Enhances P53 Activity Research Articles

Abstract 5425: Investigating the effects of p53 activation and HDAC inhibition on genes associated with poor prognosis prostate cancer

Abstract Background Prostate cancer (PCa) is now the most commonly diagnosed malignancy in men worldwide. SOC combines radiotherapy with ADT, however recurrence rate remains unacceptably high and many men present with late stage aggressive and metastatic disease, with poor prognosis and limited treatment options. Despite tumor suppressor p53 being mutated in approximately 50% of human tumors, it has been reported that p53 alteration occurs in only 12% of primary prostate tumors. Emerging data links epigenetic-mediated gene silencing as a major differentiator between aggressive and indolent disease that is associated with up-regulation of key cell cycle regulator FOXM1, which is known to be suppressed by p53. HDAC inhibitors (HDACi) are an emerging class of epigenetic modifying anti-cancer agents, which we hypothesises will enhance p53 activity, cell death and alter patterns of gene expression to targeting p53 dependent and independent vulnerabilities in PCa. Methods We used basally p53 deficient/proficient PCa models (PC3/LNCaP) and novel C4-2B and LNCap p53 CRISPR-Cas9 knockout models to investigate the combination effects of Nutlin 3A or radiation (IR) with class 1 HDACi Entinostat by Annexin V/PI Flow Cytometry and Western Blot. Transcriptional effects were evaluated by RT-PCR and RNA-seq analysis. TCGA mutational and RNA-seq data were used to link p53 mutation with altered gene expression and outcome. Results We have demonstrated that there is a synergistic induction of cell death when we combine N3A/IR with Entinostat that is p53-dependent. In addition, we see that p53 acts as a barrier to genes associated with poor prognosis including FOXM1 which is phenocopied by single-agent Entinostat independent of WT-p53. This suppression may potentially be downstream of p21 via the DREAM complex. Importantly p53 mutation in TCGA primary PCa patients is associated with poor outcome and elevated FOXM1 expression. Conclusion and Future Work Results to date suggest that Entinostat enhances p53 dependent cell death but also has p53 dependent and independent mechanisms to suppress genes associated with poor prognosis PCa. The mechanism looks to be dependent of p21 and may involve DREAM complex. Citation Format: Gemma M. Gregg, Fiammetta Falcone, Andrea Lees, Gerard Quinn, Peter Gallagher, Richard Kennedy, Ian I. Mills, Simon S. McDade. Investigating the effects of p53 activation and HDAC inhibition on genes associated with poor prognosis prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5425.

Inactivation of the MDM2 RING domain enhances p53 transcriptional activity in mice

The MDM2 RING domain harbors E3 ubiquitin ligase activity critical for regulating the degradation of tumor suppressor p53, which controls many cellular pathways. The MDM2 RING domain also is required for an interaction with MDMX. Mice containing a substitution in the MDM2 RING domain, MDM2C462A, disrupting MDM2 E3 function and the MDMX interaction, die during early embryogenesis that can be rescued by p53 deletion. To investigate whether MDM2C462A, which retains p53 binding, has p53-suppressing activity, we generated Mdm2C462A/C462A ;p53ER/- mice, in which we replaced the endogenous p53 alleles with an inducible p53ER/- allele, and compared survival with that of similarly generated Mdm2-/-;p53ER/- mice. Adult Mdm2-null mice died ∼7 days after tamoxifen-induced p53 activation, indicating that in the absence of MDM2, MDMX cannot suppress p53. Surprisingly, Mdm2C462A/C462A ;p53ER/- mice died ∼5 days after tamoxifen injection, suggesting that p53 activity is higher in the presence of MDM2C462A than in the absence of MDM2. Indeed, in MDM2C462A-expressing mouse tissues and embryonic fibroblasts, p53 exhibited higher transcriptional activity than in those expressing no MDM2 or no MDM2 and MDMX. This observation indicated that MDM2C462A not only is unable to suppress p53 but may have gained the ability to enhance p53 activity. We also found that p53 acetylation, a measure of p53 transcriptional activity, was higher in the presence of MDM2C462A than in the absence of MDM2. These results reveal an unexpected role of MDM2C462A in enhancing p53 activity and suggest the possibility that compounds targeting MDM2 RING domain function could produce even more robust p53 activation.

Minimal Residual Disease (MRD) Assessment By Multiparametric Flow Cytometry Is Prognostic for Progression-Free Survival in Phase 1/1b Relapsed/Refractory Acute Myeloid Leukemia (AML) Patients Treated with Idasanutlin MDM2 Antagonist

