[Frontiers in Bioscience 16, 517-530, January 1, 2011]
Functional role of Akt in macrophage-mediated innate immunity
Yong Gyu Lee1, Jaehwi Lee2, Se Eun Byeon1, Dae Sung Yoo1, Min Ho Kim1, Song Yi Lee1, Jae Youl Cho1
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TABLE OF CONTENTS
1. ABSTRACT
Akt (protein kinase B) is a serine/threonine protein kinase that regulates cell metabolism, survival and proliferation. Recent studies of the role of Akt in phagocytosis, intracellular bacterial infections, LPS tolerance, production of inflammatory cytokines and mediators, and migration during macrophage-mediated innate immunity strongly suggest a pivotal role for this enzyme in the functional activation of macrophages. Considering that a variety of inflammatory diseases, such as rheumatoid arthritis, atherosclerosis, diabetes, obesity, cancer and osteoporosis, are regulated by macrophage-mediated innate immunity, efforts should be more carefully focused on understanding the function of Akt in macrophage-mediated innate immunity. Although few studies have addressed this question, this review discusses recent findings that support an important role for Akt in macrophage-mediated innate immunity and underlines the need for trials to develop pharmaceutically useful drugs that target Akt for treatment of macrophage-mediated inflammatory diseases. The findings we review here suggest that a novel and safe Akt inhibitor with strong immunosuppressive and anti-inflammatory properties will be applied to various chronic inflammatory diseases in the near future.
2. INTRODUCTION
The immune response is a critical defense mechanism that involves neutralizing, removing, and destroying foreign materials (1). The immune system can be divided into two components, the innate immune system and the adaptive immune system. The innate immune system has several layers of defense: 1) anatomic barriers such as the skin and mucosal surfaces; 2) physiologic barriers such as temperature, pH, and chemical mediators (i.e., lysozyme and collectin); 3) phagocytic/endocytic barriers to foreign organisms and materials; and 4) resistance to infection through the inflammatory response (2). Adaptive immunity, also called acquired immunity, can be divided into the humoral immune response, which is characterized by B cell-mediated antibody production, and the cell-mediated immune response, which is characterized by CD4+ and CD8+ T cell-mediated immune responses. The adaptive immune response is defined based on four central characteristics: antigenic specificity, diversity, memory, and self/non-self recognition (3).
Macrophages represent a major component of the innate immune system and play roles in anti-cancer, anti-bacterial, and anti-viral immune responses (4). These cells are able to directly or indirectly attack tumor cells, virus-infected cells and invading bacteria by releasing cytotoxic molecules such as nitric oxide (NO) and reactive oxygen species (ROS), by producing various pro-inflammatory cytokines (tumor necrosis factor (TNF)-a , interleukin (IL)-1, IL-6) and chemokines (macrophage inflammatory protein 1, IL-8, monocyte chemoattractant protein-1), or by engulfing target pathogens or infected cells (5-7). The activation of macrophages is thus regarded as one good strategy to enhance the body's defense mechanisms. Considering that the thymus, the organ where T cell maturation and development occurs, decreases in size with age, maintenance of an immune defense system mediated by cells other than T cells, such as macrophages, is critical for elderly people. Macrophage-activating biomaterials are thus being screened for the development of immunostimulatory foods or supplements (8, 9).
The inflammation that occurs during innate immune responses is largely mediated by macrophages. This inflammation is driven by immunopathological events such as the over-production of various pro-inflammatory cytokines, including TNF-, IL-1, IL-6, and IL-12, and inflammatory mediators, including nitric oxide (NO) and prostaglandin E2 (PGE2), which are generated by activated inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 (10, 11). Production of these pro-inflammatory cytokines and inflammatory mediators is dependent upon the activation of pattern recognition receptors (PRRs), such as Toll-like receptor (TLR)-4 and TLR-2, by microbial ligands including lipopolysaccharide (LPS) (12). During the activation of PRRs, a series of intracellular signaling molecules, including mitogen activated protein kinases (MAPKs), serine/threonine protein kinases, and non-receptor type tyrosine kinases, are activated, resulting in the upregulation of inflammatory gene expression by transcription factors such as nuclear factor (NF)-B and activator protein (AP)-1 (13, 14).
Of the numerous signaling proteins that contribute to a large number of signals, Akt (protein kinase B) acts as a major player in the regulation of metabolism, cell survival, motility, transcription, and cell cycle progress (15, 16). It is a serine/threonine-specific protein kinase family member (EC 2.7.11.1) encoded by the Akt family genes Akt1, Akt2, and Akt3 (Table 1) that are widely distributed in a variety of tissues and cells (16, 17). The main functions of Akt are carried out by Akt1, which is involved in regulating cell survival and controlling the proliferation of many types of cancer (16, 18). Akt2 has been shown to play an important role in the insulin signaling pathway and is required for glucose transport (19). In contrast, the function of Akt3 is not fully understood, although defects in brain development were observed in Akt3 knockout mice (16, 17). The substrates of Akt (Figure 1) indicate its role in various cellular responses. Immune cells express the Akt substrates IB kinase (IKK), p47phox, Raf, and p70S6K (17, 20-23). These substrates play a central role in mediating chemotactic migration, NF-B-mediated pro-inflammatory gene expression, ROS-mediated respiratory burst, and phagocytic uptake (22-27). Together these findings demonstrate that Akt acts as a central player in numerous immunobiological and immunopathological events, including acute and chronic inflammatory diseases such as septic shock and rheumatoid arthritis.
Indeed, Akt has been shown to be highly expressed in immune cells such as macrophages, neutrophils, dendritic cells, natural killer cells, and T and B lymphocytes (28, 29). In particular, the expression and phosphorylation of Akt in macrophages are remarkably up-regulated in response to bacteria or bacteria-derived products such as LPS and peptidoglycan (PGN) (28) (Table 2). Because Akt has been identified as a strong positive regulator of various types of cancers and inflammatory diseases (30), strong and effective inhibition of Akt is considered a therapeutic objective for curing a variety of acute or chronic inflammatory diseases, such as septic shock, rheumatoid arthritis, and atherosclerosis, and other inflammatory diseases including cardiovascular disease, chronic obstructive pulmonary disease, inflammatory bowel disease, liver disease, and asthma (16). Although the functional importance of this enzyme in immune responses has been thoroughly demonstrated, few papers have reviewed its role in immune cells, and in particular, in macrophages. The purpose of this review is to summarize recent findings and describe the putative mechanistic role of Akt in innate immunity. Because macrophages are the key cells that mediate host inflammatory and innate immune responses, this review will focus on results of recent studies of the function of Akt in macrophages.
3. STRUCTURE AND FUNCTION OF AKT
3.1. Akt
Akt (Protein kinase B) is expressed as three different isoforms, Akt1, Akt2, and Akt3, which are encoded by distinct genes with similar DNA sequences (17). As shown in Figure 1, members of the Akt family have three functionally distinct domains, the pleckstrin homology (PH) domain, the kinase domain, and the hydrophobic motif (HM) (31). The PH domain plays a critical role in binding phosphatidylinositol-(3,4,5)-triphosphate (PIP3) in the cell membrane, and phosphorylation of the HM is required for Akt activation (18). Although the structural and biochemical features of the three Akt isoforms are very similar, these isoforms perform distinct functions in different organs. Akt1 seems to modulate immune responses, and it has also been reported to be involved in placental development (32). In addition to controlling the growth of adipose tissue, Akt2 is thought to regulate insulin signaling and thus play a role in cellular metabolism (19). Akt3 plays a role in the development of the brain, during which it controls cell number and cell size (16, 17).
3.2. Akt deficiency
Due to the critical functions of each Akt isoform, deficiency in these molecules results in severe growth retardation or lethality (17). Mice deficient in Akt1 indicated a dominant role of Akt1 in the development of placenta and embryo and their maintenance (33, 34). Thus, Akt1 knockout exhibited small placentas and embryos linked to neonatal mortality. The critical causes of this were found as the absence of spongiotrophoblast cells and the reduction of vascularization in mutant placenta (33, 34). Akt2 deficiency developed severe diabetes by suppression of insulin action seen in the case of insulin resistance with hyperglycaemia, hyperinsulinaemia and glucose intolerance (16, 35, 36). In agreement, the mass and number of pancreatic islet were greatly increased in Akt knockout mice. Furthermore, the mice exhibited mild growth retardation and an age-dependent loss of adipose tissue (lipoatrophy), suggesting that glucose metabolism, adipogenesis and maintenance, -cell function and animal growth are critically regulated by Akt2 (15, 37). Defective phenotype of Akt3 knockout condition was seen in brain size and weight without increased perinatal mortality and growth retardation syndrome (15, 34, 38). In adult Akt3 knockout mice, brain size and weight were dramatically reduced with a uniformly reduced brain size, exhibiting proportionally smaller structures (15). These results indicate that the function role of Akt3 could participate in the postnatal development of the brain in mammals.
