Different Signaling Mechanisms Are Involved in the Norepinephrine-Stimulated TORC1 and TORC2 Nuclear Translocation in Rat Pinealocytes

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 Ca2+ 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 beta-adrenoceptor/cAMP and alpha-adrenoceptor/intracellular Ca2+ pathways contrasting with TORC2 dephosphorylation being induced mainly through the beta-adrenoceptor/cAMP pathway. PhosTag gel indicated a different pattern of TORC1 desphosphorylation resulting from the selective activation of alpha- or beta-adrenoceptors. Interestingly, only the alpha-adrenoceptor/intracellular Ca2+-mediated dephosphorylation could translocate TORC1 to the nucleus, whereas the beta-adrenoceptor/cAMP-mediated dephosphorylation of TORC1 was ineffective. In comparison, translocation of TORC2 was induced predominantly by the beta-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. (Endocrinology 153: 3839-3849, 2012)