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

Functional Diversity of the CD8+ T-Cell Response to Epstein-Barr Virus (EBV): Implications for the Pathogenesis of EBV-Associated Lymphoproliferative Disorders

Epstein-Barr virus (EBV)-specific CD8+ cytotoxic T cells are thought to be critical for the control of EBV, which persists in healthy individuals as a latent infection of B cells. However, recent observations have indicated that CD8+ T-cell responses are not uniformly cytotoxic and that CD8+ T cells may be subdivided into type 1 and type 2 subsets that parallel the classically described Th1 and Th2 subsets of CD4+ T cells. Using two-color flow cytometric analysis of intracellular cytokine expression at the single-cell level, we have identified two distinct but overlapping subsets of EBV-specific CD8+ T cells, the first of which expressed high levels of interferon γ (IFNγ), but little or no interleukin-4 (IL-4), whereas the second subset was IFNγ+/IL-4+ double-positive. A significant proportion of EBV-specific CD8+ T cells also expressed IL-13. Subsequent analysis of a panel of 27 EBV-specific CD8+ T-cell clones showed inverse relationships between EBV-specific cytotoxicity and secretion of IL-4, IL-10, and IFNγ, respectively. IL-10 was not secreted by the 11 most strongly cytotoxic clones, suggesting that IL-10 secretion may provide a functional definition of an EBV-specific type 2 CD8+ T-cell subset with reduced EBV-specific cytotoxicity. Finally, we have demonstrated that EBV-specific CD8+ T cells that express type 2 cytokines possess the ability to activate resting B cells. EBV-specific CD8+ T cells thus have the potential to reactivate latent EBV infection in vivo and may contribute to the development of EBV-associated lymphoproliferative disorders and lymphoma.

Functional Diversity of the CD8+ T-Cell Response to Epstein-Barr Virus (EBV): Implications for the Pathogenesis of EBV-Associated Lymphoproliferative Disorders

Epstein-Barr virus (EBV)-specific CD8+ cytotoxic T cells are thought to be critical for the control of EBV, which persists in healthy individuals as a latent infection of B cells. However, recent observations have indicated that CD8+ T-cell responses are not uniformly cytotoxic and that CD8+ T cells may be subdivided into type 1 and type 2 subsets that parallel the classically described Th1 and Th2 subsets of CD4+ T cells. Using two-color flow cytometric analysis of intracellular cytokine expression at the single-cell level, we have identified two distinct but overlapping subsets of EBV-specific CD8+ T cells, the first of which expressed high levels of interferon γ (IFNγ), but little or no interleukin-4 (IL-4), whereas the second subset was IFNγ+/IL-4+ double-positive. A significant proportion of EBV-specific CD8+ T cells also expressed IL-13. Subsequent analysis of a panel of 27 EBV-specific CD8+ T-cell clones showed inverse relationships between EBV-specific cytotoxicity and secretion of IL-4, IL-10, and IFNγ, respectively. IL-10 was not secreted by the 11 most strongly cytotoxic clones, suggesting that IL-10 secretion may provide a functional definition of an EBV-specific type 2 CD8+ T-cell subset with reduced EBV-specific cytotoxicity. Finally, we have demonstrated that EBV-specific CD8+ T cells that express type 2 cytokines possess the ability to activate resting B cells. EBV-specific CD8+ T cells thus have the potential to reactivate latent EBV infection in vivo and may contribute to the development of EBV-associated lymphoproliferative disorders and lymphoma.

BAG-1L protein enhances androgen receptor function

BAG-1 is a regulator of heat shock protein (Hsp) 70/Hsc70 family proteins that interacts with steroid hormone receptors. The recently identified BAG-1 long (BAG-1L) protein, an isoform of BAG-1 that arises from translation initiation at a noncanonical CUG codon, was co-immunoprecipitated with androgen receptors (AR) from LNCaP prostate cancer cells and other cell lysates, whereas the shorter originally identified BAG-1 and BAG-1M (RAP 46) proteins were not. BAG-1L, but not BAG-1 or BAG-1M (RAP46), also markedly enhanced the ability of AR to transactivate reporter gene plasmids containing an androgen response element (ARE) in PC3 prostate cancer and other cell lines. A C-terminal region deletion mutant of BAG-1L failed to co-immunoprecipitate with AR and functioned as a trans-dominant inhibitor of BAG-1L, impairing AR-induced transactivation of ARE-containing reporter plasmids. In addition, BAG-1L significantly reduced the concentrations of 5alpha-dihydrotestosterone (DHT) required for AR activity but did not induce ligand-independent transactivation. BAG-1L also markedly improved the ability of AR to transactivate reporter genes when cells were cultured with DHT in combination with the anti-androgen cyproterone acetate. The effects of BAG-1L on AR could not be explained by detectable alterations in the DHT-induced translocation of AR from cytosol to nucleus, nor by BAG-1L-induced increases in the amounts of AR protein. These findings implicate BAG-1L in the regulation of AR function and may have relevance to mechanisms of prostate cancer resistance to hormone-ablative and anti-androgen therapy.

Immunohistochemical p53 protein status in nonsmall cell lung cancer is a promising indicator in determining in vitro chemosensitivity to some anticancer drugs

BACKGROUND AND OBJECTIVES

The tumor suppressor oncogene p53 abnormalities have been closely associated with resistance or sensitivity of cancer cells to some chemotherapeutic agents. We examined the association between p53 protein status in nonsmall cell lung cancer (NSCLC) and in vitro chemosensitivity to several chemotherapeutic agents.

METHODS

Using 146 surgically resected specimens of NSCLC, p53 status was immunohistochemically evaluated, and in vitro chemosensitivity to 5-fluorouracil (5-Fu), cisplatin (CDDP), mitomycin C (MMC), etoposide (VP-16), doxorubicin hydrochloride (ADM), and vindesine sulfate (VDS) was examined by a collagen gel-droplet embedded culture drug sensitivity test (CD-DST, Int J Oncol, 1997;11:449).

RESULTS

Sixty-five of 146 materials (45%) showed immunohistochemically abnormal p53 protein accumulation in >10% of cancer cells within the tumor tissue, being regarded as p53+, whereas 81 (55%) were to p53-, in which no or less than 10% positive immunostaining cancer cells were detected. By CD-DST, the incidence of chemosensitive, borderline, and resistant p53- materials (N=81) to 5-Fu was 37%(N=30), 14%(N=11), and 49%(N=40), whereas that of p53+ materials (N=65) was 20%(N=13), 6%(N=4), and 74%(N=48), respectively, showing that p53- materials were significantly more sensitive to 5-Fu than p53+ materials (P=0.011), especially in the adenocarcinoma type. As similar borderline association between p53 protein status and in vitro chemosensitivity was also shown in ADM (P=0.078), but not in other chemoagents.

CONCLUSIONS

Immunohistochemically detected p53 protein status in NSCLC patients may be a promising indicator in determining in vitro chemosensitivity to some anticancer drugs, especially 5-Fu and ADM.