Introduction. Despite considerable efforts towards novel therapeutics research and discovery, outcomes in AML remain poor. Although composite Complete Remission (cCR; CR, CRp, CRi) is routinely used as a measure of therapeutic clinical activity, cCR frequently does not translate to survival benefit. On this basis, the characterization and tracking of minimal residual disease (MRD) has emerged as a tool to help better define the depth of such cCR to offer prognostic utility on AML patients likely to experience survival benefit from a given experimental therapeutic.The MDM2 antagonist idasanutlin has shown promising clinical activity in AML. Idasanutlin enhances p53 activity through antagonism of the MDM2:p53 interaction. Disruption of this protein:protein interaction inhibits MDM2 targeting of p53 for ubiquitination and degradation, thus stabilizing p53 protein to exert tumor suppressor transcriptional regulation and induction of apoptotic pathways.Patients and Methods. Trial NP28679 (NCT01773408) is a Phase 1/1b study evaluating idasanutlin as monotherapy or in combination with cytarabine in relapsed or refractory AML patients with safety as primary and complete remission as secondary endpoints, respectively (Martinelli, EHA, 2016.) Duration of response was available as exploratory clinical data for a subset of patient. Patients' pre-treatment bone marrow aspirate specimens were evaluated by multiparametric flow cytometry using an 18 marker surface antigen-based panel. MRD assessment occurred per protocol recommendation at the time of hematological malignancy response assessment (HMRA) at Day 28 and for those patients initially experiencing cCR at each subsequent HMRA. Further flow cytometry analyses were conducted for expression changes of known p53 regulated proteins in CD45+(dim) blasts correlating with drug exposure, consistent with mechanistic engagement.Results. PFS analyses for cCR patients versus non-CR Kaplan-Meier plots indicate the median for responders is 315d (95%CI: 282, NA) versus non-responders is 43.5d (95%CI: 30, NA). When MRD<1% versus >1% is applied as a cut-point, analytics show a statistical association with median PFS (log-rank p-value < .001) at 367d (95%CI: 219, NA) for <1%MRD versus >1% is 84d (95%CI: 30, NA.) Median MRD values for CR/CRp/CRi vs PR/HI vs PD are 0.42%, 1.79%, and 19.16%, respectively, again consistent with MRD serving as a surrogate for clinical activity (log rank test for trend p-value = .001) Additionally, multiparametric flow cytometry analysis of idasanutlin pharmacodynamic (PD) protein expression changes comparing pretreatment patient blood specimens to 24 hours following first dose administration indicates that increases in both p53 and MDM2 in CD45+(dim) blasts is associated with steady state drug exposure levels ([Spearman’s Correlation =0.27; p=.013] and [Spearman’s Correlation=0.24; p=.026,] respectively.) Interestingly, these changes in protein expression for p53 and MDM2 are associated with orthologous PD changes in serum protein macrophage inhibitory cytokine 1 (MIC-1) ([Spearman’s Correlation=0.23; p=.035] and [Spearman’s Correlation=0.22; p=.042,] respectively.) These PD changes are mechanistically consistent with enhanced p53 resulting from diminished MDM2 ubiquitination and degradation of p53.Conclusions. In summary, the results presented here are consistent with multiparametric flow cytometry MRD assessment as an early indication aligning with cCR in relapsed/refractory AML patients treated with idasanutlin. Further, assessment for association with progression-free survival indicates that the lowest quartile patients by MRD flow cytometry measurement (<1%) are likely to exhibit a pronounced survival benefit over those patients with higher detectable levels of MRD (>1%). As such, the data presented here support inclusion of MRD assessment by flow cytometry as a prognostic indicator to provide guiding information for assignment of depth of AML patient response. We will continue to monitor this biomarker for diagnostic potential as a prognostic indicator of survival-based outcomes in future randomized clinical studies of idasanutlin. DisclosuresLanza:Roche-Genentech: Employment. Martinelli:Pfizer: Consultancy, Speakers Bureau; MSD: Consultancy; Novartis: Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Genentech: Consultancy; Celgene: Consultancy, Speakers Bureau; Ariad: Consultancy, Speakers Bureau; Roche: Consultancy, Speakers Bureau; BMS: Speakers Bureau. Yee:Novartis Canada: Membership on an entity's Board of Directors or advisory committees, Research Funding. Jukofsky:Roche Pharma: Employment. Reis:Roche Pharma: Employment. Blotner:Roche Pharma: Employment. Drummond:Pfizer: Honoraria, Speakers Bureau; celgene: Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria, Speakers Bureau; Roche: Honoraria, Speakers Bureau. Vey:Sunesis: Honoraria. Dickinson:GlaxoSmithKline: Consultancy, Research Funding. Kelly:Novartis: Consultancy, Speakers Bureau; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Consultancy, Speakers Bureau. Theron:Roche Pharma: Employment. Venstrom:Roche-Genentech: Employment. Middleton:Roche Pharma: Employment. Chen:Roche Pharma: Employment. Kinnersley:Roche-Genentech: Employment, Equity Ownership. Nichols:Roche Pharma: Employment. Pierceall:Roche Pharma: Employment.

Abstract P2-03-08: miR-621 suppresses the metastatic cascade in breast cancer patients

Abstract Purpose: In previous study, we had shown that miR-621 could sensitize breast cancer to chemotherapy by suppressing FBXO11 and enhancing p53 activity. In this study, we aimed to define miR-621 prognosis value in breast cancer patients, and to explore the potential molecular mechanisms. Experimental Design: 70 patients with stages II and III breast cancer were included as validation set. The correlation between miR-621 expression level and prognosis in breast cancer patients was confirmed. In parallel, in vitro and in vivo analyses were carried out to determine the potential mechanisms of miRNA-dependent prognosis. Results: We validated that lower than higher miR-621 expression level was markedly associated with poor metastasis-free survival in breast cancer patients(P=0.03). In breast cancer cell lines, ectopic overexpression of miR-621 inhibited proliferation, migration, invasion, and metastasis both in vitro and in vivo. The potential miR-621-target genes were determined by TargetScan and miRNA CLIP-seq database. Among those, PAK7 was verified as one of the direct targets of miR-621 in breast cancer cells, whose expression level positively associated with recurrence and metastasis in breast cancer patients. The molecular mechanisms by which miR-621/PAK7 axis regulates recurrence and metastasis may involve regulation of epithelial-mesenchymal transition (EMT) in breast cancer cells. Conclusions: Our study revealed a strong correlation between miR-621 expression and metastasis in breast cancers. High level of miR-621 was negatively associated with poor metastasis-free survival. The increased metastasis-free survival may be mediated by down-regulation of PAK7 gene, which leads to reduced EMT in breast cancer cells. Therefore, miR-621 may represent a therapeutic target for early metastasis breast cancer. Citation Format: Xue J, Chi Y, Chen J, Yang B, Wu J. miR-621 suppresses the metastatic cascade in breast cancer patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-03-08.

Combination of Dasatinib with Conventional Chemotherapy Is Associated with a High Response Rate in High Risk Acute Myeloid Leukemia (AML)

Background: High risk AML patients (pts) have poor outcome with low complete remission (CR) rate and long term survival despite intensive chemotherapy.Tyrosine kinases play an important role in AML pathogenesis. Pre-clinical studies performed in our center (Blood. 2013 122:1900) have shown that Src family tyrosine kinases (SFK) including Lyn, Hck and Fgr are abnormally activated in AML compared to normal hematopoietic stem cell and progenitor cells. Other studies have shown that the c-Kit receptor is over-activated in a subset of AML pts and contributes to abnormal leukemia cell growth. We further show that the small molecule SFK and c-Kit inhibitor dasatinib reduces proliferation and survival of AML stem and progenitor cells. Importantly, dasatinib enhances the sensitivity of AML stem and progenitor cells to chemotherapeutic agents by inhibiting Akt signaling, increasing mdm2 phosphorylation and enhancing p53 activity in AML cells. Based on this data we conducted a phase I/II clinical study of the combination of dasatinib with conventional cytarabine-idarubicin ("7+3")-based induction chemotherapy in high-risk AML.Methods: Between September 20013 and July 2015, 18 adult AML pts were enrolled in the study. Eligibility criteria were high-risk AML, age >18 years, and suitability for intensive therapy. High risk AML was defined by one of the following criteria: older age (> 60 yrs), poor-risk cytogenetic and molecular abnormalities (ELN criteria), secondary disease (AML evolving from myelodysplasia or myeloproliferative neoplasm), therapy related (t-AML), or relapsed/refractory.This Phase I study used a 3 + 3 dose escalation design for dasatinib while keeping a fixed dose of cytarabine and idarubicin (cytarabine 200 mg/m2 CIV days 1-7, idarubicin 12 mg/m2 IV days 1-3). Dasatinib was started at a dose of 70 mg (dose level 1; DL-1) days 1-7, and escalated to 100 mg orally days 1-7 (DL 1). Pts who failed to achieve CR received second re-induction with the same regimen. Pts who achieved CR received consolidation high dose cytarabine and/or allogeneic stem cell transplantation (SCT) based on donor availability.Results: Of the 18 pts enrolled on the study, 7 pts (39%) had secondary AML, 5 pts (28%) relapsed AML, 2 pts (11%) t-AML, and 4 (22%) were newly diagnosed older AML pts (one with complex karyotype, one with trisomy 8 and one cytogenetically normal with FTL3-ITD). The median age of all pts was 62 yrs (range 27-73). Of the 18 pts, 13 pts are currently evaluable for response; of which 10 (77%) achieved CR/Cri. Of the 5 non-evaluable pts, one pt withdrew from study after 2 days of therapy, one pt was taken off study after 3 days due to cytarabine neurotoxicity, one pt died of intracranial hemorrhage before the day 14 bone marrow biopsy, one pt had therapy interrupted secondary to pneumonia and sepsis, and one is still receiving therapy. None of the pts required more than one induction to achieve CR. Of the 10 pts who achieved CR/Cri, 8 patients went on to receive allogeneic SCT. As expected, the most commonly reported grade 3 and 4 adverse events (AE) were anemia 50%, thrombocytopenia 44%, neutropenia 38%, and fatigue 27%. The most common grade 1-2 AE were GI toxicities 61% and rash 33%.Correlative studies performed on blood samples obtained from pts on day 3 after initiation of treatment (n=9) demonstrated significant decrease in of SRC activity (as indicated by reduction in phospho-SRC levels on immunoblotting, 0.52±0.11 of control, p=0.01), and increased expression of p53-target genes as evaluated by Q-RT-PCT [including Puma (16.2±6.9 fold, p=0.015), P21 (4.9±1.1 fold, p=0.004), DR5 (3.4±0.9, p=0.004), Bax (3.7±0.9 fold, p=0.001) and HDM2 (2.1±0.5, p=0.02)].Conclusion: Combination of dasatinib with conventional "7+3" induction chemotherapy is feasible in high-risk AML and leads to higher CR rate compared to historical data without increase in toxicity rate, allowing more pts to receive allogeneic transplantation. Correlative laboratory studies are consistent with pre-clinical studies suggesting that this combination is associated with significant inhibition of SRC activity and enhanced activation of p53-target genes. DisclosuresDos Santos:Amgen: Employment. Stein:Amgen: Speakers Bureau. Chen:Seattle Genetics: Consultancy, Research Funding, Speakers Bureau; Millennium: Consultancy, Research Funding, Speakers Bureau; Merck: Consultancy, Research Funding; genentech: Consultancy, Speakers Bureau. Khaled:Sequenom: Research Funding.

