Cycloheximide can rescue heat-shocked L cells from death by blocking stress-induced apoptosis

Lowering Etoposide Doses Shifts Cell Demise From Caspase-Dependent to Differentiation and Caspase-3-Independent Apoptosis via DNA Damage Response, Inducing AML Culture Extinction

Cytotoxic chemotherapy, still the most widely adopted anticancer treatment, aims at eliminating cancer cells inducing apoptosis with DNA damaging agents, exploiting the differential replication rate of cancer vs. normal cells; efficiency is evaluated in terms of extent of induced apoptosis, which depends on the individual cell sensitivity to a given drug, and on the dose. In this in vitro study, we report that the concentration of etoposide, a topoisomerase II poison widely used in clinics, determines both the kinetics of cell death, and the type of apoptosis induced. We observed that on a set of myeloid leukemia cell lines, etoposide at high (50 uM) dose promoted a rapid caspase-3-mediated apoptosis, whereas at low (0.5 uM) dose, it induced morphological and functional granulocytic differentiation and caspase-2-dependent, but caspase-3-independent, cell death, displaying features consistent with apoptosis. Both differentiation and caspase-2- (but not 3)-mediated apoptosis were contrasted by caffeine, a well-known inhibitor of the cellular DNA damage response (DDR), which maintained cell viability and cycling, indicating that the effects of low etoposide dose are not the immediate consequence of damage, but the result of a signaling pathway. DDR may be thus the mediator responsible for translating a mere dosage-effect into different signal transduction pathways, highlighting a strategic action in regulating timing and mode of cell death according to the severity of induced damage. The evidence of different molecular pathways induced by high vs. low drug doses may possibly contribute to explain the different effects of cytotoxic vs. metronomic therapy, the latter achieving durable clinical responses by treating cancer patients with stable, low doses of otherwise canonical cytotoxic drugs; intriguingly caspase-3, a major promoter of wounded tissue regeneration, is also a key factor of post-therapy cancer repopulation. All this suggests that cancer control in response to cytotoxic drugs arises from complex reprogramming mechanisms in tumor tissue, recently described as anakoinosis.

Redox modulation of the DNA damage response

Lesions to DNA trigger the DNA-damage response (DDR), a complex, multi-branched cell-intrinsic process targeted to DNA repair, or elimination of the damaged cells by apoptosis. DDR aims at reducing permanence of mutated cells, decreasing the risk of tumor development: the more stringent the response, the lower the likelihood that sub-lethally damaged, unrepaired cells survive and proliferate. Accordingly, leakage often occurs in tumor cells with compromised DDR, accumulating mutations and accelerating tumor progression. Oxidations mediate DNA damage upon different insults such as UV, X and γ radiation, pollutants, poisons, or endogenous disequilibria, producing different types of lesions that trigger DDR, which can be alleviated by antioxidants. But reactive oxygen species (ROS), and the enzymes involved in their production or scavenging, also participate in DDR signaling, modulating the activity of key enzymes, and regulating the stringency of DDR. Accordingly, antioxidant enzymes such as superoxide dismutase play intimate and complex roles in tumor development, exceeding the basal roles of preventing the initial DNA damage. Likewise, it is emerging that dietary antioxidants help controlling tumor onset and progression by preventing DNA damage and by acting on cell cycle checkpoints, opening a novel and promising frontier to anticancer therapy.

The cleavage mode of apoptotic nuclear vesiculation is related to plasma membrane blebbing and depends on actin reorganization

In U937 monocytic cells induced to apoptosis, plasma membrane blebbing of different intensities appears, before the development of nuclear alterations; this latter phenomenon can occur through two major pathways, namely the cleavage and the budding mode (Dini et al., 1996). Strongly blebbing cells develop deep nuclear constrictions leading to nuclear fragmentation according to the cleavage mode, while cells with milder forms of blebbing, or no blebbing at all, undergo nuclear fragmentation along the budding mode. Compounds interfering with different cytoskeletal components affect blebbing, which is completely inhibited by the actin polymerization inhibitors, cytochalasins, while disturbance of tubulin network with taxol limits blebbing to milder forms. At the same time, the cytoskeletal poisons affect the type of nuclear fragmentation, abolishing the cleavage mode, shifting all events into the budding pathway. Adherent cells, which possess a more structured cytoskeleton, do not develop strong blebs and undergo nuclear fragmentation via budding. These observations suggest that the deep cytoskeletal movements that cause the strongest forms of plasma membrane blebbing strangle the nucleus, leading to the constrictions that later evolve into nuclear fragmentation by cleavage. The trigger for the cytoskeletal movements, known to be redox-sensitive, is probably the apoptotic GSH extrusion.

