Involvement of CREB-regulated transcription coactivators (CRTC) in transcriptional activation of steroidogenic acute regulatory protein (Star) by ACTH

Activation and expression of endogenous CREB‐regulated transcription coactivators (CRTC) 1, 2 and 3 in the rat adrenal gland

“…In the present study, we demonstrate that nuclear translocation of endogenous CRTC2 and CRTC3 in the rat adrenal gland occurs in response to both basal, ultradian HPA axis activity, and following endotoxic stress, thus complimenting the findings from previous in vitro and in vivo studies in which activation of CRTC2 and CRCT3 was shown in response to ACTH and restraint stress 13,14,16‐18 . Here, we show that an increase in CRTC2 and CRTC3 nuclear localisation parallels, or precedes, the increase in CREB phosphorylation and Star transcription, as measured by Star hnRNA levels.…”

“…Similarly, peak nuclear localisation of endogenous CRTC2 and CRTC3 was seen at 5 minutes following an ultradian ACTH pulse, and this is consistent with the activation profile of CRTC2 following administration of a small dose of ACTH in methylprednisolone‐suppressed rats 18 . We have previously demonstrated that activation of CRTC1, CRTC2 and CRTC3 occurs within 3‐7 minutes of ACTH treatment in adrenocortical cell lines, 16 in contrast to earlier in vitro studies showing activation of CRTC2, although not of CRTC1 or CRTC3, in response to cAMP 13 . Nuclear localisation of CRTC2 following HPA axis activation by restraint stress has previously been reported 17 and, in the present study, we show that activation of CRTC2 and CRTC3 also occurs following endotoxic stress induced by LPS injection, with peak nuclear levels seen at 30‐60 minutes after exposure, returning to basal by 180 minutes.…”

“…Immediately following collection adrenal glands (n = 3‐4 independent rats per group) were fixed and chromatin was extracted as described previously 23 . Eighty‐five micrograms of sheared chromatin were immunoprecipitated as described previously, 16 with either anti‐TORC2 antibody (1 µg mL ‐1 ; catalogue no. ab109081; ; Abcam, Cambridge, MA, USA), anti‐CRTC3 antibody (2 µg mL ‐1 ; catalogue no.…”

“…This allows CRTC to translocate into the nucleus and bind CREB at the transcription site 15 . Three isoforms (CRTC1, 2 and 3) have been identified, with CRTC2 and CRTC3 shown to be the most highly expressed in the adrenal gland 12,16 . CRTC2 has long been implicated in the regulation of Star transcription in vitro 13,14 and in vivo, where nuclear levels of phosphorylated CREB (pCREB) and CRTC2 in the rat adrenal gland have been shown to increase in response to both high and low dose ACTH and restraint stress 17,18 .…”

Prolonged treatment with the synthetic glucocorticoid methylprednisolone affects adrenal steroidogenic function and response to inflammatory stress in the rat

“…The transcription of adrenal steroidogenic genes is regulated by a number of transcription factors, nuclear receptors and regulators, and the activity and expression of most of these are also under the control of ACTH. Specifically, ACTH-induced phosphorylation of CREB require the activation of several nuclear receptors and co-regulators, including members of the CRTC family (CRTC1-3) (Smith et al, 2019), Nur77 and steroidogenic factor 1 (SF-1) (Sugawara et al, 1996), and the repression of a number of negative regulators, including salt inducible kinase 1 (SIK1) (Takemori and Okamoto, 2008) and dosage sensitive sex-reversal, adrenal hypoplasia (Zazopoulos et al, 1997). Interestingly, GCs can inhibit the transcription of steroidogenic genes through a mechanism that involves increase in the expression of the steroidogenic co-repressor dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1 (DAX-1) (Gummow et al, 2006) as well as by inhibiting both the transcription and the activity of Nur77 via a mechanism that involves active GR (Song et al, 2004;.…”