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Sachan V, Le Dévéhat M, Roubtsova A, Essalmani R, Laurendeau JF, Garçon D, Susan-Resiga D, Duval S, Mikaeeli S, Hamelin J, Evagelidis A, Chong M, Paré G, Chernetsova E, Gao ZH, Robillard I, Ruiz M, Trinh VQH, Estall JL, Faraj M, Austin RC, Sauvageau M, Prat A, Kiss RS, Seidah NG. PCSK7: A novel regulator of apolipoprotein B and a potential target against non-alcoholic fatty liver disease. Metabolism 2024; 150:155736. [PMID: 37967646 DOI: 10.1016/j.metabol.2023.155736] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 10/17/2023] [Accepted: 11/08/2023] [Indexed: 11/17/2023]
Abstract
BACKGROUND Epidemiological evidence links the proprotein convertase subtilisin/kexin 7 (PCSK7) to triglyceride (TG) metabolism. We associated the known PCSK7 gain-of-function non-coding SNP rs236918 with higher levels of plasma apolipoprotein B (apoB) and the loss-of-function coding variant p.Pro777Leu (SNP rs201598301) with lower apoB and TG. Herein, we aimed to unravel the in vivo role of liver PCSK7. METHODS We biochemically defined the functional role of PCSK7 in lipid metabolism using hepatic cell lines and Pcsk7-/- mice. Our findings were validated following subcutaneous administration of hepatocyte-targeted N-acetylgalactosamine (GalNAc)-antisense oligonucleotides (ASOs) against Pcsk7. RESULTS Independent of its proteolytic activity, membrane-bound PCSK7 binds apoB100 in the endoplasmic reticulum and enhances its secretion. Mechanistically, the loss of PCSK7/Pcsk7 leads to apoB100 degradation, triggering an unfolded protein response, autophagy, and β-oxidation, eventually reducing lipid accumulation in hepatocytes. Non-alcoholic fatty liver disease (NAFLD) was induced by a 12-week high fat/fructose/cholesterol diet in wild type (WT) and Pcsk7-/- mice that were then allowed to recover on a 4-week control diet. Pcsk7-/- mice recovered more effectively than WT mice from all NAFLD-related liver phenotypes. Finally, subcutaneous administration of GalNAc-ASOs targeting hepatic Pcsk7 to WT mice validated the above results. CONCLUSIONS Our data reveal hepatic PCSK7 as one of the major regulators of apoB, and its absence reduces apoB secretion from hepatocytes favoring its ubiquitination and degradation by the proteasome. This results in a cascade of events, eventually reducing hepatic lipid accumulation, thus supporting the notion of silencing PCSK7 mRNA in hepatocytes for targeting NAFLD.
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Affiliation(s)
- Vatsal Sachan
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Maïlys Le Dévéhat
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Anna Roubtsova
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Rachid Essalmani
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Jean-Francois Laurendeau
- RNA and Noncoding Mechanisms of Disease, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Damien Garçon
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Delia Susan-Resiga
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Stéphanie Duval
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Sahar Mikaeeli
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Josée Hamelin
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Alexandra Evagelidis
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Michael Chong
- Department of Biochemistry & Biomedical Sciences, McMaster University Faculty of Health Sciences, Hamilton, Ontario, Canada
| | - Guillaume Paré
- Department of Biochemistry & Biomedical Sciences, McMaster University Faculty of Health Sciences, Hamilton, Ontario, Canada
| | | | - Zu-Hua Gao
- Department of Pathology, McGill University Health Centre, Montréal, QC, Canada
| | - Isabelle Robillard
- Montreal Heart Institute, Metabolomics Platform, Montreal, Quebec, Canada; Department of Nutrition, Université de Montréal, Montréal, QC, Canada
| | - Matthieu Ruiz
- Montreal Heart Institute, Metabolomics Platform, Montreal, Quebec, Canada; Department of Nutrition, Université de Montréal, Montréal, QC, Canada
| | - Vincent Quoc-Huy Trinh
- Departement of Pathology and Cellular Biology, Institut de Recherche en Immunologie et Cancérologie, Université de Montréal, Montréal, QC, Canada
| | - Jennifer L Estall
- Molecular Mechanisms of Diabetes, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - May Faraj
- Nutrition Department, Université de Montréal, Research Unit on Nutrition, Lipoproteins and Cardiometabolic Diseases, Institut de Recherches Cliniques de Montréal (IRCM), Montréal, QC, Canada
| | - Richard C Austin
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe's Hamilton and the Hamilton Center for Kidney Research, Hamilton, ON, Canada
| | - Martin Sauvageau
- RNA and Noncoding Mechanisms of Disease, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Annik Prat
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada
| | - Robert S Kiss
- McGill University Health Centre Research Institute, Montréal, QC, Canada
| | - Nabil G Seidah
- Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal (IRCM), affiliated to the Université de Montréal, Montréal, QC, Canada.
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Essalmani R, Andréo U, Evagelidis A, Le Dévéhat M, Pereira Ramos OH, Fruchart Gaillard C, Susan-Resiga D, Cohen ÉA, Seidah NG. SKI-1/S1P Facilitates SARS-CoV-2 Spike Induced Cell-to-Cell Fusion via Activation of SREBP-2 and Metalloproteases, Whereas PCSK9 Enhances the Degradation of ACE2. Viruses 2023; 15:v15020360. [PMID: 36851576 PMCID: PMC9959508 DOI: 10.3390/v15020360] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 01/23/2023] [Accepted: 01/24/2023] [Indexed: 01/31/2023] Open
Abstract
Proprotein convertases activate various envelope glycoproteins and participate in cellular entry of many viruses. We recently showed that the convertase furin is critical for the infectivity of SARS-CoV-2, which requires cleavage of its spike protein (S) at two sites: S1/S2 and S2'. This study investigates the implication of the two cholesterol-regulating convertases SKI-1 and PCSK9 in SARS-CoV-2 entry. The assays used were cell-to-cell fusion in HeLa cells and pseudoparticle entry into Calu-3 cells. SKI-1 increased cell-to-cell fusion by enhancing the activation of SREBP-2, whereas PCSK9 reduced cell-to-cell fusion by promoting the cellular degradation of ACE2. SKI-1 activity led to enhanced S2' formation, which was attributed to increased metalloprotease activity as a response to enhanced cholesterol levels via activated SREBP-2. However, high metalloprotease activity resulted in the shedding of S2' into a new C-terminal fragment (S2″), leading to reduced cell-to-cell fusion. Indeed, S-mutants that increase S2″ formation abolished S2' and cell-to-cell fusion, as well as pseudoparticle entry, indicating that the formation of S2″ prevents SARS-CoV-2 cell-to-cell fusion and entry. We next demonstrated that PCSK9 enhanced the cellular degradation of ACE2, thereby reducing cell-to-cell fusion. However, different from the LDLR, a canonical target of PCSK9, the C-terminal CHRD domain of PCSK9 is dispensable for the PCSK9-induced degradation of ACE2. Molecular modeling suggested the binding of ACE2 to the Pro/Catalytic domains of mature PCSK9. Thus, both cholesterol-regulating convertases SKI-1 and PCSK9 can modulate SARS-CoV-2 entry via two independent mechanisms.
