Huang Y, Hui D Y
Department of Pathology and Laboratory Medicine, University of Cincinnati, College of Medicine, Ohio 45267-0529.
J Biol Chem. 1991 Apr 15;266(11):6720-5.
This study used the rat pancreatoma AR42J as a model system to investigate the possible regulation of cholesterol esterase biosynthesis in pancreas. Initial experiments were performed to verify the synthesis of pancreatic cholesterol esterase by the AR42J cells. Results indicated that this pancreatoma cell line synthesized two forms of cholesterol esterase (Mr = 71,000 and 74,000). The 74-kDa protein is most likely the precursor protein, and the 71-kDa protein is the matured enzyme secreted by the AR42J cells. The synthesis and secretion of cholesterol esterase were stimulated 2-5-fold by incubating the cells with 0.5-4 nM of cholecystokinin or 0.5-2 nM of secretin. Analysis of the RNA isolated from the hormone-stimulated cells revealed that stimulation of cholesterol esterase biosynthesis was not due to an increase in cholesterol esterase mRNA. Furthermore, inhibition of transcription with actinomycin D has no effect on the hormone-induced cholesterol esterase biosynthesis. Therefore, the mechanism of hormone stimulation was not dependent on de novo RNA synthesis. In vitro translation studies showed that the cholesterol esterase mRNA isolated from stimulated AR42J cells were translated more efficiently than those from control cells. Thus, the increased cholesterol esterase biosynthesis induced by gastric hormones was most likely mediated by posttranscriptional modification of the cholesterol esterase mRNA.
本研究以大鼠胰腺瘤AR42J作为模型系统，来研究胰腺中胆固醇酯酶生物合成的可能调控机制。进行了初步实验以验证AR42J细胞是否能合成胰腺胆固醇酯酶。结果表明，该胰腺瘤细胞系合成了两种形式的胆固醇酯酶（分子量分别为71,000和74,000）。74 kDa的蛋白很可能是前体蛋白，而71 kDa的蛋白是AR42J细胞分泌的成熟酶。用0.5 - 4 nM的胆囊收缩素或0.5 - 2 nM的促胰液素孵育细胞，可使胆固醇酯酶的合成和分泌增加2 - 5倍。对从激素刺激的细胞中分离出的RNA进行分析发现，胆固醇酯酶生物合成的刺激并非由于胆固醇酯酶mRNA的增加。此外，用放线菌素D抑制转录对激素诱导的胆固醇酯酶生物合成没有影响。因此，激素刺激的机制不依赖于从头合成RNA。体外翻译研究表明，从受刺激的AR42J细胞中分离出的胆固醇酯酶mRNA比从对照细胞中分离出的翻译效率更高。因此，胃激素诱导的胆固醇酯酶生物合成增加很可能是由胆固醇酯酶mRNA的转录后修饰介导的。
