Increased Internalization of p120-uncoupled E-cadherin and a Requirement for a Dileucine Motif in the Cytoplasmic Domain for Endocytosis of the Protein

Abstract

E-cadherin is a member of the cadherin family of Ca2+-dependent cell-cell adhesion molecules. E-cadherin associates with β-catenin at the membrane-distal region of its cytosolic domain and with p120 at the membrane-proximal region of its cytoplasmic domain. It has been shown that a pool of cell surface E-cadherin is constitutively internalized and recycled back to the surface. Further, p120 knockdown by small interference RNA resulted in dose-dependent elimination of cell surface E-cadherin. Consistent with these observations, we found that selective uncoupling of p120 from E-cadherin by introduction of amino acid substitutions in the p120-binding site increased the level of E-cadherin endocytosis. The increased endocytosis was clathrin-dependent, because it was blocked by expression of a dominant-negative form of dynamin or by hypertonic shock. A dileucine motif in the juxtamembrane cytoplasmic domain is required for E-cadherin endocytosis, because substitution of these residues to alanine resulted in impaired internalization of the protein. The alanine substitutions in the p120-uncoupled construct reduced endocytosis of the protein, indicating that this motif was dominant to p120 binding in the control of E-cadherin endocytosis. Therefore, these results are consistent with the idea that p120 regulates E-cadherin endocytosis by masking the dileucine motif and preventing interactions with adaptor proteins required for internalization. E-cadherin is a member of the cadherin family of Ca2+-dependent cell-cell adhesion molecules. E-cadherin associates with β-catenin at the membrane-distal region of its cytosolic domain and with p120 at the membrane-proximal region of its cytoplasmic domain. It has been shown that a pool of cell surface E-cadherin is constitutively internalized and recycled back to the surface. Further, p120 knockdown by small interference RNA resulted in dose-dependent elimination of cell surface E-cadherin. Consistent with these observations, we found that selective uncoupling of p120 from E-cadherin by introduction of amino acid substitutions in the p120-binding site increased the level of E-cadherin endocytosis. The increased endocytosis was clathrin-dependent, because it was blocked by expression of a dominant-negative form of dynamin or by hypertonic shock. A dileucine motif in the juxtamembrane cytoplasmic domain is required for E-cadherin endocytosis, because substitution of these residues to alanine resulted in impaired internalization of the protein. The alanine substitutions in the p120-uncoupled construct reduced endocytosis of the protein, indicating that this motif was dominant to p120 binding in the control of E-cadherin endocytosis. Therefore, these results are consistent with the idea that p120 regulates E-cadherin endocytosis by masking the dileucine motif and preventing interactions with adaptor proteins required for internalization. Cadherins are a family of structurally and functionally related molecules that mediate Ca2+-dependent cell-cell adhesion in a homophilic manner (1Takeichi M. Development. 1988; 102: 639-655Crossref PubMed Google Scholar, 2Gumbiner B.M. Nat. Rev. Mol. Cell. Biol. 2005; 6: 622-634Crossref PubMed Scopus (1199) Google Scholar). Ca2+ protects the extracellular domains of cadherins from proteolytic degradation and is necessary for their function. Cadherin-based adhesion is a central determinant of cell patterning during development and is necessary for the preservation of established tissue architecture in mature organisms. E-cadherin is a prototypic member of the family and is required for the establishment and maintenance of cell-cell adhesion and cell polarity in epithelia and plays key roles in tissue morphogenesis and tumorigenesis. Genetic studies have shown that E-cadherin is essential for epithelial integrity during development in Xenopus and mice (3Levine E. Lee C.H. Kintner C. Gumbiner B.M. Development. 1994; 120: 901-909Crossref PubMed Google Scholar, 4Hermiston M.L. Gordon J.I. J. Cell Biol. 1995; 129: 489-506Crossref PubMed Scopus (381) Google Scholar, 5Young P. Boussadia O. Halfter H. Grose R. Berger P. Leone D.P. Robenek H. Charnay P. Kemler R. Suter U. EMBO J. 2003; 22: 5723-5733Crossref PubMed Scopus (113) Google Scholar). At the cellular level, E-cadherin facilitates assembly of specialized intercellular junctions (desmosomes, gap, and tight junctions) necessary to link epithelial cells into functional monolayers (6Gumbiner B. Stevenson B. Grimaldi A. J. Cell Biol. 1988; 107: 1575-1587Crossref PubMed Scopus (655) Google Scholar, 7Wheelock M.J. Jensen P.J. J. Cell Biol. 1992; 117: 415-425Crossref PubMed Scopus (204) Google Scholar). The adhesive strength of cell-cell contacts depends on factors such as dimerization and lateral clustering of cadherin molecules (8Shapiro L. Fannon A.M. Kwong P.D. Thompson A. Lehmann M.S. Grubel G. Legrand J.F. Als-Nielsen J. Colman D.R. Hendrickson W.A. Nature. 1995; 374: 306-307Crossref PubMed Scopus (971) Google Scholar, 9Yap A.S. Brieher W.M. Pruschy M. Gumbiner B.M. Curr. Biol. 1997; 7: 308-315Abstract Full Text Full Text PDF PubMed Scopus (302) Google Scholar). Cadherins also form high affinity complexes with catenins and other molecules that participate in the overall function and stability of adherens junctions (10Ozawa M. Baribault H. Kemler R. EMBO J. 1989; 8: 1711-1717Crossref PubMed Scopus (1143) Google Scholar, 11Ozawa M. Kemler R. J. Cell Biol. 1992; 116: 989-996Crossref PubMed Scopus (324) Google Scholar). E-cadherin interacts with β-catenin and α-catenin, which links the complex to the actin cytoskeleton (11Ozawa M. Kemler R. J. Cell Biol. 1992; 116: 989-996Crossref PubMed Scopus (324) Google Scholar, 12Rimm D.L. Koslov E.R. Kebriaei P. Cianci C.D. Morrow J.S. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 8813-8817Crossref PubMed Scopus (631) Google Scholar). The Rho family GTPases Rho, Rac, and Cdc42 produce different configurations of actin in cells (13Hall A. Science. 1998; 279: 509-514Crossref PubMed Scopus (5199) Google Scholar) and have been implicated in remodeling actin for the regulation of E-cadherin-mediated adhesion (14Takaishi K. Sasaki T. Kotani H. Nishioka H. Takai Y. J. Cell Biol. 1997; 139: 1047-1059Crossref PubMed Scopus (474) Google Scholar, 15Braga V.M.M. Del Maschio A. Machesky L. Dejana E. Mol. Biol. Cell. 1999; 10: 9-22Crossref PubMed Scopus (226) Google Scholar). The trafficking of E-cadherin, its delivery to or removal from the cell surface, is one aspect of cadherin regulation that is not yet thoroughly understood. There is a growing body of evidence that shows that cell surface E-cadherin can be endocytosed and trafficked back into the cell. Ca2+ depletion induces internalization of cadherins and the subsequent disruption of junctions (16Kartenbeck J. Schmelz M. Franke W.W. Geiger B. J. Cell Biol. 1991; 113: 881-892Crossref PubMed Scopus (150) Google Scholar, 17Kamei T. Matozaki T. Sakisaka T. Kodama A. Yokoyama S. Peng Y.F. Nakano K. Takaishi K. Takai Y. Oncogene. 1999; 18: 6776-6784Crossref PubMed Scopus (176) Google Scholar, 18Izumi G. Sakisaka T. Baba T. Tanaka S. Morimoto K. Takai Y. J. Cell Biol. 2004; 166: 237-248Crossref PubMed Scopus (152) Google Scholar). It was shown that E-cadherin undergoes endocytosis and recycling in Madin-Darby canine kidney (MDCK) 2The abbreviations used are: MDCK, Madin-Darby canine kidney cell; EA substitution, amino acid substitutions in which two conserved glutamic acid residues and a conserved aspartic acid residue in the p120-binding site were substituted with alanine residues; GFP, green fluorescent protein; HA, hemagglutinin; LA substitution, amino-acid substitutions in which a dileucine motif was changed to a dialanine motif; mAb, monoclonal antibody; siRNA, small interference RNA; Ecad, E-cadherin; EAEcad, Ecad with EA substitution; LAEcad, Ecad with LA substitution; EALAEcad, Ecad with EA and LA substitutions. 2The abbreviations used are: MDCK, Madin-Darby canine kidney cell; EA substitution, amino acid substitutions in which two conserved glutamic acid residues and a conserved aspartic acid residue in the p120-binding site were substituted with alanine residues; GFP, green fluorescent protein; HA, hemagglutinin; LA substitution, amino-acid substitutions in which a dileucine motif was changed to a dialanine motif; mAb, monoclonal antibody; siRNA, small interference RNA; Ecad, E-cadherin; EAEcad, Ecad with EA substitution; LAEcad, Ecad with LA substitution; EALAEcad, Ecad with EA and LA substitutions. cell monolayers under physiological conditions (19Le T.L. Yap A.S. Stow J.L. J. Cell Biol. 1999; 146: 219-232Crossref PubMed Scopus (482) Google Scholar). The adhesive strength at cell-cell contacts depends, in part, on the amount of E-cadherin at the cell surface (20Steinberg M.S. Takeichi M. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 206-209Crossref PubMed Scopus (488) Google Scholar). Therefore, endocytosis and recycling of E-cadherin provides one mechanism for dynamically regulating cadherin-based adhesion, by balancing the relative amounts of surface-exposed and sequestered intracellular E-cadherin. How the endocytosis and recycling of E-cadherin are regulated is therefore of prime importance to the control of cell-cell adhesion. In addition to β-catenin, which binds to the distal portion of the E-cadherin cytoplasmic domain, another member of the armadillo family, p120, interacts with cadherins at the membrane-proximal region of the cytosolic domain (21Reynolds A.B. Daniel J. McCrea P.D. Wheelock M.J. Wu J. Zhang Z. Mol. Cell Biol. 1994; 14: 8333-8342Crossref PubMed Google Scholar, 22Ohkubo T. Ozawa M. J. Biol. Chem. 1999; 274: 21409-21415Abstract Full Text Full Text PDF PubMed Scopus (144) Google Scholar, 23Thoreson M.A. Anastasiadis P.Z. Daniel J.M. Ireton R.C. Wheelock M.J. Johnson K.R. Hummingbird D.K. Reynolds A.B. J. Cell Biol. 2000; 148: 189-202Crossref PubMed Scopus (385) Google Scholar). Although not directly involved in coupling cadherins to the cytoskeleton, p120 has emerged as a critical regulator of cadherin adhesive activity and cytoskeletal organization (22Ohkubo T. Ozawa M. J. Biol. Chem. 1999; 274: 21409-21415Abstract Full Text Full Text PDF PubMed Scopus (144) Google Scholar, 23Thoreson M.A. Anastasiadis P.Z. Daniel J.M. Ireton R.C. Wheelock M.J. Johnson K.R. Hummingbird D.K. Reynolds A.B. J. Cell Biol. 2000; 148: 189-202Crossref PubMed Scopus (385) Google Scholar). In addition to regulating adhesion and actin cytoskeletal organization, recent studies have demonstrated a core function for p120 in regulating cadherin expression levels. Separate studies have shown that p120 regulates steady-state levels of E-cadherin in epithelial cells (24Davis M.A. Ireton R.C. Reynolds A.B. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar) and in cells K. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar). In the of p120, cadherins and for The mechanism by which p120 regulates cadherin levels is not understood. of evidence that p120 regulates the of cell surface cadherins into a degradation (24Davis M.A. Ireton R.C. Reynolds A.B. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar, K. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar). In the of p120, E-cadherin is to the cell surface is (24Davis M.A. Ireton R.C. Reynolds A.B. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar). cell surface that p120 regulates the degradation of cell surface of K. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar). that p120 at the to cadherin internalization. In this we to the amino acid residues in E-cadherin that are required for internalization of the protein. A recent demonstrated that the for the endocytosis of in the cytoplasmic domain K. J. Dejana E. Mol. Biol. Cell. 2005; PubMed Scopus Google Scholar). A dileucine motif that was to mediate with was at in the juxtamembrane region of the E-cadherin cytoplasmic domain. two residues were substituted with two alanine of the substituted E-cadherin was that this motif was required for internalization of the protein. the binding of E-cadherin to p120 increased the at which E-cadherin was introduction of the substitution in the p120-uncoupled construct its endocytosis. the dileucine motif is dominant to p120 in the control of E-cadherin endocytosis. on these observations, we a p120 regulates E-cadherin endocytosis by masking the motif to interactions with adaptor proteins required for internalization. from canine E-cadherin, proteins to a at their the the were M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, M. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google E-cadherin and a E-cadherin construct in which two conserved glutamic acid residues and a conserved aspartic acid residue in the p120-binding site were substituted with alanine residues The EA substitution results in uncoupling of p120 binding M. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). the two residues at and to alanine residues the and were EALAEcad, a E-cadherin construct the EA and LA was by a from the construct with the from the were and into expression for green fluorescent and dominant-negative dynamin and K. C. K. K. J. 1999; PubMed Scopus Google were by and cells were in with were with the expression the (10Ozawa M. Baribault H. Kemler R. EMBO J. 1989; 8: 1711-1717Crossref PubMed Scopus (1143) Google Scholar). the of dynamin expression on the of EAEcad, cell were with expression for or dynamin as K. C. K. K. J. 1999; PubMed Scopus Google Scholar). canine p120 were from and of was was by and was used for and were from was by Kemler was from p120 and were from and were from were from and and were as M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In cells were in and were with to of cells was as (22Ohkubo T. Ozawa M. J. Biol. Chem. 1999; 274: 21409-21415Abstract Full Text Full Text PDF PubMed Scopus (144) Google Scholar). In cells were with in for at were with and with and were a with a of Cell were in with for at in the of Ca2+ or were by Cell surface are to in the of Ca2+ can be in the of the E-cadherin the pool of E-cadherin, intracellular E-cadherin and were on and tight cell monolayers were with in the or at The cells were with in at were with for and or a of was and proteins were for and was as with (19Le T.L. Yap A.S. Stow J.L. J. Cell Biol. 1999; 146: 219-232Crossref PubMed Scopus (482) Google Scholar). were with at cells were in at for the of Cell surface was by with or with acid at were in as proteins were with recycling of endocytosed proteins at cells were or acid at and to for in were to and in E-cadherin to during the was E-cadherin was from the by in addition of of E-cadherin was by with The were by and with of p120 from E-cadherin in of the studies have shown in a pool of cell surface E-cadherin is constitutively internalized and recycled back to the surface (19Le T.L. Yap A.S. Stow J.L. J. Cell Biol. 1999; 146: 219-232Crossref PubMed Scopus (482) Google Scholar). A construct E-cadherin with was into and were In Ecad was on the lateral of the two conserved glutamic acid residues and a conserved aspartic acid residue in the p120-binding site of E-cadherin with alanine residues has been shown to the with p120 M.A. Anastasiadis P.Z. Daniel J.M. Ireton R.C. Wheelock M.J. Johnson K.R. Hummingbird D.K. Reynolds A.B. J. Cell Biol. 2000; 148: 189-202Crossref PubMed Scopus (385) Google Scholar). the substitutions into the E-cadherin construct to a p120-uncoupled construct construct is to the by M.A. Anastasiadis P.Z. Daniel J.M. Ireton R.C. Wheelock M.J. Johnson K.R. Hummingbird D.K. Reynolds A.B. J. Cell Biol. 2000; 148: 189-202Crossref PubMed Scopus (385) Google from this construct in cells not p120 In to E-cadherin, a of was the of the intracellular EAEcad, cells were with to and for the Although in the which the not the overall of was not indicating that the intracellular not a pool of a portion of was on the lateral the intracellular that a pool of was internalized from the cell surface. in the cellular of were uncoupling of p120 binding not results are consistent with that p120 knockdown by expression resulted in dose-dependent elimination of cell surface E-cadherin (24Davis M.A. Ireton R.C. Reynolds A.B. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar) and that of p120 internalization from the by endocytosis of the K. J. Dejana E. Mol. Biol. Cell. 2005; PubMed Scopus Google surface expression of E-cadherin and its p120 not with E-cadherin and its were on a and with and and that a of E-cadherin and its were on the surface of the for EAEcad, which a the the were with for at in the of Ca2+ or were with of other construct the of the intracellular pool of E-cadherin and its The relative amounts of the intracellular of and shown in were and as a of the pool of the of the the were on and their or were the proteins were of cells not the expression of cells Ecad or were for in with or or The results shown in and are of in we the amount of on the surface of It is established that Ca2+ protects cell surface cadherins from proteolytic were in the of Ca2+ or of cells or demonstrated that of E-cadherin was and In of the p120-uncoupled construct was of on the cell surface. Cell surface of the and of cells on that E-cadherin, to the Therefore, intracellular of was not by of the protein. The p120-uncoupled E-cadherin with the site of cells were with a for not with the a of the with J.M. O. H. J. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google also with internalized from the cell surface that it in and that with p120 endocytosis. The steady-state levels of not from of E-cadherin consistent with the that in of cells with to not the expression of of the p120-uncoupled of in that with p120 binding the endocytosis of the protein. the of endocytosis of different E-cadherin proteins in we used a (19Le T.L. Yap A.S. Stow J.L. J. Cell Biol. 1999; 146: 219-232Crossref PubMed Scopus (482) Google Scholar) that the internalization of cell surface E-cadherin. of cell surface proteins at cells were for of at a that the of internalized proteins in or by preventing into the or recycling (19Le T.L. Yap A.S. Stow J.L. J. Cell Biol. 1999; 146: 219-232Crossref PubMed Scopus (482) Google Scholar). was from the cell surface, and the sequestered was these the amount of internalized Ecad increased the A and at the internalized pool of the E-cadherin at the of the In the pool of internalized increased A and the intracellular pool of was that of E-cadherin. Therefore, uncoupling of p120 binding to E-cadherin internalization of the protein. of the p120-uncoupled E-cadherin endocytosis a and can be by hypertonic Mol. Biol. Cell. PubMed Scopus Google Scholar) or dominant-negative a that is a key regulator of endocytosis C. Stow J.L. Yap A.S. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). the internalization of the p120-uncoupled E-cadherin is by a cells were with expression for or dominant dynamin with K. C. K. K. J. 1999; PubMed Scopus Google and the on were dynamin internalization of to cells not In cells dominant-negative dynamin by green to and intracellular of the p120-uncoupled E-cadherin is internalized by endocytosis of endocytosis, we used hypertonic a that has been shown to of the J. Cell Biol. 1989; PubMed Scopus Google Scholar) and other shown in of cells with hypertonic blocked endocytosis of E-cadherin. the the internalization of was also these we that the p120-uncoupled E-cadherin is internalized by endocytosis. for of are to mediate endocytosis into J.S. Rev. 2003; PubMed Scopus Google Scholar) and to a or the that E-cadherin the the dileucine we the that the conserved dileucine is required for E-cadherin endocytosis. of the residues to alanine a on the of E-cadherin at the with the cells substitution of the residues to alanine in the p120-uncoupled E-cadherin resulted in of intracellular of the and Although this dileucine motif has been to be critical for the of E-cadherin to the of and epithelial cells T. P. T.L. Yap A.S. Stow J.L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Yap A.S. Stow J.L. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google we expression of and on the of cells under these conditions that the of internalized was reduced A and consistent with the idea that the dileucine motif is involved in internalization. of the dileucine motif in the p120-uncoupled E-cadherin also resulted in reduced internalization of from the cell surface the dileucine motif is required for the internalization of E-cadherin. the of p120 cells E-cadherin and were by and by with p120 reduced p120 to of the control A and Consistent with (24Davis M.A. Ireton R.C. Reynolds A.B. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar, K. J. Cell Biol. 2003; 163: PubMed Scopus Google the p120 knockdown of of E-cadherin levels A and levels of were not A and of which is were cells were for at to internalized proteins in or by preventing from into the the also of proteins from the was and during the shown in the p120 knockdown cells a cell surface and increased intracellular of E-cadherin to E-cadherin, was on the cell surface at cell-cell contacts of the p120 knockdown of E-cadherin and was of E-cadherin was by p120 that of was not Although the amount of E-cadherin internalized under the conditions used is the internalization is consistent with the of intracellular of E-cadherin in the p120 knockdown of p120-uncoupled to that used to the surface expression of in cells A. E. J. Cell Biol. 1991; PubMed Scopus Google we to the recycling of internalized E-cadherin back to the cell surface. proteins were at and cells were for at to the internalization and of E-cadherin. with to from cell surface the cells were at to were with and E-cadherin to was by with The were with to E-cadherin. The was by and with E-cadherin was on the surface of cells that were not at E-cadherin was on the surface a at E-cadherin increased for the at which the A and At the of of internalized E-cadherin recycled back to the cell surface. The amount of recycled increased at a E-cadherin for at at of the internalized recycled that internalized can also be recycled to the cell surface at a E-cadherin. In this we that E-cadherin and E-cadherin for p120 binding endocytosis by a found that the p120-uncoupled E-cadherin is