Inhibition by glucocorticoids of tumor necrosis factor-mediated cytotoxicity. Evidence against lipocortin involvement

Glucocorticoids as cytokine inhibitors: role in neuroendocrine control and therapy of inflammatory diseases

Glucocorticoids are potent inhibitors of inflammation and endotoxic shock. This probably occurs through an inhibition of the synthesis of pro-inflammatory cytokines as well as of many of their toxic activities. Therefore, endogenous glucocorticoids (GC) might represent a major mechanism in the control of cytokine mediated pathologies. GC inhibit the synthesis of cytokines in various experimental models. Adrenalectomy or GC antagonists potentiate TNF, IL-1 and IL-6 production in LPS treated mice. GC inhibit the formation of arachidonic acid metabolites and the induction of NO synthase. They also inhibit various activities of cytokines including toxicity, haemodynamic shock and fever. Adrenalectomy sensitizes to the toxic effects of LPS, TNF and IL-1. On the other hand, GC potentiate the synthesis of several cytokine induced APP by the liver. Since many of these proteins have anti-toxic activities (antioxidant, antiprotease etc.) or bind cytokines, this might well represent a GC mediated protective feedback mechanism involving the liver. Not only do GC inhibit cytokines, but in vivo LPS and various cytokines (TNF, IL-1, IL-6) increase blood GC levels through a central mechanism involving the activation of the HPA. Thus, this neuroendocrine response to cytokines constitutes an important immunoregulatory feedback involving the brain.

Novel Treatments for Drug-Induced Toxic Epidermal Necrolysis (Lyell’s Syndrome)

Drug-induced toxic epidermal necrolysis (TEN) is a life-threatening disease characterized by extensive destruction of the epidermis. It apparently results from the formation of specific toxic drug metabolites by the keratinocytes. The mortality rate which averages 25-30% is mainly due to secondary septicemia, and to ionic and metabolic disturbances following loss of epidermal integrity. Apoptosis is the likely mechanism leading to massive keratinocyte death in TEN. Dysregulations in the tumor necrosis factor-alpha (TNF-alpha) pathway, CD95 system (Fas ligand, CD95L; Fas receptor, CD95R) and calcium homeostasis in the epidermis are involved in this apoptotic process. An active role has also been ascribed to T lymphocytes, macrophages and factor XIIIa-positive dermal dendrocytes. Despite progress, treatment of TEN remains controversial. In the past, systemic glucocorticoids were used in order to target the inflammatory reaction in TEN. However, there was no evidence for improvement of the healing process, while corticosteroids worsened the prognosis by increasing the risk of septicemia. Only a few cases have been treated with other drugs including cyclophosphamide, pentoxyfilline, thalidomide, anti-TNF-alpha antibodies and cyclosporin A. In the recent past, some TEN patients were treated with intravenous human immunoglobulins (IVIG). The rationale for such a treatment was to block the CD95 system on keratinocytes. The early promising clinical results of IVIG treatment in TEN were subsequently challenged. This review compares the effectiveness and drawbacks of the major drugs presently used in TEN treatment. Some future prospects in TEN management are also discussed.

Lipocortin-1 fails to ameliorate ischemic brain edema in the cat

It has been reported that corticosteroids exert their anti-inflammatory action through de novo synthesis of phospholipase-inhibitory proteins called lipocortins (annexins). We postulated that the following may lessen the effectiveness of corticosteroids on acute ischemic brain edema: 1) lipocortins are induced several hours after administration of steroids; 2) de novo synthesis of lipocortins is suppressed in the ischemic brain; and 3) lipocortins induced systemically do not pass through the blood-brain barrier (BBB) to reach the sites of ischemic edema. To test this hypothesis, we examined whether dexamethasone, given long before ischemia or direct administration of recombinant lipocortin-1, combined with or without BBB opening, ameliorate ischemic brain edema. Three hours before occlusion of the middle cerebral artery (MCA) in the cat, 4 mg/kg of dexamethasone was injected intravenously. The animals were subjected to 4 hours of ischemia. Alternatively, 2 ug/ml (total volume 10 ml) of recombinant human lipocortin-1 (annexin-I) was perfused intermittently into the ischemic focus by catheterization into the MCA. Artificial opening of the BBB was performed by intra-arterial mannitol infusion. None of these strategies demonstrated amelioration of ischemic edema. We conclude that: Dexamethasone and recombinant lipocortin-1 seem unlikely to have robust effects on amelioration of acute ischemic edema.