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Affiliation(s)
- Rachid Essalmani
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Université de Montréal, Montreal, QC H2W 1R7, Canada
| | - Ursula Andréo
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Université de Montréal, Montreal, QC H2W 1R7, Canada
| | - Alexandra Evagelidis
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Université de Montréal, Montreal, QC H2W 1R7, Canada
| | - Maïlys Le Dévéhat
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Université de Montréal, Montreal, QC H2W 1R7, Canada
| | - Oscar Henrique Pereira Ramos
- Département Médicaments et Technologies pour la Santé (DMTS), Université Paris-Saclay, CEA, INRAE, SI-MoS, 91191 Gif-sur-Yvette, France
| | - Carole Fruchart Gaillard
- Département Médicaments et Technologies pour la Santé (DMTS), Université Paris-Saclay, CEA, INRAE, SI-MoS, 91191 Gif-sur-Yvette, France
| | - Delia Susan-Resiga
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Université de Montréal, Montreal, QC H2W 1R7, Canada
| | - Éric A. Cohen
- Laboratory of Human Retrovirology, Montreal Clinical Research Institute (IRCM), Université de Montréal, 110 Pine Ave West, Montreal, QC H2W 1R7, Canada
- Department of Microbiology, Infectiology and Immunology, Université de Montréal, Montreal, QC H3C 3J7, Canada
| | - Nabil G. Seidah
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Université de Montréal, Montreal, QC H2W 1R7, Canada
- Correspondence: ; Tel.: +1-514-987-5609
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3
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Fruchart Gaillard C, Ouadda ABD, Ciccone L, Girard E, Mikaeeli S, Evagelidis A, Le Dévéhat M, Susan-Resiga D, Lajeunesse EC, Nozach H, Ramos OHP, Thureau A, Legrand P, Prat A, Dive V, Seidah NG. Molecular interactions of PCSK9 with an inhibitory nanobody, CAP1 and HLA-C: Functional regulation of LDLR levels. Mol Metab 2022; 67:101662. [PMID: 36566984 PMCID: PMC9816786 DOI: 10.1016/j.molmet.2022.101662] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Revised: 12/13/2022] [Accepted: 12/16/2022] [Indexed: 12/24/2022] Open
Abstract
OBJECTIVE The liver-derived circulating PCSK9 enhances the degradation of the LDL receptor (LDLR) in endosomes/lysosomes. PCSK9 inhibition or silencing is presently used in clinics worldwide to reduce LDL-cholesterol, resulting in lower incidence of cardiovascular disease and possibly cancer/metastasis. The mechanism by which the PCSK9-LDLR complex is sorted to degradation compartments is not fully understood. We previously suggested that out of the three M1, M2 and M3 subdomains of the C-terminal Cys/His-rich-domain (CHRD) of PCSK9, only M2 is critical for the activity of extracellular of PCSK9 on cell surface LDLR. This likely implicates the binding of M2 to an unknown membrane-associated "protein X" that would escort the complex to endosomes/lysosomes for degradation. We reported that a nanobody P1.40 binds the M1 and M3 domains of the CHRD and inhibits the function of PCSK9. It was also reported that the cytosolic adenylyl cyclase-associated protein 1 (CAP1) could bind M1 and M3 subdomains and enhance the activity of PCSK9. In this study, we determined the 3-dimensional structure of the CHRD-P1.40 complex to understand the intricate interplay between P1.40, CAP1 and PCSK9 and how they regulate LDLR degradation. METHODS X-ray diffraction of the CHRD-P1.40 complex was analyzed with a 2.2 Å resolution. The affinity and interaction of PCSK9 or CHRD with P1.40 or CAP1 was analyzed by atomic modeling, site-directed mutagenesis, bio-layer interferometry, expression in hepatic cell lines and immunocytochemistry to monitor LDLR degradation. The CHRD-P1.40 interaction was further analyzed by deep mutational scanning and binding assays to validate the role of predicted critical residues. Conformational changes and atomic models were obtained by small angle X-ray scattering (SAXS). RESULTS We demonstrate that PCSK9 exists in a closed or open conformation and that P1.40 favors the latter by binding key residues in the M1 and M3 subdomains of the CHRD. Our data show that CAP1 is well secreted by hepatic cells and binds extracellular PCSK9 at distinct residues in the M1 and M3 modules and in the acidic prodomain. CAP1 stabilizes the closed conformation of PCSK9 and prevents P1.40 binding. However, CAP1 siRNA only partially inhibited PCSK9 activity on the LDLR. By modeling the previously reported interaction between M2 and an R-X-E motif in HLA-C, we identified Glu567 and Arg549 as critical M2 residues binding HLA-C. Amazingly, these two residues are also required for the PCSK9-induced LDLR degradation. CONCLUSIONS The present study reveals that CAP1 enhances the function of PCSK9, likely by twisting the protein into a closed configuration that exposes the M2 subdomain needed for targeting the PCSK9-LDLR complex to degradation compartments. We hypothesize that "protein X", which is expected to guide the LDLR-PCSK9-CAP1 complex to these compartments after endocytosis into clathrin-coated vesicles, is HLA-C or a similar MHC-I family member. This conclusion is supported by the PCSK9 natural loss-of-function Q554E and gain-of-function H553R M2 variants, whose consequences are anticipated by our modeling.
