397 research outputs found
Plasma Membrane Calcium ATPase Regulates Stoichiometry of CD4+ T-Cell Compartments
Immune responses involve mobilization of T cells within naïve and memory compartments.
Tightly regulated Ca2+ levels are essential for balanced immune outcomes. How Ca2+
contributes to regulating compartment stoichiometry is unknown. Here, we show that
plasma membrane Ca2+ ATPase 4 (PMCA4) is differentially expressed in human CD4+ T
compartments yielding distinct store operated Ca2+ entry (SOCE) profiles. Modulation of
PMCA4 yielded a more prominent increase of SOCE in memory than in naïve CD4+ T cell.
Interestingly, downregulation of PMCA4 reduced the effector compartment fraction and
led to accumulation of cells in the naïve compartment. In silico analysis and chromatin
immunoprecipitation point towards Ying Yang 1 (YY1) as a transcription factor regulating
PMCA4 expression. Analyses of PMCA and YY1 expression patterns following activation
and of PMCA promoter activity following downregulation of YY1 highlight repressive role of
YY1 on PMCA expression. Our findings show that PMCA4 adapts Ca2+ levels to cellular
requirements during effector and quiescent phases and thereby represent a potential
target to intervene with the outcome of the immune response
On the Connections between TRPM Channels and SOCE
Plasma membrane protein channels provide a passageway for ions to access the intracellular
milieu. Rapid entry of calcium ions into cells is controlled mostly by ion channels, while Ca2+-ATPases
and Ca2+ exchangers ensure that cytosolic Ca2+ levels ([Ca2+]cyt) are maintained at low (~100 nM)
concentrations. Some channels, such as the Ca2+-release-activated Ca2+ (CRAC) channels and voltagedependent Ca2+ channels (CACNAs), are highly Ca2+-selective, while others, including the Transient
Receptor Potential Melastatin (TRPM) family, have broader selectivity and are mostly permeable
to monovalent and divalent cations. Activation of CRAC channels involves the coupling between
ORAI1-3 channels with the endoplasmic reticulum (ER) located Ca2+ store sensor, Stromal Interaction
Molecules 1-2 (STIM1/2), a pathway also termed store-operated Ca2+ entry (SOCE). The TRPM
family is formed by 8 members (TRPM1-8) permeable to Mg2+, Ca2+, Zn2+ and Na+
cations, and is
activated by multiple stimuli. Recent studies indicated that SOCE and TRPM structure-function are
interlinked in some instances, although the molecular details of this interaction are only emerging.
Here we review the role of TRPM and SOCE in Ca2+ handling and highlight the available evidence
for this interaction
Redox regulation of calcium ion channels: Chemical and physiological aspects
Reactive oxygen species (ROS) are increasingly recognized as second messengers in many cellular processes.
While high concentrations of oxidants damage proteins, lipids and DNA, ultimately resulting in
cell death, selective and reversible oxidation of key residues in proteins is a physiological mechanism
that can transiently alter their activity and function. Defects in ROS producing enzymes cause disturbed
immune response and disease.
Changes in the intracellular free Ca2+ concentration are key triggers for diverse cellular functions. Ca2+
homeostasis thus needs to be precisely tuned by channels, pumps, transporters and cellular buffering
systems. Alterations of these key regulatory proteins by reversible or irreversible oxidation alter the
physiological outcome following cell stimulation. It is therefore necessary to understand which proteins
are regulated and if this regulation is relevant in a physiological- and/or pathophysiological context.
