Cysteinyl leukotriene type I receptor desensitization sustains Ca2+-dependent gene expression

House dust mite allergens, store-operated Ca2+ channels and asthma

The house dust mite is the principal source of aero-allergen worldwide. Exposure to mite-derived allergens is associated with the development of asthma in susceptible individuals, and the majority of asthmatics are allergic to the mite. Mite-derived allergens are functionally diverse and activate multiple cell types within the lung that result in chronic inflammation. Allergens activate store-operated Ca2+ release-activated Ca2+ (CRAC) channels, which are widely expressed in multiple cell types within the lung that are associated with the pathogenesis of asthma. Opening of CRAC channels stimulates Ca2+ -dependent transcription factors, including nuclear factor of activated T cells and nuclear factor-κB, which drive expression of a plethora of pro-inflammatory cytokines and chemokines that help to sustain chronic inflammation. Here, I describe drivers of asthma, properties of mite-derived allergens, how the allergens are recognized by cells, the signalling pathways used by the receptors and how these are transduced into functional effects, with a focus on CRAC channels. In vivo experiments that demonstrate the effectiveness of targeting CRAC channels as a potential new therapy for treating mite-induced asthma are also discussed, in tandem with other possible approaches.

Plasma Membrane Ca2+ ATPase Activity Enables Sustained Store-operated Ca2+ Entry in the Absence of a Bulk Cytosolic Ca2+ Rise

In many cell types, the rise in cytosolic Ca2+ due to opening of Ca2+ release-activated Ca2+ (CRAC) channels drives a plethora of responses, including secretion, motility, energy production, and gene expression. The amplitude and time course of the cytosolic Ca2+ rise is shaped by the rates of Ca2+ entry into and removal from the cytosol. However, an extended bulk Ca2+ rise is toxic to cells. Here, we show that the plasma membrane Ca2+ ATPase (PMCA) pump plays a major role in preventing a prolonged cytosolic Ca2+ signal following CRAC channel activation. Ca2+ entry through CRAC channels leads to a sustained sub-plasmalemmal Ca2+ rise but bulk Ca2+ is kept low by the activity of PMCA4b. Despite the low cytosolic Ca2+, membrane permeability to Ca2+ is still elevated and Ca2+ continues to enter through CRAC channels. Ca2+-dependent NFAT activation, driven by Ca2+ nanodomains near the open channels, is maintained despite the return of bulk Ca2+ to near pre-stimulation levels. Our data reveal a central role for PMCA4b in determining the pattern of a functional Ca2+ signal and in sharpening local Ca2+ gradients near CRAC channels, whilst protecting cells from a toxic Ca2+ overload.

Role of the Purinergic P2Y2 Receptor in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH), group 1 pulmonary hypertension (PH), is a fatal disease that is characterized by vasoconstriction, increased pressure in the pulmonary arteries, and right heart failure. PAH can be described by abnormal vascular remodeling, hyperproliferation in the vasculature, endothelial cell dysfunction, and vascular tone dysregulation. The disease pathomechanisms, however, are as yet not fully understood at the molecular level. Purinergic receptors P2Y within the G-protein-coupled receptor family play a major role in fluid shear stress transduction, proliferation, migration, and vascular tone regulation in systemic circulation, but less is known about their contribution in PAH. Hence, studies that focus on purinergic signaling are of great importance for the identification of new therapeutic targets in PAH. Interestingly, the role of P2Y2 receptors has not yet been sufficiently studied in PAH, whereas the relevance of other P2Ys as drug targets for PAH was shown using specific agonists or antagonists. In this review, we will shed light on P2Y receptors and focus more on the P2Y2 receptor as a potential novel player in PAH and as a new therapeutic target for disease management.

Regulation of Store-Operated Ca2+ Entry by SARAF

Calcium (Ca²⁺) signaling plays a dichotomous role in cellular biology, controlling cell survival and proliferation on the one hand and cellular toxicity and cell death on the other. Store-operated Ca²⁺ entry (SOCE) by CRAC channels represents a major pathway for Ca²⁺ entry in non-excitable cells. The CRAC channel has two key components, the endoplasmic reticulum Ca²⁺ sensor stromal interaction molecule (STIM) and the plasma-membrane Ca²⁺ channel Orai. Physical coupling between STIM and Orai opens the CRAC channel and the resulting Ca²⁺ flux is regulated by a negative feedback mechanism of slow Ca²⁺ dependent inactivation (SCDI). The identification of the SOCE-associated regulatory factor (SARAF) and investigations of its role in SCDI have led to new functional and molecular insights into how SOCE is controlled. In this review, we provide an overview of the functional and molecular mechanisms underlying SCDI and discuss how the interaction between SARAF, STIM1, and Orai1 shapes Ca²⁺ signaling in cells.

The N terminus of Orai1 couples to the AKAP79 signaling complex to drive NFAT1 activation by local Ca2+ entry

To avoid conflicting and deleterious outcomes, eukaryotic cells often confine second messengers to spatially restricted subcompartments. The smallest signaling unit is the Ca2+ nanodomain, which forms when Ca2+ channels open. Ca2+ nanodomains arising from store-operated Orai1 Ca2+ channels stimulate the protein phosphatase calcineurin to activate the transcription factor nuclear factor of activated T cells (NFAT). Here, we show that NFAT1 tethered directly to the scaffolding protein AKAP79 (A-kinase anchoring protein 79) is activated by local Ca2+ entry, providing a mechanism to selectively recruit a transcription factor. We identify the region on the N terminus of Orai1 that interacts with AKAP79 and demonstrate that this site is essential for physiological excitation-transcription coupling. NMR structural analysis of the AKAP binding domain reveals a compact shape with several proline-driven turns. Orai2 and Orai3, isoforms of Orai1, lack this region and therefore are less able to engage AKAP79 and activate NFAT. A shorter, naturally occurring Orai1 protein that arises from alternative translation initiation also lacks the AKAP79-interaction site and fails to activate NFAT1. Interfering with Orai1-AKAP79 interaction suppresses cytokine production, leaving other Ca2+ channel functions intact. Our results reveal the mechanistic basis for how a subtype of a widely expressed Ca2+ channel is able to activate a vital transcription pathway and identify an approach for generation of immunosuppressant drugs.

Montelukast alleviates inflammation in experimental autoimmune encephalomyelitis by altering Th17 differentiation in a mouse model

Montelukast is a leukotriene receptor antagonist that is known to prevent allergic rhinitis and asthma. Blocking the Cysteinyl leukotriene receptor (CysLTR1), one of the primary receptors of leukotrienes, has been demonstrated to be efficacious in ameliorating experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), through disrupting chemotaxis of infiltrating T cells. However, the role of CysLTR1 in the pathogenesis of MS is not well understood. Here, we show that MS patients had higher expression of CysLTR1 in the circulation and central nervous system (CNS). The majority of CD4⁺ T cells expressed CysLTR1 in MS lesions. Among T-cell subsets, Th17 cells had the highest expression of CysLTR1, and blocking CysLTR1 signalling abrogated their development in vitro. Inhibition of CysLTR1 by montelukast suppressed EAE development in both a prophylactic and therapeutic manner and inhibited myelin loss in EAE mice. Similarly, the in vivo results showed that montelukast inhibited Th17 response in EAE mice and that Th17 cells treated with montelukast had reduced encephalitogenic in adoptive EAE. Our findings strongly suggest that targeting Th17 response by inhibiting CysLTR1 signalling could be a promising therapeutic strategy for the treatment of MS and CNS inflammatory diseases.

The Ca2+ export pump PMCA clears near-membrane Ca2+ to facilitate store-operated Ca2+ entry and NFAT activation

Ca²⁺ signals, which facilitate pluripotent changes in cell fate, reflect the balance between cation entry and export. We found that overexpression of either isoform of the Ca²⁺-extruding plasma membrane calcium ATPase 4 (PMCA4) pump in Jurkat T cells unexpectedly increased activation of the Ca²⁺-dependent transcription factor nuclear factor of activated T cells (NFAT). Coexpression of the endoplasmic reticulum-resident Ca²⁺ sensor stromal interaction molecule 1 (STIM1) with the PMCA4b splice variant further enhanced NFAT activity; however, coexpression with PMCA4a depressed NFAT. No PMCA4 splice variant dependence in STIM1 association was observed, whereas partner of STIM1 (POST) preferentially associated with PMCA4b over PMCA4a, which enhanced, rather than inhibited, PMCA4 function. A comparison of global and near-membrane cytosolic Ca²⁺ abundances during store-operated Ca²⁺ entry revealed that PMCA4 markedly depressed near-membrane Ca²⁺ concentrations, particularly when PMCA4b was coexpressed with STIM1. PMCA4b closely associated with both POST and the store-operated Ca²⁺ channel Orai1. Furthermore, POST knockdown increased the near-membrane Ca²⁺ concentration, inhibiting the global cytosolic Ca²⁺ increase. These observations reveal an unexpected role for POST in coupling PMCA4 to Orai1 to promote Ca²⁺ entry during T cell activation through Ca²⁺ disinhibition.

The whole-cell Ca2+ release-activated Ca2+ current, ICRAC , is regulated by the mitochondrial Ca2+ uniporter channel and is independent of extracellular and cytosolic Na. J Physiol 2019;598:1753-1773. [PMID: 30582626 PMCID: PMC7318671 DOI: 10.1113/jp276551]

Key points

Ca²⁺ entry through Ca²⁺ release‐activated Ca²⁺ channels activates numerous cellular responses. Under physiological conditions of weak intracellular Ca²⁺ buffering, mitochondrial Ca²⁺ uptake regulates CRAC channel activity.

