Advising patients on dealing with acute chest pain

Instructions about using GTN and when to call an ambulance need to be clearer

Flecainide cardiotoxicity precipitated by electrolyte imbalance. Caution with thiazide diuretics

A man presented with recurrent syncope, weakness and fatigue. His ECG showed marked QRS widening and he had gross hyponatraemia and hypokalaemia. His medications included bendroflumethiazide (long term) and flecainide (started 2 months previously). This presentation was consistent with flacainide cardiotoxicity exacerbated by electrolyte disturbance. The syncopal episodes probably represented life-threatening arrhythmias. The ECG and symptoms resolved completely once the electrolytes were corrected. Increased cardiotoxicity with hypokalaemia is documented, but not widely recognised. Hyponatraemia-induced flecainide cardiotoxicity has not been documented. The clinical effects of flecainide are due to use-dependent block of sodium channels. There are reports that support the use of hypertonic sodium salts to reverse flecainide toxicity via antagonism at the receptor. By this rationale, hyponatraemia would lead to Flecainide toxicity. Flecainide has been shown to reduce salt absorption in animal bowel. It is possible that in combination with bendroflumethiazide it acted synergistically to produce profound electrolyte disturbance. Flecainide cardiotoxicity has a significant mortality and can present non-specifically. Thus, early recognition is essential. This case demonstrates the importance of strict electrolyte control in patients who are on flecainide. We would discourage concomitant use of flecainide and bendroflumethiazide.

Acute coronary syndrome

Glycoprotein IIb/IIIa inhibitors are still underused, especially in patients at high risk

Oxidative stress regulated expression of Ubiquitin Carboxyl-terminal Hydrolase-L1: Role in cell survival

The ubiquitin Carboxyl-terminal Hydrolase-L1 gene (UCHL1) is a key enzyme in the protein degradation pathway; however, its precise role in protecting cells under stress conditions is unclear. In the present study we investigated the activity of this gene in human NT2/D1 embryonal carcinoma cells subjected to oxygen-glucose deprivation (OGD) and reoxygenation. OGD/reoxygenation cause global metabolic changes due to energy withdrawal and the subsequent generation of reactive oxygen species which initiates either a stress-adaptation-survival response or cell death, depending on the severity of the insult. A bi-phasic change in UCHL1 expression was observed by Q-PCR, Western blotting and flow cytometry. Down regulation of UCHL1 was detected immediately after OGD treatment and its expression was subsequently restored and increased 6 h after OGD treatment as well as during reoxygenation. Furthermore, flow cytometry analysis detected a lower level of UCHL1 only in apoptotic cells that had severe loss of mitochondrial membrane potential. Accordingly, down-regulation of endogenous UCHL1 by antisense cDNA in mouse N2a neuroblastoma cells increased the cell's sensitivity to OGD treatment. This down-regulation of endogenous UCHL1 led to the accumulation of p27, suggesting that UCHL1 is an essential gene to maintain cell homeostasis under normal growth and oxidative stress conditions.

S/MAR-binding properties of Sox2 and its involvement in apoptosis of human NT2 neural precursors

DNA fragmentation in apoptosis, especially in lymphocytic cells, is initiated at scaffold/matrix attachment regions (S/MARs) and is preceded by the degradation of nuclear proteins. The present study was performed to establish whether the same mechanism occurred in human NT2 cells subjected to oxygen and glucose deprivation (OGD). We analyzed the integrity of c-myc S/MAR containing a base-unpairing region (BUR)-like element, which we established to be a binding site of the transcription factor Sox2. An accumulation of DNA breaks in close proximity to this element and a degradation of Sox2 were observed early in the OGD-induced apoptotic response. Identification of Sox2 as a novel c-myc BUR-binding protein was achieved through yeast one-hybrid screening and the Sox2/DNA interaction was confirmed by electrophoretic mobility shift assay and immunoprecipitation with Sox2 antibody. Our data support the notion that early proteolysis of unique BUR-binding proteins might represent a universal mechanism that renders these DNA sites vulnerable to endonucleolysis.

Regulation of DNaseY activity by actinin-α4 during apoptosis

DNaseY, a Ca(2+)- and Mg(2+)-dependent endonuclease, has been implicated in apoptotic DNA degradation; however, the molecular mechanisms controlling its involvement in this process have not been fully elucidated. We have obtained evidence from yeast two-hybrid screening and coimmunoprecipitation experiments that DNaseY interacted physically with actinin-alpha4 and this interaction significantly enhanced its endonuclease activity. Accordingly, simultaneous overexpression of both proteins in PC12 cells dramatically increased the rate of apoptosis in response to teniposide' VM26. However, overexpression of DNaseY alone neither triggered apoptosis nor facilitated cell death in response to VM26 or serum deprivation. Instead, the overexpression of DNaseY increased the production of single-strand DNA breaks and evoked a profound upregulation of DNA repair pathways. Taken together, our results point to a novel regulatory mechanism of DNaseY activity and offer an explanation for why cells must first cleave key DNA repair and replication proteins before the successful execution of apoptosis.

Mapping the initial DNA breaks in apoptotic Jurkat cells using ligation-mediated PCR

Apoptotic DNA degradation could be initiated by the accumulation of single-strand (ss) breaks in vulnerable chromatin regions, such as base unpairing regions (BURs), which might be preferentially targeted for degradation by both proteases and nucleases. We tested this hypothesis in anti-Fas-treated apoptotic Jurkat cells. Several nuclear proteins known for their association with both MARs and the nuclear matrix, that is, PARP, NuMA, lamin B and SATB1, were degraded, but the morphological rearrangement of the BUR-binding SATB1 protein was one of the earliest detected changes. Subsequently, we have identified several genes containing sequences homologous to the 25 bp BUR element of the IgH gene, a known SATB1-binding site, and examined the integrity of genomic DNA in their vicinity. Multiple ss breaks were found in close proximity to these sites relative to adjacent regions of DNA. Consistent with our prediction, the results indicated that the initiation of DNA cleavage in anti-Fas-treated Jurkat cells occurred within the BUR sites, which likely became accessible to endonucleases due to the degradation of BUR-binding proteins.

Paper alert. Immunology

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in immunology.

Melanoma patients respond to a cytotoxic T lymphocyte-defined self-peptide with diverse and nonoverlapping T-cell receptor repertoires

HLA-A2+ melanoma patients develop naturally a strong CD8+ T cell response to a self-peptide derived from Melan-A. Here, we have used HLA-A2/peptide tetramers to isolate Melan-A-specific T cells from tumor-infiltrated lymph nodes of two HLA-A2+ melanoma patients and analyzed their TCR beta chain V segment and complementarity determining region 3 length and sequence. We found a broad diversity in Melan-A-specific immune T-cell receptor (TCR) repertoires in terms of both TCR beta chain variable gene segment usage and clonal composition. In addition, immune TCR repertoires selected in the patients were not overlapping. In contrast to previously characterized CD8+ T-cell responses to viral infections, this study provides evidence against usage of highly restricted TCR repertoire in the natural response to a self-differentiation tumor antigen.

Loss of Fas (CD95/APO-1) expression by antigen-specific cytotoxic T cells is reversed by inhibiting DNA methylation

Elimination of clonally expanded peripheral CD8 T cells was thought to involve apoptosis induction mediated principally by TNF, but recently Fas (CD95/APO-1) has been shown to play a role in certain responses. Here we study Fas expression and sensitivity to its ligation on murine CD8 cells specific for the CW3 antigen expressed by transfected P815 cells. Fas was progressively downregulated after successive in vitro restimulations of antigen-specific CD8 cells, until clones became Fas negative and totally resistant to the effects of recombinant Fas ligand. In contrast, Fas expression by in vivo restimulated antigen-specific cells did not diminish. Loss of Fas expression in vitro was not totally irreversible, since it could be reinduced by inhibition of DNA methylation. Understanding how Fas may be differentially regulated in vivo and in vitro is an important issue for the optimal manipulation of T cells for adoptive immunotherapy protocols.

TWEAK stimulation of astrocytes and the proinflammatory consequences

Astrocytes exert many active roles in brain homeostasis, potentially including the regulation of immune reactions. They possess a substantial aptitude for plasticity and, indeed, functional and phenotypic changes are frequently encountered in reactive gliosis observed in brain injuries. The significance of reactive astrocytes is still poorly defined, but it is clear that these cells are an important source of cytokines in inflamed brain. How tumor necrosis factor (TNF) and TNF-receptor family members contribute to this reaction is an interesting issue that is currently being explored. It was previously shown that reactive astrocytes express high levels of Fas (CD95) and respond to Fas ligand (CD95L) by apoptosis or IL-8 production. TWEAK (Apo-3 ligand) is a recently identified member of the TNF family that is produced mainly by leukocytes that can infiltrate the inflamed brain and thus influence astrocyte behavior. Here we show that human astrocytes derived from different regions of the brain specifically bind TWEAK and are totally resistant to TWEAK mediated apoptosis. In addition, high amounts of IL-8 and IL-6 were secreted by astrocytes after TWEAK exposure. Finally, expression of cell surface molecules involved in the propagation and/or maintenance of brain inflammation was determined. TWEAK significantly increased ICAM-1 expression on astrocytes, whereas no modification was detected in the expression of Fas, TNFRI, B7-1, or MHC molecules. In conclusion, the proinflammatory effects induced by TWEAK on astrocytes in culture recapitulate many characteristics of reactive astrocytes observed in vivo, suggesting that TWEAK could play a significant role in brain inflammation.

