Project description:The tumor suppressor p53 is mainly involved in the transcriptional regulation of a large number of growth-arrest- and apoptosis-related genes. However, a clear understanding of which factor/s influences the choice between these two opposing p53- dependent outcomes remains largely elusive. We have previously described that in response to DNA damage, the RNA polymerase II binding protein Che-1/AATF transcriptionally activates p53. Here, we show that Che-1 binds directly p53. This interaction essentially occurs in the first hours of DNA damage, whereas it is lost when cells undergo to apoptosis in response to post-transcriptional modifications. Moreover, Che-1 sits in a ternary complex with p53 and the oncosuppressor Brca1. Accordingly, our analysis of genome-wide chromatin occupancy by p53 revealed that p53/Che1 interaction results in preferential transactivation of growth-arrest p53 target genes over its pro-apoptotic target genes. Notably, exposure of Che-1+/- mice to ionizing radiations resulted in enhanced apoptosis of thymocytes, compared to wild-type mice. These results confirm Che-1 as an important regulator of p53 activity and suggest Che-1 to be a promising yet attractive drug target for cancer therapy.
Project description:In response to stress, the p53 tumor suppressor induces arrest or apoptosis by transcriptionally regulating genes that mediate these processes. It has been proposed that the levels of p53 can influence the choice between these different outcomes, but the mechanisms involved are not clear. To gain mechanistic understanding of this p53-dependent cell fate decision, we generated a p53 inducible system that allowed tight regulation of p53 expression in human mammary epithelial cells. We used microarrays to detail the global programme of gene expression underlying cellularisation and identified distinct classes of up-regulated genes during this process. Using microarray and chromatin immunoprecipitation analysis, we showed that low and high levels of p53 bind to and activate the same set of pro arrest and pro apoptotic target genes, induced to lower and higher levels, respectively. We propose that the cell fate decision between arrest and apoptosis in these cells is determined by a higher threshold required for p53 dependent apoptosis. We suggest that high level p53 activation is crucial in order to achieve maximum efficacy of p53 targeted cancer therapies.
Project description:The p53 transcription factor is a regulator of key cellular processes including DNA repair, cell cycle arrest, and apoptosis. In this theoretical study, we investigate how the complex circuitry of the p53 network allows for stochastic yet unambiguous cell fate decision-making. The proposed Markov chain model consists of the regulatory core and two subordinated bistable modules responsible for cell cycle arrest and apoptosis. The regulatory core is controlled by two negative feedback loops (regulated by Mdm2 and Wip1) responsible for oscillations, and two antagonistic positive feedback loops (regulated by phosphatases Wip1 and PTEN) responsible for bistability. By means of bifurcation analysis of the deterministic approximation we capture the recurrent solutions (i.e., steady states and limit cycles) that delineate temporal responses of the stochastic system. Direct switching from the limit-cycle oscillations to the "apoptotic" steady state is enabled by the existence of a subcritical Neimark-Sacker bifurcation in which the limit cycle loses its stability by merging with an unstable invariant torus. Our analysis provides an explanation why cancer cell lines known to have vastly diverse expression levels of Wip1 and PTEN exhibit a broad spectrum of responses to DNA damage: from a fast transition to a high level of p53 killer (a p53 phosphoform which promotes commitment to apoptosis) in cells characterized by high PTEN and low Wip1 levels to long-lasting p53 level oscillations in cells having PTEN promoter methylated (as in, e.g., MCF-7 cell line).
Project description:Che-1 is a RNA Polymerase II binding protein involved in the regulation of gene transcription. We have observed that Che-1 depletion induces apoptosis in several cancer cells expressing mutated forms of p53. We used microarrays to investigate classes of genes regulated by Che-1 in one of these cell lines.
Project description:Che-1 is a RNA Polymerase II binding protein involved in the regulation of gene transcription. Che-1 emerges as an important adaptor that connects transcriptional regulation, cell-cycle progression, checkpoint control, and apoptosis. We have observed that Che-1 depletion sensitizes cells to chemotherapy. We used microarrays analysis to investigate classes of genes regulated by Che-1. Total RNA was extracted from control and Che-1 depleted HCT 116 cells 48 hours after transient transfection of siRNA.
Project description:WTX encodes a tumor suppressor, frequently inactivated in Wilms tumor, with both plasma membrane and nuclear localization. WTX has been implicated in beta-catenin turnover, but its effect on nuclear proteins is unknown. We report an interaction between WTX and p53, derived from the unexpected observation of WTX, p53 and E1B 55K colocalization within the characteristic cytoplasmic body of adenovirus-transformed kidney cells. In other cells without adenovirus expression, the C-terminal domain of WTX binds to the DNA binding domain of p53, enhances its binding to CBP, and increases CBP/p300-mediated acetylation of p53 at Lys 382. WTX knockdown accelerates CBP/p300 protein turnover and attenuates this modification of p53. In p53-reconstitution experiments, cell cycle arrest, apoptosis, and p53-target gene expression are suppressed by depletion of WTX. Together, these results suggest that WTX modulates p53 function, in part through regulation of its activator CBP/p300. Affymetrix microarray gene expression profiling was performed to identify differentially expressed genes following overexpression of WTX in HEK293 clones after 12 hour induction of WTX
Project description:Che-1 is a RNA Polymerase II binding protein involved in the regulation of gene transcription. Che-1 emerges as an important adaptor that connects transcriptional regulation, cell-cycle progression, checkpoint control, and apoptosis. We have observed that Che-1 depletion sensitizes cells to chemotherapy. We used microarrays analysis to investigate classes of genes regulated by Che-1.
Project description:Tumor suppressor p53 regulates various role in the cell including cell cycle arrest, DNA repair and apoptosis. Current research achieved to investigate p53 target genes in human osteosarcoma cell line-SaOS2 cell. Examination of p53 binding protein by transfecting flag-tagged wild type p53 into SaOS2 cells.
Project description:After DNA damage, cells activate p53, a tumor suppressor gene, and select a cell fate (e.g., DNA repair, cell cycle arrest, or apoptosis). Recently, a p53 oscillatory behavior was observed following DNA damage. However, the relationship between this p53 oscillation and cell-fate selection is unclear. Here, we present a novel model of the DNA damage signaling pathway that includes p53 and whole cell cycle regulation and explore the relationship between p53 oscillation and cell fate selection. The simulation run without DNA damage qualitatively realized experimentally observed data from several cell cycle regulators, indicating that our model was biologically appropriate. Moreover, the comprehensive sensitivity analysis for the proposed model was implemented by changing the values of all kinetic parameters, which revealed that the cell cycle regulation system based on the proposed model has robustness on a fluctuation of reaction rate in each process. Simulations run with four different intensities of DNA damage, i.e. Low-damage, Medium-damage, High-damage, and Excess-damage, realized cell cycle arrest in all cases. Low-damage, Medium-damage, High-damage, and Excess-damage corresponded to the DNA damage caused by 100, 200, 400, and 800 J/m(2) doses of UV-irradiation, respectively, based on expression of p21, which plays a crucial role in cell cycle arrest. In simulations run with High-damage and Excess-damage, the length of the cell cycle arrest was shortened despite the severe DNA damage, and p53 began to oscillate. Cells initiated apoptosis and were killed at 400 and 800 J/m(2) doses of UV-irradiation, corresponding to High-damage and Excess-damage, respectively. Therefore, our model indicated that the oscillatory mode of p53 profoundly affects cell fate selection.