The p53 circuit board

Navigating the complexity of p53-DNA binding: implications for cancer therapy

Abstract

The tumor suppressor protein p53, a transcription factor playing a key role in cancer prevention, interacts with DNA as its primary means of determining cell fate in the event of DNA damage. When it becomes mutated, it opens damaged cells to the possibility of reproducing unchecked, which can lead to formation of cancerous tumors. Despite its critical role, therapies at the molecular level to restore p53 native function remain elusive, due to its complex nature. Nevertheless, considerable information has been amassed, and new means of investigating the problem have become available.

Objectives

We consider structural, biophysical, and bioinformatic insights and their implications for the role of direct and indirect readout and how they contribute to binding site recognition, particularly those of low consensus. We then pivot to consider advances in computational approaches to drug discovery.

Materials and methods

We have conducted a review of recent literature pertinent to the p53 protein.

Results

Considerable literature corroborates the idea that p53 is a complex allosteric protein that discriminates its binding sites not only via consensus sequence through direct H-bond contacts, but also a complex combination of factors involving the flexibility of the binding site. New computational methods have emerged capable of capturing such information, which can then be utilized as input to machine learning algorithms towards the goal of more intelligent and efficient de novo allosteric drug design.

Conclusions

Recent improvements in machine learning coupled with graph theory and sector analysis hold promise for advances to more intelligently design allosteric effectors that may be able to restore native p53-DNA binding activity to mutant proteins.

Clinical relevance

The ideas brought to light by this review constitute a significant advance that can be applied to ongoing biophysical studies of drugs for p53, paving the way for the continued development of new methodologies for allosteric drugs. Our discoveries hold promise to provide molecular therapeutics which restore p53 native activity, thereby offering new insights for cancer therapies.

Graphical Abstract

Structural representation of the p53 DBD (PDBID 1TUP). DNA consensus sequence is shown in gray, and the protein is shown in blue. Red beads indicate hotspot residue mutations, green beads represent DNA interacting residues, and yellow beads represent both.

Inclusion of Nitrofurantoin into the Realm of Cancer Chemotherapy via Biology-Oriented Synthesis and Drug Repurposing

Structural modifications of the antibacterial drug nitrofurantoin were envisioned, employing drug repurposing and biology-oriented drug synthesis, to serve as possible anticancer agents. Eleven compounds showed superior safety in non-cancerous human cells. Their antitumor efficacy was assessed on colorectal, breast, cervical, and liver cancer cells. Three compounds induced oxidative DNA damage in cancer cells with subsequent cellular apoptosis. They also upregulated the expression of Bax while downregulated that of Bcl-2 along with activating caspase 3/7. The DNA damage induced by these compounds, demonstrated by pATM nuclear shuttling, was comparable in both MCF7 and MDA-MB-231 (p53 mutant) cell lines. Mechanistic studies confirmed the dependence of these compounds on p53-mediated pathways as they suppressed the p53-MDM2 interaction. Indeed, exposure of radiosensitive prostatic cancer cells to low non-cytotoxic concentrations of compound 1 enhanced the cytotoxic response to radiation indicating a possible synergistic effect. In vivo antitumor activity was verified in an MCF7-xenograft animal model.

Emerging Insight Into the Role of Circadian Clock Gene BMAL1 in Cellular Senescence

Cell senescence is a crucial process in cell fate determination and is involved in an extensive array of aging-associated diseases. General perceptions and experimental evidence point out that the decline of physical function as well as aging-associated diseases are often initiated by cell senescence and organ ageing. Therefore, regulation of cell senescence process can be a promising way to handle aging-associated diseases such as osteoporosis. The circadian clock regulates a wide range of cellular and physiological activities, and many age-linked degenerative disorders are associated with the dysregulation of clock genes. BMAL1 is a core circadian transcription factor and governs downstream genes by binding to the E-box elements in their promoters. Compelling evidence has proposed the role of BMAL1 in cellular senescence and aging-associated diseases. In this review, we summarize the linkage between BMAL1 and factors of cell senescence including oxidative stress, metabolism, and the genotoxic stress response. Dysregulated and dampened BMAL1 may serve as a potential therapeutic target against aging- associated diseases.

Cooperative effects of RIG-I-like receptor signaling and IRF1 on DNA damage-induced cell death

Properly responding to DNA damage is vital for eukaryotic cells, including the induction of DNA repair, growth arrest and, as a last resort to prevent neoplastic transformation, cell death. Besides being crucial for ensuring homeostasis, the same pathways and mechanisms are at the basis of chemoradiotherapy in cancer treatment, which involves therapeutic induction of DNA damage by chemical or physical (radiological) measures. Apart from typical DNA damage response mediators, the relevance of cell-intrinsic antiviral signaling pathways in response to DNA breaks has recently emerged. Originally known for combatting viruses via expression of antiviral factors including interferons (IFNs) and establishing of an antiviral state, RIG-I-like receptors (RLRs) were found to be critical for adequate induction of cell death upon the introduction of DNA double-strand breaks. We here show that presence of IRF3 is crucial in this process, most likely through direct activation of pro-apoptotic factors rather than transcriptional induction of canonical downstream components, such as IFNs. Investigating genes reported to be involved in both DNA damage response and antiviral signaling, we demonstrate that IRF1 is an obligatory factor for DNA damage-induced cell death. Interestingly, its regulation does not require activation of RLR signaling, but rather sensing of DNA double-strand breaks by ATM and ATR. Hence, even though independently regulated, both RLR signaling and IRF1 are essential for full-fledged induction/execution of DNA damage-mediated cell death programs. Our results not only support more broadly developing IRF1 as a biomarker predictive for the effectiveness of chemoradiotherapy, but also suggest investigating a combined pharmacological stimulation of RLR and IRF1 signaling as a potential adjuvant regimen in tumor therapy.

Recent Advances in Zinc Oxide Nanoparticles (ZnO NPs) for Cancer Diagnosis, Target Drug Delivery, and Treatment

Cancer is regarded as one of the most deadly and mirthless diseases and it develops due to the uncontrolled proliferation of cells. To date, varieties of traditional medications and chemotherapies have been utilized to fight tumors. However, their immense drawbacks, such as reduced bioavailability, insufficient supply, and significant adverse effects, make their use limited. Nanotechnology has evolved rapidly in recent years and offers a wide spectrum of applications in the healthcare sectors. Nanoscale materials offer strong potential for curing cancer as they pose low risk and fewer complications. Several metal oxide NPs are being developed to diagnose or treat malignancies, but zinc oxide nanoparticles (ZnO NPs) have remarkably demonstrated their potential in the diagnosis and treatment of various types of cancers due to their biocompatibility, biodegradability, and unique physico-chemical attributes. ZnO NPs showed cancer cell specific toxicity via generation of reactive oxygen species and destruction of mitochondrial membrane potential, which leads to the activation of caspase cascades followed by apoptosis of cancerous cells. ZnO NPs have also been used as an effective carrier for targeted and sustained delivery of various plant bioactive and chemotherapeutic anticancerous drugs into tumor cells. In this review, at first we have discussed the role of ZnO NPs in diagnosis and bio-imaging of cancer cells. Secondly, we have extensively reviewed the capability of ZnO NPs as carriers of anticancerous drugs for targeted drug delivery into tumor cells, with a special focus on surface functionalization, drug-loading mechanism, and stimuli-responsive controlled release of drugs. Finally, we have critically discussed the anticancerous activity of ZnO NPs on different types of cancers along with their mode of actions. Furthermore, this review also highlights the limitations and future prospects of ZnO NPs in cancer theranostic.

MDM2/X Inhibitors as Radiosensitizers for Glioblastoma Targeted Therapy

Inhibition of the MDM2/X-p53 interaction is recognized as a potential anti-cancer strategy, including the treatment of glioblastoma (GB). In response to cellular stressors, such as DNA damage, the tumor suppression protein p53 is activated and responds by mediating cellular damage through DNA repair, cell cycle arrest and apoptosis. Hence, p53 activation plays a central role in cell survival and the effectiveness of cancer therapies. Alterations and reduced activity of p53 occur in 25-30% of primary GB tumors, but this number increases drastically to 60-70% in secondary GB. As a result, reactivating p53 is suggested as a treatment strategy, either by using targeted molecules to convert the mutant p53 back to its wild type form or by using MDM2 and MDMX (also known as MDM4) inhibitors. MDM2 down regulates p53 activity via ubiquitin-dependent degradation and is amplified or overexpressed in 14% of GB cases. Thus, suppression of MDM2 offers an opportunity for urgently needed new therapeutic interventions for GB. Numerous small molecule MDM2 inhibitors are currently undergoing clinical evaluation, either as monotherapy or in combination with chemotherapy and/or other targeted agents. In addition, considering the major role of both p53 and MDM2 in the downstream signaling response to radiation-induced DNA damage, the combination of MDM2 inhibitors with radiation may offer a valuable therapeutic radiosensitizing approach for GB therapy. This review covers the role of MDM2/X in cancer and more specifically in GB, followed by the rationale for the potential radiosensitizing effect of MDM2 inhibition. Finally, the current status of MDM2/X inhibition and p53 activation for the treatment of GB is given.

The Genomic Response to TGF-β1 Dictates Failed Repair and Progression of Fibrotic Disease in the Obstructed Kidney

Tubulointerstitial fibrosis is a common and diagnostic hallmark of a spectrum of chronic renal disorders. While the etiology varies as to the causative nature of the underlying pathology, persistent TGF-β1 signaling drives the relentless progression of renal fibrotic disease. TGF-β1 orchestrates the multifaceted program of kidney fibrogenesis involving proximal tubular dysfunction, failed epithelial recovery or re-differentiation, capillary collapse and subsequent interstitial fibrosis eventually leading to chronic and ultimately end-stage disease. An increasing complement of non-canonical elements function as co-factors in TGF-β1 signaling. p53 is a particularly prominent transcriptional co-regulator of several TGF-β1 fibrotic-response genes by complexing with TGF-β1 receptor-activated SMADs. This cooperative p53/TGF-β1 genomic cluster includes genes involved in cellular proliferative control, survival, apoptosis, senescence, and ECM remodeling. While the molecular basis for this co-dependency remains to be determined, a subset of TGF-β1-regulated genes possess both p53- and SMAD-binding motifs. Increases in p53 expression and phosphorylation, moreover, are evident in various forms of renal injury as well as kidney allograft rejection. Targeted reduction of p53 levels by pharmacologic and genetic approaches attenuates expression of the involved genes and mitigates the fibrotic response confirming a key role for p53 in renal disorders. This review focuses on mechanisms underlying TGF-β1-induced renal fibrosis largely in the context of ureteral obstruction, which mimics the pathophysiology of pediatric unilateral ureteropelvic junction obstruction, and the role of p53 as a transcriptional regulator within the TGF-β1 repertoire of fibrosis-promoting genes.

Global Analyses to Identify Direct Transcriptional Targets of p53

The transcription factor p53 controls a gene expression program with pleiotropic effects on cell biology including cell cycle arrest and apoptosis. Identifying direct p53 target genes within this network and determining how they influence cell fate decisions downstream of p53 activation is a prerequisite for designing therapeutic approaches that target p53 to effectively kill cancer cells. Here we describe a comprehensive multi-omics approach for identifying genes that are direct transcriptional targets of p53. We provide detailed procedures for measuring global RNA polymerase activity, defining p53 binding sites across the genome, and quantifying changes in steady-state mRNA in response to p53 activation.

Nutlin-Induced Apoptosis Is Specified by a Translation Program Regulated by PCBP2 and DHX30

Activation of p53 by the small molecule Nutlin can result in a combination of cell cycle arrest and apoptosis. The relative strength of these events is difficult to predict by classical gene expression analysis, leaving uncertainty as to the therapeutic benefits. In this study, we report a translational control mechanism shaping p53-dependent apoptosis. Using polysome profiling, we establish Nutlin-induced apoptosis to associate with the enhanced translation of mRNAs carrying multiple copies of an identified 3' UTR CG-rich motif mediating p53-dependent death (CGPD-motif). We identify PCBP2 and DHX30 as CGPD-motif interactors. We find that in cells undergoing persistent cell cycle arrest in response to Nutlin, CGPD-motif mRNAs are repressed by the PCBP2-dependent binding of DHX30 to the motif. Upon DHX30 depletion in these cells, the translation of CGPD-motif mRNAs increases, and the response to Nutlin shifts toward apoptosis. Instead, DHX30 inducible overexpression in SJSA1 cells leads to decreased translation of CGPD-motif mRNAs.

Curcumin stabilizes p53 by interaction with NAD(P)H:quinone oxidoreductase 1 in tumor-derived cell lines

Curcumin is a natural phytochemical with potent anti-neoplastic properties including modulation of p53. Targeting p53 activity has been suggested as an important strategy in cancer therapy. The purpose of this study was to describe a mechanism by which curcumin restores p53 levels in human cancer cell lines. HeLa, SiHa, CaSki and MDA-MB-231 cells were exposed to curcumin and a pulse and chase and immunoprecipitation assays were performed. Here we showed that curcumin increases the half-life of p53 by a physical interaction between p53-NQO1 (p53 - NAD(P)H:quinone oxidoreductase 1) proteins after treatment with curcumin. Interestingly, the cell viability assay after treatment with curcumin showed that the cytotoxic activity was selectively higher in cervical cancer cells contained wild type p53 but not in breast cancer cells contained mutated p53. The cytotoxic effect of curcumin in cervical cancer cells was related to the complex p53-NQO1 that avoids the interaction between p53 and its negative regulator ubiquitin ligase E6-associated protein (E6AP). Finally, we demonstrated that in pancreatic epithelioid carcinoma cells (PANC1) that are knockout for NQO1, the reestablishment of NQO1 expression can stabilize p53 in presence of curcumin. Collectively, our findings showed that curcumin is necessary to promote the protein interaction of NQO1 with p53, therefore, it increases the half-life of p53, and permits the cytotoxic effect of curcumin in cancer cells containing wild type p53. Our findings suggest that the use of curcumin may reactivate the p53 pathway in cancer cells with p53 wild-type.

Age- and Nicotine-Associated Gene Expression Changes in the Hippocampus of APP/PS1 Mice

The etiology of Alzheimer's disease (AD) has been intensively studied. However, little is known about the molecular alterations in early-stage and late-stage AD. Hence, we performed RNA sequencing and assessed differentially expressed genes (DEGs) in the hippocampus of 18-month and 7-month-old APP/PS1 mice. Moreover, the DEGs induced by treatment with nicotine, the nicotinic acetylcholine receptor agonist that is known to improve cognition in AD, were also analyzed in old and young APP/PS1 mice. When comparing old APP/PS1 mice with their younger littermates, we found an upregulation in genes associated with calcium overload, immune response, cancer, and synaptic function; the transcripts of 14 calcium ion channel subtypes were significantly increased in aged mice. In contrast, the downregulated genes in aged mice were associated with ribosomal components, mitochondrial respiratory chain complex, and metabolism. Through comparison with DEGs in normal aging from previous reports, we found that changes in calcium channel genes remained one of the prominent features in aged APP/PS1 mice. Nicotine treatment also induced changes in gene expression. Indeed, nicotine augmented glycerolipid metabolism, but inhibited PI3K and MAPK signaling in young mice. In contrast, nicotine affected genes associated with cell senescence and death in old mice. Our study suggests a potential network connection between calcium overload and cellular signaling, in which additional nicotinic activation might not be beneficial in late-stage AD.

The cytotoxic properties of zinc oxide nanoparticles on the rat liver and spleen, and its anticancer impacts on human liver cancer cell lines

INTRODUCTION

Due to their unique properties including cellular uptake and the delivery efficiency to biological systems, nanoparticles are used in various preclinical and clinical applications. The aim of this study was to investigate the toxicity impacts of zinc oxide nanoparticles (ZnO-NPs) on morphology and functionality of the rat's liver and spleen and illustrated its safe-therapeutic doses.

METHODS

The 28 female Swiss albino rats (180-220 g) and two human hepatocyte cell lines (HepG2 and HUH7) were designed as an in vivo and in vitro study, respectively. Samples were treated with certain doses of ZnO-NPs. The rat's liver morphology and functionality and apoptotic genes expression profile (Bax, Bcl-2, and P53) were analyzed to detect the cytotoxicity and antitumor impacts of ZnO-NPs, respectively.

RESULTS

The results showed a positive significant association between the increasing doses of ZnO-NPs and alanine aminotransferase/aspartate aminotransferase values. Moreover, a meaningful correlation was detected between the rat's liver and spleen weight and ZnO-NPs doses. Furthermore, the histopathological analysis of rat's liver showed the individual cytotoxic properties of ZnO-NPs. Finally, the positive significant correlation was detected among the expression of Bax and P53 genes with ZnO-NPs. In addition, the negative correlation was demonstrated between the expression of Bcl-2 and ZnO-NPs.

CONCLUSION

In general, in the current study, the antitumor effects of ZnO-NPs were confirmed by the enhancement of P53 and Bax genes expression profile, which are indicated the apoptotic induction in HUH7 cell line. Moreover, we introduced a safe-clinical ZnO-NPs dosage, have antitumor effects.

Transcriptional repression of IKKβ by p53 in arsenite-induced GADD45α accumulation and apoptosis

Our previous studies revealed that GADD45α is a liable protein, which undergoes MDM2-dependent constitutive ubiquitination and degradation in resting HepG2 hepatoma cells. Arsenite exposure induces ribosomal stress responses mediated by the ribosomal protein S7, which can block MDM2 activity and result in GADD45α accumulation and cell apoptosis. In the present study, we found that one of the catalytic subunits of IκB kinase (IKK), IKKβ, exerted a novel IKKα- and NF-κB-independent function in stabilizing MDM2 and therefore contributed to ubiquitination-dependent degradation of GADD45α in resting HepG2 cells. Arsenite stimulation induced transactivation of p53, which formed a complex with its downstream target, Ets-1, and then synergistically repressed IKKβ transcription, reduced MDM2 stability, and ultimately removed the inhibitory effect of MDM2 on GADD45α induction. In addition, DAPK1 functioned as an upstream protein kinase triggering p53/Ets-1-dependent IKKβ and MDM2 reduction and GADD45α accumulation, thus promoting apoptosis in HepG2 cells. Subsequent studies further revealed that the activation of the DAPK1/p53/Ets-1/IKKβ/MDM2/GADD45α cascade was a common signaling event in mediating apoptosis of diverse cancer cells induced by arsenite and other tumor therapeutic agents. Therefore, we conclude that data in the current study have revealed a novel role for IKKβ in negatively regulating GADD45α protein stability and the contribution of p53-dependent IKKβ reduction to mediating cancer cell apoptosis.

Angiogenesis in human brain tumors: screening of drug response through a patient-specific cell platform for personalized therapy

Gliomas are the most common brain tumors, with diverse biological behaviour. Glioblastoma (GBM), the most aggressive and with the worst prognosis, is characterized by an intense and aberrant angiogenesis, which distinguishes it from low-grade gliomas (LGGs) and benign expansive lesions, as meningiomas (MNGs). With increasing evidence for the importance of vascularization in tumor biology, we focused on the isolation and characterization of endothelial cells (ECs) from primary GBMs, LGGs and MNGs. Gene expression analysis by Real-Time PCR, immunofluorescence and flow cytometry analysis, tube-like structures formation and vascular permeability assays were performed. Our results showed a higher efficiency of ECs to form a complex vascular architecture, as well as a greater impairment of a brain blood barrier model, and an overexpression of pro-angiogenic mediators in GBM than in LGG and MNG. Furthermore, administration of temozolomide, bevacizumab, and sunitinib triggered a different proliferative, apoptotic and angiogenic response, in a dose and time-dependent manner. An increased resistance to temozolomide was observed in T98G cells co-cultured in GBM-EC conditioned media. Therefore, we developed a novel platform to reproduce tumor vascularization as “disease in a dish”, which allows us to perform screening of sensitivity/resistance to drugs, in order to optimize targeted approaches to GBM therapy.

Studying the expression rate and methylation of Reprimo gene in the blood of patients suffering from gastric cancer

As gastric cancer has no exclusive signals in its initial phases, it is usually diagnosed in advanced phases. Although many researches have been conducted on methylation and diagnosis of cancer’s markers, the methylation and expression of Reprimo gene and its correlation with gastric cancer has not been thoroughly studied. Methylation of Reprimo promoter is a repetitive procedure exclusive to cancer which nullifies its expression and performance. The present research seeks to study the expression and methylation of Reprimo among people suffering with gastric cancer so that it may be used as a biomarker for early diagnosis. Fifty blood samples taken from healthy people (normal samples) and 50 blood samples obtained from gastric cancer patients were analyzed using Real-Time PCR. The methylation status of the promoter of Reprimo was studied using Methylation Specific PCR technique in normal samples and in gastric cancer Iranian patients. We observed reduction in expression rate of Reprimo in the blood samples of patients suffering with gastric cancer in comparison to normal blood samples. A significant correlation was also observed between the expression rate of this gene, age and methylation of its promoter among patients suffering with gastric cancer and various analysis points to a correlation between reduced expressions of Reprimo gene in gastric cancer patients. In conclusion, reduced expression of Reprimo gene and greater levels of methylation of its promoter seems to be promising biomarkers for early diagnosis of gastric cancer.

Hypoxia exposure induced cisplatin resistance partially via activating p53 and hypoxia inducible factor-1α in non-small cell lung cancer A549 cells

Lung cancer is one of the most frequently occurring and fatal cancer types worldwide. Cisplatin is widely used for chemotherapy of non-small cell lung cancer (NSCLC). However, the use of cisplatin has been met with the challenge of chemoresistance as a result of hypoxia, which is common in adult solid tumors and is a principal cause of a poor patient outcome. In the present study, the effects of hypoxia on the response of the NSCLC A549 cell line to the clinically relevant cytotoxic cisplatin were evaluated via regulating hypoxia inducible facor-1α (HIF-1α) and p53. Hypoxia exposure upregulated the expression levels of HIF-1α and p53, and promoted glycolysis in A549 cells, which was attenuated by HIF-1α knockdown by siRNA introduction, indicating the critical roles of HIF-1α in regulating glycolysis under hypoxic conditions. HIF-1α-knockdown also sensitized A549 cells to cisplatin in hypoxia-exposed, but not in normoxia-exposed A549 cells, suggesting that hypoxia-induced cisplatin resistance partially contributes toward the upregulation of HIF-1α by hypoxia exposure. The present study also determined that hypoxia-upregulated p53 activated its downstream target gene p21 transcriptionally and blocked the cell cycle at the G1-G0 phase, thereby leading to inhibition of cell proliferation. As a result, activated p53 desensitized A549 cells to cisplatin potentially through increasing the non-proliferation status of A549 cells and therefore minimizing the influence of cisplatin. Taken together, these results identified the exact effects of HIF-1α and p53 induced by hypoxia and potentially elucidated their protective effects on A549 cells against cisplatin.

Dependence of prevalence of contiguous pathways in proteins on structural complexity

Allostery is a regulatory mechanism in proteins where an effector molecule binds distal from an active site to modulate its activity. Allosteric signaling may occur via a continuous path of residues linking the active and allosteric sites, which has been suggested by large conformational changes evident in crystal structures. An alternate possibility is that the signal occurs in the realm of ensemble dynamics via an energy landscape change. While the latter was first proposed on theoretical grounds, increasing evidence suggests that such a control mechanism is plausible. A major difficulty for testing the two methods is the ability to definitively determine that a residue is directly involved in allosteric signal transduction. Statistical Coupling Analysis (SCA) is a method that has been successful at predicting pathways, and experimental tests involving mutagenesis or domain substitution provide the best available evidence of signaling pathways. However, ascertaining energetic pathways which need not be contiguous is far more difficult. To date, simple estimates of the statistical significance of a pathway in a protein remain to be established. The focus of this work is to estimate such benchmarks for the statistical significance of contiguous pathways for the null model of selecting residues at random. We found that when 20% of residues in proteins are randomly selected, contiguous pathways at the 6 Å cutoff level were found with success rates of 51% in PDZ, 30% in p53, and 3% in MutS. The results suggest that the significance of pathways may have system specific factors involved. Furthermore, the possible existence of false positives for contiguous pathways implies that signaling could be occurring via alternate routes including those consistent with the energetic landscape model.

Hyperthermia exposure induces apoptosis and inhibits proliferation in HCT116 cells by upregulating miR-34a and causing transcriptional activation of p53

Hyperthermia, as an anticancer therapeutic strategy, presents notable advantages in conjunction with irradiation and/or chemotherapy in the treatment of cancer by promoting apoptosis and inhibiting proliferation. A number of studies have documented that hyperthermia inhibits cancer progression through transcriptional activation of p53, which promotes cell cycle arrest and apoptosis. However, the underlying molecular mechanisms of hyperthermia-regulated apoptosis and proliferation dependent on p53 remain largely unknown. To investigate the effects and molecular mechanism of hyperthermia on the apoptosis and proliferation of colorectal carcinoma (CRC) HCT116 cells, the present study assessed cell apoptosis and proliferation following exposure to hyperthermia (42°C for 2–4 h). The results indicated that, compared with the control group at 0 h, hyperthermia exposure for 2 and 4 h induced the apoptosis of HCT116 cells (P<0.05), inhibited cell proliferation by causing cell cycle arrest at G1/G0 phase (P<0.05), and significantly increased microRNA (miR)-34a expression (P<0.05), but not miR-34b, miR-34c, miR-215 and miR-504 expression. The transcriptional activity of p53 on its consensus sequence and downstream target genes, namely p21, B cell lymphoma 2-associated X protein, mouse double minute 2 homolog, p53 upregulated modulator of apoptosis and growth arrest and DNA-damage-inducible 45α, was subsequently detected. The data indicated significantly higher transcriptional activity of p53 following hyperthermia exposure for 2 and 4 h (P<0.05), and these observations were similar to the effects of transfection with miR-34a mimics in HCT116 cells. Furthermore, transfection with miR-34a antagomiR supressed hyperthermia-induced apoptosis and promoted cell cycle progression following hyperthermia exposure when compared with transfection controls (P<0.05). Collectively, these findings indicate that miR-34a may serve an important role in hyperthermia-regulated apoptosis and proliferation in HCT116 cells by influencing the transcriptional activity of p53.

Putting p53 in Context

TP53 is the most frequently mutated gene in human cancer. Functionally, p53 is activated by a host of stress stimuli and, in turn, governs an exquisitely complex anti-proliferative transcriptional program that touches upon a bewildering array of biological responses. Despite the many unveiled facets of the p53 network, a clear appreciation of how and in what contexts p53 exerts its diverse effects remains unclear. How can we interpret p53's disparate activities and the consequences of its dysfunction to understand how cell type, mutation profile, and epigenetic cell state dictate outcomes, and how might we restore its tumor-suppressive activities in cancer?

Heterogeneity of p53 dependent genomic responses following ethanol exposure in a developmental mouse model of fetal alcohol spectrum disorder

Prenatal ethanol exposure can produce structural and functional deficits in the brain and result in Fetal Alcohol Spectrum Disorder (FASD). In rodent models acute exposure to a high concentration of alcohol causes increased apoptosis in the developing brain. A single causal molecular switch that signals for this increase in apoptosis has yet to be identified. The protein p53 has been suggested to play a pivotal role in enabling cells to engage in pro-apoptotic processes, and thus figures prominently as a hub molecule in the intracellular cascade of responses elicited by alcohol exposure. In the present study we examined the effect of ethanol-induced cellular and molecular responses in primary somatosensory cortex (SI) and hippocampus of 7-day-old wild-type (WT) and p53-knockout (KO) mice. We quantified apoptosis by active caspase-3 immunohistochemistry and ApopTag™ labeling, then determined total RNA expression levels in laminae of SI and hippocampal subregions. Immunohistochemical results confirmed increased incidence of apoptotic cells in both regions in WT and KO mice following ethanol exposure. The lack of p53 was not protective in these brain regions. Molecular analyses revealed a heterogeneous response to ethanol exposure that varied depending on the subregion, and which may go undetected using a global approach. Gene network analyses suggest that the presence or absence of p53 alters neuronal function and synaptic modifications following ethanol exposure, in addition to playing a classic role in cell cycle signaling. Thus, p53 may function in a way that underlies the intellectual and behavioral deficits observed in FASD.

Ataxia Telangiectasia-Mutated (ATM)Polymorphisms and Risk of Lung Cancer in a Chinese Population

BACKGROUND

The ataxia telangiectasia-mutated (ATM) gene has a key role in DNA repair including activation and stabilization of p53, which implicates the importance of ATM polymorphisms in the development of cancer. This study aims to investigate the association of two ATM single-nucleotide polymorphisms (SNPs) with lung cancer, as well as their potential interaction with p53 gene and other known risk factors of lung cancer.

METHODS

A population-based case-control study was conducted in Taiyuan city, China with 399 cases and 466 controls matched on the distribution of age and sex of cases. The two ATM gene SNPs, ATMrs227060 and ATMrs228589 as well as p53 gene SNP, p53rs1042522 were genotyped using Sequenom platform. Unconditional logistic regression models were used to estimate crude and adjusted odds ratios (aOR) and 95% confidence intervals (CIs). Adjusted models controlled for age, sex, and smoking status.

RESULTS

The study showed that TT genotype of ATMrs227060 (aOR = 1.58, 95% CI: 1.06-2.35) and AA genotype of ATMrs228589 were significantly associated with lung cancer (aOR = 1.50, 95% CI: 1.08-2.08) in a recessive model. Additionally, carrying variant genotypes of ATMrs227060 (TT), ATMrs228589 (AA), and p53rs1042522 (CC) concomitantly was associated with much higher risk (aOR = 3.68, 95% CI: 1.43-9.45) of lung cancer than carrying variant genotypes of any one of the above three SNPs. We also found multiplicative and additive interaction between tea drinking and ATMrs227060 in association with lung cancer.

CONCLUSION

This study indicates that ATM gene variants might be associated with development of lung cancer in Chinese population. These results need to be validated in larger and different population samples.

Depletion of NFBD1/MDC1 Induces Apoptosis in Nasopharyngeal Carcinoma Cells Through the p53-ROS-Mitochondrial Pathway

NFBD1, a signal amplifier of the p53 pathway, is vital for protecting cells from p53-mediated apoptosis and the early phase of DNA damage response under normal culture conditions. Here we investigated its expression in patients with nasopharyngeal carcinoma (NPC), and we describe the biological functions of the NFBD1 gene. We found that NFBD1 mRNA and protein were more highly expressed in NPC tissues than in nontumorous tissues. To investigate the function of NFBD1, we created NFBD1-depleted NPC cell lines that exhibited decreased cellular proliferation and colony formation, an increase in their rate of apoptosis, and an enhanced sensitivity to chemotherapeutic agents compared with in vitro controls. However, N-acetyl cysteine (NAC) and downregulation of p53 expression could partially reverse the apoptosis caused by the loss of NFBD1. Further analysis showed that loss of NFBD1 resulted in increased production of intracellular reactive oxygen species (ROS) depending on p53, which subsequently triggered the mitochondrial apoptotic pathway. Using a xenograft model in nude mice, we showed that silencing NFBD1 also significantly inhibited tumor growth and led to apoptosis. Taken together, our data suggest that inhibition of NFBD1 in NPC could be therapeutically useful.

Is p53 Involved in Tissue-Specific Insulin Resistance Formation?

p53 constitutes an extremely versatile molecule, primarily involved in sensing the variety of cellular stresses. Functional p53 utilizes a plethora of mechanisms to protect cell from deleterious repercussions of genotoxic insults, where senescence deserves special attention. While the impressive amount of p53 roles has been perceived solely by the prism of antioncogenic effect, its presence seems to be vastly connected with metabolic abnormalities underlain by cellular aging, obesity, and inflammation. p53 has been found to regulate multiple biochemical processes such as glycolysis, oxidative phosphorylation, lipolysis, lipogenesis, β-oxidation, gluconeogenesis, and glycogen synthesis. Notably, p53-mediated metabolic effects are totally up to results of insulin action. Accumulating amount of data identifies p53 to be a factor activated upon hyperglycemia or excessive calorie intake, thus contributing to low-grade chronic inflammation and systemic insulin resistance. Prominent signs of its actions have been observed in muscles, liver, pancreas, and adipose tissue being associated with attenuation of insulin signalling. p53 is of crucial importance for the regulation of white and brown adipogenesis simultaneously being a repressor for preadipocyte differentiation. This review provides a profound insight into p53-dependent metabolic actions directed towards promotion of insulin resistance as well as presenting experimental data regarding obesity-induced p53-mediated metabolic abnormalities.

RECQL: a new breast cancer susceptibility gene

Identifying and characterizing novel genetic risk factors for BRCA1/2 negative breast cancers is highly relevant for early diagnosis and development of a management plan. Mutations in a number of DNA repair genes have been associated with genomic instability and development of breast and various other cancers. Whole exome sequencing efforts by 2 groups have led to the discovery in distinct populations of multiple breast cancer susceptibility mutations in RECQL, a gene that encodes a DNA helicase involved in homologous recombination repair and response to replication stress. RECQL pathogenic mutations were identified that truncated or disrupted the RECQL protein or introduced missense mutations in its helicase domain. RECQL mutations may serve as a useful biomarker for breast cancer. Targeting RECQL associated tumors with novel DNA repair inhibitors may provide a new strategy for anti-cancer therapy.

