Abstract
Hepatitis B virus X protein (HBx) of the hepatitis B virus was strongly implicated in angiogenesis and metastasis during hepatocarcinogenesis. Here, we explored the possibility of cross-talk between HBx and hypoxia-inducible factor-1alpha (HIF-1alpha), a potent transcriptional inducer of angiogenic factors. First, we showed that stability of HIF-1alpha protein was increased by HBx in HBx-inducible Chang liver cells as well as in transient HBx expression system of non-hepatic cells. Immunofluorescence studies revealed that the HBx-induced HIF-1alpha was partially translocated into the nucleus in majority of cells while additional CoCl2-induced hypoxic condition caused complete nuclear translocation. Second, HBx induced both phosphorylation of HIF-1alpha and activation of p42/p44 mitogen-activated protein kinases (MAPKs), which were synergistically enhanced in the presence of CoCl2. Furthermore, HBx enhanced transcriptional activity of HIF-1alpha in the reporter genes encoding hypoxia response element or VEGF promoter. Either treatment of MEK inhibitor PD98059 or coexpression of dominant-negative MAPK mutants abolished the HBx-induced transcriptional activity and protein stability as well as nuclear translocation of HIF-1alpha, suggesting that HBx activates HIF-1alpha through MAPK pathway. Third, the association of HIF-1alpha with von Hippel-Lindau was decreased but the association with CREB-binding protein was enhanced in the presence of HBx, suggesting the molecular mechanism by which HBx enhances the protein stability and transactivation function of HIF-1alpha. Finally, we demonstrated that expression of HIF-1alpha and vascular endothelial growth factor was increased in the liver of HBx-transgenic mice, suggesting that the cross-talk between HIF-1alpha and HBx may lead to transcriptional activation of HIF-1alpha target genes, which play a critical role in hepatocarcinogenesis.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Active Transport, Cell Nucleus
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Androstadienes / pharmacology
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Animals
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Blotting, Western
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Cell Line
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Cell Nucleus / metabolism
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Cobalt / pharmacology
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Endothelial Growth Factors / metabolism
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Enzyme Inhibitors / pharmacology
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Flavonoids / pharmacology
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Flow Cytometry
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Genes, Reporter
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HeLa Cells
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Humans
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Hypoxia
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Hypoxia-Inducible Factor 1, alpha Subunit
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Immunohistochemistry
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Intercellular Signaling Peptides and Proteins / metabolism
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Ligases / metabolism
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Lymphokines / metabolism
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MAP Kinase Signaling System*
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Mice
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Mice, Transgenic
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Microscopy, Fluorescence
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases / metabolism
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Phosphorylation
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Plasmids / metabolism
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Precipitin Tests
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Promoter Regions, Genetic
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Protein Transport
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Reverse Transcriptase Polymerase Chain Reaction
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Signal Transduction
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Time Factors
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Trans-Activators / metabolism
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Trans-Activators / physiology*
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Transcription Factors / metabolism*
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Transcription, Genetic*
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Transcriptional Activation
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Transfection
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Tumor Cells, Cultured
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Tumor Suppressor Proteins*
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Ubiquitin-Protein Ligases*
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Vascular Endothelial Growth Factor A
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Vascular Endothelial Growth Factors
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Viral Regulatory and Accessory Proteins
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Von Hippel-Lindau Tumor Suppressor Protein
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Wortmannin
Substances
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Androstadienes
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Endothelial Growth Factors
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Enzyme Inhibitors
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Flavonoids
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HIF1A protein, human
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Hypoxia-Inducible Factor 1, alpha Subunit
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Intercellular Signaling Peptides and Proteins
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Lymphokines
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Trans-Activators
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Transcription Factors
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Tumor Suppressor Proteins
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Vascular Endothelial Growth Factor A
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Vascular Endothelial Growth Factors
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Viral Regulatory and Accessory Proteins
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hepatitis B virus X protein
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Cobalt
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Ubiquitin-Protein Ligases
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Von Hippel-Lindau Tumor Suppressor Protein
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases
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Ligases
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VHL protein, human
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cobaltous chloride
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2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one
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Wortmannin