title: Phosphorylation of the 165-kDa dihydropyridine/phenylalkylamine receptor from skeletal muscle by protein kinase C.
abstract: Dihydropyridine-sensitive Ca2+ channels exist in many different types of cells and are believed to be regulated by various protein phosphorylation and dephosphorylation reactions. The present study concerns the phosphorylation of a putative component of dihydropyridine-sensitive Ca2+ channels by the calcium and phospholipid-dependent protein kinase, protein kinase C. A skeletal muscle peptide of 165 kDa, which is known to contain receptors for dihydropyridines, phenylalkylamines, and other Ca2+ channel effectors, was found to be an efficient substrate for protein kinase C when the peptide was phosphorylated in its membrane-bound state. Protein kinase C incorporated 1.5-2.0 mol of phosphate/mol of peptide within 2 min into the 165-kDa peptide in incubations carried out at 37 degrees C. In contrast to the membrane-bound peptide, the purified 165-kDa peptide in detergent solution was phosphorylated to a markedly less extent than its membrane-bound counterpart; less than 0.1 mol of phosphate/mol of peptide was incorporated. Preincubation of the membranes with several types of drugs known to be Ca2+ channel activators or inhibitors had no specific effects on the rate and/or extent of phosphorylation of the 165-kDa peptide by protein kinase C. The phosphorylation of the membrane-bound 165-kDa peptide by protein kinase C was compared to that catalyzed by cAMP-dependent protein kinase and was found to be not additive. Prior phosphorylation of the 165-kDa peptide by cAMP-dependent protein kinase prevented subsequent phosphorylation of the peptide by protein kinase C. Phosphoamino acid analysis indicated that protein kinase C phosphorylated the 165-kDa peptide at both serine and threonine residues. Phosphopeptide mapping experiments showed that protein kinase C phosphorylated one unique site in the 165-kDa peptide, and, in addition, other sites that were phosphorylated by either cAMP-dependent protein kinase or a multifunctional Ca2+/calmodulin-dependent protein kinase. The results suggest that the 165-kDa dihydropyridine/phenylalkylamine receptor could serve as a physiological substrate of protein kinase C in intact cells. It is therefore possible that the regulation of dihydropyridine-sensitive Ca2+ channels by activators of protein kinase C may occur at the level of this peptide.
authors.affiliation: Department of Biological Chemistry and Structure, University of Health Sciences, Chicago Medical School, Illinois 60064.
authors.forename: C M
authors.initials: CM
authors.lastname: O'Callahan
authors.forename: J
authors.initials: J
authors.lastname: Ptasienski
authors.forename: M M
authors.initials: MM
authors.lastname: Hosey
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism; D015220:Calcium Channels; D002462:Cell Membrane / Q000378:metabolism; D015151:Immunoblotting; D007700:Kinetics; D008970:Molecular Weight; D009132:Muscles / Q000378:metabolism*; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000032:analysis; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011817:Rabbits; D011978:Receptors, Nicotinic / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010748:Phosphopeptides; D011978:Receptors, Nicotinic; D011493:Protein Kinase C