Human EHMT2/G9a activates p53 through methylation-independent mechanism

p53 is a critical tumor suppressor in humans. It functions mostly as a transcriptional factor and its activity is regulated by numerous post-translational modifications. Among different covalent modifications found on p53 the most controversial one is lysine methylation. We found that human G9a (hG9a) unlike its mouse orthologue (mG9a) potently stimulated p53 transcriptional activity. Both ectopic and endogenous hG9a augmented p53-dependent transcription of pro-apoptotic genes, including Bax and Puma, resulting in enhanced apoptosis and reduced colony formation. Significantly, shRNA-mediated knockdown of hG9a attenuated p53-dependent activation of Puma. On the molecular level, hG9a interacted with histone acetyltransferase, p300/CBP, resulting in increased histone acetylation at the promoter of Puma. The bioinformatics data substantiated our findings showing that positive correlation between G9a and p53 expression is associated with better survival of lung cancer patients. Collectively, this study demonstrates that depending on the cellular and organismal context, orthologous proteins may exert both overlapping and opposing functions. Furthermore, this finding has important ramifications on the use of G9a inhibitors in combination with genotoxic drugs to treat p53-positive tumors.

Theaflavin-3, 3'-digallate induces apoptosis and G2 cell cycle arrest through the Akt/MDM2/p53 pathway in cisplatin-resistant ovarian cancer A2780/CP70 cells

Ovarian cancer is the most lethal gynecological cancer among women worldwide. Adverse side effects and acquired resistance to conventional platinum based chemotherapy are major impediments in ovarian cancer treatment, and drive the development of more selective anticancer drugs that target cancer-specific defects. In this study, theaflavin-3, 3′-digallate (TF3), the major theaflavin monomer in black tea, exhibited a potent growth inhibitory effect on the cisplatin-resistant ovarian cancer A2780/CP70 cells (IC₅₀, 23.81 μM), and was less cytotoxic to a normal ovarian IOSE-364 cells (IC₅₀, 59.58 μM) than to the cancer cells. Flow cytometry analysis indicated that TF3 induced preferential apoptosis and G2 cell cycle arrest in A2780/CP70 cells with respect to IOSE-364 cells. TF3 induced apoptosis through both the intrinsic and extrinsic apoptotic pathways, and caused G2 cell cycle arrest via cyclin B1 in A2780/CP70 cells. The p53 protein played an important role in TF3-induced apoptosis and G2 cell cycle arrest. TF3 might upregulate the p53 expression via the Akt/MDM2 pathway. Our findings help elucidate the mechanisms by which TF3 may contribute to the prevention and treatment of platinum-resistant ovarian cancer.

Tetraploidization or autophagy: The ultimate fate of senescent human endometrial stem cells under ATM or p53 inhibition

Previously we demonstrated that endometrium-derived human mesenchymal stem cells (hMESCs) via activation of the ATM/p53/p21/Rb pathway enter the premature senescence in response to oxidative stress. Down regulation effects of the key components of this signaling pathway, particularly ATM and p53, on a fate of stressed hMESCs have not yet been investigated. In the present study by using the specific inhibitors Ku55933 and Pifithrin-α, we confirmed implication of both ATM and p53 in H(2)O(2)-induced senescence of hMESCs. ATM or p53 down regulation was shown to modulate differently the cellular fate of H(2)O(2)-treated hMESCs. ATM inhibition allowed H(2)O(2)-stimulated hMESCs to escape the permanent cell cycle arrest due to loss of the functional ATM/p53/p21/Rb pathway, and induced bypass of mitosis and re-entry into S phase, resulting in tetraploid cells. On the contrary, suppression of the p53 transcriptional activity caused a pronounced cell death of H(2)O(2)-treated hMESCs via autophagy induction. The obtained data clearly demonstrate that down regulation of ATM or p53 shifts senescence of human endometrial stem cells toward tetraploidization or autophagy.

Bim directly antagonizes Bcl-xl in doxorubicin-induced prostate cancer cell apoptosis independently of p53

Doxorubicin and other anthracycline compounds exert their anti-cancer effects by causing DNA damage and initiating cell cycle arrest in cancer cells, followed by apoptosis. DNA damage generally activates a p53-mediated pathway to initiate apoptosis by increasing the level of the BH3-only protein, Puma. However, p53-mediated apoptosis in response to DNA damage has not yet been validated in prostate cancers. In the current study, we used LNCaP and PC3 prostate cancer cells, representing wild type p53 and a p53-null model, to determine if DNA damage activates p53-mediated apoptosis in prostate cancers. Our results revealed that PC3 cells were 4 to 8-fold less sensitive than LNCaP cells to doxorubicin-inuced apoptosis. We proved that the differential response of LNCaP and PC3 to doxorubicin was p53-independent by introducing wild-type or dominant negative p53 into PC3 or LNCaP cells, respectively. By comparing several apoptosis-related proteins in both cell lines, we found that Bcl-xl proteins were much more abundant in PC3 cells than in LNCaP cells. We further demonstrated that Bcl-xl protects LNCaP and PC3 cells from doxorubicin-induced apoptosis by using ABT-263, an inhibitor of Bcl-xl, as a single agent or in combination with doxorubicin to treat LNCaP or PC3 cells. Bcl-xl rather than p53, likely contributes to the differential response of LNCaP and PC3 to doxorubicin in apoptosis. Finally, co-immunoprecipitation and siRNA analysis revealed that a BH3-only protein, Bim, is involved in doxorubicin-induced apoptosis by directly counteracting Bcl-xl.

Abnormalities in Alternative Splicing of Apoptotic Genes and Cardiovascular Diseases

Apoptosis is required for normal heart development in the embryo, but has also been shown to be an important factor in the occurrence of heart disease. Alternative splicing of apoptotic genes is currently emerging as a diagnostic and therapeutic target for heart disease. This review addresses the involvement of abnormalities in alternative splicing of apoptotic genes in cardiac disorders including cardiomyopathy, myocardial ischemia and heart failure. Many pro-apoptotic members of the Bcl-2 family have alternatively spliced isoforms that lack important active domains. These isoforms can play a negative regulatory role by binding to and inhibiting the pro-apoptotic forms. Alternative splicing is observed to be increased in various cardiovascular diseases with the level of alternate transcripts increasing elevated in diseased hearts compared to healthy subjects. In many cases these isoforms appear to be the underlying cause of the disease, while in others they may be induced in response to cardiovascular pathologies. Regardless of this, the detection of alternate splicing events in the heart can serve as useful diagnostic or prognostic tools, while those splicing events that seem to play a causative role in cardiovascular disease make attractive future drug targets.

Genetic susceptibility to cervical cancer: role of common polymorphisms in apoptosis-related genes

Cervical cancer is a common malignancy which poses a significant health burden among women, especially those living in the developing countries. Although human papillomavirus (HPV) infection has been unequivocally implicated in the etiopathogenesis of the cancer, it alone is not adequate to contribute to the malignant transformation of cervical cells. Most HPV infections regress spontaneously, and only a small proportion of women have persistent infections which eventually lead to malignancy. This suggests that interplays between HPV infection and other cofactors certainly exist during the process of cervical carcinogenesis, which synergistically contribute to the differential susceptibility of an individual to the malignancy. Undoubtedly, host genetic factors represent a major element involved in such a synergistic interaction, and accumulating evidence suggests that polymorphisms in apoptosis-related genes play an important role in the genetic susceptibility to cervical cancer. This review consolidates the recent literatures on the role of common polymorphisms in apoptosis-related genes in genetic susceptibility to cervical cancer.

miR-34 and p53: New Insights into a Complex Functional Relationship

miR-34, a tumor suppressor miRNA family transcriptionally activated by p53, is considered a critical mediator of p53 function. However, knockout of the mouse miR-34 family has little or no effect on the p53 response. The relative contribution of different miR-34 family members to p53 function or how much p53 relies on miR-34 in human cells is unclear. Here we show that miR-34a has a complex effect on the p53 response in human cells. In HCT116 cells miR-34a overexpression enhances p53 transcriptional activity, but the closely related family members, miR-34b and miR-34c, even when over-expressed, have little effect. Both TP53 itself and MDM4, a strong p53 transactivation inhibitor, are direct targets of miR-34a. The genes regulated by miR-34a also include four other post-translational inhibitors of p53. miR-34a overexpression leads to variable effects on p53 levels in p53-sufficient human cancer cell lines. In HCT116, miR-34a overexpression increases p53 protein levels and stability. About a quarter of all mRNAs that participate in the human p53 network bind to biotinylated miR-34a, suggesting that many are direct miR-34a targets. However, only about a fifth of the mRNAs that bind to miR-34a also bind to miR-34b or miR-34c. Two human cell lines knocked out for miR-34a have unimpaired p53-mediated responses to genotoxic stress, like mouse cells. The complex positive and negative effects of miR-34 on the p53 network suggest that rather than simply promoting the p53 response, miR-34a might act at a systems level to stabilize the robustness of the p53 response to genotoxic stress.

