Expression Of P53 Target Genes Research Articles

Dose escalation results of a phase 1b study of the MDM2 inhibitor AMG 232 with or without trametinib in patients (Pts) with relapsed/refractory (r/r) acute myeloid leukemia (AML).

7027 Background: The ubiquitin ligase MDM2 inhibits the tumor suppressor p53. In preclinical AML models, MDM2 inhibitors have antitumor activity as monotherapy that is synergistic when combined with MEK inhibitors. This open-label phase 1b study assessed the maximum tolerated dose (MTD), pharmacokinetics (PK), and preliminary antitumor activity of the investigational oral, selective MDM2 inhibitor AMG 232 as monotherapy or combined with the MEK kinase inhibitor trametinib in pts with r/r AML. Methods: Pts with r/r AML received AMG 232 for 7 days every 2 weeks (7 days on/7 days off) at 60, 120, 240, 480, and 960 mg PO QD as monotherapy (Arm 1) or combined with trametinib 2 mg PO QD (Arm 2). Primary endpoints were the incidence of adverse events (AEs), dose-limiting toxicities (DLTs), and PK. Additional endpoints included best response (revised IWG) and serum MIC-1 level (increased MIC-1 suggests p53 activation). p53 target gene ( P21, BAX, and PUMA) expression in bone marrow was assessed by microarray. Results: In total, 35 pts (Arm 1, n = 26; Arm 2, n = 9; median age, 68 y; range, 26–86) were treated. Arm 1 enrolled AMG 232 at 60 mg (n = 4), 90 mg (n = 4), 180 mg (n = 5), 240 mg (n = 3), and 360 (n = 10). Twenty-two (85%) pts in Arm 1 had treatment-related AEs; the most common were nausea (n = 14), diarrhea (n = 14), and vomiting (n = 6). No DLTs occurred; one pt is still on treatment. The MTD was determined as 360 mg based on tolerance of gastrointestinal toxicity. Arm 2 enrollment is ongoing at a fixed AMG 232 dose of 60 mg plus trametinib (n = 9). AMG 232 plasma exposure increased with dose escalation; PK was unaffected by trametinib. Trametinib PK was as expected. Increases from baseline (BL) to day 10 in serum MIC-1 were dose dependent. Evidence of increased P21, BAX, and PUMA expression (BL to day 7 or 8) was seen (n = 3). One pt (Arm 2) had complete remission (CR); three pts (Arm 1) achieved CRi/MLFS. Median response duration was 66 days [range, 21–377+]). Conclusions: AMG 232 monotherapy was tolerable in pts with r/r AML at doses up to 360 mg on a 7 days on/7 days off schedule with expected PK, on-target biological effects, and early evidence of antileukemia activity. Clinical trial information: NCT02016729.

P53 pathway determines the cellular response to alcohol-induced DNA damage in MCF-7 breast cancer cells.

Alcohol consumption is associated with increased breast cancer risk; however, the underlying mechanisms that contribute to mammary tumor initiation and progression are unclear. Alcohol is known to induce oxidative stress and DNA damage; likewise, p53 is a critical modulator of the DNA repair pathway and ensures genomic integrity. p53 mutations are frequently detected in breast and other tumors. The impact of alcohol on p53 is recognized, yet the role of p53 in alcohol-induced mammary carcinogenesis remains poorly defined. In our study, we measured alcohol-mediated oxidative DNA damage in MCF-7 cells using 8-OHdG and p-H2AX foci formation assays. p53 activity and target gene expression after alcohol exposure were determined using p53 luciferase reporter assay, qPCR, and Western blotting. A mechanistic study delineating the role of p53 in DNA damage response and cell cycle arrest was based on isogenic MCF-7 cells stably transfected with control (MCF-7/Con) or p53-targeting siRNA (MCF-7/sip53), and MCF-7 cells that were pretreated with Nutlin-3 (Mdm2 inhibitor) to stabilize p53. Alcohol treatment resulted in significant DNA damage in MCF-7 cells, as indicated by increased levels of 8-OHdG and p-H2AX foci number. A p53-dependent signaling cascade was stimulated by alcohol-induced DNA damage. Moderate to high concentrations of alcohol (0.1–0.8% v/v) induced p53 activation, as indicated by increased p53 phosphorylation, reporter gene activity, and p21/Bax gene expression, which led to G0/G1 cell cycle arrest. Importantly, compared to MCF-7/Con cells, alcohol-induced DNA damage was significantly enhanced, while alcohol-induced p21/Bax expression and cell cycle arrest were attenuated in MCF-7/sip53 cells. In contrast, inhibition of p53 degradation via Nutlin-3 reinforced G0/G1 cell cycle arrest in MCF-7 control cells. Our study suggests that functional p53 plays a critical role in cellular responses to alcohol-induced DNA damage, which protects the cells from DNA damage associated with breast cancer risk.

MP60-14 THE VON HIPPEL LINDAU (VHL) TUMOR SUPPRESSOR INHIBITS P53 TARGET GENE EXPRESSION TO PROMOTE APOPTOSIS-RESISTANCE IN CANCER

You have accessJournal of UrologyKidney Cancer: Basic Research & Pathophysiology II1 Apr 2017MP60-14 THE VON HIPPEL LINDAU (VHL) TUMOR SUPPRESSOR INHIBITS P53 TARGET GENE EXPRESSION TO PROMOTE APOPTOSIS-RESISTANCE IN CANCER Adam Kinnaird, Peter Dromparis, Aristeidis Boukouris, Vikram Gurtu, Bruno Saleme, Sotirios Zervopoulos, Gopinath Sutendra, and Evangelos Michelakis Adam KinnairdAdam Kinnaird More articles by this author , Peter DromparisPeter Dromparis More articles by this author , Aristeidis BoukourisAristeidis Boukouris More articles by this author , Vikram GurtuVikram Gurtu More articles by this author , Bruno SalemeBruno Saleme More articles by this author , Sotirios ZervopoulosSotirios Zervopoulos More articles by this author , Gopinath SutendraGopinath Sutendra More articles by this author , and Evangelos MichelakisEvangelos Michelakis More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2017.02.1851AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES VHL is characterized as a tumour suppressor, being suppressed in up to 90% of clear cell Renal Cell Carcinomas (ccRCC). Canonically, VHL binds to and mediates degradation of hypoxia inducible factors (HIF). However, VHL has been discovered to bind other proteins, like p53, thereby altering the cell in more ways than just HIF degradation. Furthermore, there are conflicting reports on the impact of VHL on cancer proliferation and apoptosis, which can be regulated by p53 target genes, like p21 and PUMA. We hypothesize that VHL inhibits p53 activation paradoxically leading to increased proliferation and reduced apoptosis in cancer cells. METHODS VHL-deficient cells were transiently (adenoviral) or stably (lentiviral) transduced with VHL. We generated VHL knockout cells using CRISPR/Cas9 genome editing technology. HIF overexpression was achieved using hypoxia or a non-degradable HIF-expressing adenovirus. Immunodeficient nude mice were injected with tumor cells bilaterally (left, -VHL; right, +VHL) and treated with weekly injections of doxorubicin (2mg/kg, IP). Co-immunoprecipitations, immunoblots, confocal imaging and siRNA transfections were performed using standard techniques. RESULTS Transient and stable VHL overexpression robustly decreased, while knockout of VHL increased p21/PUMA mRNA and protein levels. VHL-deficient cells lacking HIF (via siRNA) had unaltered p21. Conversely, VHL and non-degradable HIF mutant co-expressing cells exhibited low p21 levels compared to VHL-deficient cells. Taken together, these data suggest that VHL-mediated p53 regulation is independent of HIF. VHL over-expression significantly attenuated induction of apoptosis in doxorubicin (p53 activator) treated cells. Prior to treatment, VHL-deficient tumors grew larger than VHL expressing tumors. However, doxorubicin resulted in a more significant reduction in tumor size in VHL-deficient tumors. CONCLUSIONS These results suggest an inhibitory interaction between VHL and p53, in which VHL mediates reduces p53 target gene expression. Furthermore, the attenuation of doxorubicin treatment in VHL-expressing cancer cells suggests that this chemotherapy may be more effective against VHL-deficient tumors or in combination with a VHL inhibitor. This work suggests that through a previously undescribed mechanism, a known tumor suppressor may paradoxically be capable of potentiating cancer growth and apoptosis resistance. © 2017FiguresReferencesRelatedDetails Volume 197Issue 4SApril 2017Page: e795 Advertisement Copyright & Permissions© 2017MetricsAuthor Information Adam Kinnaird More articles by this author Peter Dromparis More articles by this author Aristeidis Boukouris More articles by this author Vikram Gurtu More articles by this author Bruno Saleme More articles by this author Sotirios Zervopoulos More articles by this author Gopinath Sutendra More articles by this author Evangelos Michelakis More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

