Mammalian target of rapamycin regulates expression of β-catenin in hepatocellular carcinoma

Although evidence has shown that both the mammalian target of rapamycin and beta-catenin are involved in hepatocellular carcinoma, little is known about their relationship in pathogenesis of hepatocellular carcinoma. To investigate the expression of phosphorylated mammalian target of rapamycin and beta-catenin and their prognostic impacts, as well as their relationship in hepatocellular carcinoma, we analyzed 63 human hepatocellular carcinoma samples by immunohistochemistry. Phosphorylated mammalian target of rapamycin cytoplasmic and beta-catenin cytoplasmic/nuclear-positive immunoreactivities were observed in 63.5% (40/63) and 55.6% (35/63) of the hepatocellular carcinoma specimens, respectively. Significant associations were found between cytoplasmic beta-catenin and phosphorylated mammalian target of rapamycin expression and tumor size (both P < .01) and metastasis (P < .01 and P < .05, respectively). In addition, beta-catenin expression in the cytoplasm was closely associated with the expression of phosphorylated mammalian target of rapamycin. To further explore the relationship between mammalian target of rapamycin and beta-catenin, hepatocellular carcinoma HepG2 and Hep3B cells were treated with beta-catenin siRNA and mammalian target of rapamycin inhibitor, rapamycin; and the expression of phosphorylated mammalian target of rapamycin and beta-catenin in cells was then measured by Western blot. The activity of Wnt/beta-catenin signaling pathway was also assessed by luciferase reporter assay. The cell viability and proliferation were evaluated by thiazolyl blue tetrazolium bromide assay and [H-3]-thymidine incorporation assay. The results showed that the level of beta-catenin protein expression was markedly decreased by rapamycin in HepG2 and Hep3B cells. The reduction of beta-catenin and mammalian target of rapamycin resulted in inhibition of cell viability proliferation, but the combination of reduction of beta-catenin and mammalian target of rapamycin did not show a synergistic effect on the inhibition of cell viability and proliferation in HepG2 and Hep3B cells. In conclusion, the present study showed that, for the first time, mammalian target of rapamycin regulated the expression level of beta-catenin in hepatocellular carcinoma. Both mammalian target of rapamycin and beta-catenin play important roles in the growth, metastasis, and prognosis of hepatocellular carcinoma. (C) 2011 Elsevier Inc. All rights reserved.