Abstract A156: Preclinical activity of MDM2 antagonist RO6839921, a pegylated prodrug for intravenous administration

Abstract The p53 tumor suppressor is a transcription factor that inhibits tumorigenesis by inducing cell cycle arrest or apoptosis in response to diverse stresses. In normal cells, p53 levels are tightly controlled by MDM2 which binds p53 and negatively regulates its activity and stability. MDM2 is overproduced in many human cancers, thereby impairing p53 function. Antagonists of p53-MDM2 interaction can enhance p53 activity and offer a novel approach to cancer therapy. The first potent and selective small-molecule inhibitors of p53-MDM2 binding, the nutlins, provided preclinical proof-of-concept for MDM2 antagonists as therapeutics for patients with tumors expressing wild-type p53. The nutlin family member idasanutlin (RG7388, RO5503781) is an oral small molecule inhibitor of MDM2 currently in clinical testing. Here we describe RO6839921, a pegylated prodrug formulated for intravenous administration. This IV MDM2 antagonist has been developed in order to improve variability in exposure seen with the oral compound, and to allow expansion into indications where patients cannot swallow or absorb the oral idasanutlin. RO6839921 is rapidly metabolized to the active principle (AP) idasanutlin which then binds selectively to the p53 site on the surface of the MDM2 molecule. In vitro testing with the AP shows high affinity with effective displacement of p53 from MDM2, leading to stabilization and accumulation of p53 protein and activation of the p53 pathway. Studies focused on in vivo investigation of activity of the prodrug RO6839921 since esterase cleavage is required to release the AP. The anti-tumor activity of RO6839921 was investigated in several sarcoma xenograft models including highly responsive wild-type (WT) p53, MDM2 overexpressing osteosarcoma models SJSA-1 and MHM. Sustained survival was seen in the WT p53 HT1080 fibrosarcoma model when combined with Doxil. Activity was also seen in the WT p53 MOLM-13 disseminated AML model alone and in combination with cytarabine, in the CRPC model 22rv1, and in the ER+ BCa model MCF-7. In these studies we see an increase in dose commensurate with exposure and activity (prodrug vs oral), less variability, and potentiated activity in combination with relevant therapeutics. Clinical studies with the oral AP (idasanutlin) have shown that p53 may be activated by this novel therapeutic strategy that releases p53 from MDM2 inhibition. In particular, patients with AML exhibit significant clinical activity (ASH 2014). In view of the existing unmet medical need in advanced cancers, and the promising activity seen with idasanutlin, RO6839921 is believed to be a promising agent that may offer new therapeutic options, and is therefore currently in clinical testing in both solid and hematologic malignancies. Citation Format: Brian Higgins, Christian Tovar, Kelli Glen, Aruna Railkar, Zoran Filipovic, Farooq Qureshi, Binh Vu, George Ehrlich, Dan Fishlock, Lin-Chi Chen, Steven Middleton, Gwen Nichols, Kathryn Packman, Lyubomir Vassilev. Preclinical activity of MDM2 antagonist RO6839921, a pegylated prodrug for intravenous administration. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A156.

Estradiol induces apoptosis via activation of miRNA-23a and p53: implication for gender difference in liver cancer development.

Estrogen (E2) has been suggested to have a protective role in attenuating hepatocellular carcinoma (HCC) development. miRNAs have great potential as biomarkers and therapeutic agents owing to their ability to control gene expression. However, little is known about the mechanism underlying the protective role of E2 in hepatocarcinogenesis and the effects of E2 on apoptotic miRNAs expression. Using miRNA PCR array, we found more than 2-fold alteration was observed in 25 upregulated and 10 downregulated apoptotic miRNAs in E2-treated cells. Among these miRNAs, we found expression of miR-23a was related to p53 functional status in the male-derived liver cell-lines. We demonstrated that E2 via ERα transcriptionally activated miR-23a and p53 expression, and thus enhanced p53 activation of miR-23a expression. Moreover, miR-23a expression correlated inversely with the expression of target gene X-linked inhibitor of apoptosis protein (XIAP), but positively with the caspase-3/7 activity. Decreasing of XIAP might contribute to caspase-3 activity and cell apoptosis. Taken together, our findings reveal a novel E2-signaling mechanism in regulating miRNAs expression for controlling apoptosis in liver cells. Delineating the role of E2 in regulating the activation of p53 and miR-23a, expression in HCC is crucial to the understanding of the sex difference observed in HCC.

