Interleukin-2-activated natural killer cells can induce both apoptosis and necrosis in rat hepatocytes

MHCI promotes developmental synapse elimination and aging-related synapse loss at the vertebrate neuromuscular junction

Synapse elimination at the developing neuromuscular junction (NMJ) sculpts motor circuits, and synapse loss at the aging NMJ drives motor impairments that are a major cause of loss of independence in the elderly. Here we provide evidence that at the NMJ, both developmental synapse elimination and aging-related synapse loss are promoted by specific immune proteins, members of the major histocompatibility complex class I (MHCI). MHCI is expressed at the developing NMJ, and three different methods of reducing MHCI function all disrupt synapse elimination during the second postnatal week, leaving some muscle fibers multiply-innervated, despite otherwise outwardly normal synapse formation and maturation. Conversely, overexpressing MHCI modestly accelerates developmental synapse elimination. MHCI levels at the NMJ rise with aging, and reducing MHCI levels ameliorates muscle denervation in aged mice. These findings identify an unexpected role for MHCI in the elimination of neuromuscular synapses during development, and indicate that reducing MHCI levels can preserve youthful innervation of aging muscle.

Bacteria-induced phagocyte secondary necrosis as a pathogenicity mechanism

Triggering of phagocyte apoptosis is a major virulence mechanism used by some successful bacterial pathogens. A central issue in the apoptotic death context is that fully developed apoptosis results in necrotic cell autolysis (secondary necrosis) with release of harmful cell components. In multicellular animals, this occurs when apoptosing cells are not removed by scavengers, mainly macrophages. Secondary necrotic lysis of neutrophils and macrophages may occur in infection when extensive phagocyte apoptosis is induced by bacterial cytotoxins and removal of apoptosing phagocytes is defective because the apoptotic process exceeds the available scavenging capacity or targets macrophages directly. Induction of phagocyte secondary necrosis is an important pathogenic mechanism, as it combines the pathogen evasion from phagocyte antimicrobial activities and the release of highly cytotoxic molecules, particularly of neutrophil origin, such as neutrophil elastase. This pathogenicity mechanism therefore promotes the unrestricted multiplication of the pathogen and contributes directly to the pathology of several necrotizing infections, where extensive apoptosis and necrosis of macrophages and neutrophils are present. Here, examples of necrotizing infectious diseases, where phagocyte secondary necrosis is implicated, are reviewed.

Liver natural killer and natural killer T cells: immunobiology and emerging roles in liver diseases

Hepatic lymphocytes are enriched in NK and NKT cells that play important roles in antiviral and antitumor defenses and in the pathogenesis of chronic liver disease. In this review, we discuss the differential distribution of NK and NKT cells in mouse, rat, and human livers, the ultrastructural similarities and differences between liver NK and NKT cells, and the regulation of liver NK and NKT cells in a variety of murine liver injury models. We also summarize recent findings about the role of NK and NKT cells in liver injury, fibrosis, and repair. In general, NK and NKT cells accelerate liver injury by producing proinflammatory cytokines and killing hepatocytes. NK cells inhibit liver fibrosis via killing early-activated and senescent-activated stellate cells and producing IFN-gamma. In regulating liver fibrosis, NKT cells appear to be less important than NK cells as a result of hepatic NKT cell tolerance. NK cells inhibit liver regeneration by producing IFN-gamma and killing hepatocytes; however, the role of NK cells on the proliferation of liver progenitor cells and the role of NKT cells in liver regeneration have been controversial. The emerging roles of NK/NKT cells in chronic human liver disease will also be discussed.Understanding the role of NK and NKT cells in the pathogenesis of chronic liver disease may help us design better therapies to treat patients with this disease.

