NF-kappaB mediates the protein loss induced by TNF-alpha in differentiated skeletal muscle myotubes.
Nuclear factor-kappaB (NF-kappaB) regulates the transcription of a variety of genes involved in immune responses, cell growth, and cell death. However, the role of NF-kappaB in muscle biology is poorly understood. We recently reported that tumor necrosis factor-alpha (TNF-alpha) rapidly activates NF-kappaB in differentiated skeletal muscle myotubes and that TNF-alpha acts directly on the muscle cell to induce protein degradation. In the present study, we ask whether NF-kappaB mediates the protein loss induced by TNF-alpha. We addressed this problem by creating stable, transdominant negative muscle cell lines. C2C12 myoblasts were transfected with viral plasmid constructs that induce overexpression of mutant I-kappaBalpha proteins that are insensitive to degradation via the ubiquitin-proteasome pathway. These mutant proteins selectively inhibit NF-kappaB activation. We found that differentiated myotubes transfected with the empty viral vector (controls) underwent a drop in total protein content and in fast-type myosin heavy-chain content during 72 h of exposure to TNF-alpha. In contrast, total protein and fast-type myosin heavy-chain levels were unaltered by TNF-alpha in the transdominant negative cell lines. TNF-alpha did not induce apoptosis in any cell line, as assessed by DNA ladder and annexin V assays. These data indicate that NF-kappaB is an essential mediator of TNF-alpha-induced catabolism in differentiated muscle cells.
Li
Y P
YP
Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
Reid
M B
MB
D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020672:I-kappa B Proteins; D007700:Kinetics; D051379:Mice; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D009124:Muscle Proteins; D016328:NF-kappa B; C000606205:Nfkbia protein, mouse; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; D018995:Myosin Heavy Chains