cAMP-independent G protein signaling in yeast

酿酒酵母中的假菌丝和侵入性生长需要由G蛋白β亚基Gpa 2 p及其偶联受体Gpr 1介导的信号传导途径。gpr 1 p是一种低亲和力的葡萄糖受体，对环境中高浓度的葡萄糖有反应。从Gpr 1 p到Gpa 2 p的信号传递导致与高水平细胞内cAMP相关的表型。我们最近已经确定KRH 1和KRH 2的基因编码的Gpa 2 p信号通路的组件。我们已经表明，Krh 1 p和Krh 2 p的腺苷酸环化酶的下游作用，以抑制蛋白激酶A（PKA）的过程中，不涉及生产的细胞内cAMP。Gpa 2 p的激活被认为可以缓解 通过Krh 1 p和Krh 2 p抑制PKA，导致高水平的PKA活性。该项目的长期目标是：1）获得组成Gpa 2 p信号转导通路的分子过程的完整描述; 2）了解Gpa 2 p通路在整个细胞群体经历假菌丝生长方面的生物学功能。 该项目的第一个具体目标是确定Krh 1 p和Krh 2 p如何调节PKA。这些研究将调查Krh 1 p和Krh 2 p与PKA的结合是否是直接的，以及结合是否抑制PKA激酶活性。第二个具体目标是确定Krh 1 p和Krh 2 p是否通过影响PKA的定位来控制信号传导。第三个具体目的是通过确定GPA 2的非活化和组成型等位基因对Krh 1 p和Krh 2 p功能的影响，研究Gpa 2 p的GTP结合形式是否阻断Krh 1 p和Krh 2 p的抑制功能。第四个具体目标是测试Gpa 2 p是否在生长菌落边缘的细胞中特异性激活，以抑制应激和饥饿反应，并促进生长和假菌丝发育。这一目标的目标是发展一个 报告系统，以允许在整个菌落的水平上检测活化的Gpa 2 p， 假菌丝生长。这些研究将提供有关G蛋白介导的信号通路的新信息，这些信号通路对于人类许多生理过程的正常运作至关重要。

Pseudohyphal and invasive growth in the yeast Saccharomyces cerevisiae require a signaling pathway that is mediated by the G protein beta-subunit Gpa2p and its coupled receptor Gpr1. Gpr1p is a low affinity glucose receptor that responds to high concentrations of glucose in the environment. Transmission of a signal from Gpr1p to Gpa2p results in phenotypes associated with high levels of intracellular cAMP. We have recently identified KRH1 and KRH2 as genes that encode components of the Gpa2p signaling pathway. We have shown that Krh1p and Krh2p act downstream of adenylyl cyclase to inhibit protein kinase A (PKA) by a process that does not involve production of intracellular cAMP. Activation of Gpa2p is thought to relieve the inhibition of PKA by Krh1p and Krh2p, resulting in high levels of PKA activity. The long-term objectives of this project are: 1) To obtain a complete description of the molecular processes that comprise the Gpa2p signal transduction pathway; 2) To understand the biological function of the Gpa2p pathway in terms of an entire cell population undergoing pseudohyphal growth. The first specific aim of this project is to determine how Krh1p and Krh2p regulate PKA. These studies will investigate whether binding of Krh1p and Krh2p to PKA is direct and whether binding inhibits PKA kinase activity. The second specific aim is to determine whether Krh1p and Krh2p control signaling by affecting the localization of PKA. The third specific aim is to investigate whether the GTP-bound form of Gpa2p blocks the inhibitory function of Krh1p and Krh2p by determining the effects of non-activatable and constitutive alleles of GPA2 on Krh1p and Krh2p function. The fourth specific aim is to test whether Gpa2p is specifically activated in cells at the edge of a growing colony in order to suppress stress and starvation responses and to promote growth and pseudohyphal development. The goal of this aim is to develop a reporter system to allow detection of activated Gpa2p at the level of a whole colony undergoing pseudohyphal growth. These studies will provide new information about G protein-mediated signaling pathways, which are essential for the proper functioning of many physiological processes in humans.