Gene expression profiling of Ca2+-atpase inhibitor DTBHQ and antigen-stimulated RBL-2H3 mast cells

Use of humanized rat basophilic leukemia reporter cell lines as a diagnostic tool for detection of allergen-specific IgE in allergic patients: time for a reappraisal?

The interaction between allergens and specific IgE is at the heart of the allergic response and as such lies at the center of techniques used for diagnosis of allergic sensitization. Although serological tests are available, in vivo tests such as double-blind placebo-controlled food challenges (DBPCFC) and skin prick test (SPT) associated to the patients' clinical history are still the main guides to clinicians in many practices around the world. More recently, complex protein arrays and basophil activation tests, requiring only small amounts of whole blood, have been developed and refined, but are yet to enter clinical practice. Similarly, the use of rat basophilic leukemia (RBL) cell lines for detection of allergen-specific IgE has been made possible by stable transfection of the human FcεRI α chain into this cell line more than 20 years ago, but has not found widespread acceptance among clinicians. Here, we review the perceived limitations of diagnostic applications of humanized RBL systems. Furthermore, we illustrate how the introduction of reporter genes into humanized RBL cells is able to overcome most of these limitations, and has the potential to become a new powerful tool to complement the armamentarium of allergists. A demonstration of the usefulness of humanized RBL reporter systems for elucidation of complex IgE sensitization patterns against wheat proteins and a section on the use of fluorescence-based reporter systems in combination with allergen arrays close the review.

Deciphering the structure and function of FcεRI/mast cell axis in the regulation of allergy and anaphylaxis: a functional genomics paradigm

Allergy and anaphylaxis are inflammatory disorders caused by immune reactions mainly induced by immunoglobulin-E that signal through the high-affinity FcεRI receptor to release the inflammatory mediators from innate immune cells. The FcεRI/mast cell axis is potently involved in triggering various intracellular signaling molecules to induce calcium release from the internal stores, induction of transcription factors such as NF-kB, secretion of various cytokines as well as lipid mediators, and degranulation, resulting in the induction of allergy and anaphylaxis. In this review, we discuss various cellular and molecular mechanisms triggered through FcεRI/mast cell axis in allergy and anaphylaxis with a special emphasis on the functional genomics paradigm.

A convenient and sensitive allergy test: IgE crosslinking-induced luciferase expression in cultured mast cells

Background

For the detection of allergen-specific IgE in sera, solid-phase IgE-binding assays like the CAP test are commonly used. Although such immunochemical methods are very sensitive, they frequently produce false positives. Degranulation of the human IgE receptor (FcεRI)-transfected rat mast cell (RBL) lines seems to be a possible indicator for human IgE, but spontaneous mediator release from these cells in the presence of human sera is not negligible.

Methods

The nuclear factor of activated T-cells (NFAT)-responsive luciferase reporter gene was stably transfected into human FcεRI-expressing RBL-SX38 cells. One established clone (RS-ATL8) was sensitized with 1 : 100 dilution of sera from patients with egg white allergy and then stimulated with purified or a crude extract of egg white allergen.

Results

Sensitization with 15 pg/ml IgE was sufficient to detect IgE crosslinking–induced luciferase expression (EXiLE) by anti-IgE stimulation. Allergen-specific EXiLE was elicited by as little as 1 fg/ml of egg white protein without cytotoxicity. There was a good correlation between results with EXiLE and oral food challenge tests on patients with egg allergy (P = 0.001687, Fisher's exact test). The measured values of EXiLE and the CAP test also correlated well (R = 0.9127, Spearman's test).

Conclusion

The EXiLE test using RS-ATL8 cells is a promising in vitro IgE test to evaluate the biological activity of the binding between IgE and allergens.

