Regulation of pituitary corticotropin releasing factor type-1 receptor mRNA binding proteins by modulation of the hypothalamic-pituitary-adrenal axis.

Abstract

Long-term adrenalectomy (ADX) is associated with marked down-regulation of pituitary corticotropin releasing factor type-1 receptors (CRF-R1) but normal CRF-R1 mRNA levels, suggesting that regulation of receptor levels occurs at post-transcriptional sites. We have reported that adrenal cytosolic proteins, which bind to cis elements in the 5' leader sequence (5'LS) of the rat angiotensin II type 1a receptor (AT(1a)R) mRNA, participate in the regulation of AT(1a)R density by inhibiting AT(1a)R mRNA translation. In this study, we examined anterior pituitary cytosolic proteins that form RNA protein complexes (RPC) with the 5'LS of the CRF-R1 and the AT(1a)R. Competition studies and ultraviolet-crosslinking analysis suggest that formation of CRF-R1 and AT(1a)R 5'LS RPC require at least some proteins that are common to both receptor mRNAs. Pituitaries isolated from male Sprague-Dawley rats six days after ADX showed significant (P < 0.05) increases of 2.9-fold in CRF-R1 5'LS RNA binding protein (BP) activity compared to pituitaries from sham-operated rats; this effect of ADX was prevented by glucocorticoid replacement. By contrast, no differences in the number of pituitary AT(1a)R binding sites or pituitary AT(1a)R 5'LS BP activity were observed between sham and ADX rats, indicating that the effect of ADX on RPC formation was specific for CRF-R1 mRNA. Addition of pituitary cytosolic extracts inhibited in vitro translation of CRF-R1 mRNA by 79% under conditions that had no significant effects on the translation of a control mRNA. The data suggest that CRF-R1 translation is regulated by modulation of the HPA axis through pituitary cytosolic proteins binding to the CRF-R1 5'LS.