Overlapping domains on the p53 protein regulate its transcriptional activation and repression functions.
Wild-type p53 has been shown to inhibit transcription from several viral and cellular promoters without known p53-binding sites, while transactivating promoters with p53-binding sites. Using a series of N- and C-terminal p53 deletion mutants and wild-type p53, we have defined the domains on p53 responsible for its transcriptional functions. To test transcriptional activation by p53 we have used a promoter-chloramphenicol acetyltransferase (CAT) construct containing synthetic p53-binding sites. To check transcriptional inhibition by p53 we have used a human cytomegalovirus immediate-early promoter construct, CMV-CAT. Using transient transfection-transcription assays in Saos-2 cells, we determined that the p53 transcriptional activation and repression domains overlap at the N-terminus. This suggests the possibility that the same transcriptional machinery is involved in both functions. A C-terminal deletion up to amino acid 327 (del 393-327) eliminated repression of CMV-CAT, while preserving the transactivation function to a large extent. Using gluteraldehyde cross-linking experiments, we observed that the mutant del 393-327, which is transactivation-competent, but repression-defective, could not oligomerize. Thus, oligomerization of p53 is not required for transactivation, but may be essential for repression. Interestingly, transactivation by the oligomerization-defective mutant could be inhibited by cotransfection with a plasmid expressing the transforming mutant p53-175H.
Subler
M A
MA
Department of Microbiology, University of Texas Health Science Center at San Antonio 78284.
Martin
D W
DW
Deb
S
S
D017353:Gene Deletion; D016158:Genes, p53; D006367:HeLa Cells; D006801:Humans; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D016159:Tumor Suppressor Protein p53