HIGH-FREQUENCY OF P53 MUTATIONS IN HUMAN ORAL EPITHELIAL DYSPLASIA AND PRIMARY SQUAMOUS-CELL CARCINOMA DETECTED BY YEAST FUNCTIONAL ASSAY

To determine the timing and actual incidence of p53 mutations in oral epithelial lesions, we examined 33 primary squamous cell carcinomas (S CCs), 14 dysplasias and six hyperplasias from Japanese patients by a c ombination of yeast functional assay and DNA sequencing, The assay det ects mutations of p53 mRNA between codons 67 and 347 on the basis of t he DNA-binding activity of the protein, Twenty-six SCCs (79%) and five dysplasias (36%) were positive for p53 mutation, while all six hyperp lasias were negative for the mutation, Human papillomavirus type 16 E6 mRNA was detected in one of seven p53 mutation-negative SCCs by rever se transcription polymerase chain reaction (RT-PCR), We further examin ed p53 mutations in 17 Sri Lankan oral SCCs using the yeast functional assay and the single-strand conformation polymorphism analysis of PCR -amplified DNA fragments (PCR-SSCP) of exon 5-8. The mutations were co nfirmed by DNA sequencing and the detection sensitivity was compared b etween the two methods, Six samples (35%) were positive for p53 mutati on in PCR-SSCP analysis, while nine samples (53%) were positive in yea st functional assay, This suggests that the incidence of p53 mutations has been considerably underestimated in the conventional SSCP analysi s, The present data indicate that p53 mutations are extremely frequent in oral cancers in the Japanese, and suggest that the timing and sign ificance of p53 mutation in oral tumor progression vary in different e thnic populations and areas.