Glucocorticoids inhibit serum depletion-induced apoptosis in T lymphocytes expressing Bcl-2

Enhanced chemosensitization of anoikis-resistant melanoma cells through syndecan-2 upregulation upon anchorage independency

Syndecan family proteins are heparan sulfate proteoglycans, which involved in various cellular activities and associating with metastatic potential and chemosensitivity of tumor cells. Melanoma is one of malignant tumors with poor prognosis upon metastasis. Previously, we had shown that melanoma cells remained survived under cell detachment, which was similar to the initial steps of tumor metastasis. Downregulation of syndecan-1 and upregulation of syndecan-2 in melanoma A375 cells were observed by different suspension conditions. Specific gene alterations also increased melanoma malignancy under anchorage independency. Thus, we would like to investigate in further the role of specific gene alteration, so that it could be used to develop novel strategy to treat melanoma.

In this paper, we found that syndecan-2 expression level as well the kinase phosphorylation levels increased upon anchorage independency. The pathway to regulate syndecan-2 expression shifted from PKCα/β-dependent under adhesion into PKCδ-dependent under cell suspension. Manipulation of syndecan-2 expression showed that PI3K and ERK phosphorylation as well the migratory ability increased with increased syndecan-2 expression level. In addition, suspended melanoma cells were more sensitive to chemoagents, which correlated with syndecan-2 overexpression, PI3K and ERK activations, serum level, and the presence of glycosaminoglycans.

In conclusion, we showed upregulation of syndecan-2 in anoikis-resistant melanoma cells enhanced chemosensitivity through PI3K and ERK activation. This observation would support and refine the strategy of adjuvant chemotherapy to overcome metastatic melanoma.

Splenic micronodular T-cell/histiocyte-rich large B-cell lymphoma: effect of prior corticosteroid therapy

We report on three patients who were treated with corticosteroids only prior to the diagnosis of splenic lymphoma. Corticosteroids were administered for different conditions, at different doses, and for various periods of time. The primary diagnosis was splenic micronodular T-cell/histiocyte-rich large B-cell lymphoma in the three cases, and it was reached with variable difficulty. We suggest that the corticosteroid treatment was one of the causes for the complications in reaching a diagnosis. The morphologic appearance of the microscopic splenic nodules was the most variable feature and may possibly reflect the dose and duration of the corticosteroid therapy. However, the histopathologic changes are probably not related with Epstein-Barr virus-induced immunosuppression.

Mecanismos adaptativos do sistema imunológico em resposta ao treinamento físico

O treinamento físico, de intensidade moderada, melhora os sistemas de defesa, enquanto que o treinamento intenso causa imunossupressão. Os mecanismos subjacentes estão associados à comunicação entre os sistemas nervoso, endócrino e imunológico, sugerindo vias autonômicas e modulação da resposta imune. Células do sistema imune, quando expostas a pequenas cargas de estresse, desenvolvem mecanismo de tolerância. Em muitos tecidos tem-se demonstrado que a resposta a situações agressivas parece ser atenuada pelo treinamento físico aplicado previamente, isto é, o treinamento induz tolerância para situações agressivas/estressantes. Nesta revisão são relatados estudos sugerindo os mecanismos adaptativos do sistema imunológico em resposta ao treinamento físico.

High tolerance to apoptotic stimuli induced by serum depletion and ceramide in side-population cells: high expression of CD55 as a novel character for side-population

Cancer stem cells are supposed to be resistant to apoptosis, but information for this is quite limited. Cancer stem cells are usually isolated as dye-effluxing cells with Hoechst 33342 staining, called side-population (SP) cells. Because Hoechst 33342 dye itself induces apoptosis, the SP cells isolated by such method are not suitable for evaluation of apoptosis. For accurate assessment, SP cells must be isolated without Hoechst 33342. Here, we found that CD55 was highly expressed in SP cells of two mammary gland carcinoma cell lines. Then, the high expression of CD55 was used for isolation of cancer stem cells among mammary carcinoma cell lines as a surrogate character. Cells expressing high level of CD55 (CD55(hi)) were resistant to apoptosis induced by serum depletion as in the case of SP cells. In ceramide-inducing apoptosis, CD55(hi) cells showed high tolerance. Anti-apoptotic molecules such as Bcl-2 were abundantly expressed in both SP cells and CD55(hi) cells. These findings indicated that SP cells as revealed to be CD55(hi) cells were tolerant to apoptosis. The high expression of CD55 may be a useful character for SP cells in evaluating their functions.

