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Biomedical subjects

K Schulze-Osthoff

Publications and source records attributed to K Schulze-Osthoff.

At least 73 records · Page 4Linked to original sources
PubMed1999

Anticancer drugs induce caspase-8/FLICE activation and apoptosis in the absence of CD95 receptor/ligand interaction.

Proteases of the caspase family are the critical executioners of apoptosis. Their activation has been mainly studied upon triggering of death receptors, such as CD95 (Fas/APO-1) and tumor necrosis factor-R1, which recruit caspase-8/FLICE as the most proximal effector to the receptor complex. Because apoptosis induced by anticancer drugs has been proposed to involve CD95/CD95 ligand interaction, we investigated the mechanism of caspase activation by daunorubicin, doxorubicin, etoposide, and mitomycin C. In Jurkat leukemic T cells, all drugs induced apoptosis and the cleavage of procaspase-8 to its active p18 subunit. However, cells resistant to CD95 were equally susceptible to anticancer drugs and activated caspase-8 with a similar kinetic and dose response as CD95-sensitive cells. The broad caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone prevented apoptosis and caspase-8 activation in response to CD95 and drug treatment, whereas a neutralizing CD95 decoy as well as a dominant-negative FADD construct selectively abrogated CD95, but not drug-induced effects. A potent activation of caspase-8 was also induced by cycloheximide, indicating that it was independent of protein synthesis. Our data, therefore, show that (1) anticancer drug-induced apoptosis does not require de novo synthesis of death ligands or CD95 interaction, and (2) that caspase-8 can be activated in the absence of a death receptor signaling.

Amino Acid Chloromethyl Ketones↗
PubMed1999

Mistletoe lectin activates caspase-8/FLICE independently of death receptor signaling and enhances anticancer drug-induced apoptosis.

Mistletoe lectin I (ML-I) is a major active component in plant extracts of Viscum album that is increasingly used in adjuvant cancer therapy. ML-I exerts potent immunomodulating and cytotoxic effects, although its mechanism of action is largely unknown. We show that treatment of leukemic T- and B-cell lines with ML-I induced apoptosis, which required the prior activation of proteases of the caspase family. The involvement of caspases is demonstrated because (a) a peptide caspase inhibitor almost completely prevented ML-I-induced cell death and (b) proteolytic activation of caspase-8, caspase-9, and caspase-3 was observed. Because caspase-8 has been implicated as a regulator of apoptosis mediated by death receptors, we further investigated a potential receptor involvement in ML-I-induced effects. Cell death triggered by ML-I was neither attenuated in cell clones resistant to CD95 nor in cells that were rendered refractory to other death receptors by overexpressing a dominant-negative FADD mutant. In contrast, ML-I triggered a receptor-independent mitochondria-controlled apoptotic pathway because it rapidly induced the release of cytochrome c into the cytosol. Because ML-I was also observed to enhance the cytotoxic effect of chemotherapeutic drugs, these data may provide a molecular basis for clinical trials using MLs in anticancer therapy.

Amino Acid Chloromethyl Ketones↗
PubMed1999

P2Z purinoreceptor ligation induces activation of caspases with distinct roles in apoptotic and necrotic alterations of cell death.

Myeloic cells express a peculiar surface receptor for extracellular ATP, called the P2Z/P2X7 purinoreceptor, which is involved in cell death signalling. Here, we investigated the role of caspases, a family of proteases implicated in apoptosis and the cytokine secretion. We observed that extracellular ATP induced the activation of multiple caspases including caspase-1, -3 and -8, and subsequent cleavage of the caspase substrates PARP and lamin B. Using caspase inhibitors, it was found that caspases were specifically involved in ATP-induced apoptotic damage such as chromatin condensation and DNA fragmentation. In contrast, inhibition of caspases only marginally affected necrotic alterations and cell death proceeded normally whether or not nuclear damage was blocked. Our results therefore suggest that the activation of caspases by the P2Z receptor is required for apoptotic but not necrotic alterations of ATP-induced cell death.

Adenosine Triphosphate↗
PubMed1999

Plant extracts from stinging nettle (Urtica dioica), an antirheumatic remedy, inhibit the proinflammatory transcription factor NF-kappaB.

