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Activation of cJun NH2-terminal kinase/stress-activated protein kinase by insulin
B S Miller1, U T Shankavaram, M J Horney
1Department of Cell and Molecular Pharmacology, Medical University of South Carolina, Charleston, 29425 USA.
Abstract:
One of insulin's many biological effects is the increased transcription of AP-1-regulated genes. cJun is the principal component of the AP-1 transcription complex, which is regulated by the newly discovered members of the MAPK superfamily referred to as cJun NH2-terminal kinases (JNKs) or stress-activated protein kinases (SAPKs). We show that insulin stimulates a dose- and time-dependent increase in JNK activity in Rat 1 fibroblasts overexpressing human insulin receptors (Rat 1 HIR cells). Using two different polyclonal anti-JNK antibodies, JNK activity was measured after immunoprecipitation from whole cell extracts by phosphorylation of GSTcJun(1-79). Peak activation occurred 15 min after insulin addition, resulting in a 2.5-fold increase in GSTcJun(1-79) phosphorylation over unstimulated controls. Maximal JNK activation correlated with the onset of AP-1 DNA binding activity. Both insulin-stimulated JNK activity and insulin-induced AP-1 transcriptional activity were found to be Ras-dependent. These data suggest that in Rat 1 cells, JNK activation may play a role in insulin-regulated AP-1 transcriptional activity leading to a mitogenic response.
Insights
Insulin boosts cJun NH-terminal kinase (JNK) activity, a key regulator of AP-1 transcription. This activation, dependent on Ras, may contribute to insulin
Area of Science:
- Cellular Biology
- Molecular Biology
- Endocrinology
Background:
- Insulin influences gene transcription, including AP-1-regulated genes.
- cJun NH-terminal kinases (JNKs), also known as stress-activated protein kinases (SAPKs), are key regulators of the AP-1 transcription complex.
Purpose of the Study:
- To investigate the effect of insulin on JNK activity and AP-1 transcriptional activity in Rat 1 fibroblasts.
- To determine the role of Ras in insulin-mediated JNK and AP-1 activation.
Main Methods:
- Measuring JNK activity via immunoprecipitation and GSTcJun phosphorylation in Rat 1 HIR cells treated with insulin.
- Assessing AP-1 DNA binding activity.
- Investigating the involvement of Ras signaling pathways.
Main Results:
- Insulin induced a dose- and time-dependent increase in JNK activity, peaking at 15 minutes with a 2.5-fold increase.
- Maximal JNK activation correlated with increased AP-1 DNA binding activity.
- Both insulin-stimulated JNK activity and AP-1 transcriptional activity were Ras-dependent.
Conclusions:
- Insulin activates JNK in Rat 1 cells, suggesting a role for JNK in insulin-regulated AP-1 transcriptional activity.
- Ras signaling is crucial for insulin's effects on JNK and AP-1 activity, potentially mediating a mitogenic response.