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17ß-Hydroxysteroid Dehydrogenase Type 1, 2, 3, and 4 Expression and Enzyme Activity in Human Anterior Pituitary Adenomas

Department of Medicine, University of Hull, and Neurosurgical Unit, Walton Hospital (P.M.F.), Liverpool, United Kingdom HU6 7RX; and Seestrusse 285 (A.M.L.), CH-8038 Zurich, Switzerland

Address all correspondence and requests for reprints to: Dr. V. L. Green, Department of Medicine, Wolfson Building, University of Hull, Cottingham Road, Hull, United Kingdom HU6 7RX.

17ß-Hydroxysteroid dehydrogenase (17ßHSD) isoforms reversibly catalyze the final step in the formation of estradiol (E₂) from estrone (E₁) and the formation of testosterone from androstenedione. We have investigated 17ßHSD type 1, 2, 3, and 4 gene expression and 17ßHSD estrogenic activity in human anterior pituitary adenomas. 17ßHSD messenger ribonucleic acid (mRNA) expression was studied by RT-PCR in 42 pituitary tumors and 3 normal pituitaries, 17ßHSD activity was studied in 11 tumors and 17ßHSD type 1 was immunolocalized in vitro in 6 tumors. 17ßHSD type 1 gene expression was detected in 34 of 42 adenomas in all tumor subtypes; 17ßHSD type 2 mRNA was detected in 18 of 42 adenomas, but not in prolactinomas; 17ßHSD type 3 mRNA was detected in 12 of 42 adenomas, but not in corticotropinomas; 17ßHSD type 4 was expressed in 20 of 42 adenomas by all adenoma subtypes. Reversible 17ßHSD activity was found in 9 of 11 adenomas, and 17ßHSD type 1 immunopositivity was cytoplasmically distributed in all 6 adenomas in vitro. All 4 17ßHSD isoforms are variably expressed in human anterior pituitary adenomas, which also show 17ßHSD enzyme activity, suggesting that 17ßHSD may play an important role in regulating the local cellular levels of estradiol.