Regulation of Cell Polarity and Exocytosis

描述（由申请人提供）：将蛋白质递送到细胞表面的适当位置对于大量细胞生物学过程非常重要，包括细胞不对称和极性的发展。细胞表面成分的递送主要是通过运输囊泡的递送来完成的，这些运输囊泡与原质膜的特定区域融合。我们正在研究酵母（Saccharomyces cerevisiae）的质膜靶向事件，以便利用这种生物中可用的遗传和细胞生物学工具。SNARE蛋白被认为在运输囊泡与质膜的靶向和/或融合中起着核心作用，我们已经鉴定并广泛表征了一组SNARE蛋白，它们是酵母中细胞表面运输所必需的。我们对这些蛋白质的遗传和生化分析使我们确定了一个新的调控途径，涉及Rho GTPases Cdc42和Rho3，以及一个新的Sec9结合蛋白，称为Sro7，与果蝇肿瘤抑制致死巨型幼虫有关。我们实验室最近的工作表明，Cdc42在胞吐作用中的作用仅限于芽出的早期，而Rho3似乎在整个细胞周期中都在这方面发挥作用。这表明，这一途径可能是肌动蛋白细胞骨架极性与细胞表面递送极性整体协调的核心。来自哺乳动物上皮细胞培养模型的证据表明，Sro7/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 gtpase在胞吐作用中的功能以及揭示质膜上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的极性以及向细胞表面极化传递蛋白质和脂质的关键机制。最后，来自其他系统的研究表明，这一途径的功能丧失与上皮细胞极性的丧失有关，这可能在上皮细胞的致瘤转化中起关键作用——上皮细胞是人类最常见的癌症来源。

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.