Enhancement of FcɛRI-mediated degranulation response in the rat basophilic leukemia cell line RBL2H3 by the fluorosurfactants perfluorooctanoic acid and perfluorooctane sulfonate

The effect of two fluorosurfactants, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), on degranulation of rat basophilic leukemia RBL2H3 cells was investigated. PFOA and PFOS promoted IgE-mediated release of granule components of RBL2H3 cells at 10-300μM. At low concentrations (<30μM), the fluorosurfactants failed to induce degranulation, but promoted IgE-mediated degranulation without affecting cell viability. The absence of extracellular Ca(2+) removed the promoting effect of the fluorosurfactants on IgE-mediated degranulation. On the other hand, the fluorosurfactants at high concentrations (>100μM) induced release of granule components without IgE-mediated activation in parallel with cell death. Pretreatment of tetradecanoyl-phorbol-acetate, a protein kinase C activator, inhibited both the promoting effect of the fluorosurfactants at low concentration on IgE-mediated degranulation and cell death-associated granule component release by high concentration of the fluorosurfactants. These findings indicate that PFOA and PFOS affect granule component release of mast cells by two different mechanisms, namely enhancement of active degranulation machinery at low concentrations and cell lysis at high concentrations.

eIF2alpha kinases GCN2 and PERK modulate transcription and translation of distinct sets of mRNAs in mouse liver

In eukaryotes, selective derepression of mRNA translation through altered utilization of upstream open reading frames (uORF) or internal ribosomal entry sites (IRES) regulatory motifs following exposure to stress is regulated at the initiation stage through the increased phosphorylation of eukaryotic initiation factor 2 on its alpha-subunit (eIF2alpha). While there is only one known eIF2alpha kinase in yeast, general control nonderepressible 2 (GCN2), mammals have evolved to express at least four: GCN2, heme-regulated inhibitor kinase (HRI), double-stranded RNA-activated protein kinase (PKR), and PKR-like endoplasmic reticulum-resident kinase (PERK). So far, the main known distinction among these four kinases is their activation in response to different acute stressors. In the present study, we used the in situ perfused mouse liver model and hybridization array analyses to assess the general translational response to stress regulated by two of these kinases, GCN2 and PERK, and to differentiate between the downstream effects of activating GCN2 versus PERK. The resulting data showed that at least 2.5% of mouse liver mRNAs are subject to derepressed translation following stress. In addition, the data demonstrated that eIF2alpha kinases GCN2 and PERK differentially regulate mRNA transcription and translation, which in the latter case suggests that increased eIF2alpha phosphorylation is not sufficient for derepression of translation. These findings open an avenue for more focused future research toward groups of mRNAs that code for the early cellular stress response proteins.

Genome-wide gene expression profiling of human mast cells stimulated by IgE or FcepsilonRI-aggregation reveals a complex network of genes involved in inflammatory responses

Background

Mast cells are well established effectors of IgE-triggered allergic reactions and immune responses to parasitic infections. Recent studies indicate that mast cells may play roles in adaptive and innate immunity, suggesting an innovative view of the regulation of immune responses. Here, we profiled the transcriptome of human mast cells sensitized with IgE alone, or stimulated by FcεRI aggregation.

Results

Our data show that among 8,793 genes examined, 559 genes are differentially regulated in stimulated mast cells when compared with resting/unstimulated mast cells. The major functional categories of upregulated genes include cytokines, chemokines, and other genes involved in innate and adaptive immune-responses. We observed the increased expression of over 63 gene-transcripts following IgE-sensitization alone. Our data was validated using Real-Time-PCR; ELISA and western blot. We confirmed that IgE alone does not trigger mast cell-immediate responses, such as calcium signals, degranulation or protein-phosphorylation.

Conclusion

This report represents a substantial advance in our understanding of the genome wide effects triggered by "passive sensitization" or active stimulation of human mast cells, supporting mast cells' potential involvement in a wide range of inflammatory responses.

