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

Mechanisms of differential activation of target gene promoters by p53 hinge domain mutants with impaired apoptotic function

Suppression of tumor cell growth by p53 results from the activation of both apoptosis and cell cycle arrest functions that have been shown to be separable activities of p53. We report here that some mutants in the p53 hinge domain, a short linker between the DNA binding and tetramerization domains, differentially activated the promoters of p53 target genes and possessed an impaired apoptotic function. Our results indicate that the hinge domain may play an important role in differentially regulating p53 cell cycle arrest and apoptotic functions. However, the mechanisms by which p53 hinge domain mutants differentially activate its target genes, e.g. p21(WAF1/CIP1) and Bax, remain unknown. To investigate the possible mechanisms, recombinant p21(WAF1/CIP1) and Bax promoters were constructed, resulting in rearrangement of the existing p53 binding sites within a given promoter or actually swapping p53 binding sites between the two promoters. Our results suggest that multiple mechanisms of differential transactivation occur, depending on the molecular nature of the relevant hinge domain mutant, such as the possibility that dual separate DNA binding sites in the p21(WAF1/CIP1) promoter are responsible for the selective transactivation activity of p53 hinge domain mutant del300-327, which has a large deletion in the hinge domain. Lack of ideal p53 binding sites in the Bax promoter results in less potent activation than that seen with the p21(WAF1/CIP1) promoter when it is transactivated by hinge domain point mutant mutR306P or short deletion mutant del300-308 proteins. How the single mutation or the short deletion affect the conformation of p53 and consequently the transactivation of the Bax promoter will require further investigation of the relevant p53 protein: DNA-binding domain by NMR and x-ray crystallographic techniques.

DNA damage-inducible gene p33ING2 negatively regulates cell proliferation through acetylation of p53

The p33ING1 protein is a regulator of cell cycle, senescence, and apoptosis. Three alternatively spliced transcripts of p33ING1 encode p47ING1a, p33ING1b, and p24ING1c. We cloned an additional ING family member, p33ING2/ING1L. Unlike p33ING1b, p33ING2 is induced by the DNA-damaging agents etoposide and neocarzinostatin. p33ING1b and p33ING2 negatively regulate cell growth and survival in a p53-dependent manner through induction of G(1)-phase cell-cycle arrest and apoptosis. p33ING2 strongly enhances the transcriptional-transactivation activity of p53. Furthermore, p33ING2 expression increases the acetylation of p53 at Lys-382. Taken together, p33ING2 is a DNA damage-inducible gene that negatively regulates cell proliferation through activation of p53 by enhancing its acetylation.

No significant association of Epstein-Barr virus infection with invasive breast carcinoma

We studied 48 cases of invasive breast carcinoma for evidence of Epstein-Barr virus (EBV), which is associated with many human malignancies. In situ hybridization studies to detect the presence of EBV-encoded small nonpolyadenylated RNA (EBER)-1 were performed in paraffin sections. Immunohistochemical studies to detect EBV nuclear antigen (EBNA)-1, latent membrane protein (LMP)-1, and the transactivating immediate-early BZLF1 (ZEBRA) protein were also performed in paraffin sections. The presence of EBV genomic DNA was studied by polymerase chain reaction (PCR) amplification using sets of primers flanking the EBNA-4 and the EBV-LMP-1 genes in frozen tissues. Southern blot analysis using a probe flanking the EBV terminal repeat region was then attempted in cases that were PCR-positive. Five of 48 cases (10%) of breast carcinoma showed focal EBER-positive tumor cells. Twelve cases (25%) were positive for EBNA-1 by immunohistochemistry, all but one different from the EBER-positive cases. None of the cases were positive for LMP-1 or ZEBRA protein by immunohistochemistry. PCR studies for EBNA-4 and LMP-1 were each positive in five cases (including three cases in common). However, Southern blot studies successfully performed in all but one of the PCR-positive cases were completely negative. The identification of EBV by any methodology was not correlated with tumor size, grade, or lymph node status. This study demonstrated evidence of EBV infection in tissues involved by invasive breast carcinomas in a significant subset of cases. However, the lack of localization of EBV infection to a significant population of the tumor cells in any case, the negativity by Southern blot hybridization, and the lack of expression of multiple antigens in any case strongly argue against a significant role for EBV in the pathogenesis of breast carcinoma.

All-trans-retinoic acid enhances the effect of adenovirus-mediated wild-type p53 gene transfer in head and neck squamous cell carcinoma

OBJECTIVES

Adenovirus-mediated p53 (AdCMVp53) gene therapy for cancer is currently undergoing phase III clinical trials. One problematic aspect of this therapy is that the current protocols result in low transduction of the therapeutic virus in vivo. To search new modalities that can enhance the effect of AdCMVp53 gene therapy, we focused on retinoids.

METHODS

To study the effect of ATRA in combination with AdCMVp53 gene therapy, we pretreated head and neck squamous cell carcinoma (HNSCC) cells for 72 hours with a low-dose All-trans-retinoic acid (ATRA) (10-7 M-10-8 M) which will not affect the in vitro cell growth, and then infected the cells with low MOI (30MOI) AdCMVp53. In vitro cell proliferation assays, cell cycle assays were performed. Expression of p53 and p53-related gene products, BAX and p21, were examined.

RESULTS

The combined treatment with ATRA and Ad-p53 suppressed cell growth and induced apoptosis significantly more than AdCMVp53 treatment alone (P <.05). p53 expression significantly increased more after the combined treatment than after either treatment alone, at both the transcription and protein levels. In addition, increased expression of p21 and BAX, which are downstream gene products of p53, was observed in the combination. ATRA also enhanced the expression of green fluorescent protein (GFP) transduced by an adenovirus-cytomegalovirus (CMV)-GFP vector suggesting ATRA enhances adenovirus-CMV-promoted vectors through transcription.

CONCLUSIONS

Our results indicate that ATRA enhances AdCMVp53 expression through transcriptional mechanisms and can synergistically induce apoptosis in HNSCC cells. ATRA has a potential to enhance the effect of adenovirus-mediated p53 gene therapy for HNSCC.

Huperzine A protects rat pheochromocytoma cells against oxygen-glucose deprivation

The effect of huperzine A (HupA) on oxygen-glucose deprivation (OGD)-induced injury was investigated in the rat pheochromocytoma cell line PC12. OGD for 3 h and reoxygenation for 24 h triggered apoptosis characterized by chromatin condensation, nucleus fragmentation and DNA laddering. The temporal profile of c-jun, p53, bcl-2 and bax mRNA after OGD indicated that these genes played important roles in apoptosis. Pre-incubation of the cells for 2 h with 1 microM HupA significantly attenuated apoptosis. The same treatment also reduced the up-regulation of c-jun and bax as well as the down-regulation of bcl-2. These data suggest the ability of HupA to attenuate apoptosis induced by OGD may result from its capability to alter the expression of apoptosis-related genes.

Expression of caspases-3, -6 and -8 and their relation to apoptosis in non-small cell lung carcinoma

We analyzed a set of 103 non-small cell lung carcinomas (NSCLCs) for caspase-3, -6 and -8 expression and apoptosis. Additionally, the expression of bcl-2, bax and p53 were studied. Caspase-3 positivity appeared as diffuse, cytoplasmic staining and was restricted to the tumor area. In contrast, the immunoreactivity for caspase-6 was intense, granular and mostly located in single cells or groups of tumor cells showing apoptotic morphology. The caspase-8 expression pattern was a combination of the two other caspases studied, featuring both diffuse and single-cell patterns restricted to the tumor area. No significant differences were seen in caspase -3, -6 and -8 expression between tumors of different histological types or grades. The number of apoptotic cells and bodies was significantly higher in NSCLCs, in which caspase-8 immunostaining was mainly seen in single cells (p = 0.017), whereas caspase -3 and -6 expression had no association with apoptosis. It is apparent that, in lung tissue, up-regulation of caspase expression is a phenomenon associated solely with neoplasia and reflects the readiness of the tumor cells to undergo apoptosis. Interestingly, caspases -3, -6 and -8 each have an individual staining pattern in NSCLC, perhaps reflecting their different position in the caspase hierarchy.