Disruption of a regulatory loop between DUSP1 and p53 contributes to hepatocellular carcinoma development and progression

Altered expression of dual specificity phosphatase 1 (DUSP1) is common in tumors including hepatocellular carcinoma (HCC), and is predictive of tumor progression and poor prognosis. However, the tumor suppressive role of DUSP1 has yet to be clearly elucidated. The molecular mechanisms of tumor suppression that were investigated were induction of apoptosis, cell cycle inhibition, and regulation of p53. Additionally, the antitumor effect of DUSP1 was assessed using a mouse model. Associated signaling pathways in HCC cells and tissues were examined. Downregulation of DUSP1 expression was significantly correlated with poor differentiation (p<0.001) and advanced HCC stage (p=0.023). DUSP1 expression resulted in HCC suppression and longer survival (p=0.0002) in a xenoplant mice model. DUSP1 inhibited p38 MAPK phosphorylation and subsequently suppressed HSP27 activation, resulting in enhanced p53 phosphorylation at sites S15, S20, and S46 in HCC cells. Enhanced p53 activation induced the expression of target genes p21 and p27, which are linked to cell cycle arrest and apoptosis. Thus, DUSP1 was potentially linked to p53 activation via the p38 MAPK/HSP27 pathway. Wild-type but not mutant p53 transcriptionally upregulated DUSP1 via its DNA-binding domain. DUSP1 and p53 might collaborate to suppress tumors in hepatocarcinogenesis via a positive regulatory loop. Our results revealed that disruption of a positive regulatory loop between DUSP1 and p53 promoted HCC development and progression, providing a rationale for a therapeutic agent that restores DUSP1 in HCC.

Macrophage functions in atherosclerosis.

Atherosclerosis is a chronic inflammatory disease of the arterial wall instigated by the excessive accumulation of lipoproteins; monocyte recruitment and their differentiation into macrophages in the subendothelial space. Repeated failure of innate immune responses to clear subintimal low-density lipoprotein (LDL), results in the deposition of lipid-laden macrophages or foam cells. Foam cells secrete proinflammatory mediators that facilitate lipoprotein retention and maintain vascular inflammation.1 Advancement of lesion is characterized by the apoptosis of these macrophages in the lipid core. Macrophage apoptosis plays a dual role in atherosclerosis. In early fatty streaks lesions, efferocytosis removes apoptotic cells and prevents lesion development, whereas in the advanced lesions, efferocytosis is not efficient to clear the apoptotic debri, leading to the formation of necrotic core which further enhances inflammation and atherogenesis.2 Accumulating indirect evidence suggests that the antiatherogenic role of high density lipoprotein (HDL) could at least in part, be due to its ability to stimulate cholesterol efflux from macrophages by ATP-binding cassette transporter A1 and G1 (ABCA1 and ABCG1). Complementing this notion, recent studies by Westerterp et al3 show that macrophage deficiency of ABCA1/G1 enhances lipid accumulation in macrophages, atherosclerosis and lesion inflammation. These authors observed that macrophage foam cells in spleen facilitate monocytosis which is inhibited by ABCA1/G1 and high levels of HDL. Studies by Ramirez et al4 demonstrate that activation of liver X receptor (LXR) augments the transcription of microRNA 144 (miR144) and inhibition of miR144 in macrophages upregulates ABCA1 expression and cholesterol efflux. In vivo, supplementation of mice with miR144 suppresses ABCA1 expression in the liver and reduces plasma HDL levels. Silencing of miR144 …

Abstract 5138: Histone deacetylase 2 and N-Myc reduce p53 protein phosphorylation at serine 46 by repressing gene transcription of tumor protein 53-induced nuclear protein 1

