TRANSCRIPTIONAL REPRESSION IN NORMAL HUMAN KERATINOCYTES BY WILD-TYPEAND MUTANT P53

Wild-type p53 is a nuclear phosphoprotein that inhibits cell prolifera tion and represses transcriptionally most TATA box-containing promoter s in transformed or tumor-derived cell lines. This study demonstrates that p53 alters transcription of the long control region (LCR) of huma n papillomavirus type 18 (HPV-18), Wild-type and mutant p53 143(Val to Ala) repressed the HPV-18 LCR promoter in normal human keratinocytes, the natural host cell for HPV infections. Repression by wild-type p53 was also observed in C-33A cells and in an HPV-16-immortalized cell l ine with an inducible wild-type p53, However, when C-33A cells were co transfected with the HPV-18 LCR and mutant 143(Val to Ala), repression did not occur. Mutant p53 135(Cys to Ser) did not induce repression i n either normal human keratinocytes or in the C-33A line; although lik e 143(Val to Ala), it is thought to affect the DNA binding activity of the wild-type protein. The ability of mutant p53 143(Val to Ala) to i nactivate the HPV early promoter in normal cells (by approximately 60% reduction) suggests that this mutant may be able to associate with wi ld-type p53 and interact with TATA box-binding proteins, Therefore, th ese results demonstrate that the transcriptional activities of p53 mut ants may be dependent upon the cell type assayed and the form of its e ndogenous p53, Furthermore, normal human keratinocytes represent an al ternative model for determining the activities of p53 mutants.