Knockdown of the mitochondrial Ca²⁺ uniporter channel prevented the development of I_CRAC in weak buffer but not when strong buffer was used instead.

Removal of either extracellular or intra‐pipette Na⁺ had no effect on the selectivity, kinetics, amplitude, rectification or reversal potential of whole‐cell CRAC current.

Knockdown of the mitochondrial Na⁺–Ca²⁺ exchanger did not prevent the development of I_CRAC in strong or weak Ca²⁺ buffer.

Whole cell CRAC current is Ca²⁺‐selective.

Mitochondrial Ca²⁺ channels, and not Na⁺‐dependent transport, regulate CRAC channels under physiological conditions.

Abstract

Ca²⁺ entry through store‐operated Ca²⁺ release‐activated Ca²⁺ (CRAC) channels plays a central role in activation of a range of cellular responses over broad spatial and temporal bandwidths. Mitochondria, through their ability to take up cytosolic Ca²⁺, are important regulators of CRAC channel activity under physiological conditions of weak intracellular Ca²⁺ buffering. The mitochondrial Ca²⁺ transporter(s) that regulates CRAC channels is unclear and could involve the 40 kDa mitochondrial Ca²⁺ uniporter (MCU) channel or the Na⁺–Ca²⁺–Li⁺ exchanger (NCLX). Here, we have investigated the involvement of these mitochondrial Ca²⁺ transporters in supporting the CRAC current (I_CRAC) under a range of conditions in RBL mast cells. Knockdown of the MCU channel impaired the activation of I_CRAC under physiological conditions of weak intracellular Ca²⁺ buffering. In strong Ca²⁺ buffer, knockdown of the MCU channel did not inhibit I_CRAC development demonstrating that mitochondria regulate CRAC channels under physiological conditions by buffering of cytosolic Ca²⁺ via the MCU channel. Surprisingly, manipulations that altered extracellular Na⁺, cytosolic Na⁺ or both failed to inhibit the development of I_CRAC in either strong or weak intracellular Ca²⁺ buffer. Knockdown of NCLX also did not affect I_CRAC. Prolonged removal of external Na⁺ also had no significant effect on store‐operated Ca²⁺ entry, on cytosolic Ca²⁺ oscillations generated by receptor stimulation or on CRAC channel‐driven gene expression. In the RBL mast cell, Ca²⁺ flux through the MCU but not NCLX is indispensable for activation of I_CRAC.

Ca²⁺ entry through Ca²⁺ release‐activated Ca²⁺ channels activates numerous cellular responses. Under physiological conditions of weak intracellular Ca²⁺ buffering, mitochondrial Ca²⁺ uptake regulates CRAC channel activity.

Knockdown of the mitochondrial Ca²⁺ uniporter channel prevented the development of I_CRAC in weak buffer but not when strong buffer was used instead.

Removal of either extracellular or intra‐pipette Na⁺ had no effect on the selectivity, kinetics, amplitude, rectification or reversal potential of whole‐cell CRAC current.

Knockdown of the mitochondrial Na⁺–Ca²⁺ exchanger did not prevent the development of I_CRAC in strong or weak Ca²⁺ buffer.

Whole cell CRAC current is Ca²⁺‐selective.

Mitochondrial Ca²⁺ channels, and not Na⁺‐dependent transport, regulate CRAC channels under physiological conditions.

Roles of cysteinyl leukotrienes and their receptors in immune cell-related functions

The cysteinyl leukotrienes (cys-LTs), leukotriene C₄, (LTC₄), LTD₄, and LTE₄, are lipid mediators of inflammation. LTC₄ is the only intracellularly synthesized cys-LT through the 5-lipoxygenase and LTC₄ synthase pathway and after transport is metabolized to LTD₄ and LTE₄ by specific extracellular peptidases. Each cys-LT has a preferred functional receptor in vivo; LTD₄ to the type 1 cys-LT receptor (CysLT₁R), LTC₄ to CysLT₂R, and LTE₄ to CysLT₃R (OXGR1 or GPR99). Recent studies in mouse models revealed that there are multiple regulatory mechanisms for these receptor functions and each receptor plays a distinct role as observed in different mouse models of inflammation and immune responses. This review focuses on the integrated host responses to the cys-LT/CysLTR pathway composed of sequential ligands with preferred receptors as seen from mouse models. It also discusses potential therapeutic targets for LTC₄ synthase, CysLT₂R, and CysLT₃R.