The brain parenchyma is permissive for full antitumor CTL effector function, even in the absence of CD4 T cells

Effective antitumor immune responses against cerebral malignancies have been demonstrated in several models, but precise cellular function of specific effector cells is poorly understood. We have explored this topic by analyzing the MHC class I-restricted T cell response elicited after implantation of HLA-CW3-transfected P815 mastocytoma cells (P815-CW3) in syngeneic mice. In this model, tumor-specific CTLs use a distinctive repertoire of TCRs that allows ex vivo assessment of the response by immunophenotyping and TCR spectratyping. Thus, for the first time in a brain tumor model, we are able to directly visualize ex vivo CTLs specific for a tumor-expressed Ag. Tumor-specific CTLs are detected in the CNS after intracerebral implantation of P815-CW3, together with other inflammatory cells. Moreover, despite observations in other models suggesting that CTLs infiltrating the brain may be functionally compromised and highly dependent upon CD4 T cells, in this syngeneic P815-CW3 model, intracerebral tumors were efficiently rejected, whether or not CD4 T cells were present. This observation correlated with potent ex vivo cytotoxicity of brain-infiltrating CTLs, specific for the immunodominant epitope CW3170-179 expressed on P815-CW3 tumor cells.

Caspase-dependent and independent cell death in rat hepatoma 5123tc cells

The objective of this study was to establish whether apoptosis in 5123tc rat hepatoma cells required the caspase-3 dependent pathway. Apoptosis was induced by either growth factor deprivation or treatment with a topoisomerase II inhibitor, VM26, in the absence or presence of caspase inhibitors (DEVD-fmk, z-VAD-fmk and BAF). The results indicated that, although these inhibitors at 10 microM concentration completely blocked caspase-3 activity, they had no effect on either the rate of cell death or on any other apoptotic features, e.g., chromatin condensation, DNA fragmentation, protein cleavage, suggesting that caspase-3 was not required to mediate nuclear destruction in these hepatoma cells. At higher concentrations, up to 100 microM, z-VAD-fmk and BAF, but not DEVD-fmk, did block apoptosis, however, they also caused cell swelling and membrane permeabilization, which are the hallmarks of necrotic cell death. Clearly, high concentrations of these inhibitors must have interfered non-specifically with other metabolic pathways, e.g., z-VAD-fmk at a high concentration blocked protein phosphorylation, and caused cell death by a different mechanism.

Effects of neoplastic transformation and teniposide (VM26) on protein kinase C isoform expression in rodent fibroblasts

This study examined changes in protein kinase C (PKC) isoforms in rodent fibroblasts (rat F111 and mouse NIH3T3), transformed by the polyoma virus middle T antigen (mT) and undergoing apoptosis in response to teniposide (VM26). The mT-transformed cells up-regulated PKC delta and down-regulated both PKC epsilon and PKC lambda expression, and were more sensitive to the drug than their non-transformed counterparts. The drug treatment further lowered the expression of PKC epsilon, triggered nuclear translocation of PKC delta and its site-specific proteolysis, consistent with the notion that changes in specific PKC isoforms play a role not only in the neoplastic transformation of fibroblasts, but also in their apoptotic response.

Neither caspase-3 nor DNA fragmentation factor is required for high molecular weight DNA degradation in apoptosis

In this paper, we show that there is a two-step process of DNA fragmentation in apoptosis; DNA is first cleaved to large fragments of 50-300 kb that are subsequently cleaved to smaller oligonucleosomes in some, but not all cells. Significantly, only the first stage is considered essential for cell death since some cells, for example human MCF7 breast carcinoma cells and human NT2 neuronal cells, do not show this behavior but still display normal nuclear morphological apoptotic changes. In cells that usually produce small fragments blocking the second (internucleosomal) stage of DNA fragmentation prevents neither nuclear condensation nor apoptosis. We are beginning to understand why the extent of DNA fragmentation during apoptosis varies enormously and why it appears to be a function of the cell type not the inducer. Presumably, this reflects the content of not only endonuclease activit(ies) but also on the ability of the cells to activate caspases, particularly caspase-3, and other proteases that may be involved in endonuclease activation. Since NT2 cells activate caspase-3, but do not correctly process DFF45, other factors must also impinge on the inevitability of that process.

Apoptosis-related functional features of the DNaseI-like family of nucleases

Rat DNaseYb and its human homolog DHP2 are members of a new family of DNaseI-like endonucleases. They contain all the conserved amino acid residues to engage a DNaseI-like catalytic activity and the same molecular mechanisms of DNA hydrolysis. The sequence similarity can be extended to other families of nucleases, such as FEN-1, DNA polymerases, RNaseH and exonuclease III, involved in the ion-dependent hydrolysis of nucleic acids. Their unique features include the NLS signals that place them in the nuclei and a high content of positively charged amino acid residues that results in their high affinity for the substrate. Their properties are consistent with a role in the early stage DNA degradation during apoptosis. The caspase-DFF45/CIDE-CPAN pathway is most likely involved in the second stage of internucleosomal DNA degradation. However, cells express constitutively multiple transcripts encoding DNA degrading enzymes and related molecules, hence they have the molecular diversity to engage the self-destructive pathway appropriate to a given trigger.

