title: Rack1 promotes epithelial cell-cell adhesion by regulating E-cadherin endocytosis.
abstract: E-cadherin and its cytoplasmic partners, catenins, mediate epithelial cell-cell adhesion. Disruption of this adhesion allows cancer cells to invade and metastasize. Aberrant activation of the Src tyrosine kinase disrupts cell-cell contacts through an E-cadherin/catenin-dependent mechanism. Previously we showed that Rack1 regulates the growth of colon cells by suppressing Src activity at G(1) and mitotic checkpoints, and in the intrinsic apoptotic and Akt cell survival pathways. Here we show that Rack1, partly by inhibiting Src, promotes cell-cell adhesion and reduces the invasive potential of colon cancer cells. Rack1 stabilizes E-cadherin and catenins at cell-cell contacts by inhibiting the Src phosphorylation of E-cadherin, the ubiquitination of E-cadherin by the E3 ligase Hakai and the endocytosis of E-cadherin. Upon depletion and restoration of extracellular calcium, Rack1 facilitates the re-assembly of E-cadherin-containing cell-cell contacts. Rack1 also blocks HGF-induced endocytosis of E-cadherin, disruption of cell-cell contacts and cell scatter. Our results uncover a novel function of Rack1 in maintaining the junctional homeostasis of intestinal epithelial cells by regulation of the Src- and growth factor-induced endocytosis of E-cadherin.
authors.affiliation: Department of Medicine, Stanford University, Stanford, CA 94305-5187, USA.
authors.forename: G
authors.initials: G
authors.lastname: Swaminathan
authors.forename: C A
authors.initials: CA
authors.lastname: Cartwright
mesh_terms: D015820:Cadherins / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology*; D004705:Endocytosis; D019204:GTP-Binding Proteins / Q000378:metabolism*; D057809:HEK293 Cells; D017228:Hepatocyte Growth Factor / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism / Q000473:pathology*; D009361:Neoplasm Invasiveness; D009363:Neoplasm Proteins / Q000378:metabolism*; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D015820:Cadherins; C066855:HGF protein, human; D009363:Neoplasm Proteins; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D017228:Hepatocyte Growth Factor; D044767:Ubiquitin-Protein Ligases; D019061:src-Family Kinases; D019204:GTP-Binding Proteins; D002118:Calcium