EFFECT OF DIETARY-FAT ON CODON-12 AND CODON-13 HA-RAS GENE-MUTATIONS IN NO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE-INDUCED RAT MAMMARY-GLAND TUMORS

Activating mutations in and expression of the Ha-ras gene were examine d in benign and malignant female Sprague-Dawley rat mammary gland tumo rs induced by the heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[ 4,5-b]pyridine (PhlP) and promoted by a diet high in polyunsaturated f at. Ha-ras mutations were detected in codons 12 and 13 by selective po lymerase chain reaction amplification of mutated sequences and nucleot ide sequencing. The percentage of Ha-ras mutations in carcinomas from PhlP-treated rats was significantly higher in rats on a low-fat diet t han 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 w ith 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 do uble mutations. Ha-ras mutations were also detected in benign tumors ( largely adenomas) induced by PhlP in rats on different diets; two of e ight and three of four benign tumors examined from rats on low-fat and high-fat diets, respectively, had Ha-ras mutations, suggesting that a ctivating Ha-ras mutations alone are not sufficient for PhlP-induced t umors to become malignant. No differences were observed in the level o f Ha-ras mRNA expression in the different groups. In our animal model, a high-fat diet increased the incidence and percentage of malignant P hlP-induced mammary gland tumors yet decreased the percentage of carci nomas showing Ha-ras mutations. Thus, the complement of genetic altera tions associated with PhlP-induced mammary gland carcinogenesis is pro bably altered by the level of dietary fat. (C) 1997 Wiley-Liss, Inc.