Analysis of oncogenes and tumor-suppressor genes in oral cancers and the application to diagnosis

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Human cancers emerge from a normal cell after multiple genetic changes of protooncogenes and tumor suppressor genes by multistep process. In the present research we focused on squamous cell carcinomas (SCC) in the oral cavity and examined abnormalities of ras and erbB1 (EGFR) protooncogenes, and p53 tumor suppressor gene.ras mutation : 29 tumor lesions of oral SCC were examined for the activational mutations of codons 12, 13, and 61 of N-, H- K-ras genes. Mutations were detected by hybridization of PCR (polymerase chain reaction)-amplified DNA with allele specific oligonucleotide probes or by PCR-SSCP (single strand conformation polymorphysm) analysis. As a result we could not detect mutation except for two cell lines which had mutations of codons 12 (HOC313) and 13 (ZA) of H-ras. Analysis of parafin-embedded sections showed that the tumor sample of HOC313 had the mutation at the time of initial diagnosis. Although the mutation of ZA was detected in the tumor tissue used for the cell l … More ine establishment, the normal epithelium and leukoplakia lesion were negative. From these results frequency of ras mutation in oral SCC is considerablly low compared with those of adenomas, thus suggesting that ras mutation may not important in tumorigenesis of oral SCC.p53 gene mutation : 15 oral SCC cell lines were examined for the presence of the mutation by cDNA-SSCP and exon-SSCP anlaysis, followed by direct sequencing. As a result, p53 gene mutations were found in 14 cell lines and were localized from cadon 126 to cadon 305. Two mutational hot-spots were found in codon 248 (3 cases) and the spliincg donor sequence of exon 6 (2 cases). Thirteen out of 14 mutations were point mutations including 10 missense mutations.Analysis of EGFR : increased capacity for EGF binding was observed in all the examined 4 cases of oral SCC.From these results it is anticipated that p53 gone mutations and increased capacity for EGF binding play important roles in the genesis of oral SCC, thus suggesting that both will be good diagnostic markers for SCC. Less