ABSTRACT
Inborn defects in nucleotide excision DNA repair (NER) can paradoxically result in elevated cancer incidence (xeroderma pigmentosum [XP]) or segmental progeria without cancer predisposition (Cockayne syndrome [CS] and trichothiodystrophy [TTD]). We report generation of a knockin mouse model for the combined disorder XPCS with a G602D-encoding mutation in the Xpd helicase gene. XPCS mice are the most skin cancer-prone NER model to date, and we postulate an unusual NER dysfunction that is likely responsible for this susceptibility. XPCS mice also displayed symptoms of segmental progeria, including cachexia and progressive loss of germinal epithelium. Like CS fibroblasts, XPCS and TTD fibroblasts from human and mouse showed evidence of defective repair of oxidative DNA lesions that may underlie these segmental progeroid symptoms.
Subject(s)
Cockayne Syndrome/pathology , Progeria/pathology , Skin Neoplasms/pathology , Xeroderma Pigmentosum Group D Protein/metabolism , Xeroderma Pigmentosum/pathology , Animals , Carcinoma, Squamous Cell/etiology , Carcinoma, Squamous Cell/metabolism , Carcinoma, Squamous Cell/pathology , Cell Line, Transformed , Cockayne Syndrome/complications , Cockayne Syndrome/metabolism , DNA Repair , Disease Models, Animal , Disease Susceptibility , Female , Fibroblasts/metabolism , Fibroblasts/pathology , Humans , Male , Mice , Mice, Mutant Strains , Mutation , Papilloma/etiology , Papilloma/metabolism , Papilloma/pathology , Phenotype , Progeria/complications , Progeria/metabolism , Skin Neoplasms/etiology , Skin Neoplasms/metabolism , Xeroderma Pigmentosum/complications , Xeroderma Pigmentosum/metabolism , Xeroderma Pigmentosum Group D Protein/geneticsABSTRACT
One of the factors postulated to drive the aging process is the accumulation of DNA damage. Here, we provide strong support for this hypothesis by describing studies of mice with a mutation in XPD, a gene encoding a DNA helicase that functions in both repair and transcription and that is mutated in the human disorder trichothiodystrophy (TTD). TTD mice were found to exhibit many symptoms of premature aging, including osteoporosis and kyphosis, osteosclerosis, early greying, cachexia, infertility, and reduced life-span. TTD mice carrying an additional mutation in XPA, which enhances the DNA repair defect, showed a greatly accelerated aging phenotype, which correlated with an increased cellular sensitivity to oxidative DNA damage. We hypothesize that aging in TTD mice is caused by unrepaired DNA damage that compromises transcription, leading to functional inactivation of critical genes and enhanced apoptosis.
Subject(s)
Aging, Premature/etiology , Aging , DNA Damage , DNA Helicases/physiology , DNA Repair , Proteins/physiology , Transcription Factors , Animals , Apoptosis , Bone Density , Cachexia/etiology , Crosses, Genetic , DNA Helicases/genetics , DNA-Binding Proteins/genetics , DNA-Binding Proteins/physiology , Female , Fertility , Gene Targeting , Growth Disorders/etiology , Growth Disorders/genetics , Hair Diseases/genetics , Kyphosis/etiology , Kyphosis/genetics , Kyphosis/pathology , Male , Mice , Mutation , Oxidative Stress , Phenotype , Point Mutation , Proteins/genetics , RNA-Binding Proteins/genetics , RNA-Binding Proteins/physiology , Transcription, Genetic , Xeroderma Pigmentosum Group A Protein , Xeroderma Pigmentosum Group D ProteinABSTRACT
mHR23B encodes one of the two mammalian homologs of Saccharomyces cerevisiae RAD23, a ubiquitin-like fusion protein involved in nucleotide excision repair (NER). Part of mHR23B is complexed with the XPC protein, and this heterodimer functions as the main damage detector and initiator of global genome NER. While XPC defects exist in humans and mice, mutations for mHR23A and mHR23B are not known. Here, we present a mouse model for mHR23B. Unlike XPC-deficient cells, mHR23B(-/-) mouse embryonic fibroblasts are not UV sensitive and retain the repair characteristics of wild-type cells. In agreement with the results of in vitro repair studies, this indicates that mHR23A can functionally replace mHR23B in NER. Unexpectedly, mHR23B(-/-) mice show impaired embryonic development and a high rate (90%) of intrauterine or neonatal death. Surviving animals display a variety of abnormalities, including retarded growth, facial dysmorphology, and male sterility. Such abnormalities are not observed in XPC and other NER-deficient mouse mutants and point to a separate function of mHR23B in development. This function may involve regulation of protein stability via the ubiquitin/proteasome pathway and is not or only in part compensated for by mHR23A.