The tumor suppressor capability of p53 is dependent on non-muscle myosin IIA function in head and neck cancer

Over 300,000 patients develop squamous cell carcinoma of the head and neck (HNSCC) worldwide with 25-30% of patients ultimately dying from their disease. Currently, molecular biomarkers are not used in HNSCC but several genes have been identified including mutant TP53 (mutp53) Our recent work has identified an approach to stratify patients with tumors harboring high or low risk TP53 mutations. Non-muscle Myosin IIA (NMIIA) was recently identified as a tumor suppressor in HNSCC. We now demonstrate that low MYH9 expression is associated with decreased survival in patients with head and neck cancer harboring low-risk mutp53 but not high-risk mutp53. Furthermore, inhibition of NMIIA leads to increased invasion in cells harboring wildtype p53 (wtp53), which was not observed in high-risk mutp53 cells. This increased invasiveness of wtp53 following NMIIA inhibition was associated with reduced p53 target gene expression and was absent in cells expressing mutp53. This reduced expression may be due, in part, to a decrease in nuclear localization of wtp53. These findings suggest that the tumor suppressor capability of wtp53 is dependent upon functional NMIIA and that the invasive phenotype of high-risk mutp53 is independent of NMIIA.

Usp7 promotes medulloblastoma cell survival and metastasis by activating Shh pathway

The ubiquitin-specific protease Usp7 plays roles in multiple cellular processes through deubiquitinating and stabilizing numerous substrates, including P53, Pten and Gli. Aberrant Usp7 activity has been implicated in many disorders and tumorigenesis, making it as a potential target for therapeutic intervention. Although it is clear that Usp7 is involved in many types of cancer, its role in regulating medulloblastoma (MB) is still unknown. In this study, we show that knockdown of Usp7 inhibits the proliferation and migration of MB cells, while Usp7 overexpression exerts an opposite effect. Furthermore, we establish Usp7 knockout MB cell line using the CRISPR/Cas9 system and further confirm that Usp7 knockout also blocks MB cell proliferation and metastasis. In addition, we reveal that knockdown of Usp7 compromises Shh pathway activity and decrease Gli protein levels, while P53 level and P53 target gene expression have no obvious changes. Finally, we find that Usp7 inhibitors apparently inhibit MB cell viability and migration. Taken together, our findings suggest that Usp7 is important for MB cell proliferation and metastasis by activating Shh pathway, and is a putative therapeutic target for MBs.

TRIAD1 Is a Novel Transcriptional Target of p53 and Regulates Nutlin-3a-Induced Cell Death.

Nutlin-3a is a non-genotoxic, p53-activating, MDM2 inhibitor being investigated as an anticancer agent. Although Nutlin-3a selectively antagonizes the ubiquitin E3 ligase activity of MDM2, its efficacy is not entirely regulated by MDM2 levels in cancer cells. Here, we report that the cytotoxic effects of Nutlin-3a are regulated by TRIAD1 via a positive feedback loop with p53. We found that Nutlin-3a enhanced TRIAD1 transcription in a p53-dependent manner. Using in silico analysis and promoter luciferase assays, we demonstrated that p53-mediated transcription of TRIAD1 is mediated by a p53 consensus sequence in the TRIAD1 promoter region. Silencing TRIAD1 expression in wild-type p53 (p53WT ) cancer cells suppressed Nutlin-3a-mediated p53 activation and p53 target gene expression. These effects were enhanced in TRIAD1-overexpressing p53WT cancer cells, but not in p53-deficient cancer cells. Furthermore, TRIAD1 knockdown significantly reduced the growth inhibitory and cytotoxic effects of Nutlin-3a in p53WT cancer cells, as demonstrated by cell viability assays, cell cycle analysis, clonogenic growth, and soft-agar colony forming assays. Together, these data indicate that TRIAD1 regulates Nutlin-3a-mediated p53 activation and the cytotoxic activity of Nutlin-3a. J. Cell. Biochem. 118: 1733-1740, 2017. © 2016 Wiley Periodicals, Inc.

P53-independent DUX4 pathology in cell and animal models of facioscapulohumeral muscular dystrophy.

