Evan T. Keller^1,2,3, Jon Wanagat¹, W.B. Ershler^1,3

¹Glennan Center for Geriatrics and Gerontology, Departments of ²Pathology and ³Internal Medicine, Eastern Virginia Medical School.

Received 10/21/96; Accepted 11/01/96; On-line //96

TABLE OF CONTENTS

1. Abstract

2. Introduction

3. An overview of interleukin-6

3.1. Physiology and pathophysiology of interleukin-6

3.2. Interleukin-6 structure and function

3.3. Control of interleukin-6 promoter activity

4. Steroids and regulation of interleukin-6 expression

4.1. Glucocorticoid and interleukin-6 expression

4.2. Estrogen and interleukin-6 expression

4.3. Androgen and interleukin-6 expression

5. The interleukin-6 receptor

5.1. The interleukin-6 receptor: Structure and function

5.2. Expression of the interleukin-6 receptor

6. Summary

7. Acknowledgments

8. References

1. ABSTRACT

Interleukin-6 (IL-6) is a member of the family of cytokines collectively termed "the interleukin-6 type cytokines." Among its many functions, IL-6 plays an active role in immunology, bone metabolism, reproduction, arthritis, neoplasia, and aging. IL-6 expression is regulated by a variety of factors, including steroidal hormones, at both the transcriptional and post-transcriptional levels. IL-6 achieves its effects through the ligand-specific IL-6 receptor (IL-6R). Unlike most other cytokine receptors, the IL-6R is active in both membrane bound and soluble forms. Defining mechanisms to control IL-6 or IL-6R expression may prove useful for therapy of the many clinical disorders in IL-6 plays a role.

2. INTRODUCTION

Interleukin-6 (IL-6) contributes to a myriad of physiologic and pathophysiologic processes. Because of the large scope of its effects, the cellular and molecular biology of IL-6 has been explored by a variety of investigators representing a great number of basic biological and medical fields. In this review, we will describe the cellular and molecular biology of IL-6 and its receptor, delineate sources and targets of IL-6 and the IL-6 receptor (IL-6R), and correlate the basic biology of IL-6 with its role in pathophysiology.

3. AN OVERVIEW OF INTERLEUKIN-6

3.1. Physiology and pathophysiology of interleukin-6

IL-6 is involved in a myriad of biologic processes, perhaps explaining its long list of synonyms (B-cell stimulatory factor-2, B cell differentiation factor, T cell-replacing factor, interferon-ß₂, 26-kDa protein, hybridoma growth factor, interleukin hybridoma plasmacytoma factor 1, plasmacytoma growth factor, hepatocyte-stimulating factor, macrophage granulocyte-inducing factor 2, cytotoxic T cell differentiation factor, thrombopoietin) (1). Though not an exclusive representation, the several biologic activities of IL-6 are depicted in Figure 1.

Figure 1: Roles of Interleukin-6 in Physiology

Interleukin-6, termed at the time interferon-ß₂, was first cloned during an effort to isolate and characterize the viral-induced protein interferon-ß. This strategy included treating cultured human fibroblasts with the double-stranded RNA, poly(I)·poly(C), which mimics viral activity (2). IL-6 is now well recognized for its role in the acute phase inflammatory response which is characterized by production of a variety of hepatic proteins termed acute phase proteins (e.g., C-reactive protein, serum amyloid A, fibrinogen, complement, alpha₁-antitrypsin) (reviewed in (3)). In addition to its role in the acute phase response, IL-6 is important for the development of specific immunologic responses. IL-6 induces differentiation of activated, but not resting, B cells (4-6) culminating in production of immunoglobulin (7, 8). Along with B cell differentiation, IL-6 stimulates proliferation of thymic and peripheral T cells (9, 10) and in cooperation with IL-1 (11), induces T cell differentiation to cytolytic-T cells (12, 13) and activates natural killer cells (14). These observations emphasize the importance of IL-6 in both non-specific and specific immune responses.

In addition to its immunologic/inflammatory role, IL-6 appears to play an important role in bone metabolism through induction of osteoclastogenesis and osteoclast activity (15, 16). In rodents, inhibition of IL-6 gene expression is in part responsible for estrogen's ability to inhibit osteoclast activation (17-20). These findings are further supported by the observation that IL-6 gene knockout mice are protected from cancellous bone loss associated with ovariectomy (21).

In addition to the activities described above, IL-6 functions in a wide variety of other systems including the reproductive system by participating in menses (22, 23) and spermatogenesis (24), skin proliferation (25-27), megakaryocytopoiesis (28-30), macrophage differentiation (31-33), and neural cell differentiaion and proliferation (34, 35).

Because of its multidimensional and complex actions, dysregulation of IL-6 results in a myriad of disorders (summarized in Fig. 2) including a variety of neoplastic processes. For example, it may affect cancer progression by its actions on cell adhesion and motility (36), thrombopoiesis (30, 37), tumor specific antigen expression (38) and cancer cell proliferation. Depending on the cell type and the presence or absence of IL-6R, IL-6 can either inhibit (39-41) or stimulate (42) cancer cell proliferation. A great variety of tumor types are stimulated by IL-6, including melanoma (43), renal cell carcinoma (44, 45), prostate carcinoma (46), Kaposi's sarcoma (47), ovarian carcinoma (48), lymphoma and leukemia (49-51), and multiple myeloma (52-59). In many of these tumors, IL-6R have been detected and a direct proliferative signal has been proposed. Yet, when tumor cells are devoid of IL-6R, a tumor inhibiting effect of IL-6 has been demonstrated, presumably because of its immune enhancing properties.

Figure 2: Roles of Interleukin-6 in Pathophysiology

Recently, IL-6 like other cytokines and growth factors (e.g., IL1-alpha, IL1-ß, and TNF-alpha) has been shown to contribute to the bone remodeling process (for review see references (60, 61)). IL-6 exerts its effect on bone by stimulating osteoclast progenitor cell differentiation and osteoclast proliferation as mentioned above. Conditioned media from marrow cultures obtained from patients with Paget's disease (characterized by increased osteoclastogenesis), stimulated osteoclast-like cell formation in normal human marrow cultures and this was reversed by addition of neutralizing antibody to IL-6 (62). IL-6 neutralizing antibody also blocks bone resorption induced by a variety of agents including TNF (18, 63). In addition to increasing osteoclast numbers, IL-6 has been shown to stimulate bone resorption in rat long bones (64) and fetal mouse metacarpi (65) , calvaria (66), and bone resorption pit assays (62, 67). Although it is not clear that IL-6 alone is sufficient to mediate these activities (68), these data demonstrate the importance of IL-6 in enhancing osteoclastic activity thus providing a mechanism for IL-6 promoting osteoporosis.

Although a normal physiologic process, aging is accompanied by a variety of disorders (reviewed in (69)) including, Alzheimer's disease, arteriosclerosis, and thyroiditis. Because IL-6 levels are directly correlated with aging in a variety of species (reviewed in (70)), it may play an important role in the aging process. Intriguingly, dietary restriction, the only experimental intervention that reproducibly prolongs maximum lifespan in mammals (71) can restore to the young phenotype a variety of physiologic parameters, including IL-6 secretion and serum levels.(72, 73). Similarly, DHEA, currently thought to influence various aging processes (74), also has been shown to diminish the age-associated rise in serum IL-6 (75).

IL-6 may be an important mediator of several infectious and autoimmune diseases. These include human immunodeficiency virus (76, 77), rheumatoid arthritis (78), Castleman's disease (79, 80), and the paraneoplastic symptoms associated with cardiac myxoma (81-83). Furthermore, elevated serum and cerebrospinal fluid levels of IL-6 can be found in sepsis (84, 85). Inflammatory joint disease, particularly rheumatoid arthritis (78), is associated with increased synovial fluid levels of IL-6 (86).

In spite of the great variety of health consequences associated with IL-6, it manifests its activity by binding to a specific receptor, the IL-6R, which is described below.

3.2. Interleukin-6 structure and function

Human IL-6 has a molecular weight of between 21 to 28 Kd depending on post-translational processing such as glycosylation and phosphorylation (87, 88). The IL-6 peptide contains 212 amino acids (aa) of which a 28 aa hydrophobic signal peptide is cleaved off resulting in a mature protein of 184 aa. Even though the homology between human and mouse IL-6 is 65% at the nucleic acid level and only 42% at the amino acid level (89), human IL-6 can stimulate murine IL-6 responsive cells. This may be due to the highly conserved central region (57% homology at the amino acid level) of the molecule which contains four cysteine residues that can be perfectly aligned between mouse and human IL-6 (90). Additionally, the carboxy-terminus appears to be critical for IL-6 activity (91, 92). When just four aa were deleted from the carboxy-terminus, IL-6 activity was completely lost (93). In contrast, deletion of 28 aa from the amino-terminus did not affect IL-6 activity (94).

The human IL-6 gene, located on chromosome 7p21 (95-97), is approximately 5 Kb (compared to 7 Kb for the mouse (98)) and consists of four introns and five exons (99). The human IL-6 gene contains three transcriptional initiation sites which correspond with three TATA-like sequences (99).

3.3. Control of interleukin-6 promoter activity

Characterization of the IL-6 gene 5' flanking region has revealed a very complex control region. The importance of this region is underscored by the observation that the proximal 300 bp of the human and murine IL-6 gene 5'-flanking region share approximately 80% homology (98). Figure 3 summarizes the regulatory elements in the IL-6 promoter. Table 1 and Table 2 summarize factors which induce or repress the IL-6 promoter, respectively.

Figure 3: Schematic representation of the IL-6 promoter. See text for abbreviation definitions.

Briefly, several cis-acting response elements mediate activation of the IL-6 promoter including those for AP-1, nuclear factor IL-6 (NF-IL6), NF-kappaB, and the multiple response element (MRE), The MRE and NF-IL6 response element are components of the serum response element (SRE). The SRE was first identified in c-fos and induces gene transcription when serum-starved cells are exposed to serum (122, 123). The MRE confers induction of the IL-6 promoter to TPA, serum, forskolin, IL-1alpha, and TNF (115). Repression of the IL-6 promoter can be mediated by various combinations of trans-acting factors and cis-acting elements including Fos binding to the SRE, retinoblastoma protein binding to the retinoblastoma control element (RCE), and a variety of steroids (described below)

4. Steroids and regulation of interleukin-6 expression

4.1. Glucocorticoid and interleukin-6 expression

Glucocorticoids repress expression of a variety of genes including proliferin, pro-opiomelanocortin, prolactin, and the a-subunit of glycoprotein hormone. Similarly, glucocorticoids inhibit IL-6 expression. During times of stress or inflammation IL-6 levels are increased. IL-6, in turn, can induce release of corticotrophin-releasing factor (124, 125), which results in elevated systemic levels of corticosteroids. These findings along with the observations that natural and synthetic corticosteroids inhibit IL-6 production from a variety of tissues (126-129), provide a mechanism for a negative-feedback loop. It was these observations along with the availability of the IL-6 promoter which were the impetus to analyze how glucocorticoid mediates repression of IL-6 expression at the molecular level. The initial studies demonstrated that dexamethasone could inhibit IL-1-induced transcriptional activation of the proximal 225 bp of the IL-6 promoter (130). Additionally, it was observed that dexamethasone abrogated the activity of the thymidine kinase (TK) minimal promoter fused downstream of either MRE I and MRE II when induced by IL-1, phorbol ester, or forskolin. These findings taken together with the observation that the glucocorticoid receptor (GR) could inhibit pseudorabies virus-induced activation of the proximal 110 bp fragment of the IL-6 promoter, in which the MRE had been deleted, prompted the investigators to examine for interaction of GR and the IL-6 promoter by DNAse I footprinting (130). They found that GR protected the MRE, the TATA box, the major transcription initiation site (similar to the initiator (Inr) (131)), and an as yet functionally uncharacterized region between -201 to -210. These findings were further supported by results from a DNA-binding immunoprecipitation assay which showed that cell extract from HeLa cells transfected with wildtype GR cDNA was capable of binding to the -225 fragment of the IL-6 promoter (albeit not as strongly as to the GRE in the MMTV promoter) (119). Additionally, mutation of the DNA binding domain resulted in loss of GR's ability to repress transcriptional activation (119). These data are compatible with a model in which corticosteroid activates GR which then occludes the IL-6 promoter at these activation sites, thus blocking the binding of positive-acting and basal transcription factors to the IL-6 promoter.

Because the above studies demonstrated that GR bound weakly to the IL-6 promoter and it had been previously documented that GR was capable of protein:protein interactions with c-Jun (132, 133), Ray et al. examined the possibility that GR interacted with NF-kB and NF-IL6; transcription factors known to stimulate the IL-6 promoter (120). Using murine F9 embryonal carcinoma cells, which are devoid of endogenous NF-IL6, AP-1, and Rel-like activities, Ray et al. demonstrated that expression plasmids encoding NF-IL6, or p65 alone could not stimulate the IL-6 promoter, whereas when used together, the IL-6 promoter was stimulated. Furthermore, dexamethasone could inhibit this activation (120). In contrast, transfection of HeLa cells with either plasmid alone, resulted in activation of the IL-6 promoter, suggesting that the transgenic protein interacted with the endogenous co-activating protein. Regardless, in HeLa cells, dexamethasone was capable of inhibiting NF-IL6 and p65-induced IL-6 promoter activity (120). Finally, in cross precipitation assays, it was demonstrated that GR bound to p65, but not NF-IL6. These results suggest that GR mediates inhibition of p65-induced activation of the IL-6 promoter through protein:protein interactions. This mechanism may occur in combination with the promoter occlusion mechanism described earlier.

Yet, additional clues on the action of GR on the IL-6 promoter may be gleaned from studies by Scheinman et. al. and Auphan et al. (134, 135). Though not evaluated on the IL-6 promoter itself, these groups demonstrated that dexamethasone induces IkappaBalpha protein and mRNA expression. Auphan et al. further demonstrated that dexamethasone could inhibit TNF-alpha-stimulated nuclear translocation of p65 (135). These data suggest that GR induces IkappaBalpha protein synthesis which results in cytoplasmic sequestration of NFkappaB culminating in decreased activation of the target promoter. This mechanism does not preclude the previously described mechanisms of promoter occlusion and GR:p65 protein interactions.

4.2. Estrogen and interleukin-6 expression

Estrogen's ability to repress IL-6 expression was first recognized in human endometrial stromal cells (23). Additional clues came from the observations that menopause or ovariectomy resulted in increased IL-6 serum levels (136) , increased IL-6 mRNA levels in bone cells (137), and increased IL-6 secretion by mononuclear cells (75, 138, 139). Further evidence for estrogen's ability to repress IL-6 expression is derived from studies which demonstrated that estradiol inhibits bone marrow stromal cell and osteoblastic cell IL-6 protein and mRNA production in vitro (18, 140) and that estradiol was as effective as neutralizing antibody to IL-6 to suppress osteoclast development in murine bone cell cultures (18) or in ovariectomized mice (19). Taken together, these data provide strong evidence for the occurrence of estrogen-mediated repression of IL-6 expression.

To explore estrogen's effect on the IL-6 promoter, Pottratz et al. (117) and Ray et al. (116) performed transient transfection assays using either a 1.2 Kb fragment of the promoter or a 225 bp fragment of the promoter. They found that basal IL-6 promoter activity was very low when used to drive a chloramphenicol acetyltransferase (CAT) gene in both HeLa, which does not express the estrogen receptor (ER), and the murine bone marrow stromal cell line MBA 13.2, which constitutively expresses the ER. However, phorbol-13-myristate acetate (PMA), IL-1, or TNF stimulated the promoter and 17ß-estradiol inhibited this activity in both cell lines. Transfection of the HeLa cells with ER was required to observe the suppression. These results suggest that 17ß-estradiol inhibits IL-6 gene transcriptional activation by an ER-dependent mechanism.

To investigate whether the ER-mediated repression was due to direct interaction between the ER and the IL-6 promoter, Pottratz et al. performed competition assays which assessed for the 225 bp IL-6 promoter fragment's ability to compete for binding of ER to a labeled estrogen response element (ERE) (117). However, even though ER bound to the labeled ERE, the 225 bp fragment did not compete with the ERE. Additionally, upon electrophoretic mobility shift assay (EMSA) the ERE could not compete shifted complexes formed from incubation of HeLa or MBA 13.2 nuclear extracts with the labeled 225 bp fragment and this fragment could not bind to ER (116, 117). In summary, these results suggested that ER does not bind to the 225 bp IL-6 promoter fragment even though it inhibits its activity. These results were not entirely surprising based on the observation that there was no ERE within the 225 bp IL-6 promoter fragment. However, they led to the hypothesis that ER was working through inhibition of positive acting transcription factors by protein:protein interactions.

At nearly the same time, Ray et al. reported that wildtype ER, but not ER with mutated or deleted DNA-binding domain (DBD), could mediate repression of IL-1-induced IL-6 promoter activity, yet if the ER DBD was replaced with a GR DBD, the resulting chimeric receptor was capable of mediating repression (116). These results were also observed if the IL-6 promoter activity was induced by co-transfection of HeLa cells with NF-IL6 and NFkappaB p65 subunit. However, the chimeric receptor, which could mediate repression, could not stimulate a ERE-reporter construct, thus suggesting that repression was not dependent on direct binding to the IL-6 promoter. Furthermore, overexpression of NFkappaB p65 by transient transfection inhibited ER's ability to transactivate an ERE-reporter construct (116). This result provided evidence for interaction between NFkappaB p65 and ER.

These studies were extended into the U2-OS human osteoblast and MCF-7 breast carcinoma cell lines by Stein and Yang (141). Similar to the observations in HeLa cells described above, the IL-6 promoter, even when deleted to 109 bp, was stimulated by IL-1alpha and this activation was repressed by 17ß-estradiol in the presence of either co-transfected ER (U2-OS cells) or native ER (MCF-7 cells). Further deletion of the promoter to 49 bp, in which both NF-IL6 and NFkappaB response elements are deleted, resulted in loss of promoter induction by IL-1b. Based on these data, Stein and Yang concluded that the ER target is between -109 and -49 (141). However, since the 49 bp promoter region was not stimulated, they could not observe ER-mediated repression if it was present, hence this conclusion may be premature.

To deduce which regions of the ER were necessary for repression, Stein and Yang performed a series of transient co-transfection experiments using mutated ER constructs and the IL-6 promoter (141). Deletion of the amino-terminus including the transcription accessory factor (TAF)-1 (delta1-179) domain still allowed for ER-mediated repression. Extending this deletion to include the DBD (delta1-281) resulted in loss of repression as did isolated deletion of the DBD (delta185-251). Additionally, deletion of the carboxy-terminus (delta271-595) including TAF-2 domain and the LBD resulted in loss of repression. Based on these data, the author's concluded that the DBD contributed to transrepression.

Based on the previous data that ER does not appear to bind to the IL-6 promoter (116, 117), yet can mediate transrepression of the IL-6 promoter, Stein and Yang explored for direct interaction between ER and NFkappaB p65, NFkappaB p50, or NF-IL6 (141). They found that all these in vitro translated proteins bound with bacterially expressed ER. Intriguingly, this interaction was not dependent on estrogen and deletion of the DBD did not effect the interaction. Furthermore, they demonstrated that ER and NFkappaB p65 or NF-IL-6 mutually represses each others transactivation abilities through a mechanism which does not induce IkappaBalpha. Based on these data, Stein and Yang concluded that binding of NFkappaB p65 or NF-IL-6 is the driving force which mediates transrepression. However, when considered with the observation described above that isolated deletion of the ER DBD results in loss of transrepression, these data suggest that ER's binding capability for these transcription factors and its ability to mediate transrepression are in fact on different domains of the ER and are mediated by some mechanism which involves more than just binding of these transcription factors. Further studies are needed to resolve these issues.

4.3. Androgen and interleukin-6 expression

Androgens can repress expression of a variety of gene products (142-157). The first demonstration of androgen's ability to repress IL-6 expression was made in +/+LDA11 murine bone marrow stromal cell line which had been stimulated with IL-1 and TNF (18). In this study, 10 nM T was able to repress bioactive IL-6 expression by approximately 20% (as opposed to approximately 60% for 10 nM 17ßE₂). Curiously, when HeLa cells were co-transfected with ER and a CAT-reporter plasmid driven by a 225 bp fragment of the IL-6 promoter, 10 nM DHT inhibited PMA-induced activation by approximately 50% (as opposed to approximately 90% for 10 nM 17ß-estradiol (17ßE₂) (117). The authors accounted for this effect as due to T's affinity for the ER (117). However, this is unlikely as it has been previously demonstrated that T and DHT inhibits PMA-induced IL-6 promoter activation in HeLa cells transfected with AR, but not ER (158). This supports an earlier study in which it was reported that DHT antagonizes estrogen's effect in the uterus by decreasing estrogen-induced RNA transcription at a point subsequent to estrogen receptor binding (159). Several adrenal androgens which are not known to bind the AR (i.e., androstenedione, androstenediol, and dehydroepiandrosterone sulfate) mediate repression of the IL-6 promoter in HeLa cells transfected with AR. These experiments suggest that androgens are capable of mediating transrepression of IL-6 promoter activation.

