title: ERK1/2 contributes negative regulation to STAT3 activity in HSS-transfected HepG2 cells.
abstract: Signal transducer and activator of transcription 3 (STAT3) is a recently characterized transcription factor which is essential to liver regeneration. We have previously reported that hepatic stimulator substance (HSS), a novel growth-promoting substance, phosphorylated the epidermal growth factor (EGF) receptors and activated downstream Ras-MAP kinase (extracellular signal-regulated kinases, ERK1/2) cascade. However, whether HSS signal is related to STAT3 pathway remains unclear. The present study is aiming to explore the regulatory effect of activation of ERK1/2 evoked by HSS on STAT3 phosphorylation and STAT3 signaling. Human hepatoma cell line HepG2 was stably transfected with HSS cDNA and HSS expression was measured by Northern blot. The results showed that the transfection of HSS into HepG2 resulted in remarkable increase in cellular proliferation as compared with the non-transfected cells, and it was further proved that the cellular proliferation in the HSS-transfected cells was related to ERK1/2 activation. Treatment of the cells with 50 mM of PD98059, an ERK1/2 specific upstream inhibitor, resulted in ERK1/2 inactivation completely. Inhibition of ERK1/2 allowed the tyrosine of STAT3 to be phosphorylated in a dose-dependent manner to PD98059. Furthermore, transient transfection of STAT3 mutant (STAT3S727A) into HSS-bearing cells could remarkably reverse the inhibitory effect of ERK1/2 on STAT3 phosphorylation. Based upon these results, it is concluded that ERK1/2 negatively modulates STAT3 phosphorylation and this function is dependent on residual serine-727 (S727) of STAT3.
authors.affiliation: Department of Cell Biology, Capital University of Medical Science, 10 Xitoutiao, You An Men Beijing 100054, China.
authors.forename: Ze Jun
authors.initials: ZJ
authors.lastname: Tian
authors.forename: Wei
authors.initials: W
authors.lastname: An
mesh_terms: D019943:Amino Acid Substitution; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D006133:Growth Substances / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D008934:Mitogens / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D050796:STAT3 Transcription Factor; D012694:Serine; D015398:Signal Transduction / Q000187:drug effects; D015534:Trans-Activators; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; D005419:Flavonoids; D006133:Growth Substances; D036341:Intercellular Signaling Peptides and Proteins; D008934:Mitogens; D010455:Peptides; D011994:Recombinant Proteins; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; C073456:hepatic stimulator substance; D012694:Serine; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one