Abstract
Estrogen sulfotransferase (EST) is a cytosolic enzyme that catalyzes the sulfonation of estrogens at the 3-hydroxyl position by use of 3′-phosphoadenosine-5′-phosphosulfate as an activated sulfate donor. Although largely known and studied as a phase II metabolic enzyme with prominent expression in the liver, the high substrate specificity of EST (with a highVmax/Km value for estrogen) suggests that expression of the enzyme in extrahepatic, estrogen target tissues, such as the breast epithelium, may constitute an effective mechanism for local estrogen regulation as well. In this study, we have evaluated the physiological significance of EST expression by cDNA transfection studies with use of the estrogen-dependent MCF-7 breast cancer cell line as a model system. We show that expression of EST in MCF-7 cells effectively reduces the cells’ response to physiological concentrations of estradiol (10 nM) by up to 70% as determined in an estrogen-responsive reporter gene assay. In addition, we demonstrate that expression of EST similarly inhibits estrogen-stimulated DNA synthesis and cell proliferation by 21% and 46%, respectively. (The thymidine incorporation rate was measured 3 days after and the cell numbers were counted 8 days after transfection.) These results provide direct evidence for the functional significance of in situ EST expression in the breast epithelium and suggest that abnormal regulation of the enzyme may have pathological implications in the development and maintenance of hormone-dependent breast carcinomas.
Footnotes
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Send reprint requests to: Wen-chao Song, Ph.D., Center for Experimental Therapeutics, University of Pennsylvania School of Medicine, 905 Stellar-Chance Laboratories, 422 Curie Blvd, Philadelphia, PA 19104.
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↵1 Supported in part by National Institutes of Health grant R21CA66179. Preliminary findings were presented at the 79th Annual Meeting of The Endocrine Society.
- Abbreviations:
- CAT
- chloramphenicol acetyltransferase
- ER
- estrogen receptor
- EST
- estrogen sulfotransferase
- FBS
- fetal bovine serum
- HME
- human mammary epithelial
- HSST
- hydroxysteroid sulfotransferase
- MEM
- minimum essential medium
- PBS
- phosphate-buffered saline
- PST
- phenol sulfotransferase
- TLC
- thin-layer chromatography
- Received December 15, 1997.
- Accepted March 30, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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