Using ribosome profiling to investigate the effect of p53 on translation in cancer cells
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ABSTRACT: p53 is deleted or dysfunctional, or develops these features during the course of disease, with a frequency of about 50% in human cancers. This is clinically important because this group of patients respond very poorly to treatment. Our approach to discovering novel biomarkers or targets for therapy for p53 deleted/dysfunctional disease is to find genes that are translationally regulated by p53. The aim of this experiment is to compare translational efficiencies in cancer cells that are p53 WT, p53-/-, or p53 R175H, in response to doxorubicin.
Project description:Oncogene-induced senescence (OIS) is a p53-dependent defence mechanism against uncontrolled proliferation. Consequently, many human tumours harbour p53 mutations while others show a dysfunctional p53 pathway, frequently by unknown mechanisms. We identified BRD7, a bromodomain-containing protein whose inhibition allows full neoplastic transformation in the presence of wild-type p53. Intriguingly, in human breast tumours harbouring wild-type, but not mutant p53, the BRD7 gene locus was frequently deleted and low BRD7 expression was found in a subgroup of tumours. Functionally, BRD7 is required for efficient p53-mediated transcription of a subset of target genes. BRD7 interacts with p53 and p300, and is recruited to target gene promoters, affecting histone acetylation, p53 acetylation, and promoter activity. Thus, BRD7 suppresses tumourigenicity by serving as a p53 cofactor required for efficient induction of p53-dependent OIS. We recorded mRNA expression profiles of BJ primary fibroblasts expressing the oncogene RasV12 and either control vector, one of two BRD7 knockdown vectors, or p53 knockdown vector. In addition, we profiled genome-wide protein DNA interactions for p53 and BRD7 using ChIP-Seq. p53- and BRD7-binding sites were recorded in RasV12-expressing BJ cells; as a control we used knockdown of the gene of interest (BRD7 or p53).
Project description:RNA-sequencing was performed to determine the differences between cells that contain mutant p53 and a transactivation deficient mutant of p53 to determine why the TAD mutant cells don't form tumors.
Project description:This experiment was performed to determine which gene promoters mutant p53 binds and transcriptionally regulates in order to understand how mutant p53 accomplishes its gain of function phenotype.
Project description:The tetrameric tumor suppressor p53 represents a great challenge for 3D structural analysis due to its high degree of intrinsic disorder (ca. 40%). We developed and applied an integrative structural biology approach combining complementary techniques of structural mass spectrometry (MS), namely cross-linking mass spectrometry (XL-MS), protein footprinting, and hydrogen/deuterium exchange mass spectrometry (HDX-MS), with advanced protein structure prediction approaches to gain insights into the disordered C-terminal region of p53. Additionally, we evaluate possible differences in p53 regarding solvent accessibility and topology upon DNA binding. Our quantitative XL-MS and lysine labeling data show no major conformational differences in p53 between DNA-bound and DNA-free states. Integration of experimental data generate p53 models for p53’s intrinsically disordered regions (IDRs) that reflect substantial compaction of the molecule. Our models provide the most detailed description of the relationship between p53’s folded regions and IDRs that is available to date. The synergies between complementary structural MS techniques and computational modeling as pursued in our integrative approach is envisioned to serve as general strategy for studying intrinsically disordered proteins (IDPs) and IDRs.
Project description:This experiment aimed to determine the genes that were upregulated when mutant p53 (R273H) was expressed. We used H1299 lung cancer cells that are endogenously p53-null and overexpressed the p53 mutant.