We have further demonstrated that DHT requires the AR to mediated DHT's repressive effect in a transient transfection assay system (118). In our system, DHT inhibited PMA-induced activation of the IL-6 promoter by inhibiting translocation of NFkappaB. This was achieved through maintenance of IkappaBalpha levels even in the presence of PMA. Currently, it is unknown how DHT maintains IkappaBalpha levels, but decreased phosphorylation or increased protein production are two possibilities.

The in vivo relevance of the above observations was demonstrated by Bellido et al. in an orchiectomized mouse model (158). Though they did not report serum or bone marrow IL-6 levels, they found that orchiectomy resulted in increased replication of bone marrow osteoclast progenitors and found that this could be prevented by administration of IL-6 neutralizing antibody or implantation of a slow release form of T. However, because T is converted to 17ßE₂, these results are not conclusive evidence of androgen's action. In fact, the observation of decreased bone density observed in a male patient whom had normal androgen levels, but a mutation resulting in a non-functional ER, suggests that estrogen's effects on bone in men are as important as androgen's (160). This hypothesis is supported by the observation that 17ßE₂ can inhibit bone loss observed in men treated by orchiectomy for prostate cancer (161). However, estrogen's ability to inhibit bone loss may be mediated through its transrepression of the IL-6 promoter, and thus these observations are still consistent with androgen loss resulting in increased IL-6 activity. Finally, that orchiectomy of mice without the IL-6 gene (generated by knockout technology) do not demonstrate the increased osteoclast proliferative effects, strongly supports that loss of androgen results in increased IL-6 levels (158).

5. THE INTERLEUKIN-6 RECEPTOR

5.1. The interleukin-6 receptor: Structure and function

The human IL-6R (also known as gp80 and the IL-6Ra subunit), was first cloned by Yamasaki et al. from a human natural killer-like cell line, YT, (162) followed by Schooltink et al. from a human hepatoma cell line, HepG2 (163). IL-6R is a 80 Kd protein consisting of 467 aa. Located on chromosome 1 band q21 (164), the IL-6R gene encodes for a 5 Kb mRNA containing a coding region of 1401 bp (162). The 3'-untranslated region (3'-UTR) consists of approximately 1.5 Kb, suggesting that the 5'-UTR compromises approximately 2.1 Kb. The human IL-6R shares 53% identity with the rat hepatic IL-6R aa sequence (165). However, the mRNA structures are strikingly different. Although both human and rat IL-6 mRNAs are approximately 5 Kb, the rat 3'-UTR consists of approximately 3.1 Kb, which combined with the observation that the coding region, similar to the human IL-6R coding region, is 1.4 Kb, suggests that the 5'-UTR is much shorter in the rat than the human IL-6R mRNA (approximately 0.6 vs 2.1 Kb, respectively). A definitive conclusion on the length of the 5'-UTRs of these mRNAs awaits for localization of the transcription initiation site(s).

The structure of IL-6R has been deduced by comparative sequence analysis. A hydropathy plot revealed two major hydrophobic regions; one which encodes for the signal peptide between residues 1 and 20, and the other which encodes for the transmembrane domain in the region of residues 359 to 386 (162). The latter region is followed by a putative transmembrane anchoring stop codon consisting of several positively charged residues. These findings suggest the IL-6R has a 339 aa extracellular region, 28 aa transmembrane region, and 82 aa intracellular region. Intriguingly, the intracellular region does not contain any kinase domains suggesting that this molecule is not capable of signaling activity (162).

Upon homology search, it was identified that the extracellular component of the IL-6R contains a domain which shares extensive homology with the Ig superfamily (162) and two tandem fibronectin type III motifs (166) present in a 200 aa region. This region defines the cytokine receptor family domain, a domain which is found in a variety of other cytokine and growth factor receptors. It contains highly conserved components consisting of four cysteine residues in its amino-terminal region, and a tryptophan-serine-X-tryptophan-serine (WSXWS) motif penultimate of the transmembrane region (166, 167). Fibronectin type III domains are observed in cell-adhesion molecules, which implies that cytokine receptors evolved from an ancestral adhesive molecule (168).

As the protein structure suggests, the IL-6R is not capable of inducing signal transduction directly. It is now understood that in order for IL-6 to mediate signal, it first binds to gp-80 forming a low affinity receptor complex. This complex then associates with the non-ligand-binding transmembrane glycoprotein, gp-130 (169). Homodimerization of gp-130 is required for IL-6 signal transduction (170). Although it was originally considered that one unit of IL-6 and the IL-6R bound to a gp-130 homodimer (170), the stochiometry and number of this reaction appears to involve a hexameric complex consisting of two molecules each of IL-6, IL-6R gp-80, and gp-130 (171). This complex forms a high affinity binding site for IL-6, as opposed to the low affinity binding observed with IL-6 and IL-6R gp-80 in the absence of gp-130.

Mutational analyses of the IL-6R has identified that the region of amino acids 106-322, which comprise the cytokine receptor family domain of IL-6R, is responsible both for IL-6-binding and for binding to gp-130 (172). In fact, the Ig-like domain, whose action in the context of IL-6R is not currently identified, is not required for either of these functions.

The IL-6R has an isoform which was first identified in human urine, the soluble IL-6R (sIL-6R) (173). In contrast to other soluble cytokine receptors (e.g., sIL-2R) which inhibit cytokine induced signaling, the sIL-6R forms a fully active hexameric IL-6:sIL-6R:gp-130 complex which induces cell signaling. How sIL-6R is generated is not currently known , but both alternative splicing, resulting in loss of the transmembrane domain (174), or proteolyis of the mature cell surface IL-6R (175, 176) have been proposed.

As mentioned in our opening comments, IL-6 is one of a family of cytokines collectively termed "the interleukin-6-type cytokines". The cytokines which make up this family are IL-6, leukemia inhibitory factor (LIF), oncostatin-M (OSM), ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT-1), and interleukin-11 (177). The common characteristic which define this group is they activate gp-130 to induce cell signaling. That these cytokines converge on gp-130 underscores the redundancy present in the cytokine system. However, specificity of cytokine action is mediated, in part, through cell specific repertoire of cytokine specific a chain receptors, such as gp80 for IL-6

5.2. Expression of the Interleukin-6 Receptor

The IL-6R is expressed in a variety of cells (Table 3). In general it is expressed in the range of 100 to 2000 sites/cell (178). However, in myeloma lines and Epstein-Barr virus transformed lines up to 29,000 sites/cell have been identified (178). Except for the effects of dexamethasone, modulation of IL-6 expression by various factors has not given consistent results. Snyer et al. demonstrated that A23187 (a calcium ionophore), lipopolysaccharide, prostaglandin E1, IL-1, tumor necrosis factor (TNF), and muramyl dipeptide did not significantly alter IL-6R expression in either CESS (Epstein-Barr Virus B cell immortalized line), HL-60, U937, Hep-G, UAC cell lines. In contrast, several other groups have demonstrated that IL-1 does modulate IL-6R expression in several cell lines and tissues (summarized in Table 3). Perhaps cell specific differences in response account for the discordant results. On the other hand, dexamethasone has been consistently demonstrated to increase IL-6R in a variety of tissues including liver primary cells and cell lines, monocyte primary cultures, myeloma cell lines, and an amniotic cell line.

In spite of the great variety of cells which express the IL-6R and its importance in many facets of physiology, the molecular mechanisms which regulate transcriptional control of the IL-6R gene have not been defined to date. Cloning and analysis of the IL-6R promoter will help define these mechanisms.

6. SUMMARY

IL-6 is active in a great number of physiologic and pathophysiologic processes. A wide variety of factors have been demonstrated to modulate IL-6 expression. While may of these stimulate IL-6 expression, only a few factors have been demonstrated to inhibit IL-6 expression. Among the inhibitors of IL-6 gene expression are steroids, including corticosteroids, estrogen, and androgens. Steroids appear to inhibit IL-6 expression thorugh repressing transcriptional activation of the IL-6 gene. In addition to regulation of IL-6 levels, modulation of IL-6R levels is another mechanism by which IL-6 activity is controlled. Both the soluble and membrane bound form of IL-6R mediate IL-6 activity by stimulating cell signalling through activation of gp130. Even though the importance of the IL-6R for manifestation of IL-6 activity is recognized, the molecular mechanisms by which transcriptional control of the IL-6R gene is achieved have not been reported to date. Future studies aimed at elucidating these mechanisms may contribute to understanding how IL-6 is active in a variety of disorders.

