The endocytic protein Epsin regulates the Cdc42 signal transduction pathway through binding Cdc42 GTPase Activating Proteins

C. AGUILAR, S.A. LONGHI, J.D. SHAW, L.-Y. YEH, S. KIM, A. SCHÖN E. FREIRE, A. HSU, W.K. MCCORMICK, H.A. WATSON, B. WENDLAND

Saint Feliu de Guixols, Costa Brava, España

Conferencia; ESF Research Conference; 2005

EMBO

Epsins are endocytic proteins with a structured Epsin N-terminal Homology (ENTH) domain that binds phosphoinositides and a poorly structured carboxy-terminal region that interacts with ubiquitin and components of the endocytic machinery, including clathrin and endocytic scaffolding proteins. Yeast has two redundant genes encoding epsins, ENT1 and ENT2; deletion of both genes results in lethality. Here we show that the ENTH domain is both necessary and sufficient for viability of ent1∆ent2∆ cells, and that this essential function is independent of lipid binding. Instead, we mapped a distinct surface patch that is essential and that binds and regulates guanine nucleotide triphosphatase activating proteins (GAPs) for Cdc42, a critical regulator of cell polarity in all eukaryotes. Interaction between epsin and Cdc42 GAPs contributes to the regulation of Cdc42; impairing this interaction decreases the levels of activated Cdc42. Moreover, our results also suggest that the epsin-GAP complex plays a role in signal transduction, most likely facilitating the activation of specific Cdc42-dependent pathways. We also show evidence that this function is conserved in higher eukaryotes. We propose that epsin coordinates endocytosis and cell polarity, linking these two physiological events spatially and temporally.