Effects of serum on calcium mobilization in the submandibular cell line A253

Human salivary gland cells express bradykinin receptors that modulate the expression of proinflammatory cytokines

Bradykinin is an important peptide modulator that affects the function of neurons and immune cells. However, there is no evidence of the bradykinin receptors and their functions in human salivary glands. Here we have identified and characterized bradykinin receptors on human submandibular gland cells. Both bradykinin B1 and B2 receptors are expressed on human submandibular gland cells, A253 cells, and HSG cells. Bradykinin increased the intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) in a concentration-dependent manner. Interestingly, a specific agonist of the B1 receptor did not have any effect on [Ca²⁺ ]_i in HSG cells, whereas specific agonists of the B2 receptor had a Ca²⁺ mobilizing effect. Furthermore, application of the B1 receptor antagonist, R715, did not alter the bradykinin-mediated increase in cytosolic Ca²⁺ , whereas the B2 receptor antagonist, HOE140, showed a strong inhibitory effect, which implies that bradykinin B2 receptors are functional in modulating the concentration of cytosolic Ca²⁺ . Bradykinin did not affect a carbachol-induced rise of [Ca²⁺ ]_i and did not modulate translocation of aquaporin-5. However, bradykinin did promote the expression of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), implying the role of bradykinin in salivary gland inflammation. These data suggest that bradykinin receptors are involved in Ca²⁺ signaling in human submandibular gland cells and serve a unique role, which is separate from that of other salivary gland G protein-coupled receptors.

Sphingosine-1-phosphate Signaling in Human Submandibular Cells

Sphingosine-1-phosphate (S1P) is a significant lipid messenger modulating many physiological responses. S1P plays a critical role in autoimmune disease and is suggested to be involved in Sjögren’s syndrome pathology. However, the mechanism of S1P signaling in salivary glands is unclear. Here we studied the effects of S1P on normal human submandibular gland cells. S1P increased levels of the intracellular Ca2+ concentration ([Ca2+]i), which was inhibited by pre-treatment with U73122 or 2-aminoethoxydiphenyl borate (2-APB). Pre-treated S1P did not inhibit subsequent carbachol-induced [Ca2+]i increase, which suggests that S1P and muscarinic signaling are independent of each other. S1P1, S1P2, and S1P3 receptors SphK1 and SphK2 were commonly expressed in human salivary gland cells. S1P, but not carbachol, induces the expression of interleukin-6 and Fas. Our results suggest that S1P triggers Ca2+ signaling and the apoptotic pathway in normal submandibular gland cells, which suggests in turn that S1P affects the progression of Sjögren’s syndrome.

Promoting effects of IL-13 on Ca2+ release and store-operated Ca2+ entry in airway smooth muscle cells

Th2 cytokine interleukin (IL)-13 plays a central role in the pathogenesis of allergic asthma. IL-13 exhibits a direct effect on airway smooth muscle cells (ASMCs) to cause airway hyperresponsiveness. IL-13 has been demonstrated to regulate Ca(2+) signaling in ASMCs, but the underlying mechanisms are not fully understood. Store-operated Ca(2+) entry (SOCE) plays an important role in regulating Ca(2+) signaling and cellular responses of ASMCs, whether IL-13 affects SOCE in ASMCs has not been reported. In this study, by using confocal Ca(2+) fluorescence imaging, we found that IL-13 (10 ng/ml) treatment increased basal intracellular Ca(2+) ([Ca(2+)](i)) level, Ca(2+) release and SOCE induced by SERCA inhibitor thapsigargin in rat bronchial smooth muscle cells. The glucocorticoid dexamethasone and the short-acting beta2 adrenergic agonist (beta2 agonist) salbutamol suppressed IL-13-augumented basal [Ca(2+)](i), Ca(2+) release and SOCE, whereas the long-acting beta2 agonist salmeterol had no effect on altered Ca(2+) signaling in IL-13-treated ASMCs. Membrane-permeable cAMP analog dibutyryl-cAMP (db-cAMP) similarly decreased Ca(2+) release and SOCE induced by thapsigargin in IL-13-treated ASMCs, confirmed a role of cAMP/PKA signaling pathway in the regulation of SOCE. IL-13 promoted the proliferation of ASMCs stimulated by serum; this effect was inhibited by nonspecific Ca(2+) channel blockers SKF-96365 and NiCl(2), by salmeterol, but not by salbutamol and dexamethasone. IL-13 treatment did not change the expression of SOC channel-associated molecules STIM1, Orai1 and TRPC1 at mRNA level. Our findings identified a promoting effect of IL-13 on Ca(2+) release and SOCE in ASMCs, which partially contributes to its effect on the proliferation of ASMCs; the differences of glucocorticoids and beta2 agonists in inhibiting Ca(2+) signal and proliferation potentiated by IL-13 suggest that these therapies of asthma may have distinct effect on the relief of airway contraction and remodeling in bronchial asthma.

JNK and ceramide kinase govern the biogenesis of lipid droplets through activation of group IVA phospholipase A2

The biogenesis of lipid droplets (LD) induced by serum depends on group IVA phospholipase A(2) (cPLA(2)alpha). This work dissects the pathway leading to cPLA(2)alpha activation and LD biogenesis. Both processes were Ca(2+)-independent, as they took place after pharmacological blockade of Ca(2+) transients elicited by serum or chelation with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester). The single mutation D43N in cPLA(2)alpha, which abrogates its Ca(2+) binding capacity and translocation to membranes, did not affect enzyme activation and formation of LD. In contrast, the mutation S505A did not affect membrane relocation of the enzyme in response to Ca(2+) but prevented its phosphorylation, activation, and the appearance of LD. Expression of specific activators of different mitogen-activated protein kinases showed that phosphorylation of cPLA(2)alpha at Ser-505 is due to JNK. This was confirmed by pharmacological inhibition and expression of a dominant-negative form of the upstream activator MEKK1. LD biogenesis was accompanied by increased synthesis of ceramide 1-phosphate. Overexpression of its synthesizing enzyme ceramide kinase increased phosphorylation of cPLA(2)alpha at Ser-505 and formation of LD, and its down-regulation blocked the phosphorylation of cPLA(2)alpha and LD biogenesis. These results demonstrate that LD biogenesis induced by serum is regulated by JNK and ceramide kinase.

Ultra low concentrations of morphine increase neurite outgrowth in cultured rat spinal cord and cerebral cortical neurons

The present study was undertaken to evaluate the effects of ultra low concentrations (10(-9) or 10(-14)M) of morphine on neurite elongation in cultured neurons dissociated from rat spinal cords and cerebral cortex. In fetal serum (FS) or fetal serum-free supplemented with cAMP media, the length of longest neurite was significantly increased by 10(-9) or 10(-14)M morphine. For example, 10(-14)M morphine increased neurite length by 24 +/- 0.5% and 27 +/- 0.3% in spinal cord neurons, and 18 +/- 0.2% and 17 +/- 0.6% in cortical neurons. Morphine (10(-6)M) had no significant effect on neurite length of spinal and cortical neurons. The relative frequency distribution of neurite length revealed 61 +/- 2.7% of spinal neurons and 48 +/- 2.6% of cortical neurons are responsive to ultra low concentrations of morphine. In the responsive populations, morphine (10(-14)M) enhanced the neurite outgrowth in spinal neurons by 58 +/- 0.9% and 48 +/- 1.2% and in cortical neurons by 31 +/- 0.6% and 28 +/- 0.9% in FS and cAMP-supplemented media, respectively. Pretreatment with naloxone did not prevent the morphine effect. The result shows that morphine at ultra low concentrations enhances neurite outgrowth of spinal and cortical neurons via a naloxone-independent mechanism.

Store-operated Ca2+ entry activates the CREB transcription factor in vascular smooth muscle