7. ACKNOWLEDGMENTS

This work was supported by the American Federation for Aging Research A96169 (to E.T.K.), a National Institutes of Health Training Fellowship AG00213 (to E.T.K. and W.B.E.), and grants AG11970 (to W.B.E.) and AG00451 (to W.B.E)

8. REFERENCES

1. S. Akira, T. Taga & T. Kishimoto: Interleukin-6 in biology and medicine. Adv Immunol 54, 1-78 (1993)

2. J. Weissenbach, Y. Chernajovsky, M. Zeevi, L. Shulman, H. Sorecq, U. Nir, D. Wallach, M. Perricaude, P. Tiollais & M. Revel: Two interferon mRNA in human fibroblasts: In vitro translation and Escheria coli cloning studies. Proc Natl Acad Sci USA 77, 7152-7156 (1980)

3. P. B. Sehgal, G. Greininger & G. Tosato: Acute Phase and Immune Responses: Interleukin-6. Ann NY Acad Sci 557, 1-583 (1989)

4. T. Hirano, T. Teranishi, B. H. Lin & K. Onoue: Human helper T cell factor(s). IV. Demonstration of a human late-acting B cell differentiation factor actin on Staphylococcus aureus Cowen I-stimulated B cells. J Immunol 133, 798-802 (1984)

5. A. Muraguchi, T. Hirano, B. Tang, T. Matsuda, Y. Horii, K. Nakamima & T. Kishimoto: The essential role of B cell stimulatory factor 2 (BSF-2/IL-6) for the terminal differentiation of B cells. J Exp Med 67, 332-344 (1988)

6. T. Taga, Y. Kawanishi, T. T. Hardy, T. Hirano & T. Kishimoto: Receptors for B cell stimulatory factor 2. J Exp Med 166, 967-981 (1987)

7. D. M. Ambrosino, N. R. Delaney & R. C. Shamberger: Human polysaccharide-specific B cells are responsive to pokeweed mitogen and IL-6. J Immunol 144, 1221-1226 (1990)

8. F. Takatsuki, A. Okano, C. Suzuki, R. Chieda, Y. Takahara, T. Hirano, T. Kishimoto, J. Hamuro & Y. Akiyama: Human recombinant IL-6/B cell-stimulatory factor 2 augments murine antigen-specific antibody responses in vitro and in vivo. J Immunol 141, 3072-3077 (1988)

9. C. Uyttenhove, P. G. Coulie & J. Van Snick: T cell growth and differentiation induced by interleukin HP1/IL-6, the murine hybridoma/plasmacytoma growth factor. J Exp Med 167, 1414-1427 (1988)

10. M. Lotz, F. Jirik, R. Kabouridis, C. Tsoukas, T. Hirano, T. Kishimoto & D. Carson: B cell stimulating factor 2/interleukin 6 is a costimulant for human thymocytes and T lymphocytes. J Exp Med 167, 1253-1258 (1988)

11. M. Helle, J. P. J. Brakenhoff, E. T. DeGroot & L. A. Aarden: Interleukin-6 is involved in interleukin-1-induced activities. Eur J Immunol 18, 957-959 (1988)

12. M. Okada, N. Kitahara, S. Kishimoto, T. Matsuda, T. Hirano & T. Kishimoto: IL-6/BSF-2 functions as a killer helper factor in the in vitro induction of cytotoxic T cells. J Immunol 141, 1543-1549 (1988)

13. J. C. Renauld, A. Vink & J. Van Snick: IL1 and IL6 in CTL induction-accessory signals in murine cytolytic T cell responses: Dual requirement for IL1 and IL6. J Immunol 143, 1894-1898 (1989)

14. T. A. Luger, J. Krutman, T. Kirnbauer, A. Urbanski, T. Schwarz, G. Klappacher, A. Kock, M. Micksche, K. J. Malejczy, E. Schauer, L. T. May, & P. B. Sehgal: IFNß/IL-6 augments the activity of human natural killer cells. J Immunol 143, 1206-1209 (1989)

15. N. Kurihara, D. Bertolini, T. Suda, Y. Akiyama & G. D. Roodman: IL-6 stimulates osteoclast-like multinucleated cell formation in long term human marrow cultures by inducing IL-1 release. J Immunol 144, 4226-4230 (1990)

16. T. Tamura, N. Udagawa, N. Takahashi, C. Miyaura, S. Tanaka, Y. Koishihara, Y. Ohsugi, K. Kumaki, T. Taga, T. Kishimoto & T. Suda: Soluble interleukin-6 receptor triggers osteoclast formation by interleukin-6. Proc Natl Acad Sci USA 90, 11924-11928 (1993)

17. G. Passeri, G. Girasole, T. Markus, J. S. Abrams, S. C. Manolagas & R. L. Jilka: 17ß-estradiol regulates IL-6 production and osteoclast development in murine calvaria cell cultures. J Bone Miner Res 6, S263 (1991)

18. G. Girasole, R. L. Jilka, F. Passeri, S. Boswell, G. Boder, D. C. Williams & S. C. Manologas: 17ß-Estradiol inhibits interleukin-6 production by bone marrow-derived stromal cells and osteoblasts in vitro: a potential mechanism for the antiosteoporotic effect of estrogens. J Clin Invest 89, 883-891 (1992)

19. R. L. Jilka, C. Hangoc, G. Girasole, G. Passeri, D. C. Williams, J. S. Abrams, B. Boyce, H. Broxmeyer & S. C. Manolagas: Increased osteoclast development after estrogen loss: Mediation by interleukin-6. Science 257, 88-91 (1992)

20. C. Miyaura, K. Kusano, T. Masuzawa, O. Chaki, Y. Onoe, M. Aoyagi, T. Sasaki, T. Tamura, Y. Koishihara, Y. Ohsugi & T. Suda: Endogenous bone-resorbing factors in estrogen deficiency: Cooperative effects of IL-1 and IL-6. J Bone Miner Res 10, 1365-1373 (1995)

21. V. Poli, R. Balena, E. Fattori, A. Markatos, M. Yamamoto, H. Tanaka, G. Ciliberto, G. Rodan & C. A: Interleukin-6 deficient mice are protected from bone loss caused by estrogen depletion. EMBO 13, 1189-1196 (1994)

22. S. Tabibzadeh, Q. F. Kong, A. Babaknia & L. T. May: Progressive rise in the expression of intereleukin-6 in human endometrium during menstrual cycle is initiated during the implantation window. Mol Hum Reprod 1, 2793-2799 (1995)

23. S. S. Tabibzadeh, U. Santhanam, P. B. Sehgal & L. T. May: Cytokine-induced production of IFN-ß2/IL-6 by freshly explanted human endometrial stromal cells. Modulation by estradiol-17ß. J Immunol 142, 3134-3139 (1989)

24. H. Hakovirta, V. Syed, B. Jegou & M. Parvinen: Function of interleukin-6 as an inhibitor of meiotic DNA synthesis in the rat seminiferous epithelium. Mol Cell Endocrinol 108, 193-198 (1995)

25. J. G. Krueger, J. F. Krane, D. M. Carter & A. B. Gottlieb: Role of growth factors, cytokines, and their receptors in the pathogenesis of psoriasis. J Invest Dermatol 94(suppl), 135S-140S (1990)

26. R. M. Grossman, J. Kreuger, D. Yourish, A. Granelli-Piperno, D. P. Murphy, L. T. May, T. S. Kupper, P. B. Sehgal & A. B. Gottlieb: Interleukin 6 is expressed in high levels in psoriatic skin and stimulates proliferation of cultured human keratin0cytes. Proc Natl Acad Sci USA 86, 6367-6371 (1989)

27. K. Yoshizaki, N. Nishimoto, K. Matsumoto, H. Tagoh, T. Taga, Y. Deguchi, T. Kuritani, T. Hirano, I. Hashimoto, N. Okada & T. Kishimoto: Interleukin-6 and eexpression of its receptor on epidermal keratinocytes. Cytokines 2, 381-387 (1990)

28. S. Navarro, N. Devili, J. P. LeCouedic, B. Klein, J. Bretonn-Gorius, J. Doly & W. Vainchenker: Interleukin-6 and its receptor are expressed by human megakaryocytes: In vitro effects on proliferation and endoreplication. Blood 77, 461-471 (1991)

29. W. H. Sun, N. Binkley, D. W. Bidwell & W. B. Ershler: The influence of recombinant human interleukin-6 on Blood and immune parameters in middle-aged and old rhesus monkeys. Lymphokine & Cytokine Research 12, 449-455 (1993)

30. R. J. Hill, M. K. Warren, P. Stenberg, H. Levin, L. Corash, R. Drummond, G. Baker, F. Levin & Y. Mok: Stimulation of megakaryocytopoiesis in mice by human recombinant interleukin-6. Blood 77, 42-48 (1991)

31. Y. Shabo, L. J, M. Rubinstein, M. Revel, S. C. Clark, S. F. Wolf, R. Kamen & L. Sachs: The myeloid Blood cell differentiation inducting protein MGI-2A is interleukin-6. Blood 72, 2070-2073 (1988)

32. C. P. Chiu, F. Lee, T. J. Fero, A. Johnson, J. Everitt & A. B. Malik: IL-6 is a differentiation factor for M1 and WEHI-3B myeloid leukemic cells. J Immunol 142, 1909-1915 (1989)

33. J. Lotem, Y. Shabo & L. Sachs: Clonal variation in susceptibility to differentiation by different protein inducers in the myeloid Leukemia cell line M1. Leukemia 3, 804-807 (1989)

34. T. Hama, M. Miyamoto, H. Tsukui, C. Nishio & M. Hatanaka: Interleukin-6 as a neurotrophic factor for promoting the survival of cultured basal forebrain cholinergic neurons from postnatal rats. Neurosci Lett 104, 340-344 (1989)

35. T. Satoh, S. Nakamura, T. Taga, T. Matsuda, T. Hirano, T. Kishimoto & Y. Kaziro: Induction of neuronal differentiation in PC12 cells by B-cell stimulatory factor 2/interleukin 6. Mol Cell Biol 8, 3546-3549 (1988)

36. I. Tamm, I. Cardinale & P. Sehgal: Interleukin-6 and 12-O-tetradecanoyl phorbol-13-acetate act synergistically in inducing cell-cell separation and migration of human breast carcinoma cells. Cytokine 3, 212-223 (1991)

37. T. Ishibashi, Y. Shikama, H. Kimura, M. Kawaguchi, T. Uchida, T. Yamamoto, A. Okano, Y. Akiyama, T. Hirano, T. Kishimoto & Y. Maruyama: Thrombopoietic effects of interleukin-6 in long-term administration in mice. Exp Hematol 21, 640-646 (1993)

38. C. D. Ullmann, J. Schlom & J. W. Greiner: Interleukin-6 increases carcinoembryonic antigen and histocompatibility leukocyte antigen expression on the surface of human colorectal carcinoma cells. J Immunother 12, 231-241 (1992)

39. W. H. Sun, R. A. Kreisle, A. W. Philips & W. B. Ershler: In vivo and in vitro characteristics of interleukin 6-transfected B16 melanoma cells. Cancer Res 52, 5412-5415 (1992)

40. L. Chen, Y. Mory, A. Zilberstein & M. Revel: Growth inhibition of human breast carcinoma and Leukemia/lymphoma cell lines by recombinant interferon-beta2. Proc Natl Acad Sci USA 85, 8037 (1988)

41. J. J. MulŽ, M. C. Custer, W. D. Travis & S. A. Rosenberg: Cellular mechanisms of the antitumor activity of recombinant IL-6 in mice. J Immunol 8, 2622-2629 (1992)

