A novel form of Epstein-Barr virus latency in normal B cells in vivo

Activation of p53-regulated pro-apoptotic signaling pathways in PrP-mediated myopathy

BACKGROUND

We have reported that doxycycline-induced over-expression of wild type prion protein (PrP) in skeletal muscles of Tg(HQK) mice is sufficient to cause a primary myopathy with no signs of peripheral neuropathy. The preferential accumulation of the truncated PrP C1 fragment was closely correlated with these myopathic changes. In this study we use gene expression profiling to explore the temporal program of molecular changes underlying the PrP-mediated myopathy.

RESULTS

We used DNA microarrays, and confirmatory real-time PCR and Western blot analysis to demonstrate deregulation of a large number of genes in the course of the progressive myopathy in the skeletal muscles of doxycycline-treated Tg(HQK) mice. These include the down-regulation of genes coding for the myofibrillar proteins and transcription factor MEF2c, and up-regulation of genes for lysosomal proteins that is concomitant with increased lysosomal activity in the skeletal muscles. Significantly, there was prominent up-regulation of p53 and p53-regulated genes involved in cell cycle arrest and promotion of apoptosis that paralleled the initiation and progression of the muscle pathology.

CONCLUSION

The data provides the first in vivo evidence that directly links p53 to a wild type PrP-mediated disease. It is evident that several mechanistic features contribute to the myopathy observed in PrP over-expressing mice and that p53-related apoptotic pathways appear to play a major role.

Nonlinear cooperation of p53-ING1-induced bax expression and protein S-nitrosylation in GSNO-induced thymocyte apoptosis: a quantitative approach with cross-platform validation

Increasing evidence has been gathered for p53-dependent apoptosis, but it is still unclear how p53 initiates apoptosis by employing its transcriptional program. Pair-wise interactions of p53 with expression of other genes fail to predict p53 levels or rate of apoptosis. A more sophisticated approach, using neural networks, permits prediction of interaction among three or more genes (p53, bax, and ING1). These interactions are decidedly nonlinear. Careful measurements and advanced mathematical treatments will permit us not only to understand how expression of pro- and anti-apoptotic genes is regulated, but also to integrate cross-platform and cross-experimental data for the validation of predicted interactions.

Leukocyte elastase induces lung epithelial apoptosis via a PAR-1-, NF-kappaB-, and p53-dependent pathway

Leukocyte elastase induces apoptosis of lung epithelial cells via alterations in mitochondrial permeability, but the signaling pathways regulating this response remain uncertain. Here we investigated the involvement of proteinase-activated receptor-1 (PAR-1), the transcription factor NF-kappaB, and the protooncogene p53 in this pathway. Elastase-induced apoptosis of lung epithelial cells correlated temporally with activation of NF-kappaB, phosphorylation, and nuclear translocation of p53, increased p53 up-regulated modulator of apoptosis (PUMA) expression, and mitochondrial translocation of Bax resulting in enhanced permeability. Elastase-induced apoptosis was also prevented by pharmacologic inhibitors of NF-kappaB and p53 and by short interfering RNA knockdown of PAR-1, p53, or PUMA. These inhibitors prevented elastase-induced PUMA expression, mitochondrial translocation of Bax, increased mitochondrial permeability, and attenuated apoptosis. NF-kappaB inhibitors also reduced p53 phosphorylation. We conclude that elastase-induced apoptosis of lung epithelial cells is mediated by a PAR-1-triggered pathway involving activation of NF-kappaB and p53, and a PUMA- and Bax-dependent increase in mitochondrial permeability leading to activation of distal caspases. Further, p53 contributes to elastase-induced apoptosis by both transcriptional and post-transcriptional mechanisms.

Genes of cell-cell interactions, chemotherapy detoxification and apoptosis are induced during chemotherapy of acute myeloid leukemia

Background

The molecular changes in vivo in acute myeloid leukemia cells early after start of conventional genotoxic chemotherapy are incompletely understood, and it is not known if early molecular modulations reflect clinical response.

Methods

The gene expression was examined by whole genome 44 k oligo microarrays and 12 k cDNA microarrays in peripheral blood leukocytes collected from seven leukemia patients before treatment, 2–4 h and 18–24 h after start of chemotherapy and validated by real-time quantitative PCR. Statistically significantly upregulated genes were classified using gene ontology (GO) terms. Parallel samples were examined by flow cytometry for apoptosis by annexin V-binding and the expression of selected proteins were confirmed by immunoblotting.

Results

Significant differential modulation of 151 genes were found at 4 h after start of induction therapy with cytarabine and anthracycline, including significant overexpression of 31 genes associated with p53 regulation. Within 4 h of chemotherapy the BCL2/BAX and BCL2/PUMA ratio were attenuated in proapoptotic direction. FLT3 mutations indicated that non-responders (5/7 patients, 8 versus 49 months survival) are characterized by a unique gene response profile before and at 4 h. At 18–24 h after chemotherapy, the gene expression of p53 target genes was attenuated, while genes involved in chemoresistance, cytarabine detoxification, chemokine networks and T cell receptor were prominent. No signs of apoptosis were observed in the collected cells, suggesting the treated patients as a physiological source of pre-apoptotic cells.

Conclusion

Pre-apoptotic gene expression can be monitored within hours after start of chemotherapy in patients with acute myeloid leukemia, and may be useful in future determination of therapy responders. The low number of patients and the heterogeneity of acute myeloid leukemia limited the identification of gene expression predictive of therapy response. Therapy-induced gene expression reflects the complex biological processes involved in clinical cancer cell eradication and should be explored for future enhancement of therapy.

Medical management update: Non-Hodgkin lymphoma

Lymphoma is a heterogeneous malignancy of the lymphatic system characterized by proliferation of lymphoid cells or their precursors. Non-Hodgkin lymphoma (NHL) is associated with significant morbidity and is the seventh leading cause of death in the United States. Manifestations of NHL as well as complications of the disease and its management are frequently encountered in the head and neck region and often require specific treatment and modifications in the provision of oral health care. The purpose of this article is to review current concepts of the pathophysiology, as well as medical and oral health care management of NHL.

