Investigation of nanotopography on SOCE mediated cell migration via live-cell : Imaging on opaque implant surface

The exploration of cell response to nanotopography has attracted considerable attentions for years. This article focuses on the influence of nanotopography on the intracellular Ca2+ dynamics, the most ubiquitous but ignored second messenger. The classic titanium nanotubes (NT) were fabricated by anodization to formulate nanoporous surfaces. Firstly, the store operative calcium entry (SOCE) in endoplasmic reticulum (ER) and functional Ca2+ release-activated Ca2+ (CRAC) channels were significantly enhanced on NT surfaces that revealed by live-cell Ca2+ imaging and fluorescence resonance energy transfer (FRET) identification of orai1-stim1 connection. To investigate the potential implication of Ca2+ elevation, the dynamic cell migration trajectory was monitored by a self-made holder, which could not only be suitable for the opaque implant surface but also guarantee the focus fields identical during samples shifting. The cell migration on NT surface was more vigorous and rapid, which was correlated with higher focal adhesion proteins expression, Ca2+-dependent calpain activity and stim1 level. In conclusion, this study has confirmed the novel ER Ca2+ hemostasis pathway on nanosurfaces and its crucial role in cell migration regulation, which may help for more biofavorable implant surface design.

ATP promotes resident CD34+ cell migration mainly through P2Y2-Stim1-ERK/p38 pathway

Extracellular adenosine triphosphate (ATP) is one of the most abundant biochemical constitutes within the stem cell microenvironment and is postulated to play critical roles in cell migration. However, it is unclear whether ATP regulates the cell migration of CD34+ vascular wall-resident stem/progenitor cells (VW-SCs) and participates in angiogenesis. Therefore, the biological mechanisms of cell migration mediated by ATP was determined by in vivo subcutaneous matrigel plug assay, ex vivo aortic ring assay, in vitro transwell migration assay, and other molecular methods. In the present study, ATP dose-dependently promoted CD34+ VW-SCs migration, which was more obviously attenuated by inhibiting or knocking down P2Y2 than P2Y6. Furthermore, it was confirmed that ATP potently promoted the migration of resident CD34+ cells from cultured aortic artery rings and differentiation into endothelial cells in matrigel plugs by using inducible lineage tracing Cd34-CreERT2; R26-tdTomato mice, whereas P2Y2 and P2Y6 blocker greatly inhibited the effect of ATP. In addition, ATP enhanced the protein expression of stromal interaction molecule 1 (STIM1) on cell membrane, blocking the calcium release-activated calcium (CRAC) channel with shSTIM1 or BTP2 apparently inhibited ATP-evoked intracellular Ca2+ elevation and channel opening, thereby suppressing ATP-driven cell migration. Moreover, extracellular signal-regulated protein kinase (ERK) inhibitor PD98059 and p38 inhibitor SB203580 remarkably inhibited ERK and p38 phosphorylation, cytoskeleton rearrangement, and subsequent cell migration. Unexpectedly, it was found that knocking down STIM1 greatly inhibited ATP-triggered ERK/p38 activation. Taken together, it was suggested that P2Y2 signaled through the CRAC channel mediated Ca2+ influx and ERK/p38 pathway to reorganize the cytoskeleton and promoted the migration of CD34+ VW-SCs.NEW & NOTEWORTHY In this study, we observed that the purinergic receptor P2Y2 is critical in the regulation of vascular wall-resident CD34+ cells' migration. ATP could activate STIM1-mediated extracellular Ca2+ entry by triggering STIM1 translocation to the plasma membrane, and knockdown of STIM1 prevented ERK/p38 activation-mediated cytoskeleton rearrangement and cell migration.

PKC-β modulates Ca2+ mobilization through Stim1 phosphorylation

BACKGROUND

Calcium ions play a pivotal role in cell proliferation, differentiation, and migration. Under basal conditions, the calcium level is tightly regulated; however, cellular activation by growth factors increase the ion level through calcium pumps in the plasma membrane and endoplasmic reticulum for calcium signaling. Orai1 is a major calcium channel in the cell membrane of non-excitable cells, and its activity depends on the stromal interaction molecule 1 (Stim1). Several groups reported that the store-operated calcium entry (SOCE) can be modulated through phosphorylation of Stim1 by protein kinases such as extracellular signal-regulated kinase (ERK), protein kinase A (PKA), and p21-activated kinase (PAK). PKC is a protein kinase that is activated by calcium and diacylglycerol (DAG), but it remains unclear what role activated PKC plays in controlling the intracellular calcium pool.