42. J. Serve, G. Steinhauser, D. Oberberg, W. A. Fiegel, J. Northoff & W. E. Berdel: Studies on the interaction between interelukin 6 and human malignant nonhematopoietic cell lines. Cancer Res 51, 3862-3866 (1991)

43. C. Lu & R. S. Kerbel: Interleukin-6 undergoes transition from paracrine growth inhibitor to autocrine stimulator during human melanoma progression. J Cell Biol 120, 1281-1288 (1993)

44. J. Fujita, J. Takenawa, Y. Kaneko, K. Okumura & O. Yoshida: Anti-interleukin-6 (IL-6) therapy of IL-6-producing renal cell carcinoma. Acta Urol Jpn 38, 1333-1336 (1992)

45. A. S. Koo, C. Armstrong, B. Bochner, T. Shimabukuro, C. Tso, J. B. deKernion & A. Belldegrun: Interleukin-6 and renal cell cancer: production, regulation, and growth effects. Cancer Immunol Immunother 35, 97-105 (1992)

46. P. H. Gumerlock & J. H. Li: Antisense inhibition of interleukin-6 production by and growth of human prostate cancer cells. Proc Annu Meet Am Assoc Cancer Res 34, A2950 (1993)

47. S. A. Miles, A. R. Rezai, J. F. Salazar-Gonzalez, M. V. Meyden, R. H. Stevens, D. M. Logan, R. T. Mitsuyasu, T. Taga, T. Hirano, Y. Kishimoto & O. Martinez-Maza: AIDS Kaposi sarcoma-derived cells produce and respond to interleukin 6. Proc Natl Acad Sci USA 87, 4068-4072 (1990)

48. S. Wu, K. Rodabaugh, O. Martinez-Maza, J. M. Watson, D. S. Silberstein, C. M. Boyer, W. P. Peters, J. B. Weinberg, J. S. Berek & R. C. Bast Jr: Stimulation of ovarian tumor cell proliferation with monocyte products including interleukin-1, interleukin-6, and tumor necrosis factor-a. Am J Obstet Gynecol 166, 997-1007 (1992)

49. S. Shimuzu, T. Hirano, R. Yoshioka, S. Sugai, T. Matsuda, T. Taga, T. Kishimoto & S. Konda: Interleukin 6 (B-cell stimulatory factor 2) dependent growth of a Lennert's lymphoma derived T-cell line (KT-3). Blood 72, 1826-1828 (1988)

50. C. A. Schirren, H. Volpel & S. C. Meuer: Spontaneous responsiveness to cytokines by human T-cell leukemias. Leukemia 6, 574-581 (1992)

51. B. Barut, D. Chauhan, H. Uchiyama & K. C. Anderson: Interleukin-6 functions as an intracellular growth factor in hairy cell leukemia in vitro. J Clin Invest 92, 2346-2352 (1993)

52. Y. Okuno, T. Takahashi, A. Suzuki, M. Fukumoto, K. Nakamura, H. Fukui, Y. Koishihara, Y. Ohsugi & H. Imura: Acquisition of growth autonomy and tumorigenicity by an interleukin 6-dependent human myeloma cell line transfected with interleukin 6 cDNA. Exp Hematol 20, 395-400 (1992)

53. M. Kawano, T. Hirano, T. Matsuda, T. Taga, Y. Horii, K. Iwato, H. Asaoku, B. Tang, O. Tanabe, H. Tanaka, A. Kuramoto & T. Kishimoto: Autocrine generation and requirement of BSF-2/IL-6 for human multiple myeloma. Nature 332, 83-85 (1988)

54. K. C. Anderson, R. M. Jones, C. Morimoto, P. Leavitt & B. A. Barut: Response patterns of purified myeloma cells to hematopoietic growth factors. Blood 73, 1915-1924 (1989)

55. M. Kawano, H. Tanaka, H. Ishikawa, M. Nobuyoshi, K. Iwato, H. Asaoku, O. Tanabe & A. Kuramato: Interleukin-1 accelerates autocrine growth of myeloma cells through interleukin-6 in human myeloma. Blood 73, 2145-2148 (1989)

56. B. Klein, X. Zhang, M. Jourdan, J. Content, F. Houssiau, L. Aarden, M. Pichaczyk & R. Bataille: Paracrine rather than autocrine regulation of myeloma-cell growth and differentiation by interleukin-6. Blood 73, 517-526 (1989)

57. H. Jernberg, M. Pettersson, T. Kishimoto & K. Nilsson: Heterogeneity in response to interleukin 6 (IL-6), expression of IL-6 and IL-6 receptor mRNA in a panel of established human multiple myeloma cell lines. Leukemia 5, 255-265 (1991)

58. O. Tanabe, M. Kawano, H. Tanaka, K. Iwato, H. Asaoku, H. Ishikawa, M. Nobuyoshi, T. Hirano, T. Kishimoto & A. Kuramoto: BSF-2/IL-6 does not augment Ig secretion but stimulates proliferation of myeloma cells. Am J Hematol 31, 258-262 (1989)

59. X. G. Zhang, B. Klein & R. Bataille: Interleukin-6 is a potent myeloma-cell growth factor in patients with aggressive multiple myeloma. Blood 74, 11-13 (1989)

60. S. C. Manolagas: Role of Cytokines in bone resorption. Bone 17, 63S-67S (1995)

61. J. A. Lorenzo: The role of Cytokines in the regulation of local bone resorption. Crit Rev Immunol 11, 195-213 (1991)

62. G. D. Roodman, N. Kurihara, Y. Ohsaki, T. Kukita, D. Hosking, A. Demulder & F. R. Singer: Interleukin-6: a potential autocrine/paracrine factor in Paget's disease of bone. J Clin Invest 89, 46-52 (1992)

63. K. S. Black, G. R. Mundy & I. R. Garrett: Interleukin-6 causes hypercalcemia in vivo, and enhances the bone resorbing potency of interleukin-1 and tumor necrosis factor by two orders of magnitude in vitro. J Bone Miner Res 6, S271 (1991)

64. E. M. Greenfield, S. M. Shaw, S. A. Gornik & M. A. Banks: Adenyl cyclase and interleukin 6 are downstream effectors of parathyroid hormone resulting in stimulation of bone resorption. J Clin Invest 96, 1238-1244 (1995)

65. C. W. G. M. Löwik, G. van der Pluijm, H. Bloys, K. Hoekman, O. L. M. Bijvoet, L. A. Asrden & S. E. Papapoulos: Parathyroid hormone (PTH) and PTH-like protein (PLP) stimulate interleukin-6 production by osteogenic cells: A possible role of interleukin-6 in osteoclastogenesis. Biochem Biophys Res Comm 162, 1546-1552 (1989)

66. Y. Ishimi, C. Miyaura, C. H. Jin, T. Akatsu, E. Abe, Y. Nakamura, A. Yamaguchi, S. Yoshiki, T. Matsuda, T. Hirano, T. Kishimoto & T. Suda: IL-6 is produced by osteoblasts and induces bone resorption. J Immunol 145, 3297-3303 (1990)

67. Y. Ohsaki, S. Takahashi, T. Scarcez, A. Demulder, T. Nishihara, R. Williams & G. D. Roodman: Evidence for an autocrine/paracrine role for interleukin-6 in bone resorption by giant cells from giant cell tumors of bone. Endocrinology 131, 2229-2234 (1992)

68. J. De La Mata, H. L. Uy, T. A. Guise, B. Story, B. F. Boyce, G. R. Mundy & G. D. Roodman: Interleukin-6 enhances hypercalcemia and bone resorption mediated by parathyroid hormone-related protein in vivo. J Clin Invest 95, 2846-2852 (1995)

69. W. B. Ershler, W. H. Sun & N. Binkley: The role of interleukin-6 in certain age-related diseases. Drugs Aging 5, 358-365 (1994)

70. W. B. Ershler: Interleukin-6: A cytokine for gerontologists. J Am Geriatr Soc 41, 176-181 (1993)

71. R. Weindruch: Caloric restriction and aging. Scientific American 274, 46-52 (1996)

72. M. J. Volk, T. D. Pugh, M. J. Kim, C. H. Frith, R. A. Daynes, W. B. Ershler & R. Weindruch: Dietary restriction from middle age attenuates age-associated lymphoma development and IL-6 dysregulation in C57BL/6 mice. Cancer Res 54, 3054-3063 (1993)

73. W. B. Ershler, W. H. Sun, N. Binkley, S. Gravenstein, M. J. Volk, G. Kamoske, R. G. Klopp, E. B. Roecker, R. A. Daynes & R. Weindruch: Interleukin-6 and aging: blood levels and mononuclear cell production increase with advancing age and in vitro production is modifiable by dietary restriction. Lymphokine Cytokine Res 12, 225-230 (1993)

74. W. Regelson, R. Loria & M. Kalimi: Hormonal intervention: "buffer hormones" or "state dependency". The role of dehydroepiandrosterone (DHEA), thyroid hormone, estrogen and hypophysectomy in aging. Ann NY Acad Sci 521, 260-273 (1988)

75. R. A. Daynes, B. A. Araneo, W. B. Ershler, C. Maloney, G. Z. Li & S. Y. Ryu: Altered regulation of IL-6 production with normal aging. Possible linkage to the age-associated decline in dehydroepiandrosterone and its sulfated derivative. J Immunol 150, 5219-5230 (1993)

76. G. Scala, M. R. Ruocco, C. Ambrosino, M. Mallardo, V. Giordano, F. Baldassarre, E. Dragonetti, I. Quinto & S. Venuta: The expression of the interleukin 6 gene is induced by the human immunodeficiency virus 1 TAT protein. J Exp Med 179, 961-971 (1994)

77. M. Honda, S. Yamamoto, M. Cheng, K. Yasukawa, H. Suzuki, T. Saito, Y. Osugi, T. Tokunaga & T. Kishimoto: Human soluble IL-6 receptor: Its detection and enhanced release by HIV infection. J Immunol 148, 2175-2180 (1992)

78. S. Kotake, K. Sato, K. J. Kim, N. Takahashi, N. Udagawa, I. Nakamura, A. Yamaguchi, T. Kishimoto, T. Suda & S. Kashiwazaki: Interleukin-6 and soluble interleukin-6 receptors in the synovial fluids form rheumatoid arthritis patients are responsible for osteoclast-like cell formation. J Bone Miner Res 11, 88-95 (1996)

