Poderoso C, Cornejo Maciel F, Gorostizaga A, Bey P, Paz C, Podestá E J
Department of Biochemistry, School of Medicine, University of Buenos Aires, Argentina.
Endocr Res. 2002 Nov;28(4):413-7. doi: 10.1081/erc-120016816.
A key regulatory step in the steroidogenic hormones signaling pathway is the synthesis of steroidogenic acute regulatory protein (StAR). This protein facilitates the delivery of cholesterol to the inner mitochondrial membrane, the rate-limiting step in steroidogenesis. ACTH and LH pathway also includes tyrosine dephosphorylation processes. Indeed, our previous studies have demonstrated that both hormones increase protein tyrosine phosphatase (PTP) activity by a PKA-dependent mechanism and that the action of PTPs is required for the stimulation of steroid biosynthesis in adrenal and Leydig cells. In order to test the putative relationship between PTP activity and StAR protein induction in adrenocortical cells, in the present study we evaluated steroid production and StAR protein level in Y1 adrenocortical cells under PTP inhibition. Phenylarsine oxide (PAO), a powerful cell permeable PTP inhibitor, reduced ACTH-stimulated steroidogenesis in a concentration-dependent fashion. A concentration of 2.5 microM of this compound inhibited steroid synthesis in a 56% (ACTH = 318 +/- 30, ACTH + PAO = 145 +/- 18 ng progesterone/mL, P < 0.001) and also abrogated StAR protein induction. Phenylarsine oxide reduced the protein level after 60 min and this effect still remained at 120 min. A second PTP inhibitor, benzyl phosphonic acid, acting by a different mechanism, reproduced PAO effects on both steroidogenesis and StAR protein. Taken together, these results indicate that PTP activity participates in StAR protein induction and led us to attribute to the PKA-mediated PTP activation in steroidogenic systems a functional role, as mediator of StAR protein induction.
类固醇生成激素信号通路中的一个关键调节步骤是类固醇生成急性调节蛋白（StAR）的合成。这种蛋白质促进胆固醇向线粒体内膜的转运，这是类固醇生成中的限速步骤。促肾上腺皮质激素（ACTH）和促黄体生成素（LH）信号通路也包括酪氨酸去磷酸化过程。事实上，我们之前的研究表明，这两种激素都通过依赖蛋白激酶A（PKA）的机制增加蛋白酪氨酸磷酸酶（PTP）的活性，并且PTP的作用是肾上腺和睾丸间质细胞中类固醇生物合成刺激所必需的。为了测试肾上腺皮质细胞中PTP活性与StAR蛋白诱导之间的假定关系，在本研究中，我们评估了PTP抑制下Y1肾上腺皮质细胞中的类固醇生成和StAR蛋白水平。苯胂酸氧化物（PAO）是一种强大的可穿透细胞的PTP抑制剂，它以浓度依赖的方式降低ACTH刺激的类固醇生成。2.5微摩尔浓度的该化合物抑制类固醇合成达56%（ACTH = 318 +/- 30，ACTH + PAO = 145 +/- 18纳克孕酮/毫升，P < 0.001），并且还消除了StAR蛋白的诱导。苯胂酸氧化物在60分钟后降低了蛋白水平，并且这种作用在120分钟时仍然存在。第二种PTP抑制剂苄基膦酸通过不同机制起作用，重现了PAO对类固醇生成和StAR蛋白的影响。综上所述，这些结果表明PTP活性参与了StAR蛋白的诱导，并使我们将类固醇生成系统中PKA介导的PTP激活归因于作为StAR蛋白诱导介质的功能作用。