STIM1 and Orai1 regulate Ca2+ microdomains for activation of transcription

Since calcium (Ca²⁺) regulates a large variety of cellular signaling processes in a cell's life, precise control of Ca²⁺ concentrations within the cell is essential. This enables the transduction of information via Ca²⁺ changes in a time-dependent and spatially defined manner. Here, we review molecular and functional aspects of how the store-operated Ca²⁺ channel Orai1 creates spatiotemporal Ca²⁺ microdomains. The architecture of this channel is unique, with a long helical pore and a six-fold symmetry. Energetic barriers within the Ca²⁺ channel pathway limit permeation to allow an extensive local Ca²⁺ increase in close proximity to the channel. The precise timing of the Orai1 channel function is controlled by direct binding to STIM proteins upon Ca²⁺ depletion in the endoplasmic reticulum. These induced Ca²⁺ microdomains are tailored to, and sufficient for, triggering long-term activation processes, such as transcription factor activation and subsequent gene regulation. We describe the principles of spatiotemporal activation of the transcription factor NFAT and compare its signaling characteristics to those of the autophagy regulating transcription factors, MITF and TFEB.

IL-33 Upregulates Cysteinyl Leukotriene Receptor Type 1 Expression in Human Peripheral Blood CD4+ T Lymphocytes

IL-33 and cysteinyl leukotrienes (cysLTs) are key components of asthma pathogenesis, and both contribute to the initiation and maintenance of the type 2 inflammatory environment. However, little is known about the potential interactions between the two mediators. In this work, we aimed at studying the regulation of expression of the cysLT receptors CysLT1 and CysLT2 by IL-33 in human PBLs. Our results show that the IL-33/ST2L axis increases CysLT1 but not CysLT2 expression in a concentration- and time-dependent manner in PBLs. IL-33-induced CysLT1 upregulation was observed at the protein but not at the mRNA level and was accompanied by an increase in LTD₄-induced calcium mobilization and migration of CD4⁺ T lymphocytes. We also show that purified naive CD4⁺ T lymphocytes expressed ST2L and responded to IL-33 in the absence of Ag or TCR stimulation, suggesting a mechanism independent of Ag presentation. These results contribute to expanding our knowledge in the field of IL-33 by proposing a new mode of action of the cytokine on T cells and by extending its role to the regulation of naive T cell trafficking, therefore reinforcing its interest as a potential therapeutic target for the treatment of asthma.

Sequential forward and reverse transport of the Na+ Ca2+ exchanger generates Ca2+ oscillations within mitochondria

Mitochondrial Ca²⁺ homoeostasis regulates aerobic metabolism and cell survival. Ca²⁺ flux into mitochondria is mediated by the mitochondrial calcium uniporter (MCU) channel whereas Ca²⁺ export is often through an electrogenic Na⁺–Ca²⁺ exchanger. Here, we report remarkable functional versatility in mitochondrial Na⁺–Ca²⁺ exchange under conditions where mitochondria are depolarised. Following physiological stimulation of cell-surface receptors, mitochondrial Na⁺–Ca²⁺ exchange initially operates in reverse mode, transporting cytosolic Ca²⁺ into the matrix. As matrix Ca²⁺ rises, the exchanger reverts to its forward mode state, extruding Ca²⁺. Transitions between reverse and forward modes generate repetitive oscillations in matrix Ca²⁺. We further show that reverse mode Na⁺–Ca²⁺ activity is regulated by the mitochondrial fusion protein mitofusin 2. Our results demonstrate that reversible switching between transport modes of an ion exchanger molecule generates functionally relevant oscillations in the levels of the universal Ca²⁺ messenger within an organelle.

Mitochondrial Ca²⁺ homoeostasis is tightly regulated and export of Ca²⁺ is mediated by an Na⁺Ca²⁺ exchanger. Here authors show that in depolarised mitochondria the exchanger initially operates in reverse mode, transporting cytosolic Ca²⁺ into the matrix before it reverts to its forward mode state.

Spatial Ca2+ profiling: decrypting the universal cytosolic Ca2+ oscillation

Stimulation of cell-surface receptors that couple to phospholipase C to generate the second messenger inositol trisphosphate often evokes repetitive oscillations in cytosolic Ca²⁺ . Signalling information is encoded in both the amplitude and frequency of the Ca²⁺ spikes. Recent studies have revealed that the spatial profile of the oscillation also imparts signalling power; Ca²⁺ microdomains near store-operated CRAC channels in the plasma membrane and inositol trisphosphate-gated channels in the endoplasmic reticulum both signal to distinct downstream targets. Spatial profiling therefore increases the transduction power of the universal oscillatory cytosolic Ca²⁺ signal.

Regulation of CRAC channels by Ca2+-dependent inactivation

CRAC channels are a major route for Ca²⁺ influx in eukaryotic cells. The channels show prominent Ca²⁺-dependent inactivation through two spatially and temporally distinct mechanisms: fast inactivation, which develops over milliseconds and is triggered by Ca²⁺ near the mouth of the channel and slow inactivation, which arises over tens of seconds and requires a rise in global cytosolic Ca²⁺. Slow inactivation is controlled physiologically by Ca²⁺ uptake into mitochondria through the MCU. Site-directed mutagenesis studies on STIM1 and Orai1 have led to new molecular insight into how fast inactivation occurs. This review describes properties and molecular mechanisms that contribute to these important Ca²⁺-dependent inhibitory pathways.

Control of NFAT Isoform Activation and NFAT-Dependent Gene Expression through Two Coincident and Spatially Segregated Intracellular Ca2+ Signals

Excitation-transcription coupling, linking stimulation at the cell surface to changes in nuclear gene expression, is conserved throughout eukaryotes. How closely related coexpressed transcription factors are differentially activated remains unclear. Here, we show that two Ca2+-dependent transcription factor isoforms, NFAT1 and NFAT4, require distinct sub-cellular InsP3 and Ca2+ signals for physiologically sustained activation. NFAT1 is stimulated by sub-plasmalemmal Ca2+ microdomains, whereas NFAT4 additionally requires Ca2+ mobilization from the inner nuclear envelope by nuclear InsP3 receptors. NFAT1 is rephosphorylated (deactivated) more slowly than NFAT4 in both cytoplasm and nucleus, enabling a more prolonged activation phase. Oscillations in cytoplasmic Ca2+, long considered the physiological form of Ca2+ signaling, play no role in activating either NFAT protein. Instead, effective sustained physiological activation of NFAT4 is tightly linked to oscillations in nuclear Ca2+. Our results show how gene expression can be controlled by coincident yet geographically distinct Ca2+ signals, generated by a freely diffusible InsP3 message.

The role of Orai-STIM calcium channels in melanocytes and melanoma

Calcium signalling within normal and cancer cells regulates many important cellular functions such as migration, proliferation, differentiation and cytokine secretion. Store operated Ca(2+) entry (SOCE) via the Ca(2+) release activated Ca(2+) (CRAC) channels, which are composed of the plasma membrane based Orai channels and the endoplasmic reticulum stromal interaction molecules (STIMs), is a major Ca(2+) entry route in many cell types. Orai and STIM have been implicated in the growth and metastasis of multiple cancers; however, while their involvement in cancer is presently indisputable, how Orai-STIM-controlled Ca(2+) signals affect malignant transformation, tumour growth and invasion is not fully understood. Here, we review recent studies linking Orai-STIM Ca(2+) channels with cancer, with a particular focus on melanoma. We highlight and examine key molecular players and the signalling pathways regulated by Orai and STIM in normal and malignant cells, we expose discrepancies, and we reflect on the potential of Orai-STIMs as anticancer drug targets. Finally, we discuss the functional implications of future discoveries in the field of Ca(2+) signalling.

Ca2+ Influx through Store-operated Calcium Channels Replenishes the Functional Phosphatidylinositol 4,5-Bisphosphate Pool Used by Cysteinyl Leukotriene Type I Receptors

Oscillations in cytoplasmic Ca²⁺ concentration are a universal mode of signaling following physiological levels of stimulation with agonists that engage the phospholipase C pathway. Sustained cytoplasmic Ca²⁺ oscillations require replenishment of the membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PIP₂), the source of the Ca²⁺-releasing second messenger inositol trisphosphate. Here we show that cytoplasmic Ca²⁺ oscillations induced by cysteinyl leukotriene type I receptor activation run down when cells are pretreated with Li⁺, an inhibitor of inositol monophosphatases that prevents PIP₂ resynthesis. In Li⁺-treated cells, cytoplasmic Ca²⁺ signals evoked by an agonist were rescued by addition of exogenous inositol or phosphatidylinositol 4-phosphate (PI4P). Knockdown of the phosphatidylinositol 4-phosphate 5 (PIP5) kinases α and γ resulted in rapid loss of the intracellular Ca²⁺ oscillations and also prevented rescue by PI4P. Knockdown of talin1, a protein that helps regulate PIP5 kinases, accelerated rundown of cytoplasmic Ca²⁺ oscillations, and these could not be rescued by inositol or PI4P. In Li⁺-treated cells, recovery of the cytoplasmic Ca²⁺ oscillations in the presence of inositol or PI4P was suppressed when Ca²⁺ influx through store-operated Ca²⁺ channels was inhibited. After rundown of the Ca²⁺ signals following leukotriene receptor activation, stimulation of P2Y receptors evoked prominent inositol trisphosphate-dependent Ca²⁺ release. Therefore, leukotriene and P2Y receptors utilize distinct membrane PIP₂ pools. Our findings show that store-operated Ca²⁺ entry is needed to sustain cytoplasmic Ca²⁺ signaling following leukotriene receptor activation both by refilling the Ca²⁺ stores and by helping to replenish the PIP₂ pool accessible to leukotriene receptors, ostensibly through control of PIP5 kinase activity.

