Genetic Variation at the Human MGMT Locus and its Biological Consequences

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 ranging from carcinogens present in cigarette smoke to drugs used in cancer chemotherapy. There is a considerable amount of interindividual variation of MGMT activity and recent work has uncovered a series of polymorphisms that affect protein activity or are associated with differences in expression levels. On the other hand, current evidence for an association with cancer risk is tenuous: while some studies find such associations, others fail to support them. However, all published studies are based on small sample numbers. Not yet addressed are issues such as the relationship between sequence variation and the extent of the side effects of chemotherapy involving O 6 -alkylating agents. This review summarises the current state of knowledge in these areas.

Molecular Basis of Selectivity of Nucleoside Triphosphate Incorporation Opposite O6-Benzylguanine by Sulfolobus solfataricus DNA Polymerase Dpo4

“…Calcium was used as a cofactor during crystallization, because magnesium (which facilitates polymerization during crystallization) failed to provide diffraction quality crystals under the conditions used here. Crystals were grown using the sitting drop vapor diffusion method by mixing 1 l of complex with 1 l of solution containing 5-10% polyethylene glycol 3350 (w/v) and 100 mM Ca(OAc) 2 and equilibrated against a well solution containing 25 mM Tris-HCl (pH 7.4 at 25°C) buffer, 5-10% polyethylene glycol 3350 (w/v), 100 mM Ca(OAc) 2 , and 2.5% glycerol (v/v). Crystals were soaked in mother liquor containing an additional 25% polyethylene glycol 3350 (w/v) and 15% ethylene glycol (v/v) and then swiped through paratone-N (Hampton Research, Aliso Viejo, CA) and flash frozen in a stream of liquid nitrogen.…”

“…Alkyl and aryl modifications are some of the most extensively studied forms of DNA damage (1), with O 6 -alkylation providing one of the more mutagenic examples of this type of lesion (2,3). Alkylating agents have been used in warfare (i.e.…”

Sulfolobus solfataricus DNA Polymerase Dpo4 Is Partially Inhibited by “Wobble” Pairing between O6-Methylguanine and Cytosine, but Accurate Bypass Is Preferred

“…Guanine is generally considered the most easily oxidized of the bases, and the N7 position is the most nucleophilic atom of guanine. One prevalent form of guanine oxidation occurs at the O6 position, with a simple and widely studied process being addition of a methyl group to form O 6 -MeG 2 (4). Methylation of the O6 atom results in alternate pairing schemes that include a O 6 -MeG:C "wobble" pairing and a pseudo-"Watson-Crick" O 6 -MeG:T pair ( Fig.…”

“…Cells can repair O 6 -MeG by recognition and/or removal of the lesion through either the mismatch repair pathway or through the actions of (O 6 -alkylguanine DNA alkyltransferase) (8 -10). O 6 -MeG is even observed in the DNA of the general population, although the level measured between studies has varied (4,11). Substantially increased levels of O 6 -MeG are found in patients treated with chemotherapeutic regimes that include methylating agents (4,12,13).…”

Association between lung cancer risk and single nucleotide polymorphisms in the first intron and codon 178 of the DNA repair gene, O6‐alkylguanine–DNA alkyltransferase

“…[21][22][23] The reasons for these differences are also unclear but as many of these studies were small, they lacked the power to reveal small changes in risk. 24 The purpose of this study was to investigate whether the 2 intragenic SNPs, identified in previous work to be significantly associated with MGMT expression, 16 influence lung cancer risk in a Caucasian population.…”