title: O6-methylguanine-DNA methyltransferase Leu84Phe and Ile143Val polymorphisms and risk of colorectal cancer in the Nurses' Health Study and Physicians' Health Study (United States).
abstract: OBJECTIVE
  O6-methylguanine-DNA methyltransferase (MGMT) removes mutagenic adducts from the O6-position of guanine in DNA. Unrepaired O6-methylguanines result in G:C to A:T transitions in mutated K-ras and p53 in colorectal tumors. Two non-synonymous MGMT coding region variants, Leu84Phe and Ile143Val, lie in close proximity to the reactive 145Cys residue and to a conserved estrogen receptor interacting helix.
  
  
  METHODS
  We assessed the association between the MGMT Leu84Phe and Ile143Val polymorphisms and risk of colorectal cancer in two nested case-control studies: one each in the Nurses' Health Study (NHS) and the Physicians' Health Study (PHS) cohorts.
  
  
  RESULTS
  Among 197 female cases and 2,500 controls from the NHS, the variant 143Val allele was significantly associated with reduced risk of colorectal cancer [odds ratio (OR) = 0.52, 95% confidence interval (CI) 0.33-0.80]. In women, statistically significant gene-environment interactions were found between the Leu84Phe polymorphism and alcohol intake (P = 0.03), BMI (P = 0.04) and postmenopausal hormone use (P = 0.03). The Leu84Phe and Ile143Val polymorphisms were not significantly associated with risk of colorectal cancer among 271 male cases and 451 controls from the PHS.
  
  
  CONCLUSIONS
  Our results suggest that the common Leu84Phe and Ile143Val polymorphisms in MGMT influence risk of colorectal cancer in women possibly through modulating estrogen receptor-dependent transcriptional activation, which has previously been shown to occur in response to DNA alkylation damage.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA. gtranah@psg.ucsf.edu
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Tranah
authors.forename: James
authors.initials: J
authors.lastname: Bugni
authors.forename: Edward
authors.initials: E
authors.lastname: Giovannucci
authors.forename: Jing
authors.initials: J
authors.lastname: Ma
authors.forename: Charles
authors.initials: C
authors.lastname: Fuchs
authors.forename: Lisa
authors.initials: L
authors.lastname: Hines
authors.forename: Leona
authors.initials: L
authors.lastname: Samson
authors.forename: David J
authors.initials: DJ
authors.lastname: Hunter
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000209:etiology* / Q000235:genetics; D004311:Double-Blind Method; D005260:Female; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics*; D011110:Polymorphism, Genetic; D011960:Receptors, Estrogen / Q000032:analysis; D012307:Risk Factors
chemical_list: D011960:Receptors, Estrogen; D019853:O(6)-Methylguanine-DNA Methyltransferase