ABSTRACTFacioscapulohumeral muscular dystrophy (FSHD) is a genetically dominant myopathy caused by mutations that disrupt repression of the normally silent DUX4 gene, which encodes a transcription factor that has been shown to interfere with myogenesis when misexpressed at very low levels in myoblasts and to cause cell death when overexpressed at high levels. A previous report using adeno-associated virus to deliver high levels of DUX4 to mouse skeletal muscle demonstrated severe pathology that was suppressed on a p53-knockout background, implying that DUX4 acted through the p53 pathway. Here, we investigate the p53 dependence of DUX4 using various in vitro and in vivo models. We find that inhibiting p53 has no effect on the cytoxicity of DUX4 on C2C12 myoblasts, and that expression of DUX4 does not lead to activation of the p53 pathway. DUX4 does lead to expression of the classic p53 target gene Cdkn1a (p21) but in a p53-independent manner. Meta-analysis of 5 publicly available data sets of DUX4 transcriptional profiles in both human and mouse cells shows no evidence of p53 activation, and further reveals that Cdkn1a is a mouse-specific target of DUX4. When the inducible DUX4 mouse model is crossed onto the p53-null background, we find no suppression of the male-specific lethality or skin phenotypes that are characteristic of the DUX4 transgene, and find that primary myoblasts from this mouse are still killed by DUX4 expression. These data challenge the notion that the p53 pathway is central to the pathogenicity of DUX4.

ΔN-ASPP2, a novel isoform of the ASPP2 tumor suppressor, promotes cellular survival

ASPP2 is a tumor suppressor that works, at least in part, through enhancing p53-dependent apoptosis. We now describe a new ASPP2 isoform, ΔN-ASPP2, generated from an internal transcription start site that encodes an N-terminally truncated protein missing a predicted 254 amino acids. ΔN-ASPP2 suppresses p53 target gene transactivation, promoter occupancy, and endogenous p53 target gene expression in response to DNA damage. Moreover, ΔN-ASPP2 promotes progression through the cell cycle, as well as resistance to genotoxic stress-induced growth inhibition and apoptosis. Additionally, we found that ΔN-ASPP2 expression is increased in human breast tumors as compared to adjacent normal breast tissue; in contrast, ASPP2 is suppressed in the majority of these breast tumors. Together, our results provide insight into how this new ASPP2 isoform may play a role in regulating the ASPP2-p53 axis.

Tifab, a Del(5q) MDS/AML Gene, Regulates USP15 Activity and p53

Interstitial deletion of a single copy of chromosome 5q is the most frequent cytogenetic alteration in Myelodysplastic Syndromes (MDS), which results in reduced dosage of numerous genes. TRAF-interacting protein with forkhead-associated domain B (TIFAB) resides within the proximal commonly-deleted region on band 5q31.1, and belongs to a family of forkhead-associated domain proteins. TIFAB is deleted in nearly all reported cases of del(5q) MDS and AML. As expected, TIFAB expression is significantly lower in CD34+ and BM mononuclear cells isolated from MDS patients with del(5q) as compared with cells from MDS patients diploid at chr 5q. Recently we have shown that hematopoietic-specific deletion of Tifab results in progressive BM and blood defects, including aberrant HSPC proportions, altered myeloid differentiation, and progressive cytopenia (Varney and Niederkorn et al., JEM 2015). Approximately 10% of mice transplanted with Tifab KO HSPCs develop a BM failure with neutrophil dysplasia and cytopenia. Gene expression analysis of Tifab KO lineage-Sca1+cKit+ (LSK) cells identified dysregulation of immune-related signatures, and hypersensitivity to Toll-like receptor stimulation. To investigate the molecular function of TIFAB, we performed a tandem-affinity tag purification and mass-spectrometry analysis of TIFAB complexes in a del(5q) AML cell line (HL60), and identified unique TIFAB-interacting proteins. The top interacting candidate was an ubiquitin-specific peptidase (USP), USP15. USPs play a major role in ubiquitin-dependent processes including DNA damage response signaling, protein degradation, and kinase activation. Specifically, USP15 has been shown to promote p53 degradation via deubiquitination and stabilization of its major negative regulator, MDM2. Through biochemical assays and a series of deletion mutants, we confirmed that TIFAB interacts with USP15. Moreover, we find that TIFAB enhances the deubiquitination of USP15 substrates, including MDM2 and histone 2B. To examine whether TIFAB directly regulates USP15 DUB activity, we performed in vitro deubiquitination assays in a cell-free system using fluorescent reporter di-ubiquitin substrates with purified USP15. We found that the addition of purified TIFAB increases the rate of USP15 catalytic activity on both lysine (K)48 and K63-linked di-ubiquitins in a dose-dependent manner. Collectively, these findings indicated that the USP15-TIFAB interaction leads to increased USP15 activity.USP15 stabilizes MDM2 via its DUB function, and MDM2 is known to bind and inhibit p53. Moreover, p53 is implicated in the pathogenesis of del(5q) MDS: 1) BM cells from murine models and BM from del(5q) patients exhibit increased p53 activity, which is thought to contribute to ineffective hematopoiesis and anemia; and 2) del(5q) MDS patients often acquire concurrent TP53 mutations that result in rapid transformation to AML and poor treatment response. To examine the effects of TIFAB on p53 function, we examined p53 target genes in TIFAB-overexpressing and -deficient cells. Gene expression profiling and qRT-PCR analysis of Tifab KOHSPCs revealed significant upregulation of p53 regulatory genes. In contrast, overexpression of TIFAB in a p53-competent cell line reduced the expression of p53 target gene, p21. Collectively, our findings identify a novel role for TIFAB as an activating adapter of USP15 and mediator of p53 activity. These findings have important implications in the potential role of TIFAB and p53 signaling in the pathogenesis of del(5q) MDS and transformation to AML. DisclosuresNo relevant conflicts of interest to declare.

1800MHz Microwave Induces p53 and p53-Mediated Caspase-3 Activation Leading to Cell Apoptosis In Vitro.

Recent studies have reported that exposure of mammalian cells to microwave radiation may have adverse effects such as induction of cell apoptosis. However, the molecular mechanisms underlying microwave induced mammalian cell apoptosis are not fully understood. Here, we report a novel mechanism: exposure to 1800MHz microwave radiation induces p53-dependent cell apoptosis through cytochrome c-mediated caspase-3 activation pathway. We first measured intensity of microwave radiation from several electronic devices with an irradiation detector. Mouse NIH/3T3 and human U-87 MG cells were then used as receivers of 1800MHz electromagnetic radiation (EMR) at a power density of 1209 mW/m2. Following EMR exposure, cells were analyzed for viability, intracellular reactive oxygen species (ROS) generation, DNA damage, p53 expression, and caspase-3 activity. Our analysis revealed that EMR exposure significantly decreased viability of NIH/3T3 and U-87 MG cells, and increased caspase-3 activity. ROS burst was observed at 6 h and 48 h in NIH/3T3 cells, while at 3 h in U-87 MG cells. Hoechst 33258 staining and in situ TUNEL assay detected that EMR exposure increased DNA damage, which was significantly restrained in the presence of N-acetyl-L-cysteine (NAC, an antioxidant). Moreover, EMR exposure increased the levels of p53 protein and p53 target gene expression, promoted cytochrome c release from mitochondrion, and increased caspase-3 activity. These events were inhibited by pretreatment with NAC, pifithrin-α (a p53 inhibitor) and caspase inhibitor. Collectively, our findings demonstrate, for the first time, that 1800MHz EMR induces apoptosis-related events such as ROS burst and more oxidative DNA damage, which in turn promote p53-dependent caspase-3 activation through release of cytochrome c from mitochondrion. These findings thus provide new insights into physiological mechanisms underlying microwave-induced cell apoptosis.

Effective Codelivery of lncRNA and pDNA by Pullulan‐Based Nanovectors for Promising Therapy of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers. Maternally expressed gene 3 (MEG3, one kind of long noncoding RNA [lncRNA]) can act as a tumor suppressor and regulate P53 target gene expression. However, lncRNA MEG3 demonstrates relatively low or no expression in human HCC. This study provides a promising concept to codeliver lncRNA and pDNA for cancer therapy. As proof‐of‐concept, the pcDNA‐MEG3 and pcDNA‐P53 plasmids‐condensed nanocomplexes with the liver‐targeting polycation gene vector, pullulan‐based ethanolamine‐modified poly(glycidyl methacrylate) (denoted as PuPGEA), are proposed to codeliver lncRNA and pDNA to treat HCC. Pullulan‐containing nanovectors are shown to be able to effectively mediate gene delivery in liver cells. To assess gene delivery performances of PuPGEA, a series of assays such as in vitro gene transfection, HCC cell proliferation, colony formation, migration, matrigel transwell assays, and in vivo xenograft animal models are carried out. The codelivery system with PuPGEA/(MEG3+P53) nanocomplexes demonstrates additive effects in suppressing HCC compared to PuPGEA/MEG3 or PuPGEA/P53 nanocomplexes alone. These results suggest that codelivery of lncRNA and pDNA by polycation nanovectors is a promising method to treat cancers.

Effect and Safety of Recombinant Adenovirus-p53 Transfer Combined with Radiotherapy on Long-Term Survival of Locally Advanced Cervical Cancer.

Detection of exogenous p53 gene and target gene expression in cervical cancer cell lines SiHa and C33A infected by recombinant adenovirus-p53 (rAd-p53) in vitro. The rAd-p53 infection evidently increased the expression of exogenous p53 gene, p21 gene, and Bax gene. The radiosensitization rates of rAd-p53 were 1.19 in SiHa and 1.18 in C33A in vitro. To evaluate the effect and safety of rAd-p53 transfer combined with radiotherapy (RT) in patients with cervical cancer, rAd-p53 transfer combined with radiotherapy (group PRT) in 69 patients with cervical cancer was compared with a control group treated with radiotherapy alone (group RT) in 35 patients with cervical cancer. Patients were intratumorally injected with rAd-p53 (1 × 1012 virus particles) once a week for 6 weeks. Concurrent pelvic RT plus brachytherapy to take point A to 76.0 Gray units (Gy) (range 75-80 Gy). The 5-year overall survival rate of the PRT group was 17.5% higher than that of the RT group (HR = 0.551, 95% CI 0.278-1.095, p = 0.084). The 5-year progress-free survival rate of the PRT group was 17.1% higher than that of the RT group (HR = 0.485, 95% CI 0.234-1.006, p = 0.047). rAd-p53 administration did not increase the adverse events caused by radiotherapy, except for transient fever after rAd-p53 administration. rAd-p53 was safe and biologically active in improving radiotherapeutic survival rates in patients with cervical cancer.

Abstract 1228: Indolo-pyrido-isoquinolin based alkaloid inhibits epithelial-mesenchymal transition and stemness via activation of p53-miR34a axis

Abstract The tumor suppressor p53 plays a critical role in suppressing cancer growth and progression and is the most frequently mutated and functionally inactivated gene in all human malignancies. Owing to its widespread alteration/inactivation in cancer, p53 is an attractive target for the development of new targeted therapies. We synthesized several indolo-pyrido-isoquinolin based alkaloids to restore/activate p53 function and examined their therapeutic efficacy using NCI-60 screening. Here, we provide molecular evidence that one of these compounds, 11-Methoxy-2,3,4,13-tetrahydro-1H-indolo[2’,3’:3,4]pyrido[1,2-b]isoquinolin-6-ylium-bromide (termed P18 or NSC-768219) inhibits growth and clonogenic potential of cancer cells. P18 treatment results in downregulation of mesenchymal markers and concurrent upregulation of epithelial markers as well as inhibition of migration and invasion. Experimental epithelial-mesenchymal-transition (EMT) induced by exposure to TGFβ/TNFα is also completely reversed by P18. Importantly, P18 also inhibits mammosphere-formation along with a reduction in the expression of stemness factors, Oct4, Nanog and Sox2. We show that P18 induces expression, phosphorylation and accumulation of p53 in cancer cells. P18-mediated induction of p53 leads to increased nuclear localization and elevated expression of p53 target genes. Using isogenic cancer cells differing only in p53 status, we show that the alteration of mesenchymal and epithelial genes, inhibition of migration and invasion of cancer cells mediated by P18 is p53-dependent. Furthermore, P18 increases miR-34a expression in p53-dependent manner and inhibition of mammosphere-formation by P18 is further enhanced by miR-34a mimic. Collectively, these data provide evidence that p53-miR-34a activation by P18 may represent a promising therapeutic strategy for the inhibition of growth and progression of cancer. Citation Format: Arumugam Nagalingam, Dimiter. B Avtanski, Joesph Tomaszewski, Risbood Prabhakar, Michael Difillippantonio, Brian Mears, Neeraj Saxena, Sanjay Malhotra, Sanjay Malhotra, Dipali Sharma. Indolo-pyrido-isoquinolin based alkaloid inhibits epithelial-mesenchymal transition and stemness via activation of p53-miR34a axis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1228.

