Autosomal mutants of proton-exposed kidney cells display frequent loss of heterozygosity on nonselected chromosomes.
High-energy protons found in the space environment can induce mutations and cancer, which are inextricably linked. We hypothesized that some mutants isolated from proton-exposed kidneys arose through a genome-wide incident that causes loss of heterozygosity (LOH)-generating mutations on multiple chromosomes (termed here genomic LOH). To test this hypothesis, we examined 11 pairs of nonselected chromosomes for LOH events in mutant cells isolated from the kidneys of mice exposed to 4 or 5 Gy of 1 GeV protons. The mutant kidney cells were selected for loss of expression of the chromosome 8-encoded Aprt gene. Genomic LOH events were also assessed in Aprt mutants isolated from isogenic cultured kidney epithelial cells exposed to 5 Gy of protons in vitro. Control groups were spontaneous Aprt mutants and clones isolated without selection from the proton-exposed kidneys or cultures. The in vivo results showed significant increases in genomic LOH events in the Aprt mutants from proton-exposed kidneys when compared with spontaneous Aprt mutants and when compared with nonmutant (i.e., nonselected) clones from the proton-exposed kidneys. A bias for LOH events affecting chromosome 14 was observed in the proton-induced Aprt mutants, though LOH for this chromosome did not confer increased radiation resistance. Genomic LOH events were observed in Aprt mutants isolated from proton-exposed cultured kidney cells; however the incidence was fivefold lower than in Aprt mutants isolated from exposed intact kidneys, suggesting a more permissive environment in the intact organ and/or the evolution of kidney clones prior to their isolation from the tissue. We conclude that proton exposure creates a subset of viable cells with LOH events on multiple chromosomes, that these cells form and persist in vivo, and that they can be isolated from an intact tissue by selection for a mutation on a single chromosome.
a  Center for Research on Occupational and Environmental Toxicology (CROET), Oregon Health & Science University, Portland, Oregon 97239;
Dmytro
D
Grygoryev
Cristian
C
Dan
Stacey
S
Gauny
Bradley
B
Eckelmann
Anna P
AP
Ohlrich
Marissa
M
Connolly
Michael
M
Lasarev
Gianfranco
G
Grossi
Amy
A
Kronenberg
Mitchell S
MS
Turker
D000228:Adenine Phosphoribosyltransferase / Q000172:deficiency / Q000235:genetics; D000818:Animals; D002470:Cell Survival; D002478:Cells, Cultured; D002869:Chromosome Aberrations; D020223:Chromosome Painting; D002875:Chromosomes / Q000235:genetics / Q000528:radiation effects*; D002999:Clone Cells; D004307:Dose-Response Relationship, Radiation; D006579:Heterozygote; D007668:Kidney / Q000166:cytology / Q000528:radiation effects*; D019656:Loss of Heterozygosity; D008661:Metabolism, Inborn Errors / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D016296:Mutagenesis; D011522:Protons / Q000009:adverse effects; D011833:Radiation Injuries, Experimental / Q000235:genetics* / Q000473:pathology; D011836:Radiation Tolerance; D011995:Recombination, Genetic / Q000528:radiation effects; D052878:Urolithiasis / Q000235:genetics; D014916:Whole-Body Irradiation
D011522:Protons; D000228:Adenine Phosphoribosyltransferase