Effect of dietary fat on codon 12 and 13 Ha-ras gene mutations in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced rat mammary gland tumors.
Activating mutations in and expression of the Ha-ras gene were examined in benign and malignant female Sprague-Dawley rat mammary gland tumors induced by the heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and promoted by a diet high in polyunsaturated fat. Ha-ras mutations were detected in codons 12 and 13 by selective polymerase chain reaction amplification of mutated sequences and nucleotide sequencing. The percentage of Ha-ras mutations in carcinomas from PhIP-treated rats was significantly higher in rats on a low-fat diet than in rats on a high-fat diet (82% (nine of 11) vs 26% (seven of 27), respectively, P < 0.01). In addition, whereas 56% of the carcinomas with Ha-ras mutations from rats on a low-fat diet carried double Ha-ras mutations, none of the carcinomas from rats on a high-fat diet had double mutations. Ha-ras mutations were also detected in benign tumors (largely adenomas) induced by PhIP in rats on different diets; two of eight and three of four benign tumors examined from rats on low-fat and high-fat diets, respectively, had Ha-ras mutations, suggesting that activating Ha-ras mutations alone are not sufficient for PhIP-induced tumors to become malignant. No differences were observed in the level of Ha-ras mRNA expression in the different groups. In our animal model, a high-fat diet increased the incidence and percentage of malignant PhIP-induced mammary gland tumors yet decreased the percentage of carcinomas showing Ha-ras mutations. Thus, the complement of genetic alterations associated with PhIP-induced mammary gland carcinogenesis is probably altered by the level of dietary fat.
Roberts-Thomson
S J
SJ
Chemical Carcinogenesis Section, National Cancer Institute, Bethesda, Maryland 20892-4255, USA.
Snyderwine
E G
EG
D000818:Animals; D001483:Base Sequence; D002273:Carcinogens; D003062:Codon; D004042:Dietary Fats, Unsaturated; D005260:Female; D011905:Genes, ras; D007093:Imidazoles; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics*; D016296:Mutagenesis; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic
D002273:Carcinogens; D003062:Codon; D004042:Dietary Fats, Unsaturated; D007093:Imidazoles; D012333:RNA, Messenger; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine