Faure M, Voyno-Yasenetskaya T A, Bourne H R
Department of Pharmacology, University of California, San Francisco 94143.
J Biol Chem. 1994 Mar 18;269(11):7851-4.
Mitogen-activated protein kinases (MAPKs) are activated by a variety of extracellular stimuli, including agonists for G protein-coupled receptors. Using transient transfection of COS-7 cells, we have studied the stimulation of a hemagglutinin-tagged p44mapk (p44HA-mapk) by receptors coupled to Gs, Gq, and Gi. Agonists that act via all three G proteins stimulated p44HA-mapk activity. A constitutively activated alpha s mutant, forskolin, and a cAMP analog also increased p44HA-mapk activity, indicating that cAMP in COS-7 cells, in contrast to other cell types, activates the MAPK pathway. Similarly, a constitutively activated alpha q mutant, overexpression of phospholipase C-beta 2, and a phorbol ester also stimulated p44HA-mapk, suggesting that Gq-coupled receptors stimulate the MAPK pathway by increasing phosphatidylinositol turnover and probably stimulating protein kinase C. In COS-7 cells, in contrast to Rat-1 cells, mutationally activated alpha i did not stimulate the MAPK pathway. G protein beta and gamma subunits, overexpressed together, did activate p44HA-mapk; this finding suggests that in COS-7 cells Gi-coupled receptors may stimulate the MAPK pathway through beta gamma. These unexpected results in COS-7 cells show that G proteins and second messengers regulate the MAPK pathway differently in different cell types.
丝裂原活化蛋白激酶（MAPKs）可被多种细胞外刺激激活，包括G蛋白偶联受体的激动剂。通过瞬时转染COS-7细胞，我们研究了与Gs、Gq和Gi偶联的受体对血凝素标记的p44mapk（p44HA-mapk）的刺激作用。通过所有三种G蛋白起作用的激动剂均可刺激p44HA-mapk活性。组成型激活的αs突变体、福斯可林和一种环磷酸腺苷（cAMP）类似物也可增加p44HA-mapk活性，这表明与其他细胞类型不同，COS-7细胞中的cAMP可激活MAPK途径。同样，组成型激活的αq突变体、磷脂酶C-β2的过表达和佛波酯也可刺激p44HA-mapk，这表明与Gq偶联的受体通过增加磷脂酰肌醇周转率并可能刺激蛋白激酶C来刺激MAPK途径。与大鼠1细胞不同，在COS-7细胞中，突变激活的αi不会刺激MAPK途径。一起过表达的G蛋白β和γ亚基确实可激活p44HA-mapk；这一发现表明，在COS-7细胞中，与Gi偶联的受体可能通过βγ刺激MAPK途径。COS-7细胞中的这些意外结果表明，G蛋白和第二信使在不同细胞类型中对MAPK途径的调节方式不同。
