Punn Anu, Levine Michael A, Grammatopoulos Dimitris K
Endocrinology and Metabolism, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom.
Mol Endocrinol. 2006 Dec;20(12):3179-95. doi: 10.1210/me.2006-0255. Epub 2006 Sep 7.
In most target cells, activation of the type 1 CRH receptor (CRH-R1) by CRH or urocortin (UCN I) leads to stimulation of the Gs-protein/adenylyl cyclase/protein kinase A cascade. Signal transduction of CRH-R1 also involves alternative pathways such as phosphorylation of ERK1/2 and p38 MAPK, two members of the MAPK family that mediate important pathophysiological responses. The intracellular pathways by which CRH-R1 activates these MAPK are only partially understood; here we characterized further signaling mechanisms and molecules involved in CRH-R1-mediated ERK1/2 and p38 MAPK activation. In human embryonic kidney 293 cells overexpressing recombinant CRH-R1alpha, UCN I induced ERK1/2 and p38 MAPK activation was dependent on signaling molecules involved in agonist-induced CRH-R1alpha trafficking and endocytosis. Furthermore, time course studies and use of selective inhibitors demonstrated that ERK1/2 activation occured within 5 min, was sustained for at least 60 min, and was dependent on both phosphatidylinositol 3-kinase (PI3-K)/Akt activation and epidermoid growth factor receptor transactivation involving matrix metelloproteinases. UCN I effect on p38 MAPK phosphorylation was more transient, returned to basal within 40 min and was dependent on epidermoid growth factor receptor transactivation, but not PI3-K/Akt activation. Overexpression of G(alpha-)transducin, showed that G(betagamma)-subunit activation is only partially required for ERK1/2 phosphorylation and does not play a role in p38 MAPK phosphorylation, whereas overexpression of a dominant-negative Ras (Ras N17) attenuated both ERK and p38 MAPK activation. In conclusion, a complex signaling network appears to mediate CRH-R1alpha-MAPK interactions; PI3-K might play a critical role in the regulation of CRH-R1alpha signaling selectivity and cellular responses.
在大多数靶细胞中，促肾上腺皮质激素释放激素（CRH）或尿皮质素（UCN I）激活1型CRH受体（CRH-R1）会刺激Gs蛋白/腺苷酸环化酶/蛋白激酶A级联反应。CRH-R1的信号转导还涉及其他途径，如ERK1/2和p38丝裂原活化蛋白激酶（MAPK）的磷酸化，这两种MAPK家族成员介导重要的病理生理反应。CRH-R1激活这些MAPK的细胞内途径仅得到部分了解；在此，我们进一步表征了参与CRH-R1介导的ERK1/2和p38 MAPK激活的信号传导机制和分子。在过表达重组CRH-R1α的人胚肾293细胞中，UCN I诱导的ERK1/2和p38 MAPK激活依赖于参与激动剂诱导的CRH-R1α转运和内吞作用的信号分子。此外，时间进程研究和选择性抑制剂的使用表明，ERK1/2激活在5分钟内发生，持续至少60分钟，并且依赖于磷脂酰肌醇3激酶（PI3-K）/Akt激活以及涉及基质金属蛋白酶的表皮生长因子受体转活化。UCN I对p38 MAPK磷酸化的作用更短暂，在40分钟内恢复到基础水平，并且依赖于表皮生长因子受体转活化，但不依赖于PI3-K/Akt激活。G（α）-转导蛋白的过表达表明，G（βγ）亚基激活对于ERK1/2磷酸化仅部分需要，并且在p38 MAPK磷酸化中不起作用，而显性负性Ras（Ras N17）的过表达减弱了ERK和p38 MAPK激活。总之，一个复杂的信号网络似乎介导CRH-R1α-MAPK相互作用；PI3-K可能在CRH-R1α信号传导选择性和细胞反应的调节中起关键作用。
