title: IQ-domain GTPase-activating protein 1 regulates beta-catenin at membrane ruffles and its role in macropinocytosis of N-cadherin and adenomatous polyposis coli.
abstract: Beta-catenin is an integral component of E-cadherin dependent cell-cell junctions. Here we show that beta-catenin co-localizes with IQ-domain GTPase-activating protein 1 (IQGAP1), adenomatous polyposis coli (APC), and N-cadherin at actin-positive membrane ruffles in NIH 3T3 fibroblasts. We used deletion mapping to identify the membrane ruffle-targeting region of beta-catenin, localizing it to amino acids 47-217, which overlap the IQGAP1 binding site. Knockdown by small interference RNA (siRNA) revealed IQGAP1-dependent membrane targeting of beta-catenin, APC, and N-cadherin. Transient overexpression of IQGAP1 or N-cadherin increased beta-catenin at membrane ruffles. IQGAP1/APC regulates cell migration, and using a wound healing assay we demonstrate that siRNA-mediated loss of beta-catenin also caused a modest reduction in the rate of cell migration. More significantly, we discovered that beta-catenin is internalized by Arf6-dependent macropinocytosis near sites of membrane ruffling. The beta-catenin macropinosomes co-stained for APC, N-cadherin, and to a lesser extent IQGAP1, and internalization of each binding partner was abrogated by siRNA-dependent knockdown of beta-catenin. In addition, beta-catenin macropinosomes co-localized with the lysosomal marker, lysosome associated membrane protein 1, consistent with their recycling by the late endosomal machinery. Our findings expand on current knowledge of beta-catenin function. We propose that in motile cells beta-catenin is recruited by IQGAP1 and N-cadherin to active membrane ruffles, wherein beta-catenin mediates the internalization and possible recycling of the membrane-associated proteins N-cadherin and APC.
authors.affiliation: Westmead Institute for Cancer Research, University of Sydney, Westmead Millennium Institute at Westmead Hospital, Westmead, New South Wales 2145, Australia.
authors.forename: Manisha
authors.initials: M
authors.lastname: Sharma
authors.forename: Beric R
authors.initials: BR
authors.lastname: Henderson
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000378:metabolism*; D000818:Animals; D015820:Cadherins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D002465:Cell Movement; D004847:Epithelial Cells / Q000378:metabolism; D006801:Humans; D051379:Mice; D008954:Models, Biological; D041681:NIH 3T3 Cells; D010873:Pinocytosis; D011485:Protein Binding; D051176:beta Catenin / Q000096:biosynthesis*; D020703:ras GTPase-Activating Proteins / Q000502:physiology*
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D015820:Cadherins; C101203:IQ motif containing GTPase activating protein 1; D051176:beta Catenin; D020703:ras GTPase-Activating Proteins