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Regulation of Aromatase Expression in Human Ovarian Surface Epithelial Cells¹

Division of Immunology (T.O., S.C.), Beckman Research Institute of the City of Hope, Duarte, California 91010; and Laboratory of Gynecology Oncology, Department of Obstetrics, Gynecology and Reproductive Biology (S.C.M.), Brigham and Women’s Hospital, Harvard Medical School. Boston, Massachusetts 02115

Address correspondence and requests for reprints to: Dr. Shiuan Chen, Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, California 91010. E-mail: schen{at}coh.org

Ovarian cancer originates mainly from surface epithelial cells, which are potential targets of estrogen action. Using immunohistochemistry and RT-PCR analysis, aromatase (estrogen synthetase) can be detected in human ovarian surface epithelial tumors. In this study, we functionally characterized the aromatase expressed in a primary cell culture, normal human ovarian surface epithelial (HOSE) 17. The apparent K_m and V_max values were determined to be 5.8 ± 0.5 nM, and 0.3 ± 0.0 pmol/mg·h, respectively. The aromatase activity in HOSE 17 cells can be induced effectively by phorbol esters and forskolin, suggesting that estrogen biosynthesis in HOSE 17 cells is mainly regulated through protein kinase C- and protein kinase A-mediated mechanisms. Exon I-specific RT-PCR revealed that phorbol esters predominantly up-regulated promoter II. Whereas forskolin treatment increased exon I.3A-containing messenger RNA, the aromatase activity remained low in the cells treated with this agent. In vitro transcription/translation analysis using plasmids containing T7 promoter and the human snail gene (SnaH) as a reporter capped with different untranslated exon Is revealed that exon PII-containing transcripts were translated more effectively than exon I.3-containing transcripts. These findings explain why aromatase activity is higher in cells with the PII-containing transcripts than is cells with the I.3-containing transcripts. Our results indicate that aromatase is functionally expressed in human ovarian surface epithelial cells and its expression is regulated at both the transcriptional and translational levels.

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