title: Role for IkappaBalpha, but not c-Rel, in skeletal muscle atrophy.
abstract: Skeletal muscle atrophy is associated with a marked and sustained activation of nuclear factor-kappaB (NF-kappaB) activity. Previous work showed that p50 is one of the NF-kappaB family members required for this activation and for muscle atrophy. In this work, we tested whether another NF-kappaB family member, c-Rel, is required for atrophy. Because endogenous inhibitory factor kappaBalpha (IkappaBalpha) was activated (i.e., decreased) at 3 and 7 days of muscle disuse (i.e., hindlimb unloading), we also tested if IkappaBalpha, which binds and retains Rel proteins in the cytosol, is required for atrophy and intermediates of the atrophy process. To do this, we electrotransferred a dominant negative IkappaBalpha (IkappaBalphaDeltaN) in soleus muscles, which were either unloaded or weight bearing. IkappaBalphaDeltaN expression abolished the unloading-induced increase in both NF-kappaB activation and total ubiquitinated protein. IkappaBalphaDeltaN inhibited unloading-induced fiber atrophy by 40%. The expression of certain genes known to be upregulated with atrophy were significantly inhibited by IkappaBalphaDeltaN expression during unloading, including MAFbx/atrogin-1, Nedd4, IEX, 4E-BP1, FOXO3a, and cathepsin L, suggesting these genes may be targets of NF-kappaB transcription factors. In contrast, c-Rel was not required for atrophy because the unloading-induced markers of atrophy were the same in c-rel(-/-) and wild-type mice. Thus IkappaBalpha degradation is required for the unloading-induced decrease in fiber size, the increase in protein ubiquitination, activation of NF-kappaB signaling, and the expression of specific atrophy genes, but c-Rel is not. These data represent a significant advance in our understanding of the role of NF-kappaB/IkappaB family members in skeletal muscle atrophy, and they provide new candidate NF-kappaB target genes for further study.
authors.affiliation: Department of Health Sciences, Boston University, 635 Commonwealth Avenue, 4th Fl., Boston, MA 02215, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Judge
authors.forename: Alan
authors.initials: A
authors.lastname: Koncarevic
authors.forename: R Bridge
authors.initials: RB
authors.lastname: Hunter
authors.forename: Hsiou-Chi
authors.initials: HC
authors.lastname: Liou
authors.forename: Robert W
authors.initials: RW
authors.lastname: Jackman
authors.forename: Susan C
authors.initials: SC
authors.lastname: Kandarian
mesh_terms: D000818:Animals; D005260:Female; D005456:Fluorescent Dyes; D005799:Genes, Dominant; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D009133:Muscular Atrophy / Q000378:metabolism* / Q000473:pathology* / Q000503:physiopathology; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000235:genetics; D020569:Proto-Oncogene Proteins c-rel / Q000172:deficiency / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D025801:Ubiquitin / Q000378:metabolism; D016474:Weight-Bearing
chemical_list: D005456:Fluorescent Dyes; D020672:I-kappa B Proteins; D009124:Muscle Proteins; D016328:NF-kappa B; C000606205:Nfkbia protein, mouse; C000606206:Nfkbia protein, rat; D020569:Proto-Oncogene Proteins c-rel; D012333:RNA, Messenger; D025801:Ubiquitin; C485184:enhanced green fluorescent protein; D000072000:NF-KappaB Inhibitor alpha; D049452:Green Fluorescent Proteins