Activation of transcription factor NF-kappaB is elevated in several chronic inflammatory diseases and is responsible for the enhanced expression of many proinflammatory gene products. Extracts from leaves of stinging nettle (Urtica dioica) are used as antiinflammatory remedies in rheumatoid arthritis. Standardized preparations of these extracts (IDS23) suppress cytokine production, but their mode of action remains unclear. Here we demonstrate that treatment of different cells with IDS23 potently inhibits NF-kappaB activation. An inhibitory effect was observed in response to several stimuli, suggesting that IDS23 suppressed a common NF-kappaB pathway. Inhibition of NF-kappaB activation by IDS23 was not mediated by a direct modification of DNA binding, but rather by preventing degradation of its inhibitory subunit IkappaB-alpha. Our results suggests that part of the antiinflammatory effect of Urtica extract may be ascribed to its inhibitory effect on NF-kappaB activation.

Animals↗
PubMed1999

The non-steroidal anti-inflammatory drug tepoxalin inhibits interleukin-6 and alpha1-anti-chymotrypsin synthesis in astrocytes by preventing degradation of IkappaB-alpha.

Tepoxalin is a structurally and functionally novel non-steroidal anti-inflammatory drug (NSAID) with potent anti-inflammatory and analgesic properties. Apart from its inhibitory effect on cyclooxygenase activity, tepoxalin is able to inhibit production of cytokines in peripheral cells outside the CNS. No data, however, are available concerning the effects of this drug in the CNS. Since cytokines such as interleukin-1 (IL-1) or interleukin-6 (IL-6) as well as acute-phase proteins such as alpha1-anti-chymotrypsin (ACT) participate in the etiopathology of Alzheimer's disease (AD), we were interested whether tepoxalin is able to inhibit the synthesis of these immunomodulators in primary rat microglia and astrocytes as well as in the human astrocytoma cell line U373 MG. We found that tepoxalin markedly inhibits IL-1beta-induced IL-6 and ACT synthesis in astrocytes and the synthesis of IL-1beta and IL-6 in lipopolysaccharide (LPS)-stimulated microglial cells. Electrophoretic mobility shift and reporter gene assays revealed that tepoxalin exerts its inhibitory effect through the inhibition of nuclear factor kappaB (NF-kappaB), a transcription factor involved in the induction of IL-1, IL-6 and ACT gene expression. We show that inhibition of NF-kappaB activation by tepoxalin is mediated by preventing IkappaB-alpha degradation. Based on this inhibitory effect of tepoxalin on cytokine and ACT synthesis and the documented therapeutic efficacy of NSAIDs in AD, we conclude that tepoxalin may be of therapeutic benefit for the treatment of AD patients and should therefore be tested in clinical trials.

Alzheimer Disease↗
PubMed1999

Ionizing radiation and the activation of caspase-8 in highly apoptosis-sensitive lymphoma cells.

PURPOSE: Ionizing radiation induces apoptosis in human lymphoma cells. However, the participating molecules and their exact order is unknown. Caspases are reported as essential cysteine proteases required for the activation and execution of programmed cell death. The activator caspase-8 is a key component of the CD95/Fas/APO-1 death receptor-triggered apoptosis pathway. Since contributing molecules for radiation-induced apoptosis and their exact order have not been analyzed in greater detail, the involvement of caspase-8 for radiation-induced apoptosis in human lymphoma cell lines was studied. MATERIALS AND METHODS: Apoptosis induction by CD95 stimulation and ionizing radiation was analyzed in eight different cell lines. In parallel, Western blotting tested activation of caspase-8. RESULTS: Activation of caspase-8 by ionizing radiation occurred in five cell lines and was associated with high apoptosis sensitivity. Caspase-8 activation and apoptosis was detectable in cells resistant to CD95 stimulation, so suggesting separate pathways for CD95 and radiation-induced caspase-8 activation. CONCLUSION: The activator caspase-8 is activated during radiation-induced cell death and, in some cases, ionizing radiation induces caspase-8 independently of the CD95 system.

Apoptosis↗
PubMed1999

Sendai virus infection induces apoptosis through activation of caspase-8 (FLICE) and caspase-3 (CPP32).