A novel Arabidopsis thaliana protein protects tumor cells from tumor necrosis factor-induced apoptosis

Recently we have cloned and characterized a novel, oxidative stress-induced Arabidopsis thaliana gene (oxy5), and showed that expression of oxy5 protects bacterial cells from death caused by oxidative stress. As oxidative stress is one pathway of TNF cytotoxicity, we investigated whether the encoded protein could also protect human tumor cells from TNF killing. We stably transfected the oxy5 gene into TNF-sensitive HeLa D98 cells (D98/O.5), and found that all examined transfectants were highly TNF-resistant in the absence of the protein synthesis inhibitor cycloheximide. The acquired TNF resistance of these clones was accompanied by a sharp decrease in the intracellular formation of reactive oxygen species, suggesting the activation of antioxidant enzymes like superoxide dismutases (SODs). Indeed, D98/O.5 clones showed an increased manganous superoxide dismutase (MnSOD) mRNA and protein expression in the absence or presence of TNF stimulation, whereas the expression of the Cu/ZnSOD was not affected. Furthermore, the elevated MnSOD expression in the D98/O.5 clones correlated well with an increased antioxidative activity, which was specifically due to MnSOD as measured by the suppression of xanthine oxidase. Our results demonstrate a novel role for a plant-derived protein in resistance to TNF cytotoxicity, and that the Arabidopsis thaliana protein Oxy5 can exert its protective function across evolutionary boundaries through activation of antioxidant enzymes like MnSOD.

Casein kinase-1 phosphorylates the p75 tumor necrosis factor receptor and negatively regulates tumor necrosis factor signaling for apoptosis

Cellular responses initiated by tumor necrosis factor (TNF) are mediated by two different cell surface receptors with respective molecular masses of 55 kDa (p55) and 75 kDa (p75). p55 is functional in almost every cell type and can independently transmit most biological activities of TNF. In contrast, TNF signaling via p75 seems so far largely restricted to cells of lymphoid origin, where it can induce proliferation, cytokine production, and/or apoptosis. The mechanisms that regulate TNF receptor activity are largely unknown. Here we report that the p75 of unstimulated p75-responsive PC60 T cells is phosphorylated on serine by a kinase activity present in p75 immune complexes. Several lines of evidence indicate that the latter kinase is casein kinase-1 (CK-1). Previous results have shown that the p75 TNF receptor is constitutively phosphorylated in vivo. Our data show that the latter in vivo phosphorylation is also at least partially due to CK-1. Pretreatment of cells with TNF had no detectable effect on p75 phosphorylation in vitro or in vivo. However, a specific CK-1 inhibitor potentiated TNF-induced apoptosis mediated by p75, suggesting an inhibitory role for phosphorylation by CK-1. Although in vivo p75 phosphorylation could be seen in both p75-unresponsive and p75-responsive cell lines, in vitro p75 phosphorylation in p75 coimmunoprecipitates could not be observed in cell lines that were biologically unresponsive to p75 stimulation. The latter observation further indicates a regulatory role for p75 phosphorylation in p75-mediated signaling. Taken together, our data demonstrate that the p75 TNF receptor is phosphorylated and associated with CK-1, which negatively regulates p75-mediated TNF signaling.

Levels and localization of group II phospholipase A2 and annexin I in interleukin- and dexamethasone-treated rat mesangial cells: evidence against annexin mediation of the dexamethasone-induced inhibition of group II phospholipases A2

