title: Mislocalization of XPF-ERCC1 nuclease contributes to reduced DNA repair in XP-F patients.
abstract: Xeroderma pigmentosum (XP) is caused by defects in the nucleotide excision repair (NER) pathway. NER removes helix-distorting DNA lesions, such as UV-induced photodimers, from the genome. Patients suffering from XP exhibit exquisite sun sensitivity, high incidence of skin cancer, and in some cases neurodegeneration. The severity of XP varies tremendously depending upon which NER gene is mutated and how severely the mutation affects DNA repair capacity. XPF-ERCC1 is a structure-specific endonuclease essential for incising the damaged strand of DNA in NER. Missense mutations in XPF can result not only in XP, but also XPF-ERCC1 (XFE) progeroid syndrome, a disease of accelerated aging. In an attempt to determine how mutations in XPF can lead to such diverse symptoms, the effects of a progeria-causing mutation (XPF(R153P)) were compared to an XP-causing mutation (XPF(R799W)) in vitro and in vivo. Recombinant XPF harboring either mutation was purified in a complex with ERCC1 and tested for its ability to incise a stem-loop structure in vitro. Both mutant complexes nicked the substrate indicating that neither mutation obviates catalytic activity of the nuclease. Surprisingly, differential immunostaining and fractionation of cells from an XFE progeroid patient revealed that XPF-ERCC1 is abundant in the cytoplasm. This was confirmed by fluorescent detection of XPF(R153P)-YFP expressed in Xpf mutant cells. In addition, microinjection of XPF(R153P)-ERCC1 into the nucleus of XPF-deficient human cells restored nucleotide excision repair of UV-induced DNA damage. Intriguingly, in all XPF mutant cell lines examined, XPF-ERCC1 was detected in the cytoplasm of a fraction of cells. This demonstrates that at least part of the DNA repair defect and symptoms associated with mutations in XPF are due to mislocalization of XPF-ERCC1 into the cytoplasm of cells, likely due to protein misfolding. Analysis of these patient cells therefore reveals a novel mechanism to potentially regulate a cell's capacity for DNA repair: by manipulating nuclear localization of XPF-ERCC1.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Anwaar
authors.initials: A
authors.lastname: Ahmad
authors.forename: Jacqueline H
authors.initials: JH
authors.lastname: Enzlin
authors.forename: Nikhil R
authors.initials: NR
authors.lastname: Bhagwat
authors.forename: Nils
authors.initials: N
authors.lastname: Wijgers
authors.forename: Anja
authors.initials: A
authors.lastname: Raams
authors.forename: Esther
authors.initials: E
authors.lastname: Appledoorn
authors.forename: Arjan F
authors.initials: AF
authors.lastname: Theil
authors.forename: Jan H
authors.initials: JH
authors.lastname: J Hoeijmakers
authors.forename: Wim
authors.initials: W
authors.lastname: Vermeulen
authors.forename: Nicolaas G
authors.initials: NG
authors.lastname: J Jaspers
authors.forename: Orlando D
authors.initials: OD
authors.lastname: Schärer
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Niedernhofer
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D016466:CHO Cells; D002470:Cell Survival; D006224:Cricetinae; D003412:Cricetulus; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004720:Endonucleases / Q000235:genetics / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006801:Humans; D009154:Mutation / Q000235:genetics; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014983:Xeroderma Pigmentosum / Q000201:enzymology* / Q000235:genetics / Q000473:pathology
chemical_list: D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; C095888:xeroderma pigmentosum group F protein; C071447:ERCC1 protein, human; D004720:Endonucleases