OBJECTIVES

Here, we investigated whether PKC-β controls intracellular calcium dynamics through Stim1.

METHODS

Several biochemical methods such as immune-precipitation, site directed mutagenesis, in vitro kinase assay were employed to investigate PKC interaction with and phosphorylation of Stim1. Intracellular calcium mobilization, via Stim1 mediated SOCE channel, were studied using in the presence of PKC activator or inhibitor under a confocal microscope.

RESULTS

Our data demonstrate that PKC interacts with and phosphorylates Stim1 in vitro. phosphorylation of Stim1 at its C-terminal end appears to be important in the regulation of SOCE activity in HEK293 and HeLa cells. Additionally, transient intracellular calcium mobilization assays demonstrate that the SOCE activity was inhibited by PKC activators or activated by PKC inhibitors.

CONCLUSION

In sum, our data suggest a repressive role of PKC in regulating calcium entry through SOCE.

Deficiency of ER Ca2+ sensor STIM1 in AgRP neurons confers protection against dietary obesity

Store-operated calcium entry (SOCE) is pivotal in maintaining intracellular Ca2+ level and cell function; however, its role in obesity development remains largely unknown. Here, we show that the stromal interaction molecule 1 (Stim1), an endoplasmic reticulum (ER) Ca2+ sensor for SOCE, is critically involved in obesity development. Pharmacological blockade of SOCE in the brain, or disruption of Stim1 in hypothalamic agouti-related peptide (AgRP)-producing neurons (ASKO), significantly ameliorates dietary obesity and its associated metabolic disorders. Conversely, constitutive activation of Stim1 in AgRP neurons leads to an obesity-like phenotype. We show that the blockade of SOCE suppresses general translation in neuronal cells via the 2',5'-oligoadenylate synthetase 3 (Oas3)-RNase L signaling. While Oas3 overexpression in AgRP neurons protects mice against dietary obesity, deactivation of RNase L in these neurons significantly abolishes the effect of ASKO. These findings highlight an important role of Stim1 and SOCE in the development of obesity.

Lysosomal agents inhibit store-operated Ca2+ entry

Pharmacological manipulation of lysosome membrane integrity or ionic movements is a key strategy for probing lysosomal involvement in cellular processes. However, we have found an unexpected inhibition of store-operated Ca²⁺ entry (SOCE) by these agents. Dipeptides [glycyl-L-phenylalanine 2-naphthylamide (GPN) and L-leucyl-L-leucine methyl ester] that are inducers of lysosomal membrane permeabilization (LMP) uncoupled endoplasmic reticulum Ca²⁺-store depletion from SOCE by interfering with Stim1 oligomerization and/or Stim1 activation of Orai. Similarly, the K⁺/H⁺ ionophore, nigericin, that rapidly elevates lysosomal pH, also inhibited SOCE in a Stim1-dependent manner. In contrast, other strategies for manipulating lysosomes (bafilomycin A1, lysosomal re-positioning) had no effect upon SOCE. Finally, the effects of GPN on SOCE and Stim1 was reversed by a dynamin inhibitor, dynasore. Our data show that lysosomal agents not only release Ca²⁺ from stores but also uncouple this release from the normal recruitment of Ca²⁺ influx.

Summary: Lysosomal agents uncouple ER Ca²⁺-release from store-operated Ca²⁺ entry, predominantly by inhibiting Stim1 oligomerization and its activation of Orai.

The role of Stim1 in the progression of lupus nephritis in mice

OBJECTIVE

To investigate the expression of Stim1 in the kidneys of mice with lupus, and the effect of Stim1 on the progression of renal interstitial fibrosis.

METHODS

Mice (MRL/lpr) with spontaneous lupus nephritis (LN) and normal control mice (C57/BL) were selected. Immunohistochemistry and Masson staining were used to determine the degree of renal interstitial fibrosis in kidney tissues. The expression of Stim1 and fibronectin in tissues was measured by qRT-PCR, western blotting, and immunohistochemistry. Urine protein, blood urea nitrogen, and serum creatinine levels in the mice were analyzed, and Spearman analysis was conducted to determine the correlation with Stim1 expression levels. Mouse renal tubular epithelial cells (mRTECs) were chosen as the experimental objects. After various treatments, the cells were divided into the blank control group, lipopolysaccharide (LPS) treatment group, LPS+siRNA-NC group and LPS+siRNA-Stim1 group. Western blotting and immunofluorescence were used to measure epithelial-mesenchymal transition (EMT)-related protein levels.