Necrosis, a well-orchestrated form of cell demise: signalling cascades, important mediators and concomitant immune response

Necrosis has long been described as a consequence of physico-chemical stress and thus accidental and uncontrolled. Recently, it is becoming clear that necrotic cell death is as well controlled and programmed as caspase-dependent apoptosis, and that it may be an important cell death mode that is both pathologically and physiologically relevant. Necrotic cell death is not the result of one well-described signalling cascade but is the consequence of extensive crosstalk between several biochemical and molecular events at different cellular levels. Recent data indicate that serine/threonine kinase RIP1, which contains a death domain, may act as a central initiator. Calcium and reactive oxygen species (ROS) are main players during the propagation and execution phases of necrotic cell death, directly or indirectly provoking damage to proteins, lipids and DNA, which culminates in disruption of organelle and cell integrity. Necrotically dying cells initiate pro-inflammatory signalling cascades by actively releasing inflammatory cytokines and by spilling their contents when they lyse. Unravelling the signalling cascades contributing to necrotic cell death will permit us to develop tools to specifically interfere with necrosis at certain levels of signalling. Necrosis occurs in both physiological and pathophysiological processes, and is capable of killing tumour cells that have developed strategies to evade apoptosis. Thus detailed knowledge of necrosis may be exploited in therapeutic strategies.

Effect of Ligustrazine on liver injury after burn trauma

This study was designed to investigate the effect of Ligustrazine on burn-induced liver injury as well as the activation of nuclear factor kappaB (NF-kappaB) in severely burned rats. Sprague-Dawley rats were divided into three groups: (1) sham group, rats who underwent sham burn; (2) control group, rats given third-degree burns over 30% total body surface area (TBSA) and lactated Ringer solution for resuscitation; (3) Ligustrazine group, rats given burn and lactated Ringer's solution with Ligustrazine inside for resuscitation. Liver injury was assessed at 24 h post-burn by serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), as well as liver wet/dry weight ratio. Liver myeloperoxidase (MPO) activity was also analyzed. Hepatic NF-kappaB activity was examined by electrophoretic mobility shift assay (EMSA). Burn results in hepatic dysfunction and increased hepatic NF-kappaB activity, elevated liver wet/dry ratio and hepatic MPO activity. Ligustrazine inhibited these changes and alleviated burn-mediated hepatic dysfunction. The data indicated that Ligustrazine has a protective effect on burn-induced liver injury and possible mechanism may be attributed to its inhibitory action on the activation of NF-kappaB following burn trauma.

Catecholamine-induced apoptosis and necrosis in cardiac and skeletal myocytes of the rat in vivo: the same or separate death pathways?

High levels of catecholamines are myotoxic but the relative amounts of apoptosis and necrosis have not been established in vivo in cardiac and skeletal muscles. Immunohistochemistry was used to detect and quantify myocyte-specific necrosis (myosin antibody in vivo) and apoptosis (caspase-3 antibody in vitro) in the heart and soleus muscles of male Wistar rats that had received single subcutaneous injections of isoprenaline over the range 1 microg to 5 mg [kg body weight (BW)](-1). Peak myocyte apoptosis occurred 3-6 h after, and necrosis 18 h after, a single injection of 5 mg (kg BW)(-1) isoprenaline in vivo. In the heart myocyte death was mediated through the beta1-adrenergic receptor whereas myocyte death in the soleus muscle was mediated through the beta2-adrenergic receptor. Cardiomyocyte death was heterogeneously distributed throughout the heart, being greatest in the left ventricle (LV) subendocardium and peaking close to the apex, but with significantly more necrosis than apoptosis. Extensive co-localization of caspase-3 and myosin labelling was found in the myocytes of both the heart and the slow-twitch soleus muscle. This, together with similar spatial distributions and responses to catecholamine doses, suggests that either caspase-3 activation occurs in necrotic as well as apoptotic myocytes or that a large proportion of apoptotic myocytes progress to secondary necrosis in vivo.