3.3. Akt substrate proteins
The functions of Akt can be understood by studying its substrate binding capacity. Akt phosphorylates serine or threonine residues within the minimal consensus sequence RxRxx(S/T), in which x is any amino acid, and S/T is the phosphorylation site (17). Many proteins are known to have such sequences. The Akt substrate eNOS is important for angiogenesis (39), WNK1, IRS1, TSC2, GSK3, BRF1, and PLK1 are critical for metabolism (40), IKK, MyK1, Mdm2, p27, p21, Raf, mTOR, and p70S6K are critical for cell growth, protein synthesis, and transcription (41-43), and Bad and Bax are critical for cell survival signaling (44). Some of these Akt substrates are found in macrophage-mediated innate immune responses such as migration, invasion, repiratory burst, inflammatory signaling and phagocytosis as summarized in Figure 1.
3.4. Expression and activity in macrophages
Akt1 and Akt2 are expressed in most cell types and tissues; however, Akt3 expression is largely limited to brain tissue (45). Macrophages and monocytes predominantly express Akt1 and Akt2 but not Akt3 (45). In contrast, most cancer cells have been reported to express all members of the Akt family.
3.5. Akt-mediated activation signaling in macrophages
Two major transcription factors, NF-B and interferon regulatory factor (IRF)-3, are activated by various TLRs to promote the production of inflammatory mediators such as cytokines and PGE2 and enhance chemotactic migration and phagocytosis (46). The association of common adaptor proteins such as MyD88, IRAKs (IRAK1 and 4), TRAF6, and TAK1 with the cytoplasmic TIR domain of the Toll like receptors has been shown to be critical for the activation of NF-B (47). The activation of TAK1 continuously triggers the IKK complex, which consists of IKK, IKK, and NEMO/IKK. The activated IKK complex in turn phosphorylates IB, leading to its ubiquitination (49). The resultant degradation of IB results in the release of bound NF-B, enabling NF-B to translocate into the nucleus and induce the expression of inflammatory mediators such as TNF-, IL-1, iNOS, and COX-2. Akt acts upstream to activate IKK, resulting in activation of the NF-B pathway. A variety of mitogens and TLR ligands have been reported to activate the Akt/IKK/NF-B pathway (see Figure 2).
In particular, it is suggested that Akt-mediated NF-B activation is mainly found to evoke its classical activation pathway, which is managed by MKK3, IKK, and NF-B (p50/p65) for macrophage-mediated innate immunity and inflammatory responses (50).
4. AKT IN MACROPHAGE-MEDIATED INNATE IMMUNITY
4.1. Inflammatory gene expression
Several in vitro model systems have been employed to evaluate the mechanisms by which Akt regulates the expression and production of inflammatory genes and mediators. In these models, macrophage-like J774 and RAW264.7 cells or primary peritoneal macrophages were stimulated with bacteria-derived inflammatory stimuli such as LPS and PGN (51-53), and production of various proinflammatory cytokines, including TNF-, IL-1, IL-6, and IL-12, and inflammatory mediators, including NO and PGE2, were measured (54-56).
Most previous reports have focused on the molecular interactions between TLRs and their counter adaptors during inflammatory responses. Some of these studies have reported the cellular location of Akt in TLR-mediated pro-inflammatory signaling cascades. The activation of macrophages by LPS initially requires the molecular association of CD14 and TLR4 to build signaling complexes including adaptor molecules such as MyD88, TRIF, and IRAK and signaling enzymes, such as non-receptor type protein tyrosine kinases (e.g., c-Src and Janus kinase (JAK)-2)), protein kinase C, and protein kinase A (57). Signaling through TLR4-mediated pathways is also associated with the activation of various enzymes, such as nuclear factor (NF)-B-inducing kinase (NIK), phosphoinositide 3-kinase (PI3K), phosphoinositide-dependent kinase 1 (PDK1), Akt, and MAPKs (such as extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38) (57). These proteins play central roles in controlling several redox-sensitive transcription factors such as NF-B, cAMP responsive element binding protein (CREB), and AP-1. The inhibition of Akt has been found to prevent NF-B activation by suppressing IKK phosphorylation and subsequent degradation of IB.
4.2. Phagocytosis
The prime function of monocytes and macrophages in innate host defense is known as phagocytosis, a process in which pathogen-infected or apoptotic cells are engulfed into a cytoplasmic compartment in receptor-mediated or non-receptor-mediated manners. Although phagocytic cells further contribute to the induction of inflammatory responses by producing various inflammatory cytokines and mediators, these cells function to remove inflammatory materials by up-regulating phagocytosis. Receptors known to regulate phagocytic function in macrophages include Fc receptors, such as FcRI and FcRIIIa, which are associated with the low molecular weight -subunit and bear immunoreceptor tyrosine-based activation motifs (ITAMs) (58). The phosphorylation of this motif plays a critical role in recruiting several signaling enzymes and adaptor molecules that are required for phagocytosis. One of the major enzymes that phosphorylates ITAMs is Src kinase. After activation of Src kinase, additional signaling enzymes, including PIP3-dependent signaling enzymes such as PI3K, PDK1, and Akt, form biochemically active complexes. Ganesan et al. (2004) found a novel role for Akt in Fc receptor-mediated phagocytosis (23). This study demonstrated that myristoylated Akt but not dominant-negative CAAX-Akt significantly increased phagocytosis by activating p70S6K (23). Rac has also been reported to act as an upstream regulator of p70S6K (59). Akt-mediated phagocytosis is thus thought to be regulated by various substrate proteins such as Rac and p70S6K. More interestingly, Akt1 plays a critical role in the modulation of intracellular growth of phagocytosed bacteria in macrophages (60). To this end, Neefjes et al. screened inhibitors of signaling enzymes for anti-bacterial activity against intracellular bacteria such as Salmonella typhimurium, and two inhibitors targeted to Akt1, H-89 and ETB067, were found to be the most promising drugs (60). The results of this study further demonstrate that Akt1 regulates intracellular survival of Salmonella typhimurium via SopB by modulating the actin cytoskeleton through PAK4 and modulating phagosome-lysosome function through the AS160-RAB14 pathway (60). Because the doses of ETB067 and its derivatives tested did not affect mouse viability or cause any detectable tissue damage, the authors of this study suggested that Akt1 could be targeted for development of novel antibiotics with no side effects (60). Akt has also been reported to play a critical role in controlling the apoptosis of macrophages that have phagocytosed bacteria such as Salmonella typhimurium (61). Similar to the general apoptotic pathway, infection with S. typhimurium stimulated a signaling cascade composed of Rho-GTPases, c-Jun N-terminal kinase (JNK), p38, Akt and Raf-1 (61).
4.3. Macrophage migration and chemotaxis
Migration of macrophages to the proximity of inflamed areas or tumors is an important immunobiological event. To clear apoptotic bodies, macrophages must interact with various pathogens or cancer cells; migration thus plays a critical role in the ability of macrophages to encounter their phagocytic targets. Macrophage migration is usually modulated by chemokines such as colony stimulating factor (CSF)-1, growth factors such as insulin-like growth factor (IGF-1), adhesion molecules such as LFA-1 and integrins, and surface proteoglycans such as osteoprotegerin (62). Stimulation of macrophages by chemokines and growth factors through chemokine receptors, a subfamily of G-protein-coupled receptors, results in the activation of a variety of intracellular signaling cascades composed of PI3K, PTEN, Rho A, PKC, LIM domain kinase (LIMK), syndecan, and cofilin (62-66). Although the exact molecular mechanisms driving macrophage chemotaxis are not clearly defined, several lines of evidence obtained using molecular biological and pharmacological inhibitory strategies suggest that Akt acts as an upstream signaling regulator of intracellular chemotactic processes. First, knocking down Akt2 expression resulted in a strong impairment in chemotaxis and migration of monocytic THP-1 cells and mouse peritoneal macrophages to CSF-1 and MCP-1 (64). Second, Akt2 siRNA strikingly reduced both actin polymerization and the phosphorylation of PKC and LIMK/cofilin, which are essential events for chemotaxis (64). Furthermore, cryptotanshinone, the major tanshinone isolated from Salvia miltiorrhiza Bungea, a strong anti-inflammatory drug, impaired chemotactic migration of macrophages to complement 5a (C5a) or macrophage inflammatory protein-1 by inhibiting PI3K (p110) membrane translocation and Akt phosphorylation (67). Similarly, osteoprotegerin-stimulated monocyte chemotaxis is associated with signaling events mediated by protein kinase C, PI3K/Akt, and tyrosine kinase via syndecan-1 (62).
