Nuclear co-translocation of myotrophin and p65 stimulates myocyte growth. Regulation by myotrophin hairpin loops.
Myotrophin, a 12-kDa ankyrin repeat protein, stimulates protein synthesis and cardiomyocyte growth to initiate cardiac hypertrophy by activating the NF-kappaB signaling cascade. We found that, after internalization into myocytes, myotrophin cotranslocates into the nucleus with p65 to stimulate myocyte growth. We used structure-based mutations on the hairpin loops of myotrophin to determine the effect of the loops on myotrophin and p65 localization, induction of protein synthesis, and cardiac hypertrophy. Loop mutants, most prominently glutamic acid 33-->alanine (E33A), stimulated protein synthesis much less than wild type. Myotrophin-E33A internalized into myocytes but did not translocate into the nucleus and failed to promote nuclear translocation of p65. In addition, two cardiac hypertrophy marker genes, atrial natriuretic factor and beta-myosin heavy chain, were not up-regulated in E33A-treated cells. Myotrophin-induced myocyte growth and initiation of hypertrophy thus require nuclear co-translocation of myotrophin and p65, in a manner that depends crucially on the myotrophin hairpin loops.
Das
Biswajit
B
Department of Molecular Cardiology, Cleveland Clinic, Cleveland, Ohio 44195.
Gupta
Sudhiranjan
S
Department of Molecular Cardiology, Cleveland Clinic, Cleveland, Ohio 44195.
Vasanji
Amit
A
Image Processing and Analysis Center, Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195.
Xu
Zhen
Z
Department of Molecular Cardiology, Cleveland Clinic, Cleveland, Ohio 44195.
Misra
Saurav
S
Department of Molecular Cardiology, Cleveland Clinic, Cleveland, Ohio 44195.
Sen
Subha
S
Department of Molecular Cardiology, Cleveland Clinic, Cleveland, Ohio 44195. Electronic address: sens@ccf.org.
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D019943:Amino Acid Substitution; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000096:biosynthesis; D015415:Biomarkers / Q000378:metabolism; D006332:Cardiomegaly / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D005260:Female; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D020125:Mutation, Missense; D032383:Myocytes, Cardiac / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects*; D017433:Protein Structure, Secondary / Q000235:genetics; D051381:Rats; D011921:Rats, Inbred WKY; D013329:Structure-Activity Relationship; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*; D024723:Ventricular Myosins / Q000096:biosynthesis
D015415:Biomarkers; D036341:Intercellular Signaling Peptides and Proteins; C498145:Rela protein, rat; D051996:Transcription Factor RelA; C065700:myotrophin; D009320:Atrial Natriuretic Factor; D024723:Ventricular Myosins