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Title: Functions of the dynamin-like protein VPS1 in actin organization in Saccharomyces Cerevisiae
Keywords: endocytosis/GTPase/dynamin/actin/Vps1p/Sla1p
Issue Date: 28-Sep-2005
Citation: YU XIANWEN (2005-09-28). Functions of the dynamin-like protein VPS1 in actin organization in Saccharomyces Cerevisiae. ScholarBank@NUS Repository.
Abstract: Endocytosis, the retrograde vesicle trafficking event originated from the plasma membrane, serves multiple fundamental roles in eukaryotic cells such as the recycle of membrane materials, down regulation of receptor-mediated signalling, and uptake of nutrients. This process is highly conserved through evolution from yeast to mammal. In mammalian cells, one of the best known factors which participate in the first step of endocytosis (membrane invagination) is the large GTPase dynamin. Dynamin is believed to promote membrane constriction, fission, and vesicle formation through anchoring to the neck of membrane invaginations and undergoing conformational changes upon GTP hydrolysis. Dynamin-interacting proteins including syndapin, intersectin and cortactin, serve as bridge molecules to connect actin cytoskeleton to the endocytosis via interacting with actin assembly activators such as WASP and Arp2/3 complex to modulate the actin organization at the endocytic sites. In budding yeast Saccharomyces cerevisiae, interestingly, the endocytic machinery shares an evolutionary conservation with that identified in higher eukaryotic cells and the crucial roles of actin cytoskeleton organization in the endocytosis of budding yeast also have been demonstrated. However, the roles of yeast dynamin-related proteins in endocytosis have not been thoroughly investigated so far. The primary aim of our study was to examine the possible involvement of yeast dynamin-related protein in endocytosis and actin organization. In this study, we found that one of the yeast dynamin-related proteins, Vps1p, is required for normal actin cytoskeleton organization. At both permissive and nonpermissive temperatures, the vps1 mutants exhibit various degrees of phenotypes commonly associated with actin cytoskeleton defects: depolarized and aggregated actin structures, hypersensitivity to the actin cytoskeleton toxin Latrunculin-A, randomized bud site selection and chitin deposition, and impaired efficiency in the internalization of membrane receptors. Overexpression of the GTPase mutants of VPS1 also leads to actin abnormalities. Consistent with these actin-related defects, Vps1p is found to physically interact, and partially co-localize, with the actin-regulatory protein Sla1p. The normal cellular localization of Sla1p requires Vps1p and can be altered by overexpression of a region of Vps1p that is involved in the interaction with Sla1p. The same region also promotes missorting of the vacuolar protein carboxypeptidase Y upon overexpression. Our studies on Vps1p also suggest a close connection between actin organization and protein sorting at Golgi. Taken together, our results indicate that the yeast Vps1p is required for actin cytoskeleton organization and it may be involved in endocytosis through a mechanism different from that of mammalian dynamins.
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