Pandey Amit V, Mellon Synthia H, Miller Walter L
Department of Pediatrics, University of California, San Francisco, California 94143-0978, USA.
J Biol Chem. 2003 Jan 31;278(5):2837-44. doi: 10.1074/jbc.M209527200. Epub 2002 Nov 19.
Cytochrome P450c17 catalyzes 17 alpha-hydroxylation needed for cortisol synthesis and 17,20 lyase activity needed to produce sex steroids. Serine phosphorylation of P450c17 specifically increases 17,20 lyase activity, but the physiological factors regulating this effect remain unknown. Treating human adrenal NCI-H295A cells with the phosphatase inhibitors okadaic acid, fostriecin, and cantharidin increased 17,20 lyase activity, suggesting involvement of protein phosphatase 2A (PP2A) or 4 (PP4). PP2A but not PP4 inhibited 17,20 lyase activity in microsomes from cultured cells, but neither affected 17 alpha-hydroxylation. Inhibition of 17,20 lyase activity by PP2A was concentration-dependent, could be inhibited by okadaic acid, and was restored by endogenous protein kinases. PP2A but not PP4 coimmunoprecipitated with P450c17, and suppression of PP2A by small interfering RNA increased 17,20 lyase activity. Phosphoprotein SET found in adrenals inhibited PP2A, but not PP4, and fostered 17,20 lyase activity. The identification of PP2A and SET as post-translational regulators of androgen biosynthesis suggests potential additional mechanisms contributing to adrenarche and hyperandrogenic disorders such as polycystic ovary syndrome.
细胞色素P450c17催化皮质醇合成所需的17α-羟化作用以及产生性类固醇所需的17,20裂解酶活性。P450c17的丝氨酸磷酸化特异性增加17,20裂解酶活性，但调节这种效应的生理因素仍不清楚。用磷酸酶抑制剂冈田酸、福司曲星和斑蝥素处理人肾上腺NCI-H295A细胞可增加17,20裂解酶活性，提示蛋白磷酸酶2A（PP2A）或4（PP4）参与其中。PP2A而非PP4抑制培养细胞微粒体中的17,20裂解酶活性，但两者均不影响17α-羟化作用。PP2A对17,20裂解酶活性的抑制呈浓度依赖性，可被冈田酸抑制，并可被内源性蛋白激酶恢复。PP2A而非PP4与P450c17共免疫沉淀，小干扰RNA抑制PP2A可增加17,20裂解酶活性。肾上腺中发现的磷蛋白SET抑制PP2A而非PP4，并促进17,20裂解酶活性。PP2A和SET作为雄激素生物合成的翻译后调节因子的鉴定提示了可能导致肾上腺初现和多囊卵巢综合征等高雄激素性疾病的额外机制。
