title: Homozygous mutation of MTPAP causes cellular radiosensitivity and persistent DNA double-strand breaks.
abstract: The study of rare human syndromes characterized by radiosensitivity has been instrumental in identifying novel proteins and pathways involved in DNA damage responses to ionizing radiation. In the present study, a mutation in mitochondrial poly-A-polymerase (MTPAP), not previously recognized for its role in the DNA damage response, was identified by exome sequencing and subsequently associated with cellular radiosensitivity. Cell lines derived from two patients with the homozygous MTPAP missense mutation were radiosensitive, and this radiosensitivity could be abrogated by transfection of wild-type mtPAP cDNA into mtPAP-deficient cell lines. Further analysis of the cellular phenotype revealed delayed DNA repair, increased levels of DNA double-strand breaks, increased reactive oxygen species (ROS), and increased cell death after irradiation (IR). Pre-IR treatment of cells with the potent anti-oxidants, α-lipoic acid and n-acetylcysteine, was sufficient to abrogate the DNA repair and clonogenic survival defects. Our results firmly establish that mutation of the MTPAP gene results in a cellular phenotype of increased DNA damage, reduced repair kinetics, increased cell death by apoptosis, and reduced clonogenic survival after exposure to ionizing radiation, suggesting a pathogenesis that involves the disruption of ROS homeostasis.
authors.affiliation: 1] UCLA Department of Pathology and Laboratory Medicine, MacDonald Research Laboratories, Los Angeles, CA, USA [2] UCLA Biomedical Physics Interdepartmental Graduate Program, Los Angeles, CA, USA.
authors.forename: N T
authors.initials: NT
authors.lastname: Martin
authors.affiliation: UCLA Department of Pathology and Laboratory Medicine, MacDonald Research Laboratories, Los Angeles, CA, USA.
authors.forename: K
authors.initials: K
authors.lastname: Nakamura
authors.affiliation: Department of Public Health Sciences, Center for Public Health Genomics, University of Virginia, Charlottesville, VA, USA.
authors.forename: U
authors.initials: U
authors.lastname: Paila
authors.affiliation: UCLA Department of Pathology and Laboratory Medicine, MacDonald Research Laboratories, Los Angeles, CA, USA.
authors.forename: J
authors.initials: J
authors.lastname: Woo
authors.affiliation: UCLA Department of Pathology and Laboratory Medicine, MacDonald Research Laboratories, Los Angeles, CA, USA.
authors.forename: C
authors.initials: C
authors.lastname: Brown
authors.affiliation: Genetics Institute, University of Florida, Gainesville, FL, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Wright
authors.affiliation: Genetics Institute, University of Florida, Gainesville, FL, USA.
authors.forename: S N
authors.initials: SN
authors.lastname: Teraoka
authors.affiliation: UCLA Department of Pathology and Laboratory Medicine, MacDonald Research Laboratories, Los Angeles, CA, USA.
authors.forename: S
authors.initials: S
authors.lastname: Haghayegh
authors.affiliation: UCLA Department of Pediatrics, Los Angeles, CA, USA.
authors.forename: D
authors.initials: D
authors.lastname: McCurdy
authors.affiliation: Carle Physician Group, Urbana, IL, USA.
authors.forename: M
authors.initials: M
authors.lastname: Schneider
authors.affiliation: UCLA Department of Pathology and Laboratory Medicine, MacDonald Research Laboratories, Los Angeles, CA, USA.
authors.forename: H
authors.initials: H
authors.lastname: Hu
authors.affiliation: Department of Public Health Sciences, Center for Public Health Genomics, University of Virginia, Charlottesville, VA, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Quinlan
authors.affiliation: 1] UCLA Department of Pathology and Laboratory Medicine, MacDonald Research Laboratories, Los Angeles, CA, USA [2] UCLA Biomedical Physics Interdepartmental Graduate Program, Los Angeles, CA, USA [3] UCLA Department of Human Genetics, Los Angeles, CA, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Gatti
authors.affiliation: 1] Genetics Institute, University of Florida, Gainesville, FL, USA [2] Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, USA.
authors.forename: P
authors.initials: P
authors.lastname: Concannon
mesh_terms: D061365:Amish / Q000235:genetics; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000528:radiation effects; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D019610:Cytoprotection; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects*; D012321:DNA-Directed RNA Polymerases / Q000235:genetics* / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D005838:Genotype; D006720:Homozygote; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes / Q000187:drug effects / Q000201:enzymology / Q000473:pathology / Q000528:radiation effects*; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D020125:Mutation, Missense; D010641:Phenotype; D017382:Reactive Oxygen Species / Q000378:metabolism; D014162:Transfection
chemical_list: D000975:Antioxidants; D024101:Mitochondrial Proteins; D017382:Reactive Oxygen Species; D012321:DNA-Directed RNA Polymerases; C555258:MTPAP protein, human