Because ROS are inherently difficult to identify and to measure, we first review basic oxygen redox
chemistry and methods of ROS detection with special emphasis on electron paramagnetic resonance
(EPR) spectroscopy. We then focus on the present knowledge of redox regulation of Ca2+ permeable ion
channels such as voltage-gated (CaV) Ca2+ channels, transient receptor potential (TRP) channels and Orai
channels
Supra-Molecular Assemblies of ORAI1 at Rest Precede Local Accumulation into Puncta after Activation
The Ca2+ selective channel ORAI1 and endoplasmic reticulum (ER)-resident STIM proteins
form the core of the channel complex mediating store operated Ca2+ entry (SOCE). Using liquid phase
electron microscopy (LPEM), the distribution of ORAI1 proteins was examined at rest and after SOCEactivation at nanoscale resolution. The analysis of over seven hundred thousand ORAI1 positions
revealed a number of ORAI1 channels had formed STIM-independent distinct supra-molecular
clusters. Upon SOCE activation and in the presence of STIM proteins, a fraction of ORAI1 assembled
in micron-sized two-dimensional structures, such as the known puncta at the ER plasma membrane
contact zones, but also in divergent structures such as strands, and ring-like shapes. Our results thus
question the hypothesis that stochastically migrating single ORAI1 channels are trapped at regions
containing activated STIM, and we propose instead that supra-molecular ORAI1 clusters fulfill an
amplifying function for creating dense ORAI1 accumulations upon SOCE-activation
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High glucose distinctively regulates Ca2+ influx in cytotoxic T lymphocytes upon target recognition and thapsigargin stimulation
In CTLs: High glucose‐culture enhances thapsigargin‐induced SOCE but decreases target recognition‐induced Ca2+ influx.
High glucose‐culture regulates expression of ORAIs and STIMs without affecting glucose uptake.
More high glucose‐cultured CTLs are prone to necrosis after execution of killing. (...
Acute Downregulation but Not Genetic Ablation of Murine MCU Impairs Suppressive Capacity of Regulatory CD4 T Cells
By virtue of mitochondrial control of energy production, reactive oxygen species (ROS)
generation, and maintenance of Ca2+ homeostasis, mitochondria play an essential role in modulating
T cell function. The mitochondrial Ca2+ uniporter (MCU) is the pore-forming unit in the main protein
complex mediating mitochondrial Ca2+ uptake. Recently, MCU has been shown to modulate Ca2+
signals at subcellular organellar interfaces, thus fine-tuning NFAT translocation and T cell activation.
The mechanisms underlying this modulation and whether MCU has additional T cell subpopulationspecific effects remain elusive. However, mice with germline or tissue-specific ablation of Mcu did
not show impaired T cell responses in vitro or in vivo, indicating that ‘chronic’ loss of MCU can
be functionally compensated in lymphocytes. The current work aimed to specifically investigate
whether and how MCU influences the suppressive potential of regulatory CD4 T cells (Treg). We show
that, in contrast to genetic ablation, acute siRNA-mediated downregulation of Mcu in murine Tregs
results in a significant reduction both in mitochondrial Ca2+ uptake and in the suppressive capacity
of Tregs, while the ratios of Treg subpopulations and the expression of hallmark transcription factors
were not affected. These findings suggest that permanent genetic inactivation of MCU may result in
compensatory adaptive mechanisms, masking the effects on the suppressive capacity of Tregs
Modulation of intracellular calcium signaling by microRNA-34a-5p
Adjusting intracellular calcium signaling is an important feature in the regulation of immune cell function and survival. Here we show that miR-34a-5p, a small non-coding RNA that is deregulated in many common diseases, is a regulator of store-operated Ca2+ entry (SOCE) and calcineurin signaling. Upon miR-34a-5p overexpression, we observed both a decreased depletion of ER calcium content and a decreased Ca2+ influx through Ca2+ release-activated Ca2+ channels. Based on an in silico target prediction we identified multiple miR-34a-5p target genes within both pathways that are implicated in the balance between T-cell activation and apoptosis including ITPR2, CAMLG, STIM1, ORAI3, RCAN1, PPP3R1, and NFATC4. Functional analysis revealed a decrease in Ca2+ activated calcineurin pathway activity measured by a reduced IL-2 secretion due to miR-34a-5p overexpression. Impacting SOCE and/or downstream calcineurin/NFAT signaling by miR-34a-5p offers a possible future approach to manipulate immune cells for clinical interventions
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