79. J. T. Beck, S.-H. Jsu, J. Wijdenes, R. Bataille, B. Klein, D. Vesole, K. Hayden, S. Jagannath & B. Barlogie: Brief report: Alleviation of systemic manifestations of Castleman's disease by monoclonal anti-interleukin-6 antibody. N Eng J Med 330, 602-605 (1994)

80. S. J. Brandt, D. M. Bodine, C. E. Dunbar & A. W. Nienhuis: Dysregulated interlukin 6 expression produces a syndrome resembling Castleman's disease in mice. J Clin Invest 86, 592-599 (1990)

81. Y. Seino, U. Ikeda & K. Shimada: Increased expression of interleukin 6 mRNA in cardiac myxomas. Br Heart J 69, 565-567 (1993)

82. T. Kanda, S. Umeyama, A. Sasaki, Y. Nakazato, Y. Morishita, S. Imai, T. Suzuki & K. Murata: Interleukin-6 and cardiac myxoma. Am J Cardiol 74, 965-967 (1994)

83. J. R. Seguin, J. Y. Beigbeder, U. Hvass, J. Langlois, R. Grolleau, M. Jourdan, B. Klein, R. Bataille & P. A. Chaptal: Interleukin 6 production by cardiac myxomas may explain constitutional symptoms. J Thoracic Cardiovas Surg 103, 599-600 (1992)

84. A. Wagge, P. Brandtzaeg, A. Halstensen, P. Kierulf & T. Espevik: The complex pattern of Cytokines in serum from patients with meningococcal septic shock. J Exp Med 169, 333-338 (1989)

85. F. A. Houssiau, K. Bukasa, C. J. M. Sindic, J. Van Damme & J. Van Snick: Elevated levels of the 26k human hybridoma growth factor (interleukin 6) in cerebrospinal fluid of patients with acute infection of the central nervous system. Clin Exp Immunol 71, 320-323 (1988)

86. F. Houssiau, J. P. Devoglaer, J. Van Damme, C. Nagant de Deuxchaisnes & J. Van Snick: Interleukin 6 in synovial fluid and serum of patients with rheumatoid arthritis and other inflammatory arthritides. Arthritis Rheum 31, 784-788 (1988)

87. L. T. May, J. Grayeb, U. Santhanam, S. B. Tatter, Z. Sthoeger, D. C. Helfgott, N. Chiorazzi, G. Grieninger & P. B. Sehgal: Synthesis and secretion of multiple forms of b2-interferon/B-cell differentiation factor 2/hepatocyte-stimulating factor by human fibroblasts and monocytes. J Biol Chem 263, 7760-7766 (1988)

88. L. T. May, U. Santhanam, S. B. Tatter, D. C. Helfgott, A. Ray, J. Grayeb & P. B. Sehgal: Phosphorylation of secreted froms of human b2-interferon/hepatocyte-stimulating factor/interleukin-6. Biochem Biophys Res Commun 152, 1144-1150 (1988)

89. J. Van Snick: Interleukin-6: An overview. Annu Rev Immunol 8, 253-278 (1990)

90. J. Van Snick, S. Cayphas, J.-P. Szikora, J.-C. Renauld, E. Van Roost, T. Boon & R. J. Simpson: cDNA cloning of murine interleukin-HP1: homology with human interleukin-6. Eur J Immunol 18, 193-198 (1988)

91. N. Ida, S. Sakurai, T. Hosaka, K. Hosoi, T. Kunitomo, T. Shimazu, T. Maruyama & M. Kahase: Establishment of strongly neutralizing monoclonal antibody to human interleukin-6 and its epitope analysis. Biochem Biophys Res Commun 165, 728-734 (1989)

92. H. N. Snouwaert, K. Kariya & D. M. Fowlkes: Effects of site-specific mutations on biologic activities of recombinant human IL-6. J Immunol 146, 585-591 (1991)

93. A. Krüttgen, S. Rosejohn, C. Möller, B. Wroblowski, A. Wollmer, J. Mü:llberg, T. Hirano, T. Kishimoto & P. C. Heinrich: Structure-function analysis of human interleukin-6-Evidence for the involvement of the carboxy-terminus in function. FEBS Lett 262, 323-326 (1990)

94. J. P. Brakenhoff, M. Hart & L. A. Aarden: Analysis of human IL-6 mutants expressed in Escheria coli. Biologic activities are not affected by deletion of aminon acids 1-28. J Immunol 143, 1175-1182 (1989)

95. P. B. Sehgal, A. Zilberstein, M. R. Ruggieri, L. T. May, A. Ferguson-Smith, D. L. Sate, M. Revel & F. H. Ruddle: Human chromosome 7 carries the ß2 interferon gene. Proc Natl Acad Sci USA 83, 8957-8961 (1986)

96. A. M. Bowcock, J. R. Kidd, N. Lathrop, L. Daneshvar, L. T. Mary, A. Ray, P. B. Sehgal, K. K. Kidd & L. L. Cavalli-Sforza: The human "ß2 interferon/hepatocyte stimulating factor/interleukin-6" gene: DNA polymorphism studies and localization to chromosome 7p21. Genomics 3, 8-16 (1988)

97. A. C. Ferguson-Smith, Y. F. Chen, M. S. Newman, L. T. May, P. B. Sehgal & F. H. Ruddle: Regional localization of the beta2-interferon/B-cell stimulatory factor 2/hepatocyte stimulating factor gene to human chromosome 7p15-p21. Genomics 2, 203-208 (1988)

98. O. Tanabe, S. Akira, T. Kamiya, G. G. Wong, T. Hirano & T. Kishimoto: Genomic structure of the murine IL-6 gene: High degree of conservation of potential regulatory sequences between mouse and human. J Immunol 141, 3875-3881 (1988)

99. K. Yasukawa, T. Hirano, Y. Watanabe, K. Muratani, T. Matsuda, S. Nakai & T. Kishimoto: Structure and expression of human B cell stimulatory factor-2 (BSF-2/IL-6) gene. EMBO J 6, 2939-2945 (1987)

100. Y. Zhang, M. Broser & W. N. Rom: Activation of the interleukin 6 gene by Mycobacterium tuberculosis or lipopolysaccharide is mediated by nuclear factors NF-IL6 and NF-kappa B. Proc Natl Acad Sci USA 91, 2225-2229 (1994)

101. O. Muraoka, T. Kaisho, M. Tanabe & T. Hirano: Transcriptonal activation of the interleukin-6 gene by HTLV-1 p40tax through an NF-kappaB-like binding site. Immunol Letters 37, 159-165 (1993)

102. N. Mori, F. Shirakawa, H. Shimizu, S. Murakami, S. Oda, K. Yamamoto & S. Eto: Transcriptional regulation of the human interleukin-6 gene promoter in human T-cell leukemia virus type I-infected T-cell lines: evidence for the involvement of NF-kappa B. Blood 84, 2904-2911 (1994)

103. I. Yamashita, S. Katamine, R. Moriuchi, Y. Nakamura, T. Miyamoto, K. Eguchi & S. Nagataki: Transactivation of the human interleukin-6 gene by human T-lymphotropic virus type 1 Tax protein. Blood 84, 1573-1578 (1994)

104. S. F. Yan, I. Tritto, D. Pinsky, H. Liao, J. Huang, G. Fuller, J. Brett, L. May & D. Stern: Induction of interleukin 6 (IL-6) by hypoxia in vascular cells. Central role of the binding site for nuclear factor-IL-6. J Biol Chem 270, 11463-11471 (1995)

105. U. Dendorfer, P. Oettgen & T. A. Libermann: Multiple regulatory elements in the interleukin-6 gene mediate induction by prostaglandins, cyclic AMP, and lipopolysaccharide. Mol Cell Biol 14, 4443-4454 (1994)

106. M. A. Brach, H. J. Gruss, T. Kaisho, Y. Asano, T. Hirano & F. Herrmann: Ionizing radiation induces expression of interleukin 6 by human fibroblasts involving activation of nuclear factor-kappa B. J Biol Chem 268, 8466-72 (1993)

107. L. Margulies & P. B. Sehgal: Modulation of the human interleukin-6 promoter (IL-6) and transcription factor C/EBPß (NF-IL6) activity by p534 species. J Biol Chem 268, 15096-15100 (1993)

108. P. M. Janaswami, D. V. Kalvakolanu, Y. Zhang & G. C. Sen: Transcriptional repression of interleukin-6 gene by adenoviral E1A proteins. J Biol Chem 267, 24886-24891 (1992)

109. M. A. Brach, S. de Vos, C. Arnold, H. J. Gruss, R. Mertelsmann & F. Herrmann: Leukotriene B4 transcriptionally activates interleukin-6 expression involving NK-chi B and NF-IL6. Eur J Immunol 22, 2705-11 (1992)

110. H. J. Gruss, M. A. Brach & F. Herrmann: Involvement of nuclear factor-kappa B in induction of the interleukin-6 gene by leukemia inhibitory factor. Blood 80, 2563-2570 (1992)

111. C. S. Yee, H. A. Messner & M. D. Minden: Regulation of interleukin-6 expression in the lymphoma cell line OCI-LY3. J Cell Physiol 148, 426-429 (1991)

112. Y. Zhang, J.-X. Lin & J. Vilcek: Interleukin-6 induction by tumor necrosis factor and interleukin-1 in human fibroblasts involves activation of a nuclear factor binding to a kappa B-like sequence. Mol Cell Biol 10, 3818-3823 (1990)

113. H. Shimuzu, K. Mitomo, T. Watanbe, S. Okamoto & K. Yamamoto: Involvement of a NF-kB-like transcription factor in the activation of the interleukin-6 gene by inflammatory lymphokines. Mol Cell Biol 10, 561-568 (1990)

114. U. Santhanam, A. Ray & P. B. Sehgal: Repression of the interleukin 6 gene promoter by p53 and the retinoblastoma susceptibility gene product. Proc Natl Acad Sci USA 88, 7605-7609 (1991)

115. A. Ray, P. Sassone-Corsi & P. B. Sehgal: A multiple Cytokine- and second messenger-responsive element in the enhancer of the human interleukin-6 gene: Similarities with c-fos gene regulation. Mol Cell Biol 9, 5537-5547 (1989)

116. A. Ray, K. E. Prefontaine & P. Ray: Down-modulation of interleukin-6 gene expression by 17 beta-estradiol in the absence of high affinity DNA estrogen receptor. J Biol Chem 269, 12940-12946 (1994)

