Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
Endocrinology. 2012 Aug;153(8):3839-49. doi: 10.1210/en.2012-1315. Epub 2012 Jun 8.
The distribution of transducers of regulated cAMP-response element-binding protein activity (TORC) between the cytoplasm and the nucleus is tightly regulated and represents one of the main mechanisms whereby the cAMP response element activation activities of TORC are controlled. Whereas both cAMP and Ca(2+) pathways can cause translocation of TORC, the relative importance of these two pathways in regulating different TORC within the same cell is unclear. In this study, we determined the mechanism that regulated TORC1 translocation and compared it with that of TORC2 in rat pinealocytes. Stimulation of pinealocytes with norepinephrine (NE), although having no effect on Torc1 transcription, caused rapid dephosphorylation of TORC1. Although NE also caused rapid dephosphorylation of TORC2, pharmacological studies revealed that TORC1 dephosphorylation could be induced by both β-adrenoceptor/cAMP and α-adrenoceptor/intracellular Ca(2+) pathways contrasting with TORC2 dephosphorylation being induced mainly through the β-adrenoceptor/cAMP pathway. PhosTag gel indicated a different pattern of TORC1 desphosphorylation resulting from the selective activation of α- or β-adrenoceptors. Interestingly, only the α-adrenoceptor/intracellular Ca(2+)-mediated dephosphorylation could translocate TORC1 to the nucleus, whereas the β-adrenoceptor/cAMP-mediated dephosphorylation of TORC1 was ineffective. In comparison, translocation of TORC2 was induced predominantly by the β-adrenoceptor/cAMP pathway. Studies with different protein phosphatase (PP) inhibitors indicated that the NE-mediated translocation of TORC1 was blocked by cyclosporine A, a PP2B inhibitor, but that of TORC2 was blocked by okadaic acid, a PP2A inhibitor. Together these results highlight different intracellular signaling pathways that are involved in the NE-stimulated dephosphorylation and translocation of TORC1 and TORC2 in rat pinealocytes.
调节环腺苷酸反应元件结合蛋白活性（TORC）转导子的分布在细胞质和细胞核之间受到严格调控，是 TORC 的环腺苷酸反应元件激活活性受到控制的主要机制之一。虽然 cAMP 和 Ca(2+) 途径都可以导致 TORC 的易位，但这两种途径在调节同一细胞内不同 TORC 的相对重要性尚不清楚。在这项研究中，我们确定了调节 TORC1 易位的机制，并将其与大鼠松果体细胞中 TORC2 的机制进行了比较。去甲肾上腺素（NE）刺激松果体细胞虽然对 Torc1 转录没有影响，但会导致 TORC1 的快速去磷酸化。尽管 NE 也会导致 TORC2 的快速去磷酸化，但药理学研究表明，TORC1 的去磷酸化可以通过β-肾上腺素能受体/cAMP 和 α-肾上腺素能受体/细胞内 Ca(2+) 途径诱导，而 TORC2 的去磷酸化主要通过β-肾上腺素能受体/cAMP 途径诱导。PhosTag 凝胶表明，通过选择性激活α或β肾上腺素能受体，会导致 TORC1 去磷酸化的不同模式。有趣的是，只有 α-肾上腺素能受体/细胞内 Ca(2+)-介导的去磷酸化才能将 TORC1 易位到细胞核，而 TORC1 的β-肾上腺素能受体/cAMP 介导的去磷酸化则无效。相比之下，TORC2 的易位主要是由β-肾上腺素能受体/cAMP 途径诱导的。用不同的蛋白磷酸酶（PP）抑制剂进行的研究表明，NE 介导的 TORC1 易位被环孢素 A（一种 PP2B 抑制剂）阻断，但 TORC2 的易位被 okadaic 酸（一种 PP2A 抑制剂）阻断。这些结果共同强调了不同的细胞内信号通路，这些通路参与了 NE 刺激的大鼠松果体细胞中 TORC1 和 TORC2 的去磷酸化和易位。