Evidence that DNA fragmentation in apoptosis is initiated and propagated by single-strand breaks

Apoptosis is characterised by the degradation of DNA into a specific pattern of high and low molecular weight fragments seen on agarose gels as a distribution of sizes between 50-300 kb and sometimes, but not always, a ladder of smaller oligonucleosomal fragments. Using a 2D pulsed field-conventional agarose gel electrophoresis technique, where the second dimension is run under either normal or denaturing conditions, we show that single-strand breaks are introduced into DNA at the initial stages of fragmentation. Using single-strand specific nuclease probes we further show that the complete fragmentation pattern, including release of small oligonucleosomal fragments can also be generated by a single-strand endonuclease. Three classes of sites where single-strand breaks accumulate were identified. The initial breaks produce a distribution of fragment sizes (50 kb to >1 Mb) similar to those generated by Topoisomerase II inhibitors suggesting that cleavage may commence at sites of attachment of DNA to the nuclear matrix. A second class of rare sites is also cut further reducing the size distribution of the fragments to 50-300 kb. Thirdly, single-strand breaks accumulate at the linker region between nucleosomes eventually causing double-strand scissions which release oligonucleosomes. These observations further define the properties of the endonuclease responsible for DNA fragmentation in apoptosis.

A quantitative, single-cell PCR analysis of an antigen-specific TCR repertoire selected during an in vivo CD8 response: direct evidence for a wide range of clone sizes with uniform tissue distribution

The development of T cell effector and memory responses against foreign antigens (Ags) involves the activation, differentiation and proliferation of naive T cells expressing distinct Ag-specific TCRs. Understanding the complexity of Ag-selected TCR repertoires in individual responders in terms of the sequences selected and their relative frequencies may provide indications about how a repertoire is established and suggest ways to influence the outcome of an immune response. Most methods of repertoire analysis are unsuitable for calculating the relative in vivo frequencies of Ag-specific clones (expressing distinct TCRs) selected during an immune response, whereas sequence data obtained by single-cell PCR analysis directly reflect cell frequencies if a sufficiently large number of cells is sampled. Using a CD8 T cell response in normal mice in which Ag-selected cells are identified by cell surface phenotype and rearranged TCRBV sequences are determined by PCR amplification of genomic DNA directly from single cells, we have analyzed a large number (>200 per animal) of structurally-related Ag-specific TCRs to calculate the frequencies of distinct TCRs selected by individual mice. We found that each responder selects a unique Ag-specific TCR repertoire in which the various TCRBV sequences are present in a wide range of frequencies. However, the overall distribution of sequences is quite similar for different responder animals. Moreover, an individual's selected TCR repertoire is uniformly represented among Ag-specific CD8 cells circulating in the blood or localized in the spleen or liver. Relatively few sequences make up the bulk of the repertoire and account for the oligoclonality observed in earlier studies. We discuss various models that could account for this skewed distribution of an Ag-selected TCR repertoire.

Astrocytoma infiltrating lymphocytes include major T cell clonal expansions confined to the CD8 subset

Anaplastic astrocytoma and glioblastoma are frequent and malignant brain tumors that are infiltrated by T lymphocytes. Whether these cells result from non-specific inflammation following blood-brain barrier disruption or an antigen-driven specific immune response is unknown. In this study, an in-depth characterization of TCR diversity in tumor and blood RNA biopsies was performed in a series of 16 patients with malignant astrocytoma. Whilst there was no obvious restriction of the AV and BV gene segment usage, complementarity-determining region 3 size analysis and sequencing of amplified TCR transcripts revealed multiple T cell oligoclonal expansions in all astrocytomas analyzed. Unique T cell clones were present in different adjacent areas of a given tumor, but never detected in the blood. Quantification of the number of TCR clonal transcripts per microg of tumor RNA indicated that certain T cell clonal expansions may represent at least 300 cells/10(6) tumor cells. Furthermore, we demonstrated that the in vivo expanded clones were almost exclusively confined to the CD8(+) subset. Overall, these data suggest that spontaneous antigen-driven immune responses may be elicited against human astrocytoma despite the immunosuppressive microenvironment generated by the brain and the tumor itself. However, the ultimate failure of the immune system to control tumor growth could be the consequence of a deficient CD4 T(h) component of the response. This observation could have important consequences for the development of immunotherapies for astrocytoma patients.

