Ki-ras oncogene activation in transplantable rat thyroid carcinoma induced by N-bis(2-hydroxypropyl)nitrosamine

We have established 17 transplantable rat thyroid carcinoma cell lines from primary thyroid tumors of rats induced by N-bis(2-hydroxypropyl)nitrosamine (DHPN) (Cancer Res. (1993) 53, 4408-4412). The present study was designed to evaluate point mutations in the murine c-Ki-ras gene of these carcinoma cell lines. Using PCR amplification and direct sequencing, we found that the activated form of the Ki-ras oncogene was present in 4 (23%) of a total of 17 cell lines, all the Ki-ras gene mutations being GC-->AT transitions. In three of the cell lines, the mutations occurred in codon 12 (GTP-binding domain), and in the remaining one the first nucleotide of codon 63 was affected. Histologically, three of the carcinomas with Ki-ras mutation were diagnosed as well-differentiated carcinomas, and the other as poorly differentiated carcinoma. Mutations of the ras gene are relatively uncommon in tumors of these histological types. From these experimental results, we suggest that the mutation induced by DHPN is due to damage to guanine in cellular DNA. In addition, Ki-ras activation may play an important role in the initiation of thyroid carcinogenesis.