Indolo-pyrido-isoquinolin based alkaloid inhibits growth, invasion and migration of breast cancer cells via activation of p53-miR34a axis

The tumor suppressor p53 plays a critical role in suppressing cancer growth and progression and is an attractive target for the development of new targeted therapies. We synthesized several indolo-pyrido-isoquinolin based alkaloids to activate p53 function and examined their therapeutic efficacy using NCI-60 screening. Here, we provide molecular evidence that one of these compounds, 11-methoxy-2,3,4,13-tetrahydro-1H-indolo[2′,3′:3,4]pyrido[1,2-b]isoquinolin-6-ylium-bromide (termed P18 or NSC-768219) inhibits growth and clonogenic potential of cancer cells. P18 treatment results in downregulation of mesenchymal markers and concurrent upregulation of epithelial markers as well as inhibition of migration and invasion. Experimental epithelial–mesenchymal-transition (EMT) induced by exposure to TGFβ/TNFα is also completely reversed by P18. Importantly, P18 also inhibits mammosphere-formation along with a reduction in the expression of stemness factors, Oct4, Nanog and Sox2. We show that P18 induces expression, phosphorylation and accumulation of p53 in cancer cells. P18-mediated induction of p53 leads to increased nuclear localization and elevated expression of p53 target genes. Using isogenic cancer cells differing only in p53 status, we show that p53 plays an important role in P18-mediated alteration of mesenchymal and epithelial genes, inhibition of migration and invasion of cancer cells. Furthermore, P18 increases miR-34a expression in p53-dependent manner and miR-34a is integral for P18-mediated inhibition of growth, invasion and mammosphere-formation. miR-34a mimics potentiate P18 efficacy while miR-34a antagomirs antagonize P18. Collectively, these data provide evidence that P18 may represent a promising therapeutic strategy for the inhibition of growth and progression of breast cancer and p53-miR-34a axis is important for P18 function.

The common stress responsive transcription factor ATF3 binds genomic sites enriched with p300 and H3K27ac for transcriptional regulation

BackgroundDysregulation of the common stress responsive transcription factor ATF3 has been causally linked to many important human diseases such as cancer, atherosclerosis, infections, and hypospadias. Although it is believed that the ATF3 transcription activity is central to its cellular functions, how ATF3 regulates gene expression remains largely unknown. Here, we employed ATF3 wild-type and knockout isogenic cell lines to carry out the first comprehensive analysis of global ATF3-binding profiles in the human genome under basal and stressed (DNA damage) conditions.ResultsAlthough expressed at a low basal level, ATF3 was found to bind a large number of genomic sites that are often associated with genes involved in cellular stress responses. Interestingly, ATF3 appears to bind a large portion of genomic sites distal to transcription start sites and enriched with p300 and H3K27ac. Global gene expression profiling analysis indicates that genes proximal to these genomic sites were often regulated by ATF3. While DNA damage elicited by camptothecin dramatically altered the ATF3 binding profile, most of the genes regulated by ATF3 upon DNA damage were pre-bound by ATF3 before the stress. Moreover, we demonstrated that ATF3 was co-localized with the major stress responder p53 at genomic sites, thereby collaborating with p53 to regulate p53 target gene expression upon DNA damage.ConclusionsThese results suggest that ATF3 likely bookmarks genomic sites and interacts with other transcription regulators to control gene expression.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2664-8) contains supplementary material, which is available to authorized users.

VprBP, an HIV target protein, is vital for immune responses by controlling T cell growth, proliferation and senescence.

Abstract Naïve mature T cells are maintained in a quiescent state with a low rate of cell size growth (biomass increase due to enhanced metabolism and biosynthesis) and proliferation. Disturbances inflicted by infection and inflammation, often trigger cells to exit quiescence and enter cell cycle, followed by rapid proliferation to restore homeostasis. Cell size growth is imperative for proliferating cells to compensate for the halving of cellular constituents for each division. Thus, proper coordination of cell growth and cell cycle entry of T cells is essential to mount effective immune response. Nonetheless, little is known about how cell cycle entry is controlled and even less about how cell size growth is regulated in T cells. We studied protein expression during T cell growth and cell cycle entry using quantitative proteomic approach. VprBP, an HIV target protein, was identified to be one of the highly upregulated factors. We found that VprBP was required for the cell growth and cell cycle entry of activated T cells. VprBP deletion abrogated T cell expansion during antiviral and autoimmune responses in vivo. VprBP-deficient cells drastically stabilized p53 protein with elevated expression of p53 target genes. Intriguingly, we found that although p53 deletion failed to correct the T cell growth defect due to VprBP deletion, it largely restored the cell cycle entry of VprBP-deficient T cells. In addition, VprBP deletion led to a premature senescence phenotype in T cells associating with increased cellular aging markers. These results suggest that VprBP controls T cell growth, cell cycle entry and senescence via discrete molecular programs. The recent findings and the underlying mechanisms will be discussed in detail in this presentation.