Regulation of cell cycle progression following DNA damage

DNA damage causes an arrest in cell cycle progression. Checkpoints, which monitor the state of the DNA, exist throughout the cycle and negatively regulate cell cycle transitions when damage is detected. The molecular basis of how these checkpoints are activated, and interact with the cell cycle machinery, is just beginning to be understood. Studies in yeast have identified a number of genes involved in a G2 DNA damage checkpoint, while in mammalian cells a G1 checkpoint has been extensively studied.

Cellular responses to antimetabolite anticancer agents: cytostasis versus cytotoxicity

Thymineless death is an important cytotoxic response to several classes of antimetabolite agents used in the treatment of patients with carcinomas and hematopoeitic malignancies. Cell death induced by lack of dThd results in the formation of DNA nucleosomal ladders, and hence would be defined as a form of apoptosis. Although drug resistance to these agents has been extensively studied, relatively little attention has been focused on events downstream of dTTP depletion that determine the ultimate fate of the cancer cell. In this article we review some of the emerging data that suggests the role of p53 in determining whether the cellular response to dThd deprivation is cytostasis or cytotoxicity (apoptosis).

Apoptosis and the cell cycle

Apoptosis is a genetically controlled response by which eukaryotic cells undergo programmed cell death. This phenomenon plays a major role in developmental pathways (1), provides a homeostatic balance of cell populations, and is deregulated in many diseases including cancer. Control of cell number is determined by an intricate balance of cell death and cell proliferation. Accumulation of cells through suppression of death can contribute to cancer and to persistent viral infections, while excessive death can result in impaired development and in degenerative diseases. Identification of genes that control cell death, and understanding of the impact of apoptosis in both development and disease has advanced our knowledge of apoptosis in the past few years. There appears to be a linkage between apoptosis and cell cycle control mechanisms. Elucidating the mechanisms that link cell cycle control with apoptosis will be of key importance in understanding tumour progression and designing new models of effective tumour therapy.

Bax directly induces release of cytochrome c from isolated mitochondria

Bax is a pro-apoptotic member of the Bcl-2 protein family that resides in the outer mitochondrial membrane. It is controversial whether Bax promotes cell death directly through its putative function as a channel protein versus indirectly by inhibiting cellular regulators of the cell death proteases (caspases). We show here that addition of submicromolar amounts of recombinant Bax protein to isolated mitochondria can induce cytochrome c (Cyt c) release, whereas a peptide representing the Bax BH3 domain was inactive. When placed into purified cytosol, neither mitochondria nor Bax individually induced proteolytic processing and activation of caspases. In contrast, the combination of Bax and mitochondria triggered release of Cyt c from mitochondria and induced caspase activation in cytosols. Supernatants from Bax-treated mitochondria also induced caspase processing and activation. Recombinant Bcl-XL protein abrogated Bax-induced release of Cyt c from isolated mitochondria and prevented caspase activation. In contrast, the broad-specificity caspase inhibitor benzyloxycarbonyl-valinyl-alaninyl-aspartyl-(0-methyl)- fluoromethylketone (zVAD-fmk) and the caspase-inhibiting protein X-IAP had no effect on Bax-induced release of Cyt c from mitochondria in vitro but prevented the subsequent activation of caspases in cytosolic extracts. Unlike Ca2+, a classical inducer of mitochondrial permeability transition, Bax did not induce swelling of mitochondria in vitro. Because the organellar swelling caused by permeability transition causes outer membrane rupture, the findings, therefore, dissociate these two events, implying that Bax uses an alternative mechanism for triggering release of Cyt c from mitochondria.

Sensitivity and reproducibility of RT-PCR to detect Borna disease virus (BDV) RNA in blood: implications for BDV epidemiology

Borna disease virus (BDV) infection of domestic animals and humans appears to have a worldwide distribution. There is evidence suggesting an association of BDV with certain psychiatric disorders. However, more comprehensive epidemiological studies are required to establish rigorously a link between BDV and human mental disorders, and to evaluate the role of carrier animals as potential source of BDV for human infection. The use of RT-PCR to detect BDV RNA in peripheral blood mononuclear cells (PBMCs) of infected individuals is a powerful tool to address these questions. The comparison of discrepant results reported by different investigators using this approach is hampered by the lack of controls to assess the sensitivity and reproducibility of the assays. Procedures are now described that allow the establishment of standardized controls to evaluate the performance of the RT-PCR assays. This RT-PCR assay detected reproducibly 100 copies of BDV p40 RNA in 5 microg of RNA. The data illustrate that the number of PBMCs used for RNA preparation, rather than the amount of RNA, has a critical influence on the outcome of the RT-PCR assay. Evidence is provided that levels of BDV in blood do not necessarily reflect viral load in brain.

Phenotype-Dependent Differences in Proteasome Subunit Composition and Cleavage Specificity in B Cell Lines

We have compared the subunit composition and enzymatic activity of purified 26S proteasomes from Burkitt’s lymphoma (BL) cells and in vitro EBV-transformed lymphoblastoid cell lines (LCLs) of normal B cell origin. Low expression of the IFN-γ-regulated β low molecular mass polypeptide (Lmp)2, Lmp7, and MECL-1 was demonstrated in a panel of seven BL lines that express the germinal center cell phenotype of the original tumor. Coexpression of Lmp2 and Lmp7 with the constitutively expressed subunits δ and MB1 was demonstrated in the BL lines by immunoprecipitation and two-dimensional gel fractionation of the 20S proteasomes. Coexpression of these subunits correlated with reduced levels of chymotrypsin- and trypsin-like activities detected by the cleavage of fluorogenic substrates. Down-regulation of Lmp2 and Lmp7 and decreased chymotrypsin- and trypsin-like activities were also observed in purified proteasomes from a c-myc-transfected subline of the ER/EB2–5 LCL that has adopted a BL-like phenotype. A synthetic peptide analogue of the immunodominant epitope from the EBV nuclear Ag 4 (E4416–424Y) was cleaved by proteasomes from BLs and A1, while proteasomes from LCLs were inactive. Cleavage of the E4416–424Y peptide was not affected by treatment of the BL cells with IFN-γ despite both significant up-regulation of Lmp2 and Lmp7 and reconstitution of chymotrypsin and trypsin-like activities against fluorogenic substrates to LCL-like levels. The results demonstrate that B cell lines representing different stages of B cell activation and differentiation express proteasomes with different subunit compositions and enzymatic activity. This may result in the generation of a distinct set of endogenous peptides and influence the immunogenicity of these cells.

