The role of Ataxia telangiectasia and the DNA-dependent protein kinase in the p53-mediated cellular response to ionising radiation.

The DNA-dependent protein kinase (DNA-PK), whose catalytic subunit shows structural similarities to the Ataxia telangiectasia (AT) gene product (ATM), has also been implicated in the p53-mediated signal transduction pathway that activates the cellular response to DNA damage produced by ionizing radiation. DNA-PK activity however was not found to be related to the transcriptional induction of WAFl/CIP1(p2l) in AT lymphoblastoid cell lines, following treatment with ionizing radiation. Normal protein and transcription levels of Ku70 and Ku80, as well as DNA-PK activity, were found in six different AT cell lines, 1-4 h following exposure to ionizing radiation, timepoints where reduced and delayed transcriptional induction of WAF1/CIP1 (p21) was observed.

The role of the Ataxia telangiectasia gene in the p53, WAF1/CIP1(p21)- and GADD45-mediated response to DNA damage produced by ionising radiation.

The inducible response of the tumour suppressor gene p53 has been examined following exposure to DNA-damaging agents in Ataxia telangiectasia (AT) cell lines, an autosomal recessive disorder with multiple clinical and biological abnormalities including sensitivity to ionising radiation. The p53 induction was significantly delayed and reduced in the 8 AT cell lines examined over the 6 h following irradiation with no dose response in p53 induction being observed compared to control cells. The increase of WAF1/CIP1(p21) and GADD45 mRNA, two genes transcriptionally activated by p53, was also reduced in the AT cell lines after such treatment.

Alkylation and oxidative-DNA damage repair activity in blood leukocytes of smokers and non-smokers.

The levels of 3 DNA repair enzymes involved in alkylation and oxidative DNA damage repair in human peripheral blood leukocytes were measured in 20 smokers and 17 non-smokers. No differences in O6-alkylguanine-DNA-alkyltransferase (AGT) activity were found between the 2 groups and the AGT distribution within the population appeared to be unimodal. In contrast, the mean activities of both the methylpurine (MeP)- and the 2-6-diamino-4-hydroxy-5N formamidopyrimidine (FaPy)-DNA glycosylases were higher in the smokers, although only the difference between the MeP-DNA glycosylase means was statistically significant.

Some safety procedures for handling 32P during postlabelling assays.

32P is a high-energy (1.7 MeV) beta-emitter. Its handling is therefore subject to regulation and very strict control.

Modulation of O6-methylguanine-DNA methyltransferase in rat and hamster liver after treatment with dimethylnitrosamine.

Distinct species differences exist between BDIV rats and Syrian Golden hamsters in the repair of methylated DNA lesions, after single exposures to dimethylnitrosamine (DMN). The promutagenic lesions O6-methylguanine (O6-MeG) and O4-methylthymidine were actively repaired in rat liver; in contrast, in hamster liver the levels of O6-MeG remained relatively stable while O4-methylthymidine levels were reduced. Species differences in the levels of two enzymes involved in the repair of DNA alkylation damage were also noted.