Regulation of muscle creatine kinase by phosphorylation in normal and diabetic hearts.
Protein kinase C (PKC) is an important signaling molecule in the heart, but its targets remain unclear. Using a PKC substrate antibody, we detected a 40-kDa phosphorylated cardiac protein that was subsequently identified by tandem mass spectroscopy as muscle creatine kinase (M-CK) with phosphorylation at serine 128. The forward reaction using ATP to generate phosphocreatine was reduced, while the reverse reaction using phosphocreatine to generate ATP was increased following dephosphorylation of immunoprecipitated M-CK with protein phosphatase 2A (PP2A) or PP2C. Despite higher PKC levels in diabetic hearts, decreased phosphorylation of M-CK was more prominent than the reduction in its expression. Changes in CK activity in diabetic hearts were similar to those found following dephosphorylation of M-CK from control hearts. The decrease in phosphorylation may act as a compensatory mechanism to maintain CK activity at an appropriate level for cytosolic ATP regeneration in the diabetic heart.
Lin
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G
Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia, 2146 East Mall, Vancouver, BC V6T 1Z3, Canada.
Liu
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Y
MacLeod
K M
KM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D052283:Creatine Kinase, MM Form / Q000737:chemistry / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology* / Q000378:metabolism; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D054645:Protein Phosphatase 1 / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012694:Serine / Q000737:chemistry; D053719:Tandem Mass Spectrometry
D020033:Protein Isoforms; D012694:Serine; D000255:Adenosine Triphosphate; D011493:Protein Kinase C; D052283:Creatine Kinase, MM Form; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2