Dexamethasone induces cell death in insulin-secreting cells, an effect reversed by exendin-4

Glucocorticoid excess induces hyperglycemia, which may result in diabetes. The present experiments explored whether glucocorticoids trigger apoptosis in insulin-secreting cells. Treatment of mouse beta-cells or INS-1 cells with the glucocorticoid dexamethasone (0.1 micromol/l) over 4 days in cell culture increased the number of fractionated nuclei from 2 to 7 and 14%, respectively, an effect that was reversed by the glucocorticoid receptor antagonist RU486 (1 micromol/l). In INS-1 cells, dexamethasone increased the number of transferase-mediated dUTP nick-end labeling-staining positive cells, caspase-3 activity, and poly-(ADP-) ribose polymerase protein cleavage; decreased Bcl-2 transcript and protein abundance; dephosphorylated the proapoptotic protein of the Bcl-2 family (BAD) at serine155; and depolarized mitochondria. Dexamethasone increased PP-2B (calcineurin) activity, an effect abrogated by FK506. FK506 (0.1 micromol/l) and another calcineurin inhibitor, deltamethrin (1 micromol/l), attenuated dexamethasone-induced cell death. The stable glucagon-like peptide 1 analog, exendin-4 (10 nmol/l), inhibited dexamethasone-induced apoptosis in mouse beta-cells and INS-1 cells. The protective effect of exendin-4 was mimicked by forskolin (10 micromol/l) but not mimicked by guanine nucleotide exchange factor with the specific agonist 8CPT-Me-cAMP (50 micromol/l). Exendin-4 did not protect against cell death in the presence of cAMP-dependent protein kinase (PKA) inhibition by H89 (10 micromol/l) or KT5720 (5 micromol/l). In conclusion, glucocorticoid-induced apoptosis in insulin-secreting cells is accompanied by a downregulation of Bcl-2, activation of calcineurin with subsequent dephosphorylation of BAD, and mitochondrial depolarization. Exendin-4 protects against glucocorticoid-induced apoptosis, an effect mimicked by forskolin and reversed by PKA inhibitors.

Physiological and pathological consequences of the interactions of the p53 tumor suppressor with the glucocorticoid, androgen, and estrogen receptors

The p53 tumor suppressor plays a key role in protection from the effects of different physiological stresses (DNA damage, hypoxia, transcriptional defects, etc.), and loss of its activity has dire consequences, such as cancer. Its activity is finely tuned through interactions with other important regulatory circuits in the cell. Recently, striking evidence has emerged for crosstalk with another class of important regulators, the steroid hormone receptors, and in particular the glucocorticoid (GR), androgen (AR), and estrogen (ER) receptors. These receptors are important in maintaining homeostasis in response to internal and external stresses (GR) and in the development, growth, and maintenance of the male and female reproductive systems (AR and ER, respectively). We review how p53 interacts closely with these receptors, to the extent that they share the same E3 ubiquitin ligase, the MDM2 oncoprotein. We discuss the different physiological contexts in which such interactions occur, and also how these interactions have been undermined in various pathological situations. We will describe future areas for research, with special emphasis on GR, and how certain common features, such as cytoplasmic anchoring of p53 by the receptors, may become targets for the development of therapeutic interventions. Given the importance of GR in inflammation, erythropoiesis, and autoimmune diseases, and the importance of AR and ER in prostate and breast cancer (respectively), the studies on p53 interactions with the steroid receptors will be an important domain in the near future.

Bioelectrical impedance assay to monitor changes in cell shape during apoptosis

Apoptosis is a strictly regulated and genetically encoded cell 'suicide' that may be triggered by cytokines, depletion of growth factors or certain chemicals. It is morphologically characterized by severe alterations in cell shape like cell shrinkage and disintegration of cell-cell contacts. We applied a non-invasive electrochemical technique referred to as electric cell-substrate impedance sensing (ECIS) in order to monitor the apoptosis-induced changes in cell shape in an integral and quantitative fashion with a time resolution in the order of minutes. In ECIS the cells are grown directly on the surface of small gold-film electrodes (d = 2 mm). From readings of the electrical impedance of the cell-covered electrode, performed with non-invasive, low amplitude sensing voltages, it is possible to deduce alterations in cell-cell and cell-substrate contacts. To improve the sensitivity of this impedance assay we used endothelial cells derived from cerebral micro-vessels as cellular model systems since these are well known to express electrically tight intercellular junctions. Apoptosis was induced by cycloheximide (CHX) and verified by biochemical and cytological assays. The time course of cell shape changes was followed with unprecedented time resolution by impedance readings at 1 kHz and correlated with biochemical parameters. From impedance readings along a broad frequency range of 1-10(6) Hz we could assign the observed impedance changes to alterations on the subcellular level. We observed that disassembly of barrier-forming tight junctions precedes changes in cell-substrate contacts and correlates strongly with the time course of protease activation.