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Affiliation(s)
- Carole Fruchart Gaillard
- Université Paris-Saclay, CEA, INRAE, Département Médicaments et Technologies pour la Santé (DMTS), SIMoS, 91191 Gif-sur-Yvette, France
| | - Ali Ben Djoudi Ouadda
- Montreal Clinical Research Institute (IRCM), affiliated to the University of Montreal, Laboratory of Biochemical Neuroendocrinology, Montreal, Quebec H2W 1R7, Canada
| | - Lidia Ciccone
- Synchrotron SOLEIL, HelioBio group, l'Orme des Merisiers, 91190 Saint-Aubin, France; Department of Pharmacy, University of Pisa, Via Bonanno, 6, 56126 Pisa, Italy
| | - Emmanuelle Girard
- Montreal Clinical Research Institute (IRCM), affiliated to the University of Montreal, Laboratory of Biochemical Neuroendocrinology, Montreal, Quebec H2W 1R7, Canada
| | - Sepideh Mikaeeli
- Montreal Clinical Research Institute (IRCM), affiliated to the University of Montreal, Laboratory of Biochemical Neuroendocrinology, Montreal, Quebec H2W 1R7, Canada
| | - Alexandra Evagelidis
- Montreal Clinical Research Institute (IRCM), affiliated to the University of Montreal, Laboratory of Biochemical Neuroendocrinology, Montreal, Quebec H2W 1R7, Canada
| | - Maïlys Le Dévéhat
- Montreal Clinical Research Institute (IRCM), affiliated to the University of Montreal, Laboratory of Biochemical Neuroendocrinology, Montreal, Quebec H2W 1R7, Canada
| | - Delia Susan-Resiga
- Montreal Clinical Research Institute (IRCM), affiliated to the University of Montreal, Laboratory of Biochemical Neuroendocrinology, Montreal, Quebec H2W 1R7, Canada
| | - Evelyne Cassar Lajeunesse
- Université Paris-Saclay, CEA, INRAE, Département Médicaments et Technologies pour la Santé (DMTS), SIMoS, 91191 Gif-sur-Yvette, France
| | - Hervé Nozach
- Université Paris-Saclay, CEA, INRAE, Département Médicaments et Technologies pour la Santé (DMTS), SIMoS, 91191 Gif-sur-Yvette, France
| | - Oscar Henrique Pereira Ramos
- Université Paris-Saclay, CEA, INRAE, Département Médicaments et Technologies pour la Santé (DMTS), SIMoS, 91191 Gif-sur-Yvette, France
| | - Aurélien Thureau
- Synchrotron SOLEIL, HelioBio group, l'Orme des Merisiers, 91190 Saint-Aubin, France
| | - Pierre Legrand
- Synchrotron SOLEIL, HelioBio group, l'Orme des Merisiers, 91190 Saint-Aubin, France
| | - Annik Prat
- Montreal Clinical Research Institute (IRCM), affiliated to the University of Montreal, Laboratory of Biochemical Neuroendocrinology, Montreal, Quebec H2W 1R7, Canada
| | - Vincent Dive
- Université Paris-Saclay, CEA, INRAE, Département Médicaments et Technologies pour la Santé (DMTS), SIMoS, 91191 Gif-sur-Yvette, France
| | - Nabil G Seidah
- Montreal Clinical Research Institute (IRCM), affiliated to the University of Montreal, Laboratory of Biochemical Neuroendocrinology, Montreal, Quebec H2W 1R7, Canada.
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Susan-Resiga D, Girard E, Essalmani R, Roubtsova A, Marcinkiewicz J, Derbali RM, Evagelidis A, Byun JH, Lebeau PF, Austin RC, Seidah NG. Asialoglycoprotein receptor 1 is a novel PCSK9-independent ligand of liver LDLR cleaved by furin. J Biol Chem 2021; 297:101177. [PMID: 34508778 PMCID: PMC8479480 DOI: 10.1016/j.jbc.2021.101177] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 08/26/2021] [Accepted: 09/07/2021] [Indexed: 01/06/2023] Open
Abstract
The hepatic carbohydrate-recognizing asialoglycoprotein receptor (ASGR1) mediates the endocytosis/lysosomal degradation of desialylated glycoproteins following binding to terminal galactose/N-acetylgalactosamine. Human heterozygote carriers of ASGR1 deletions exhibit ∼34% lower risk of coronary artery disease and ∼10% to 14% reduction of non-HDL cholesterol. Since the proprotein convertase PCSK9 is a major degrader of the low-density lipoprotein receptor (LDLR), we investigated the degradation and functionality of LDLR and/or PCSK9 by endogenous/overexpressed ASGR1 using Western blot and immunofluorescence in HepG2-naïve and HepG2-PCSK9-knockout cells. ASGR1, like PCSK9, targets LDLR, and both independently interact with/enhance the degradation of the receptor. This lack of cooperativity between PCSK9 and ASGR1 was confirmed in livers of wildtype (WT) and Pcsk9−/− mice. ASGR1 knockdown in HepG2-naïve cells significantly increased total (∼1.2-fold) and cell-surface (∼4-fold) LDLR protein. In HepG2-PCSK9-knockout cells, ASGR1 silencing led to ∼2-fold higher levels of LDLR protein and DiI (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate)-LDL uptake associated with ∼9-fold increased cell-surface LDLR. Overexpression of WT-ASGR1/2 primarily reduced levels of immature non-O-glycosylated LDLR (∼110 kDa), whereas the triple Ala-mutant of Gln240/Trp244/Glu253 (characterized by loss of carbohydrate binding) reduced expression of the mature form of LDLR (∼150 kDa), suggesting that ASGR1 binds the LDLR in both a sugar-dependent and -independent fashion. The protease furin cleaves ASGR1 at the RKMK103↓ motif into a secreted form, likely resulting in a loss of function on LDLR. Altogether, we demonstrate that LDLR is the first example of a liver-receptor ligand of ASGR1. We conclude that silencing of ASGR1 and PCSK9 may lead to higher LDL uptake by hepatocytes, thereby providing a novel approach to further reduce LDL cholesterol levels.