internalized from the cell surface at a that of E-cadherin. internalization of p120-uncoupled E-cadherin to on in this A conserved dileucine motif at in the juxtamembrane cytoplasmic domain was as a and shown to be necessary for E-cadherin endocytosis. of the dileucine motif with two alanine residues resulted in reduced endocytosis of and p120-uncoupled E-cadherin. that the dileucine motif is to be a for the E-cadherin The dileucine motif of E-cadherin is as it the amino in the or J.S. Rev. 2003; PubMed Scopus Google Scholar). it is to the domain dileucine in other proteins J.S. Rev. 2003; PubMed Scopus Google Scholar). Although dileucine have been shown to be to mediate endocytosis and to or residues to the motif to be for to or not for internalization J.S. Rev. 2003; PubMed Scopus Google Scholar). The of residues to the dileucine the of E-cadherin. Consistent with this E-cadherin for p120 binding is internalized and is in not of cells with to not the expression of p120-uncoupled E-cadherin, indicating that the was not for A recent that is essential for the of E-cadherin to J.S. Y. C. Mol. Cell Biol. 2005; PubMed Scopus Google Scholar). Therefore, it is that p120 binding to E-cadherin not in steady-state because another such as is the uncoupling p120 binding was not for and subsequent Although p120 binding to E-cadherin not steady-state level of the protein, depletion of p120 E-cadherin levels. At we not the for this of E-cadherin was by the p120 knockdown cells at which is a that of Therefore, it is that other binding interactions involved in internalization are by the The dileucine motif of E-cadherin mediate binding to adaptor such as and the to J.S. Rev. 2003; PubMed Scopus Google Scholar). The dileucine motif was by amino from the residues necessary for p120 binding that p120 for these interactions and to the of cadherins into the It has been shown that of p120 reduced the internalization of a of the extracellular domain and the cytoplasmic domain, not a with amino acid substitutions in the p120-binding site that p120 binding K. J. Dejana E. Mol. Biol. Cell. 2005; PubMed Scopus Google Scholar). p120 to the cadherin to function as a The p120 is selective for and not the endocytosis because p120 on internalization K. J. Dejana E. Mol. Biol. Cell. 2005; PubMed Scopus Google Scholar). on these we a in which p120 binding to the dileucine motif of preventing interactions with adaptor proteins and subsequent endocytosis. A has been by the K. J. Dejana E. Mol. Biol. Cell. 2005; PubMed Scopus Google Scholar). Consistent with this we found that p120 knockdown endocytosis of E-cadherin not that of the E-cadherin the dileucine found that the uncoupling of p120 binding not increased the of E-cadherin, also its recycling back to the cell surface, that p120 binding at two in in trafficking of the in of the in and on the cell surface at Although studies not evidence to p120 as a regulator of E-cadherin p120 has been implicated in other trafficking such as the of of intercellular junctions S. J. Cell Biol. 2003; 163: PubMed Scopus Google Scholar). of in the region of cells with the of intracellular pool of the p120-uncoupled E-cadherin. results that the p120-uncoupled E-cadherin recycled back to the cell surface at a that of E-cadherin to be consistent with this studies that trafficking of E-cadherin is regulated by cell-cell (19Le T.L. Yap A.S. Stow J.L. J. Cell Biol. 1999; 146: 219-232Crossref PubMed Scopus (482) Google Scholar) or by cellular proteins that Rho family G. Sakisaka T. Baba T. Tanaka S. Morimoto K. Takai Y. J. Cell Biol. 2004; 166: 237-248Crossref PubMed Scopus (152) Google Scholar). At we not internalization and subsequent recycling of the p120-uncoupled E-cadherin constitutively or of p120 binding has been shown to the of E-cadherin to M. M.A. Reynolds A.B. Yap A.S. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). it has been shown that p120 is involved in of Rho by to domains cadherins M.A. J. Reynolds A.B. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). it is to the that endocytosis of this protein. The results of this the that p120 regulates E-cadherin endocytosis by masking the dileucine motif to interactions with adaptor proteins required for internalization. Although adaptor proteins to to dileucine are proteins that be for the internalization of E-cadherin J.S. Rev. 2003; PubMed Scopus Google the one or molecules for the of the dileucine motif have yet to be to the binding of the dileucine motif is in in