OBJECTIVETo investigate the roles of p53 and K-ras gene in carcinogenesis and development of the lung carcinoma induced by 3-methylcholanthrene (MCA) and diethylinitrosamine (DEN) in Wistar rats, and to elucidate the relationships between the protein expression and gene mutation of p53 and K-ras.

METHODSMicrodissection was used to obtain pure cell populations of each phase in the carcinogenesis and development of lung carcinoma induced by MCA and DEN. DNA of the microdissected cell populations was extracted and used to analyze the mutations of p53 exons 5 approximately 8 and K-ras exons 1 approximately 2 by PCR-SSCP. The expressions of p53 and K-ras protein in each phase were detected by immunohistochemistry.

RESULTSNo mutation and protein expression of p53 and K-ras was found in the 30 cases with normal bronchial epithelium. Mutation of p53 was detected in 3.1% of 18 hyperplasia and 14 squamous metaplasia cases, 28.6% of 21 dysplasia, 30.0% of 12 carcinomas in situ, 51.2% of 43 infiltration carcinomas, 52.9% of 17 metastases. The positive immunostaining rate of p53 protein was 0, 42.9%, 50.0%, 60.5% and 64.7% respectively. K-ras mutation rate was 0, 4.8%, 8.3%, 9.3%, 11.8% respectively, while the overexpression rate of K-ras protein was 15.6%, 19.0%, 25.0%, 41.9%, 52.9% respectively. p53 protein expression was closely related with p53 mutation (P < 0.005, Pearson's R = 0.599 6). There was no relationship between the protein expression and gene mutation of K-ras (P > 0.500).

CONCLUSIONSp53 gene mutation and K-ras overexpression were early events in the carcinogenesis and development of rat lung carcinoma induced by MCA and DEN, while K-ras mutation does not play any important role.