Therapeutic potential of recombinant p53 overexpression in breast cancer cells expressing endogenous wild-type p53

Reconstitution of the p53-dependent apoptotic pathway by gene transfer of a recombinant wild-type p53 minigene leads to rapid apoptotic cell death in breast and other cancer cell types expressing null or mutant p53. Tumour cells expressing wild-type p53 have been reported to be more resistant to this treatment strategy, presumably as a result of mutations in downstream regulators of p53-dependent apoptotic signalling. The MCF-7 breast cancer cell line is representative of this class of tumour cell. Our recent observation of a p53-dependent apoptotic response following adenovirus-mediated HSV thymidine kinase gene transfer and gancyclovir treatment led us to reexamine recombinant p53 cytotoxicity in MCF-7 cells. Infection with a recombinant adenovirus expressing wild-type p53 resulted in a dramatic increase in p53 protein levels and was accompanied by an increase in p21WAF/CIP1 protein levels and G1 arrest within 24 hours post-infection. A significant decrease in MCF-7 cell viability was first observed at 5 days post-infection and coincided with the appearance of morphological and biochemical changes consistent with apoptotic cell death. By day 7 post-treatment, cell viability decreased to 45% and clonogenic survival was reduced to 12% of controls. The results demonstrate that persistent, high level expression of recombinant p53 can induce programmed cell death in MCF-7 cells. While the mechanism by which p53 overexpression overcomes the defect in downstream apoptotic signalling is not clear, our data suggests that this treatment strategy may be beneficial for the class of tumour cells represented by the MCF-7 cell line.

In situ amplification of the Epstein-Barr virus genome in cell suspensions

Epstein-Barr virus (EBV) is distributed widely throughout the world. Apart from a association with two geographically-restricted malignancies (Burkitt's lymphoma and nasopharyngeal carcinoma), EBV is thought to be implicated in the etiology of B-cell lymphoma in immunocompromised individuals. In these patients, monitoring the viral load in serum can provide useful information on the timing of the instigation of antiviral therapy, i.e. as soon as a rise is detected. PCR technology, owing to its high sensitivity, is used frequently in such situations. In order to gain further insight into the nature of the peripheral blood cells carrying the viral genome on a cell-by-cell basis, an in situ amplification technique was developed as a model using two cell lines growing in suspension, with the aim of distinguishing between EBV-positive and EBV-negative cells. Preliminary experiments were undertaken subsequently on clinical samples from patients with infectious mononucleosis and patients with lymphoma indicating that this technique might be useful clinically.

Defects in the ubiquitin pathway induce caspase-independent apoptosis blocked by Bcl-2

Apoptosis requires the activation of caspases (formerly interleukin 1beta-converting enzyme-like proteases), in particular those related to the caspase-3/7/6 subfamily. Recent data, however, revealed that, although caspase-specific inhibitors delay apoptosis, they are often incapable of preventing it. To obtain evidence for caspase-independent steps of apoptosis, we artificially created a high amount of short-lived or aberrant proteins by blocking the ubiquitin degradation pathway. A temperature-sensitive defect in the ubiquitin-activating enzyme E1 induced apoptosis independent of the activation of caspase-3 and -6 and the cleavage of their respective substrates poly(ADP-ribose) polymerase and lamin A. In addition, neither the caspase 3/7-specific inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone nor the general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone were capable of blocking this type of cell death. By contrast, Bcl-2 overexpression effectively protected cells from apoptosis induced by a defect in the E1 enzyme at the nonpermissive temperature. Bcl-2 acted downstream of the accumulation of short-lived or aberrant proteins because it did not prevent the overexpression of the short-lived proteins p53, p27(kip1), and cyclins D1 and B1 under conditions of decreased ubiquitination. These results suggest the existence of short-lived proteins that may serve the role of caspase-independent effectors of apoptosis and attractive targets of the death-protective action of Bcl-2.

No induced apoptosis accompanying the change of oncoprotein expression and the activation of CPP32 protease

Previously we have shown that nitric oxide (NO) donors induced apoptosis in vascular smooth muscle cells (VSMCs). However, the mechanisms by which NO induced apoptosis in VSMCs are entirely unknown. In the present study, we intended to identify the mechanism by which NO donors induce apoptosis in VSMCs. First, we evaluated the expression of c-Myc, P53, and Bcl-2 proteins in VSMCs treated by NO donors. c-Myc and P53 protein expression increased after VSMCs were incubated with NO donors for 6 hr and reached a maximum level at 24 hr, while Bcl-2 protein decreased after 12 hr incubation. Next we investigated to see whether the CPP32 protease activation was involved in NO donors-induced apoptosis. In VSMCs treated by NO donors, the increase of CPP32 protease activity was observed and specific inhibition of CPP32 activity significantly prevented apoptosis induced by NO donors in a dose-dependent manner. These results suggest that NO donors induced apoptosis through proto-oncoprotein expression and CPP32-like protease activation.

Molecular regulation of neuronal apoptosis

Apoptosis is a fundamental biological process used by all muticellular organisms to eliminate unwanted or superfluous cells, and is a prominent feature of normal neural development. Developmentally occurring neuronal apoptosis serves to match the number of neurons to the requirements of their synaptic targets and to rid the nervous system of inappropriate connections. While it is generally accepted that apoptosis is a "suicide program" inherent in all cells, the molecular basis of this program is just beginning to be unraveled. Evidence from numerous recent studies indicate that a variety of proteins are involved in the transmission of external signals to the cell-death machinery within the cell. This review describes many of the recent findings of the regulatory pathways and genes that have been implicated in the induction or suppression of apoptosis in neurons.

Bax immunohistochemical expression in breast carcinoma: a study with long term follow-up

Bax and Bcl2 are functionally antagonistic proteins which control apoptosis, whose expression in human tumours could be of prognostic value. We evaluated Bax and Bcl2 expression in 239 breast carcinomas (99 N0, 140 N1/2) with long term follow-up (median 79 months, range 11-140) in relation to clinico-pathologic parameters, clinical outcome, adjuvant therapy and expression of oestrogen receptor protein and p53. The prognostic value of Bax was investigated in the whole series of patients and in subgroups of homogeneously staged and treated patients (i.e., node-negative, N1/2 CMF-treated, N1/2 tamoxifen-treated). Bax immunostaining was cytoplasmic and heterogeneous. Cases were scored as Bax-positive if there were more than 20% reacting cells. High Bax expression was associated with positive nodal status (p = 0.03) and high Bcl2 expression (p = 0.01) and was more frequent in high-grade tumours. In the node-negative subgroup, Bax expression was associated with small tumour size. No association was seen with other parameters or with clinical outcome in any subgroup of patients. Since the apoptotic rate of a tumour is influenced by the ratio Bcl2/Bax, we investigated the combined effects of Bax and Bcl2 expression in relation to clinical outcome. However, no differences in survival were seen in the Bcl2-negative and Bcl2-positive groups when they were subdivided on the basis of the level of Bax expression and vice versa. In experimental systems, p53 is a direct transcriptional activator of the human bax gene. However, we could not observe any relation between Bax and p53 expression. We investigated whether the combined p53/Bax expression could have any prognostic value since it is predicted that tumours with normal p53 expression and concurrent high levels of Bax should be less aggressive and more susceptible to therapy. However, while p53 itself was of prognostic value, Bax expression was not related to prognosis in p53-negative or in p53-positive groups.