Abstract Myc oncoproteins and histone deacetylases (HDACs) exert oncogenic effects by modulating gene transcription. Paradoxically, N-Myc induces p53 gene expression. Tumor protein 53-induced nuclear protein 1 (TP53INP1) phosphorylates p53 protein at serine 46, leading to enhanced p53 activity, transcriptional activation of p53 target genes and programmed cell death. We aimed to identify the mechanism through which N-Myc overexpressing p53 wild-type neuroblastoma cells acquired resistance to apoptosis.Gene and protein expression was analysed by real-time RT-PCR and immunoblot. Cell survival/death was examined by flow cytometry study of Annexin V-staining. The prognostic value of TP53INP1 expression in tumor tissues was investigated in three independent cohorts of neuroblastoma patients. TP53INP1 was one of the genes most significantly repressed by HDAC2 and N-Myc according to Affymetrix microarray gene expression datasets. HDAC2 and N-Myc reduced TP53INP1 gene expression by direct binding to the TP53INP1 gene promoter, leading to transcriptional repression of TP53INP1, p53 protein de-phosphorylation at serine 46, neuroblastoma cell proliferation and survival. Moreover, low levels of TP53INP1 expression in human neuroblastoma tissues correlated with high levels of N-Myc expression and poor patient outcome, and the BET bromodomain inhibitors JQ1 and I-BET151 reduced N-Myc expression and reactivated TP53INP1 expression in neuroblastoma cells. These findings identify TP53INP1 repression as an important co-factor for N-Myc oncogenesis, and provide further evidence for the potential application of BET bromodomain inhibitors in the therapy of N-Myc-induced neuroblastoma. Citation Format: Jeyran Shahbazi, Christopher J. Scarlett, Murray Norris, Bing Liu, Michelle Haber, Andrew E. Tee, Alice Carrier, Andrew V. Biankin, Wendy B. London, Glenn M. Marshall, Richard Lock, Tao Liu. Histone deacetylase 2 and N-Myc reduce p53 protein phosphorylation at serine 46 by repressing gene transcription of tumor protein 53-induced nuclear protein 1. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5138. doi:10.1158/1538-7445.AM2014-5138

LincRNA-p21 regulates neointima formation, vascular smooth muscle cell proliferation, apoptosis, and atherosclerosis by enhancing p53 activity.

Long noncoding RNAs (lncRNAs) have recently been implicated in many biological processes and diseases. Atherosclerosis is a major risk factor for cardiovascular disease. However, the functional role of lncRNAs in atherosclerosis is largely unknown. We identified lincRNA-p21 as a key regulator of cell proliferation and apoptosis during atherosclerosis. The expression of lincRNA-p21 was dramatically downregulated in atherosclerotic plaques of ApoE(-/-) mice, an animal model for atherosclerosis. Through loss- and gain-of-function approaches, we showed that lincRNA-p21 represses cell proliferation and induces apoptosis in vascular smooth muscle cells and mouse mononuclear macrophage cells in vitro. Moreover, we found that inhibition of lincRNA-p21 results in neointimal hyperplasia in vivo in a carotid artery injury model. Genome-wide analysis revealed that lincRNA-p21 inhibition dysregulated many p53 targets. Furthermore, lincRNA-p21, a transcriptional target of p53, feeds back to enhance p53 transcriptional activity, at least in part, via binding to mouse double minute 2 (MDM2), an E3 ubiquitin-protein ligase. The association of lincRNA-p21 and MDM2 releases MDM2 repression of p53, enabling p53 to interact with p300 and to bind to the promoters/enhancers of its target genes. Finally, we show that lincRNA-p21 expression is decreased in patients with coronary artery disease. Our studies identify lincRNA-p21 as a novel regulator of cell proliferation and apoptosis and suggest that this lncRNA could serve as a therapeutic target to treat atherosclerosis and related cardiovascular disorders.

Abstract 32: LincRNA-p21 Regulates Neointima Formation and Atherosclerosis by Enhancing p53 Activity

Background: Long non-coding RNAs (lncRNAs) recently have been implicated in many biological processes and diseases. Atherosclerosis is a major risk factor for cardiovascular disease. However, the functional role of lncRNAs in atherosclerosis is largely unknown. Methods and Results: The downstream targets of p53 also been detected by un-bias mRNA array and specific qPCR. Furthermore, bioinformatics prediction, RNA-Immunoprecipitation, biotin-labeled RNA-pulldown and deletion mapping were performed to test the potential interaction between lincRNA-p21 and MDM2. Co-IP, genome-wide ChIP-seq and ChIP-qPCR were preformed to verify the possible influence on p53 transcriptional activity. We further investigated the function of lincRNA-p21 in vivo, therefore recombinant lincRNA-p21 knockdown lentivirus were injected into the injured area of carotid arteries injury mouse model. Then the expression of lincRNA-p21 in vascular samples of clinical coronary disease patients were also detected. We identified lincRNA-p21 as a key regulator of atherosclerosis. Expression of lincRNA-p21 was dramatically down-regulated in atherosclerotic plaques of ApoE-/- mice, an animal model for AS. Through loss- and gain-of function approaches, we showed that lincRNA-p21 represses cell proliferation and induces apoptosis in VSMCs in vitro. Moreover, we found that inhibition of lincRNA-p21 results in neointimal hyperplasia in vivo in a carotid artery injury model. Mechanistically, we revealed that lincRNA-p21, which is a transcriptional target of p53, feeds back to enhance p53 transcriptional activity via binding to mouse double minute 2 (MDM2), an E3 ubiquitin-protein ligase. The association of lincRNA-p21 and MDM2 releases MDM2 repression of p53, enabling p53 to interact with p300 to regulate apoptosis, cell proliferation and suppress neointima formation. Conclusions: Our studies identified lincRNA-p21 as a novel regulator of cell proliferation and apoptosis and suggest that this lncRNA could serve as a therapeutic target to treat atherosclerosis.

