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Alkyltransferase-like proteins (ATLs) share functional motifs with the cancer chemotherapy target O6-alkylguanine-DNA alkyltransferase (AGT) and paradoxically protect cells from the biological effects of DNA alkylation damage, despite lacking the reactive cysteine and alkyltransferase activity of AGT. Here we determine Schizosaccharomyces pombe ATL structures without and with damaged DNA containing the endogenous lesion O6-methylguanine or cigarette-smoke-derived O6-4-(3-pyridyl)-4-oxobutylguanine. These results reveal non-enzymatic DNA nucleotide flipping plus increased DNA distortion and binding pocket size compared to AGT. Our analysis of lesion-binding site conservation identifies new ATLs in sea anemone and ancestral archaea, indicating that ATL interactions are ancestral to present-day repair pathways in all domains of life. Genetic connections to mammalian XPG (also known as ERCC5) and ERCC1 in S. pombe homologues Rad13 and Swi10 and biochemical interactions with Escherichia coli UvrA and UvrC combined with structural results reveal that ATLs sculpt alkylated DNA to create a genetic and structural intersection of base damage processing with nucleotide excision repair. [ABSTRACT FROM AUTHOR]

Abstract: O 6-Alkylguanine–DNA alkyltransferase (MGMT) repairs DNA adducts that result from alkylation at the O 6 position of guanine. These lesions are mutagenic and toxic and can be produced by a variety of agents including the tobacco-specific nitrosamines, carcinogens present in cigarette smoke. Here, we review some of our work in the context of inter-individual differences in MGMT expression and their potential influence on lung cancer risk. In humans there are marked inter-individual differences in not only levels of DNA damage in the lung (N7-methylguanine) that can arise from exposure to methylating agents but also in MGMT activity in lung tissues. In the presence of such exposure, this variability in MGMT activity may alter cancer susceptibility, particularly as animal models have demonstrated that the complete absence of MGMT activity predisposes to alkylating-agent induced cancer while overexpression is protective. Recent studies have uncovered a series of polymorphisms that affect protein activity or are associated with differences in expression levels. The associations between these (and other) polymorphisms and cancer risk are inconsistent, possibly because of small sample sizes and inter-study differences in lung cancer histology. We have recently analysed a consecutive series of case–control studies and found evidence that lung cancer risk was lower in subjects with the R178 allele. [Copyright &y& Elsevier]

Objectives: MGMT (O[sup 6] -alkylguanine-DNA alkyltransferase) reverses the carcinogenic, mutagenic and cytotoxic effects of alkylating agents. Measurement of MGMT activity in tumours might thus be of use in selecting those patients with colorectal cancer who may be sensitive to adjuvant alkylating agent therapy. The aim of this study was to assess whether measurement of MGMT activity in a single tumour biopsy is representative of the whole tumour. Methods: Multiple symmetrically spaced biopsies were taken from colorectal cancers obtained from 9 patients. MGMT activity was then measured in cell-free extracts by quantifying the transfer of [[sup 3] H]methyl group from calf thymus DNA methylated in vitro with N-nitroso-N-[[sup 3] H]-methylurea to the MGMT protein. Results: MGMT activity was detected in all tumour samples with the activity ranging between 3.6 and 36.2 fmol/μg DNA and 202–1,986 fmol/mg protein. Heterogeneity in MGMT activity (ratio of maximum/minimum MGMT levels per tumour) varied between 1.3 and 5.4. Conclusions: Measurement of MGMT activity in a single biopsy is not necessarily indicative of the level throughout the tumour. The response of colorectal cancers to alkylating agent treatment is likely to be non-uniform both within the tumour and between patients.Copyright © 2002 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Examines the role of DNA alkylation damage in the etiology of human colorectal cancer. Detection of O[sup 6]-methylguanine in human colorectal DNA; Association of the O[sup 6]-methylguanine persistence with the induction of colon tumors; Removal of O[sup 6]-Alkylguanine adducts by the DNA repair protein.

Presents information on a study which examined the role of O[sup6]-alkylguanine-DNA alkyltransferase (ATase) in carcinogenesis and chemotherapy. Genotoxic mechanisms of alkylation damage; Expression and regulation of ATase; Physiological role of ATase; Evolution of ATase; Conclusions.

Abstract: To examine associations between two different classes of DNA damage that can occur through endogenous processes or exogenous exposures such as smoking, N7-methyldeoxyguanosine (N7-MedG) and 8-oxodeoxyguanosine (8-oxodG) levels were measured in lymphocyte DNA from 22 bronchoscopy patients. 8-OxodG and N7-MedG was detected in 100% and 91% of samples, respectively with 8-oxodG levels being approx 20 times higher (mean 8.39±3.578-oxodG/106dG versus 0.41±0.33 N7-MedG/106 dG) which provides an indication of the relative importance of the agents that induce oxidative DNA damage or alkylation damage. The sources of these genotoxic lesions remain to be established but N7-MedG and 8-oxodG levels were not correlated (r 2 <0.01) suggesting that there is no association between alkylating agent and reactive oxygen species exposure, their metabolism and/or the DNA repair processes that can remove this DNA damage. [Copyright &y& Elsevier]