Epstein-Barr Virus (EBV) in Endemic Burkitt's Lymphoma: Molecular Analysis of Primary Tumor Tissue

Many aspects of Epstein-Barr virus (EBV) and tumor biology have been studied in Burkitt's lymphoma (BL)-derived cell lines. However, in tissue culture, patterns of gene expression and C promoter-G (CpG) methylation often change and viral strain selection may occur. In this report, 10 cases of snap-frozen endemic BL tumors are characterized in terms of viral gene expression, promoter usage, methylation, and viral strain. EBNA1 and BamHI-A rightward transcripts (BART) were detected in 7 of 7 and LMP2A transcripts in 5 of 7 tumors with well-preserved RNA. Transcripts for the other EBNAs and for LMP1 were not detected in any tumor. These tumors differ from BL cell lines in that they lack a variety of lytic cycle transcripts. This pattern of viral gene expression in endemic BL is similar to that reported in peripheral blood mononuclear cells (PBMCs) from healthy EBV–seropositive individuals. EBNA1 transcripts originated from the Q promoter (Qp) but not C, W, or F promoters that drive transcription of EBNA1 in other circumstances. Whereas Cp has been previously shown to be entirely CpG methylated in BL, bisulfite genomic sequencing showed virtually no methylation in Qp. Type-A EBV was detected in 6 of 10 and type B in 4 of 10 cases. A previously reported 30bp deletion variant in the carboxyl terminal of LMP1 gene was detected in 5 of 10 cases. The association with both A and B strains contrasts with EBV–associated Hodgkin's disease, nasopharyngeal carcinoma, and post-transplant lymphoproliferative disease, which are much more consistently associated with A strain virus.

Pore formation domain of human pro-apoptotic Bax induces mammalian apoptosis as well as bacterial death without antagonizing anti-apoptotic factors

A trace amount of the pro-apoptotic factor human Bax was sufficient to kill host Escherichia coli (Asoh, S., Nishimaki, K., Nanbu-Wakao, R., and Ohta, S., submitted). The region of Bax lethal to E. coli cells was determined by introducing truncated human bax mutant genes. A peptide corresponding to amino acid residues 115 to 144 of Bax was the smallest peptide capable of inducing cell death of E. coli. A truncated bax gene (Bax112-192) containing the region lethal to E. coli was then introduced into a murine promyeloid cell line, FDC-P1. Constitutively expressed Bax112-192 induced apoptosis as judged by decrease of transfectants surviving and DNA fragmentation. These results indicate that Bax112-192 contains the region directly responsible for mammalian apoptosis as well as bacterial death. Flow cytometric analysis by FITC-Annexin V showed that the transfectant cells expressing Bax112-192 or native Bax became apoptotic even without external stimuli. The apoptotic population in the cells expressing Bax112-192 was not decreased by co-expression of Bcl-2 or Bcl-XL, while Bcl-2 or Bcl-XL suppressed apoptosis in the cells expressing native Bax. Therefore, Bax induces apoptosis by its own activity without blocking the anti-apoptotic activity involved in Bcl-2 or Bcl-XL.

Apoptosis was promoted at a nonpermissive temperature in DNA replication-defective temperature-sensitive mutants of mouse FM3A cells

Apoptosis was promoted at the nonpermissive temperature in some temperature-sensitive (ts) mutant strains of mouse FM3A cells deficient in initiation of DNA replication. We examined expression of cell cycle regulation genes in the four ts mutant strains and found that two strains, tsFT107 and tsFT111, exhibited marked accumulation of p53 protein by a posttranscriptional mechanism at 16 h after temperature up-shift. These two strains also exhibited high levels of p21 mRNA expression, repression of cyclin A and D1 mRNAs, and obvious accumulation of underphosphorylated retinoblastoma protein. Only these two strains died by apoptosis at day 3 after up-shift, although no change was observed in the level of bax mRNA. These results suggest the existence of two types of responses after temperature up-shift in the four temperature-sensitive cell strains of the initiation of DNA replication: one type directs inappropriate DNA replication that then may produce endogenous DNA damage, p53-mediated cell cycle arrest, and subsequent apoptosis, while the other type exhibits only the p53-independent cell cycle arrest.

Molecular mechanisms of c-Jun N-terminal kinase-mediated apoptosis induced by anticarcinogenic isothiocyanates

Isothiocyanates have strong chemopreventive properties against many carcinogen-induced cancers in experimental animal models. Here, we report that phenylmethyl isocyacyanate (PMITC) and phenylethyl isothiocyanate (PEITC) induced sustained c-Jun N-terminal kinase (JNK) activation in a dose-dependent manner. The sustained JNK activation caused by isothiocyanates was associated with apoptosis induction in various cell types. An inhibitor of the caspase/interleukin-1 beta-converting enzyme blocked isothiocyanate-induced apoptosis without inhibiting the JNK activation, which suggests that JNK activation by isothiocyanates is an event that is independent or upstream of the activation of caspase/interleukin-1 beta-converting enzyme proteases. PEITC-induced apoptosis was suppressed by interfering with the JNK pathway with a dominant-negative mutant of JNK1 or MEKK1 (JNK1(APF) and MEKK1 (KR), respectively), implying that the JNK pathway is required for apoptotic signaling. Isothiocyanate-induced JNK activation was blocked by the antioxidants 2-mercaptoethanol and N-acetyl-L-cysteine, suggesting that the death signaling was triggered by oxidative stress. Overexpression of Bcl-2 suppressed PEITC-induced JNK activation. In addition, Bcl-2 and Bcl-xL suppressed PEITC-induced apoptosis, but failed to protect cells from death induced by overexpression of activated JNK1. These results suggest that Bcl-2 and Bcl-xL are upstream of JNK. Taken together, our results indicate (i) that JNK mediates PMITC- and PEITC-induced apoptosis and (ii) that PMITC and PEITC may have chemotherapeutic functions besides their chemopreventive functions.

Induction of apoptosis in human keratinocytes containing mutated p53 alleles and its inhibition by both the E6 and E7 oncoproteins

Induction of apoptosis is a function of external stimuli and cellular gene expression. Many cells respond to DNA damage by the induction of apoptosis, which depends on a functional p53 protein and is signaled by elevation of p53 levels. We have investigated the response of immortalized human keratinocytes (HaCaT) bearing mutated alleles of p53 to genotoxic stress and the effect of human papillomavirus (HPV) 16 E6 and E7 on this response. UVC irradiation triggered HaCaT's cell death with several characteristics of apoptosis, including DNA laddering, chromatin condensation and fragmentation, and the appearance of cells with a low content of DNA (categorized as sub-G1 by cell sorter analysis). This response was accompanied by accumulation of cells in S phase of the cell cycle. HaCaT cells infected with retroviruses carrying HPV16 E6 or E7 showed a significant reduction in their apoptotic response, which was not observed in cells infected with the LXSN vector DNA-carrying virus. Reduced apoptosis in HaCaT cells expressing E6 or E7 also was observed after treatment with the alkylating agent mitomycin C. Western blot analysis of p53 and p21/WAF-1/CIP-1, a downstream effector of p53, did not reveal any changes in the levels of these proteins after UVC irradiation in either HaCaT cells or HaCaT cells expressing HPV16 E6 or E7.

