Gender-specific interplay of signaling through β-catenin and CAR in the regulation of xenobiotic-induced hepatocyte proliferation.

Aberrant signaling through the Wnt/β-catenin pathway is a critical determinant in human and rodent liver carcinogenesis and generally accepted to be a potent driver of proliferation. Xenobiotic agonists of the constitutive androstane receptor (CAR) induce massive acute hyperplasia of mouse liver and facilitate the outgrowth of hepatocellular carcinomas with activated β-catenin. In the present study, the interplay of β-catenin-dependent and CAR-dependent signaling in the liver and its effect on hepatocyte proliferation were analyzed in transgenic mice with hepatocyte-specific knockout of Ctnnb1 (encoding β-catenin) following treatment with two CAR agonists, 1,4-bis[2-(3,5-dichloropyridyloxy)]-benzene (TCPOBOP) and phenobarbital. Hepatocyte-specific knockout of β-catenin inhibited CAR agonists-induced hepatocyte proliferation in male mice. By contrast, the proliferative effect of CAR agonists was strongly augmented in female β-catenin knockout animals. This was due to prolonged proliferation of the knockout hepatocytes. CAR-mediated hepatocyte proliferation was, at least in part, dependent on estrogen signaling and was associated with enhanced expression of FoxM1 and elevated activity of the PDK1/p90RSK pathway. In conclusion, our study shows that gender-specific factors determine whether β-catenin signaling plays a pro- or an antiproliferative role in the regulation of mouse hepatocyte proliferation induced by CAR agonists.