Effects of modulators of cytosolic Ca2+ on phytohemagglutin-dependent Ca2+ response and interleukin-2 production in Jurkat cells

Acidic Ca2+ stores and immune-cell function

Acidic organelles act as intracellular Ca²⁺ stores; they actively sequester Ca²⁺ in their lumina and release it to the cytosol upon activation of endo-lysosomal Ca²⁺ channels. Recent data suggest important roles of endo-lysosomal Ca²⁺ channels, the Two-Pore Channels (TPCs) and the TRPML channels (mucolipins), in different aspects of immune-cell function, particularly impacting membrane trafficking, vesicle fusion/fission and secretion. Remarkably, different channels on the same acidic vesicles can couple to different downstream physiology. Endo-lysosomal Ca²⁺ stores can act under different modalities, be they acting alone (via local Ca²⁺ nanodomains around TPCs/TRPMLs) or in conjunction with the ER Ca²⁺ store (to either promote or suppress global ER Ca²⁺ release). These different modalities impinge upon functions as broad as phagocytosis, cell-killing, anaphylaxis, immune memory, thrombostasis, and chemotaxis.

Tweeters, Woofers and Horns: The Complex Orchestration of Calcium Currents in T Lymphocytes

Elevation of intracellular calcium ion (Ca²⁺) levels is a vital event that regulates T lymphocyte homeostasis, activation, proliferation, differentiation, and apoptosis. The mechanisms that regulate intracellular Ca²⁺ signaling in lymphocytes involve tightly controlled concinnity of multiple ion channels, membrane receptors, and signaling molecules. T cell receptor (TCR) engagement results in depletion of endoplasmic reticulum (ER) Ca²⁺ stores and subsequent sustained influx of extracellular Ca²⁺ through Ca²⁺ release-activated Ca²⁺ (CRAC) channels in the plasma membrane. This process termed store-operated Ca²⁺ entry (SOCE) involves the ER Ca²⁺ sensing molecule, STIM1, and a pore-forming plasma membrane protein, ORAI1. However, several other important Ca²⁺ channels that are instrumental in T cell function also exist. In this review, we discuss the role of additional Ca²⁺ channel families expressed on the plasma membrane of T cells that likely contribute to Ca²⁺ influx following TCR engagement, which include the TRP channels, the NMDA receptors, the P2X receptors, and the IP₃ receptors, with a focus on the voltage-dependent Ca²⁺ (Ca_V) channels.

Weft, warp, and weave: the intricate tapestry of calcium channels regulating T lymphocyte function

Calcium (Ca(2+)) is a universal second messenger important for T lymphocyte homeostasis, activation, proliferation, differentiation, and apoptosis. The events surrounding Ca(2+) mobilization in lymphocytes are tightly regulated and involve the coordination of diverse ion channels, membrane receptors, and signaling molecules. A mechanism termed store-operated Ca(2+) entry (SOCE), causes depletion of endoplasmic reticulum (ER) Ca(2+) stores following T cell receptor (TCR) engagement and triggers a sustained influx of extracellular Ca(2+) through Ca(2+) release-activated Ca(2+) (CRAC) channels in the plasma membrane. The ER Ca(2+) sensing molecule, stromal interaction molecule 1 (STIM1), and a pore-forming plasma membrane protein, ORAI1, have been identified as important mediators of SOCE. Here, we review the role of several additional families of Ca(2+) channels expressed on the plasma membrane of T cells that likely contribute to Ca(2+) influx following TCR engagement, particularly highlighting an important role for voltage-dependent Ca(2+) channels (CaV) in T lymphocyte biology.

Modulation of intracellular Cl- homeostasis by lectin-stimulation in Jurkat T lymphocytes

We investigated changes in intracellular Cl(-) concentration ([Cl(-)](i)) during lectin-induced activation and proliferation in human Jurkat T lymphocytes. [Cl(-)](i) was measured using Cl(-) fluorescence dye (N-(6-methoyquinolyl) acetoxy-acetyl-ester, MQAE) methods. Lectins, phytohemagglutinin and concanavalin A, dose-dependently increased [Cl(-)](i) and triggered intracellular Cl(-) oscillation in human Jurkat T lymphocytes. However, some mitochondria metabolism inhibitors, such as m-chlorocarbonylcyanide phenylhydrazone (CCP) and 2,4-dinitrophenol, increased [Cl(-)](i) without triggering any Cl(-) oscillation. Furthermore, both lectins and metabolism inhibitors-induced elevation in [Cl(-)](i) were blocked by removal of extracellular Cl(-) from perfusion solution or by application of anthracene-9-carboxylate, a blocker of Cl(-) channels. Since an extracellular Cl(-)-free condition and application of 9-AC also inhibited PHA-induced proliferation, we suggested that elevation of [Cl(-)](i) via activation of Cl(-) channels and increase in incidence of Cl(-) oscillation would play an important role in modulation of Jurkat T cell activation and proliferation.

Mechanisms involved in alpha6beta1-integrin-mediated Ca(2+) signalling

Contact of Jurkat T-lymphocytes with the extracellular matrix (ECM) protein laminin resulted in long-lasting alpha6beta1-integrin-mediated Ca(2+) signalling. Both Ca(2+) release from thapsigargin-sensitive Ca(2+) stores and capacitative Ca(2+) entry via Ca(2+) channels sensitive to SKF 96365 constitute important parts of this process. Inhibition of alpha6beta1-integrin-mediated Ca(2+) signalling by (1) the src kinase inhibitor PP2, (2) the PLC inhibitor U73122, and (3) the cyclic adenosine diphosphoribose (cADPR) antagonist 7-deaza-8-Br-cADPR indicate the involvement of src tyrosine kinases and the Ca(2+)-releasing second messengers D-myo-inositol 1,4,5-trisphosphate (InsP3) and cADPR.

Modulation of cytosolic calcium levels of human lymphocytes by yessotoxin, a novel marine phycotoxin

Yessotoxin (YTX) is a polyether toxin of marine origin that has been classified among the diarrheic shellfish poisoning (DSP) toxins group due to its lipophilic nature. However, unlike other DSP toxins, YTX does not produce diarrhea and its mechanisms of action are unknown. We studied the effect of YTX on the cytosolic calcium levels of freshly isolated human lymphocytes by means of fluorescence imaging microscopy. We showed that YTX produced a calcium influx through nifedipine and SKF 96365 (1-[beta-[3-(4-methoxyphenyl)propoxyl]-4-methoxyphenyl]-1H-imidazole hydrochloride)-sensitive channels. This Ca2+ entry was not affected by the DSP toxin okadaic acid, which inhibits protein phosphatases. In addition, YTX also produced an inhibition of capacitative calcium entry activated by thapsigargin or by preincubation in a Ca2+-free medium. This capacitative calcium entry was not sensitive to nifedipine. Furthermore, the inhibitory effect of YTX was dependent on the time of addition of the toxin. We suggest that YTX may interact with calcium channels in a way similar to that described for other polyether marine compounds such as brevetoxins and maitotoxin, although an involvement of other second messengers is also likely.

Macrophages and lymphocyte subpopulations in nifedipine- and cyclosporin A-associated human gingival overgrowth

BACKGROUND

Nifedipine and cyclosporin A (CsA) induce gingival overgrowth. Both drugs have immunomodulating effects. It has been suggested that altered immune response is associated with drug-induced gingival overgrowth. In this study, we evaluated whether there were differences in macrophages and lymphocyte subpopulations in human nifedipine- and CsA-associated gingival overgrowth as compared with those in normal gingiva.

METHODS

Biopsy samples of overgrown gingiva were obtained from 9 nifedipine-treated cardiac outpatients, 13 CsA-treated renal transplant recipients including 9 patients who were also receiving nifedipine, and 30 healthy control individuals undergoing dental treatment. Serial 5 microm thick cryostat sections were stained with mAbs for CD20 (B-pan), CD68 (macrophages), CD4 (T-helper/inducer), and CD8 (T-cytotoxic/suppressor) using an avidin-biotin-horseradish peroxidase complex method. Numbers of mAb-labeled and all nucleated cells were determined in 3 areas: the connective tissue beneath the sulcular epithelium, the middle connective tissue, and the connective tissue beneath the oral epithelium. Distributions of each type of cell were expressed as percentages of mAb-labeled cells in relation to total number of nucleated cells in a counting zone. Significances of differences between groups were tested by means of the Kruskal-Wallis test, and between pairs of results by means of the Mann-Whitney U-test.

RESULTS

The proportion of CD8-labeled cells was significantly higher in connective tissue beneath the sulcular epithelium in the nifedipine group than in the controls (P = 0.014). In both medicated groups, the proportions of CD68-labeled cells were higher in all counting zones than in the controls, but statistically significantly only in the nifedipine group in the connective tissue beneath the oral epithelium (P = 0.008). No intergroup differences were found with respect to CD4- and CD20-labeled cells. The CD4/CD8 ratio was significantly lower in connective tissue beneath the sulcular epithelium in the nifedipine group than in the controls (P= 0.013).

CONCLUSION

The results support the idea that immune response may be altered in drug-induced gingival overgrowth.

The antiinflammatory activity of topically applied novel calcium-channel antagonists

The antiinflammatory activities of two novel calcium-channel antagonists, AGN 190742 and AGN 190744, were evaluated in murine models of cutaneous inflammation. These 2(5H)-furanone ring compounds block both depolarization-dependent Ca2+ entry and receptor-mediated responses in GH3 cells. Topical application of AGN 190742 or AGN 190744 inhibits neutrophil infiltration and epidermal hyperplasia induced by repeated treatment of mouse skin with phorbol ester. AGN 190744 also is active in an arachidonic acid model of acute inflammation. These data suggest that topical application of calcium-channel antagonists can inhibit cutaneous inflammatory responses and that AGN 190742 and/or AGN 190744 may serve as useful pharmacological probes for examining these responses in vivo.