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Affiliation(s)
- Delia Susan-Resiga
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Affiliated to the University of Montreal, Montreal, Quebec, Canada
| | - Emmanuelle Girard
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Affiliated to the University of Montreal, Montreal, Quebec, Canada
| | - Rachid Essalmani
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Affiliated to the University of Montreal, Montreal, Quebec, Canada
| | - Anna Roubtsova
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Affiliated to the University of Montreal, Montreal, Quebec, Canada
| | - Jadwiga Marcinkiewicz
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Affiliated to the University of Montreal, Montreal, Quebec, Canada
| | - Rabeb M Derbali
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Affiliated to the University of Montreal, Montreal, Quebec, Canada
| | - Alexandra Evagelidis
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Affiliated to the University of Montreal, Montreal, Quebec, Canada
| | - Jae H Byun
- Division of Nephrology, Department of Medicine, McMaster University, St. Joseph's Healthcare Hamilton, Hamilton, Ontario, Canada
| | - Paul F Lebeau
- Division of Nephrology, Department of Medicine, McMaster University, St. Joseph's Healthcare Hamilton, Hamilton, Ontario, Canada
| | - Richard C Austin
- Division of Nephrology, Department of Medicine, McMaster University, St. Joseph's Healthcare Hamilton, Hamilton, Ontario, Canada
| | - Nabil G Seidah
- Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM), Affiliated to the University of Montreal, Montreal, Quebec, Canada.
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Durand L, Duval S, Evagelidis A, Guillemot J, Dianati V, Sikorska E, Schu P, Day R, Seidah NG. The motif E XE XXXL in the cytosolic tail of the secretory human proprotein convertase PC7 regulates its trafficking and cleavage activity. J Biol Chem 2020; 295:2068-2083. [PMID: 31915245 DOI: 10.1074/jbc.ra119.011775] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 12/17/2019] [Indexed: 02/05/2023] Open
Abstract
Many secretory proteins are activated by cleavage at specific sites. The proprotein convertases (PCs) form a family of nine secretory subtilisin-like serine proteases, seven of which cleave at specific basic residues within the trans-Golgi network, granules, or at the cell surface/endosomes. The seventh member, PC7, is a type-I transmembrane (TM) protein with a 97-residue-long cytosolic tail (CT). PC7 sheds human transferrin receptor 1 (hTfR1) into soluble shTfR1 in endosomes. To better understand the physiological roles of PC7, here we focused on the relationship between the CT-regulated trafficking of PC7 and its ability to shed hTfR1. Deletion of the TMCT resulted in soluble PC7 and loss of its hTfR1 shedding activity. Extensive CT deletions and mutagenesis analyses helped us zoom in on three residues in the CT, namely Glu-719, Glu-721, and Leu-725, that are part of a novel motif, EXEXXXL725, critical for PC7 activity on hTfR1. NMR studies of two 14-mer peptides mimicking this region of the CT and its Ala variants revealed that the three exposed residues are on the same side of the molecule. This led to the identification of adaptor protein 2 (AP-2) as a protein that recognizes the EXEXXXL725 motif, thus representing a potentially new regulator of PC7 trafficking and cleavage activity. Immunocytochemistry of the subcellular localization of PC7 and its Ala variants of Leu-725 and Glu-719 and Glu-721 revealed that Leu-725 enhances PC7 localization to early endosomes and that, together with Glu-719 and Glu-721, it increases the endosomal activity of PC7 on hTfR1.
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Affiliation(s)
- Loreleï Durand
- Laboratory of Biochemical Neuroendocrinology, Clinical Research of Montreal, affiliated with Université de Montréal, Montreal, Quebec H2W 1R7, Canada
| | - Stéphanie Duval
- Laboratory of Biochemical Neuroendocrinology, Clinical Research of Montreal, affiliated with Université de Montréal, Montreal, Quebec H2W 1R7, Canada
| | - Alexandra Evagelidis
- Laboratory of Biochemical Neuroendocrinology, Clinical Research of Montreal, affiliated with Université de Montréal, Montreal, Quebec H2W 1R7, Canada
| | - Johann Guillemot
- CIRI, Centre International de Recherche en Infectiologie, Team Pathogenesis of Legionella, INSERM U1111, Université Claude Bernard Lyon 1, CNRS UMR5308, École Normale Supérieure de Lyon, Université Lyon, Villeurbanne, 69100 France
| | - Vahid Dianati
- Institut de Pharmacologie de Sherbrooke, Department of Surgery/Urology Division, and Faculté de Médecine et des Sciences de la Santé, Sherbrooke, Quebec J 1H 5N4, Canada
| | - Emilia Sikorska
- Faculty of Chemistry, University of Gdańsk, Gdańsk, 80-233 Poland
| | - Peter Schu
- Department of Cellular Biochemistry, University Medical Center, Göttingen, Humboldtallee 23, 37073 Goettingen, Germany
| | - Robert Day
- Institut de Pharmacologie de Sherbrooke, Department of Surgery/Urology Division, and Faculté de Médecine et des Sciences de la Santé, Sherbrooke, Quebec J 1H 5N4, Canada
| | - Nabil G Seidah
- Laboratory of Biochemical Neuroendocrinology, Clinical Research of Montreal, affiliated with Université de Montréal, Montreal, Quebec H2W 1R7, Canada.
