DNA Sequence Analysis of $HPRT^{-}$ Mutants Induced in Human Lymphoblastoid Cells Adapted to Ionizing Radiation

• Published in: Radiation research 1995-11, Vol.144 (2), p.181-189
• Main Authors: Rigaud, O., Laquerbe, A., Moustacchi, E.
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Base Sequence; Biological and medical sciences; Biological effects of radiation; Cells, Cultured; Chromosome Mapping; Complementary DNA; DNA Primers - chemistry; Dose-Response Relationship, Radiation; Exons; Fundamental and applied biological sciences. Psychology; Gamma Rays; Gene Expression - radiation effects; Genetic mutation; Humans; Hypoxanthine Phosphoribosyltransferase - genetics; Ionizing radiation; Ionizing radiations; Lymphocytes - radiation effects; Messenger RNA; Molecular Sequence Data; Point Mutation; Polymerase chain reaction; Radiation dosage; RNA, Messenger - genetics; Sequence Deletion; Sequencing; Splicing; Tissues, organs and organisms biophysics
• ISSN: 0033-7587; 1938-5404
• DOI: 10.2307/3579257

Radioadaptation to the mutagenic effect of ionizing radiation by pre-exposure of human cells to a low dose has been shown to decrease the proportion of $HPRT^{-}$ mutants of the deletion type. To determine whether point mutations would be affected by the adaptive treatment, the molecular nature of mutations induced after exposure to low, high or low plus high doses was established. DNA sequencing of 38 point mutants which still expressed mRNA was performed using reverse transcription/polymerase chain reaction amplification. Under all conditions, base substitutions were the most common mutational event (range 72-80%), the remainder being frameshift and small deletions. The types and proportions of base changes did not appear to be differentially modified. A clustering of mutations was observed in exon 8, independently of the radiation protocol. About 40% of the mutants exhibited incorrect splicing of mRNA. The lack of striking modifications between the different molecular spectra of point mutations suggests that the low-dose pre-exposure does not affect the production and/or the processing of lesions leading to point mutations. Thus the highly significant effect triggered by the low dose is the preferential reduction of deletion-type mutations. In view of the actual small data set, definitive conclusions will be drawn only when our observations are confirmed or can be generalized to human endogenous loci other than the HPRT locus, which is particularly prone to the recovery of deletion-type mutations.