Cellular mechanisms of neuronal damage from hyperthermia

Hyperthermia can cause brain damage and also exacerbate the brain damage produced by stroke and amphetamines. The developing brain is especially sensitive to hyperthermia. The severity of, and mechanisms underlying, hyperthermia-induced neuronal death depend on both temperature and duration of exposure. Severe hyperthermia can produce necrotic neuronal death. For a window of less severe heat stresses, cultured neurons exhibit a delayed death with apoptotic characteristics including cytochrome c release and caspase activation. Little is known about mechanisms of hyperthermia-induced damage upstream of these late apoptotic effects. This chapter considers several possible upstream mechanisms, drawing on both in vivo and in vitro studies of the nervous system and other tissues. Hyperthermia-induced damage in some non-neuronal cells includes endoplasmic reticular stress due to denaturing of nascent polypeptide chains, as well as nuclear and cytoskeletal damage. Evidence is presented that hyperthermia produces mitochondrial damage, including depolarization, in cultured mammalian neurons.

Involvement of apoptosis in hydrazine induced toxicity in rat primary hepatocytes

The current study was undertaken to investigate the role of apoptosis in hydrazine induced hepatotoxicity. Hepatocytes were exposed to hydrazinium nitrate (HzN) at two doses (50 and 75 mM) for 2 h then placed in fresh HzN-free media and cultured for an additional 24 h. Post-exposure, cell viability was evaluated at several time points by lactate dehydrogenase (LDH) leakage and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction. Markers of apoptosis (mitochondrial membrane potential, annexin binding, DNA fragmentation, caspase activation, and cytochrome c release) were measured 24 h post-exposure. The viability data showed time dependent increase in LDH leakage at 75 mM of HzN, with only a slight increase at 50 mM. MTT reduction showed a decrease in mitochondrial activity at both doses immediately after the 2 h continuous exposure. However, MTT reduction returned to normal at 50 mM while at 75 mM, MTT reduction initially recovered but then deteriorated to approximately 50% of controls at 24 h post-exposure. Based on viability data, exposure to 50 mM HzN for 2 h is a marginally toxic dose while 75 mM is a significantly toxic dose. The results for apoptosis biomarkers showed a reduction in mitochondrial membrane potential, an increase in annexin binding, an increase in total caspase activity, moderate activation of caspase-3, and release of cytochrome c. However, the appearance of DNA fragmentation in HzN exposed cells was very low compared to positive controls (cadmium and cyclosporine). The possibility that HzN induces apoptosis without the involvement of DNA fragmentation can not be ruled out. The present results, overall, suggest that apoptosis may be a contributing factor in acute HzN toxicity.

Cycloheximide and 4-OH-TEMPO suppress chloramphenicol-induced apoptosis in RL-34 cells via the suppression of the formation of megamitochondria

