Related Experiment Videos
Insulin activates Stat3 independently of p21ras-ERK and PI-3K signal transduction
P J Coffer1, A van Puijenbroek, B M Burgering
1Department of Pulmonary Diseases, University Hospital Utrecht, The Netherlands.
Abstract:
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.
Insights
Insulin rapidly activates the transcription factor Stat3, independent of p21ras, MAP kinases, and PI-3K. This insulin-induced Stat3 activation is crucial for regulating gene expression in cellular processes.
Area of Science:
- Molecular Biology
- Cell Signaling
- Transcription Factor Regulation
Background:
- Insulin receptor signaling regulates critical cellular functions like proliferation and glucose transport.
- STAT (Signal Transducer and Activator of Transcription) family proteins mediate gene induction by cytokines and hormones.
- Constitutive STAT activation is linked to cellular transformation.
Purpose of the Study:
- To investigate the activation of a transcriptional complex in response to insulin.
- To identify the specific transcription factor involved in insulin-induced gene regulation.
- To elucidate the signaling pathways mediating insulin-induced STAT activation.
Main Methods:
- Analysis of a transcriptional complex binding to a STAT-element after insulin stimulation.
- Supershift analysis to identify specific transcription factors within the complex.
- Inhibition studies using tyrosine kinase inhibitors, serine/threonine kinase inhibitors, dominant-negative p21ras, MEK inhibitor PD098059, and PI-3K inhibitor wortmannin.
Main Results:
- Insulin rapidly induces a DNA-binding complex containing the transcription factor Stat3.
- This insulin-induced Stat3 DNA-binding and transactivation are independent of p21ras.
- Insulin-induced Stat3 phosphorylation and transactivation do not require MAP kinases (ERKs) or PI-3K activation.
Conclusions:
- Insulin directly activates the transcription factor Stat3 through a pathway that bypasses p21ras, MAP kinases, and PI-3K.
- This novel insulin signaling pathway contributes to the regulation of cellular processes controlled by Stat3.
- Understanding this pathway offers insights into insulin action and potential therapeutic targets.