Lincrna-p21 regulates neointima formation and atherosclerosis by enhancing p53 activity

Lincrna-p21 regulates neointima formation and atherosclerosis by enhancing p53 activity

Nemo-like kinase is critical for p53 stabilization and function in response to DNA damage.

The DNA damage response (DDR) acts as a protective mechanism for maintaining cell homeostasis. Nemo-like kinase (NLK) is a serine/threonine-protein kinase that has an important role in many pathways; however, its function in the DDR has not yet been defined. In our study, NLK-deficient HCT116 cells were found to be resistant to etoposide-induced cell death. We demonstrated that NLK is required for p53 activation in response to DNA damage. Remarkably, mechanistic studies revealed that NLK interacts with p53 and stabilizes p53 by blocking MDM2-mediated p53 ubiquitination and degradation. Furthermore, NLK enhances p53 activity and affects expression downstream of p53. Interestingly, these functions of NLK are not related to its kinase activity. Consistent with these results, NLK-deficient cells have a resistance effect on DNA damage. Therefore, these findings emphasize that NLK is a novel factor in DDR mechanisms.

Histone deacetylase 2 and N-Myc reduce p53 protein phosphorylation at serine 46 by repressing gene transcription of tumor protein 53-induced nuclear protein 1.

Myc oncoproteins and histone deacetylases (HDACs) exert oncogenic effects by modulating gene transcription. Paradoxically, N-Myc induces p53 gene expression. Tumor protein 53-induced nuclear protein 1 (TP53INP1) phosphorylates p53 protein at serine 46, leading to enhanced p53 activity, transcriptional activation of p53 target genes and programmed cell death. Here we aimed to identify the mechanism through which N-Myc overexpressing p53 wild-type neuroblastoma cells acquired resistance to apoptosis. TP53INP1 was found to be one of the genes most significantly repressed by HDAC2 and N-Myc according to Affymetrix microarray gene expression datasets. HDAC2 and N-Myc reduced TP53INP1 gene expression by direct binding to the TP53INP1 gene promoter, leading to transcriptional repression of TP53INP1, p53 protein de-phosphorylation at serine 46, neuroblastoma cell proliferation and survival. Moreover, low levels of TP53INP1 expression in human neuroblastoma tissues correlated with high levels of N-Myc expression and poor patient outcome, and the BET bromodomain inhibitors JQ1 and I-BET151 reduced N-Myc expression and reactivated TP53INP1 expression in neuroblastoma cells. These findings identify TP53INP1 repression as an important co-factor for N-Myc oncogenesis, and provide further evidence for the potential application of BET bromodomain inhibitors in the therapy of N-Myc-induced neuroblastoma.

The Nucleolar Protein Myb-binding Protein 1A (MYBBP1A) Enhances p53 Tetramerization and Acetylation in Response to Nucleolar Disruption

Tetramerization of p53 is crucial to exert its biological activity, and nucleolar disruption is sufficient to activate p53. We previously demonstrated that nucleolar stress induces translocation of the nucleolar protein MYBBP1A from the nucleolus to the nucleoplasm and enhances p53 activity. However, whether and how MYBBP1A regulates p53 tetramerization in response to nucleolar stress remain unclear. In this study, we demonstrated that MYBBP1A enhances p53 tetramerization, followed by acetylation under nucleolar stress. We found that MYBBP1A has two regions that directly bind to lysine residues of the p53 C-terminal regulatory domain. MYBBP1A formed a self-assembled complex that provided a molecular platform for p53 tetramerization and enhanced p300-mediated acetylation of the p53 tetramer. Moreover, our results show that MYBBP1A functions to enhance p53 tetramerization that is necessary for p53 activation, followed by cell death with actinomycin D treatment. Thus, we suggest that MYBBP1A plays a pivotal role in the cellular stress response.

A novel cell-penetrating peptide derived from WT1 enhances p53 activity, induces cell senescence and displays antimelanoma activity in xeno- and syngeneic systems

The Wilms tumor protein 1 (WT1) transcription factor has been associated in malignant melanoma with cell survival and metastasis, thus emerging as a candidate for targeted therapy. A lysine–arginine rich peptide, WT1-pTj, derived from the ZF domain of WT1 was evaluated as an antitumor agent against A2058 human melanoma cells and B16F10-Nex2 syngeneic murine melanoma. Peptide WT1-pTj quickly penetrated human melanoma cells and induced senescence, recognized by increased SA-β-galactosidase activity, enhanced transcriptional activity of p53, and induction of the cell cycle inhibitors p21 and p27. Moreover, the peptide bound to p53 and competed with WT1 protein for binding to p53. WT1-pTj treatment led to sustained cell growth suppression, abrogation of clonogenicity and G2/M cell cycle arrest. Notably, in vivo studies showed that WT1-pTj inhibited both the metastases and subcutaneous growth of murine melanoma in syngeneic mice, and prolonged the survival of nude mice challenged with human melanoma cells. The 27-amino acid cell-penetrating WT1-derived peptide, depends on C3 and H16 for effective antimelanoma activity, inhibits proliferation of WT1-expressing human tumor cell lines, and may have an effective role in the treatment of WT1-expressing malignancies.

