Schuetz E G, Schuetz J D, May B, Guzelian P S
Department of Pathology, Medical College of Virginia, Richmond 23298-0267.
J Biol Chem. 1990 Jan 15;265(2):1188-92.
Growth hormone (GH) may directly affect the expression of some liver cytochromes P-450 inducible by xenobiotics, but this has been difficult to establish with pituitary ablation in living animals. Therefore, we incubated adult rat hepatocytes on a laminin-rich matrix, matrigel, a new system that permits hepatocytes to respond to xenobiotics with induction of the microsomal hemoproteins, the cytochromes P-450, in culture as they do in the intact liver (Schuetz, E. G., Li, D., Omiecinski, C. J., Muller-Eberhard, U., Kleinman, H. K., Elswick, B., and Guzelian, P. S. (1988) J. Cell. Physiol. 134, 309-323). Indeed, when cultures were treated with phenobarbital, there was a rise in mRNAs for the cytochromes P-450b/e and P-450p accompanied by a rise in mRNA for 5-aminolevulinate synthase, the rate-limiting enzyme in heme biosynthesis. Analysis of nuclei from the matrigel cultures established that phenobarbital treatment had activated transcription of the P-450b/e gene. Co-incubation of the cultures with physiologic concentrations of growth hormone completely blocked the induction of these P-450 mRNAs and partially blocked the rise in 5-aminolevulinate synthase mRNA. Induction of P-450p by isosafrole also was inhibited strongly by GH, whereas P-450p induction by pregnenolone 16 alpha-carbonitrile or dexamethasone was affected only weakly by GH. The effect of GH was specific inasmuch as phenobarbital-inducible expression of P-450 reductase, glucocorticoid-inducible expression of tyrosine aminotransferase, and basal expression of albumin were unaffected by the presence or absence of growth hormone. Nuclear analysis revealed that growth hormone inhibited phenobarbital-induced P-450b/e gene transcription, whereas the hormone was without effect on transcription of the liver-specific gene, tyrosine aminotransferase. In contrast, the addition of another peptide hormone, insulin-like growth factor I, was without inhibitory effect on P-450 gene expression. We conclude that growth hormone acts specifically and selectively in direct contact with the hepatocyte to control xenobiotic induction of some liver drug-metabolizing enzymes.
生长激素（GH）可能直接影响一些由异生素诱导的肝细胞色素P-450的表达，但在活体动物中通过垂体切除来证实这一点一直很困难。因此，我们将成年大鼠肝细胞在富含层粘连蛋白的基质Matrigel上进行培养，这是一种新的系统，能使肝细胞在培养中像在完整肝脏中一样，对外源化学物质作出反应，诱导微粒体血红素蛋白即细胞色素P-450的产生（舒茨，E.G.，李，D.，奥米辛斯基，C.J.，米勒-埃伯哈德，U.，克莱曼，H.K.，埃尔兹威克，B.，和古泽利安，P.S.（1988年）《细胞生理学杂志》134卷，309 - 323页）。实际上，当用苯巴比妥处理培养物时，细胞色素P-450b/e和P-450p的mRNA水平升高，同时血红素生物合成中的限速酶5-氨基酮戊酸合酶的mRNA水平也升高。对Matrigel培养物细胞核的分析表明，苯巴比妥处理激活了P-450b/e基因的转录。将培养物与生理浓度的生长激素共同孵育，完全阻断了这些P-450 mRNA的诱导，并部分阻断了5-氨基酮戊酸合酶mRNA的升高。异黄樟素对P-450p的诱导也受到生长激素的强烈抑制，而孕烯醇酮16α-腈或地塞米松对P-450p的诱导仅受到生长激素的微弱影响。生长激素的作用具有特异性，因为苯巴比妥诱导的P-450还原酶表达、糖皮质激素诱导的酪氨酸转氨酶表达以及白蛋白的基础表达不受生长激素存在与否的影响。细胞核分析显示，生长激素抑制苯巴比妥诱导的P-450b/e基因转录，而该激素对肝脏特异性基因酪氨酸转氨酶的转录没有影响。相反，添加另一种肽类激素胰岛素样生长因子I对P-450基因表达没有抑制作用。我们得出结论，生长激素在与肝细胞直接接触时发挥特异性和选择性作用，以控制某些肝脏药物代谢酶的异生素诱导。
