Myotrophin-kappaB DNA interaction in the initiation process of cardiac hypertrophy.
To investigate how cardiac hypertrophy and heart failure develop, we isolated and characterized a candidate initiator, the soluble 12-kDa protein myotrophin, from rat and human hearts. Myotrophin stimulates protein synthesis and myocardial cell growth associated with increased levels of hypertrophy marker genes. Recombinant myotrophin from the cloned gene showed structural/functional motifs, including ankyrin repeats and putative phosphorylation sites for protein kinase C (PKC) and casein kinase II. One repeat, homologous with I kappaB, interacts with rel/NF-kappaB in vitro. We analyzed the interaction of recombinant myotrophin and nuclear extracts prepared from neonatal and adult cardiomyocytes; gel mobility shift assay showed that myotrophin bound to kappaB DNA. To define PKC's role in myotrophin-induced myocyte growth, we incubated neonatal rat myocytes (normal and stretch) with specific inhibitors and found that myotrophin inhibits [3H]leucine incorporation into myocytes and different hypertrophic gene expression in neonatal myocytes. Using confocal microscopy, we observed that a basal level of myotrophin was present in both cytoplasm and nucleus under normal conditions, but under cyclic stretch, myotrophin levels became elevated in the nucleus. Myotrophin gene levels were upregulated when myocytes underwent cyclic stretch or were treated with tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta and also when excised beating hearts were exposed to high pressure. Our data showed that the myotrophin-kappaB interaction was increased with age in spontaneously hypertensive rats (SHRs) only. Our data provide evidence that myotrophin-kappaB DNA interaction may be an important step in initiating cardiac hypertrophy.
Gupta
Sudhiranjan
S
Department of Molecular Cardiology (NB 50), Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, OH 44195, USA.
Sen
Subha
S
D000818:Animals; D000831:Animals, Newborn; D009320:Atrial Natriuretic Factor / Q000096:biosynthesis; D001665:Binding Sites; D015152:Blotting, Northern; D006332:Cardiomegaly / Q000209:etiology*; D004247:DNA / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D004926:Escherichia coli / Q000235:genetics; D006133:Growth Substances / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology*; D006801:Humans; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D018613:Microscopy, Confocal; D009206:Myocardium / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology; D011312:Pressure; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
D006133:Growth Substances; D020672:I-kappa B Proteins; D036341:Intercellular Signaling Peptides and Proteins; D009281:Naphthalenes; D016271:Proto-Oncogene Proteins c-myc; D014409:Tumor Necrosis Factor-alpha; C065700:myotrophin; C061462:calphostin B; D009320:Atrial Natriuretic Factor; D004247:DNA