MAP kinase activator from insulin-stimulated skeletal muscle is a protein threonine/tyrosine kinase

S. Nakielny, P. Cohen, J. Wu, T. Sturgill

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    Abstract

    A 'MAP kinase activator' was purified several thousand-fold from insulin-stimulated rabbit skeletal muscle, which resembled the 'activator' from nerve growth factor-stimulated PC12 cells in that it could be inactivated by incubation with protein phosphatase 2A, but not by protein tyrosine phosphatases and its apparent molecular mass was 45-50 kDa. In the presence of MgATP, 'MAP kinase activator' converted the normal 'wild-type' 42 kDa MAP kinase from an inactive dephosphorylated form to the fully active diphosphorylated species. Phosphorylation occurred on the same threonine and tyrosine residues which are phosphorylated in vivo in response to growth factors or phorbol esters. A mutant MAP kinase produced by changing a lysine at the active centre to arginine was phosphorylated in an identical manner by the 'MAP kinase activator', but no activity was generated. The results demonstrate that 'MAP kinase activator' is a protein kinase (MAP kinase kinase) and not a protein that stimulates the autophosphorylation of MAP kinase. MAP kinase kinase is the first established example of a protein kinase that can phosphorylate an exogenous protein on threonine as well as tyrosine residues.

    Original languageEnglish
    Pages (from-to)2123-2129
    Number of pages7
    JournalEMBO Journal
    Volume11
    Issue number6
    Publication statusPublished - 1992

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    Keywords

    • Growth factor
    • Insulin
    • MAP kinase
    • Protein kinase
    • Skeletal muscle

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