Tumor necrosis factor alpha receptor- and Fas-associated FLASH inhibit transcriptional activity of the glucocorticoid receptor by binding to and interfering with its interaction with p160 type nuclear receptor coactivators

Tumor necrosis factor alpha (TNF alpha) and its downstream transcription factor nuclear factor kappa B (NF-kappa B) suppress glucocorticoid action, contributing to tissue resistance to glucocorticoids in several pathologic inflammatory states. p160 nuclear receptor coactivators on the other hand, contribute to the transcriptional signal of the glucocorticoid receptor (GR) through interaction with it via LXXLL motifs in their nuclear receptor-binding (NRB) domain. To discover TNF alpha-induced factors that regulate GR activity at the coactivator level, we performed yeast two-hybrid screening using the NRB domain of the glucocorticoid receptor-interacting protein 1 (GRIP1) as bait. We found that FLICE-associated huge protein (FLASH), which transduces TNF alpha and Fas ligand signals, bound the NRB domain of GRIP1 at a region between the second and third LXXLL motifs. FLASH suppressed both GR transactivation and GRIP1 enhancement of the glucocorticoid signal and inhibited the physical interaction between GR and the GRIP1 NRB domain. Transfected green fluorescent protein-fused FLASH was located in both the cytoplasm and nucleus, while endogenous FLASH shifted its subcellular localization from the cytoplasm into the nucleus in response to TNF alpha. FLASH antisense and super-repressor I kappa B alpha inhibited the action of TNF alpha independently of each other and additively. These findings indicate that FLASH participates in TNF alpha-induced blockade of GR transactivation at the nuclear receptor coactivator level, upstream and independently of NF-kappa B.

Molecular basis of rifampicin-induced inhibition of anti-CD95-induced apoptosis of peripheral blood T lymphocytes: the role of CD95 ligand and FLIPs

Rifampicin modulates immune response; however, mechanisms by which it exerts these effects are incompletely understood. Recently, rifampicin has been shown to bind to and activate glucocorticoid receptors. Because of the evidence for a role of glucocorticoids in lymphocyte apoptosis, we hypothesized that rifampicin may exert its influence on the immune system by regulating apoptosis. Therefore, we examined the effect of rifampicin on signaling pathway of anti-CD95-induced apoptosis in peripheral blood lymphocytes. Rifampicin, in a concentration-dependent manner, inhibited anti-CD95-induced apoptosis in both CD4+ and CD8+ T cells, which was associated with the inhibition of activation of both caspase-3 and caspase-8. In addition, rifampicin down-regulated the expression of CD95L and Bax. The inhibitory effects of rifampicin on apoptosis and caspase activation as well as its effect on the expression of CD95L and FLIPs were reversed by RU486, an antagonist of glucocorticoid receptor. These data suggest that rifampicin inhibits anti-CD95-mediated apoptosis in lymphocytes by modulating the expression of certain proteins that regulate apoptosis, at least in part, via glucocorticoid receptors.

Cell-specific regulation of apoptosis by glucocorticoids: implication to their anti-inflammatory action

Glucocorticoids play a major role in attenuation of the inflammatory response. These steroid hormones are able to induce apoptosis in cells of the hematopoietic system such as monocytes, macrophages, and T lymphocytes that are involved in the inflammation reaction. In contrast, it was discovered recently that in glandular cells such as the mammary gland epithelia, hepatocytes, ovarian follicular cells, and in fibroblasts glucocorticoids protect against apoptotic signals evoked by cytokines, cAMP, tumor suppressors, and death genes. The anti-apoptotic effect of glucocorticoids is exerted by modulation of several survival genes such as Bcl-2, Bcl-x(L), and NFkB, in a cell-specific manner. Moreover, upregulation or downregulation of the same gene product can occur in a cell-dependent manner following stimulation by glucocorticoids. This phenomenon is probably due to composite regulatory cross-talk among multiple nuclear coactivators or corepressors, which mediate the transcription regulation of the genes, by their interaction with the glucocorticoid receptor. These observations suggest that the anti-inflammatory action of glucocorticoids is exerted by two complementary mechanisms: on one hand, they induce death of the cells that provoke the inflammation, and on the other hand they protect the resident cells of the inflamed tissue by arresting apoptotic signals. Moreover, the complementary action of glucocorticoids provides a new insight to the therapeutic potential of these hormones.

Phosphorylation status modulates Bcl-2 function during glucocorticoid-induced apoptosis in T lymphocytes

Glucocorticoids are known to induce apoptosis in lymphoid cells, and Bcl-2 overexpression can block the apoptosis-inducing action of glucocorticoids. Since phosphorylation of Bcl-2 is implicated in regulating Bcl-2 function, we considered the role of Bcl-2 phosphorylation in protecting lymphoid cells from glucocorticoid-induced cell death. Five stably transfected cell lines of WEHI 7.1 cells expressing either wild-type Bcl-2 or alanine mutants of Bcl-2 at amino acids threonine 56, serine 70, threonine 74, or serine 87 were created. Expression of the mutant Bcl-2 proteins was documented by flow cytometry and Western blot analysis. Mutation of Bcl-2 on T56 and S87 eliminated the ability of Bcl-2 to inhibit glucocorticoid-induced cell shrinkage, mitochondrial depolarization, DNA fragmentation, and cell death. Mutation of T74 only partially impaired the ability of Bcl-2 to block glucocorticoid-induced apoptosis whereas mutation of S70 in Bcl-2 did not alter its ability to block glucocorticoid-induced apoptosis.

The anti-inflammatory action of glucocorticoids is mediated by cell type specific regulation of apoptosis

Glucocorticoids play a major role in attenuation of the inflammatory response. These steroid hormones are able to induce apoptosis in cells of the hematopoietic system such as monocytes, macrophages and T-lymphocytes that are involved in the inflammation reaction. In contrast, it was discovered recently that in glandular cells such as the mammary gland epithelia, hepatocytes, ovarian follicular cells and in fibroblasts glucocorticoids protect against apoptotic signals evoked by cytokines, cAMP, tumor suppressors and death genes. The anti-apoptotic effect of glucocorticoids is exerted by modulation of several survival genes such as Bcl-2, Bcl-x(L) and NFkappaB, in a cell type-specific manner. Moreover, up regulation or down regulation of the same gene product can occur in a cell type-dependent manner following stimulation by glucocorticoids. This phenomenon is probably due to composite regulatory cross-talk among multiple nuclear coactivators or corepressors, which mediate the transcriptional regulation of the genes, by their interaction with the glucocorticoid receptor (GR). These observations suggest that the anti-inflammatory action of glucocorticoids is exerted by two complementary mechanisms: on the one hand, they induce death of the cells that provoke the inflammation, and on the other hand, they protect the resident cells of the inflamed tissue by arresting apoptotic signals.

Rifampicin inhibits CD95-mediated apoptosis of Jurkat T cells via glucocorticoid receptors by modifying the expression of molecules regulating apoptosis

Rifampicin and its analogues are increasingly used in the treatment and prophylaxis of mycobacterial infections. Recently, it has been demonstrated that rifampicin binds to and activates glucocorticoid receptors (GR). Glucocorticoids may inhibit or promote apoptosis in various cell types. Therefore, we investigated the effect of rifampicin on anti-CD95-induced apoptosis in Jurkat T cells. Rifampicin, in a concentration-dependent manner, inhibited anti-CD95-induced apoptosis. Furthermore, rifampicin down-regulated the expression of Bax and CD95L and up-regulated the expression of Bcl-2, Bcl-xL, and Flice-inhibitory protein-L (FLIPL); however, rifampicin had no effect on CD95 or XIAP expression. Rifampicin did not inhibit the binding of anti-CD95 monoclonal antibody to CD95 receptor. A GR-specific antagonist RU480 reversed the inhibition of apoptosis by rifampicin. Furthermore, rifampicin failed to inhibit anti-CD95-induced apoptosis in a dominant negative IKBalpha (IKBaM) Jurkat T cells. Taken together, these findings suggest that rifampicin inhibits anti-CD95-induced apoptosis in Jurkat T cells by modulating the expression of various molecules regulating apoptosis and its effect appears to be mediated via GR and at least in part through NF-kappaB signaling pathway.