Project description:Advanced colorectal cancer (CRC) is an unresolved clinical problem. Epigenetic drugs belonging to the group of histone deacetylase inhibitors (HDACi) may combat CRC in rationally designed treatment schedules. Unfortunately, there is sparse evidence on molecular mechanisms and markers that determine cellular sensitivity to HDACi. Irinotecan is widely used to treat CRC and causes replication stress (RS) and DNA damage as topoisomerase-I inhibitor. We applied irinotecan and the class I HDACi entinostat (MS-275) to isogenic p53-positive and -negative CRC cells. Combinations of irinotecan and MS-275 evoke mitochondrial damage, caspase-mediated apoptosis, and RS-associated DNA damage synergistically and p53-dependently. Targeted mass spectrometry and immunoblot show that irinotecan induces phosphorylation, acetylation, and accumulation of p53 and its target genes. Addition of MS-275 augments the irinotecan-induced acetylation of C-terminal lysine residues of p53 but decreases its phosphorylation and p53 target gene induction. Furthermore, MS-275 increases the amount of acetylated p53 at mitochondria and dysregulates the expression of pro- and anti-apoptotic BCL2 proteins in irinotecan-treated cells. Regarding DNA repair, we see that MS-275 represses the homologous recombination (HR) filament protein RAD51, which limits DNA damage and pro-apoptotic effects of irinotecan. These data suggest that key class I HDAC-dependent functions of p53 in cells with RS are linked to mitochondrial damage and a breakdown of HR. Most importantly, combinations of irinotecan plus MS-275 also kill short-term primary CRC cell cultures and organoids from CRC patients but spare organoids of adjacent matched normal tissue. Thus, irinotecan/HDACi treatment is a promising new approach for the therapy of p53-proficient tumors with clinically tractable inhibitors.
Project description:It has been recently shown that the transcription factor p53 induces the expression of multiple lincRNAs. However, relatively little is known about the role that lincRNAs play in this pathway. Here we characterize a lincRNA named PINT (p53 Induced Noncoding Transcript). We show that PINT is a ubiquitously expressed lincRNA that is finely regulated by p53. In mouse cells, PINT promotes cell proliferation and survival by regulating the expression of genes of TGF-beta, MAPK and p53 pathways. PINT is a nuclear lincRNA that directly interacts with Polycomb Repressive Complex 2 (PRC2), being required for PRC2 targeting of specific genes for repression. Furthermore, PINT functional activity is dependent on PRC2 expression, representing a connection between the p53 pathway and epigenetic regulation by PRC2. We have also identified PINT human ortholog (hPINT), which presents suggestive analogies with the mouse lincRNA. hPINT is similarly regulated by p53, and its expression correlates significantly with the same cellular pathways as the mouse ortholog, including the p53 pathway. Interestingly, hPINT is significantly downregulated in colon cancer, representing a novel tumor suppressor candidate. Our results not only help our understanding of the role of p53 and lincRNAs in cancer, but also contribute to the open debate regarding the utility of mouse models for the study of lincRNAs. Inhibition of PINT or p53 gene expression and subsequent treatment with 150 nM doxorubicine for 12h in MEF LSL p53 +/+ cells.
Project description:Loss of the p53-inducible LINC01021 in p53-proficient CRC cell lines results in increased sensitivity to DNA-damaging chemotherapeutics. Here, we comprehensively analyzed how LINC01021 affects the p53-induced transcriptional program. Using a CRISPR/Cas9-approach we deleted the p53 binding site in the LINC01021 promoter of SW480 colorectal cancer cells and subjected them to RNA-Seq analysis after activation of ectopic p53. RNA affinity purification followed by mass spectrometry was used identify proteins associated with LINC01021.
Project description:Wild type and mutant p53 were transfected in H1299 cells and the associated complexes were affinity purified. The p53 interacting proteins then analyzed by ms/ms.
Project description:Here we identify PURB, a dual DNA/RNA-binding protein, as a key mediator for LncRNAs to interact with p53. PURB is overexpressed in human cancers and loss of PURB expression in human cancer cells induces tumor growth suppression by activating p53. Interestingly, PURB knockdown activates only a subset of p53 target genes without affecting p53 protein levels and PURB is specifically recruited by p53 to the target genes in a promoter-specific manner. Moreover, a unique cis-regulatory element is identified at the target promoters recognized by PURB; loss of this element does not affect p53-mediated transactivation but abrogates the ability of p53 to recruit PURB to the promoters for repression. Notably, the ability of PURB in transcriptional repression requires its sequence-specific binding with HOTAIR, one of LncRNAs tightly associated with PURB. HOTAIR interacts directly with SUV39H1 and, bridging by the PURB/HOTAIR complex, p53 is able to recruit SUV39H1 histone methyltransferase to the target promoters for transcriptional repression. These data establish a new mode of LncRNA-mediated regulation of p53 transcription in a sequence-specific manner and also reveal, a previously unanticipated mechanism for promoter-specific regulation through a unique cis-regulatory element recognized by the LncRNA-protein complex.