Over-expression of APAF-1 and caspase-9 augments radiation-induced apoptosis in U-373MG glioma cells

The p53 tumor-suppressor gene plays a critical role in radiation-induced apoptosis. Several genes, including Bax and Fas, are involved in p53-mediated apoptosis, and their over-expression enhances the degree of radiation-induced apoptosis. Apaf-1 and caspase-9 have been reported to be downstream components of p53-mediated apoptosis, suggesting that these genes play a role in radiation-induced apoptosis. In this study, we transduced U-373MG cells harboring mutant p53 with the Apaf-1 and/or caspase-9 genes via adenoviral (Adv) vectors concomitant with X-ray irradiation and evaluated the degree of apoptosis. The percentage of apoptotic cells in U-373MG cells co-infected with the Adv for Apaf-1 (Adv-APAF-1) and that for caspase-9 (Adv-Casp9) and treated with irradiation (24%) was much higher than that in cells co-infected with Adv-APAF-1 and Adv-Casp9 and not treated with irradiation (0.86%) and that in cells infected with either Adv-APAF-1 or Adv-Casp9 and treated with irradiation (2.0% or 2.6%, respectively). The apoptosis induced by co-transduction of Apaf-1 and caspase-9 and irradiation was repressed in cells that were co-infected with the Adv for Bcl-X(L) but not in cells co-infected with the Adv for Bcl-2. These results indicate that Apaf-1 and caspase-9 play a role in radiation-induced apoptosis in cancer cells harboring mutant p53. Bcl-X(L) may be critically involved in the radioresistance of cancer cells by repressing Apaf-1- and caspase-9-mediated apoptosis. Expression of Apaf-1 and caspase-9 in tumors may be an important determinant of the therapeutic effect of irradiation in cancer treatment.

Orphan G protein-coupled receptor, GPR41, induces apoptosis via a p53/Bax pathway during ischemic hypoxia and reoxygenation

Orphan receptors that couple to G protein without known ligands are considered to relate directly to drug discovery. Here, we examine the expression of various orphan receptors in H9c2 cells during ischemic hypoxia and reoxygenation. Among orphan receptors examined, the level of G protein-coupled receptor 41 (GPR41) mRNA increases significantly, with a peak at 2 h after reoxygenation, and recovers to the control level by 3 h after reoxygenation. The level of glyceraldehyde-3-phosphate dehydrogenase mRNA used as an internal control remains almost constant. The levels of c-fos and c-jun mRNA increase significantly with ischemic hypoxia and reoxygenation. The transfection of GPR41 into H9c2 cells results in a significant decrease in cell number, with DNA fragmentation observed by in vitro and in situ assay. The amount of p53 protein increases significantly in the nuclei of cells expressing GPR41, accompanying an increase in the transcriptional activity of p53. Consistent with the activation of p53, the level of bax mRNA is significantly increased, which leads to an increase in Bax protein. Furthermore, the expression of a deletion mutant of a GPR41, which lacks the G protein binding site and shows an attenuation of intracellular phosphorylation signals to H9c2 cells, inhibits cell death and the increase in p53 protein within 24 h after reoxygenation. These observations demonstrate that GPR41 is a novel receptor that activates p53 leading to apoptosis during reoxygenation after ischemic hypoxia in H9c2 cells. We have designated GPR41 as the hypoxia-induced apoptosis receptor, HIA-R.

Promoter-proximal regulatory elements involved in oriP-EBNA1-independent and -dependent activation of the Epstein-Barr virus C promoter in B-lymphoid cell lines

The identification of the cellular factors that control the transcription regulatory activity of the Epstein-Barr virus C promoter (Cp) is fundamental to the understanding of the molecular mechanisms that control virus latent gene expression. Using transient transfection of reporter plasmids in group I phenotype B-lymphoid cells, we have previously shown that the -248 to -55 region (-248/-55 region) of Cp contains elements that are essential for oriPI-EBNA1-dependent as well as oriPI-EBNA1-independent activation of the promoter. We now establish the importance of this region by a detailed mutational analysis of reporter plasmids carrying Cp regulatory sequences together with or without oriPI. The reporter plasmids were transfected into group I phenotype Rael cells and group III phenotype cbc-Rael cells, and the Cp activity measured was correlated with the binding of candidate transcription factors in electrophoretic mobility shift assays and further assessed in cotransfection experiments. We show that the NF-Y transcription factor interacts with the previously identified CCAAT box in the -71/-63 Cp region (M. T. Puglielli, M. Woisetschlaeger, and S. H. Speck, J. Virol. 70:5758-5768, 1996). We also show that members of the C/EBP transcription factor family interact with a C/EBP consensus sequence in the -119/-112 region of Cp and that this interaction is important for promoter activity. A central finding is the identification of a GC-rich sequence in the -99/-91 Cp region that is essential for oriPI-EBNA1-independent as well as oriPI-EBNA1-dependent activity of the promoter. This region contains overlapping binding sites for Sp1 and Egr-1, and our results suggest that Sp1 is a positive and Egr-1 is a negative regulator of Cp activity. Furthermore, we demonstrate that a reporter plasmid that in addition to oriPI contains only the -111/+76 region of Cp still retains the ability to be activated by EBNA1.

Epstein-Barr virus associated lymphoproliferations in the AIDS setting

Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus that is associated with a variety of malignancies. In vivo infection of B lymphocytes is initially associated with the broad expression of immunodominant viral latency genes and proliferation of infected cells. Ultimately, a viral reservoir is established in resting B cells with restricted expression of viral latency genes and no expression of immunodominant viral genes. Among the tumours associated with EBV that are relevant to a consideration of EBV in HIV-associated malignancies are posttransplant lymphoproliferative disease, Burkitt's lymphoma (BL) and Hodgkin's disease (HD). BL carries whereas EBV in only a minority of cases whereas HD in patients infected with HIV is virtually always EBV-associated. EBV-directed T cell therapies have proven effective in posttransplant lymphomas in bone marrow transplantation patients. In patients with HIV infection, primary central nervous system (CNS) and immunoblastic lymphomas show similarities with posttransplant lymphoproliferative disease. EBV detection studies in cerebrospinal fluid are useful diagnostically in primary CNS lymphoma. T cell therapies may be useful in the treatment of EBV-associated lymphomas. Thus, a better understanding of the relationship between EBV and these tumours will not only help to clarify their pathogenesis, but may facilitate the development of new diagnostic and therapeutic strategies.

New concepts in radiation-induced apoptosis: 'premitotic apoptosis' and 'postmitotic apoptosis'

Formerly, the mechanisms responsible for the killing of cells by ionizing radiation were regarded as being divided into two distinct forms, interphase death and reproductive death. Since they were defined based on the classical radiobiological concepts using a clonogenic cell survival assay, biochemical and molecular biological mechanisms involved in the induction of radiation-induced cell death were not fully understood in relation to the modes of cell death. Recent multidisciplinary approaches to cell death mechanism have revealed that radiation-induced cell death is divided into several distinct pathways by the time course and cell-cycle position, and that apoptotic cell death plays a key role in almost every mode of cell death. This review discusses the mechanisms of radiation-induced apoptosis in relation to cell-cycle progression and highlights a new concept of the mode of cell death: 'premitotic apoptosis' and 'postmitotic apoptosis'. The former is a rapid apoptotic cell death associated with a prompt activation of caspase-3, a key enzyme of intracellular signaling of apoptosis. A rapid execution of cell killing in premitotic apoptosis is presumably due to the prompt activation of a set of pre-existed molecules following DNA damages. In contrast, the latter is a delayed apoptotic cell death after cell division, and unlike premitotic apoptosis, it neither requires a rapid activation of caspase-3 nor is inhibited by a specific inhibitor, Ac-DEVD-CHO. A downregulation of anti-apoptotic genes such as MAPK and Bcl-2 may play a key role in this mode of cell death. Characterization of these two types of apoptotic cell death regarding the cell cycle regulation and intracellular signaling will greatly help to understand the mechanisms of radiation-induced apoptosis.

Early molecular changes in irradiated aortic endothelium

Irradiated aortic endothelial cells (EC) exhibit distinct morphological, functional, and physiological responses to ionizing radiation (IR). However, the molecular basis for these responses has not been fully characterized. Cultured bovine and rat aortic endothelial cells were exposed to single fraction doses (0-30 Gy) of gamma radiation. IR caused dose-dependent DNA strand breaks which were repaired to near baseline levels within 30 min. A dose-dependent inhibition of cell growth was noted for IR greater than 1 Gy. At doses greater than 2.5 Gy, morphologic changes consistent with apoptosis and loss of cell viability were present beginning 12-16 h after radiation, with subsequent detachment of EC from the cell monolayer. By Western blot analysis, expression of p53, gadd45, p21, and bax protein increased in a time-and dose-dependent manner; p53 expression was maximal at 3 h after IR, and gadd45, bax and p21 levels peaked at 6 h. By Reverse Transcriptase Polymerase Chain Reaction (RT-PCR), levels of p53 mRNA were not significantly increased after IR, whereas gadd45 exhibited time- and dose-dependent increase in mRNA synthesis after IR. Activation of intracellular caspases, manifest by proteolytic poly (ADP-ribose) polymerase (PARP) and lamin B cleavage, was maximal at 15 h after IR, concident with other indices of EC apoptosis, including oligonucleosomal DNA degradation, TUNEL immunostaining, and morphologic changes. The tripeptide protease inhibitor z-Val-Ala-Asp (zVAD) prevented PARP and lamin cleavage, DNA fragmentation, morphological changes, and cell detachment in irradiated EC. The combined data suggested that gamma radiation induces a dose- and time-dependent sequence of early events in cultured EC with modulate growth arrest, apoptosis, and possibly premature senescence in surviving cells.

Expression of p53, bcl-2 and ras oncoproteins and apoptosis levels in acute leukaemias and myelodysplastic syndromes

We analysed by immunocytochemistry the expression of p53, bcl-2 and ras proteins in bone marrow blasts from 59 patients with acute leukaemia (AL), 36 myeloid (AML) and 23 lymphoid (ALL), and from 22 patients with myelodysplastic syndrome (MDS); our aim was to examine if abnormalities in their expression were associated with peculiar biological and clinical findings, or with an altered apoptosis rate, as measured by TUNEL technique. The oncoproteins were expressed with extreme variability, without significant differences among the various morphological or immunological AL subtypes. The mean percentages of bcl-2+ blasts were significantly higher in AML than in MDS (p = 0.01), and in MDS with bone marrow blastosis than in the forms without excess of blasts (p = 0.007). The lowest percentages of apoptotic cells were observed in ALL (mean 1%, p = 0.006), whereas in MDS the apoptotic index was higher (16.7%) than in AML (8.6%) and than in the normal controls (10.8%). but the difference tended to be statistically significant only for cases of refractory anaemia. Whereas in AML and MDS the apoptotic rate was independent of the oncoprotein expression, in ALL there was a significant linear relationship between TUNEL and ras positivity (p = 0.01). Among AML patients treated with intensive polychemotherapy, no differences were observed in oncoprotein expression and apoptotic rate between responders and resistant cases. In conclusion, our data are in agreement with the hypothesis that decreased apoptosis and enhanced cell survival are associated with AL, whereas a high level of apoptosis may be responsible for the ineffective hematopoiesis in MDS; abnormal expression of oncoproteins, even if not strictly related to apoptosis level, may influence disease behaviour.

Evidence that the death receptor DR4 is a DNA damage-inducible, p53-regulated gene

DR4 (TRAIL-R1), a member of the tumor necrosis factor receptor superfamily, is a cell surface receptor that triggers the apoptotic machinery upon binding to its ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Although three other TRAIL receptors DR5, DcR1, and DcR2 are induced by DNA damage and are regulated by the wild-type p53 tumor suppressor, it was not known whether these factors also affect DR4 expression. In this study, we found that DR4 expression is also enhanced by DNA damage whether induced by ionizing radiation or by chemotherapeutic agents. The induction was observed predominantly in cells containing wild-type p53 and was similar to the regulation patterns of DR5 and Fas, two other members of the family which are known to be regulated by p53. Transfection of HPV 16 E6 gene into cells with wild-type p53, which decreased the level of p53 protein, resulted in suppression of DR4 induction by DNA-damaging agents. Conversely, introduction of exogenous wild-type p53 through adenovirus infection has led to upregulation of endogenous DR4 in cells with mutant p53. Moreover, the transcription inhibitor actinomycin D abolished DNA-damaging agent-induced DR4 expression. Thus, DR4 appears to be a DNA damage-inducible, p53-regulated gene.

A diverse family of proteins containing tumor necrosis factor receptor-associated factor domains

We have identified three new tumor necrosis factor-receptor associated factor (TRAF) domain-containing proteins in humans using bioinformatics approaches, including: MUL, the product of the causative gene in Mulibrey Nanism syndrome; USP7 (HAUSP), an ubiquitin protease; and SPOP, a POZ domain-containing protein. Unlike classical TRAF family proteins involved in TNF family receptor (TNFR) signaling, the TRAF domains (TDs) of MUL, USP7, and SPOP are located near the NH(2) termini or central region of these proteins, rather than carboxyl end. MUL and USP7 are capable of binding in vitro via their TDs to all of the previously identified TRAF family proteins (TRAF1, TRAF2, TRAF3, TRAF4, TRAF5, and TRAF6), whereas the TD of SPOP interacts weakly with TRAF1 and TRAF6 only. The TD of MUL also interacted with itself, whereas the TDs of USP7 and SPOP did not self-associate. Analysis of various MUL and USP7 mutants by transient transfection assays indicated that the TDs of these proteins are necessary and sufficient for suppressing NF-kappaB induction by TRAF2 and TRAF6 as well as certain TRAF-binding TNF family receptors. In contrast, the TD of SPOP did not inhibit NF-kappaB induction. Immunofluorescence confocal microscopy indicated that MUL localizes to cytosolic bodies, with targeting to these structures mediated by a RBCC tripartite domain within the MUL protein. USP7 localized predominantly to the nucleus, in a TD-dependent manner. Data base searches revealed multiple proteins containing TDs homologous to those found in MUL, USP7, and SPOP throughout eukaryotes, including yeast, protists, plants, invertebrates, and mammals, suggesting that this branch of the TD family arose from an ancient gene. We propose the moniker TEFs (TD-encompassing factors) for this large family of proteins.

PY motifs of Epstein-Barr virus LMP2A regulate protein stability and phosphorylation of LMP2A-associated proteins

Latent membrane protein 2A (LMP2A) is expressed in latent Epstein-Barr virus (EBV) infection. We have demonstrated that Nedd4 family ubiquitin-protein ligases (E3s), AIP4, WWP2/AIP2, and Nedd4, bind specifically to two PY motifs present within the LMP2A amino-terminal domain. In this study, LMP2A PY motif mutant viruses were constructed to investigate the role of the LMP2A PY motifs. AIP4 was found to specifically associate with the LMP2A PY motifs in EBV-transformed lymphoblastoid cell lines (LCLs), extending our original observation to EBV-infected cells. Mutation of both of the LMP2A PY motifs resulted in an absence of binding of AIP4 to LMP2A, which resulted in an increase in the expression of Lyn and the constitutive hyperphosphorylation of LMP2A and an unknown 120-kDa protein. In addition, there was a modest increase in the constitutive phosphorylation of Syk and an unidentified 60-kDa protein. These results indicate that the PY motifs contained within LMP2A are important in regulating phosphorylation in EBV-infected LCLs, likely through the regulation of Lyn activity by specifically targeting the degradation of Lyn by ubiquination by Nedd4 family E3s. Despite differences between PY motif mutant LCLs and wild-type LCLs, the PY motif mutants still exhibited a block in B-cell receptor (BCR) signal transduction as measured by the induction of tyrosine phosphorylation and BZLF1 expression following BCR activation. EBV-transformed LCLs with mutations in the PY motifs were not different from wild-type LCLs in serum-dependent cell growth. Protein stability of LMP1, which colocalizes with LMP2A, was not affected by the LMP2A-associated E3s.

Expression of the cell cycle phosphatase cdc25C is down-regulated by the tumor suppressor protein p53 but not by p73

The cdc25C phosphatase dephosphorylates cdc2 kinase which then in complex with cyclin B can catalyse transition from the G(2) phase to mitosis. We demonstrate that transcription of cdc25C is repressed by p53 in a dose-dependent manner. In stably transfected DLD-1 colorectal adenocarcinoma cells, cdc25C expression is down-regulated when p53 is induced from a (tet)-off-regulated system. In contrast to p53, its homologue p73 is not able to down-modulate cdc25C expression. A previously identified site in the cdc25C promoter can bind p53 in vitro and, when placed in a heterologous construct, is able to activate transcription. However, transcriptional repression by p53 is not mediated through this site but is dependent on a segment containing three CCAAT-boxes. In general down-regulation of cdc25C transcription by reducing the levels of active cdc2 kinase contributes to G(2) arrest and G(2)/M checkpoint control. This reveals functional differences between p73 and p53 in regulating cell division.

Detection of Epstein-Barr virus DNA in the peripheral-blood cells of patients with nasopharyngeal carcinoma: relationship to distant metastasis and survival

PURPOSE

Nasopharyngeal carcinoma (NPC) has been proved to be an Epstein-Barr virus (EBV)-associated cancer. By use of nested polymerase chain reactions (PCRs), we examined whether the presence of EBV DNA in the peripheral-blood cells (PBC) can serve as a prognostic indicator for NPC.

PATIENTS AND METHODS

Peripheral blood from 124 patients with NPC who had no evidence of distant metastasis and 114 healthy volunteers with serologically positive findings for EBV infection was collected prospectively. Plasma and erythrocytes were separated. DNA was extracted from PBCs and analyzed by a nested PCR using primers specific to Epstein-Barr virus nuclear antigen 1 (EBNA-1). All patients were treated by radiotherapy with or without chemotherapy. Clinical parameters and status of EBNA-1 in PBCs were used for survival analysis using the Kaplan-Meier method and the Cox proportional hazards model.

RESULTS

Positive rates of EBNA-1 DNA in PBCs of NPC patients and healthy volunteers are 71% and 14%, respectively (P =.001). No significant difference was observed with regard to the clinical characteristics of patients who were EBNA-1-positive (n = 88) and those who were EBNA-1-negative (n = 36). After a median follow-up period of 38 months (range, 24 to 56 months), 29 of 88 EBNA-1-positive patients and only one of 36 EBNA-1-negative patients developed distant metastases (P =.00015). Kaplan-Meier estimates of overall survival (P =.0010), metastasis-free survival (P =.0004), and progression-free survival (P =.0004) were significantly lower for the patients in the EBNA-1-positive group than for those in the EBNA-1-negative group. Multivariate Cox analysis confirmed the same results.

CONCLUSION

The presence of EBNA-1 DNA in PBCs is a novel, important risk factor for patients with NPC that indicates a significantly higher risk of developing distant metastasis as well as a lower survival rate.

Activation of TRAF5 and TRAF6 signal cascades negatively regulates the latent replication origin of Epstein-Barr virus through p38 mitogen-activated protein kinase

Latent Epstein-Barr virus (EBV) is maintained by the virus replication origin oriP that initiates DNA replication with the viral oriP-binding factor EBNA1. However, it is not known whether oriP's replicator activity is regulated by virus proteins or extracellular signals. By using a transient replication assay, we found that a low level of expression of viral signal transduction activator latent membrane protein 1 (LMP1) suppressed oriP activity. The binding site of the tumor necrosis factor receptor-associated factor (TRAF) of LMP1 was essential for this suppressive effect. Activation of the TRAF signal cascade by overexpression of TRAF5 and/or TRAF6 also suppressed oriP activity. Conversely, blocking of TRAF signaling with dominant negative mutants of TRAF5 and TRAF6, as well as inhibition of a downstream signal mediator p38 MAPK, released the LMP1-induced oriP suppression. Furthermore, activation of TRAF6 signal cascade by lipopolysaccharides (LPS) resulted in loss of EBV from Burkitt's lymphoma cell line Akata, and inhibition of p38 MAPK abolished the suppressive effect of LPS. These results suggested that the level of oriP activity is regulated by LMP1 and extracellular signals through TRAF5- and TRAF6-mediated signal cascades.

Nucleoside analogues: mechanisms of drug resistance and reversal strategies

Nucleoside analogues (NA) are essential components of AML induction therapy (cytosine arabinoside), effective treatments of lymphoproliferative disorders (fludarabine, cladribine) and are also used in the treatment of some solid tumors (gemcitabine). These important compounds share some general common characteristics, namely in terms of requiring transport by specific membrane transporters, metabolism and interaction with intracellular targets. However, these compounds differ in regard to the types of transporters that most efficiently transport a given compound, and their preferential interaction with certain targets which may explain why some compounds are more effective against rapidly proliferating tumors and others on neoplasia with a more protracted evolution. In this review, we analyze the available data concerning mechanisms of action of and resistance to NA, with particular emphasis on recent advances in the characterization of nucleoside transporters and on the potential role of activating or inactivating enzymes in the induction of clinical resistance to these compounds. We performed an extensive search of published in vitro and clinical data in which the levels of expression of nucleoside-activating or inactivating enzymes have been correlated with tumor response or patient outcome. Strategies aiming to increase the intracellular concentrations of active compounds are presented.

Immunotherapeutic strategies for EBV-associated malignancies

Advances in our understanding of the role of cytotoxic T lymphocytes (CTLs) in the control of Epstein-Barr virus (EBV)-associated malignancies and the overall biology of these diseases have led to the development of novel therapeutic strategies designed to specifically target viral antigens expressed in these malignancies. Long-term success of many of these strategies is constrained by the latency phenotypes adopted by different diseases. Adoptive transfer of polyclonal virus-specific CTLs has been used successfully to reverse the outgrowth of malignancies such as post-transplant lymphoproliferative disease (PTLD). On the other hand, limited viral gene expression in other EBV-associated malignancies such as Burkitt's lymphoma, Hodgkin's disease and nasopharyngeal carcinoma limits the efficacy of immunotherapeutic strategies used for PTLD. Preclinical studies based on specific targeting of viral antigens expressed in these malignancies have provided very encouraging results and thus are likely to serve as an important platform for the treatment of human patients.

Autostimulation of the Epstein-Barr virus BRLF1 promoter is mediated through consensus Sp1 and Sp3 binding sites

As an essential step in the lytic cascade, the Rta homologues of gammaherpesviruses all activate their own expression. Consistent with this biologic function, the Epstein-Barr virus (EBV) Rta protein powerfully stimulates the promoter of its own gene, Rp, in EBV-positive B cells in transient-transfection reporter-based assays. We analyzed the activity of RpCAT in response to Rta by deletional and site-directed mutagenesis. Two cognate Sp1 binding sites located at -279 and -45 relative to the transcriptional start site proved crucial for Rta-mediated activation. Previously described binding sites for the cellular transcription factor Zif268 and the viral transactivator ZEBRA were found to be dispensable for activation of RpCAT by Rta. Gel shift analysis, using extracts of B cells in latency or induced into the lytic cycle, identified Sp1 and Sp3 as the predominant cellular proteins bound to Rp near -45. During the lytic cycle, ZEBRA bound Rp near the Sp1/Sp3 site. The binding of Sp1 and Sp3 to Rp correlated with the reporter activities in the mutagenesis study, establishing a direct link between transcriptional activation of Rp by Rta and DNA binding by Sp1 and/or Sp3. The relative abundance or functional state of the cellular Sp1 and Sp3 transcription factors may be altered in response to stimuli that induce the BRLF1 promoter and thereby contribute to the activation of the viral lytic cycle.

Signaling pathways and effector mechanisms pre-programmed cell death

Apoptosis is a complex biochemical process that involves all aspects of the cell from the plasma membrane to the nucleus. Apoptosis stimuli are mediated by many different cellular processes including protein synthesis and degradation, the alteration in protein phosphorylation states, the activation of lipid second messenger systems, and disruption of normal mitochondrial function. Despite this diversity in signal transduction, all apoptotic pathways are believed to converge ultimately with the activation of caspases leading to the characteristic morphological changes of apoptosis. In this review, we discuss what is known about these pathways and its implication for normal cellular function.

Bax protein expression in DCIS of the breast in relation to invasive ductal carcinoma and other molecular markers

This study describes the incidence of Bax protein expression in a series of 106 cases of breast cancer including 56 cases of ductal carcinoma in situ (DCIS) and 50 cases of invasive ductal carcinoma (IDC). Relationships of Bax expression to the histological grades of DCIS & IDC, and to the expression of Ki67, ER, p53, cerbB2 & Bcl2 are described. The expression of Bax, Ki67, ER, p53, cerbB2 and Bcl2 proteins is determined immunohistochemically. Cases were regarded positive for Bax, Bcl2 and cerbB2 when they showed either moderate or strong staining for these markers. The nuclear stains (Ki67, ER, and p53) were quantified in terms of percentage positive cells and cases for ER and p53 were considered positive when more than 10% cells were labelled. DCIS were graded histologically as well (n=18), intermediately (n=18), and poorly differentiated (n=20) Invasive ductal carcinoma was graded as grade I (well-differentiated) n=7, grade II (intermediate) n=24 and grade III (poorly differentiated) n=19. 65/106 cases (61%) were Bax positive including 37/56 (66%) of DCIS and 28/50 (56%) of IDC. Bax expression did not correlate to increasing histological grades of either DCIS or IDC. It did not correlate to Ki67, ER, p53 or cerbB2 but positive correlation was seen with Bcl2 (p=0.003). Bcl2 immunostaining displayed a negative correlation with increasing histological grades both of DCIS and IDC (p=0.026), (p=0.041) respectively. There was a trend of negative correlation of Bcl2 with Ki67 (p=0.062). It correlated positively with Bax (p=0.003) and ER (p<0.0001). Results suggest that the regulation of apoptosis is important in ductal carcinoma in situ of the breast as well as invasive ductal carcinomas. Bcl2 is associated with good prognostic markers in both DCIS and IDC, whereas the regulation of Bax is complex and does not necessarily correlate with mutant p53.

The tumor suppressor protein p53 requires a cofactor to activate transcriptionally the human BAX promoter

An important regulator of the proapoptotic BAX is the tumor suppressor protein p53. Unlike the p21 gene, in which p53-dependent transcriptional activation is mediated by a response element containing two consensus p53 half-sites, it previously was reported that activation of the BAX element by p53 requires additional sequences. Here, it is demonstrated that the minimal BAX response element capable of mediating p53-dependent transcriptional activation consists of two p53 half-sites plus an adjacent 6 base pairs (5'-GGGCGT-3'). This GC-rich region constitutes a "GC box" capable both of binding members of the Sp family of transcription factors, including Sp1 in vitro, and of conferring Sp1-dependent transcriptional activation on a minimal promoter in cells. Mutations within this GC box abrogated the ability of p53 to activate transcription without affecting the affinity of p53 for its binding site, demonstrating that these 6 bases are required for p53-dependent activation. In addition, a positive correlation was observed between the ability of p53 to activate transcription in cells and the ability of Sp1 to bind this response element in vitro. Mutations that inhibited Sp1 binding also blocked the ability of p53 to activate transcription through this element. Together, these results suggest a model in which p53 requires the cooperation of Sp1 or a Sp1-like factor to mediate transcriptional activation of the human BAX promoter.

Injury-induced apoptosis of neurons in adult brain is mediated by p53-dependent and p53-independent pathways and requires Bax

The mechanisms of injury-induced apoptosis of neurons within the CNS are not understood. We used a model of cortical injury in rat and mouse to induce retrograde neuronal apoptosis in thalamus. In this animal model, unilateral ablation of the occipital cortex causes unequivocal apoptosis of corticopetal projection neurons in the dorsal lateral geniculate nucleus (LGN) by 7 days postlesion. We tested the hypothesis that p53 and Bax regulate this retrograde neuronal apoptosis. We found, by using immunocytochemistry, that p53 accumulates in nuclei of neurons destined to undergo apoptosis. By immunoblotting, p53 levels increase ( approximately 150% of control) in nuclear-enriched fractions of the ipsilateral LGN by 5 days after occipital cortex ablation. p53 is functionally activated in nuclear fractions of the ipsilateral LGN at 5 days postlesion, as shown by DNA binding assay (approximately fourfold increase) and by immunodetection of phosphorylated p53. The levels of procaspase-3 increase at 4 days postlesion, and caspase-3 is activated prominently at 5 days postlesion. To identify whether neuronal apoptosis in the adult brain is dependent on p53 and Bax, cortical ablations were done on p53 and bax null mice. Neuronal apoptosis in the dorsal LGN is significantly attenuated (approximately 34%) in p53(-/-) mice. In lesioned p53(+/+) mice, Bax immunostaining is enhanced in the ipsilateral dorsal LGN and Bax immunoreactivity accumulates at perinuclear locations in dorsal LGN neurons. The enhancement and redistribution of Bax immunostaining is attenuated in lesioned p53(-/-) mice. Neuronal apoptosis in the dorsal LGN is blocked completely in bax(-/-) mice. We conclude that neuronal apoptosis in the adult thalamus after cortical injury requires Bax and is modulated by p53.

Physical interaction with Yes-associated protein enhances p73 transcriptional activity

Specific protein-protein interactions are involved in a large number of cellular processes and are mainly mediated by structurally and functionally defined domains. Here we report that the nuclear phosphoprotein p73 can engage in a physical association with the Yes-associated protein (YAP). This association occurs under physiological conditions as shown by reciprocal co-immunoprecipitation of complexes from lysates of P19 cells. The WW domain of YAP and the PPPPY motif of p73 are directly involved in the association. Furthermore, as required for ligands to group I WW domains, the terminal tyrosine (Y) of the PPPPY motif of p73 was shown to be essential for the association with YAP. Unlike p73alpha, p73beta, and p63alpha, which bind to YAP, the endogenous as well as exogenously expressed wild-type p53 (wt-p53) and the p73gamma isoform do not interact with YAP. Indeed, we documented that YAP interacts only with those members of the p53 family that have a well conserved PPXY motif, a target sequence for WW domains. Overexpression of YAP causes an increase of p73alpha transcriptional activity. Differential interaction of YAP with members of the p53 family may provide a molecular explanation for their functional divergence in signaling.

