Sergey M. Troyanovsky

Department of Dermatology, Northwestern University, The Feinberg School of Medicine, Chicago, IL 60611

TABLE OF CONTENTS

1. Abstracts

2. Introduction (Horizontals and verticals of cadherin adhesion)

3. Interrelated array of cadherin internalization pathways

4. Endocytic disruption of adherens junctions is one of possible mechanisms for junction dynamics

5. Acknowledgements

6. References

1. ABSTRACT

Regulation of cadherin-based adhesion is an important but poorly studied question. Little is known which mechanisms control the size, number, strength, dynamics, and motility of adherens junctions. Cadherin endocytosis has been suggested to be one such mechanism. Recent studies have revealed several pathways of cadherin endocytosis, each of which appears to have specific functions. These pathways are surprisingly similar to those responsible for endocytosis of growth factor receptors. They could mediate the uptake of cadherin from both the inside and outside of adherens junctions thereby controlling different parameters of cell-cell adhesion structures.

2. HORIZONTALS AND VERTICALS OF CADHERIN ADHESION

Adherens junctions are some of the most prominent cell-cell adhesion structures to be found in any of our cells. They not only interconnect the cells into highly organized tissues, but also serve as platforms for forming other intercellular junctions. Yet adherens junctions are not static structures. Recent progress in live cell imaging shows that adherens junctions are in constant, directional motion (1). This observation suggests that adherens junctions are linked to some kinds of intracellular motors. It also suggests that the adhesive bonds interconnecting the two halves of the junction are strong enough to sustain the stress induced by this motion, which is unlikely to be completely synchronized in two neighboring cells. Adding even more complexity to this model, numerous FRAP (fluorescence recovery after photobleaching) experiments have shown that individual cadherin molecules continuously move in and out of adherens junctions (2-4). This exchange of cadherin has been traditionally regarded as a lateral (horizontal) diffusion of cadherin molecules (5). Recent progress in understanding cadherin traffic (reviewed recently in 6, 7) suggests, however, that the lateral diffusion might not be a primary mechanism of the continuous remodeling of adherens junctions. Instead, cadherin endocytosis, which emerged as a vertical dimension of cadherin junction dynamics, may play the leading role in this process.

The endocytosis of growth factor receptors has been shown to regulate many parameters of downstream receptor signaling. To fulfill this regulatory function, two types of endocytosis execute the receptor uptake from the cell surface. Constitutive but slow-rate endocytosis, often mediated by AP2-clathrin interactions, regulates the overall amounts of the receptors on the cell surface. Once receptors are activated, they are rapidly internalized by alternative endocytic mechanisms. The latter process, which in many cases is stimulated by receptor monoubiquitination, determines the duration of growth factor signaling. Molecular mechanisms of cadherin endocytosis are not as well studied as those for growth factor receptors. Even less is known about which cadherin pool, engaged or unengaged in adhesion at the moment of endocytosis, is subject to internalization. Recent data, however, shows that cadherin endocytosis and endocytosis of growth factor receptors share many of the same critical molecules. In this review we briefly discuss the emerging mechanisms and functions of cadherin internalization.

3. INTERRELATED ARRAY OF CADHERIN INTERNALIZATION PATHWAYS

Available data show that cadherin constitutive endocytosis is mediated by a clathrin-dependent pathway (8, 9). One of the suggested mechanisms that couple cadherin with the clathrin endocytic machinery is a binding of the adaptor complex AP2 to the dileucine motif located at the juxtamembrane region of E-cadherin. A point mutation of this motif was shown to inhibit cadherin internalization in MDCK cells (10). The authors proposed a simple model suggesting that this motif becomes accessible for AP2 only once E-cadherin dissociates from one of its major intracellular partner p120ctn. Therefore, p120ctn, in agreement with earlier works of other authors (9, 11, 12), regulates the cell surface retention and lifetime of E-cadherin. However, the work of the Stow group did not support the role of dileucine motif in cadherin endocytosis; their biochemical and live-imaging experiments suggested that this motif is required for Rab11-dependent targeting of E-cadherin to the basolateral membrane (13, 14). In either case, however, the dileuicine motif cannot be the sole motif responsible for constitutive cadherin endocytosis. First, VE-cadherin, which like E-cadherin is constitutively endocytosed by clathrin under the regulation of p120ctn, does not posses diluicine motif (9). Second, intracellular regions lacking diluicine motif of another classic cadherin, N-cadherin, were able to mediate an efficient constitutive endocytosis (15). Third, proteasome inhibitors blocked p120ctn-controlled cadherin degradation (11). Since proteasome inhibitors rapidly deplete the intracellular pool of free ubiquitin (16, 17), this observation suggests that cadherin ubiquitination plays an important role for selecting p120ctn-unbound cadherin for the degradation pathway.

