Transgenic expression of human MGMT protects against azoxymethane-induced aberrant crypt foci and G to A mutations in the K-ras oncogene of mouse colon.
Transgenic mice over-expressing MGMT, which codes for the human protein O6-alkylguanine-DNA alkyltransferase, are protected from methylating agent-induced thymic lymphomas. In this study we evaluated the ability of transgenic overexpression of MGMT in the colon to protect mice from the development of azoxymethane(AOM)-induced aberrant crypt foci (ACF) and mutations in K-ras. Colonic alkyltransferase in MGMT+ transgenic mice was > 5-fold higher than in nontransgenics: 10.5 +/- 1.1 vs 2.2 +/- 1.1 fmol/micrograms DNA, P = < 0.0001. Mice received 20 mg AOM/kg i.p. at 6 weeks or 15 mg AOM/kg at 6 and 7 weeks of age, and 8 wks later colons were examined for ACF. A significant protective effect of MGMT was seen in mice given single dose of 20 mg AOM/kg. The incidence of ACF/colon was lower in MGMT+ mice (2.0 +/- 1.2) than in nontransgenic mice (3.9 +/- 1.8, P = 0.02). G to A mutations in codon 12 of K-ras were detected by PCR-RFLP in ACF and in random samples of normal appearing mucosa. The incidence of ACF with mutant K-ras in MGMT transgenic mice (0.6 +/- 0.7/colon) was significantly reduced compared to nontransgenic mice (2.3 +/- 1.7/colon, P = 0.02). We propose that AOM induces at least two overlapping but not identical premalignant lesions (aberrant crypt foci and K-ras mutations) which can be prevented by over-expression of MGMT. Thus, MGMT may protect colonic mucosa from carcinogenesis involving methylating agents such as AOM.
Zaidi
N H
NH
Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH.
Pretlow
T P
TP
O'Riordan
M A
MA
Dumenco
L L
LL
Allay
E
E
Gerson
S L
SL
D000225:Adenine; D000818:Animals; D001397:Azoxymethane / Q000633:toxicity*; D001483:Base Sequence; D003062:Codon; D003106:Colon / Q000187:drug effects* / Q000473:pathology; D017931:DNA Primers; D004260:DNA Repair; D011905:Genes, ras; D006147:Guanine; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects / Q000473:pathology; D008780:Methyltransferases / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase
D003062:Codon; D017931:DNA Primers; D006147:Guanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000225:Adenine; D001397:Azoxymethane