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

Early events in the anoikis program occur in the absence of caspase activation

Adhesion of many cell types to the extracellular matrix is essential to maintain their survival. In the absence of integrin-mediated signals, normal epithelial cells undergo a form of apoptosis termed anoikis. It has been proposed that the activation of initiator caspases is an early event in anoikis, resulting in Bid cleavage and cytochrome c release from mitochondria. We have previously demonstrated that the loss of integrin signaling in mammary epithelial cells results in apoptosis and that this is dependent upon translocation of Bax from the cytosol to the mitochondria. In this paper, we ask whether caspases are required for Bax activation and the associated changes within mitochondria. We show that Bax activation occurs extremely rapidly, within 15 min after loss of integrin-mediated adhesion to extracellular matrix. The conformational changes associated with Bax activation are independent of caspases including the initiator caspase-8. We also examined downstream events in the apoptosis program and found that cytochrome c release occurs after a delay of at least 1 h, with subsequent activation of the effector caspase-3. This delay is not due to a requirement for new protein synthesis, since cycloheximide has no effect on the kinetics of Bax activation, cytochrome c release, caspase-3 cleavage, or apoptosis. Together, our data indicate that the cellular decision for anoikis in mammary epithelial cells occurs in the absence of caspase activation. Moreover, although the conformational changes in Bax are rapid and synchronous, the subsequent events occur stochastically and with considerable delays.

Nitric oxide induces phosphorylation of p53 and impairs nuclear export

The tumor suppressor p53 accumulates under diverse stress conditions and affects cell cycle progression and/or apoptosis. This has been exemplified for endogenously produced or exogenously supplied nitric oxide (NO) and thus accounts at least in part for pathophysiological signaling of that bioactive molecule, although detailed mechanisms remain to be elucidated. By using luciferase reporter assays, we show that NO stabilized a transcriptionally active p53 protein. Considering that p53 is targeted by murine double minute (Mdm2) for ubiquitination and subsequent proteasomal degradation and knowing that this interaction is impaired by, for example, UV-treatment with concomitant stabilization of p53 we questioned the p53/Mdm2 interaction in the presence of NO. Although p53 became phosphorylated at serine 15 under the impact of NO, coimmunoprecipitation with Mdm2 and ubiquitination remained intact, thus excluding any interference of NO with this pathway. The importance of N-terminal p53 phosphorylation was verified with p53 mutants where the first six serine residues have been converted to alanine, and which do not accumulate in response to NO. Regulation of p53 stability can be also achieved by affecting nuclear-cytoplasmic shuttling and it was presented that leptomycin B, an inhibitor of nuclear export, caused p53 accumulation. Cell fractionation and immunofluorescence staining following NO-treatment revealed predominant nuclear accumulation of p53 in close association with serine 15-phosphorylation, which suggests impaired nuclear-cytoplasmic shuttling. This was verified by heterokaryon analysis. We conclude that attenuated nuclear export contributes to stabilization and activation of p53 under the influence of NO.

Polo-like kinase (Plk)1 depletion induces apoptosis in cancer cells

Elevated expression of mammalian polo-like kinase (Plk)1 occurs in many different types of cancers, and Plk1 has been proposed as a novel diagnostic marker for several tumors. We used the recently developed vector-based small interfering RNA technique to specifically deplete Plk1 in cancer cells. We found that Plk1 depletion dramatically inhibited cell proliferation, decreased viability, and resulted in cell-cycle arrest with 4 N DNA content. The formation of dumbbell-like chromatin structure suggests the inability of these cells to completely separate the sister chromatids at the onset of anaphase. Plk1 depletion induced apoptosis, as indicated by the appearance of subgenomic DNA in fluorescence-activated cell-sorter (FACS) profiles, the activation of caspase 3, and the formation of fragmented nuclei. Plk1-depletion-induced apoptosis was partially reversed by cotransfection of nondegradable mouse Plk1 constructs. In addition, the p53 pathway was shown to be involved in Plk1-depletion-induced apoptosis. DNA damage occurred in Plk1-depleted cells and inhibition of ATM strongly potentiated the lethality of Plk1 depletion. Although p53 is stabilized in Plk1-depleted cells, DNA damage also occurs in p53(-/-) cells. These data support the notion that disruption of Plk1 function could be an important application in cancer therapy.

The activation domains, the proline-rich domain, and the C-terminal basic domain in p53 are necessary for acetylation of histones on the proximal p21 promoter and interaction with p300/CREB-binding protein

The p53 transcription factor contains two separate tandem activation domains (AD1 and AD2), a proline-rich domain (PRD), and a C-terminal basic domain (BD). Previously, we have shown that these domains are necessary for transcriptional activity. To further characterize the role of these domains in transactivation, we analyzed the regulation of p21, a well characterized p53 target gene, by various p53 mutants deficient in one or more of these domains. We found that the induction of endogenous p21 is compromised by AD1-deficient p53 (p53(AD1(-))), AD2-deficient p53 (p53(AD2(-))), both AD1- and AD2-deficient p53 (p53(AD1(-)AD2(-))), p53(deltaPRD), which lacks PRD, and p53(deltaBD), which lacks BD. However, p53(AD2(-)), p53(deltaPRD), and p53(deltaBD) are still capable of activating exogenous p21 promoter to an extent comparable with that by wild-type p53. Thus, we performed chromatin immunoprecipitation assay to measure the DNA binding ability of various p53 mutants in vivo. We found that like wild-type p53, these p53 mutants are capable of binding to the p53 response elements in the p21 promoter. In contrast, we found that the extent of acetylated histones on the p21 promoter, especially the proximal promoter, and the amount of interaction with p300/CREB-binding protein, which contain histone acetyltransferase activity, directly correlate with the activity of p53 to induce endogenous p21. Furthermore, we showed that down-regulation of p300/CBP by short interference RNA markedly decreases the ability of p53 to induce endogenous p21. These data lead us to hypothesize that when p53 binds to the responsive element(s) of a target gene, its ability to interact with histone acetyltransferase-containing proteins and subsequently the acetylation of histones bound to the proximal promoter dictate the induction level of a target gene.

hCDC4b, a regulator of cyclin E, as a direct transcriptional target of p53

To identify p53-target genes we have been using a cDNA-microarray system to assess gene expression in a p53-mutated glioblastoma cell line (U373MG) after adenovirus-mediated transfer of wild-type p53 into the p53-deficient cells. In the work reported here, expression of hCDC4b, which encodes one of the four subunits of the SCF (ubiquitin ligase) complex responsible for degradation of cyclin E, was dramatically up-regulated by infection with Ad-p53. An electrophoretic mobility-shift assay and a chromatin immunoprecipitation assay indicated that a potential p53-binding site (p53BS) present in exon 1b of the hCDC4 gene was able to bind to p53, and a reporter assay confirmed that this p53BS had p53-dependent transcriptional activity. Expression of endogenous hCDC4b, but not the alternative transcript of this gene, hCDC4a, was induced in a p53-dependent manner in response to genotoxic stresses caused by UV irradiation and adriamycin treatment, suggesting that each transcript has a different functional role. These results suggest that hCDC4b is a previously unrecognized transcriptional target of the p53 protein, and that by negatively regulating cyclin E through induction of hCDC4b, p53 might stop cell-cycle progression at G0-G1. This would represent a novel mechanism for p53-dependent control of the cell cycle, in addition to the well-known p21(WAF1) machinery.

Temporal alterations in cellular Bax:Bcl-2 ratio following traumatic brain injury in the rat

Cell death/survival following CNS injury may be a result of alterations in the intracellular ratio of death and survival factors. Using immunohistochemistry, Western analysis and in situ hybridization, the expression of the anti-cell death protein, Bcl-2, and the pro-cell death protein, Bax, was evaluated following lateral fluid-percussion (FP) brain injury of moderate severity (2.3-2.6 atm) in adult male Sprague-Dawley rats. By 2 h post-injury, a marked reduction of cellular Bcl-2-immunoreactivity (IR) and a mild decrease in cellular Bax IR were observed in the temporal and occipital cortices, and in the hippocampal CA3 ipsilateral to the site of impact. These decreases in Bcl-2 and Bax IR appeared to precede the overt cell loss in these regions that was evident at 24 h. Immunoblot analysis supported the immunohistochemical data, with a modest but significant reduction in the intensities of both the Bcl-2 and Bax protein bands at 2 h (p < 0.05 compared to sham levels). However, the Bax:Bcl-2 ratio increased significantly at 2 h (2.28 +/- 0.13) and remained elevated up to 7 days (2.05 +/- 0.13) post-injury compared to sham-injured control tissue (1.62 +/- 0.10, p < 0.05). Furthermore, cortical, but not hippocampal, levels of Bax protein increased by 25% (p < 0.05 compared to sham-injured controls) at 24 h post-injury, and returned to control levels by 7 days. In situ hybridization analysis of Bax mRNA revealed increased cellular grain density in the injured cortex (p < 0.05 compared to sham-injured brains), but not in the CA3 region of the injured hippocampus. No injury-induced changes in the expression of Bcl-2 mRNA were observed in any brain region. Taken together, these data suggest that the association between regional post-traumatic cell death and alterations in the cellular ratio of Bcl-2 and Bax may be, in part, due to alterations in mRNA and/or protein expression of the Bcl-2 family of proteins.

B lymphocytes in the normal brain: contrasts with HIV-associated lymphoid infiltrates and lymphomas

In recent years evidence has accumulated which suggests that the brain may not be the immunologically privileged site it was once considered to be. It is now widely accepted that T lymphocytes perform surveillance functions in normal brain parenchyma. However, as yet there are no reports of B lymphocytes entering brain parenchyma in the healthy state. This study aimed to determine first the prevalence of B lymphocytes in normal brain, and subsequently whether advancing HIV infection led to changes in the brain B lymphocyte population, which might contribute to the increased risk of lymphoma seen in AIDS. Our results show that B lymphocytes do enter all parts of the normal human brain in very low numbers and that the B lymphocytes within the brain parenchyma display an activated (CD23 positive) phenotype. In contrast, intravascular B lymphocytes have a much lower expression of activation markers. B lymphocytes were found in increased numbers in both the brain parenchyma and perivascular spaces of pre-AIDS brains. However, brains from the majority of AIDS subjects, including those with primary CNS lymphoma (PCNSL) (outside the area of neoplastic involvement) contained fewer B lymphocytes than normal or pre-symptomatic HIV-infected brains. A subset of AIDS brains, previously shown to have pleomorphic lymphoid infiltrates in the perivascular spaces, had significantly increased numbers of B lymphocytes in both the brain parenchyma and perivascular spaces. Virtually all AIDS-related PCNSL are known to be Epstein-Barr Virus (EBV) positive, in contrast to non-HIV PCNSL and non-CNS AIDS-related lymphomas. We examined the EBV status of brain parenchymal B lymphocytes to investigate whether EBV-positive B lymphocytes are more frequent in HIV-infected brains than normal, thus explaining the propensity for CNS lymphomas in AIDS. In situ hybridization studies showed EBV positivity only in AIDS-related PCNSL cases within the lymphoma deposits. PCR-based studies detected high EBV copy numbers in PCNSL tumour tissue, and low copy numbers in AIDS cases with pleomorphic lymphoid infiltrates. As none of the B lymphocytes in this latter group were EBV positive on in situ hybridization, bearing in mind that this appears to be a prerequisite for PCNSL development, we find no evidence that pleomorphic infiltrates represent a pre-malignant PCNSL state.

Bcl-2 controls caspase activation following a p53-dependent cyclin D1-induced death signal

MCF-7 and ZR-75 breast cancer cells infected with an adenovirus constitutively expressing high levels of cyclin D1 demonstrated widespread mitochondrial translocation of Bax and cytochrome c release that was approximately doubled after the addition of all-trans retinoic acid (RA) or Bcl-2 antisense oligonucleotide. By comparison, the percentage of cells in Lac Z virus-infected cultures containing translocated Bax and cytoplasmic cytochrome c was markedly less even after RA treatment. Despite this, RA-treated Lac Z and untreated cyclin D1 virus-infected cultures contained similarly low proportions of cells with active caspase or cells that were permeable to propidium iodide. Bax activation was p53-dependent and accompanied by arrest in G(2) phase. Although constitutive Bcl-2 expression prevented Bax activation, it did not alter cyclin D1-induced cell cycle arrest, illustrating the independence of these events. Both RA and antisense Bcl-2 oligonucleotide decreased Bcl-2 protein levels and markedly increased caspase activity and apoptosis in cyclin D1-infected cells. Thus amplified cyclin D1 expression initiates an apoptotic signal inhibited by different levels of cellular Bcl-2 at two points. Whereas high cellular levels of Bcl-2 prevent mitochondrial Bax translocation, lower levels can prevent apoptosis by inhibition of caspase activation.

Drosophila p53 preserves genomic stability by regulating cell death

When animal cells are exposed to stressful conditions, the tumor suppressor protein p53 restrains growth by promoting an arrested cell cycle or initiating a cell death program. How these distinct fates are specified through the action of a single protein is not known. To study its functions in vivo we produced a targeted mutation at the Drosophila p53 (Dmp53) locus. We show that Dmp53 is required for damage-induced apoptosis but not for cell-cycle arrest. Dmp53 function is also required for damage-induced transcription of two tightly linked cell death activators, reaper and sickle. When challenged by ionizing radiation, Dmp53 mutants exhibit radiosensitivity and genomic instability. Hence, elevated mutant loads were not caused by defective checkpoint functions but instead correlated with failures in p53-associated cell death. Our studies support the notion that core ancestral functions of the p53 gene family are intimately coupled to cell death as an adaptive response to maintain genomic stability.

The BZLF1 promoter of Epstein-Barr virus is controlled by E box-/HI-motif-binding factors during virus latency

The BZLF1 open reading frame of Epstein-Barr virus (EBV) encodes an important transactivator of replication. During latency, transcription of this gene is switched off. HI motifs have been shown to cause negative regulation of the promoter. Using yeast one-hybrid assays, we isolated the E box-binding protein, E2-2, interacting with these motifs. Electrophoretic mobility shift assays demonstrated that E2-2 binds to HI alpha, HI beta and HI gamma, which contain E box consensus binding sites. Deletion of the HI-associated E boxes and overexpression of E2-2 in transfection assays revealed that these elements act as repressors in lymphoid cells. In contrast, in epithelial cells they contribute to the increased responsiveness of the promoter to transactivation by the BZLF1 protein. The data presented are in accord with an alternative and exclusive binding of different cell type- and differentiation-specific factors, such as E2-2, to the HI-associated E boxes in lymphoid and epithelial cells. This implies a role in cell type-specific virus replication.

p53 triggers apoptosis in oncogene-expressing fibroblasts by the induction of Noxa and mitochondrial Bax translocation

The mechanism of p53-dependent apoptosis is still only partly defined. Using early-passage embryonic fibroblasts (MEF) from wild-type (wt), p53(-/-) and bax(-/-) mice, we observe a p53-dependent translocation of Bax to the mitochondria and a release of mitochondrial Cytochrome c during stress-induced apoptosis. These events proceed independent of zVAD-inhibitable caspase activation, are not prevented by dominant negative FADD (DN-FADD), but are negatively regulated by Mdm-2. Bcl-x(L) expression prevents the release of mitochondrial Cytochrome c and apoptosis, but not Bax translocation. At a single-cell level, enforced expression of p53 is sufficient to induce Bax translocation and Cytochrome c release. Real-time RT-PCR analysis reveals a significant induction of RNA expression of Noxa and Bax in p53(+/+), but not in p53(-/-) MEF. Noxa protein expression becomes detectable prior to Bax translocation, and downregulation of endogenous Noxa by RNA interference protects wt MEF against p53-dependent apoptosis. Hence, in oncogene-expressing MEF p53 induces apoptosis by BH3 protein-dependent caspase activation.

Combined p53/Bax mutation results in extremely poor prognosis in gastric carcinoma with low microsatellite instability

Gastric cancer is highly refractory to DNA-damaging therapies. We therefore studied both gene mutation and protein expression of p53 and Bax in a cohort of 116 patients with gastric cancer who underwent R0-resection with a curative intent. Bax mutation was independent from severe microsatellite instability (MSI), that is, global mismatch repair deficiency as determined by analysis of BAT-25/BAT-26 microsatellite markers. Thus, Bax-frameshift mutation is a feature of tumors with low MSI. In contrast and as expected, no p53 mutations were observed in the microsatellite instable tumors. p53 Mutation or p53 overexpression did not have an impact on disease prognosis. p53-Inactivation was, however, associated with an extremely poor prognosis in the subgroup of patients with Bax-mutated tumors. Thus, we show for the first time that the combined mutation of p53 and Bax, two key regulators of the mitochondrial apoptosis pathway, results in an extremely aggressive tumor biology and poor clinical prognosis.

Evaluation of clinical significance of TP53, BCL-2, BAX and MEK1 expression in 229 ovarian carcinomas treated with platinum-based regimen

In cell line studies, BCL-2, BAX, as well as novel MEK1 protein levels have strong influence on ovarian cancer response to cisplatin-based chemotherapy. However, such associations have not been demonstrated clinically. We evaluated prognostic/predictive significance of these proteins with regard to TP53 status. Immunohistochemical analysis was performed on 229 ovarian carcinomas FIGO stage IIB-IV treated with platinum-based chemotherapy; the results were analysed by the Cox and logistic regression models. Clinical parameters (residual tumour size, patient age, FIGO stage) were the only indicators of overall survival (OS) and the strongest predictors of complete remission (CR). On the other hand, BAX expression was the strongest (P=0.005) or the only (in FIGO IIIC, P=0.02) prognostic indicator of disease-free survival (DFS) in the TP53(+) group. TP53(+) and TP53(-) ovarian carcinomas differed in clinical and molecular prognostic and predictive factors. Another novel finding is that CR was negatively influenced by high BAX expression in all patients group (P=0.047) and by BCL2 expression in the TP53(-) group (P=0.05). High MEK1 expression was associated with endometrioid and clear cell carcinomas (P=0.049); its loss was found with advancing FIGO stage (P=0.002). Our results suggest that binomial TP53 status divides ovarian carcinomas into two biologically distinct groups. BAX expression is an important factor of DFS in the TP53(+) group. BCL-2 and BAX, but not MEK1 expressions have predictive value in ovarian cancer patients treated with platinum-based chemotherapy.

Early growth response 1 protein, an upstream gatekeeper of the p53 tumor suppressor, controls replicative senescence

The proliferation of most primary cells in culture is limited by replicative senescence and crisis, p53-dependent events. However, the regulation of p53 itself has not been defined. We find that deletion of the early growth response 1 (EGR1) transcription factor leads to a striking phenotype, including complete bypass of senescence and apparent immortal growth consistent with loss of a suppressor gene. EGR1-null mouse embryo fibroblasts (MEFs) exhibit decreased expression of p53, p21(Cip1/Waf1), and other p53 "marker" proteins. Precrisis WT but not EGR1-null cells exhibit irradiation-induced arrest. WT MEFs that emerge from crisis exhibit a mutated p53 (sequence confirmed), colony formation, and tumorigenicity. In contrast, high-passage EGR1-null MEFs retain the WT p53 sequence but with much reduced expression, remain untransformed, and grow continuously. An EGR1-expressing retrovirus restores p53 expression and sencescence to EGR1-null but not p53-null MEFs or postcrisis WT cells. Taken together, the results establish EGR1 as a major regulator of cell senescence and previously undescribed upstream "gatekeeper" of the p53 tumor suppressor pathway.

Hypoxic neuronal necrosis: protein synthesis-independent activation of a cell death program

Hypoxic necrosis of dentate gyrus neurons in primary culture required the activation of an orderly cell death program independent of protein synthesis. Early mitochondrial swelling and loss of the mitochondrial membrane potential were accompanied by release of cytochrome c and followed by caspase-9-dependent activation of caspase-3. Caspase-3 and -9 inhibitors reduced neuronal necrosis. Calcium directly induced cytochrome c release from isolated mitochondria. Hypoxic neuronal necrosis may be an active process in which the direct effect of hypoxia on mitochondria may lead to the final common pathway of caspase-3-mediated neuronal death.

The p53-inducible TSAP6 gene product regulates apoptosis and the cell cycle and interacts with Nix and the Myt1 kinase

The p53 tumor suppressor protein plays a crucial role in tumorigenesis by controlling cell-cycle progression and apoptosis. We have previously described a transcript designated tumor suppressor activated pathway-6 (TSAP6) that is up-regulated in the p53-inducible cell line, LTR6. Cloning of the murine and human full-length TSAP6 cDNA revealed that it encodes a 488-aa protein with five to six transmembrane domains. This gene is the murine and human homologue of the recently published rat pHyde. Antibodies raised against murine and human TSAP6 recognize a 50- to 55-kDa band induced by p53. Analysis of the TSAP6 promoter identified a functional p53-responsive element. Functional studies demonstrated that TSAP6 antisense cDNA diminished levels of the 50- to 55-kDa protein and decreased significantly the levels of p53-induced apoptosis. Furthermore, TSAP6 small interfering RNA inhibited apoptosis in TSAP6-overexpressing cells. Yeast two-hybrid analysis followed by GST/in vitro-transcribed/translated pull-down assays and in vivo coimmunoprecipitations revealed that TSAP6 associated with Nix, a proapoptotic Bcl-2-related protein and the Myt1 kinase, a negative regulator of the G(2)/M transition. Moreover, TSAP6 enhanced the susceptibility of cells to apoptosis and cooperated with Nix to exacerbate this effect. Cell-cycle studies indicated that TSAP6 could augment Myt1 activity. Overall, these data suggest that TSAP6 may act downstream to p53 to interface apoptosis and cell-cycle progression.

Assessment of p53 gene transfer and biological activities in a clinical study of adenovirus-p53 gene therapy for recurrent ovarian cancer

A cohort study was designed to evaluate the efficiency of gene transfer and whether biological activity from the expressed therapeutic gene resulted after administration of a recombinant adenovirus containing the human wild-type p53 (p53(wt)) gene (rAd-p53 SCH 58500). The cohort study was conducted in five trial subjects with recurrent ovarian cancer. Each trial subject received multiple cycles of rAd-p53 SCH 58500, each cycle comprised of doses of 7.5 x 10(13) particles on each of five consecutive days. Subjects were treated with rAd-p53 SCH 58500 alone during Cycle 1 and in combination with gemcitabine during the subsequent cycles. Both tumor biopsies and peritoneal aspirates were collected and evaluated for gene transfer and evidence of the biological activities of the expressed p53(wt) gene. Using quantitative PCR and RT-PCR, and in situ PCR, gene transfer and expression were documented in tumor biopsies (four of five patients) collected from Cycle 1. Furthermore, upregulation of p21/WAF1, bax and mdm-2, and downregulation of survivin were observed in these same tumor biopsy samples, suggesting that intraperitoneal administration of rAd-p53 SCH 58500 leads to detectable p53 biological activity in target tumor tissue. In addition, gene transfer and its expression were observed in cells obtained from peritoneal aspirates. These fluids were mainly comprised of polymorphonuclear neutrophils, indicating that successful gene transfer can be achieved by multiple cycle intraperitoneal administration of recombinant adenovirus.

p53RDL1 regulates p53-dependent apoptosis

Although a number of targets for p53 have been reported, the mechanism of p53-dependent apoptosis still remains to be elucidated. Here we report a new p53 target-gene, designated p53RDL1 (p53-regulated receptor for death and life; also termed UNC5B). The p53RDL1 gene product contains a cytoplasmic carboxy-terminal death domain that is highly homologous to rat Unc5H2, a dependence receptor involved in the regulation of apoptosis, as well as in axon guidance and migration of neural cells. We found that p53RDL1 mediated p53-dependent apoptosis. Conversely, when p53RDL1 interacted with its ligand, Netrin-1, p53-dependent apoptosis was blocked. Therefore, p53RDL1 seems to be a previously un-recognized target of p53 that may define a new pathway for p53-dependent apoptosis. We suggest that p53 might regulate the survival of damaged cells by balancing the regulation of Netrin-p53RDL1 signalling, and cell death through cleavage of p53RDL1 for apoptosis.

Epstein-Barr virus-recent advances

Epstein-Barr virus is a tumorigenic herpes virus that is ubiquitous in the adult population. The virus is generally spread to and between young children through salivary contact, and only causes clinical illness where primary infection is delayed until adolescence or beyond, when an intense immunopathological reaction leads to the symptoms of infectious mononucleosis in roughly 50% of cases. More than 90% of the world's population carry Epstein-Barr virus as a life-long, latent infection of B lymphocytes. Recent data show that by mimicking B-cell antigen-activation pathways the virus enters the long-lived memory B lymphocyte pool where it evades immune elimination by severely restricting its own gene expression. By influencing B-cell survival mechanisms Epstein-Barr virus may induce tumours such as B lymphoproliferative disease and Hodgkin's disease. Vaccines are being developed to prevent and/or treat these conditions, but an animal model is required to study pathogenesis before a rational vaccine strategy can be formulated.

Activated protein C blocks p53-mediated apoptosis in ischemic human brain endothelium and is neuroprotective

Activated protein C (APC) is a systemic anti-coagulant and anti-inflammatory factor. It reduces organ damage in animal models of sepsis, ischemic injury and stroke and substantially reduces mortality in patients with severe sepsis. It was not known whether APC acts as a direct cell survival factor or whether its neuroprotective effect is secondary to its anti-coagulant and anti-inflammatory effects. We report that APC directly prevents apoptosis in hypoxic human brain endothelium through transcriptionally dependent inhibition of tumor suppressor protein p53, normalization of the pro-apoptotic Bax/Bcl-2 ratio and reduction of caspase-3 signaling. These mechanisms are distinct from those involving upregulation of the genes encoding the anti-apoptotic Bcl-2 homolog A1 and inhibitor of apoptosis protein-1 (IAP-1) by APC in umbilical vein endothelial cells. Cytoprotection of brain endothelium by APC in vitro required endothelial protein C receptor (EPCR) and protease-activated receptor-1 (PAR-1), as did its in vivo neuroprotective activity in a stroke model of mice with a severe deficiency of EPCR. This is consistent with work showing the direct effects of APC on cultured cells via EPCR and PAR-1 (ref. 9). Moreover, the in vivo neuroprotective effects of low-dose mouse APC seemed to be independent of its anti-coagulant activity. Thus, APC protects the brain from ischemic injury by acting directly on brain cells.

Replicative senescence of activated human hepatic stellate cells is accompanied by a pronounced inflammatory but less fibrogenic phenotype

Limited proliferative capacity is a characteristic of most normal human cells and results in a growth-arrested state, called replicative senescence. Functional expression of the telomerase catalytic subunit (human telomerase reverse transcriptase; hTERT) in human activated hepatic stellate cells (HSCs) rescues them from death with immortalization and maintains an activated HSC phenotype. The aim of this study was to evaluate alterations in gene and protein expression of in vitro aged human activated HSCs and to define the pathway by which senescent-activated HSCs are eliminated in culture. Altered patterns of gene expression in senescent human HSCs were assessed using DNA microarray analysis and compared with early passage HSCs or hTERT immortalized HSCs. Senescent HSCs showed higher expression of inflammation and stress-associated genes as compared with early passage HSCs. Senescent HSCs expressed reduced levels of extracellular matrix proteins, including collagens, tenascin, and fibronectin. TUNEL staining of senescent HSCs showed approximately 21% positive cells, indicating DNA fragmentation and apoptosis. Apoptosis involved the mitochondrial pathway with decreased levels of Bcl-2 and Bcl-x(L) protein, release of cytochrome c, and increased caspase-3 activity. In contrast, 4% to 5% of early activated HSCs or telomerase positive HSCs were TUNEL positive. In conclusion, cultured human HSCs undergo a switch from a fibrogenic to an inflammatory phenotype, suggesting that senescent human HSCs might modulate chronic wound healing processes. Maintenance of telomere length represents an important survival factor for activated human HSCs.

Catalase protects HepG2 cells from apoptosis induced by DNA-damaging agents by accelerating the degradation of p53

Oxidants such as H(2)O(2) play a role in the toxicity of certain DNA-damaging agents, a process that often involves the tumor suppressor p53. H(2)O(2) is rapidly degraded by catalase, which protects cells against oxidant injury. To study the effect of catalase on apoptosis induced by DNA-damaging agents, HepG2 cells were infected with adenovirus containing the cDNA of catalase (Ad-Cat). Forty-eight hours after infection, catalase protein and activity was increased 7-10-fold compared with control cells infected with Ad-LacZ. After treatment with Vp16 or mitomycin C, control cells underwent apoptosis in a p53-dependent manner; however, overexpression of catalase inhibited this apoptosis. Basal levels as well as Vp16- or mitomycin C-stimulated levels of p53 and p21 protein were decreased in the catalase-overexpressing cells as compared with control cells; however, p53 mRNA levels were not decreased by catalase. There was no difference in p53 protein synthesis between catalase-overexpressing cells and control cells. However, pulse-chase experiments indicated that p53 protein degradation was enhanced in the catalase-overexpressing cells. Proteasome inhibitors but not calpeptin prevented the catalase-mediated decrease of p53 content. Whereas Vp16 increased, catalase overexpression decreased the phosphorylation of p53. The protein phosphatase inhibitor okadaic acid did not prevent the catalase-mediated down-regulation of p53 or phosphorylated p53. These results demonstrate that catalase protects HepG2 cells from apoptosis induced by DNA-damaging agents in association with decreasing p53 phosphorylation; the latter may lead to an acceleration in the degradation of p53 protein by the proteasome complex. This suggests that the level of catalase may play a critical role in cell-induced resistance to the effects of anti-cancer drugs which up-regulate p53.

H9c2 cardiac myoblasts undergo apoptosis in a model of ischemia consisting of serum deprivation and hypoxia: inhibition by PMA

Cardiac myocytes undergo apoptosis under condition of ischemia. Little is known, however, about the molecular pathways that mediate this response. We show that serum deprivation and hypoxia, components of ischemia in vivo, resulted in apoptosis of rat ventricular myoblast cells H9c2. Hypoxia alone did not induce significant apoptosis for at least 48 h, but largely increased the proapoptotic action of serum deprivation. H9c2 cells apoptosis is evidenced by an increase in terminal (TdT)-mediated dUTP nick end-labeling-positive nuclei and by activation of caspases 3, 6, 7 and 9, and loss of mitochondrial functions. In this model of simulated ischemia, represented by serum deprivation plus hypoxia, cardiomyoblasts apoptosis was associated with a p53-independent Bax accumulation and with a down-regulation of Bcl-xL, whereas the levels of cIAP-1, cIAP-2 and X-IAP proteins did not change. Phorbol-12-myristate-13-acetate significantly reduced the induction of apoptosis, inhibiting caspase 3 cleavage, Bax accumulation, Bcl-xL down-regulation as well as restoring cell viability.

Diverse p53 alterations in ulcerative colitis-associated low-grade dysplasia: full-length gene sequencing in microdissected single crypts

In long-standing ulcerative colitis (UC), p53 mutations have been shown to occur by indirect detection methods such as PCR-SSCP. To clarify whether p53 gene mutations are early events in UC-associated neoplasia and to analyse clonality within dysplasia-associated lesions or masses (DALMs), the entire coding region of the p53 gene was analysed in DNA of microdissected single crypts by the polymerase chain reaction (PCR)-direct sequencing method. With a novel microdissection method using serial histological sections, the p53 gene (exons 2-11) was analysed in a total of 11 regenerative crypts and 76 single crypts within seven DALMs selected from three colectomy specimens of long-standing UC patients. Although p53 point mutations were found in at least one crypt in each DALM, heterogeneity in terms of the presence and the type of genetic change was marked, except in one carcinoma. As early events, p53 gene mutations were apparent even in some regenerative crypts (8/12 crypts). Some were of silent type. Altered p53 protein expression was confirmed in only 14/32 mutated crypts and was also evident in 24 other non-mutated examples by immunostaining of serial sections. Polyclonal p53 gene mutations were found in regenerative (REG) crypts and low-grade dysplasia (LGD), but monoclonal changes were noted in high-grade dysplasia (HGD) or carcinoma (Ca) in long-standing UC. At the single crypt level, however, p53 point mutations were not always linked to p53 overexpression, indicating a discrepancy between gene alteration and protein accumulation in LGD.

Apoptosis or growth arrest: modulation of the cellular response to p53 by proliferative signals

Activation of the tumor suppressor p53 after genotoxic insults may result in two different responses: growth arrest or apoptosis. In this study, we analysed how mitogenic stimulation of primary mouse lymphocytes influences p53 signaling upon gamma-irradiation. We found that G(0) lymphocytes rapidly went into p53-dependent apoptosis, whereas stimulated lymphocytes went into a p53-dependent, p21-mediated growth arrest. The switch in p53 response upon stimulation did neither result from a switch in transcriptional activation of major p53 target genes, nor from the high level of p21 expressed in stimulated, irradiated cells. Growth stimulation, however, led to the upregulation of the antiapoptotic factors Bcl-x(L) and Bfl-1. In resting cells, p53 induced apoptosis after gamma-irradiation was accompanied by a breakdown of the mitochondrial membrane potential (psi(m)) that was counteracted by growth stimulation. We propose that growth stimulation intercepted p53 proapoptotic signaling at the level of mitochondrial integrity, most likely by upregulating the antiapoptotic factors Bcl-x(L) and Bfl-1. Upregulation of Bcl-x(L) and of Bfl-1 upon growth stimulation was mediated by the PKC-dependent activation of NF-kappaB. Consequently, blocking PKC activity restored apoptosis in stimulated, irradiated splenocytes. The inherent coupling of growth stimulation with antiapoptotic signaling in primary lymphocytes might provide hints as to how precancerous lymphocytes bypass the need for mutational inactivation of p53. Thus, our findings might explain the relatively low frequency of p53 mutations in lymphomas in comparison to other tumor entities.

A novel PHD-finger motif protein, p47ING3, modulates p53-mediated transcription, cell cycle control, and apoptosis

A candidate tumor suppressor gene, p33ING1, was previously identified by using the genetic suppressor element methodology. p33ING1 cooperates with p53 and plays a significant role in p53-mediated cellular processes. Recently, we have identified p33ING2, which shows a sequence homology similar to p33ING1 and modulates p53 function. In the present study, we identified and characterized another 'ING family' gene. The estimated molecular weight of the encoded protein is 46.8 kDa, thus, we named it p47ING3. The p47ING3 gene is located at chromosome 7q31.3 and consists of 12 exons that encode 418 amino acids. A computational domain search revealed a C-terminal PHD-finger motif. Such motifs are common in proteins involved in chromatin remodeling. p47ING3 is highly expressed in some normal human tissues or organs, including the spleen, testis, skeletal muscle, and heart. p47ING3 expression levels varied among cancer cell lines. p47ING3 overexpression resulted in a decreased population of cells in S phase, a diminished colony-forming efficiency, and induced apoptosis in RKO cells, but not in RKO-E6 cells with inactivated p53. p47ING3 activates p53-transactivated promoters, including promoters of p21/waf1 and bax. Thus, we have isolated a novel ING family gene, p47ING3, which modulates p53-mediated transcription, cell cycle control, and apoptosis.

Beta2-microglobulin induces caspase-dependent apoptosis in the CCRF-HSB-2 human leukemia cell line independently of the caspase-3, -8 and -9 pathways but through increased reactive oxygen species

Exogenous beta(2)-microglobulin (beta(2)m) induces significant apoptosis in the CCRF-HSB-2 human lymphoblastic leukemia cell line as detected by DNA fragmentation, DAPI staining and annexin V binding assay. beta(2)m treatment induced the release of cytochrome c and apoptosis-inducing factor (AIF) from the mitochondria, but no change in mitochondrial membrane potential (DeltaPsim) was observed during apoptosis, suggesting that cytochrome c may be released through a mechanism independent of mitochondrial permeability transition (MPT) pore formation. Moreover, the beta(2)m-induced release of cytochrome c and AIF from the mitochondria in CCRF-HSB-2 cells was caspase-independent, since Z-VAD-fmk, a general inhibitor of caspases, did not block the release of these factors. However, Z-VAD-fmk treatment significantly blocked beta(2)m-induced apoptosis, while Western blot analysis revealed that caspases-1, -2, -3, -6, -7, -8 and -9 are not activated during beta(2)m-induced apoptosis in these cells. These results collectively indicate that a post-mitochondrial caspase-dependent mechanism is involved in beta(2)m-induced apoptosis. Moreover, beta(2)m significantly enhanced the production of reactive oxygen species (ROS) during 12-48 hr treatment, and beta(2)m-induced apoptosis was almost totally inhibited in cells pre-treated with the antioxidant N-acetylcysteine (NAC), providing evidence that beta(2)m-induced apoptosis in CCRF-HSB-2 cells is ROS-dependent. Therefore, these results reveal that beta(2)m-induced apoptosis in CCRF-HSB-2 cells may occur through an unknown caspase-dependent and ROS-dependent mechanism(s) that is associated with cytochrome c and AIF release from mitochondria, but is independent of the caspase -3, -8 and -9 pathways.

Adenoviral vector-mediated mRTVP-1 gene therapy for prostate cancer

We previously identified the mouse RTVP-1 (mRTVP-1; related to testes-specific, vespid, and pathogenesis proteins) gene as a direct target of p53 with proapoptotic activities in various cancer cell lines, including prostate cancer. To test the therapeutic potential of mRTVP-1 we constructed an adenoviral vector capable of efficient transduction and expression of mRTVP-1 (AdmRTVP-1) and used this vector in an orthotopic, metastatic mouse model of prostate cancer. A single intratumoral administration of AdmRTVP-1 gene therapy significantly reduced primary tumor wet weight compared with control Adbetagal-injected tumors at two time points after injection with two different vector doses (p < or = 0.01 at 7 and 14 days). Spontaneous metastasis to lung was also significantly reduced (p < or = 0.02). Evaluation of treated tumors revealed increased apoptosis and lower microvessel density counts. In a rat aortic ring sprouting assay, AdmRTVP-1 inhibited endothelial cell sprouting compared with Adbetagal, confirming its antiangiogenic activity. These therapeutic activities were associated with a significant increase in survival from 22.9 to 26.8 days (p = 0.003) in this aggressive model of prostate cancer. Interestingly, there were significant increases in the infiltration of tumor-associated macrophages, dendritic cells, and CD8+ T cells, which persisted at 14 days posttreatment in the AdmRTVP-1-treated tumors compared with Adbetagal control-treated tumors. In addition, significantly increased natural killer and cytotoxic T lymphocyte activities were demonstrated in the mice with AdmRTVP-1-treated tumors. The unique therapeutic properties of AdmRTVP-1 gene therapy demonstrated in this study provide new opportunities for gene and immunotherapy of prostate cancer and potentially other malignancies.

Testicular germ-cell apoptosis in stressed rats following combined exposure to pyridostigmine bromide, N,N-diethyl m-toluamide (DEET), and permethrin

This study reports and characterizes the testicular apoptosis following daily exposure of male Sprague-Dawley rats to subchronic combined doses of pyridostigmine bromide (PB, 1.3 mg/kg/d in water, oral), a drug used for treatment of myasthenia gravis and prophylactic treatment against nerve agents during the Persian Gulf War; the insect repellent N,N-diethyl m-toluamide (DEET, 40 mg/kg/d in ethanol, dermal); and the insecticide permethrin (0.13 mg/kg in ethanol, dermal), with and without stress for 28 d. Combined exposure to these chemicals was implicated in the development of illnesses including genitourinary disorders among many veterans of the Persian Gulf War. Previous studies from this laboratory have shown that exposure to combination of these chemicals produced greater toxicity compared to single components. Exposure to stress alone did not cause any significant histopathological alterations in the testes. Administration of combination of these chemicals induced apoptosis in rat testicular germ cells, Sertoli cells, and Leydig cells, as well as in the endothelial lining of the blood vessels. Testicular damage was significantly augmented when the animals were further exposed to a combination of chemicals and stress. Histopathological examination of testicular tissue sections showed that apoptosis was confined to the basal germ cells and spermatocytes, indicating suppression of spermatogenesis. Increased apoptosis of testicular cells coincided, in timing and localization, with increased expression of the apoptosis-promoting proteins Bax and p53. Furthermore, significant increase of 3-nitrotyrosine immunostaining in the testis revealed oxidative and/or nitrosation induction of cell death. In conclusion, combined exposure to real-life doses of test compounds caused germ-cell apoptosis that was significantly enhanced by stress.

Inducing cancer cell death by targeting transcription factors

We review the biological significance of transcription factors such as p53, Myc, E2F family and AP-1 (Jun/Fos) in anticancer drug-induced apoptosis. It is likely that the functional role of these transcription factors is complex in response to DNA damage depending on cancer cell type. Regulation of apoptosis following DNA damage is mediated by cell cycle arrest for DNA repair and subsequent signal transduction pathways leading to apoptosis, which is associated with mitochondrial dysfunction. Activation of transcription factors following anticancer drugs is located upstream of signal transduction pathways, thereby the downstream pathway is promoted, which is connected to activation or suppression of apoptosis-related proteins. Switching on apoptotic signals by anticancer drugs is amplified in mitochondria by releasing cytochrome from the ion channel to activate the caspase cascade, which is regulated by Bcl-2 families in the central gate for drug-induced apoptosis. Activation of transcription factors targeting downstream genes, some of which are apoptosis-related genes, can play a critical role in promoting apoptosis following treatment with anticancer drugs. The strategy of identification of downstream target proteins or transcription factors involved in apoptosis will be necessary for the development of an effective transcription factor-targeted chemotherapy for cancer.

Pathogenic roles for Epstein-Barr virus (EBV) gene products in EBV-associated proliferative disorders

Epstein-Barr virus (EBV) is associated with a still growing spectrum of clinical disorders, ranging from acute and chronic inflammatory diseases to lymphoid and epithelial malignancies. Based on a combination of in vitro and in vivo findings, EBV is thought to contribute in the pathogenesis of these diseases. The different EBV gene expression patterns in the various disorders, suggest different EBV-mediated pathogenic mechanisms. In the following pages, an overview of the biology of EBV-infection is given and functional aspects of EBV-proteins are discussed and their putative role in the various EBV-associated disorders is described. EBV gene expression patterns and possible pathogenic mechanisms are discussed. In addition, expression of the cellular genes upregulated by EBV in vitro is discussed, and a comparison with the in vivo situation is made.

Functional interaction of nuclear factor y and sp1 is required for activation of the epstein-barr virus C promoter

Two Epstein-Barr virus (EBV) latent cycle promoters, Wp and Cp, are activated sequentially during virus-induced transformation of primary B lymphocytes. Immediately postinfection, viral transcription initiates from Wp, leading to expression of EBV nuclear antigen 2 (EBNA2) and EBNA5. Within 36 h, there is a switch in promoter usage from Wp to the upstream Cp, which leads to expression of EBNA1 to EBNA6. EBNA2 appears to be required for the Wp-to-Cp switch, but the switching mechanism is not fully understood at the molecular level. In a previous investigation we showed that there is an EBNA2-independent activity of reporter constructs containing deletion fragments of Cp in B-lymphoid cell lines, and we demonstrated that Cp activity is highly dependent on several cellular transcription factors, including nuclear factor Y (NF-Y) and Sp1. In the present work, we analyzed the effect of NF-Y on Cp activity in greater detail. We demonstrate that (i) a dominant negative analogue of NF-Y abolishes Cp activity, (ii) NF-Y and Sp1 costimulate Cp, and (iii) the oriPI-EBNA1-induced transactivation of Cp requires concomitant expression of NF-Y and Sp1, although additional factors seem necessary for optimal activation. Furthermore, using the lymphoblastoid cell line EREB2-5, in which EBNA2 function is regulated by estrogen, we demonstrate that inactivation of EBNA2 results in decreased expression of NF-Y and down-regulation of Cp. On reconstitution of the EBNA2 function, the cells enter the cell cycle, NF-Y levels increase, and a concomitant Wp-to-Cp switch occurs. Taken together, our results suggest that NF-Y is essential for Cp activation and that up-regulation of NF-Y may contribute to a successful Wp-to-Cp switch during B-cell transformation.

Avoiding proteasomal processing: the case of EBNA1

Ubiquitin/proteasome-dependent proteolysis is involved in the regulation of a large variety of cellular processes including cell cycle progression, tissue development and atrophy, flux of substrates through metabolic pathways, selective elimination of abnormal proteins and processing of intracellular antigens for major histocompatibility complex (MHC) class I-restricted T-cell responses. Many viruses tamper with this proteolytic machinery by encoding proteins that interact with various components of the pathway. A particularly interesting example of a viral protein that interferes with proteasomal processing is the Epstein-Barr virus (EBV) nuclear antigen-1 (EBNA1). EBNA1 contains an internal repeat exclusively composed of glycines and alanines that inhibits in cis the presentation of MHC class I-restricted T-cell epitopes and prevents ubiquitin/proteasome-dependent proteolysis in vitro and in vivo. The glycine-alanine repeat acts as a transferable element on a variety of proteasomal substrates and may therefore provide a new approach to the modification of cellular proteins for therapeutic purposes.

8-Cl-cAMP affects glioma cell-cycle kinetics and selectively induces apoptosis

8-Chloro-cyclic-adenosine-3',5'-monophosphate (8-Cl-cAMP), a site-selective synthetic cyclic adenosine 3',5'-monophosphate (cAMP) analog exhibits growth inhibition in a broad spectrum of human cancer lines. However, detailed studies on the effects exerted by cAMP analogs on cell-cycle kinetics have been lacking. We have examined and compared the effect of 8-Cl-cAMP on cell-cycle kinetics in two human glioma cell lines, U87MG (p53wt) and U251MG (p53mt). A flow cytometric analysis of cell-cycle distribution as well as apoptosis evaluation were performed by univariate DNA analysis after 24-72 hr of treatment with 10-50 M concentrations of 8-Cl-cAMP. Longer incubation with 8-Cl-cAMP induced dose related accumulation of cells in S phase and a subsequent decrease in the proportion of cells in G0/G1 phase of cell cycle in both cell lines. Time-dependent suppression of cyclin B1 was detected in both glioma cell lines and could be associated with observed G2 delay. However, 8-aCl-cAMP selectively induced apoptotic cell death only in U87MG, but not in U251MG cells. Induction of apoptosis was revealed both by flow cytometry and apoptotic cell morphology. These results provide an insight into the mechanism of 8-aCl-cAMP action, suggesting that the disturbance of cell-cycle kinetics and induction of apoptosis might contribute to its growth-inhibitory effect on cancer cells.

Nuclear factor-kappaB, induced in human carcinoma cell line A2780 by the new anthracycline men 10755, is devoid of transcriptional activity

The new disaccharide anthracycline MEN 10755 induces activation of both NF-kappaB and p53 transcription factors in A2780 cells. Nevertheless, pharmacologic inhibition of NF-kappaB activation does not modify the sensitivity of A2780 cells to MEN 10755 treatment. To better characterize the role of NF-kappaB in MEN 10755-induced cytotoxicity, we analyzed the expression of a number of genes that are known to be regulated by NF-kappaB. None of these genes is modified by MEN 10755 treatment. On the contrary, our results suggest that the p53 DNA damage-responsive pathway is fully activated in A2780 cells, several genes controlled by p53 being up- or downregulated according to the described action of p53 on their promoters. Thus, in the A2780 cell line, the role of p53 in transducing the DNA-damage signal appears to be relevant, whereas NF-kappaB, although activated, appears to be nonfunctional. Other human carcinoma cell lines besides A2780 activate NF-kappaB DNA binding in response to MEN 10755 treatment, but again, this binding does not always lead to target gene activation. These results suggest that other factors, tumor type-specific and different from mere activation, could influence NF-kappaB transcriptional activity. Therefore, care should be taken when considering the pharmacologic inhibition of NF-kappaB as a means to improve anticancer therapy efficacy.

Corticosteroids: sculptors of the hippocampal formation

The influence of corticosteroids on hippocampus-dependent learning and memory processes is now indisputable. On the other hand, closer scrutiny of early studies together with interpretations from newer studies would suggest that the proposition that corticosteroid-induced hippocampal cell death accounts fully for the associated cognitive deficits is only partially correct. Firstly, it is now clear that a specific sub-population of hippocampal neurons, the granule cells of the dentate gyrus, is more sensitive to changes in the corticosteroid environment; this fact raises the interesting question of what might be the unique properties of granule cells that render them more vulnerable to these hormones, since virtually all hippocampal cells express corticosteroid receptors. Secondly, from a critical analysis of the available data, the picture that emerges is that corticosteroids, by acting through two distinct receptors, influence not only cell birth and death, but probably also cell differentiation. Mineralocorticoid receptor (MR) occupation appears to be essential for the survival of existing and newly generated granule neurons. In contrast, while glucocorticoid receptors (GR) can induce loss of neurons in the absence of MR activation, it appears that their occupation usually results in less drastic effects involving only dendritic atrophy and loss of synaptic contacts. This revised scheme of corticosteroid actions on hippocampal structure should explain earlier observations that many of the cognition- impairing effects of corticosteroids are reversible.

Apoptosis and growth arrest induced by platinum compounds in U2-OS cells reflect a specific DNA damage recognition associated with a different p53-mediated response

Mononuclear and multinuclear platinum complexes are known to induce distinct types of DNA lesions and exhibit different profiles of antitumor activity, in relation to p53 mutational status. In this study, we investigated the cellular effects of exposure to two platinum compounds (cisplatin and the multinuclear platinum complex BBR 3464), in the osteosarcoma cell line, U2-OS, carrying the wild-type p53 gene and capable of undergoing apoptosis or cell cycle arrest in response to diverse genotoxic stresses. In spite of the ability of both compounds to up-regulate p53 at cytotoxic concentrations, exposure to BBR 3464 resulted in cell cycle arrest but only cisplatin was capable of inducing significant levels of apoptosis and phosphorylation at the Ser15 residue of p53. The cisplatin-induced protein phosphorylation, not detectable in cells treated with BBR 3464, was associated with RPA phosphorylation, a specific up-regulation of Bax and down-regulation of p21(WAF1). Cells treated with BBR 3464 displayed a different cellular response with evidence of cytostasis associated with a high induction of p21(WAF1). The regulation of p21(WAF1) after cisplatin or BBR 3464 exposure required a p53 signal, as documented using stable transfectants expressing a dominant-negative form of p53 (175(his)). Taken together, these results indicate that cellular response to different genotoxic lesions (i.e. apoptosis or growth arrest) is associated with a specific recognition of DNA damage and a different p53-mediated signaling pathway. Multinuclear platinum complexes could be regarded as useful tools for investigating the p53-mediated process of cell cycle arrest in response to DNA damage.

Immunological aspects of Epstein-Barr virus infection

Epstein-Barr virus (EBV) is a member of ubiquitous gamma herpes viruses, which primarily induces acute infectious mononucleosis (IM) or subclinical infection in susceptible subjects. The host reactions account for the clinical manifestation of IM. This virus also contributes to the development of lymphoid or epithelial malignancies. The outgrowth of EBV-infected B-cells is first controlled by interferon (IFN)-gamma and natural killer (NK) cells, and later by EBV-specific cytotoxic T-lymphocytes (CTL). To overcome the host responses and establish the persistent infection, EBV conducts the protean strategies of immune evasion. Several EBV genes modulate apoptotic signals and cytokine balances to persist B-cell infection without insulting the host. Uncontrolled lymphoproliferation occurs as EBV(+) B-cell lymphoproliferative disease (LPD)/lymphoma in AIDS, posttransplant, or primary immunodeficiency diseases (PID). On the other hand, EBV(+) T/NK cells are involved in EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) or chronic active EBV infection (CAEBV) in children having no underlying immunodeficiencies, and at times lead to the clonal evolution of T/NK-cell LPD/lymphomas. Recent advance in molecular techniques has enabled us to analyze the clonality of EBV-infected lymphocytes and to quantify the gene expression of EBV and cytokines. Dominant autocrine loop of T helper (Th) 2 and Th1 may exert in EBV(+) B-LPD and T-LPD, respectively. Intensive studies on the immunological interface between effector components and EBV(+) target cells will provide more information on clarifying the pathogenesis of EBV-associated lymphoid malignancies, as well as on exploiting the therapeutic and preventive strategies for the formidable EBV-associated disease in childhood.

Nocodazole-induced p53-dependent c-Jun N-terminal kinase activation reduces apoptosis in human colon carcinoma HCT116 cells

Microtubule-interfering agents are widely used in cancer chemotherapy, and prognostic results vary significantly from tumor to tumor, depending on the p53 status. In preliminary experiments, we compared the expression and phosphorylation profiles of more than 100 protein kinases and protein phosphatases in human colorectal carcinoma cell line HCT116 between p53+/+ and p53-/- cells in response to short term nocodazole treatment through application of Kinetworks immunoblotting screens. Among the proteins tracked, the regulation of the phosphorylation of c-Jun N-terminal kinase (JNK)1/2 at Thr-183/Tyr-185 was the major difference between p53+/+ and p53-/- cells. With the loss of the p53 gene, the levels of phosphorylation of Ser-63 of c-Jun and Thr-183/Tyr-185 of JNK1/2 in p53-/- cells did not increase as markedly as in p53+/+ cells in response to a 1-h treatment with nocodazole or other microtubule-disrupting drugs such as vinblastine and colchicine. Similar observations were also made in MCF-7 and A549 tumor cells, which were rendered p53-deficient by E6 oncoprotein expression. However, arsenate-induced JNK activation in p53-/- cells was preserved. Inhibition of p53 expression by its antisense oligonucleotide also attenuated nocodazole-induced JNK activation in p53+/+ cells. Surprisingly, cotransfection of p53+/+ cells with dominant negative mutants of JNK isoforms and treatment of p53+/+ cells with the JNK inhibitor SP600125 actually further enhanced apoptosis in p53+/+ cells by up to 2-fold in response to nocodazole. These findings indicate that inhibition of p53-mediated JNK1/2 activity in certain tumor cells could serve to enhance the apoptosis-inducing actions of cancer chemotherapeutic agents that disrupt mitotic spindle function.

Modulation of caspase activation and p27(Kip1) degradation in the p53-induced apoptosis in IW32 erythroleukemia cells

To examine the p53-mediated biological activities and signalling pathways, we generated stable transfectants of the p53-null IW32 murine erythroleukemia cells expressing the temperature-sensitive p53 mutant DNA, tsp53(val135). Two clones with different levels of p53 protein expression were selected for further characterization. At permissive temperature, clone 1-5 cells differentiated along the erythroid pathway, and clone 3-2 cells that produced greater levels (3.5-fold) of p53 underwent apoptosis. Apoptosis of 3-2 cells was accompanied by mitochondrial cytochrome c release and caspase activation as well as by cleavage of caspase substrates. Bax protein was induced to a similar extent in these clones by wild-type p53; expression of p21(Cip1/Waf1) and p27(Kip1) proteins was also increased. However, significantly lesser extent of induction for both CDK inhibitors was detected in the apoptotic 3-2 clone. The general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD.fmk) blocked the p53-induced apoptosis in 3-2 cells, with a concomitant elevation of p27(Kip1), suggesting that p27(Kip1) protein underwent caspase-dependent proteolysis in the apoptotic 3-2 cells. Together these results linked a pathway involving cytochrome c release, caspase activation and p27(Kip1) degradation to the p53-induced apoptosis in IW32 erythroleukemia cells.

To kill or be killed: viral evasion of apoptosis

In the struggle between virus and host, control over the cell's death machinery is crucial for survival. Viruses are obligatory intracellular parasites and, as such, must modulate apoptotic pathways to control the lifespan of their host in order to complete their replication cycle. Many of the counter-assaults mounted by the immune system incorporate activation of the apoptotic pathway-particularly by members of the tumor necrosis factor cytokine family-as a mechanism to restrict viral replication. Thus, apoptosis serves as a powerful selective pressure for the virus to evade. However, for the host, success is harsh and potentially costly, as apoptosis often contributes to pathogenesis. Here we examine some of the molecular mechanisms by which viruses manipulate the apoptotic machinery to their advantage and how we (as vertebrates) have evolved and learned to cope with viral evasion.

BID regulation by p53 contributes to chemosensitivity

The role of the p53 protein (encoded by TP53) in tumour suppression relies partly on the ability of p53 to regulate the transcription of genes that are important in cell-cycle arrest and in apoptosis. But the apoptotic pathway mediated by p53 is not fully understood. Here we show that BID, a member of the pro-apoptotic Bcl-2 family of proteins, is regulated by p53. BID mRNA is increased in a p53-dependent manner in vitro and in vivo, with strong expression in the splenic red pulp and colonic epithelium of gamma-irradiated mice. Both the human and the mouse BID genomic loci contain p53-binding DNA response elements that bind p53 and mediate p53-dependent transactivation of a reporter gene. In addition, BID-null mouse embryonic fibroblasts are more resistant than are wild-type fibroblasts to the DNA damaging agent adriamycin and the nucleotide analogue 5-fluorouracil, both of which stabilize endogenous p53. Our results indicate that BID is a p53-responsive 'chemosensitivity gene' that may enhance the cell death response to chemotherapy.

Bacterial redox protein azurin, tumor suppressor protein p53, and regression of cancer

The use of live bacteria in the treatment of cancer has a long and interesting history. We report the use of a purified bacterial redox protein, azurin, that enters human cancer (melanoma UISO-Mel-2) cells and induces apoptosis. The induction of apoptosis occurs readily in melanoma cells harboring a functional tumor suppressor protein p53, but much less efficiently in p53-null mutant melanoma (UISO-Mel-6) cells. A redox-negative mutant form of azurin (M44K/M64E) demonstrates much less cytotoxicity to the UISO-Mel-2 cells than the wild-type protein. Azurin has been shown to be internalized in UISO-Mel-2 cells and is localized predominantly in the cytosol and in the nuclear fraction. In the p53-null UISO-Mel-6 cells, azurin is localized only in the cytosol. Thus, intracellular trafficking of azurin to the nucleus is p53-dependent. Azurin forms a complex with p53, thereby stabilizing it and raising its intracellular level in cytosolic, mitochondrial, and nuclear fractions. Corresponding to an increasing level of p53, an inducer of apoptosis, the level of Bax also increases in mitochondria, allowing significant release of mitochondrial cytochrome c into the cytosol, thus initiating the onset of apoptosis. The M44K/M64E mutant form of azurin, deficient in cytotoxicity, is also deficient in forming a complex with p53 and is less efficient in stabilizing p53 than wild-type azurin. Azurin has been shown to allow regression of human UISO-Mel-2 tumors xenotransplanted in nude mice and may potentially be used in cancer treatment.

Specific interaction of p53 with target binding sites is determined by DNA conformation and is regulated by the C-terminal domain

Transcriptional activation of p53-regulated genes is initiated by sequence-specific DNA binding of p53 to target binding sites. Regulation of sequence-specific DNA binding is complex and occurs at various levels. We demonstrate that DNA topology is an important parameter for regulating the selective and highly specific interaction of p53 with its target binding sites. Specific binding of wild-type p53 is greatly enhanced when cognate binding sites are present in a non-linear stem-loop conformation. The C-terminal domain plays a key role in regulating the specific interactions of p53 with target binding sites in a DNA conformation-dependent manner. The C-terminal domain is required for binding to target sites in a non-linear DNA conformation in contrast to the strong inhibitory effects of the C terminus on p53 interaction with linear DNA. We propose that selective binding of p53 to various promoters may be determined by the DNA conformation within p53 cognate sites.

Molecular mechanisms of pre-T cell receptor-induced survival

En route to maturing as T cell receptor (TCR) alphabeta-expressing cells, the development of thymocytes is contingent on expression of a pre-TCR complex comprising a TCRbeta chain paired with a surrogate TCRalpha chain, pre-Talpha (pTalpha). The pre-TCR has been proposed to promote cell survival, proliferation, differentiation, and lineage commitment. However, the precise molecular mechanisms governing this variety of effects remain elusive. Here, we present a cellular system designed to biochemically dissect signals elicited upon pre-TCR expression. Using the T cell line 4G4 stably transfected with one of the two known pTalpha isoforms or selective pTalpha deletion mutants and TCRbeta, we were able to observe that expression of a functional pre-TCR complex is sufficient to control the levels of surface Fas protein, the stimulation of mitogen-activated and stress-regulated kinases, and the activation status of the p53 antioncogene. We demonstrate that this regulation has a major impact on the expression of important regulators of apoptosis, such as Bcl-2 family members, and the cell cycle, such as p21(WAF). Furthermore, we show here that cells expressing a functional pre-TCR are more resistant to different types of DNA damage-induced apoptosis and that these effects are contingent on an intact cytoplasmic tail of pTalpha. We finally propose that the presence of a functional pre-TCR complex triggers many intracellular pathways capable of driving and ensuring thymocyte survival in the presence of DNA damage.

Transcriptional regulation during p21WAF1/CIP1-induced apoptosis in human ovarian cancer cells

In this study we used adenovirus vector-mediated transduction of either the p53 gene (rAd-p53) or the p21(WAF1/CIP1) gene (rAd-p21) to mimic both p53-dependent and -independent up-regulation of p21(WAF1/CIP1) within a human ovarian cancer cell line, 2774, and the derivative cell lines, 2774qw1 and 2774qw2. We observed that rAd-p53 can induce apoptosis in both 2774 and 2774qw1 cells but not in 2774qw2 cells. Surprisingly, overexpression of p21(WAF1/CIP1) also triggered apoptosis within these two cell lines. Quantitative reverse transcription-PCR analysis revealed that the differential expression of BAX, BCL2, and caspase 3 genes, specific in rAd-p53-induced apoptotic cells, was not altered in rAd-p21-induced apoptotic cells, suggesting p21(WAF1/CIP1)-induced apoptosis through a pathway distinguishable from p53-induced apoptosis. Expression analysis of 2774qw1 cells infected with rAd-p21 on 60,000 cDNA microarrays identified 159 genes in response to p21(WAF1/CIP1) expression in at least one time point with 2.5-fold change as a cutoff. Integration of the data with the parallel microarray experiments with rAd-p53 infection allowed us to extract 66 genes downstream of both p53 and p21(WAF1/CIP1) and 93 genes in response to p21(WAF1/CIP1) expression in a p53-independent pathway. The genes in the former set may play a dual role in both p53-dependent and p53-independent pathways, and the genes in the latter set gave a mechanistic molecular explanation for p53-independent p21(WAF1/CIP1)-induced apoptosis. Furthermore, promoter sequence analysis suggested that transcription factor E2F family is partially responsible for the differential expression of genes following p21(WAF1/CIP1). This study has profound significance toward understanding the role of p21(WAF1/CIP1) in p53-independent apoptosis.

Ketoconazole potentiates terfenadine-induced apoptosis in human Hep G2 cells through inhibition of cytochrome p450 3A4 activity

Terfenadine (TF) is a highly potent histamine H1 receptor antagonist that in clinically effective doses is free of significant central nervous system side effects. Ketoconazole (KT) is a worldwide used oral antifungal agent with a broad spectrum of activity against both superficial and systemic mycosis. Simultaneously administration of KT and TF has been reported to induce several potent symptoms including cardiotoxicity, excitotoxicity, inhibition of blood mononuclear cells proliferation, and cardiovascular toxicity. However, the intracellular molecular mechanisms of TF-KT interactions in cells were still uncertain. In this study, we first demonstrated that TF (5-30 microM) induced apoptosis in several types of human cancer cell lines including human hepatoma (Hep G2), colorectal cancer (COLO 205), and fibroblast (CCD 922SK) cells for 24 h. The cellular responses to TF-induced apoptosis were demonstrated to be associated with the p53-signaling pathway, including induction of p53, p21/Cip1, p27/Kip1, bax protein expression and inhibition of bcl-2 protein expression. To realized the role of H1 receptor involved in TF-induced apoptosis, different H1 receptor antagonists including promethazine, mequitazine, and chlorpheniramin (50-100 microM) were administered and demonstrated that these chemicals cannot induced apoptosis through the H1 receptor signaling pathway. Interestingly, we found that the apoptotic effect of TF (2.5 microM) was significantly potentiated by KT (1 microM) treatment in Hep G2 cells through inhibition of the cytochrome p450 3A4 (CYP 3A4) activity. Such results were demonstrated by decreased of the TF activity with recombinant CYP 3A4, which prepared from baculovirus-infected insect cells. Our results provide the molecular basis of TF-KT interaction and this information should allow more rational forecasting of the risk for TF therapy during co-administration of KT.

Bleomycin sensitivity of mice expressing dominant-negative p53 in the lung epithelium

The chemotherapeutic drug bleomycin causes DNA damage and apoptosis in the lungs of mice within hours of endotracheal instillation followed by inflammation and fibrosis weeks later. The p53 tumor suppressor protein mediates cellular responses to DNA damage, including induction of apoptosis, but the effects of p53 activation in the various cell types of the lung during bleomycin-induced pulmonary fibrosis remain unclear. We show here that a transgene with a dominant-negative mutant form of human p53 expressed from the surfactant protein C promoter sensitizes mice to bleomycin-induced lung injury. The bleomycin-exposed transgenic animals display more severe lung pathology with associated collagen deposition and more pronounced lung eosinophilia than simultaneously exposed nontransgenic littermates. These observations suggest that compromising p53 function in the alveolar epithelium impairs recovery of the lung from bleomycin-induced injury.