title: A non-canonical ESCRT pathway, including histidine domain phosphotyrosine phosphatase (HD-PTP), is used for down-regulation of virally ubiquitinated MHC class I.
abstract: 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.
authors.affiliation: 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.
authors.forename: Michael D J
authors.initials: MD
authors.lastname: Parkinson
authors.affiliation: 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.
authors.forename: Siân C
authors.initials: SC
authors.lastname: Piper
authors.affiliation: 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.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Bright
authors.affiliation: 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.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Evans
authors.affiliation: 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.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Boname
authors.affiliation: 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.
authors.forename: Katherine
authors.initials: K
authors.lastname: Bowers
authors.affiliation: 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.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Lehner
authors.affiliation: 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. JPL10@cam.ac.uk.
authors.forename: J Paul
authors.initials: JP
authors.lastname: Luzio
mesh_terms: D015536:Down-Regulation; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D019288:Herpesvirus 8, Human / Q000235:genetics / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D054558:Protein Tyrosine Phosphatases, Non-Receptor / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D015395:Histocompatibility Antigens Class I; C456022:K3 protein, Kaposi's sarcoma-associated herpesvirus; D014764:Viral Proteins; C114102:PTPN23 protein, human; D054558:Protein Tyrosine Phosphatases, Non-Receptor
keywords: endocytosis; endosomal sorting complex required for transport (ESCRT); histidine domain phosphotyrosine phosphatase (HD-PTP); histidine-domain protein tyrosine phosphatase non-receptor type 23 (PTPN23); lysosome; ubiquitination (ubiquitylation)