4.4. LPS tolerance
Activation of macrophages by LPS triggers a negative feedback regulatory pathway involved in maintaining balanced inflammatory responses. The two major events that have been demonstrated to provide this negative feedback are regulation of TLR4 gene expression and activation of negative modulators including suppressor of cytokine signaling 1 (SOCS1) and interleukin-1 receptor-associated kinase-M (IRAK-M) (68, 69). Strong induction of these responses is linked to LPS tolerance, and defects in these responses promote hyperresponsiveness to LPS and consequently, suppress the development of endotoxin tolerance (68). Numerous studies have added to the understanding of the major signaling enzymes that mediate these negative regulatory responses. For example, activation of the PI3K/Akt pathway has been shown to block LPS-induced MAPK and NF-B signaling cascades in monocytes and dendritic cells, resulting in diminished secretion of pro-inflammatory cytokines (70). More interestingly, Akt1-deficient macrophages demonstrate enhanced responsiveness to endotoxin, and Akt1-deficient mice do not exhibit LPS tolerance in vivo (71). Tsatsanis et al. found that the key molecules regulating this enhanced sensitivity to LPS are microRNAs (71). Indeed, expression levels of miR-155 and let-72 are remarkably different between wild type and Akt1-deficient mice, and these molecules have been demonstrated to modulate the expression levels of SOCS-1 and TLR4 (71). These findings suggest that Akt1 may modulate LPS sensitivity or tolerance by regulating miR-155 and let-72, resulting in subsequent regulation of TLR4 and SOCS1 expression.
5. DEVELOPMENT OF AKT INHIBITORS AS NEW IMMUNOSUPPRESSIVE DRUGS
5.1. Akt inhibitor development
Understanding the functional and biological significance of Akt in tumorigenesis has led to the development of novel Akt inhibitors. For several years, greatly increased numbers of chemical compounds have been designed and synthesized as novel inhibitors of Akt. Structural understanding of the functions of Akt has allowed the development of selective and strong inhibitors that are structurally optimized to bind target areas such as the ATP binding motif or other allosteric sites (72, 73). GSK690693, Se,Se'-1,4-phenylenebis(1,2-ethanediyl)bisisoselenourea, 4-(4-aminopiperidin-1-yl)-7H-pyrrolo(2,3-d)pyrimidines, orally bioavailable indazole-pyridine series, a series of N(1)-(5-(heterocyclyl)-thiazol-2-yl)-3-(4-trifluoromethylphenyl)-1,2-propanediamines, 5-methyl-4-phenyl-1H-pyrazole, tetrasubstituted pyridines, aminofurazans, 2,3,5-trisubstituted pyridines, and 2,3,5-trisubstituted pyridines are examples of recently developed Akt inhibitors with IC50 values ranging from 0.001 to 50 M (74-77). In addition to direct assessment of enzymatic activity, the biological activities of these inhibitors have mostly been tested in cancer and cardiovascular disease settings; for example, studies have addressed the ability of Akt inhibitors to reduce hypotension and to arrest tumor growth in human breast carcinoma, colon cancer, and glioblastoma (74, 76). Because no trials have assessed the immunopharmacological efficacy of these inhibitors under inflammatory conditions in vitro and in vivo, systematic approaches could lead to the discovery of promising immunosuppressive or anti-inflammatory drugs that target the pivotal role of Akt during inflammatory responses.
5.2. Akt inhibitors that inhibit production of inflammatory mediators
Although few experimental trials of selective Akt inhibitors have been reported, a large amount of evidence suggest that naturally occurring anti-inflammatory agents and plant extracts act by suppressing the PI3K/Akt pathway (Table 3 and 4). For example, Eleutherococcus senticosus extract has been reported to attenuate LPS-induced iNOS expression by inhibiting the Akt and JNK pathways in murine macrophages (78). It has been reported that treatment with a 70% ethanol extract of Acer tegmentosum results in a dose-dependent reduction in the production of NO, TNF-, and PGE2 in LPS-activated RAW264.7 cells and peritoneal macrophages through a transcriptional mechanism (79). E. senticosus extract was further shown to regulate the activation of NF-B, AP-1, and CREB by effectively inhibiting upstream inflammatory signals, including Akt, p38, and JNK (79). Notably, treatment with an aqueous extract of Dichroa febrifuga was shown to result in a decrease in inflammatory mediator production in LPS-activated peritoneal macrophages by suppressing the activity of IKK/IB/NF-B and the phosphorylation of Akt, ERK1/2, and JNK (80). Furthermore, the inhibitory effects of tetramethylpyrazine on LPS-induced over-production of NO and iNOS in N9 microglial cells have also been found to be mediated by blocking MAPK and PI3K/Akt activation and suppressing ROS production (81). Cordycepin, which is derived from Cordyceps militaris, a traditional medicinal mushroom that parasitizes caterpillars, inhibits the production of NO by suppressing NF-B activation and phosphorylation of Akt and p38, resulting in down-regulation of iNOS and COX-2 gene expression (82). Natural products and chemical compounds that inhibit Akt are summarized in Table II.
5.3. Akt inhibitors with in vivo therapeutic effects in inflammatory models
Acute and chronic mouse and rat models have been widely used to investigate the efficacy of potential anti-inflammatory agents identified in in vitro screens. In these models, croton oil, carageenan, arachidonic acid, and collagen have been employed to induce inflammation (51, 83). Similar to the results of in vitro experiments, histamine, prostaglandins and some pro-inflammatory cytokines, such as TNF- and IL-1, were shown to be important in boosting inflammatory symptoms (51). Septic shock provides a representative model of acute inflammation triggered by Gram-negative bacteria-derived endotoxins like LPS that results in significant production of TNF- and NO. In the ear edema model, inflammation is acutely induced by croton oil and arachidonic acid (84). Rat and mouse models of arthritis induced by adjuvant containing type II collagen or Mycobacteria are also used as representative chronic inflammatory models for drug efficacy tests (54).
Few studies have examined the relevance of Akt in the onset of septic shock or sepsis. The Akt inhibitory compound ferulaldehyde, a natural intermediate of polyphenol metabolism of intestinal microflora, enhances the survival rate of LPS-treated mice (85), and endotoxin-induced cardiac dysfunction and lethality are closely associated with the activity of PI3K and the Akt pathway (86), suggesting a potential role for Akt in acute inflammatory septic shock. Despite these findings, no reports on the therapeutic activity of known Akt inhibitors in septic shock have been published. Recently, however, the novel Akt inhibitor JS-III-049 was shown to protect mice against lethal responses to LPS/D-galactosamine (D-GalN) (28), suggesting that these Akt inhibitors may be considered a new class of therapeutic drugs to treat septic shock or endotoxemia.
Similarly, the pathological roles of Akt in rheumatoid arthritis have not been fully elucidated. It has been reported that PI3K deficiency does not alter the recruitment of inflammatory cells, but significantly reduces cartilage damage through reduced expression of matrix metalloproteinases in fibroblasts and chondrocytes (87). Imatinib mesylate, a specific inhibitor of the PDGF receptor tyrosine kinase, the novel A3AR agonist CF502, which has high affinity and selectivity for the human A3AR, and the colchicine-derived compound CT20126 have been reported to mediate anti-arthritic activity by suppressing the Akt pathway (88). More interestingly, adenovirus-mediated PTEN gene transfer remarkably attenuated collagen-induced arthritis in rats and simultaneously suppressed the PI3K/Akt pathway in rheumatoid arthritis synovial tissue (89). Although these findings clearly implicate the Akt pathway as a therapeutic target for the treatment of rheumatoid arthritis, no trials of specific Akt inhibitors have been reported. Further evaluation of the therapeutic use of Akt inhibitors will provide an opportunity to begin to develop a novel class of anti-rheumatoid arthritis drugs.
5.4. Novel Akt binding site: implications for development of a novel class of anti-inflammatory Akt inhibitors
Although novel Akt inhibitors are often tested for their anti-cancer activity, few studies have examined the therapeutic activity of these newly developed inhibitors in various inflammatory diseases. Numerous lines of evidence indicating that Akt plays a critical role in the regulation of macrophage-mediated immune responses suggest that novel Akt inhibitors may also be useful in the treatment of a variety of immunological diseases. Indeed, our group found that the dihydroxyl benzene metabolite hydroquinone and its derivatives demonstrated strong anti-inflammatory properties in the LPS/D-GalN-induced septic shock model by suppressing activation of NF-B (28). Interestingly, these compounds were found to significantly inhibit Akt kinase activity by binding to the sulfhydryl group of C310 (28). That the sulfhydryl group of C310 serves as a novel allosteric site was demonstrated by the ability of hydroquinone derivatives to dramatically reduce the phosphorylation of T308 and S473 (28). Due to this pharmacological activity, the survival rate of mice undergoing endotoxin shock was remarkably enhanced by hydroquinone derivatives (28). Akt inhibitory compounds have also been demonstrated to strongly suppress the up-regulation of serum TNF-, a major septic shock-causing pro-inflammatory cytokine that results from NF-B activation, in response to LPS and D-GalN treatment (90, 91). These results suggest that in addition to the in vivo anti-inflammatory activities of Akt inhibitors that target C310, the biochemical and pharmacological significance of the C310 residue as a novel allosteric site could be considerable. The C310 reside was also proposed as a pharmacological target residue by the Yu group (92, 93). The Yu group explored the mechanisms driving the anti-cancer activity of natural antibiotics such as lactoquinomycin and demonstrated that similar to hydroquinone derivatives, these drugs function by targeting the Akt residue C310 (92). Derivatives of these antibiotics also exhibited Akt inhibitory and anti-cancer activities (93), confirming the critical function of residue C310 in the regulation of Akt activity. Indeed, it has been proposed that pyranonaphthoquinone lactones can be considered a new class of Akt-selective kinase inhibitors that are capable of alkylating a regulatory loop cysteine with IC50 values of 0.04 to 1.5 M (93). Ongoing studies aim to prove the anti-inflammatory activities of these novel Akt inhibitors.