A distinct role for apoptosis in the changes in lymphopoiesis and myelopoiesis created by deficiencies in zinc

Reduced numbers of lymphocytes in the peripheral immune system appeared to be a significant cause of the loss in host defense capacity in humans and animals that are zinc deficient (ZD). A series of studies verified that ZD substantially reduced the lymphocyte compartment of both the marrow and thymus in young adult mice, with large losses noted among the pre-B and pre-T cells. Suboptimal nutriture along with chronic production of glucocorticoids generated during ZD had accelerated apoptosis among these precursor lymphocytes two- to threefold. Thus, the primary cause of the lymphopenia created by ZD was reduced production of lymphocytes and heightened cell death among precursor cells. The data will also show that myelopoiesis in the marrow was protected and enhanced numbers of myeloid progenitor cells were found in S and G2/M. Thus, as zinc became limiting the second line of defense appeared to be down-regulated via reduction of lymphopoiesis while cells of the myeloid lineage were protected to maintain the first line of defense that provides innate immunity. This may represent an important adaptation of the immune system to suboptimal nutriture that deserves further exploration.

Cdc42-independent activation and translocation of the cytostatic p21-activated protein kinase gamma-PAK by sphingosine

Autophosphorylation of p21-activated protein kinase gamma-PAK is stimulated at 10 microM sphingosine in vitro and is maximal at 100 microM. Sites autophosphorylated on gamma-PAK in response to sphingosine are identical to those obtained with Cdc42(GTP). Autophosphorylation is paralleled by stimulation of gamma-PAK activity as measured with peptide and protein substrates. In 3T3-L1 cells, sphingosine stimulates the autophosphorylation and activity of gamma-PAK associated with the membrane-containing particulate fraction by 2.8-fold, but does not stimulate the activity of the soluble enzyme. Thus, gamma-PAK is activatable via a Cdc42-independent mechanism, suggesting sphingosine has a role in gamma-PAK activation under conditions of cell stress.

Ligand-dependent interaction of the glucocorticoid receptor with p53 enhances their degradation by Hdm2

The glucocorticoid receptor (GR) and the tumor suppressor p53 mediate different stress responses. We have studied the mechanism of their mutual inhibition in normal endothelial cells (HUVEC) in response to hypoxia, a physiological stress, and mitomycin C, which damages DNA. Dexamethasone (Dex) stimulates the degradation of endogenous GR and p53 by the proteasome pathway in HUVEC under hypoxia and mitomycin C treatments, and also in hepatoma cells (HepG2) under normoxia. Dex inhibits the functions of p53 (apoptosis, Bax, and p21(WAF1/CIP1) expression) and GR (PEPCK and G-6-Pase expression). Endogenous p53 and GR form a ligand-dependent trimeric complex with Hdm2 in the cytoplasm. Disruption of the p53-HDM2 interaction prevents Dex-induced ubiquitylation of GR and p53. The ubiquitylation of GR requires p53, the interaction of p53 with Hdm2, and E3 ligase activity of Hdm2. These results provide a mechanistic basis for GR and p53 acting as opposing forces in the decision between cell death and survival.

The effect of drugs and toxins on the process of apoptosis

In this review we examine the modifying effect of specific drugs on apoptosis. Apoptosis is a type of cell death prevalent during many physiological and pathological conditions, consisting of several steps, namely, initiating stimuli, transduction pathways, effector mechanisms, nuclear fragmentation, and phagocytosis. Pharmacological substances such as glucocorticoids can either induce or inhibit the process of apoptosis in various cells depending on the type of drug and its concentration. Understanding the mechanisms of interaction of drugs with cells undergoing apoptosis could encourage novel therapeutic approaches to human diseases in which apoptosis has a critical role.

Light-dependent generation of reactive oxygen species in cell culture media

Cell culture media (RPMI 1640, Dulbecco's Minimal Essential Medium and yeast extract-peptone-glucose medium) were found to oxidize dichlorodihydrofluorescein diacetate and dihydrorhodamine 123, and to generate spin adduct of 5,5'-dimethyl-1-pyrroline N-oxide, which indicates formation of reactive oxygen species (ROS). The production of ROS was light dependent. The main component of the media responsible for the generation of ROS was riboflavin, but tryptophan, tyrosine, pyridoxine, and folic acid enhanced the effect of riboflavin. These observations point to exposure of cells to ROS under in vitro culture conditions.