Ca(2+) Channel Re-localization to Plasma-Membrane Microdomains Strengthens Activation of Ca(2+)-Dependent Nuclear Gene Expression

In polarized cells or cells with complex geometry, clustering of plasma-membrane (PM) ion channels is an effective mechanism for eliciting spatially restricted signals. However, channel clustering is also seen in cells with relatively simple topology, suggesting it fulfills a more fundamental role in cell biology than simply orchestrating compartmentalized responses. Here, we have compared the ability of store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels confined to PM microdomains with a similar number of dispersed CRAC channels to activate transcription factors, which subsequently increase nuclear gene expression. For similar levels of channel activity, we find that channel confinement is considerably more effective in stimulating gene expression. Our results identify a long-range signaling advantage to the tight evolutionary conservation of channel clustering and reveal that CRAC channel aggregation increases the strength, fidelity, and reliability of the general process of excitation-transcription coupling.

Microarray analysis of tick-infested skin in resistant and susceptible cattle confirms the role of inflammatory pathways in immune activation and larval rejection

Tick bites promote activation of an inflammatory process that is influenced by bovine genetic composition and its history of previous exposure. Taurine and indicine breeds are known to differ on its immune response development against Rhipicephalus microplus. Nevertheless, further investigation about the complex molecular pathways involved in the development of immune response to tick infestation in cattle presenting the same genetic background is mandatory. The aim of this work was to access the early immune response triggered by R. microplus larvae attachment in previously selected resistant and susceptible animals in a bovine F2 population derived from Gyr (Bos indicus)×Holstein (Bos taurus) crosses. Microarray data analysis of RNA samples from tick infested skin was used to evaluate the gene expression at 0, 24 and 48h after R. microplus larvae attachment. Our experimental design allowed us to deeply explore the immune response related to R. microplus infestation avoiding the innate differences between these breeds. The differentially expressed genes found reveal networks and pathways that suggest a key role of lipid metabolism in inflammation control and impairment of tick infestation in resistant animals. Acute phase response also seems to be impaired in susceptible animals. These results provide new insights about early immune response against ticks and raise the possibility of using immunomodulation processes to improve and develop novel tools for tick control.

Mitochondrial calcium uniporter MCU supports cytoplasmic Ca2+ oscillations, store-operated Ca2+ entry and Ca2+-dependent gene expression in response to receptor stimulation

Ca²⁺ flux into mitochondria is an important regulator of cytoplasmic Ca²⁺ signals, energy production and cell death pathways. Ca²⁺ uptake can occur through the recently discovered mitochondrial uniporter channel (MCU) but whether the MCU is involved in shaping Ca²⁺ signals and downstream responses to physiological levels of receptor stimulation is unknown. Here, we show that modest stimulation of leukotriene receptors with the pro-inflammatory signal LTC₄ evokes a series of cytoplasmic Ca²⁺ oscillations that are rapidly and faithfully propagated into mitochondrial matrix. Knockdown of MCU or mitochondrial depolarisation, to reduce the driving force for Ca²⁺ entry into the matrix, prevents the mitochondrial Ca²⁺ rise and accelerates run down of the oscillations. The loss of cytoplasmic Ca²⁺ oscillations appeared to be a consequence of enhanced Ca²⁺-dependent inactivation of InsP₃ receptors, which arose from the loss of mitochondrial Ca²⁺ buffering. Ca²⁺ dependent gene expression in response to leukotriene receptor activation was suppressed following knockdown of the MCU. In addition to buffering Ca²⁺ release, mitochondria also sequestrated Ca²⁺ entry through store-operated Ca²⁺ channels and this too was prevented following loss of MCU. MCU is therefore an important regulator of physiological pulses of cytoplasmic Ca²⁺.

Caveolin-1 alters the pattern of cytoplasmic Ca2+ oscillations and Ca2+-dependent gene expression by enhancing leukotriene receptor desensitization

Cytoplasmic Ca²⁺ oscillations constitute a widespread signaling mode and are often generated in response to stimulation of G protein-coupled receptors that activate phospholipase C. In mast cells, repetitive Ca²⁺ oscillations can be evoked by modest activation of cysteinyl leukotriene type I receptors by the physiological trigger, leukotriene C₄. The Ca²⁺ oscillations arise from regenerative Ca²⁺ release from inositol 1,4,5-trisphosphate-sensitive stores followed by Ca²⁺ entry through store-operated Ca²⁺ channels, and the latter selectively activate the Ca²⁺-dependent transcription factor NFAT. The cysteinyl leukotriene type I receptors desensitize through negative feedback by protein kinase C, which terminates the oscillatory Ca²⁺ response. Here, we show that the scaffolding protein caveolin-1 has a profound effect on receptor-driven Ca²⁺ signals and downstream gene expression. Overexpression of caveolin-1 increased receptor-phospholipase C coupling, resulting in initially larger Ca²⁺ release transients of longer duration but which then ran down quickly. NFAT-activated gene expression, triggered in response to the Ca²⁺ signal, was also reduced by caveolin-1. Mutagenesis studies revealed that these effects required a functional scaffolding domain within caveolin-1. Mechanistically, the increase in Ca²⁺ release in the presence of caveolin-1 activated protein kinase C, which accelerated homologous desensitization of the leukotriene receptor and thereby terminated the oscillatory Ca²⁺ response. Our results reveal that caveolin-1 is a bimodal regulator of receptor-dependent Ca²⁺ signaling, which fine-tunes the spatial and temporal profile of the Ca²⁺ rise and thereby its ability to activate the NFAT pathway.

