The dual sex hormone specificity for human reductive 17β-hydroxysteroid dehydrogenase type 7: Synergistic function in...

Human 17β-hydroxysteroid dehydrogenase (17β-HSD) type 1 and 7 catalyze the final step of estrogen activation and the first step in androgen inactivation. It has been shown in breast cancer cells that DHT has a suppression effect on cell proliferation, counteracting the estrogen growth effect. However, the exact kinetic function of 17β-HSD7 in steroidogenesis was not determined. Here we report the steady-state kinetics and binding study for 17β-HSD7 with estrone or DHT as substrates and NADPH as cofactor. 17β-HSD7 has been overexpressed in E. coli and purified. For both substrates, kinetics of 17β-HSD7 demonstrates positive cooperativity. The K_0.5 value is 5.2 ± 0.4 μM and 14.4 ± 0.8 μM and the k_cat is 0.0063 ± 0.0003 s^-1 and 0.0153 ± 0.0007 s^-1 for the reduction of E1 and DHT, respectively. The binding study shows a similar affinity with a dissociation constant of 5.2 ± 0.5 μM and 11 ± 1 μM for E1 and DHT, respectively. Our kinetic and binding results reveal a positive cooperativity for 17β-HSD7 to both the E1 and DHT with a similar affinity, while 17β-HSD1 demonstrated a significantly higher affinity toward E1 than DHT, but with a strong E1 substrate inhibition. These results strongly support that the inhibition of 17β-HSD7 constitutes the basis of breast cancer cell proliferation decreasing that led to the shrinkage of xenograft ER + breast tumor mice model.