Specific Ki‐ras codon 61 mutations may determine the development of urethan‐induced mouse lung adenomas or adenocarcinomas

Abstract

In A/J strain mice, the carcinogen urethan induces lung adenomas and adenocarcinomas that contain Ki‐ras‐activating mutations primarily in codon 61. These mutations affect the middle adenine in codon 61 resulting in the substitution of either arginine (AT→GC transition) or leucine (AT→TA transversion) for the wild‐type gluta‐mine. To analyze the expression of the wild‐type and mutant Ki‐ras mRNAs in primary mouse lung tumors and transformed mouse lung cell lines, we utilized reverse transcription of total mRNA and DNA amplification by the polymerase chain reaction. The wild‐type allele of coden 61 was expressed in all normal lung and primary tumor samples and in all transformed cell lines, except one. Significantly, the leucine‐substituted allele was expressed primarily in very small lung adenomas, whereas the arginine‐substituted allele was expressed in large lung adenocarcinomas and transformed lung cell lines. The relative amounts of expression of the mutant versus wild‐type Ki‐ras alleles and the total Ki‐ras mRNA expression was similar in both lung adenomas and adenocarcinomas. Further, the arginine mutant allele was present in adenocarcinomas having either alveolar or papillary tumor morphologies. These results suggest that the specific activating Ki‐ras mutation is more critical to either lung adenoma or adenocarcinoma development than is the tumor's cell of origin or the extent to which the mutant alleles are expressed. A distinct role of the specific activating Ki‐ras mutations in affecting lung tumor growth or malignant potential is indicated.