Transactivation of the TIEG1 confers growth inhibition of transforming growth factor-β-susceptible hepatocellular carcinoma cells

AIM: To investigate the role of transforming growth factor (TGF)-beta-inducible early gene 1 (TIEG1) in TGF-beta-induced growth inhibition in hepatocellular carcinoma (HCC) cells. METHODS: Human hepatocyte and HCC cell lines with varied susceptibilities to TGF-beta were tested by methylthiazoletetrazolium (MU) assay. The expression changes of Smad2, Smad3, Smad4, Smad7, TIEG1 and TIEG2 gene following treatment with TGF-beta 1 in a TGF-beta-sensitive hepatocyte cell line (MIHA), a TGF-beta-sensitive hepatoma cell line (Hep3B) and two TGF-beta-sensitive hepatoma cell lines (HepG2 and Bel7404) were examined. SiRNA targeting TIEG1 was transfected into Hep3B cells and the sensitivity of cells to TGF-beta 1 was examined. Overexpression of TIEG1 was induced by lentiviral-mediated transduction in TGF-beta-resistant hepatoma cell lines (Bel7404 and HepG2). MU assay and 4,6-Diamidino-2-phenylindole staining were used to identify cell viability and apoptosis, respectively. The expression level of stathmin was measured by reverse transcriptase polymerase chain reaction and Western-blotting analysis, and stathmin promoter activity by TIEG1 was monitored by a luciferase reporter gene system. RESULTS: TIEG1 was significantly upregulated by TGF-beta 1 in the TGF-beta 1-sensitive HCC cell line, Hep3B, but not in the resistant cell lines. The suppression of TIEG1 by siRNAs decreased the sensitivity of Hep3B cells to TGF-beta 1, whereas the overexpression of TIEG1 mediated growth inhibition and apoptosis in TGF-beta 1-resistant HCC cell lines, which resembled those of TGF-beta 1-sensitive HCC cells treated with TGF-beta 1. Our data further suggested that stathmin was a direct target of TIEG1, as stathmin was significantly downregulated by TIEG1 overexpression, and stathmin promoter activity was inhibited by TIEG1 in a dose-dependent manner. CONCLUSION: Our data suggest that transactivation of TIEG1 conferred growth inhibition of TGF-beta-susceptible human HCC cells. (C) 2012 Baishideng. All rights reserved.