title: In vitro inhibition of MAP kinase (ERK1/ERK2) activity by phosphorylated glia maturation factor (GMF).
abstract: We report that recombinant glia maturation factor (GMF), a 17-kDa brain protein, inhibits the activity of mitogen-activated protein (MAP) kinase in the test tube assay, in particular the ERK1/ERK2 isoforms. A preliminary phosphorylation of GMF by protein kinase A (PKA) dramatically increases its inhibitory effect by over 600-fold (Ki approximately 3 nM), making it the most potent MAP kinase inhibitor ever reported. Immunoprecipitation of GMF from cell extracts using its specific antibody coprecipitates ERK (and vice versa), suggesting the association of the two proteins in the cell. The inhibitory effect of PKA-phosphorylated GMF is specific, as it does not suppress the activity of cdc2 kinase, another proline-directed kinase. Nor does it inhibit MAP kinase kinase (MEK) and MAP kinase-activated protein (MAPKAP) kinase-2, the two enzymes immediately upstream and downstream, respectively, of ERK. Of the other three enzymes that can phosphorylate GMF, only p90 ribosomal S6 kinase (RSK) enhances the inhibitory function of GMF on ERK; protein kinase C (PKC) and casein kinase II (CKII) are without effect. The inhibition of ERK by PKA-phosphorylated GMF suggests that GMF could be one of the mediators of the suppressive effect of the PKA pathway on the MAP kinase pathway. On the other hand, that RSK-phosphorylated GMF also inhibits ERK implies a negative feedback loop in the regulation of MAP kinase activity.
authors.affiliation: Department of Neurology (Division of Neurochemistry and Neurobiology), University of Iowa College of Medicine, Iowa City, USA.
authors.forename: A
authors.initials: A
authors.lastname: Zaheer
authors.forename: R
authors.initials: R
authors.lastname: Lim
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D005246:Feedback; D020904:Glia Maturation Factor; D006801:Humans; D066298:In Vitro Techniques; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D020904:Glia Maturation Factor; D009419:Nerve Tissue Proteins; D010455:Peptides; D011994:Recombinant Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases