Zakar T, Hirst J J, Mijovic J E, Olson D M
Department of Obstetrics and Gynaecology, University of Alberta, Edmonton, Canada.
Endocrinology. 1995 Apr;136(4):1610-9. doi: 10.1210/endo.136.4.7895671.
Corticosteroids increase the production of prostaglandin E2 (PGE2) and the activity of prostaglandin endoperoxide H synthase (PGHS) in cultured amnion cells, although they inhibit prostanoid biosynthesis in numerous other cell types. This suggests that glucocorticoids control the level of PGHS in amnion cells by a hitherto unexplored, positive regulatory mechanism. We have tested the possibility that corticosteroids act by stimulating the expression of messenger RNAs (mRNAs) encoding one or both isoforms of PGHS. Ribonuclease protection assays were used to determine the levels of PGHS-1 and -2 mRNAs and, for reference, gamma-actin mRNA levels in confluent primary cultures of human amnion cells. In untreated cultures, PGHS-1 and -2 mRNA levels were low, often not reaching the level of detection. Dexamethasone (DEX) treatment for 4 h resulted in a measurable level of PGHS-2 mRNA, which increased further 10-fold and 20-fold after incubation with the glucocorticoid for 8 h and 16 h, respectively. The stimulation was dependent on DEX concentration, and was concomitant with an increase in the capacity of the cells to metabolize arachidonic acid to PGE2. PGHS-1 mRNA levels remained low in DEX-treated cells, while the gamma-actin message level showed no change. Estradiol and progesterone had no influence on PGHS-2 mRNA expression, but cortisol increased the PGHS-2 mRNA abundance. The glucocorticoid antagonist RU486 blocked the effect of DEX. Conditioned media of DEX-treated cells did not contain steroid-induced factor(s) stimulating PGE2 production. Inhibition of protein synthesis by cycloheximide potentiated the effect of DEX, and raised the abundance of PGHS-1, PGHS-2, and gamma-actin mRNAs in untreated cells. DEX did not affect the stability of the PGHS-2 mRNA. These results show that glucocorticoids promote PGE2 synthesis by amnion cells by stimulating the expression of PGHS-2 mRNA in a receptor-dependent, selective, and immediate fashion.
皮质类固醇可增加培养羊膜细胞中前列腺素E2（PGE2）的生成以及前列腺素内过氧化物H合酶（PGHS）的活性，尽管它们在许多其他细胞类型中抑制类前列腺素生物合成。这表明糖皮质激素通过一种迄今尚未探索的正向调节机制来控制羊膜细胞中PGHS的水平。我们测试了皮质类固醇通过刺激编码PGHS一种或两种同工型的信使核糖核酸（mRNA）表达起作用的可能性。采用核糖核酸酶保护分析法来测定人羊膜细胞汇合原代培养物中PGHS-1和-2 mRNA的水平，作为对照，同时测定γ-肌动蛋白mRNA水平。在未处理的培养物中，PGHS-1和-2 mRNA水平较低，常常未达到检测水平。地塞米松（DEX）处理4小时导致可检测到的PGHS-2 mRNA水平，在用糖皮质激素孵育8小时和16小时后，该水平分别进一步增加了10倍和20倍。这种刺激依赖于DEX浓度，并且与细胞将花生四烯酸代谢为PGE2的能力增加相伴。在DEX处理的细胞中，PGHS-1 mRNA水平仍然较低，而γ-肌动蛋白信使水平没有变化。雌二醇和孕酮对PGHS-2 mRNA表达没有影响，但皮质醇增加了PGHS-2 mRNA丰度。糖皮质激素拮抗剂RU486阻断了DEX的作用。DEX处理细胞的条件培养基中不含有刺激PGE2产生的类固醇诱导因子。用环己酰亚胺抑制蛋白质合成增强了DEX的作用，并提高了未处理细胞中PGHS-1、PGHS-2和γ-肌动蛋白mRNA的丰度。DEX不影响PGHS-2 mRNA的稳定性。这些结果表明，糖皮质激素通过以受体依赖、选择性和即时的方式刺激PGHS-2 mRNA的表达来促进羊膜细胞合成PGE2。
