Wild-type p53 and p73 negatively regulate expression of proliferation related genes

Abstract

When normal cells come under stress, the wild-type (WT) p53 level increases resulting in the regulation of gene expression responsible for growth arrest or apoptosis. Here we show that elevated levels of WT p53 or its homologue, p73, inhibit expression of a number of cell cycle regulatory and growth promoting genes. Our analysis also identified a group of genes whose expression is differentially regulated by WT p53 and p73. We have infected p53-null H1299 human lung carcinoma cells with recombinant adenoviruses expressing WT p53, p73 or b-galactosidase, and have undertaken microarray hybridization analyses to identify genes whose expression profile is altered by p53 or p73. Quantitative real-time PCR verified the repression of E2F-5, centromere protein A and E, minichromosome maintenance proteins (MCM)-2, -3, -5, -6 and -7 and human CDC25B after p53 expression. 5-Fluorouracil treatment of colon carcinoma HCT116 cells expressing WT p53 results in a reduction of the cyclin B2 protein level suggesting that DNA damage may indeed cause repression of these genes. Transient transcriptional assays verified that WT p53 repressed promoters of a number of these genes. Interestingly, a gain-of-function p53 mutant instead upregulated a number of these promoters in transient transfection. Using promoter deletion mutants of MCM-7 we have found that WT p53-mediated repression needs a minimal promoter that contains a single E2F site and surrounding sequences. However, a single E2F site cannot be significantly repressed by WT p53. Many of the genes identified are also repressed by p21. Thus, our work shows that WT p53 and p73 repress a number of growth-related genes and that in many instances this repression may be through the induction of p21.

Cdc25B is negatively regulated by p53 through Sp1 and NF-Y transcription factors

“…However, the downregulation was not as pronounced in p21À/À HCT116 as that observed with WT cells. This results probably from the upregulation of the p53 target gene p21 in nutlin-treated WT HCT116 cells, as in earlier studies Cdc25B was also repressed by overexpression of p21 (Scian et al, 2008). Therefore, it is likely that there exist p21-dependent and -independent pathways of repression.…”

“…It has been previously shown that a 941-bp fragment of the human Cdc25B promoter was able to mediate the repression by overexpressed p53 (Scian et al, 2008). In silico analyses of this sequence revealed no consensus p53-binding sites.…”

“…It has been suggested that overexpression of p53 may repress Cdc25B expression through the induction of p21 (Scian et al, 2008). To investigate the role of p21 in the p53-dependent regulation of Cdc25B, we invalidated p53 in the p21 null derivative of HCT116 cells (HCT116 p21À/À).…”

“…Recent studies show that p53 can regulate expression of genes in the absence of any cellular stresses, uncovering an additional role of the p53 protein that is expressed under basal physiological and cell-culture stress conditions (Vousden and Prives, 2009). Using microarray analysis, Cdc25B has been recently identified as a gene transcriptionally repressed upon p53 overexpression (Scian et al, 2008). However, no molecular mechanism has been described concerning this repression.…”

Udu Deficiency Activates DNA Damage Checkpoint

“…Third, Udu localizes in chromatin during the S phase in synchronized cells. Fourth, mcm2, mcm4, and mcm5 expression level is down-regulated in udu sq1 mutants (Liu et al, 2007), probably due to the elevated p53 expression (Scian et al, 2008) and/or cross-regulation between MCM proteins (Fitch et al, 2003. And last, Udu contains PAH-L and SANT-L domains, which have been shown to be involved in transcription and/or chromatin remodeling.…”