Gene expression profiles of livers from thermally injured rats

The liver plays an important role in a severe thermal injury by modulating immune function, inflammatory processes and the acute phase response, which are an orchestrated attempt to restore homeostasis. Using high-density oligonucleotide arrays, we examined the gene expression profile in the livers of rats between 2 and 240 h after a 40% total body surface area (TBSA) burn. Alterations in gene expression unique to a thermal injury were identified. Approximately 39 genes out of 8700 genes on each array across all the time points showed a significant change in expression patterns. Real time reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses verified significant changes in early growth response-1 (Egr-1) messenger RNA (mRNA) and protein levels corresponding to the array data. Significant increases in serum levels of alpha-2-macroglobulin that correspond to changes in its mRNA levels were observed at 6 and 24 h after burn, p<0.05. The genomic pattern for liver in the hypermetabolic phase after the burn injury involves transcription factors, stress and inflammatory responses, cytoskeletal and extracellular matrix modifications, and regulation of cell proliferation and differentiation. During the initial phase of thermal injury gene expression profiles in the liver may provide some insight into how cellular protection mechanisms and systemic hypermetabolism are initiated and controlled. The genome wide changes observed may provide a rational therapeutic strategy to improve burn care.

Rat colon carcinoma cells that survived systemic immune surveillance are less sensitive to NK-cell mediated apoptosis

In order to form distant metastases, cells from the primary tumor have to detach, enter the blood- or lymph-compartment and escape immune surveillance. Here, we describe the selection of rat colon carcinoma cell lines (CC531s-m1 and CC531s-m2) that escaped from systemic immune surveillance; CC531s cells were injected into the v. jugularis of Wag/Rij rats, after three weeks the lung tumors were isolated, the tumor cells were cultured, characterized and injected again. The m1- and m2-cell lines were less susceptible for killing by syngeneic NK cells. Further characterization of this cell line showed a decreased sensitivity towards TRAIL- and CD95L-, but not to granzyme B-mediated apoptosis. In the m1- and m2-cells log-phase growth started earlier as compared to the parental cell line, whereas no changes were found in anchorage-dependent or anchorage-independent growth. After subcapsular injection of the m2-cell line into the liver of rats much more lung metastases were formed in comparison to injection of the parental cell line. In conclusion, the results suggest that the resistance of the m1- and m2-cells to NK cell-mediated apoptosis was associated with their capability to survive systemic immune surveillance and form metastases in vivo.

Interleukin-2 activated NK cells do not use the CD95L- and TRAIL-pathways in the rapid induction of apoptosis of rat colon carcinoma CC531s cells

Natural Killer (NK) cells can induce apoptosis in target cells in at least four ways: by secretion of granzyme B/perforin (GrB/P) and via the CD95L, TRAIL and TNF-alpha pathways. In this study we examined the pathways used by interleukin-2 activated rat NK (A-NK) cells to induce apoptosis in the rat colon carcinoma cell line CC531s. Co-incubation of A-NK cells with CC531s cells for three hours resulted in 70% apoptosis in the latter. Addition of the GrB/P pathway-inhibitor concanamycin A reduced the number of apoptotic cells to 54%. Blockade of the CD95L, TRAIL and TNF-alpha pathways by specific antibodies hardly had an additional effect. However, co-incubation with transfected MEC cells that expressed CD95L or 2PK3-cells that expressed TRAIL did induce apoptosis in CC531s cells. Furthermore the A-NK cells contained CD95L and TRAIL. However, comparison of non- and permeabilized cells revealed that the majority of TRAIL was present in the cytosol of A-NK cells and was not available for induction of apoptosis. The presence of elevated levels of bcl-2 in CC531 cells reduced the sensitivity towards induction of apoptosis both by A-NK cells as well as the CD95L and TRAIL expressing cell lines. Using the caspase-inhibitors ac-IEPD-CHO, ac-DEVD-CHO and zVAD-fmk, it was shown that inhibition of the effector caspase-3 prevented A-NK cell induced apoptosis in CC531-bcl-2 cells, but not in CC531s cells. In conclusion, A-NK cells kill by secretion of GrB/P and not by the CD95L, TRAIL or TNF pathways albeit both CD95L and TRAIL are produced by the A-NK cells.

IL-4 enhances antitumor effect of IL-2 induced A-NK Cells on human colon carcinoma

AIM

Using IL-4 combined with IL-2 to induce A-NK cells and to evaluate the cytotoxicity of A-NK cells and its inhibiting effect on colon tumor growth.

METHODS

The A-NK cells were activated with recombinant lymphokine IL-2 combined IL-4, the cytotoxicity of the effector cells was determined by LDH-L release assay. Its antitumor effect was investigated through growth inhibiting of human colon carcinoma cells in nude mice.

RESULTS

IL-2 alone or combined with IL-4 could induce the activity of A-NK cells successively which could kill K562, Anip973 and CC95 tumor cells in vitro by LDH-L release assay (39.00 ± 9.16 vs 77.68 ± 12.80, 43.10 ± 10.05 vs 80.02 ± 13.74, 42.14 ±9.72 vs 79.10 ±12.65, P <0.01) and inhibit the growth of human colon carcinoma cells in nude mice (1.04 ± 0.15 vs 0.62 ± 0.16, P <0.01).The results suggested that there was expression of IL-4 receptor on the surface of A-NK cells.

CONCLUSION

IL-4 can enhance the antitumor activity of IL-2 induced A-NK cells. The method may have some potential application value in human cancer treatment.

Regional loss of the mitochondrial membrane potential in the hepatocyte is rapidly followed by externalization of phosphatidylserines at that specific site during apoptosis

The spatio-temporal relationship between a decrease in the mitochondrial membrane potential (MMP) and externalization of phosphatidylserines (PS) during induction of apoptosis was investigated in single freshly isolated hepatocytes. Apoptosis was induced in the hepatocytes in three different ways: attack by activated Natural Killer cells, exposure to ATP, or exposure to the inhibitor of protein synthesis cycloheximide. Fluorescence microscopy showed staining of externalized PS at those areas where the staining for MMP was lost whereas in other areas the mitochondria remained intact for longer periods of time, indicating coupling between local loss of MMP and local PS exposure. To discriminate whether the decrease in MMP itself or a decrease in ATP induced PS externalization, hepatocytes were treated with rotenone, which resulted in a rapid collapse of cellular ATP but left the MMP intact for a much longer period. Addition of fructose prevented the decrease of ATP to approximately 30% and also delayed the collapse of the MMP. This indicates that ATP was needed for the maintenance of the MMP probably via reverse action of the ATP synthase. In a subsequent study hepatocytes were incubated with Natural Killer cells for induction of apoptosis followed by addition of rotenone to deplete ATP. Under these conditions the PS staining co-localized with mitochondrial MMP indicating that PS externalization does not require a collapse in MMP. Moreover, exposure of PS was evenly distributed over the whole plasma membrane. In conclusion, we propose that after an apoptotic stimulus some mitochondria start to loose their MMP, which results in cessation of ATP production and perhaps even consumption of ATP. This results in an overall decrease in cellular ATP. ATP-consuming enzyme reactions most distal from still intact mitochondria will be most sensitive to such a decrease. Apparently the translocase that keeps phosphatidylserines inward-oriented is such a sensitive enzyme.

Necrosis: a specific form of programmed cell death?

For a long time necrosis was considered as an alternative to programmed cell death, apoptosis. Indeed, necrosis has distinct morphological features and it is accompanied by rapid permeabilization of plasma membrane. However, recent data indicate that, in contrast to necrosis caused by very extreme conditions, there are many examples when this form of cell death may be a normal physiological and regulated (programmed) event. Various stimuli (e.g., cytokines, ischemia, heat, irradiation, pathogens) can cause both apoptosis and necrosis in the same cell population. Furthermore, signaling pathways, such as death receptors, kinase cascades, and mitochondria, participate in both processes, and by modulating these pathways, it is possible to switch between apoptosis and necrosis. Moreover, antiapoptotic mechanisms (e.g., Bcl-2/Bcl-x proteins, heat shock proteins) are equally effective in protection against apoptosis and necrosis. Therefore, necrosis, along with apoptosis, appears to be a specific form of execution phase of programmed cell death, and there are several examples of necrosis during embryogenesis, a normal tissue renewal, and immune response. However, the consequences of necrotic and apoptotic cell death for a whole organism are quite different. In the case of necrosis, cytosolic constituents that spill into extracellular space through damaged plasma membrane may provoke inflammatory response; during apoptosis these products are safely isolated by membranes and then are consumed by macrophages. The inflammatory response caused by necrosis, however, may have obvious adaptive significance (i.e., emergence of a strong immune response) under some pathological conditions (such as cancer and infection). On the other hand, disturbance of a fine balance between necrosis and apoptosis may be a key element in development of some diseases.

Mitochondrial membrane potential is reduced in peripheral natural killer cells following partial hepatectomy

The mechanism underlying immunosuppression after partial hepatectomy remains unclear. Hepatectomy induces lymphopenia, which is related to immunomodulation. The aim of this study was to determine whether peripheral blood lymphocytes (PBL) are susceptible to mitochondria-mediated apoptosis after hepatic resection. We compared the changes in mitochondrial membrane potential in lymphocytes from hepatectomized patients with metastatic liver tumor with the corresponding changes in lymphocytes from cholechystectomized patients, because changes in mitochondrial membrane potential have been reported to frequently occur during the early stages of apoptosis. Mitochondrial membrane potential, subpopulation, and apoptosis of lymphocytes were estimated with flow cytometry. Hepatectomy significantly (P<0.001) reduced postoperative mitochondrial membrane potential, while cholecystectomy slightly decreased it. Apoptosis of lymphocytes was increased on post-hepatectomy day, and this increase was correlated with the extent of mitochondrial membrane potential reduction. The major subset of lymphocytes with low mitochondrial membrane potential consisted of CD56(+) natural killer (NK) cells, and NK cell activity and cell counts significantly decreased after hepatectomy. Mitochondrial membrane potential of PBL was reduced after hepatectomy, and some lymphocytes underwent apoptosis through the mitochondrial pathway, which was one of the causes for lymphopenia. NK cells were more responsible for the decrease of mitochondrial membrane potential after hepatectomy than other lymphocytes, and the reduction in mitochondrial membrane potential in NK cells appeared to reflect modulation of the innate immune system.

The role of calpains in apoptotic changes in isolated hepatocytes after attack by Natural Killer cells

Previously, we showed that interleukin-2 activated Natural Killer cells (A-NK cells) in vitro rapidly induced apoptosis in freshly isolated rat hepatocytes (Blom et al., 1999. Hepatology 29 (3): 785-792) which was caused by a rapid decrease in the mitochondrial membrane potential and activation of caspases. In the present study we investigated the involvement of calpains in A-NK cell-induced apoptosis in isolated hepatocytes. When NK cells and hepatocytes were incubated in the presence of a calpain inhibitor the number of apoptotic cells decreased from 46 to 36%. However, more hepatocytes became necrotic (48 vs. 30%) as compared to the uninhibited situation. Inhibition of the calpains alone could not prevent the induction of the nuclear and cytoskeletal disruptions occurring in the hepatocytes. Inhibition of both calpains and caspases increased the number of necrotic cells as compared to incubation with a single inhibitor. However, the damage to the cytoskeleton of the surviving cells was completely inhibited. We conclude that calpains play a role in induction of apoptosis by NK cells. However, their role is limited as compared to caspases.

Differential regulation of phosphatidylserine externalization and DNA fragmentation by caspases in anticancer drug-induced apoptosis of rat mammary adenocarcinoma MTLn3 cells

Caspase activation is a central event in the execution phase of apoptosis and is associated with phosphatidylserine (PS) externalization and DNA fragmentation. We investigated the role of caspase activity in anticancer drug-induced PS externalization and DNA fragmentation in MTLn3 cells. Caspase activation (DEVD-AMC cleavage) occurred in a time- and concentration-dependent manner after exposure to doxorubicin, in association with cleavage of poly(ADP) ribose polymerase and protein kinase C delta, two caspase-3 substrates. Caspase activation was closely followed by oligonucleosomal DNA fragmentation and PS externalization as determined by flow cytometric analysis. Similar observations were made for etoposide and cisplatin. Inhibition of caspases with zVAD-fmk inhibited almost completely doxorubicin-induced DNA fragmentation as well as proteolysis of protein kinase C delta. In contrast, PS externalization induced by doxorubicin was only partly affected by caspase inhibition. Flow cytometric cell sorting demonstrated that DNA fragmentation in the remaining PS positive cells after doxorubicin treatment in the presence of zVAD-fmk was fully blocked. In conclusion, these data indicate that while DNA fragmentation in anticancer drug-induced apoptosis of MTLn3 cells is fully dependent on caspase activity, PS externalization is controlled by both caspase-dependent and caspase-independent pathways.

Remodeling of the actin cytoskeleton of target hepatocytes and NK cells during induction of apoptosis

Natural Killer cells are immune cells that recognize and eliminate altered and non-self cells from the circulation. To study the interaction between NK cells and target cells, we set up an experimental system consisting of rat Interleukin-2 activated Natural Killer cells (A-NK cells) and rat hepatocytes with a masked Major Histocompatibility Complex (MHC). The masking of the MHC induces recognition of the hepatocytes by the NK cells as non-self. We showed that in vitro apoptosis is rapidly induced in the hepatocytes [Blom et al., 1999] after co-incubation with A-NK cells. Now we describe the morphological changes that occur during and after interaction of A-NK cells with hepatocytes. Confocal laser scanning microscopy showed that the actin cytoskeleton of the NK cells was remodeled during attack of hepatocytes. Some NK cells were in close contact with the hepatocytes while others had formed actin-containing dendrites of varying length that made contact with the hepatocytes. However, dendrite formation is not obligatory for induction of apoptosis because cells that were unable to form these did induce FAS-dependent apoptosis in hepatocytes. Apparently both direct as well as distant contact resulted in apoptosis. Formation of the dendrites was calcium-dependent as EGTA largely prevented it. Importantly, chelation of the calcium also suppressed killing of the hepatocytes. Within 1 h after addition of the A-NK cells, morphological changes in hepatocytes that are characteristic of apoptosis, such as the formation of apoptotic bodies and fragmented nuclei, became apparent. Specifically, the actin cytoskeleton of the hepatocytes was remodeled resulting in the formation of the apoptotic bodies. Inhibition of caspase activity by z-Val-Ala-DL-Asp-fluoromethylketone (100 microM) partly protected against the rearrangement of the actin filaments in the hepatocytes.

Cell proliferation, apoptosis, NF-kappaB expression, enzyme, protein, and weight changes in livers of burned rats

Thermal injury has been shown to alter gut epithelium and heart myocyte homeostasis by inducing programmed cell death. The effect of thermal injury on hepatocyte apoptosis and proliferation, however, has not been established. The purpose of this study was to determine whether a large thermal injury increases liver cell apoptosis and proliferation and whether these changes were associated with alterations in hepatic nuclear factor kappaB (NF-kappaB) expression and changes in liver enzymes and amount of protein. Sprague-Dawley rats received a 40% total body surface area scald burn or sham burn. Rats were killed and livers were harvested at 1, 2, 5, and 7 days after burn. Liver cell apoptosis was determined by terminal deoxyuridine nick end labeling (TUNEL) assay and cell proliferation by immunohistochemistry for proliferating cell nuclear antigen. Hepatic NF-kappaB expression was determined by Western blot, and total hepatic protein content was determined by protein assay. Protein concentration decreased after burn compared with sham controls (P < 0.05). Liver cell apoptosis, proliferation, and NF-kappaB expression in hepatocytes increased in burned rats compared with controls (P < 0.05). It was concluded that thermal injury induces hepatic cell apoptosis and proliferation associated with an increase in hepatic NF-kappaB expression and a decrease in hepatic protein concentration.