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Ben Djoudi Ouadda A, Gauthier MS, Susan-Resiga D, Girard E, Essalmani R, Black M, Marcinkiewicz J, Forget D, Hamelin J, Evagelidis A, Ly K, Day R, Galarneau L, Corbin F, Coulombe B, Çaku A, Tagliabracci VS, Seidah NG. Ser-Phosphorylation of PCSK9 (Proprotein Convertase Subtilisin-Kexin 9) by Fam20C (Family With Sequence Similarity 20, Member C) Kinase Enhances Its Ability to Degrade the LDLR (Low-Density Lipoprotein Receptor). Arterioscler Thromb Vasc Biol 2019; 39:1996-2013. [PMID: 31553664 DOI: 10.1161/atvbaha.119.313247] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
OBJECTIVE PCSK9 (proprotein convertase subtilisin-kexin 9) enhances the degradation of the LDLR (low-density lipoprotein receptor) in endosomes/lysosomes. This study aimed to determine the sites of PCSK9 phosphorylation at Ser-residues and the consequences of such posttranslational modification on the secretion and activity of PCSK9 on the LDLR. Approach and Results: Fam20C (family with sequence similarity 20, member C) phosphorylates serines in secretory proteins containing the motif S-X-E/phospho-Ser, including the cholesterol-regulating PCSK9. In situ hybridization of Fam20C mRNA during development and in adult mice revealed a wide tissue distribution, including liver, but not small intestine. Here, we show that Fam20C phosphorylates PCSK9 at Serines 47, 666, 668, and 688. In hepatocytes, phosphorylation enhances PCSK9 secretion and maximizes its induced degradation of the LDLR via the extracellular and intracellular pathways. Replacing any of the 4 Ser by the phosphomimetic Glu or Asp enhanced PCSK9 activity only when the other sites are phosphorylated, whereas Ala substitutions reduced it, as evidenced by Western blotting, Elisa, and LDLR-immunolabeling. This newly uncovered PCSK9/LDLR regulation mechanism refines our understanding of the implication of global PCSK9 phosphorylation in the modulation of LDL-cholesterol and rationalizes the consequence of natural mutations, for example, S668R and E670G. Finally, the relationship of Ser-phosphorylation to the implication of PCSK9 in regulating LDL-cholesterol in the neurological Fragile X-syndrome disorder was investigated. CONCLUSIONS Ser-phosphorylation of PCSK9 maximizes both its secretion and activity on the LDLR. Mass spectrometric approaches to measure such modifications were developed and applied to quantify the levels of bioactive PCSK9 in human plasma under normal and pathological conditions.
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Affiliation(s)
- Ali Ben Djoudi Ouadda
- From the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM; affiliated to the Université de Montréal), QC, Canada (A.B.D.O., D.S.-R., E.G., R.E., J.M., J.H., A.E., N.G.S.)
| | - Marie-Soleil Gauthier
- Translational Proteomics Research Unit, Clinical Research Institute of Montreal (IRCM, affiliated to the Université de Montréal), QC, Canada (M.-S.G., D.F., B.C.)
| | - Delia Susan-Resiga
- From the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM; affiliated to the Université de Montréal), QC, Canada (A.B.D.O., D.S.-R., E.G., R.E., J.M., J.H., A.E., N.G.S.)
| | - Emmanuelle Girard
- From the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM; affiliated to the Université de Montréal), QC, Canada (A.B.D.O., D.S.-R., E.G., R.E., J.M., J.H., A.E., N.G.S.)
| | - Rachid Essalmani
- From the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM; affiliated to the Université de Montréal), QC, Canada (A.B.D.O., D.S.-R., E.G., R.E., J.M., J.H., A.E., N.G.S.)
| | - Miles Black
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas (M.B., V.S.T.)
| | - Jadwiga Marcinkiewicz
- From the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM; affiliated to the Université de Montréal), QC, Canada (A.B.D.O., D.S.-R., E.G., R.E., J.M., J.H., A.E., N.G.S.)
| | - Diane Forget
- Translational Proteomics Research Unit, Clinical Research Institute of Montreal (IRCM, affiliated to the Université de Montréal), QC, Canada (M.-S.G., D.F., B.C.)
| | - Josée Hamelin
- From the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM; affiliated to the Université de Montréal), QC, Canada (A.B.D.O., D.S.-R., E.G., R.E., J.M., J.H., A.E., N.G.S.)
| | - Alexandra Evagelidis
- From the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM; affiliated to the Université de Montréal), QC, Canada (A.B.D.O., D.S.-R., E.G., R.E., J.M., J.H., A.E., N.G.S.)
| | - Kevin Ly
- Institut de Pharmacologie, Université de Sherbrooke, QC, Canada (K.L., R.D.)
| | - Robert Day
- Institut de Pharmacologie, Université de Sherbrooke, QC, Canada (K.L., R.D.)
| | - Luc Galarneau
- Department of Biochemistry, Université de Sherbrooke, and Centre de Recherche du CHUS, QC, Canada (L.G., F.C., A.Ç.)
| | - Francois Corbin
- Department of Biochemistry, Université de Sherbrooke, and Centre de Recherche du CHUS, QC, Canada (L.G., F.C., A.Ç.)
| | - Benoit Coulombe
- Translational Proteomics Research Unit, Clinical Research Institute of Montreal (IRCM, affiliated to the Université de Montréal), QC, Canada (M.-S.G., D.F., B.C.)
| | - Artuela Çaku
- Department of Biochemistry, Université de Sherbrooke, and Centre de Recherche du CHUS, QC, Canada (L.G., F.C., A.Ç.)
| | - Vincent S Tagliabracci
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas (M.B., V.S.T.)
| | - Nabil G Seidah
- From the Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute (IRCM; affiliated to the Université de Montréal), QC, Canada (A.B.D.O., D.S.-R., E.G., R.E., J.M., J.H., A.E., N.G.S.)
