Heterotrimeric G Protein-Mediated Cellular Polarization in Yeast

异源三聚体 G 蛋白介导的酵母细胞极化

• 批准号: 0218081
• 负责人: David Stone
• 金额: $ 9万
• 依托单位: University of Illinois at Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-09-15 至 2004-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0218081&HistoricalAwards=false
• 关键词: Heterotrimeric; Protein; Mediated; Cellular; Polarization

Cellular polarization is essential to morphogenesis, immune response, neuronal development, chemotropism, and motility. The budding yeast, Saccharomyces cerevisiae, is a well studied model eukaryote that exhibits numerous polarization phenomena, including signal-induced changes in cell shape and nuclear position. In the life cycle of S. cerevisiae, two haploid cells of opposite mating type, MATa and MATa, can conjugate to form a MATa/a diploid cell. Each mating type constitutively secretes a peptide mating pheromone that transforms vegetatively growing cells of opposite type into gametes. To prepare haploids for cellular and nuclear fusion, pheromone triggers the induction of mating specific genes, arrest in the G1 phase of the cell cycle, polarized growth toward the mating partner, and nuclear migration to the tip of the mating projection. The molecular mechanisms underlying transmission of the mating signal are well understood. Communication of the signal from the plasma membrane to the cytoplasm is mediated by a receptor-coupled heterotrimeric G protein. When occupied by ligand, the pheromone receptors activate the pheromone-responsive Ga protein (encoded by GPA1) via guanine nucleotide exchange and the concomitant dissociation of Ga?GTP from the Gbg dimer (encoded by STE4 and STE18). The signal is then transmitted by Gbg to a mitogen?activated protein (MAP) kinase cascade. The MAP kinase module consists of Ste11 (the MEKK), Ste7 (the MEK), and Fus3 (the MAPK). In addition to stimulating the mating signal, Gbg serves as a positional cue. It directs the dual function protein, Far1, to the growth site. Far1 serves as a scaffold. It brings together elements that stimulate polarization of the actin cytoskeleton. Under physiological conditions, the Gbg-Far1 complex is presumed to assemble in the region of the cell surface that experiences the highest concentration of pheromone, and to mark this area for growth. Thus, the cell orients its growth toward the source of pheromone. This is called chemotropism. Recent results implicate the pheromone-responsive Ga protein, Gpa1, in control of signal-induced polarization and nuclear movement. In cells responding to pheromone, Gpa1 interacts directly with the mating-specific MAP kinase, Fus3, and with Kar3, a kinesin-like protein that is essential for nuclear movement during mating. Disruption of the Gpa1-Fus3 interaction confers defects in chemotropism and nuclear migration. The goals of this investigation are to determine which chemotropic factors depend on the recruitment of Fus3 by Gpa1, and to determine how Gpa1 affects nuclear movement during mating. In the work funded by NSF, the following hypothesis will be tested: Gpa1 co-localizes Fus3 and Kar3 so that Fus3 can activate Kar3. Because there is no precedent for regulation of kinesins by Ga proteins or MAP kinases, and because it is not known how kinesins are activated, this work promises to be of great value to those studying microtubule-associated motor proteins. The broader impact of this investigation is that it will enhance our understanding of chemotropism and nuclear movement, two fundamental aspects of cellular function. Students at all levels will be involved in this research.

细胞极化对于形态发生、免疫应答、神经元发育、趋化性和运动性是必不可少的。 芽殖酵母（Saccharomyces cerevisiae）是一种经过充分研究的模式真核生物，它表现出许多极化现象，包括信号诱导的细胞形状和核位置的变化。 在S.在酿酒酵母中，相反交配类型的两个单倍体细胞MATa和MATa可以缀合以形成MATa/a二倍体细胞。 每种交配类型组成性地分泌肽交配信息素，其将相反类型的植物生长细胞转化为配子。 为了制备用于细胞和核融合的单倍体，信息素触发交配特异性基因的诱导，在细胞周期的G1期停滞，向交配伴侣极化生长，以及核迁移到交配突起的尖端。 交配信号传递的分子机制已经很清楚了。 从质膜到细胞质的信号传递是由受体偶联的异源三聚体G蛋白介导的。 当被配体占据时，信息素受体通过鸟嘌呤核苷酸交换和伴随的Ga解离激活信息素响应Ga蛋白（由GPA 1编码）？来自Gbg二聚体的GTP（由STE 4和STE 18编码）。 然后信号通过Gbg传输到有丝分裂原？活化蛋白（MAP）激酶级联。 MAP激酶模块由Ste 11（MEK）、Ste 7（MEK）和Fus 3（MAPK）组成。 除了刺激交配信号外，Gbg还充当位置线索。 它将双功能蛋白Far 1引导到生长位点。 Far 1充当脚手架。 它汇集了刺激肌动蛋白细胞骨架极化的元素。 在生理条件下，Gbg-Far 1复合物被推测在经历最高浓度的信息素的细胞表面的区域中组装，并标记该区域用于生长。 因此，细胞的生长方向是信息素的来源。 这被称为趋化性。最近的研究结果牵连的信息素响应Ga蛋白，Gpa 1，在控制信号诱导的极化和核运动。 在对信息素作出反应的细胞中，Gpa 1直接与交配特异性MAP激酶Fus 3和Kar 3相互作用，Kar 3是一种驱动蛋白样蛋白，在交配过程中对核运动至关重要。 Gpa 1-Fus 3相互作用的破坏赋予向化性和核迁移的缺陷。 本研究的目的是确定哪些趋化因子依赖于Gpa 1对Fus 3的招募，并确定Gpa 1如何影响交配过程中的核运动。 在NSF资助的工作中，将测试以下假设：Gpa 1共定位Fus 3和Kar 3，以便Fus 3可以激活Kar 3。 由于没有Ga蛋白或MAP激酶调节驱动蛋白的先例，并且还不知道驱动蛋白是如何被激活的，因此这项工作对研究微管相关马达蛋白的人具有很大的价值。 这项研究的更广泛的影响是，它将提高我们对趋化性和核运动的理解，这是细胞功能的两个基本方面。各级学生都将参与这项研究。