THE INFLUENCE OF CELLULAR APOPTOTIC CAPACITY ON N-NITROSODIMETHYLAMINE-INDUCED LOSS OF HETEROZYGOSITY MUTATIONS IN HUMAN-CELLS

The induction of loss of heterozygosity (LOH) by the environmental car cinogen N-nitrosodimethylamine (NDMA), and the factors that influence the recovery of LOH mutations were studied in two directly related hum an lymphoblastoid cell lines, AHH-1 (h2E1.v2) and MCL-5. Initially, th e NDMA-induced mutation frequency at the heterozygous tk locus in AHH- 1 cells was observed to be 5-fold higher in AHH-1 compared with MCL-5. Molecular analysis of NDMA-induced TK- mutants indicated that the ind uced mutant fraction attributable to small intragenic mutations was si milar in both cell lines, However, the induced mutant fraction, becaus e of LOH, was 18-fold greater in AHH-1, In addition, LOH mutations wer e more extensive among TK- mutants derived from AHH-1 cells, We hypoth esized that the increased recovery of large LOH mutations in AHH-1 cel ls could be attributable to reduced apoptotic capacity, as it has been reported that AHH-1 cells carry a heterozygous mutation in the p53 lo cus, whereas MCL-5 cells are homozygous wild-type, Analysis of the kin etics of apoptosis showed that the apoptotic response of the AHH-1 cel l line was diminished and delayed compared with MCL-5. Based on the an alyses presented here, and several recent reports, it is suggested tha t the recovery of LOH mutations in p53 deficient cell lines is affecte d not only by abnormalities in cellular apoptotic response, but also i nvolves a number of p53-mediated responses to DNA damage.