Abrogation of constitutive STAT3 activity sensitizes human hepatoma cells to TRAIL-mediated apoptosis

Abstract

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated and regulates cell growth and survival of various cancer cells. We investigated the anti-tumor effect of AG490, a Janus kinase 2 specific inhibitor, inhuman hepatoma cells. Effects of AG490 on STAT3 activation, on cell-growth and survival, and on the expression of cell-cycle- and apoptosis-related proteins were evaluated in Huh-1, Huh-7, HepG2 and Hep3B cells. Next, whether AG490 renders hepatoma cells susceptible to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) was examined in vitro and in vivo. Constitutively activated STAT3 through tyrosine phosphorylation was detected in all hepatoma cells. AG490 inhibited the phosphorylation of STAT3 and its activity. AG490 induced cell cycle arrest in Huh-1, Huh-7 and HepG2 through cyclin D1 downregulation, and induced marked apoptosis in Hep3B. AG490 downregulated at least one of the anti-apoptotic proteins, Bcl-xL, survivin or XIAP in all hepatoma cells. AG490 sensitized Huh-1, Huh-7 and HepG2 to TRAIL-induced apoptosis in vitro. Intraperitoneal injection of AG490, the combination of AG490 and TRAIL more greatly, repressed the growth of subcutaneous Huh-7 tumors in athymic mice. Abrogation of constitutive activation of STAT3 by AG490 enhances the anti-tumor activity of TRAIL against human hepatoma cells.