title: Interleukin-6 inhibits transforming growth factor-beta-induced apoptosis through the phosphatidylinositol 3-kinase/Akt and signal transducers and activators of transcription 3 pathways.
abstract: The multifunctional cytokine interleukin-6 (IL-6) regulates growth and differentiation of many cell types and induces production of acute-phase proteins in hepatocytes. Here we report that IL-6 protects hepatoma cells from apoptosis induced by transforming growth factor-beta (TGF-beta), a well known apoptotic inducer in liver cells. Addition of IL-6 blocked TGF-beta-induced activation of caspase-3 while showing no effect on the induction of plasminogen activator inhibitor-1 and p15(INK4B) genes, indicating that IL-6 interferes with only a subset of TGF-beta activities. To further elucidate the mechanism of this anti-apoptotic effect of IL-6, we investigated which signaling pathway transduced by IL-6 is responsible for this effect. IL-6 stimulation of hepatoma cells induced a rapid tyrosine phosphorylation of the p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase) and its kinase activity followed by the activation of Akt. Inhibition of PI 3-kinase by wortmannin or LY294002 abolished the protection of IL-6 against TGF-beta-induced apoptosis. A dominant-negative Akt also abrogated this anti-apoptotic effect. Dominant-negative inhibition of STAT3, however, only weakly attenuated the IL-6-induced protection. Finally, inhibition of both STAT3 and PI 3-kinase by treating cells overexpressing the dominant-negative STAT3 with LY294002 completely blocked IL-6-induced survival signal. Thus, concomitant activation of the PI 3-kinase/Akt and the STAT3 pathways mediates the anti-apoptotic effect of IL-6 against TGF-beta, with the former likely playing a major role in this anti-apoptosis.
authors.affiliation: Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: R H
authors.initials: RH
authors.lastname: Chen
authors.forename: M C
authors.initials: MC
authors.lastname: Chang
authors.forename: Y H
authors.initials: YH
authors.lastname: Su
authors.forename: Y T
authors.initials: YT
authors.lastname: Tsai
authors.forename: M L
authors.initials: ML
authors.lastname: Kuo
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism / Q000494:pharmacology*; D008113:Liver Neoplasms / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: D053148:Caspase 3; D020169:Caspases; D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D019869:Phosphatidylinositol 3-Kinases; D017395:Plasminogen Activator Inhibitor 1; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D050796:STAT3 Transcription Factor; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; C493966:CDKN2B protein, human; C494086:STAT3 protein, human; C494918:AKT1 protein, human; C505407:CASP3 protein, human