Dexamethasone induces rapid tyrosine-phosphorylation of ZAP-70 in Jurkat cells

Beyond Corticoresistance, A Paradoxical Corticosensitivity Induced by Corticosteroid Therapy in Pediatric Acute Lymphoblastic Leukemias

Known as a key effector in relapse of acute lymphoblastic leukemia (ALL), resistance to drug-induced apoptosis, is tightly considered one of the main prognostic factors for the disease. ALL cells are constantly developing cellular strategies to survive and resist therapeutic drugs. Glucocorticoids (GCs) are one of the most important agents used in the treatment of ALL due to their ability to induce cell death. The mechanisms of GC resistance of ALL cells are largely unknown and intense research is currently focused on this topic. Such resistance can involve different cellular and molecular mechanisms, including the modulation of signaling pathways involved in the regulation of proliferation, apoptosis, autophagy, metabolism, epigenetic modifications and tumor suppressors. Recently, several studies point to the paradoxical role of GCs in many survival processes that may lead to therapy-induced resistance in ALL cells, which we called "paradoxical corticosensitivity". In this review, we aim to summarize all findings on cell survival pathways paradoxically activated by GCs with an emphasis on previous and current knowledge on gene expression and signaling pathways.

Malignant ascite-derived extracellular vesicles inhibit T cell activity by upregulating Siglec-10 expression

Background and purpose: To evade immune defense, cancer cells can employ extracellular vesicles (EVs) to inhibit the anti-tumor activity of lymphocytes in the tumor microenvironment. However, the mechanisms and key molecules that mediate the effects of EVs on lymphocytes are unclear.

Patients and methods: We used Quantibody^® Human Cytokine Antibody Array 440 to determine the tumor immunity-related cytokine profile of peripheral blood lymphocytes (PBLs) stimulated with EVs derived from peritoneal washes or malignant ascites. We detected 21 upregulated and 27 downregulated proteins, including the immunosuppressive receptors Siglec-10, SLAM, PD-1, and TIM-3.

Results: Flow cytometry analysis of PBLs or ovarian cancer ascites suggested that Siglec-10 expression on CD3+ T cells was higher in ovarian cancer patients than in healthy controls and in the malignant ascites of ovarian cancer patients than in their blood. Moreover, the expression of CD24, the Siglec-10 ligand, was associated with tumor stage and cancer cell metastasis. Finally, compared to the benign peritoneal wash-derived EVs, the malignant EVs significantly upregulated Siglec-10 expression on Jurkat T cells, inhibited the protein kinase C activity induced by phorbol 12-myristate 13-acetate and ionomycin, and impaired the phosphorylation of the tyrosine kinase ZAP-70 activated by crosslinking with an anti-CD3 antibody.

Conclusion: The EVs secreted by malignant ovarian cells upregulated Siglec-10 expression on T cells and impaired T cell activation in the tumor microenvironment. We believe that a comprehensive understanding of the regulation of Siglec-10 and CD24 by malignant EVs has clinical importance, as it will aid in the development of better immunotherapeutic strategies for ovarian cancer.

Nongenomic glucocorticoid effects and their mechanisms of action in vertebrates

Glucocorticoids (GC) act on multiple organ systems to regulate a variety of physiological processes in vertebrates. Due to their immunosuppressive and anti-inflammatory actions, glucocorticoids are an attractive target for pharmaceutical development. Accordingly, they are one of the most widely prescribed classes of therapeutics. Through the classical mechanism of steroid action, glucocorticoids are thought to mainly affect gene transcription, both in a stimulatory and suppressive fashion, regulating de novo protein synthesis that subsequently leads to the physiological response. However, over the past three decades multiple lines of evidence demonstrate that glucocorticoids may work through rapid, nonclassical mechanisms that do not require alterations in gene transcription or translation. This review assimilates evidence across the vertebrate taxa on the diversity of nongenomic actions of glucocorticoids and the membrane-associated cellular mechanisms that may underlie rapid glucocorticoid responses to include potential binding sites characterized to date.

Glucocorticoid-independent modulation of GR activity: Implications for immunotherapy

Pharmacological doses of glucocorticoids (GCs), acting via the glucocorticoid receptor (GR) to repress inflammation and immune function, remain the most effective therapy in the treatment of inflammatory and immune diseases. Since many patients on GC therapy exhibit GC resistance and severe side-effects, much research is focused on developing more selective GCs and combination therapies, with greater anti-inflammatory potency. GCs mediate their classical genomic transcriptional effects by binding to the cytoplasmic GR, followed by nuclear translocation and modulation of transcription of target genes by direct DNA binding of the GR or its tethering to other transcription factors. Recent evidence suggests, however, that the responses mediated by the GR are much more complex and involve multiple parallel mechanisms integrating simultaneous signals from other receptors, both in the absence and presence of GCs, to shift the sensitivity of a target cell to GCs. The level of cellular stress, immune activation status, or the cell cycle phase may be crucial for determining GC sensitivity and GC responsiveness as well as subcellular localization of the GR and GR levels. Central to the development of new drugs that target GR signaling alone or as add-on therapies, is an in-depth understanding of the molecular mechanisms of GC-independent GR desensitization, priming and activation of the unliganded GR, as well as synergy and cross-talk with other signaling pathways. This review will discuss the information currently available on these topics and their relevance to immunotherapy, as well as identify unanswered questions and future areas of research.

