Regulation of p53 stability and activity in response to genotoxic stress

BH3-mimetics or DNA-damaging agents in combination with RG7388 overcome p53 mutation-induced resistance to MDM2 inhibition

The development of drug resistance reduces the efficacy of cancer therapy. Tumor cells can acquire resistance to MDM2 inhibitors, which are currently under clinical evaluation. We generated RG7388-resistant neuroblastoma cells, which became more proliferative and metabolically active and were less sensitive to DNA-damaging agents in vitro and in vivo, compared with wild-type cells. The resistance was associated with a mutation of the p53 protein (His193Arg). This mutation abated its transcriptional activity via destabilization of the tetrameric p53-DNA complex and was observed in many cancer types. Finally, we found that Cisplatin and various BH3-mimetics could enhance RG7388-mediated apoptosis in RG7388-resistant neuroblastoma cells, thereby partially overcoming resistance to MDM2 inhibition.

Oxidative stress induced by hydrogen peroxide disrupts zebrafish visual development by altering apoptosis, antioxidant and estrogen related genes

Hydrogen peroxide is considered deleterious molecule that cause cellular damage integrity and function. Its key redox signaling molecule in oxidative stress and exerts toxicity on a wide range of organisms. Thus, to understand whether oxidative stress alters visual development, zebrafish embryos were exposed to H2O2 at concentration of 0.02 to 62.5 mM for 7 days. Eye to body length ratio (EBR) and apoptosis in retina at 48 hpf, and optomotor response (OMR) at 7 dpf were all measured. To investigate whether hydrogen peroxide-induced effects were mediated by oxidative stress, embryos were co-incubated with the antioxidant, glutathione (GSH) at 50 μM. Results revealed that concentrations of H2O2 at or above 0.1 mM induced developmental toxicity, leading to increased mortality and hatching delay. Furthermore, exposure to 0.1 mM H2O2 decreased EBR at 48 hpf and impaired OMR visual behavior at 7 dpf. Additionally, exposure increased the area of apoptotic cells in the retina at 48 hpf. The addition of GSH reversed the effects of H2O2, suggesting the involvement of oxidative stress. H2O2 decreased the expression of eye development-related genes, pax6α and pax6β. The expression of apoptosis-related genes, tp53, casp3 and bax, significantly increased, while bcl2α expression decreased. Antioxidant-related genes sod1, cat and gpx1a showed decreased expression. Expression levels of estrogen receptors (ERs) (esr1, esr2α, and esr2β) and ovarian and brain aromatase genes (cyp19a1a and cyp19a1b, respectively) were also significantly reduced. Interestingly, co-incubation of GSH effectivity reversed the impact of H2O2 on most parameters. Overall, these results demonstrate that H2O2 induces adverse effects on visual development via oxidative stress, which leads to alter apoptosis, diminished antioxidant defenses and reduced estrogen production.

Molecular docking study of frequently used food additives for selected targets depending on the chromosomal abnormalities they cause

Food additives (FAs) (flavor enhancers, sweeteners, etc.) protect foods during storage and transportation, making them attractive to consumers. Today, while the desire to access natural foods is increasing, the chemicals added to foods have started to be questioned. In this respect, genotoxicity tests have gained importance. Studies show that some food additives may have genotoxic risks. Previous studies carried out in our laboratory also revealed genotoxic effects of Monopotassium glutamate (MPG), Monosodium glutamate (MSG), Magnesium diglutamate (MDG) as flavor enhancers; Potassium benzoate (PB), Potassium sorbate (PS), Sodium benzoate (SB), Sodium sorbate (SS) as preservatives; Acesulfame potassium (ACE-K), Xylitol (XYL) as sweeteners. In this study, we determined the interactions of these food additives with ATM and p53 proteins, which are activated in the cell due to genotoxic effects, and with DNA by employing the molecular docking method for the first time. Among the food additives, SB (-4.307) for ATM, XYL (-4.629) for p53, and XYL (-4.927) for DNA showed the highest affinity. Therefore, flexible docking (IFD) scores were determined for SB, XYL, and MDG from flavor enhancers. The potential binding modes of the food additives to target molecules' possible inhibition mechanisms were determined by molecular docking. Thus, new information was obtained to show how these additives cause chromosomal abnormalities.

Anti-inflammatory effects of PRIMA-1MET (mutant p53 reactivator) induced by inhibition of nuclear factor-κB on rheumatoid arthritis fibroblast-like synoviocytes

Fibroblast-like synoviocytes (FLSs), the main pathological cells in rheumatoid arthritis (RA), display tumor-like phenotype, including hyper-proliferation, apoptosis resistance, and aggressive phenotype. Excessive proliferation and insufficient apoptosis of RA-FLSs can lead to hyperplastic synovial pannus tissue, excess production of inflammatory mediators, and destruction of joints. In this article, we investigate the effect of PRIMA-1^MET on the apoptosis induction and inhibition of pro-inflammatory cytokines in RA-FLSs. Synovial tissue samples were obtained from 10 patients with RA. The FLSs were treated with different concentrations of PRIMA-1^MET. The rate of apoptosis and cell survival was assessed by flow cytometry and MTT assay and Real-time quantitative PCR was performed to evaluate the transcription of p53, IL-6, IL-1β, TNF-α, Noxa, p21, PUMA, Bax, Survivin, and XIAP in treated RA-FLSs. The protein level of p53, IκBα, and phospho-IκBα were measured using Western blotting. The results showed that PRIMA-1^MET induced apoptosis in RA-FLSs and increased significantly the expression of Noxa, and decreased significantly IL-6, IL-1β, p53, and phospho-IκBα expression. PRIMA-1^MET can induce apoptosis in RA-FLSs through induction of Noxa expression while p53 was downregulated. Furthermore, PRIMA-1^MET treatment results in the suppression of pro-inflammatory cytokine production and NF-κB inhibition. Given the role of p53 and NF-κB in RA-FLSs, PRIMA-1^MET can be considered as a new therapeutic strategy for rheumatoid arthritis.

Transcription profiling of feline mammary carcinomas and derived cell lines reveals biomarkers and drug targets associated with metabolic and cell cycle pathways

The molecular heterogeneity of feline mammary carcinomas (FMCs) represents a prognostic and therapeutic challenge. RNA-Seq-based comparative transcriptomic profiling serves to identify recurrent and exclusive differentially expressed genes (DEGs) across sample types and molecular subtypes. Using mass-parallel RNA-Seq, we identified DEGs and performed comparative function-based analysis across 15 tumours (four basal-like triple-negative [TN], eight normal-like TN, and three luminal B fHER2 negative [LB fHER2-]), two cell lines (CL, TiHo-0906, and TiHo-1403) isolated from the primary tumours (LB fHER2-) of two cats included in this study, and 13 healthy mammary tissue controls. DEGs in tumours were predominantly upregulated; dysregulation of CLs transcriptome was more extensive, including mostly downregulated genes. Cell-cycle and metabolic-related DEGs were upregulated in both tumours and CLs, including therapeutically-targetable cell cycle regulators (e.g. CCNB1, CCNB2, CDK1, CDK4, GTSE1, MCM4, and MCM5), metabolic-related genes (e.g. FADS2 and SLC16A3), heat-shock proteins (e.g. HSPH1, HSP90B1, and HSPA5), genes controlling centrosome disjunction (e.g. RACGAP1 and NEK2), and collagen molecules (e.g. COL2A1). DEGs specifically upregulated in basal-like TN tumours were involved in antigen processing and presentation, in normal-like TN tumours encoded G protein-coupled receptors (GPCRs), and in LB fHER2- tumours were associated with lysosomes, phagosomes, and endosomes formation. Downregulated DEGs in CLs were associated with structural and signalling cell surface components. Hence, our results suggest that upregulation of genes enhancing proliferation and metabolism is a common feature among FMCs and derived CLs. In contrast, the dissimilarities observed in dysregulation of membrane components highlight CLs' disconnection with the tumour microenvironment. Furthermore, recurrent and exclusive DEGs associated with dysregulated pathways might be useful for the development of prognostically and therapeutically-relevant targeted panels.

Bisdemethoxycurcumin sensitizes the response of cisplatin resistant non-small cell lung carcinoma cell lines by activating apoptosis and autophagy

Lung cancer belongs to the most frequent and deadliest cancer types worldwide, non-small cell lung carcinoma (NSCLC) being the most frequent type. Development of chemoresistance in NSCLC patients is common and responsible for bad outcome. Curcuminoids are naturally occurring substances with prominent cytotoxic effects in different cancer cells. Here we analyzed influence of bisdemethoxycurcumin (BDMC) on phenotype and molecular mechanisms in cisplatin-sensitive NSCLC cell lines (A549 and H460) and their cisplatin-resistant counterparts. NSCLC cell lines were exposed to BDMC and analyzed by cell viability, proliferation, and motility assays, as well as fluorescence-activated cell sorting. Immunoblotting was assessed to detect apoptosis and autophagy. Colony-formation assay and multicellular tumor spheroid model were used to investigate the effects of BDMC. Expression levels of different Hedgehog-pathway genes were determined by RT-qPCR analysis. We identified substantial cytotoxic effects of BDMC on NSCLC cells in general and on cisplatin-resistant NSCLC cells in special. BDMC markedly decreased the cell viability by inducing apoptosis and autophagy in a cell-type specific manner. BDMC emphasized cisplatin-induced cell death and inhibited cell cycle progression of cisplatin-resistant NSCLC cells. Scratch-closure, colony formation, and multicellular spheroid growth in cisplatin-resistant NSCLC cell lines were inhibited by BDMC. Expression profile analyses of different Hedgehog-pathway regulatory genes showed that Gli1, the mean transcriptional regulator of this pathway, was markedly decreased upon the BDMC treatment, this decrement being most prominent in cisplatin-resistant cells. Our data identified BDMC as a potent substance that may be suitable for combined cisplatin-based therapy in cisplatin-resistant subpopulation of NSCLC patients.

Tick tock, tick tock: Mouse culture and tissue aging captured by an epigenetic clock

Aging is associated with dramatic changes to DNA methylation (DNAm), although the causes and consequences of such alterations are unknown. Our ability to experimentally uncover mechanisms of epigenetic aging will be greatly enhanced by our ability to study and manipulate these changes using in vitro models. However, it remains unclear whether the changes elicited by cells in culture can serve as a model of what is observed in aging tissues in vivo. To test this, we serially passaged mouse embryonic fibroblasts (MEFs) and assessed changes in DNAm at each time point via reduced representation bisulfite sequencing. By developing a measure that tracked cellular aging in vitro, we tested whether it tracked physiological aging in various mouse tissues and whether anti-aging interventions modulate this measure. Our measure, termed CultureAGE, was shown to strongly increase with age when examined in multiple tissues (liver, lung, kidney, blood, and adipose). As a control, we confirmed that the measure was not a marker of cellular senescence, suggesting that it reflects a distinct yet progressive cellular aging phenomena that can be induced in vitro. Furthermore, we demonstrated slower epigenetic aging in animals undergoing caloric restriction and a resetting of our measure in lung and kidney fibroblasts when re-programmed to iPSCs. Enrichment and clustering analysis implicated EED and Polycomb group (PcG) factors as potentially important chromatin regulators in translational culture aging phenotypes. Overall, this study supports the concept that physiologically relevant aging changes can be induced in vitro and used to uncover mechanistic insights into epigenetic aging.

MDMX is essential for the regulation of p53 protein levels in the absence of a functional MDM2 C-terminal tail

BACKGROUND

MDM2 is an E3 ubiquitin ligase that is able to ubiquitinate p53, targeting it for proteasomal degradation. Its homologue MDMX does not have innate E3 activity, but is able to dimerize with MDM2. Although mouse models have demonstrated both MDM2 and MDMX are individually essential for p53 regulation, the significance of MDM2-MDMX heterodimerization is only partially understood and sometimes controversial. MDM2C462A mice, where the C462A mutation abolishes MDM2 E3 ligase activity as well as its ability to dimerize with MDMX, die during embryogenesis. In contrast, the MDM2Y487A mice, where the Y487A mutation at MDM2 C-terminus significantly reduces its E3 ligase activity without disrupting MDM2-MDMX binding, survive normally even though p53 is expressed to high levels. This indicates that the MDM2-MDMX heterodimerization plays a critical role in the regulation of p53. However, it remains unclear whether MDMX is essential for the regulation of p53 protein levels in the context of an endogenous MDM2 C-terminal tail mutation.

RESULTS

Here, we studied the significance of MDM2-MDMX binding in an MDM2 E3 ligase deficient context using the MDM2Y487A mouse embryonic fibroblast (MEF) cells. Surprisingly, down-regulation of MDMX in MDM2Y487A MEFs resulted in a significant increase of p53 protein levels. Conversely, ectopic overexpression of MDMX reduced p53 protein levels in MDM2Y487A MEFs. Mutations of the RING domain of MDMX prevented MDMX-MDM2 binding, and ablated MDMX-mediated suppression of p53 protein expression. Additionally, DNA damage treatment and nuclear sequestration of MDMX inhibited MDMX activity to suppress p53 protein expression.

CONCLUSIONS

These results suggest that MDMX plays a key role in suppressing p53 protein expression in the absence of normal MDM2 E3 ligase activity. We found that the ability of MDMX to suppress p53 levels requires MDM2 binding and its cytoplasmic localization, and this ability is abrogated by DNA damage. Hence, MDMX is essential for the regulation of p53 protein levels in the context of an MDM2 C-terminal mutation that disrupts its E3 ligase activity but not MDMX binding. Our study is the first to examine the role of MDMX in the regulation of p53 in the context of endogenous MDM2 C-terminal mutant MEF cells.

Divergence of the PIERCE1 expression between mice and humans as a p53 target gene

PIERCE1, p53 induced expression 1 in Rb null cells, is a novel p53 target involved in the DNA damage response and cell cycle in mice. These facts prompted us to study the function of PIERCE1 with respect to p53-associated pathophysiology of cancer in humans. Unexpectedly, PIERCE1 did not respond to overexpression and activation of p53 in humans. In this study, we swapped p53 protein expression in human and mouse cells to find the clue of this difference between species. Human p53 expression in mouse cells upregulated PIERCE1 expression, suggesting that p53-responsive elements on the PIERCE1 promoter are crucial, but not the p53 protein itself. Indeed, in silico analyses of PIERCE1 promoters revealed that p53-responsive elements identified in mice are not conserved in humans. Consistently, chromatin immunoprecipitation-sequencing (ChIP-seq) analyses confirmed p53 enrichment against the PIERCE1 promoter region in mice, not in human cells. To complement the p53 study in mice, further promoter analyses suggested that the human PIERCE1 promoter is more similar to guinea pigs, lemurs, and dogs than to rodents. Taken together, our results confirm the differential responsiveness of PIERCE1 expression to p53 due to species differences in PIERCE1 promoters. The results also show partial dissimilarity after p53 induction between mice and humans.

Contributory role of microRNAs in anti-cancer effects of small molecule inhibitor of telomerase (BIBR1532) on acute promyelocytic leukemia cell line

Telomerase-mediated immortalization and proliferation of tumor cells is a promising anti-cancer treatment strategy and development of potent telomerase inhibitors is believed to open new window of treatments in human malignancies. In the present study, we found that BIBR1532, a small molecule inhibitor of human telomerase, exerted cytotoxic effects on a panel of human cancer cells spanning from solid tumors to hematologic malignancies; however, as compared with solid tumors, leukemic cells were more sensitive to this inhibitor. This was independent of molecular status of p53 in the leukemic cells. The results of a miRNA PCR array revealed that BIBR1532-induced cytotoxic effects in NB4, the most sensitive cell line, was coupled with alteration in a substantial number of cancer-related miRNAs. Interestingly, most of these miRNAs were found to act as tumor suppressors with validated targets in cell cycle or nuclear factor (NF)-κB-mediated apoptosis. In accordance with a bioinformatics analysis, our experimental studies showed that BIBR1532-induced apoptosis is mediated, at least partly, by inhibition of NF-κB. Moreover, we found that the alteration in the expression of miRNAs was coupled with the alteration in the cell cycle progression. To sum up with, a straightforward interpretation of our results is that telomerase inhibition using BIBR1532 not only induced CDKN1A-mediated G1 arrest in NB4, but also resulted in a caspase-3-dependent apoptotic cell death mostly through suppression of NF-κB axis.

Clinorotation-induced autophagy via HDM2-p53-mTOR pathway enhances cell migration in vascular endothelial cells

Individuals exposed to long-term spaceflight often experience cardiovascular dysfunctions characterized by orthostatic intolerance, disability on physical exercise, and even frank syncope. Recent studies have showed that the alterations of cardiovascular system are closely related to the functional changes of endothelial cells. We have shown previously that autophagy can be induced by simulated microgravity in human umbilical vein endothelial cells (HUVECs). However, the mechanism of enhanced autophagy induced by simulated microgravity and its role in the regulation of endothelial function still remain unclear. We report here that 48 h clinorotation promoted cell migration in HUVECs by induction of autophagy. Furthermore, clinorotation enhanced autophagy by the mechanism of human murine double minute 2 (HDM2)-dependent degradation of cytoplasmic p53 at 26S proteasome, which results in the suppression of mechanistic target of rapamycin (mTOR), but not via activation of AMPK in HUVECs. These results support the key role of HDM2–p53 in direct downregulation of mTOR, but not through AMPK in microgravity-induced autophagy in HUVECs.

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

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

Cyanobacterial Toxins of the Laurentian Great Lakes, Their Toxicological Effects, and Numerical Limits in Drinking Water

Cyanobacteria are ubiquitous phototrophic bacteria that inhabit diverse environments across the planet. Seasonally, they dominate many eutrophic lakes impacted by excess nitrogen (N) and phosphorus (P) forming dense accumulations of biomass known as cyanobacterial harmful algal blooms or cyanoHABs. Their dominance in eutrophic lakes is attributed to a variety of unique adaptations including N and P concentrating mechanisms, N₂ fixation, colony formation that inhibits predation, vertical movement via gas vesicles, and the production of toxic or otherwise bioactive molecules. While some of these molecules have been explored for their medicinal benefits, others are potent toxins harmful to humans, animals, and other wildlife known as cyanotoxins. In humans these cyanotoxins affect various tissues, including the liver, central and peripheral nervous system, kidneys, and reproductive organs among others. They induce acute effects at low doses in the parts-per-billion range and some are tumor promoters linked to chronic diseases such as liver and colorectal cancer. The occurrence of cyanoHABs and cyanotoxins in lakes presents challenges for maintaining safe recreational aquatic environments and the production of potable drinking water. CyanoHABs are a growing problem in the North American (Laurentian) Great Lakes basin. This review summarizes information on the occurrence of cyanoHABs in the Great Lakes, toxicological effects of cyanotoxins, and appropriate numerical limits on cyanotoxins in finished drinking water.

Dihydroartemisin inhibits glioma invasiveness via a ROS to P53 to β-catenin signaling

Dihydroartemisinin(DHA) is the active metabolic derivative of artemisinin. DHA has potential therapeutic effects on glioma but the detailed mechanism is unclear. In this study, we investigated the role and the underlying mechanisms of DHA in its inhibition of glioma cells. U87 cells are wild-type p53 glioblastoma cells and U251 cells contain mutant p53. DHA inhibited the proliferation, migration and invasion of glioma cells in a dose-dependent manner. DHA promoted reactive oxygen species production and activated p53 in two glioma cell lines, U87 and U251. In U87 cells, DHA significantly up-regulated the expression of p-β-catenin (S45) and inhibited EGFR, β-catenin, p-β-catenin (Y333) and matrix metalloprotease7/9 activity. In U251 cells, DHA significantly up-regulated p-β-catenin (S45), p-β-catenin (Y333) and EGFR, but the expression of β-cateninwas unchanged. We also found that DHA and sh-β-catenin prevented the proliferation of U87 and U251 cells in vivo. In conclusion, DHA inhibited the migration and invasion of human glioma cells with different types of p53 via different pathways.

Cadmium-induced apoptosis of Siberian tiger fibroblasts via disrupted intracellular homeostasis

Background

Heavy metals can cause great harm to Siberian tigers in the natural environment. Cadmium (Cd²⁺) is an environmental contaminant that affects multiple cellular processes, including cell proliferation, differentiation, and survival. It has been shown to induce apoptosis in a variety of cell types and tissues.

Results

We investigated the apoptotic effects of Cd²⁺ on Siberian tiger fibroblasts in vitro. Our research revealed the typical signs of apoptosis after Cd²⁺ exposure. Apoptosis was dose- (0–4.8 μM) and duration-dependent (12–48 h), and proliferation was strongly inhibited. Cd²⁺ increased the activity of caspase-3, -8, and -9 and disrupted calcium homeostasis by causing oxidative stress and mitochondrial dysfunction. It also increased K⁺ efflux and altered the mRNA levels of Bax, Bcl-2, caspase-3, caspase-8, Fas, and p53.

Conclusions

Our results suggest that Cd²⁺ triggers the apoptosis of Siberian tiger fibroblasts by disturbing intracellular homeostasis. These results will aid in our understanding of the effects of Cd²⁺ on Siberian tigers and in developing interventions to treat and prevent cadmium poisoning.

Radio-Sensitization of Human Leukaemic MOLT-4 Cells by DNA-Dependent Protein Kinase Inhibitor, NU7026

In this paper we describe the influence of NU7026, a specific inhibitor of DNA-dependent protein kinase, phosphoinositide 3-kinase, and ATM-kinase on molecular and cellular mechanisms triggered by ionising irradiation in human T-lymphocyte leukaemic MOLT-4 cells. We studied the effect of this inhibitor (10 μM) combined with gammaradiation (1 Gy) leading to DNA damage response and induction of apoptosis. We used methods for apoptosis assessment (cell viability count and flow-cytometric analysis) and cell cycle analysis (DNA content measurement) and we detected expression and post-translational modifications (Western blotting) of proteins involved in DNA repair signalling pathways. Pre-treatment with NU7026 resulted into decreased activation of checkpoint kinase-2 (Thr68), p53 (Ser15and Ser392), and histone H2A.X (Ser139) 2 hours after irradiation. Subsequently, combination of radiation and inhibitor led to decreased amount of cells in G2-phase arrest and into increased apoptosis after 72 hours. Our results indicate that in leukaemic cells the pre-incubation with inhibitor NU7026 followed by low doses of ionising radiation results in radio-sensitising of MOLT-4 cells via diminished DNA repair and delayed but pronounced apoptosis. This novel approach might offer new strategies in combined treatment of leukaemia diseases.

New insights on NOX enzymes in the central nervous system

SIGNIFICANCE

There is increasing evidence that the generation of reactive oxygen species (ROS) in the central nervous system (CNS) involves the NOX family of nicotinamide adenine dinucleotide phosphate oxidases. Controlled ROS generation appears necessary for optimal functioning of the CNS through fine-tuning of redox-sensitive signaling pathways, while overshooting ROS generation will lead to oxidative stress and CNS disease.

RECENT ADVANCES

NOX enzymes are not only restricted to microglia (i.e. brain phagocytes) but also expressed in neurons, astrocytes, and the neurovascular system. NOX enzymes are involved in CNS development, neural stem cell biology, and the function of mature neurons. While NOX2 appears to be a major source of pathological oxidative stress in the CNS, other NOX isoforms might also be of importance, for example, NOX4 in stroke. Globally speaking, there is now convincing evidence for a role of NOX enzymes in various neurodegenerative diseases, cerebrovascular diseases, and psychosis-related disorders.

CRITICAL ISSUES

The relative importance of specific ROS sources (e.g., NOX enzymes vs. mitochondria; NOX2 vs. NOX4) in different pathological processes needs further investigation. The absence of specific inhibitors limits the possibility to investigate specific therapeutic strategies. The uncritical use of non-specific inhibitors (e.g., apocynin, diphenylene iodonium) and poorly validated antibodies may lead to misleading conclusions.

FUTURE DIRECTIONS

Physiological and pathophysiological studies with cell-type-specific knock-out mice will be necessary to delineate the precise functions of NOX enzymes and their implications in pathomechanisms. The development of CNS-permeant, specific NOX inhibitors will be necessary to advance toward therapeutic applications.

Bisdemethoxycurcumin suppresses MCF-7 cells proliferation by inducing ROS accumulation and modulating senescence-related pathways

BACKGROUND

Bisdemethoxycurcumin (BDMC) is a natural derivative of curcumin present in the phenolic components extracted from the dried rhizome of Curcuma longa L. BDMC demonstrated potential chemotherapeutic activities but the underlying mechanisms have not been fully clarified. In the present study, the role of reactive oxidative species (ROS) in the anti-cancer effects of BDMC was investigated.

METHODS

MCF-7 cells were exposed to BDMC, and then the cell proliferation, colony formation ability and cell cycle profile were analyzed. Cellular ROS level was determined by flow cytometry and fluorescent microscope observation using specific fluorescent probes. Mitochondrial membrane potential (ψm) was assessed using JC-1. In addition, effects of BDMC on senescence-related molecules were analyzed by western blot assay.

RESULTS

BDMC significantly inhibited MCF-7 breast cancer cell proliferation, while a rapid rise of the intracellular ROS level accompanied with a reduction of Dym were observed. In addition, BDMC activated the pro-apoptotic protein p53 and its downstream effector p21 as well as the cell cycle regulatory proteins p16 and its downstream effector retinoblastoma protein (Rb). All of these BDMC-induced effects were counteracted with the pre-incubation of the antioxidant N-acetylcysteine (NAC).

CONCLUSIONS

These results suggested that BDMC-induced ROS accumulation may contribute to its inhibitory effect on MCF-7 cell viability through regulation of p53/p21 and p16/Rb pathways.

Hydrogen peroxide sensing, signaling and regulation of transcription factors

The regulatory mechanisms by which hydrogen peroxide (H₂O₂) modulates the activity of transcription factors in bacteria (OxyR and PerR), lower eukaryotes (Yap1, Maf1, Hsf1 and Msn2/4) and mammalian cells (AP-1, NRF2, CREB, HSF1, HIF-1, TP53, NF-κB, NOTCH, SP1 and SCREB-1) are reviewed. The complexity of regulatory networks increases throughout the phylogenetic tree, reaching a high level of complexity in mammalians. Multiple H₂O₂ sensors and pathways are triggered converging in the regulation of transcription factors at several levels: (1) synthesis of the transcription factor by upregulating transcription or increasing both mRNA stability and translation; (ii) stability of the transcription factor by decreasing its association with the ubiquitin E3 ligase complex or by inhibiting this complex; (iii) cytoplasm–nuclear traffic by exposing/masking nuclear localization signals, or by releasing the transcription factor from partners or from membrane anchors; and (iv) DNA binding and nuclear transactivation by modulating transcription factor affinity towards DNA, co-activators or repressors, and by targeting specific regions of chromatin to activate individual genes. We also discuss how H₂O₂ biological specificity results from diverse thiol protein sensors, with different reactivity of their sulfhydryl groups towards H₂O₂, being activated by different concentrations and times of exposure to H₂O₂. The specific regulation of local H₂O₂ concentrations is also crucial and results from H₂O₂ localized production and removal controlled by signals. Finally, we formulate equations to extract from typical experiments quantitative data concerning H₂O₂ reactivity with sensor molecules. Rate constants of 140 M⁻¹ s⁻¹ and ≥1.3 × 10³ M⁻¹ s⁻¹ were estimated, respectively, for the reaction of H₂O₂ with KEAP1 and with an unknown target that mediates NRF2 protein synthesis. In conclusion, the multitude of H₂O₂ targets and mechanisms provides an opportunity for highly specific effects on gene regulation that depend on the cell type and on signals received from the cellular microenvironment.

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Complexity of redox regulation increases along the phylogenetic tree.

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Complex regulatory networks allow for a high degree of H₂O₂ biological plasticity.

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H₂O₂ modulates gene expression at all steps from transcription to protein synthesis.

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Fast response (s) is mediated by sensors with high H₂O₂ reactivity.

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Low reactivity H₂O₂ sensors may mediate slow (h) or localized H₂O₂ responses.

An R132H mutation in isocitrate dehydrogenase 1 enhances p21 expression and inhibits phosphorylation of retinoblastoma protein in glioma cells

Cytosolic isocitrate dehydrogenase 1 (IDH1) with an R132H mutation in brain tumors loses its enzymatic activity for catalyzing isocitrate to α-ketoglutarate (α-KG) and acquires new activity whereby it converts α-KG to 2-hydroxyglutarate. The IDH1 mutation induces down-regulation of tricarboxylic acid cycle intermediates and up-regulation of lipid metabolism. Sterol regulatory element-binding proteins (SREBPs) regulate not only the synthesis of cholesterol and fatty acids but also acyclin-dependent kinase inhibitor p21 that halts the cell cycle at G1. Here we show that SREBPs were up-regulated in U87 human glioblastoma cells transfected with an IDH1^R132H-expression plasmid. Small interfering ribonucleic acid (siRNA) for SREBP1 specifically decreased p21 messenger RNA (mRNA) levels independent of the p53 pathway. In IDH1^R132H-expressing U87 cells, phosphorylation of Retinoblastoma (Rb) protein also decreased. We propose that metabolic changes induced by the IDH1 mutation enhance p21 expression via SREBP1 and inhibit phosphorylation of Rb, which slows progressionof the cell cycle and may be associated with non-aggressive features of gliomas with an IDH1 mutation.

Radiation enhances the invasiveness of irradiated and nonirradiated bystander hepatoma cells through a VEGF-MMP2 pathway initiated by p53

Recent evidence has shown that irradiation can promote the invasiveness of hepatocellular carcinoma cells and have an impact on the invasive behavior of nonirradiated surrounding cancer cells, which may enhance overall tumor aggressiveness. However, the role of the TP53 tumor suppressor gene in the invasion of irradiated hepatoma cells and their nonirradiated bystanders remain largely unknown. In the present study, we found that irradiation increased the invasiveness of human hepatoma HepG2 cells, and pretreatment of the cells with SU1498 (an inhibitor of vascular endothelial growth factor receptor 2, VEGFR2) and GM6001 (an inhibitor of matrix metalloproteinases 2, MMP2) demonstrated that radiation-enhanced invasiveness is associated with the interplay between MMP2 and VEGF signaling. In addition, while radiation-induced expression and phosphorylation of p53, inhibition of p53 function with pifithrin-α or transfection of cells with p53 siRNA significantly reduced the activation of both MMP2 and VEGF and resulted in a reduction of radiation-induced invasiveness. Interestingly, we also found that the invasiveness of the nonirradiated bystander cells was also elevated after co-culturing with irradiated cells and that bystander invasive potential was regulated paracrine in a manner by MMP2 and VEGF from the irradiated cells through a p53-dependent mechanism. Taken together, our data demonstrate that radiation-induced up-regulation of p53 is responsible for the promotion of VEGF-MMP2 pathway involved in the enhancement of invasiveness of both irradiated and bystander hepatoma cells.

Glucosidase II exhibits similarity to the p53 tumor suppressor in regards to structure and behavior in response to stress signals: a potential novel cancer biomarker

Early diagnosis of cancer is a key factor for the success of treatment. For this reason, identification of highly sensitive and specific novel tumor markers is urgently needed. In the present study, the CM5 polyclonal antibody (CM5 pAb) raised against p53 of mouse origin was used to identify p53 structurally related protein(s) that may also play an important role in promoting or preventing lung cancer. Western blot analysis was performed on tumor tissues and corresponding normal tissues obtained from lung cancer patients. CM5 pAb reacted with a human protein with an apparent molecular weight of 90 kDa in the lung tumor tissue. The levels of this protein were greatly increased in 35 of the 37 (94.6%) lung tumor samples assessed, with only minimal expression in the normal adjacent tissues. The 90-kDa protein was immunoprecipitated by CM5 pAb and was subsequently identified by LC-MS/MS to be glucosidase II, a key protein involved in the quality control mechanism of glycoprotein folding. An investigation of the response to genotoxic stress and endoplasmic reticulum (ER) stress using A549 human lung adenocarcinoma cells demonstrated that glucosidase II exhibited a similar pattern of response as the p53 tumor suppressor. Protein levels of both p53 and glucosidase II were increased in response to UV irradiation but decreased in response to tunicamycin-induced ER stress. In conclusion, we demonstrated that a polyclonal antibody raised against mouse p53 could cross-react with human glucosidase II, which was found to be frequently overexpressed in human lung tumor tissues and exhibited a stress response similar to p53. The high frequency of glucosidase II overexpression, which to the best of our knowledge has not been previously described, indicates its crucial roles in lung tumorigenesis and is thus a valuable biomarker for facilitating the screening and/or diagnosis of lung cancer. However, further investigations concerning its relationship to p53 and its roles in ER and genotoxic stress are warranted.

hnRNP Q regulates translation of p53 in normal and stress conditions

The responses to numerous stress signals are important for cellular growth and survival. The p53 tumor-suppressor protein is stabilized under stress conditions and induces transcription of several genes to regulate cell cycle and apoptosis. Regarding p53 protein accumulation, inhibition of proteasomal degradation of p53 protein, which is mainly mediated by Mdm2, has received much attention. Here, we demonstrate that regulation of translation initiation is also crucial for p53 protein accumulation. Furthermore, we report that heterogeneous nuclear ribonucleoprotein (hnRNP) Q binds to the 5'-untranslated region (UTR) of mouse p53 mRNA and regulates translation efficiency of p53 and apoptosis progression. We also suggest that changes in cytosolic hnRNP Q levels contribute to cell cycle-dependent translational differences in p53 mRNA.

The mouse lymphoma assay

The mouse lymphoma TK assay (MLA) is part of an in vitro battery of tests designed to predict risk assessment prior to in vivo testing. The test has the potential to detect mutagenic and clastogenic events at the thymidine kinase (tk) locus of L5178Y mouse lymphoma tk ( +/- ) cells by measuring resistance to the lethal nucleoside analogue triflurothymidine (TFT). Cells may be plated for viability and mutation in semi-solid agar (agar assay) or in 96-well microtitre plates (microwell assay). When added to selective medium containing TFT, wild-type tk ( +/- ) cells die, but TFT cannot be incorporated into the DNA of mutant tk ( -/- ) cells, which survive to form colonies that may be large (indicative of gene mutation) or small (indicative of chromosomal mutation) in nature. Mutant frequency is expressed as the number of mutants per 10(6) viable cells.

Resistance and gain-of-resistance phenotypes in cancers harboring wild-type p53

Chemotherapy is the bedrock for the clinical management of cancer, and the tumor suppressor p53 has a central role in this therapeutic modality. This protein facilitates favorable antitumor drug response through a variety of key cellular functions, including cell cycle arrest, senescence, and apoptosis. These functions essentially cease once p53 becomes mutated, as occurs in ∼50% of cancers, and some p53 mutants even exhibit gain-of-function effects, which lead to greater drug resistance. However, it is becoming increasingly evident that resistance is also seen in cancers harboring wild-type p53. In this review, we discuss how wild-type p53 is inactivated to render cells resistant to antitumor drugs. This may occur through various mechanisms, including an increase in proteasomal degradation, defects in post-translational modification, and downstream defects in p53 target genes. We also consider evidence that the resistance seen in wild-type p53 cancers can be substantially greater than that seen in mutant p53 cancers, and this poses a far greater challenge for efforts to design strategies that increase drug response in resistant cancers already primed with wild-type p53. Because the mechanisms contributing to this wild-type p53 "gain-of-resistance" phenotype are largely unknown, a concerted research effort is needed to identify the underlying basis for the occurrence of this phenotype and, in parallel, to explore the possibility that the phenotype may be a product of wild-type p53 gain-of-function effects. Such studies are essential to lay the foundation for a rational therapeutic approach in the treatment of resistant wild-type p53 cancers.

Activation of p53 signaling and inhibition of androgen receptor mediate tanshinone IIA induced G1 arrest in LNCaP prostate cancer cells

Our group previously reported that tanshinone IIA induced apoptosis via a mitochondria dependent pathway in LNCaP prostate cancer cells. In the present study, the roles of androgen receptor (AR) and p53 signaling pathways were investigated in tanshinone IIA-induced G1 arrest in LNCaP cells. Tanshinone IIA significantly inhibited the growth and proliferation of LNCaP cells by colony formation and BrdU incorporation assays, respectively. Tanshinone IIA induced cell cycle arrest at G1 phase and down-regulated cyclin D1, CDK2 and CDK4. Furthermore, tanshinone IIA activated the phosphorylation of p53 at Ser 15 residue and its downstream p21 and p27. Additionally, tanshinone IIA suppressed the expression of AR and prostate specific antigen (PSA). Conversely, silencing p53 using its specific siRNA reversed cyclin D1 expression inhibited by tanshinone IIA. However, knockdown of AR had no effect on the p53/p21/p27 signaling pathway activated by tanshinone IIA in LNCaP cells. In AR siRNA-transfected cells, tanshinone IIA did not cause cell cycle arrest and reduce cyclin D1, implying that AR is essential to induce G1 arrest by tanshinone IIA in LNCaP cells. Taken together, the findings suggest that tanshinone IIA induces G1 arrest via activation of p53 signaling and inhibition of AR in LNCaP cells.

Pharmacological inhibition of Mdm2 triggers growth arrest and promotes DNA breakage in mouse colon tumors and human colon cancer cells

The p53 tumor suppressor protein performs a number of cellular functions, ranging from the induction of cell cycle arrest and apoptosis to effects on DNA repair. Modulating p53 activity with Mdm2 inhibitors is a promising approach for treating cancer; however, it is presently unclear how the in vivo application of Mdm2 inhibitors impact the myriad processes orchestrated by p53. Since approximately half of all colon cancers (predominately cancers with microsatellite instability) are p53-normal, we assessed the anticancer activity of the Mdm2 inhibitor Nutlin-3 in the mouse azoxymethane (AOM) colon cancer model, in which p53 remains wild type. Using a cell line derived from an AOM-induced tumor, we found that four daily exposures to Nutlin-3 induced persistent p53 stabilization and cell cycle arrest without significant apoptosis. A 4-day dosing schedule in vivo generated a similar response in colon tumors; growth arrest without significantly increased apoptosis. In adjacent normal colon tissue, Nutlin-3 treatment reduced both cell proliferation and apoptosis. Surprisingly, Nutlin-3 induced a transient DNA damage response in tumors but not in adjacent normal tissue. Nutlin-3 likewise induced a transient DNA damage response in human colon cancer cells in a p53-dependent manner, and enhanced DNA strand breakage and cell death induced by doxorubicin. Our findings indicate that Mdm2 inhibitors not only trigger growth arrest, but may also stimulate p53's reported ability to slow homologous recombination repair. The potential impact of Nutlin-3 on DNA repair in tumors suggests that Mdm2 inhibitors may significantly accentuate the tumoricidal actions of certain therapeutic modalities.

Resveratrol and apoptosis

Resveratrol is a naturally occurring stilbene with desirable cardioprotective and anti-cancer properties. We have demonstrated the existence of a plasma membrane receptor for resveratrol near the arginine-glycine-aspartate (RGD) recognition site on integrin α(v)β₃ that is involved in stilbene-induced apoptosis of cancer cells. Resveratrol treatment in vitro causes activation and nuclear translocation of mitogen-activated protein kinase (ERK1/2), consequent phosphorylation of Ser-15 of p53, and apoptosis. An RGD peptide blocks these actions of resveratrol. By a PD98059-inhibitable process, resveratrol causes inducible COX-2 to accumulate in the nucleus where it complexes with pERK1/2 and p53. Chromatin immunoprecipitation reveals binding of nuclear COX-2 to promoters of certain p53-responsive genes, including PIG3 and Bax. NS-398, a specific pharmacologic inhibitor of COX-2, prevents resveratrol-induced complexing of nuclear ERK1/2 with COX-2 and with pSer-15-p53 and subsequent apoptosis; cyclooxygenase enzyme activity is not involved. Molecular steps in the pro-apoptotic action of resveratrol in cancer cells include induction of intranuclear COX-2 accumulation relevant to activation of p53. Epidermal growth factor, estrogen, and thyroid hormone act downstream of ERK1/2 to prevent resveratrol-induced apoptosis.

Mechanisms associated with mitochondrial-generated reactive oxygen species in cancer

The mitochondria are unique cellular organelles that contain their own genome and, in conjunction with the nucleus, are able to transcribe and translate genes encoding components of the electron transport chain (ETC). To do so, the mitochondria must communicate with the nucleus via the production of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), which are produced as a byproduct of aerobic respiration within the mitochondria. Mitochondrial signaling is proposed to be altered in cancer cells, where the mitochondria are frequently found to harbor mutations within their genome and display altered functional characteristics leading to increased glycolysis. As signaling molecules, ROS oxidize and inhibit MAPK phosphatases resulting in enhanced proliferation and survival, an effect particularly advantageous to cancer cells. In terms of transcriptional regulation, ROS affect the phosphorylation, activation, oxidation, and DNA binding of transcription factors such as AP-1, NF-kappaB, p53, and HIF-1alpha, leading to changes in target gene expression. Increased ROS production by defective cancer cell mitochondria also results in the upregulation of the transcription factor Ets-1, a factor that has been increasingly associated with aggressive cancers.

Spatiotemporal aspects of MicroRNA-mediated gene regulation

MicroRNA-mediated modulation of translation has been recently discovered as a new dimension in gene expression regulation. In this chapter we review how this regulation operates in time between the fast protein modification and degradation steps on the one hand and the slow transcriptional reprogramming associated with more stable changes in gene expression patterns on the other hand. We also discuss the additional layer of complexity associated with spatial redistribution of the RNA silencing machinery in subcellular structures. Various stress conditions induce both a transient change in microRNA expression within the first few hours after exposure and a redistribution of the RNA silencing machinery from P-bodies to Stress Granules, which differ in their function and protein content. Insight into the spatiotemporal aspects of the microRNA response will be indispensable for a full understanding of this level of gene regulation.

Growth inhibition and induction of apoptosis in MCF-7 breast cancer cells by oridonin nanosuspension

The mechanism for anti-tumor activity of oridonin (ORI) nanosuspension, prepared by the high pressure homogenization method, was studied using MCF-7 human breast carcinoma cells in vitro. MTT assay, observation of morphologic changes, flow cytometric analysis, and western blot analysis indicated that ORI nanosuspension could significantly intensify the in vitro anti-tumor activity to MCF-7 cells, as compared with ORI solution. Furthermore, ORI nanosuspension induced G₂/M stage proliferation arrest and apoptosis in MCF-7 cells depending on its concentration. In addition, western blot analysis indicated that the pro-caspase-3 protein was not cleaved into the activated form and the expression of anti-apoptotic Bcl-2 protein decreased, on the contrary, the expression of pro-apoptotic Bax protein increased in a dose-dependent manner in ORI nanosuspension-treated cells. These observations indicated that the anti-tumor activity of ORI nanosuspension was intensified by cell-cycle arrest and apoptosis induction.