Mitochondrial impairment increases FL-PINK1 levels by calcium-dependent gene expression

Mutations of the PTEN-induced kinase 1 (PINK1) gene are a cause of autosomal recessive Parkinson's disease (PD). This gene encodes a mitochondrial serine/threonine kinase, which is partly localized to mitochondria, and has been shown to play a role in protecting neuronal cells from oxidative stress and cell death, perhaps related to its role in mitochondrial dynamics and mitophagy. In this study, we report that increased mitochondrial PINK1 levels observed in human neuroblastoma SH-SY5Y cells after carbonyl cyanide m-chlorophelyhydrazone (CCCP) treatment were due to de novo protein synthesis, and not just increased stabilization of full length PINK1 (FL-PINK1). PINK1 mRNA levels were significantly increased by 4-fold after 24h. FL-PINK1 protein levels at this time point were significantly higher than vehicle-treated, or cells treated with CCCP for 3h, despite mitochondrial content being decreased by 29%. We have also shown that CCCP dissipated the mitochondrial membrane potential (Δψm) and induced entry of extracellular calcium through L/N-type calcium channels. The calcium chelating agent BAPTA-AM impaired the CCCP-induced PINK1 mRNA and protein expression. Furthermore, CCCP treatment activated the transcription factor c-Fos in a calcium-dependent manner. These data indicate that PINK1 expression is significantly increased upon CCCP-induced mitophagy in a calcium-dependent manner. This increase in expression continues after peak Parkin mitochondrial translocation, suggesting a role for PINK1 in mitophagy that is downstream of ubiquitination of mitochondrial substrates. This sensitivity to intracellular calcium levels supports the hypothesis that PINK1 may also play a role in cellular calcium homeostasis and neuroprotection.

Prostaglandin E2 deficiency causes a phenotype of aspirin sensitivity that depends on platelets and cysteinyl leukotrienes

Aspirin-exacerbated respiratory disease (AERD) is characterized by asthma, tissue eosinophilia, overproduction of cysteinyl leukotrienes (cysLTs), and respiratory reactions to nonselective cyclooxygenase (COX) inhibitors. Ex vivo studies suggest that functional abnormalities of the COX-2/microsomal prostaglandin (PG)E2 synthase-1 system may underlie AERD. We demonstrate that microsomal PGE2 synthase-1 null mice develop a remarkably AERD-like phenotype in a model of eosinophilic pulmonary inflammation. Lysine aspirin (Lys-ASA)-challenged PGE2 synthase-1 null mice exhibit sustained increases in airway resistance, along with lung mast cell (MC) activation and cysLT overproduction. A stable PGE2 analog and a selective E prostanoid (EP)2 receptor agonist blocked the responses to Lys-ASA by ∼90%; EP3 and EP4 agonists were also active. The increases in airway resistance and MC products were blocked by antagonists of the type 1 cysLT receptor or 5-lipoxygenase, implying that bronchoconstriction and MC activation were both cysLT dependent. Lys-ASA-induced cysLT generation and MC activation depended on platelet-adherent granulocytes and T-prostanoid (TP) receptors. Thus, lesions that impair the inducible generation of PGE2 remove control of platelet/granulocyte interactions and TP-receptor-dependent cysLT production, permitting MC activation in response to COX-1 inhibition. The findings suggest applications of antiplatelet drugs or TP receptor antagonists for the treatment of AERD.

Differential regulation of cysteinyl leukotriene receptor signaling by protein kinase C in human mast cells

Cysteinyl leukotrienes (cys-LTs) are a group of lipid mediators that are potent bronchoconstrictors, powerful inducers of vascular leakage and potentiators of airway hyperresponsiveness. Cys-LTs play an essential role in asthma and are synthesized as well as activated in mast cells (MCs). Cys-LTs relay their effects mainly through two known GPCRs, CysLT₁R and CysLT₂R. Although protein kinase C (PKC) isoforms are implicated in the regulation of CysLT₁R function, neither the role of PKCs in cys-LT-dependent MC inflammatory signaling nor the involvement of specific isoforms in MC function are known. Here, we show that PKC inhibition augmented LTD₄ and LTE₄-induced calcium influx through CysLT₁R in MCs. In contrast, inhibition of PKCs suppressed c-fos expression as well MIP1β generation by cys-LTs. Interestingly, cys-LTs activated both PKCα and PKCε isoforms in MC. However, knockdown of PKCα augmented cys-LT mediated calcium flux, while knockdown of PKCε attenuated cys-LT induced c-fos expression and MIP1β generation. Taken together, these results demonstrate for the first time that cys-LT signaling downstream of CysLT₁R in MCs is differentially regulated by two distinct PKCs which modulate inflammatory signals that have significant pathobiologic implications in allergic reactions and asthma pathology.

