title: A defect in DNA double strand break processing in cells from unaffected parents of retinoblastoma patients and other apparently normal humans.
abstract: Cells from unaffected parents of retinoblastoma (RB) patients were previously shown to be hypersensitive to radiation induced G(1) arrest and cell killing [1]. The hypersensitivity was similar to that reported for cells from ATM heterozygotes. The latter was consistent with a mild DNA DSB rejoining defect which we demonstrated using a gamma-H2AX focus assay after low dose-rate (LDR) irradiation of non-cycling G(0) cells [2,3]. Since neither parent carried the mutant RB allele of the RB heterozygous probands, these results suggested the possibility of an enhanced germline mutation rate, perhaps resulting from some mild defect in genome maintenance. We therefore examined levels of gamma-H2AX foci for cells from these RB parents in this G(0) LDR assay, which reflects the non-homologous end joining (NHEJ) capacity of cells and in a G(2)/M assay, which reflects additional contributions from other G(2)-related damage processing systems. For several of the cell strains parallel radiosensitivity comparisons were made for cell killing and for G(2) chromosomal radiosensitivities. G(0) cells from the RB parents were clearly hypersensitive both in the LDR gamma-H2AX assay, and for cell killing. In addition, cultured fibroblasts from 6 of 15 apparently normal individuals in this study (and one of six in a previous study) were also hypersensitive in the same assays. In the G(2)/M gamma-H2AX assay, the relative sensitivities were similar to those seen in the low dose-rate G(0) assay and tracked with chromosomal radiosensitivity, but some differences were observed.
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, United States.
authors.forename: Takamitsu A
authors.initials: TA
authors.lastname: Kato
authors.forename: Paul F
authors.initials: PF
authors.lastname: Wilson
authors.forename: Hatsumi
authors.initials: H
authors.lastname: Nagasawa
authors.forename: Markus M
authors.initials: MM
authors.lastname: Fitzek
authors.forename: Michael M
authors.initials: MM
authors.lastname: Weil
authors.forename: John B
authors.initials: JB
authors.lastname: Little
authors.forename: Joel S
authors.initials: JS
authors.lastname: Bedford
mesh_terms: D002453:Cell Cycle; D002455:Cell Division; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D004260:DNA Repair; D005192:Family Health; D016195:G2 Phase; D018095:Germ-Line Mutation; D006657:Histones / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D011995:Recombination, Genetic; D016192:Resting Phase, Cell Cycle; D012175:Retinoblastoma / Q000235:genetics*; D013997:Time Factors
chemical_list: C468783:H2AX protein, human; D006657:Histones