pp54 microtubule-associated protein 2 kinase. A novel serine/threonine protein kinase regulated by phosphorylation and stimulated by poly-L-lysine.
An hepatic protein kinase that phosphorylates microtubule-associated protein 2 (MAP-2) on Ser/Thr residues is markedly activated after intraperitoneal injection of cycloheximide in the rat. The enzyme has been purified greater than 10,000-fold to near homogeneity and corresponds to a 54-kDa polypeptide, based on auto-phosphorylation, renaturation of activity from sodium dodecyl sulfate gels, and gel filtration. The protein kinase activity is unaffected by prior autophosphorylation, Ca2+, diacylglycerol and phospholipids, cyclic nucleotides, staurosporine, and protein kinase inhibitor, but can be totally and specifically deactivated by the Ser/Thr protein phosphatase 2A. The enzyme is inhibited completely but reversible by transition metals and p-chloromercuribenzoate, and is strongly stimulated by poly-L-lysine toward most, but not all protein substrates. The activity of the cycloheximide-stimulated MAP-2 kinase (pp54 MAP-2 kinase) toward potential polypeptide substrates was compared to that of an insulin-stimulated MAP-2 kinase (pp42 MAP-2 kinase). Although both MAP-2 kinases exhibited little or no ability to phosphorylate histones and casein, the two kinases had a distinguishable substrate specificity. At comparable MAP-2 phosphorylating activities, pp42 MAP-2 kinase, but not pp54 MAP-2 kinase, phosphorylated and activated the Xenopus S6 protein kinase II. Moreover, pp42 MAP-2 kinase phosphorylated myelin basic protein at 10-12-fold higher rates than did pp54 MAP-2 kinase. Cycloheximide-activated pp54 MAP-2 protein kinase appears to be a previously uncharacterized protein kinase that is itself regulated through Ser/Thr phosphorylation and, perhaps, polypeptide regulators with basic domains. The identity of the upstream regulatory elements and the native substrates remain to be established.
Kyriakis
J M
JM
Department of Medicine, Harvard Medical School, Massachusetts General Hospital, Boston 02129.
Avruch
J
J
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003513:Cycloheximide / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D006706:Homeostasis; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008970:Molecular Weight; D010766:Phosphorylation; D011107:Polylysine / Q000494:pharmacology*; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D012694:Serine; D013912:Threonine
D007328:Insulin; D011107:Polylysine; D013912:Threonine; D012694:Serine; D003513:Cycloheximide; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases