Ubiquitin ligase Hrd1 enhances the degradation and suppresses the toxicity of polyglutamine-expanded huntingtin |
| |
Authors: | Yang Hui Zhong Xiaoyan Ballar Petek Luo Shouqing Shen Yuxian Rubinsztein David C Monteiro Mervyn J Fang Shengyun |
| |
Institution: | Medical Biotechnology Center, University of Maryland Biotechnology Institute, 725 W. Lombard Street, Baltimore, MD 21201, USA. |
| |
Abstract: | E3 ubiquitin ligases catalyze the conjugation of ubiquitin onto proteins, which acts as a signal for targeting proteins for degradation by the proteasome. Hrd1 is an endoplasmic reticulum (ER) membrane-spanning E3 with its catalytic active RING finger facing the cytosol. We speculated that this topology might allow Hrd1 to ubiquitinate misfolded proteins in the cytosol. We tested this idea by using polyglutamine (polyQ)-containing huntingtin (htt) protein as a model substrate. We found that the protein levels of Hrd1 were increased in cells overexpressing the N-terminal fragment of htt containig an expanded polyQ tract (httN). Forced expression of Hrd1 enhanced the degradation of httN in a RING finger-dependent manner, whereas silencing of endogenous Hrd1 expression by RNA interference stabilized httN. Degradation of httN was found to be p97/VCP-dependent, but independent of Ufd1 and Npl4, all of which are thought to form a complex with Hrd1 during ER-associated degradation. Consistent with its role as an E3 for httN, we demonstrate that Hrd1 interacts with and ubiquitinates httN. Subcellular fractionation and confocal microscopy revealed that Hrd1recruits HttN to the ER and co-localizes with juxtanuclear aggregates of httN in cells. Interaction of Hrd1 with httN was found to be independent of the length of the polyglutamine tract. However, httN with expanded polyglutamine tracts appeared to be a preferred substrate for Hrd1. Functionally, we found that Hrd1 protects cells against the httN-induced cell death. These results suggest that Hrd1 is a novel htt-interacting protein that can target pathogenic httN for degradation and is able to protect cells against httN-induced cell death. |
| |
Keywords: | ER endoplasmic reticulum htt huntingtin httN htt exon I or the N-terminal 588 amino acids with various numbers of glutamines ERAD ER-associated degradation GST glutathione S-transferase HA hemagglutinin IB immunoblotting IP immunoprecipitation RING really interesting new gene GFP green fluorescent protein E3 ubiquitin ligase GFP-polyQ GFP fusion of huntingtin exon I with various numbers of glutamines CHIP carboxyl terminus of Hsc70-interacting protein CHX cycloheximide |
本文献已被 ScienceDirect PubMed 等数据库收录! |
|