Adenomatous polyposis coli truncation mutations in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced intestinal tumours of multiple intestinal neoplasia mice.
The heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induces intestinal tumours in C57BL/6J-multiple intestinal neoplasia (Min)/+ mice. The main mechanism for PhIP-induced tumour induction in Min/+ mice is loss of the wild-type adenomatous polyposis coli (Apc) allele, i.e. loss of heterozygosity (LOH). In this study, single injections of either 10, 17.5 or 25 mg/kg PhIP on days 3-6 after birth all increased the mean number of small intestinal tumours two to three-fold, from 37.7 in controls to 124.8 in the PhIP-treated Min/+ mice. In total, we analysed 292 small intestinal tumours and 253 of these had LOH. The frequency of LOH in the Apc gene was 88, 93, 83 and 84% in tumours of 0, 10, 17.5 and 25 mg/kg PhIP-treated mice, respectively. Therefore, these lower doses of PhIP did not reduce the frequency of LOH, as found in our previous study with a single injection of 50 mg/kg PhIP (Mutat. Res. 1-2 (2002) 157). In the second part of this study, we wanted to characterise Apc truncation mutations from tumour samples apparently retaining the Apc wild-type allele from this and two previous experiments with PhIP-exposed Min/+ mice. In the first half of exon 15 in Apc, we verified 25 mutations from 804 tumour samples of PhIP-treated mice. Of these were 60% G-->T transversions, and 16% G deletions, indicating that these are the predominant types of PhIP-induced truncation mutations in the Apc gene in Min/+ mice. Most of the mutations were located between codon 989 and 1156 corresponding to the first part of the beta-catenin binding region. We also identified two Apc truncation mutations from 606 spontaneously formed intestinal tumours from untreated Min/+ mice, one C-->T transition and one T insertion, which were different from those induced by PhIP.
Møllersen
Linda
L
Department of Food Toxicology, Division of Environmental Medicine, Norwegian Institute of Public Health, P.O. Box 4404 Nydalen, N-0403 Oslo, Norway.
Vikse
Rose
R
Andreassen
Ashild
A
Steffensen
Inger-Lise
IL
Mikalsen
Arne
A
Paulsen
Jan Erik
JE
Alexander
Jan
J
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D017491:Genes, APC; D007093:Imidazoles / Q000633:toxicity*; D007414:Intestinal Neoplasms / Q000139:chemically induced / Q000235:genetics*; D019656:Loss of Heterozygosity; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation
D007093:Imidazoles; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine