Insulin activates the kinase activity of the Raf-1 proto-oncogene by increasing its serine phosphorylation.
Insulin was found to stimulate the serine/threonine kinase activity of the proto-oncogene product Raf-1. This stimulation was observed in HeLa, NIH 3T3, and Chinese hamster ovary cells, all overexpressing the human insulin receptor. In the HeLa cells, 100 pM insulin gave a significant increase in Raf-1 kinase activity, and 100 nM insulin caused a maximal 2-5-fold increase in activity. The increase in activity was detected after 2 min of insulin treatment and peaked after 5 min. In addition to stimulating Raf-1 kinase activity, insulin caused a shift in the electrophoretic mobility of the Raf-1 protein and an increase in the amount of serine phosphorylation of Raf-1. Moreover, a serine/threonine-specific phosphatase, phosphatase 1, but not two tyrosine-specific phosphatases, was found to deactivate the insulin-activated Raf-1 kinase activity. These findings indicate that insulin activates the serine/threonine kinase activity of the Raf-1 proto-oncogene by increasing its content of phosphoserine.
Kovacina
K S
KS
Department of Pharmacology, Stanford University School of Medicine, California 94305-5332.
Yonezawa
K
K
Brautigan
D L
DL
Tonks
N K
NK
Rapp
U R
UR
Roth
R A
RA
D000595:Amino Acid Sequence; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D013997:Time Factors
D007328:Insulin; C000715470:MAS1 protein, human; D009842:Oligopeptides; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D010768:Phosphoserine; D011494:Protein Kinases; D019908:Proto-Oncogene Proteins c-raf