Extracellular adenosine-induced apoptosis in mouse neuroblastoma cells: studies on involvement of adenosine receptors and adenosine uptake

The induction of apoptosis by adenosine was studied in the mouse neuroblastoma cell line N1E-115. Apoptosis was characterized by fluorescence and electron microscopy, fluorescence-activated cell sorter (FACS) analysis, and caspase activity assays. A sixteen-hour exposure to 100 microM of adenosine led to chromatin condensation and caspase activation. However, selective agonists for all four adenosine receptors were ineffective. Caspase activation could be blocked partially by an inhibitor of the nucleoside transporter, dipyridamole, and completely by uridine, a competing substrate for adenosine transport. 2'-Deoxycoformycin, an inhibitor of adenosine deaminase, enhanced caspase activation by adenosine but had no effect by itself. Caspase activation could be blocked by 5'-amino-5'-deoxyadenosine, which inhibits the phosphorylation of adenosine by adenosine kinase. These results indicate that adenosine receptors are not involved in adenosine-induced apoptosis in N1E-115 cells, but that uptake of adenosine and its subsequent phosphorylation is required.

Murine polyomavirus infection of 3T6 mouse cells shows evidence of predominant necrosis as well as limited apoptosis

The current study was developed to determine if polyomavirus infected 3T6 mouse cells evoked an apoptotic or a necrotic mechanism during infection. Infected cells were analyzed by flow cytometry, transmission electron microscopy (TEM), DNA electrophoresis and by measuring caspase-3 enzymatic activity. Infected cells that were analyzed at 72 h post-infection showed the following: flow cytometry analysis revealed a 5% increase in apoptotic cells and a 46% increase in necrotic cells when compared to uninfected cells; electron microscopy showed 10% cells with characteristic apoptotic morphology and 40% with necrotic appearance; caspase-3 activity was found to increase two fold when compared to uninfected cells and DNA fragmentation (laddering) was clearly evident late in infection. It was concluded that infected cells predominantly showed necrosis, although some cells showed apoptosis in late infection. Recombinant capsid-like particles composed of the polyomavirus structural proteins were not able to induce cell death.

Prevention of cycloheximide-induced apoptosis in hepatocytes by adenosine and by caspase inhibitors

The mechanism by which cycloheximide induces apoptosis in isolated rat hepatocytes was studied. Cycloheximide (1-300 microM) induced apoptosis within 3-4 hr in the hepatocytes. Specific apoptotic characteristics such as blebbing, phosphatidyl serine (PS) exposure, chromatin condensation, and nuclear fragmentation were induced. Cycloheximide (CHX) dose dependently activated the caspase-3-like proteases, but not the caspase-1-like proteases. Pretreatment of the hepatocytes with 100 microM of the caspase inhibitors z-Val-Ala-DL-Asp-fluoromethylketone or Ac-Asp-Glu-Val-Asp-aldehyde completely abrogated the caspase activation and the apoptosis. Addition of adenosine (100 microM) reduced phosphatidyl serine exposure and other morphological characteristics of apoptosis by 50%; however, it did not prevent the activation of the caspases, suggesting that adenosine inhibited downstream of caspase activation. The adenosine receptor antagonist 8-[4-[[[[(2-aminoethyl)amino]-carbonyl]methyl]oxy]phenyl]-1,3-dipropylxa nthine abolished the capacity of adenosine to prevent apoptosis, indicating that prevention was receptor-mediated. During apoptosis, the mitochondrial membrane potential in apoptotic cells (cells with PS exposition) was decreased to 50-60% of the control value; in the population viable cells, however, the mitochondrial membrane potential remained stable. Prevention of apoptosis by the caspase inhibitor z-Val-Ala-DL-Asp-fluoromethylketone or adenosine prevented the decrease in mitochondrial membrane potential. In conclusion, CHX rapidly induces apoptosis in isolated rat hepatocytes, which is inhibited by adenosine at a relatively late step.

Adenovirus-mediated gene expression in vivo is enhanced by the antiapoptotic bcl-2 gene

An adenovirus vector encoding the human Bcl-2 gene (hBcl-2) was derived. In vivo expression of hBcl-2 in murine livers enhanced and prolonged adenovirus-mediated gene expression. Furthermore, in the hBcl-2-treated group a significant reduction in the apoptosis induced by the adenovirus vector was observed. Thus, the cytoprotection of the vector-infected cells with antiapoptotic genes appears promising for successful in vivo gene therapy.