Another possible form of constitutive cadherin endocytosis is macropinocytosis. This form of internalization is proposed to be specific for a cadherin pool unengaged in adhesion at the moment of endocytosis (18). It could be responsible for the formation of large intracellular vesicles found in keratinocytes in low calcium media or after disruption of the cadherin junction by a cadherin-specific antibody (19). Available data could not exclude, however, that this form of endocytosis uptakes E-cadherin only upon E-cadherin overexpression or after the application of some specific external stimuli (see below).

Various growth factors, such as TGFbeta (20); EGF (21, 22), HGF (23, 24), FGF (25) were shown to increase the rate of cadherin internalization that in some cells resulted in the complete disintegration of adherens junctions. This rapid event might be a critical cause of the epithelial-mesenchimal transition. And again, different endocytic pathways have been suggested to mediate this regulated endocytosis. For example microinjection of the constitutively active Rac1 mutant destroyed adherens junctions and delivered cadherin (as well as other cell surface receptors, like transferrin receptor) to the large intracellular vesicles (19). It is possible that this effect is caused by intensive macropinocytosis, the activation of which compensates a deficiency of the clathrin-mediated endocytosis that is blocked by Rac1 hyperactivation. In good agreement with this hypothesis, it was recently shown that the activation of EGF receptors dramatically increased cadherin macropinocytosis in MCF-7 cells and that this increase depended on Rac1 activation (26). Alternatively, some authors interpreted the EGF-induced increase in cadherin internalization as activation of the caveolin-dependent endocytosis (21). In favor to this idea, they showed that cadherin associates with caveolin1 in A-431 cells and cholesterol-sequestering reagents, like beta-cyclodextrin or filipin blocked cadherin internalization (21).

Another pathway potentially regulating the level of cadherin on the cell surface is cadherin monoubiquitination and its subsequent internalization via clathrin-dependent endocytosis. Rapid cadherin internalization and dissolution of adherens junctions was shown to accompany the activation of ts-v-Src mutant in MDCK cells resulting in cell-cell contact disruption and in the recruitment of cadherin into recycling endosomes (27-29). Upon Src activation, two tyrosines of E-cadherin (Y755 and Y756) are phosporylated, producing a binding site for E3 ubiquitin-ligase Hakai. After binding, this ligase ubiquitinates E-cadherin-catenin complex that eventually facilitates cadherin internalization (28) and targeting for lysosomal degradation (30).

Finally, some pool of surface-located cadherin molecules apparently associates with growth factor receptors such as EGF receptor, ErbB-1 (31, 32 ) and HGF receptor, c-Met (33, 34). E-cadherin apparently directly interacts with both of them via its extracellular domain (32, 35). These interactions are very likely to be critical for targeting c-Met to the basolateral surface of epithelial cells where they co-localize with E-cadherin-catenin complex. Interestingly, endocytosis of these two proteins, c-Met and E-cadherin, was markedly accelerated by the same stimuli such as HGF, low calcium media, and TPA (36). These data suggest that internalizations of these two proteins from the cell surface are somehow coordinated. There are several obvious mechanisms for such coordination. First, if indeed the same mechanisms are responsible for the internalization of activated growth factor receptors and cadherin, then activation of this mechanism by any stimuli (for example by growth factors) inevitably would result in accelerated internalization of both proteins. Another possibility is that both proteins are coendocytosed because of their physical interactions (37). Finally, it was found that in some cells the formation of adherens junctions seems to activate EGF receptors via EGF-independent activation (32, 38 see however 39). Another work suggests the opposite: adherens junctions downregulate ErbB-1 activity (40). Nevertheless, modulation of ErbB-1 activity by cadherin may modulate the rate and mechanisms of ErbB-1 endocytic pathways, which, in turn, by coendocytosis, modulate E-cadherin internalization. Clearly, a lot of work is needed to fully understand the relationships between growth factor receptors and cadherin endocytosis.