Sendai virus (SV) infection and replication lead to a strong cytopathic effect with subsequent death of host cells. We now show that SV infection triggers an apoptotic program in target cells. Incubation of infected cells with the peptide inhibitor z-VAD-fmk abrogated SV-induced apoptosis, indicating that proteases of the caspase family were involved. Moreover, proteolytic activation of two distinct caspases, CPP32/caspase-3 and, as shown for the first time in virus-infected cells, FLICE/caspase-8, could be detected. So far, activation of FLICE/caspase-8 has been described in apoptosis triggered by death receptors, including CD95 and tumor necrosis factor (TNF)-R1. In contrast, we could show that SV-induced apoptosis did not require TNF or CD95 ligand. We further found that apoptosis of infected cells did not influence the maturation and budding of SV progeny. In conclusion, SV-induced cell injury is mediated by CD95- and TNF-R1-independent activation of caspases, leading to the death of host cells without impairment of the viral life cycle.

Animals↗
PubMed1998

Human T cell leukemia virus-I (HTLV-I) Tax-mediated apoptosis in activated T cells requires an enhanced intracellular prooxidant state.

We have shown that an estradiol-dependent activation of human T cell leukemia virus-I Tax leads to the inhibition of cell proliferation and to the induction of apoptosis. The present study demonstrates that a hormone-dependent activation of Tax promotes an enhanced prooxidant state in stably transfected Jurkat cells as measured by changes in the intracellular levels of glutathione and H2O2; these changes are followed by apoptotic cell death. Additional stimulation of the CD3/TCR pathway enhances the oxidative and apoptotic effects. Both Tax-mediated apoptosis and oxidative stress can be potently suppressed by antioxidants, as is seen with the administration of recombinant thioredoxin (adult T cell leukemia-derived factor) or pyrrolidine dithiocarbamate. Hormone-induced Tax activation induces a long-lasting activation of NF-kappaB, which is a major target of reactive oxygen intermediates. The long-term exposure of Jurkat cells to hormone eventually results in a selection of cell clones that have lost Tax activity. A subsequent transfection of these apparently "nonresponsive" clones allows the recovery of Tax responses in these cells. Our observations indicate that changes in the intracellular redox status may be a determining factor in Tax-mediated DNA damage, apoptosis, and selection against the long-term expression of Tax function.

Antibodies, Monoclonal↗
PubMed1998

Differential regulation and ATP requirement for caspase-8 and caspase-3 activation during CD95- and anticancer drug-induced apoptosis.

Apoptosis is induced by different stimuli, among them triggering of the death receptor CD95, staurosporine, and chemotherapeutic drugs. In all cases, apoptosis is mediated by caspases, although it is unclear how these diverse apoptotic stimuli cause protease activation. Two regulatory pathways have been recently identified, but it remains unknown whether they are functionally independent or linked to each other. One is mediated by recruitment of the proximal regulator caspase-8 to the death receptor complex. The other pathway is controlled by the release of cytochrome c from mitochondria and the subsequent ATP-dependent activation of the death regulator apoptotic protease-activating factor 1 (Apaf-1). Here, we report that both pathways can be dissected by depletion of intracellular ATP. Prevention of ATP production completely inhibited caspase activation and apoptosis in response to chemotherapeutic drugs and staurosporine. Interestingly, caspase-8, whose function appeared to be restricted to death receptors, was also activated by these drugs under normal conditions, but not after ATP depletion. In contrast, inhibition of ATP production did not affect caspase activation after triggering of CD95. These results suggest that chemotherapeutic drug-induced caspase activation is entirely controlled by a receptor-independent mitochondrial pathway, whereas CD95-induced apoptosis can be regulated by a separate pathway not requiring Apaf-1 function.

Adenosine Triphosphate↗
PubMed1998

Apoptosis signaling by death receptors.

Death receptors have been recently identified as a subgroup of the TNF-receptor superfamily with a predominant function in induction of apoptosis. The receptors are characterized by an intracellular region, called the death domain, which is required for the transmission of the cytotoxic signal. Currently, five different such death receptors are known including tumor necrosis factor (TNF) receptor-1, CD95 (Fas/APO-1), TNF-receptor-related apoptosis-mediated protein (TRAMP) and TNF-related apoptosis-inducing ligand (TRAIL) receptor-1 and -2. The signaling pathways by which these receptors induce apoptosis are rather similar. Ligand binding induces receptor oligomerization, followed by the recruitment of an adaptor protein to the death domain through homophilic interaction. The adaptor protein then binds a proximal caspase, thereby connecting receptor signaling to the apoptotic effector machinery. In addition, further pathways have been linked to death receptor-mediated apoptosis, such as sphingomyelinases, JNK kinases and oxidative stress. These pro-apoptotic signals are counteracted by several mechanisms which inhibit apoptosis at different levels. This review summarizes the current and rapidly expanding knowledge about the biological functions of death receptors and the mechanisms to trigger or to counteract cell death.

