Identification of p53 regulators by genome-wide functional analysis

Abstract

The p53 tumor-suppressor protein is a critical mediator of cellular growth arrest and the induction of apoptosis. To identify proteins involved in the modulation of p53 transcriptional activity, a gainof-function cellular screen was carried out with an arrayed matrix of Ϸ20,000 cDNAs. Nine genes previously unknown to be involved in regulating p53 activity were identified. Overexpression of seven of these genes (Hey1, Hes1, TFAP4, Osr1, NR2F2, SFRS10, and FLJ11339) resulted in up-regulation of p53 activity; overexpression of two genes (M17S2 and cathepsin B) resulted in down-regulation of p53 activity in mammalian cells. HES1, HEY1, and TFAP4, which are members of the basic helix-loop-helix transcription family, and OSR1 were shown to activate p53 through repression of HDM2 transcription. Ectopic expression of these basic helix-loop-helix transcription factors in both zebrafish and avian developmental systems activated p53 and induced apoptosis in vivo, resulting in a phenotype similar to that of p53 overexpression. Furthermore, ras-and myc-mediated transformation of mouse embryonic fibroblasts was abrogated by expression of HEY1 in a p53-dependent manner. These results suggest that these transcription factors are members of an evolutionarily conserved network that governs p53 function.

Deregulated expression of pro-survival and pro-apoptotic p53-dependent genes upon Elongator deficiency in colon cancer cells

“…3C). As expected these p53-dependent genes [29][30][31] were no longer induced upon IKAP/hELP1 depletion in p53 deficient HCT116 cells (Fig. 3C).…”

The notch pathway positively regulates programmed cell death during erythroid differentiation

“…Previous reports have attempted to link Notch induction of apoptosis through the p53 pathway in other systems. 36,37 We have also explored that possibility in erythroid cells, since there is increasing evidence of p53-mediated apoptosis at different stages of erythroid differentiation; 13,38 however, our results show that crucial p53 pathway genes are not affected in the RBPjk À/À erythroid cells suggesting that this pathway is not responsible for the protection of apoptosis in the RBPjk mutants. In fact, we found an erythroid-specific upregulation of the proapoptotic p53-target gene, puma, in the RBPjk À/À Ter119 þ cells, which is surprising since this population has a lower apoptotic rate.…”

GC-selective DNA-binding antibiotic, Mithramycin A, reveals multiple points of control in the regulation of Hdm2 protein synthesis

“…This response to p53 is the key in regulating the duration of the p53-response to genotoxic stress (Lev Bar-Or et al, 2000). A number of other signalling pathways and transcription factors also impinge upon the activity of the p53-Hdm2 module via the regulation of the activity of the P2-promoter, including thyroid hormone receptors (Qi et al, 1999), HEY1 and HES1 transcriptional repressors (Huang et al, 2004), MYCN (Slack et al, 2005) and Ras-Raf-MEK-ERK signalling (Ries et al, 2000;Phelps et al, 2003Phelps et al, , 2005. Hdm2 protein synthesis is also subject to post-transcriptional control; the export of hdm2 message from the nucleus to the cytoplasm is controlled by cellular MEK activity (Phelps et al, 2005), and hdm2 mRNA translation rates are elevated in some cancer cells (Landers et al, 1997;Trotta et al, 2003).…”