Hepatitis B virus X protein inhibits transforming growth factor-beta -induced apoptosis through the activation of phosphatidylinositol 3-kinase pathway.
Transforming growth factor-beta (TGF-beta) is a potent inducer of apoptosis in Hep 3B cells. This work investigated how hepatitis B virus X protein (HBx) affects TGF-beta-induced apoptosis. Trypan blue exclusion and colony formation assays revealed that HBx increased the ID(50) toward TGF-beta. In the presence of HBx, TGF-beta-induced DNA laddering was decreased, indicating that HBx had the ability to block TGF-beta-induced apoptosis. Furthermore, HBx did not alter the expression levels of type I and type II TGF-beta receptors. HBx did not affect TGF-beta-induced activation of promoter activities of the plasminogen activator inhibitor-1 (PAI-1) gene. These results indicate that HBx interferes with only a subset of TGF-beta activity. In the presence of phosphatidylinositol (PI) 3-kinase inhibitors, wortmannin or LY294002, the HBx-mediated inhibitory effect on TGF-beta-induced apoptosis was alleviated. In addition, the tyrosine phosphorylation levels of the regulatory subunit p85 of phosphatidylinositol 3-kinase (PI 3-kinase) and PI 3-kinase activity were elevated in stable clones with HBx expression. Transactivation-deficient mutants of HBx lost their ability to inhibit TGF-beta-induced apoptosis. Phosphorylation of the p85 subunit of PI 3-kinase and Akt, a downstream target of PI 3-kinase, was not observed in stable clones with transactivation-deficient HBx mutant's expression. Thus, the anti-apoptotic effect of HBx against TGF-beta can be mediated through the activation of the PI 3-kinase signaling pathway, and the transactivation function of HBx is required for its anti-apoptosis activity.
Shih
W L
WL
Graduate Institute of Microbiology, Taipei, Taiwan.
Kuo
M L
ML
Chuang
S E
SE
Cheng
A L
AL
Doong
S L
SL
D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis; D029681:Arabidopsis Proteins; D002470:Cell Survival / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D016895:Culture Media, Serum-Free / Q000378:metabolism; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D011233:Precipitin Tests; D020079:Terminal Repeat Sequences; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D054334:Viral Regulatory and Accessory Proteins; D000077191:Wortmannin
D000730:Androstadienes; D029681:Arabidopsis Proteins; D002867:Chromones; D016895:Culture Media, Serum-Free; D004791:Enzyme Inhibitors; D008156:Luciferases; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D010940:Plant Proteins; D015221:Potassium Channels; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D054334:Viral Regulatory and Accessory Proteins; D000077191:Wortmannin; C057628:hepatitis B virus X protein; C074500:AKT1 protein, Arabidopsis; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one