OR45-4 Signaling pathways involved in mediating ACTH-induced StAR transcription

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: OR45-HPA Axis
Tuesday, June 18, 2013: 9:15 AM-10:45 AM
Presentation Start Time: 10:00 AM
Room 135 (Moscone Center)
Lorna Ionie Freda Smith*1, Mark Olah2, Greti Aguilera3 and Victoria Huang1
1NIH/NICHD, Bethesda, MD, 2NIH, NICHD, Bethesda, MD, 3NIH - NICHD, Bethesda, MD
Glucocorticoids, secreted by the adrenal cortex, are the end product of activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis. Glucocorticoid secretion is episodic, following hourly ultradian pulsatility, as well as showing marked but transient increases during stress. We have previously demonstrated that secretory episodes are associated with episodes of transcription of rate limiting proteins involved in steroidogenesis, such as the labile protein, steroidogenic acute regulatory protein (StAR). Stimulation of steroid secretion and StAR transcription are mediated by adrenocorticotropic hormone (ACTH), through activation of adenylate cyclase and cyclic AMP production. ACTH also induces CREB phosphorylation (pCREB), and nuclear translocation of the CREB co-activator, transducer of regulated CREB activity, TORC, as well as activation of other transcription factors. To determine the signaling pathways mediating ACTH stimulation of StAR transcription, we examined the effects of signaling activators and inhibitors on StAR transcription, measured as changes in StAR hnRNA levels in the adrenocortical cell line Y1. Stimulation of Y1 cells with ACTH rapidly increased StAR transcription and nuclear levels of pCREB, TORC and phospho-ERK. The effects of ACTH on StAR hnRNA were mimicked by 8-bromo cyclic AMP and the adenylate cyclase stimulator, forskolin, but not by activation of protein kinase C by phorbolesters, or the MAP kinase pathway by EGF, suggesting that the effect is mediated by protein kinase A. This was supported by studies in adrenal-specific PKA regulatory subunit 1a knockout mice showing 3-fold elevations in basal StAR hnRNA, and reduced stimulation by ACTH. Nevertheless, the PKA inhibitors, H89 and PKI, only slightly attenuated ACTH-induced StAR transcription. Inhibition of the MAP kinase pathway by the MEK inhibitors, UO126 or SL327 produced a similar, minor reduction of ACTH-induced StAR transcription. A combination of inhibitors for the two pathways, however, markedly reduced basal and ACTH- or 8Br-cAMP-stimulated StAR transcription. Inhibition of PKA using H89 decreased ACTH-induced nuclear accumulation of TORC, while the MAPK inhibitor, UO126, had no effect on TORC translocation but inhibited ERK phosphorylation. The data shows that the full stimulatory effect of ACTH on StAR transcription requires cAMP-dependent activation of both PKA and MAPK pathways.  The data is consistent with the recognized role of PKA on TORC activation. In addition, it suggests that activation of the MAP kinase pathway is required for full transcriptional activation of StAR, probably by mediating phosphorylation of other transcription factors such as SF1.

Nothing to Disclose: LIFS, MO, GA, VH

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: NICHD Intramural Program