title: Autosomal mutations in mouse kidney epithelial cells exposed to high-energy protons in vivo or in culture.
abstract: Proton exposure induces mutations and cancer, which are presumably linked. Because protons are abundant in the space environment and significant uncertainties exist for the effects of space travel on human health, the purpose of this study was to identify the types of mutations induced by exposure of mammalian cells to 4-5 Gy of 1 GeV protons. We used an assay that selects for mutations affecting the chromosome 8-encoded Aprt locus in mouse kidney cells and selected mutants after proton exposure both in vivo and in cell culture. A loss of heterozygosity (LOH) assay for DNA preparations from the in vivo-derived kidney mutants revealed that protons readily induced large mutational events. Fluorescent in situ hybridization painting for chromosome 8 showed that >70% of proton-induced LOH patterns resembling mitotic recombination were in fact the result of nonreciprocal chromosome translocations, thereby demonstrating an important role for DNA double-strand breaks in proton mutagenesis. Large interstitial deletions, which also require the formation and resolution of double-strand breaks, were significantly induced in the cell culture environment (14% of all mutants), but to a lesser extend in vivo (2% of all mutants) suggesting that the resolution of proton-induced double-strand breaks can differ between the intact tissue and cell culture microenvironments. In total, the results demonstrate that double-strand break formation is a primary determinant for proton mutagenesis in epithelial cell types and suggest that resultant LOH for significant genomic regions play a critical role in proton-induced cancers.
authors.affiliation: Center for Research on Occupational and Environmental Toxicology CROET, Oregon Health & Science University, Portland, Oregon 97239, USA. turkerm@ohsu.edu
authors.forename: Mitchell S
authors.initials: MS
authors.lastname: Turker
authors.forename: Dmytro
authors.initials: D
authors.lastname: Grygoryev
authors.forename: Cristian
authors.initials: C
authors.lastname: Dan
authors.forename: Bradley
authors.initials: B
authors.lastname: Eckelmann
authors.forename: Michael
authors.initials: M
authors.lastname: Lasarev
authors.forename: Stacey
authors.initials: S
authors.lastname: Gauny
authors.forename: Ely
authors.initials: E
authors.lastname: Kwoh
authors.forename: Amy
authors.initials: A
authors.lastname: Kronenberg
mesh_terms: D000228:Adenine Phosphoribosyltransferase / Q000235:genetics; D000818:Animals; D002460:Cell Line; D033481:Chromosomes, Mammalian / Q000235:genetics* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism* / Q000528:radiation effects; D005260:Female; D056426:Genetic Loci / Q000235:genetics / Q000528:radiation effects; D008297:Male; D051379:Mice; D009154:Mutation / Q000528:radiation effects*; D011522:Protons / Q000009:adverse effects*
chemical_list: D011522:Protons; D000228:Adenine Phosphoribosyltransferase