Expression Of P53-regulated Genes Research Articles

A dual role of RBM42 in modulating splicing and translation of CDKN1A/p21 during DNA damage response

p53-mediated cell cycle arrest during DNA damage is dependent on the induction of p21 protein, encoded by the CDKN1A gene. p21 inhibits cyclin-dependent kinases required for cell cycle progression to guarantee accurate repair of DNA lesions. Hence, fine-tuning of p21 levels is crucial to preserve genomic stability. Currently, the multilayered regulation of p21 levels during DNA damage is not fully understood. Herein, we identify the human RNA binding motif protein 42 (RBM42) as a regulator of p21 levels during DNA damage. Genome-wide transcriptome and interactome analysis reveals that RBM42 alters the expression of p53-regulated genes during DNA damage. Specifically, we demonstrate that RBM42 facilitates CDKN1A splicing by counteracting the splicing inhibitory effect of RBM4 protein. Unexpectedly, we also show that RBM42, underpins translation of various splicing targets, including CDKN1A. Concordantly, transcriptome-wide mapping of RBM42-RNA interactions using eCLIP further substantiates the dual function of RBM42 in regulating splicing and translation of its target genes, including CDKN1A. Collectively, our data show that RBM42 couples splicing and translation machineries to fine-tune gene expression during DNA damage response.

Low expression of the dynamic network markers FOS/JUN in pre-deteriorated epithelial cells is associated with the progression of colorectal adenoma to carcinoma

BackgroundDeterioration of normal intestinal epithelial cells is crucial for colorectal tumorigenesis. However, the process of epithelial cell deterioration and molecular networks that contribute to this process remain unclear.MethodsSingle-cell data and clinical information were downloaded from the Gene Expression Omnibus (GEO) database. We used the recently proposed dynamic network biomarker (DNB) method to identify the critical stage of epithelial cell deterioration. Data analysis and visualization were performed using R and Cytoscape software. In addition, Single-Cell rEgulatory Network Inference and Clustering (SCENIC) analysis was used to identify potential transcription factors, and CellChat analysis was conducted to evaluate possible interactions among cell populations. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and gene set variation analysis (GSVA) analyses were also performed.ResultsThe trajectory of epithelial cell deterioration in adenoma to carcinoma progression was delineated, and the subpopulation of pre-deteriorated epithelial cells during colorectal cancer (CRC) initialization was identified at the single-cell level. Additionally, FOS/JUN were identified as biomarkers for pre-deteriorated epithelial cell subpopulations in CRC. Notably, FOS/JUN triggered low expression of P53-regulated downstream pro-apoptotic genes and high expression of anti-apoptotic genes through suppression of P53 expression, which in turn inhibited P53-induced apoptosis. Furthermore, malignant epithelial cells contributed to the progression of pre-deteriorated epithelial cells through the GDF signaling pathway.ConclusionsWe demonstrated the trajectory of epithelial cell deterioration and used DNB to characterize pre-deteriorated epithelial cells at the single-cell level. The expression of DNB-neighboring genes and cellular communication were triggered by DNB genes, which may be involved in epithelial cell deterioration. The DNB genes FOS/JUN provide new insights into early intervention in CRC.

The Mettl3 epitranscriptomic writer amplifies p53 stress responses

The p53 transcription factor drives anti-proliferative gene expression programs in response to diverse stressors, including DNA damage and oncogenic signaling. Here, we seek to uncover new mechanisms through which p53 regulates gene expression using tandem affinity purification/mass spectrometry to identify p53-interacting proteins. This approach identified METTL3, an m6A RNA-methyltransferase complex (MTC) constituent, as a p53 interactor. We find that METTL3 promotes p53 protein stabilization and target gene expression in response to DNA damage and oncogenic signals, by both catalytic activity-dependent and independent mechanisms. METTL3 also enhances p53 tumor suppressor activity in invivo mouse cancer models and human cancer cells. Notably, METTL3 only promotes tumor suppression in the context of intact p53. Analysis of human cancer genome data further supports the notion that the MTC reinforces p53 function in human cancer. Together, these studies reveal a fundamental role for METTL3 in amplifying p53 signaling in response to cellular stress.

Structure of the p53/RNA polymerase II assembly

The tumor suppressor p53 protein activates expression of a vast gene network in response to stress stimuli for cellular integrity. The molecular mechanism underlying how p53 targets RNA polymerase II (Pol II) to regulate transcription remains unclear. To elucidate the p53/Pol II interaction, we have determined a 4.6 Å resolution structure of the human p53/Pol II assembly via single particle cryo-electron microscopy. Our structure reveals that p53’s DNA binding domain targets the upstream DNA binding site within Pol II. This association introduces conformational changes of the Pol II clamp into a further-closed state. A cavity was identified between p53 and Pol II that could possibly host DNA. The transactivation domain of p53 binds the surface of Pol II’s jaw that contacts downstream DNA. These findings suggest that p53’s functional domains directly regulate DNA binding activity of Pol II to mediate transcription, thereby providing insights into p53-regulated gene expression.

P55PIK Regulates P53-Dependent Apoptosis in Cancer Cells by Interacting with P53 DNA-Specific Domain.

PurposePhosphatidylinositol 3-kinase (PI3K) plays an important role in tumorigenesis by cross-talking with several signaling pathways. p55PIK is a unique regulatory subunit of PI3K and contains an extra 24-residue N-terminal domain (N24). This study aimed to explore the interaction of p55PIK with p53 and the role of p55PIK in regulating p53-dependent apoptosis in cancer cells.Materials and MethodsThe expression of p55PIK was detected in cancer cells, and the interaction of p55PIK with p53 was examined by immunoprecipitation and pull-down assay. The expression of p53-dependent apoptosis-related genes was detected by PCR.ResultsN24 domain of p55PIK interacted with DNA-specific binding domain (DBD) of p53. The increase or decrease of p55PIK expression led to the change of the expression of p53 and p53-regulated genes in cancer cells. Moreover, N24 peptide led to the change of the expression of p53-regulated genes. Moreover, a membrane-permeable N24 peptide enhanced p53-dependent apoptosis induced by methyl methanesulfonate.ConclusionOur results reveal a novel mechanism that regulates p53-dependent apoptosis in cancer cells via p55PIK-p53 interaction.

Honey bee (Apis mellifera) gut microbiota promotes host endogenous detoxification capability via regulation of P450 gene expression in the digestive tract.

SummaryThere is growing number of studies demonstrating a close relationship between insect gut microbiota and insecticide resistance. However, the contribution of the honey bee gut microbiota to host detoxification ability has yet to be investigated. In order to address this question, we compared the expression of cytochrome P450s (P450s) genes between gut microbiota deficient (GD) workers and conventional gut community (CV) workers and compared the mortality rates and the pesticide residue levels of GD and CV workers treated with thiacloprid or tau‐fluvalinate. Our results showed that gut microbiota promotes the expression of P450 enzymes in the midgut, and the mortality rate and pesticide residue levels of GD workers are significantly higher than those of CV workers. Further comparisons between tetracycline‐treated workers and untreated workers demonstrated that antibiotic‐induced gut dysbiosis leads to attenuated expression of P450s in the midgut. The co‐treatment of antibiotics and pesticides leads to reduced survival rate and a significantly higher amount of pesticide residues in honey bees. Taken together, our results demonstrated that honey bee gut symbiont could contribute to bee health through the modification of the host xenobiotics detoxification pathways and revealed a potential negative impact of antibiotics to honey bee detoxification ability and health.

