Abayasekara D R, Ford S L, Persaud S J, Jones P M
Department of Physiology, Royal Free Hospital School of Medicine, London, UK.
J Endocrinol. 1996 Aug;150(2):213-21. doi: 10.1677/joe.0.1500213.
The key role of protein kinases and protein phosphorylation in the regulation of luteal steroidogenesis is well documented. However the role of phosphoprotein phosphatases (PP) and dephosphorylation in the regulation of luteal cell progesterone secretion is as yet unknown. We have recently demonstrated the presence and activity of PP1 and PP2A in rat luteal cells and the present study was undertaken to determine the consequences of inhibiting PP activity in terms of progesterone secretion. Three structurally dissimilar inhibitors of PP1/2A, okadaic acid, calyculin A and cantharidin each caused a dose-dependent inhibition of LH-induced progesterone secretion without affecting cyclic AMP accumulation. The less potent derivative of okadaic acid, norokadaone, had no effect on either parameter, suggesting that the inhibitory actions on progesterone secretion are due to their specific actions on PP activity and that this inhibition occurs principally at a locus which is distal to the generation of cyclic AMP. In contrast to the inhibitory effects of PP1/2A inhibitors on progesterone biosynthesis, a PP2B inhibitor, cypermethrin, had no effect on LH-stimulated steroidogenesis. The three PP1/2A inhibitors also caused a concentration-dependent inhibition of dibutyryl cyclic AMP-stimulated progesterone secretion. However, none of the inhibitors affected 22R-hydroxycholesterol-supported steroidogenesis, clearly demonstrating that the inhibitors did not interfere with the activity of steroidogenic enzymes. These results suggest that cycles of phosphorylation/dephosphorylation of specific proteins are required for the sustained production of progesterone. Whilst the precise location and function of putative PP substrates is uncertain, the present results indicate that they are involved in regulating the availability of free cholesterol to steroidogenic enzymes within mitochondria.
蛋白激酶和蛋白磷酸化在黄体类固醇生成调节中的关键作用已有充分记载。然而，磷蛋白磷酸酶（PP）和去磷酸化在黄体细胞孕酮分泌调节中的作用尚不明确。我们最近已证实大鼠黄体细胞中存在PP1和PP2A及其活性，本研究旨在确定抑制PP活性对孕酮分泌的影响。三种结构不同的PP1/2A抑制剂，冈田酸、花萼海绵诱癌素A和斑蝥素，均引起LH诱导的孕酮分泌呈剂量依赖性抑制，而不影响环磷酸腺苷（cAMP）的积累。冈田酸的低效衍生物去甲冈田酮对这两个参数均无影响，这表明对孕酮分泌的抑制作用是由于它们对PP活性的特异性作用，且这种抑制主要发生在环磷酸腺苷生成的远端位点。与PP1/2A抑制剂对孕酮生物合成的抑制作用相反，PP2B抑制剂氯氰菊酯对LH刺激的类固醇生成无影响。这三种PP1/2A抑制剂还引起二丁酰环磷酸腺苷刺激的孕酮分泌呈浓度依赖性抑制。然而，这些抑制剂均不影响22R-羟基胆固醇支持的类固醇生成，清楚地表明这些抑制剂并未干扰类固醇生成酶的活性。这些结果表明，特定蛋白质的磷酸化/去磷酸化循环是孕酮持续产生所必需的。虽然假定的PP底物的确切位置和功能尚不确定，但目前的结果表明它们参与调节线粒体中类固醇生成酶可利用的游离胆固醇的供应。