Increased expression of genes linked to FcepsilonRI Signaling and to cytokine and chemokine production in Lyn-deficient mast cells

Cross-linking the high-affinity IgE receptor, FcepsilonRI, on mast cells activates signaling pathways leading to the release of preformed inflammatory mediators and the production of cytokines and chemokines associated with allergic disorders. Bone marrow-derived mast cells (BMMCs) from Lyn-deficient (Lyn-/-) mice are hyperresponsive to FcepsilonRI cross-linking with multivalent Ag. Previous studies linked the hyperresponsive phenotype in part to increased Fyn kinase activity and reduced SHIP phosphatase activity in the Lyn-/- BMMCs in comparison with wild-type (WT) cells. In this study, we compared gene expression profiles between resting and Ag-activated WT and Lyn-/- BMMCs to identify other factors that may contribute to the hyperresponsiveness of the Lyn-/- cells. Among genes implicated in the positive regulation of FcepsilonRI signaling, mRNA for the tyrosine kinase, Fyn, and for several proteins contributing to calcium regulation are more up-regulated following Ag stimulation in Lyn-/- BMMCs than in WT BMMCs. Conversely, mRNA for the low-affinity IgG receptor (FcgammaRIIB), implicated in negative regulation of FcepsilonRI-mediated signaling, is more down-regulated in Ag-stimulated Lyn-/- BMMCs than in WT BMMCs. Genes coding for proinflammatory cytokines and chemokines (IL-4, IL-6, IL-13, CSF, CCL1, CCL3, CCL5, CCL7, CCL9, and MIP1beta) are all more highly expressed in Ag-stimulated Lyn-/- mast cells than in WT cells. These microarray data identify Lyn as a negative regulator in Ag-stimulated BMMCs of the expression of genes linked to FcepsilonRI signaling and also to the response pathways that lead to allergy and asthma.

Gene expression profiling of dexamethasone-treated RBL-2H3 cells: induction of anti-inflammatory molecules

Glucocorticoids are well known for their anti-inflammatory effect through the regulation of gene expression in many types of immune cells, including mast cells. However, the genes that are involved in suppression of mast cell-mediated inflammation by glucocorticoids have not been fully identified. Therefore, we examined the dexamethasone (Dex)-responsive genes in RBL-2H3 mast cells using a high-density oligonucleotide microarray technique. Gene expression profiling revealed that the antigen-induced up-regulation of pro-inflammatory factors, including monocyte chemoattractant protein-1, was markedly inhibited by 100 nM Dex. On the other hand, Dex treatment itself caused the substantial up-regulation of many genes, including phenylethanolamine-N-methyl transferase (PNMT) and cytokine-inducible SH2-containing protein (CISH), in the mast cells. The expression of these two genes significantly increased 6 h after Dex exposure and lasted for more than 24 h. Considering that PNMT is the rate-determining enzyme in epinephrine synthesis and that CISH is a suppressor of cytokine signaling, these Dex-responsive genes may be potential anti-inflammatory factors. Thus, gene expression profiling suggested that Dex might exert its anti-inflammatory effect through two pathways in mast cells: the suppression and induction of potentially pro- and anti-inflammatory factors, respectively.

Gene expression profiles in HEK-293 cells with low or high store-operated calcium entry: can regulatory as well as regulated genes be identified?

Gene expression profiles were generated using cDNA microarray technology for clones of human embryonic kidney (HEK)-293 cells selected to have either high or low levels of store-operated Ca2+ entry (SOCE). For five high clones, three low clones, and control HEK-293 cells, duplicate Affymetrix U133A human gene arrays were run after extraction of total RNA from cells growing in the presence of serum. Of the approximately 22,000 genes represented on the microarray, 58 genes had readings at least twofold higher, while 32 genes had readings at least twofold lower, in all five high SOCE clones compared with control HEK-293 cells. In the low SOCE clones, 92 genes had readings at least twofold higher, while 58 genes had readings at least twofold lower, than in HEK-293 cells. Microarray results were confirmed for 18 selected genes by real-time RT-PCR analysis; for six of those genes, predicted changes in the low SOCE clone were confirmed by an alternative method, monitoring mRNA levels in HEK-293 with SOCE decreased by expression of small interfering (si)RNA to canonical transient receptor potential protein-1. Genes regulated by SOCE are involved in signal transduction, transcription, apoptosis, metabolism, and membrane transport. These data provide insight into the physiological role of SOCE. In addition, a potential regulator of SOCE, insulin receptor substrate (IRS)-2, has been identified. A reduction of IRS-2 levels by siRNA methods in two high clones dramatically reduced SOCE, whereas overexpression of IRS-2 in a low SOCE clone elevated SOCE.