Molecular mechanism of steroid transporter P-glycoprotein

p -糖蛋白作为一种能量依赖的外排泵，将抗癌药物输出细胞外，将其细胞内浓度降低到亚致死水平，被认为在人类肿瘤的多药耐药（MDR）中起重要作用。p -糖蛋白在几种正常人体组织中均有表达，但p -糖蛋白的生理底物尚未完全了解。为了分析药物转运机制和生理底物，我们建立了经上皮转运系统。我们在猪肾近端小管LLC-PK1细胞中表达了从人正常肾上腺中分离的MDR1 cDNA。其中一种转化（LLC-GA5-COL300）对秋水仙碱、长春花碱和阿霉素的抗性分别是LLC-PK1细胞的54倍、150倍和167倍。lc - pk_1和表达P-糖蛋白的转染细胞形成高度极化的上皮，利用单克隆抗体MRK16的电镜免疫细胞化学表明，人P- pk_1在转染细胞的顶端表面特异性表达了更多的糖蛋白。通过使用这个经上皮运输系统，我们测量了^ 3h标记的醛固酮、皮质酮、皮质醇、脱氧皮质酮、地塞米松、雌二醇、雌三醇、孕酮、睾酮的运输。与宿主细胞相比，转染细胞中醛固酮、皮质醇、雌三醇和地塞米松从基部到基部的转运增加，而从基部到基部的转运减少。但在两种细胞系中，皮质酮、脱氧皮质酮、雌二醇、孕酮、睾酮的转运没有区别。维拉帕米可抑制醛固酮、皮质醇、雌三醇和地塞米松的上皮转运。这些结果表明，人p糖蛋白转运醛固酮、皮质醇、雌三醇和地塞米松。皮质醇是一种糖皮质激素，是人体肾上腺产生的主要类固醇。醛固酮是人体肾上腺产生的主要矿物皮质激素。雌三醇是妊娠期间胎胎盘单位产生的主要雌激素。p -糖蛋白在人肾上腺皮质、孕妇子宫和胎盘中表达。这些结果表明，人p糖蛋白在妊娠期间作为类固醇转运体在肾上腺皮质和胎胎盘单位中起作用。少

P-glycoprotein acts as an energy-dependent efflux pump that exports anticancer agents out of the cell, lowering their intracellular concentration to sublethal levels, and is considered to be important in multidrug resistance (MDR) of human tumors. P-glycoprotein is expressed in several normal human tissues, but physiological substrates of P-glycoprotein have not been fully understood.To analyze the mechanism of drug transport and physiological substrates, we established a transepithelial transport system. We expressed MDR1 cDNA isolated from human normal adrenal in LLC-PK1 cells, which are derived from porcine kidney proximal tubule. One transformant (LLC-GA5-COL300) showed 54-, 150-, and 167-fold resistance to colchicine, vinblastine, and adriamycin, respectively, compared to LLC-PK1 cells. LLC-PK_1 and the P-glycoprotein-expressing transfectant cells form a highly polarized epithelium, and electron microscopic immunocytochemistry using a monoclonal antibody MRK16 showed that human P- … More glycoprotein is specifically expressed on the apical surface of the transfectant cells.By using this transepithelial transport system, we measured transport of ^3H-labeled aldosterone, corticosterone, cortisol, deoxycorticosterone, dexamethasone, estradiol, estriol, progesterone, testesterone. In the transfectant cells, basal to apical transport of aldosterone, cortisol, estriol and dexamethasone increased and their apical to basal transport decreased compared to those in the host cells. But transport of corticosterone, deoxycorticosterone, estradiol, progesterone, testesterone was indistinguishable in both cell lines. Transepithelial transport of aldosterone, cortisol, estriol and dexamethasone was inhibited by verapamil. These results indicate that human P-glycoprotein transports aldosterone, cortisol, estriol and dexamethasone.Cortisol, a glucocorticoid, is the main steroid produced in the human adrenal. Aldosterone is the main mineralocorticoid produced in the human adrenal. Estriol is the main estrogen produced during pregnancy in the fetoplacental unit. P-glycoprotein is expressed in the human adrenal cortex and the pregnant uterus and placenta. These results suggest that human P-glycoprotein functions as a steroid transporter in the adrenal cortex and in the fetoplacental unit during pregnancy. Less