Histone 3 Lysine 9 Methylating Enzyme G9a Regulates Transcriptional Expression of Nuclear Receptors and Cytochrome P450 Genes in HepaRG Cells

Histone modification transcriptionally regulate gene expression. Cytochrome P450 genes are studied extensively in terms of regulation of expression through histone modification. Histone 3 lysine 4 (H3K4) and Histone 3 lysine 27 (H3K27) methylation are studied extensively in regulation of P450 gene expression. Another histone modification Histone 3 lysine 9 methylation, is well known for transcriptional repression of genes but not studies well in regulation of nuclear receptors and cytochrome P450 gene expression. In this study, the role of histone methyl transferase G9a, which is responsible for mono and di‐methylation of histone 3 lysine 9 residue, was studied in regulation of drug metabolizing enzymes and nuclear receptors. We treated HepaRG cell with small interfering RNA to selectively knockdown EHMT2 mRNA and using adenovirus, G9a was overexpressed to study the effect on nuclear receptors CAR (NR1I3), PXR (NR1I2), AHR and heterodimer partner RXRα along with the selected drug metabolizing cytochrome P450 genes. In pathological conditions such as steatosis, the expression of nuclear receptors and cytochrome P450 genes is affected along with G9a in a mice model treated with high fat diet. In this study, we treated HepaRG cells with fatty acids to induce steatosis. In conclusion we observed that loss of G9a shown to decrease mRNA expression of nuclear receptors and cytochrome P450 genes whereas overexpression of G9a increased expression of nuclear receptors CAR (NR1I3), PXR (NR1I2)and selected drug metabolizing enzymes CYP1A2, CYP2B6, CYP2C9, CYP3A4 etc. In fatty acid treated cells overexpression of G9a was observed to prevent fatty acid mediated down regulation of nuclear receptor CAR (NR1I3) and drug metabolizing enzyme genes CYP2C19, CYP2C8 and CYP3A4.Support or Funding InformationThis project work was funded by Boehringer Ingelheim Pharmaceuticals

Carfilzomib Induces Drug Resistance in A2780 Ovarian Cancer Cells Through p53-Dependent and Caspase-3 Independent Pathways

Introduction: Resistance to selective small-molecule inhibitors has been a substantial factor for limiting the efficacy of ovarian cancer. Recent studies have revealed that proteasome inhibitors induce acquired drug resistance. The possible mechanisms underlying the resistance to carfilzomib (CFZ), a recently developed inhibitor of proteasome, has not been well studied. This experimental study has aimed to determine if CFZ induces drug resistance in A2780 ovarian cancer cells through p53- and caspase-3 dependent pathways. Materials and Methods: The A2780CFZ cells were generated by continuous culturing of A2780S cells in the presence of CFZ for 4 months. The MTT cytotoxic assay was applied to compare the survival rates in A2780CFZ and A2780S cells. Also, the relative expression of p53 and caspase-3 genes were evaluated using quantitative real-time polymerase chain reaction (qRT-PCR). The nonparametric ANOVA and Friedman tests were used for data analysis. Results: A significant difference was observed between the viability of resistant- and sensitive-A2780 cells exposed to various concentrations of CFZ, indicating that A2780S cells have become resistant to this drug under long-term culture. Compared with A2780CFZ cells, the mRNA levels of p53 gene in A2780S cells were significantly increased after 12 (P = 0.008), and 24 hours (P = 0.034) . Also, no significant differences were observed regarding caspase-3 mRNA levels between both cell lines (P > 0.05). Conclusions: The findings of this study suggest that regulation of p53 gene expression in A2780CFZ cells might be the possible primary mechanism for gaining resistance against CFZ, but this might be independent of caspase cascades activation. Further studies are required to find strategies for overcoming CFZ resistance.

MSK1 functions as a transcriptional coactivator of p53 in the regulation of p21 gene expression

Mitogen- and stress-activated kinase 1 (MSK1) is a chromatin kinase that facilitates activator-dependent transcription by altering chromatin structure through histone H3 phosphorylation. The kinase activity of MSK1 is activated by intramolecular autophosphorylation, which is initially triggered by the activation of upstream mitogen-activated protein kinases (MAPKs), such as p38 and ERK1/2. MSK1 has been implicated in the expression of p21, a p53 target gene; however, the precise connection between MSK1 and p53 has not been clearly elucidated. Here, using in vitro and cell-based transcription assays, we show that MSK1 functions as a transcriptional coactivator of p53 in p21 expression, an action associated with MAPK-dependent phosphorylation of MSK1 and elevated kinase activity. Of special significance, we show that MSK1 directly interacts with p53 and is recruited to the p21 promoter, where it phosphorylates histone H3 in a p53-dependent manner. In addition, phosphomimetic mutant analysis demonstrated that negative charges in the hydrophobic motif are critical for serine 212 phosphorylation in the N-terminal kinase domain, which renders MSK1 competent for histone kinase activity. These studies suggest that MSK1 acts through a direct interaction with p53 to function as a transcriptional coactivator and that MSK1 activation by upstream MAPK signaling is important for efficient p21 gene expression.

Adenovirus 5 E1A-Mediated Suppression of p53 via FUBP1.

Far-upstream element (FUSE) binding protein 1 (FUBP1) was originally identified as a regulator of the oncogene c-Myc via binding to the FUSE within the c-Myc promoter and activating the expression of the gene. Recent studies have identified FUBP1 as a regulator of transcription, translation, and splicing via its DNA and RNA binding activities. Here we report the identification of FUBP1 as a novel binding partner of E1A. FUBP1 binds directly to E1A via the N terminus (residues 1 to 82) and conserved region 3 (residues 139 to 204) of adenovirus 5 E1A. The depletion of FUBP1 via short interfering RNAs (siRNA) reduces virus growth and drives the upregulation of the cellular stress response by activating the expression of p53-regulated genes. During infection, FUBP1 is relocalized within the nucleus, and it is recruited to viral promoters together with E1A while at the same time being lost from the FUSE upstream of the c-Myc promoter. The depletion of FUBP1 affects viral and cellular gene expression. Importantly, in FUBP1-depleted cells, p53-responsive genes are upregulated, p53 occupancy on target promoters is enhanced, and histone H3 lysine 9 is hyperacetylated. This is likely due to the loss of the FUBP1-mediated suppression of p53 DNA binding. We also observed that E1A stabilizes the FUBP1-p53 complex, preventing p53 promoter binding. Together, our results identify, for the first time, FUBP1 as a novel E1A binding protein that participates in aspects of viral replication and is involved in the E1A-mediated suppression of p53 function.IMPORTANCE Viral infection triggers innate cellular defense mechanisms that have evolved to block virus replication. To overcome this, viruses have counterevolved mechanisms that ensure that cellular defenses are either disarmed or not activated to guarantee successful replication. One of the key regulators of cellular stress is the tumor suppressor p53 that responds to a variety of cellular stress stimuli and safeguards the integrity of the genome. During infection, many viruses target the p53 pathway in order to deactivate it. Here we report that human adenovirus 5 coopts the cellular protein FUBP1 to prevent the activation of the p53 stress response pathway that would block viral replication. This finding adds to our understanding of p53 deactivation by adenovirus and highlights its importance in infection and innate immunity.

40 Years of Research Put p53 in Translation.

Since its discovery in 1979, p53 has shown multiple facets. Initially the tumor suppressor p53 protein was considered as a stress sensor able to maintain the genome integrity by regulating transcription of genes involved in cell cycle arrest, apoptosis and DNA repair. However, it rapidly came into light that p53 regulates gene expression to control a wider range of biological processes allowing rapid cell adaptation to environmental context. Among them, those related to cancer have been extensively documented. In addition to its role as transcription factor, scattered studies reported that p53 regulates miRNA processing, modulates protein activity by direct interaction or exhibits RNA-binding activity, thus suggesting a role of p53 in regulating several layers of gene expression not restricted to transcription. After 40 years of research, it appears more and more clearly that p53 is strongly implicated in translational regulation as well as in the control of the production and activity of the translational machinery. Translation control of specific mRNAs could provide yet unsuspected capabilities to this well-known guardian of the genome.

How mutations shape p53 interactions with the genome to promote tumorigenesis and drug resistance.

The tumor suppressive transcription factor p53 regulates a wide array of cellular processes that confer upon cells an essential protection against cancer development. Wild-type p53 regulates gene expression by directly binding to DNA in a sequence-specific manner. p53 missense mutations are the most common mutations in malignant cells and can be regarded as synonymous with anticancer drug resistance and poor prognosis. The current review provides an overview of how the extraordinary variety of more than 2000 different mutant p53 proteins, known as the p53 mutome, affect the interaction of p53 with DNA. We discuss how the classification of p53 mutations to loss of function (LOF), gain of function (GOF), and dominant-negative (DN) inhibition of a remaining wild-type allele, hides a complex p53 mutation spectrum that depends on the distinctive nature of each mutant protein, requiring different therapeutic strategies for each mutant p53 protein. We propose to regard the different mutant p53 categories as continuous variables, that may not be independent of each other. In particular, we suggest here to consider GOF mutations as a special subset of LOF mutations, especially when mutant p53 binds to DNA through cooperation with other transcription factors, and we present a model for GOF mechanism that consolidates many observations on the GOF phenomenon. We review how novel mutant p53 targeting approaches aim to restore a wild-type-like DNA interaction and to overcome resistance to cancer therapy.

A p53-regulated apoptotic gene signature predicts treatment response and outcome in pediatric acute lymphoblastic leukemia.

Gene signatures have been associated with outcome in pediatric acute lymphoblastic leukemia (ALL) and other malignancies. However, determining the molecular drivers of these expression changes remains challenging. In ALL blasts, the p53 tumor suppressor is the primary regulator of the apoptotic response to genotoxic chemotherapy, which is predictive of outcome. Consequently, we hypothesized that the normal p53-regulated apoptotic response to DNA damage would be altered in ALL and that this alteration would influence drug response and treatment outcome. To test this, we first used global expression profiling in related human B-lineage lymphoblastoid cell lines with either wild type or mutant TP53 to characterize the normal p53-mediated transcriptional response to ionizing radiation (IR) and identified 747 p53-regulated apoptotic target genes. We then sorted these genes into six temporal expression clusters (TECs) based upon differences over time in their IR-induced p53-regulated gene expression patterns, and found that one cluster (TEC1) was associated with multidrug resistance in leukemic blasts in one cohort of children with ALL and was an independent predictor of survival in two others. Therefore, by investigating p53-mediated apoptosis in vitro, we identified a gene signature significantly associated with drug resistance and treatment outcome in ALL. These results suggest that intersecting pathway-derived and clinically derived expression data may be a powerful method to discover driver gene signatures with functional and clinical implications in pediatric ALL and perhaps other cancers as well.

Abstract 3225: SHetA2 targets mortalin-p53 interaction in differential induction of apoptosis in ovarian cancer over normal cells

Abstract Introduction: Identical TP53 mutations observed in fallopian tube pre-neoplastic lesions and high grade serous ovarian cancer (HGSOC) from the same patient suggest that these mutations drive ovarian carcinogenesis. While elevated p53 protein expression caused by these mutations increase cell survival, persistently high levels can cause apoptosis. Mortalin (HSPA9) is a chaperone protein which plays a major role in protecting cancer cells from p53-mediated apoptosis by binding to p53 and preventing it from translocating to the nucleus where it transactivates apoptosis-inducing genes and to the mitochondria where it inhibits Bcl-2 and induces Bax pore formation. SHetA2 is an anti-cancer drug that binds mortalin and induces apoptosis in cancer, but not in normal cells. We hypothesized that release of p53 from mortalin contributes to the mechanism of SHetA2-induced apoptosis in cancer, but not in normal cells. Methods: SHetA2 effects on mortalin and p53 interaction and subcellular localization were evaluated by co-immunoprecipitation in cell extracts and fluorescent cytochemistry of human ovarian cancer cell lines and tissues and human fallopian tube secretory epithelial cells (hFTSECs) cultures and tissues. Effects of SHetA2 and manipulations of mortalin and p53 expression, function and localization in ovarian cancer cells were measured using the MTS dye to detect viable cells, Flow cytometric analysis of Annexin-V/PI cell staining to detect apoptosis and a PCR array to measure p53 regulated gene expression. Results: Mortalin bound to p53 in protein extracts of cultures and tissues from ovarian cancer, but not from hFTSECs. SHetA2 caused dose-responsive apoptosis in association with nuclear and mitochondrial accumulation of p53 in ovarian cancer cell lines harboring wild type or S215R, L130V TP53 mutants, but not in hFTSECs. Mortalin overexpression or p53 knockdown reduced SHetA2 cytotoxicity in ovarian cancer cells. Mortalin knockdown, p53 overexpression, and chemical inhibitors of p53 transcription (Pifithrin-α) and p53 mitochondrial localization (Pifithrin-µ) were lethal to ovarian cancer cells at effective concentrations and therefore ineffective tools for probing the SHetA2 apoptosis mechanism. In the A2780 cell line containing wild type p53, SHetA2 caused ≥2 fold regulation of p53 signaling genes (p21, FOXO3, IGF1R, MDM4, SESN2, SIAH1, DR5, CAPS2, CCNE1, CDC25A, E2F1, PCNA and TP63). Our analysis of p53 mutations using The Cancer Genome Atlas (TCGA) data revealed that majority of HGSOC exhibited p53 mutations spanning from exon 3-9, with the majority being missense mutations in the DNA binding domain associated with increased protein stability and gain of function. Conclusion: Release of wild type and mutant p53 proteins from mortalin contributes to the mechanism of SHetA2-induced apoptosis in cancer cells and does not occur in healthy cells. Funded by R01CA196200. Citation Format: Satish Kumar Ramraj, Richard Pelikan, Vishal Chandra, Doris Benbrook. SHetA2 targets mortalin-p53 interaction in differential induction of apoptosis in ovarian cancer over normal cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3225. doi:10.1158/1538-7445.AM2017-3225

PRIMA-1 induces caspase-mediated apoptosis in acute promyelocytic leukemia NB4 cells by inhibition of nuclear factor-κB and downregulation of Bcl-2, XIAP, and c-Myc.

Restoration of p53 function triggers cell death and eliminates tumors in vivo. Identification of p53-reactivating small molecules such as PRIMA-1 holds promise for effective new anticancer therapies. Here, we investigated the effects of small molecule PRIMA-1 on cell viability and expression of p53-regulated genes and proteins in the acute promyelocytic leukemia-derived NB4 cell line. Our results showed that PRIMA-1 had antileukemic properties in acute promyelocytic leukemia-derived NB4 cells. PRIMA-1-triggered apoptosis in a dose-dependent and time-dependent manner as indicated by the MTT assay and annexin-V staining. Apoptosis induction by PRIMA-1 was associated with caspase-9, caspase-7 activation and PARP cleavage. p21 protein expression was increased after PRIMA-1 treatment and real-time PCR analysis of proapoptotic p53 target genes indicated upregulation of Bax and Noxa. Western blot analysis showed that IκBα phosphorylation and its degradation were inhibited by PRIMA-1. Moreover, protein expression of nuclear factor-κB-regulated antiapoptotic (Bcl-2 and XIAP) and proliferative (c-Myc) gene products was decreased. Importantly, PRIMA-1 did not show any significant apoptotic effect in normal human peripheral blood mononuclear cells. These in-vitro studies imply that p53 reactivation by small compounds may become a novel anticancer therapy in acute promyelocytic leukemia.

Editor's Highlight: Hydroxyurea Exposure Activates the P53 Signaling Pathway in Murine Organogenesis-Stage Embryos.

Hydroxyurea, an anticancer agent and potent teratogen, induces oxidative stress and activates a DNA damage response pathway in the gestation day (GD) 9 mouse embryo. To delineate the stress response pathways activated by this drug, we investigated the effect of hydroxyurea exposure on the transcriptome of GD 9 embryos. Timed pregnant CD-1 mice were treated with saline or hydroxyurea (400 mg/kg or 600 mg/kg) on GD 9; embryonic gene and protein expression were examined 3 h later. Microarray analysis revealed that the expression of 1346 probe sets changed significantly in embryos exposed to hydroxyurea compared with controls; the P53 signaling pathway was highly affected. In addition, P53 related family members, P63 and P73, were predicted to be activated and had common and unique downstream targets. Western blot analysis revealed that active phospho-P53 was significantly increased in drug-exposed embryos; confocal microscopy showed that the translocation of phospho-P53 to the nucleus was widespread in the embryo. Furthermore, qRT-PCR showed that the expression of P53-regulated genes (Cdkn1A, Fas, and Trp53inp1) was significantly upregulated in hydroxyurea-exposed embryos; the concentration of the redox sensitive P53INP1 protein was also increased in a hydroxyurea dose-dependent fashion. Thus, hydroxyurea elicits a significant effect on the transcriptome of the organogenesis stage murine embryo, activating several key developmental signaling pathways related to DNA damage and oxidative stress. We propose that the P53 pathway plays a central role in the embryonic stress response and the developmental outcome after teratogen exposure.

