Testosterone regulation of cyclin E kinase is a key factor determining gender differences in hepatocarcinogenesis

Abstract

Background & Aim: While gender differences in hepatocellular carcinoma (HCC) are profound, the mechanism is unclear. Using castration and hormone replacement strategies, we tested whether these gender differences are attributable to testosterone or estradiol/progesterone (E/P) effects on cell cycle regulators and p53. Methods: We studied dysplastic liver and HCCs in intact and castrated diethylnitrosamine (DEN)-injected C57BL/6J male and female mice, with or without hormonal replacement. Effects of sex steroids on proliferation and survival of primary hepatocytes and primary HCC cells were also characterized. Results: DEN-injected females displayed fewer dysplastic foci and slower onset of HCC than males, with smaller/more differentiated tumors and fewer metastases. Castration of DEN-injected males reduced cyclin E kinase and augmented hepatocyte apoptosis compared with intact males; E/P enhanced these effects. In intact females, cyclin E kinase activity was less than in males; testosterone administered to ovariectomized females up-regulated cyclin E, increased cyclin E kinase and accelerated hepatocarcinogenesis. In vitro, testosterone increased expression of cell cycle regulators (cyclin D1, cyclin E and cyclin-dependent kinase 2) and reduced p53 and p21, which enhanced hepatocyte viability. In contrast, estradiol both suppressed hepatocyte cell cycle markers, up-regulated p53 and reduced viability of hepatocytes and HCC cells. Conclusions: Testosterone is the positive regulator of hepatocyte cell cycle via cyclin E, while estradiol plays a negative role by effects of p53 and p21. Together, both sex hormones determine the male predominance of gender differences in hepatocarcinogenesis.