The L84F polymorphism in the O6-Methylguanine-DNA-Methyltransferase (MGMT) gene is associated with increased hypoxanthine phosphoribosyltransferase (HPRT) mutant frequency in lymphocytes of tobacco smokers.
OBJECTIVE
O-methylguanine-DNA-methyltransferase (MGMT) is a crucial DNA repair protein that removes DNA adducts formed by alkylating mutagens. Several coding single nucleotide polymorphisms (cSNPs) in the MGMT gene have been reported. Their biological significance, however, is not known.


METHODS
We used a newly modified cloning HPRT mutant lymphocyte assay to test the hypothesis that inheritance of the L84F and I143V coding single nucleotide polymorphism in the MGMT gene is associated with increases in HPRT mutant frequency in lymphocytes of individuals exposed to alkylating agents. In addition, we expanded and sequenced 109 mutant clones to test the hypothesis that the mutation spectrum would shift to a larger percentage of base substitutions and G-->A transition mutations in cells with L84F and I143 V coding single nucleotide polymorphisms.


RESULTS
We observed no significant effect for the I143 V coding single nucleotide polymorphism on mutant frequency. In contrast, we observed a significant increase in mutant frequency (P<0.01) in lymphocytes from smokers with the 84F coding single nucleotide polymorphism compared with smokers homozygous for the referent L84 wild-type allele. A multiple regression analysis indicated that the mutant frequency increased significantly as a function of the 84F coding single nucleotide polymorphism and smoking, according to the model; mutant frequency (x10)=0.90+0.618 (84F polymorphism)+0.46 (smoking) with R=0.22. Mutation spectra analysis revealed an apparent increase, which was short of statistical significance (P=0.08), in base substitutions in cells with the 84F polymorphism.


CONCLUSIONS
These new data suggest that the 84F coding single nucleotide polymorphism may alter the phenotype of the MGMT protein, resulting in suboptimal repair of O-methylguanine lesions after exposure to alkylating agents.
Hill
Courtney E
CE
Department of Preventive Medicine and Community Health, The University of Texas Medical Branch, Galveston, Texas, USA.
Wickliffe
Jeffrey K
JK
Guerin
Adele T
AT
Kinslow
Carla J
CJ
Wolfe
Kevin J
KJ
Ammenheuser
Marinel M
MM
Abdel-Rahman
Sherif Z
SZ
D000328:Adult; D000367:Age Factors; D000368:Aged; D000477:Alkylating Agents / Q000633:toxicity; D001483:Base Sequence; D015254:DNA Modification Methylases / Q000235:genetics*; D017931:DNA Primers / Q000235:genetics; D004260:DNA Repair / Q000235:genetics; D045643:DNA Repair Enzymes / Q000235:genetics*; D005260:Female; D005838:Genotype; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D008214:Lymphocytes / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010597:Pharmacogenetics; D020641:Polymorphism, Single Nucleotide; D012907:Smoking / Q000235:genetics* / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics*
D000477:Alkylating Agents; D017931:DNA Primers; D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D007041:Hypoxanthine Phosphoribosyltransferase; D045643:DNA Repair Enzymes