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Riepe C, Wąchalska M, Deol KK, Amaya AK, Porteus MH, Olzmann JA, Kopito RR. Small-molecule correctors divert CFTR-F508del from ERAD by stabilizing sequential folding states. Mol Biol Cell 2024; 35:ar15. [PMID: 38019608 PMCID: PMC10881158 DOI: 10.1091/mbc.e23-08-0336] [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: 09/18/2023] [Revised: 11/13/2023] [Accepted: 11/20/2023] [Indexed: 12/01/2023] Open
Abstract
Over 80% of people with cystic fibrosis (CF) carry the F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride ion channel at the apical plasma membrane (PM) of epithelial cells. F508del impairs CFTR folding causing it to be destroyed by endoplasmic reticulum associated degradation (ERAD). Small-molecule correctors, which act as pharmacological chaperones to divert CFTR-F508del from ERAD, are the primary strategy for treating CF, yet corrector development continues with only a rudimentary understanding of how ERAD targets CFTR-F508del. We conducted genome-wide CRISPR/Cas9 knockout screens to systematically identify the molecular machinery that underlies CFTR-F508del ERAD. Although the ER-resident ubiquitin ligase, RNF5 was the top E3 hit, knocking out RNF5 only modestly reduced CFTR-F508del degradation. Sublibrary screens in an RNF5 knockout background identified RNF185 as a redundant ligase and demonstrated that CFTR-F508del ERAD is robust. Gene-drug interaction experiments illustrated that correctors tezacaftor (VX-661) and elexacaftor (VX-445) stabilize sequential, RNF5-resistant folding states. We propose that binding of correctors to nascent CFTR-F508del alters its folding landscape by stabilizing folding states that are not substrates for RNF5-mediated ubiquitylation.
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Affiliation(s)
- Celeste Riepe
- Department of Biology, Stanford University, Stanford, CA 94305
| | - Magda Wąchalska
- Department of Biology, Stanford University, Stanford, CA 94305
| | - Kirandeep K. Deol
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720
- Chan Zuckerberg Biohub Network, San Francisco, CA 94158
| | - Anais K. Amaya
- Department of Pediatrics, Stanford University, Stanford, CA 94305
| | | | - James A. Olzmann
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720
- Chan Zuckerberg Biohub Network, San Francisco, CA 94158
| | - Ron R. Kopito
- Department of Biology, Stanford University, Stanford, CA 94305
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Riepe C, Wąchalska M, Deol KK, Amaya AK, Porteus MH, Olzmann JA, Kopito RR. Small molecule correctors divert CFTR-F508del from ERAD by stabilizing sequential folding states. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.15.556420. [PMID: 37745470 PMCID: PMC10515913 DOI: 10.1101/2023.09.15.556420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/26/2023]
Abstract
Over 80% of people with cystic fibrosis (CF) carry the F508del mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride ion channel at the apical plasma membrane (PM) of epithelial cells. F508del impairs CFTR folding causing it to be destroyed by endoplasmic reticulum associated degradation (ERAD). Small molecule correctors, which act as pharmacological chaperones to divert CFTR-F508del from ERAD, are the primary strategy for treating CF, yet corrector development continues with only a rudimentary understanding of how ERAD targets CFTR-F508del. We conducted genome-wide CRISPR/Cas9 knockout screens to systematically identify the molecular machinery that underlies CFTR-F508del ERAD. Although the ER-resident ubiquitin ligase, RNF5 was the top E3 hit, knocking out RNF5 only modestly reduced CFTR-F508del degradation. Sublibrary screens in an RNF5 knockout background identified RNF185 as a redundant ligase, demonstrating that CFTR-F508del ERAD is highly buffered. Gene-drug interaction experiments demonstrated that correctors tezacaftor (VX-661) and elexacaftor (VX-445) stabilize sequential, RNF5-resistant folding states. We propose that binding of correctors to nascent CFTR-F508del alters its folding landscape by stabilizing folding states that are not substrates for RNF5-mediated ubiquitylation.
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Affiliation(s)
- Celeste Riepe
- Department of Biology, Stanford University, Stanford, CA, USA 94305
| | - Magda Wąchalska
- Department of Biology, Stanford University, Stanford, CA, USA 94305
| | - Kirandeep K. Deol
- Department of Molecular and Cell Biology, University of California, Berkeley, CA USA 94720
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA USA 94720
- Chan Zuckerberg Biohub, San Francisco, CA, USA 94158
| | - Anais K. Amaya
- Department of Pediatrics, Stanford University, Stanford, CA, USA 94305
| | | | - James A. Olzmann
- Department of Molecular and Cell Biology, University of California, Berkeley, CA USA 94720
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA USA 94720
- Chan Zuckerberg Biohub, San Francisco, CA, USA 94158
| | - Ron R. Kopito
- Department of Biology, Stanford University, Stanford, CA, USA 94305
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