Effects of Glucocorticoids in the Immune System

Glucocorticoids (GCs) are steroid hormones with widespread effects. They control intermediate metabolism by stimulating gluconeogenesis in the liver, mobilize amino acids from extra hepatic tissues, inhibit glucose uptake in muscle and adipose tissue, and stimulate fat breakdown in adipose tissue. They also mediate stress response. They exert potent immune-suppressive and anti-inflammatory effects particularly when administered pharmacologically. Understanding these diverse effects of glucocorticoids requires a detailed knowledge of their mode of action. Research over the years has uncovered several details on the molecular action of this hormone, especially in immune cells. In this chapter, we have summarized the latest findings on the action of glucocorticoids in immune cells with a view of identifying important control points that may be relevant in glucocorticoid therapy.

Lipid raft- and protein kinase C-mediated synergism between glucocorticoid- and gonadotropin-releasing hormone signaling results in decreased cell proliferation

Cross-talk between the glucocorticoid receptor (GR) and other receptors is emerging as a mechanism for fine-tuning cellular responses. We have previously shown that gonadotropin-releasing hormone (GnRH) ligand-independently activates the GR and synergistically modulates glucocorticoid-induced transcription of an endogenous gene in LβT2 pituitary gonadotrope precursor cells. Here, we investigated GR and GnRH receptor (GnRHR) cross-talk that involves co-localization with lipid rafts in LβT2 cells. We report that the GnRHR and a small population of the GR co-localize with the lipid raft protein flotillin-1 (Flot-1) at the plasma membrane and that the GR is present in a complex with Flot-1, independent of the presence of ligands. We found that the SGK-1 gene is up-regulated by Dex and GnRH alone, whereas a combination of both ligands resulted in a synergistic increase in SGK-1 mRNA levels. Using siRNA-mediated knockdown and antagonist strategies, we show that the gene-specific synergistic transcriptional response requires the GR, GnRHR, and Flot-1 as well as the protein kinase C pathway. Interestingly, although several GR cofactors are differentially recruited to the SGK-1 promoter in the presence of Dex and GnRH, GR levels remain unchanged compared with Dex treatment alone, suggesting that lipid raft association of the GR has a role in enhancing its transcriptional output in the nucleus. Finally, we show that Dex plus GnRH synergistically inhibit cell proliferation in a manner dependent on SGK-1 and Flot-1. Collectively the results support a mechanism whereby GR and GnRHR cross-talk within Flot-1-containing lipid rafts modulates cell proliferation via PKC activation and SGK-1 up-regulation.

Nongenomic actions of adrenal steroids in the central nervous system

Mineralocorticoids and glucocorticoids are steroid hormones that are released by the adrenal cortex in response to stress and hydromineral imbalance. Historically, adrenocorticosteroid actions are attributed to effects on gene transcription. More recently, however, it has become clear that genome-independent pathways represent an important facet of adrenal steroid actions. These hormones exert nongenomic effects throughout the body, although a significant portion of their actions are specific to the central nervous system. These actions are mediated by a variety of signalling pathways, and lead to physiologically meaningful events in vitro and in vivo. We review the nongenomic effects of adrenal steroids in the central nervous system at the levels of behaviour, neural system activity, individual neurone activity and subcellular signalling activity. A clearer understanding of adrenal steroid activity in the central nervous system will lead to a better ability to treat human disease as well as reduce the side-effects of the steroid treatments already in use.

Emerging pathways of non-genomic glucocorticoid (GC) signalling in T cells

In the last decade new glucocorticoid (GC)-signalling mechanisms have emerged. The evolving field of non-genomic GC actions was precipitated from two major directions: (i) some rapid/acute clinical GC applications could not be explained based on the relatively slowly appearing genomic GC action and (ii) accumulating evidence came to light about the discrepancy in the apoptosis sensitivity and GR expression of thymocytes and other lymphoid cell types. Herein, we attempt to sample the latest information in the field of non-genomic GC signalling in T cells, and correlate it with results from our laboratory. We discuss some aspects of the regulation of thymocyte apoptosis by GCs, paying special interest to the potential role(s) of mitochondrial GR signalling. The interplay between the T cell receptor (TcR) and glucocorticoid receptor (GR) signalling pathways is described in more detail, focusing on ZAP-70, which is a novel target of rapid GC action.