Ca2+-regulated gene transcription is a critical component of arterial responses to injury, hypertension, and tumor-stimulated angiogenesis. The Ca2+/cAMP response element binding protein (CREB), a transcription factor that regulates expression of many genes, is activated by Ca2+-induced phosphorylation. Multiple Ca2+ entry pathways may contribute to CREB activation in vascular smooth muscle including voltage-dependent Ca2+ channels and store-operated Ca2+ entry (SOCE). To investigate a role for SOCE in CREB activation, we measured CREB phosphorylation using immunofluorescence, intracellular Ca2+ levels using a fluorescence resonance energy transfer (FRET)-based Cameleon indicator, and c-fos transcription using RT-PCR. In this study, we report that SOCE activates CREB in both cultured smooth muscle cells and intact arteries. Depletion of intracellular Ca2+ stores with thapsigargin increased nuclear phospho-CREB levels, intracellular Ca2+ concentration, and transcription of c-fos. These effects were abolished by inhibiting SOCE through lowering extracellular Ca2+ concentration or by application of 2-aminoethoxydiphenylborate and Ni2+. Inhibition of Ca2+ influx through voltage-dependent Ca2+ channels using nimodipine partially blocked intact artery responses, but was without effect in cultured smooth muscle cells. Our findings indicate that Ca2+ entry through store-operated Ca2+ channels leads to CREB activation, suggesting that SOCE contributes to the regulation of gene expression in vascular smooth muscle.

Effects of radiation on Ca2+signaling in salivary epithelial cell lines transfected with Bcl-2 and Bcl-XL

The effects of radiation on the Ca2+ signaling system in HSY cells transfected with the Bcl-2 or Bcl-XL gene were studied. Bcl-2 overexpression did not alter carbachol (CCh)-elicited initial increase in cytosolic free Ca2+ concentrations ([Ca2+]i), but Bcl-XL overexpression dramatically reduced this response. Exposure to 10 Gy gamma-ray did not alter basal [Ca2+]i. By contrast, the CCh-stimulated initial [Ca2+]i increase was reduced at 0.5 and 4 h post-irradiation in all cell types and remained decreased at 24 h in wild-type and control-transfected cells, but recovered in Bcl-2- and Bcl-XL-transfectants. The formation of inositol 1,4,5-trisphosphate (IP3) in response to CCh at 4-h post-irradiation was decreased in wild-type and control-transfected cells, but not in Bcl-2 and Bcl-XL transfectants. The capacity of the IP3-sensitive Ca2+ store was significantly reduced by radiation in all cells except Bcl-XL transfectants. Ca2+ influx after stimulation with CCh was suppressed by exposure to radiation in wild-type and control-transfected cells, but not in Bcl-2- and Bcl-XL-transfectants. However, radiation enhanced Ca2+ influx activated by thapsigargin in all cell types. These results suggest that 1) radiation diminishes IP3 formation and Ca2+ release in response to CCh, but potentiates the store-operated Ca2+ influx; and 2) overexpression of Bcl-2 or Bcl-XL partially protects cells from radiation-induced inhibition of Ca2+ signaling.

Regulation of Ca(2+) signals in a parotid cell line Par-C5

The Ca(2+) signaling system in an established immortalized rat parotid acinar cell line, Par-C5, was examined using the Ca(2+)-sensitive fluorescent indicator fura-2 and by measuring inositol 1,4,5-trisphosphate (IP(3)) formation. Agonist-induced increase in intracellular Ca(2+) ([Ca(2+)](i)) by mobilization of intracellular stores and influx across the cell membrane was stimulated by acetylcholine (ACh) and ATP, whereas noradrenaline-(NA)-induced a small [Ca(2+)](i) increase mediated primarily by release from intracellular Ca(2+) stores. [Ca(2+)](i) increase by ACh and ATP was mediated through the phosphoinositide signal pathway since both agonists significantly increased 1,4,5-IP(3) formation and Ca(2+) mobilization was abolished by the phospholipase C inhibitor U73122. In Ca(2+)-free medium, ACh or ATP discharged the IP(3)-sensitive Ca(2+) store and essentially abolished subsequent [Ca(2+)](i) response to thapsigargin (TG). Exposure to ionomycin and monensin after TG induced a further mobilization of Ca(2+), suggesting IP(3)-insensitive stores are present. Furthermore, depletion of IP(3)-sensitive Ca(2+) stores by TG, ACh and ATP enhanced plasmalemmal Ca(2+)-entry pathways. Exposure to tumor necrosis factor-alpha (TNF-alpha), a cytokine associated with lymphocyte invasion of salivary epithelial cells in autoimmune disorders, significantly reduced ACh-stimulated Ca(2+) mobilization. TNF-alpha inhibitory effect on Ca(2+) mobilization was not directly due to an interaction on muscarinic receptors since ACh-induced 1,4,5-IP(3) formation was not altered. These results in the Par-C5 cell line indicate 1) [Ca(2+)](i) is regulated by muscarinic and P2Y-nucleotide receptors and partly by alpha(1)-adrenergic receptors; 2) IP(3)-sensitive and -insensitive Ca(2+) stores exist; 3) Ca(2+) influx activated by ACh, ATP or TG is mediated by the store-operated Ca(2+) entry pathway; and 4) muscarinic agonist-stimulated Ca(2+) mobilization is altered by the cytokine TNF-alpha.

Effects of low concentrations of paraoxon on Ca(2+) mobilization in a human parotid salivary cell-line HSY

The salivary gland is a target organ of organophosphate pesticides (OPs). Inhibition of acetylcholinesterase (AChE) by OPs leads to a decrease in acetylcholine (ACh) breakdown that results in overstimulation of muscarinic cholinergic receptors (mChR). However, OPs may also directly interact with downstream elements of the phosphoinositide (PI) signalling pathway coupled with mChR. The present study examined the effects of exposure to low concentrations of the OP paraoxon on inositol 1,4,5-trisphosphate (IP(3)) formation and Ca(2+) mobilization in response to ACh or ATP in the human parotid cell-line HSY. Exposure to 0.1 and 1 nM, but not 10 nM, paraoxon for 24 hr significantly elevated the basal cytosolic free Ca(2+) ([Ca(2+)](i)). This increase was abolished by atropine. Ca(2+) release from the IP(3)-sensitive store in response to ACh or ATP, a P2Y-nucleotide agonist, was significantly increased in cells pre-exposed to 0.1 nM paraoxon. However, IP(3) formation was inhibited by paraoxon but mChR expression was not altered. Although IP(3) receptor expression was not changed, Ca(2+) release elicited by IP(3) in streptolysin O toxin-permeabilized cells was significantly larger in cells pre-exposed to 0.1 nM paraoxon, suggesting that paraoxon increases the sensitivity of IP(3) receptors. Paraoxon exposure also induced a concentration-dependent reduction in the total capacity of intracellular Ca(2+) stores, whereas the capacity of the IP(3)-sensitive Ca(2+) store was not altered by paraoxon, as judged by discharging of the IP(3)-sensitive Ca(2+) store with thapsigargin (TG). Ca(2+) influx stimulated by ACh or ATP was also enhanced by 0.1 nM, but not 1 and 10 nM, paraoxon. On the other hand, Ca(2+) influx activated by TG was enhanced by exposure to all concentrations of paraoxon, indicating that paraoxon modulates the Ca(2+) entry pathway. These results suggest that low concentrations of paraoxon interact with elements of the PI pathway, enhancing Ca(2+) release and influx mechanisms.

Effects of forksolin, dibutyryl cAMP and H89 on Ca2+ mobilization in submandibular salivary cells of newborn rats

The effects of substances which affect cAMP or the cAMP-dependent protein kinase (PKA) on the inositol 1,4,5-trisphosphate (IP3) and Ca2+ responses to acetylcholine or thapsigargin were investigated in submandibular gland cells of newborn rats. Exposure to forskolin, dibutyryl cAMP or the PKA inhibitor H89 did not affect the formation of IP3 or the release of Ca2+ from intracellular stores elicited by acetylcholine. However, the thapsigargin-induced Ca2+ release was reduced by dibutyryl cAMP and enhanced by H89 in immature cells. Ca2+ influx activated by acetylcholine and thapsigargin was additive in immature cells but not in mature cells, suggesting the presence of a separate Ca2+ entry pathway in immature cells. Moreover, the acetylcholine-stimulated Ca2+ influx was significantly potentiated by forskolin and dibutyrylcAMP, but not by H89 in immature cells. In contrast, the thapsigargin-activated Ca2+ influx was dramatically enhanced by H89, but not by forskolin and dibutyrylcAMP in these cells. This modulation of Ca2+ mobilization by the test substances is different from that observed in mature submandibular cells in which forskolin, dibutyrylcAMP and H89 affected both IP3 formation and Ca2+ release in response to acetylcholine. Therefore, these results suggest differences in the interaction between the cAMP-PKA and the phosphoinositide-Ca2+ signalling pathways of mature and immature salivary cells. The modulation of Ca2+ influx by the cAMP-PKA pathway in immature cells is likely to play a part in the maturation of salivary cells.