Dexamethasone inhibits TNF-alpha-induced apoptosis and IAP protein downregulation in MCF-7 cells

Exposure of human mammary carcinoma cell line MCF-7 to TNF-alpha leads to apoptotic cell death within 24 h. In search for apoptosis-preventing signals, we identified glucocorticoids as potent death-preventing compounds. Ten nM dexamethasone provided a significant protective effect whereas 100 nM dexamethasone roughly blocked 80 - 90% of TNF-alpha-induced apoptosis. Surprisingly, dexamethasone exerted a protective effect even when supplied several hours after TNF-alpha. This points to a powerful inhibition of even advanced apoptotic processes by dexamethasone. To further pinpoint the anti-apoptotic glucocorticoid action, we investigated the expression levels of several members of the inhibitors of apoptosis (IAPs) family of proteins in response to TNF-alpha and dexamethasone. IAP proteins directly block caspase protease activities including caspase-3, caspase-7, and caspase-9. Exposure of MCF-7 cells to TNF caused an extensive downregulation of cIAP1, cIAP2, and XIAP protein levels. The decline of the IAP protein levels temporally paralleled the appearance of apoptotic DNA fragments which started 12 - 14 h following TNF-alpha addition and maximal effects were seen within 24 h. Coincubation of cells with TNF-alpha and dexamethasone potently blocked cIAP1, cIAP2, and XIAP downregulation. TNF-alpha-mediated IAP protein downregulation was not affected by proteasome inhibitors like lactacystin, ALLN or ALLM, whereas it was blocked by the broad-spectrum caspase inhibitor Z-VAD-fmk which also prevented TNF-alpha-induced apoptotic cell death. These data suggest that inhibition of IAP downregulation mediated by a caspase proteolytic activity constitutes the anti-apoptotic action of glucocorticoids in MCF-7 carcinoma cells.

The ataxia-telangiectasia gene product may modulate DNA turnover and control cell fate by regulating cellular redox in lymphocytes

The ATM kinase, when activated postnatally, exerts multiple functions to prevent the onset of ataxia-telangiectasia (AT). Using freshly isolated thymocytes from Atm-/- mice that were under stress during postnatal differentiation, we noted that thiol redox activity, as indicated by reduction of the tetrazolium MTS, and DNA turnover activity, as indicated by incorporation of [(3)H]thymidine into DNA, were both greatly increased compared with activities in thymocytes from Atm+/+ mice. This increased thymidine incorporation could be suppressed by the thiol N-acetylcysteine. In primary noncycling splenocytes, mitogens proportionally increased both the rate of [(3)H]thymidine incorporation and the rate of reduction of MTS. The mitogen-induced activities in splenocytes were not affected by ATM but were suppressed by the calcineurin-dependent inhibitor FK-506, which has no effect on these activities in thymocytes. These findings suggest that increased [(3)H]thymidine incorporation and reducing power indicate increased cell cycling in mitogenically stimulated splenocytes, whereas these two indicators represent increased FK-506-independent DNA turnover activities in thymocytes. Thus, a primary function of ATM is to activate the redox-sensitive checkpoint required for down-regulation of DNA turnover activities in developing lymphocytes. Cell-cycling checkpoints in undamaged quiescent lymphocytes are not activated by ATM with mitogenic stimulation. ATM may suppress abnormal DNA turnover and the resultant oncogenesis by regulating cellular thiol redox pathways.

Dexamethasone inhibits the antigen presentation of dendritic cells in MHC class II pathway

Glucocorticoids (GC) are physiological inhibitors of inflammatory responses and are widely used as anti-inflammatory and immunosuppressive agents in treatment of many autoimmune and allergic diseases. In the present study, we demonstrated that one of the mechanisms by which GC can suppress the immune responses is to inhibit the differentiation and antigen presentation of dendritic cells (DC). DC were differentiated from murine bone marrow hematopoietic progenitor cells by culture with GM-CSF and IL-4 with or without dexamethasone (Dex). Our data showed that Dex, in a dose dependent manner, down-regulated surface expression of CD86, CD40, CD54 and MHC class II molecules by DC, but the expression of MHC class I, CD80, CD95 and CD95L were not affected. In addition, Dex-treated DC showed an impaired function to activate alloreactive T cells and to secrete IL-Ibeta and IL-12p70. Moreover, Dex inhibited DC to present antigen by MHC class II pathway. However, the endocytotic activity of DC was not affected. The inhibitory effect of Dex on the expression of costimulatory molecules and the antigen-presenting capacity of DC could be blocked by the addition of RU486, a potent steroid hormone antagonist, suggesting the requirement of binding to cytosolic receptors in the above-described action of Dex. Since DC have the unique property to present antigen to responding naive T cells and are required in the induction of a primary response, the functional suppression of DC by Dex may be one of the mechanisms by which GC regulate immune responses in vivo.

