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Dröge C, Bonus M, Baumann U, Klindt C, Lainka E, Kathemann S, Brinkert F, Grabhorn E, Pfister ED, Wenning D, Fichtner A, Gotthardt DN, Weiss KH, McKiernan P, Puri RD, Verma IC, Kluge S, Gohlke H, Schmitt L, Kubitz R, Häussinger D, Keitel V. Sequencing of FIC1, BSEP and MDR3 in a large cohort of patients with cholestasis revealed a high number of different genetic variants. J Hepatol 2017; 67:1253-1264. [PMID: 28733223 DOI: 10.1016/j.jhep.2017.07.004] [Citation(s) in RCA: 83] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 06/16/2017] [Accepted: 07/07/2017] [Indexed: 12/19/2022]
Abstract
BACKGROUND & AIMS The bile salt export pump (BSEP, ABCB11), multidrug resistance protein 3 (MDR3, ABCB4) and the ATPase familial intrahepatic cholestasis 1 (FIC1, ATP8B1) mediate bile formation. This study aimed to determine the contribution of mutations and common variants in the FIC1, BSEP and MDR3 genes to cholestatic disorders of differing disease onset and severity. METHODS Coding exons with flanking intron regions of ATP8B1, ABCB11, and ABCB4 were sequenced in cholestatic patients with assumed genetic cause. The effects of new variants were evaluated by bioinformatic tools and 3D protein modeling. RESULTS In 427 patients with suspected inherited cholestasis, 149 patients carried at least one disease-causing mutation in FIC1, BSEP or MDR3, respectively. Overall, 154 different mutations were identified, of which 25 were novel. All 13 novel missense mutations were disease-causing according to bioinformatics analyses and homology modeling. Eighty-two percent of patients with at least one disease-causing mutation in either of the three genes were children. One or more common polymorphism(s) were found in FIC1 in 35.3%, BSEP in 64.3% and MDR3 in 72.6% of patients without disease-causing mutations in the respective gene. Minor allele frequencies of common polymorphisms in BSEP and MDR3 varied in our cohort compared to the general population, as described by gnomAD. However, differences in ethnic background may contribute to this effect. CONCLUSIONS In a large cohort of patients, 154 different variants were detected in FIC1, BSEP, and MDR3, 25 of which were novel. In our cohort, frequencies for risk alleles of BSEP (p.V444A) and MDR3 (p.I237I) polymorphisms were significantly overrepresented in patients without disease-causing mutation in the respective gene, indicating that these common variants can contribute to a cholestatic phenotype. LAY SUMMARY FIC1, BSEP, and MDR3 represent hepatobiliary transport proteins essential for bile formation. Genetic variants in these transporters underlie a broad spectrum of cholestatic liver diseases. To confirm a genetic contribution to the patients' phenotypes, gene sequencing of these three major cholestasis-related genes was performed in 427 patients and revealed 154 different variants of which 25 have not been previously reported in a database. In patients without a disease-causing mutation, common genetic variants were detected in a high number of cases, indicating that these common variants may contribute to cholestasis development.
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Affiliation(s)
- Carola Dröge
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, Germany
| | - Michele Bonus
- Institute for Pharmaceutical and Medicinal Chemistry, Heinrich Heine University Düsseldorf, Germany
| | - Ulrich Baumann
- Pediatric Gastroenterology and Hepatology, Department for Pediatric Kidney, Liver and Metabolic Diseases, Hannover Medical School, Germany
| | - Caroline Klindt
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, Germany
| | - Elke Lainka
- Department for Pediatric Nephrology, Gastroenterology, Endocrinology and Transplant Medicine, Clinic for Pediatrics II, University Children's Hospital Essen, University Duisburg-Essen, Germany
| | - Simone Kathemann
- Department for Pediatric Nephrology, Gastroenterology, Endocrinology and Transplant Medicine, Clinic for Pediatrics II, University Children's Hospital Essen, University Duisburg-Essen, Germany
| | - Florian Brinkert
- Pediatric Gastroenterology and Hepatology, University Children's Hospital, University Medical Center Hamburg-Eppendorf, Germany
| | - Enke Grabhorn
- Pediatric Gastroenterology and Hepatology, University Children's Hospital, University Medical Center Hamburg-Eppendorf, Germany
| | - Eva-Doreen Pfister
- Pediatric Gastroenterology and Hepatology, Department for Pediatric Kidney, Liver and Metabolic Diseases, Hannover Medical School, Germany
| | - Daniel Wenning
- Department of General Pediatrics, Heidelberg University Hospital, Germany
| | - Alexander Fichtner
- Department of General Pediatrics, Heidelberg University Hospital, Germany
| | - Daniel N Gotthardt
- Department of Internal Medicine IV, University Hospital Heidelberg, Germany
| | - Karl Heinz Weiss
- Department of Internal Medicine IV, University Hospital Heidelberg, Germany
| | - Patrick McKiernan
- Pittsburgh Liver Research Center, University of Pittsburgh and Children's Hospital of Pittsburgh of UPMC, Pittsburgh, USA
| | - Ratna Dua Puri
- Institute of Medical Genetics & Genomics, Sir Ganga Ram Hospital, New Delhi, India
| | - I C Verma
- Institute of Medical Genetics & Genomics, Sir Ganga Ram Hospital, New Delhi, India
| | - Stefanie Kluge
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, Germany
| | - Holger Gohlke
- Institute for Pharmaceutical and Medicinal Chemistry, Heinrich Heine University Düsseldorf, Germany
| | - Lutz Schmitt
- Institute of Biochemistry, Heinrich Heine University Düsseldorf, Germany
| | - Ralf Kubitz
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, Germany
| | - Dieter Häussinger
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, Germany.
| | - Verena Keitel
- Department of Gastroenterology, Hepatology and Infectious Diseases, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, Germany.