The mechanism by which glucocorticosteroids inhibit the synthesis and secretion of pro-inflammatory arachidonate metabolites is still controversial. Initially it was postulated that glucocorticoids can induce the formation of PLA2 inhibitory proteins termed annexins. We have previously shown that the cytokine-induced 14 kDa PLA2 activity and the synthesis of prostaglandin E2 in rat mesangial cells is dose-dependently blocked by pretreatment of the cells with dexamethasone (Schalkwijk et al. (1991) Biochem. Biophys. Res. Commun. 180, 46-52). Concurrently, the synthesis of 14 kDa group II PLA2 is suppressed. The regulation of PLA2 activity is complex and may well involve superimposable mechanisms. Thus, although the decrease in PLA2 protein levels could in itself explain the dexamethasone-induced decrease in PLA2 activity, a contribution of the glucocorticoid-induced anti-phospholipase A2 protein annexin cannot be ruled out a priori. To investigate this possibility we analyzed the level of annexin I by Western blotting and immunostaining in mesangial cells treated with interleukin-1 beta and/or dexamethasone. Under conditions where 14 kDa group II PLA2 activity and protein levels were dramatically affected by interleukin-1 and dexamethasone, the level of annexin I in the cells remained constant. Dexamethasone also did not induce the secretion of annexin I. In addition, no evidence for dexamethasone-induced translocation of annexin I from the cytosol to membranes, thereby possibly sequestering the substrates for PLA2, was obtained. Immunofluorescence studies localized the cytokine-induced PLA2 to the Golgi area and punctate structures in the cytoplasm. We have also studied the subcellular localization of annexin I in rat mesangial cells using confocal microscopy. These studies located annexin I mainly in the cytoplasma and the nucleus. We conclude from these experiments that the dexamethasone-induced inhibition of 14 kDa group II PLA2 in rat mesangial cells is not mediated by annexin I and is solely due to the suppression of PLA2 gene expression.

Conditional expression of human TNF-alpha: a system for inducible cytotoxicity

Tumour necrosis factor-alpha (TNF-alpha) is currently being used in clinical trials for cancer treatment, but toxic side effects, due to systemic administration and high doses, are observed. Inducible expression of TNF may permit selective killing of tumour cells in gene therapy protocols without need for prolonged and/or high-level TNF expression. A conditional TNF expression vector has been constructed in which the coding sequences of human TNF have been placed under the transcriptional control of the glucocorticoid-regulated murine mammary tumour virus long terminal repeat (MMTV-LTR). Negligible levels of TNF expression, associated with no phenotypic alterations, are observed in cells transfected with MMTV-TNF vectors in the absence of glucocorticoid. Expression levels could be stimulated by the addition of the synthetic glucocorticoid dexamethasone. Increasing expression levels of TNF were associated with enhanced cytotoxicity. Our results suggest the potential use of inducible TNF systems for the treatment of tumours in gene therapy protocols.

Molecular mechanisms of tumor necrosis factor-induced cytotoxicity. What we do understand and what we do not

Although TNF plays an important role in several physiological and pathological conditions, the hallmark of this important cytokine has been its selective cytotoxic activity on tumor cells. Since its cloning in 1984, understanding of how TNF selectively kills tumor cells has been the subject of research in many laboratories. Here we review TNF-induced post-receptor signaling mechanisms which seem to be involved in the pathway to cytotoxicity.

Mass spectrometric and Edman sequencing of lipocortin I isolated by two-dimensional SDS/PAGE of human melanoma lysates

We have integrated preparative two-dimensional polyacrylamide gel electrophoresis with high-performance tandem mass spectrometry and Edman degradation. By using this approach, we have isolated and identified, by partial sequencing, a human melanoma protein (34 kDa, pI 6.4) as lipocortin I. To our knowledge, this protein was not previously known to be associated with melanoma cells. The identity of the protein was confirmed by two-dimensional immunoblot analysis. High-energy collision-induced dissociation analysis revealed the sequence and acetylation of the N-terminal tryptic peptide and an acrylamide-modified cysteine in another tryptic peptide. Thus, knowledge concerning both the primary structure and covalent modifications of proteins isolated from two-dimensional gels can be obtained directly by this approach, which is applicable to a broad range of biological problems.

Interactions of tumor necrosis factor with local and systemic factors in fetal rat limb bones

