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Tey PY, Dufner A, Knobeloch KP, Pruneda JN, Clague MJ, Urbé S. Rapid turnover of CTLA4 is associated with a complex architecture of reversible ubiquitylation. J Cell Biol 2025; 224:e202312141. [PMID: 39404738 PMCID: PMC11486831 DOI: 10.1083/jcb.202312141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2023] [Revised: 08/14/2024] [Accepted: 09/27/2024] [Indexed: 10/20/2024] Open
Abstract
The immune checkpoint regulator CTLA4 is an unusually short-lived membrane protein. Here, we show that its lysosomal degradation is dependent on ubiquitylation at lysine residues 203 and 213. Inhibition of the v-ATPase partially restores CTLA4 levels following cycloheximide treatment, but also reveals a fraction that is secreted in exosomes. The endosomal deubiquitylase, USP8, interacts with CTLA4, and its loss enhances CTLA4 ubiquitylation in cancer cells, mouse CD4+ T cells, and cancer cell-derived exosomes. Depletion of the USP8 adapter protein, HD-PTP, but not ESCRT-0 recapitulates this cellular phenotype but shows distinct properties vis-à-vis exosome incorporation. Re-expression of wild-type USP8, but neither a catalytically inactive nor a localization-compromised ΔMIT domain mutant can rescue delayed degradation of CTLA4 or counteract its accumulation in clustered endosomes. UbiCRest analysis of CTLA4-associated ubiquitin chain linkages identifies a complex mixture of conventional Lys63- and more unusual Lys27- and Lys29-linked polyubiquitin chains that may underly the rapidity of protein turnover.
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Affiliation(s)
- Pei Yee Tey
- Biochemistry, Cell and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - Almut Dufner
- Institute of Neuropathology, Medical Faculty, University of Freiburg, Freiburg, Germany
- Signalling Research Centres BIOSS and CIBSS, University of Freiburg, Freiburg, Germany
| | - Klaus-Peter Knobeloch
- Institute of Neuropathology, Medical Faculty, University of Freiburg, Freiburg, Germany
- Signalling Research Centres BIOSS and CIBSS, University of Freiburg, Freiburg, Germany
| | - Jonathan N. Pruneda
- Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, USA
| | - Michael J. Clague
- Biochemistry, Cell and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - Sylvie Urbé
- Biochemistry, Cell and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
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Tey PY, Dufner A, Knobeloch KP, Pruneda JN, Clague MJ, Urbé S. Rapid turnover of CTLA4 is associated with a complex architecture of reversible ubiquitylation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.12.31.573735. [PMID: 38260548 PMCID: PMC10802369 DOI: 10.1101/2023.12.31.573735] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
The immune checkpoint regulator CTLA4 is an unusually short-lived membrane protein. Here we show that its lysosomal degradation is dependent on ubiquitylation at Lysine residues 203 and 213. Inhibition of the v-ATPase partially restores CTLA4 levels following cycloheximide treatment, but also reveals a fraction that is secreted in exosomes. The endosomal deubiquitylase, USP8, interacts with CTLA4 and its loss enhances CTLA4 ubiquitylation in cancer cells, mouse CD4+ T cells and in cancer cell-derived exosomes. Depletion of the USP8 adapter protein, HD-PTP, but not ESCRT-0 recapitulates this cellular phenotype, but shows distinct properties vis-à-vis exosome incorporation. Re-expression of wild-type USP8, but neither a catalytically inactive, nor a localization-compromised ΔMIT domain mutant can rescue delayed degradation of CTLA4, or counteract its accumulation in clustered endosomes. UbiCRest analysis of CTLA4-associated ubiquitin chain linkages identifies a complex mixture of conventional Lys63- and more unusual Lys27- and Lys29-linked polyubiquitin chains that may underly the rapidity of protein turnover.
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Affiliation(s)
- Pei Yee Tey
- Biochemistry, Cell and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown St., Liverpool, L69 3BX, UK
| | - Almut Dufner
- Institute of Neuropathology, Medical Faculty, University of Freiburg, 79106 Freiburg, Germany; Signalling Research Centres BIOSS and CIBSS, University of Freiburg, 79104 Freiburg, Germany
| | - Klaus-Peter Knobeloch
- Institute of Neuropathology, Medical Faculty, University of Freiburg, 79106 Freiburg, Germany; Signalling Research Centres BIOSS and CIBSS, University of Freiburg, 79104 Freiburg, Germany
| | - Jonathan N. Pruneda
- Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, OR 97239, USA
| | - Michael J. Clague
- Biochemistry, Cell and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown St., Liverpool, L69 3BX, UK
| | - Sylvie Urbé
- Biochemistry, Cell and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown St., Liverpool, L69 3BX, UK
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