Oyarce A M, Hand T A, Mains R E, Eipper B A
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, USA.
J Neurochem. 1996 Jul;67(1):229-41. doi: 10.1046/j.1471-4159.1996.67010229.x.
The biosynthesis of peptides requires the synthesis of the prohormone, several biosynthetic processing enzymes, and other granule constituents. We have investigated the regulated expression of proopiomelanocortin (POMC) and five enzymes essential for the processing of POMC to smaller, bioactive peptides in intermediate pituitary melanotropes. Rats were treated with a dopaminergic agonist (bromocriptine) or antagonist (haloperidol) for periods ranging from 1 h to 5 days, followed by analyses of mRNA levels and protein biosynthetic rates. Multiplex RNase protection assays showed that bromocriptine treatment caused a striking decrease in POMC mRNA levels, and significant decreases in mRNA levels for prohormone convertase 2 (PC2), carboxypeptidase H (CPH), and peptidylglycine alpha-amidating monooxygenase (PAM). Smaller increases in mRNA levels were seen after haloperidol stimulation. Protein biosynthetic rates changed more profoundly than mRNA levels at short drug treatment times, indicating a role for translational effects after treatment with bromocriptine and with haloperidol. The homogeneous population of melanotropes in the intermediate lobe of the pituitary allows a quantitative analysis of transcript levels and biosynthetic rates. POMC mRNA levels are 200-1,000-fold higher than levels of any of the processing enzyme mRNAs, and POMC biosynthetic rates exceed those of PC2, PC1, and PAM by 1,000-10,000-fold.
肽的生物合成需要合成前激素、几种生物合成加工酶以及其他颗粒成分。我们研究了阿片促黑激素皮质素原（POMC）以及五种将POMC加工成更小的生物活性肽所必需的酶在垂体中间叶促黑素细胞中的调控表达。用多巴胺能激动剂（溴隐亭）或拮抗剂（氟哌啶醇）处理大鼠1小时至5天，随后分析mRNA水平和蛋白质生物合成速率。多重核糖核酸酶保护分析表明，溴隐亭处理导致POMC mRNA水平显著下降，前激素转化酶2（PC2）、羧肽酶H（CPH）和肽基甘氨酸α-酰胺化单加氧酶（PAM）的mRNA水平也显著下降。氟哌啶醇刺激后，mRNA水平有较小幅度的升高。在短时间药物处理时，蛋白质生物合成速率的变化比mRNA水平更为显著，这表明溴隐亭和氟哌啶醇处理后存在翻译效应。垂体中间叶中均匀的促黑素细胞群体允许对转录水平和生物合成速率进行定量分析。POMC mRNA水平比任何一种加工酶mRNA的水平高200 - 1000倍，POMC生物合成速率比PC2、PC1和PAM的生物合成速率高1000 - 10000倍。