The intersection of Epstein-Barr virus with the germinal center

The current model of Epstein-Barr virus (EBV) infection and persistence in vivo proposes that EBV uses the germinal center (the GC model) to establish a quiescent latent infection in otherwise-normal memory B cells. However, the evidence linking EBV-infected cells and the GC is only indirect and limited. Therefore, a key portion of the model, that EBV-infected cells physically reside and participate in GCs, has yet to be verified. Furthermore, recent experiments suggested that upon infection of GC cells the viral growth latency transcription program is dominant and GC functionality and phenotype are ablated, i.e., EBV infection is not consistent with GC function. In this study we show that in vivo, EBV-infected B cells in the tonsils retain expression of functional and phenotypic markers of GC cells, including bcl-6 and AID. Furthermore, these cells are physically located in the GC and express a restricted form of latency, the default latency program. Thus, the EBV default latency transcription program, unlike the growth latency program, is consistent with the retention of GC functionality in vivo. This work verifies key components of the GC model of EBV persistence and suggests that EBV and the GC can interact to produce the latently infected memory cells found in the periphery. Furthermore, it identifies latently infected GC B cells as a potential pathogenic nexus for the development of the EBV-positive, GC-associated lymphomas Hodgkin's disease and Burkitt's lymphoma.

A function for the RING finger domain in the allosteric control of MDM2 conformation and activity

The MDM2 oncoprotein plays multiple regulatory roles in the control of p53-dependent gene expression. A picture of MDM2 is emerging where structurally discrete but interdependent functional domains are linked through changes in conformation. The domain structure includes: (i) a hydrophobic pocket at the N terminus of MDM2 that is involved in both its transrepressor and E3-ubiqutin ligase functions, (ii) a central acid domain that recognizes a ubiquitination signal in the core DNA binding domain of p53, and (iii) a C-terminal C2H2C4 RING finger domain that is required for E2 enzyme-binding and ATP-dependent molecular chaperone activity. Here we show that the binding affinity of MDM2s hydrophobic pocket can be regulated through the RING finger domain and that increases in pocket affinity are reflected by a gain in MDM2 transrepressor activity. Thus, mutations within the RING domain that affect zinc coordination, but not one that inhibits ATP binding, produce MDM2 proteins that have a higher affinity for the BOX-I transactivation domain of p53 and a reduced I(0.5) for p53 transrepression. An allosteric model for regulation of the hydrophobic pocket is supported by differences in protein conformation and pocket accessibility between wild-type and the RING domain mutant MDM2 proteins. Additionally the data demonstrate that the complex relationship between different domains of MDM2 can impact on the efficacy of anticancer drugs directed toward its hydrophobic pocket.

Involvement of c-Abl, p53 and the MAP kinase JNK in the cell death program initiated in A2E-laden ARPE-19 cells by exposure to blue light

The lipofuscin fluorophore A2E has been shown to mediate blue light-induced damage to retinal pigmented epithelial (RPE) cells. To understand the events that lead to RPE cell apoptosis under these conditions, we explored signaling pathways upstream of the cell death program. Human RPE cells (ARPE-19) that had accumulated A2E were exposed to blue light to induce apoptosis and the involvement of the transcription factors p53 and c-Abl and the mitogen activated protein kinases p38 and JNK were examined. We found that A2E/blue light caused upregulation and phosphorylation of c-Abl, and upregulation of p53. Pretreatment with the c-Abl inhibitor STI571 and transfection with siRNA specific to c-Abl and p53 prior to irradiation reduced A2E/blue light-induced cell death. Gene and protein expression of JNK and p38 was upregulated in response to A2E/blue light. Treatment with the JNK inhibitor SP600125 before irradiation resulted in increase in cell death whereas inhibition of p38 with SB203580 had no effect. This study indicates that c-Abl and p53 are important for execution of the cell death program initiated in A2E-laden RPE cells exposed to blue light, while JNK might play an anti-apoptotic role.

Targeting death-receptors in radiation therapy

The development of apoptosis resistance is a crucial step during the pathogenesis of malignant tumors. Thus, any treatment approach overcoming apoptosis resistance may be a valuable tool in oncology. Although a variety of treatments induce apoptosis, only very few specifically trigger programmed cell death. In this regard, the class of apoptosis inducing ligands may turn out to have a considerable potential in oncology. TNF-alpha-related apoptosis-inducing ligand (TRAIL/Apo2L) is the most promising candidate, either alone or in combination with established cancer therapies, since it induces apoptosis in a wide range of malignant cells while sparing most normal tissues. Since death-receptor induced apoptosis is mainly mediated via nonmitochondrial death pathways, it is possible to induce apoptosis in cancer cell systems which mainly harbor defects within the mitochondrial death cascades. Even more so it has been shown that conventional DNA damaging approaches reduced the killing threshold for receptor induced apoptosis, making TRAIL an ideal candidate for combined approaches. Thus, combined treatments might offer the chance to enhance therapeutic efficiency and overcome resistance. In combination, additive or synergistic apoptotic responses and substantially enhanced clonogenic cell kill has been documented. Furthermore, in several settings it has been shown that combined modality teatments were effective in malignant cells, which are highly resistant to either treatment, alone. Ionizing radiation is one of the most effective modalities in oncology. Thus, it is reasonable to test, how far combinations of TRAIL with ionizing radiation may increase the efficacy. Indeed, the combination of TRAIL with ionizing radiation in several in vitro settings as well as xenograft models resulted in highly increased rates of cell kill and long-term tumor control. No increase in the rate and severity of side effects has been documented, indicating that the combination really increases the therapeutic ratio. It is important to note that TRAIL and TRAIL receptor agonistic antibodies, either as single

Latent species C adenoviruses in human tonsil tissues

Although species C human adenoviruses establish persistent infections, the molecular details of this lifestyle remain poorly understood. We previously reported that adenovirus DNA is found in human mucosal T lymphocytes in a noninfectious form (C. T. Garnett, D. Erdman, W. Xu, and L. R. Gooding, J. Virol. 76:10608-10616, 2002). In this study, human tonsil and adenoid tissues were analyzed to determine the dynamics of infection, the rate of clearance of viral DNA, and the possibility of reactivation of virus from these tissues. The presence of viral DNA peaked at 4 years of age and declined thereafter. The average number of viral genomes declined with the age of the donor. The frequency of virus-bearing cells ranged from 3 x 10(-7) to 3.4 x 10(-4), while the amount of viral DNA per cell varied less, with an average of 280 copies per cell. All species C serotypes were represented in these tissues, although adenovirus type 6 was notably rare. Infectious virus was detected infrequently (13 of 94 of donors tested), even among donors with the highest levels of adenoviral DNA. Adenovirus transcripts were rarely detected in uncultured lymphocytes (2 of 12 donors) but appeared following stimulation and culture (11 of 13 donors). Viral DNA replication could be stimulated in most donor samples by lymphocyte stimulation in culture. New infectious virus was detected in 13 of 15 donors following in vitro stimulation. These data suggest that species C adenoviruses can establish latent infections in mucosal lymphocytes and that stimulation of these cells can cause viral reactivation resulting in RNA transcription, DNA replication, and infectious virus production.