Toxic effects of chloramphenicol, an antibiotic inhibitor of mitochondrial protein synthesis, on rat liver derived RL-34 cell line were completely blocked by a combined treatment with substances endowed with direct or indirect antioxidant properties. A stable, nitroxide free radical scavenger, 4-hydroxy-2,2,6, 6-tetramethylpiperidine-1-oxyl, and a protein synthesis inhibitor, cycloheximide, suppressed in a similar manner the following manifestations of the chloramphenicol cytotoxicity: (1) Oxidative stress state as evidenced by FACS analysis of cells loaded with carboxy-dichlorodihydrofluorescein diacetate and Mito Tracker CMTH2MRos; (2) megamitochondria formation detected by staining of mitochondria with MitoTracker CMXRos under a laser confocal microscopy and electron microscopy; (3) apoptotic changes of the cell detected by the phase contrast microscopy, DNA laddering analysis and cell cycle analysis. Since increases of ROS generation in chloramphenicol-treated cells were the first sign of the chloramphenicol toxicity, we assume that oxidative stress state is a mediator of above described alternations of RL-34 cells including MG formation. Pretreatment of cells with cycloheximide or 4-hydroxy-2,2, 6,6-tetramethylpiperidine-1-oxyl, which is known to be localized into mitochondria, inhibited the megamitochondria formation and succeeding apoptotic changes of the cell. Protective effects of cycloheximide, which enhances the expression of Bcl-2 protein, may further confirm our hypothesis that the megamitochondria formation is a cellular response to an increased ROS generation and raise a possibility that antiapoptotic action of the drug is exerted via the protection of the mitochondria functions.

Free radical-induced megamitochondria formation and apoptosis

Pathophysiological meaning and the mechanism of the formation of megamitochondria (MG) induced under physiological and pathological conditions remain obscure. We now provide evidence suggesting that the MG formation may be a prerequisite for free radical-mediated apoptosis. MG were detected in primary cultured rat hepatocytes, rat liver cell lines RL-34 and IAR-20 and kidney cell line Cos-1 treated for 22 h with various chemicals known to generate free radicals: hydrazine, chloramphenicol, methyl-glyoxal-bis-guanylhydrazone, indomethacin, H2O2, and erythromycin using a fluorescent dye Mito Tracker Red CMXRos (CMXRos) for confocal laser microscopy and also by electron microscopy. Remarkable elevations of the intracellular level of reactive oxygen species (ROS), monitored by staining of cells with a fluorescent dye carboxy-H2-DCFDA, were detected before MG were formed. Prolongation of the incubation time with various chemicals, specified above, for 36 h or longer has induced distinct structural changes of the cell, which characterize apoptosis: condensation of nuclei, the formation of apoptotic bodies, and the ladder formation. Cells treated with the chemicals for 22 h were arrested in G1 phase, and apoptotic sub-G1 populations then became gradually increased. The membrane potential of MG induced by chloramphenicol detected by CMXRos for flow cytometry was found to be decreased compared to that of mitochondria in control cells. Rates of the generation of H2O2 and O2- from MG isolated from the liver of rats treated with chloramphenicol or hydrazine were found to be lower than those of mitochondria of the liver of control animals. We suggest, based on the present results together with our previous findings, that the formation of MG may be an adaptive process at a subcellular level to unfavorable environments: when cells are exposed to excess amounts of free radicals mitochondria become enlarged decreasing the rate of oxygen consumption. Decreases in the oxygen consumption of MG may result in decreases in the rate of ROS production as shown in the present study. This will at the same time result in decreases in ATP production from MG. If cells are exposed to a large amount of free radicals beyond a certain period of time, lowered intracellular levels of ATP may result in apoptotic changes of the cell.

Dephosphorylation, proteolysis, and reduced activity of poly(A) polymerase associated with U937 cell apoptosis

The apoptotic trend of the widely used cell lines HL-60, U937, HeLa, Molt-3, and K562 has been found to be accompanied and reversibly related with Poly(A) polymerase (PAP; EC 2.7.7.19) activity levels. Moreover, variations in the pattern of multiple enzyme forms are revealed, being most prominent in apoptosis-prone cell lines, HL-60 and U937. Furthermore, in heat-shocked or nutrient-deprived apoptotic U937 Percoll-fractionated subpopulations, PAP lower mobility phosphorylated forms of 106 and 100 kDa as well as enzyme activity were progressively reduced along with the appearance of higher than 80 kDa mobility species. The kinetics of these alterations (dephosphorylation, proteolysis, and activity) coincided with the appearance of DNA fragmentation. In fact, PAP dephosphorylation appears to precede the appearance of DNA fragmentation. In addition, inhibition of PAP dephosphorylation, proteolysis, and decrease in its activity were tightly coupled with the concomitant prevention of apoptosis. This novel finding yields information on a possible involvement of PAP in cell commitment and execution to apoptosis.

Apoptosis precedes necrosis of fish cell line with infectious pancreatic necrosis virus infection

The current view of infectious pancreatic necrosis virus (IPNV) infection includes a necrotic process that relies primarily on the histological appearance of tissue after the degenerative process. We tested this view by examining the possibility that apoptosis is a component of double-stranded RNA virus (IPNV) that induces fish embryonic cell death. Four kinds of assays for apoptosis were used in analyzing IPNV-infected CHSE-214 cells: (1) assay with terminal deoxynucleotidyl transferase (TdT)-mediated end-labeling of DNA in nuclei of intact cells during virus infection, (2) assay for procoagulant activity, (3) assay for DNA ladders, and (4) electron microscopic assays for the ultrastructural changes in characteristic apoptotic cells. In all p.i. samples, both low and high m.o.i. groups contained apoptotic nuclei, according to TdT-mediated dUTP labeling of intact cells, but in control CHSE-214 cells, apoptotic nuclei were rare at all levels of incubation sampled by TdT-mediated dUTP labeling. Prenecrotic or postnecrotic cells were found to express phosphatidylserine on the surface by annexin V-FITC labeling, but normal cells did not. DNAs from both 4 h p.i. of high m.o.i. and 8 h p.i. of low m.o.i. were found to be cleaved into fragments indicative of preferential cleavage at internucleosomal sites. The IPNV-infected CHSE-214 cells were analyzed with an electron microscope and showed a pattern of ultrastructural change, indicating that apoptosis appears before pathological changes of necrosis, including condensed chromatin, fragmented nuclei, nuclei with chromatin marginations, and secondary necrosis from prenecrotic cells in IPNV-infected CHSE-214 cells. Together, these findings show that apoptosis precedes any detectable necrotic change in CHSE-214 cells that is currently viewed as necrosis. Thus, apoptosis characterizes the onset of pathology in host cells and is followed by necrotic processes.

Effect of heat shock treatment on the production of variant testosterone-repressed prostate message-2 (TRPM-2) mRNA in culture cells

The testosterone-repressive prostate message-2 (TRPM-2) variant mRNA lacking the exon 5 was induced in rat primary culture hepatocytes by heat shock treatment. A similar variant mRNA lacking exon 5 was also induced by heat shock treatment of the human culture cell line HepG2. On the other hand, in mouse cell line L929, heat shock treatment induced a variant TRPM-2 mRNA lacking only a small region located in exon 5. However, irrespective of the difference of mechanism of variant production, all the variant TRPM-2 mRNA species derived from each animal species encoded a putative protein constituted from the N-terminal one-third of TRPM-2 protein attached to a C-terminal TRPM-2 unrelated tail. In humans, the variant TRPM-2 species was not detected in normal tissues but was present in certain kinds of tumour cells. These results indicate that the splicing variants were induced as a direct result of heat shock treatment on cells per se and that the phenomenon of heat shock induction was observed in culture cells derived from different animal species.

Evidence of apoptosis in primary neuronal cultures after heat shock

We investigated the effects of 30-min heat shock on survival, DNA degradation, and nuclear morphology of primary rat cortical and hippocampal neurones. In cell cultures which were grown for 8 days in vitro (DIV), only a small portion of neurones showed apoptotic morphology after heat shock of 45 degrees C and typical DNA laddering was not detectable, despite the fact that nearly 50% of the neurones died within 24 h. The majority of the neurones presumably died by necrosis, as indicated by random DNA degradation. In neuronal cultures grown for 15 DIV, heat shock, however, resulted in DNA laddering, occurrence of apoptotic bodies and DNA strand breaks, typical of apoptosis. In these cultures, about 50% of the neurones showed apoptotic morphology following exposure to 45 degrees C in TUNEL and acridine orange staining, whereas glia were not affected in vitality. In addition we were interested whether the highly inducible member of the heat-shock protein family, HSP72, would be induced in apoptotic cells. Double staining for HSP72 and TUNEL revealed concomitant HSP72 induction and occurrence of DNA degradation only in very few neurones in 15-DIV cultures, which were growing adjacent to astrocytes. A clear association of the degenerative process and HSP72 expression, therefore, could not be established. These results demonstrate that environmental stress, such as heat shock, can induce apoptotic death in aged primary cultured neurones. The differentiation state and/or the presence of glial cell elements in the cultures appears to be an important factor for the occurrence of apoptotic features in cultured neurones.

Changes in metabolism of inorganic polyphosphate in rat tissues and human cells during development and apoptosis

Age-dependent studies show that the amount of inorganic polyphosphate in rat brain strongly increases after birth. Maximal levels were found in 12-months old animals. Thereafter, the concentration of total polyphosphate decreases to about 50%. This decrease in the concentration of total polyphosphate is due to a decrease in the amount of insoluble, long-chain polyphosphates. The amount of soluble, long-chain polyphosphates does not change significantly in the course of ageing. In rat embryos and newborns, mainly soluble polyphosphates could be detected. In rat liver, the age-dependent changes are less pronounced. The changes in polyphosphate level are accompanied by changes in exopolyphosphatase activity, which degrades the polymers to orthophosphate; highest enzyme activities were found when the polyphosphate level was low. Induction of apoptosis in the human leukemic cell line HL-60 by actinomycin D results in degradation of long polyphosphate chains. The total polyphosphate content does not change significantly in apoptotic cells.

Final checkpoint in the drug-promoted and poliovirus-promoted apoptosis is under post-translational control by growth factors

The treatment of HeLa subline (HeLa-B) cells with cycloheximide or Actinomycin D resulted in a rapid (approximately 1.5 h and approximately 2.5 h, respectively) development of morphological and biochemical signs of apoptosis. The addition of fetal bovine serum to the cycloheximide-treated or Actinomycin D-treated cells suppressed the apoptotic reaction, as evidenced by the postponement of the DNA fragmentation for at least 9 and 5 h, respectively. A similar suppressive effect was observed upon the serum addition to cells undergoing abortive infection with poliovirus, which died of apoptosis in the absence of the serum. The serum appeared to exert its anti-apoptotic effect without any appreciable lag and even immediately blocked further progress of ongoing DNA fragmentation. The epidermal growth factor also suppressed, although less efficiently and more transiently, the apoptotic reaction promoted by the metabolic inhibitors. It is concluded that growth factors may affect, without modulating either transcription or translation, the balance of pro-apoptotic and anti-apoptotic activities at a final checkpoint, just preceding the irreversible effector step of apoptosis.

Apoptosis: inhibitor or instigator of carcinogenesis?

Carcinogenesis is considered to require an initiating event that results in an irreversible genetic change in a subpopulation of cells. Based on the available evidence, it seems likely that apoptosis may act to attenuate this process by causing the deletion of genetically damaged cells from the host organism. Nevertheless, the existence of an active pathway leading to apoptotic cell death may be a double-edged sword, simply because it can be overcome. Some cells may exhibit preexisting genetic or epigenetic insensitivity to induction of apoptosis. Surviving cells may contain sub- lethal levels of DNA damage and be induced to proliferate as an indirect result of the carcinogen-induced apoptotic cell death of surrounding tissue. This process would facilitate the acquisition mutations in the genome, possibly resulting in further insensitivity to apoptosis through activation of the bcl-2 oncogene or inactivation of the p53 tumor suppressor gene. In this context, the propensity of a cell to undergo apoptosis could be viewed as a selection pressure that a tumor cell must overcome. For neoplastic growth to occur, an imbalance between proliferation and apoptosis must be established such that cell growth predominates. Genetic mutations or epigenetic factors that diminish the propensity of a cell to undergo apoptosis may therefore confer on that cell a growth advantage.

Increased c-fos expression associated with hyperthermia-induced apoptosis of a Burkitt lymphoma cell line

Hyperthermia (42 - 44 degrees C for 30 min to 1 h) can induce apoptosis in a variety of cell types and tumour cell lines. This process is usually, but not invariably unaffected by RNA and protein synthesis inhibition. C-fos expression has been implicated in the regulation of apoptosis occurring under diverse circumstances. By heating the Burkitt lymphoma cell line, BM 13674, for 43 degrees C for 30 min, approximately 60% of cells underwent apoptosis within 6h of treatment. Co-ordinate with the massive induction of apoptosis, a 10-fold increase in the steady state c-fos mRNA expression occurred.

Heat shock of human synovial and dermal fibroblasts induces delayed up-regulation of collagenase-gene expression

We investigated the effect of heat shock on the expression of the collagenase gene in normal human synovial and dermal fibroblasts. Heat shock (42-44 degrees C for 1 h) caused a marked increase in heat-shock protein 70 (HSP-70) mRNA levels, followed by a delayed increase in collagenase mRNA levels, in both cell types. Pretreatment with cycloheximide had no effect on the heat-shock-induced increase in HSP-70 mRNA expression, but abrogated the induction of collagenase mRNA during the recovery. To study the mechanisms of collagenase-gene induction by heat shock, the transcriptional activity of a collagenase-promoter-driven chloramphenicol acetyltransferase (CAT) reporter gene was examined in transient transfection experiments. Heat shock was followed by a > 2-fold increase in CAT activity driven by a 3.8 kb fragment of the collagenase promoter, or by a construct containing an AP-1 binding site. A mutation in the AP-1 binding site abolished the effect of heat shock. Electrophoretic-mobility-shift assays revealed a marked increase in DNA-binding activity specific for the AP-1 binding site in nuclear extracts prepared from synovial fibroblasts recovering from heat shock. These results indicate that heat shock causes a delayed increase in collagenase-gene expression in human fibroblasts, and suggests that this stimulation involves, at least in part, transcriptional activation through an AP-1 binding site. Heat shock appears to initiate a programme of cellular events resulting in collagenase-gene expression, and therefore may contribute to connective-tissue degradation in disease states.

Apoptosis-inducing and apoptosis-preventing functions of poliovirus

Data showing that an apoptotic reaction (the exit into the cytoplasm and nucleolytic internucleosomal degradation of chromosomal DNA, compaction and fragmentation of chromatin, cellular shrinkage, and cytoplasmic blebbing) developed in a subline of HeLa-S3 cells upon nonpermissive poliovirus infection with either a guanidine-sensitive poliovirus in the presence of guanidine, a guanidine-dependent mutant in the absence of guanidine, or certain temperature-sensitive mutants at a restrictive temperature are presented. Essentially, no apoptotic reaction occurred upon permissive infection of these cells. Both permissive and nonpermissive infections resulted in the inhibition of host protein synthesis. Actinomycin D or cycloheximide also elicited a rapid apoptotic reaction in uninfected cells. However, preinfection or coinfection with poliovirus prevented the apoptotic response to the addition of actinomycin D, and preinfection blocked cycloheximide-induced apoptosis as well. These data fit a model in which the cells used are prepared to develop apoptosis, with their viability due to the presence of certain short-lived mRNA and protein species. Poliovirus infection turns on two oppositely directed sets of reactions. On the one hand, the balance is driven toward apoptosis, probably via the shutoff of host macromolecular synthesis. On the other hand, viral protein exhibits antiapoptotic activity, thereby preventing premature cell death. To our knowledge, this is the first description of an antiapoptotic function for an RNA virus.

A protein produced by a monocytic human cell line can induce apoptosis on tumor cells

A serum-free medium conditioned by U937, a human cell line of monocyte/macrophage origin, was found capable of inducing apoptosis on exponentially growing U937 cells themselves (autocrine suicide). The apoptosis-inducing agent is a macromolecule and possibly a protein (SKT factor), with a relative molecular mass in the range of 18-25 kDa. All human tumor cell lines examined have been induced to apoptosis with high efficiency, whereas non transformed human lymphocytes and monocytes are insensitive to the apoptosis-inducing activity; moreover, partially differentiated U937 are not killed but induced to full maturation. These observations suggest that the SKT factor could possibly be a cytokine with a specific cytotoxic tropism, that resembles in many respects the cytokine tumor necrosis factor (TNF), even though no TNF is detectable in the conditioned medium.

Serum deprivation induces apoptotic cell death in a subset of Balb/c 3T3 fibroblasts

Little is known about the regulation of apoptosis in fibroblasts although several model systems including serum deprivation and treatment with staurosporine or topoisomerase inhibitors have been used to induce apoptosis in vitro. To validate a reproducible in vitro model for the study of apoptosis in fibroblasts, we cultured density-inhibited monolayer cultures of Balb/c 3T3 fibroblasts in Dulbecco's modified essential medium plus 15% fetal calf serum and then withdrew serum. Time-lapse video microscopy demonstrated that within minutes of serum withdrawal, cells lost substrate attachment and floated to the top of the liquid growth medium. There was a time-dependent increase in the number of non-adherent cells. Some of these cells regained attachment and spread momentarily, but they eventually rounded up and lost attachment permanently. In contrast to serum-containing cultures in which similar morphological changes were followed by mitosis, in serum-free cultures repeated attempts at mitosis were followed by permanent attachment loss and presumably cell death. To assess whether all the non-adherent cells were in fact dead, the percentages of cells that continued to proliferate upon return to serum-supplemented conditions was computed. After various periods of serum starvation a decreasing proportion (approx. 75% at 30 minutes; < 2% at 24 hours) of the non-adherent cells could be rescued by addition of serum. Transmission electron microscopy of cells 3 hours after serum withdrawal showed that the majority (approximately 60%) of non-adherent cells exhibited marked intranuclear chromatin condensation but maintained integrity of cell and nuclear membranes and cell organelles, morphological changes consistent with those of apoptotic cell death. Scanning electron microscopy of cultures 3 hours following serum withdrawal showed rounded cells with marked surface blebbing. Fluorescence and confocal microscopy revealed increased intensity of nuclear staining with DAPI while actin filaments became indistinct or collapsed around the nucleus. After cycloheximide treatment to inhibit protein synthesis, there was no reduction of apoptosis. Gel electrophoresis of DNA from both control and 3 hour-serum-deprived cells showed intact DNA with no oligonucleosomal length fragmentation. After serum withdrawal, intracellular calcium was reduced by about 32% over 5 minutes as measured by fura2 ratio fluorimetry in single cells. Serum-starved cells showed a time-dependent shrinkage in mean cell diameter compared to trypsinized, adherent control cells (at 0 hours, mean diameter = 18.0 microns--viable; at 4 hours, mean diameter = 15.5 microns--apoptotic). Flow cytometric analysis showed increased propidium iodide staining and reduced fluorescein diacetate uptake over 3 hours, changes that were contemporaneous with the reduction of cell diameter.(ABSTRACT TRUNCATED AT 400 WORDS)

Radiation response of mouse lymphoid and myeloid cell lines. Part II. Apoptotic death is shown by all lines examined

The mode of death induced by gamma-irradiation in a panel of 10 mouse lymphoid or myeloid cell lines was examined. Four of these lines were known to lose viability (membrane integrity) rapidly after irradiation, whilst the others were known to lose viability considerably more slowly. However, based on the criteria of morphology and DNA degradation pattern, all 10 lines showed apoptotic death. The occurrence of apoptosis after irradiation in rapid-dying lymphoid cell lines was consistent with published results, whilst the demonstration of apoptosis in slow-dying lines was unexpected. Cells of the slow-dying lymphoid lines underwent one or more mitoses prior to death, a feature also reported for fibroblastoid cell lines. However, the occurrence of radiation-induced necrosis in fibroblasts suggests that the pathways leading to 'mitotic death' differ between fibroblastoid and lymphoid cell lines.

Molecular cloning of a human cDNA encoding a novel protein, DAD1, whose defect causes apoptotic cell death in hamster BHK21 cells

The tsBN7 cell line, one of the mutant lines temperature sensitive for growth which have been isolated from the BHK21 cell line, was found to die by apoptosis following a shift to the nonpermissive temperature. The induced apoptosis was inhibited by a protein synthesis inhibitor, cycloheximide, but not by the bcl-2-encoded protein. By DNA-mediated gene transfer, we cloned a cDNA that complements the tsBN7 mutation. It encodes a novel hydrophobic protein, designated DAD1, which is well conserved (100% identical amino acids between humans and hamsters). By comparing the base sequences of the parental BHK21 and tsBN7 DAD1 cDNAs, we found that the DAD1-encoding gene is mutated in tsBN7 cells. The DAD1 protein disappeared in tsBN7 cells following a shift to the nonpermissive temperature, suggesting that loss of the DAD1 protein triggers apoptosis.