Altogether the data described above emphasize the robustness of the cadherin internalization process, which can be controlled by multiple independent mechanisms. Importantly, cadherin endocytic mechanisms and their regulation are, at least in general, similar to those for growth factor receptors.

4. ENDOCYTIC DISRUPTION OF ADHERENS JUNCTIONS IS ONE OF POSSIBLE MECHANISMS FOR JUNCTION DYNAMICS

Cadherin uptake from the cell surface may influence cadherin adhesion by two different nonexclusive mechanisms: endocytosis from outside and inside the adherens junctions. By the first mechanism, endocytosis would uptake cadherin molecules unengaged in adhesion and, in theory, could control the level of free cadherin on the cell surface. Indeed macropinocitosis of free cadherin was demonstrated in the experiments with preconfluent epithelial cells (8, 18). Free cadherin was also proposed to undergo endocytosis through a clathrin-dependent pathway (41, 42). Furthermore the latter two works envisioned a complex Rac/Cdc42/nectin-dependent signaling pathway inhibiting cadherin endocytosis once it is recruited into nascent adherens junctions. By this mechanism, cadherin engaged in adhesion becomes inaccessible to endocytic machinery. Nevertheless, some processes should mediate an efficient and apparently regulated removal of cadherin from cell-cell contacts. The lack of such mechanism(s) would obviously result in unlimited expansion of adherens junctions. Below we summarize the data indicating that one such mechanism is cadherin endocytosis.

The clearest evidence for internalization of cadherin from the junctions have been obtained using a calcium-switch model. The calcium-dependency of cadherin-based adhesion is a very well characterized phenomenon. The cadherin ectodomain, in the absence of calcium ions, immediately changes its conformation; it becomes accessible for trypsin digestion and cysteine-specific biotinylation (43, 44). Junctional proteins, including cadherin, are then rapidly internalized (45). The detailed molecular mechanisms underlining this remarkable and long-known effect are not completely understood. The critical and unresolved question is whether cadherin first loose their adhesive bonds and then are internalized or, vice versa, they are first internalized, forcefully breaking apart cadherin adhesive bonds. The first possibility is widely accepted and is based on the analysis of cadherin-cadherin interactions in different in vitro assays (reviewed in 44, 46).

However, a number of experimental data performed on both cellular and molecular levels indicate that the mechanism of cell-cell contact disintegration in low calcium media is far more complex. The possibility that cadherin adhesion bonds themselves are calcium-independent has been clearly suggested by crystallography works, which showed that cadherin adhesion interface does not include calcium-binding sites (47). The maintenance of cadherin adhesion bonds in low calcium has been further supported by direct biochemical experiments. We showed that cadherin adhesive dimers, which can be extracted from cells by nonionic detergents, are surprisingly stable in low calcium. The same dimers immediately dissociate, however, upon calcium depletion in living cells (48). Notably, this dissociation of cadherin adhesive dimers by calcium deficiency in living cells can be blocked by many maneuvers that inactivate cadherin endocytosis, such as hypertonic media, low temperature or ATP depletion (49). Thus, in living cells as well as solution, cadherin adhesive dimers are stable in low calcium. Their dissociation in vivo requires some active processes; one candidate for this is endocytosis. This conclusion, however, is in sharp disagreement with in vitro binding experiments, which demonstrate that cadherin-cadherin interactions are calcium-dependent. Detailed comparison of cadherin dimer formation on the cell surface and on the surface of agarose beads provided a clue for understanding this discrepancy (50): cadherin dimers, which formed at these two conditions, are structurally different. Cadherin dimers formed on the agarose surface immediately dissociate at calcium concentrations below 100 mkM threshold. By contrast, on the cell surface calcium was needed only for adhesive dimer production but not for their maintenance. We proposed that cells have a special mechanism, lacking in vitro, which mediates the assembly of such calcium-independent cadherin adhesive dimers. Taken together, biochemical and molecular examinations of cadherin-cadherin interactions suggest that just the depletion of calcium ions is not sufficient to dissolute adherens junctions.

