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Rapid Stimulation by Insulin of a Serine/Threonine Kinase in 3T3-L1 Adipocytes that Phosphorylates Microtubule-Associated Protein 2 in vitro
L. Bryan Ray and Thomas W. Sturgill
Proceedings of the National Academy of Sciences of the United States of America
Vol. 84, No. 6 (Mar. 15, 1987), pp. 1502-1506
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/29610
Page Count: 5
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Insulin treatment (Kact, 5 × 10-9 M) of serum-starved 3T3-L1 adipocytes stimulates a soluble serine/threonine kinase that catalyzes phosphorylation of microtubule-associated protein 2 (MAP-2) in vitro. Maximal activation of MAP-2 kinase activity by 80 nM insulin was observed after 10 min of hormonal stimulation, prior to maximal stimulation of S6 kinase activity (20 min). The insulin-stimulatable MAP-2 kinase activity is not adsorbed to phosphocellulose, whereas the principal S6 kinase activity is retained and elutes at ≈ 0.5 M NaCl. The insulin-stimulatable MAP-2 kinase is less stable during incubation at 30 degrees C than S6 kinase activity. Inclusion of phosphatase inhibitors decreases the rate at which the stimulated MAP-2 kinase activity is lost from extract supernatants incubated at 30 degrees C. p-Nitrophenyl phosphate is more effective than DL-phosphotyrosine, whereas DL-phosphoserine is without effect at the concentration used (40 mM). The difference in MAP-2 kinase activity in extract supernatants from control and insulin-treated cells is also preserved after rapid chromatography on Sephadex G-25. These results show that a soluble serine/threonine kinase is rapidly activated by insulin, possibly by phosphorylation of either the kinase itself or an interacting modulator.
Proceedings of the National Academy of Sciences of the United States of America © 1987 National Academy of Sciences