In many tissues the actions of tumor necrosis factor-alpha (TNF) are indirectly mediated through the production of autacoids or other cytokines. To determine the role that these factors might have in the action of TNF on bone resorption, we examined the effects of several selective inhibitors on TNF-stimulated resorption. The cyclooxygenase inhibitor indomethacin did not prevent TNF-stimulated resorption in fetal rat limb bones. Stimulation of resorption by TNF was also unaffected by the platelet activating factor antagonist WEB 2086. A 17.5 kD interleukin receptor antagonist protein, at concentrations that completely blocked the bone-resorbing actions of maximally effective concentrations of interleukin (IL)-1 beta, failed to affect the stimulatory actions of TNF. TNF-stimulated resorption was inhibited by both interferon-gamma and dexamethasone. Dexamethasone inhibited TNF-stimulated resorption more effectively than it inhibited parathyroid hormone (PTH)-stimulated resorption. When bones were treated simultaneously with low concentrations of TNF and PTH, potentiation of the bone-resorbing effects was elicited. These results suggest that TNF stimulates resorption through a pathway different from that by which PTH produces its effects. Transforming growth factor-beta (TGF-beta) enhanced responses to TNF; TGF-beta failed to inhibit the effects of TNF, even in long-term culture or when bones were pretreated with TGF-beta. Synergistic interactions between TNF and several other bone-resorbing factors have now been demonstrated. In contrast to the actions of TNF on certain other functions, the bone-resorbing effects of TNF, as determined in the fetal rat limb bone system, do not seem to be mediated by PAF, IL-1, or prostaglandins.

Cytokines involved in monocyte mediated tumor cell death and growth inhibition in serum-free medium

In a serum-free culture system, the release of TNF, lI-1, lI-6, IFN-alpha, and IFN-beta during interaction of elutriated human monocytes (MO) with human tumor cells (TC) was studied by ELISA-technique. Contributions of these cytokines to inhibition of TC-growth and to induction of TC-death by supernatants (SU) gained from such MO/TC-interaction cultures were investigated using affinity chromatography for removal of individual cytokines. Although the TC used are relatively insensitive to recombinant human TNF, withdrawal of TNF causes 50% to 75% reduction of SU-induced TC-death rates, suggesting that susceptibility to TNF is raised during MO/TC-interaction by the other cytokines. Individual removal of other cytokines does not cause reduction of SU-mediated TC-death. However, combined withdrawal of lI-1 and IFN-alpha/beta causes in 2 of 4 TC-lines significant reduction of TC-death. Combined removal of TNF, IFN-alpha/beta, lI-1, and lI-6 leads to complete prevention of SU-mediated growth inhibitory and lytic effects, suggesting that besides these cytokines other signals are not involved significantly. SU-effects can be mimicked by appropriate combinations of authentic cytokines. The response of TC to SU- or cytokine-exposure is strikingly dependent on TC-density, leading at subconfluent TC-density exclusively to inhibition of growth and at postconfluent TC-density to induction of cell death. The principal effect of SU or cytokine combinations in this context seems to be the activation of growth inhibitory signal transduction pathways leading to TC-death in postconfluent TC-populations exclusively if growth stimulatory pathways are activated at the same time. Mouse L cells do not follow this reaction pattern: Their death is exclusively dependent on the presence of TNF in SU and they die upon SU-exposure at postconfluent as well as at subconfluent cell density.

Clinical effect of intra-arterial tumor necrosis factor-alpha for malignant glioma

Recombinant human tumor necrosis factor-alpha was administered intra-arterially to treat 20 cases of malignant gliomas, mostly progressive or recurrent. The optimum dosage was determined to be 1 x 10(5) U/sq m/day. Among the 10 evaluable patients treated at this dosage, two responded (one completely and one partially), resulting in a 20% response rate. Side effects were mild and easily controllable. Improvement of neurological symptoms was noted in 47% of the patients a few days after treatment, even when computerized tomography showed no tumor regression. This might have been due to the pleiotypic biological activity of tumor necrosis factor-alpha. Neuroradiographic observations revealed narrowing of the tumor-feeding artery, a decrease in tumor staining ability, and necrosis in the central part of a tumor. The authors suggest that intra-arterial administration of tumor necrosis factor-alpha may be an effective treatment for malignant glioma, including recurrent cases.

Modulation of tumor cell susceptibility to cytokine-induced cell death by hormones, growth factors, and cell density