RESULTS

There was significant interstitial fibrosis in the kidneys of LN mice. Compared with that in normal mice, the expression of Stim1 in the kidney tissues of LN mice was significantly increased, and Stim1 expression was positively correlated with fibronectin, urine protein, blood urea nitrogen and serum creatinine levels. LPS induced the expression of Stim1, fibronectin, and α-SMA in mRTECs and decreased the protein level of E-CA, while silencing Stim1 effectively alleviated the effects of LPS.

CONCLUSION

Stim1 is significantly increased in the kidneys of lupus mice, and it is possible to promote EMT in renal tubular epithelial cells and renal interstitial fibrosis by elevating fibronectin, which ultimately contributes to renal damage.

Pathophysiological significance of Stim1 mutation in sympathetic response to stress and cardiovascular phenotypes in SHRSP/Izm: In vivo evaluation by creation of a novel gene knock-in rat using CRISPR/Cas9

Genetic approach using rat congenic lines between SHRSP/Izm and WKY/Izm identified stromal interaction molecule 1 (Stim1), an essential component of store-operated Ca²⁺ entry (SOCE), as a promising candidate gene responsible for the exaggerated sympathetic response to stress in SHRSP. Since SHRSP has a nonsense mutation in Stim1 resulting in the expression of a truncated form of STIM1 that caused reduction of SOCE activity in primary cultured cerebral astrocytes, we created SHRSP/Izm knocked-in with the wild-type Stim1 (KI SHRSP) by the CRISPR/Cas9 method to investigate whether the functional recovery of STIM1 would mitigate sympatho-excitation to stress in vivo in SHRSP. No potential off-target nucleotide substitutions/deletions/insertions were found in KI SHRSP. Western blotting and fluorescent Ca²⁺ imaging of astrocytes confirmed wild-type STIM1 expression and restored SOCE activity in astrocytes from KI SHRSP, respectively. Blood pressure (BP) measured by the tail-cuff method at 12, 16, and 20 weeks of age did not significantly differ between SHRSP and KI SHRSP, while the heart rate of KI SHRSP at 16 and 20 weeks of age was significantly lower than that of age-matched SHRSP. Unexpectedly, the sympathetic response to stress (evaluated with urinary excretion of norepinephrine under cold stress and BP elevation under cold/restraint stress) did not significantly differ between SHRSP and KI SHRSP. The present results indicated that the functional deficit of STIM1 was not a genetic determinant of the exaggerated sympathetic response to stress in SHRSP and that it would be necessary to explore other candidates within the congenic fragment on chromosome 1.

CRAC channel regulation of innate immune cells in health and disease

Calcium is a major intracellular signaling messenger in innate immune cells. Similar to other immune cell subsets, the majority of calcium entry into innate immune cells is induced by cell surface receptors that stimulate store-operated calcium entry through calcium-release activated calcium (CRAC) channels. Since the molecular description of the STIM family of calcium sensors and the ORAI family of CRAC channel proteins, the majority of studies support a dominant role for these proteins in calcium signaling in innate cells. In reviewing the literature on CRAC channel function in innate cells, several general themes emerge. All innate cells express multiple members of the STIM and ORAI family members, however the ratio and relative contribution of individual isoforms changes depending on the cell type and activation state of the cell. It is evident that study of functional roles for STIM molecules is clearly ahead of studies of specific ORAI family members in all innate cell types, and that studies of CRAC channels in innate cells are not nearly as advanced as studies in lymphocytes. However, taken together, evidence from both STIM calcium sensors and ORAI channels in innate cells indicates that deficiency of STIM and ORAI proteins tends not to affect the development of any innate cell lineage, but certainly affects their function, in particular activation of the neutrophil oxidase and mast cell activation via IgE receptors. Furthermore, there are clearly hints that therapeutic targeting of CRAC channels in innate cells offers a new approach to various inflammatory and allergic diseases.

