REGULATION OF MITOGENESIS AND APOPTOSIS BY G PROTEINS

细胞数量在一定程度上是由有丝分裂反应和凋亡反应之间的平衡调节的。异三聚体GTP结合蛋白(G蛋白)可以传递促进有丝分裂的生长信号。我们已经证明了异源三聚体G12和G13蛋白的α亚基诱导小鼠成纤维细胞有丝分裂和肿瘤转化。相反，Galpha12和Galpha13诱导人内皮细胞凋亡。我们的数据表明，Galpha12和Galpha13可以刺激多种信号通路，包括Ras和Rho家族的单体G蛋白以及丝裂原活化蛋白激酶(MAP)通路。RAS和RHO家族的G蛋白在细胞有丝分裂和肿瘤转化中起重要作用。然而，有相当多的证据表明，Ras和Rho家族的G蛋白可以促进细胞凋亡。Galpha12和Galpha13对有丝分裂和凋亡反应的不同影响可能反映了在不同环境和不同细胞类型下对多种信号通路的利用。我们将测试Galpha12和Galpha13蛋白调节多个信号通路的假设，这些信号通路产生导致有丝分裂或凋亡反应的分叉信号。为了验证这一假设，我们将结合生化、细胞和遗传学方法来研究导致G蛋白诱导有丝分裂或凋亡的特定信号通路。特别是，我们将确定Ras和Rho家族G蛋白的作用，以及MAP激酶通路在Galpha12和Galpha13蛋白诱导的有丝分裂和凋亡反应中的作用。为了了解Galpha12和Galpha13不同作用的分子基础，我们将确定caspase和Bcl-2在G蛋白诱导的细胞凋亡反应中的作用。最后，我们将使用酵母双杂交筛选cDNA文库来鉴定与Galpha12和Galpha13相互作用的效应蛋白，并将表征相互作用蛋白在介导有丝分裂或凋亡反应中的作用。这些研究对于理解组织增殖和凋亡的控制以及设计控制癌细胞增殖的新策略至关重要。

Cell number is regulated, in part, by a balance between mitogenic and apoptotic responses. Heterotrimeric GTP-binding proteins (G proteins) can transmit growth signals leading to mitogenesis. We have shown that alpha subunits of heterotrimeric G12 and G13 proteins induce mitogenesis and neoplastic transformation in mouse fibroblasts. In contrast, Galpha12 and Galpha13 induce apoptosis in human endothelial cells. Our data suggest that Galpha12 and Galpha13 can stimulate multiple signaling pathways, including Ras and Rho family of monomeric G proteins and the mitogen-activated protein kinase (MAP) pathways. Ras and Rho families of G proteins play an important role in mitogenesis and neoplastic transformation of the cell. However, there is considerably evidence that Ras and Rho families of G proteins can promote apoptosis. The variable effects of Galpha12 and Galpha13 on mitogenic and apoptotic responses could reflect the utilization of the multiple signaling pathways under different circumstances and in different cell types. We will test the hypothesis that Galpha12 and Galpha13 proteins regulate multiple signaling pathways which produce bifurcating signals leading to mitogenic or apoptotic response. To test this hypothesis, we will use the combination of biochemical, cellular, and genetic approaches to investigate the specific signaling pathways leading to G protein-induced mitogenesis or apoptosis. In particular, we will determine the role of Ras and Rho family of G proteins and the MAP kinase pathways in mitogenic and apoptotic responses induced by Galpha12 and Galpha13 proteins. To understand the molecular basis of variable effects of Galpha12 and Galpha13, we will determine the role of caspases and Bcl-2 in the G protein- induced apoptotic response. Finally, we will identify the effector proteins interacting with Galpha12 and Galpha13 using yeast two-hybrid screening of cDNA libraries and will characterize the role of interacting proteins in mediating mitogenic or apoptotic responses. These studies are critical for understanding of the control of tissue proliferation and apoptosis and for design of novel strategies to control proliferation of cancerous cells.