Li Yi-Ping, Lecker Stewart H, Chen Yuling, Waddell Ian D, Goldberg Alfred L, Reid Michael B
Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Suite 520B, Houston, Texas 77030, USA.
FASEB J. 2003 Jun;17(9):1048-57. doi: 10.1096/fj.02-0759com.
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.
在一些炎症性疾病中,肿瘤坏死因子-α(TNF-α)被认为通过一种依赖核因子-κB(NF-κB)的过程刺激肌肉分解代谢,该过程会增加泛素与肌肉蛋白的结合。这种反应的转录机制尚未确定。在此,我们研究了泛素载体蛋白UbcH2(鼠E220k的同源物)的潜在作用。我们发现UbcH2在人类骨骼肌和心肌、鼠肢体肌肉以及培养的肌管中组成性表达。TNF-α在体内和培养的肌管中均可刺激鼠肢体肌肉中UbcH2的表达。UbcH2启动子区域包含一个功能性NF-κB结合位点;TNF-α刺激会增加NF-κB与该序列的结合。NF-κB激活的显性负性抑制剂可阻断UbcH2的上调以及TNF-α刺激引起的泛素结合活性的增加。在TNF-α处理的肌管提取物中,泛素结合活性受UbcH2可用性的限制;该活性被抗UbcH2血清或UbcH2的显性负性突变体抑制,并被野生型UbcH2增强。因此,UbcH2上调是骨骼肌对TNF-α/NF-κB信号的一种新反应,似乎对该细胞因子诱导的泛素结合增加至关重要。