K-ras mutations (codon 12) are not involved in down-regulation of MHC class-I genes in colon carcinomas

Fifty-eight colorectal carcinomas were studied for HLA class-I antigen expression and for the presence of point mutations in codons 12 and 61 of the K-ras gene. Eight carcinomas were completely negative for class I by the APAAP technique. Analyses using the polymerase chain reaction (PCR) method, together with selective hybridization using mutation-specific synthetic oligonucleotides, demonstrated K-ras mutations in 14 cases (24.1%), all of them in codon 12. None of the mutations corresponded to the negative cases for class-I HLA antigen expression. We did not observe any correlation between K-ras mutations and the extent of tumor differentiation.