RAS- AND CERAMIDE-MEDIATED CONTROL OF CELL GROWTH IN YEAST

我们计划研究两个信号转导系统， 酵母菌中细胞周期的启动，两者都是 与哺乳动物细胞中的信号转导途径同源。的 第一种系统由Ras蛋白介导，Ras蛋白在结构上和 功能上与人ras蛋白同源，并提供阳性 激活细胞周期起始。第二个系统，由一个 新的脂质第二信使神经酰胺，显示出惊人的相似性， 多种哺乳动物生长调节剂-包括 TNF α和γ-干扰素调节细胞增殖。我们有 显示该途径的激活抑制细胞周期的起始 酵母中的进展，类似于哺乳动物细胞对 激活这条通路。因此，这两种途径似乎在 在酵母和哺乳动物细胞中的对立，以提供平衡的细胞 增长 对于这两种信号转导系统，我们计划研究其性质， 的相互作用的途径，该机制， 这些信号冲击每个通路，而下游目标， 负责通路激活的生理后果。 对于Ras通路，我们将重点关注以下蛋白的功能和激活： Cdc 25 p，Ras鸟嘌呤核苷酸交换因子，似乎 介导输入到通路中。此外，我们还将探讨 Ras途径在蛋白质分泌和可能的相互作用 Ras途径和细胞骨架组织。对于神经酰胺 信号转导，我们已经表明，神经酰胺诱导的抑制 酵母细胞增殖由神经酰胺活化蛋白介导 磷酸酶，这是我们所描述的。酵母还含有一种神经酰胺 与哺乳动物细胞中发现的非常相似的活化蛋白激酶。 我们提出了一个遗传分析，以确定（1）激酶的作用， 生长控制，（2）信号进入途径的性质和（3） 神经酰胺激活的磷酸酶和激酶的关键目标。的 对这些通路的拟议解剖应该提供有价值的见解 哺乳动物细胞限制其增殖的机制， 从中吸取的教训应该对理解 和治疗癌症。

We plan to investigate two signal transduction systems that regulate initiation of the cell cycle in the yeast Saccharomyces, both of which are homologous to signal transduction pathways in mammalian cells. The first system is mediated by Ras proteins, which are both structurally and functionally homologous to human ras proteins, and provides positive activation of cell cycle initiation. The second system, mediated by a novel lipid second messenger, ceramide, shows striking parallels to the pathway by which a variety of mammalian growth modulators - including TNFalpha and gamma-interferon - regulate cell proliferation. We have shown that activation of this pathway inhibits initiation of cell cycle progression in yeast, similar to the response of mammalian cells to activation of this pathway. Thus, the two pathways appear to work in opposition in both yeast and mammalian cells to provide balanced cell growth. For both signal transduction systems we plan to investigate the nature of the interactions of the components of the pathways, the mechanism by which signals impinge on each pathway, and the downstream targets that are responsible for the physiological consequences of pathway activation. For the Ras pathway, we will focus on the function and activation of Cdc25p, the Ras guanine nucleotide exchange factor, which appears to mediate input into the pathway. In addition, we will explore the role of the Ras pathway in protein secretion and in possible interactions between the Ras pathway and cytoskeletal organization of the cell. For ceramide signal transduction, we have shown that ceramide-induced inhibition of yeast cell proliferation is mediated by a ceramide activated protein phosphatase, which we have characterized. Yeast also contain a ceramide activated protein kinase quite similar to that found in mammalian cells. We propose a genetic analysis to determine (1) the role of the kinase in growth control, (2) the nature of the signal into the pathway and (3) the critical targets of the ceramide activated phosphatase and kinase. The proposed dissection of these pathways should provide valuable insight into the mechanism by which mammalian cells limit their proliferation, the lessons from which should have profound implications in understanding and treating cancer.