Molecular cloning of a human cDNA encoding a novel protein, DAD1, whose defect causes apoptotic cell death in hamster BHK21 cells

The tsBN7 cell line, one of the mutant lines temperature sensitive for growth which have been isolated from the BHK21 cell line, was found to die by apoptosis following a shift to the nonpermissive temperature. The induced apoptosis was inhibited by a protein synthesis inhibitor, cycloheximide, but not by the bcl-2-encoded protein. By DNA-mediated gene transfer, we cloned a cDNA that complements the tsBN7 mutation. It encodes a novel hydrophobic protein, designated DAD1, which is well conserved (100% identical amino acids between humans and hamsters). By comparing the base sequences of the parental BHK21 and tsBN7 DAD1 cDNAs, we found that the DAD1-encoding gene is mutated in tsBN7 cells. The DAD1 protein disappeared in tsBN7 cells following a shift to the nonpermissive temperature, suggesting that loss of the DAD1 protein triggers apoptosis.

Cytoprotective effect of NMDA receptor antagonists on prion protein (PrionSc)-induced toxicity in rat cortical cell cultures

Rat cortical cells were incubated with the Scrapie prion protein, PrionSc. At concentrations of 3 ng/ml of PrionSc and higher, the viability of the cells decreased significantly after a 12-h incubation period. Simultaneously, the degree of DNA fragmentation increased. In control experiments with antibodies against PrionSc, PrionSc lost its deleterious effect on neurons. PrionSc did not affect the viability of astrocytes. Drugs known to block NMDA receptor channels, such as memantine (1-amino-3,5-dimethyl-adamantane) (Mem), its analogue 1-N-methylamino-3,5-dimethyl-adamantane as well as (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) prevented the effect of PrionSc. Production of PrionSc in the Scrapie prion-infected subclone of N2 a cells (ScN2 a cells) was not affected by memantine. We conclude that antagonists of the NMDA receptor-channel complex (i) abolish the PrionSc-induced neuronal injury in vitro, and (ii) display no influence on the synthesis and/or the processing of PrionSc.

Thermal stress as an inducer of differentiation of U937 cells

The individual and combined effects of heat shock, all-trans retinoic acid and 1,25-dihydroxyvitamin D3 on inhibition of cell growth and initiation of differentiation were investigated on U937 human leukemia cells. Incubation of U937 cells at 43 degrees C for 1 h did not affect cell viability but induced a reduction of cell growth and the emergence of a differentiated phenotype, characterized by the acquisition of chemiluminescent responses to various oxidative burst inducers and by the capacity to produce IL-6 in response to bacterial lipopolysaccharide. Heat shock alone, therefore, appears to be an efficient inducer of cell differentiation. In addition, heat shock primed the cells to respond more efficiently to the action of retinoic acid and vitamin D, and amplified the phenotypic changes initiated by pretreatment of U937 cells with these agents.

Effect of heat shock on susceptibility of normal lymphoblasts and of a heat shock protein 70-defective tumour cell line to cytotoxic T lymphocytes in vitro

The effect of heat shock pretreatment of target cells on their lysability by cytotoxic T lymphocytes was analysed. Killing of Concanavalin A-stimulated normal lymphocytes by minor or major histocompatibility antigen-specific cytotoxic T lymphocytes is unchanged or even slightly enhanced after heat shock, whereas cells of the myeloma line Y3, which is derived from one of the lymphocyte donor strains, become nearly resistant to killing after the same pretreatment. Cold target inhibition experiments show that heat-shocked cells are recognized specifically and that untreated and heat-shocked target cells possess similar inhibitory potential. Y3 cells are unable to express the strongly heat-inducible heat shock protein of 70 kDa (hsp70) after heat shock; the acquired resistance is thus independent of hsp70 induction. Possible mechanisms of the different lysability seen in lymphoblasts and tumour cells after heat shock are discussed.