Substrate Inhibition of 17beta-HSD1 in living cells and regulation of 17beta-HSD7 by 17beta-HSD1 knockdown

Publication date: Available online 26 May 2017
Source:The Journal of Steroid Biochemistry and Molecular Biology
Author(s): Hui Han, Jean-François Thériault, Guang Chen, Sheng-Xiang Lin
This study addresses first the role of human 17beta-hydroxysteroid dehydrogenase type 1 (17β-HSD1) in breast cancer (BC). The enzyme has a high estrone-activating activity that is subject to strong substrate inhibition as shown by enzyme kinetics at the molecular level. We used BC cells to verify this phenomenon in living cells: estrone concentration increase did reduce the reaction with 0.025 to 4μM substrate. Moreover, 5α-dihydrotestosterone (DHT) demonstrated some inhibition of estrogen activation at both the molecular and cellular level. The presence of DHT did not change the tendency toward substrate inhibition for estrone conversion, but shifted the inhibition toward higher substrate concentrations. Moreover, a binding study demonstrated that both DHT and dehydroepiandrosterone (DHEA) can be bound to the enzyme, thereby supporting the multi-specificity of 17β-HSD1. We then followed the concentrations of estradiol and performed Q-RT-PCR measurements of reductive 17β-HSDs after 17β-HSD1 inhibition. The estradiol decrease by the 17β-HSD1 inhibition was demonstrated lending support to this observation. Knockdown and inhibition of 17β-HSD1 produced reduction in estradiol levels and the down-regulation of another reductive enzyme 17β-HSD7, thus "amplifying" the reduction of estradiol by the 17β-HSD1 modulation itself. The critical positioning of 17β-HSD7 in sex-hormone-regulation as well as the mutual regulation of steroid enzymes via estradiol in BC, are clearly demonstrated.Our study demonstrates that fundamental enzymological mechanisms are relevant in living cells. Moreover, further enzyme study in cells is merited to advance biological and medical research. We also demonstrated the central role of 17β-HSD7 in sex-hormone conversion and regulation, supporting it as a novel target for estrogen-dependent (ER+) BC.Summary StatementWe demonstrate that fundamental enzymology is relevant in living cells with different mechanisms. We also show the mutual regulation of reductive 17β-HSDs and the central role of 17β-HSD7 controlling sex-hormones, supporting it as a novel target for ER+ breast cancer.



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