Hepatitis B virus X protein upregulates mTOR signaling through IKKβ to increase cell proliferation and VEGF production in hepatocellular carcinoma

• Published in: PloS one Vol. 7; no. 7; p. e41931
• Main Authors: Yen, Chia-Jui, Lin, Yih-Jyh, Yen, Chia-Sheng, Tsai, Hung-Wen, Tsai, Ting-Fen, Chang, Kwang-Yu, Huang, Wei-Chien, Lin, Pin-Wen, Chiang, Chi-Wu, Chang, Ting-Tsung
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 27.07.2012; Public Library of Science (PLoS)
• Subjects: Adult; Aged; Angiogenesis; Animals; Biology; Carcinoma, Hepatocellular - blood supply; Carcinoma, Hepatocellular - diagnosis; Carcinoma, Hepatocellular - metabolism; Carcinoma, Hepatocellular - pathology; Cell growth; Cell Line, Tumor; Cell Proliferation; Clinical medicine; Deregulation; Female; Gene expression; Gene Expression Regulation, Neoplastic; HBX protein; Hepatitis; Hepatitis B; Hepatocellular carcinoma; Hepatoma; Humans; Hypoxia; I-kappa B Kinase - metabolism; Inflammation; Inhibitors; Internal medicine; Kinases; Liver; Liver cancer; Liver Neoplasms - blood supply; Liver Neoplasms - diagnosis; Liver Neoplasms - metabolism; Liver Neoplasms - pathology; Male; Medical prognosis; Medical research; Medicine; Mice; Middle Aged; Neovascularization, Pathologic; Patients; Phosphorylation; Prognosis; Proteins; Rapamycin; Rodents; Signal Transduction; Signaling; siRNA; Surgery; Tissues; TOR protein; TOR Serine-Threonine Kinases - metabolism; Trans-Activators - metabolism; Transcription factors; Transgenic mice; Tuberous sclerosis; Tuberous Sclerosis Complex 1; Tuberous Sclerosis Complex 1 Protein; Tumor necrosis factor-TNF; Tumor Suppressor Proteins - metabolism; Tumorigenesis; Up-Regulation; Vascular endothelial growth factor; Vascular Endothelial Growth Factor A - biosynthesis; Viruses; Taiwan
• DOI: 10.1371/journal.pone.0041931
• ISSN: 1932-6203

Hepatocellular carcinoma (HCC), a major cause of cancer-related death in Southeast Asia, is frequently associated with hepatitis B virus (HBV) infection. HBV X protein (HBx), encoded by a viral non-structural gene, is a multifunctional regulator in HBV-associated tumor development. We investigated novel signaling pathways underlying HBx-induced liver tumorigenesis and found that the signaling pathway involving IκB kinase β (IKKβ), tuberous sclerosis complex 1 (TSC1), and mammalian target of rapamycin (mTOR) downstream effector S6 kinase (S6K1), was upregulated when HBx was overexpressed in hepatoma cells. HBx-induced S6K1 activation was reversed by IKKβ inhibitor Bay 11-7082 or silencing IKKβ expression using siRNA. HBx upregulated cell proliferation and vascular endothelial growth factor (VEGF) production, and these HBx-upregulated phenotypes were abolished by treatment with IKKβ inhibitor Bay 11-7082 or mTOR inhibitor rapamycin. The association of HBx-modulated IKKβ/mTOR/S6K1 signaling with liver tumorigenesis was verified in a HBx transgenic mouse model in which pIKKβ, pS6K1, and VEGF expression was found to be higher in cancerous than non-cancerous liver tissues. Furthermore, we also found that pIKKβ levels were strongly correlated with pTSC1 and pS6K1 levels in HBV-associated hepatoma tissue specimens taken from 95 patients, and that higher pIKKβ, pTSC1, and pS6K1 levels were correlated with a poor prognosis in these patients. Taken together, our findings demonstrate that HBx deregulates TSC1/mTOR signaling through IKKβ, which is crucially linked to HBV-associated HCC development.