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Insulin activates the Raf-1 protein kinase.
P J Blackshear1, D M Haupt, H App
1Howard Hughes Medical Institute Laboratories, Durham, North Carolina 27710.
The Journal of Biological Chemistry
|July 25, 1990
Summary
Insulin activates Raf-1 kinase in insulin-sensitive cells, but not through direct tyrosine phosphorylation by the insulin receptor. This suggests a distinct signaling pathway for insulin-induced Raf-1 activation.
Area of Science:
- Cellular signaling
- Molecular biology
- Oncogene research
Background:
- Proto-oncogene product Raf-1 kinase is activated by growth factors via tyrosine phosphorylation.
- Insulin receptor possesses intrinsic protein tyrosine kinase activity, suggesting a potential role in Raf-1 activation.
Purpose of the Study:
- To investigate if insulin activates Raf-1 kinase.
- To determine the mechanism of insulin-induced Raf-1 activation in insulin-sensitive cells.
Main Methods:
- Stimulation of various cell lines with insulin.
- Measurement of Raf-1 protein phosphorylation and kinase activity.
- Phosphoamino acid analysis of Raf-1 protein.
Main Results:
- Insulin rapidly stimulated Raf-1 protein phosphorylation and kinase activity in H35 rat hepatoma cells.
- Activation occurred independently of protein kinase C.
- Phosphoamino acid analysis revealed only phosphoserine and phosphothreonine, not phosphotyrosine, on Raf-1 after insulin stimulation.
Conclusions:
- Insulin activates Raf-1 kinase in certain insulin-sensitive cell types.
- Activation mechanism is likely distinct from direct tyrosine phosphorylation by the insulin receptor.
- Suggests an indirect signaling pathway mediating insulin's effect on Raf-1.