Signal transducer and activator of transcription-3 serine phosphorylation by insulin is mediated by a Ras/Raf/MEK-dependent pathway.
We recently reported that insulin stimulation results in the serine phosphorylation of STAT3 (signal transducer and activator of transcription-3). In the present study, we identified serine 727 as the site of insulin-stimulated STAT3 serine phosphorylation. This phosphorylation event occurs independent of tyrosine phosphorylation. Furthermore, interleukin-6-induced tyrosine phosphorylation can occur independent of serine phosphorylation, demonstrating that these two phosphorylation pathways are mechanistically unrelated. Selective activation of the JNK and p38 family of mitogen-activated protein (MAP) kinases by anisomycin treatment did not result in the phosphorylation of STAT3. In contrast, activation of the ERK MAP kinase pathway with both insulin and osmotic shock resulted in the serine phosphorylation of STAT3. In addition, expression of a dominant-interfering Ras mutant (N17Ras) or treatment with the specific MEK inhibitor (PD98059) prevented the insulin stimulation of STAT3 serine phosphorylation. Blockade of ERK activation by expression of the MAP kinase phosphatase (MKP-1) had no effect on insulin-stimulated STAT3 serine phosphorylation. Together, these data demonstrate that the insulin-stimulated serine phosphorylation of STAT3 occurs by a MEK-dependent pathway that is independent of ERK activation.
Ceresa
B P
BP
Department of Physiology and Biophysics, University of Iowa, Iowa City 52242, USA.
Horvath
C M
CM
Pessin
J E
JE
D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015153:Blotting, Western; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism / Q000502:physiology; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D015850:Interleukin-6 / Q000494:pharmacology; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D009154:Mutation; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf; D050796:STAT3 Transcription Factor; D012694:Serine / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism; D018631:ras Proteins / Q000502:physiology*
D000900:Anti-Bacterial Agents; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007328:Insulin; D015850:Interleukin-6; D011518:Proto-Oncogene Proteins; D050796:STAT3 Transcription Factor; D015534:Trans-Activators; D014443:Tyrosine; D012694:Serine; D000841:Anisomycin; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one