Hsp90 inhibitor BIIB021 enhances triptolide-induced apoptosis of human T-cell acute lymphoblastic leukemia cells in vitro mainly by disrupting p53-MDM2 balance

To investigate the effects of BIIB021, an inhibitor of heat shock protein 90 (Hsp90) alone or in combination with triptolide (TPL) on T-cell acute lymphoblastic leukemia (T-ALL) and the mechanisms of action. Human T-ALL cells line Molt-4 was examined. The cell viability was measured using MTT assay. Apoptotic cells were studied with Hoechst 33258 staining. Cell apoptosis and cell cycle were analyzed using flow cytometry with Annexin V/PI staining and PI staining, respectively. The levels of multiple proteins, including Akt, p65, CDK4/6, p18, Bcl-2 family proteins, MDM2, and p53, were examined with Western blotting. The level of MDM2 mRNA was determined using RT-PCR. Treatment of Molt-4 cells with BIIB021 (50-800 nmol/L) inhibited the cell growth in a dose-dependent manner (the IC50 value was 384.6 and 301.8 nmol/L, respectively, at 48 and 72 h). BIIB021 dose-dependently induced G0/G1 phase arrest, followed by apoptosis of Molt-4 cells. Furthermore, BIIB021 increased the expression of p18, decreased the expression of CDK4/6, and activated the caspase pathway in Molt-4 cells. Moreover, BIIB021 (50-400 nmol/L) dose-dependently decreased the phospho-MDM2 and total MDM2 protein levels, but slightly increased the phospho-p53 and total p53 protein levels, whereas TPL (5-40 nmol/L) dose-dependently enhanced p53 activation without affecting MDM2 levels. Co-treatment with BIIB021 and TPL showed synergic inhibition on Molt-4 cell growth. The co-treatment disrupted p53-MDM2 balance, thus markedly enhanced p53 activation. In addition, the co-treatment increased the expression of Bak and Bim, followed by increased activation of caspase-9. The combination of BIIB021 and TPL may provide a novel strategy for treating T-ALL by overcoming multiple mechanisms of apoptosis resistance.

Hsp90 Inhibitors Promote p53-Dependent Apoptosis through PUMA and Bax

Hsp90 is widely overexpressed in cancer cells and believed to be essential for the maintenance of malignant phenotypes. Targeting Hsp90 by small molecules has shown promise in solid and hematologic malignancies, which likely involves degradation of client oncoproteins in a cell-type-specific manner. In this study, we found that structurally unrelated Hsp90 inhibitors induce DNA damage and apoptosis via p53-dependent induction of PUMA, which indirectly triggers Bax activation and mitochondrial dysfunction in colon cancer cells. Deficiency in PUMA, BAX, or p53, at lesser extent, abrogated 17-allylamino-17-demethoxygeldanamycin (17-AAG)-induced apoptosis and mitochondrial dysfunction, and enhanced clonogenic cell survival. Furthermore, suppression of p53-dependent p21 induction or enhanced p53 activation synergized with 17-AAG to induce PUMA-dependent apoptosis. Finally, PUMA was found to mediate apoptotic and therapeutic responses to the 17-AAG analog 17-DMAG in xenografts. These results show an important role of the p53/PUMA/Bax axis in Hsp90 inhibitor-induced killing of p53 wild-type cells, and have important implications for their clinical applications.

Regulation of the HDM2-p53 pathway by ribosomal protein L6 in response to ribosomal stress

The HDM2-p53 loop is crucial for monitoring p53 level and human pathologies. Therefore, identification of novel molecules involved in this regulatory loop is necessary for understanding the dynamic regulation of p53 and treatment of human diseases. Here, we characterized that the ribosomal protein L6 binds to and suppresses the E3 ubiquitin ligase activity of HDM2, and subsequently attenuates HDM2-mediated p53 polyubiquitination and degradation. The enhanced p53 activity further slows down cell cycle progression and leads to cell growth inhibition. Conversely, the level of p53 is dramatically decreased upon the depletion of RPL6, indicating that RPL6 is essential for p53 stabilization. We also found that RPL6 translocalizes from the nucleolus to nucleoplasm under ribosomal stress, which facilitates its binding with HDM2. The interaction of RPL6 and HDM2 drives HDM2-mediated RPL6 polyubiquitination and proteasomal degradation. Longer treatment of actinomycin D increases RPL6 ubiquitination and destabilizes RPL6, and thereby putatively attenuates p53 response until the level of L6 subsides. Therefore, RPL6 and HDM2 form an autoregulatory feedback loop to monitor the level of p53 in response to ribosomal stress. Together, our study identifies the crucial function of RPL6 in regulating HDM2-p53 pathway, which highlights the importance of RPL6 in human genetic diseases and cancers.