Apoptotic response of spermatogenic cells to the germ cell mutagens etoposide, adriamycin, and diepoxybutane

In testis, apoptosis is a way to eliminate damaged germ cells during their development. In this study, we evaluated the ability of three germ cell mutagens to induce apoptosis (or programmed cell death) at specific stages of rat seminiferous epithelial cycle. These chemicals include the cancer chemotherapy drugs etoposide and adriamycin and the butadiene metabolite diepoxybutane. According to our results, etoposide is a very potent inducer of apoptosis in male rat germ cells and the cell types most sensitive to it include all types of spermatogonia, zygotene, and early pachytene spermatocytes and meiotically dividing spermatocytes. Also, adriamycin causes an increase in apoptosis at specific stages of seminiferous epithelial cycle and the most sensitive cell types are type A3-4 spermatogonia, preleptotene, zygotene, and early pachytene spermatocytes. Diepoxybutane does not cause any significant increase in the frequency of apoptosis in rat testis. In addition, we studied whether p53 is taking part in the apoptotic response of spermatogenic cells by studying the levels of p53 protein in testis before and after chemical treatment. No accumulation of p53 in testis was seen after treatment with these three chemicals. The expression of two p53-regulated genes, p21WAF1 and mdm2, was also studied but no increase in the levels of mRNA of these genes was observed after treatment. The results indicate that apoptosis should be taken into consideration when the genotoxic effects of chemicals are evaluated in germ cells.

Expression of multiple apoptosis-regulatory genes in human breast cancer cell lines and primary tumors

The expression of several apoptosis-regulating genes was evaluated in 9 human breast cancer cell lines, 2 immortalized human mammary epithelial lines, 1 normal breast tissue biopsy, and 3 primary breast tumors, using a multiple antigen detection (MAD) immunoblotting method. The anti-apoptotic proteins Bcl-2, Bcl-X(L), Mcl-1, and BAG-1 were present at immunodetectable levels in 7, 10, 10, and 9 of the 11 lines. Comparing these 11 cell lines among themselves revealed that steady-state levels of Bcl-2, Bcl-X(L), Mcl-1, and BAG-1 were present at relatively higher levels in 4, 6, 5, and 5 of the lines, respectively. In contrast, the pro-apoptotic proteins Bax and Bak were detected in all 11 cell lines, and were present at relatively higher levels in 10 and 5 of the 11 lines, respectively. The Interleukin-1beta converting enzyme (ICE) homolog CPP32 (Caspase-3) was expressed in 10/11 breast cell lines. High levels of p53 protein, indicative of mutant p53, were found in 8 of the 11 lines and correlated inversely with Bax expression (p = 0.01). Bcl-2 and BAG-1 protein levels were positively correlated (p = 0.03). Immunoblot analysis of primary adenocarcinomas revealed expression of the anti-apoptotic proteins Bcl-2, Bcl-X(L), Mcl-1, and BAG-1, as well as the pro-apoptotic proteins Bax, Bak, and CPP32, in at least 2 of the 3 tumors examined. Immunohistochemical analysis was also performed for all of these proteins using 20 paraffin-embedded breast cancer biopsy specimens that all contained residual normal mammary epithelium in combination with both invasive cancer and carcinoma in situ. All of these apoptosis-regulating proteins were detected in primary breast cancers, though the percentage of immunopositive tumor cells varied widely in some cases. Comparisons of the intensity of immunostaining in normal mammary epithelium and invasive carcinoma suggested that Bcl-2 immunointensity tends to be lower in cancers than normal breast epithelium (p = 0.03), whereas CPP32 immunointensity was generally higher in invasive cancers (p < 0.0001). Taken together, the results demonstrate expression of multiple apoptosis-modulating proteins in breast cancer cell lines and primary tumors, suggesting complexity in the regulation of apoptosis in these neoplasms of mammary epithelial origin.

Characterization of the CBF2 binding site within the Epstein-Barr virus latency C promoter and its role in modulating EBNA2-mediated transactivation

The Epstein-Barr virus (EBV) EBNA2 protein is a transcriptional activator that regulates viral and cellular gene expression and is also essential for EBV-driven immortalization of B lymphocytes. The EBNA2-responsive enhancer in the viral latency C promoter (Cp) binds two cellular factors, CBF1 and CBF2. The precise role of the CBF2 protein for Cp enhancer function is presently unclear. CBF2 does not appear to interact with EBNA2 and binds just downstream of CBF1 between positions -339 and -368 in the Cp EBNA2 enhancer. Within this region an 8-bp sequence, CAGTGCGT, can be found, and a similar sequence is also located downstream of CBF1 binding sites in other EBNA2-responsive promoters. Previous studies have indicated that mutations and methylation in this sequence affect EBNA2 responsiveness. To investigate the requirements for CBF2 binding, we synthesized a series of oligonucleotides carrying double transversion mutations spanning both the conserved core sequence and outside flanking sequences. Surprisingly, mutations outside of the conserved core sequence in 4 bases immediately flanking the 5' end, GGTT, had the most deleterious effect on CBF2 binding. Mutations in the conserved core had a gradient effect, with those near the 5' end having the most deleterious effects on CBF2 binding. In addition, the affinities of CBF2 for binding to the LMP-1, LMP-2, and CD23 promoters were also measured. These promoters contain the conserved core but lack the 5' flanking GGTT motif and bound CBF2 weakly or not at all. Using Cp reporter plasmids containing CBF2 mutant binding sites, we were also able to show that at lower doses of EBNA2, Cp transactivation required a functional CBF2 binding site but that higher doses of EBNA2 transactivated CBF2 mutant promoters to 40% of wild-type levels. These assays indicate that CBF2 is important for EBNA2-mediated transactivation of the viral latency Cp. In addition, CBF2 activity was found to be associated with two polypeptides of 27 and 33 kDa.

Transfection of C6 glioma cells with the bax gene and increased sensitivity to treatment with cytosine arabinoside

OBJECT

Genes known to be involved in the regulation of apoptosis include members of the bcl-2 gene family, such as inhibitors of apoptosis (bcl-2 and bcl-xl) and promoters of apoptosis (bax). The authors investigated a potential approach for the treatment of malignant gliomas by using a gene transfection technique to manipulate the level of an intracellular protein involved in the control of apoptosis.