Whole-genome cartography of p53 response elements ranked on transactivation potential

Background

Many recent studies using ChIP-seq approaches cross-referenced to trascriptome data and also to potentially unbiased in vitro DNA binding selection experiments are detailing with increasing precision the p53-directed gene regulatory network that, nevertheless, is still expanding. However, most experiments have been conducted in established cell lines subjected to specific p53-inducing stimuli, both factors potentially biasing the results.

Results

We developed p53retriever, a pattern search algorithm that maps p53 response elements (REs) and ranks them according to predicted transactivation potentials in five classes. Besides canonical, full site REs, we developed specific pattern searches for non-canonical half sites and 3/4 sites and show that they can mediate p53-dependent responsiveness of associated coding sequences. Using ENCODE data, we also mapped p53 REs in about 44,000 distant enhancers and identified a 16-fold enrichment for high activity REs within those sites in the comparison with genomic regions near transcriptional start sites (TSS). Predictions from our pattern search were cross-referenced to ChIP-seq, ChIP-exo, expression, and various literature data sources. Based on the mapping of predicted functional REs near TSS, we examined expression changes of thirteen genes as a function of different p53-inducing conditions, providing further evidence for PDE2A, GAS6, E2F7, APOBEC3H, KCTD1, TRIM32, DICER, HRAS, KITLG and TGFA p53-dependent regulation, while MAP2K3, DNAJA1 and potentially YAP1 were identified as new direct p53 target genes.

Conclusions

We provide a comprehensive annotation of canonical and non-canonical p53 REs in the human genome, ranked on predicted transactivation potential. We also establish or corroborate direct p53 transcriptional control of thirteen genes. The entire list of identified and functionally classified p53 REs near all UCSC-annotated genes and within ENCODE mapped enhancer elements is provided. Our approach is distinct from, and complementary to, existing methods designed to identify p53 response elements. p53retriever is available as an R package at: http://tomateba.github.io/p53retriever.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1643-9) contains supplementary material, which is available to authorized users.

Genome wide expression profiling of p53 regulated miRNAs in neuroblastoma

Restoration of the antitumor activity of p53 could offer a promising approach for the treatment of neuroblastoma. MicroRNAs (miRNAs) are important mediators of p53 activity, but their role in the p53 response has not yet been comprehensively addressed in neuroblastoma. Therefore, we set out to characterize alterations in miRNA expression that are induced by p53 activation in neuroblastoma cells. Genome-wide miRNA expression analysis showed that miR-34a-5p, miR-182-5p, miR-203a, miR-222-3p, and miR-432-5p are upregulated following nutlin-3 treatment in a p53 dependent manner. The function of miR-182-5p, miR-203a, miR-222-3p, and miR-432-5p was analyzed by ectopic overexpression of miRNA mimics. We observed that these p53-regulated miRNAs inhibit the proliferation of neuroblastoma cells to varying degrees, with the most profound growth inhibition recorded for miR-182-5p. Overexpression of miR-182-5p promoted apoptosis in some neuroblastoma cell lines and induced neuronal differentiation of NGP cells. Using Chromatin Immunoprecipitation-qPCR (ChIP-qPCR), we did not observe direct binding of p53 to MIR182, MIR203, MIR222, and MIR432 in neuroblastoma cells. Taken together, our findings yield new insights in the network of p53-regulated miRNAs in neuroblastoma.

Nutlin-3 downregulates p53 phosphorylation on serine392 and induces apoptosis in hepatocellular carcinoma cells

Drug-resistance and imbalance of apoptotic regulation limit chemotherapy clinical application for the human hepatocellular carcinoma (HCC) treatment. The reactivation of p53 is an attractive therapeutic strategy in cancer with disrupted-p53 function. Nutlin-3, a MDM2 antagonist, has antitumor activity in various cancers. The post-translational modifications of p53 are a hot topic, but there are some controversy ideas about the function of phospho-Ser³⁹²-p53 protein in cancer cell lines in response to Nutlin-3. Therefore, we investigated the relationship between Nutlin-3 and phospho-Ser³⁹²-p53 protein expression levels in SMMC-7721 (wild-type TP53) and HuH-7 cells (mutant TP53). We demonstrated that Nutlin-3 induced apoptosis through down-regulation phospho-Ser³⁹²-p53 in two HCC cells. The result suggests that inhibition of p53 phosphorylation on Ser³⁹² presents an alternative for HCC chemotherapy. [BMB Reports 2014; 47(4): 221-226]

Bystander communication and cell cycle decisions after DNA damage

The DNA damage response (DDR) has two main goals, to repair the damaged DNA and to communicate the presence of damaged DNA. This communication allows the adaptation of cellular behavior to minimize the risk associated with DNA damage. In particular, cell cycle progression must be adapted after a DNA-damaging insult, and cells either pause or terminally exit the cell cycle during a DDR. As cells can accumulate mutations after a DDR due to error-prone DNA repair, terminal cell cycle exit may prevent malignant transformation. The tumor suppressor p53 plays a key role in promoting terminal cell cycle exit. Interestingly, p53 has been implicated in communication of a stress response to surrounding cells, known as the bystander response. Recently, surrounding cells have also been shown to affect the damaged cell, suggesting the presence of intercellular feedback loops. How such feedback may affect terminal cell cycle exit remains unclear, but its presence calls for caution in evaluating cellular outcome without controlling the cellular surrounding. In addition, such feedback may contribute to how the cellular environment affects malignant transformation after DNA damage.

Evolution of p53 transactivation specificity through the lens of a yeast-based functional assay

Co-evolution of transcription factors (TFs) with their respective cis-regulatory network enhances functional diversity in the course of evolution. We present a new approach to investigate transactivation capacity of sequence-specific TFs in evolutionary studies. Saccharomyces cerevisiae was used as an in vivo test tube and p53 proteins derived from human and five commonly used animal models were chosen as proof of concept. p53 is a highly conserved master regulator of environmental stress responses. Previous reports indicated conserved p53 DNA binding specificity in vitro, even for evolutionary distant species. We used isogenic yeast strains where p53-dependent transactivation was measured towards chromosomally integrated p53 response elements (REs). Ten REs were chosen to sample a wide range of DNA binding affinity and transactivation capacity for human p53 and proteins were expressed at two levels using an inducible expression system. We showed that the assay is amenable to study thermo-sensitivity of frog p53, and that chimeric constructs containing an ectopic transactivation domain could be rapidly developed to enhance the activity of proteins, such as fruit fly p53, that are poorly effective in engaging the yeast transcriptional machinery. Changes in the profile of relative transactivation towards the ten REs were measured for each p53 protein and compared to the profile obtained with human p53. These results, which are largely independent from relative p53 protein levels, revealed widespread evolutionary divergence of p53 transactivation specificity, even between human and mouse p53. Fruit fly and human p53 exhibited the largest discrimination among REs while zebrafish p53 was the least selective.