117. S. T. Pottratz, T. Bellido, H. Mocharla, D. Crabb & S. C. Manolagas: 17b-Estradiol inhibits expression of human promoter-reporter constructs by a receptor-dependent mechanism. J Clin Invest 93, 944-950 (1994)

118. E. T. Keller, C. Chang & W. B. Ershler: Inhibition of NFkappaB activity through maintenance of IkappaBalpha levels contributes to dihydrotestosterone-mediated repression of the interleukin-6 promoter. J Biol Chem 271, 26267-26275 (1996)

119. A. Ray, K. S. LaForge & P. B. Sehgal: Repressor to activator switch by mutations in the the glucocorticoid receptor: Is direct DNA binding necessary? Proc Natl Acad Sci USA 88, 7086-7090 (1991)

120. A. Ray & K. E. Prefontaine: Physical association and functional antagonism between subunit of transcription factor NF-kappa B and the glucocorticoid receptor. Proc Natl Acad Sci USA 91, 752-756 (1994)

121. R. J. Zitnik, N. L. Whiting & J. A. Elias: Glucocorticoid inhibition of interleukin-1-induced production by human lung fibroblasts: evidence for and post-transcriptional regulatory mechanisms. Am J Respir Cell Mol Biol 10, 643-650 (1994)

122. T. M. Fisch, R. Prywes & R. G. Roeder: c-fos sequences necessary for basal expression and induction by epidermal growth factor, 12-O-tetradecanoyl phorbol-13-acetate, and the calcium ionophore. Mol Cell Biol 7, 3490-3402 (1987)

123. M. Z. Gilman: The c-fos serum response element responds to protein kinase C-dependent and -independent signals but not to cyclic AMP. Genes Dev 2, 394-402 (1988)

124. P. Navarra, S. Tsagarakis, M. Faria, L. H. Rees, M. Besser & A. B. Grossman: Interleukin-1 and -6 stimulate the release of corticotropoin-releasing hormone from rat hypothalamus in vitro via eicosanoid cyclooxygenase pathway. Endocrinology 128, 37-44 (1990)

125. K. Lyson, K. Milenkovic & S. M. McCann: The stimulatory effect of interleukin-6 on corticotorpin-releasing factor and thyrotropin-releasing hormone secretion in vitro. Prog Neuroendocrinol Immunol 4, 161-165 (1991)

126. B. M. R. N. J. Woloski, E. M. Smith, W. J. Meyer III, G. M. Fuller & J. E. Blalock: Corticotropin-releasing activity in monokines. Science 230, 1035-1037 (1985)

127. M. Kohase, D. Henriksen-DiStefano, L. T. May & J. Vilcek: Dexamethasone inhibits feedback regulation of the mitogenic activity of tumor necrosis factor, interleukin-1 and epidermal growth factor in human fibroblasts. J Cell Physiol 132, 271-278 (1987)

128. H. J. M. Feyen, P. Elford, F. E. Ki Padova & U. Trechsel: Interleukin-6 is produced by bone and modulated by parathyroid hormone. J Bone Miner Res 4, 633-638 (1989)

129. T. Nishida, S. Nakai, T. Kawakami, K. Aihara, N. Nishino & Y. Hirai: Dexamethasone regulation of the expression of Cytokine mRNAs induced by interleukin-1 in the astrocytoma cell line U373MG. FEBS Lett 243, 25-29 (1989)

130. A. Ray, K. S. LaForge & P. B. Sehgal: On the mechanism for efficient repression of the interleukin-6 promoter by glucocorticoids: Enhancer, TATA box, and RNA start site (Inr Motif) occlusion. Mol Cell Biol 10, 5736-5746 (1990)

131. S. T. Smale, M. C. Schmidt, A. J. Berk & D. Baltimore: Transcriptional activation by Sp1 as directed throught the TATA or initiator: specific requirement for mammalian transcription factor IID. Proc Natl Acad Sci USA 87, 4509-4513 (1990)

132. M. I. Diamond, H. N. Miner, S. K. Yoshinaga & K. R. Yamamoto: Transcription factor interactions: selectors of positive or negative regulation form a single DNA element. Science 249, 1266-1272 (1990)

133. C. Jonat, H. J. Rahmsdorf, K.-K. Park, A. C. B. Cato, S. Gebel, H. Ponta & P. Herrlich: Antitumor promotion and antiinflammation: Down-modulation of AP-1 (Fos/Jun) activity by glucocorticoid hormone. Cell 62, 1189-1204 (1990)

134. R. I. Scheinman, P. C. Cogswell, A. K. Lofquist & A. S. Baldwin Jr: Role of transcriptional activation of IkappaBalpha in mediation of immunosuppression by glucocorticoids. Science 270, 283-286 (1995)

135. N. Auphan, A. SiSonato, C. Rosette, A. Helmberg & M. Karin: Immunosuppression by glucocorticoids: Inhibition of NF-kB activity through induction of IkappaB synthesis. Science 270, 286-2290 (1995)

136. D. M. Kania, N. Binkley, M. Checovich, T. Havighurst, M. Schilling & W. B. Ershler: Elevated plasma levels of interleukin-6 in postmenopausal women do not correlate with bone density. J Am Geriat Soc 43, 236-239 (1995)

137. S. H. Ralston: Analysis of gene expression in human bone biopsies by polymerase chain reaction: evidence for enhanced Cytokine expression in post-menopausal osteoporosis. J Bone Miner Res 9, 883-890 (1994)

138. R. Pacifici, C. Brown, E. Puscheck, E. Friedrich, E. Slatopolsky, D. Maggio, R. McCracken & L. V. Avioli: Effect of surgical menopause and estrogen replacement on Cytokine release from human blood mononuclear cells. Proc Natl Acad Sci USA 88, 5134-5138 (1991)

139. G. Pioli, G. Basini, M. Pedtazzoni, G. Musetti, V. Ulietti, D. Bresciani, P. Villa, A. Bacchi, D. Hughes, M. Russel & M. Passeri: Spontaneous release of interleukin-1 and interleukin-6 by peripheral blood mononuclear cells after oophorectomy. Clin Sci 83, 503-507 (1992)

140. M. Kassem, S. A. Harris, T. C. Spelsberg & R. B. L: Estrogen inhibits interleukin-6 production and gene expression in a human osteoblastic cell line with high levels of estrogen receptor. J Bone Miner Res 11, 193-199 (1996)

141. B. Stein & M. X. Yang: Repression of the interleukin-6 promoter by estrogen receptor is mediated by NF-kappaB and C/EBPß. Mol Cell Biol 15, 4971-4979 (1995)

142. S. Leppa, P. Härkönen & M. Jaikanen: Steroid-induced epithelial-fibroblastic conversion associated with syndecan suppression in S115 mouse mammary cells. Cell Regul 2, 1-11 (1991)

143. P. V. Bodine, B. L. Riggs & T. C. Spelsberg: Regulation of c-fos expression and TGF-beta production by gonadal and adrenal androgens in normal human osteoblastic cells. J Steroid Biochem Mol Biol 52, 149-158 (1995)

144. E. W. Bingaman, D. J. Magnuson, T. S. Gray & R. J. Handa: Androgen inhibits the increases in hypothalamic corticotropin-releasing hormone (CRH) and CRH-immunoreactivity following gonadectomy. Neuroendocrinology 59, 228-234 (1994)

145. C. M. Clay, R. A. Keri, A. B. Finicle, L. L. Heckert, D. L. Hamernik, K. M. Marschke, E. M. Wilson, F. S. French & J. H. Nilson: Transcriptional repression of the glycoprotein hormone alpha subunit gene by androgen may involve direct binding of androgen receptor to the proximal promoter. J Biol Chem 268, 13556-13564 (1993)

146. A. Mizokami, H. Saiga, T. Matsui, T. Mita & A. Sugita: Regulation of androgen receptor by androgen and epidermal growth factor in a human prostatic cancer cell line, LNCaP. Endocrinologia Japonica 39, 235-43 (1992)

147. M. A. Mancini, B. Chatterjee & A. K. Roy: Age-dependent reversal of the lobular distribution of androgen-inducible alpha 2u globulin and androgen-repressible SMP-2 in rat liver. J Histochem Cytochem 39, 401-5 (1991)

148. H. Persson, C.-L. Lievre, O. Söder, M. J. Villar, M. Metsis, L. Olson, M. Ritzen & T. Hökfelt: Expression of b-nerve growth factor receptor mRNA in Sertoli cells is downregulated by testosterone. Science 247, 704-707 (1990)

149. M. Metsis, T. Timmusk, R. Alikmets, M. Saarma & H. Persson: Regulatory elements and transcriptional regulation by testosterone and retinoic acid of the rat nerve growth factor receptor promoter. Gene 121, 247-254 (1992)

150. P. J. Kallio, H. Poukka, A. Moilanen, O. A. Jänne & J. J. Palvimo: Androgen receptor-mediated transcriptional regulation in the absence of direct interaction with a specific DNA element. Mol Endocrinol 9, 1017-1028 (1995)

151. M. L. Montpetit, K. R. Lawless & M. Tenniswood: Androgen-repressed messages in the rat ventral prostate. The Prostate 8, 25-36 (1986)

152. R. Buttyan, Z. Zakeri, R. Lockshin & D. Wolgemuth: Cascade induction of c-fos, c-myc, and heat shock 70K transcripts during regression of the rat ventral prostate gland. Mol Endocrinol 2, 650-657 (1988)

153. M. L. Day, S. Wu & J. W. Basler: Prostate nerve growth factor inducible A gene binds a novel element in the retinoblastoma gene promoter. Cancer Res 53, 5597-5599 (1993)

154. D. A. Wolf, F. Kohlhuber, P. Schulz, F. Fittler & D. Eick: Transcriptional down-regulation of c-myc in human prostate carcinoma cells by the synthetic androgen mibolerone. Br J Cancer 65, 376-382 (1992)

155. P. Wong, J. Pineault, J. Lakins, D. Taillefer, J. LŽger, C. Wang & M. Tenniswood: Genomic organization and expression of the rat TRPM-2 (clusterin) gene, a gene implicated in apoptosis. J Biol Chem 268, 5021-5031 (1993)

