Freeman Caroline L, Hesketh Geoffrey, Seaman Matthew N J
University of Cambridge, Cambridge Institute for Medical Research/Department of Clinical Biochemistry, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Cambridge CB2 0XY, UK.
J Cell Sci. 2014 May 1;127(Pt 9):2053-70. doi: 10.1242/jcs.144659. Epub 2014 Mar 18.
Retromer is a vital element of the endosomal protein sorting machinery and comprises two subcomplexes that operate together to sort membrane proteins (cargo) and tubulate membranes. Tubules are formed by a dimer of sorting nexins, a key component of which is SNX1. Cargo selection is mediated by the VPS35-VPS29-VPS26 trimer, which additionally recruits the WASH complex through VPS35 binding to the WASH complex subunit FAM21. Loss of function of the WASH complex leads to dysregulation of endosome tubulation, although it is unclear how this occurs. Here, we show that FAM21 also binds to the SNX1-interacting DNAJ protein RME-8. Loss of RME-8 causes altered kinetics of SNX1 membrane association and a pronounced increase in highly branched endosomal tubules. Building on previous observations from other laboratories, we show that these tubules contain membrane proteins that are dependent upon WASH complex activity for their localization to the plasma membrane. Therefore, we propose that the interaction between RME-8 and the WASH complex provides a means to coordinate the activity of the WASH complex with the membrane-tubulating function of the sorting nexins at sites where retromer-mediated endosomal protein sorting occurs.
逆转录复合物是内体蛋白分选机制的重要组成部分，由两个亚复合物组成，它们共同作用以分选膜蛋白（货物）并使膜形成微管。微管由分选连接蛋白二聚体形成，其中关键成分是SNX1。货物选择由VPS35-VPS29-VPS26三聚体介导，该三聚体还通过VPS35与WASH复合物亚基FAM21结合来招募WASH复合物。尽管尚不清楚其发生机制，但WASH复合物功能丧失会导致内体微管形成失调。在这里，我们表明FAM21还与与SNX1相互作用的DNAJ蛋白RME-8结合。RME-8的缺失导致SNX1膜结合动力学改变以及高度分支的内体微管显著增加。基于其他实验室先前的观察结果，我们表明这些微管含有膜蛋白，这些膜蛋白依赖于WASH复合物的活性才能定位于质膜。因此，我们提出RME-8与WASH复合物之间的相互作用提供了一种手段，可在发生逆转录复合物介导的内体蛋白分选的位点，将WASH复合物的活性与分选连接蛋白的膜微管形成功能协调起来。
