Autelitano D J, Sheppard K E
Molecular Physiology Laboratory, Baker Medical Research Institute, Prahran, Victoria, Australia.
Mol Cell Endocrinol. 1993 Jul;94(1):111-9. doi: 10.1016/0303-7207(93)90058-r.
Although corticotropin releasing factor (CRF) and glucocorticoid hormones (GC) act directly at the level on the anterior pituitary corticotrope cell to stimulate (CRF) or inhibit (GC) pro-opiomelanocortin (POMC) expression, the actions of GC on POMC have been shown to be impaired if corticotrope cells are coincubated or preincubated with CRF. In the present study we have measured secreted beta-endorphin (beta EP) and changes in the level of nuclear POMC hnRNA as an indirect measure of gene transcription to characterize the molecular mechanisms involved in the CRF-mediated inhibition of glucocorticoid action. In primary cultures of rat anterior pituitary cells either co-treated or pretreated with CRF, acute dexamethasone (DEX)-mediated inhibition of POMC hnRNA levels was impaired. In contrast, the ability of CRF to block glucocorticoid action was abolished if the cells were pretreated with the protein synthesis inhibitor puromycin. Since previous studies have demonstrated that components of the AP1 transcription factor can modulate glucocorticoid receptor activity in other systems, we examined the regulation of the proto-oncogenes c-fos and c-jun in response to CRF. Treatment of the corticotrope cell line (AtT-20) with CRF rapidly activated c-fos mRNA to levels 11-12-fold above control by 30 and 60 min, with no apparent elevation of c-jun mRNA levels. Pretreatment of AtT-20 cells with antisense c-fos oligonucleotides prevented CRF from blocking glucocorticoid inhibition of POMC hnRNA levels and beta EP release.(ABSTRACT TRUNCATED AT 250 WORDS)
尽管促肾上腺皮质激素释放因子（CRF）和糖皮质激素（GC）直接作用于垂体前叶促肾上腺皮质激素细胞水平，以刺激（CRF）或抑制（GC）阿片促黑激素皮质素原（POMC）的表达，但如果促肾上腺皮质激素细胞与CRF共同孵育或预孵育，GC对POMC的作用会受到损害。在本研究中，我们测量了分泌的β-内啡肽（βEP）以及核POMC hnRNA水平的变化，以此作为基因转录的间接指标，来表征CRF介导的糖皮质激素作用抑制所涉及的分子机制。在大鼠垂体前叶细胞原代培养物中，用CRF共同处理或预处理后，地塞米松（DEX）急性介导的POMC hnRNA水平抑制受到损害。相反，如果细胞用蛋白质合成抑制剂嘌呤霉素预处理，CRF阻断糖皮质激素作用的能力就会被消除。由于先前的研究表明，AP1转录因子的成分可以在其他系统中调节糖皮质激素受体活性，我们研究了原癌基因c-fos和c-jun对CRF的反应调节。用CRF处理促肾上腺皮质激素细胞系（AtT-20），30分钟和60分钟时，c-fos mRNA迅速激活至对照水平以上11 - 12倍，而c-jun mRNA水平无明显升高。用反义c-fos寡核苷酸预处理AtT-20细胞可阻止CRF阻断糖皮质激素对POMC hnRNA水平和βEP释放的抑制作用。（摘要截短于250字）