The complex cellular mechanisms responsible for cell-cell dissociation in low calcium are also evident from experiments with living cells. It was shown that several compounds, very different on first glance, could protect cell-cell contacts from degradation by low calcium. These compounds include relatively unspecific protein kinase inhibitors, such as H7 (51) or staurosporine (52), casein kinase 1 inhibitor IC261 (53), the microtubule-specific drug nocodazole (54, 55), and agents that block actin-myosin contractility (51, 56). Importantly, these drugs did not protect cadherin from low calcium-induced changes in the cadherin ectodomain conformation (51, 52). Furthermore these drugs are cell-type specific. For example, only keratinocytes but not other cells tested acquired nocodazole-induced calcium-independent adhesion in Kee and Stainert (54) experiments. The fact that the processes underlying calcium-independent cadherin adhesion are redundant underlines the complexity of the entire process. Several possibilities have been suggested. Actin filament contractility, activated by low calcium, was suspected by Citi et al (51) and Ivanov et al (56). However, it is not clear what triggers such highly organized actin-based contractility upon calcium depletion. Some evidence points to cadherin endocytosis. Ivanov et al. (57) showed that different drugs that inactivate, while not very specifically, clathrin-dependent endocytosis markedly stabilized cadherin adhesion in low calcium. Interestingly, the stabilizing effect of kinase inhibitors on cell-cell contacts in low calcium also could be based on the inhibition of endocytosis. Some protein kinase C (PKC) isozymes apparently are required for cadherin internalizations (58). Therefore the kinase inhibitor H7 potentially could block cell-cell dissociation in low calcium by inhibiting PKC and subsequent downregulation of cadherin internalization. Inactivation of cadherin endocytosis by staurosporine, which also inhibits PKC, was experimentally demonstrated (52). Finally, nocodazole may also inactivate cell-cell contact dissociation through the inhibition of endocytosis; it was shown that this agent inhibits SV40, Listeria and some other pathogen entry into cells (59, 60). Notably, nocodazole induced the protection effect independently to RhoA activation and stress fiber formation (61). Altogether, the stability of adherens junctions at low calcium at conditions that inactivate endocytosis supports the data obtained in the biochemical and structural works described above: some active processes are needed for cadherin junction disintegration, and one such process is the endocytic uptake of cadherin molecules directly from the adherens junctions.

Does cadherin uptake from adherens junctions occur at the standard calcium concentration? Clear indications that this is the case have been found in our recent work (49). Using immunoelectron microscopy we showed the presence of endocytic invaginations consuming E-cadherin directly from cell-cell contacts, including from well-organized adherens junctions in confluent cultures of A-431 and HaCat cells. Furthermore, two different approaches, hypertonic shock and ATP depletion, inhibiting practically all forms of endocytosis, resulted in the rapid accumulation of adhesive dimers in cells and led to a profound increase in cadherin cell-cell contact staining. These data suggest that cadherin endocytosis may be essential to counterbalance a continuous assembly of cadherin in adherens junctions under physiological calcium concentration. Importantly, cadherin endocytosis activated by growth factors or v-Src during epithelial to mesenhimal transition may also proceed within adherens junctions. At least Warren and Nelson in 1987 reported an appearance of numerous clathrin-coated pits in the region of adherens junction in the v-Src-transformed MDCK cells (27).

In summary, recent studies have revealed several forms of cadherin endocytosis, each of which has specific functions and mechanisms. First, cadherin is constitutively endocytosed and recycles back to the plasma membrane. This form of endocytosis is perhaps similar to the constitutive endocytosis of growth factor receptors and is mediated through a classic clathrin-mediated pathway or macropinocytosis. Whether these processes distinguish free from junctional cadherin is not clear, but apparently they both regulate the total level of cadherin on the cell surface. Deficiency of p120ctn in the cadherin-catenin complex might target cadherin to another endocytic pathway, which eventually leads to cadherin degradation in lysosomes. In different cell types or along tumor progression different forms of cadherin endocytosis may be dominant. Second, by specific internalization of the junctional cadherin, cells may regulate the strength and dynamics of existing contacts. This type of endocytosis may be analogues to the internalization of the growth factor receptors upon their activation. The similarity in mechanisms of these two processes may explain why the stimulation of EGF or HGF receptors activates cadherin endocytosis. The interrelation of these two processes might be very important during carcinogenesis. Further detailed studies of cadherin endocytosis on molecular levels are needed to fully assess the contribution of cadherin endocytosis in cell-cell junction remodeling.