Animals↗
PubMed1998

Oxidative stress and hypoxia/reoxygenation trigger CD95 (APO-1/Fas) ligand expression in microglial cells.

Apoptosis plays an important role in neurodegeneration, although the mechanisms and mediators in the brain are largely unknown. Because microglial cells have been suggested to contribute to apoptosis in neurological disorders, we investigated the expression of the death ligand CD95L in this cell type. We found that, compared to classical mediators of microglial activation, the most potent inducer of CD95L was oxidative stress. Exposure of microglial cells to H2O2 or paraquat rapidly triggered CD95L mRNA and protein expression, associated with the activation of transcription factor NF-kappaB. Enhanced expression of CD95L was further found following exposure of cells to hypoxia and subsequent reoxygenation. Our results indicate a potential role of CD95L in oxidative stress-mediated cell death, ischemia/reperfusion and other diseases with a disturbed redox balance.

Animals↗
PubMed1998

Role of reactive oxygen intermediates in activation-induced CD95 (APO-1/Fas) ligand expression.

Activation-induced cell death of T lymphocytes requires the inducible expression of CD95 (APO-1/Fas) ligand, which triggers apoptosis in CD95-bearing target cells by an autocrine or paracrine mechanism. Although execution of the CD95 death pathway is largely independent of reactive oxygen intermediates, activation-induced cell death is blocked by a variety of antioxidants. In the present study, we investigated the involvement of redox processes in the regulation of CD95 ligand (CD95L) expression in Jurkat T cells. We show that various antioxidants potently inhibited the transcriptional activation of CD95L following T cell receptor ligation or stimulation of cells with phorbol ester and ionomycin. Conversely, a prooxidant such as hydrogen peroxide alone was able to increase CD95L expression. As detected by Western blot and cytotoxicity assays, functional expression of CD95L protein was likewise diminished by antioxidants. Inhibition of CD95L expression was associated with a decreased DNA binding activity of nuclear factor (NF)-kappaB, an important redox-controlled transcription factor. Moreover, inhibition of NF-kappaB activity by a transdominant IkappaB mutant attenuated CD95L expression. Our data suggest that, although reactive oxygen intermediates do not act as mediators in the execution phase of CD95-mediated apoptosis, they are involved in the transcriptional regulation of CD95L expression.

Antioxidants↗
PubMed1998

Sesquiterpene lactones specifically inhibit activation of NF-kappa B by preventing the degradation of I kappa B-alpha and I kappa B-beta.

Extracts from certain Mexican Indian medicinal plants used in traditional indigenous medicine for the treatment of inflammations contain sequiterpene lactones (SLs), which specifically inhibit the transcription factor NF-kappa B (Bork, P. M., Schmitz, M. L., Kuhnt, M., Escher, C., and Heinrich, M. (1997) FEBS Lett. 402, 85-90). Here we show that SLs prevented the activation of NF-kappa B by different stimuli such as phorbol esters, tumor necrosis factor-alpha, ligation of the T-cell receptor, and hydrogen peroxide in various cell types. Treatment of cells with SLs prevented the induced degradation of I kappa B-alpha and I kappa B-beta by all these stimuli, suggesting that they interfere with a rather common step in the activation of NF-kappa B. SLs did neither interfere with DNA binding activity of activated NF-kappa B nor with the activity of the protein tyrosine kinases p59fyn and p60arc. Micromolar amounts of SLs prevented the induced expression of the NF-kappa B target gene intracellular adhesion molecule 1. Inhibition of NF-kappa B by SLs resulted in an enhanced cell killing of murine fibroblast cells by tumor necrosis factor-alpha. SLs lacking an exomethylene group in conjugation with the lactone function displayed no inhibitory activity on NF-kappa B. The analysis of the cellular redox state by fluorescence-activated cell sorter showed that the SLs had no direct or indirect anti-oxidant properties.

Animals↗
PubMed1998

Differential regulation of CD95 (Fas/APO-1) expression in human blood eosinophils.