Detection of DNA fragmentation and endonucleases in apoptosis

DNA degradation during apoptosis is endonuclease mediated and proceeds through an ordered series of stages commencing with the production of large DNA pieces of 300 kb which are then degraded to fragments of 50 kb. The 50-kb fragments are further degraded, in some but not all cells, to smaller pieces (10-40 kb) releasing the small oligonucleosome fragments that are detected as a characteristic DNA ladder on conventional agarose gels. Methodology is presented for the detection of both DNA ladders and the initial stages of DNA fragmentation using pulsed-field gel electrophoresis. We have developed electrophoresis conditions that resolve large fragments of DNA and also retain the smaller fragments on the same gel. Methods for the detection of endonuclease activities responsible for the cleavage of DNA during apoptosis are also presented.

CD95 (Fas/Apo-1) as a receptor governing astrocyte apoptotic or inflammatory responses: a key role in brain inflammation?

Astrocytes are a major cellular component of the brain that are capable of intense proliferation and metabolic activity during diverse inflammatory brain diseases (such as multiple sclerosis, Alzheimer's dementia, tumor, HIV encephalitis, or prion disease). In this biological process, called reactive gliosis, astrocyte apoptosis is frequently observed and could be an important mechanism of regulation. However, the factors responsible for apoptosis in human astrocytes are poorly defined. Here, we report that short term cultured astrocytes derived from different brain regions express significant levels of CD95 at their surface. Only late passage astrocytes are sensitive to CD95 ligation using either CD95 mAb or recombinant CD95 ligand. Blocking experiments using caspase inhibitors with different specificities (DEVD-CHO, z-VAD-fmk, and YVAD-cmk), an enzymatic activity assay, and immunoblotting show that CPP32/caspase-3 play a prominent role in CD95-induced astrocyte death. In contrast, early passage astrocytes are totally resistant to death, but a significant increase in astrocytic IL-8 secretion (p < 0.001, by Wilcoxon's test for paired samples) is observed after CD95 triggering. Production of IL-8 contributes to the resistance of astrocytes to CD95 ligation. Furthermore, in the presence of IFN-gamma, resistant astrocytes became sensitive to CD95-mediated death. These data suggest that microenvironmental factors can influence the consequences of CD95 ligation on astrocytes. Therefore, we propose that CD95 expressed by human astrocytes plays a pivotal role in the regulation of astrocyte life and death and may be a key factor in inflammatory processes in the brain, such as reactive gliosis.

Tumor expression of Fas ligand (CD95L) and the consequences

Tumors of diverse origin have recently been shown to express CD95 ligand and to induce apoptosis in CD95-expressing targets in vitro; however, in vivo, enhanced tumor growth and rejection have both been observed as a consequence of either immunosuppressive or proinflammatory functions of CD95 ligand. The final in vivo outcome of CD95 ligand expression will depend upon a complex balance of interactions relevant for each tumor in its particular microenvironment.

Splenic T lymphocytes die preferentially during heat-induced apoptosis: NuMA reorganization as a marker

We are investigating nuclear events during apoptosis in mouse splenic lymphocytes cultured immediately after isolation (controls) or after heat treatment (42 degreesC, 30 minutes), and have found that hyperthermia increased the level of apoptosis to double that of spontaneous apoptosis in controls within 6 hours. Immunolabelling for Nuclear Mitotic Apparatus Protein (NuMA) suggested that splenocytes were responding heterogeneously to the heat treatment. Whereas all nuclei in controls and about half of nuclei in heat-treated samples showed the usual diffuse nucleoplasmic labelling, 40–60% of nuclei in heated samples also contained numerous bright spots. We then examined whether the heterogeneity in NuMA organization might be an indication of a differential response of B and T lymphocytes to hyperthermia, and whether the presence of NuMA spots is related to the apoptotic process. NuMA labelling of heated fractionated splenocyte populations showed that 90% of nuclei in T-enriched cultures (less than or equal to 4% IgG+ cells), but only 25% of nuclei in B-enriched samples (less than or equal to 80% IgG+ cells), contained spots. As well, 2 hours after heat treatment of unfractionated cultures, greater than or equal to 90% of nuclei that were accumulating DNA strand breaks, as detected by TUNEL, exhibited NuMA spots. These data indicate that cells with NuMA spots are targetted for, or have initiated, the death program. Since most T cells, but few or no B cells, were spotty after heating, we conclude further that hyperthermia induces apoptosis preferentially in splenic T lymphocytes. The observation that the proportion of T cells was, on average, threefold greater in control than in heated samples after 24 hours in culture reinforces this conclusion.