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7
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Huang J, Shan J, Kim D, Liao J, Evagelidis A, Alper SL, Hanrahan JW. Basolateral chloride loading by the anion exchanger type 2: role in fluid secretion by the human airway epithelial cell line Calu-3. J Physiol 2012; 590:5299-316. [PMID: 22802585 DOI: 10.1113/jphysiol.2012.236919] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Anion exchanger type 2 (AE2 or SLC4A2) is an electroneutral Cl(-)/HCO(3)(-) exchanger expressed at the basolateral membrane of many epithelia. It is thought to participate in fluid secretion by airway epithelia. However, the role of AE2 in fluid secretion remains uncertain, due to the lack of specific pharmacological inhibitors, and because it is electrically silent and therefore does not contribute directly to short-circuit current (I(sc)). We have studied the role of AE2 in Cl(-) and fluid secretion by the airway epithelial cell line Calu-3. After confirming expression of its mRNA and protein, a knock-down cell line called AE2-KD was generated by lentivirus-mediated RNA interference in which AE2 mRNA and protein levels were reduced 90%. Suppressing AE2 increased the expression of the cystic fibrosis transmembrane conductance regulator (CFTR) by ∼70% without affecting the levels of NKCC1 (Na(+)-K(+)-2Cl(-) cotransporter) or NBCe1 (Na(+)-nHCO(3)(-) cotransporter). cAMP agonists stimulated fluid secretion by parental Calu-3 and scrambled shRNA cells >6.5-fold. In AE2-KD cells this response was reduced by ∼70%, and the secreted fluid exhibited elevated pH and [HCO(3)(-)] as compared with the control lines. Unstimulated equivalent short-circuit current (I(eq)) was elevated in AE2-KD cells, but the incremental response to forskolin was unaffected. The modest bumetanide-induced reductions in both I(eq) and fluid secretion were more pronounced in AE2-KD cells. Basolateral Cl(-)/HCO(3)(-) exchange measured by basolateral pH-stat in cells with permeabilized apical membranes was abolished in AE2-KD monolayers, and the intracellular alkalinization resulting from basolateral Cl(-) removal was reduced by ∼80% in AE2-KD cells. These results identify AE2 as a major pathway for basolateral Cl(-) loading during cAMP-stimulated secretion of Cl(-) and fluid by Calu-3 cells, and help explain the large bumetanide-insensitive component of fluid secretion reported previously in airway submucosal glands and some other epithelia.
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Affiliation(s)
- Junwei Huang
- Department of Physiology, McGill University, Montr´eal, QC, Canada
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8
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Balghi H, Robert R, Rappaz B, Zhang X, Wohlhuter-Haddad A, Evagelidis A, Luo Y, Goepp J, Ferraro P, Roméo P, Trebak M, Wiseman PW, Thomas DY, Hanrahan JW. Enhanced Ca2+ entry due to Orai1 plasma membrane insertion increases IL-8 secretion by cystic fibrosis airways. FASEB J 2011; 25:4274-91. [PMID: 21873556 DOI: 10.1096/fj.11-187682] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Cystic fibrosis (CF) is caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR). The most common mutation, ΔF508, causes retention of CFTR in the endoplasmic reticulum (ER). Some CF abnormalities can be explained by altered Ca(2+) homeostasis, although it remains unknown how CFTR influences calcium signaling. This study examined the novel hypothesis that store-operated calcium entry (SOCE) through Orai1 is abnormal in CF. The significance of Orai1-mediated SOCE for increased interleukin-8 (IL-8) expression in CF was also investigated. CF and non-CF human airway epithelial cell line and primary cells (obtained at lung transplantation) were used in Ca(2+) imaging, electrophysiology, and fluorescence imaging experiments to explore differences in Orai1 function in CF vs. non-CF cells. Protein expression and localization was assessed by Western blots, cell surface biotinylation, ELISA, and image correlation spectroscopy (ICS). We show here that store-operated Ca(2+) entry (SOCE) is elevated in CF human airway epithelial cells (hAECs; ≈ 1.8- and ≈ 2.5-fold for total Ca(2+)(i) increase and Ca(2+) influx rate, respectively, and ≈ 2-fold increase in the I(CRAC) current) and is caused by increased exocytotic insertion (≈ 2-fold) of Orai1 channels into the plasma membrane, which is normalized by rescue of ΔF508-CFTR trafficking to the cell surface. Augmented SOCE in CF cells is a major factor leading to increased IL-8 secretion (≈ 2-fold). CFTR normally down-regulates the Orai1/stromal interaction molecule 1 (STIM1) complex, and loss of this inhibition due to the absence of CFTR at the plasma membrane helps to explain the potentiated inflammatory response in CF cells.
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Affiliation(s)
- Haouaria Balghi
- Department of Physiology, McGill University, Montréal, Québec, Canada.
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9
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Seavilleklein G, Amer N, Evagelidis A, Chappe F, Irvine T, Hanrahan JW, Chappe V. PKC phosphorylation modulates PKA-dependent binding of the R domain to other domains of CFTR. Am J Physiol Cell Physiol 2008; 295:C1366-75. [PMID: 18799655 DOI: 10.1152/ajpcell.00034.2008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Activity of the CFTR channel is regulated by phosphorylation of its regulatory domain (RD). In a previous study, we developed a bicistronic construct called DeltaR-Split CFTR, which encodes the front and back halves of CFTR as separate polypeptides without the RD. These fragments assemble to form a constitutively active CFTR channel. Coexpression of the third fragment corresponding to the missing RD restores regulation by PKA, and this is associated with dramatically enhanced binding of the phosphorylated RD. In the present study, we examined the effect of PKC phosphorylation on this PKA-induced interaction. We report here that PKC alone enhanced association of the RD with DeltaR-Split CFTR and that binding was further enhanced when the RD was phosphorylated by both kinases. Mutation of all seven PKC consensus sequences on the RD (7CA-RD) did not affect its association under basal (unphosphorylated) conditions but abolished phosphorylation-induced binding by both kinases. Iodide efflux responses provided further support for the essential role of RD binding in channel regulation. The basal activity of DeltaR-Split/7CA-RD channels was similar to that of DeltaR-Split/wild type (WT)-RD channels, whereas cAMP-stimulated iodide efflux was greatly diminished by removal of the PKC sites, indicating that 7CA-RD binding maintains channels in an inactive state that is unresponsive to PKA. These results suggest a novel mechanism for CFTR regulation in which PKC modulates PKA-induced domain-domain interactions.
