Mesiano S, Fujimoto V Y, Nelson L R, Lee J Y, Voytek C C, Jaffe R B
Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco 94143-0556, USA.
J Clin Endocrinol Metab. 1996 Jan;81(1):340-5. doi: 10.1210/jcem.81.1.8550775.
Developmental changes in the responsiveness of the fetal adrenals to corticotropin (ACTH) play an important role in the regulation of the fetal hypothalamic-pituitary-adrenal axis. Responsiveness of adrenal cortical cells to ACTH is dependent on the extent of ACTH receptor expression. Therefore, we examined the localization and regulation of ACTH receptor expression in the midgestation (16-24 weeks) human fetal adrenal cortex. In situ hybridization analysis was used to localize messenger RNA (mRNA) encoding the ACTH receptor in sections of human fetal adrenal glands. Messenger RNA encoding the ACTH receptor was localized in cells from all cortical zones; abundance was higher in definitive zone than in fetal zone cells and was least abundant in the more central portions of the cortex. Regulation of ACTH receptor expression was studied using Northern blot analysis of total RNA extracted from primary cultures of fetal and definitive zone cells. Two major (1.5 and 3.5 kilobases) and, upon stimulation with ACTH, 3 minor (4.0, 6.0 and 10.0 kb) ACTH receptor mRNA transcripts were detected in RNA from fetal and definitive zone cells. In both cell types, ACTH-(1-24) increased the abundance of mRNA encoding the ACTH receptor 10- to 20-fold compared with untreated cells. The effects of ACTH-(1-24) on ACTH receptor expression in fetal zone cells were time- and dose-dependent. The ED50 for the stimulation of ACTH receptor expression by ACTH-(1-24) was 1-10 pM, and maximal response to 0.1 nm ACTH-(1-24) was detected after 12-16 h. Eight-bromoadenosine cAMP and forskolin also stimulated ACTH receptor expression in fetal zone cells and closely mimicked the effects of ACTH-(1-24). In contrast, stimulation of protein kinase C with 12-O-tetradecanoyl phorbol 13-acetate had no effect on ACTH receptor expression. Changes in ACTH receptor expression in response to ACTH-(1-24), cAMP and forskolin were paralleled by changes in expression of the P450 cholesterol side chain cleavage (P450scc) enzyme. These data demonstrate that expression of the ACTH receptor by the human fetal adrenal cortex is up-regulated by its own ligand and that this effect is mediated by a cAMP-dependent mechanism. In addition, the coordinate stimulation of ACTH receptor and P450scc expression by ACTH indicates that the gene for the ACTH receptor is one of a specific cohort of genes regulated by ACTH that are required to facilitate fetal adrenal cortical response to ACTH. ACTH regulation of its own receptor may represent a mechanism by which fetal adrenal responsiveness to ACTH is maintained and possibly enhanced during fetal development.
胎儿肾上腺对促肾上腺皮质激素（ACTH）反应性的发育变化在胎儿下丘脑 - 垂体 - 肾上腺轴的调节中起重要作用。肾上腺皮质细胞对ACTH的反应性取决于ACTH受体表达的程度。因此，我们研究了孕中期（16 - 24周）人胎儿肾上腺皮质中ACTH受体表达的定位和调节。采用原位杂交分析在人胎儿肾上腺切片中定位编码ACTH受体的信使核糖核酸（mRNA）。编码ACTH受体的mRNA定位于所有皮质区的细胞中；在永久区的丰度高于胎儿区细胞，且在皮质更中央部分丰度最低。使用从胎儿区和永久区细胞原代培养物中提取的总RNA进行Northern印迹分析来研究ACTH受体表达的调节。在胎儿区和永久区细胞的RNA中检测到两种主要的（1.5和3.5千碱基）以及在用ACTH刺激后3种次要的（4.0、6.0和10.0 kb）ACTH受体mRNA转录本。在两种细胞类型中，与未处理细胞相比，ACTH - (1 - 24)使编码ACTH受体的mRNA丰度增加了10至20倍。ACTH - (1 - 24)对胎儿区细胞中ACTH受体表达的影响具有时间和剂量依赖性。ACTH - (1 - 24)刺激ACTH受体表达的半数有效剂量（ED50）为1 - 10 pM，在12 - 16小时后检测到对0.1 nM ACTH - (1 - 24)的最大反应。8 - 溴腺苷环磷腺苷（8 - bromoadenosine cAMP）和福司可林也刺激胎儿区细胞中ACTH受体表达，并紧密模拟ACTH - (1 - 24)的作用。相比之下，用12 - O - 十四酰佛波醇13 - 乙酸酯刺激蛋白激酶C对ACTH受体表达没有影响。对ACTH - (1 - 24)、cAMP和福司可林反应时ACTH受体表达的变化与细胞色素P450胆固醇侧链裂解酶（P450scc）表达的变化平行。这些数据表明，人胎儿肾上腺皮质中ACTH受体的表达受其自身配体上调，且这种作用由cAMP依赖性机制介导。此外，ACTH对ACTH受体和P450scc表达的协同刺激表明，ACTH受体基因是受ACTH调节的特定基因群之一，这些基因是促进胎儿肾上腺皮质对ACTH反应所必需的。ACTH对其自身受体的调节可能代表一种机制，通过该机制胎儿肾上腺对ACTH的反应性在胎儿发育过程中得以维持并可能增强。
