Spectrum of in vivo hprt mutations in T lymphocytes from atomic bomb survivors. I. Sequence alterations in cDNA.

Recently, we found an elevated frequency of 6-thioguanine-resistant (TGr) mutations at the hyoxanthine-guanine phosphoribosyltransferase (hprt) gene in T cells of peripheral blood from atomic bomb survivors and a slight, but significant, positive correlation between the frequency of mutation and radiation dose. Southern blot analysis of DNA from TGr mutant T cells of atomic bomb survivors, however, failed to show a significant difference between the control and survivor groups. We here report mutational events at the hprt locus of TGr mutant T cell clones from atomic bomb survivors as found by (i) the multiplex polymerase chain reaction (PCR) and (ii) the reverse transcription (RT)-PCR of cDNA and sequencing. The numbers of independent TGr mutant T cell clones examined were 41 from a control group of 18 individuals who had received less than 0.005 Gy and 50 from an exposed group of 24 individuals who had received more than 1.5 Gy (mean dose 2.45 +/- 0.85 Gy). Gross structural alterations, which were detected by multiplex PCR as a loss of or shift in hprt exon-containing fragments of genomic DNA, were found in 10-15% of the clones from both groups, thus indicating that there was no significant difference between them. The altered sequences in the HPRT cDNAs recovered from both groups were of various types. Similar proportions of base substitutions (approximately 45%), deletions or insertions (approximately 25%) and exon skipping (approximately 20%) were found in both groups, indicating that neither the gross structural alterations in the genomic DNA nor sequence alterations in the hprt cDNA of both groups differ significantly. These results confirm our previous observation that A-bomb-induced HRT- mutant T cells have mostly been eliminated from the peripheral blood over the decades that have elapsed since exposure. Some unique features of the mutational sequence alterations found are also described.