Unsuspected roles of the endocytic protein epsin in cell polarity regulation

B. COON, S. LONGHI, B. WENDLAND AND RC AGUILAR

Chicago, IL, USA

Simposio; Annual Basic Science Colloqium, Northwestern University.; 2006

Northwestern University

Epsins are endocytic proteins with a structured Epsin N-terminal Homology (ENTH) domain that binds phosphoinositides and a poorly structured C-terminal region that interacts with ubiquitin and endocytic machinery, including clathrin and endocytic scaffolding proteins. Yeast has two redundant genes encoding epsins, ENT1 and ENT2; deleting both genes is lethal. We demonstrate that the ENTH domain is both necessary and sufficient for viability of double epsin KO cells. Mutational analysis of the ENTH domain revealed a surface patch that is essential for viability and that binds guanine nucleotide triphosphatase-activating proteins (GAPs) for Cdc42, a critical regulator of cell polarity in all eukaryotes. Mutations in this epsin essential region lead to severe cell polarity and viability defects, we also show that the epsins contribute to regulation of specific Cdc42 signaling pathways in yeast cells. Importantly, our results indicate conservation of this epsin-regulated Cdc42 pathway in mammalian cells (including human HeLa cells). These data support a model in which the epsins function as spatial and temporal coordinators of endocytosis and cell polarity.