Project description:Signaling trough cytoplasmic or nuclear action of p53 is a major response mechanism to cellular stresses. While p53 protein levels have been shown to increase upon nutrient stresses such as starvation, the exact signaling cascade in this context remains elusive. Here, we show in a human hepatoma cell line that nutrient withdrawal leads to robust nuclear p53 stabilization and utilize various complementary omics approaches to dissect upstream and downstream networks in the response to starvation. Using the affinity purification mass spectrometry (MS) method BioID, we determine the cytoplasmic p53 interaction network within the immediate-early starvation response and show that p53 is dissociated from several metabolic enzymes and the kinase PAK2. Direct binding of p53 DNA-binding domain and N-terminal PAK2 was confirmed with nuclear magnetic resonance (NMR) interaction studies. Furthermore, rapid immunoprecipitation MS of endogenous proteins (RIME) uncovered the nuclear interactome under prolonged starvation, where we confirmed the novel p53 interactors SORBS1, involved in insulin signaling, and UGP2, a key enzyme of glycogen synthesis. Finally, transcriptomics after p53 re-expression on a CRISPR/Cas9 knock out background revealed a distinct starvation-specific transcriptome response and suggested novel nutrient-dependent p53 target genes. Together, our complementary approaches delineate several nodes of the p53 signaling cascade in response to starvation, shedding new light on the mechanisms of p53 as a nutrient stress sensor and regulator of specific transcriptional output. Given the central role of p53 in cancer biology and the beneficial effects of fasting in cancer treatment, the identified interaction partners and networks could pinpoint novel pharmacologic targets to fine-tune p53 activity.
Project description:p53 signaling is a major response mechanism to cellular stresses through cytoplasmic or nuclear action. While p53 protein levels have been shown to increase upon nutrient stresses such as starvation, the exact signaling cascade in this context remains elusive. Here, we use proximity biotinylation (BioID), to derive the cytoplasmic p53 interaction network as immediate early starvation response.
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:H1299 cells were overexpressed miR-138 or silenced AGO2. The expression of 92 genes associated with p53 using the “Human p53 Signaling Pathway PCR Array” qPCR gene expression profiling. H1299 cells were transfected with NC mimics, AGO2 siRNA or miR-138 for 48h. Equal amount total RNA from each group was pooled prior to gene expression analysis.
Project description:H1299 cells were overexpressed miR-138 or silenced AGO2. The expression of 92 genes associated with p53 using the “Human p53 Signaling Pathway PCR Array”
Project description:Protein degradation regulates cellular homeostasis, yet many degradation events are difficult to study because they lack a readily selectable phenotype. Here, we develop Degradation-Induced Pyroptosis TArgeting Receptors (DIPTAR), a modular synthetic biology platform that couples protein degradation to CARD8-mediated pyroptosis. Using HIF-1α as a model substrate, we show that DIPTAR faithfully reports oxygen-dependent VHL-mediated degradation and enables pooled CRISPR screening to identify established and previously unrecognized regulators of HIF-1α stability. DIPTAR is functional across multiple cell types and can be programmed with diverse proteins, including BRD4, IκBα, and p53, to convert distinct degradation stimuli into a common pyroptotic output. DIPTAR also detects pathogen-mediated perturbations of host degradation pathways, including both inhibition and induction of degradation-dependent signaling. By converting protein degradation into a robust selectable phenotype, DIPTAR provides a scalable platform for functional genetic discovery, interrogation of degradation pathways, degrader characterization, and investigation of host-pathogen interactions.
Project description:Ceramides are important participants of signal transduction, regulating fundamental cellular processes. Here we report the mechanism for activation of p53 tumor suppressor by C16-ceramide. C16-ceramide tightly binds within the p53 DNA binding domain (Kd ~ 60 nM), in close vicinity to the Box V motif. This interaction is highly selective towards the ceramide acyl chain length with its C10 atom being proximal to Ser240 and Ser241. Ceramide binding stabilizes p53 and disrupts its complex with E3 ligase MDM2 leading to the p53 accumulation, nuclear translocation and activation of the downstream targets. This is a novel physiological mechanism of p53 activation, which is fundamentally different from the canonical p53 regulation through protein-protein interactions or post-translational modifications. The discovered mechanism is triggered by serum or folate deprivation implicating it in the cellular response to nutrient/metabolic stress. Our study establishes C16-ceramide as the first natural small molecule activating p53 through the direct binding.