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Affiliation(s)
- Gage Seavilleklein
- Dept. of Physiology and Biophysics, 5850 College St., Halifax, NS, Canada B3H 1X5
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10
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Chappe V, Irvine T, Liao J, Evagelidis A, Hanrahan JW. Phosphorylation of CFTR by PKA promotes binding of the regulatory domain. EMBO J 2005; 24:2730-40. [PMID: 16001079 PMCID: PMC1182242 DOI: 10.1038/sj.emboj.7600747] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2004] [Accepted: 06/21/2005] [Indexed: 11/08/2022] Open
Abstract
The unphosphorylated regulatory (R) domain of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) is often viewed as an inhibitor that is released by phosphorylation. To test this notion, we studied domain interactions using CFTR channels assembled from three polypeptides. Nucleotides encoding the R domain (aa 635-836) were replaced with an internal ribosome entry sequence so that amino- and carboxyl-terminal half-molecules would be translated from the same mRNA transcript. Although only core glycosylation was detected on SplitDeltaR, biotinylation, immunostaining, and functional studies clearly demonstrated its trafficking to the plasma membrane. SplitDeltaR generated a constitutive halide permeability, which became responsive to cAMP when the missing R domain was coexpressed. Each half-molecule was co-precipitated by antibody against the other half. Contrary to expectations, GST-R domain was pulled down only if prephosphorylated by protein kinase A, and coexpressed R domain was precipitated with SplitDeltaR much more efficiently when cells were stimulated with cAMP. These results indicate that phosphorylation regulates CFTR by promoting association of the R domain with other domains rather than by causing its dissociation from an inhibitory site.
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Affiliation(s)
- Valerie Chappe
- Department of Physiology, McGill University, Montréal, QC, Canada
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Thomas Irvine
- Department of Physiology, McGill University, Montréal, QC, Canada
| | - Jie Liao
- Department of Physiology, McGill University, Montréal, QC, Canada
| | | | - John W Hanrahan
- Department of Physiology, McGill University, Montréal, QC, Canada
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11
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Chappe V, Hinkson DA, Howell LD, Evagelidis A, Liao J, Chang XB, Riordan JR, Hanrahan JW. Stimulatory and inhibitory protein kinase C consensus sequences regulate the cystic fibrosis transmembrane conductance regulator. Proc Natl Acad Sci U S A 2004; 101:390-5. [PMID: 14695900 PMCID: PMC314195 DOI: 10.1073/pnas.0303411101] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2003] [Accepted: 10/22/2003] [Indexed: 11/18/2022] Open
Abstract
Protein kinase C (PKC) phosphorylation stimulates the cystic fibrosis transmembrane conductance regulator (CFTR) channel and enhances its activation by protein kinase A (PKA) through mechanisms that remain poorly understood. We have examined the effects of mutating consensus sequences for PKC phosphorylation and report here evidence for both stimulatory and inhibitory sites. Sequences were mutated in subsets and the mutants characterized by patch clamping. Activation of a 4CA mutant (S707A/S790A/T791A/S809A) by PKA was similar to that of wild-type CFTR and was enhanced by PKC, whereas responses of 3CA (T582A/T604A/S641A) and 2CA (T682A/S686A) channels to PKA were both drastically reduced (>90%). When each mutation in the 3CA and 2CA constructs was studied individually in a wild-type background, T582, T604, and S686 were found to be essential for PKA activation. Responses were restored when these three residues were reintroduced simultaneously into a 9CA mutant lacking all nine PKC consensus sequences (R6CA revertant); however, PKC phosphorylation was not required for this rescue. Nevertheless, two of the sites (T604 and S686) were phosphorylated in vitro, and PKC alone partially activated wild-type CFTR, the 4CA mutant, and the point mutants T582A and T604A, but not S686A channels, indicating that PKC does act at S686. The region encompassing S641 and T682 is inhibitory, because S641A enhanced activation by PKA, and T682A channels had 4-fold larger responses to PKC compared to wild-type channels. These results identify functionally important PKC consensus sequences on CFTR and will facilitate studies of its convergent regulation by PKC and PKA.
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Affiliation(s)
- Valerie Chappe
- Department of Physiology, McGill University, Montréal, QC, Canada H3G 1Y6.
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12
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Affiliation(s)
- Tang Zhu
- Department of Physiology, McGill University, Montréal, Québec, Canada
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13
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Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels are regulated tightly by protein kinases and phosphatases. The regulatory domain of CFTR has about 20 potential sites for phosphorylation by protein kinases A (PKA) and C (PKC). The reason for this large number of sites is not known, however their conservation from fish to humans implies that they play important roles in vivo. PKA is an important activator, and its stimulation of CFTR is enhanced by PKC via mechanisms which are not fully understood. The physiological stimuli of CFTR are not known for some epithelia, and it appears likely that other serine/threonine and even tyrosine kinases also regulate CFTR in particular tissues. Phosphatases that deactivate CFTR have yet to be identified definitively at the molecular level, however CFTR is regulated by a membrane-bound form of protein phosphatase-2C (PP2C) in several cell types. Patch-clamp studies of channel rundown, co-immunoprecipitation, chemical cross-linking studies, and pull-down assays all indicate that CFTR and PP2C are closely associated within a stable regulatory complex. Understanding the regulation of CFTR by PP2C is a priority due to its potential as a target for pharmacotherapies in the treatment of cystic fibrosis.
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Affiliation(s)
- D Dahan
- Department of Physiology, McGill University, Montréal, Québec, Canada
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14
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Gupta J, Evagelidis A, Hanrahan JW, Linsdell P. Asymmetric structure of the cystic fibrosis transmembrane conductance regulator chloride channel pore suggested by mutagenesis of the twelfth transmembrane region. Biochemistry 2001; 40:6620-7. [PMID: 11380256 DOI: 10.1021/bi002819v] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel contains 12 membrane-spanning regions which are presumed to form the transmembrane pore. Although a number of findings have suggested that the sixth transmembrane region plays a key role in forming the pore and determining its functional properties, the role of other transmembrane regions is currently not well established. Here we assess the functional importance of the twelfth transmembrane region, which occupies a homologous position in the carboxy terminal half of the CFTR molecule to that of the sixth transmembrane region in the amino terminal half. Five residues in potentially important regions of the twelfth transmembrane region were mutated individually to alanines, and the function of the mutant channels was examined using patch clamp recording following expression in mammalian cell lines. Three of the five mutations significantly weakened block of unitary Cl(-) currents by SCN(-), implying a partial disruption of anion binding within the pore. Two of these mutations also caused a large reduction in the steady-state channel mean open probability, suggesting a role for the twelfth transmembrane region in channel gating. However, in direct contrast to analogous mutations in the sixth transmembrane region, all mutants studied here had negligible effects on the anion selectivity and unitary Cl(-) conductance of the channel. The relatively minor effects of these five mutations on channel permeation properties suggests that, despite their symmetrical positions within the CFTR protein, the sixth and twelfth transmembrane regions make highly asymmetric contributions to the functional properties of the pore.