6. SUMMARY AND PERSPECTIVE
Numerous studies of the involvement of Akt in phagocytosis, intracellular bacterial infections, LPS tolerance, the production of inflammatory cytokine and mediators, and macrophage migration have revealed the important role of Akt in macrophage-mediated innate immunity. Importantly, a variety of inflammatory diseases such as rheumatoid arthritis, atherosclerosis, and osteoporosis are regulated by macrophage activation. The critical role of Akt in macrophage activation led us to consider that inhibiting Akt activity may be a useful therapeutic strategy in macrophage-mediated diseases. Recently, a few researchers have investigated the possibility that Akt inhibitors could be useful for this purpose. Considering that Akt-C310-targeted hydroquinone derivatives display strong anti-inflammatory and anti-septic shock activities, future studies will aim to develop these compounds as Akt-targeted immunomodulatory drugs. We expect that novel and safe Akt inhibitors with strong immunosuppressive and anti-inflammatory properties will be developed in the near future.
7. ACKNOWLEDGEMENT
Yong Gyu Lee and Jaehwi Lee equally contributed to this article. This work was supported by the Ministry of Commerce, Industry and Energy (MOCIE) and Korea Industrial Technology Foundation (KOTEF) through the Human Resource Training Project for Regional Innovation (to J. Y. C.).
8. REFERENCES
1. L. E. Bermudez: Immunobiology of Mycobacterium avium infection. Eur J Clin Microbiol Infect Dis, 13, 1000-6 (1994)
doi:10.1007/BF02111501
2. M. Naumann: Nuclear factor-kappa B activation and innate immune response in microbial pathogen infection. Biochem Pharmacol, 60, 1109-14 (2000)
doi:10.1016/S0006-2952(00)00390-7
3. R. Medzhitov and C. A. Janeway, Jr.: Innate immune recognition and control of adaptive immune responses. Semin Immunol, 10, 351-3 (1998)
doi:10.1006/smim.1998.0136
4. M. F. Linton and S. Fazio: Macrophages, inflammation, and atherosclerosis. Int J Obes Relat Metab Disord, 27 Suppl 3, S35-40 (2003)
doi:10.1038/sj.ijo.0802498
5. C. A. Biron: Role of early cytokines, including alpha and beta interferons (IFN-alpha/beta), in innate and adaptive immune responses to viral infections. Semin Immunol, 10, 383-90 (1998)
doi:10.1006/smim.1998.0138
6. F. Sanchez-Madrid and R. Gonzalez-Amaro: Drugs, inflammation and cell adhesion receptors. Expert Opin Pharmacother, 2, 3-17 (2001)
doi:10.1517/14656566.2.1.3
7. K. A. Beningo and Y. L. Wang: Fc-receptor-mediated phagocytosis is regulated by mechanical properties of the target. J Cell Sci, 115, 849-56 (2002)
8. S. E. Byeon, J. Lee, E. Lee, S. Y. Lee, E. K. Hong, Y. E. Kim and J. Y. Cho: Functional activation of macrophages, monocytes and splenic lymphocytes by polysaccharide fraction from Tricholoma matsutake. Arch Pharm Res, 32, 1565-72 (2009)
doi:10.1007/s12272-009-2108-y
9. Y. Ukawa, H. Ito and M. Hisamatsu: Antitumor effects of (1-->3)-beta-D-glucan and (1-->6)-beta-D-glucan purified from newly cultivated mushroom, Hatakeshimeji (Lyophyllum decastes Sing.). J Biosci Bioeng, 90, 98-104 (2000)
doi:10.1263/jbb.90.98 doi:10.1016/S1389-1723(00)80041-9
10. N. Qureshi, S. N. Vogel, C. Van Way, 3rd, C. J. Papasian, A. A. Qureshi and D. C. Morrison: The proteasome: a central regulator of inflammation and macrophage function. Immunol Res, 31, 243-60 (2005)
doi:10.1385/IR:31:3:243
11. I. Y. Malyshev and A. Shnyra: Controlled modulation of inflammatory, stress and apoptotic responses in macrophages. Curr Drug Targets Immune Endocr Metabol Disord, 3, 1-22 (2003)
doi:10.2174/1568008033340342
12. N. Palaniyar, J. Nadesalingam and K. B. Reid: Pulmonary innate immune proteins and receptors that interact with gram-positive bacterial ligands. Immunobiology, 205, 575-94 (2002)
doi:10.1078/0171-2985-00156
13. J. P. Butchar, K. V. Parsa, C. B. Marsh and S. Tridandapani: Negative regulators of toll-like receptor 4-mediated macrophage inflammatory response. Curr Pharm Des, 12, 4143-53 (2006)
doi:10.2174/138161206778743574
14. A. Yoshimura: Signal transduction of inflammatory cytokines and tumor development. Cancer Sci, 97, 439-47 (2006)
doi:10.1111/j.1349-7006.2006.00197.x
15. Z. Z. Yang, O. Tschopp, A. Baudry, B. Dummler, D. Hynx and B. A. Hemmings: Physiological functions of protein kinase B/Akt. Biochem Soc Trans, 32, 350-4 (2004)
doi:10.1042/BST0320350
16. B. Dummler and B. A. Hemmings: Physiological roles of PKB/Akt isoforms in development and disease. Biochem Soc Trans, 35, 231-5 (2007)
doi:10.1042/BST0350231
17. E. Fayard, L. A. Tintignac, A. Baudry and B. A. Hemmings: Protein kinase B/Akt at a glance. J Cell Sci, 118, 5675-8 (2005)
doi:10.1242/jcs.02724
18. G. Song, G. Ouyang and S. Bao: The activation of Akt/PKB signaling pathway and cell survival. J Cell Mol Med, 9, 59-71 (2005)
doi:10.1111/j.1582-4934.2005.tb00337.x
19. G. D. Cartee and J. F. Wojtaszewski: Role of Akt substrate of 160 kDa in insulin-stimulated and contraction-stimulated glucose transport. Appl Physiol Nutr Metab, 32, 557-66 (2007)
doi:10.1139/H07-026
20. D. P. Brazil, J. Park and B. A. Hemmings: PKB binding proteins. Getting in on the Akt. Cell, 111, 293-303 (2002)
doi:10.1016/S0092-8674(02)01083-8
21. V. Factor, A. L. Oliver, G. R. Panta, S. S. Thorgeirsson, G. E. Sonenshein and M. Arsura: Roles of Akt/PKB and IKK complex in constitutive induction of NF-kappaB in hepatocellular carcinomas of transforming growth factor alpha/c-myc transgenic mice. Hepatology, 34, 32-41 (2001)
doi:10.1053/jhep.2001.25270
22. Q. Chen, D. W. Powell, M. J. Rane, S. Singh, W. Butt, J. B. Klein and K. R. Mcleish: Akt phosphorylates p47phox and mediates respiratory burst activity in human neutrophils. J Immunol, 170, 5302-8 (2003)
23. L. P. Ganesan, G. Wei, R. A. Pengal, L. Moldovan, N. Moldovan, M. C. Ostrowski and S. Tridandapani: The serine/threonine kinase Akt Promotes Fc gamma receptor-mediated phagocytosis in murine macrophages through the activation of p70S6 kinase. J Biol Chem, 279, 54416-25 (2004)
doi:10.1074/jbc.M408188200
24. E. Nijhuis, J. W. Lammers, L. Koenderman and P. J. Coffer: Src kinases regulate PKB activation and modulate cytokine and chemoattractant-controlled neutrophil functioning. J Leukoc Biol, 71, 115-24 (2002)
25. B. Tilton, M. Andjelkovic, S. A. Didichenko, B. A. Hemmings and M. Thelen: G-Protein-coupled receptors and Fcgamma-receptors mediate activation of Akt/protein kinase B in human phagocytes. J Biol Chem, 272, 28096-101 (1997)
doi:10.1074/jbc.272.44.28096
26. C. Tan, A. Mui and S. Dedhar: Integrin-linked kinase regulates inducible nitric oxide synthase and cyclooxygenase-2 expression in an NF-kappa B-dependent manner. J Biol Chem, 277, 3109-16 (2002)
doi:10.1074/jbc.M108673200