Quantitative phosphoproteomic analysis reveals γ-bisabolene inducing p53-mediated apoptosis of human oral squamous cell carcinoma via HDAC2 inhibition and ERK1/2 activation.

γ-Bisabolene, one of main components in cardamom, showed potent in vitro and in vivo anti-proliferative activities against human oral squamous cell carcinoma (OSCC). γ-Bisabolene activated caspases-3/9 and decreased mitochondrial memebrane potential, leading to apoptosis of OSCC cell lines (Ca9-22 and SAS), but not normal oral fibroblast cells. Phosphoproteome profiling of OSCC cells treated with γ-bisabolene was identified using TiO2-PDMS plate and LC-MS/MS, then confirmed using Western blotting and real-time RT-PCR assays. Phosphoproteome profiling revealed that γ-bisabolene increased the phosphorylation of ERK1/2, protein phosphatases 1 (PP1), and p53, as well as decreased the phosphorylation of histone deacetylase 2 (HDAC2) in the process of apoptosis induction. Protein-protein interaction network analysis proposed the involvement of PP1-HDAC2-p53 and ERK1/2-p53 pathways in γ-bisabolene-induced apoptosis. Subsequent assays indicated γ-bisabolene eliciting p53 acetylation that enhanced the expression of p53-regulated apoptotic genes. PP1 inhibitor-2 restored the status of HDAC2 phosphorylation, reducing p53 acetylation and PUMA mRNA expression in γ-bisabolene-treated Ca9-22 and SAS cells. Meanwhile, MEK and ERK inhibitors significantly decreased γ-bisabolene-induced PUMA expression in both cancer cell lines. Notably, the results ascertained the involvement of PP1-HDAC2-p53 and ERK1/2-p53 pathways in mitochondria-mediated apoptosis of γ-bisabolene-treated cells. This study demonstrated γ-bisabolene displaying potent anti-proliferative and apoptosis-inducing activities against OSCC in vitro and in vivo, elucidating molecular mechanisms of γ-bisabolene-induced apoptosis. The novel insight could be useful for developing anti-cancer drugs.

Mutant p53 cooperates with the SWI/SNF chromatin remodeling complex to regulate VEGFR2 in breast cancer cells.

Mutant p53 impacts the expression of numerous genes at the level of transcription to mediate oncogenesis. We identified vascular endothelial growth factor receptor 2 (VEGFR2), the primary functional VEGF receptor that mediates endothelial cell vascularization, as a mutant p53 transcriptional target in multiple breast cancer cell lines. Up-regulation of VEGFR2 mediates the role of mutant p53 in increasing cellular growth in two-dimensional (2D) and three-dimensional (3D) culture conditions. Mutant p53 binds near the VEGFR2 promoter transcriptional start site and plays a role in maintaining an open conformation at that location. Relatedly, mutant p53 interacts with the SWI/SNF complex, which is required for remodeling the VEGFR2 promoter. By both querying individual genes regulated by mutant p53 and performing RNA sequencing, the results indicate that >40% of all mutant p53-regulated gene expression is mediated by SWI/SNF. We surmise that mutant p53 impacts transcription of VEGFR2 as well as myriad other genes by promoter remodeling through interaction with and likely regulation of the SWI/SNF chromatin remodeling complex. Therefore, not only might mutant p53-expressing tumors be susceptible to anti VEGF therapies, impacting SWI/SNF tumor suppressor function in mutant p53 tumors may also have therapeutic potential.

