Signaling mechanisms in cell polarity in yeast

描述（由申请人提供）：细胞极性对于发育和分化至关重要，并且在细胞迁移、跨上皮细胞的营养转运和神经元传递等基本过程中发挥重要作用。细胞极性的缺陷通常与严重的人类疾病如癌症有关。我们的长期目标是利用遗传上易处理的真核生物酿酒酵母来阐明细胞极化的原理。在这个建议中，我们将解决两个重要的问题，关于Cdc42p，一个进化保守的小GTdR，在极性发展中的核心作用。在目标1中，我们将确定Cdc42p的活动是如何时空调节其GAP，Rga1p和Bem2p，在形成一个单一的极化域，所有极化系统之间的共同问题。已知有四种GAP（Rga1p、Rga2、Bem3p和Bem2p）作用于Cdc42p。以前，我们和其他人已经表明，三个GAP（Rga1p，Rga2和Bem3p）在细胞周期开始时的septin环组装中发挥作用。最近，我们发现，Rga1p是唯一需要防止极化后胞质分裂细胞中的旧细胞分裂位点。在这个建议中，我们将测试我们的新想法，Rga1p和Bem2p冗余功能在芽颈作为“看门人”，以限制活性Cdc42p和Rho1p到一个单一的极化域，芽皮层。到目前为止，我们的研究表明，不同的GAP可以单独或共同作用，以调节特定的细胞过程，涉及Cdc42 p，并帮助建立了一个范式，研究复杂的调节哺乳动物Rho GTP酶（约17在人类基因组中）通过其众多的GAP（约68 Rho GAP在人类基因组中）。在目标2中，我们将提出实验来测试我们的综合模型Cdc42p在极化肌动蛋白和隔蛋白组织中的作用，它们共同决定了整体细胞的形状，并决定了它们在基本过程中的不同功能，如极化胞吐作用和定向细胞迁移。我们的模型指出，Cdc42p控制极化肌动蛋白和隔蛋白组织通过两个遗传上可分离的，但生物化学上的串扰途径，一个涉及进化上保守的“极化体”，这是集中在的cubbni1p，支架蛋白Spa2p，和Rab GAP Msb3p和Msb4p，和其他涉及酵母特异性Cdc42p效应Gic1p和Gic2p。在这个提议中，我们将确定极性体途径如何通过肌动蛋白细胞骨架影响隔蛋白组织，Gic途径如何通过隔蛋白影响肌动蛋白组织，以及这两种途径如何在细胞应力下通过Spa2p相互作用（如370C）进行串扰。Cdc42p的同源物参与许多细胞功能，例如细胞极性、细胞迁移和细胞生长控制。哺乳动物中Cdc42p活性的失调与严重的人类疾病如癌症有关。因此，研究Cdc42p在酵母中的信号转导机制具有重要的基础生物学和临床意义。 公共卫生相关性：Cdc42p是一种进化上保守的小G蛋白，在细胞极性、细胞迁移和细胞生长控制等多种细胞过程中发挥重要作用。哺乳动物中Cdc42p活性的失调与严重的人类疾病如癌症有关。因此，研究Cdc42p在酵母中的信号转导机制具有重要的基础生物学和临床意义。

DESCRIPTION (provided by applicant): Cell polarity is essential for development and differentiation, and it plays vital roles in fundamental processes such as cell migration, nutrient transport across epithelia, and neuronal transmission. Defects in cell polarity are often associated with serious human diseases such as cancer. Our long-term objective is to use the genetically tractable eukaryote Saccharomyces cerevisiae to elucidate the principles of cell polarization. In this proposal, we will address two important questions regarding the central role of Cdc42p, an evolutionarily conserved small GTPase, in polarity development. In Aim1, we will determine how Cdc42p activity is spatiotemporally regulated by its GAPs, Rga1p and Bem2p, in the formation of a single polarization domain, a common issue among all polarization systems. There are four GAPs (Rga1p, Rga2, Bem3p, and Bem2p) known to act on Cdc42p. Previously, we and others have shown that three GAPs (Rga1p, Rga2, and Bem3p) share a role in septin ring assembly at the beginning of the cell cycle. Recently, we discovered that Rga1p is uniquely required for preventing polarization within old cell division sites in post-cytokinesis cells. In this proposal, we will test our novel idea that Rga1p and Bem2p function redundantly at the bud neck as "gatekeepers" to restrict active Cdc42p and Rho1p to a single polarization domain, the bud cortex. To date, our studies have indicated that different GAPs can act alone or together to regulate specific cellular processes involving Cdc42p, and have helped establish a paradigm for studying complex regulation of mammalian Rho GTPases (~17 in human genome) by their numerous GAPs (~68 Rho GAPs in human genome). In Aim2, we will propose experiments to test our integrative model for the role of Cdc42p in polarized actin and septin organization, which together determine the overall cell shape and dictate their diverse functions in fundamental processes such as polarized exocytosis and directed cell migration. Our model states that Cdc42p controls polarized actin and septin organization via two genetically separable, but biochemically cross-talking pathways, one involving the evolutionarily conserved "polarisome" that is centered on the formin Bni1p, scaffold protein Spa2p, and the Rab GAPs Msb3p and Msb4p, and the other involving the yeast-specific Cdc42p effectors Gic1p and Gic2p. In this proposal, we will determine how the polarisome pathway affects septin organization via the actin cytoskeleton, how the Gic pathway affects actin organization via the septins, and how these two pathways crosstalk under cellular stresses such as 370C via Spa2p-based interactions. Homologues of Cdc42p are involved in numerous cellular functions such as cell polarity, cell migration, and cell growth control. Deregulation of Cdc42p activity in mammals is associated with serious human diseases, such as cancer. Thus, studying the signaling mechanisms of Cdc42p in yeast will have profound implication in basic biology and clinical sciences. PUBLIC HEALTH RELEVANCE: Cdc42p, an evolutionarily conserved small GTPase, plays essential roles in diverse cellular processes such as cell polarity, cell migration, and cell growth control. Deregulation of Cdc42p activity in mammals is associated with serious human diseases, such as cancer. Thus, studying the signaling mechanisms of Cdc42p in yeast will have profound implication in basic biology and clinical sciences.