title: Interleukin-6-induced STAT3 transactivation and Ser727 phosphorylation involves Vav, Rac-1 and the kinase SEK-1/MKK-4 as signal transduction components.
abstract: In the present study, signal transducer and activator of transcription 3 (STAT3) Ser(727) phosphorylation and transactivation was investigated in relation to activation of mitogen-activated protein (MAP) kinase family members including extracellular-signal-regulated protein kinase (ERK)-1, c-Jun N-terminal kinase (JNK)-1 and p38 ('reactivating kinase') in response to interleukin (IL)-6 stimulation. Although IL-6 can activate ERK-1 in HepG2 cells, STAT3 transactivation and Ser(727) phosphorylation were not reduced by using the MAP kinase/ERK kinase (MEK) inhibitor PD98059 or by overexpression of dominant-negative Raf. IL-6 did not activate JNK-1 in HepG2 cells and STAT3 was a poor substrate for JNK-1 activated by anisomycin, excluding a role for JNK1 in IL-6-induced STAT3 activation. However, SEK-1/MKK-4 [where SEK-1 stands for stress-activated protein kinase (SAPK)/ERK kinase 1, and MKK-4 stands for MAP kinase kinase 4] was activated in response to IL-6 and overexpression of dominant-negative SEK-1/MKK-4(A-L) reduced both IL-6-induced STAT3 Ser(727) phosphorylation as well as STAT3 transactivation. Subsequently, the SEK-1/MKK-4 upstream components Vav, Rac-1 and MEKK were identified as components of a signal transduction cascade that leads to STAT3 transactivation in response to IL-6 stimulation. Furthermore, inhibition of p38 kinase activity with the inhibitor SB203580 did not block STAT3 Ser(727) phosphorylation but rather increased both basal as well as IL-6-induced STAT3 transactivation, indicating that p38 may act as a negative regulator of IL-6-induced STAT3 transactivation through a presently unknown mechanism. In conclusion, these data indicate that IL-6-induced STAT3 transactivation and Ser(727) phosphorylation is independent of ERK-1 or JNK-1 activity, but involves a gp130 receptor-signalling cascade that includes Vav, Rac-1, MEKK and SEK-1/MKK-4 as signal transduction components.
authors.affiliation: Department of Genetics, Biological Center, Kerklaan 30, 9751 NN, Haren, The Netherlands.
authors.forename: J J
authors.initials: JJ
authors.lastname: Schuringa
authors.forename: L J
authors.initials: LJ
authors.lastname: Jonk
authors.forename: W H
authors.initials: WH
authors.lastname: Dokter
authors.forename: E
authors.initials: E
authors.lastname: Vellenga
authors.forename: W
authors.initials: W
authors.lastname: Kruijer
mesh_terms: D019943:Amino Acid Substitution; D006528:Carcinoma, Hepatocellular; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017930:Genes, Reporter; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology*; D048031:JNK Mitogen-Activated Protein Kinases; D008113:Liver Neoplasms; D048670:MAP Kinase Kinase 4; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D011725:Pyridines / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism; D050796:STAT3 Transcription Factor; D012694:Serine; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007093:Imidazoles; D015850:Interleukin-6; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D011725:Pyridines; D011994:Recombinant Proteins; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; C496618:VAV1 protein, human; D012694:Serine; D048031:JNK Mitogen-Activated Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; C482559:MAP2K4 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D020744:rac GTP-Binding Proteins; C093642:SB 203580