Regulation of Transcriptional Networks by PKC Isozymes: Identification of c-Rel as a Key Transcription Factor for PKC-Regulated Genes

BACKGROUND

Activation of protein kinase C (PKC), a family of serine-threonine kinases widely implicated in cancer progression, has major impact on gene expression. In a recent genome-wide analysis of prostate cancer cells we identified distinctive gene expression profiles controlled by individual PKC isozymes and highlighted a prominent role for PKCδ in transcriptional activation.

PRINCIPAL FINDINGS

Here we carried out a thorough bioinformatics analysis to dissect transcriptional networks controlled by PKCα, PKCδ, and PKCε, the main diacylglycerol/phorbol ester PKCs expressed in prostate cancer cells. Despite the remarkable differences in the patterns of transcriptional responsive elements (REs) regulated by each PKC, we found that c-Rel represents the most frequent RE in promoters regulated by all three PKCs. In addition, promoters of PKCδ-regulated genes were particularly enriched with REs for CREB, NF-E2, RREB, SRF, Oct-1, Evi-1, and NF-κB. Most notably, by using transcription factor-specific RNAi we were able to identify subsets of PKCδ-regulated genes modulated by c-Rel and CREB. Furthermore, PKCδ-regulated genes condensed under the c-Rel transcriptional regulation display significant functional interconnections with biological processes such as angiogenesis, inflammatory response, and cell motility.

CONCLUSION/SIGNIFICANCE

Our study identified candidate transcription factors in the promoters of PKC regulated genes, in particular c-Rel was found as a key transcription factor in the control of PKCδ-regulated genes. The deconvolution of PKC-regulated transcriptional networks and their nodes may greatly help in the identification of PKC effectors and have significant therapeutics implications.

STIM proteins, Orai1 and gene expression

Cytoplasmic Ca(2+) is an universal intracellular messenger that activates cellular responses over a broad temporal range, from neurotransmitter release to cell growth and proliferation. Inherent to the use of the multifarious Ca(2+) signal is the question of specificity: how can some Ca(2+)-dependent responses be activated in a cell and not others? A rise in cytoplasmic Ca(2+) can evoke a response either by binding directly to the target (as occurs with certain Ca(2+)-activated K(+) and Cl(-) channels, for example) or through recruitment of intermediary proteins, such as calmodulin and troponin C. A substantial body of evidence has now established that Ca(2+)-binding proteins differ both in their affinities for Ca(2+) and in their on- and off-rates for Ca(2+) binding/unbinding. Furthermore, different Ca(2+)-binding proteins often occupy distinct locations within the cell. Therefore, the size, kinetics and spatial profile of a cytoplasmic Ca(2+) signal are all important in determining which Ca(2+)-dependent response will be activated, when and for how long.

The leukotrienes: immune-modulating lipid mediators of disease

The leukotrienes are important lipid mediators with immune modulatory and proinflammatory properties. Classical bioactions of leukotrienes include chemotaxis, endothelial adherence, and activation of leukocytes, chemokine production, as well as contraction of smooth muscles in the microcirculation and respiratory tract. When formed in excess, these compounds play a pathogenic role in several acute and chronic inflammatory diseases, such as asthma, rheumatoid arthritis, and inflammatory bowel disease. An increasing number of diseases have been linked to inflammation implicating the leukotrienes as potential mediators. For example, recent investigations using genetic, morphological, and biochemical approaches have pointed to the involvement of leukotrienes in cardiovascular diseases including atherosclerosis, myocardial infarction, stroke, and abdominal aortic aneurysm. Moreover, new insights have changed our previous notion of leukotrienes as mediators of inflammatory reactions to molecules that can fine-tune the innate and adaptive immune response. Here, we review the most recent understanding of the leukotriene cascade with emphasis on recently identified roles in immune reactions and pathophysiology.

Coupling of P2Y receptors to G proteins and other signaling pathways

P2Y receptors are G protein-coupled receptors (GPCRs) that are activated by adenine and uridine nucleotides and nucleotide sugars. There are eight subtypes of P2Y receptors (P2Y₁, P2Y₂, P2Y₄, P2Y₆, P2Y₁₁, P2Y₁₂, P2Y₁₃, and P2Y₁₄), which activate intracellular signaling cascades to regulate a variety of cellular processes, including proliferation, differentiation, phagocytosis, secretion, nociception, cell adhesion, and cell migration. These signaling cascades operate mainly by the sequential activation or deactivation of heterotrimeric and monomeric G proteins, phospholipases, adenylyl and guanylyl cyclases, protein kinases, and phosphodiesterases. In addition, there are numerous ion channels, cell adhesion molecules, and receptor tyrosine kinases that are modulated by P2Y receptors and operate to transmit an extracellular signal to an intracellular response.