Cloning and characterization of human form 2 type 7 17β-hydroxysteroid dehydrogenase, a primarily 3β-keto reductase and estrogen activating and androgen inactivating enzyme

Type 7 17β-HSD catalyzes the transformation of estrone (E1) into estradiol (E2) and dihydrotestosterone (DHT) into 5α -androstane-3β,17β-diol (3β-diol) as well as zymosterone into zymosterol. This suggests that in addition to cholesterol metabolism, the enzyme could play a critical role in estrogen-sensitive cells, since it inactivates DHT that generally shows antagonistic effect in the cells, while producing active E2 for cell proliferation. In this report, we describe the cloning and characterization of a second form of type 7 17β-HSD (17β-HSD7_2) that shares 95.6% identity with 17β-HSD7_1. Using a 7.5 kb genomic DNA fragment of 17β-HSD7_1 as probe, we have obtained 7 BAC clones: three clones containing the 17β-HSD7_1 gene and four containing the 17β-HSD7_2 gene. The corresponding 17β-HSD7_2 cDNA fragments of the coding region were obtained by amplification using RT-PCR and subcloned into pCMV expression vector and stably transfected into human embryonic kidney (HEK-293) cells. The overexpressed 17β-HSD7_2 catalyzes efficiently the transformation of E1 into E2 and of DHT into 3β-diol. Ribonuclease protection assays (RPA) indicate that 17β-HSD7_2 is expressed in the liver, prostate, uterus and placenta. FISH mapping using the 7.5 kb genomic DNA fragment as well as 2 BAC clones of each form allowed us to map the 17β-HSD7_1 gene on chromosome band 1q23, and 17β-HSD7_2 on band 10p11.2. These results contrast with a previous report that the 17β-HSD7_1 gene was mapped to chromosomal band 10p11.2. This newly identified form of 17β-HSD7 could have a significant role by modulating active hormone levels in estrogen-sensitive cells or tissues.