METHODS

The authors transfected the murine bax gene, which had been cloned into a mammalian expression vector, into the C6 rat glioma cell line. Overexpression of the bax gene resulted in a decreased growth rate (average doubling time of 32.96 hours compared with 22.49 hours for untransfected C6, and 23.11 hours for clones transfected with pcDNA3 only), which may be caused, in part, by an increased rate of spontaneous apoptosis (0.77 +/- 0.15% compared with 0.42 +/- 0.08% for the vector-only transfected C6 cell line; p = 0.038, two-tailed Student's t-test). Treatment with 1 microM cytosine arabinoside (ara-C) resulted in significantly more cells undergoing apoptosis in the cell line overexpressing bax than in the vector-only control cell line (23.57 +/- 2.6% compared with 5.3 +/- 0.7% terminal deoxynucleotidyl transferase-mediated biotinylated-deoxyuridine triphosphate nick-end labeling technique-positive cells; p = 0.007). Furthermore, measurements of growth curves obtained immediately after treatment with 0.5 microM ara-C demonstrated a prolonged growth arrest of at least 6 days in the cell line overexpressing bax.

CONCLUSIONS

These results can be used collectively to argue that overexpression of bax results in increased sensitivity of C6 cells to ara-C and that increasing bax expression may be a useful strategy, in general, for increasing the sensitivity of gliomas to antineoplastic treatments.

Inosine-5'-monophosphate dehydrogenase is a rate-determining factor for p53-dependent growth regulation

We have proposed that reduced activity of inosine-5'-monophosphate dehydrogenase (IMPD; IMP:NAD oxidoreductase, EC 1.2.1.14), the rate-limiting enzyme for guanine nucleotide biosynthesis, in response to wild-type p53 expression, is essential for p53-dependent growth suppression. A gene transfer strategy was used to demonstrate that under physiological conditions constitutive IMPD expression prevents p53-dependent growth suppression. In these studies, expression of bax and waf1, genes implicated in p53-dependent growth suppression in response to DNA damage, remains elevated in response to p53. These findings indicate that under physiological conditions IMPD is a rate-determining factor for p53-dependent growth regulation. In addition, they suggest that the impd gene may be epistatic to bax and waf1 in growth suppression. Because of the role of IMPD in the production and balance of GTP and ATP, essential nucleotides for signal transduction, these results suggest that p53 controls cell division signals by regulating purine ribonucleotide metabolism.

Apoptosis is inversely related to bcl-2 but not to bax expression in salivary gland tumours

AIMS

We investigated the extent of apoptosis in 55 benign and malignant salivary gland tumours and its association with the immunohistochemical expression of bcl-2 and bax.

METHODS AND RESULTS

Apoptosis was detected in histological sections by the 3'-end DNA labelling method. bcl-2 and bax protein expression was determined by immunohistochemistry. The frequency of apoptosis was clearly higher in malignant than in benign tumours. In pleomorphic adenomas and Warthin's tumours the average apoptotic index was 0.01% (range 0.00-0.07%) while in the malignant salivary gland tumours it was 0.42% (range 0.00-1.75%). Immunohistochemical bcl-2 expression was observed in all pleomorphic adenomas and Warthin's tumours and in most cases the expression was strong. In malignant tumours, 9/25 cases showed no expression and in the rest of the cases, apart from adenoid cystic carcinomas, the bcl-2 expression was often weak. There were significantly more cases with no or weak bcl-2 positivity in malignant than in benign salivary gland tumours (P = 0.001). There was a statistically significant association between a weak bcl-2 expression and a high frequency of apoptosis (P = 0.02). In contrast to bcl-2, strong bax expression was found in both benign and malignant tumours and was not associated with the frequency of apoptosis.

CONCLUSIONS

The low bcl-2 expression in malignant tumours suggests that down-regulation of its expression might contribute to their higher frequency of apoptosis.

Induction of tumour-suppressor phosphoprotein p53 in the apoptosis of cultured rat cerebellar neurones triggered by excitatory amino acids

We found that primary cultures of rat cerebellar granule cells, although definitely postmitotic and terminally differentiated, express the tumour-suppressor phosphoprotein p53. In particular, granule cells both expressed significant levels of p53 mRNA and positively reacted to an anti-p53 antibody, from the first day of culturing. During neurone differentiation, p53 mRNA content did not significantly change, at least up to 12 days in vitro, while p53 immunoreactivity increased gradually. p53 expression appeared to be further modulable being upregulated after stimulation of glutamate ionotropic receptors by glutamate or kainate. Although qualitatively similar, p53 induction by glutamate and kainate differed in terms of intensity and time-course. The glutamate increase of p53 immunoreactivity appeared within 30 min after the treatment and lasted for at least 2 h. Kainate-induced increase of p53 immunoreactivity was delayed, becoming apparent within 2 h and lasting for at least 8 h. Both kainate- and glutamate-induced increases of p53 immunoreactivity were prevented by the non-competitive NMDA receptor antagonist MK 801. As shown by the electrophoretic mobility shift analysis, both glutamate and kainate induced increases of p53 DNA binding activity. Blockade of p53 induction by a specific p53 antisense oligonucleotide resulted in a partial reduction of excitotoxicity with a complete inhibition of the excitatory amino acids induced apoptosis. Our data suggest that stimulation of ionotropic glutamate receptors in neurones results in a p53-dependent apoptosis.

Cooperation of p53 loss of function and v-Ha-ras in transformation of mouse keratinocyte cell lines

We previously demonstrated that after transduction with the v-Ha-ras oncogene and grafting onto nude mouse hosts, primary epidermal keratinocytes with a null mutation in the p53 gene form tumors with increased growth rates and predisposition to malignant conversion relative to p53 wild-type keratinocytes (Weinberg WC, et al., Cancer Res 54:5584-5592, 1994). To further explore the cooperation between p53 loss of function and activation of the ras oncogene, cell lines were established from the normal epidermises of newborn and adult p53-null mice, and parallel subclones were reconstituted with the p53val135 temperature-sensitive mutant. Reconstituted lines C, G, N, and V demonstrated functional p53 transcriptional activator activity at the wild-type-permissive temperature of 32 degrees C, compared with the hygromycin-selected control line X and parental p53-null lines NHK4 and AK1b. Hygromycin-selected subclones, but not the parental lines, made normal skin in vivo; all cell lines made carcinomas after introduction of v-Ha-ras, independent of p53 status. These cell lines were compared in vitro at 32 degrees C to maximize the amount of p53val135 in the wild-type conformation. Expression of v-Ha-ras did not consistently alter p53-mediated transcriptional activity, suggesting tat ras acts downstream or independently of p53. No correlation was observed between p53-mediated transcriptional activity and in vitro growth rates, colony formation after exposure to ultraviolet light, or suppression by normal neighboring keratinocytes. However, keratinocyte cell lines devoid of p53 and expressing v-Ha-ras formed colonies in soft agar; this was blocked at 32 degrees C in all cell lines reconstituted with p53val135. These keratinocyte lines provide a model for exploring the role of p53 and the interaction of p53 and ras in keratinocyte transformation.

Corticosteroids in the brain. Cellular and molecular actions

The rat adrenal hormone corticosterone reaches the brain and binds to intracellular receptors. These receptors comprise high-affinity mineralocorticoid and lower-affinity glucocorticoid receptors that, upon activation, affect the transcription rate of specific genes. The two receptor types are discretely localized in the brain, with particularly high expression levels in the hippocampus. Here we review recent studies showing that electrical properties and structural aspects of hippocampal principal neurons are specifically regulated by mineralocorticoid- or glucocorticoid-receptor activation. The molecular mechanisms by which these cellular effects could be accomplished are discussed.

p53CP, a putative p53 competing protein that specifically binds to the consensus p53 DNA binding sites: a third member of the p53 family?

p53 tumor suppressor protein negatively regulates cell growth, mainly through the transactivation of its downstream target genes. As a sequence-specific DNA binding transcription factor, p53 specifically binds to a 20-bp consensus motif 5'-PuPuPuC(A/T) (T/A)GPyPyPyPuPuPuC(A/T)(T/A)GPyPyPy-3'. We have now identified, partially purified, and characterized an additional approximately 40-kDa nuclear protein, p53CP (p53 competing protein), that specifically binds to the consensus p53 binding sites found in several p53 downstream target genes, including Waf-1, Gadd45, Mdm2, Bax, and RGC. The minimal sequence requirement for binding is a 14-bp motif, 5'-CTTGCTTGAACAGG-3' [5'-C(A/T)(T/A)GPyPyPyPuPuPuC(A/T)(T/A)G-3'], which includes the central nucleotides of the typical p53 binding site with one mismatch. p53CP and p53 (complexed with antibody) showed a similar binding specificity to Waf-1 site but differences in Gadd45 and T3SF binding. Like p53, p53CP also binds both double- and single-stranded DNA oligonucleotides. Important to note, cell cycle blockers and DNA damaging reagents, which induce p53 binding activity, were found to inhibit p53CP binding in p53-positive, but not in p53-negative, cells. This finding suggested a p53-dependent coordinate regulation of p53 and p53CP in response to external stimuli. p53CP therefore could be a third member of the p53 family, in addition to p53 and p73, a newly identified p53 homolog. p53CP, if sequestering p53 from its DNA binding sites through competitive binding, may provide a novel mechanism of p53 inactivation. Alternatively, p53CP may have p53-like functions by binding and transactivating p53 downstream target genes. Cloning of the p53CP gene ultimately will resolve this issue.

Oncoprotein MDM2 is a ubiquitin ligase E3 for tumor suppressor p53

The tumor suppressor p53 is degraded by the ubiquitin-proteasome system. p53 was polyubiquitinated in the presence of E1, UbcH5 as E2 and MDM2 oncoprotein. A ubiquitin molecule bound MDM2 through sulfhydroxy bond which is characteristic of ubiquitin ligase (E3)-ubiquitin binding. The cysteine residue in the carboxyl terminus of MDM2 was essential for the activity. These data suggest that the MDM2 protein, which is induced by p53, functions as a ubiquitin ligase, E3, in human papillomavirus-uninfected cells which do not have E6 protein.

Role of apoptotic proteins in ischemic hippocampal damage

In this review, we have presented evidence that apoptotic proteins may be involved in ischemic cell death. We tried to keep in mind that focal and global ischemia almost certainly produces different forms of cell death. For example, necrotic cell death is clearly part of a focal cerebral infarct, although it is not seen in brief global insults. We also tried to make the point that not all apoptosis is the same and that various forms of non-necrotic cell death, including ischemic cell death after global ischemia, may share some of the same molecular mechanisms as classic forms of apoptosis. Finally, we wish to leave the reader with the clear impression that all the evidence is not in hand. More work needs to be done in animals to define the role of apoptotic proteins. For example, glial cells probably are important in necrosis and may play a role in ischemic cell death after transient global ischemia. Yet it is likely that glial cells die from injury in a different manner than neurons. A better understanding of these processes should lead to new therapeutic approaches that may make possible the salvaging of neurons well after an ischemic insult.

An increased prevalence of Epstein-Barr virus infection in young patients suggests a possible etiology for systemic lupus erythematosus

An unknown environmental agent has been suspected to induce systemic lupus erythematosus (lupus) in man. Prompted by our recent immunochemical findings, we sought evidence for an association between Epstein-Barr virus infection and lupus. Because the vast majority of adults have been infected with Epstein-Barr virus, we chose to study children and young adults. Virtually all (116 of 117, or 99%) of these young patients had seroconverted against Epstein-Barr virus, as compared with only 70% (107 of 153) of their controls (odds ratio 49.9, 95% confidence interval 9.3-1025, P < 0. 00000000001). The difference in the rate of Epstein-Barr virus seroconversion could not be explained by serum IgG level or by cross-reacting anti-Sm/nRNP autoantibodies. No similar difference was found in the seroconversion rates against four other herpes viruses. An assay for Epstein-Barr viral DNA in peripheral blood lymphocytes established Epstein-Barr virus infection in the peripheral blood of all 32 of the lupus patients tested, while only 23 of the 32 matched controls were infected (odds ratio > 10, 95% confidence interval 2.53-infinity, P < 0.002). When considered with other evidence supporting a relationship between Epstein-Barr virus and lupus, these data are consistent with, but do not in themselves establish, Epstein-Barr virus infection as an etiologic factor in lupus.

The MDM2 C-terminal region binds to TAFII250 and is required for MDM2 regulation of the cyclin A promoter

MDM2 proto-oncogene expression is aberrant in many human tumors. Its normal role is to modulate the functions of p53. The N terminus of MDM2 interacts with p53, whereas the properties of the rest of the molecule are poorly understood. We show that MDM2 binds to the general transcription factor TFIID in vivo. The C-terminal Ring finger interacts with TAFII250/CCG1, and the central acidic domain interacts with TBP. Expression of MDM2 activates the cyclin A gene promoter but not c-fos, showing that the effects of MDM2 are specific. Deletion of the C-terminal region of MDM2 abolishes activation, showing that the C-terminal domain of MDM2 is functionally important. We found that increasing MDM2 expression to higher levels inhibits the cyclin A promoter. Inhibition appears to result from titration of general transcription factors because MDM2 overexpression inhibits c-fos as well as other promoters in vivo and basal transcription in vitro. The mechanisms of repression of the cyclin A and fos promoters appear to be different. Cyclin A repression is lost by deleting the C terminus, whereas that of c-fos is lost by removal of the acidic domain. These results reinforce the conclusion that the C terminus of MDM2 mediates effects on the cyclin A promoter. MDM2 transformed cells contain elevated levels of cyclin A mRNA, showing that activation occurs under physiological conditions. There is a positive correlation between MDM2 binding to TAFII250 and MDM2 activation of the cyclin A promoter. The C-terminal region of MDM2, which contains the Ring finger, interacts with TAFII250 and is required for regulation of the cyclin A promoter by MDM2. Our results link the activity of MDM2, a transforming protein implicated in many human tumors, with cyclin A, a regulator of the cell cycle.

