Myotrophin/V-1, a protein up-regulated in the failing human heart and in postnatal cerebellum, converts NFkappa B p50-p65 heterodimers to p50-p50 and p65-p65 homodimers.
Myotrophin/V-1 is a cytosolic protein found at elevated levels in failing human hearts and in postnatal cerebellum. We have previously shown that it disrupts nuclear factor of kappaB (NFkappaB)-DNA complexes in vitro. In this study, we demonstrated that in HeLa cells native myotrophin/V-1 is predominantly present in the cytoplasm and translocates to the nucleus during sustained NFkappaB activation. Three-dimensional alignment studies indicate that myotrophin/V-1 resembles a truncated IkappaBalpha without the signal response domain (SRD) and PEST domains. Co-immunoprecipitation studies reveal that myotrophin/V-1 interacts with NFkappaB proteins in vitro; however, it remains physically associated only with p65 and c-Rel proteins in vivo during NFkappaB activation. In vitro studies indicate that myotrophin/V-1 can promote the formation of p50-p50 homodimers from monomeric p50 proteins and can convert the preformed p50-p65 heterodimers into p50-p50 and p65-p65 homodimers. Furthermore, adenovirus-mediated overexpression of myotrophin/V-1 resulted in elevated levels of both p50-p50 and p65-p65 homodimers exceeding the levels of p50-p65 heterodimers compared with Adbetagal-infected cells, where the levels of p50-p65 heterodimers exceeded the levels of p50-p50 and p65-p65 homodimers. Thus, overexpression of myotrophin/V-1 during NFkappaB activation resulted in a qualitative shift by quantitatively reducing the level of transactivating heterodimers while elevating the levels of repressive p50-p50 homodimers. Correspondingly, overexpression of myotrophin/V-1 resulted in significantly reduced kappaB-luciferase reporter activity. Because myotrophin/V-1 is found at elevated levels during NFkappaB activation in postnatal cerebellum and in failing human hearts, this study cumulatively suggests that myotrophin/V-1 is a regulatory protein for modulating the levels of activated NFkappaB dimers during this period.
Knuefermann
Pascal
P
Winters Center For Heart Failure Research, Molecular Cardiology Unit, Cardiology Section of Department of Medicine, Baylor College of Medicine, Veterans Affairs Medical Center, Houston, Texas 77030, USA.
Chen
Peter
P
Misra
Arunima
A
Shi
Shu-Ping
SP
Abdellatif
Maha
M
Sivasubramanian
Natarajan
N
D000595:Amino Acid Sequence; D001692:Biological Transport; D002467:Cell Nucleus / Q000737:chemistry; D002531:Cerebellum / Q000378:metabolism*; D003593:Cytoplasm / Q000737:chemistry; D019281:Dimerization; D019084:Fluorescent Antibody Technique, Indirect; D006133:Growth Substances / Q000032:analysis / Q000502:physiology*; D006367:HeLa Cells; D006333:Heart Failure / Q000378:metabolism*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D018832:Molecular Chaperones / Q000502:physiology; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000737:chemistry*; D052002:NF-kappa B p50 Subunit; D051996:Transcription Factor RelA; D014158:Transcription, Genetic; D015854:Up-Regulation
D006133:Growth Substances; D036341:Intercellular Signaling Peptides and Proteins; D018832:Molecular Chaperones; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D051996:Transcription Factor RelA; C065700:myotrophin