The curious case of the tumour virus: 50 years of Burkitt's lymphoma

Burkitt's lymphoma (BL) was first described 50 years ago, and the first human tumour virus Epstein-Barr virus (EBV) was discovered in BL tumours soon after. Since then, the role of EBV in the development of BL has become more and more enigmatic. Only recently have we finally begun to understand, at the cellular and molecular levels, the complex and interesting interaction of EBV with B cells that creates a predisposition for the development of BL. Here, we discuss the intertwined histories of EBV and BL and their relationship to the cofactors in BL pathogenesis: malaria and the MYC translocation.

Suberoyl bis-hydroxamic acid induces p53-dependent apoptosis of MCF-7 breast cancer cells

AIM

To study the effects of suberoyl bis-hydroxamic acid (SBHA), an inhibitor of histone deacetylases, on the apoptosis of MCF-7 breast cancer cells.

METHODS

Apoptosis in MCF-7 cells induced by SBHA was demonstrated by flow cytometric analysis, morphological observation, and DNA ladder. Mitochondrial membrane potential (DeltaPsim) was measured using the fluorescent probe JC-1. The expressions of p53, p21, Bax, and PUMA were determined using RT-PCR or Western blotting analysis after the MCF-7 cells were treated with SBHA or p53 siRNA.

RESULTS

SBHA induced apoptosis in MCF-7 cells. The expressions of p53, p21, Bax, and PUMA were induced, and DeltaPsim collapsed after treatment with SBHA. p53 siRNA abrogated the SBHA-induced apoptosis and the expressions of p53, p21, Bax, and PUMA.

CONCLUSION

The activation of the p53 pathway is involved in SBHA-induced apoptosis in MCF-7 cells.

Bcl-2 family proteins and cancer

BCL-2 was the first anti-death gene discovered, a milestone with far reaching implications for tumor biology. Multiple members of the human Bcl-2 family of apoptosis-regulating proteins have been identified, including six antiapoptotic, three structurally similar proapoptotic proteins and several structurally diverse proapoptotic interacting proteins that operate as upstream agonists or antagonists. These proteins, in turn, are regulated through myriad post-translational modifications and interactions with other proteins. Bcl-2-family proteins regulate all major types of cell death, including apoptosis, necrosis and autophagy, thus operating as nodal points at the convergence of multiple pathways with broad relevance to oncology. Experimental therapies targeting Bcl-2-family mRNAs or proteins are currently in clinical testing, raising hopes that a new class of anticancer drugs may soon be available.

Monocytic leukemia zinc finger (MOZ) interacts with p53 to induce p21 expression and cell-cycle arrest

Upon DNA damage, p53 can induce either cell-cycle arrest or apoptosis. Here we show that monocytic leukemia zinc finger (MOZ) forms a complex with p53 to induce p21 expression and cell-cycle arrest. The levels of the p53-MOZ complex increased in response to DNA damage to levels that induce cell-cycle arrest. MOZ(-/-) mouse embryonic fibroblasts failed to arrest in G1 in response to DNA damage, and DNA damage-induced expression of p21 was impaired in MOZ(-/-) cells. These results suggest that MOZ is involved in regulating cell-cycle arrest in the G1 phase. Screening of tumor-associated p53 mutants demonstrated that the G279E mutation in p53 disrupts interactions between p53 and MOZ, but does not affect the DNA binding activity of p53. The leukemia-associated MOZ-CBP fusion protein inhibits p53-mediated transcription. These results suggest that inhibition of p53/MOZ-mediated transcription is involved in tumor pathogenesis and leukemogenesis.

HIV-1 expression induces tubular cell G2/M arrest and apoptosis

Human renal biopsy studies suggest the presence of HIV-1 and associated signs of injury in renal tubular epithelial cells. Because renal epithelial cells lack conventional HIV-1 receptors, the modus operandi of HIV-1 in the induction of tubular cell injury remains a mystery. In the present study, we evaluated the role of HIV-1 gene expression in human proximal tubular cell apoptosis and cell cycle progression. HIV-1- or vector-transduced cells were assayed for cellular injury and cell cycle defect. HIV-1-transduced cells showed the progressive loss of viability in a time-dependent manner. Similarly, HIV-1-transduced cells showed greater apoptosis when compared with vector-transduced cells. A higher number of HIV-1 expressing cells showed cell cycle arrest at G2/M phase and enhanced tubular cell expression of phospho-p53(ser15), phospho-cdc-2(Tyr 15), and phospho-chk-2 (Thr 68). These findings suggest that in addition to the activation of apoptotic pathway, HIV-1-induced G2/M arrest may also contribute to tubular cell injury.

Therapeutic modulation of apoptosis: targeting the BCL-2 family at the interface of the mitochondrial membrane

A vast portion of human disease results when the process of apoptosis is defective. Disorders resulting from inappropriate cell death range from autoimmune and neurodegenerative conditions to heart disease. Conversely, prevention of apoptosis is the hallmark of cancer and confounds the efficacy of cancer therapeutics. In the search for optimal targets that would enable the control of apoptosis, members of the BCL-2 family of anti- and pro-apoptotic factors have figured prominently. Development of BCL-2 antisense approaches, small molecules, and BH3 peptidomimetics has met with both success and failure. Success-because BCL-2 proteins play essential roles in apoptosis. Failure-because single targets for drug development have limited scope. By examining the activity of the BCL-2 proteins in relation to the mitochondrial landscape and drawing attention to the significant mitochondrial membrane alterations that ensue during apoptosis, we demonstrate the need for a broader based multi-disciplinary approach for the design of novel apoptosis-modulating compounds in the treatment of human disease.

4-Hydroxynonenal induces p53-mediated apoptosis in retinal pigment epithelial cells

4-Hydroxynonenal (4-HNE) has been suggested to be involved in stress-induced signaling for apoptosis. In present studies, we have examined the effects of 4-HNE on the intrinsic apoptotic pathway associated with p53 in human retinal pigment epithelial (RPE and ARPE-19) cells. Our results show that 4-HNE causes induction, phosphorylation, and nuclear accumulation of p53 which is accompanied with down regulation of MDM2, activation of the pro-apoptotic p53 target genes viz. p21 and Bax, JNK, caspase3, and onset of apoptosis in treated RPE cells. Reduced expression of p53 by an efficient silencing of the p53 gene resulted in a significant resistance of these cells to 4-HNE-induced cell death. The effects of 4-HNE on the expression and functions of p53 are blocked in GSTA4-4 over expressing cells indicating that 4-HNE-induced, p53-mediated signaling for apoptosis is regulated by GSTs. Our results also show that the induction of p53 in tissues of mGsta4 (-/-) mice correlate with elevated levels of 4-HNE due to its impaired metabolism. Together, these studies suggest that 4-HNE is involved in p53-mediated signaling in in vitro cell cultures as well as in vivo that can be regulated by GSTs.

Clinical biomarkers and imaging for radiotherapy-induced cell death

INTRODUCTION

Radiotherapy, like most anticancer treatments, achieves its therapeutic effect by inducing different types of cell death in tumors.

CELL DEATH MARKERS AND IMAGING MODALITIES

To evaluate treatment efficacy a variety of routine anatomical imaging modalities is used. However, changes in tumor physiology, metabolism and proliferation often precede these volumetric changes. Therefore, reliable biomarkers and imaging modalities that could assess treatment response more rapidly or even predict tumor responsiveness to treatment in an early phase would be very useful to identify responders and/or avoid ineffective, toxic therapies. A better understanding of cell death mechanisms following irradiation is essential for the development of such tools.

CELL DEATH AND AVAILABLE ASSAYS

In this review the most prominent types of radiation-induced cell death are discussed. In addition, the currently available assays to detect apoptosis, necrosis, mitotic catastrophe, autophagy and senescence in vitro and, if applicable, in vivo, are presented.

p53-dependent repression of the human MCL-1 gene encoding an anti-apoptotic member of the BCL-2 family: the role of Sp1 and of basic transcription factor binding sites in the MCL-1 promoter

p53 regulates transcription of one anti-apoptotic and four pro-apoptotic members of the BCL-2 family, but nothing is known about the regulation of MCL-1, another antiapoptotic member of this family, by p53. Confocal microscopic analysis of COS1, HEK 293 and HeLa cells transfected with a p53 expression plasmid demonstrated a decrease in the signal of endogenous MCL-1 compared to neighboring non-transfected cells. Transcription regulation assays showed that the 1826 bp human MCL-1 promoter fragment was repressed up to 30-fold by wild-type p53 in a dose-dependent manner. As shown by electrophoretic mobility shift assays, Sp1 binding to the sites located in the -295 to +16 MCL-1 promoter fragment was decreased in the presence of p53. However, the MCL-1 promoter devoid of all Sp1 binding sites was still repressed by p53, albeit 2-fold weaker than the wild-type promoter. Overexpression of Sp1 reduced p53-dependent repression of the MCL-1 promoter only up to 2.2-fold. Transcription regulation assays performed with MCL-1 promoter deletion mutants showed that most of the p53 inhibitory effect was mediated by the -41 to +16 bp promoter fragment containing binding sites only for TATA-binding protein and other basal transcription factors. We propose a novel, promoter-based mechanism by which p53 down-regulates expression of the antiapoptotic MCL-1 protein.

KLF6 induces apoptosis in prostate cancer cells through up-regulation of ATF3

KLF6 (Kruppel-like factor 6) is a zinc finger transcription factor and a tumor suppressor that is frequently mutated in prostate cancer. KLF6 suppresses tumor growth and induces apoptosis in cancer cells through mechanisms still not defined. Here we show that KLF6 induces apoptosis in prostate cancer cells by ATF3 (activating transcription factor 3) expression. KLF6 binds directly to and activates the ATF3 promoter. ATF3 induced apoptosis when ectopically expressed in cells, whereas knockdown of ATF3 by small interference RNA blocked KLF6-induced apoptosis. KLF6 mutants derived from clinical prostate cancers failed to activate the ATF3 promoter and were unable to induce apoptosis. Furthermore, stress conditions (exposure to staurosporine and hypoxia induced by sodium azide) caused significant increase in ATF3 expression and induced apoptosis, whereas knockdown of KLF6 by small interference RNA blocked the increase of ATF3 as well as the induction of apoptosis in these conditions. Thus, ATF3 is a key mediator of KLF6-induced apoptosis in prostate cancer cells.

Novel synthetic triterpenoid methyl 25-hydroxy-3-oxoolean-12-en-28-oate induces apoptosis through JNK and p38 MAPK pathways in human breast adenocarcinoma MCF-7 cells

Breast cancer is the most common neoplasm in women and is the leading cause of cancer-related death for women. Therefore, new agents targeting prevention and treatment of breast cancer are urgently needed. The present study first investigates that a novel triterpenoid Methyl 25-Hydroxy-3-oxoolean-12-en-28-oate (AMR-Me) derived from 25-Hydroxy-3-oxoolean-12-en-28-oic acid (AMR) is a potent inhibitor of cell growth by inducing human breast cancer MCF-7 cells to undergo apoptosis. AMR-Me induced DNA fragmentation and PARP degradation which were preceded by changing Bax/Bcl-2 ratios, cytochrome c release, and subsequent induction of pro-caspase-9 and -7 processing in breast carcinoma MCF-7 cells, but it did not act on Fas/Fas ligand pathways and the activation of caspase-8, suggesting AMR-Me triggered the mitochondrial apoptotic pathway. The general caspase blocking peptide VAD partially blocked AMR-Me induced apoptosis. AMR-Me stimulated p38 mitogen-activated protein kinase and c-Jun NH2-terminal kinase (JNK), but not extracellular signal-regulated kinase activation during apoptosis. SP600125, a specific inhibitor for JNK and SB203580, a p38 MAPK-specific inhibitor suppressed AMR-Me induced apoptosis indicating that activation of JNK and p38 MAPKs involved in the mitochondrial activation-mediated cell death pathway. Our results suggest that AMR-Me can utilize two different MAPK signaling pathways for amplifying the apoptosis cascade, is critical for both our understanding of cell death events and development of cancer preventive/therapeutic agents.

