Abstract #88A

Localization of the yeast ortholog of the human Wiskott-Aldrich Syndrome Protein-Interacting Protein (WIP) to the cortical actin cytoskeleton is not essential for endocytosis. Gang Ren^1,2,3, Neeyor Bose², Barbara Winsor³, Alan L. Munn^1,2. 1) Institute for Molecular Bioscience, The University of Queensland, St Lucia, Queensland, AUSTRALIA; 2) Institute of Molecular and Cell Biology, A*STAR Biomedical Sciences Institutes, Singapore, 138673, Republic of Singapore; 3) Centre National Recherche Scientifique, Université Louis Pasteur, UMR7156, Strasbourg, 67084, FRANCE.
   The actin cytoskeleton is a highly dynamic network of signalling and structural proteins that regulates the gross morphology and internal organization of cells. During the cell division cycle the distribution of the actin cytoskeleton changes. Early in the cell cycle, cortical patches (spots) of actin concentrate in the bud where deposition of new cell wall material allows for bud expansion. Once the bud approaches the size of the mother cell, the cortical actin patches redistribute to the bud neck where deposition of new cell wall material separates the cytoplasm of mother and daughter cells during cytokinesis. The actin cytoskeleton functions in both exocytic membrane traffic to the cell surface and in endocytic membrane traffic from the cell surface. Either trafficking pathway (or both) may be important for cytokinesis. Cortical actin patches have been proposed to be sites of endocytosis. We have performed structure-function analysis on the cortical actin patch protein known as verprolin/Vrp1p (the yeast ortholog of the human Wiskott-Aldrich Syndrome Protein Interacting Protein). We find that the roles of verprolin in endocytic membrane traffic of membrane and fluid and in cytokinesis are indeed linked. Strikingly, however, neither endocytosis nor cytokinesis require that verprolin localize to cortical actin patches nor do they require a polarized distribution of cortical actin patches. Instead, we find that the ability of proline-rich motifs within the Hof One Trap (HOT) domain of verprolin to bind the Src Homology 3 (SH3) domain of the cytokinesis regulator Hof1p is critical for both endocytosis and cytokinesis. Verprolin may act as a chaperone to prevent SH3-mediated aggregation of Hof1p in the cytoplasm.

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