Sp1 regulates Raf/MEK/ERK-induced p21(CIP1) transcription in TP53-mutated cancer cells

We previously reported that the upregulation of mortalin, an Hsp70 family chaperone, is important for B-Raf(V600E) tumor cells to bypass p21(CIP1) expression, which is activated as a tumor-suppressive mechanism in response to aberrant MEK/ERK activation (Wu et al., 2013). Interestingly, mortalin depletion induced p21(CIP1) transcription not only in wild-type TP53 but also in TP53-mutated B-Raf(V600E) cancer cells, suggesting the presence of an additional mechanism for p21(CIP1) regulation. In the present study, using luciferase reporter truncation analysis in a TP53-mutated B-Raf(V600E) cancer cell line, SK-MEL28, we identified a proximal p21(CIP1) promoter region responsive to mortalin depletion. Interestingly, when Sp1-like cis-elements in this promoter region were mutagenized, the p21(CIP1) promoter luciferase reporter was no longer responsive to mortalin depletion. Consistent with this, our ChIP analysis revealed that mortalin knockdown could induce Sp1 binding to p21(CIP1) promoter in a MEK/ERK-dependent manner. Moreover, RNA interference of Sp1 substantially attenuated p21(CIP1) expression induced by mortalin depletion in SK-MEL28 cells. Consistent with this observation in SK-MEL28 cells, Sp1 was necessary for the tamoxifen-regulated ∆Raf-1:ER to induce p21(CIP1) transcription in U251 cells, in which TP53 is mutated. However, in contrast, Sp1 was not necessary for ∆Raf-1:ER to induce p21(CIP1) transcription in LNCaP cells, in which TP53 is wild type. These data suggest that Sp1 may address TP53-independent p21(CIP1) transcription in Raf/MEK/ERK-activated cancer cells and that its requirement in Raf/MEK/ERK-induced p21(CIP1) transcription is subject to TP53 status.

∆N-P63α and TA-P63α exhibit intrinsic differences in transactivation specificities that depend on distinct features of DNA target sites

TP63 is a member of the TP53 gene family that encodes for up to ten different TA and ΔN isoforms through alternative promoter usage and alternative splicing. Besides being a master regulator of gene expression for squamous epithelial proliferation, differentiation and maintenance, P63, through differential expression of its isoforms, plays important roles in tumorigenesis. All P63 isoforms share an immunoglobulin-like folded DNA binding domain responsible for binding to sequence-specific response elements (REs), whose overall consensus sequence is similar to that of the canonical p53 RE. Using a defined assay in yeast, where P63 isoforms and RE sequences are the only variables, and gene expression assays in human cell lines, we demonstrated that human TA- and ΔN-P63α proteins exhibited differences in transactivation specificity not observed with the corresponding P73 or P53 protein isoforms. These differences 1) were dependent on specific features of the RE sequence, 2) could be related to intrinsic differences in their oligomeric state and cooperative DNA binding, and 3) appeared to be conserved in evolution. Since genotoxic stress can change relative ratio of TA- and ΔN-P63α protein levels, the different transactivation specificity of each P63 isoform could potentially influence cellular responses to specific stresses.

ATM regulates cell fate choice upon p53 activation by modulating mitochondrial turnover and ROS levels

Despite extensive study, the mechanisms of cell fate choice upon p53 activation remain poorly understood. Using genome-wide shRNA screening, we recently identified the ATM kinase as synthetic lethal with Nutlin-3, an MDM2 inhibitor that leads to non-genotoxic p53 activation. Here, we demonstrate that while this synthetic lethal interaction relies upon components of both the intrinsic and extrinsic apoptotic pathways (e.g., BAX and BID), it is not due to significant ATM effects on the expression of p53 target genes. Instead, loss of ATM activity results in increased mitochondria and reactive oxygen species that drive apoptosis. Finally, we provide evidence that pharmacologic inhibition of ATM blocks autophagy in direct opposition to p53, which activates this process, and that inhibition of autophagy is sufficient to elicit an apoptotic response when combined with Nutlin-3.

Chaetoglobosin K induces apoptosis and G2 cell cycle arrest through p53-dependent pathway in cisplatin-resistant ovarian cancer cells

Adverse side effects and acquired resistance to conventional platinum based chemotherapy have become major impediments in ovarian cancer treatment, and drive the development of more selective anticancer drugs. Chaetoglobosin K (ChK) was shown to have a more potent growth inhibitory effect than cisplatin on two cisplatin-resistant ovarian cancer cell lines, OVCAR-3 and A2780/CP70, and was less cytotoxic to a normal ovarian cell line, IOSE-364, than to the cancer cell lines. Hoechst 33342 staining and Flow cytometry analysis indicated that ChK induced preferential apoptosis and G2 cell cycle arrest in both ovarian cancer cells with respect to the normal ovarian cells. ChK induced apoptosis through a p53-dependent caspase-8 activation extrinsic pathway, and caused G2 cell cycle arrest via cyclin B1 by increasing p53 expression and p38 phosphorylation in OVCAR-3 and A2780/CP70 cells. DR5 and p21 might play an important role in determining the sensitivity of normal and malignant ovarian cells to ChK. Based on these results, ChK would be a potential compound for treating platinum-resistant ovarian cancer.

A prolyl-hydroxylase inhibitor, ethyl-3,4-dihydroxybenzoate, induces cell autophagy and apoptosis in esophageal squamous cell carcinoma cells via up-regulation of BNIP3 and N-myc downstream-regulated gene-1

The protocatechuic acid ethyl ester ethyl-3,4-dihydroxybenzoate is an antioxidant found in the testa of peanut seeds. Previous studies have shown that ethyl-3,4-dihydroxybenzoate can effectively reduce breast cancer cell metastasis by inhibiting prolyl-hydroxylase. In this study, we investigated the cytotoxic effect of ethyl-3,4-dihydroxybenzoate on esophageal squamous cell carcinoma cells in vitro and identified key regulators of ethyl-3,4-dihydroxybenzoate-induced esophageal cancer cell death through transcription expression profiling. Using flow cytometry analysis, we found that ethyl-3,4-dihydroxybenzoate induced S phase accumulation, a loss in mitochondrial membrane permeabilization, and caspase-dependent apoptosis. Moreover, an expression profile analysis identified 46 up- and 9 down-regulated genes in esophageal cancer KYSE 170 cells treated with ethyl-3,4-dihydroxybenzoate. These differentially expressed genes are involved in several signaling pathways associated with cell cycle regulation and cellular metabolism. Consistent with the expression profile results, the transcriptional and protein expression levels of candidate genes NDRG1, BNIP3, AKR1C1, CCNG2 and VEGFA were found to be significantly increased in treated KYSE 170 cells by reverse-transcription PCR and western blot analysis. We also found that protein levels of hypoxia-inducible factor-1α, BNIP3, Beclin and NDRG1 were increased and that enriched expression of BNIP3 and Beclin caused autophagy mediated by microtubule-associated protein 1 light chain 3 in the treated cells. Autophagy and apoptosis were activated together in esophageal cancer cells after exposed to ethyl-3,4-dihydroxybenzoate. Furthermore, knock-down of NDRG1 expression by siRNA significantly attenuated apoptosis in the cancer cells, implying that NDRG1 may be required for ethyl-3,4-dihydroxybenzoate-induced apoptosis. Together, these results suggest that the cytotoxic effects of ethyl-3,4-dihydroxybenzoate were mediated by the up-regulation of NDRG1, BNIP3, Beclin and hypoxia-inducible factor-1α, initiating BNIP3 and Beclin mediated autophagy at an early stage and ultimately resulting in esophageal cancer cell apoptosis.

Caught in the cross fire: p53 in inflammation

The p53 transcription factor is a major tumor suppressor, whose diverse activities serve to ensure genome stability and inhibit neoplastic processes. In recent years, it is becoming increasingly clear that p53 also plays a broader role in maintaining cellular homeostasis, as well as contributing to tissue homeostasis in a non-cell-autonomous fashion. Chronic inflammation is a potential cancer-promoting condition, and as such is also within the radar of p53, which mounts a multifaceted attempt to prevent the escalation of chronic tissue imbalance into neoplasia. Recent understanding of the p53 pathway and other family members reveals a broad interaction with inflammatory elements such as reactive oxygen and nitrogen species, cytokines, infectious agents and major immune-regulatory pathways like nuclear factor-kappaB. This complex cross talk is highly dependent on p53 status, as different p53 isoforms and p53 mutants can mediate different responses and even promote chronic inflammation and associated cancer, acting in the tumor cells as well as in the stromal and immune compartments.