156. J. Lindzey, M. Grossmann, M. V. Kumar & D. J. Tindall: Regulation of the 5'-flanking region of the mouse androgen receptor gene by cAMP and androgen. Mol Endocrinol 7, 1530-1540 (1993)

157. V. E. Quarmby, W. C. Beckman, E. M. Wilson & F. S. French: Androgen regulation of c-myc messenger ribonucleic acid levels in rat ventral prostate. Mol Endocrinol 1, 865-874 (1987)

158. T. Bellido, R. L. Jilka, B. F. Boyce, G. Girasole, H. Broxmeyer, S. A. Dalrymple, R. Murray & S. C. Manolagas: Regulation of interleukin-6, osteoclastogenesis, and Bone mass by androgens. The role of the androgen receptor. J Clin Inv 95, 2886-2895 (1995)

159. T. T. Hung & W. E. Gibbons: Evaluation of androgen antagonism of estrogen effect by dihydrotestosterone. J Steroid Biochem 19, 1513-1520 (1983)

160. E. P. Smith, J. Boyd, G. R. Frank, H. Takahashi, T. M. Cohen, B. Specker, T. C. Williams, D. B. Lubahn & K. S. Korach: Estrogen resistance caused by a mutation in the estrogen-receptor gene in a man. N Eng J Med 331, 1056-1061 (1994)

161. S. Eriksson, A. Eriksson, R. Stege & K. Carlström: Bone mineral density in patients with prostatic cancer treated with orchidectomy and with estrogens. Calcif Tissue Int 57, 97-99 (1995)

162. K. Yamasaki, T. Taga, Y. Hirata, H. Yawata, Y. Kawanzihi, B. Seed, T. Taniguchi, T. Hirano & T. Kishimoto: Cloning and expression of the human interleukin-6 (BSF-2/IFNß 2) receptor. Science 241, 825-828 (1988)

163. H. Schooltink, T. Stoyan, D. Lenz, H. Schmitz, T. Hirano, T. Kishimoto, P. Henrich & S. Rose-John: Structural and functional studies on the human hepatic interleukin-6 receptor. Biochem J 277, 659-664 (1991)

164. P. M. C. Kluck, J. Wiegant, R. P. M. Hansen, M. W. J. Bolk, A. K. Raap, R. Willemze & J. E. Landegent: The human interleukin-6 receptor a chain gene is localized on chromosome 1 band q21. Hum Genet 90, 542-544 (1993)

165. M. Baumann, H. Baumann & G. H. Fey: Molecular cloning, characterization and functional expression of the rat liver interleukin 6 receptor. J Biol Chem 265, 19853-19862 (1990)

166. J. F. Bazan: A novel family of growth factor receptors: a common binding domain in the growht hormone, prolactin, erythropoietin and IL-6 receptors, and the p75 IL-2 receptor ß-chain. Biochem Biophys Res Commun 164, 788-795 (1989)

167. D. Cosman, S. D. Lyman, R. L. Idzerda, M. P. Beckmann, L. S. Park, R. G. Goodwin & C. J. March: A new Cytokine receptor superfamily. Trends Biol Sci 15, 265-270 (1990)

168. T. Taga, M. Hibi, M. Murakami, M. Saito, H. Yawata, T. Hirano & T. Kishimoto: Interleukin-6 receptor and signals. In: Interleukins: Molecular Biology and Immunology. Chem Immunol. (T. Kishimoto, ed.), Vol. 51, pp. 181-204. Basel, Karger 1992.

169. T. Taga, M. Hibi, Y. Hirata, K. Yamasaki, K. Yasukawa, T. Matsuda, T. Hirano & T. Kishimoto: Interleukin-6 triggers the association of its receptor with a possible signal transducer, gp 130. Cell 58, 573-581 (1989)

170. M. Murakami, M. Hibi, N. Nakagawa, T. Nakagawa, K. Yasukawa, K. Yamanishi, T. Taga & T. Kishimoto: IL-6-induced homodimerization of gp 130 and associated activation of a tyrosine kinase. Science 260, 1808-1810 (1993)

171. L. D. Ward, G. J. Howlett, G. Discolo, K. Yasukawa, A. Hammacher, R. L. Moritz & R. J. Simpson: High affinity interleukin-6 receptor is a hexameric consisting of two molecules each of interleukin-6, receptor, and gp-130. J Biol Chem 269, 23286-23289 (1994)

172. H. Yawata, K. Yasukawa, S. Natsuka, M. Murakami, K. Yamasaki, M. Hibi, T. Taga & T. Kishimoto: Structure-function analysis of human IL-6 receptor: dissociation of amino acid residues required for IL-6-binding and for IL-6 signal transduction through gp130. EMBO J 12, 1705-1712 (1993)

173. D. Novick, H. Englmann, D. Wallach & M. Rubinstein: Soluble Cytokine receptors are present in normal human urine. J Exp Med 170, 1409-1414 (1989)

174. J. A. Lust, D. F. Jelinek, K. A. Donovan, L. A. Frederick, B. K. Huntley, J. K. Braaten & N. J. Maihle: Sequence, expression and function of an mRNA encoding of the human interleukin-6 receptor (sIL-6R). Curr Topics Microbiol Immunol 194, 199-205 (1994)

175. J. Mullberg, J. Schooltink, T. Stoyan, M. Gunther, L. Graeve, G. Buse, A. Mackiewicz, P. C. Henrich & S. Rose-John: The soluble interleukin-6 receptor is generated by shedding. Eur J Immunol 23, 473-480 (1993)

176. T. Nakajima, S. Yamamoto, M. Cheng, K. Yasukawa, T. Hirano, T. Kishimoto, T. Tokunaga & M. Honda: Soluble interleukin-6 receptor is released from receptor-bearing cell line in vitro. Jpn J Cancer Res 83, 373-378 (1992)

177. P. B. Sehgal, L. Wang, R. Rayanade, H. Pan & L. Margulies: Interleukin-6 type Cytokines. In: Interleukin-6-type Cytokines. (A. Mackiewicz, A. Koji and P. B. Sehgal, eds.), Vol. 762, pp. 1-14. New York Academy of Sciences, New York 1995.

178. L. Snyers, V. Fontaine & J. Content: Modulation of interleukin-6 receptors in human cells. Ann NY Acad Sci 557, 388-393 (1989)

179. J. E. Nesbitt & G. M. Fuller: Differential regulation of interleukin-6 receptor and gp130 gene expression in rat hepatocytes. Mol Cell Biol 3, 103-112 (1992)

180. R. Hoffmann, H. P. Henninger, A. Schulze-Specking & K. Decker: Regulation of interleukin-6 receptor expression in rat cells: modulation by Cytokines, dexamethasone and. J Hepatol 21, 543-550 (1994)

181. J. Bauer, T. M. Bauer, T. Kalb, T. Taga, G. Lengyel, T. Joramp, T. Kishimoto, G. Acs, L. Mayer & W. Gerok: Regulation of interleukin 6 receptor expression in human monocytes and monocyte-derived macrophages. J Exp Med 170, 1537-1549 (1989)

182. S. Rose-John, E. Hipp, D. Lenz, L. G. LegrŽs, H. Korr, T. Hirano, T. Kishimoto & P. C. Heinrich: Structural and functional studies on the human interleukin-6 receptor. J Biol Chem 266, 3841-3846 (1991)

183. L. Snyers, L. De Witt & J. Content: Glucocorticoid up-regulation of high-affinity interleukin 6 receptors on human epithelial cells. Proc Natl Acad Sci USA 87, 2838-2842 (1990)

184. S. Marinkovic & H. Baumann: Structure, hormonal regulation, and identification of the interleukin-6- and dexamethasone-responsive element of the rat haptoglobin gene. Mol Cell Biol 10, 1573-1583 (1990)

185. E. T. Keller & W. B. Ershler: Effect of IL-6 receptor antisense oligodeoxynucleotides on in vitro proliferation of myeloma cells. J Immunol 154, 4091-4098 (1995)

186. M. Portier, D. Lees, E. Caron, M. Jourdan, J. Boiron, R. Bataille & B. Klein: Up-regulation of interleukin (IL)-6 receptor gene expression in vitro and in vivo in IL-6 deprived myeloma cells. FEBS Lett 302, 35-38 (1992)

187. R. A. Gadient & U. Otten: Differential expression of interleukin-6 (IL-6) and interleukin-6 receptor (IL-6R) mRNAs in rat hypothalamus. Neurosci Lett 153, 13-16 (1993)

188. R. A. Gadient & U. Otten: Expression of interleukin-6 (IL-6) and interleukin-6 receptor (IL-6R) mRNAs in rat brain during postnatal development. Brain Res 637, 10-14 (1994)

189. M. Jücker, H. Abts, W. Li, R. Schindler, H. Merz, A. Günther, C. von Kalle, M. Schaadt, T. Diamantstein, A. C. Feller, G. R. F. Krueger, B. Diehl, T. Blankenstein & H. Tesch: Expression of interleukin-6 and interleukin-6 receptor in Hodgkin's disease. Blood 77, 2413-2418 (1991)

190. F. J. Meyers, P. H. Gumerlock, E. S. Kawasaki, A. M. Wang, R. W. deVere White & H. A. Erlich: Human leuckocyte antigen II, interleukin-6, and interleukin-6 receptor expression determined by the polymerase chain reaction. Cancer 67, 2087-2095 (1991)

191. M. J. Siegsmund, H. Yamazki & I. Pastan: Interleukin 6 receptor mRNA in prostate carcinomas and benign prostate hyperplasia. J Urology 151, 1396-1399 (1994)

192. A. Silvani, G. Ferrari, G. Paonessa, C. Toniatti, G. Parmiani & M. P. Colombo: Down-regulation of interleukin 6 receptor a chain in interleukin 6 transduced melanoma cells causes selective resistance to interleukin 6 but not to oncostatin M. Cancer Res 55, 2200-2205 (1995)

193. A. J. Littlewood, J. Russell, G. R. Harvery, D. E. Hughes, R. G. G. Russell & M. Gowen: The modulation of the expression of IL-6 and its receptor in human osteoblasts in vitro. Endocrinology 129, 1513-1520 (1991)

194. H. Suzuki, K. Yasukawa, T. Saito, M. Narazaki, A. Hasegawa, T. Taga & T. Kishimoto: Serum soluble interleukin-6 receptor in MRL/lpr mice is elevated with age and mediates the interleukin-6 signal. Eur J Immunol 23, 1078-1082 (1993)