Orai1 and Stim1 Mediate the Majority of Store-Operated Calcium Entry in Multiple Myeloma and Have Strong Implications for Adverse Prognosis

BACKGROUND/AIMS

Multiple myeloma (MM) is a plasma cell neoplasm which constitutes about 10% of all hematologic malignancies. Despite the development and application of novel agents, MM still undergoes an aggressive and incurable course in the vast majority of patients. Ca2+ is one of the critical regulators of cell migration. Ca2+ influx is essential for the migration of various types of cells including tumor cells. However, the role of store-operated calcium entry (SOC) channels, the only Ca2+ channels of non-excitable cells, has not yet been reported in MM cell survival.

METHODS

We evaluated the expression of Stim1 and Orai1 (two key regulators of SOC) in MM tissues and cell lines by immunohistochemical assay, quantitative real-time PCR assay and western blot. MM cell lines were pretreated with pharmacological blockers and siRNAs, and then MM cell proliferation, cell cycle arrest, and apoptosis were examined by FACS (flow cytometry) assay, and Annexin V-FITC/PI staining. The correlation between the expression of Stim1 (or Orai1) level and outcome in MM were assessed by using Progress Free Survival (PFS).

RESULTS

Stim1 and Orai1 were both abundantly expressed in MM tissue and MM cell lines. Inhibition of SOCE reduced MM cell viability, and induced cell cycle arrest and apoptosis. Stim1 or Orai1 silencing also reduced cell viability, caused cell apoptosis and cell cycle arrest in MM cell lines. Over-expression of Stim1/Orai1 in MM patients was closely associated with the clinical outcome of MM.

CONCLUSION

The Stim1/Orai1-mediated signaling participates in the pathogenesis of MM, which represents an attractive target for future therapeutic intervention.

Deficient for endoplasmic reticulum calcium sensors Stim1 and Stim2 affects aberrant antibody affinity maturation in B cells

Antigen specific B cells undergo a process termed affinity maturation in the germinal centers of secondary lymphoid organs where B cells with high affinity receptors are selected to mature into antibody-producing cells or to the memory B cell pool. It is known that B cell antigen receptor (BCR) signaling plays pivotal role in this selection process. Calcium influx is an essential component of BCR signaling. The current report is to determine the effect of calcium influx on antibody affinity maturation. In our studies, mice deficient for both endoplasmic reticulum calciumsensor Stim1 and Stim2 was immunized with T-cell dependent and independent antigens. Antibody affinity was measured by ELISA. We demonstrated that Stim1 &Stim2 deficient B cells exhibit accelerated pace of affinity maturation compared to wild type controls while the overall antibody production was not dramatically impaired to T-independent antigen immunization. In conclusion, calcium influx plays an important role in antibody affinity maturation in humoral immune responses. The knowledge can be used in manipulate humoral immune response for the design of effective vaccines.

Extracellular ATP activates store-operated Ca2+ entry in white adipocytes: functional evidence for STIM1 and ORAI1

In the present study, we have applied ratiometric measurements of intracellular Ca²⁺ concentrations ([Ca²⁺]_i) to show that extracellularly applied ATP (adenosine triphosphate) (100 µM) stimulates store-operated Ca²⁺ entry (SOCE) in 3T3-L1 adipocytes. ATP produced a rapid increase in [Ca²⁺]_i consisting of an initial transient elevation followed by a sustained elevated phase that could be observed only in the presence of extracellular Ca²⁺. Gene expression data and [Ca²⁺]_i recordings with uridine-5′-triphosphate or with the phospholipase C (PLC) inhibitor U73122 demonstrated the involvement of purinergic P2Y2 receptors and the PLC/inositol trisphosphate pathway. The [Ca²⁺]_i elevation produced by reintroduction of a Ca²⁺-containing intracellular solution to adipocytes exposed to ATP in the absence of Ca²⁺ was diminished by known SOCE antagonists. The chief molecular components of SOCE, the stromal interaction molecule 1 (STIM1) and the calcium release-activated calcium channel protein 1 (ORAI1), were detected at the mRNA and protein level. Moreover, SOCE was largely diminished in cells where STIM1 and/or ORAI1 had been silenced by small interfering (si)RNA. We conclude that extracellular ATP activates SOCE in white adipocytes, an effect predominantly mediated by STIM1 and ORAI1.