Role of Cell Division Autoantigen 1 (CDA1) in Cell Proliferation and Fibrosis

Cell Division Autoantigen 1 (CDA1) was discovered following screening a human expression library with serum from a patient with Discoid Lupus Erythematosus. CDA1, encoded by TSPYL2 on the X chromosome, shares anti-proliferative, pro‑fibrotic properties with TGF-β. It inhibits cell growth through p53, pERK1/2, p21‑mediated pathways, is implicated in tumorigenesis, the DNA damage response. Its pro-fibrotic property is mediated through cross-talk with TGF-β that results in upregulation of extracellular matrix proteins. The latter properties have identified a key role for CDA1 in diabetes associated atherosclerosis. These dual properties place CDA1 as an attractive molecular target for treating tumors, vascular fibrosis including atherosclerosis, other vascular disorders associated with enhanced TGF-β action, tissue scarring.

Elevation of cyclic AMP causes an imbalance between NF-kappaB and p53 in NALM-6 cells treated by doxorubicin

We previously showed that cAMP can inhibit DNA damage-induced wild type p53 accumulation in human pre-B NALM-6 cells, leading to a profound reduction of their apoptotic response. Here, we provide evidence for the potentiation of DNA damage-induced NF-kappaB activation by cAMP. We found that inhibition of NF-kappaB activation prevents the inhibitory effect of cAMP on doxorubicin-induced apoptosis. Moreover, cAMP exerts its inhibitory effect on doxorubicin-induced apoptosis in a PKA-independent manner. The present study also shows that elevation of cAMP prolongs the phosphorylation of IkappaB and subsequent activation of NF-kappaB in doxorubicin treated NALM-6 cells in a proteasome-dependent manner. Taken together, our results demonstrate that cAMP abrogates the balance between apoptotic and antiapoptotic transcription factors that are hallmarks of DNA damage signaling.

Gossypol induces apoptosis by activating p53 in prostate cancer cells and prostate tumor-initiating cells

Prostate cancer continues to represent a burgeoning medical problem in the United States. Recent studies suggest that gossypol, a bioactive phytochemical produced by cotton plants, is a promising agent against prostate cancer. The current studies were undertaken to examine the chemotherapeutic efficacy of gossypol on human prostate cancer cell lines and prostate tumor-initiating cells. Gossypol reduced the viability of three prostate cancer cell lines (LAPC4, PC3, and DU145) with an IC(50) between 3 and 5 micromol/L. Additionally, gossypol was effective at inhibiting prostate tumor-initiating cell-driven tumor growth in a nonobese diabetic/severe combined immunodeficient xenograft model. Our integrated molecular profiling approach encompassing proteomics, activated transcription factors, and genomics suggests that the decrease in viability was associated with increased DNA damage and the induction of apoptosis. Exposure of DU145 cells to gossypol (1-10 micromol/L) resulted in the activation of 13 proteins and 7 transcription factors, and the expression of 17 genes involved in the mitochondrial pathway of apoptosis. These studies show for the first time that gossypol treatment induces DNA damage and activates p53. Collectively, these data support the use of gossypol as a novel agent for prostate cancer.

Transcriptional responses to oxidative stress: pathological and toxicological implications

The utilization of molecular oxygen as the terminal electron acceptor for energy production has in many ways shaped the evolution of complex life, physiology, and certain disease processes. The generation of reactive oxygen species (ROS), either as by-products of O(2) metabolism or by specialized enzymes, has the potential to damage cellular components and functions. Exposure to a variety of exogenous toxicants also promotes ROS production directly or through indirect means to cause toxicity. Oxidative stress activates the expression of a wide range of genes that mediate the pathogenic effect of ROS or are required for the detection and detoxification of the oxidants. In many cases, these are mediated by specific transcription factors whose expression, structure, stability, nuclear targeting, or DNA-binding affinity is regulated by the level of oxidative stress. This review examines major transcription factors that mediate transcriptional responses to oxidative stress, focusing on recent progress in the signaling pathways and mechanisms of activation of transcription factors by oxidative stress and the implications of this regulation in the development of disease and chemical toxicity.

MTA1 coregulator regulates p53 stability and function

Although metastasis-associated protein 1 (MTA1) has recently been shown as a DNA damage responsive protein, the underlying mechanism for its role in DNA double-strand break (DSB) repair remains unknown. Here, we show that MTA1 controls p53 stability through inhibiting its ubiquitination by E3 ubiquitin ligases mouse double minute 2 (Mdm2) and constitutive photomorphogenic protein 1 (COP1). The underlying mechanisms involve the ability of MTA1 to compete with COP1 to bind to p53 and/or to destabilize COP1 and Mdm2. Consequently, MTA1 regulates the p53-dependent transcription of p53R2, a direct p53 target gene for supplying nucleotides to repair damaged DNA. Depletion of MTA1 impairs p53-dependent p53R2 transcription and compromises DNA repair. Interestingly, these events could be reversed by MTA1 reintroduction, indicating that MTA1 interjects into the p53-dependent DNA repair. Given the fact that MTA1 is widely up-regulated in human cancers, these findings in conjunction with our earlier finding of a crucial role of MTA1 in DSB repair suggest an inherent role of the MTA1-p53-p53R2 pathway in DNA damage response in cancer cells.

Homeodomain interacting protein kinase 2 activation compromises endothelial cell response to laminar flow: protective role of p21(waf1,cip1,sdi1)

BACKGROUND

In the cardiovascular system, laminar shear stress (SS) is one of the most important source of endothelial protecting signals. Physical and chemical agents, however, including ionising radiations and anticancer drugs, may injure endothelial cells determining an increase in oxidative stress and genotoxic damage. Whether the SS protective function remains intact in the presence of strong oxidants or DNA damage is currently unclear.

METHODS AND RESULTS

To investigate this aspect a series of experiments were performed in which HUVEC were exposed to sub-lethal doses of the radio-mimetic compound Bleomycin (Bleo; 10 microg/ml) which generated free radicals (ROS) without significantly compromising cell survival. Remarkably, the application of a SS of 12 dyne/cm(2) did not protect endothelial cells but markedly accelerated apoptosis compared to controls kept in static culture and in the presence of Bleo. Experiments with the inducible nitric oxide synthase (iNOS) inhibitor GW274150 significantly reduced the SS-dependent apoptosis indicating that the production of NO was relevant for this effect. At molecular level, the ataxia-telangectasia-mutated (ATM) kinase, the homeodomain-interacting protein kinase-2 (HIPK2) and p53 were found activated along a pro-apoptotic signalling pathway while p21(waf1,cip1,sdi1) was prevented from its protective action. RNA interference experiments revealed that HIPK2 and p53 were both important for this process, however, only the forced expression p21(waf1,cip1,sdi1) fully restored the SS-dependent pro-survival function.

CONCLUSIONS

This study provides the first evidence that, in the presence of genotoxic damage, laminar flow contributes to endothelial toxicity and death and identifies molecular targets potentially relevant in endothelial dysfunction and cardiovascular disease pathogenesis.

Induction and loss of a TP53-dependent radioadaptive response in the human lymphoblastoid cell model TK6 and its abrogation by BCL2 over-expression

PURPOSE

To characterize the radioadaptive response in the human lymphoblastoid cell model TK6, and determine: (i) Whether repeated low dose exposures are more effective than single acute exposures in inducing resistance, (ii) the time-course for induction and loss of resistance following chronic exposures, and (iii) the effect of TP53 deletion or BCL2 over-expression on the induction of an adaptive response.

MATERIALS AND METHODS

TK6, a human B-lymphoblastoid cell line, TK6-BCL2, a TK6 line that over-expresses BCL2 and is resistant to radiation-induced apoptosis, and NH32, a TP53 knockout of TK6 that is also resistant to apoptosis were studied. Cells were exposed to chronic, daily doses of 10 cGy given over 1 -21 days before being challenged with 1 -5 Gy exposures. Cell survival and chromatid break induction following high dose challenge were used to evaluate adaptive radiation responses.

RESULTS

Exposure to 10 cGy gamma rays induced resistance to killing and chromosome break induction in TK6 cells, but not in either TK6-BCL2 or NH32 cells. Resistance in TK6 was observed 4 h after exposure, and cells remained resistant for about 48 h. Maximal resistance was induced by a single 10 cGy dose. Repeated 10 cGy exposures had no additional effect on radiation sensitivity, except to maintain the induced radioresistance.

CONCLUSION

An adaptive response is maximally and rapidly induced by a single low dose exposure in TK6 cells, and it has a limited lifespan. Induction of an adaptive response in TK6 cells can be abrogated by either TP53 loss or BCL2 over-expression. The characteristics of induced resistance in TK6 cells suggest that alterations in TP53-dependent apoptotic responses may be one mechanism for resistance.

MicroRNA-mediated gene silencing modulates the UV-induced DNA-damage response

DNA damage provokes DNA repair, cell-cycle regulation and apoptosis. This DNA-damage response encompasses gene-expression regulation at the transcriptional and post-translational levels. We show that cellular responses to UV-induced DNA damage are also regulated at the post-transcriptional level by microRNAs. Survival and checkpoint response after UV damage was severely reduced on microRNA-mediated gene-silencing inhibition by knocking down essential components of the microRNA-processing pathway (Dicer and Ago2). UV damage triggered a cell-cycle-dependent relocalization of Ago2 into stress granules and various microRNA-expression changes. Ago2 relocalization required CDK activity, but was independent of ATM/ATR checkpoint signalling, whereas UV-responsive microRNA expression was only partially ATM/ATR independent. Both microRNA-expression changes and stress-granule formation were most pronounced within the first hours after genotoxic stress, suggesting that microRNA-mediated gene regulation operates earlier than most transcriptional responses. The functionality of the microRNA response is illustrated by the UV-inducible miR-16 that downregulates checkpoint-gene CDC25a and regulates cell proliferation. We conclude that microRNA-mediated gene regulation adds a new dimension to the DNA-damage response.

p53 and MDM2 protein expression in actinic cheilitis

Actinic cheilitis is a potentially malignant lip lesion caused by excessive and prolonged exposure to ultraviolet radiation, which can lead to histomorphological alterations indicative of abnormal cell differentiation. In this pathology, varying degrees of epithelial dysplasia may be found. There are few published studies regarding the p53 and MDM2 proteins in actinic cheilitis. Fifty-eight cases diagnosed with actinic cheilitis were histologically evaluated using Banóczy and Csiba (1976) parameters, and were subjected to immunohistochemical analysis using the streptavidin-biotin method in order to assess p53 and MDM2 protein expression. All studied cases expressed p53 proteins in basal and suprabasal layers. In the basal layer, the nuclei testing positive for p53 were stained intensely, while in the suprabasal layer, cells with slightly stained nuclei were predominant. All cases also tested positive for the MDM2 protein, but with varying degrees of nuclear expression and a predominance of slightly stained cells. A statistically significant correlation between the percentage of p53 and MDM2-positive cells was established, regardless of the degree of epithelial dysplasia. The expression of p53 and MDM2 proteins in actinic cheilitis can be an important indicator in lip carcinogenesis, regardless of the degree of epithelial dysplasia.

Emodin induces apoptosis in human prostate cancer cell LNCaP

AIM

To elucidate effects and mechanisms of emodin in prostate cancer cells.

METHODS

Viability of emodin-treated LNCaP cells and PC-3 cells was measured by MTT assay. Following emodin treatments, DNA fragmentation was assayed by agarose gel electrophoresis. Apoptosis rate and the expression of Fas and FasL were assayed by flow cytometric analysis. The mRNA expression levels of androgen receptor (AR), prostate-specific antigen (PSA), p53, p21, Bcl-2, Bax, caspase-3, -8, -9 and Fas were detected by RT-PCR, and the protein expression levels of AR, p53 and p21 were detected by Western blot analysis.

RESULTS

In contrast to PC-3, emodin caused a marked increase in apoptosis and a decrease in cell proliferation in LNCaP cells. The expression of AR and PSA was decreased and the expression of p53 and p21 was increased as the emodin concentrations were increased. In the same time, emodin induced apoptosis of LNCaP cells through the upregulation of caspase-3 and -9, as well as the increase of Bax /Bcl-2 ratio. However, it did not involve modulation of Fas or caspase-8 protein expression.

CONCLUSION

In prostate cancer cell line, LNCaP, emodin inhibites the proliferation by AR and p53-p21 pathways, and induces apoptosis via the mitochondrial pathway.

Role of p53, PUMA, and Bax in wogonin-induced apoptosis in human cancer cells

We observed that treatment of prostate cancer cells for 24 h with wogonin, a naturally occurring monoflavonoid, induced cell death in a dose- and time-dependent manner. Exposure of wogonin to LNCaP cells was associated with increased intracellular levels of p21(Cip-1), p27(Kip-1), p53, and PUMA, oligomerization of Bax, release of cytochrome c from the mitochondria, and activation of caspases. We also confirmed the role of p53 by noting that knock-in in p53 expression by transfecting p53 DNA increased wogonin-induced apoptosis in p53-null PC-3 cells. To study the mechanism of PUMA up-regulation, we determined the activities of PUMA promoter in the wogonin treated and untreated cells. Increase of the intracellular levels of PUMA protein was due to increase in transcriptional activity. Data from chromatin immunoprecipitation (ChIP) analyses revealed that wogonin activated the transcription factor p53 binding activity to the PUMA promoter region. We observed that the up-regulation of PUMA mediated wogonin cytotoxicity. Further characterization of the transcriptional response to wogonin in HCT116 human colon cancer cells demonstrated that PUMA induction was p53-dependent; deficiency in either p53 or PUMA significantly protected HCT116 cells against wogonin-induced apoptosis. Also, wogonin promoted mitochondrial translocation and multimerization of Bax. Interestingly, wogonin (100 microM) treatment did not affect the viability of normal human prostate epithelial cells (PrEC). Taken together, these results indicate that p53-dependent transcriptional induction of PUMA and oligomerization of Bax play important roles in the sensitivity of cancer cells to apoptosis induced by caspase activation through wogonin.