ABSTRACT
Individual differences in response to radiation are well known, but the molecular basis for these differences is not well understood, and molecular indicators that are useful in assessing individual variation are lacking. Cells from patients developing unexpected radiation responses have occasionally been analyzed for rare genetic anomalies (such as alleles of the ATM gene), but few data exist on the long-term effects of genetic variation on radiation response. We hypothesize that much of the variation in the response to radiation is due to differences in the genes that respond to radiation exposure, and that changes in gene expression may serve as surrogate markers of individual response. As a first step in developing a selection of suitable markers of gene expression, we used cDNA microarrays to identify genes that were altered in expression in lymphoblastoid cells 4 h after exposure to 1 Gy X rays. We found changes in gene expression ranging from a 10-fold repression to a 12-fold induction. Some of the responsive genes have been noted previously in other cell types, whereas others are reported for the first time. Using these data, we are beginning to characterize the range of structural, temporal and functional variations in the responsive genes. The results of this work will assist in developing response markers both for prescreening for sensitive individuals and for risk assessment.
Subject(s)
Gene Expression/radiation effects , Gene Expression Regulation/radiation effects , Gene Silencing/radiation effects , Humans , Oligonucleotide Array Sequence Analysis , RNA, Messenger/metabolism , RNA, Messenger/radiation effects , Radiation , Tumor Cells, Cultured/physiology , Tumor Cells, Cultured/radiation effects , X-RaysABSTRACT
2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a food-borne mutagen and carcinogen that induces tumors of the colon and the prostate gland in male rats and of the mammary gland in female rats. In this study we describe the frequency and specificity of PhIP-induced mutations in the cecum, proximal colon and distal colon of male and female lacI transgenic rats. This is the first report of mutational data from discrete regions of the colon. After 61 days of treatment with 200 p.p.m. PhIP mixed into the diet, PhIP-induced mutant frequencies were elevated 7-fold in the cecum and 14- to 21-fold in the colon of male and female rats compared with untreated controls. PhIP-induced mutant frequencies increased significantly (overall trend, P < 10(-4)) along the length of the colon of both males and females, with cecum < proximal colon < distal colon. A total of 754 PhIP mutants (363 male, 391 female) were sequenced to provide the mutational spectra for each of the three tissue sections from males and females. These mutational spectra consisted predominantly of G:C-->T:A and G:C-->C:G transversions and deletions of G:C base pairs. There were no significant differences between the mutational spectra with respect to sex or position in the colon. Therefore, we surmise that following induction of mutations by PhIP in male and female colons, non-mutagenic factors, possibly hormonal, preferentially influence the formation of tumors in the colon of male rats.
Subject(s)
Bacterial Proteins/genetics , Cecum/drug effects , Colon/drug effects , Escherichia coli Proteins , Imidazoles/toxicity , Mutation/drug effects , Mutation/genetics , Repressor Proteins/genetics , Animals , Animals, Genetically Modified , Bacterial Proteins/metabolism , Cecum/metabolism , Colon/metabolism , Eating/drug effects , Female , Lac Repressors , Male , Mutagenicity Tests/methods , Mutagens/toxicity , Rats , Rats, Inbred F344 , Repressor Proteins/metabolismABSTRACT
The cII assay provides an alternative choice to the lacI transgene for mutational studies involving Big Blue(R) transgenic mice and rats, or permits the evaluation of mutational responses in both genes. Here, we compare the mutational response of the cII gene from colon of Big Blue(R) F344 rats treated with a dietary mutagen and animal carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), to those previously determined in the lacI transgene from colon of the same group of animals. A cursory inspection of PhIP-induced mutational spectra (MS) in cII and lacI suggests that the two transgenes respond differently to PhIP-induced mutation. However, a more thorough analysis of the MS in the two transgenes, including consideration of the number of mutational target sequences in each gene and nearest neighbor analyses of mutated nucleotides, indicates that PhIP-induced mutational specificity is similar in both genes. The evaluation of PhIP-induced mutational responses in these two transgenes serves as a model for intergenic mutational analyses.