Characterization of nuclear factors binding to AT-rich element in the rat p53 promoter

In this study, we identified AT-rich element located at positions -504 to -516 in the rat p53 promoter by DNase I foot printing assay. This region was previously identified as a positive regulatory element in the murine p53 promoter and designated as PBF1 (p53 binding factor 1) binding site. However, the proteins binding to this AT-rich element have not been identified yet. Therefore, we characterized the binding protein by various biochemical methods. First, we confirmed that by the oligonucleotide competition assay, nuclear factors bound to the AT-rich element in a sequence-specific manner. Two binding proteins were identified in southwestern blotting analysis and the molecular masses of the proteins were 60 and 40 kDa, respectively. The proteins were stable to denaturants or ionic strength. Treatment of chelators showed that the binding proteins did not require divalent cation for DNA-binding activity. In addition, the binding proteins were labile to protease treatment. This study showed that 60 and 40 kDa proteins bound to AT-rich element and the physico-chemical properties provided new insights into the binding proteins.

Apoptotic response to homoharringtonine in human wt p53 leukemic cells is independent of reactive oxygen species generation and implicates Bax translocation, mitochondrial cytochrome c release and caspase activation

In the present study, we investigated the in vitro apoptotic response of leukemic cells to the cellular stress induced by homoharringtonine (HHT), a plant alkaloid with antileukemic activity which is currently being tested for treatment of acute and chronic leukemias. A comparison of leukemic cell lines with different p53 gene status revealed a considerably higher sensitivity to HHT-induced apoptosis in the cells with a wt p53, and apoptotic events in wt p53 leukemia cells (MOLT-3 cell line) were studied in more detail. To this end, we examined components of apoptotic cascades including Bax expression and its intracellular localization, changes of mitochondrial membrane potential (MMP), reactive oxygen species (ROS) levels, cytochrome c release from mitochondria and activation of caspases. Bax protein levels did not increase despite an up-regulation of bax at mRNA level. However, Bax translocation from cytosol towards mitochondria was observed. In addition, we observed a release of cytochrome c from the mitochondria, and the localization changes of both Bax and cytochrome c were found already at the early, annexin V-negative stage of HHT-induced apoptosis. HHT-treated MOLT-3 cells revealed loss of MMP as well as activation of caspases demonstrated by DEVD-, IETD- and LEHD-tetrapeptide cleavage activity in the cell lysates. ROS levels only slightly increased in HHT-treated cells and antioxidants did not prevent apoptosis and MMP changes. Therefore, wt p53 leukemic cells respond to HHT-specific cellular stress by induction of ROS-independent apoptotic pathway characterized by translocation of Bax, mitochondrial cytochrome c release and activation of caspases.

Gene therapy: principles and applications to hematopoietic cells

Ever since the development of technology allowing the transfer of new genes into eukaryotic cells, the hematopoietic system has been an obvious and desirable target for gene therapy. The last 10 years have witnessed an explosion of interest in this approach to treat human disease, both inherited and acquired, with the initiation of multiple clinical protocols. All gene therapy strategies have two essential technical requirements. These are: (1) the efficient introduction of the relevant genetic material into the target cell and (2) the expression of the transgene at therapeutic levels. Conceptual and technical hurdles involved with these requirements are still the objects of active research. To date, the most widely used and best understood vectors for gene transfer in hematopoietic cells are derived from retroviruses, although they suffer from several limitations. However, as gene transfer mechanisms become more efficient and long-term gene expression is enhanced, the variety of diseases that can be tackled by gene therapy will continue to expand. However, until the problem of delivery and subsequent expression is adequately resolved, gene therapy will not realize its full potential. The first part of this review gives an overview of the gene delivery technology available at present to transfer genetic sequences in human somatic cells. The relevance of the hematopoietic system to the development of gene therapy strategies as well as hematopoietic cell-based gene therapy is discussed in the second part.

Biology and disease associations of Epstein-Barr virus

Epstein-Barr virus (EBV) is a human herpesvirus which infects almost all of the world's population subclinically during childhood and thereafter remains in the body for life. The virus colonizes antibody-producing (B) cells, which, as relatively long-lived resting cells, are an ideal site for long-term residence. Here EBV evades recognition and destruction by cytotoxic T cells. EBV is passed to naive hosts in saliva, but how the virus gains access to this route of transmission is not entirely clear. EBV carries a set of latent genes that, when expressed in resting B cells, induce cell proliferation and thereby increase the chances of successful virus colonization of the B-cell system during primary infection and the establishment of persistence. However, if this cell proliferation is not controlled, or if it is accompanied by additional genetic events within the infected cell, it can lead to malignancy. Thus EBV acts as a step in the evolution of an ever-increasing list of malignancies which are broadly of lymphoid or epithelial cell origin. In some of these, such as B-lymphoproliferative disease in the immunocompromised host, the role of the virus is central and well defined; in others, such as Burkitt's lymphoma, essential cofactors have been identified which act in concert with EBV in the evolution of the malignant clone. However, in several diseases in which the presence of EBV has more recently been discovered, the role of the virus is unclear. This review describes recent views on the EBV life cycle and its interlinks with normal B-cell biology, and discusses how this interrelationship may be upset and result in EBV-associated disease.

Molecular virology of Epstein-Barr virus

Epstein-Barr virus (EBV) interacts with its host in three distinct ways in a highly regulated fashion: (i) EBV infects human B lymphocytes and induces proliferation of the infected cells, (ii) it enters into a latent phase in vivo that follows the proliferative phase, and (iii) it can be reactivated giving rise to the production of infectious progeny for reinfection of cells of the same type or transmission of the virus to another individual. In healthy people, these processes take place simultaneously in different anatomical and functional compartments and are linked to each other in a highly dynamic steady-state equilibrium. The development of a genetic system has paved the way for the dissection of those processes at a molecular level that can be studied in vitro, i.e. B-cell immortalization and the lytic cycle leading to production of infectious progeny. Polymerase chain reaction analyses coupled to fluorescent-activated cell sorting has on the other hand allowed a descriptive analysis of the virus-host interaction in peripheral blood cells as well as in tonsillar B cells in vivo. This paper is aimed at compiling our present knowledge on the process of B-cell immortalization in vitro as well as in vivo latency, and attempts to integrate this knowledge into the framework of the viral life cycle in vivo.

Expression of p53, bcl-2, and bax as predictors of response to radiotherapy in esophageal cancer

The sensitivity of cancers to radiotherapy or chemotherapy may be influenced by susceptibility to apoptosis. We evaluated whether expression of three proteins regulating apoptosis, p53, bcl-2, and bax, could predict the effect of radiotherapy in esophageal cancers. We used immunohistochemical staining for these protein regulators of apoptosis to study biopsy specimens obtained from 25 patients with esophageal squamous cell carcinoma before they underwent preoperative radiotherapy. Effectiveness of radiotherapy was assessed by barium esophagography, esophagoscopy, and computed tomography. Radiotherapy was effective in 12 patients and ineffective in 13 patients. Biopsy specimens from the 25 patients showed expression of p53, bcl-2, and bax to be 48.0%, 32.0%, and 76.0% respectively. Effectiveness of radiotherapy was correlated with p53 expression (p = 0.047), but bcl-2 and bax expression showed no relationship to effectiveness of radiotherapy. Expression of p53 protein in biopsy specimens may predict effectiveness of preoperative radiotherapy in esophageal cancers.

Different effects of genistein on molecular markers related to apoptosis in two phenotypically dissimilar breast cancer cell lines

The association between consumption of genistein-containing soybean products and lower risk of breast cancer suggests a cancer chemopreventive role for genistein. Consistent with this suggestion, exposing cultured human breast cancer cells to genistein inhibits cell proliferation, although this is not completely understood. To better understand how genistein works, the ability of genistein to induce apoptosis was compared in phenotypically dissimilar MCF-7 and MDA-MB-231 human breast cancer cells that express the wild-type and mutant p53 gene, respectively. After 6 days of incubation with 50 microM genistein, MCF-7 but not MDA-MB-231 cells, showed morphological signs of apoptosis. Marginal proteolytic cleavage of poly-(ADP-ribose)-polymerase and significant DNA fragmentation were also detected in MCF-7 cells. In elucidating these findings, it was determined that after 2 days of incubation with genistein, MCF-7 but not MDA-MB-231 cells, had significantly higher levels of p53. Accordingly, the expression of certain proteins modulated by p53 was studied next. Levels of p21 increased in both of the genistein-treated cell lines, suggesting that p21 gene expression was activated but in a p53-independent manner, whereas no significant changes in levels of the pro-apoptotic protein, Bax, were found. In MCF-7 cells, levels of the anti-apoptotic protein, Bcl-2, decreased slightly at 18-24 h but then increased considerably after 48 h. Hence, the Bax:Bcl-2 ratio initially increased but later decreased. These data suggest that at the genistein concentration tested, MCF-7 cells in contrast to MDA-MB-231 cells were sensitive to the induction of apoptosis by genistein, but Bax and Bcl-2 did not play clear roles.

Pediatric solid-organ transplant recipients carry chronic loads of Epstein-Barr virus exclusively in the immunoglobulin D-negative B-cell compartment

Solid-organ transplant recipients are at risk for development of lymphoproliferative diseases. The purpose of this study was to examine the distribution of Epstein-Barr virus (EBV) load in the peripheral blood of pediatric transplant recipients who had become chronic viral load carriers (>8 copies/10(5) lymphocytes for >2 months). A total of 19 patients with viral loads ranging from 20 to 5,000 viral genome copies/10(5) lymphocytes were studied. Ten patients had no previous diagnosis of posttransplant lymphoproliferative disease (PT-LPD), while nine had recovered from a diagnosed case of PT-LPD. No portion of the peripheral blood viral load was detected in the cell-free plasma fraction. Viral DNA was found in a population of cells characterized as CD19(hi) and immunoglobulin D negative, a phenotype that is consistent with the virus being carried exclusively in the memory B-cell compartment of the peripheral blood. There was no difference in the compartmentalization based upon either the level of the viral load or the past diagnosis of an episode of PT-LPD. These results have implications for the design of tests to detect EBV infection and for the interpretation and use of positive EBV PCR assays in the management of transplant recipients.

Nuclear and mitochondrial apoptotic pathways of p53

In contrast to p53-mediated cell cycle arrest, the mechanisms of p53-mediated apoptosis in response to cellular stresses such as DNA damage, hypoxia and oncogenic signals still remain poorly understood. Elucidating these pathways is all the more pressing since there is good evidence that the activation of apoptosis rather than cell cycle arrest is crucial in p53 tumor suppression. Moreover, the therapeutic interest in p53 as the molecular target of anticancer intervention rests mainly on its powerful apoptotic capability. This puzzling elusiveness suggests that p53 not only engages a plethora of downstream pathways but itself might possess a biochemical flexibility that goes beyond its role as a mere transcription factor. Recent evidence of a direct pro-apoptotic role of p53 protein at mitochondria suggests a synergistic effect with its transcriptional activation function and brings an unexpected new level of complexity into p53 apoptotic pathways.

Repression of human reduced folate carrier gene expression by wild type p53

The relationship between loss of functional p53 and human reduced folate carrier (hRFC) levels and function was examined in REH lymphoblastic leukemia cells, which express wild type p53, and in p53-null K562 cells (K562(pTet-on/p53)) engineered to express wild type p53 under control of a tetracycline-inducible promoter. Activation of p53 in REH cells by treatment with daunorubicin was accompanied by decreased ( approximately 5-fold) levels of hRFC transcripts and methotrexate transport. Treatment of K562(pTet-on/p53) cells with doxycycline resulted in a dose-dependent expression of p53 protein and transcripts, increased p21 protein, decreased dihydrofolate reductase, and G(1) arrest with decreased numbers of cells in S-phase. p53 induction was accompanied by up to 3-fold decreases in hRFC transcripts transcribed from the upstream hRFC-B promoter and similar losses of hRFC protein and methotrexate uptake capacity. Expression of p15 in an analogous inducible system in K562 cells resulted in a nearly identical decrease of S-phase cells and dihydrofolate reductase without effects on hRFC levels or activity. When the hRFC-B promoter was expressed as full-length and basal promoter-luciferase reporter constructs in K562(pTet-on/p53) cells, induction of p53 with doxycycline resulted in a 3-fold loss of promoter activity, which was reversed by cotransfection with a trans-dominant-negative p53. These studies show that wild type p53 acts as a repressor of hRFC gene expression, via a mechanism that is independent of its effects on cell cycle progression.

Epstein-Barr virus BamHi-a rightward transcript-encoded RPMS protein interacts with the CBF1-associated corepressor CIR to negatively regulate the activity of EBNA2 and NotchIC

The Epstein-Barr virus (EBV) BamHI-A rightward transcripts (BARTs) are expressed in all EBV-associated tumors as well as in latently infected B cells in vivo and cultured B-cell lines. One of the BART family transcripts contains an open reading frame, RPMS1, that encodes a nuclear protein termed RPMS. Reverse transcription-PCR analysis revealed that BART transcripts with the splicing pattern that generates the RPMS1 open reading frame are commonly expressed in EBV-positive lymphoblastoid cell lines and are also detected in Hodgkin's disease tissues. Experiments undertaken to determine the function of RPMS revealed that RPMS interacts with both CBF1 and components of the CBF1-associated corepressor complex. RPMS interaction with CBF1 was demonstrated in a glutathione S-transferase (GST) affinity assay and by the ability of RPMS to alter the intracellular localization of a mutant CBF1. A Gal4-RPMS fusion protein mediated transcriptional repression, suggesting an additional interaction between RPMS and corepressor proteins. GST affinity assays revealed interaction between RPMS and the corepressor Sin3A and CIR. The RPMS-CIR interaction was further substantiated in mammalian two-hybrid, coimmunoprecipitation, and colocalization experiments. RPMS has been shown to interfere with NotchIC and EBNA2 activation of CBF1-containing promoters in reporter assays. Consistent with this function, immunofluorescence assays performed on cotransfected cells showed that there was colocalization of RPMS with NotchIC and with EBNA2 in intranuclear punctate speckles. The effect of RPMS on NotchIC function was further examined in a muscle cell differentiation assay where RPMS was found to partially reverse NotchIC-mediated inhibition of differentiation. The mechanism of RPMS action was examined in cotransfection and mammalian two-hybrid assays. The results revealed that RPMS blocked relief of CBF1-mediated repression and interfered with SKIP-CIR interactions. We conclude that RPMS acts as a negative regulator of EBNA2 and Notch activity through its interactions with the CBF1-associated corepressor complex.

Activators of the Epstein-Barr virus lytic program concomitantly induce apoptosis, but lytic gene expression protects from cell death

Expression of the lytic cycle genes of Epstain-Barr virus (EBV) is induced in type I Burkitt's lymphoma-derived cells by treatment with phorbol esters (e.g., phorbol myristate acetate [PMA]), anti-immunoglobulin, or the cytokine transforming growth factor beta (TGF-beta). Concomitantly, all these agents induce apoptosis as judged by a sub-G1 fluorescence-activated cell sorter (FACS) profile, proteolytic cleavage of poly(ADP-ribose) polymerase (PARP) and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. However, caspase activation is not required for induction of the lytic cycle since the latter is not blocked by the caspase inhibitor ZVAD. Furthermore, not all agents that induce apoptosis in these cultures (for example, cisplatin and ceramide) induce the EBV lytic programme. Although it is closely associated with the lytic cycle, apoptosis is neither necessary nor sufficient for its activation. Multiparameter FACS analysis of cultures treated with PMA, anti-Ig, or TGF-beta revealed BZLF1-expressing cells distributed in different phases of the cell cycle according to which inducer was used. However, BZLF1-positive cells did not appear to undergo apoptosis and accumulate with a sub-G1 DNA content, irrespective of the inducer used. This result, which suggests that lytic gene expression is protective, was confirmed and extended by immunofluorescence staining doubled with TUNEL analysis. BZLF1- and also gp350-expressing cells were almost always shown to be negative for TUNEL staining. Similar experiments using EBV-positive and -negative subclones of Akata BL cells carrying an episomal BZLF1 reporter plasmid confirmed that protection from apoptosis was associated with the presence of the EBV genome. Finally, treatment with phosphonoacetic acid or acyclovir prior to induction with PMA, anti-Ig, or TGF-beta blocked the protective effect in Mutu-I cells. These data suggest that a late gene product(s) may be particularly important for protection against caspase activity and cell death.

In situ hybridization of Epstein-Barr virus in tumor cells and tumor-infiltrating lymphocytes of the gastrointestinal tract

Unlike gastric carcinoma, associations of the Epstein-Barr virus (EBV) with carcinomas of other sites in the gastrointestinal tract have not yet been clarified. To elucidate these associations, we investigated the presence of EBV in 142 cases of esophageal carcinoma, 107 cases of ampulla of Vater carcinoma, and 274 cases of colorectal carcinoma in Korean patients using EBV-encoded small RNAs (EBER)-in situ hybridization (ISH). In all cases, none of the tumor cells showed a positive signal, indicating that EBV is not generally related to the carcinogenesis of these cancers. Some EBV-positive tumor-infiltrating lymphocytes (TILs) were found in 8 of 142 cases (5.6%) of esophageal carcinoma, 8 of 107 cases (7.5%) of ampulla of Vater cancer, and 35 of 274 cases (12.8%) of colorectal carcinoma. For comparison, EBER-ISH was performed in consecutive gastric carcinomas; the EBER signal on tumor cells was observed in 17 of 306 cases (5.6%), and EBV-positive TILs were seen in 31 of the 289 cases (10.7%). There was no statistically significant difference in the frequencies of cases with EBV-positive TILs among the gastrointestinal tract cancers. We suggest that the reservoir lymphocytes carrying EBV, like other inflammatory cells, are able to reach anywhere, and that the chance for an epithelial cell to be exposed to EBV is similar at different sites of the gastrointestinal tract, regardless of its carcinogenic effect on the epithelial cell. HUM PATHOL 32:297-301.

Diagnostic and prognostic tumor markers in the gastrointestinal tract

The gastrointestinal tract is the most common site of malignancies of any anatomic system in the body. An early detection of primary tumors of the bowel, pancreas, liver, stomach, and esophagus is often difficult in asymptomatic patients and for this reason these tumors are often detected at a relatively advanced stage, when symptoms lead to a diagnostic evaluation. Furthermore, gastrointestinal tract tumors have an extremely variable prognosis; thus, the identification of new prognostic parameters may be useful for selecting patients to more tailored therapies. In this work, the main molecular, genetic, tissular, and circulating tumor markers proposed for diagnosis and prognosis of gastrointestinal malignancies are reviewed and discussed.

Expression of Bcl-2 during the development of rabbit retina

AIM

Programmed cell death or apoptosis plays an important role in retinal development. Bcl-2 is one of the genes whose endproducts regulate apoptosis. This study has examined the expression of Bcl-2 during the development of rabbit retina.

METHOD

Bcl-2 was detected by immunohistochemistry in developing rabbit retinas from embryonic day (E) 15, 22, 26, 29 and postnatal day (PN) 0, 3, 7, 15 and adults.

RESULTS

Faint immunoreactivity in the anuclear layer was observed at E 15, which increased in E 19. Immunoreactivity in certain radially aligned neuroepithelial cells/immature Müller cells could be recognized at E 22 and it progressively increased until in mature Müller cells radial processes were immunoreactive beyond the outer plexiform layer in PN 15 retinas. Immunoreactivity was already present in the optic nerve at E 15 but it decreased with increasing age until it disappeared at the time of birth.

CONCLUSIONS

Observations suggest that Bcl-2 is transiently expressed by ganglion cell axons during embryonic development. Detection of Bcl-2 immunoreactivity in the endfeet and proximal processes of radially aligned neuroepithelial cells/immature Müller cells early during the development, and its persistence in the endfeet and much of radial processes of Müller cells in adult life suggest that these cells possibly play a role in the development of the retinal ganglion cells, and also in the maintenance of the retinal neurons in the adults.

Gene expression in neurotrauma

It has been established that following injury to the central nervous system two types of damage take place, the initial insult and the secondary response to injury. This review will focus on the secondary molecular aspects of neurotrauma. These responses may be either deleterious or have protective effects upon the injured cell population. Molecular responses include the regulation of genes which change cellular architecture, up-regulate of growth factors, induce reparative stress responses, influence apoptosis and regulate the transcriptional process. The purpose of this study is to provide the reader with a brief overview of some of the molecular mechanisms which are activated following a neurological insult.

Linkage between STAT regulation and Epstein-Barr virus gene expression in tumors

Epstein-Barr virus (EBV) latency gene expression in lymphoblastoid cell lines is regulated by EBNA2. However, the factors regulating viral expression in EBV-associated tumors that do not express EBNA2 are poorly understood. In EBV-associated tumors, EBNA1 and frequently LMP1 are synthesized. We found that an alternative latent membrane protein 1 (LMP1) promoter, L1-TR, located within the terminal repeats is active in both nasopharyngeal carcinoma and Hodgkin's disease tissues. Examination of the L1-TR and the standard ED-L1 LMP1 promoters in electrophoretic mobility shift assays revealed that both promoters contain functional STAT binding sites. Further, both LMP1 promoters responded in reporter assays to activation of JAK-STAT signaling. Cotransfection of JAK1 or v-Src or treatment of cells with the cytokine interleukin-6 upregulated expression from ED-L1 and L1-TR reporter plasmids. Cotransfection of a dominant negative STAT3 beta revealed that STAT3 is likely to be the biologically relevant STAT for EBNA1 Qp and LMP1 L1-TR promoter regulation. In contrast, LMP1 expression from ED-L1 was not abrogated by STAT3 beta, indicating that the two LMP1 promoters are regulated by different STAT family members. Taken together with the previous demonstration of JAK-STAT activation of Qp driven EBNA1 expression, this places two of the EBV genes most commonly expressed in tumors under the control of the same signal transduction pathway. Immunohistochemical analyses of nasopharyngeal carcinoma tumors revealed that STAT3, STAT5, and STAT1 are constitutively activated in these tumors while STAT3 is constitutively activated in the malignant cells of Hodgkin's disease. We hypothesize that chronic or aberrant STAT activation may be both a necessary and predisposing event for EBV-driven tumorigenesis in immunocompetent individuals.