Full-length hdmX transcripts decrease following genotoxic stress

Previous studies have suggested that the mdmX gene is constitutively transcribed, and that MdmX protein activity is instead controlled by cellular localization and DNA damage induced Mdm2-mediated ubiquitination leading to proteasomal degradation. In these studies, we report that the human mdmX (hdmX) mRNA is reproducibly decreased in various human cell lines following treatment with various DNA-damaging agents. Repression of hdmX transcripts is observed in DNA-damaged HCT116 colon cancer cells and in isogenic p53(-/-) cells, suggesting that this effect is p53-independent. Reduction in the amount of hdmX transcript occurs in both human tumor cell lines and primary human diploid fibroblasts, and results in a significant reduction of HdmX protein. Examination of hdmX promoter activity suggests that damage-induced repression of hdmX mRNA is not significantly impacted by transcription initiation. In contrast, changes in hdmX mRNA splicing appear to partly explain the reduction in full-length hdmX mRNA levels in tumor cell lines with the destabilization of full-length hdmX transcripts, potentially through microRNA miR-34a regulation, also impacting transcript levels. Taken together, this study uncovers previously unrecognized cellular mechanisms by which hdmX mRNA levels are kept low following genotoxic stress.

Caspase-2 activation in neural stem cells undergoing oxidative stress-induced apoptosis

Oxidative stress occurs as a consequence of disturbance in the balance between the generation of reactive oxygen species (ROS) and the antioxidant defence mechanisms. The interaction of ROS with DNA can cause single-, or double-strand breaks that subsequently can lead to the activation of p53, which is central for the regulation of cellular response, e.g. apoptosis, to a range of environmental and intracellular stresses. Previous reports have suggested a regulatory role of p53 in the early activation of caspase-2, upstream of mitochondrial apoptotic signaling. Here we show that excessive ROS formation, induced by 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) exposure, induces apoptosis in primary cultured neural stem cells (NSCs) from cortices of E15 rat embryos. Following DMNQ exposure cells exhibited apoptotic hallmarks such as Bax oligomerization and activation, cytochrome c release, caspase activation and chromatin condensation. Additionally, we could show early p53 accumulation and a subsequent activation of caspase-2. The attenuation of caspase-2 activity with selective inhibitors could antagonize the mitochondrial signaling pathway and cell death. Overall, our results strongly suggest that DMNQ-induced oxidative stress causes p53 accumulation and consequently caspase-2 activation, which in turn initiates apoptotic cell death via the mitochondria-mediated caspase-dependent pathway in NSCs.

Triggering of Bcl-2-related pathway is associated with apoptosis of photoreceptors in Rpe65-/- mouse model of Leber's congenital amaurosis

Mutations in RPE65 protein is characterized by the loss of photoreceptors, although the molecular pathways triggering retinal cell death remain largely unresolved. The role of the Bcl-2 family of proteins in retinal degeneration is still controversial. However, alteration in Bcl-2-related proteins has been observed in several models of retinal injury. In particular, Bax has been suggested to play a crucial role in apoptotic pathways in murine glaucoma model as well as in retinal detachment-associated cell death. We demonstrated that Bcl-2-related signaling pathway is involved in Rpe65-dependent apoptosis of photoreceptors during development of the disease. Pro-apoptotic Bax alpha and beta isoforms were upregulated in diseased retina. This was associated with a progressive reduction of anti-apoptotic Bcl-2, reflecting imbalanced Bcl-2/Bax ratio as the disease progresses. Moreover, specific translocation of Bax beta from cytosol to mitochondria was observed in Rpe65-deficient retina. This correlated with the initiation of photoreceptor cell loss at 4 months of age, and further increased during disease development. Altogether, these data suggest that Bcl-2-apoptotic pathway plays a crucial role in Leber's congenital amaurosis disease. They further highlight a new regulatory mechanism of Bax-dependent apoptosis based on regulated expression and activation of specific isoforms of this protein.

Identification of a protective role for protein phosphatase 1cgamma1 against oxidative stress-induced vascular smooth muscle cell apoptosis

The development of therapeutic strategies to inhibit reactive oxygen species (ROS)-mediated damage in blood vessels has been limited by a lack of specific targets for intervention. Targeting ROS-mediated events in the vessel wall is of interest, because ROS play important roles throughout atherogenesis. In early atherosclerosis, ROS stimulate vascular smooth muscle cell (VSMC) growth, whereas in late stages of lesion development, ROS induce VSMC apoptosis, causing atherosclerotic plaque instability. To identify putative protective genes against oxidative stress, mouse aortic VSMC were infected with a retroviral human heart cDNA expression library, and apoptosis was induced in virus-infected cells by 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) treatment. A total of 17 different, complete cDNAs were identified from the DMNQ-resistant VSMC clones by PCR amplification and sequencing. The cDNA encoding PP1cgamma1 (catalytic subunit of protein phosphatase 1) was present in several independent DMNQ-resistant VSMC clones. DMNQ increased mitochondrial ROS production, caspase-3/7 activity, DNA fragmentation, and decreased mitochondrial transmembrane potential in VSMC while decreasing PP1cgamma1 activity and expression. Depletion of PP1cgamma1 expression by short hairpin RNA significantly enhanced basal as well as DMNQ-induced VSMC apoptosis. PP1cgamma1 overexpression abrogated DMNQ-induced JNK1 activity, p53 Ser(15) phosphorylation, and Bax expression and protected VSMC against DMNQ-induced apoptosis. In addition, PP1cgamma1 overexpression attenuated DMNQ-induced caspase-3/7 activation and DNA fragmentation. Inhibition of p53 protein expression using small interfering RNA abrogated DMNQ-induced Bax expression and significantly attenuated VSMC apoptosis. Together, these data indicate that PP1cgamma1 overexpression promotes VSMC survival by interfering with JNK1 and p53 phosphorylation cascades involved in apoptosis.

Oligomerization of BAK by p53 utilizes conserved residues of the p53 DNA binding domain

Genotoxic stress triggers a rapid translocation of p53 to the mitochondria, contributing to apoptosis in a transcription-independent manner. Using immunopurification protocols and mass spectrometry, we previously identified the proapoptotic protein BAK as a mitochondrial p53-binding protein and showed that recombinant p53 directly binds to BAK and can induce its oligomerization, leading to cytochrome c release. In this work we describe a combination of molecular modeling, electrostatic analysis, and site-directed mutagenesis to define contact residues between BAK and p53. Our data indicate that three regions within the core DNA binding domain of p53 make contact with BAK; these are the conserved H2 alpha-helix and the L1 and L3 loop. Notably, point mutations in these regions markedly impair the ability of p53 to oligomerize BAK and to induce transcription-independent cell death. We present a model whereby positively charged residues within the H2 helix and L1 loop of p53 interact with an electronegative domain on the N-terminal alpha-helix of BAK; the latter is known to undergo conformational changes upon BAK activation. We show that mutation of acidic residues in the N-terminal helix impair the ability of BAK to bind to p53. Interestingly, many of the p53 contact residues predicted by our model are also direct DNA contact residues, suggesting that p53 interacts with BAK in a manner analogous to DNA. The combined data point to the H2 helix and L1 and L3 loops of p53 as novel functional domains contributing to transcription-independent apoptosis by this tumor suppressor protein.

Regulation of programmed cell death by the p53 pathway

The p53 pathway is targeted for inactivation in most human cancers either directly or indirectly, highlighting its critical function as a tumor suppressor gene. p53 is normally activated by cellular stress and mediates a growth-suppressive response that involves cell cycle arrest and apoptosis. In the case of cell cycle arrest, p21 appears sufficient to block cell cycle progression out of G1 until repair has occurred or the cellular stress has been resolved. The p53-dependent apoptotic response is more complex and involves transcriptional activation of multiple proapoptotic target genes, tissue, and signal specificity, as well as additional events that are less well understood. In this chapter, we summarize the apoptosis pathway regulated by p53 and include some open questions in this field.

Brn-3a/POU4F1 interacts with and differentially affects p73-mediated transcription

The Brn-3a/POU4F1 POU transcription factor is critical for the survival and differentiation of specific sensory neurons during development or upon injury; by regulating expression of target genes, either directly or indirectly upon interaction with other proteins. In this study, we demonstrated the physical interaction of Brn-3a with different p73 isoforms and showed co-localization in sensory neurons arising from the neural crest. The biological effects of p73/ Brn-3a interaction depend on the particular p73 isoform, because co-expression of Brn-3a with TAp73 enhanced cell cycle arrest, whereas Brn-3a and DeltaNp73 cooperated to increase protection from apoptosis. Brn-3a antagonized TAp73 transactivation of pro-apoptotic Bax, but co-operated to increase transcription of the cell cycle regulator p21 CIP1/Waf1. The region 425-494 amino acids within the TAp73 C terminus were critical for Brn-3a to repress Bax transactivation, but not for cooperation on the p21 CIP1/Waf1 promoter. Our results suggest that co-factors binding to the p73 C terminus facilitate maximal activation on the Bax but not p21 CIP1/Waf1 promoter and that Brn-3a modulates this interaction. Thus, the physical interaction of Brn-3a with specific p73 isoforms will be critical for determining cell fate during neuronal development or in injured neurons expressing both factors.

A new triterpenoid from Panax ginseng exhibits cytotoxicity through p53 and the caspase signaling pathway in the HepG2 cell line

A new triterpenoid, 20(R),22(xi),24(S)-dammar-25(26)-ene-3beta,6 alpha,12 beta,20,22,24-hexanol (1), and three known triterpenoids, beta-D-glucopyranoside,(3beta,12 beta)-12,20-dihydroxydammar-24-en-3-yl,6-acetate (2), 20(R)-ginsenoside Rg3 (3), and 20(R)-ginsenoside Rh2 (4), were isolated from the leaves of Panax ginseng. Their structures were determined by chemical analysis and spectral methods (IR, 1D and 2D NMR, HR-ESI-MS). Compounds 1-4 were exhibited various degrees of cytotoxicity in the human hepatoma cell line, HepG2. Compound 1 had the highest cytotoxic potency, with an IC50 value of 20.1 microM, by stimulating p53-mediated cell cycle arrest at the G1 to S phase transition, leading to apoptosis via activation of the caspase signaling pathway.

Rapid quantitative PCR assays for the simultaneous detection of herpes simplex virus, varicella zoster virus, cytomegalovirus, Epstein-Barr virus, and human herpesvirus 6 DNA in blood and other clinical specimens

Rapid diagnosis of human herpesvirus primary infections or reactivations is facilitated by quantitative PCRs. Quantitative PCR assays with a standard thermal cycling profile permitting simultaneous detection of herpes simplex virus (HSV), varicella zoster virus (VZV), cytomegalovirus (CMV), Epstein-Barr virus (EBV), and human herpesvirus 6 (HHV6) DNA were developed and validated for diagnostic use. High specificity and sensitivity were achieved and the new PCR assays correlated well with commercial PCR assays. Twenty two thousand eight hundred sixty eight PCR tests were undertaken on specimens obtained from immunosuppressed patients. DNAemia was frequent with EBV (43.5%), HHV6 (32.4%), CMV (12.8%), and VZV (12.9%). As already described for EBV and CMV, high virus loads of HHV6 and VZV were associated with clinical symptoms and poor clinical outcome, for example, three of four patients with VZV virus loads >10(5) copies/ml died. A high proportion of lower respiratory specimens was positive for EBV- (38.8%), HHV6- (29.4%), and CMV-DNA (18.2%). For CMV, infection was confirmed in 66.7% of patients by virus isolation or positive pp65 antigenaemia. Differentiation of HHV6A, -B and HSV-1, -2 by melting curve analysis revealed that HHV6A and HSV-2 represented only 1.8% and 3.3% of all positive specimens, respectively. In conclusion, these results indicate significant improvements for the early diagnosis of primary infections or reactivations of five human herpesviruses especially in immunosuppressed patients. Detection of coinfections with multiple herpesviruses is facilitated. Quantitative results enable monitoring of virus load during antiviral therapy. A standard thermal cycling profile permits time and cost effective use in a routine diagnostic setting.

Management of oral infections in cancer patients

The myelosuppressive and mucosal-damaging consequences of cancer and cancer therapies place patients at high risk for developing infectious complications. Bacterial, fungal, and viral infections are all commonly encountered in the oral cavity, contributing to both morbidity and mortality in this patient population. Prevention, early and definitive diagnosis, and appropriate management are critical to ensure optimal treatment outcomes. With the majority of cancer patients treated as outpatients in the community setting, oral health care professionals play an important role in managing such infectious complications of cancer therapy.

Protein kinase C epsilon confers resistance of MCF-7 cells to TRAIL by Akt-dependent activation of Hdm2 and downregulation of p53

Protein kinase C epsilon (PKC epsilon ) acts as an antiapoptotic protein and inhibits tumor necrosis factor-alpha (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in MCF-7 breast cancer cells. Members of the TNF receptor superfamily trigger apoptosis independent of the tumor suppressor protein p53, which primarily affects DNA damage-induced apoptosis. We have previously shown that PKC epsilon acts upstream of Akt to inhibit receptor-initiated cell death. Since Akt can regulate p53, we have examined the involvement of p53 in PKC epsilon-mediated TRAIL resistance. Overexpression of PKC epsilon in MCF-7 cells (MCF-7/PKC epsilon ) caused a decrease in p53 and an increase in human homolog of murine double minute 2 (Hdm2) and phospho-Hdm2. Depletion of p53 by siRNA attenuated, whereas depletion of Hdm2 enhanced TRAIL-mediated apoptosis. Knockdown of Akt decreased Hdm2 phosphorylation, increased p53 level and potentiated TRAIL-induced cell death. Depletion of epsilon from MCF-7 cells caused an increase in p53, whereas knockdown of p53 caused a decrease in Bid mRNA. Depletion of Akt from MCF-7/PKC epsilon cells resulted in an increase in p53 and Bid. These results suggest that PKC epsilon mediates TRAIL resistance by Akt-mediated phosphorylation of Hdm2 resulting in suppression of p53 expression and downregulation of Bid in MCF-7 breast cancer cells.

Molecular docking analysis of the protein-protein interaction between RelA-associated inhibitor and tumor suppressor protein p53 and its inhibitory effect on p53 action

RelA-associated inhibitor (RAI) was initially identified as a protein that interacts with the p65 subunit (RelA) of nuclear factor-kappaB. It was recently found to interact with the p53 tumor suppressor protein. RAI is a structural homolog of the p53-binding protein 2 and I kappaB family proteins, and is known to inhibit the DNA-binding activities of p65 and p53. In the present study, we have attempted to predict the 3-dimensional structure of RAI in complex with p53 using computational chemistry. In order to evaluate the predicted structure model, we created a series of RAI mutants in which the amino acid residues involved in the interaction with p53 were mutated, and examined their activities in blocking p53-mediated bax gene expression. Our observations support the validity of the predicted 3-dimensional model of the p53-RAI protein complex. Based on the p53-RAI complex model, we have demonstrated the biological importance of the R248 and R273 residues of p53, and the D775 and E795 residues of RAI, in the protein-protein interaction between p53 and RAI and the biological actions of these proteins. These findings will further clarify the biological actions of RAI in carcinogenesis and can be used for the development of a novel strategy in blocking the actions of RAI. The possible biological implications of RAI are also discussed.

BAF60a interacts with p53 to recruit the SWI/SNF complex

To understand the tumor-suppressing mechanism of the SWI/SNF chromatin remodeling complex, we investigated its molecular relationship with p53. Using the pREP4-luc episomal reporter, we first demonstrated that p53 utilizes the chromatin remodeling activity of the SWI/SNF complex to initiate transcription from the chromatin-structured promoter. Among the components of the SWI/SNF complex, we identified BAF60a as a mediator of the interaction with p53 by the yeast two-hybrid assay. p53 directly interacted only with BAF60a, but not with other components of the SWI/SNF complex, such as BRG1, SRG3, SNF5, or BAF57. We found out that multiple residues at the amino acid 108-150 region of BAF60a were involved in the interaction with the tetramerization domain of p53. The N-terminal fragment of BAF60a containing the p53-interacting region as well as small interfering RNA for baf60a inhibited the SWI/SNF complex-mediated transcriptional activity of p53. The uncoupling of p53 with the SWI/SNF complex resulted in the repression of both p53-dependent apoptosis and cell cycle arrest by the regulation of target genes. These results suggest that the SWI/SNF chromatin remodeling complex is involved in the suppression of tumors by the interaction with p53.

Paraquat induces apoptosis in human lymphocytes: protective and rescue effects of glucose, cannabinoids and insulin-like growth factor-1

In order to establish causal or protective treatments for Parkinson's disease (PD), it is necessary to identify the cascade of deleterious events that lead to the dysfunction and death of dopaminergic neurons. Paraquat (PQ) is a pesticide used as xenobiotic compound to model PD. However, the mechanism(s) of PQ-induced cell death and the mechanism(s) of cytoprotection in a single cell model are still unknown. In this study, lymphocytes were treated with (0.1-1 mM) PQ. Apoptotic morphology was assessed with acridine orange/ethidium bromide staining. Further evaluation included (i) superoxide radicals, reflected by nitroblue tetrazolium reduction to formazan, (ii) the production of hydrogen peroxide, reflected by rhodamine-positive fluorescent cells, (iii) the generation of hydroxyl radicals, reflected by dimethylsulfoxide and melatonin ( radical)OH scavengers, (iv) activation and/or translocation of NF-kappaB, p53 and c-Jun transcription factors showed by immunocytochemical staining, and by ammonium pyrrolidinedithiocarbamate, pifithrin-alpha and SP600125 inhibition and (V) caspase-3 activation, reflected by caspase Ac-DEVD-cho inhibition. To elucidate the mechanism of cytoprotection, lymphocytes were treated with PQ in the presence of cannabinoids, insulin-like growth factor-1 and glucose. We provide evidence that PQ induces apoptosis in lymphocytes in a concentration- and time-dependent fashion by an oxidative stress mechanism involving O(2)( radical - ), H(2)O(2)/(( radical)OH) generation, simultaneous activation of NF-kappaB/p53/c-Jun transcription factors, mitochondrial depolarization and caspase-3 activation leading to morphological apoptosis. Moreover, dying lymphocytes are protected and rescued from PQ noxious stimuli by direct antioxidant effect by cannabinoids, receptor mediated signaling by IGF-1, and/or energetic protection by glucose. It is concluded that PQ-induced apoptosis in lymphocytes by a mechanism involving reactive oxygen species generation, mitochondrial dysfunction, transcriptional factors and caspase-3 activation. However, this cell death routine can be reversed by the action of cannabinoids, IGF-1 and glucose. These data may provide innovating therapeutic strategies to intervene environmentally or genetically susceptible PD population to oxidative stress.

Runx2-mediated activation of the Bax gene increases osteosarcoma cell sensitivity to apoptosis

The Runx family of transcription factors regulate cell growth and differentiation, and control the expression of target genes involved in cell fate decisions. We examined the role of the bone-related member of this family, Runx2, in regulating apoptosis via modulation of the Bcl2 family of genes in the osteosarcoma cell line Saos2. Our data demonstrate that Runx2 directly binds to two Runx-specific regulatory elements on the human bax promoter thereby inducing Bax expression. Furthermore, bone morphogenetic protein-induced or vector-mediated expression of Runx2 resulted in upregulation of Bax expression, and subsequent increased sensitivity of Saos2 cells to apoptosis. Finally, the observed upregulation of Bax expression and increased apoptosis were Runx2 dependent as Runx2 loss of function abrogated these effects. Our study provides the first evidence for Bax as a direct target of Runx2, suggesting that Runx2 may act as a proapoptotic factor in osteosarcoma cells.

Capture of p53 by electrodes modified with consensus DNA duplexes and amplified voltammetric detection using ferrocene-capped gold nanoparticle/streptavidin conjugates

p53, a tumor suppressor protein and a transcription factor, is capable of inhibiting the growth of tumor cells by eliciting either cell-cycle arrest or apoptosis through a cascade of events. p53 binds sites within the promoters of several genes that conform to a sequence commonly defined as the consensus site. In more than 50% of cancer cases, the p53 gene has been found to be mutated and the p53 protein loses its ability to bind the consensus DNA. In this work, double-stranded (ds-) oligonucleotides (ODNs) containing the consensus site are immobilized onto gold electrodes to capture wild-type p53. The cysteine residues on the exterior of the p53 molecule were derivatized for the attachment of gold nanoparticle/streptavidin conjugates capped with multiple ferrocene (Fc) groups. Well-defined voltammetric peaks of high signal intensity were obtained, and p53 concentration as low as 2.2 pM was measured. The peak heights were found to be dependent on the surface density of the consensus ds-ODN, the sequence of the immobilized ODNs, and the p53 concentration. With base pair(s) in the full consensus binding sequence altered, the level of p53 binding was found to decrease sharply, and no p53 binding occurred at electrodes covered with nonconsensus ds-ODNs. The amenability of this method to the analyses of p53 from normal and cancer cell lysates was also demonstrated. Owing to the p53 mutation in the cancer cells, the concentration of the wild-type p53 was found to decrease significantly (by about 50-182 times). The sensitivity and amenability for real sample analysis of the method compared well with enzyme-linked immunosorbant assay (ELISA), and complements ELISA in that wild-type p53, instead of total p53 (wild-type and mutant p53) concentration, is measured. The method described herein is simple and selective and does not require the use of p53 antibodies.

ATR-Chk2 signaling in p53 activation and DNA damage response during cisplatin-induced apoptosis

Cisplatin is one of the most effective anti-cancer drugs; however, the use of cisplatin is limited by its toxicity in normal tissues, particularly injury of the kidneys. The mechanisms underlying the therapeutic effects of cisplatin in cancers and side effects in normal tissues are largely unclear. Recent work has suggested a role for p53 in cisplatin-induced renal cell apoptosis and kidney injury; however, the signaling pathway leading to p53 activation and renal apoptosis is unknown. Here we demonstrate an early DNA damage response during cisplatin treatment of renal cells and tissues. Importantly, in the DNA damage response, we demonstrate a critical role for ATR, but not ATM (ataxia telangiectasia mutated) or DNA-PK (DNA-dependent protein kinase), in cisplatin-induced p53 activation and apoptosis. We show that ATR is specifically activated during cisplatin treatment and co-localizes with H2AX, forming nuclear foci at the site of DNA damage. Blockade of ATR with a dominant-negative mutant inhibits cisplatin-induced p53 activation and renal cell apoptosis. Consistently, cisplatin-induced p53 activation and apoptosis are suppressed in ATR-deficient fibroblasts. Downstream of ATR, both Chk1 and Chk2 are phosphorylated during cisplatin treatment in an ATR-dependent manner. Interestingly, following phosphorylation, Chk1 is degraded via the proteosomal pathway, whereas Chk2 is activated. Inhibition of Chk2 by a dominant-negative mutant or gene deficiency attenuates cisplatin-induced p53 activation and apoptosis. In vivo in C57BL/6 mice, ATR and Chk2 are activated in renal tissues following cisplatin treatment. Together, the results suggest an important role for the DNA damage response mediated by ATR-Chk2 in p53 activation and renal cell apoptosis during cisplatin nephrotoxicity.

P53 mediated regulation of metallothionein transcription in breast cancer cells

Recent studies have shown that only breast cancer epithelial cells with intact p53 can induce metallothionein (MT) synthesis after exposure to metals. In this study, the potential role of p53 on regulation of MT was investigated. Results demonstrate that zinc and copper increased metal response elements (MREs) activity and MTF-1 expression in p53 positive MN1 and parental MCF7 cells. However, inactivation of p53 by treatment with pifithrin-alpha or the presence of inactive p53 inhibited MRE-dependent reporter gene expression in response to metals. MTF-1 levels remained unchanged after treatment with zinc in cells with nonfunctional p53. The introduction of wild-type p53 in MDD2 cells, containing nonfunctional p53, enhanced the ability of zinc to increase MRE-dependent reporter gene expression. The cellular level of p21Cip1/WAF1 was increased in MDD2 cells after p53 transfection, confirming the presence of active p53. The treatment of MN1 and parental MCF7 with trichostatin A led to a sixfold increase in the MRE activity in response to zinc. On the contrary, MRE activity remained unaltered in MDD2 cells with inactive p53. The above results demonstrate that activation of p53 is an important factor in metal regulation of MT.