5. Acknowledgements

Works from the author's laboratory were supported by grants from the National Institute of Health 2RO1 AR44016-04 and 1R21 AR054472-01, with additional support from Zell Scholar Award from The Robert H. Lurie Comprehensive Cancer Center Northwestern University.

6. REFERENCES

1. Kametani Y, Takeichi M.: Basal-to-apical cadherin flow at cell junctions. Nat Cell Biol. 9, 92-98 (2007)
doi:10.1038/ncb1520

2. Yamada S, Pokutta S, Drees F, Weis WI, Nelson WJ.: Deconstructing the cadherin-catenin-actin complex. Cell 123, 889-901 (2005)
doi:10.1016/j.cell.2005.09.020

3. Stehbens SJ, Paterson AD, Crampton MS, Shewan AM, Ferguson C, Akhmanova A, Parton RG, Yap AS.: Dynamic microtubules regulate the local concentration of E-cadherin at cell-cell contacts. J Cell Sci. 119, 1801-1811 (2006)
doi:10.1242/jcs.02903

4. Thoumine O, Lambert M, M�ge RM, Choquet D.: Regulation of N-cadherin dynamics at neuronal contacts by ligand binding and cytoskeletal coupling. Mol Biol Cell 17, 862-875 (2006)
doi:10.1091/mbc.E05-04-0335

5. Kusumi A, Suzuki K, Koyasako K.: Mobility and cytoskeletal interactions of cell adhesion receptors. Curr Opin Cell Biol. 11, 582-590 (1999)
doi:10.1016/S0955-0674(99)00020-4

6. Bryant DM, Stow JL.: The ins and outs of E-cadherin trafficking. Trends Cell Biol. 14, 427-434 (2004)
doi:10.1016/j.tcb.2004.07.007

7. Yap AS, Crampton MS, Hardin J.: Making and breaking contacts: the cellular biology of cadherin regulation. Curr Opin Cell Biol. 19, 508-514 (2007)
doi:10.1016/j.ceb.2007.09.008

8. Le TL, Yap AS, Stow JL.: Recycling of E-cadherin: a potential mechanism for regulating cadherin dynamics. J Cell Biol. 146, 219-232 (1999)

9. Xiao K, Garner J, Buckley KM, Vincent PA, Chiasson CM, Dejana E, Faundez V, Kowalczyk AP.: p120-Catenin regulates clathrin-dependent endocytosis of VE-cadherin. Mol Biol Cell 16, 5141-5151 (2005)
doi:10.1091/mbc.E05-05-0440

10. Miyashita Y, Ozawa M.: Increased internalization of p120-uncoupled E-cadherin and a requirement for a dileucine motif in the cytoplasmic domain for endocytosis of the protein. J Biol Chem. 282, 11540-11548 (2007)
doi:10.1074/jbc.M608351200

11. Davis MA, Ireton RC, Reynolds AB.: A core function for p120-catenin in cadherin turnover. J Cell Biol. 163, 525-534 (2003)
doi:10.1083/jcb.200307111

12. Xiao K, Allison DF, Buckley KM, Kottke MD, Vincent PA, Faundez V, Kowalczyk AP.: Cellular levels of p120 catenin function as a set point for cadherin expression levels in microvascular endothelial cells. J Cell Biol. 163, 535-545 (2003)
doi:10.1083/jcb.200306001

13. Miranda KC, Joseph SR, Yap AS, Teasdale RD, Stow JL.: Contextual binding of p120ctn to E-cadherin at the basolateral plasma membrane in polarized epithelia. J Biol Chem. 278, 43480-43488 (2003)
doi:10.1074/jbc.M305525200

14. Lock JG, Stow JL.: 2005. Rab11 in recycling endosomes regulates the sorting and basolateral transport of E-cadherin. Mol Biol Cell. 16:1744-1755.
doi:10.1091/mbc.E04-10-0867

15. Tai CY, Mysore SP, Chiu C, Schuman EM.: Activity-regulated N-cadherin endocytosis. Neuron 54, 771-785 (2007)
doi:10.1016/j.neuron.2007.05.013

16. Patnaik A, Chau V, Wills JW.: Ubiquitin is part of the retrovirus budding machinery. Proc Natl Acad Sci U S A. 97, 13069-13074 (2000)
doi:10.1073/pnas.97.24.13069