27. D. L. Laskin, L. Fakhrzadeh, D. E. Heck, D. Gerecke and J. D. Laskin: Upregulation of phosphoinositide 3-kinase and protein kinase B in alveolar macrophages following ozone inhalation. Role of NF-kappaB and STAT-1 in ozone-induced nitric oxide production and toxicity. Mol Cell Biochem, 234-235, 91-8 (2002)
doi:10.1023/A:1015963217045
28. J. Y. Lee, Y. G. Lee, J. Lee, K. J. Yang, A. R. Kim, J. Y. Kim, M. H. Won, J. Park, B. C. Yoo, S. Kim, W. J. Cho and J. Y. Cho: Akt Cys-310-targeted inhibition by hydroxylated benzene derivatives is tightly linked to their immunosuppressive effects. J Biol Chem, 285, 9932-48 (2010)
doi:10.1074/jbc.M109.074872
29. K. Jiang, B. Zhong, C. Ritchey, D. L. Gilvary, E. Hong-Geller, S. Wei and J. Y. Djeu: Regulation of Akt-dependent cell survival by Syk and Rac. Blood, 101, 236-44 (2003)
doi:10.1182/blood-2002-04-1251
30. D. Kim, H. C. Dan, S. Park, L. Yang, Q. Liu, S. Kaneko, J. Ning, L. He, H. Yang, M. Sun, S. V. Nicosia and J. Q. Cheng: AKT/PKB signaling mechanisms in cancer and chemoresistance. Front Biosci, 10, 975-87 (2005)
doi:10.2741/1592
31. M. Hanada, J. Feng and B. A. Hemmings: Structure, regulation and function of PKB/AKT--a major therapeutic target. Biochim Biophys Acta, 1697, 3-16 (2004)
doi:10.1016/j.bbapap.2003.11.009
32. P. Luthra, D. Sun, M. Wolfgang and B. He: AKT1-dependent activation of NF-kappaB by the L protein of parainfluenza virus 5. J Virol, 82, 10887-95 (2008)
doi:10.1128/JVI.00806-08
33. Z. Z. Yang, O. Tschopp, M. Hemmings-Mieszczak, J. Feng, D. Brodbeck, E. Perentes and B. A. Hemmings: Protein kinase B alpha/Akt1 regulates placental development and fetal growth. J Biol Chem, 278, 32124-31 (2003)
doi:10.1074/jbc.M302847200
34. Z. Z. Yang, O. Tschopp, N. Di-Poi, E. Bruder, A. Baudry, B. Dummler, W. Wahli and B. A. Hemmings: Dosage-dependent effects of Akt1/protein kinase Balpha (PKBalpha) and Akt3/PKBgamma on thymus, skin, and cardiovascular and nervous system development in mice. Mol Cell Biol, 25, 10407-18 (2005)
doi:10.1128/MCB.25.23.10407-10418.2005
35. H. Cho, J. L. Thorvaldsen, Q. Chu, F. Feng and M. J. Birnbaum: Akt1/PKBalpha is required for normal growth but dispensable for maintenance of glucose homeostasis in mice. J Biol Chem, 276, 38349-52 (2001)
doi:10.1074/jbc.C100462200
36. K. F. Leavens, R. M. Easton, G. I. Shulman, S. F. Previs and M. J. Birnbaum: Akt2 is required for hepatic lipid accumulation in models of insulin resistance. Cell Metab, 10, 405-18 (2009)
doi:10.1016/j.cmet.2009.10.004
37. X. D. Peng, P. Z. Xu, M. L. Chen, A. Hahn-Windgassen, J. Skeen, J. Jacobs, D. Sundararajan, W. S. Chen, S. E. Crawford, K. G. Coleman and N. Hay: Dwarfism, impaired skin development, skeletal muscle atrophy, delayed bone development, and impeded adipogenesis in mice lacking Akt1 and Akt2. Genes Dev, 17, 1352-65 (2003)
doi:10.1101/gad.1089403
38. Y. Nonaka, M. Miyajima, I. Ogino, M. Nakajima and H. Arai: Analysis of neuronal cell death in the cerebral cortex of H-Tx rats with compensated hydrocephalus. J Neurosurg Pediatr, 1, 68-74 (2008)
doi:10.3171/PED-08/01/068
39. M. Schleicher, J. Yu, T. Murata, B. Derakhshan, D. Atochin, L. Qian, S. Kashiwagi, A. Di Lorenzo, K. D. Harrison, P. L. Huang and W. C. Sessa: The Akt1-eNOS axis illustrates the specificity of kinase-substrate relationships in vivo. Sci Signal, 2, ra41 (2009)
doi:10.1126/scisignal.2000343
40. O. Kaidanovich and H. Eldar-Finkelman: The role of glycogen synthase kinase-3 in insulin resistance and type 2 diabetes. Expert Opin Ther Targets, 6, 555-61 (2002)
doi:10.1517/14728222.6.5.555
41. H. Hacker and M. Karin: Regulation and function of IKK and IKK-related kinases. Sci STKE, 2006, re13 (2006)
doi:10.1126/stke.3572006re13
42. T. Asano, M. Fujishiro, A. Kushiyama, Y. Nakatsu, M. Yoneda, H. Kamata and H. Sakoda: Role of phosphatidylinositol 3-kinase activation on insulin action and its alteration in diabetic conditions. Biol Pharm Bull, 30, 1610-6 (2007)
doi:10.1248/bpb.30.1610
43. Q. Zhou, S. E. Leeman and S. Amar: Signaling mechanisms involved in altered function of macrophages from diet-induced obese mice affect immune responses. Proc Natl Acad Sci U S A, 106, 10740-5 (2009)
doi:10.1073/pnas.0904412106
44. S. R. Datta, A. Brunet and M. E. Greenberg: Cellular survival: a play in three Akts. Genes Dev, 13, 2905-27 (1999)
doi:10.1101/gad.13.22.2905
45. H. Shiratsuchi and M. D. Basson: Akt2, but not Akt1 or Akt3 mediates pressure-stimulated serum-opsonized latex bead phagocytosis through activating mTOR and p70 S6 kinase. J Cell Biochem, 102, 353-67 (2007)
doi:10.1002/jcb.21295
46. M. Hallman, M. Ramet and R. A. Ezekowitz: Toll-like receptors as sensors of pathogens. Pediatr Res, 50, 315-21 (2001)
doi:10.1203/00006450-200109000-00004
47. B. Beutler, K. Hoebe, X. Du and R. J. Ulevitch: How we detect microbes and respond to them: the Toll-like receptors and their transducers. J Leukoc Biol, 74, 479-85 (2003)
doi:10.1189/jlb.0203082
48. E. H. Kim and D. K. Rhee: Anti-oxdative properties of ginseng. J Ginseng Res, 33, 1-7 (2009)
49. M. Funakoshi-Tago, N. Kamada, T. Shimizu, Y. Hashiguchi, K. Tago, Y. Sonoda and T. Kasahara: TRAF6 negatively regulates TNFalpha-induced NF-kappaB activation. Cytokine, 45, 72-9 (2009)
doi:10.1016/j.cyto.2008.10.010
50. D. G. Jackson-Bernitsas, H. Ichikawa, Y. Takada, J. N. Myers, X. L. Lin, B. G. Darnay, M. M. Chaturvedi and B. B. Aggarwal: Evidence that TNF-TNFR1-TRADD-TRAF2-RIP-TAK1-IKK pathway mediates constitutive NF-kappaB activation and proliferation in human head and neck squamous cell carcinoma. Oncogene, 26, 1385-97 (2007)
doi:10.1038/sj.onc.1209945
51. Y. H. Kong, Y. C. Lee and S. Y. Choi: Neuroprotective and anti-inflammatory effects of phenolic compounds in Panax ginseng C. A. Meyer. J Ginseng Res, 33, 111-114 (2009)
52. K. H. Kim, S. A. Jang, K. S. Kim, S. Park, H. J. Park, S. J. Lee, S. Pyo and E. H. Sohn: Effects of non-saponin red ginseng components (NSRG) on functions of macrophages isolated from young and aged mice. J Ginseng Res, 33, 177-182 (2009)
53. B. H. Kim and J. Y. Cho: Anti-inflammatory effect of honokiol is mediated by PI3K/Akt pathway suppression. Acta Pharmacol Sin, 29, 113-22 (2008)
doi:10.1111/j.1745-7254.2008.00725.x
54. J. H. Jin, H. Lim, S. Y. Kwon, K. H. Son and H. P. Kim: Anti-inflammatory activity of the total flavonoid fraction from Broussonetia papyrifera in combination with Lonicera japonica. Biomol Ther, 18, 197-204 (2010)
doi: 10.4062/biomolther.2010.18.2.197
55. Y. G. Lee, W. M. Lee, J. Y. Kim, J. Y. Lee, I. K. Lee, B. S. Yun, M. H. Rhee and J. Y. Cho: Src kinase-targeted anti-inflammatory activity of davallialactone from Inonotus xeranticus in lipopolysaccharide-activated RAW264.7 cells. Br J Pharmacol, 154, 852-63 (2008)
doi:10.1038/bjp.2008.136
56. S. K. Gurung, H. Lim, H. P. Kim and H. Park: Structural alterations of wogonin significantly reduce the inhibitory activity against COX-2 catalyzed PGE2 production from LPS-induced RAW264.7 cells. Biomol Ther, 17, 418-421 (2009)
