title: Repression of Stat3 activity by activation of mitogen-activated protein kinase (MAPK).
abstract: STAT proteins are activated by phosphorylation at specific tyrosine residue at the carboxy-terminus which is required for dimer-formation, nuclear translocation, DNA binding and transcriptional activity in cells treated with cytokines and growth factors. Recent studies have indicated that STATs are also phosphorylated by MAPK, or extracellular signal-regulated kinase (ERK) on serine. We investigated the role of ERK on the regulation of STAT activity. Here, we report that ERK2 activated by its upstream kinase, MEK1, represses Stat3 transcriptional activity induced by Src or Jak-2. To unravel the mechanism of repression, we further showed that Stat3 DNA binding activity and its tyrosine phosphorylation are also inhibited under the same conditions. ERK2 phosphorylates Stat3 on three serine-containing peptides and decreases its tyrosine phosphorylation induced by EGF treatment. We also detected an association of ERK2 and Stat3 in vivo which is modulated positively by activation of ERK2, but negatively by Jak2. We propose that MAP kinase cascade may negatively regulate Stat3 activities by decreasing its tyrosine phosphorylation and also possibly by association.
authors.affiliation: Signal Transduction Laboratory, Institute of Molecular and Cell Biology, National University of Singapore.
authors.forename: N
authors.initials: N
authors.lastname: Jain
authors.forename: T
authors.initials: T
authors.lastname: Zhang
authors.forename: S L
authors.initials: SL
authors.lastname: Fong
authors.forename: C P
authors.initials: CP
authors.lastname: Lim
authors.forename: X
authors.initials: X
authors.lastname: Cao
mesh_terms: D016475:3T3 Cells; D000818:Animals; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D002461:Cell Line, Transformed; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D015688:Oncogene Protein pp60(v-src) / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014443:Tyrosine
chemical_list: D004268:DNA-Binding Proteins; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; C494088:Stat3 protein, rat; D015534:Trans-Activators; D014443:Tyrosine; D015688:Oncogene Protein pp60(v-src); D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1