RESEARCH ARTICLE Src Family Tyrosine Kinase Signaling Regulates FilGAP through Association with

FilGAP is a Rac-specific GTPase-activating protein (GAP) that suppresses lamellae forma-tion. In this study, we have identified RBM10 (RNA Binding Motif domain protein 10) as a Fil-GAP-interacting protein. Although RBM10 is mostly localized in the nuclei in human melanoma A7 cells, forced expression of Src family tyrosine kinase Fyn induced transloca-tion of RBM10 from nucleus into cell peripheries where RBM10 and FilGAP are co-local-ized. The translocation of RBM10 from nucleus appears to require catalytic activity of Fyn since kinase-negative Fyn mutant failed to induce translocation of RBM10 in A7 cells. When human breast carcinoma MDA-MB-231 cells are spreading on collagen-coated coverslips, endogenous FilGAP and RBM10 were localized at the cell periphery with tyrosine-phos-phorylated proteins. RBM10 appears to be responsible for targeting FilGAP at the cell periphery because depletion of RBM10 by siRNA abrogated peripheral localization of Fil-GAP during cell spreading. Association of RBM10 with FilGAP may stimulate RacGAP activity of FilGAP. First, forced expression of RBM10 suppressed FilGAP-mediated cell spreading on collagen. Conversely, depletion of endogenous RBM10 by siRNA abolishe