Coso O A, Chiariello M, Kalinec G, Kyriakis J M, Woodgett J, Gutkind J S
Molecular Signaling Unit, NIDR, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1995 Mar 10;270(10):5620-4. doi: 10.1074/jbc.270.10.5620.
The expression of human muscarinic acetylcholine receptors (mAChRs) in NIH 3T3 cells has been used as a model for studying proliferative signaling through G protein-coupled receptors. In this biological system, the m1 class of mAChRs can effectively transduce mitogenic signals (Stephens, E.V., Kalinec, G., Brann, M.R., and Gutkind, J.S. (1993) Oncogene 8, 19-26) and induce malignant transformation if persistently activated (Gutkind, J.S., Novotny, E.A., Brann, M.R., and Robbins, K.C. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 4703-4708). Moreover, available evidence suggests that the m1-signaling pathway converges at the level of p21ras with that emerging from tyrosine kinase receptors (Crespo, P., Xu, N., Simonds, W.F., and Gutkind, J.S. (1994) Nature 369, 418-420). To explore nuclear events involved in growth regulation by G protein-coupled receptors in this setting, we compared the effect of platelet-derived growth factor (PDGF) and the cholinergic agonist, carbachol, on the expression of mRNA for members of the jun and fos family of nuclear proto-oncogenes. We found that activation of m1 receptors by carbachol induces the expression of a distinct set of nuclear transcription factors. In particular, carbachol caused a much greater induction of c-jun mRNA and AP-1 activity. These responses did not correlate with protein kinase C stimulation nor with the activation of mitogen-activated protein (MAP) kinases. Recently, it has been shown that a novel family of kinases structurally related to MAP kinases, stress-activated protein kinases, or Jun kinases (JNKs), phosphorylate in vivo the amino-terminal transactivating domain of the c-Jun protein, thereby increasing its transcriptional activity. In view of our results, this observation prompted us to ask whether m1 and PDGF can differentially activate JNKs. Here, we show that m1 mAChRs can induce a remarkable increase in JNK activity, which was temporally distinct from that of MAP kinase and was entirely protein kinase C independent. In contrast, PDGF failed to activate JNK in these cells, although it stimulated MAP kinase to an extent even greater than that for carbachol. These findings demonstrate that G protein-coupled receptors can signal through pathways leading to the activation of JNK, thus diverging at this level with those signaling routes utilized by tyrosine kinase receptors.
人类毒蕈碱型乙酰胆碱受体（mAChRs）在NIH 3T3细胞中的表达已被用作通过G蛋白偶联受体研究增殖信号传导的模型。在这个生物系统中，mAChRs的m1类可以有效地转导促有丝分裂信号（斯蒂芬斯，E.V.，卡利内克，G.，布兰，M.R.，和古特金德，J.S.（1993年）《癌基因》8卷，19 - 26页），如果持续激活则可诱导恶性转化（古特金德，J.S.，诺沃特尼，E.A.，布兰，M.R.，和罗宾斯，K.C.（1991年）《美国国家科学院院刊》88卷，4703 - 4708页）。此外，现有证据表明，m1信号通路在p21ras水平与酪氨酸激酶受体产生的信号通路汇合（克雷斯波，P.，徐，N.，西蒙兹，W.F.，和古特金德，J.S.（1994年）《自然》369卷，418 - 420页）。为了探索在这种情况下G蛋白偶联受体参与生长调节的核内事件，我们比较了血小板衍生生长因子（PDGF）和胆碱能激动剂卡巴胆碱对核原癌基因jun和fos家族成员mRNA表达的影响。我们发现，卡巴胆碱激活m1受体可诱导一组独特的核转录因子的表达。特别是，卡巴胆碱对c - jun mRNA和AP - 1活性的诱导作用要强得多。这些反应与蛋白激酶C的刺激以及丝裂原活化蛋白（MAP）激酶的激活均无关。最近，已表明与MAP激酶结构相关的一个新的激酶家族，即应激激活蛋白激酶或Jun激酶（JNKs），在体内使c - Jun蛋白的氨基末端反式激活结构域磷酸化，从而增加其转录活性。鉴于我们的结果，这一观察促使我们询问m1和PDGF是否能差异激活JNKs。在此，我们表明m1 mAChRs可诱导JNK活性显著增加，其在时间上与MAP激酶不同，且完全不依赖于蛋白激酶C。相反，PDGF在这些细胞中未能激活JNK，尽管它对MAP激酶的刺激程度甚至大于卡巴胆碱。这些发现表明，G蛋白偶联受体可通过导致JNK激活的途径发出信号，从而在这一水平上与酪氨酸激酶受体利用的信号途径不同。