Mitochondrial translocation of the glucocorticoid receptor in double-positive thymocytes correlates with their sensitivity to glucocorticoid-induced apoptosis

Glucocorticoid receptor (GR) signaling plays an important role in the selection and apoptosis of thymocytes. Besides nuclear translocation, mitochondrial translocation of the ligand-bound GR in lymphoid cells was also shown, which might determine glucocorticoid (GC)-induced apoptosis sensitivity. In the present work, we followed the ligand-induced GR trafficking in CD4+CD8+ double-positive (DP) thymocytes. Using confocal microscopy, we found that upon short-term in vitro GC analog [dexamethasone (DX)] treatment, the GR translocates into the mitochondria but not into the nucleus in DP cells. We also analyzed the GR redistribution in cytosolic, nuclear and mitochondrial fractions of unseparated thymocytes by western blot and confirmed that in DX-treated cells a significant fraction of the GR translocates into the mitochondria. DX reduced the mitochondrial membrane potential of DP cells within 30 min, measured by flow cytometry, which refers to a direct modulatory activity of mitochondrial GR translocation. The abundant mitochondrial GR found in DP cells well correlates with their high GC-induced apoptosis sensitivity.

Steroid effects on ZAP-70 and SYK in relation to apoptosis in poor prognosis chronic lymphocytic leukemia

There is resurgent interest in glucocorticoids (GCs) in the treatment of poor prognosis chronic lymphocytic leukemia (CLL). Little is known however on how GCs induce apoptosis in CLL. Methylprednisolone (MP) induces apoptosis in ZAP-70 positive CLL more readily than in ZAP-70 negative CLL, which is in contrast to the effects of radiation and chemotherapy. The increased GC sensitivity of ZAP-70+ CLL was studied in relation to the expression status of ZAP-70 and the related signal transducing tyrosine kinase SYK. Both ZAP-70 and SYK were downregulated by GC treatment. Moreover, SYK was dephosphorylated by the phosphatase PTP1B of which the expression and translation levels were induced by GCs. Inhibition of PTP1B successfully restored ZAP-70 expression and SYK phosphorylation but did not interfere with GC-induced apoptosis. Therefore, the downregulation of ZAP-70 and P-SYK per se during treatment with GCs is not sufficient to induce apoptosis, and different mechanisms must therefore be responsible for the increased steroid sensitivity of ZAP-70+ CLL.

Zap70 Signaling Pathway Mediates Glucocorticoid Receptor-Dependent Transcriptional Activation: Role in the Regulation of Annexin 1 Expression in T Cells

We have recently shown that Zap70 is important in retinoid receptor-dependent transactivation in T lymphocytes. We report that Zap70 signaling is also essential in dexamethasone-inducible glucocorticoid receptor (GR)-mediated transactivation in T lymphocytes. Zap70-negative Jurkat T cells and cells reconstituted with inactive Zap70 exhibited attenuated GR-mediated activation as compared with Zap70 reconstituted and wild-type cells. Lck-lacking Jurkat cells were also found to show markedly reduced GR activation, and reconstitution with Lck restored the activation. Gene array and protein analysis showed that the level of annexin 1 (ANXA1), an anti-inflammatory protein known to be induced and released by the glucocorticoid action, was significantly reduced in Zap70-negative and Zap70-inactive Jurkat cells as compared with wild-type cells. Lck-lacking cells were also found to have markedly reduced ANXA1 levels and reconstitution with Lck restored the ANXA1 expression. RNA interference-induced knockdown of Zap70 or Lck in Jurkat cells and peripheral blood T lymphocytes also resulted in the loss of ANXA1 expression. Transcriptional analysis revealed that dexamethasone-inducible GR-mediated activation of ANXA1 promoter was compromised in both Zap70 knocked down peripheral blood T cells and Zap70 or Lck-deficient/Lck-inactive Jurkat cells, indicating an essential role of these kinases in GR-mediated ANXA1 promoter activation in T lymphocytes. To summarize, our data demonstrate an important role for Zap70 signaling in GR-mediated transactivation in T lymphocytes and also point out a crucial role of this kinase in maintaining normal ANXA1 levels in these cells.