Glucocorticoids protect against apoptosis induced by serum deprivation, cyclic adenosine 3',5'-monophosphate and p53 activation in immortalized human granulosa cells: involvement of Bcl-2

Glucocorticoid hormones are known to enhance gonadotropin/cAMP-induced steroidogenesis in rat and human granulosa cells. As glucocorticoids induce apoptosis in numerous cell types, we investigated the role of glucocorticoids in the control of apoptosis in immortalized human granulosa cells (HO-23) transfected with a temperature-sensitive mutant of p53 (Val(135)). When HO-23 were incubated with forskolin in the presence or absence of dexamethasone (Dex) at 32 or 37 C, progesterone production was higher by 4- and 8-fold in the presence of Dex at 37 or 32 C, respectively (P: < 0. 01). The expression of adrenodoxin (ADX), which is an intrinsic part of the cytochrome P450 side-chain cleavage enzyme system, remained the same in the presence or absence of Dex in forskolin-stimulated cells. Dex reduced apoptosis (to 33% of control) in cultures after activation of p53 by shifting the temperature from 37 to 32 C. Moreover, Dex suppressed apoptosis induced by serum deprivation (to 40% of control) or forskolin stimulation (to 28% and 40% at 37 and at 32 C, respectively). The protective effect of Dex on cAMP-, p53-, and serum deprivation-induced apoptosis was confirmed by both 4',6-diamido-2-phenylindole hydrochloride DNA staining and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling with an ED(50) of 7 nM Dex. Hydrocortisone showed a similar antiapoptotic effect. The protective effect of glucocorticoids against apoptosis was completely abolished by RU486 when cells were coincubated with 10 nM Dex and 10-100 nM RU486. The protection against apoptosis by glucocorticoid involved a sharp elevation in intracellular levels of Bcl-2 (3-7.6 fold; P: < 0.01). In contrast to the effect of Dex in the prevention of apoptosis in HO-23 granulosa cells, Dex dramatically stimulated apoptosis by 3-fold in LTR-6 myeloid leukemia cells expressing the same temperature-sensitive mutant (Val(135) p53) and the same amount of glucocorticoid receptor-alpha. Forskolin did not stimulate apoptosis when incubated with these cells. However, it augmented by 1.2-fold the p53-induced apoptosis in cells shifted from 37 to 32 C. Dex further enhanced apoptosis by 1.9-fold in p53-activated cultures (32 C). Incubation of the cells with Dex dramatically reduced Bcl-2 levels to 15% of control at 37 C (P: < 0.01) or 32 C in the presence or absence of forskolin (P: < 0.01). Our data suggest that glucocorticoids exert a protective effect against induced apoptosis in immortalized granulosa cells and a stimulatory effect on apoptosis in myeloid leukemia cells. Moreover, modulation of Bcl-2 levels plays an important role in mediating the glucocorticoid effect on cell survival. The opposite effect of glucocorticoids on Bcl-2 levels in the two cell lines may be due to the different ontogeneses of the two cell types: epithelial for granulosa cells vs. mesenchymal for myeloid cells studied in the present work.

Negative cross-talk between p53 and the glucocorticoid receptor and its role in neuroblastoma cells

The tumour suppressor p53 and the glucocorticoid receptor (GR) respond to different types of stress. We found that dexamethasone-activated endogenous and exogenous GR inhibit p53-dependent functions, including transactivation, up- (Bax and p21(WAF1/CIP1)) and down- (Bcl2) regulation of endogenous genes, cell cycle arrest and apoptosis. GR forms a complex with p53 in vivo, resulting in cytoplasmic sequestration of both p53 and GR. In neuroblastoma (NB) cells, cytoplasmic retention and inactivation of wild-type p53 involves GR. p53 and GR form a complex that is dissociated by GR antagonists, resulting in accumulation of p53 in the nucleus, activation of p53-responsive genes, growth arrest and apoptosis. These results suggest that molecules that efficiently disrupt GR-p53 interactions would have a therapeutic potential for the treatment of neuroblastoma and perhaps other diseases in which p53 is sequestered by GR.

Dual effect of glucocorticoids on apoptosis of human autoreactive and foreign antigen-specific T cells

The efficacy of glucocorticoids in the treatment of multiple sclerosis may involve the induction of T cell apoptosis. Here, we report that glucocorticoids have two different effects on the vulnerability of human antigen-specific T cells: (i) steroids induce T cell apoptosis in a CD95-independent, but caspase-dependent manner; (ii) steroids protect T cells from CD95-mediated apoptosis which, however, is also caspase-dependent. An increase in BCL-2 expression is observed upon incubation with steroids. Thus, inhibition of CD95-mediated T cell apoptosis may be an undesirable side-effect resulting in survival of activated T cells and the maintenance of pathogenic immune responses might explain the lack of long-term glucocorticoid therapy.