17. Melikova MS, Kondratov KA, Kornilova ES.: Two different stages of epidermal growth factor (EGF) receptor endocytosis are sensitive to free ubiquitin depletion produced by proteasome inhibitor MG132. Cell Biol Int. 30, 31-43 (2006)

18. Paterson AD, Parton RG, Ferguson C, Stow JL, Yap AS.: Characterization of E-cadherin endocytosis in isolated MCF-7 and chinese hamster ovary cells: the initial fate of unbound E-cadherin. J Biol Chem. 278, 21050-21057 (2003)
doi:10.1074/jbc.M300082200

19. Akhtar N, Hotchin NA.: RAC1 regulates adherens junctions through endocytosis of E-cadherin. Mol Biol Cell 12, 847-862 (2001)

20. Janda E, Nevolo M, Lehmann K, Downward J, Beug H, Grieco M.: Raf plus TGFbeta-dependent EMT is initiated by endocytosis and lysosomal degradation of E-cadherin. Oncogene 25, 7117-7130 (2006)
doi:10.1038/sj.onc.1209701

21. Lu Z, Ghosh S, Wang Z, Hunter T.: Downregulation of caveolin-1 function by EGF leads to the loss of E-cadherin, increased transcriptional activity of beta-catenin, and enhanced tumor cell invasion. Cancer Cell 4, 499-515 (2003)
doi:10.1016/S1535-6108(03)00304-0

22. Hirao T, Nanba D, Tanaka M, Ishiguro H, Kinugasa Y, Doki Y, Yano M, Matsuura N, Monden M, Higashiyama S.: Overexpression of ADAM9 enhances growth factor-mediated recycling of E-cadherin in human colon cancer cell line HT29 cells. Exp Cell Res. 312, 331-339 (2006)

23. Palacios F, Price L, Schweitzer J, Collard JG, D'Souza-Schorey C.: An essential role for ARF6-regulated membrane traffic in adherens junction turnover and epithelial cell migration. EMBO J. 20, 4973-4986 (2001)
doi:10.1093/emboj/20.17.4973

24. Kimura T, Sakisaka T, Baba T, Yamada T, Takai Y.: Involvement of the Ras-Ras-activated Rab5 guanine nucleotide exchange factor RIN2-Rab5 pathway in the hepatocyte growth factor-induced endocytosis of E-cadherin. J Biol Chem. 281, 10598-10609 (2006)
doi:10.1074/jbc.M510531200

25. Bryant DM, Wylie FG, Stow JL.: Regulation of endocytosis, nuclear translocation, and signaling of fibroblast growth factor receptor 1 by E-cadherin. Mol Biol Cell 16, 14-23 (2005)
doi:10.1091/mbc.E04-09-0845

26. Bryant DM, Kerr MC, Hammond LA, Joseph SR, Mostov KE, Teasdale RD, Stow JL.: EGF induces macropinocytosis and SNX1-modulated recycling of E-cadherin. J Cell Sci. 120, 1818-1828 (2007)
doi:10.1242/jcs.000653

27. Warren SL, Nelson WJ.: Nonmitogenic morphoregulatory action of pp60v-src on multicellular epithelial structures. Mol Cell Biol. 7, 1326-1337 (1987)

28. Fujita Y, Krause G, Scheffner M, Zechner D, Leddy HE, Behrens J, Sommer T, Birchmeier W.: Hakai, a c-Cbl-like protein, ubiquitinates and induces endocytosis of the E-cadherin complex. Nat Cell Biol. 4, 222-231 (2002)
doi:10.1038/ncb758

29. Palovuori R, Sormunen R, Eskelinen S.: SRC-induced disintegration of adherens junctions of madin-darby canine kidney cells is dependent on endocytosis of cadherin and antagonized by Tiam-1. Lab Invest. 83, 1901-1915 (2003)
doi:10.1097/01.LAB.0000107009.75152.03

30. Shen Y, Hirsch DS, Sasiela CA, Wu WJ.: CDC42 regulates E-cadherin ubiquitination and degradation through an EGF receptor to SRC-mediated pathway. J Biol Chem. 283, 5127-5137 (2008)
doi:10.1074/jbc.M703300200

31. Dumstrei K, Wang F, Shy D, Tepass U, Hartenstein V.: Interaction between EGFR signaling and DE-cadherin during nervous system morphogenesis. Development 129, 3983-3994 (2002)

