Klaij I A, Timmerman M A, Blok L J, Grootegoed J A, de Jong F H
Department of Endocrinology and Reproduction, Medical Faculty, Erasmus University Rotterdam, Netherlands.
Mol Cell Endocrinol. 1992 Jun;85(3):237-46. doi: 10.1016/0303-7207(92)90262-5.
In Sertoli cells from 21-day-old rats, the expression of the mRNA encoding the alpha-subunit of inhibin, and the production of immunoreactive inhibin are stimulated by follicle-stimulating hormone (FSH). In contrast, the amount of beta B-subunit mRNA is not increased after FSH treatment of the cells, and the ratio between bioactive and immunoactive inhibin decreases after stimulation with FSH. These data suggest that the beta B-subunit is the limiting factor in the production of bioactive inhibin. The aim of the present experiments was to investigate the effect of changes in the amount of beta B-subunit mRNA on the production of bioactive and immunoreactive inhibin. During early postnatal testicular development, the relative amounts of the 4.2 kb and 3.5 kb mRNAs encoding the beta B-subunit of inhibin changed markedly. The meaning of this changing ratio between beta B-subunit mRNAs is not clear, since both mRNAs are actively translated, as demonstrated by polysomal analysis. The total amount of beta B-subunit mRNA correlated with the in vitro production of bioactive inhibin as published earlier. Prolonged stimulation of cultured Sertoli cells from 14-day-old rats with 4 beta-phorbol 12-myristate 13-acetate (PMA) caused a decreased expression of the beta B-subunit mRNAs, presumably by down-regulation of protein kinase C. A similar effect was obtained after addition of the calcium ionophore A23187. Concomitantly, a decreased production of bioactive inhibin was observed. Furthermore, Western blotting revealed that secretion of the 32 kDa inhibin alpha beta-dimer was decreased, whereas secretion of the combination of the C-terminal part with the pro-region of the alpha-subunit was increased. It is concluded that the level of the beta B-subunit of inhibin is rate-limiting for the production of bioactive inhibin in cultured Sertoli cells, and that its expression can be influenced by modulation of protein kinase C, and/or intracellular calcium levels.
在21日龄大鼠的支持细胞中，促卵泡激素（FSH）可刺激编码抑制素α亚基的mRNA表达以及免疫反应性抑制素的产生。相比之下，用FSH处理细胞后，βB亚基mRNA的量并未增加，且FSH刺激后生物活性抑制素与免疫活性抑制素的比例降低。这些数据表明，βB亚基是生物活性抑制素产生的限制因素。本实验的目的是研究βB亚基mRNA量的变化对生物活性和免疫反应性抑制素产生的影响。在出生后早期睾丸发育过程中，编码抑制素βB亚基的4.2 kb和3.5 kb mRNA的相对量发生了显著变化。βB亚基mRNA之间这种变化比例的意义尚不清楚，因为多核糖体分析表明这两种mRNA都能被积极翻译。如先前报道，βB亚基mRNA的总量与生物活性抑制素的体外产生相关。用4β-佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）长期刺激14日龄大鼠的培养支持细胞，可能通过下调蛋白激酶C导致βB亚基mRNA的表达降低。添加钙离子载体A23187后也获得了类似的效果。同时，观察到生物活性抑制素的产生减少。此外，蛋白质印迹法显示32 kDa抑制素αβ二聚体的分泌减少，而α亚基C末端部分与前区域组合的分泌增加。结论是，抑制素βB亚基的水平是培养支持细胞中生物活性抑制素产生的限速因素，其表达可受蛋白激酶C和/或细胞内钙水平调节的影响。
