title: Tumor necrosis factor-regulated biphasic activation of NF-kappa B is required for cytokine-induced loss of skeletal muscle gene products.
abstract: NF-kappaB activation is classically defined as a transient response initiated by the degradation of IkappaB inhibitor proteins leading to nuclear import of NF-kappaB and culminating with the resynthesis of IkappaBalpha and subsequent inactivation of the transcription factor. Although this type of regulation is considered the paradigm for NF-kappaB activation, other regulatory profiles are known to exist. By far the most common of these is chronic or persistent activation of NF-kappaB. In comparison, regulation of NF-kappaB in a biphasic manner represents a profile that is scarcely documented and whose biological significance remains poorly understood. Here we show using differentiated skeletal muscle cells, that tumor necrosis factor (TNF) induces NF-kappaB activation in a biphasic manner. Unlike the first transient phase, which is terminated within 1 h of cytokine addition, the second phase persists for an additional 24-36 h. Biphasic activation is mediated at both the levels of NF-kappaB DNA binding and transactivation function, and both phases are dependent on the IKK/26 S proteasome pathway. We find that regulation of the first transient phase is mediated by the degradation and subsequent resynthesis of IkappaBalpha, as well as by a TNF-induced expression of A20. Second phase activity correlates with persistent down-regulation of both IkappaBalpha and IkappaBbeta proteins, derived from a continuous TNF signal. Finally, we demonstrate that inhibition of NF-kappaB prior to initiation of the second phase of activity inhibits cytokine-mediated loss of muscle proteins. We propose that the biphasic activation of NF-kappaB in response to TNF may play a key regulatory role in skeletal muscle wasting associated with cachexia.
authors.affiliation: Division of Human Cancer Genetics, Comprehensive Cancer Center, The Ohio State University, Columbus 43210, USA.
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Ladner
authors.forename: Michael A
authors.initials: MA
authors.lastname: Caligiuri
authors.forename: Denis C
authors.initials: DC
authors.lastname: Guttridge
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002100:Cachexia / Q000378:metabolism; D002460:Cell Line; D016207:Cytokines / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D007371:Interferon-gamma / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D016207:Cytokines; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C000606205:Nfkbia protein, mouse; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; D007371:Interferon-gamma; D004247:DNA; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease