title: Involvement of Ca2+/calmodulin-dependent protein kinase II in the activation of carnitine palmitoyltransferase I by okadaic acid in rat hepatocytes.
abstract: The present work was undertaken to study the mechanism by which okadaic acid (OA), an inhibitor of protein phosphatases 1 and 2A, stimulates carnitine palmitoyltransferase I (CPT-I) in isolated rat hepatocytes [Guzmán, Kolodziej, Caldwell, Costorphine and Zammit (1994) Biochem. J. 300, 693-699]. The OA-induced stimulation of CPT-I was abolished by the general protein kinase inhibitor K-252a as well as by KN-62, a specific inhibitor of Ca2+/calmodulin-dependent protein kinase II (Ca2+/CM-PKII). However, neither the protein kinase C-specific inhibitor bisindolylmaleimide nor the protein kinase A/protein kinase C inhibitor H-7 was able to prevent the OA-induced stimulation of CPT-I. Hepatocyte-shrinkage-induced stimulation of CPT-I as well as OA-induced hepatocyte shrinkage was prevented by KN-62. KN-62 also antagonized the OA-enhanced release of lactate dehydrogenase from digitonin-permeabilized hepatocytes. Exposure of 32P-labelled hepatocytes to OA increased the degree of phosphorylation of Ca2+/CM-PKII, as immunoprecipitated by a monoclonal antibody raised against the alpha-subunit of rat brain kinase. This effect of OA was also antagonized by KN-62. The results thus indicate that the OA-dependent stimulation of CPT-I may be mediated (at least in part) by increased phosphorylation and subsequent activation of Ca2+/CM-PKII.
authors.affiliation: Department of Biochemistry and Molecular Biology I, Faculty of Biology, Complutense University, Madrid, Spain.
authors.forename: G
authors.initials: G
authors.lastname: Velasco
authors.forename: M
authors.initials: M
authors.lastname: Guzmán
authors.forename: V A
authors.initials: VA
authors.lastname: Zammit
authors.forename: M J
authors.initials: MJ
authors.lastname: Geelen
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D019319:Okadaic Acid / Q000494:pharmacology*; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar
chemical_list: D004791:Enzyme Inhibitors; D019319:Okadaic Acid; C063302:KN 62; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D007770:L-Lactate Dehydrogenase; D002334:Carnitine O-Palmitoyltransferase; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases