Rainey W E, Naville D, Mason J I
Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas 75235.
Endocr Res. 1991;17(1-2):281-96. doi: 10.1080/07435809109027202.
The maintenance of optimal steroidogenesis in adrenocortical cells primarily depends on the chronic action of ACTH to promote the synthesis of the various steroid metabolizing enzymes. In the steroidogenic pathway, the ratio of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) to 17 alpha-hydroxylase cytochrome P450 (P-450(17 alpha)) plays a key role in determining the final steroid products released by adrenal cells. The differences in these enzymes are particularly important when one considers the adrenal zones and the secretion of the zone-specific steroids. In the present study we have investigated the regulation of 3 beta HSD with regard to its enzyme activity, levels of protein and changes in specific mRNA encoding for this enzyme. Following eight days in primary culture, bovine adrenocortical (BAC) cells were found to respond to both ACTH and Bu2 cAMP by increased cortisol production. In addition, 3 beta HSD activity, enzyme protein and mRNA levels were increased in response to both factors. The increases varied from 2-fold for activity to 5-7 fold for mRNA. ACTH and Bu2cAMP also greatly increased P-450(17 alpha) from the near undetectable levels in control cells. In order to examine the possibility of differential regulation of these adrenal steroidogenic enzymes we determined the effects of angiotensin II (A-II) and transforming growth factor beta (TGF beta) on the levels of these enzymes. Both of these factors decreased the ACTH-stimulated levels of P-450(17 alpha) enzyme and mRNA to near nondetectable levels observed within control cells. In addition, these compounds inhibited the ACTH induction of 3 beta HSD. While the mechanism of TGF beta action is not clear, A-II probably is acting through protein kinase C. Indeed the protein kinase C activating phorbol ester, TPA, mimicked the inhibitory effects of A-II on 3 beta HSD and P450(17 alpha). It is important to point out, however, that the effects of A-II and TGF beta on P450(17 alpha) activity appeared more pronounced than their action of 3 beta HSD. This observation may relate to the relative stability of 3 beta HSD as compared to P450(17 alpha). Taken together these data indicate that, while A-II and TGF beta each decrease the levels of steroid-metabolizing enzymes, a differential regulation is observed in that P-450(17 alpha) protein and activity levels are much more sensitive to treatment with these factors.
肾上腺皮质细胞中最佳类固醇生成的维持主要依赖于促肾上腺皮质激素（ACTH）的长期作用，以促进各种类固醇代谢酶的合成。在类固醇生成途径中，3β-羟基类固醇脱氢酶（3β-HSD）与17α-羟化酶细胞色素P450（P-450(17α)）的比例在决定肾上腺细胞释放的最终类固醇产物方面起着关键作用。当考虑到肾上腺区域和区域特异性类固醇的分泌时，这些酶的差异尤为重要。在本研究中，我们研究了3β-HSD在酶活性、蛋白质水平以及编码该酶的特定mRNA变化方面的调节情况。在原代培养八天后，发现牛肾上腺皮质（BAC）细胞对ACTH和双丁酰环磷腺苷（Bu2 cAMP）均有反应，皮质醇生成增加。此外，3β-HSD活性、酶蛋白和mRNA水平对这两种因子均有增加反应。增加幅度从活性增加2倍到mRNA增加5 - 7倍不等。ACTH和Bu2 cAMP还使对照细胞中几乎检测不到的P-450(17α)水平大幅增加。为了研究这些肾上腺类固醇生成酶的差异调节可能性，我们测定了血管紧张素II（A-II）和转化生长因子β（TGFβ）对这些酶水平的影响。这两种因子均将ACTH刺激的P-450(17α)酶和mRNA水平降低至对照细胞中观察到的几乎检测不到的水平。此外，这些化合物抑制ACTH对3β-HSD的诱导作用。虽然TGFβ的作用机制尚不清楚，但A-II可能是通过蛋白激酶C起作用。实际上，激活蛋白激酶C的佛波酯TPA模拟了A-II对3β-HSD和P450(17α)的抑制作用。然而，需要指出的是，A-II和TGFβ对P450(17α)活性的影响似乎比对3β-HSD的作用更为明显。这一观察结果可能与3β-HSD与P450(17α)相比的相对稳定性有关。综合这些数据表明，虽然A-II和TGFβ各自降低了类固醇代谢酶的水平，但观察到一种差异调节现象，即P-450(17α)蛋白和活性水平对这些因子的处理更为敏感。