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Affiliation(s)
- J Gupta
- Department of Physiology & Biophysics, Dalhousie University, Halifax, Nova Scotia, B3H 4H7, Canada
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15
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Luo J, Zhu T, Evagelidis A, Pato MD, Hanrahan JW. Role of protein phosphatases in the activation of CFTR (ABCC7) by genistein and bromotetramisole. Am J Physiol Cell Physiol 2000; 279:C108-19. [PMID: 10898722 DOI: 10.1152/ajpcell.2000.279.1.c108] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Genistein and bromotetramisole (Br-t) strongly activate cystic fibrosis transmembrane conductance regulator (CFTR; ABCC7) chloride channels on Chinese hamster ovary cells and human airway epithelial cells. We have examined the possible role of phosphatases in stimulation by these drugs using patch-clamp and biochemical methods. Genistein inhibited the spontaneous rundown of channel activity that occurs after membrane patches are excised from cAMP-stimulated cells but had no effect on purified protein phosphatase type 1 (PP1), PP2A, PP2B, PP2C, or endogenous phosphatases when assayed as [(32)P]PO(4) release from prelabeled casein, recombinant GST-R domain fusion protein, or immunoprecipitated full-length CFTR. Br-t also slowed rundown of CFTR channels, but, in marked contrast to genistein, it did inhibit all four protein phosphatases tested. Half-maximal inhibition of PP2A and PP2C was observed with 0.5 and 1.5 mM Br-t, respectively. Protein phosphatases were also sensitive to (+)-p-Br-t, a stereoisomer of Br-t that does not inhibit alkaline phosphatases. Br-t appeared to act exclusively through phosphatases since it did not affect CFTR channels in patches that had low apparent endogenous phosphatase activity (i.e., those lacking spontaneous rundown). We conclude that genistein and Br-t act through different mechanisms. Genistein stimulates CFTR without inhibiting phosphatases, whereas Br-t acts by inhibiting a membrane-associated protein phosphatase (probably PP2C) that presumably allows basal phosphorylation to accumulate.
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Affiliation(s)
- J Luo
- Department of Physiology, McGill University, Montréal, Québec H3G 1Y6, Canada S7N 0W0
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16
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Linsdell P, Evagelidis A, Hanrahan JW. Molecular determinants of anion selectivity in the cystic fibrosis transmembrane conductance regulator chloride channel pore. Biophys J 2000; 78:2973-82. [PMID: 10827976 PMCID: PMC1300881 DOI: 10.1016/s0006-3495(00)76836-6] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Ionic selectivity in many cation channels is achieved over a short region of the pore known as the selectivity filter, the molecular determinants of which have been identified in Ca(2+), Na(+), and K(+) channels. However, a filter controlling selectivity among different anions has not previously been identified in any Cl(-) channel. In fact, because Cl(-) channels are only weakly selective among small anions, and because their selectivity has proved so resistant to site-directed mutagenesis, the very existence of a discrete anion selectivity filter has been called into question. Here we show that mutation of a putative pore-lining phenylalanine residue, F337, in the sixth membrane-spanning region of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel, dramatically alters the relative permeabilities of different anions in the channel. Specifically, mutations that reduce the size of the amino acid side chain present at this position virtually abolish the relationship between anion permeability and hydration energy, a relationship that characterizes the anion selectivity not only of wild-type CFTR, but of most classes of Cl(-) channels. These results suggest that the pore of CFTR may indeed contain a specialized region, analogous to the selectivity filter of cation channels, at which discrimination between different permeant anions takes place. Because F337 is adjacent to another amino acid residue, T338, which also affects anion selectivity in CFTR, we suggest that selectivity is predominantly determined over a physically discrete region of the pore located near these important residues.
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Affiliation(s)
- P Linsdell
- Department of Physiology, McGill University, Montréal, Québec H3G 1Y6, Canada.
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17
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Zhu T, Dahan D, Evagelidis A, Zheng S, Luo J, Hanrahan JW. Association of cystic fibrosis transmembrane conductance regulator and protein phosphatase 2C. J Biol Chem 1999; 274:29102-7. [PMID: 10506164 DOI: 10.1074/jbc.274.41.29102] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels are rapidly deactivated by a membrane-bound phosphatase activity. The efficiency of this regulation suggests CFTR and protein phosphatases may be associated within a regulatory complex. In this paper we test that possibility using co-immunoprecipitation and cross-linking experiments. A monoclonal anti-CFTR antibody co-precipitated type 2C protein phosphatase (PP2C) from baby hamster kidney cells stably expressing CFTR but did not co-precipitate PP1, PP2A, or PP2B. Conversely, a polyclonal anti-PP2C antibody co-precipitated CFTR from baby hamster kidney membrane extracts. Exposing baby hamster kidney cell lysates to dithiobis (sulfosuccinimidyl propionate) caused the cross-linking of histidine-tagged CFTR (CFTR(His10)) and PP2C into high molecular weight complexes that were isolated by chromatography on Ni(2+)-nitrilotriacetic acid-agarose. Chemical cross-linking was specific for PP2C, because PP1, PP2A, and PP2B did not co-purify with CFTR(His10) after dithiobis (sulfosuccinimidyl propionate) exposure. These results suggest CFTR and PP2C exist in a stable complex that facilitates regulation of the channel.
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Affiliation(s)
- T Zhu
- Department of Physiology, McGill University, Montréal, Québec H3G 1Y6, Canada
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