Project description:The downstream events and target genes of p53 in senescence responses are not fully understood. Here, we report a novel function of the forkhead transcription factor Foxp3, a key player in mediating T cell inhibitory function, in p53-mediated cellular senescence. Overexpression of Foxp3 in mouse embryonic fibroblasts (MEFs) accelerates senescence, whereas Foxp3 knockdown leads to escape from p53-mediated senescence in p53-expressing MEFs. Consistently, Foxp3 expression resulted in the induction of senescence in epithelial cancer cells, including MCF7 and HCT116. Foxp3 overexpression also increased the intracellular levels of reactive oxygen species (ROS). The ROS inhibitor N-acetyl-L-cysteine rescued Foxp3 expression-induced senescence. Furthermore, the elevated ROS levels that accompanied Foxp3 overexpression were paralleled by an increase in p21 expression. Knockdown of p21 in Foxp3-expressing MEFs abrogated the Foxp3-dependent increase in ROS levels, indicating that Foxp3 acts through p21 induction and subsequent ROS elevation to trigger senescence. Collectively, these results suggest that Foxp3 is a downstream target of p53 that is sufficient to induce p21 expression and ROS production and is necessary for p53-mediated senescence. control and treated samples (human), young passage (p3) or old passage (p7) samples (mouse)
Project description:The downstream events and target genes of p53 in the process of senescence are not fully understood. Here, we report a novel function of the forkhead transcription factor Foxp3, which is a key player in mediating T cell inhibitory functions, in p53-mediated cellular senescence. The overexpression of Foxp3 in mouse embryonic fibroblasts (MEFs) accelerates senescence, whereas Foxp3 knockdown leads to escape from p53-mediated senescence in p53-expressing MEFs. Consistent with these results, Foxp3 expression resulted in the induction of senescence in epithelial cancer cells, including MCF7 and HCT116 cells. Foxp3 overexpression also increased the intracellular levels of reactive oxygen species (ROS). The ROS inhibitor N-acetyl-L-cysteine rescued cells from Foxp3-expression-induced senescence. Furthermore, the elevated ROS levels that accompanied Foxp3 overexpression were paralleled by an increase in p21 expression. Knockdown of p21 in Foxp3-expressing MEFs abrogated the Foxp3-dependent increase in ROS levels, indicating that Foxp3 acts through the induction of p21 and the subsequent ROS elevation to trigger senescence. Collectively, these results suggest that Foxp3 is a downstream target of p53 that is sufficient to induce p21 expression and ROS production and is necessary for p53-mediated senescence.
Project description:As a critical cellular stress sensor, p53 mediates a variety of defensive processes including cell-cycle arrest, apoptosis, and senescence to prevent propagation of hyperproliferative cells or cells with a damaged genome, hence the formation of neoplasia. Transactivation of downstream genes plays an important while sometimes controversial role in regulating these cellular processes. To evaluate the dependence on transcriptional activation in p53’s activities, we generated genetically-modified mouse lines carrying mutations in the transactivation domains (TADs) of p53. These transactivatio-deficient mutants serve as unique reagents to probe the dependence on robust transactivation in p53-mediated cellular functions, as well as the underneath mechanisms. To identify genes differentially regulated by these p53 mutants, we performed gene expression profiling analysis on mouse embryonic fibroblast cells (MEFs) from these mice in the context of oncogenic Ras-induced premature cellular senescence. Mouse embryonic fibroblasts (MEFs) with different p53 genotypes were infected with retroviral H-Ras V12, which induces premature cellular senescence in p53 wild-type MEFs but not in p53 null MEFs. 5 genotypic groups of MEFs were used in the study: (i) p53L25Q/W26S, or "25,26", in which the first TAD (transactivation domain) of p53 is disrupted by the mutation, 5 biological samples; (ii) p53W53Q/F54S, or "53,54", in which the second TAD of p53 is disrupted by the mutation, 3 biological samples; (iii) p53L25Q/W26S/W53Q/F54S, or "QM", in which both TADs or p53 are disrupted, 3 biological samples; (iv) p53 wild-type, or "WT", 6 biological samples; (v) p53 null, or "Null", 6 biological samples.
Project description:As a critical cellular stress sensor, p53 mediates a variety of defensive processes including cell-cycle arrest, apoptosis, and senescence to prevent propagation of hyperproliferative cells or cells with a damaged genome, hence the formation of neoplasia. Transactivation of downstream genes plays an important while sometimes controversial role in regulating these cellular processes. To evaluate the dependence on transcriptional activation in p53’s activities, we generated genetically-modified mouse lines carrying mutations in the transactivation domains (TADs) of p53. These transactivatio-deficient mutants serve as unique reagents to probe the dependence on robust transactivation in p53-mediated cellular functions, as well as the underneath mechanisms. To identify genes differentially regulated by these p53 mutants, we performed gene expression profiling analysis on mouse embryonic fibroblast cells (MEFs) from these mice in the context of oncogenic Ras-induced premature cellular senescence.
Project description:Mice on two different ketogenic diets induce p53 and cellular senescence in multiple organs, including heart and kidney. This is mediated through inactivation of MDM2 by caspase-2 cleavage, leading to p53 accumulation and induction of p21. Ketogenic diet also induced pAMPK, suggesting that persistent activation leads to p53-dependent senescence.
Project description:Deregulated expression of the c-MYC oncogene induces unscheduled DNA replication, DNA damage, and activation of the p53 tumor suppressor. The AP4 transcription factor is a direct c-MYC target gene involved in cell proliferation, epithelial-mesenchymal transition, and stemness, as well as suppression of DNA damage and senescence. Here, we analyzed the role of AP4 and p53 downstream of c-MYC activation using a CRISPR/Cas9-approach in MCF-7 cells.