Developmental shift in TcR-mediated rescue of thymocytes from glucocorticoid-induced apoptosis

Glucocorticoid hormone (GC) production by thymic epithelial cells influences TcR signalling in DP thymocytes and modifies their survival. In the present work, we focused on exploring details of GC effects on DP thymocyte apoptosis with or without parallel TcR activation in AND transgenic mice, carrying TcR specific for pigeon cytochrome C, in vivo. Here we show that the glucocorticoid receptor (GR) protein level was the lowest in DP thymocytes, and it was slightly down-regulated by GC analogue, anti-CD3, PCC and combined treatments as well. Exogenous GC analogue treatment or TcR stimulation alone lead to marked DP cell depletion, coupled with a significant increase of early apoptotic cell ratio (AnnexinV staining), marked abrogation of the mitochondrial function in DP cells (CMXRos staining), and significant decrease in the Bcl-2(high) DP thymocyte numbers, respectively. On the other hand, the simultaneous exposure to these two proapototic signals effectively reversed all the above-described changes. The parallel analysis of CD4 SP cell numbers, AnnexinV, CMXRos, Bcl-2 and GR stainings revealed, that the GR and TcR signals were not antagonistic on the mature thymocytes. These data provide experimental evidence in TcR transgenic mice, in vivo, that when TcR activation and GR signals are present simultaneously, they rescue double positive thymocytes from programmed cell death. The two separate signalling pathways merge in DP thymocytes at such important apoptosis regulating points as the Bcl-2 and GR, showing that their balanced interplay is essential in DP cell survival.

Intermolecular relations between the glucocorticoid receptor, ZAP-70 kinase, and Hsp-90

The glucocorticoid receptor (GR) participates in both genomic and non-genomic glucocorticoid hormone (GC) actions by interacting with other cytoplasmic signalling proteins. Previously, we have shown that high dose Dexamethasone (DX) treatment of Jurkat cells causes tyrosine phosphorylation of ZAP-70 within 5 min in a GR-dependent manner. By using co-immunoprecipitation and confocal microscopy, here we demonstrate that the liganded GR physically associates with ZAP-70, in addition to its phosphorylation changes. The association of the ligand-bound GR and ZAP-70 was also observed in HeLa cells transfected with ZAP-70, suggesting that this co-clustering is independent of lymphocyte specific factors. Furthermore, the ZAP-70 was found to also co-precipitate with Hsp-90 chaperone both in Jurkat and transgenic HeLa cells, independent of the presence of DX. These findings raise the possibility that ZAP-70 may serve as an important link between GC and TcR-induced signaling, thereby transmitting non-genomic GC action in T-cells.

Still waiting for the toll?

Multicellular organisms including invertebrates and vertebrates live in various habitats that may be aquatic or terrestrial where they are constantly exposed to deleterious pathogens. These include viruses, bacteria, fungi, and parasites. They have evolved various immunodefense mechanisms that may protect them from infection by these microorganisms. These include cellular and humoral responses and the level of differentiation of the response parallels the evolutionary development of the species. The first line of innate immunity in earthworms is the body wall that prevents the entrance of microbes into the coelomic cavity that contains fluid in which there are numerous leukocyte effectors of immune responses. When this first barrier is broken, a series of host responses is set into motion activating the leukocytes and the coelomic fluid. The responses are classified as innate, natural, non-specific, non-anticipatory, non-clonal (germ line) in contrast to the vertebrate capacity that is considered adaptive, induced, specific, anticipatory and clonal (somatic). Specific memory is associated with the vertebrate response and there is information that the innate response of invertebrates may under certain conditions possess specific memory. The invertebrate system when challenged affects phagocytosis, encapsulation, agglutination, opsonization, clotting and lysis. At least two major leukocytes, small and large mediate lytic reactions against several tumor cell targets. Destruction of tumor cells in vitro shows that phagocytosis and natural killer cell responses are distinct properties of these leukocytes. This has prompted newer searches for immune function and regulation in other systems. The innate immune system of the earthworm has been analyzed for more than 40 years with every aspect examined. However, there are no known entire sequences of the earthworm as exists in these other invertebrates. Because the earthworm lives in soil and has been utilized as a successful monitor for pollution, there are studies that reveal up and down regulation of responses in the immune system after exposure to a variety of environmental pollutants. Moreover, there are partial sequences that appear in earthworms after exposure to environmental pollutants such as cadmium and copper. There are now attempts to define the AHR receptor crucial for intracellular signaling after exposure to pollutants, but without linking the signals to changes in the immune system. There are several pathways for signal transduction, including JAK/STAT, TOLL, TRAF PIP3, known in invertebrates and vertebrates. For resistance to pathogens, conserved signal transduction components are required and these include a Toll/IL-1 receptor domain adaptor protein that functions upstream of a conserved p38 MAP kinase pathway. This pathway may be an ancestral innate immune signaling pathway found in a putative common ancestor of nematodes, arthropods and even vertebrates. It could also help us to link pollution, innate immunity and transduction in earthworms.