Glucocorticoid-induced, caspase-dependent organ apoptosis early after burn injury

Immune suppression and increased apoptotic loss of circulating lymphocytes have been reported after burn injury. However, little is known about the underlying mechanisms responsible for the increased apoptosis of lymphoid and parenchymal cells in solid organs and the role played by inflammatory mediators, such as tumor necrosis factor-alpha (TNF-alpha) and Fas ligand (FasL), as well as by glucocorticoids. To evaluate the role of endogenously produced glucocorticoids and FasL, mice subjected to a 20% steam burn were pretreated with a glucocorticoid receptor antagonist (mifepristone) or a neutralizing murine Fas fusion protein. Three and twenty-four hours after burn injury, histological analysis, caspase-3 activity, and in situ terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and phenotyping of lymphocyte populations for apoptosis were evaluated. Burn injury increased the number of apoptotic cells and caspase-3 activity in thymus and spleen, but not in other solid organs. Increased apoptosis was seen in several T and B cell populations from both thymus and spleen. Mifepristone pretreatment significantly reduced the apoptosis and caspase-3 activity after burn injury, whereas blocking FasL activity had only minimal effects. We conclude that corticosteroids, and not FasL, are primarily responsible for the increased caspase-3 activity and apoptosis in thymus and spleen cell populations early after burn injury.

Suppression of apoptosis by glucocorticoids in glomerular endothelial cells: effects on proapoptotic pathways

Tumour necrosis factor-alpha (TNF-alpha)- and lipopolysaccharide (LPS)-induced apoptosis of bovine glomerular endothelial cells is now recognized as an important part in the pathogenesis of glomerulonephritis characterized by early mitochondrial cytochrome c release, mitochondrial permeability transition, Bak protein upregulation, Bcl-X(L) protein downregulation and caspase-3 activation. Co-treatment of cells with 10 nM dexamethasone and TNF-alpha or LPS blocked roughly 90% of apoptotic cell death in glomerular endothelial cells. The action of glucocorticoids could be documented in that they prevented all apoptotic markers such as DNA laddering, DNA fragmentation measured by the diphenylamine assay as well as morphological alterations. To mechanistically elucidate the action of glucocorticoids we evaluated whether glucocorticoids elicit a time-dependent effect. For dexamethasone, to maximally inhibit DNA fragmentation a preincubation period was not required. Even if dexamethasone was supplemented 6 h following TNF-alpha or LPS we observed a maximal inhibitory effect. Concerning its influence on TNF-alpha and LPS signal transduction, we found that dexamethasone only partially prevented cytochrome-c-release as a first sign of apoptotic cell death but efficiently blocked mitochondrial permeability transition. Moreover, TNF-alpha- and LPS-induced Bak upregulation, Bcl-X(L)-downregulation, and the activation of caspase-3-like proteases, measured fluorometrically using DEVD-AMC and PARP cleavage, were efficiently blocked by dexamethasone. We postulate that glucocorticoids exert their inhibitory action upstream of the terminal death pathways but downstream of primary receptor mediated signals by blocking pro-apoptotic signals pre- and/or post cytochrome c release and mitochondrial signalling.

p21-activated protein kinase gamma-PAK is activated by ionizing radiation and other DNA-damaging agents. Similarities and differences to alpha-PAK

The p21-activated protein kinase gamma-PAK is activated 2-5-fold in response to ionizing radiation (IR) in 3T3-L1 fibroblasts and U937 leukemia cells. gamma-PAK is activated in a dose- and time-dependent manner. Doses from 1 to 100 Gy result in significant stimulation of activity at 30 min, whereas maximal stimulation is observed at 120 min after irradiation. UV (80 J/m(2)) and the DNA-damaging drugs cytosine beta-D-arabinofuranoside (AraC) and cis-platinum(II)diammine dichloride (cisplatin) also induce gamma-PAK activation. The activation of gamma-PAK in response to IR or AraC is dependent on tyrosine kinase and phosphoinositide 3-kinase activity, as demonstrated by use of the inhibitors genistein and wortmannin; in contrast activation of gamma-PAK by cisplatin and UV is not affected significantly by these inhibitors, suggesting that gamma-PAK can be activated by more than one pathway in response to different types of DNA damage. In contrast to gamma-PAK, alpha-PAK and JNK are activated only by cisplatin and UV in 3T3-L1 cells, suggesting differential regulation of the protein kinases. This is the first time that members of the Ste20/PAK family of protein kinases have been shown to be involved in the cellular response to IR and other DNA-damaging agents.