Project description:Telomere erosion contributes to age-associated tissue dysfunction and senescence, and p53 plays a crucial role in this response. We undertook a genome-wide screen to identify gene deletions that sensitized p53-positive human cells to loss of telomere integrity, and uncovered a previously unannotated gene, C16ORF72, which we term Telomere Attrition and p53 Response 1: TAPR1. CRISPR-Cas9 mediated deletion of TAPR1 led to elevated p53 and induction of p53 transcriptional targets. TAPR1-disrupted cells exhibited a synthetic-sick relationship with the loss of telomerase, or treatment with the topoisomerase II inhibitor doxorubicin. Stabilization of p53 with nutlin-3a further decreased cell fitness in cells lacking TAPR1 or telomerase, whereas deletion of TP53 rescued the decreased fitness of TAPR1-deleted cells. We propose that TAPR1 regulates p53 turnover, thereby tapering the p53-dependent response to telomere erosion. We discuss the possible implications of such a mechanism in the preservation of genome integrity during senescence or aging.
Project description:Regulatory T (Treg) cells are important regulators of the immune system and have versatile functions for the homeostasis and repair of tissues. They express the forkhead box transcription factor Foxp3 as a lineage-defining protein. In mature Treg cells, the Foxp3 core promoter is unmethylated indicating that this area could harbor a transcription factor complex to initiate or repress gene expression, respectively. We used an unbiased method to identify Foxp3-promoter-binding transcription factors (TFs) by inverted chromatin immunoprecipitation (IP) followed by quantitative mass spectrometry. We identified several candidate factors which showed Foxp3-promoter suppressive capacity, one of which was T-cell factor 1 (Tcf1). Using viral overexpression and CRISPR/Cas knockout studies, we identified Tcf1 as a repressor of Foxp3 expression in primary conventional CD4 T cells (Tconv). In Tcf1-deficient animals, increased levels of Foxp3intermediateCD25negative T cells were identified in secondary lymphoid tissues, implicating that Tcf1 protects Foxp3-negative T cells from inadvertent Foxp3 expression.
Project description:Defective glucose-stimulated insulin secretion (GSIS) and β-cell senescence are hallmarks in diabetes. The mitochondrial enzyme pyruvate carboxylase (PC) has been shown to promote GSIS and β-cell proliferation in the clonal β-cell lines, yet its physiological relevance remains unknown. Here, we provide animal and human data showing a role of PC in protecting β-cells against senescence and maintaining GSIS under different physiological and pathological conditions. β-cell-specific deletion of PC impaired GSIS and induced β-cell senescence in the mouse models under either a standard chow diet or prolonged high-fat diet feeding. Transcriptomic analysis indicated that p53-related senescence and cell cycle arrest are activated in PC-deficient islets. Overexpression of PC inhibited hyperglycemia- and aging-induced p53-related senescence in human and mouse islets as well as INS-1E β-cells, whereas knockdown of PC provoked senescence. Mechanistically, PC interacted with MDM2 to prevent its degradation via the MDM2 binding motif, which in turn restricts the p53-dependent senescent program in β-cells. On the contrary, the regulatory effects of PC on GSIS and the tricarboxylic acid (TCA) anaplerotic flux are p53-independent. We illuminate a function of PC in controlling β-cell senescence through the MDM2–p53 axis.
Project description:Cellular senescence is a program of irreversible cell cycle arrest that normal cells undergo in response to progressive shortening of telomeres, changes in telomeric structure, oncogene activation or oxidative stress. The underlying signalling pathways, potentially of major clinicopathological relevance, are unknown. A major stumbling block to studying senescence has been the absence of suitable model systems because of the asynchrony of this process in heterogeneous cell populations. To simplify this process many investigators study oncogene-induced senescence due to expression of activated oncogenes where senescence occurs prematurely without telomere attrition and can be induced acutely in a variety of cell types. We have taken a different approach by making use of the finding that reconstitution of telomerase activity by introduction of the catalytic subunit of human telomerase alone is incapable of immortalising all human somatic cells, but inactivation of the p16-pRB and p53-p21 pathways are required in addition. The ability of SV40 large T antigen to inactivate the p16-pRB and p53-p21 pathways has enabled us to use a thermolabile mutant of LT antigen, in conjunction with hTERT, to develop conditionally immortalised human (HMF3A) fibroblasts that are immortal but undergo an irreversible growth arrest when the thermolabile LT antigen is inactivated leading to activation of pRB and p53. When these cells cease dividing, senescence-associated- b-galactosidase activity is induced and the growth-arrested cells have morphological features and express genes in common with senescent cells. Since these cells growth arrest in a synchronous manner they are an excellent starting point for dissecting the pathways that underlie cellular senescence and act downstream of p16-pRB and p53-p21 pathways. We have combined genome-wide expression profiling with genetic complementation to undertake identification of genes that are differentially expressed when these conditionally immortalised human fibroblasts undergo senescence upon activation of the p16-pRB and p53-p21 tumour suppressor pathways. Genes differentially expressed upon senescence will be identified by comparing arrays from growing versus senescent cells. Changes in gene expression due to the temperature shift will be eliminated by comparing with array data from the non-conditional HMF3S cells grown at 34°C ±0.5°C and 38°C ±0.5°C. To determine if the changes in gene expression upon senescence are specific and reversible, the set of differential genes will then be overlaid with array data from cells in which senescence has been bypassed by inactivation of the p16-pRB and p53-p21 tumour suppressor pathways