STATE OF P53, RB AND DCC TUMOR-SUPPRESSOR GENES IN HUMAN ORAL-CANCER CELL-LINES

The tumor suppressor genes p53, Rb, and DCC were studied in five human oral cancer cell lines (FaDu, SCC-4, HEp-2, 1483, and OEC-M1) and in primary normal human oral keratinocytes (NHOK). All tested cancer line s had similar amount of p53 messages to normal cells, but the cancer l ines FaDu and SCC-4 contained significantly higher p53 protein levels than did the normal counterpart. Sequencing p53 cDNA for these cancer cells showed point mutations: In the FaDu cell line, a mutation of CGG to CTG occurred at codon 248; and in the SCC-4 cell line, a mutation. of CCC to TCC occurred at codon 151. The HEp-2 and 1483 cancer lines translated very low levels of p53 protein compared to the normal count erpart. Sequencing of p53 cDNA for HEp-2 and 1483 lines showed no muta tions. Southern and Northern analyses revealed that these cell lines h arbored HPV-18 DNA and expressed the viral E6/E7 protein. The OEC-M1 l ine showed different restriction fragment length polymorphism for the p53 gene compared with other cells, and did not express p53. All oral cancer cell lines except the OEC-M1 cells expressed both phosphorylate d and hypophosphorylated Rb proteins. Further, the OEC-M1 line express ed smaller sized hypophosphorylated Rb proteins compared with normal c ells. Unlike the other cancer lines, the HEp-2 and OEC-M1 lines also d id not contain DCC mRNAs. These data indicate that <<high risk>> HPV i nfections and mutations of p53, Rb, and DCC genes are frequently found in oral cancer cells and may be associated with oral cancer.