Department of Pediatrics, University of California, San Francisco, California 94143, USA.
J Biol Chem. 2013 Aug 16;288(33):23903-13. doi: 10.1074/jbc.M113.460048. Epub 2013 Jul 8.
Cytochrome P450c17, a steroidogenic enzyme encoded by the CYP17A1 gene, catalyzes the steroid 17α-hydroxylation needed for glucocorticoid synthesis, which may or may not be followed by 17,20 lyase activity needed for sex steroid synthesis. Whether or not P450c17 catalyzes 17,20 lyase activity is determined by three post-translational mechanisms influencing availability of reducing equivalents donated by P450 oxidoreductase (POR). These are increased amounts of POR, the allosteric action of cytochrome b5 to promote POR-P450c17 interaction, and Ser/Thr phosphorylation of P450c17, which also appears to promote POR-P450c17 interaction. The kinase(s) that phosphorylates P450c17 is unknown. In a series of kinase inhibition experiments, the pyridinyl imidazole drugs SB202190 and SB203580 inhibited 17,20 lyase but not 17α-hydroxylase activity in human adrenocortical HCI-H295A cells, suggesting an action on p38α or p38β. Co-transfection of non-steroidogenic COS-1 cells with P450c17 and p38 expression vectors showed that p38α, but not p38β, conferred 17,20 lyase activity on P450c17. Antiserum to P450c17 co-immunoprecipitated P450c17 and both p38 isoforms; however, knockdown of p38α, but not knockdown of p38β, inhibited 17,20 lyase activity in NCI-H295A cells. Bacterially expressed human P450c17 was phosphorylated by p38α in vitro at a non-canonical site, conferring increased 17,20 lyase activity. This phosphorylation increased the maximum velocity, but not the Michaelis constant, of the 17,20 lyase reaction. p38α phosphorylates P450c17 in a fashion that confers increased 17,20 lyase activity, implying that the production of adrenal androgens (adrenarche) is a regulated event.
细胞色素 P450c17 是一种类固醇生成酶，由 CYP17A1 基因编码，催化糖皮质激素合成所需的类固醇 17α-羟化作用，而 17,20 裂解酶活性是否需要进行性甾体合成。P450c17 是否催化 17,20 裂解酶活性取决于三种影响 P450 氧化还原酶 (POR) 提供的还原当量可用性的翻译后机制。这些机制包括 POR 数量的增加、细胞色素 b5 的别构作用以促进 POR-P450c17 相互作用，以及 P450c17 的 Ser/Thr 磷酸化，这似乎也促进了 POR-P450c17 的相互作用。磷酸化 P450c17 的激酶尚不清楚。在一系列激酶抑制实验中，吡啶基咪唑类药物 SB202190 和 SB203580 抑制了人肾上腺皮质 HCI-H295A 细胞中的 17,20 裂解酶但不抑制 17α-羟化酶活性，表明其作用于 p38α 或 p38β。将 P450c17 和 p38 表达载体共转染非甾体生成性 COS-1 细胞显示，p38α而非 p38β赋予 P450c17 17,20 裂解酶活性。抗 P450c17 抗体共沉淀了 P450c17 和两种 p38 同工型；然而，p38α 的敲低而非 p38β 的敲低抑制了 NCI-H295A 细胞中的 17,20 裂解酶活性。来自大肠埃希菌的人 P450c17 在体外被 p38α 在非典型位点磷酸化，赋予了增加的 17,20 裂解酶活性。这种磷酸化增加了 17,20 裂解酶反应的最大速度，但没有改变米氏常数。p38α 以赋予增加的 17,20 裂解酶活性的方式磷酸化 P450c17，这意味着肾上腺雄激素（肾上腺皮质功能亢进）的产生是一个受调节的事件。