32. Fedor-Chaiken M, Hein PW, Stewart JC, Brackenbury R, Kinch MS.: E-cadherin binding modulates EGF receptor activation. Cell Commun Adhes. 10, 105-118 (2003)
doi:10.1080/714040416

33. Hiscox S, Jiang WG.: Association of the HGF/SF receptor, c-met, with the cell-surface adhesion molecule, E-cadherin, and catenins in human tumor cells. Biochem Biophys Res Commun. 261, 406-411 (1999)
doi:10.1006/bbrc.1999.1002

34. Davies G, Jiang WG, Mason MD.: HGF/SF modifies the interaction between its receptor c-Met, and the E-cadherin/catenin complex in prostate cancer cells. Int J Mol Med. 7, 385-388 (2001)

35. Reshetnikova G, Troyanovsky S, Rimm DL.: Definition of a direct extracellular interaction between Met and E-cadherin. Cell Biol Int. 31, 366-373 (2007)
doi:10.1016/j.cellbi.2007.01.022

36. Kamei T, Matozaki T, Sakisaka T, Kodama A, Yokoyama S, Peng YF, Nakano K, Takaishi K, Takai Y.: Coendocytosis of cadherin and c-Met coupled to disruption of cell-cell adhesion in MDCK cells--regulation by Rho, Rac and Rab small G proteins. Oncogene 18, 6776-6784 (1999)
doi:10.1038/sj.onc.1203114

37. Zhao Y, He D, Stern R, Usatyuk PV, Spannhake EW, Salgia R, Natarajan V.: Lysophosphatidic acid modulates c-Met redistribution and hepatocyte growth factor/c-Met signaling in human bronchial epithelial cells through PKC delta and E-cadherin. Cell Signal. 19, 2329-2338 (2007)
doi:10.1016/j.cellsig.2007.07.005

38. Pece S, Gutkind JS.: Signaling from E-cadherins to the MAPK pathway by the recruitment and activation of epidermal growth factor receptors upon cell-cell contact formation. J Biol Chem. 275, 41227-41233 (2000)
doi:10.1074/jbc.M006578200

39. Sovov� V, Kucerov� D, Vojtechov� M, Sloncov� E, Tuh�ckov� Z.: Transactivation of E-cadherin is not involved in the activity of EGF receptor in colorectal carcinoma cells. Int J Oncol. 25, 1459-1464 (2004)

40. Perrais M, Chen X, Perez-Moreno M, Gumbiner BM.: E-cadherin homophilic ligation inhibits cell growth and epidermal growth factor receptor signaling independently of other cell interactions. Mol Biol Cell 18, 2013-2025 (2007)
doi:10.1091/mbc.E06-04-0348

41. Izumi G, Sakisaka T, Baba T, Tanaka S, Morimoto K, Takai Y.: Endocytosis of E-cadherin regulated by Rac and Cdc42 small G proteins through IQGAP1 and actin filaments. J Cell Biol. 166, 237-248 (2004)
doi:10.1083/jcb.200401078

42. Hoshino T, Sakisaka T, Baba T, Yamada T, Kimura T, Takai Y.: Regulation of E-cadherin endocytosis by nectin through afadin, Rap1, and p120ctn. J Biol Chem. 280, 24095-24103 (2005)
doi:10.1074/jbc.M414447200

43. Pokutta S, Herrenknecht K, Kemler R, Engel J.: Conformational changes of the recombinant extracellular domain of E-cadherin upon calcium binding. Eur J Biochem. 223, 1019-1026 (1994)
doi:10.1111/j.1432-1033.1994.tb19080.x

44. Troyanovsky SM:. Cadherin dimers in cell-cell adhesion. Eur J Cell Biol. 84, 225-233 (2005)
doi:10.1016/j.ejcb.2004.12.009

45. Kartenbeck J, Schmelz M, Franke WW, Geiger B.: Endocytosis of junctional cadherins in bovine kidney epithelial (MDBK) cells cultured in low Ca2+ ion medium. J Cell Biol. 113, 881-892 (1991)
doi:10.1083/jcb.113.4.881

46. Pokutta S, Weis WI.: Structure and mechanism of cadherins and catenins in cell-cell contacts. Annu Rev Cell Dev Biol. 23, 237-261 (2007)
doi:10.1146/annurev.cellbio.22.010305.104241