DNaseY: a rat DNaseI-like gene coding for a constitutively expressed chromatin-bound endonuclease

A rat gene, designated DNaseY, encoding a 36 kDa endonuclease was identified and cloned. Sequence analysis of the cDNA showed it to be the rat homologue of human DNAS1L3. The DNaseY gene product had 42% identity to DNaseI, including conserved critical active site residues, the essential disulfide bridge, the calcium binding domain, and a signal peptide, as well as 2 of the 3 signature boxes. Significantly, DNaseY had 2 nuclear localization signals and was more basic (pI 9.5) than DNaseI (pI 4.8). The DNaseY gene contained a number of exons similar to that of DNaseI, separated by much larger introns, resulting in a gene of >17 kb compared to <4 kb gene of DNaseI. The 36 kDa DNaseY gene product was catalytically inactive but was converted to an active 33 kDa endonuclease following processing of the hydrophobic signal peptide. Antibody generated against peptides representing the predicted amino acid sequence of DNaseY cross-reacted with a 33 kDa nuclear protein which possessed endonucleolytic activity. The enzyme was active over a broad pH range (optimum pH 7-8), was Ca2+/Mg2+-dependent, was inhibited by Zn2+, and was capable of both single- and double-stranded DNA cleavage, producing DNA fragments with 3'-OH ends. Furthermore, the DNaseY gene was expressed constitutively in all cells and tissues tested, but it was not transcriptionally up-regulated in apoptotic cells. All these features were consistent with a role in the early stages of apoptotic DNA fragmentation.

New aspects of the mechanism of DNA fragmentation in apoptosis

In this article we review the current status of research into the mechanism of DNA fragmentation in apoptosis. There is accumulating evidence that there is no single conserved endonuclease that is responsible for DNA fragmentation in all cells. Not only are the two stages of high molecular weight fragment and DNA ladder formation likely to be catalysed by different activities, but multiple activities appear to be involved in internucleosomal DNA fragmentation in various cells. In addition to any one of a number of Ca2+/Mg2+-dependent endonucleases, acidic enzymes (i.e., endonucleases that are active at acid pH) also appear to be involved. Moreover, some enzymes currently being identified are active over a broad range of acidic and neutral pH values and have complex cation requirements that are a function of pH. DNA fragmentation in apoptosis appears to be controlled by either Ca2+ ions or a decrease in pH, depending on the cell type. DNA degradation to oligonucleosomes is not essential for apoptosis, but all cells must undergo DNA degradation to produce the large fragments. This is believed to occur in regions of DNA attached to the nuclear matrix, but the activity responsible has not yet been identified. Changes in both Ca2+ ions and pH have been recorded in a variety of cells, indicating that both mechanisms of regulation of endonuclease activation are involved in apoptosis.

Unique behaviour of NuMA during heat-induced apoptosis of lymphocytes

Nuclear collapse is a key feature of apoptosis, reflecting the DNA and protein fragmentation observed biochemically. We have compared nuclear events during spontaneous and heat-induced (42 degrees C for 30 min) apoptosis at the level of individual cells, monitoring overall chromatin organization by staining with 4,6'-diamidino-2-phenylindole (DAPI), DNA cleavage by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL), and the nuclear antigens NuMA, PI2, and lamin B by immunofluorescence microscopy. The data were correlated with analyses at the population level by flow cytometry and immunoblotting. We show that heat treatment doubles the level of apoptotic splenocytes with respect to the spontaneous apoptosis in controls within 6 honThe organization and disassembly of nuclear envelope antigens is identical during spontaneous and heat-induced apoptosis and proceeds in a temporally and spatially ordered manner relative to DNA fragmentation and chromatin collapse. In contrast, NuMA organization is affected by heat treatment, with about half of the cells containing many bright spots in addition to the usual diffuse labelling. The spots were still visible in many fully collapsed apoptotic nuclei. Further, this novel reorganization of NuMA and the hyperinduction of apoptosis by heat are correlated, suggesting that lymphocytes with reorganized NuMA are destined to undergo apoptosis. The data also indicate that DNA fragmentation precedes extensive remodelling of the nucleoplasm in these cells, and that chromatin begins to collapse before disassembly of nuclear envelope components.

Induction of Apoptosis in neoplastic cells by depletion of vitamin B12

Methionine synthase, a critical enzyme in deoxyribonucleotide biosynthesis for DNA replication, requires vitamin B12 as a cofactor. We have tested the hypothesis that depletion of cells of vitamin B12 would block growth of neoplastic cells and divert them into apoptosis and could form the basis of a new therapeutic strategy for cancer treatment. Using nitrous oxide to inactivate vitamin B12 we show that, in a variety of cell lines in vitro, methionine synthase is rapidly inhibited, the cells cease proliferation and undergo apoptosis. The kinetics of cell death, once started, are similar to those observed following methotrexate treatment or serum withdrawal. This is the first observation of apoptosis being induced following depletion of an essential metabolite as opposed to the more conventional strategy of adding a toxic drug to damage cells thereby triggering apoptosis. Moreover, vitamin B12 depletion has no effect on the nonproliferating cell population.

DNase I primary transcript is alternatively spliced in both normal and apoptotic cells: no evidence of up-regulation in apoptosis

The reverse transcriptase polymerase chain reaction (RT-PCR) was used to elucidate the expression of DNase I and its possible involvement in apoptotic genome degradation. Multiple PCR products were obtained from cDNAs of different rat and human cells. The subsequent cloning and sequence analysis of seven PCR products revealed that only one of them had the expected size (639 bp) and sequence identity to that of rat DNase I cDNA. The other six PCR products were characterized by either sequence insertions or deletions. To establish the origin of this molecular diversity, a genomic fragment of the rat DNase I gene was also isolated, subcloned, and sequenced. Sequence comparison of six cDNAs with the rat genomic DNA revealed that they, indeed, resulted from inclusion of introns or deletion of exons. Southern hybridizations of the RT-PCR products from a variety of mammalian cell lines, using the major DNase I cDNA fragment as a probe, showed that in some cells as many as 20 alternatively spliced transcripts could be detected. This complexity of splice variants was widespread, and cell-specific profiles differed by the relative concentration of each transcript. None of these spliced transcripts maintained an open reading frame containing an intact catalytic site, suggesting that they do not encode any functional proteins. These complicated alternative splicing events might, however, significantly contribute to the regulation of DNase I expression. There was no apparent increase of the major DNase I transcript after induction of apoptosis in the cell lines studied. Apoptotic cells appeared to have similar normal/alternative transcript ratios as the control cells, suggesting that DNase I may not be the endonuclease involved in DNA degradation during apoptosis.

TCR analysis reveals significant repertoire selection during in vitro lymphocyte culture

The in vitro stimulation of T lymphocytes is frequently used as a technique to expand specific cells present at low precursor frequency in vivo. However, cells analysed after such procedures may no longer reflect those originally present in vivo because of the variable efficiency of outgrowth of different T cell subpopulations. To systematically assess this and to complement functional assays, we have analysed the TCR repertoire using a new high resolution RT-PCR method to determine TCR beta chain CDR3 transcript length. In the ex vivo analysis of tumor infiltrating lymphocytes (TIL) of renal cell carcinoma and glioblastoma patients, we observed and quantified oligoclonally expanded populations of T cells that were very susceptible to repertoire modification upon subsequent in vitro culture with autologous tumor cells. This in vitro repertoire skewing occurred preferentially with TIL rather than peripheral blood lymphocytes and we noted that tumor cells rather than normal cells of the same tissue type were the most potent inducers of the effect. It was striking that this selection was sometimes negative: certain prominent T cell populations that were highly represented in vivo disappeared after in vitro re-stimulation. This suggests that the presentation of tumor associated antigens during culture may eliminate rather than enrich for in vivo primed T cells. It is clear that in vitro functional tests cannot adequately describe all T cells with tumor specificity. Approaches that allow the assessment of potentially antigen-reactive T cell populations ex vivo are thus an important advance in the global appraisal of anti-tumor T cell immune responses.

Role of Fas ligand (CD95L) in immune escape: the tumor cell strikes back

Several different tumor types have recently been shown to express functional Fas ligand (FasL), which may represent an additional mechanism of tumor escape. However, the in vivo significance of these findings in the context of potent adversaries such as activated CTL or NK cells remains to be fully established. The potential interactions between tumor cells and the host immune response are thus more complex than previously thought; their elucidation will benefit the rational design of cancer immunotherapy strategies.

Role of Fas ligand (CD95L) in immune escape: the tumor cell strikes back

Several different tumor types have recently been shown to express functional Fas ligand (FasL), which may represent an additional mechanism of tumor escape. However, the in vivo significance of these findings in the context of potent adversaries such as activated CTL or NK cells remains to be fully established. The potential interactions between tumor cells and the host immune response are thus more complex than previously thought; their elucidation will benefit the rational design of cancer immunotherapy strategies.

Fas ligand expression by astrocytoma in vivo: maintaining immune privilege in the brain?

Astrocytomas are among the most common brain tumors that are usually fatal in their malignant form. They appear to progress without significant impedance from the immune system, despite the presence of intratumoral T cell infiltration. To date, this has been thought to be the result of T cell immunosuppression induced by astrocytoma-derived cytokines. Here, we propose that cell contact-mediated events also play a role, since we demonstrate the in vivo expression of Fas ligand (FasL/CD95L) by human astrocytoma and the efficient killing of Fas-bearing cells by astrocytoma lines in vitro and by tumor cells ex vivo. Functional FasL is expressed by human, mouse, and rat astrocytoma and hence may be a general feature of this nonlymphoid tumor. In the brain, astrocytoma cells can potentially deliver a death signal to Fas+ cells which include infiltrating leukocytes and, paradoxically, astrocytoma cells themselves. The expression of FasL by astrocytoma cells may extend the processes that are postulated to occur in normal brain to maintain immune privilege, since we also show FasL expression by neurons. Overall, our findings suggest that FasL-induced apoptosis by astrocytoma cells may play a significant role in both immunosuppression and the regulation of tumor growth within the central nervous system.

