Role of the HBx oncoprotein in carbonic anhydrase 9 induction.
Carbonic anhydrase 9 (CA9), as one of the most hypoxia-responsive genes, has been associated almost exclusively with hypoxic tumors. Its principal role is in pH regulation which helps tumor cells overcome intracellular acidosis and survive extended periods of time with low oxygen. Hypoxia-inducible factor 1 (HIF-1) is the main transcriptional activator of CA9. Hepatitis B virus X protein (HBx) has been shown to increase the transcriptional activity of HIF-1. HBx is often expressed from the gene integrated in the hepatocytes infected persistently and contributes significantly to alterations in host gene expression that can lead to the development of hepatocellular carcinoma (HCC) associated with Hepatitis B virus (HBV). The aim of this study was to determine the effect of HBx on expression of CA9. Transient transfection of HBx led to an increase in the expression of CA9 as assessed by RT-PCR and Western blotting. HBx was able to increase CA9 promoter activity significantly in several cell lines. The effect was mediated via HIF-1 and a functional HRE element located -10/-3 bp upstream of the CA9 transcription initiation site. These data suggest that CA9 may be involved in the development of HCC by contributing to the survival of hepatocytes infected with HBV in liver tissue with fibrosis.
Holotnakova
Tereza
T
Institute of Virology, Slovak Academy of Sciences, Bratislava, Slovak Republic.
Tylkova
Lucia
L
Takacova
Martina
M
Kopacek
Juraj
J
Petrik
Juraj
J
Pastorekova
Silvia
S
Pastorek
Jaromir
J
D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000235:genetics / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000503:physiopathology; D002460:Cell Line; D045744:Cell Line, Tumor; D015971:Gene Expression Regulation, Enzymologic; D006515:Hepatitis B virus / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D022781:Hepatocytes / Q000821:virology*; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics / Q000502:physiology; D051379:Mice; D051381:Rats; D020218:Response Elements; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D054334:Viral Regulatory and Accessory Proteins
D000951:Antigens, Neoplasm; D051793:Hypoxia-Inducible Factor 1; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases