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

p53 involvement in the pathogenesis of fatty liver disease

Obesity is a major health problem in industrialized societies, and fatty liver disease (hepatic steatosis) is common in obese individuals. Oxidative stress originating from increased intracellular levels of fatty acids has been implicated as a cause of hepatocellular injury in steatosis, although the precise mechanisms remain to be elucidated. p53, widely known as a tumor suppressor, has been shown often to be activated in stressed cells, inducing cell cycle arrest or death. Here we demonstrate that p53 is involved in the molecular mechanisms of hepatocellular injury associated with steatosis. We found that p53 in the nucleus is induced in the liver from two mouse models of fatty liver disease, ob/ob and a transgenic mouse model that overexpresses an active form of sterol regulatory element-binding protein-1 in the liver (TgSREBP-1), the one with obesity and the other without obesity. This activation of the p53 pathway leads to the elevation of p21 mRNA expression, which can be considered an indicator of p53 activity, because ob/ob mice lacking p53 generated by targeting gene disruption exhibited the complete restoration of the p21 elevation to wild type levels. Consistent with these results, the amelioration of hepatic steatosis caused by Srebp-1 gene disruption in ob/ob mice lowered the p21 expression in a triglyceride content-dependent manner. Moreover, p53 deficiency in ob/ob mice resulted in a marked improvement of plasma alanine aminotransferase levels, demonstrating that p53 is involved in the mechanisms of hepatocellular injury. In conclusion, we revealed that p53 plays an important role in the pathogenesis of fatty liver disease.

Apoptosis induction in peripheral leukemia cells by remission induction treatment in vivo: selective depletion and apoptosis in a CD34+ subpopulation of leukemia cells

In vitro studies demonstrating the induction of programmed cell death by cytotoxic drugs used in anticancer chemotherapy suggested that antileukemic treatment eliminates leukemia cells by apoptosis. We therefore analyzed apoptosis induction and activation of apoptosis signaling molecules in patients receiving remission induction treatment for AML and ALL during the initial phase of leukemia cell reduction. A coexistence of distinct populations of CD34(+) and CD34(-) leukemia cells could be identified. During chemotherapy, CD34(+) leukemia cells were more rapidly depleted than CD34(-) cells. Furthermore, a significant increase in leukemia cell apoptosis ex vivo was detected in CD34(+) cells, while no such increase was observed in the CD34(-) subpopulation, suggesting that CD34(+) leukemia cells are the main targets for apoptosis induction through antileukemic treatment. No alterations in Bax and Bcl-2 expression were found during in vivo chemotherapy, and CD95 expression and sensitivity remained low, indicating the induction of apoptosis independent of the CD95 system or regulation of protein levels of Bax and Bcl-2. The data suggest that analysis of leukemia cell subpopulations is required for further identification of apoptosis signaling molecules relevant for response to treatment and assessment of drug efficacy in vivo and in vitro.

Epstein-Barr virus plays no role in the tumorigenesis of small-cell carcinoma of the lung

Epstein-Barr virus infection has been associated with lymphoepithelioma-like carcinoma of the lung in Asian patients. Recently, Epstein-Barr virus proteins or genomic DNAs were detected in pulmonary squamous-cell carcinoma, adenocarcinoma, and undifferentiated small-cell carcinoma in American patients. We studied 23 cases of small-cell carcinoma of the lung for evidence of Epstein-Barr virus infection by in situ hybridization, immunohistochemistry, and polymerase chain reaction methods. Of the 23 cases, 13 cases were primary small-cell carcinoma of the lung and 10 cases were metastatic small-cell carcinoma of the lung to the brain (one case), liver (two cases), and lymph nodes (seven cases). None of the 23 cases was positive for Epstein-Barr virus-encoded small nonpolyadenylated RNA (EBER)-1 by in situ hybridization. By immunohistochemistry, eight cases showed focal positivity for Epstein-Barr virus nuclear antigen-1. The positive immunostaining was focal and was observed in tumor cells, vascular endothelial cells, and lymphocytes, suggesting nonspecific staining. None of the 23 cases was positive for the transactivating immediate-early BZLF1 (ZEBRA) and latent membrane protein (LMP-1). Only one case was positive for the BamHI W region and LMP-1 gene by polymerase chain reaction assay. Some tumor cells in the BamHI W region positive case were also positive for Epstein-Barr virus nuclear antigen-1. Our study indicates that rare cases of American small-cell carcinoma of the lung may contain Epstein-Barr virus-infected cells, but it is unlikely that Epstein-Barr virus plays a role in the tumorigenesis of small-cell carcinoma of the lung.

ASC is a Bax adaptor and regulates the p53-Bax mitochondrial apoptosis pathway

The apoptosis-associated speck-like protein (ASC) is an unusual adaptor protein that contains the Pyrin/PAAD death domain in addition to the CARD protein-protein interaction domain. Here, we present evidence that ASC can function as an adaptor molecule for Bax and regulate a p53-Bax mitochondrial pathway of apoptosis. When ectopically expressed, ASC interacted directly with Bax, colocalized with Bax to the mitochondria, induced cytochrome c release with a significant reduction of mitochondrial membrane potential and resulted in the activation of caspase-9, -2 and -3. The rapid induction of apoptosis by ASC was not observed in Bax-deficient cells. We also show that induction of ASC after exposure to genotoxic stress is dependent on p53. Blocking of endogenous ASC expression by small-interfering RNA (siRNA) reduced the apoptotic response and inhibited translocation of Bax to mitochondria in response to p53 or genotoxic insult, suggesting that ASC is required to translocate Bax to the mitochondria. Our findings demonstrate that ASC has an essential role in the intrinsic mitochondrial pathway of apoptosis through a p53-Bax network.

Mechanisms of cancer chemoprevention by hop bitter acids (beer aroma) through induction of apoptosis mediated by Fas and caspase cascades

The bitter acids of hops (Humulus lupulus L.) mainly consist of alpha-acids, beta-acids, and their oxidation products that contribute the unique aroma of the beer beverage. Hop bitter acids displayed a strong growth inhibitory effect against human leukemia HL-60 cells, with an estimated IC(50) value of 8.67 microg/mL, but were less effective against human histolytic lymphoma U937 cells. Induction of apoptosis was confirmed in HL-60 cells by DNA fragmentation and the appearance of a sub-G1 DNA peak, which were preceded by dissipation of mitochondrial membrane potential, cytochrome c release, and subsequent induction of pro-caspase-9 and -3 processing. Cleavages of PARP and DFF-45 were accompanied with activation of caspase-9 and -3 triggered by hop bitter acids in HL-60 cells. The change in the expression of Bcl-2, Bcl-X(L), and Bax in response to hop bitter acids was studied, and the Bcl-2 protein level slightly decreased; however, the Bcl-X(L) protein level was obviously decreased, whereas the Bax protein level was dramatically increased, indicating that the control of Bcl-2 family proteins by hop bitter acids might participate in the disruption of mitochondrial integrity. In addition, the results showed that hop bitter acids promoted the up-regulation of Fas and FasL prior to the processing and activation of pro-caspase-8 and cleavage of Bid, suggesting the involvement of a Fas-mediated pathway in hop bitter acids-induced cells. Taken together, these findings suggest that a certain intimate link might exist between receptor- and mitochondria-mediated death signalings that committed to cell death induced by hop bitter acids. The induction of apoptosis by hop bitter acids may offer a pivotal mechanism for their chemopreventive action.

Phosphorylation of p53 at serine 37 is important for transcriptional activity and regulation in response to DNA damage

The p53 tumor suppressor protein plays a critical role in mediating cellular response to stress. Upon DNA damage, post-translational modifications stabilize and activate this nuclear phosphoprotein. To determine the effect of phosphorylation site mutants in the context of the whole p53 protein, we performed reporter assays in p53 and MDM2 knockout mouse embryonic fibroblasts transfected with full-length p53 constructs. We show that mutation of S37 causes a decrease in p53 transcriptional activity compared to wild-type p53. Our data further suggest that the dephosphorylation of p53 at S37 is a regulated event involving protein phosphatase 2A (PP2A). Coimmunoprecipitation and immunofluorescence microscopy studies demonstrate that PP2A and p53 associate with one another in vivo following gamma-irradiation. Consistent with these observations, phosphorylated S37 accumulates in cell extracts prepared from gamma-irradiated Molt-4 cells in the presence of okadaic acid. Furthermore, in vitro phosphatase assays show that PP2A dephosphorylates p53 at S37. These results suggest that dephosphorylation of p53 at S37 plays a role in the transcriptional regulation of the p53 protein in response to DNA damage.

Induction of p53-independent apoptosis by the BH3-only protein ITM2Bs

The p53 tumor suppressor protein is critically involved in cell cycle regulation and programmed cell death. Here we show that expression of the BH3-only protein ITM2Bs is able to induce apoptotic cell death in p53+/+, as well as in p53-/- cell lines. This cell death involves neither subcellular redistribution of p53 nor transcriptional regulation of p53 target genes such as Bax, Ras, Puma or Bcl-2. Together, our data provide evidence for a p53-independent apoptotic role of ITM2Bs.

Adenovirus-mediated p53AIP1 gene transfer as a new strategy for treatment of p53-resistant tumors

The p53AIP1 gene, which we recently identified as a novel p53-target, mediates p53-dependent apoptosis. We evaluated the effects of adenovirus-mediated introduction of p53AIP1 (Ad-p53AIP1) on 30 human cancer-cell lines in vitro, and two cell lines in vivo, in comparison with the effects of p53 (Ad-p53). In 20 of the 30 cell lines, p53AIP1-induced apoptosis was observed, and in 12 of these p53AIP1-sensitive cancer cell lines, the apoptotic effects of p53AIP1 were greater than those of p53 itself. Cancers with wild-type p53, which were thought to be p53-resistant, were likely to be sensitive to p53AIP1-induced apoptosis. p53-resistant cancers such as LS174T (p53 +/+) and A549 (p53 +/+), in which no increase of p53AIP1 mRNA expression was observed when Ad-p53 was introduced, were killed effectively by Ad-p53AIP1. Furthermore, co-introduction of p53 and p53AIP1 had a synergistic effect on the induction of apoptosis, regardless of p53 status. Finally, adenovirus-mediated introduction of p53AIP1 suppressed tumor growth in vivo. These results suggested that p53AIP1 gene transfer might become a new strategy for the treatment of p53-resistant cancers.

Secreted Frizzled-related Protein 1 (SFRP1) Protects Fibroblasts from Ceramide-induced Apoptosis

Secreted frizzled-related proteins (SFRPs) are soluble proteins that have highly restricted tissue distribution. Although not fully understood, a role of SFRP1 in the regulation of apoptosis has been suggested. Our previous study disclosed a much greater level of SFRP1 expression in periodontal ligament fibroblasts (PDLFs), which have been suggested to maintain a reduced level of apoptosis compared with gingival fibroblasts. We have tested the role of SFRP1 in the regulation of fibroblast apoptosis both in vitro and in vivo. Our data showed that SFRP1 was significantly up-regulated in cultured human PDLFs during ceramide-induced apoptosis. In vivo study demonstrated an increased SFRP1 expression in mice periodontal ligament during force-induced apoptosis. While inhibition of endogenous SFRP1 increased the percentage of cell death in cultured human PDLFs, exogenous SFRP1 substantially reduced apoptosis in cultured human gingival fibroblasts, which do not maintain a high level of endogenous SFRP1 expression. The effect of SFRP1 on apoptosis was linked to the regulation of several apoptosis-related genes, including p53, caspase-3, caspase-9, and BCL-2-interacting killer (BIK). Furthermore our results indicated that the addition of exogenous SFRP1 could reduce the level of apoptosis in dermal fibroblasts in vivo, and this effect was also linked to the regulation of similar apoptosis-related genes as observed in in vitro studies. Collectively our results suggest that the constitutive up-regulation of SFRP1 could be an adaptive cell survival mechanism inherent to functionally specialized fibroblasts, and the addition of SFRP1 may contribute to the inhibition of apoptosis in fibroblast-related cells.

Oxidative stress induces p53-mediated apoptosis in glia: p53 transcription-independent way to die

Oxidative stress has been implicated in the pathogenesis of stroke, traumatic brain injuries, and neurodegenerative diseases affecting both neuronal and glial cells in the central nervous system (CNS). The tumor suppressor protein p53 plays a pivotal function in neuronal apoptosis triggered by oxidative stress. We investigated the role of p53 and related molecular mechanisms that support oxidative stress-induced apoptosis in glia. For this purpose, we exposed C6 glioma cells and primary cultures of rat cortical astrocytes to an H(2)O(2)-induced oxidative stress protocol followed by a recovery period. We evaluated the effects of pifithrin-alpha (PF-alpha), which has been reported to protect neurons from ischemic insult by specifically inhibiting p53 DNA-binding activity. Strikingly, PF-alpha was unable to prevent oxidative stress-induced astrocyte apoptosis. We demonstrate that p53 is able to mediate an apoptotic response by direct signaling at mitochondria, despite its transcriptional activity. The z-VAD-fmk-sensitive apoptotic response requires a caspase-dependent MDM-2 degradation, leading to p53 mitochondrial targeting accompanied by cytochrome c release and nucleosomal fragmentation.

Synthetic retinoids as inducers of apoptosis in ovarian carcinoma cell lines

Apoptosis is also known as programmed cell death. Apoptosis plays an essential role in maintaining normal tissue and cell physiology in multicellular organisms. Clearance of aberrant or pre-cancerous cells occurs through the induction of apoptosis. It has been reported that many tumors and tumor cell lines have dysfunctional apoptosis signaling, causing these tumors to escape immune monitoring and internal cellular control mechanisms. One potential cause of this dysfunctional apoptosis is the tumor suppressor p53, an important regulator of growth arrest and apoptosis that is mutated in over 50% of all cancers. Retinoids have great potential in the areas of cancer therapy and chemoprevention. While some tumor cells are sensitive to the growth inhibitory effects of natural retinoids such as all-trans-retinoic acid (ATRA), many ovarian tumor cells are not. 6-[3-(1-Admantyl)]-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) and fenretinide N-[4-hydroxyphenyl] retinamide (4-HPR) are conformationally restricted synthetic retinoids that induce growth arrest and apoptosis in both ATRA-sensitive and ATRA-resistant ovarian tumor cell lines. Recently, we have identified the molecular pathways of apoptosis induced by treatment of ovarian carcinoma cells with mutated p53 by CD437 and 4-HPR.

Epstein-Barr virus signal transduction and B-lymphocyte growth transformation

Latent EBV growth transformation of resting B-cells into indefinitely proliferating cell lines is a successful viral strategy for survival in its host and the basis of several human malignancies. EBV transforms cell growth through viral proteins that modify cell gene expression at the level of transcription or by appropriating signaling pathways. Analyses of the EBV-transforming protein LMP1 have begun to reveal that this receptor transduces critical signals by appropriating the TNF receptor signal transduction pathway to activate NF-kappaB and MAPK. While this has brought an important aspect into clearer focus, future progress in delineating the underlying mechanism of transformation, which will be essential to devising effective therapies to treat EBV-associated malignancies, will depend on resolving the intricacies of TRAF signal transduction. Since expression of cytokines, receptors, and anti-apoptotic proteins are regulated by TRAF signaling, another critical issue is delineating the genes that are specifically targeted by LMP1 in order to transform B-lymphocyte growth.

Host cell-dependent expression of latent Epstein-Barr virus genomes: regulation by DNA methylation

Epstein-Barr virus (EBV) is a ubiquitous human gammaherpesvirus associated with a wide spectrum of malignant neoplasms. Expression of latent (growth transformation-associated) EBV genes is host cell specific. Transcripts for EBV-encoded nuclear antigens (EBNAs) are initiated at one of the alternative promoters: Wp, Cp (for EBNA1-6), or Qp (for EBNA1 only). Wp is active shortly after EBV infection of human B cells in vitro but is progressively methylated and silenced in established lymphoblastoid cell lines (LCLs). In parallel Cp, an unmethylated, lymphoid-specific promoter is switched on. In contrast, Cp is methylated and silent in Burkitt's lymphoma (BL) cell lines, which keep the phenotype of BL biopsy cells (group I BL lines). These cells use Qp for the initiation of EBNA1 messages. Qp is unmethylated both in group I BLs (Qp on) and in LCLs (Qp off). Thus, DNA methylation does not play a role in silencing Qp. In LCLs and nasopharyngeal carcinoma (NPC) cells, transcripts for latent membrane protein 1 (LMP1) are initiated from LMP1p, a promoter regulated by CpG methylation. LMPlp is silent in group I BL lines but can be activated by demethylating agents. Promoter silencing by CpG methylation involves both direct interference with transcription factor binding (Wp, Cp) and indirect mechanisms involving the recruitment of histone deacetylases (LMPlp). A dyad symmetry sequence(DS) within oriP (the latent origin of EBV replication) and intragenic RNA polymerase III control regions of EBER 1 and 2 transcription units are invariably unmethylated in EBV-carrying cells.

Death and more: DNA damage response pathways in the nematode C. elegans

Genotoxic stress is a threat to our cells' genome integrity. Failure to repair DNA lesions properly after the induction of cell proliferation arrest can lead to mutations or large-scale genomic instability. Because such changes may have tumorigenic potential, damaged cells are often eliminated via apoptosis. Loss of this apoptotic response is actually one of the hallmarks of cancer. Towards the effort to elucidate the DNA damage-induced signaling steps leading to these biological events, an easily accessible model system is required, where the acquired knowledge can reveal the mechanisms underlying more complex organisms. Accumulating evidence coming from studies in Caenorhabditis elegans point to its usefulness as such. In the worm's germline, DNA damage can induce both cell cycle arrest and apoptosis, two responses that are spatially separated. The latter is a tightly controlled process that is genetically indistinguishable from developmental programmed cell death. Upstream of the central death machinery, components of the DNA damage signaling cascade lie and act either as sensors of the lesion or as transducers of the initial signal detected. This review summarizes the findings of several studies that specify the elements of the DNA damage-induced responses, as components of the cell cycle control machinery, the repairing process or the apoptotic outcome. The validity of C. elegans as a tool to further dissect the complex signaling network of these responses and the high potential for it to reveal important links to cancer and other genetic abnormalities are addressed.

Demonstration of the Burkitt's lymphoma Epstein-Barr virus phenotype in dividing latently infected memory cells in vivo

Epstein-Barr virus (EBV) is a herpesvirus that establishes a lifelong, persistent infection. It was first discovered in the tumor Burkitt's lymphoma (BL). Despite intensive study, the role of EBV in BL remains enigmatic. One striking feature of the tumor is the unique pattern of viral latent protein expression, which is restricted to EBV-encoded nuclear antigen (EBNA) 1. EBNA1 is required to maintain the viral genome but is not recognized by cytotoxic T cells. Consequently, it was proposed that this expression pattern was used by latently infected B cells in vivo. This would be the site of long-term, persistent infection by the virus and, by implication, the progenitor of BL. We now know that EBV persists in memory B cells in the peripheral blood and that BL is a tumor of memory cells. However, a normal B cell expressing EBNA1 alone has been elusive. Here we show that most infected cells in the blood express no detectable latent mRNA or proteins. The exception is that when infected cells divide they express EBNA1 only. This is the first detection of the BL viral phenotype in a normal, infected B cell in vivo. It suggests that BL may be a tumor of a latently infected memory B cell that is stuck proliferating because it is a tumor and, therefore, constitutively expressing only EBNA1.

Caspase regulation of genotoxin-induced neural precursor cell death

Neural precursor cells (NPCs) critically regulate brain morphogenesis and recent studies have revealed an unexpectedly high frequency of NPC chromosomal abnormalities and apoptosis in the developing brain. We have shown previously that the apoptotic response of NPCs to genotoxic agents is dependent on p53 and caspase-9, but not Bax or caspase-3 expression. In this study, we found that NPCs deficient in Apaf-1, or both the pro-apoptotic multidomain Bcl-2 family members Bax and Bak, were resistant to cytosine arabinoside and gamma-irradiation-induced apoptosis. Inhibitors of gene transcription, protein translation, and caspase activity also blocked genotoxin-induced NPC apoptosis. Although caspase-3 and caspase-6 were both cleaved in response to DNA damage, neither of these effector caspases was critical for apoptosis. Genotoxin-induced NPC death was accompanied by the generation of reactive oxygen species and could be inhibited by several known antioxidants. Conversely, DNA damage-induced reactive oxygen species generation was inhibited significantly by gene disruption of p53, Apaf-1, or caspase-9, and combined deficiency of Bax and Bak, but not by caspase-3 or caspase-6 deficiency. These studies suggest that caspase-9 activation is both necessary and sufficient for genotoxin-induced neural precursor cell reactive oxygen species generation and death.

Induction of GADD gene expression by phenethylisothiocyanate in human colon adenocarcinoma cells

Phenethylisothiocyanate (PEITC), a potential cancer chemopreventive agent, induces colon cancer cell death, but the mechanism is not entirely clear. Therefore, the aim of this study was to further clarify the molecular effects of PEITC in causing death of human colon adenocarcinoma cells. When incubated with PEITC, HCT-116 colonocytes showed morphological features characteristic of apoptosis, such as irregular cell shape, translocation of plasma membrane phosphatidylserine, and also chromatin condensation and fragmentation. These changes occurred after single-strand breaks in DNA were detected, suggesting that PEITC induced irreparable DNA damage, which in turn triggered the process of apoptosis. DNA macroarray analysis of a selected small cluster of apoptosis-related genes revealed noticeably higher expression of only GADD45, which was confirmed by gene-specific relative RT-PCR analysis. This led to investigation of other GADD gene members possibly affected by PEITC. Whereas GADD34 mRNA expression increased just slightly, there was an appreciable elevation of the mRNA for GADD153, which is recognized as a pro-apoptotic gene. The effect of PEITC on GADD153 was attenuated by either actinomycin D or N-acetylcysteine, suggesting that PEITC-induced upregulation of GADD153 mRNA expression was partly at the level of transcriptional activation involving reactive oxygen species. Additionally, PEITC-induced upregulation of GADD153 mRNA expression did not appear to require p53, based on the observation that PEITC also increased GADD153 mRNA expression in HCT-15 colonocytes, which are known to express mutant p53. These findings suggest that PEITC creates an oxidative cellular environment that induces DNA damage and GADD153 gene activation, which in turn helps trigger apoptosis.

A comprehensive assessment of p53-responsive genes following adenoviral-p53 gene transfer in Bcl-2-expressing prostate cancer cells

The p53 protein can induce cell cycle arrest or apoptosis following activation in response to DNA damage. The function of p53 is largely mediated by regulating the expression of downstream target genes. Adenoviral-p53 gene transfer (Ad-p53) is currently being evaluated in clinical trials as a therapeutic intervention. Tumor response is likely to be influenced by context-dependent variables, such as expression of bcl-2. Bcl-2 is upregulated in a variety of neoplasms, and can inhibit p53-dependent apoptosis. It was therefore of interest to use a global genomic strategy to assess gene expression following Ad-p53 gene transfer and to determine if the expression of specific Ad-p53-responsive genes could be modulated in the context of bcl-2 gene deregulation. cDNA arrays were used to identify p53-responsive genes following Ad-p53 gene transfer in control and bcl-2-overexpressing PC3 prostate cancer cells. A total of 40 transcripts were significantly upregulated by Ad-p53 in both control and bcl-2-transfectant PC3 cells. Conversely, 19 transcripts were significantly repressed in both cell lines. These Ad-p53-responsive transcripts included previously identified p53 targets, known genes representing candidate p53 targets, and transcripts identified as expressed sequence tags. A subset of 15 transcripts was differentially modulated by Ad-p53 in the context of bcl-2. Some of these genes were also differentially modulated in LNCaP (wt p53) cells following DNA damage. These results document a number of potential p53 targets and mediators of therapeutically relevant genotoxic stress. The findings further suggest that bcl-2 may inhibit cell death at multiple points downstream of p53 activation.

MDM4 (MDMX) overexpression enhances stabilization of stress-induced p53 and promotes apoptosis

Rescue of embryonic lethality in MDM4(-/-) mice through concomitant loss of p53 has revealed a functional partnership between the two proteins. Biochemical studies have suggested that MDM4 may act as a negative regulator of p53 levels and activity. On the other hand, MDM4 overexpression has been reported to stabilize p53 levels and to counteract MDM2-degradative activity. We have investigated the functional role of MDM4 overexpression on cell behavior. In both established and primary cells cultured under stress conditions, overexpression of MDM4 significantly increased p53-dependent cell death, in correlation with enhanced induction of the endogenous p53 protein levels. This phenomenon was associated with induced p53 transcriptional activity and increased levels of the proapoptotic protein, Bax. Further, p53 stabilization was accompanied by decreased association of the protein to its negative regulator, MDM2. These findings reveal a novel role for MDM4 by demonstrating that in non-tumor cells under stress conditions it may act as a positive regulator of p53 activity, mainly by controlling p53 levels. They also indicate a major distinction between the biological consequences of MDM4 and MDM2 overexpression.

c-Myc sensitization to oxygen deprivation-induced cell death is dependent on Bax/Bak, but is independent of p53 and hypoxia-inducible factor-1

Deregulated expression of c-Myc can sensitize cells to a variety of death stimuli, including loss of growth factors and oxygen. In this study, we examined whether rodent fibroblasts that conditionally express c-Myc undergo a similar mechanism of cell death in response to serum or oxygen deprivation. Our results demonstrate that murine embryonic fibroblasts from bax-/-bak-/- mice that conditionally express c-Myc did not die in response to either oxygen or serum deprivation. Fibroblasts from p53-/- mice that conditionally express c-Myc died in response to oxygen (but not serum) deprivation. The inability of p53 to regulate oxygen deprivation-induced cell death was due to the lack of induction of p53 target genes Puma, Noxa, and Pten. In contrast, serum deprivation transcriptionally induced Puma and Pten in cells that conditionally express c-Myc. The failure of p53 to regulate oxygen deprivation-induced cell death led us to hypothesize whether hypoxia-inducible factor (HIF) might be a critical regulator of cell death during oxygen deprivation. Fibroblasts from HIF-1beta-/- cells that conditionally express c-Myc were not able to transcriptionally activate HIF during oxygen deprivation. These cells died in response to oxygen deprivation. Thus, oxygen deprivation-induced cell death in fibroblasts with deregulated expression of c-Myc is independent of p53 or HIF-1 status, but is dependent on the Bcl-2 family member Bax or Bak to initiate mitochondrial dependent cell death.

Epidermal growth factor receptor-dependent, NF-kappaB-independent activation of the phosphatidylinositol 3-kinase/Akt pathway inhibits ultraviolet irradiation-induced caspases-3, -8, and -9 in human keratinocytes

Both phosphatidylinositol 3-kinase (PI3K)/Akt and NF-kappaB pathways function to promote cellular survival following stress. Recent evidence indicates that the anti-apoptotic activity of these two pathways may be functionally dependent. Ultraviolet (UV) irradiation causes oxidative stress, which can lead to apoptotic cell death. Human skin cells (keratinocytes) are commonly exposed to UV irradiation from the sun. We have investigated activation of the PI3K/Akt and NF-kappaB pathways and their roles in protecting human keratinocytes (KCs) from UV irradiation-induced apoptosis. This activation of PI3K preceded increased levels (3-fold) of active/phosphorylated Akt. UV (50 mJ/cm2 from UVB source) irradiation caused rapid recruitment of PI3K to the epidermal growth factor receptor (EGFR). Pretreatment of KCs with EGFR inhibitor PD169540 abolished UV-induced Akt activation/phosphorylation, as did the PI3K inhibitors LY294002 or wortmannin. This inhibition of Akt activation was associated with a 3-4-fold increase of UV-induced apoptosis, as measured by flow cytometry and DNA fragmentation ELISA. In contrast to Akt, UV irradiation did not detectably increase nuclear localization of NF-kappaB, indicating that it was not strongly activated. Consistent with this observation, interference with NF-kappaB activation by adenovirus-mediated overexpression of dominant negative IKK-beta or IkappaB-alpha did not increase UV-induced apoptosis. However, adenovirus-mediated overexpression of constitutively active Akt completely blocked UV-induced apoptosis observed with PI3K inhibition by LY294002, whereas adenovirus mediated overexpression of dominant negative Akt increased UV-induced apoptosis by 2-fold. Inhibition of UV-induced activation of Akt increased release of mitochondrial cytochrome c 3.5-fold, and caused appearance of active forms of caspase-9, caspase-8, and caspase-3. Constitutively active Akt abolished UV-induced cytochrome c release and activation of caspases-9, -8, and -3. These data demonstrate that PI3K/Akt is essential for protecting human KCs against UV-induced apoptosis, whereas NF-kappaB pathway provides little, if any, protective role.

Targeted therapy for epithelial ovarian cancer: Current status and future prospects

Despite advances in surgery and chemotherapy, less than 20% of patients with stage III or IV ovarian cancer survive long-term. In the past, cytotoxic regimens have been developed empirically, combining active agents at maximally tolerated doses, often without a clear rationale for their interaction. Advances in understanding the biology of ovarian cancer have identified multiple molecular targets that differ in normal and malignant cells. Targets include cell cycle regulators, growth factor receptors, signal transduction pathways, molecules that confer drug resistance, and angiogenic mechanisms. A number of targeted agents have entered clinical trials. Small molecular weight inhibitors, monoclonal antibodies, and antisense and gene therapy are all being evaluated alone and in combination with cytotoxic drugs. In contrast to earlier studies, the impact of each agent on the designated target can be assessed and agents can be matched to the genotype and phenotype of malignant and normal cells. In the long run, this should facilitate individualization of more effective, less toxic therapy for women with ovarian cancer.

Expression of antisense bcl-2 cDNA abolishes tumorigenicity and enhances chemosensitivity of human malignant glioma cells

Bcl-2 is a key antiapoptotic protein, and it confers survival advantages on many types of tumors by inhibiting apoptotic cell death. Malignant gliomas are the most common primary central nervous system tumors, but the role of bcl-2 in these tumors has not been defined. We investigated the impact of bcl-2 on malignant gliomas by suppressing its expression. Antisense human bcl-2 cDNA was transfected into human malignant glioma cells. The effects of bcl-2 protein down-regulation on glioma cell morphology, in vitro tumor growth, and tumorigenicity in nude mice, as well as chemosensitivity to cisplatin, were studied. Expression of antisense bcl-2 cDNA decreased bcl-2 protein by more than sixfold. Antisense bcl-2 stable transfectants (AS-bcl-2) showed profound morphological change and markedly retarded cell growth in vitro. Transplantation of AS-bcl-2 cells resulted in no tumor formation, whereas backbone plasmid transfectant control formed tumors in each mouse transplanted. Expression of antisense bcl-2 in glioma cells resulted in significantly increased cytotoxicity of cisplatin. In conclusion, antisense bcl-2 expression can effectively reduce glioma survival, including retarding in vitro growth, complete loss of tumorigenicity, and significantly enhanced cisplatin cytotoxicity. These results suggest that bcl-2 plays an important role in glioma malignancy and chemoresistance. Development of strategies targeted at bcl-2 has the potential to advance treatment for malignant gliomas.

Ursodeoxycholic acid modulates E2F-1 and p53 expression through a caspase-independent mechanism in transforming growth factor beta1-induced apoptosis of rat hepatocytes

Transforming growth factor beta1 (TGF-beta1)-induced hepatocyte apoptosis is associated with activation of E2F transcription factors and p53 stabilization through Mdm-2, thus potentially modulating a number of target genes. In previous studies, we have shown that ursodeoxycholic acid (UDCA) prevents TGF-beta1-induced hepatocyte apoptosis by inhibiting the mitochondrial pathway of cell death. In this study we examined the role of p53 in the induction of apoptosis by TGF-beta1, and identified additional antiapoptosis targets for UDCA. Our data show a significant transcriptional activation of E2F-1 in primary rat hepatocytes incubated with TGF-beta1, as well as a 5-fold increase in p53 and a 2-fold decrease in its inhibitor, Mdm-2 (p < 0.05). In addition, bax mRNA expression was significantly induced at 36 h (p < 0.01), resulting in increased levels of Bax protein. In contrast, Bcl-2 transcript and protein levels were decreased at all time points (p < 0.01). Notably, UDCA inhibited E2F-1 transcriptional activation, p53 stabilization and Bcl-2 family expression (p < 0.05), in part, through a caspase-independent mechanism. Moreover, in the absence of TGF-beta1, UDCA prevented induction of p53 and Bax by overexpression of E2F-1 and p53, respectively (p < 0.05). In addition, UDCA inhibited TGF-beta1-induced degradation of nuclear factor kappaB (NF-kappaB) and its inhibitor IkappaB (p < 0.05). In conclusion, these results demonstrate that UDCA inhibits E2F-1 transcriptional activation of hepatocyte apoptosis, thus modulating p53 stabilization, NF-kappaB degradation, and expression of Bcl-2 family members.

TP53INP1s and homeodomain-interacting protein kinase-2 (HIPK2) are partners in regulating p53 activity

The TP53INP1 gene encodes two protein isoforms, TP53INP1alpha and TP53INP1beta, located into the nucleus. Their synthesis is increased during cellular stress by p53-mediated activation of transcription. Overexpression of these isoforms induces apoptosis, suggesting an involvement of TP53INP1s in p53-mediated cell death. It was recently shown that p53-dependent apoptosis is promoted by homeodomain-interacting protein kinase-2 (HIPK2), which is known to bind p53 and induce its phosphorylation in promyelocytic leukemia protein nuclear bodies (PML-NBs). In this work we show that TP53INP1s localize with p53, PML-IV, and HIPK2 into the PML-NBs. In addition, we show that TP53INP1s interact physically with HIPK2 and p53. In agreement with these results we demonstrate that TP53INP1s, in association with HIPK2, regulate p53 transcriptional activity on p21, mdm2, pig3, and bax promoters. Furthermore, TP53INP1s overexpression induces G1 arrest and increases p53-mediated apoptosis. Although a TP53INP1s and HIPK2 additive effect was observed on apoptosis, G1 arrest was weaker when HIPK2 was transfected together with TP53INP1. These results indicate that TP53INP1s and HIPK2 could be partners in regulating p53 activity.

Identification and characterization of the cytoplasmic protein TRAF4 as a p53-regulated proapoptotic gene

The role of p53 in tumor suppression partly relies on its ability to transcriptionally regulate target genes involved in the initiation of cell cycle arrest or the activation of programmed cell death. In recent years many genes have been identified as p53-regulated genes; however, no single target gene has been shown to be required for the full apoptotic effect. We have identified TRAF4 as a p53-regulated gene in a microarray screen using a Murine 11K Affymetrix GeneChip hybridized with cRNA from the p53 temperature-sensitive cell line, Vm10. TRAF4 is a member the TRAF family of adaptor proteins that mediate cellular signaling by binding to various members of the tumor necrosis family receptor superfamily and interleukin-1/Toll-like receptor super-family. In contrast to its other family members, TRAF4 has not been shown to bind to a member of the tumor necrosis factor receptor superfamily in vivo, nor has it been shown to regulate signaling pathways common to its other family members. Therefore the role of TRAF4 in a signaling pathway has not yet been established and requires further study. TRAF4 is specifically regulated by p53 in response to temperature sensitive p53, overexpression of p53 by use of an adenovirus, and stabilization of p53 in response to DNA damage. The murine TRAF4 promoter contains a functional p53 DNA-binding site approximately 1 kilobase upstream of the initiating methionine. TRAF4 localizes to the cytoplasm and appears to remain in the cytoplasm following DNA damage. Interestingly, the overexpression of TRAF4 induces apoptosis and suppresses colony formation. These data suggest a correlation that the orphan adaptor protein TRAF4 may play a role in p53-mediated proapoptotic signaling in the response to cellular stress.

Oxidative stress induces nuclear loss of DNA repair proteins Ku70 and Ku80 and apoptosis in pancreatic acinar AR42J cells

Cell death linked to oxidative DNA damage has been implicated in acute pancreatitis. The severe DNA damage, which is beyond the capacity of the DNA repair proteins, triggers apoptosis. It has been hypothesized that oxidative stress may induce a decrease in the Ku70 and Ku80 levels and apoptosis in pancreatic acinar cells. In this study, it was found that oxidative stress caused by glucose oxidase (GO) acting on beta-d-glucose, glucose/glucose oxidase (G/GO), induced slight changes in cytoplasmic Ku70 and Ku80 but drastically induced a decrease in nuclear Ku70 and Ku80 both time- and concentration-dependently in AR42J cells. G/GO induced apoptosis determined by poly(ADP-ribose) polymerase cleavage, an increase in expression of p53 and Bax, and a decrease in Bcl-2 expression. G/GO-induced apoptosis was in parallel with the loss of nuclear Ku proteins in AR42J cells. Caspase-3 inhibitor prevented G/GO-induced nuclear Ku loss and cell death. G/GO did not induce apoptosis in the cells transfected with either the Ku70 or Ku80 expression gene but increased apoptosis in those transfected with the Ku dominant negative mutant. Pulse and pulse-chase results show that G/GO induced Ku70 and Ku80 syntheses, even though Ku70 and Ku80 were degraded both in cytoplasm and nucleus. G/GO-induced decrease in Ku binding to importin alpha and importin beta reflects possible modification of nuclear import of Ku proteins. The importin beta level was not changed by G/GO. These results demonstrate that nuclear decrease in Ku70 and Ku80 may result from the decrease in Ku binding to nuclear transporter importins and the degradation of Ku proteins. The nuclear loss of Ku proteins may underlie the mechanism of apoptosis in pancreatic acinar cells after oxidative stress.

The Y-box-binding protein, YB1, is a potential negative regulator of the p53 tumor suppressor

The p53 tumor suppressor plays a major role in preventing tumor development by transactivating genes to remove or repair potentially tumorigenic cells. Here we show that the Y-box-binding protein, YB1, acts as a negative regulator of p53. Using reporter assays we show that YB1 represses transcription of the p53 promoter in a sequence-specific manner. We also show that YB1 reduces endogenous levels of p53, which in turn reduces p53 activity. Conversely, inhibiting YB1 in a variety of tumor cell lines induces p53 activity, resulting in significant apoptosis via a p53-dependent pathway. These data suggest that YB1 may, in some situations, protect cells from p53-mediated apoptosis, indicating that YB1 may be a good target for the development of new therapeutics.

Hypoxia induces apoptosis in SV40-immortalized rat proximal tubular cells through the mitochondrial pathways, devoid of HIF1-mediated upregulation of Bax

Chronic hypoxia is a major contributor to tubulointerstitial injury in various renal diseases and apoptosis is apparently involved. Although many studies report hypoxia-induced apoptosis in cultured tubular cells, information has been limited in proximal tubular cells, those from the most susceptible portion of renal tubules against hypoxia. This study was to confirm a role for apoptosis in hypoxic proximal tubular cells and to investigate its association with HIF-1. Temperature-sensitive SV40-immortalized rat proximal tubular cells (IRPTCs) showed apoptosis in 21.9+/-2.9% by hypoxia (0.2% O(2), 48h), with alterations in mitochondrial signaling such as Bcl2 and caspase-9. Bax mRNA was unaffected during the process. However, treating IRPTCs at the nonpermissive temperature showed an upregulation of Bax by hypoxia, which was abrogated by overexpressing dominant-negative HIF-1alpha. These findings extend previous reports on hypoxia-mediated tubular cell apoptosis and demonstrate the possible involvement of HIF-1 as an upstream molecule of Bax.

Cytosine arabinoside rapidly activates Bax-dependent apoptosis and a delayed Bax-independent death pathway in sympathetic neurons

Cytosine arabinoside (ara-C) is a nucleoside analog used in the treatment of hematologic malignancies. One of the major side effects of ara-C chemotherapy is neurotoxicity. In this study, we have further characterized the cell death induced by ara-C in sympathetic neurons. Similar to neurons undergoing trophic factor deprivation-induced apoptosis, ara-C-exposed neurons became hypometabolic before death and upregulated c-myb, c-fos, and Bim. Bax deletion delayed, but did not prevent, ara-C toxicity. Neurons died by apoptosis, indicated by the release of mitochondrial cytochrome-c and caspase-3 activation. p53-deficient neurons demonstrated decreased sensitivity to ara-C, but neither p53 nor multiple p53-regulated genes were induced. Mature neurons showed increased ara-C resistance. These results demonstrate that molecular mechanisms underlying ara-C-induced death are similar to those responsible for trophic factor deprivation-induced apoptosis. However, substantial differences in neuronal death after these two distinct stress stimuli exist since ara-C toxicity, unlike the developmental death, can proceed in the absence of Bax.

Dual-specificity phosphatase 5 (DUSP5) as a direct transcriptional target of tumor suppressor p53

Dual-specificity phosphatase 5 (DUSP5), a VH1-like enzyme that hydrolyses nuclear substrates phosphorylated on both tyrosine and serine/threonine residues, has a potential role in deactivation of mitogen- or stress-activated protein kinases. Using cDNA-microarray technology, we found that the expression of DUSP5 mRNA was dramatically increased by exogenous p53 in U373MG, a p53-mutant glioblastoma cell line. Transcription of DUSP5 was also remarkably activated by endogenous p53 in response to DNA damage in colon-cancer cells (p53+/+) that contained wild-type p53, but not in p53-/- cells. Chromatin-immunoprecipitation (ChIP) and reporter assays demonstrated that endogenous p53 protein would bind directly to the promoter region of the DUSP5 gene, implying p53-dependent transcriptional activity. Overexpression of DUSP5 suppressed the growth of several types of human cancer cells, in which Erk1/2 was significantly dephosphorylated. If, as the results suggest, DUSP5 is a direct target of p53, it represents a novel mechanism by which p53 might negatively regulate cell-cycle progression by downregulating mitogen- or stress-activated protein kinases.

In vivo p53 function is indispensable for DNA damage-induced apoptotic signaling in Drosophila

p53 is a representative tumor suppressor whose dysfunction is a major cause of human cancer syndrome. Here we isolated flies lacking Dmp53, which encodes the single Drosophila orthologue of mammalian p53 family. Dmp53 null mutants well developed into adults, only displaying mild defects in longevity and fertility. However, genomic stability and viability of Dmp53 mutants dramatically decreased upon ionizing irradiation. Moreover, mutating Dmp53 abolished irradiation-induced apoptosis and reaper induction. These results indicate that Dmp53 is a central component of DNA damage-dependent apoptotic signaling.

Epstein-Barr virus DNA is detected in peripheral blood mononuclear cells of EBV-seronegative infants with infectious mononucleosis-like symptoms

We demonstrated Epstein-Barr virus (EBV) DNA in peripheral blood mononuclear cells (PBMCs) from infants with infectious mononucleosis- (IM) like symptoms. Thirteen of the 17 patients did not have EBV antibodies; however, EBV DNA was detected in 8 PBMC from the 13 seronegative patients by PCR. The 4 patients were retested in 6-12 months later. Three patients were still seronegative; however EBV DNA wasnot detected. One patient seroconverted and EBV DNA could still be detected. The transcript of EBNA1 was detected in one patient, but neither EBNA2 nor LMP2A were detected in all PBMC from the 4 tested patients. Type 1 EBV DNA was detected in 5 PBMC of 7 tested patients, and type 2 EBV DNA was detected in type 1 positive PBMC of one patient as well. The IL-1 beta polymorphism that is reported to be one of the immunological factors of EBV seronegativity revealed no difference in IM-like patients. These results indicated that EBV infection occurs in EBV-seronegative IM-like infants; however, the modes of infection are clearly different from IM.

Epstein-Barr virus DNA is detected in peripheral blood mononuclear cells of EBV-seronegative infants with infectious mononucleosis-like symptoms

We demonstrated Epstein-Barr virus (EBV) DNA in peripheral blood mononuclear cells (PBMCs) from infants with infectious mononucleosis- (IM) like symptoms. Thirteen of the 17 patients did not have EBV antibodies; however, EBV DNA was detected in 8 PBMC from the 13 seronegative patients by PCR. The 4 patients were retested in 6-12 months later. Three patients were still seronegative; however EBV DNA wasnot detected. One patient seroconverted and EBV DNA could still be detected. The transcript of EBNA1 was detected in one patient, but neither EBNA2 nor LMP2A were detected in all PBMC from the 4 tested patients. Type 1 EBV DNA was detected in 5 PBMC of 7 tested patients, and type 2 EBV DNA was detected in type 1 positive PBMC of one patient as well. The IL-1 beta polymorphism that is reported to be one of the immunological factors of EBV seronegativity revealed no difference in IM-like patients. These results indicated that EBV infection occurs in EBV-seronegative IM-like infants; however, the modes of infection are clearly different from IM.

Impaired function of p53R2 in Rrm2b-null mice causes severe renal failure through attenuation of dNTP pools

p53R2, which is regulated by tumor suppressor p53, is a small subunit of ribonucleotide reductase. To determine whether it is involved in DNA repair by supplying deoxyribonucleotides (dNTPs) for resting cells in vivo, we generated a strain of mice lacking Rrm2b (encoding p53R2). These mice developed normally until they were weaned but from then on had growth retardation and early mortality. Pathological examination indicated that multiple organs had failed, and all Rrm2b-null mice died from severe renal failure by the age of 14 weeks. TUNEL staining showed a greater number of apoptotic cells in kidneys of 8-week-old Rrm2b-/- mice relative to wild-type mice. p53 was activated in kidney tissues of Rrm2b-/- mice, leading to transcriptional induction of p53 target genes. Rrm2b-/- mouse embryonic fibroblasts (MEFs) became immortal much earlier than Rrm2b+/+ MEFs. dNTP pools were severely attenuated in Rrm2b-/- MEFs under oxidative stress. Rrm2b deficiency caused higher rates of spontaneous mutation in the kidneys of Rrm2b-/- mice. Our results suggest that p53R2 has a pivotal role in maintaining dNTP levels for repair of DNA in resting cells. Impairment of this pathway may enhance spontaneous mutation frequency and activate p53-dependent apoptotic pathway(s) in vivo, causing severe renal failure, growth retardation and early mortality.

Differential expression of proliferation- and apoptosis-related markers in lentigo maligna and solar keratosis keratinocytes

Keratinocytes influence the number, morphology, and proliferation of melanocytes. An interference in the melanocyte-keratinocyte relationship may contribute to melanoma development. This study examined the expression of apoptotic and proliferative markers in keratinocytes in lentigo maligna to characterize the epidermis permissive to these lesions. Formalin-fixed and paraffin-embedded tissues from 25 samples of lentigo maligna, 20 samples of solar keratoses, and 5 samples each of normal sun-exposed and non-sun-exposed skin (controls) were immunostained with antibodies directed against the proapoptotic markers bax and p53, the antiapoptotic marker bcl-2, and the proliferation marker ki-67. Eight percent of the lentigo maligna samples were positive for keratinocyte expression of bcl-2, 24% were positive for p53, and 76% were positive for bax; respective findings for solar keratoses were 35%, 85%, and 90%. Comparison with normal sun-exposed skin yielded lower rates of keratinocyte proliferation in 56% of the lentigo maligna samples, similar rates in 36%, and higher rates in 8%; for solar keratoses, proliferation was higher than controls in 60% of samples, similar in 35%, and lower in 5%. All these differences were statistically significant. These findings indicate that there are variable patterns of epidermal reaction to chronic sun exposure. The epidermis in lentigo maligna shows overall low proliferation and an apparently low apoptotic tendency. The dysfunctional epidermis may be permissive to aberrant melanocyte proliferation in the early stages of melanoma development.

Tumor outgrowth in peripheral blood mononuclear cell-injected SCID mice is not associated with early Epstein-Barr virus reactivation

Epstein-Barr virus (EBV)-positive B-cell lymphoproliferative disease develops in severe combined immunodeficient (SCID) mice inoculated with peripheral blood mononuclear cells (PBMC) from EBV(+) individuals (SCID/hu mice). In this study, we investigated the contribution of EBV reactivation and de novo infection of B lymphocytes to tumor outgrowth in SCID/hu mice. Evaluation of BZLF-1, an early EBV activation transcript, in cells recovered from the mouse peritoneal cavity within 16 days following PBMC transfer did not reveal EBV reactivation, while BZLF-1 expression was only detected in tumor masses or in vitro established lymphoblastoid cell lines. To confirm these data by a different strategy, we coinjected PBMC from seropositive donors with purified B cells from seronegative donors of different sex. Fluorescence in situ hydridization analysis of the resulting tumor masses disclosed that the overwhelming majority of lymphoma cells originated from the seropositive donor, implying that no substantial in vivo production and transmission of virus had occurred. Further, treatment of SCID/hu mice with ganciclovir did not prevent lymphoma development. Our results suggest that in the SCID/hu mouse, early EBV replication and secondary infection of bystander B cells does not occur, and that the direct outgrowth of the transformed B lymphocytes present within the PBMC inoculum is the predominant mechanism, which leads to lymphoma generation in this experimental model.

p53-induced inhibition of protein synthesis is independent of apoptosis

Activation of a temperature-sensitive form of p53 in murine erythroleukaemia cells results in a rapid impairment of protein synthesis that precedes inhibition of cell proliferation and loss of cell viability by several hours. The inhibition of translation is associated with specific cleavages of polypeptide chain initiation factors eIF4GI and eIF4B, a phenomenon previously observed in cells induced to undergo apoptosis in response to other stimuli. Although caspase activity is enhanced in the cells in which p53 is activated, both the effects on translation and the cleavages of the initiation factors are completely resistant to inhibition of caspase activity. Moreover, exposure of the cells to a combination of the caspase inhibitor z-VAD.FMK and the survival factor erythropoietin prevents p53-induced cell death but does not reverse the inhibition of protein synthesis. We conclude that the p53-regulated cleavages of eIF4GI and eIF4B, as well as the overall inhibition of protein synthesis, are caspase-independent events that can be dissociated from the induction of apoptosis per se.

Latency pattern of Epstein-Barr virus and methylation status in Epstein-Barr virus-associated hemophagocytic syndrome

Expression of different panels of latent gene transcripts is controlled by usage of three distinct Epstein-Barr virus (EBV) nuclear antigen (EBNA) promoters (Wp, Cp, and Qp). EBV-associated hemophagocytic syndrome, which is often a fatal disease and generally occurs after primary EBV infection, is characterized by monoclonal or oligoclonal proliferation of EBV-infected T cells. The latency pattern and EBNA promoter (Wp, Cp, and Qp) usage in EBV-infected cells from three patients with EBV-associated hemophagocytic syndrome were examined by reverse transcription-polymerase chain reaction (PCR). Three samples from the patients expressed EBER, EBNA1, EBNA2, latent membrane protein (LMP)1, and LMP2A transcripts. The transcripts of EBNA1 were initiated from not only Wp/Cp but also Qp. Lytic cycle Fp-initiated EBNA1 and EBV lytic gene BZLF1 transcripts were not detected. The methylation statuses of three EBNA promoters in three patients with EBV-associated hemophagocytic syndrome and in two patients with infectious mononucleosis were also analyzed using bisulfite PCR analysis. Wp was hypermethylated, and Qp was unmethylated in both diseases. Cp was highly methylated in EBV-associated hemophagocytic syndrome, however, whereas Cp was almost unmethylated in infectious mononucleosis. These results suggest that there may be distinct EBV-infected cell populations in EBV-associated hemophagocytic syndrome, which exhibit different patterns of EBV latent gene expression. The methylation status in Cp and phenotype of EBV-infected cells may be critical differences in EBV-associated hemophagocytic syndrome and infectious mononucleosis.

Etoposide upregulates Bax-enhancing tumour necrosis factor-related apoptosis inducing ligand-mediated apoptosis in the human hepatocellular carcinoma cell line QGY-7703

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted much attention because of its ability to kill tumour cells. In this study, we demonstrated that treatment of QGY-7703 cells with the combination of TRAIL and etoposide resulted in synergistic cytotoxic effects. In dissecting the mechanism underlying this synergistic effect, we found that treatment with etoposide alone resulted in the upregulation of Bax, while the level of truncated Bid (tBid) was unchanged. In contrast, while treatment with TRAIL alone significantly increased the level of tBid, the expression of Bax remained unaffected. The enhanced apoptosis was accompanied by an increased release of cytochrome c and second mitochondria-derived activator of caspase/direct IAP binding protein with low pI (DIABLO) from mitochondria, leading to the activation of cellular caspase-8, -9, -3 and -7, as well as poly ADP-ribose polymerase. This enhanced release of cytochrome c and second mitochondria-derived activator of caspase/DIABLO was inhibited by the general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. The RT-PCR and Western blotting results demonstrated that the levels of both mRNA and protein for death receptor-4, death receptor-5 and decoy receptor-2 remained unchanged in response to etoposide, indicating that the synergistic effect of TRAIL and etoposide is not a result of increasing the expression for TRAIL receptors, but rather is associated with amplification of the mitochondrial signal pathway.

Effect of an adenoviral vector that expresses the canine p53 gene on cell growth of canine osteosarcoma and mammary adenocarcinoma cell lines

OBJECTIVE

To generate an adenoviral vector that expressed the canine p53 gene and investigate its growth-inhibiting effect on canine osteosarcoma and mammary adenocarcinoma cell lines.

SAMPLE POPULATION

2 canine osteosarcoma cell lines (HOS, OOS) and 3 canine mammary adenocarcinoma cell lines (CHMp, CIPm, and CNMm).

PROCEDURE

An adenoviral vector that expressed the canine p53 gene (AxCA-cp53) was generated. p53 gene expression was examined by use of reverse transcription (RT)-polymerase chain reaction (PCR) assay and immunohistochemistry. Susceptibility of cell lines to the adenoviral vector was determined by infection with an adenoviral vector that expresses beta-galactosidase (AxCA-LacZ) and 3-indolyl-beta-D-galactopyranoside staining. Growth inhibitory effects were examined by monitoring the numbers of cells after infection with mock (PBS) solution, AxCA-LacZ, or AxCA-cp53. The DNA contents per cell were measured by flow cytometry analysis. Apoptotic DNA fragmentation was detected by use of a terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay.

RESULTS

AxCA-cp53-derived p53 gene mRNA and P53 protein were detected by RT-PCR analysis and immunohistochemistry, respectively. Multiplicity of infection at which 50% of cells had positive 3-indolyl-beta-D-galactopyranoside staining results ranged from 10 to 50. AxCA-cp53 induced growth inhibition in a dose-dependent manner. Arrest of the G1-phase population and apoptotic DNA fragmentation were observed in cells infected with AxCA-cp53.

CONCLUSIONS AND CLINICAL RELEVANCE

AxCA-cp53 inhibits cell growth via induction of cell cycle arrest and apoptosis in canine osteosarcoma and mammary adenocarcinoma cell lines that lack a functional p53 gene. AxCA-cp53 may be useful to target the p53 gene in the treatment of dogs with tumors.

Expression of p53, bcl-2 and growth hormone receptor in actinic keratosis, hypertrophic type

According to novel investigations, actinic keratosis (AK) is not a premalignant lesion but is a malignant lesion in the evolution to invasive squamous cell carcinoma (SCC). Thus, we analyzed p53, bcl-2 and growth hormone receptor (GHR) expression in hypertrophic-type AK (HAK) to determine the relative importance of these protooncogenes in the biological behavior of HAK. Expression of p53, bcl-2 and GHR was determined by immunohistochemistry in 33 HAK specimens and surrounding perilesional normal skin (PNS). The relative proportions of immunoreactive cells were determined. Of the 33 HAK specimens, 30 (91%) showed immunopositive staining for p53, 33 (100%) for bcl-2, and 12 (36%) for GHR. Highly positive p53 expression in HAK lesions could indicate that p53 mutation is an early and crucial event in lesion development. The detected pattern of the p53/ bcl-2 ratio in HAK suggests an important role for another gene: the proapoptotic gene bax. Our findings indicate that GHR expression could be a biological marker of progression of HAK to SCC.

The complex interactions of p53 with target DNA: we learn as we go

The most import biological function of the tumor suppressor p53 is that of a sequence-specific transactivator. In response to a variety of cellular stress stimuli, p53 induces the transcription of an ever-increasing number of target genes, leading to growth arrest and repair, or to apoptosis. Long considered as a "latent" DNA binder that requires prior activation by C-terminal modification, recent data provide strong evidence that the DNA binding activity of p53 is strongly dependent on structural features within the target DNA and is latent only if the target DNA lacks a certain structural signal code. In this review we discuss evidence for complex interactions of p53 with DNA, which are strongly dependent on the dynamics of DNA structure, especially in the context of chromatin. We provide a model of how this complexity may serve to achieve selectivity of target gene regulation by p53 and how DNA structure in the context of chromatin may serve to modulate p53 functions.

Mutational analysis of Noxa gene in human cancers

There has been mounting evidence that dysregulation of apoptosis is involved in the mechanisms of cancer development and somatic mutations of apoptosis-related genes have been reported in human cancers. Noxa, a Bcl-2 homology 3 (BH3)-only member of the Bcl-2 family, is known to interact with anti-apoptotic Bcl-2 family members and induces apoptosis. The aim of this study was to explore the possibility that the Noxa gene is mutated in human cancers. We have analyzed the entire coding region and all splice sites of the Noxa gene for the detection of somatic mutations in a series of human cancers, including carcinomas from stomach, colon, liver, urinary bladder and lung by polymerase chain reaction (PCR), single strand conformation polymorphism (SSCP), and DNA sequencing. We found one somatic mutation of the Noxa gene in a transitional cell carcinoma (TCC) of the urinary bladder. To evaluate the functional alterations of the mutant in apoptosis, we overexpressed the mutant and wild-type Noxa in 293T and HeLa cells, but could not find any significant difference in cell death between the wild-type and mutant Noxa. These data suggest that Noxa is rarely mutated in human carcinomas and that the contribution of Noxa gene mutation in the pathogenesis of human cancer might not be related to cell death mechanisms.

Lymphoma development in Bax transgenic mice is inhibited by Bcl-2 and associated with chromosomal instability

Bax is a Bcl-2 family member that promotes apoptosis but has paradoxical effects on lymphoma development in p53-deficient mice. To better understand the mechanism of Bax-induced lymphoma development, the effect of Bax levels, p53 status and Bcl-2 coexpression on lymphoma development were determined. In addition, DNA content and cytogenetics were performed on young (premalignant) Lck-Bax mice as measures of genetic instability. Bax promoted lymphoma development in p53-deficient mice in a dose-dependent manner. Bax expression also led to lymphoma development in both p53 +/- and +/+ animals. Ploidy analysis in mice prior to the onset of overt thymic lymphomas demonstrated that Lck-Bax transgenic mice were more likely to be aneuploid and demonstrate increased chromosome instability. With tumor progression, aneuploidy increased and Bax expression was maintained. Importantly, coexpression of Bcl-2 delayed lymphoma development in Lck-Bax transgenic mice. These data support a model in which increased sensitivity to apoptosis leads directly to chromosome instability in developing T cells and may explain a number of paradoxical observations regarding Bcl-2 family members and the regulation of cancer.

Multiple Epstein-Barr virus infections in healthy individuals

We employed a newly developed genotyping technique with direct representational detection of LMP-1 gene sequences to study the molecular epidemiology of Epstein-Barr virus (EBV) infection in healthy individuals. Infections with up to five different EBV genotypes were found in two of nine individuals studied. These results support the hypothesis that multiple EBV infections of healthy individuals are common. The implications for the development of an EBV vaccine are discussed.