Endocrine Abstracts

Corticotropin-releasing hormone (CRH) and urocortins (UCN) bind to two types of GPCRs (CRH-R1 and CRH-R2), activating a plethora of signalling cascades, including the mitogen-activated protein kinases (MAPKs) pathways. Although previous studies have identified that CRH directly regulates adrenal steroidogenesis¹, the second messenger systems and downstream effectors remain poorly defined. The adrenal cell line H295R, which express both CRH-Rs¹ was used to investigate CRH-R signalling characteristics and UCN-I effects on enzymes involved in adrenal steroidogenesis. Confocal analysis identified receptor ‘hotspots’ on the plasma membrane and diffuse, low level specific staining throughout the cytoplasm, which may represent unprocessed receptors or cytoplasmic CRH-R variants. Functional coupling of the activated receptors to Gs/adenylyl cyclase resulted in a 3–4 fold increase in cAMP levels following treatment of cells with 100 nM UCN-I. Using phospho-specific antibodies for ERK1/2 we observed a transient increase in ERK1/2 activation (maximal response 4–7 fold above basal at 5–10 min) in response to UCN-I (100 nM). However, UCN-I did not induce any significant activation of p38 MAPK. Confocal microscopy studies showed that active ERK1/2 was exclusively localised to the cytoplasm at the time points measured (0–30 min). UCN-I treatment for 4 h significantly induced StAR mRNA and protein levels, and appeared to involve ERK1/2 activation since pretreatment with the specific MEK1/2 inhibitor (U0126) abolished this effect. Real-time PCR experiments also showed that treatment of H295R cells with 100 nM UCN-I for 24 h significantly up-regulated CYP11A, CYP17 and 3βHSD. However, ERK1/2 activation was found to be important for CYP17 and 3(HSD but not CYP11A up-regulation. We conclude that H295R cells express functional CRH-Rs, which couple to both cAMP and ERK1/2 signalling pathways. UCN-I can induce expression of specific enzymes involved in adrenal steroidogenesis through an ERK1/2-dependent pathway.

(1) Willenberg HS et al., Neuroendocrinology 2005 (82) 274–281.