TNF-alpha increases ubiquitin-conjugating activity in skeletal muscle by up-regulating UbcH2/E220k.
In some inflammatory diseases, TNF-alpha is thought to stimulate muscle catabolism via an NF-kappaB-dependent process that increases ubiquitin conjugation to muscle proteins. The transcriptional mechanism of this response has not been determined. Here we studied the potential role of UbcH2, a ubiquitin carrier protein and homologue of murine E220k. We find that UbcH2 is constitutively expressed by human skeletal and cardiac muscles, murine limb muscle, and cultured myotubes. TNF-alpha stimulates UbcH2 expression in mouse limb muscles in vivo and in cultured myotubes. The UbcH2 promoter region contains a functional NF-kappaB binding site; NF-kappaB binding to this sequence is increased by TNF-alpha stimulation. A dominant negative inhibitor of NF-kappaB activation blocks both UbcH2 up-regulation and the increase in ubiquitin-conjugating activity stimulated by TNF-alpha. In extracts from TNF-alpha-treated myotubes, ubiquitin-conjugating activity is limited by UbcH2 availability; activity is inhibited by an antiserum to UbcH2 or a dominant negative mutant of UbcH2 and is enhanced by wild-type UbcH2. Thus, UbcH2 up-regulation is a novel response to TNF-alpha/NF-kappaB signaling in skeletal muscle that appears to be essential for the increased ubiquitin conjugation induced by this cytokine.
Li
Yi-Ping
YP
Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Suite 520B, Houston, Texas 77030, USA.
Lecker
Stewart H
SH
Chen
Yuling
Y
Waddell
Ian D
ID
Goldberg
Alfred L
AL
Reid
Michael B
MB
D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D004790:Enzyme Induction; D006801:Humans; D008025:Ligases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D044763:Ubiquitin-Conjugating Enzymes; D014452:Ubiquitins / Q000378:metabolism*; D015854:Up-Regulation
D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D014452:Ubiquitins; C086376:UBE2H protein, human; D044763:Ubiquitin-Conjugating Enzymes; D008025:Ligases