Regulation of Cell Polarity and Exocytosis

描述（由申请人提供）：将蛋白质递送至细胞表面的适当位置对于大量细胞生物学过程（包括细胞不对称性和极性的发展）是重要的。细胞表面组分的递送主要通过与质膜的特定区域融合的转运囊泡的递送来实现。我们正在研究质膜靶向事件的酵母，酿酒酵母，以利用遗传和细胞生物学工具，在这种生物体。SNARE蛋白被认为在转运囊泡与质膜的靶向和/或融合中起核心作用，并且我们已经鉴定并广泛表征了一组SNARE蛋白，其是酵母中细胞表面转运所需的。我们对这些蛋白质的遗传和生化分析使我们确定了一种新的调控途径，涉及Rho GTPases Cdc 42和Rho 3，以及一种新的Sec 9结合蛋白，称为Sro 7，与果蝇肿瘤抑制因子致死性巨型幼虫有关。我们实验室最近的工作表明，Cdc 42在胞吐作用中的功能仅限于芽出现的非常早期，而Rho 3似乎在整个细胞周期中在这方面发挥作用。这表明，这一途径可能是中央的整体协调的极性的肌动蛋白细胞骨架与极性的细胞表面交付。来自哺乳动物上皮细胞培养模型的证据表明，Sro 7/Lgl在胞吐中的功能在高等真核细胞中是保守的。这些研究将对理解Rho GTP酶在胞吐中的功能以及揭示质膜t-SNARE功能调节的新机制具有重要意义。这种调节可能代表了真核细胞调节和协调肌动蛋白细胞骨架极性与蛋白质和脂质向细胞表面的极化递送的关键机制。最后，来自其他系统的研究表明，该途径的功能丧失与上皮细胞的极性丧失有关，这可能在上皮细胞的致瘤性转化中发挥关键作用-这是人类癌症最常见的来源。

DESCRIPTION (provided by applicant): Delivery of proteins to the proper place on the cell surface is important for a large number of cell biological processes, including the development of cellular asymmetry and polarity. The delivery of ceil surface components is accomplished primarily by the delivery of transport vesicles that fuse with a specific region of the ptasma membrane. We are examining plasma membrane targeting events in the yeast, Saccharomyces cerevisiae, in order to take advantage of the genetic and cell biological tools available in this organism. SNARE proteins are thought to play a central role in the targeting and/or fusion of transport vesicles with the plasma membrane, and we have identified and extensively characterized a set of SNARE proteins, which are required for ceil surface transport in yeast. Our genetic and biochemical analysis of these proteins has led us to the identification of a new regulatory pathway involving the Rho GTPases Cdc42 and Rho3, as well as a novel Sec9 binding protein, called Sro7, related to the Drosophila tumor suppressor lethal giant larvae. Recent work from our lab suggests that Cdc42 function in exocytosis is restricted to very early in bud emergence while Rho3 appears to function in this regard throughout the cell cycle. This suggests that this pathway may be central to the overall coordination of the polarity of the actin cytoskeleton with the polarity of cell surface delivery. Evidence from a mammalian epithelial cell culture model suggests that Sro7/Lgl function in exocytosis is conserved in higher eukaryotic cells. These studies will have important implications in both understanding the function of Rho GTPases in exocytosis as well as m unraveling a novel mechanism for regulation of t-SNARE function at the plasma membrane. This regulation may represent a key mechanism by which eukaryotic cells regulate and coordinate the polarity of the actin cytoskeleton with the polarized delivery of protein and lipid to the cell surface. Finally studies from other systems suggest that loss of function in this pathway is tied to the loss of polarity in epithelial cells, which may play a key role in the tumorigenic transformation of epithelial cells--the most common source of cancer in humans.