THE P53 STATUS OF CULTURED HUMAN PREMALIGNANT ORAL KERATINOCYTES

Around 60% of oral squamous cell carcinomas (SCCs) have been shown to harbour p53 mutations, and other studies have demonstrated mutant p53 genes in normal and dysplastic squamous epithelium adjacent to these S CCs. In line with these earlier studies we show here that DOK, a kerat inocyte cell line derived from a dysplasia, displays elevated levels o f p53 protein and harbours a 12 bp in-frame deletion of the p53 gene s panning codons 188-191. In contrast, the coding region of the p53 gene was normal in a series of six benign recurrent laryngeal papillomas a nd a series of four premalignant oral erythroplakia biopsies and their cell cultures. All but one of these lesions were free of malignancy a t the time of biopsy, in contrast to the premalignant lesions studied by previous investigators, but keratinocytes cultured from these lesio ns all displayed a partially transformed phenotype that was less prono unced than that of DOK. Since three out of four of the erythroplakia p atients developed SCC within 1 year of biopsy, these lesions were by d efinition premalignant. The availability of strains of partially trans formed keratinocytes from premalignant erythroplakia which possess nor mal p53 genes should enable us to test the role of mutant p53 in the p rogression of erythroplakia to SCC. The premalignant tissues and cultu res were also tested for the presence of human papillomavirus (HPV), w hich is known to inactivate p53 function in some cases. Only the benig n papillomas were shown to contain high levels of either HPV 6 or HPV 11 E6 DNA, but not both, and none of the samples contained detectable levels of HPV 16, HPV 18 or HPV 33 E6 DNA or L1 DNA of several other H PV types. There was therefore no evidence to suggest that p53 was bein g inactivated by a highly oncogenic HPV in these samples.