A CHEMICAL AND GENETIC APPROACH TOGETHER DEFINE THE BIOLOGICAL CONSEQUENCES OF 3-METHYLADENINE LESIONS IN THE MAMMALIAN GENOME

DNA-damaging agents produce a plethora of cellular responses that incl ude p53 induction, cell cycle arrest, and apoptosis, It is generally a ssumed that it is the DNA damage produced by these agents that trigger s such responses, but there is limited direct evidence to support this assumption, Here, we used DNA alkylation repair proficient and defici ent isogenic mouse cell lines to demonstrate that the signal to trigge r p53 induction, cell cycle arrest, and apoptosis in response to alkyl ating agents does emanate from DNA damage. Moreover, we established th at 3-methyladenine, a relatively minor DNA lesion produced by most met hylating agents (which form mainly 7-methylguanine), can specifically induce sister chromatid exchange, chromatid and chromosome gaps and br eaks, S phase arrest, the accumulation of p53, and apoptosis, This stu dy was made possible by the generation of 3-methyladenine DNA glycosyl ase null mutant cells by targeted homologous recombination and by the chemical synthesis of a methylating agent that almost exclusively prod uces 3-methyladenine DNA lesions, The combined use of these two experi mental tools has defined the biological consequences of 3-methyladenin e, a DNA lesion produced by endogenous cellular metabolites, environme ntal carcinogens, and chemotherapeutic alkylating agents.