doi: 10.4062/biomolther.2010.18.2.197
57. M. Fujihara, M. Muroi, K. Tanamoto, T. Suzuki, H. Azuma and H. Ikeda: Molecular mechanisms of macrophage activation and deactivation by lipopolysaccharide: roles of the receptor complex. Pharmacol Ther, 100, 171-94 (2003)
doi:10.1016/j.pharmthera.2003.08.003
58. J. V. Ravetch and S. Bolland: IgG Fc receptors. Annu Rev Immunol, 19, 275-90 (2001)
doi:10.1146/annurev.immunol.19.1.275
59. G. Y. Oudit, H. Sun, B. G. Kerfant, M. A. Crackower, J. M. Penninger and P. H. Backx: The role of phosphoinositide-3 kinase and PTEN in cardiovascular physiology and disease. J Mol Cell Cardiol, 37, 449-71 (2004)
doi:10.1016/j.yjmcc.2004.05.015
60. C. Kuijl, N. D. Savage, M. Marsman, A. W. Tuin, L. Janssen, D. A. Egan, M. Ketema, R. Van Den Nieuwendijk, S. J. Van Den Eeden, A. Geluk, A. Poot, G. Van Der Marel, R. L. Beijersbergen, H. Overkleeft, T. H. Ottenhoff and J. Neefjes: Intracellular bacterial growth is controlled by a kinase network around PKB/AKT1. Nature, 450, 725-30 (2007)
doi:10.1038/nature06345
61. M. Forsberg, R. Blomgran, M. Lerm, E. Sarndahl, S. M. Sebti, A. Hamilton, O. Stendahl and L. Zheng: Differential effects of invasion by and phagocytosis of Salmonella typhimurium on apoptosis in human macrophages: potential role of Rho-GTPases and Akt. J Leukoc Biol, 74, 620-9 (2003)
doi:10.1189/jlb.1202586
62. B. A. Mosheimer, N. C. Kaneider, C. Feistritzer, A. M. Djanani, D. H. Sturn, J. R. Patsch and C. J. Wiedermann: Syndecan-1 is involved in osteoprotegerin-induced chemotaxis in human peripheral blood monocytes. J Clin Endocrinol Metab, 90, 2964-71 (2005)
doi:10.1210/jc.2004-1895
63. V. Furundzija, J. Fritzsche, J. Kaufmann, H. Meyborg, E. Fleck, K. Kappert and P. Stawowy: IGF-1 increases macrophage motility via PKC/p38-dependent alphavbeta3-integrin inside-out signaling. Biochem Biophys Res Commun, 394, 786-91 (2010)
doi:10.1016/j.bbrc.2010.03.072
64. B. Zhang, Y. Ma, H. Guo, B. Sun, R. Niu, G. Ying and N. Zhang: Akt2 is required for macrophage chemotaxis. Eur J Immunol, 39, 894-901 (2009)
doi:10.1002/eji.200838809
65. E. A. Papakonstanti, O. Zwaenepoel, A. Bilancio, E. Burns, G. E. Nock, B. Houseman, K. Shokat, A. J. Ridley and B. Vanhaesebroeck: Distinct roles of class IA PI3K isoforms in primary and immortalised macrophages. J Cell Sci, 121, 4124-33 (2008)
doi:10.1242/jcs.032763
66. E. A. Papakonstanti, A. J. Ridley and B. Vanhaesebroeck: The p110delta isoform of PI 3-kinase negatively controls RhoA and PTEN. EMBO J, 26, 3050-61 (2007)
doi:10.1038/sj.emboj.7601763
67. M. J. Don, J. F. Liao, L. Y. Lin and W. F. Chiou: Cryptotanshinone inhibits chemotactic migration in macrophages through negative regulation of the PI3K signaling pathway. Br J Pharmacol, 151, 638-46 (2007)
doi:10.1038/sj.bjp.0707271
68. H. Fan and J. A. Cook: Molecular mechanisms of endotoxin tolerance. J Endotoxin Res, 10, 71-84 (2004)
doi:10.1179/096805104225003997 doi:10.1177/09680519040100020301
69. V. Zacharioudaki, A. Androulidaki, A. Arranz, G. Vrentzos, A. N. Margioris and C. Tsatsanis: Adiponectin promotes endotoxin tolerance in macrophages by inducing IRAK-M expression. J Immunol, 182, 6444-51 (2009)
doi:10.4049/jimmunol.0803694
70. A. Arranz, A. Androulidaki, V. Zacharioudaki, C. Martinez, A. N. Margioris, R. P. Gomariz and C. Tsatsanis: Vasoactive intestinal peptide suppresses toll-like receptor 4 expression in macrophages via Akt1 reducing their responsiveness to lipopolysaccharide. Mol Immunol, 45, 2970-80 (2008)
doi:10.1016/j.molimm.2008.01.023
71. A. Androulidaki, D. Iliopoulos, A. Arranz, C. Doxaki, S. Schworer, V. Zacharioudaki, A. N. Margioris, P. N. Tsichlis and C. Tsatsanis: The kinase Akt1 controls macrophage response to lipopolysaccharide by regulating microRNAs. Immunity, 31, 220-31 (2009)
doi:10.1016/j.immuni.2009.06.024
72. V. Calleja, M. Laguerre and B. Larijani: 3-D structure and dynamics of protein kinase B-new mechanism for the allosteric regulation of an AGC kinase. J Chem Biol, 2, 11-25 (2009)
doi:10.1007/s12154-009-0016-8
73. C. C. Kumar and V. Madison: AKT crystal structure and AKT-specific inhibitors. Oncogene, 24, 7493-501 (2005)
doi:10.1038/sj.onc.1209087
74. D. A. Heerding, N. Rhodes, J. D. Leber, T. J. Clark, R. M. Keenan, L. V. Lafrance, M. Li, I. G. Safonov, D. T. Takata, J. W. Venslavsky, D. S. Yamashita, A. E. Choudhry, R. A. Copeland, Z. Lai, M. D. Schaber, P. J. Tummino, S. L. Strum, E. R. Wood, D. R. Duckett, D. Eberwein, V. B. Knick, T. J. Lansing, R. T. Mcconnell, S. Zhang, E. A. Minthorn, N. O. Concha, G. L. Warren and R. Kumar: Identification of 4-(2-(4-amino-1,2,5-oxadiazol-3-yl)-1-ethyl-7-{((3S)-3-piperidinylmethyl)o xy}-1H-imidazo(4,5-c)pyridin-4-yl)-2-methyl-3-butyn-2-ol (GSK690693), a novel inhibitor of AKT kinase. J Med Chem, 51, 5663-79 (2008)
doi:10.1021/jm8004527
75. M. B. Rouse, M. A. Seefeld, J. D. Leber, K. C. Mcnulty, L. Sun, W. H. Miller, S. Zhang, E. A. Minthorn, N. O. Concha, A. E. Choudhry, M. D. Schaber and D. A. Heerding: Aminofurazans as potent inhibitors of AKT kinase. Bioorg Med Chem Lett, 19, 1508-11 (2009)
doi:10.1016/j.bmcl.2009.01.002
76. G. D. Zhu, V. B. Gandhi, J. Gong, S. Thomas, K. W. Woods, X. Song, T. Li, R. B. Diebold, Y. Luo, X. Liu, R. Guan, V. Klinghofer, E. F. Johnson, J. Bouska, A. Olson, K. C. Marsh, V. S. Stoll, M. Mamo, J. Polakowski, T. J. Campbell, R. L. Martin, G. A. Gintant, T. D. Penning, Q. Li, S. H. Rosenberg and V. L. Giranda: Syntheses of potent, selective, and orally bioavailable indazole-pyridine series of protein kinase B/Akt inhibitors with reduced hypotension. J Med Chem, 50, 2990-3003 (2007)
doi:10.1021/jm0701019
77. H. Lin, D. S. Yamashita, R. Xie, J. Zeng, W. Wang, J. Leber, I. G. Safonov, S. Verma, M. Li, L. Lafrance, J. Venslavsky, D. Takata, J. I. Luengo, J. A. Kahana, S. Zhang, K. A. Robell, D. Levy, R. Kumar, A. E. Choudhry, M. Schaber, Z. Lai, B. S. Brown, B. T. Donovan, E. A. Minthorn, K. K. Brown and D. A. Heerding: Tetrasubstituted pyridines as potent and selective AKT inhibitors: Reduced CYP450 and hERG inhibition of aminopyridines. Bioorg Med Chem Lett, 20, 684-8 (2010)
doi:10.1016/j.bmcl.2009.11.061
78. C. H. Jung, H. Jung, Y. C. Shin, J. H. Park, C. Y. Jun, H. M. Kim, H. S. Yim, M. G. Shin, H. S. Bae, S. H. Kim and S. G. Ko: Eleutherococcus senticosus extract attenuates LPS-induced iNOS expression through the inhibition of Akt and JNK pathways in murine macrophage. J Ethnopharmacol, 113, 183-7 (2007)
doi:10.1016/j.jep.2007.05.023
79. T. Yu, J. Lee, Y. G. Lee, S. E. Byeon, M. H. Kim, E. H. Sohn, Y. J. Lee, S. G. Lee and J. Y. Cho: In vitro and in vivo anti-inflammatory effects of ethanol extract from Acer tegmentosum. J Ethnopharmacol, 128, 139-47 (2010)
