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¹ Medical and Research Services, WJB Dorn Veterans Medical Center, Columbia, South Carolina 29201, USA
² Department of Medicine, Medical Library Building, Suite 316, School of Medicine, University of South Carolina School of Medicine, Columbia, South Carolina 29208, USA
³ Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA

(Requests for offprints should be addressed to T Lin at Department of Medicine, University of South Carolina; Email: lin{at}med.sc.edu)

This study was performed to compare the effects of three well-known phytoestrogens such as genistein, resveratrol, and quercetin on steroidogenesis in MA-10 mouse tumor Leydig cells. Addition of genistein or resveratrol to MA-10 cells resulted in decreases in the cAMP-stimulated progesterone secretion, but quercetin had an opposite response. Steroidogenic acute regulatory (StAR) mRNA expression and StAR promoter activity in transiently transfected MA-10 cells were significantly reduced by genistein or resveratrol, but increased by quercetin. Genistein was found to inhibit MA-10 cell proliferation, while resveratrol and quercetin had no effect. Quercetin-induced increase in cAMP-stimulated progesterone secretion was reversed by ICI 182,780, an estrogen receptor (ER) antagonist. However, ICI 182,780 had no effect on cAMP plus quercetin-stimulated StAR promoter activity. To examine whether non-ER factors are associated with quercetin-stimulated progesterone production, we treated MA-10 cells with EGTA to deprive them of extracellular Ca²⁺. We found that EGTA inhibited quercetin-plus cAMP-stimulated progesterone secretion and StAR promoter activity. Blocking of Ca²⁺ influx through L- or T-type voltage-gated Ca²⁺ channels with verapamil or mibefradil respectively, attenuated quercetin-stimulated progesterone secretion, while they had no effect on quercetin-plus cAMP-stimulated StAR promoter activity. Blocking of intracellular Ca²⁺ efflux by sodium orthovanadate, a Ca²⁺-pump inhibitor, blocked quercetin- plus cAMP-stimulated progesterone secretion and StAR promoter activity in MA-10 cells. Finally, EGTA or vanadate reduced quercetin and cAMP-increased in StAR mRNA expression in MA-10 cells, while ICI 182,780 had no effect. Taken together, these results indicate that phytoestrogens have differential effects on steroidogenesis in MA-10 cells.