Traffic-independent function of the Sar1p/COPII machinery in proteasomal sorting of the cystic fibrosis transmembrane conductance regulator
Traffic-independent function of the Sar1p/COPII machinery in proteasomal sorting of the cystic fibrosis transmembrane conductance regulator
复制标题
DOI：
10.1083/jcb.200210086
复制
发表时间：
2003-01-20
影响因子：
7.8
通讯作者：
Sztul, E
中科院分区：
文献类型：
--
作者：
Fu, LW;Sztul, E
新合成的蛋白质在ER中不能正确折叠，通过不同的分选机制被靶向ER相关蛋白降解(ERAD)；可溶性ERAD底物需要ER-高尔基转运和回收才能降解，而跨膜ERAD底物保留在ER中。保留的跨膜蛋白通常被隔离在专门的内质网亚结构域中，但这种隔离与蛋白酶体降解的相关性尚未被探索。我们使用酿酒酵母和一种模型ERAD底物，囊性纤维化跨膜电导调节因子(CFTR)，来探索CFTR在降解之前是否被隔离，确定调节隔离的分子机制，并分析隔离和降解之间的关系。我们报道了CFTR被隔离在含有伴侣Kar2p的ER亚域中，并且在限制温度下生长的sec12(Ts)菌株(Sar1p的鸟核苷酸交换因子突变)、sec13(Ts)菌株(COPII的Sec13p成分的突变)和sec23(Ts)菌株(COPII的Sec23p成分的突变)的隔离和CFTR降解被破坏。Sar1p/COPII机制在CFTR封存和降解中的作用独立于其在ER-Golgi交通中的作用。我们认为，Sar1p/COPII介导的CFTR到ER亚区的分选是其进入蛋白酶体降解途径的关键。这些发现揭示了降解机制的一个新方面，并表明分泌和降解途径之间存在功能上的串扰。
Newly synthesized proteins that do not fold correctly in the ER are targeted for ER-associated protein degradation (ERAD) through distinct sorting mechanisms; soluble ERAD substrates require ER-Golgi transport and retrieval for degradation, whereas transmembrane ERAD substrates are retained in the ER. Retained transmembrane proteins are often sequestered into specialized ER subdomains, but the relevance of such sequestration to proteasomal degradation has not been explored. We used the yeast Saccharomyces cerevisiae and a model ERAD substrate, the cystic fibrosis transmembrane conductance regulator (CFTR), to explore whether CFTR is sequestered before degradation, to identify the molecular machinery regulating sequestration, and to analyze the relationship between sequestration and degradation. We report that CFTR is sequestered into ER subdomains containing the chaperone Kar2p, and that sequestration and CFTR degradation are disrupted in sec12(ts) strain (mutant in guanine-nucleotide exchange factor for Sar1p), sec13(ts) strain (mutant in the Sec13p component of COPII), and sec23(ts) strain (mutant in the Sec23p component of COPII) grown at restrictive temperature. The function of the Sar1p/COPII machinery in CFTR sequestration and degradation is independent of its role in ER-Golgi traffic. We propose that Sar1p/COPII-mediated sorting of CFTR into ER subdomains is essential for its entry into the proteasomal degradation pathway. These findings reveal a new aspect of the degradative mechanism, and suggest functional crosstalk between the secretory and the degradative pathways.