doi:10.1016/j.jep.2009.12.042
80. S. Y. Park, G. Y. Park, W. S. Ko and Y. Kim: Dichroa febrifuga Lour. inhibits the production of IL-1beta and IL-6 through blocking NF-kappaB, MAPK and Akt activation in macrophages. J Ethnopharmacol, 125, 246-51 (2009)
doi:10.1016/j.jep.2009.07.003
81. H. T. Liu, Y. G. Du, J. L. He, W. J. Chen, W. M. Li, Z. Yang, Y. X. Wang and C. Yu: Tetramethylpyrazine inhibits production of nitric oxide and inducible nitric oxide synthase in lipopolysaccharide-induced N9 microglial cells through blockade of MAPK and PI3K/Akt signaling pathways, and suppression of intracellular reactive oxygen species. J Ethnopharmacol (2010)
doi:10.1016/j.jep.2010.03.037
82. H. G. Kim, B. Shrestha, S. Y. Lim, D. H. Yoon, W. C. Chang, D. J. Shin, S. K. Han, S. M. Park, J. H. Park, H. I. Park, J. M. Sung, Y. Jang, N. Chung, K. C. Hwang and T. W. Kim: Cordycepin inhibits lipopolysaccharide-induced inflammation by the suppression of NF-kappaB through Akt and p38 inhibition in RAW 264.7 macrophage cells. Eur J Pharmacol, 545, 192-9 (2006)
doi:10.1016/j.ejphar.2006.06.047
83. M. L. Deschoolmeester and K. J. Else: Cytokine and chemokine responses underlying acute and chronic Trichuris muris infection. Int Rev Immunol, 21, 439-67 (2002)
doi:10.1080/08830180213278
84. J. Y. Cho, J. D. Yeon, J. Y. Kim, E. S. Yoo, Y. H. Yu and M. H. Park: Hepatoprotection by human epidermal growth factor (hEGF) against experimental hepatitis induced by D-galactosamine (D-galN) or D-GalN/lipopolysaccharide. Biol Pharm Bull, 23, 1243-6 (2000)
85. B. Radnai, Z. Tucsek, Z. Bognar, C. Antus, L. Mark, Z. Berente, F. Gallyas, Jr., B. Sumegi and B. Veres: Ferulaldehyde, a water-soluble degradation product of polyphenols, inhibits the lipopolysaccharide-induced inflammatory response in mice. J Nutr, 139, 291-7 (2009)
doi:10.3945/jn.108.097386
86. W. You, X. Min, X. Zhang, B. Qian, S. Pang, Z. Ding, C. Li, X. Gao, R. Di, Y. Cheng and L. Liu: Cardiac-specific expression of heat shock protein 27 attenuated endotoxin-induced cardiac dysfunction and mortality in mice through a PI3K/Akt-dependent mechanism. Shock, 32, 108-17 (2009)
doi:10.1097/SHK.0b013e318199165d
87. S. Hayer, N. Pundt, M. A. Peters, C. Wunrau, I. Kuhnel, K. Neugebauer, S. Strietholt, J. Zwerina, A. Korb, J. Penninger, L. A. Joosten, S. Gay, T. Ruckle, G. Schett and T. Pap: PI3Kgamma regulates cartilage damage in chronic inflammatory arthritis. FASEB J, 23, 4288-98 (2009)
doi:10.1096/fj.09-135160
88. F. Terabe, M. Kitano, M. Kawai, Y. Kuwahara, T. Hirano, J. Arimitsu, K. Hagihara, Y. Shima, M. Narazaki, T. Tanaka, I. Kawase, H. Sano and A. Ogata: Imatinib mesylate inhibited rat adjuvant arthritis and PDGF-dependent growth of synovial fibroblast via interference with the Akt signaling pathway. Mod Rheumatol, 19, 522-9 (2009)
doi:10.1007/s10165-009-0193-x
89. C. R. Wang, A. L. Shiau, S. Y. Chen, L. L. Lin, M. H. Tai, G. S. Shieh, P. R. Lin, Y. T. Yo, C. H. Lee, S. M. Kuo, M. F. Liu, I. M. Jou, C. Y. Yang, P. C. Shen, H. L. Lee and C. L. Wu: Amelioration of collagen-induced arthritis in rats by adenovirus-mediated PTEN gene transfer. Arthritis Rheum, 58, 1650-6 (2008)
doi:10.1002/art.23517
90. D. Altavilla, G. Squadrito, L. Minutoli, B. Deodato, A. Bova, A. Sardella, P. Seminara, M. Passaniti, G. Urna, S. F. Venuti, A. P. Caputi and F. Squadrito: Inhibition of nuclear factor-kappaB activation by IRFI 042, protects against endotoxin-induced shock. Cardiovasc Res, 54, 684-93 (2002)
doi:10.1016/S0008-6363(02)00276-6
91. K. Takahashi, A. Morikawa, Y. Kato, T. Sugiyama, N. Koide, M. M. Mu, T. Yoshida and T. Yokochi: Flavonoids protect mice from two types of lethal shock induced by endotoxin. FEMS Immunol Med Microbiol, 31, 29-33 (2001)
doi:10.1111/j.1574-695X.2001.tb01582.x
92. L. Toral-Barza, W. G. Zhang, X. Huang, L. A. Mcdonald, E. J. Salaski, L. R. Barbieri, W. D. Ding, G. Krishnamurthy, Y. B. Hu, J. Lucas, V. S. Bernan, P. Cai, J. I. Levin, T. S. Mansour, J. J. Gibbons, R. T. Abraham and K. Yu: Discovery of lactoquinomycin and related pyranonaphthoquinones as potent and allosteric inhibitors of AKT/PKB: mechanistic involvement of AKT catalytic activation loop cysteines. Mol Cancer Ther, 6, 3028-38 (2007)
doi:10.1158/1535-7163.MCT-07-0211
93. E. J. Salaski, G. Krishnamurthy, W. D. Ding, K. Yu, S. S. Insaf, C. Eid, J. Shim, J. I. Levin, K. Tabei, L. Toral-Barza, W. G. Zhang, L. A. Mcdonald, E. Honores, C. Hanna, A. Yamashita, B. Johnson, Z. Li, L. Laakso, D. Powell and T. S. Mansour: Pyranonaphthoquinone lactones: a new class of AKT selective kinase inhibitors alkylate a regulatory loop cysteine. J Med Chem, 52, 2181-4 (2009)
doi:10.1021/jm900075g
94. T. Sugatani and K. A. Hruska: Akt1/Akt2 and mammalian target of rapamycin/Bim play critical roles in osteoclast differentiation and survival, respectively, whereas Akt is dispensable for cell survival in isolated osteoclast precursors. J Biol Chem, 280, 3583-9 (2005)
doi:10.1074/jbc.M410480200
95. N. Kawamura, F. Kugimiya, Y. Oshima, S. Ohba, T. Ikeda, T. Saito, Y. Shinoda, Y. Kawasaki, N. Ogata, K. Hoshi, T. Akiyama, W. S. Chen, N. Hay, K. Tobe, T. Kadowaki, Y. Azuma, S. Tanaka, K. Nakamura, U. I. Chung and H. Kawaguchi: Akt1 in osteoblasts and osteoclasts controls bone remodeling. PLoS One, 2, e1058 (2007)
doi:10.1371/journal.pone.0001058
96. Y. Wang, M. M. Zeigler, G. K. Lam, M. G. Hunter, T. D. Eubank, V. V. Khramtsov, S. Tridandapani, C. K. Sen and C. B. Marsh: The role of the NADPH oxidase complex, p38 MAPK, and Akt in regulating human monocyte/macrophage survival. Am J Respir Cell Mol Biol, 36, 68-77 (2007)
doi:10.1165/rcmb.2006-0165OC
97. S. Francois, J. El Benna, P. M. Dang, E. Pedruzzi, M. A. Gougerot-Pocidalo and C. Elbim: Inhibition of neutrophil apoptosis by TLR agonists in whole blood: involvement of the phosphoinositide 3-kinase/Akt and NF-kappaB signaling pathways, leading to increased levels of Mcl-1, A1, and phosphorylated Bad. J Immunol, 174, 3633-42 (2005)
98. S. Santos-Sierra, S. D. Deshmukh, J. Kalnitski, P. Kuenzi, M. P. Wymann, D. T. Golenbock and P. Henneke: Mal connects TLR2 to PI3Kinase activation and phagocyte polarization. Embo J, 28, 2018-27 (2009)
doi:10.1038/emboj.2009.158
99. B. C. Chen, J. C. Kang, Y. T. Lu, M. J. Hsu, C. C. Liao, W. T. Chiu, F. L. Yeh and C. H. Lin: Rac1 regulates peptidoglycan-induced nuclear factor-kappaB activation and cyclooxygenase-2 expression in RAW 264.7 macrophages by activating the phosphatidylinositol 3-kinase/Akt pathway. Mol Immunol, 46, 1179-88 (2009)
doi:10.1016/j.molimm.2008.11.006
100. J. Y. Lee, J. Y. Kim, Y. G. Lee, M. H. Rhee, E. K. Hong and J. Y. Cho: Molecular mechanism of macrophage activation by Exopolysaccharides from liquid culture of Lentinus edodes. J Microbiol Biotechnol, 18, 355-64 (2008)
