Parkinson Michael D J, Piper Siân C, Bright Nicholas A, Evans Jennifer L, Boname Jessica M, Bowers Katherine, Lehner Paul J, Luzio J Paul
Department of Clinical Biochemistry, Cambridge Institute for Medical Research, University of Cambridge School of Clinical Medicine, Wellcome Trust/MRC Building, Biomedical Campus, Hills Road, Cambridge, CB2 0XY, U.K.
Department of Medicine, Cambridge Institute for Medical Research, University of Cambridge School of Clinical Medicine, Wellcome Trust/MRC Building, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0XY, U.K.
Biochem J. 2015 Oct 1;471(1):79-88. doi: 10.1042/BJ20150336. Epub 2015 Jul 28.
The Kaposi's sarcoma-associated herpes virus (KSHV) K3 viral gene product effectively down-regulates cell surface MHC class I. K3 is an E3 ubiquitin ligase that promotes Lys(63)-linked polyubiquitination of MHC class I, providing the signal for clathrin-mediated endocytosis. Endocytosis is followed by sorting into the intralumenal vesicles (ILVs) of multivesicular bodies (MVBs) and eventual delivery to lysosomes. The sorting of MHC class I into MVBs requires many individual proteins of the four endosomal sorting complexes required for transport (ESCRTs). In HeLa cells expressing the KSHV K3 ubiquitin ligase, the effect of RNAi-mediated depletion of individual proteins of the ESCRT-0 and ESCRT-I complexes and three ESCRT-III proteins showed that these are required to down-regulate MHC class I. However, depletion of proteins of the ESCRT-II complex or of the ESCRT-III protein, VPS20 (vacuolar protein sorting 20)/CHMP6 (charged MVB protein 6), failed to prevent the loss of MHC class I from the cell surface. Depletion of histidine domain phosphotyrosine phosphatase (HD-PTP) resulted in an increase in the cell surface concentration of MHC class I in HeLa cells expressing the KSHV K3 ubiquitin ligase. Rescue experiments with wild-type (WT) and mutant HD-PTP supported the conclusion that HD-PTP acts as an alternative to ESCRT-II and VPS20/CHMP6 as a link between the ESCRT-I and those ESCRT-III protein(s) necessary for ILV formation. Thus, the down-regulation of cell surface MHC class I, polyubiquitinated by the KSHV K3 ubiquitin ligase, does not employ the canonical ESCRT pathway, but instead utilizes an alternative pathway in which HD-PTP replaces ESCRT-II and VPS20/CHMP6.
卡波西肉瘤相关疱疹病毒（KSHV）的K3病毒基因产物可有效下调细胞表面的MHC I类分子。K3是一种E3泛素连接酶，可促进MHC I类分子的赖氨酸（63）连接的多聚泛素化，为网格蛋白介导的内吞作用提供信号。内吞作用之后是分选进入多泡体（MVB）的腔内小泡（ILV），最终被递送至溶酶体。MHC I类分子分选至MVB需要运输所需的四种内体分选复合物（ESCRT）中的许多单个蛋白质。在表达KSHV K3泛素连接酶的HeLa细胞中，RNA干扰介导的ESCRT-0和ESCRT-I复合物的单个蛋白质以及三种ESCRT-III蛋白质的消耗作用表明，这些蛋白质是下调MHC I类分子所必需的。然而，ESCRT-II复合物的蛋白质或ESCRT-III蛋白质VPS20（液泡蛋白分选20）/CHMP6（带电荷的MVB蛋白6）的消耗未能阻止MHC I类分子从细胞表面丢失。组氨酸结构域磷酸酪氨酸磷酸酶（HD-PTP）的消耗导致在表达KSHV K3泛素连接酶的HeLa细胞中MHC I类分子的细胞表面浓度增加。野生型（WT）和突变型HD-PTP的拯救实验支持了以下结论：HD-PTP作为ESCRT-II和VPS20/CHMP6的替代物，充当ESCRT-I与ILV形成所需的那些ESCRT-III蛋白质之间的连接。因此，由KSHV K3泛素连接酶多聚泛素化的细胞表面MHC I类分子的下调不采用经典的ESCRT途径，而是利用一种替代途径，其中HD-PTP取代了ESCRT-II和VPS20/CHMP6。
