title: Role of troponin I phosphorylation in protein kinase C-mediated enhanced contractile performance of rat myocytes.
abstract: Our goal was to define the role of phosphorylated cardiac troponin-I in the adult myocyte contractile performance response to activated protein kinase C. In agreement with earlier work, endothelin enhanced both adult rat myocyte contractile performance and cardiac troponin-I phosphorylation. Protein kinase C participated in both responses. The role of cardiac troponin-I phosphorylation in the contractile function response to protein kinase C was further investigated using gene transfer into myocytes of troponin-I isoforms/mutants lacking one or more phosphorylation sites previously identified in purified cardiac troponin-I. Sarcomeric replacement with slow skeletal troponin-I-abrogated protein kinase C-mediated troponin-I phosphorylation. In functional studies, endothelin slowed relaxation in myocytes expressing slow skeletal troponin-I, while the relaxation rate increased in myocytes expressing cardiac troponin-I. Based on these results, acceleration of myocyte relaxation during protein kinase C activation largely depended on cardiac troponin-I phosphorylation. Experiments with troponin-I isoform chimeras provided evidence that phosphorylation sites in the amino portion of cardiac troponin I-mediated the protein kinase C acceleration of relaxation. The cardiac troponin-I Thr-144 phosphorylation site identified in earlier biochemical studies was not significantly phosphorylated during the acute contractile response. Thus, amino-terminal protein kinase C-dependent phosphorylation sites in cardiac troponin-I are likely responsible for the accelerated relaxation observed in adult myocytes.
authors.affiliation: Department of Surgery, University of Michigan, Ann Arbor, Michigan 48109-0686, USA. wfall@umich.edu
authors.forename: Margaret V
authors.initials: MV
authors.lastname: Westfall
authors.forename: Andrea R
authors.initials: AR
authors.lastname: Borton
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D018014:Gene Transfer Techniques; D006801:Humans; D009119:Muscle Contraction; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009206:Myocardium / Q000166:cytology*; D010766:Phosphorylation; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051381:Rats; D013912:Threonine / Q000737:chemistry; D013997:Time Factors; D014162:Transfection; D019210:Troponin I / Q000737:chemistry* / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D019210:Troponin I; D013912:Threonine; D011493:Protein Kinase C