Steroid-metabolizing enzymes in human breast cancer cells. II. 5 alpha-Reductase, 3 alpha-hydroxysteroid oxidoreductase, and 17 beta-hydroxysteroid oxidoreductase.

Evidence that some human breast cancers can form biologically active sex steroids from extracellular precursors has prompted us to investigate several human breast cancer cell lines for similar steroidogenic capability. We have previously reported that MCF-7 and MDA-MB-231 human breast cancer cells can transform testosterone to estradiol but that aromatase activity is not apparent in the HBL-100 human breast cell line. We report here the presence of 17 beta-hydroxysteroid oxidoreductase, 5 alpha-reductase, and 3 alpha-hydroxysteroid oxidoreductase activities in all three cell lines. Characterization of these enzymes in MCF-7 cells indicated that the intracellular location, temperature and pH optima, cofactor requirements, and apparent substrate affinities for each are generally similar to those described in several other mammalian systems. The presence of 17-hydroxysteroid oxidoreductase, aromatase, 5 alpha-reductase, and 3-hydroxysteroid oxidoreductase activities in MCF-7 suggests the possibility that the hormonal regulation of these human breast cancer cells may be mediated in part by intracellular estrogen and/or androgen biosynthesis.