Inactivation of the p53 Gene by Either Mutation or HPV Infection is Extremely Frequent in Human Oral Squamous Cell Carcinoma Cell Lines

Abstract

The state of p53 tumour suppressor and the frequency of high-risk human papillomavirus (HPV) infections were studied in nine human oral cancer cell lines. Three cancer cell lines (SCC-4, Tu-177 and FaDu) had similar amounts of p53 transcripts to normal cells, but contained significantly higher levels of p53 protein than the normal control cells. Sequencing highly conserved open reading frames of the p53 gene of these cancer cells showed point mutations in the SCC-4 and Tu-177 cell lines, a base transition from CCC to TCC occurred at codon 151; and in the line FaDu, a mutation of CGG to CTG occurred at codon 248. The HEp-2 and 1483 cancer lines contained significantly lower levels of p53 protein compared to the normal counterpart. Sequencing of p53 cDNA for HEp-2 and 1483 lines showed no mutations, but northern analysis revealed that these cell lines expressed HPV-18 E6/E7 messages. Four cell lines (SCC-9, SCC-15, SCC-25, and Tu-139) expressed negligible amounts of p53 transcripts compared to the normal counterpart and undetectable levels of p53 protein. These cell lines contained mutations in the highly conserved open reading frames of the p53 gene as follows: the SCC-9 had a deletion of 32 base pairs between codons 274 and 285; the line SCC-15 had an insertion of five base pairs between codons 224 and 225; the line SCC-25 had a deletion of two base pairs in codon 209; and the Tu-139 line had a deletion of 46 base pairs between codons 171 and 186. These data indicate that aberrant expression of p53 and altered levels of p53 protein are extremely frequent in oral cancer cell lines, and that these changes may result from either mutations or infection with high-risk HPV.