47. Boggon TJ, Murray J, Chappuis-Flament S, Wong E, Gumbiner BM, Shapiro L.: C-cadherin ectodomain structure and implications for cell adhesion mechanisms. Science 296, 1308-1313 (2002)
doi:10.1126/science.1071559

48. Chitaev NA, Troyanovsky SM.: Adhesive but not lateral E-cadherin complexes require calcium and catenins for their formation. J Cell Biol. 142, 837-846 (1998)
doi:10.1083/jcb.142.3.837

49. Troyanovsky RB, Sokolov EP, Troyanovsky SM.: Endocytosis of cadherin from intracellular junctions is the driving force for cadherin adhesive dimer disassembly. Mol Biol Cell 17, 3484-3493 (2006)
doi:10.1091/mbc.E06-03-0190

50. Troyanovsky RB, Laur O, Troyanovsky SM.: Stable and unstable cadherin dimers: mechanisms of formation and roles in cell adhesion. Mol Biol Cell 18, 4343-4352 (2007)
doi:10.1091/mbc.E07-01-0084

51. Citi S, Volberg T, Bershadsky AD, Denisenko N, Geiger B.: Cytoskeletal involvement in the modulation of cell-cell junctions by the protein kinase inhibitor H-7. J Cell Sci. 107, 683-692 (1994)

52. Alexander JS, Jackson SA, Chaney E, Kevil CG, Haselton FR.: The role of cadherin endocytosis in endothelial barrier regulation: involvement of protein kinase C and actin-cadherin interactions. Inflammation 22, 419-433 (1998)
doi:10.1023/A:1022325017013

53. Dupre-Crochet S, Figueroa A, Hogan C, Ferber EC, Bialucha CU, Adams J, Richardson EC, Fujita Y.: Casein kinase 1 is a novel negative regulator of E-cadherin-based cell-cell contacts. Mol Cell Biol. 27, 3804-3816 (2007)
doi:10.1128/MCB.01590-06

54. Kee SH, Steinert PM.: Microtubule disruption in keratinocytes induces cell-cell adhesion through activation of endogenous E-cadherin. Mol Biol Cell 12, 1983-1993 (2001)

55. Ivanov AI, McCall IC, Babbin B, Samarin SN, Nusrat A, Parkos CA.: Microtubules regulate disassembly of epithelial apical junctions. BMC Cell Biol. 7, 12. (2006)
doi:10.1186/1471-2121-7-12

56. Ivanov AI, Hunt D, Utech M, Nusrat A, Parkos CA.: Differential roles for actin polymerization and a myosin II motor in assembly of the epithelial apical junctional complex. Mol Biol Cell 16, 2636-2650 (2005)
doi:10.1091/mbc.E05-01-0043

57. Ivanov AI, Nusrat A, Parkos CA.: Endocytosis of epithelial apical junctional proteins by a clathrin-mediated pathway into a unique storage compartment. Mol Biol Cell 15, 176-188 (2004)
doi:10.1091/mbc.E03-05-0319

58. Le TL, Joseph SR, Yap AS, Stow JL.: Protein kinase C regulates endocytosis and recycling of E-cadherin. Am J Physiol Cell Physiol. 283, C489-C499 (2002)

59. Kuhn M.: The microtubule depolymerizing drugs nocodazole and colchicine inhibit the uptake of Listeria monocytogenes by P388D1 macrophages. FEMS Microbiol Lett. 160, 87-90 (1998)
doi:10.1111/j.1574-6968.1998.tb12895.x

60. Damm EM, Pelkmans L, Kartenbeck J, Mezzacasa A, Kurzchalia T, Helenius A.: Clathrin- and caveolin-1-independent endocytosis: entry of simian virus 40 into cells devoid of caveolae. J Cell Biol. 168, 477-488 (2005)
doi:10.1083/jcb.200407113

61. Kee SH, Jang SI, Ahvazi B, Larsen M, Yamada KM, Steinert PM.: Cell-cell adhesion and RhoA-mediated actin polymerization are independent phenomena in microtubule disrupted keratinocytes. J Invest Dermatol. 119, 440-448 (2002)
doi:10.1046/j.1523-1747.2002.01826.x

Key Words Adhesion, Endocytosis, Adherens junctions, Cadherin, Review