Identification of intracellular pathways through which TGF-beta 1 upregulates URG-4/URGCP gene expression in hepatoma cells

Abstract

Aims: Up-regulated gene 4 (URG-4/URGCP) was strongly expressed in Hepatitis B infected liver and correlated with HBxAG (Hepatitis B x Antigen) protein and found to promote hepatocellular cancer. Transforming growth factor (TGF-beta 1) is a multifunctional protein that effects cell proliferation, growth inhibition, differentiation and other functions. However, the mechanism of URG-4/URGCP regulation by TGF-beta 1 and its significance in cancer progression remains largely unknown. Main methods: The effect of TGF-beta 1 on URG-4/URGCP gene was determined using REAL TIME PCR at mRNA level and Western blotting/immunofluorescence at protein level. Transient transfection assays were carried out to find out which site of promoter is upregulated by TGF-beta 1.Key Findings: We report the upregulation of URG-4/URGCP gene expression by TGF-beta 1 in hepatoma cells along with prostate cancer cells, PC3. Transient transfection assays showed that the - 109 to + 63 promoter region contained the minimal TGF-beta 1 response elements. TGF-beta 1 markedly stimulated the URG-4/URGCP mRNA and protein that was blocked by MEK1 [MAPK (Mitogen-Activated Protein Kinase)/ERK (extracellular signal-regulated kinase) kinase 1] inhibitor, PD98059 and PI3K inhibitor, wortmannin. Significance: These studies show for the first time that TGF-beta 1 upregulates the expression of URG-4/URGCP in human hepatocytes and identifies the signaling pathways underlying this response.