Interactions of Chromatin Context, Binding Site Sequence Content, and Sequence Evolution in Stress-Induced p53 Occupancy and Transactivation

Cellular stresses activate the tumor suppressor p53 protein leading to selective binding to DNA response elements (REs) and gene transactivation from a large pool of potential p53 REs (p53REs). To elucidate how p53RE sequences and local chromatin context interact to affect p53 binding and gene transactivation, we mapped genome-wide binding localizations of p53 and H3K4me3 in untreated and doxorubicin (DXR)-treated human lymphoblastoid cells. We examined the relationships among p53 occupancy, gene expression, H3K4me3, chromatin accessibility (DNase 1 hypersensitivity, DHS), ENCODE chromatin states, p53RE sequence, and evolutionary conservation. We observed that the inducible expression of p53-regulated genes was associated with the steady-state chromatin status of the cell. Most highly inducible p53-regulated genes were suppressed at baseline and marked by repressive histone modifications or displayed CTCF binding. Comparison of p53RE sequences residing in different chromatin contexts demonstrated that weaker p53REs resided in open promoters, while stronger p53REs were located within enhancers and repressed chromatin. p53 occupancy was strongly correlated with similarity of the target DNA sequences to the p53RE consensus, but surprisingly, inversely correlated with pre-existing nucleosome accessibility (DHS) and evolutionary conservation at the p53RE. Occupancy by p53 of REs that overlapped transposable element (TE) repeats was significantly higher (p<10−7) and correlated with stronger p53RE sequences (p<10−110) relative to nonTE-associated p53REs, particularly for MLT1H, LTR10B, and Mer61 TEs. However, binding at these elements was generally not associated with transactivation of adjacent genes. Occupied p53REs located in L2-like TEs were unique in displaying highly negative PhyloP scores (predicted fast-evolving) and being associated with altered H3K4me3 and DHS levels. These results underscore the systematic interaction between chromatin status and p53RE context in the induced transactivation response. This p53 regulated response appears to have been tuned via evolutionary processes that may have led to repression and/or utilization of p53REs originating from primate-specific transposon elements.

Oncoprotein E7 from Beta Human Papillomavirus 38 Induces Formation of an Inhibitory Complex for a Subset of p53-Regulated Promoters

Our previous studies on cutaneous beta human papillomavirus 38 (HPV38) E6 and E7 oncoproteins highlighted a novel activity of IκB kinase beta (IKKβ) in the nucleus of human keratinocytes, where it phosphorylates and stabilizes ΔNp73α, an antagonist of p53/p73 functions. Here, we further characterize the role of the IKKβ nuclear form. We show that IKKβ nuclear translocation and ΔNp73α accumulation are mediated mainly by HPV38 E7 oncoprotein. Chromatin immunoprecipitation (ChIP)/Re-ChIP experiments showed that ΔNp73α and IKKβ are part, together with two epigenetic enzymes DNA methyltransferase 1 (DNMT1) and the enhancer of zeste homolog 2 (EZH2), of a transcriptional regulatory complex that inhibits the expression of some p53-regulated genes, such as PIG3. Recruitment to the PIG3 promoter of EZH2 and DNMT1 resulted in trimethylation of histone 3 on lysine 27 and in DNA methylation, respectively, both events associated with gene expression silencing. Decreases in the intracellular levels of HPV38 E7 or ΔNp73α strongly affected the recruitment of the inhibitory transcriptional complex to the PIG3 promoter, with consequent restoration of p53-regulated gene expression. Finally, the ΔNp73α/IKKβ/DNMT1/EZH2 complex appears to bind a subset of p53-regulated promoters. In fact, the complex is efficiently recruited to several promoters of genes encoding proteins involved in DNA repair and apoptosis, whereas it does not influence the expression of the prosurvival factor Survivin. In summary, our data show that HPV38 via E7 protein promotes the formation of a multiprotein complex that negatively regulates the expression of several p53-regulated genes.