A novel PTEN/mutant p53/c-Myc/Bcl-XL axis mediates context-dependent oncogenic effects of PTEN with implications for cancer prognosis and therapy

Phosphatase and tensin homolog located on chromosome 10 (PTEN) is one of the most frequently mutated tumor suppressors in human cancer including in glioblastoma. Here, we show that PTEN exerts unconventional oncogenic effects in glioblastoma through a novel PTEN/mutant p53/c-Myc/Bcl-XL molecular and functional axis. Using a wide array of molecular, genetic, and functional approaches, we demonstrate that PTEN enhances a transcriptional complex containing gain-of-function mutant p53, CBP, and NFY in human glioblastoma cells and tumor tissues. The mutant p53/CBP/NFY complex transcriptionally activates the oncogenes c-Myc and Bcl-XL, leading to increased cell proliferation, survival, invasion, and clonogenicity. Disruption of the mutant p53/c-Myc/Bcl-XL axis or mutant p53/CBP/NFY complex reverses the transcriptional and oncogenic effects of PTEN and unmasks its tumor-suppressive function. Consistent with these data, we find that PTEN expression is associated with worse patient survival than PTEN loss in tumors harboring mutant p53 and that a small molecule modulator of p53 exerts greater antitumor effects in PTEN-expressing cancer cells. Altogether, our study describes a new signaling pathway that mediates context-dependent oncogenic/tumor-suppressive role of PTEN. The data also indicate that the combined mutational status of PTEN and p53 influences cancer prognosis and anticancer therapies that target PTEN and p53.

Bacterial programmed cell death: making sense of a paradox

Although the concept of programmed cell death (PCD) in bacteria has been met with scepticism, a growing body of evidence suggests that it can no longer be ignored. Several recent studies indicate that the phenotypic manifestations of apoptosis, which are processes that are associated with ordered cellular disassembly in eukaryotes, are conserved in bacteria. In this Opinion article, I propose a model for the coordinated control of potential bacterial PCD effectors and argue that the processes involved are functionally analogous to eukaryotic PCD systems.

A mortalin/HSPA9-mediated switch in tumor-suppressive signaling of Raf/MEK/extracellular signal-regulated kinase

Dysregulated Raf/MEK/extracellular signal-regulated kinase (ERK) signaling, a common hallmark of tumorigenesis, can trigger innate tumor-suppressive mechanisms, which must be inactivated for carcinogenesis to occur. This innate tumor-suppressive signaling may provide a potential therapeutic target. Here we report that mortalin (HSPA9/GRP75/PBP74) is a novel negative regulator of Raf/MEK/ERK and may provide a target for the reactivation of tumor-suppressive signaling of the pathway in cancer. We found that mortalin is present in the MEK1/MEK2 proteome and is upregulated in human melanoma biopsy specimens. In different MEK/ERK-activated cancer cell lines, mortalin depletion induced cell death and growth arrest, which was accompanied by increased p21(CIP1) transcription and MEK/ERK activity. Remarkably, MEK/ERK activity was necessary for mortalin depletion to induce p21(CIP1) expression in B-Raf(V600E)-transformed cancer cells regardless of their p53 status. In contrast, in cell types exhibiting normal MEK/ERK status, mortalin overexpression suppressed B-Raf(V600E)- or ΔRaf-1:ER-induced MEK/ERK activation, p21(CIP1) expression, and cell cycle arrest. Other HSP70 family chaperones could not effectively replace mortalin for p21(CIP1) regulation, suggesting a unique role for mortalin. These findings reveal a novel mechanism underlying p21(CIP1) regulation in MEK/ERK-activated cancer and identify mortalin as a molecular switch that mediates the tumor-suppressive versus oncogenic result of dysregulated Raf/MEK/ERK signaling. Our study also demonstrates that p21(CIP1) has dual effects under mortalin-depleted conditions, i.e., mediating cell cycle arrest while limiting cell death.

Cell cycle regulation by long non-coding RNAs

The mammalian cell cycle is precisely controlled by cyclin-dependent kinases (CDKs) and related pathways such as the RB and p53 pathways. Recent research on long non-coding RNAs (lncRNAs) indicates that many lncRNAs are involved in the regulation of critical cell cycle regulators such as the cyclins, CDKs, CDK inhibitors, pRB, and p53. These lncRNAs act as epigenetic regulators, transcription factor regulators, post-transcription regulators, and protein scaffolds. These cell cycle-regulated lncRNAs mainly control cellular levels of cell cycle regulators via various mechanisms, and may provide diversity and reliability to the general cell cycle. Interestingly, several lncRNAs are induced by DNA damage and participate in cell cycle arrest or induction of apoptosis as DNA damage responses. Therefore, deregulations of these cell cycle regulatory lncRNAs may be involved in tumorigenesis, and they are novel candidate molecular targets for cancer therapy and diagnosis.

Association between a rare novel TP53 variant (rs78378222) and melanoma, squamous cell carcinoma of head and neck and lung cancer susceptibility in non-Hispanic Whites

Recently, several studies have investigated the association between a newly reported rare functional single nucleotide polymorphism (SNP) in TP53 (rs78378222) and cancer risk, but generated inconsistent findings. The present study further investigated this association with risk of melanoma, squamous cell carcinoma of head and neck (SCCHN) and lung cancer. Using volunteers of non-Hispanic Whites recruited for three large case–control studies, we genotyped the TP53 rs78378222 SNP in 1329 patients with melanoma, 1096 with SCCHN, 1013 with lung cancer and 3000 cancer-free controls. Overall, we did not observe any variant homozygotes in this study population, nor significant associations between the TP53 rs78378222AC genotype or C allele and risk for melanoma (P = 0.680 and 0.682 respectively) and lung cancer (P = 0.379 and 0.382 respectively), but a protection against SCCHN (P = 0.008 and 0.008 respectively), compared with the AA genotype or A allele. An additional meta-analysis including 19,423 cancer patients and 54,050 controls did not support such a risk association either. Our studies did not provide statistical evidence of an association between this rare TP53 variant and increased risk of melanoma, nor of lung cancer, but a possible protection against SCCHN.

A genetic screen identifies TCF3/E2A and TRIAP1 as pathway-specific regulators of the cellular response to p53 activation

The p53 transcription factor participates in diverse cellular responses to stress, including cell-cycle arrest, apoptosis, senescence, and autophagy. The molecular mechanisms defining the ultimate outcome of p53 activation remain poorly characterized. We performed a genome-wide genetic screen in human cells to identify pathway-specific coregulators of the p53 target gene CDKN1A (p21), an inhibitor of cell-cycle progression, versus BBC3 (PUMA), a key mediator of apoptosis. Our screen identified numerous factors whose depletion creates an imbalance in the p21:PUMA ratio upon p53 activation. The transcription factor TCF3, also known as E2A, drives p21 expression while repressing PUMA across cancer cell types of multiple origins. Accordingly, TCF3/E2A depletion impairs the cell-cycle-arrest response and promotes apoptosis upon p53 activation by chemotherapeutic agents. In contrast, TRIAP1 is a specific repressor of p21 whose depletion slows down cell-cycle progression. Our results reveal strategies for driving cells toward specific p53-dependent responses.

Terpenoids from Zingiber officinale (Ginger) induce apoptosis in endometrial cancer cells through the activation of p53

Novel strategies are necessary to improve chemotherapy response in advanced and recurrent endometrial cancer. Here, we demonstrate that terpenoids present in the Steam Distilled Extract of Ginger (SDGE) are potent inhibitors of proliferation of endometrial cancer cells. SDGE, isolated from six different batches of ginger rhizomes, consistently inhibited proliferation of the endometrial cancer cell lines Ishikawa and ECC-1 at IC(50) of 1.25 µg/ml. SDGE also enhanced the anti-proliferative effect of radiation and cisplatin. Decreased proliferation of Ishikawa and ECC-1 cells was a direct result of SDGE-induced apoptosis as demonstrated by FITC-Annexin V staining and expression of cleaved caspase 3. GC/MS analysis identified a total of 22 different terpenoid compounds in SDGE, with the isomers neral and geranial constituting 30-40%. Citral, a mixture of neral and geranial inhibited the proliferation of Ishikawa and ECC-1 cells at an IC(50) 10 µM (2.3 µg/ml). Phenolic compounds such as gingerol and shogaol were not detected in SDGE and 6-gingerol was a weaker inhibitor of the proliferation of the endometrial cancer cells. SDGE was more effective in inducing cancer cell death than citral, suggesting that other terpenes present in SDGE were also contributing to endometrial cancer cell death. SDGE treatment resulted in a rapid and strong increase in intracellular calcium and a 20-40% decrease in the mitochondrial membrane potential. Ser-15 of p53 was phosphorylated after 15 min treatment of the cancer cells with SDGE. This increase in p53 was associated with 90% decrease in Bcl2 whereas no effect was observed on Bax. Inhibitor of p53, pifithrin-α, attenuated the anti-cancer effects of SDGE and apoptosis was also not observed in the p53(neg) SKOV-3 cells. Our studies demonstrate that terpenoids from SDGE mediate apoptosis by activating p53 and should be therefore be investigated as agents for the treatment of endometrial cancer.