Accumulation of human immunodeficiency virus-specific cytotoxic T lymphocytes away from the predominant site of virus replication during primary infection

Down-regulation of the initial burst of viremia during primary human immunodeficiency virus (HIV) infection is thought to be mediated predominantly by HIV-specific CD8+ cytotoxic T lymphocytes (CTL). This response is associated with major perturbations in the T cell receptor (TCR) repertoire. To investigate the failure of the cellular immune response to adequately control viral spread and replication and to prevent establishment of HIV infection, changes in the TCR repertoire and in the distribution of virus-specific CTL between blood and lymph node were analyzed in three patients with primary infection. By the combined use of clonotype-specific polymerase chain reaction and analysis of the frequency of in vivo activated HIV-specific CTL, it was shown that HIV-specific CTL clones preferentially accumulated in blood as opposed to lymph node. Accumulation of HIV-specific CTL in blood occurred prior to effective down-regulation of virus replication in both blood and lymph node. These findings should provide new insights into how HIV, and possibly other viruses, elude the immune response of the host during primary infection.

Atm selectively regulates distinct p53-dependent cell-cycle checkpoint and apoptotic pathways

Atm is part of a pathway that responds to DNA damage from ionizing radiation (IR). This pathway involves p53, as Atm-deficient cell lines and mice are defective in p53 induction after IR. p53 is a multi-functional protein that simultaneously regulates distinct downstream pathways controlling cell-cycle progression and apoptosis. However, the mechanisms by which p53 differentially activates downstream pathways are unknown. To determine the relationship between Atm and p53, we examined cell-cycle and apoptotic responses in Atm-, p53-(ref. 8) and p21-deficient mice after IR in the whole animal. As expected, p53 protein levels were not induced by IR in thymus of Atm-deficient mice. IR-induced cell-cycle checkpoint function was also defective, and induction of p21 was attenuated in thymus from Atm-deficient mice. However, IR-induced apoptosis and Bax induction were completely normal; both of which are mediated by p53. IR-induced thymic apoptosis was suppressed in Atm/p53 double-mutant mice but not in Atm/p21 double mutants, demonstrating p53 dependence and Atm independence. Thus, Atm deficiency results in lack of p53 induction by IR, but only selective disruption of p53-dependent functions. Our results support a model in which upstream effectors such as Atm selectively activate p53 to regulate specific downstream pathways, providing a mechanism for controlling distinct cell-cycle and apoptotic responses.

Partial rescue of the prophase I defects of Atm-deficient mice by p53 and p21 null alleles

Patients with the human disorder ataxia-telangiectasia (A-T; refs 1,2) and Atm-deficient mice have a pleiotropic phenotype that includes infertility. Here we demonstrate that male gametogenesis is severely disrupted in Atm-deficient mice in the earliest stages of meiotic prophase I, resulting in apoptotic degeneration. Atm is required for proper assembly of Rad51 onto the chromosomal axial elements during meiosis. In addition, p53, p21 and Bax are elevated in testes from Atm-deficient mice. To determine whether these elevated protein levels are important factors in the meiotic disruption of Atm-deficient mice, we analysed the meiotic phenotype of Atm/p53 or Atm/p21 double mutants. In these double mutants, meiosis progressed to later stages but was only partly rescued. Assembly of Rad51 foci on axial elements remained defective, and gametogenesis proceeded only to pachytene of prophase I. Previous results demonstrated that mice homozygous for a null mutation in Rad51 (ref. 6) display an early embryonic lethal phenotype that can be partly rescued by removing p53 and/or p21. Because Atm-deficient mice are viable but completely infertile, our studies suggest that the Rad51 assembly defects and elevated levels of p53, p21 and Bax represent tissue-specific responses to the absence of Atm.

Methylation of the Epstein-Barr Virus Genome in Normal Lymphocytes

Epstein-Barr virus (EBV) latent infection in B cells persists over years or decades despite a sustained cytotoxic immune response to viral antigens. We present data that methylated EBV DNA can be detected in the normal lymphocytes of healthy volunteers. Whereas methylation of foreign DNA has been recognized as a potential cellular defense mechanism, methylation of EBV DNA may be an essential part of the virus life cycle in vivo, explaining the persistence of virus-infected B cells in the face of immune surveillance. Methylation of the C promoter helps to prevent expression of the immunodominant antigens expressed from this promoter. First recognized in tumors, methylation-associated evasion of immune surveillance is not an aberration restricted to tumor tissue but is detected in normal EBV-infected lymphocytes. Methylation of the viral genome in latency also provides an explanation for the CpG suppression associated with EBV but not other large DNA viruses.

Methylation of the Epstein-Barr Virus Genome in Normal Lymphocytes

Epstein-Barr virus (EBV) latent infection in B cells persists over years or decades despite a sustained cytotoxic immune response to viral antigens. We present data that methylated EBV DNA can be detected in the normal lymphocytes of healthy volunteers. Whereas methylation of foreign DNA has been recognized as a potential cellular defense mechanism, methylation of EBV DNA may be an essential part of the virus life cycle in vivo, explaining the persistence of virus-infected B cells in the face of immune surveillance. Methylation of the C promoter helps to prevent expression of the immunodominant antigens expressed from this promoter. First recognized in tumors, methylation-associated evasion of immune surveillance is not an aberration restricted to tumor tissue but is detected in normal EBV-infected lymphocytes. Methylation of the viral genome in latency also provides an explanation for the CpG suppression associated with EBV but not other large DNA viruses.

Apoptosis-associated signaling pathways are required for chemotherapy-mediated female germ cell destruction

Female sterility resulting from oocyte destruction is an unfortunate, and in many cases inevitable, consequence of chemotherapy. We show that unfertilized mouse oocytes exposed to therapeutic levels of the antitumor drug, doxorubicin (DXR), undergo apoptosis; however, fertilized oocytes do not initiate apoptosis, but enter cell-cycle arrest, when treated with DXR. Apoptosis induced by DXR in oocytes is blocked by sphingosine-1-phosphate, an inhibitor of ceramide-promoted cell death. Oocytes from Bax-deficient, but not p53-null, female mice display complete resistance to DXR-induced apoptosis in vivo and in vitro. Pretreatment of oocytes with a specific peptide inhibitor of caspases also abrogates the apoptotic response to DXR. These findings indicate that oocyte destruction caused by chemotherapy can be prevented by manipulation of apoptosis-associated signaling pathways.

p53 tumor-suppressor gene: clues to molecular carcinogenesis

The tumor-suppressor gene product p53 is clearly a component in several biochemical pathways, including transcription, DNA repair, genomic stability, cell-cycle control and apoptosis, that are central to human carcinogenesis. The p53 is functionally inactivated by mutational, viral, and cellular mechanisms in the majority of human cancers. Analysis of the spectrum of p53 mutations provides clues to the etiology and molecular pathogenesis of cancer. Recent insight into the p53-mediated biochemical pathways of cell-cycle arrest and apoptosis has provided further understanding of the mechanisms related to p53-mediated tumor suppression. This insight in turn may provide the potential molecular targets for the development of rational multimodality cancer therapy, including chemo-, immuno-, and gene-therapeutic strategies. The convergence of previously parallel lines of basic, clinical, and epidemiologic investigation may provide an opportunity to transfer research findings rapidly from the laboratory to the clinic.