Steroid-Metabolizing Enzymes in Human Breast Cancer Cells. II. 5α-Reductase, 3α-Hydroxysteroid Oxidoreductase, and 17β-Hydroxysteroid Oxidor educt ase*

Abstract

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.

Sex steroid-producing enzymes in human breast cancer

“…Activity of 5a-reductase was previously detected in human breast carcinoma cell lines (MacIndoe & Woods 1981), and 5a-reductase activity was elevated 4-8 times in breast cancer tissues compared with non-tumorous breast tissues (Wiebe et al 2000). mRNA expression of 5a-reductase type 1 was detected in all the breast carcinoma tissues examined (Suzuki et al 2001a, Lewis et al 2004, Ji et al 2004, while that of 5a-reducatase type 2 was detected in 38-100% of the tumors ( (Suzuki et al 2001a, Lewis et al 2004.…”

Biosynthesis of catalytically active rat testosterone 5 alpha-reductase in microinjected Xenopus oocytes: evidence for tissue-specific differences in translatable mRNA.

“…Moreover, the levels oftranslatable tissue-specific 5a-reductase mRNAs as monitored in the Xenopus oocytes correlated with the variable 5a-reductase activities in female rat liver, male rat liver, and prostate homogenates; the ratio of their specific activities was of 2500:630:1, respectively. Altogether, these results provide supporting evidence in favor of the transcriptional control of 5a-reductase expression in rat tissues.ical inactivation of 4-ene-3-ketosteroids, mainly adrenal corticosteroids (19).Previous biochemical studies of 5a-reductase have revealed kinetic parameters, such as affinity constants to steroid hormones, as well as the enzyme subcellular distribution in the rough endoplasmic reticulum and/or nuclei of various tissues (1,(20)(21)(22)(23)(24). Because the activity of Sareductase is extremely unstable in cell-free preparations (1, 20), it has not been purified, and therefore the regulation of its expression could not be studied at the molecular level.…”

“…Previous biochemical studies of 5a-reductase have revealed kinetic parameters, such as affinity constants to steroid hormones, as well as the enzyme subcellular distribution in the rough endoplasmic reticulum and/or nuclei of various tissues (1,(20)(21)(22)(23)(24). Because the activity of Sareductase is extremely unstable in cell-free preparations (1, 20), it has not been purified, and therefore the regulation of its expression could not be studied at the molecular level.…”

Dehydroepiandrosterone and estrone 17-ketosteroid reductases in MCF-7 human breast cancer cells

“…We now report the results of experiments which have identified and partially characterized separate cytosolic E1 and DHEA 17-ketosteroid reductase activities (17-KSR's) within MCF-7 cells, each of which appears to be different from the previously identified particulate 17-KSR that mediates the conversion of androstenedione (AE) to testosterone (T) in this cell line [18]. and have been maintained as described previously [19].…”

“…We have reported previously that MCF-7 cells also contain particulate enzyme activity that interconverts androstenedione (AE) and testosterone (T) using NADP (H) [18]. It is not yet clear whether or not NAD(H) can be utilized by this system, whether the AE/T interconversion is mediated by one or more enzymes, or whether this particulate enzyme activity is the same or different from the particulate activity which mediates the interconversion of E1 and E2.…”