Interaction of lp-dlg/KIAA0583, a membrane-associated guanylate kinase family protein, with vinexin and beta-catenin at sites of cell-cell contact.

Vinexin is a recently identified cytoskeletal protein and plays a key role in the regulation of cytoskeletal organization and signal transduction. Vinexin localizes at sites of cell-extracellular matrix adhesion in NIH3T3 fibroblasts and at sites of cell-cell contact in epithelial LLC-PK1 cells. Expression of vinexin promotes the formation of actin stress fiber, but the role of vinexin at sites of cell-cell contact is unclear. Here we identified lp-dlg/KIAA0583 as a novel binding partner for vinexin by using yeast two-hybrid screening. lp-dlg/KIAA0583 has a NH2-terminal coiled-coil-like domain, in addition to four PDZ domains, an Src homology (SH) 3 domain, and a guanylate kinase domain, which are conserved structures in membrane-associated guanylate kinase family proteins. The third SH3 domain of vinexin bound to the region between the second and third PDZ domain of lp-dlg, which contains a proline-rich sequence. lp-dlg colocalized with vinexin at sites of cell-cell contact in LLC-PK1 cells. Furthermore, lp-dlg colocalized with beta-catenin, a major adherens junction protein, in LLC-PK1 cells. Co-immunoprecipitation experiments revealed that both endogenous and epitope-tagged deletion mutants of lp-dlg/KIAA0583 associated with beta-catenin. We also showed that these three proteins could form a ternary complex. Together these findings suggest that lp-dlg/KIAA0583 is a novel scaffolding protein that can link the vinexin-vinculin complex and beta-catenin at sites of cell-cell contact.