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

p38 kinase regulates nitric oxide-induced apoptosis of articular chondrocytes by accumulating p53 via NFkappa B-dependent transcription and stabilization by serine 15 phosphorylation

Nitric oxide (NO) during primary culture of articular chondrocytes causes apoptosis via p38 mitogen-activated protein kinase in association with elevation of p53 protein level, caspase-3 activation, and differentiation status. In this study, we characterized the molecular mechanism by which p38 kinase induces apoptosis through activation of p53. We report here that NO-induced activation of p38 kinase leads to activation of NFkappaB, which in turn induces transcription of the p53 gene. Activated p38 kinase also physically associates and phosphorylates the serine 15 residue of p53, which results in accumulation of p53 protein during NO-induced apoptosis. Ectopic expression of wild-type p53 enhanced NO-induced apoptosis, whereas expression of a dominant negative p53 blocked it, indicating that p53 plays an essential role in NO-induced apoptosis of chondrocytes. The increased accumulation of p53 caused expression of Bax, a pro-apoptotic member of the Bcl-2 family that is known to cause apoptosis via release of cytochrome c and caspase activation. These results suggest that NO-activated p38 kinase activates p53 function in two different ways, transcriptional activation by NFkappaB and direct phosphorylation of p53 protein, leading to apoptosis of articular chondrocytes.

Epstein-Barr virus EBNA2 blocks Nur77- mediated apoptosis

Epstein-Barr virus infection in vitro immortalizes primary B cells. EBNA2 is an Epstein-Barr virus-encoded transcriptional transactivator that mimics the effects of activated Notch signaling and is essential for this proliferative response. An assay using Sindbis virus (SV) as a cell death inducer revealed that, like Notch, EBNA2 also has antiapoptotic activity. We show that Nur77 is a mediator of SV-induced cell death and that EBNA2 antiapoptotic activity results from interaction with Nur77. EBNA2 colocalized with Nur77 in transfected cells and coprecipitated with Nur77 in IB4 B cells. EBNA2 binds to Nur77 through sequences in the EBNA2 amino acid 123-147 conserved domain and an EBNA2 mutant unable to bind Nur77 also lost the ability to protect cells from SV-induced apoptosis. EBNA2 exerted its antideath function by retaining Nur77 in the nucleus and preventing Nur77 from targeting mitochondria in response to apoptotic stimuli. Thus, targeting of Nur77 can be added to the list of strategies used by viruses to counter apoptosis.

Markers of viral infection in monozygotic twins discordant for chronic fatigue syndrome

To estimate the prevalence of viruses associated with chronic fatigue syndrome (CFS) and to control for genetic and environmental factors, we conducted a co-twin control study of 22 monozygotic twin pairs, of which one twin met criteria for CFS and the other twin was healthy. Levels of antibodies to human herpesvirus (HHV)-8, cytomegalovirus, herpes simplex virus 1 and 2, and hepatitis C virus were measured. Polymerase chain reaction (PCR) assays for viral DNA were performed on peripheral blood mononuclear cell specimens to detect infection with HHV-6, HHV-7, HHV-8, cytomegalovirus, Epstein-Barr virus, herpes simplex virus, varicella zoster virus, JC virus, BK virus, and parvovirus B19. To detect lytic infection, plasma was tested by PCR for HHV-6, HHV-8, cytomegalovirus, and Epstein-Barr virus DNA, and saliva was examined for HHV-8 DNA. For all assays, results did not differ between the group of twins with CFS and the healthy twins.

Identification of Epstein-Barr virus-specific CD8+ T lymphocytes in the circulation of pediatric transplant recipients

BACKGROUND

Pediatric transplant recipients are at increased risk for Epstein Barr virus (EBV)-related B cell lymphomas. In healthy individuals, the expansion of EBV-infected B cells is controlled by CD8+ cytotoxic T cells. However, immunosuppressive therapy may compromise antiviral immunity. We identified and determined the frequency of EBV-specific T cells in the peripheral blood of pediatric transplant recipients.

METHODS

HLA-B*0801 and HLA-A*0201 tetramers folded with immunodominant EBV peptides were used to detect EBV-specific CD8+ T cells by flow cytometry in peripheral blood mononuclear cells from 24 pediatric liver and kidney transplant recipients. The expression of CD38 and CD45RO on EBV-specific, tetramer-binding cells was also examined in a subset of patients by immunofluorescent staining and flow cytometry.

RESULTS

Tetramer-binding CD8+ T cells were identified in 21 of 24 transplant recipients. EBV-specific CD8+ T cells were detected as early as 4 weeks after transplant in EBV seronegative patients receiving an organ from an EBV seropositive donor. The frequencies (expressed as a percentage of the CD8+ T cells) of the tetramer-binding cells were HLA-B8-RAKFKQLL (BZLF1 lytic antigen peptide) tetramer, range=0.96 to 3.94%; HLA-B8-FLRGRAYGL (EBNA3A latent antigen peptide) tetramer, range=0.03 to 0.59%; and HLA-A2-GLCTLVAML (BMLF1 lytic antigen peptide) tetramer, range=0.06 to 0.76%. The majority of tetramer reactive cells displayed an activated/memory phenotype.

CONCLUSIONS

Pediatric transplant recipients receiving immunosuppression can generate EBV-specific CD8+ T cells. Phenotypic and functional analysis of tetramer cells may prove useful in defining and monitoring EBV infection in the posttransplant patient.

Differential regulation of transcription and induction of programmed cell death by human p53-family members p63 and p73

The p53 tumor suppressor acts as a transcription factor and has a central function in controlling apoptosis. With p63 and p73 two genes coding for proteins homologous to p53 have been identified. We describe the properties of seven human p63 and p73 proteins as transcriptional activators of p21WAF1/CIP1 expression and apoptotic inducers in direct comparison to p53 in the same assay systems employing DLD-1-tet-off colon cells. Programmed cell death is detected in cells expressing high levels of p53 and p73alpha. Cells overexpressing TAp63alpha, TAp63gamma, TA*p63alpha, TA*p63gamma, DeltaNp63alpha, and DeltaNp63gamma display low or no detectable apoptosis.

Chronic myelogenous leukemia: mechanisms underlying disease progression

Chronic myelogenous leukemia (CML), characterized by the BCR-ABL gene rearrangement, has been extensively studied. Significant progress has been made in the area of BCR-ABL-mediated intracellular signaling, which has led to a better understanding of BCR-ABL-mediated clinical features in chronic phase CML. Disease progression and blast crisis CML is associated with characteristic non-random cytogenetic and molecular events. These can be viewed as increased oncogenic activity or loss of tumor suppressor activity. However, what causes transformation and disease progression to blast crisis is only poorly understood. This is in part due to the lack of a good in vivo model of chronic phase CML even though animal models developed over the last few years have started to provide insights into blast crisis development. Thus, additional in vitro and in vivo studies will be needed to provide a complete understanding of the contribution of BCR-ABL and other genes to disease progression and to improve therapeutic approaches for blast crisis CML.

Role and function of the 26S proteasome in proliferation and apoptosis

The 26S proteasome constitutes the central proteolytic machinery of the highly conserved ubiquitin/proteasome system, the cell's major tool for extralysosomal protein degradation. Recently, a plethora of cell proteins implicated in the regulation of basic cellular processes, such as proliferation, differentiation, cell cycling, and apoptosis have been discovered to undergo processing and functional limitation by entering the ubiquitin/proteasome pathway with the final destination to be proteolytically degraded by the 26S proteasome. Because both negative and positive regulators of proliferation and apoptosis undergo proteasomal degradation in a tightly regulated and temporally controlled fashion, the 26S proteasome can play opposite roles in the regulation of proliferation and apoptosis. These roles are apparently defined by the cell's environment and proliferative state. Finally, proteasomal protein degradation is deregulated in a number of human diseases, including cancer and neurodegenerative and myodegenerative diseases, which all exhibit an imbalance of proliferation and apoptosis. An improved understanding of the modes of proteasomal action should lead to the development of beneficial therapeutic and diagnostic strategies in the future.

The Epstein-Barr virus ZEBRA protein activates transcription from the early lytic F promoter by binding to a promoter-proximal AP-1-like site

The ZEBRA protein encoded by the Epstein-Barr virus (EBV) genome activates a switch from the latent to the lytic gene expression programme of the virus. ZEBRA, a member of the basic leucine zipper family of DNA-binding proteins, is a transcriptional activator capable of inducing expression from several virus lytic cycle promoters by binding to activator protein 1 (AP-1)-like sites. The Epstein-Barr virus BamHI F promoter, Fp, was for some time believed to initiate EBNA1-specific transcription in EBV-transformed latent cells. More recent data, however, show that Fp is an early lytic promoter and that the dominant EBNA1 gene promoter in latent cells is Qp, located about 200 bp downstream of Fp. In the present investigation we confirm that Fp displays the characteristics of a lytic promoter. Fp is downregulated in latently EBV-infected cells, both in the endogenous virus genome and in reporter plasmids that carry Fp regulatory sequences upstream of position -136 and down to +10 relative to the Fp transcription start site (+1), and is activated on induction of the virus lytic cycle. We show that the repression of Fp in latent stages of infection can be abolished by ZEBRA, and demonstrate that ZEBRA activates Fp through a direct interaction with an AP-1-like site at position -52/-46 in the promoter-proximal Fp region.

Adenovirus-mediated gene transfer of P16INK4/CDKN2 into bax-negative colon cancer cells induces apoptosis and tumor regression in vivo

The tumor-suppressor gene p16INK4/CDKN2 (p16) is a cyclin-dependent kinase (cdk) inhibitor and important cell cycle regulator. Here, we show that adenovirus-mediated gene transfer of p16 (AdCMV.p16) into colon cancer cells induces uncoupling of S phase and mitosis and subsequently apoptosis. Flow cytometric analysis revealed that cells infected with AdCMV.p16 showed an initial G2-like arrest followed by S phase without intervening mitosis (DNA >4N). Using microscopic analysis, deformed polyploid cells were detectable only in cells infected with AdCMV.p16 but not in control-infected cells. Subsequently, AdCMV.p16-infected polyploid cells underwent apoptosis, as assessed by AnnexinV staining and DNA fragmentation, suggesting that cell cycle dysregulation is upstream of the onset of apoptosis. Treatment of mice with subcutaneously transplanted tumors of colorectal cancer cells with AdCMV.p16 but not AdCMV.p53 resulted in significantly reduced tumor volume and prolonged survival. Using an orthotopic model of liver metastasis, we observed both reduced local tumor growth and secondary intrahepatic metastasis after AdCMV.p16 treatment. Importantly, induction of apoptosis in vitro and reduction of tumor growth in vivo by p16 was p53- as well as bax-independent because identical results were obtained using cancer cells, either wild type or mutant for p53 or bax. The studies suggest that an AdCMV.p16-based treatment may be especially effective in patients with bax-negative colon cancer where overexpression of p53 appears not to be of therapeutic value.

A novel p53-inducible apoptogenic gene, PRG3, encodes a homologue of the apoptosis-inducing factor (AIF)

The p53 tumor suppressor protein induces cell cycle arrest or apoptosis in response to cellular stresses. We have identified PRG3 (p53-responsive gene 3), which is induced specifically under p53-dependent apoptotic conditions in human colon cancer cells, and encodes a novel polypeptide of 373 amino acids with a predicted molecular mass of 40.5 kDa. PRG3 has significant homology to bacterial oxidoreductases and the apoptosis-inducing factor, AIF, and the gene was assigned to chromosome 10q21.3-q22.1. Expression of PRG3 was induced by the activation of endogenous p53 and it contains a p53-responsive element. Unlike AIF, PRG3 localizes in the cytoplasm and its ectopic expression induces apoptosis. An amino-terminal deletion mutant of PRG3 that lacks a putative oxidoreductase activity retains its apoptotic activity, suggesting that the oxidoreductase activity is dispensable for the apoptotic function of PRG3. The PRG3 gene is thus a novel p53 target gene in a p53-dependent apoptosis pathway.

Identification of functional p53-binding motifs in the mouse wig-1 promoter

We previously identified wig-1 as a p53-induced mouse gene that encodes a nuclear zinc finger protein with unknown function. To investigate whether wig-1 is a direct target of p53-dependent transactivation, a DNA fragment corresponding to the promoter region was cloned and sequenced. Three regions containing consensus p53-binding sites were identified. Two p53-binding motifs formed DNA-protein complexes with p53 and were able to drive p53-dependent transcription in a luciferase reporter assay. Our results demonstrate that wig-1 is a direct target of p53-mediated transcriptional transactivation.

Persistent Epstein-Barr virus infection: unrestricted latent and lytic viral gene expression in healthy immunosuppressed transplant recipients

BACKGROUND

Posttransplant lymphoproliferative disease (PTLD) is a common Epstein-Barr virus (EBV)-associated complication of transplantation which, despite treatment, is often fatal. This study was undertaken to monitor persistent EBV infection in transplant recipients, to compare EBV load and gene expression in healthy individuals and EBV-associated diseases, and to highlight differences in PTLD that could be used to define those at risk of the disease.

METHODS

A cohort of 96 cardiothoracic transplant recipients was monitored posttransplant for up to 1110 days (median 268 days). Levels of EBV DNA and viral mRNA transcripts in peripheral blood mononuclear cells (PBMs) were measured at regular intervals and compared with those found in healthy individuals, infectious mononucleosis (IM) patients, and 12 PTLD patients bled at the time of diagnosis. Overall posttransplant levels were significantly higher than pretransplant and healthy subjects, and correlate with dose of immunosuppression. EBV DNA levels in both IM and PTLD were significantly higher than in healthy recipients, with the highest levels in PTLD patients. Individual measurements in 12 healthy transplant recipients reached levels seen in PTLD, and thus single estimations are not of predictive significance for PTLD development.

RESULTS

Analysis of viral gene expression in peripheral blood mononuclear cells showed a restricted (LMP 2 only) pattern in healthy subjects, and an unrestricted (latency 3) pattern with lytic replication in 14% of IM blood and 45% of cases of PTLD. A total of 55% of healthy transplant recipients had additional transcripts in one or more blood samples, and this finding correlated with high viral load. Analysis of the 12 samples from healthy recipients with viral loads equivalent to those seen in PTLD showed additional transcripts in all cases and latency 3 with lytic replication in 33%. Thus, an isolated finding of high viral load and/or unrestricted latent and lytic gene expression is not indicative of PTLD.

Adenovirus-mediated p14ARF gene transfer cooperates with Ad5CMV-p53 to induce apoptosis in human cancer cells

p14(ARF), a product of the INK4A/ARF locus, induces p53 upregulation by neutralizing the effects of MDM2, a transcriptional target of p53 that antagonizes its function. Here we report that adenovirus-mediated p14(ARF) gene transfer leads to the accumulation of ectopically transduced p53 and to apoptosis in human cancer cells. We constructed an adenoviral vector expressing p14(ARF) (Ad-ARF) and examined its synergistic effect with p53-expressing adenovirus (Ad5CMV-p53 or Ad-p53) in human lung and esophageal cancer cells. Simultaneous Ad-ARF and Ad-p53 infection increased p53 protein levels not only in a wild-type p53-expressing cell line, but also in cell lines with deleted p53. This resulted in a significant in vitro cytotoxicity compared with Ad-p53 infection alone. Coinfection of Ad-ARF and Ad-p53 also resulted in an increase in expression of p53-inducible genes, including p21(WAF-1/Cip1), p53R2, and Noxa. In addition, the growth of human lung cancer tumors subcutaneously implanted into nu/nu mice was inhibited significantly by intratumoral injection with Ad-ARF and Ad-p53. Our data demonstrate that overexpression of ectopic p14(ARF) may render cells more sensitive to p53-mediated apoptosis, an outcome that has important implications for the treatment of human cancers.

Induction of p73beta by a naphthoquinone analog is mediated by E2F-1 and triggers apoptosis in HeLa cells

Recently, p73 was identified as a structural and functional homolog of p53. The p73 protein activates the transcription of genes downstream of p53 and induces apoptosis when overexpressed in several cell lines, similar to the tumor suppressor p53. However, the extracellular stimuli and molecular mechanisms regulating p73 activity remain to be elucidated. In this paper, we present evidence that the naphthoquinone analog, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone (NA), is a novel apoptotic stimulus that induces p73beta expression. Treatment with NA induced the expression of p73beta mRNA and protein and its downstream genes, p21 and bax, in HeLa cells. Similar results were obtained in MCF7 cells (p53(+/+), p73(+/+)). In the MCF7 cells, p53 protein level was rather decreased by NA treatment. Overexpression of p73beta led to the apoptosis of HeLa cells and enhancement of NA-induced cell death. Expression of p73beta was mediated by E2F-1, which was activated via release from pRB after exposure of cells to NA. We additionally observed that overexpression of pRB inhibited NA-induced apoptosis. These results imply that p53-independent p73beta-dependent p21 expression is involved in NA-induced apoptosis of HeLa cells.

Interaction between p53 and p16 expressed by adenoviral vectors in human malignant glioma cell lines

OBJECT

Multiple gene replacements have been examined as a potential treatment modality for malignant gliomas. Nevertheless, no reports are available that detail the synergy, additivity, or antagonism of multiple genes. The aim of this study was to assess the interaction between p53 and p16 genes in the growth of glioma cell lines.

METHODS

The human glioma cell lines U87MG and U373MG were transduced using an adenoviral vector with Ad-p53, Ad-p16, or both. Western blotting was performed to determine the expression of the protein products of the transduced p53 and p16 genes. To establish whether the combination of Ad-p53 and Ad-p16 would be beneficial, the effects of gene combinations at the median inhibitory concentration level were analyzed using the isobologram method. Annexin assays and cell cycle analyses were performed on the transduced cells. Western blotting demonstrated the expression of p53 and p16 in transduced cells. Simultaneous exposure to Ad-p53 and Ad-p16 produced additive effects in both glioma cell lines. Experimental data points in U373MG lay near the Mode I line, indicating that the vectors had a different mode of action. The restoration of normal p53-encoded protein in the mutant cell lines induced apoptosis, whereas in the wild-type p53 cell lines, the overexpression of wild-type p53 resulted in a moderate degree of apoptosis and G1 arrest. Furthermore, Ad-p16 induced more marked G1 arrest than Ad-p53 in cells with wild-type p53.

CONCLUSIONS

The results show that interaction between Ad-p53 and Ad-p16 is additive, regardless of p53 gene status.

Expression of p21/WAF-1, status of apoptosis and p53 mutation in esophageal squamous cell carcinoma with HPV infection

Human papilloma virus (HPV) is regarded as a causative carcinogenic agent in anogenital squamous cell carcinoma (SCC), but there is controversy about its etiologic role in esophageal SCC (ESCC). In this study, we attempted to clarify whether HPV infection plays a crucial role in the development of ESCC by analysis of multiple factors. These included: detection of HPV DNA; evaluation of immunohistochemical assays for HPV-related cell cycle regulators and apoptosis by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method; and genetic analysis of the p53 gene. Twenty of the 48 ESCC examined (42%) were found to be positive for the HPV genome by polymerase chain reaction. They comprised 16 cases with the HPV16 subtype, three with the HPV18 subtype, and one with both HPV16 and 18. Immunohistochemical analysis revealed that the expression of p21/WAF-1 was significantly decreased in HPV-positive cases (chi2 = 9.2614; P = 0.0023). Furthermore, the 10 apoptosis-negative (< or =10%) cases of HPV-positive SCC were almost exclusively p21/WAF-1-negative (chi2 = 12.1406; P = 0.0005), indicating the significance of the relationship between HPV infection and the phenotype that is expected from HPV-induced inhibition of p53. Although 14 cases possessed missense and deletion mutations of the p53 gene (of which four mutations were found in HPV-positive ESCC), no accumulation of the mutation was defined in the phenotype, suggesting that distinct mutation processes might be involved in HPV-negative and -positive ESCC. The data provide significant support for the hypothesis that HPV infection may play a crucial role in the oncogenesis of some ESCC.

Detection of Epstein-Barr virus genomes in peripheral blood B cells from solid-organ transplant recipients by fluorescence in situ hybridization

Resolution of Epstein-Barr Virus (EBV) infection in pediatric solid-organ transplant recipients often leads to an asymptomatic carrier state characterized by a persistently elevated circulating EBV load that is 2 to 4 orders of magnitude greater than the load typical of healthy latently infected individuals. Elevated EBV loads in immunosuppressed individuals are associated with an increased risk for development of posttransplant lymphoproliferative disease. We have performed fluorescence in situ hybridization (FISH) studies with peripheral blood B cells from carriers of persistent EBV loads in order to directly quantitate the number of EBV genomes per infected cell. Patients were assigned to two groups on the basis of the level of the persistent load (low-load carriers, 8 to 200 genomes/10(5) peripheral blood lymphocytes; high-load carriers, >200 genomes/10(5) peripheral blood lymphocytes). FISH analysis revealed that the low-load carriers predominantly had circulating virus-infected cells harboring one or two genome copies/cell. High-load carriers also had cells harboring one or two genome copies/cell; in addition, however, they carried a distinct population of cells with high numbers of viral genome copies. The increased viral loads correlated with an increase in the frequency of cells containing high numbers of viral genomes. We conclude that low-load carriers possess EBV-infected cells that are in a state similar to normal latency, whereas high-load carriers possess two populations of virus-positive B cells, one of which carries an increased number of viral genomes per cell and is not typical of normal latency.

p53 Gene therapy for lung cancer

The gene transfer of the tumor suppressor p53 gene has been shown to induce tumor regression in preclinical models. Recent phase I and II studies have been completed in lung cancer with adenoviral-mediated transfer of wild-type p53 (Ad-p53) either alone or in combination with chemotherapy or radiotherapy. These studies have demonstrated acceptable toxicity and evidence of tumor regression with intratumoral delivery of Ad-p53. The predominant clinical effect appears to be locoregional in the area of intratumoral delivery. Further phase III studies are needed to determine if Ad-p53 will play a therapeutic role as a novel agent to treat non-small-cell lung cancer.

Mutational analysis of human thioredoxin reductase 1. Effects on p53-mediated gene expression and interferon and retinoic acid-induced cell death

The interferon (IFN)-beta and all-trans-retinoic acid combination suppresses tumor growth by inducing apoptosis in several tumor cell lines. A genetic technique permitted the isolation of human thioredoxin reductase (TR) as a critical regulator of IFN/all-trans-retinoic acid-induced cell death. Our recent studies have shown that TR1:thioredoxin 1-regulated cell death is effected in part through the activation of p53-dependent responses. To understand its death regulatory function, we have performed a mutational analysis of TR. Human TR1 has three major structural domains, the FAD binding domain, the NADPH binding domain, and an interface domain (ID). Here, we show that the deletion of the C-terminal interface domain results in a constitutive activation of TR-dependent death responses and promotes p53-dependent gene expression. TR mutant without the ID still retains its dependence on thioredoxin for promoting these responses. Thus, our data suggest that TR-ID acts as a regulatory domain.

SWI/SNF complex interacts with tumor suppressor p53 and is necessary for the activation of p53-mediated transcription

The SWI/SNF complex is required for the transcription of several genes and has been shown to alter nucleosome structure in an ATP-dependent manner. The tumor suppressor protein p53 displays growth and transformation suppression functions that are frequently lost in mutant p53 proteins detected in various cancers. Using genetic and biochemical approaches, we show that several subunits of the human SWI/SNF complex bind to the tumor suppressor protein p53 in vivo and in vitro. The transactivation function of p53 is stimulated by overexpression of hSNF5 and BRG-1 and dominant forms of hSNF5 and BRG-1 repress p53-dependent transcription. Chromatin immunoprecipitation assay shows that hSNF5 and BRG-1 are recruited to a p53-dependent promoter in vivo. Overexpression of dominant negative forms of either hSNF5 or BRG-1 inhibited p53-mediated cell growth suppression and apoptosis. Molecular connection between p53 and the SWI/SNF complex implicates that (i) the SWI/SNF complex is necessary for p53-driven transcriptional activation, and (ii) the SWI/SNF complex plays an important role in p53-mediated cell cycle control.

Peg3/Pw1 is a mediator between p53 and Bax in DNA damage-induced neuronal death

Neuronal cell death after DNA damage requires p53 and Bax, but the mechanism by which p53 activation leads to Bax translocation and cell death in neurons is not known. We report here that Peg3/Pw1 is up-regulated after DNA damage in cortical neurons in a p53-dependent manner. Overexpression of Peg3/Pw1 leads to decreased neuronal viability. The deleterious effect of Peg3/Pw1 on neuronal survival is abrogated by deletion of either p53 or Bax, indicating an essential role for both in Peg3/Pw1-mediated neuronal death. Moreover, overexpression of a Peg3/Pw1 dominant negative protein inhibits Bax translocation and neuronal cell death after DNA damage. These findings implicate Peg3/Pw1 as a mediator between p53 and Bax in a neuronal cell death pathway activated by DNA damage.

Induction of p53 accumulation by Moloney murine leukemia virus-ts1 infection in astrocytes via activation of extracellular signal-regulated kinases 1/2

SUMMARY

We previously reported that Moloney murine leukemia virus-ts1-mediated neuronal degeneration in mice is likely a result of both loss of glial support and release of cytokines and neurotoxins from ts1-infected glial cells. Viral infection in some cell types regulates expression of p53 protein, a key regulator of cell proliferation and death. Therefore, we hypothesized that p53 and its dependent genes may be linked with ts1-mediated neuropathology. We examined the presence of p53 and its dependent gene product, a proapoptotic protein bax-alpha, in ts1-induced spongiform encephalomyelopathy. Compared with controls, the lesions of infected animals contained increased levels of p53 and bax-alpha in astrocytes, as shown by strong nuclear p53 and cytoplasmic bax-alpha immunoreactivity in astrocytes. To determine how ts1 affects p53 expression in astrocytes, we then assessed the expression of p53 and its dependent genes, such as bax-alpha and p21, in infected and uninfected immortalized C1 astrocytes and studied possible pathways responsible for p53 accumulation in infected astrocytes. In these studies using mitogen-activated protein kinase inhibitors, infection-induced increases in the p53 level were partially blocked by PD98059, a synthetic inhibitor of MEK1 that is the immediate upstream kinase of extracellular signal-regulated kinases 1/2 (ERK1/2), but not by SB202190, a potent p38 kinase inhibitor. Furthermore, treatment with PD98059 significantly decreased the level of p21 protein, a p53-dependent gene product. These results suggest that ts1 infection may stabilize p53 protein through activation of ERKs in C1 astrocytes, leading to increased expression of the p21 and bax-alpha proteins, both of which induce cell cycle arrest and apoptosis. Our studies suggest that ts1 neuropathology in mice may result from changes in expression and activity of p53, brought about in part by ts1 activation of ERK.

Redox control of cell death

Cellular redox is controlled by the thioredoxin (Trx) and glutathione (GSH) systems that scavenge harmful intracellular reactive oxygen species (ROS). Oxidative stress also evokes many intracellular events including apoptosis. There are two major pathways through which apoptosis is induced; one involves death receptors and is exemplified by Fas-mediated caspase-8 activation, and another is the stress- or mitochondria-mediated caspase-9 activation pathway. Both pathways converge on caspase-3 activation, resulting in nuclear degradation and cellular morphological change. Oxidative stress induces cytochrome c release from mitochondria and activation of caspases, p53, and kinases, including apoptosis signal-regulating kinase 1 (ASK1), c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase. Trx inhibits apoptosis signaling not only by scavenging intracellular ROS in cooperation with the GSH system, but also by inhibiting the activity of ASK1 and p38. Mitochondria-specific thioredoxin (Trx-2) and Trx peroxidases (peroxiredoxins) are suggested to regulate cytochrome c release from mitochondria, which is a critical early step in the apoptotis-signaling pathway. dATP/ATP and reducing factors including Trx determine the manifestation of cell death, apoptosis or necrosis, by regulating the activation process and the activity of redox-sensitive caspases. As mitochondria are the most redox-active organelle and indispensable for cells to initiate or inhibit the apoptosis process, the regulation of mitochondrial function is the central focus in the research field of apoptosis and redox.

Physical interaction with human tumor-derived p53 mutants inhibits p63 activities

The p53 tumor suppressor gene is the most frequent target for genetic alterations in human cancers, whereas the recently discovered homologues p73 and p63 are rarely mutated. We and others have previously reported that human tumor-derived p53 mutants can engage in a physical association with different isoforms of p73, inhibiting their transcriptional activity. Here, we report that human tumor-derived p53 mutants can associate in vitro and in vivo with p63 through their respective core domains. We show that the interaction with mutant p53 impairs in vitro and in vivo sequence-specific DNA binding of p63 and consequently affects its transcriptional activity. We also report that in cells carrying endogenous mutant p53, such as T47D cells, p63 is unable to recruit some of its target gene promoters. Unlike wild-type p53, the binding to specific p53 mutants markedly counteracts p63-induced growth inhibition. This effect is, at least partially, mediated by the core domain of mutant p53. Thus, inactivation of p53 family members may contribute to the biological properties of specific p53 mutants in promoting tumorigenesis and in conferring selective survival advantage to cancer cells.

The course of etoposide-induced apoptosis from damage to DNA and p53 activation to mitochondrial release of cytochrome c

Treatment of L929 fibroblasts by the topoisomerase II inhibitor etoposide killed 50% of the cells within 72 h. The cell killing was preceded by the release of cytochrome c from the mitochondria. Simultaneous treatment of the cells with wortmannin, cycloheximide, furosemide, cyclosporin A, or decylubiquinone prevented the release of cytochrome c and significantly reduced the loss of viability. Etoposide caused the phosphorylation of p53 within 6 h, an effect prevented by wortmannin, an inhibitor of DNA-dependent protein kinase (DNA-PK). The activation of p53 by etoposide resulted in the up-regulation of the pro-apoptotic protein Bax, a result that was prevented by the protein synthesis inhibitor cycloheximide. The increase in the content of Bax was followed by the translocation of this protein from the cytosol to the mitochondria, an event that was inhibited by furosemide, a chloride channel inhibitor. Stably transfected L929 fibroblasts that overexpress Akt were resistant to etoposide and did not translocate Bax to the mitochondria or release cytochrome c. Bax levels in these transfected cells were comparable with the wild-type cells. The release of cytochrome c upon translocation of Bax has been attributed to induction of the mitochondrial permeability transition (MPT). Cyclosporin A and decylubiquinone, inhibitors of MPT, prevented the release of cytochrome c without affecting Bax translocation. These data define a sequence of biochemical events that mediates the apoptosis induced by etoposide. This cascade proceeds by coupling DNA damage to p53 phosphorylation through the action of DNA-PK. The activation of p53 increases Bax synthesis. The translocation of Bax to the mitochondria induces the MPT, the event that releases cytochrome c and culminates in the death of the cells.

A zinc-finger protein, PLAGL2, induces the expression of a proapoptotic protein Nip3, leading to cellular apoptosis

Pleomorphic adenomas gene-like 2 (PLAGL2) protein containing seven C(2)H(2) zinc finger motifs exhibits DNA binding and transcriptional activation activity and is expressed in response to hypoxia or iron deficiency. To identify the target genes of PLAGL2, we transfected mouse PLAGL2 cDNA into Balb/c3T3 fibroblasts and neuroblastoma Neuro2a cells. Both cells were induced to undergo apoptosis by the expression of PLAGL2 as judged by assays of TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling), DNA fragmentation, propidium iodide staining, and the binding of annexin V to the cell surface. The treatment of the cells with an iron chelator, desferrioxamine, resulted in the induction of apoptosis with a concomitant accumulation of PLAGL2 in the nucleus. The expression of PLAGL2 in Balb/c3T3 cells led to the mRNA expression of a proapoptotic factor, Nip3, which can dimerize with Bcl-2. Nip3 mRNA was also induced in desferrioxamine-treated cells. Furthermore, the Nip3 promoter containing a hypoxia-responsive element was activated by PLAGL2, independent of hypoxia-inducible factor-1 (HIF-1). The transfection of antisense oligonucleotide to mouse Nip3 mRNA into PLAGL2-expressing cells led to a decrease in apoptotic cells compared with sense oligonucleotide-transfected cells. Despite the activation of DNA-HIF-1 binding activity under hypoxic conditions, neither an accumulation of HIF-1 alpha nor the activation of HIF-1 was observed following the expression of PLAGL2. These results indicate that PLAGL2 is located downstream of HIF-1 and suggest that PLAGL2 functions as a tumor suppressor in association with HIF-1.

Epstein-Barr virus latent membrane protein 2B (LMP2B) co-localizes with LMP2A in perinuclear regions in transiently transfected cells

Epstein-Barr virus is a human gammaherpesvirus that infects and establishes latency in B lymphocytes in vivo. The latent membrane protein 2 (LMP2) gene is expressed in latently infected B cells and encodes two protein isoforms, LMP2A and LMP2B, that are identical except for an additional N-terminal 119 aa cytoplasmic domain which is present in the LMP2A isoform. A panel of fusion proteins was constructed in which the fluorescent enhanced green fluorescent protein and DsRed protein domains were fused to the N- and C-termini of LMP2A and LMP2B. By fluorescence microscopy, LMP2B localized to perinuclear regions of both live and fixed transiently transfected cells. Co-localization was detected with markers for the endoplasmic reticulum and the trans-Golgi network. No evidence of co-localization of LMP2B with endosomes or surface expression was obtained. Transiently expressed LMP2B co-localized with transiently or constitutively expressed LMP2A. Confocal microscopy confirmed that LMP2A proteins localized to intracellular perinuclear compartments with markers for the trans-Golgi network. Only LMP2A proteins with C-terminal truncations were detected in the plasma membrane with extracellular loop1 epitope tags. These results indicate that the transmembrane domain of LMP2 proteins possess intracellular retention signals and suggest that LMP2A-mediated signalling effects are likely to be ectopic, originating from sites inside the cell close to the nucleus.

p53 leans on its siblings

Despite the common assumption that p53 by itself can induce apoptosis, results of a recent study implicate the homologous genes p63 and p73 in p53-mediated programmed cell death.

Cancer gene therapy: scientific basis

Gene therapy of cancer has been one of the most exciting and elusive areas of therapeutic research in the past decade. Critical developments have occurred in gene therapy targeting cancer cells, cancer vasculature, the immune system, and the bone marrow, itself often the target for severe toxicity from therapeutic agents. We review some recent developments in the field. In each instance, clear preclinical models validated the therapeutic approach and efforts have been made to evaluate the target impact in both preclinical and early clinical trials. Although no cures can consistently be expected from today's cancer gene therapy, the rapid progress may imply that such cures are a few short years away.

A mutant P53 can activate apoptosis through a mechanism distinct from those induced by wild type P53

A common mutation in P53 protein occurs at amino acid residue 281 in the DNA binding domain (P53(gly(281))), which results in loss of transcriptional regulation of P53 target genes and has been reported to gain pro-oncogenic functions. In the present study, we investigated the activity of P53(gly(281)) in P53-null PC3 human prostate cancer cells and found that the P53(gly(281)) induced apoptosis as efficiently as the wild-type P53 (wtP53). However, in contrast to wtP53-induced apoptosis, the P53(gly(281))-induced apoptosis was insensitive to overexpression of bcl-2. Thus, our findings indicate that while a mutation in the DNA binding domain of p53 may result in a more oncogenic form of the protein, it may also paradoxically result in the 'gain' of a new, alternative pathway for apoptosis.

Bax and Bak independently promote cytochrome C release from mitochondria

Pro-apoptotic Bax and Bak have been implicated in the regulation of p53-dependent apoptosis. We assessed the ability of primary baby mouse kidney (BMK) epithelial cells from bax(-/-), bak(-/-), and bax(-/-) bak(-/-) mice to be transformed by E1A alone or in conjunction with dominant-negative p53 (p53DD). Although E1A alone transformed BMK cells from p53-deficient mice, E1A alone did not transform BMK cells from bax(-/-), bak(-/-), or bax(-/-) bak(-/-) mice. Thus, the loss of both Bax and Bak was not sufficient to relieve p53-dependent suppression of transformation in epithelial cells. To test the requirement for Bax and Bak in other death signaling pathways, stable E1A plus p53DD-transformed BMK cell lines were derived from the bax(-/-), bak(-/-), and bax(-/-) bak(-/-) mice and characterized for their response to tumor necrosis factor-alpha (TNF-alpha)-mediated apoptosis. The loss of both Bax and Bak severely impaired TNF-alpha-mediated apoptosis, but the presence of either Bax or Bak alone was sufficient for cell death. Cytochrome c was released from mitochondria, and caspase-9 was activated in Bax- or Bak-deficient cells in response to TNF-alpha but not in cells deficient in both. Thus, either Bax or Bak is required for death signaling through mitochondria in response to TNF-alpha, but both are dispensable for p53-dependent transformation inhibition.

Tumor suppressor p53 mediates apoptotic cell death triggered by cyclosporin A

The tumor suppressor p53 can induce growth arrest and cell death via apoptosis in response to a number of cellular stresses. We have shown previously that the immunosuppressant cyclosporin A (CsA) induces programmed cell death with typical features of apoptosis in rat glioma cells. We report that CsA treatment results in increased level of the p53 tumor suppressor, its nuclear accumulation, and transcriptional activation of p53-dependent genes. The increase of p53 correlates with the elevation of p21(Waf1) and Bax protein expression. The increased level of Bax protein was accompanied with changes in its subcellular localization and association with mitochondria. Importantly, we demonstrate that glioma cells stably transfected with a mutant p53 (p53Val135) fail to increase p21 and Bax protein levels and are less sensitive to CsA-induced apoptosis. Furthermore, primary fibroblasts from p53-/- knockout mice are significantly more resistant to CsA-induced apoptosis compared with their corresponding counterparts containing functional p53. Together, our results suggest that the apoptotic program activated by CsA can be mediated by activation of p53 tumor suppressor and potentiation of its ability to initiate apoptosis.

Topoisomerase IIalpha gene expression is regulated by the p53 tumor suppressor gene in nonsmall cell lung carcinoma patients

BACKGROUND

Topoisomerase IIalpha (Topo IIalpha) is an essential nuclear enzyme for chromosome segregation during mitosis. Previous experimental studies using cell lines reported that Topo IIalpha expression was negatively regulated by wild-type p53 through the gene's promoter region.

METHODS

Surgically resected tumor specimens from 98 nonsmall cell lung carcinoma (NSCLC) patients who were not treated with preoperative chemotherapy were studied. Quantitative reverse-transcription polymerase chain reaction analysis was done to evaluate Topo IIalpha gene expression. Polymerase chain reaction single strand conformation polymorphism following sequencing was performed to investigate mutations of p53.

RESULTS

Topo IIalpha gene expression in squamous cell carcinomas was significantly higher than in adenocarcinomas (P = 0.0007). Topo IIalpha gene expression in moderately differentiated tumors and poorly differentiated tumors was significantly higher than in well differentiated tumors (P = 0.0032 and P = 0.0005, respectively). Thirty nine tumors (40%) had mutations of p53. Topo IIalpha gene expression in tumors with mutant p53 was significantly higher than in those with wild-type p53 (P = 0.0224).

CONCLUSIONS

The current study suggests that Topo IIalpha gene expression is regulated by p53 gene status in NSCLC patients and that the overexpression of Topo IIalpha induced by mutant p53 might cause more aggressive carcinogenesis.

Biogenesis of p53 involves cotranslational dimerization of monomers and posttranslational dimerization of dimers. Implications on the dominant negative effect

Precisely how mutant p53 exerts a dominant negative effect over wild type p53 has been an enigma. To understand how wild type and mutant p53 form hetero-oligomers, we studied p53 biogenesis in vitro. We show here that p53 dimers are formed cotranslationally (on the polysome), whereas tetramers are formed posttranslationally (by the dimerization of dimers in solution). Coexpression of wild type and mutant p53 therefore results in 50% of the p53 generated being heterotetramers comprised of a single species: wild type dimer/mutant dimer. Using hot spot mutants of p53 and a variety of natural target sites, we show that all wild type/mutant heterotetramers manifest impaired DNA binding activity. This impairment is not due to the mutant dimeric subunit inhibiting association of the complex with DNA but rather due to the lack of significant contribution (positive cooperativity) from the mutant partner. For all heterotetramers, bias in binding is particularly pronounced against those sequences in genes responsible for apoptosis rather than cell growth arrest. These results explain the molecular basis of p53 dominant negative effect and suggest a functional role in the regulation of p53 tetramerization.

The molecular pathology of p53 in primitive neuroectodermal tumours of the central nervous system

One hundred and one pre-treatment primary central primitive neuroectodermal tumours were analysed for the expression of p53 protein by immunohistochemistry using the monoclonal antibody DO-7. The staining intensity was classified into four groups: strong, medium, weak and negative and strong staining intensity was associated with the poorest survival. DNA sequencing of the p53 gene was performed in 28 cases representing all four staining groups. Mutations were found in only three of the strong staining tumours suggesting that DNA mutations were not common events and that in the majority of the tumours with over-expressed p53, the protein was likely to be wild-type. Results of immunohistochemistry showed a significantly positive relationship between the expression of p53 and Bax and Bcl-2 proteins, but not Waf-1. Multivariate analyses supported the prognostic value of p53 immunostaining in central primitive neuroectodermal tumours and also of age and gender of patients.

Resistance of colon cancer cells to long-term 5-fluorouracil exposure is correlated to the relative level of Bcl-2 and Bcl-X(L) in addition to Bax and p53 status

Defects in apoptosis have been implicated in chemoresistance of colon cancer cells. We report here the ability to resist to 5-fluorouracil-induced apoptosis of 8 colon cancer cell lines differing in p53 and bax status: p53(-/0)bax(+/+) for TC7, SW480, HT-29; p53(+/+)bax(-/-) for LS174T, LoVo; p53(+/+) bax(+/-) for HCT116; p53(+/+) or p53(+/0)bax(+/+) for LS513 or HCT-EB, respectively. To approximate to the in vivo therapy, the cell lines were exposed to a long-term treatment of 5-FU. The analysis of proteins implicated in the apoptotic pathway has shown that the independent analysis of p53 or bax status was not sufficient to predict the extent of drug-resistance of all cell lines. In p53(+/+) cell lines but not in p53(-/0) cell lines, a low level of the pro-apoptotic Bax protein was correlated with a greater resistance of cells to 5-FU. In addition, we found that high levels of anti-apoptotic Bcl-2 and Bcl-x(L) proteins combined with a low level of Bax were correlated to high 5-FU resistance of wild-type p53 cell lines. The same correlation was obtained for 2 out of 3 mutated p53 cell lines. In conclusion, the relative levels of Bcl-2, Bcl-x(L) and Bax may altogether contribute to determine the resistance of a majority of colon tumor cells to long-term 5-FU treatment, whatever their p53 status.

Death and anti-death: tumour resistance to apoptosis

Every cell in a multicellular organism has the potential to die by apoptosis, but tumour cells often have faulty apoptotic pathways. These defects not only increase tumour mass, but also render the tumour resistant to therapy. So, what are the molecular mechanisms of tumour resistance to apoptosis and how can we use this knowledge to resensitize tumour cells to cancer therapy?

Replication licensing of the EBV oriP minichromosome

The latent EBV genome may persist in the integrated form as well as the circular episomal form. However, most of the latent viral DNA molecules are known to exist in the circular episomal form, which binds to host chromosomes during mitosis. The DS element of oriP in the circular episomal DNA functions as a replication origin. As it replicates once in a single S phase, it is possible that oriP is regulated by the cellular replication licensing mechanism including the MCM family of replication licensing factors. Transient replication analysis using the oriP plasmid and HeLa/EB1 cells revealed that the DS element requires early G1 phase for the next round of replication, the same cell-cycle window in which the replication licensing of cellular chromatin occurs. After this phase, the sedimentation velocity of the oriP minichromosome increases. MCM2 associates with the oriP minichromosome at late G1 but not at G2/M, and this association requires the DS element in the plasmid. The interaction of EBNA1 and the MCM proteins on the DS element was also suggested. These results suggested that the cellular licensing mechanism controls the replication from oriP. This also suggested a similarity in the replication machinery of the cellular chromatin and the latent EBV genome. In addition to DS-dependent replication, the EBV genome replicates in a manner independent of the DS element in several cultured cell lines. The DS-dependent replication is likely to be suppressed in these cell lines by the expression of other viral proteins. In contrast, EBV-positive Burkitt's lymphoma and circulating EBV-infected B cells express only EBNA1 or both EBNA1 and LMP2. DS-dependent replication may play a major role in these EBNA1-only cells, and the licensing regulation of oriP is important for maintenance of the EBV genome during this latent period of the viral life cycle. EBNA1 is required for efficient nuclear retention and partitioning of oriP-carrying plasmid by its binding to the FR element, thus providing stable persistence of the latent EBV genome during cell division. The copy number of latent EBV DNA molecules in B-cell lines remains fairly constant during multiple passage in culture. However, very little is known about the mechanism by which the viral DNA molecules are equally segregated into daughter cells. To understand the mechanisms responsible for stable nuclear retention and partitioning of the latent viral genome, it is essential to analyze the episomal and integrated viral DNAs at a single-cell level by FISH and other techniques.

Wild-type and mutated presenilins 2 trigger p53-dependent apoptosis and down-regulate presenilin 1 expression in HEK293 human cells and in murine neurons

Presenilins 1 and 2 are two homologous proteins that, when mutated, account for most early onset Alzheimer's disease. Several lines of evidence suggest that, among various functions, presenilins could modulate cell apoptotic responses. Here we establish that the overexpression of presenilin 2 (PS2) and its mutated form Asn-141-Ile-PS2 alters the viability of human embryonic kidney (HEK)293 cells as established by combined trypan blue exclusion, sodium 3'-[1-(phenylamino-carbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene sulfonic acid hydrate assay, and propidium iodide incorporation FACS analyses. The two parent proteins increase the acetyl-DEVD-al-sensitive caspase-3-like activity in both HEK293 cells and Telencephalon specific murine neurons, modulate Bax and bcl-2 expressions, and enhance cytochrome C translocation into the cytosol. We show that overexpression of both wild-type and mutated PS2 increases p53-like immunoreactivity and transcriptional activity. We also establish that wild-type- and mutated PS2-induced caspase activation is reduced by p53 antisense approach and by pifithrin-alpha, a chemical inhibitor of p53. Furthermore, mouse fibroblasts in which the PS2 gene has been knocked out exhibited strongly reduced p53-transcriptional activity. Finally, we establish that the overexpression of both wild-type and mutated PS2 is accompanied by a drastic reduction of endogenous presenilin 1 (PS1) expression. Interestingly, pifithrin-alpha diminished endogenous PS2 immunoreactivity, whereas the inhibitor increases PS1 expression. Altogether, our data demonstrate that wild-type and familial Alzheimer's disease-linked PS2 trigger apoptosis and down-regulate PS1 expression through p53-dependent mechanisms.

Integrins regulate the apoptotic response to DNA damage through modulation of p53

p53 mediates apoptosis of cells after DNA damage including tumor cells after radiation or chemotherapy. Survival of isolated cancer cells after therapy leads to recurrence of therapy-resistant tumors. We now show that for some melanoma, sarcoma, or fibroblastic cell types that survive without integrin-mediated adhesion, apoptosis in response to DNA damage requires cell adhesion. This effect correlates with rapid changes in levels of p14/p19 Arf and its downstream component, p53. Killing of nonadherent cells is increased by treatment with antiintegrin antibodies or by increasing levels of p53 or Arf. Consistent with low p53 levels, suspended cells show chromosomal instability after irradiation. Thus, loss of normal adhesion in susceptible tumor cells during genotoxic stress may play a role in therapy resistance and promote survival of cells with aberrant DNA.

Bax and Bak promote apoptosis by modulating endoplasmic reticular and mitochondrial Ca2+ stores

Alterations in intracellular Ca(2+) homeostasis and cytochrome c release from mitochondria have been implicated in the regulation of apoptosis, but the relationship between these events remains unclear. Here we report that enforced expression of either Bax or Bak via adenoviral gene delivery results in the accumulation of the proteins in the endoplasmic reticulum (ER) and mitochondria, resulting in early caspase-independent BCL-2-sensitive release of the ER Ca(2+) pool and subsequent Ca(2+) accumulation in mitochondria. The inhibition of ER-to-mitochondrial Ca(2+) transport with a specific inhibitor of mitochondrial Ca(2+) uptake attenuates cytochrome c release and downstream biochemical events associated with apoptosis. Bax and Bak also directly sensitize mitochondria to cytochrome c release induced by immediate emptying of ER Ca(2+) pool. Our results demonstrate that the effects of the "multidomain" proapoptotic BCL-2 family members Bak and Bax involve direct effects on the endoplasmic reticular Ca(2+) pool with subsequent sensitization of mitochondria to calcium-mediated fluxes and cytochrome c release. These effects modulate the kinetics of cytochrome c release and apoptosis.

Hepatitis B virus X protein differentially regulates cell cycle progression in X-transforming versus nontransforming hepatocyte (AML12) cell lines

Hepatitis B virus (HBV) X protein (pX) is implicated in hepatocarcinogenesis of chronically infected HBV patients. To understand mechanism(s) of pX-mediated cellular transformation, we employed two tetracycline-regulated, pX-expressing cell lines, constructed in AML12 immortalized hepatocytes: one a differentiated (3pX-1) and the other a de-differentiated (4pX-1) hepatocyte cell line. Only 3pX-1 cells undergo pX-mediated transformation, via sustained Ras-Raf-mitogen-activated protein kinase pathway activation. pX-nontransforming 4pX-1 cells display sustained, pX-dependent JNK pathway activation. To understand how pX mediates different growth characteristics in 3pX-1 and 4pX-1 cells, we report, herein, comparative cell cycle analyses. pX-transforming 3pX-1 cells display pX-dependent G(1), S, and G(2)/M progression evidenced by cyclin D(1), A, and B(1) induction, and Cdc2 kinase activation. pX-nontransforming 4pX-1 cells display pX-dependent G(1) and S phase entry, followed by S phase pause and absence of Cdc2 kinase activation. Interestingly, 4pX-1 cells exhibit selective pX-induced expression of cyclin-dependent kinase inhibitor p21(Cip1), tumor suppressor p19(ARF), and proapoptotic genes bax and IGFBP-3. Despite the pX-mediated induction of growth arrest and apoptotic genes and the absence of pX-dependent Cdc2 activation, 4pX-1 cells do not undergo pX-dependent G(2)/M arrest or apoptosis. Nocodazole-treated, G(2)/M-arrested 4pX-1 cells exhibit pX-dependent formation of multinucleated cells, similar to human T-cell lymphotropic virus type I Tax-expressing cells. We propose that in 4pX-1 cells, pX deregulates the G(2)/M checkpoint, thus rescuing cells from pX-mediated apoptosis.

An analysis of p53, BAX and vascular endothelial growth factor expression in node-positive rectal cancer. Relationships with tumour recurrence and event-free survival of patients treated with adjuvant chemoradiation

Tumours of patients with node-positive rectal cancer were studied by immunohistochemistry for p53, BAX and vascular endothelial growth factor expressions. Results were correlated to the relapse rate, the pattern of relapse and the event-free survival after radical surgery and adjuvant chemoradiation. After a median follow-up of 60 months, 39 patients remained disease-free and 40 patients relapsed (18 local relapses and 22 distant metastases). The majority of disease-free patients showed p53 negative and vascular endothelial growth factor negative tumours. Local relapses occurred more frequently in patients with p53 overexpressing tumours (P<0.01), while distant metastases were in patients with vascular endothelial growth factor positive tumours (P<0.003). Patients with p53 negative or vascular endothelial growth factor negative tumours showed better event-free survival than patients with p53 positive or vascular endothelial growth factor positive tumours. BAX analysis did not show any association with patients' outcome and it was unrelated to the p53 status. Adjuvant treatment strategies for node-positive rectal cancer may be improved by identifying categories of high-risk patients. In this study, vascular endothelial growth factor and p53 expressions correlated with recurrent disease, pattern of relapse and poor event-free survival.

An effective immunization and cancer treatment with activated dendritic cells transduced with full-length wild-type p53

P53-based immunization is an attractive approach to cancer immunotherapy due to the accumulation of p53 protein in tumor, but not in normal cells. However, it was not known whether immune response against self-protein (p53) could be generated in vivo. Mouse dendritic cells (DCs) were transduced with adenoviral construct containing murine full-length wild-type p53 (Ad-p53). Repeated immunizations with these cells protected 60% of mice against challenge with MethA sarcoma cells bearing point mutations in p53 gene. Activation of DCs via ligation of CD40 significantly improved the results of immunization: all mice were protected against MethA sarcoma. The treatment of MethA tumor-bearing mice with activated Ad-p53-transduced DCs showed complete tumor rejection in four out of six mice. The specificity of antitumor immune response was confirmed by CTL assay. The analysis of phenotype and function of DCs demonstrated that the effect of CD40 ligation on these cells was enhanced by their infection with Ad-p53. The level of neutralizing anti-adenovirus antibody was moderately elevated in these mice. No signs of autoimmune reaction were evident during detailed pathological evaluation of treated mice. These data demonstrate that activated Ad-p53-infected DCs are able to break tolerance to this protein and can be used in immunotherapy of cancer.

Head and neck cancer: gene therapy approaches. Part II: genes delivered

In Part I, the review summarised the safety of adenoviral vectors and provided insight into approaches being undertaken to improve the specificity, durability and potency of adenoviral delivery vehicles. In Part II, brief discussions are held regarding results of preclinical and clinical trials with a variety of different genes, which have demonstrated antitumour activity in squamous cell carcinoma of the head and neck region (HNSCC). Studies have been performed with a variety of immune modulatory genes. Preliminary results demonstrate activity with several cytokine genes, tumour antigen genes and co-stimulatory molecule genes. Despite only preliminary results, thus far, a theoretical attractive feature for the use of gene therapy for the enhancement of immune modulation is that local injection of the gene product appears to be well tolerated. It is also successful in inducing systemic immune response, potentially providing effect to metastatic sites distal from the injected site. Animal studies have confirmed efficacy in the use of specific targeting of molecules regulating cancer growth (EGF receptor [EGFR], super oxide dismutase [SOD], cyclin D1, E1A and Bcl-2). These approaches are discussed. However, the most significant clinical advances for the use of gene therapy in advanced HNSCC involves two agents: Adp53 and ONYX-015. Preliminary Phase I and II results suggest evidence of efficacy and justify accrual Phase III trials, which are currently ongoing.

HMGB1 and HMGB2 cell-specifically down-regulate the p53- and p73-dependent sequence-specific transactivation from the human Bax gene promoter

The recently cloned gene p73 is a close homologue of p53, which is a crucial tumor suppressor gene for preventing the malignant transformation of cells by inducing cell cycle arrest and apoptosis. Previous reports have shown that architectural DNA-bending/looping chromosomal proteins HMGB1 and HMGB2 (formerly known as HMG1 and HMG2), which function in a number of biological processes including transcription and DNA repair, interact in vitro with p53 and stimulate p53 binding to DNA containing p53 consensus sites. Here, we report that HMGB1 physically interacts with two splicing variants of p73, alpha and beta (pull-down assay), and enhances binding of p73 to specific cognate DNA sites (gel-shift assay). Both HMG box domains of HMGB1, A and B, interact with p73alpha. Association of HMGB1 with p73, like the demonstrated ability of HMGB1 to stimulate p73 binding to different p53-responsive elements, requires the oligomerization region and/or region between DNA-binding domain and oligomerization domain of p73 (residues 312-381). Transient transfections revealed that ectopically expressed or endogenous HMGB1 and HMGB2 (antisense strategy) significantly inhibit in vivo both p73alpha/beta- and p53-dependent transactivation from the Bax gene promoter (and much less from Mdm2 and p21(waf1) promoters) in p53-deficient SAOS-2 cells. In contrast, HMGB1 and HGMB2 stimulate p73- or p53-dependent transactivation in p53-deficient H1299 cells, irrespective of the promoter used. Our results suggest that ubiquitously expressed HMGB1 and HMGB2 have potential to cell- and promoter-specifically down- or up-regulate in vivo transcriptional activity of different members of the p53 family. A possible mechanism of HMGB1-mediated modulation of p73- and p53-dependent transactivation is discussed.

Injury-induced spinal motor neuron apoptosis is preceded by DNA single-strand breaks and is p53- and Bax-dependent

The mechanisms of injury-induced apoptosis of neurons within the spinal cord are not understood. We used a model of peripheral nerve-spinal cord injury in the rat and mouse to induce motor neuron degeneration. In this animal model, unilateral avulsion of the sciatic nerve causes apoptosis of motor neurons. We tested the hypothesis that p53 and Bax regulate this neuronal apoptosis, and that DNA damage is an early upstream signal. Adult mice and rats received unilateral avulsions causing lumbar motor neurons to achieve endstage apoptosis at 7-14 days postlesion. This motor neuron apoptosis is blocked in bax(-/-) and p53(-/-) mice. Single-cell gel electrophoresis (comet assay), immunocytochemistry, and quantitative immunogold electron microscopy were used to measure molecular changes in motor neurons during the progression of apoptosis. Injured motor neurons accumulate single-strand breaks in DNA by 5 days. p53 accumulates in nuclei of motor neurons destined to undergo apoptosis. p53 is functionally activated by 4-5 days postlesion, as revealed by immunodetection of phosphorylated p53. Preapoptotically, Bax translocates to mitochondria, cytochrome c accumulates in the cytoplasm, and caspase-3 is activated. These results demonstrate that motor neuron apoptosis in the adult spinal cord is controlled by upstream mechanisms involving DNA damage and activation of p53 and downstream mechanisms involving upregulated Bax and cytochrome c and their translocation, accumulation of mitochondria, and activation of caspase-3. We conclude that adult motor neuron death after nerve avulsion is DNA damage-induced, p53- and Bax-dependent apoptosis.

Curcumin induces apoptosis in human breast cancer cells through p53-dependent Bax induction

The aim of this study was to determine the mechanisms of curcumin-induced human breast cancer cell apoptosis. From quantitative image analysis data showing an increase in the percentage of cells with a sub-G0/G1 DNA content, we demonstrated curcumin-induced apoptosis in the breast cancer cell line MCF-7, in which expression of wild-type p53 could be induced. Apoptosis was accompanied by an increase in p53 level as well as its DNA-binding activity followed by Bax expression at the protein level. Further experiments using p53-null MDAH041 cell as well as low and high p53-expressing TR9-7 cell, in which p53 expression is under tight control of tetracycline, established that curcumin induced apoptosis in tumor cells via a p53-dependent pathway in which Bax is the downstream effector of p53. This property of curcumin suggests that this molecule could have a possible therapeutic potential in breast cancer patients.

Co-transduction of Apaf-1 and caspase-9 highly enhances p53-mediated apoptosis in gliomas

Mutation of the p53 gene plays a critical role in the development of cancer and response to cancer therapy. To analyze the mechanism of cancer development and to improve cancer therapy, it is important to assess which genes are downstream components of p53 in cancers, and whether the expression levels of these genes affect p53-mediated apoptosis. In this study, we transduced the wild type p53 gene along with the Apaf-1 and caspase-9 genes via adenovirus vectors into U251 and U-373MG glioma cells harbouring a mutated p53, and evaluated the degree of apoptosis. Co-induction of Apaf-1 and caspase-9 genes highly enhanced p53-mediated apoptosis in glioma cells. Induction of wild type p53 enhanced the expression levels of Bax, p21/WAF1, and Fas protein. To determine which gene is activated by wild type p53 induction and, in turn, activates Apaf-1 and caspase-9, we transduced the Bax, p21/WAF1 or Fas gene via adenovirus vector to U251 cells to achieve a similar expression level as that induced by the Adv for p53 in U251 cells. U251 cells transduced with Fas concomitant with the Apaf-1 and caspase-9 genes underwent drastic apoptosis. This suggests that induction of wild type p53 upregulates Fas, which in turn may play a role in the activation of Apaf-1 and caspase-9. These results are important for analyzing the mechanism of tumour development and for predicting the therapeutic effect of p53 replacement gene therapy in a particular patient.