The mechanisms controlling "spontaneous" cellular death rates in normal and tumorigenic tissues are largely unknown. An important parameter in this respect is the susceptibility of the target cell to induction of the lytic pathway by appropriate signals. In the present article it is demonstrated in a serum-free in vitro system that the susceptibility of human tumor cells (TC) to induction of lysis by cytokine signals generated during interaction of TC with elutriated human monocytes (MO) is a highly dynamic parameter subject to modulation by hormones, growth factors, and tumor cell density. It was found that growth stimulatory signals such as insulin, and especially epidermal growth factor (EGF), increase lytic susceptibility, whereas hydrocortisone, which does not exert significant growth modulatory effects in these examples, protects TC against the induction of lysis. Increasing TC density above confluence dramatically enhances lytic susceptibility, suggesting interactions between TC to be involved in the induction of their death. In conjunction with previous data demonstrating the insusceptibility of TC, which are forced out of the cell cycle into the quiescent state (G0), the hypothesis is put forward that growth stimulatory factors increase a TC's lytic susceptibility by preventing its transit from G1 to G0 in response to growth inhibitory signals generated during MO/TC interaction. The data support the concept that TC susceptibility to the induction of cell death is a consequence of simultaneously activated growth stimulatory and growth inhibitory signalling pathways.

Transforming growth factors type-beta and dexamethasone attenuate group II phospholipase A2 gene expression by interleukin-1 and forskolin in rat mesangial cells

Treatment of rat mesangial cells with interleukin-1 beta (IL-1 beta) and forskolin induced, in a synergistic fashion, the expression of group II phospholipase A2 (PLA2) mRNA, with subsequent increased synthesis and secretion of PLA2. In contrast, interleukin-6 did not increase PLA2 mRNA levels of PLA2 activity. Transforming growth factor (TGF) beta 1, TGF beta 2 and TGF beta 3 equipotently attenuated the IL-1 beta- and forskolin-induced elevation of PLA2 mRNA, as well as PLA2 synthesis and secretion. The glucocorticoid dexamethasone only partially suppressed the IL-1 beta- and forskolin-induced elevation of PLA2 mRNA, but totally inhibited PLA2 synthesis and secretion.

Cytokine- and forskolin-induced synthesis of group II phospholipase A2 and prostaglandin E2 in rat mesangial cells is prevented by dexamethasone

We have previously described that treatment of rat glomerular mesangial cells with interleukin-1 beta, tumor necrosis factor or forskolin stimulates the synthesis and secretion of prostaglandin E2 and group II phospholipase A2. We now report that pretreatment of the mesangial cells with dexamethasone dose-dependently suppresses the cytokines- and forskolin-induced synthesis of prostaglandin E2 as well as the induced synthesis and secretion of group II phospholipase A2. These observations implicate that the inhibition of the cellular or secreted phospholipase A2 activity by dexamethasone in rat mesangial cells is not due to induced synthesis of phospholipase A2 inhibitory proteins but caused by direct inhibition of phospholipase A2 protein expression.

Tumor necrosis factor. Characterization at the molecular, cellular and in vivo level

TNF was originally characterized as an antitumor agent and a factor cytotoxic for many malignant cells. It is now clear that it plays an important role in the defense against viral, bacterial and parasitic infections, - and in (auto-)immune responses. Natural induction of TNF is protective, but its overproduction may be detrimental and even lethal to the host. The structure of TNF and its interaction with the two types of cellular receptor are becoming better understood. TNF elicits a variety of events in different cell types. It subverts the electron transport system or the mitochondria into production of oxygen radicals, which can kill the (malignant) cells when these do not contain or produce protective enzymes. Furthermore, TNF induces a set of genes and at least part of this transcriptional activation is mediated by NF kappa B. The prospects of TNF as an antitumor drug can be improved on the one hand by agents such as LI+, which synergizes, and on the other hand by inhibitors of the systemic toxicity which do not interfere with the antitumor efficacy. Also, in tumor-bearing animals which have been rendered tolerant by administration of small doses of TNF, an effective and complete elimination of the tumors can be obtained by the combined action of TNF plus interferon.

Production of lipocortin-like proteins by cultured human tracheal submucosal gland cells

Evidence is obtained for the presence of lipocortin-like proteins in human tracheal gland cells in culture. Using polyclonal antibodies to lipocortin I, indirect immunofluorescence studies demonstrate that lipocortin I is mainly confined to the tracheal gland cell surface. From cell membranes, four Ca2(+)-dependent proteins (35, 40, 45 and 67 kDa) were identified as lipocortin related proteins by using immunoblotting and fluorography following [35S]methionine metabolic labeling experiments. A strong immunoreactivity for the 35 kDa protein was observed. In addition, lipocortin-like proteins with apparent Mr33, 35, 37 and 67 kDa, respectively, were released in the apical culture medium by tracheal gland cells cultured on microporous membrane of a double chamber culture system.