101. B. W. Jones, K. A. Heldwein, T. K. Means, J. J. Saukkonen and M. J. Fenton: Differential roles of Toll-like receptors in the elicitation of proinflammatory responses by macrophages. Ann Rheum Dis, 60 Suppl 3, iii6-12 (2001)
102. S. N. Sarkar, K. L. Peters, C. P. Elco, S. Sakamoto, S. Pal and G. C. Sen: Novel roles of TLR3 tyrosine phosphorylation and PI3 kinase in double-stranded RNA signaling. Nat Struct Mol Biol, 11, 1060-7 (2004)
doi:10.1038/nsmb847
103. J. L. Herrera, E. Gonzalez-Rey, R. Fernandez-Montesinos, F. J. Quintana, R. Najmanovich and D. Pozo: Toll-like receptor stimulation differentially regulates vasoactive intestinal peptide type 2 receptor in macrophages. J Cell Mol Med, 13, 3209-17 (2009)
doi:10.1111/j.1582-4934.2009.00662.x
104. D. P. Sester, K. Brion, A. Trieu, H. S. Goodridge, T. L. Roberts, J. Dunn, D. A. Hume, K. J. Stacey and M. J. Sweet: CpG DNA activates survival in murine macrophages through TLR9 and the phosphatidylinositol 3-kinase-Akt pathway. J Immunol, 177, 4473-80 (2006)
105. J. H. Kim, G. Lee, Y. L. Cho, C. K. Kim, S. Han, H. Lee, J. S. Choi, J. Choe, M. H. Won, Y. G. Kwon, K. S. Ha and Y. M. Kim: Desmethylanhydroicaritin inhibits NF-kappaB-regulated inflammatory gene expression by modulating the redox-sensitive PI3K/PTEN/Akt pathway. Eur J Pharmacol, 602, 422-31 (2009)
doi:10.1016/j.ejphar.2008.10.062
106. O. H. Kang, H. S. Chae, J. G. Choi, Y. C. Oh, Y. S. Lee, J. H. Kim, M. J. Seung, H. J. Jang, K. H. Bae, J. H. Lee, D. W. Shin and D. Y. Kwon: Ent-pimara-8(14), 15-dien-19-oic acid isolated from the roots of Aralia cordata inhibits induction of inflammatory mediators by blocking NF-kappaB activation and mitogen-activated protein kinase pathways. Eur J Pharmacol, 601, 179-85 (2008)
doi:10.1016/j.ejphar.2008.10.012
107. M. H. Pan, M. C. Hsieh, P. C. Hsu, S. Y. Ho, C. S. Lai, H. Wu, S. Sang and C. T. Ho: 6-Shogaol suppressed lipopolysaccharide-induced up-expression of iNOS and COX-2 in murine macrophages. Mol Nutr Food Res, 52, 1467-77 (2008)
doi:10.1002/mnfr.200700515
108. M. H. Pan, C. S. Lai, Y. J. Wang and C. T. Ho: Acacetin suppressed LPS-induced up-expression of iNOS and COX-2 in murine macrophages and TPA-induced tumor promotion in mice. Biochem Pharmacol, 72, 1293-303 (2006)
doi:10.1016/j.bcp.2006.07.039
109. K. R. Roy, K. M. Arunasree, A. Dhoot, R. Aparna, G. V. Reddy, S. Vali and P. Reddanna: C-Phycocyanin inhibits 2-acetylaminofluorene-induced expression of MDR1 in mouse macrophage cells: ROS mediated pathway determined via combination of experimental and In silico analysis. Arch Biochem Biophys, 459, 169-77 (2007)
doi:10.1016/j.abb.2007.01.006
110. Y. C. Kuo, C. S. Lai, J. M. Wang, V. Badmaev, K. Nagabhushanam, C. T. Ho and M. H. Pan: Differential inhibitory effects of inotilone on inflammatory mediators, inducible nitric oxide synthase and cyclooxygenase-2, in LPS-stimulated murine macrophage. Mol Nutr Food Res, 53, 1386-95 (2009)
doi:10.1002/mnfr.200800583
111. A. Xagorari, A. Papapetropoulos, A. Mauromatis, M. Economou, T. Fotsis and C. Roussos: Luteolin inhibits an endotoxin-stimulated phosphorylation cascade and proinflammatory cytokine production in macrophages. J Pharmacol Exp Ther, 296, 181-7 (2001)
112. K. T. Ku, Y. L. Huang, Y. J. Huang and W. F. Chiou: Miyabenol A inhibits LPS-induced NO production via IKK/IkappaB inactivation in RAW 264.7 macrophages: possible involvement of the p38 and PI3K pathways. J Agric Food Chem, 56, 8911-8 (2008)
doi:10.1021/jf8019369
113. M. H. Pan, Y. H. Chang, M. L. Tsai, C. S. Lai, S. Y. Ho, V. Badmaev and C. T. Ho: Pterostilbene suppressed lipopolysaccharide-induced up-expression of iNOS and COX-2 in murine macrophages. J Agric Food Chem, 56, 7502-9 (2008)
doi:10.1021/jf800820y
114. C. S. Lai, J. H. Lee, C. T. Ho, C. B. Liu, J. M. Wang, Y. J. Wang and M. H. Pan: Rosmanol potently inhibits lipopolysaccharide-induced iNOS and COX-2 expression through downregulating MAPK, NF-kappaB, STAT3 and C/EBP signaling pathways. J Agric Food Chem, 57, 10990-8 (2009)
doi:10.1021/jf9025713
115. J. H. Kim, H. J. Na, C. K. Kim, J. Y. Kim, K. S. Ha, H. Lee, H. T. Chung, H. J. Kwon, Y. G. Kwon and Y. M. Kim: The non-provitamin A carotenoid, lutein, inhibits NF-kappaB-dependent gene expression through redox-based regulation of the phosphatidylinositol 3-kinase/PTEN/Akt and NF-kappaB-inducing kinase pathways: role of H(2)O(2) in NF-kappaB activation. Free Radic Biol Med, 45, 885-96 (2008)
doi:10.1016/j.freeradbiomed.2008.06.019
116. D. W. Park, K. Baek, J. R. Kim, J. J. Lee, S. H. Ryu, B. R. Chin and S. H. Baek: Resveratrol inhibits foam cell formation via NADPH oxidase 1- mediated reactive oxygen species and monocyte chemotactic protein-1. Exp Mol Med, 41, 171-9 (2009)
doi:10.3858/emm.2009.41.3.020
117. K. V. Parsa, L. P. Ganesan, M. V. Rajaram, M. A. Gavrilin, A. Balagopal, N. P. Mohapatra, M. D. Wewers, L. S. Schlesinger, J. S. Gunn and S. Tridandapani: Macrophage pro-inflammatory response to Francisella novicida infection is regulated by SHIP. PLoS Pathog, 2, e71 (2006)
doi:10.1371/journal.ppat.0020071
118. H. G. Kim, D. H. Yoon, C. H. Kim, B. Shrestha, W. C. Chang, S. Y. Lim, W. H. Lee, S. G. Han, J. O. Lee, M. H. Lim, G. Y. Kim, S. Choi, W. O. Song, J. M. Sung, K. C. Hwang and T. W. Kim: Ethanol extract of Inonotus obliquus inhibits lipopolysaccharide-induced inflammation in RAW 264.7 macrophage cells. J Med Food, 10, 80-9 (2007)
doi:10.1089/jmf.2006.156
Abbreviations: NO: nitric oxide, ROS: reactive oxygen species, TNFtumor necrosis factor, IL: interleukin, iNOS: nitric oxide synthase, COX: cyclooxygenase, PRRs: pattern recognition receptors, TLR: Toll-like receptor, LPS: lipopolysaccharide, MPAKs: mitogen activated protein kinases, NF-B: nuclear factor-B, AP-1: activator protein-1, IKK: IB kinase, PGN: peptidoglycan, PH: pleckstrin homology, HM: hydrophobic motif, PIP3: phosphatidylinositol-(3,4,5)-triphosphate, IRF: interferon regulatory factor, JAK-2: Janus kinase-2, NIK: nuclear factor-B-inducing kinase, PI3K: phosphoinositide 3-kinase, PDK1: phosphoinositide-dependent kinase 1, ERK: extracellular signal-regulated kinase, JNK: c-Jun N-terminal kinase, CREB: cAMP responsive element binding protein, ITAMs: immunoreceptor tyrosine-based activation motifs, CSF-1: colony stimulating factor-1, IGF-1: insulin-like growth factor-1, LIMK: LIM domain kinase, C5a: complement 5a, SOCS1: suppressor of cytokine signaling 1, IRAK-M: interleukin-1 receptor-associated kinase-M, D-GalN: D-galactosamine
Key Words: Protein kinase B, Akt, macrophages, cytokine production, phagocytosis, LPS tolerance, Review
Send correspondence to: Jae Youl Cho, College of Biomedical Science, Kangwon National University, 192-1 Hyoja-2-dong, Chuncheon 192-1, South Korea. Tel: 82-33-250-6488, Fax: 82-33-241-6480, E-mail:jaecho@kangwon.ac.kr