Insulin-stimulated microtubule associated protein kinase is detectable by analytical gel chromatography as a 35-kDa protein in myocytes, adipocytes, and hepatocytes.
Insulin stimulates a novel Ser/Thr kinase, which phosphorylates microtubule associated protein-2 (MAP-2) in vitro. MAP kinase was studied in cell models of the principal insulin responsive tissues using analytical fast-protein liquid chromatography for partial purification of the enzyme. Stimulation of MAP kinase (1.3- to 2-fold) by insulin was readily detected in BC3H1 smooth and 23A2 skeletal muscle cells; 3T3-L1 adipocytes; and isolated rat hepatocytes and adipocytes. No phosphatase activity was detectable under the assay conditions used, proving that stimulation of a kinase, not inhibition of a phosphatase, is responsible for the increased incorporation of 32PO4 catalyzed by supernatants from insulin-treated 3T3-L1 cells. In H4 hepatoma cells, stimulation of MAP kinase was much less evident after gel filtration in comparison to the other cell types. The activated enzyme present in supernatants from insulin-treated cells migrated as a single peak of approximately 35 kDa apparent molecular mass (except in the case of isolated hepatocytes in which a shoulder was present). These results suggest that the insulin-stimulatable MAP kinase may be ubiquitous in insulin responsive cells.
Ray
L B
LB
Department of Internal Medicine, University of Virginia School of Medicine, Charlottesville 22908.
Sturgill
T W
TW
D000273:Adipose Tissue / Q000166:cytology / Q000201:enzymology*; D000818:Animals; D002478:Cells, Cultured; D002850:Chromatography, Gel; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D008297:Male; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000201:enzymology*; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000166:cytology / Q000201:enzymology; D009132:Muscles / Q000166:cytology / Q000201:enzymology*; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D007328:Insulin; D008869:Microtubule-Associated Proteins; D011494:Protein Kinases