FREQUENT MUTATIONS OF KI-RAS BUT NO MUTATIONS OF HA-RAS AND P53 IN LUNG LESIONS INDUCED BY N-NITROSOBIS(2-HYDROXYPROPYL)AMINE IN RATS

Point mutations of the Ki-ras and p53 genes in rat lung lesions induce d by N-nitrosobis(2-hydroxypropyl)amine (BHP) were investigated by pol ymerase chain reaction-single-strand conformation polymorphism analysi s followed by direct sequencing using paraffin-embedded tissues. Male Wistar rats 6 wk old were given 2000 ppm BHP in drinking water for 15 wk. Another group was given drinking water without BHP. The rats were killed 20-27 wk after the beginning of the experiment. Lung adenomatou s and squamous lesions, including carcinomas, were induced. The freque ncies of Ki-ras mutations were 40% (six of 15) in alveolar hyperplasia s, 36% (five of 14) in adenomas, 72% (18 of 25) in adenocarcinomas, 20 % (three of 15) in squamous metaplasias, 50% (three of six) in squamou s cell carcinomas, and 50% (five of 10) in adenosquamous carcinomas. T he mutations were all G --> A transitions at the second position of co don 12; no other mutations were detected. However, Haras mutations in exons 1 and 2 and p53 mutations in exons 5, 6, and 7 were not detected in adenocarcinomas and squamous cell carcinomas. These results indica te that Ki-ras mutation is an early genetic event in some adenomatous and squamous lung carcinogeneses and that Ki-ras mutations can cause b enign lesions to convert to malignant lesions. The results also show t hat Ha-ras and p53 mutations are not involved in rat lung carcinogenes is induced by BHP. (C) 1996 Wiley-Liss, Inc.