CD95 (Fas, APO-1) is a cell surface receptor expressed on many cells including eosinophils which mediates apoptosis when ligated by agonistic antibodies or its natural ligand FasL. Since inhibition of apoptosis may play an important role in controlling tissue eosinophilia, we investigated the expression of CD95 on purified peripheral blood eosinophils from normal donors. Freshly isolated eosinophils expressed CD95 on the cell surface as well as CD95-specific mRNA at low levels which did not change during 24-h culture. Incubation of eosinophils with IL-3, IL-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF) did not modulate the basal expression of CD95. IFN-gamma as well as TNF-alpha, however, induced a significant, dose- and time-dependent increase in CD95 mRNA and cell surface expression as measured by reverse transcription-PCR and flow cytometry. Co-stimulation with IFN-gamma and TNF-alpha had synergistic effects on the CD95 surface expression on eosinophils. Addition of IL-3, IL-5 or GM-CSF to IFN-gamma- and TNF-alpha-stimulated eosinophils caused in a reduction of CD95 expression. Functional activity for CD95 following incubation with IFN-gamma and TNF-alpha was demonstrated by increased apoptosis in response to cross-linking with FasL. From these data, we conclude that IFN-gamma and TNF-alpha can up-regulate cell surface expression of CD95 on eosinophils, which leads to an increased susceptibility of eosinophils to Fas-mediated apoptosis. Thus, our results suggest that receptors involved in eosinophil apoptosis can be regulated by antagonistic cytokines.

Apoptosis↗
PubMed1998

Substance P and histamine induce interleukin-6 expression in human astrocytoma cells by a mechanism involving protein kinase C and nuclear factor-IL-6.

Interleukin-6 (IL-6) is a proinflammatory cytokine whose synthesis is induced by a variety of stimuli including interleukin-1 (IL-1), substance P (SP), and histamine. Because IL-6 has been implicated in the etiopathology of different human diseases including multiple myeloma, rheumatoid arthritis, multiple sclerosis, acquired immunodeficiency syndrome dementia complex, and Alzheimer's disease, its inhibition may be of therapeutic interest. A main demand on an effective inhibitor of IL-6 expression is that it inhibits IL-6 synthesis independently of the inducing stimulus. We therefore used human astrocytoma cells to search for signal transduction cascades and transcription factors whose inhibition suppresses IL-6 synthesis after stimulation with three different inductors, IL-1beta, SP, and histamine. Whereas the antioxidant pyrrolidinedithiocarbamate was only able to inhibit IL-1beta-induced IL-6 expression, inhibition of protein kinase C prevented IL-6 expression induced by all three substances. Promoter deletion analysis revealed that IL-1beta-induced IL-6 expression required the transcription factor nuclear factor-kappaB (NF-kappaB), whereas SP- and histamine-induced IL-6 synthesis was essentially controlled by NF-IL-6. These findings suggest that inhibition of protein kinase C or a combinatory inhibition of NF-IL-6 and NF-kappaB binding are strategies to effectively suppress IL-6 synthesis. They therefore provide the basis for the development of antiinflammatory drugs used to treat disorders in which IL-6 is pathogenically involved.

Astrocytoma↗
PubMed1998

Radiation-induced apoptosis in human lymphocytes and lymphoma cells critically relies on the up-regulation of CD95/Fas/APO-1 ligand.

Ionizing radiation is known to induce death by apoptosis in malignant and nonmalignant human lymphocytes. The mechanism which initiates the induction of apoptosis has not been identified. Here we demonstrate that a radiation-induced up-regulation of CD95/Fas/APO-1 ligand (CD95-L) is involved in the induction of apoptosis in lymphocytes and lymphoma cells. Using antibodies against CD95-L, we detected a rapid and persistent up-regulation of CD95-L in Jurkat cells and blood lymphocytes after irradiation. Blocking of interactions between CD95/Fas/APO-1 and CD95-L with inhibitory antibodies reduces apoptosis after irradiation. The hypothesis that an interaction between CD95 and CD95-L is involved in radiation-induced apoptosis is supported by the finding that only peripheral blood lymphocytes that are stimulated with interleukin 2 for 5 days and thus are rendered sensitive to CD95-L show pronounced levels of apoptosis in response to low radiation doses, whereas resting peripheral blood lymphocytes show very low levels of apoptosis after treatment with CD95-L and radiation. The finding that the caspase FLICE is degraded proteolytically after irradiation and the observation of a radiation-induced CD95 receptor capping confirm the functional activation of the CD95 receptor.

Apoptosis↗