Tsu R C, Wong Y H
Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon.
J Neurosci. 1996 Feb 15;16(4):1317-23. doi: 10.1523/JNEUROSCI.16-04-01317.1996.
Synergism between Gs- and Gi- or Gq-dependent signaling pathways has been demonstrated in the stimulation of type II adenylyl cyclase (AC-II). Provision of activated alpha s is known to allow numerous Gi-coupled receptors to stimulate AC-II and to potentiate the responses to Gq-coupled receptors. To explore possible interactions between Gi- and Gq-coupled receptors that are independent of alpha s, the activity of AC-II was determined after the activation of Gi- and Gq-regulated pathways. Human embryonic kidney 293 cells were transiently cotransfected with cDNAs encoding AC-II and various G-protein-coupled receptors. Agonist-bound Gi-coupled receptors (including the formyl peptide, dopamine-D2, and delta-opioid receptors) stimulated AC-II activity in the absence of activated alpha s, provided that the cells were treated with 100 nM phorbol 12-myristate 13-acetate. Activation of protein kinase C (PKC) thus appears to relieve the requirement for the presence of activated alpha s. Stimulation of PKC via Gq-coupled receptors also allowed Gi-coupled receptors to activate AC-II. Coexpression of the m1 muscarinic receptor with the dopamine-D2 receptor permitted dopamine to stimulate AC-II in the presence of carbachol. The phorbol ester-permissive and alpha s-independent stimulation was mediated by G-protein beta gamma subunits because it was blocked by the beta gamma scavengers alpha t and beta-adrenergic receptor kinase. These results show that AC-II can efficiently integrate signals generated by Gq- and Gi-coupled receptors via a mechanism that is independent of Gs.
Gs 依赖性信号通路与 Gi 或 Gq 依赖性信号通路之间的协同作用已在 II 型腺苷酸环化酶（AC-II）的刺激中得到证实。已知提供活化的αs可使许多与 Gi 偶联的受体刺激 AC-II，并增强对与 Gq 偶联受体的反应。为了探索与αs无关的 Gi 和 Gq 偶联受体之间可能的相互作用，在激活 Gi 和 Gq 调节的信号通路后测定了 AC-II 的活性。将编码 AC-II 和各种 G 蛋白偶联受体的 cDNA 瞬时共转染到人胚肾 293 细胞中。只要用 100 nM 佛波醇 12-肉豆蔻酸酯 13-乙酸酯处理细胞，激动剂结合的 Gi 偶联受体（包括甲酰肽、多巴胺 D2 和δ-阿片受体）在没有活化αs的情况下就能刺激 AC-II 活性。因此，蛋白激酶 C（PKC）的激活似乎消除了对活化αs存在的需求。通过 Gq 偶联受体刺激 PKC 也能使 Gi 偶联受体激活 AC-II。m1 毒蕈碱受体与多巴胺 D2 受体的共表达使多巴胺在存在卡巴胆碱的情况下能够刺激 AC-II。佛波醇酯允许的且与αs无关的刺激是由 G 蛋白βγ亚基介导的，因为它被βγ清除剂αt 和β-肾上腺素能受体激酶阻断。这些结果表明，AC-II 可以通过一种与 Gs 无关的机制有效地整合由 Gq 和 Gi 偶联受体产生的信号。
