Insulin activates Stat3 independently of p21ras-ERK and PI-3K signal transduction.
The binding of insulin to its receptor initiates multiple signal transduction pathways regulating such diverse processes as proliferation, differentiation, glucose transport, and glycogen metabolism. The STAT-family of transcription factors has been demonstrated to play a critical role in gene induction by a variety of hemopoietic cytokines and hormones. Furthermore, constitutive activation of STATs is observed in transformed cells. Here we describe activation of a transcriptional complex binding to a consensus STAT-transcriptional element in response to insulin challenge. This complex is induced rapidly after tyrosine autophosphorylation of the insulin receptor, and is sustained for several hours. Supershift analysis of the insulin-induced complex reveals that it specifically contains the transcription factor Stat3. DAN binding of this complex is inhibited by pre-incubation with tyrosine, but not serine/threonine protein kinase inhibitors, whereas transcriptional activation is inhibited by both. Utilising a dominant negative mutant of p21ras we demonstrate that both insulin-induced Stat3 DNA-binding and also transactivation do not require p21ras. Furthermore, although previous studies have suggested a role for MAP kinases (ERKs) and PI-3K in STAT activation, utilising the specific MEK inhibitor PD098059 and the PI-3K inhibitor wortmannin, we demonstrate that activation of ERKs or PI-3K are not required for insulin induced Stat3 phosphorylation or transactivation.
Coffer
P J
PJ
Department of Pulmonary Diseases, University Hospital Utrecht, The Netherlands.
van Puijenbroek
A
A
Burgering
B M
BM
Klop-de Jonge
M
M
Koenderman
L
L
Bos
J L
JL
Kruijer
W
W
D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology*; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects*; D015534:Trans-Activators / Q000378:metabolism*; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; D007328:Insulin; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D016283:Proto-Oncogene Proteins p21(ras)