Jun and JNK kinase are activated in thymocytes in response to VM26 and radiation but not glucocorticoids

In order to establish what role members of the activating protein-1 (AP-1) gene families, i.e., c-fos, c-jun, junB, and junD, play in thymic apoptosis, we have analyzed changes in their expression in response to three different agents: a glucocorticoid analog dexamethasone, an inhibitor of topoisomerase II teniposide VM26, and gamma radiation. All three agents induced thymic death at a similar rate and with the same morphological and biochemical features. There was a rapid and transient increase in the steady-state mRNA level of junB and c-fos genes in all treatments, including control cultures, reminiscent rather of cellular stress response to the environmental changes than to the apoptotic stimuli. On the other hand, treatments with the DNA-damaging agents, VM26 and gamma radiation, resulted in superinduction of the c-jun mRNA and in the activation of the stress response signaling pathway of c-Jun N-terminal kinase. Gene transcription ceased completely in cells with fragmented DNA and the down-regulation of genes such as junD and tubulin was reflective of the thymocytes' commitment to apoptosis. The DNA-binding activities of the serum response factors, cyclic AMP response element binding proteins, and AP-1 factors, indicative of their transcriptional competence, were compromised shortly after induction of apoptosis regardless of the agent employed, consistent with previously reported enhancement in cellular proteolysis which is an essential component of the apoptotic cell death.

Identification of a novel 97 kDa endonuclease capable of internucleosomal DNA cleavage

The two steps of DNA digestion seen in apoptotic cells were recreated in nuclei isolated from 5123tc rat hepatoma cells. The initial DNA cleavage, into high molecular weight fragments (300-50 kb), was stimulated by magnesium ions alone, whereas the second step required both calcium and magnesium ions and produced the ladder of oligonucleosomes. Endonucleolytic activities involved in both steps of DNA cleavage could be separated under appropriate conditions since the magnesium-modulated activity was tightly bound to the chromatin whereas the calcium/magnesium-dependent internucleosomal cleaving activity was easily extractable with a low ionic strength buffer. This calcium/ magnesium-dependent activity was attributed to a novel 97 kDa endonuclease which was also activated by manganese and cobalt and inhibited by millimolar concentrations of zinc, consistent with the properties ascribed to the apoptotic endonuclease. Furthermore, this activity became resistant to extraction with a low salt buffer in nuclei of apoptotic cells. Isoelectrofocusing revealed that the p97 protein existed in multiple forms of different isoelectric points (pI range 4.6-5.0), indicative of its postranslational modification. The p97 enzyme was present constitutively in a variety of cultured cells and rat tissues. It was active over a broad range of pH (6-9), but it was inactivated by reducing agents. In vitro, it displayed both endo- and exonucleolytic activities, and it was capable of both single- and double-stranded DNA cleavage. Rabbit polyclonal anti-p97 antibodies were generated and used to further distinguish this protein from other known cellular nucleases, namely, DNases I and II.

Alpha interferon-2b, leucovorin, and 5-fluorouracil (ALF) in non-small cell lung cancer

Eighteen patients with non-small cell lung cancer (NSCLC) who had previously received no systemic chemotherapy, were treated on this phase II study with interferon-alfa-2b 8 MU tiw, leucovorin 500 mg/m2 IVPB over 2 hours and 5-Fluorouracil 500 mg/m2 i.v. for 6 weeks followed by a 2-week rest. There were was no rest period for interferon. Median age of patients on this study was 63 years. Fatigue, nausea, and diarrhea were the most common toxicities. There were no grade IV toxicities and no treatment-related deaths. Seven partial responses (39%) with median duration of 4.5 months were seen. An additional patient has had stable disease/minor response for 12+ months. Median survival is 10 months. ALF has activity in NSCLC.

Memory TCR repertoires analyzed long-term reflect those selected during the primary response

Normal T cell repertoire selection and evolution in antigen-specific responses is poorly understood. We have recently described an MHC class I-restricted response characterized by an overwhelming expansion of CD8 cells expressing a Vbeta10 TCR, thus allowing the identification of antigen-selected cells directly ex vivo. Our present strategy to follow the overall TCR repertoire selection was to monitor the expression of a particular TCR alpha chain (Valpha8) on antigen-selected Vbeta10(+) cells by four-color flow cytometry. We demonstrate that while there is substantial variation among the responder mice in Valpha8 usage, the repertoires of individual animals remain relatively stable over long periods of time (>1 year), with or without repeated antigenic challenge. Thus if any evolution of this response occurs upon re-exposure to antigen, it would appear not to skew the TCR repertoire established during the primary response.