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The cystic fibrosis V232D mutation inhibits CFTR maturation by disrupting a hydrophobic pocket rather than formation of aberrant interhelical hydrogen bonds. Biochem Pharmacol 2014; 88:46-57. [PMID: 24412276 DOI: 10.1016/j.bcp.2013.12.027] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Revised: 12/30/2013] [Accepted: 12/31/2013] [Indexed: 11/21/2022]
Abstract
Processing mutations that inhibit folding and trafficking of CFTR are the main cause of cystic fibrosis. Repair of CFTR mutants requires an understanding of the mechanisms of misfolding caused by processing mutations. Previous studies on helix-loop-helix fragments of the V232D processing mutation suggested that its mechanism was to lock transmembrane (TM) segments 3 and 4 together by a non-native hydrogen bond (Asp232(TM4)/Gln207(TM3)). Here, we performed mutational analysis to test for Asp232/Gln207 interactions in full-length CFTR. The rationale was that a V232N mutation should mimic V232D and a V232D/Q207A mutant should mature if the processing defect was caused by hydrogen bonds. We report that only Val232 mutations to charged amino acids severely blocked CFTR maturation. The V232N mutation did not mimic V232D as V232N showed 40% maturation compared to 2% for V232D. Mutation of Val232 to large nonpolar residues (Leu, Phe) had little effect. The Q207L mutation did not rescue V232D because Q207L showed about 50% maturation in the presence of corrector VX-809 while V232D/Q207A could no longer be rescued. These results suggest that V232D inhibits maturation by disrupting a hydrophobic pocket between TM segments rather than forming a non-native hydrogen bond. Disulfide cross-linking analysis of cysteines W356C(TM6) and W1145C(TM12) suggest that the V232D mutation inhibits maturation by trapping CFTR as a partially folded intermediate. Since correctors can efficiently rescue V232D CFTR, the results suggest that hydrophilic processing mutations facing a hydrophobic pocket are good candidates for rescue with pharmacological chaperones.
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Loo TW, Clarke DM. Drug rescue distinguishes between different structural models of human P-glycoprotein. Biochemistry 2013; 52:7167-9. [PMID: 24083983 PMCID: PMC3798097 DOI: 10.1021/bi401269m] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
There
is no high-resolution crystal structure of the human P-glycoprotein
(P-gp) drug pump. Homology models of human P-gp based on the crystal
structures of mouse or Caenorhabditis elegans P-gps
show large differences in the orientation of transmembrane segment
5 (TM5). TM5 is one of the most important transmembrane segments involved
in drug–substrate interactions. Drug rescue of P-gp processing
mutants containing an arginine at each position in TM5 was used to
identify positions facing the lipid or internal aqueous chamber. Only
the model based on the C. elegans P-gp structure
was compatible with the drug rescue results.
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Affiliation(s)
- Tip W Loo
- Departments of Medicine and Biochemistry, University of Toronto , Toronto, Ontario M5S 1A8, Canada
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Loo TW, Clarke DM. A salt bridge in intracellular loop 2 is essential for folding of human p-glycoprotein. Biochemistry 2013; 52:3194-6. [PMID: 23634976 PMCID: PMC3656768 DOI: 10.1021/bi400425k] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
There is no high-resolution structure
of the human P-glycoprotein
(P-gp, ABCB1) drug pump. Homology models based on the crystal structures
of mouse and Caenorhabditis elegans P-gps show extensive
contacts between intracellular loop 2 (ICL2, in the first transmembrane
domain) and the second nucleotide-binding domain. Human P-gp modeled
on these P-gp structures yields different ICL2 structures. Only the
model based on the C. elegans P-gp structure predicts
the presence of a salt bridge. We show that the Glu256–Arg276
salt bridge was critical for P-gp folding.
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Affiliation(s)
- Tip W Loo
- Departments of Medicine and Biochemistry, University of Toronto , Toronto, Ontario M5S 1A8, Canada
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Abstract
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Deletion of Phe508 from the first nucleotide-binding domain of the CFTR chloride channel causes cystic fibrosis because it inhibits protein folding. Indirect approaches such as incubation at low temperatures can partially rescue ΔF508 CFTR, but the protein is unstable at the cell surface. Here, we show that direct binding of benzbromarone to the transmembrane domains promoted maturation and stabilized ΔF508 CFTR because its half-life at the cell surface was ∼10-fold longer than that for low-temperature rescue. Therefore, a search for small molecules that can rescue and stabilize ΔF508 CFTR could lead to the development of an effective therapy for cystic fibrosis.
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Affiliation(s)
- Tip W Loo
- Departments of Medicine and Biochemistry, University of Toronto, Toronto, Ontario, Canada
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