P53 Pulses Diversify Target Gene Expression Dynamics in an mRNA Half-Life-Dependent Manner and Delineate Co-regulated Target Gene Subnetworks

The transcription factor p53 responds to DNA double-strand breaks by increasing in concentration in a series of pulses of fixed amplitude, duration, and period. How p53 pulses influence the dynamics ofp53 target gene expression is not understood. Here, we show that, in bulk cell populations, patterns of p53 target gene expression cluster into groups with stereotyped temporal behaviors, including pulsing and rising dynamics. These behaviors correlate statistically with the mRNA decay rates of target genes: short mRNA half-lives produce pulses of gene expression. This relationship can be recapitulated by mathematical models of p53-dependent gene expression in single cells and cell populations. Single-cell transcriptional profiling demonstrates that expression of a subset of p53 target genes is coordinated across time within single cells; p53 pulsing attenuates this coordination. These results help delineate how p53 orchestrates the complex DNA damage response and give insight into the function of pulsatile signaling pathways.

A novel cytoprotective function for the DNA repair protein Ku in regulating p53 mRNA translation andfunction.

Ku heterodimer is a DNA binding protein with a prominent role in DNA repair. Here, we investigate whether and how Ku impacts the DNA damage response by acting as a post-transcriptional regulator of gene expression. We show that Ku represses p53 protein synthesis and p53-mediated apoptosis by binding to a bulged stem-loop structure within the p53 5' UTR However, Ku-mediated translational repression of the p53 mRNA is relieved after genotoxic stress. The underlying mechanism involves Ku acetylation which disrupts Ku-p53 mRNA interactions. These results suggest that Ku-mediated repression of p53 mRNA translation constitutes a novel mechanism linking DNA repair and mRNA translation.

ERβ decreases the invasiveness of triple-negative breast cancer cells by regulating mutant p53 oncogenic function.

Most (80%) of the triple-negative breast cancers (TNBCs) express mutant p53 proteins that acquire oncogenic activities including promoting metastasis. We previously showed that wild-type ERβ (ERβ1) impedes epithelial to mesenchymal transition (EMT) and decreases the invasiveness of TNBC cells. In the present study we searched for signaling pathways that ERβ1 uses to inhibit EMT and invasion in TNBC cells. We show that ERβ1 binds to and opposes the transcriptional activity of mutant p53 at the promoters of genes that regulate metastasis. p63 that transcriptionally cooperates with mutant p53 also binds to ERβ1. Downregulation of p63 represses the epithelial phenotype of ERβ1-expressing cells and alters the expression of mutant p53 target genes. These results describe a novel mechanism through which ERβ1 can disturb oncogenic signals to inhibit aggressiveness in TNBCs.

NAT10 regulates p53 activation through acetylating p53 at K120 and ubiquitinating Mdm2.

As a genome guardian, p53 maintains genome stability by arresting cells for damage repair or inducing cell apoptosis to eliminate the damaged cells in stress response. Several nucleolar proteins stabilize p53 by interfering Mdm2–p53 interaction upon cellular stress, while other mechanisms by which nucleolar proteins activate p53 remain to be determined. Here, we identify NAT10 as a novel regulator for p53 activation. NAT10 acetylates p53 at K120 and stabilizes p53 by counteracting Mdm2 action. In addition, NAT10 promotes Mdm2 degradation with its intrinsic E3 ligase activity. After DNA damage, NAT10 translocates to nucleoplasm and activates p53‐mediated cell cycle control and apoptosis. Finally, NAT10 inhibits cell proliferation and expression of NAT10 decreases in human colorectal carcinomas. Thus, our data demonstrate that NAT10 plays a critical role in p53 activation via acetylating p53 and counteracting Mdm2 action, providing a novel pathway by which nucleolar protein activates p53 as a cellular stress sensor.