Contacts between the endoplasmic reticulum and other membranes in neurons

Close appositions between the membrane of the endoplasmic reticulum (ER) and other intracellular membranes have important functions in cell physiology. These include lipid homeostasis, regulation of Ca²⁺ dynamics, and control of organelle biogenesis and dynamics. Although these membrane contacts have previously been observed in neurons, their distribution and abundance have not been systematically analyzed. Here, we have used focused ion beam-scanning electron microscopy to generate 3D reconstructions of intracellular organelles and their membrane appositions involving the ER (distance ≤30 nm) in different neuronal compartments. ER-plasma membrane (PM) contacts were particularly abundant in cell bodies, with large, flat ER cisternae apposed to the PM, sometimes with a notably narrow lumen (thin ER). Smaller ER-PM contacts occurred throughout dendrites, axons, and in axon terminals. ER contacts with mitochondria were abundant in all compartments, with the ER often forming a network that embraced mitochondria. Small focal contacts were also observed with tubulovesicular structures, likely to be endosomes, and with sparse multivesicular bodies and lysosomes found in our reconstructions. Our study provides an anatomical reference for interpreting information about interorganelle communication in neurons emerging from functional and biochemical studies.

Enhanced Stim1 expression is associated with acquired chemo-resistance of cisplatin in osteosarcoma cells

Osteosarcoma is the most common primary malignant bone tumor. Although cisplatin is the primary chemotherapy used in osteosarcoma treatment, the cisplatin resistance remains a big challenge for improving overall survival. The store-operated calcium (Ca²⁺) entry (SOCE) and its major mediator Stim1 have been shown to be implicated in a number of pathological processes typical for cancer. In this study, we showed that Stim1 expression was significantly increased in chemo-resistant osteosarcoma tissues compared with chemo-sensitivity tissues. Patients with Sitm1 expression exhibited poorer overall survival than Stim1-negative patients. Moreover, un-regulation of Stim1 expression and SOCE were also observed in cisplatin-resistant MG63/CDDP cells compared with their parental cells. Cisplatin treatment obviously reduced Stim1 expression and SOCE in cisplatin-sensitivity MG63 cells, but had no effects on MG63/CDDP cells. In addition, cisplatin resulted in a more pronounced increase of endoplasmic reticulum (ER) stress in MG63 cells than in their resistant variants, which was evidenced by the activation of molecular markers of ER stress, GRP78, CHOP and ATF4. Knockdown of Stim1 using siRNA remarkably enhanced cisplatin-induced apoptosis and ER stress in MG63/CDDP cells, thereby sensitizing cancer cells to cisplatin. On the other hand, overexpression of Stim1 markedly reversed apoptosis and ER stress following cisplatin treatment. Taken together, these results demonstrate that Stim1 as well as Ca²⁺ entry contributes cisplatin resistance via inhibition of ER stress-mediated apoptosis, and provide important clues to the mechanisms involved in cisplatin resistance for osteosarcoma treatment. Stim1 represents as a target of cisplatin and blockade of Stim1-mediated Ca²⁺ entry may be a useful strategy to improve the efficacy of cisplatin to treat osteosarcoma.

Orai1 and Orai3 in Combination with Stim1 Mediate the Majority of Store-operated Calcium Entry in Astrocytes

Astrocytes are non-excitable cells in the brain and their activity largely depends on the intracellular calcium (Ca²⁺) level. Therefore, maintaining the intracellular Ca²⁺ homeostasis is critical for proper functioning of astrocytes. One of the key regulatory mechanisms of Ca²⁺ homeostasis in astrocytes is the store-operated Ca²⁺ entry (SOCE). This process is mediated by a combination of the Ca²⁺-store-depletion-sensor, Stim, and the store-operated Ca²⁺-channels, Orai and TrpC families. Despite the existence of all those families in astrocytes, previous studies have provided conflicting results on the molecular identification of astrocytic SOCE. Here, using the shRNA-based gene-silencing approach and Ca²⁺-imaging from cultured mouse astrocytes, we report that Stim1 in combination with Orai1 and Orai3 contribute to the major portion of astrocytic SOCE. Gene-silencing of Stim1 showed a 79.2% reduction of SOCE, indicating that Stim1 is the major Ca²⁺-store-depletion-sensor. Further gene-silencing showed that Orai1, Orai2, Orai3, and TrpC1 contribute to SOCE by 35.7%, 20.3%, 26.8% and 12.2%, respectively. Simultaneous gene-silencing of all three Orai subtypes exhibited a 67.6% reduction of SOCE. Based on the detailed population analysis, we predict that Orai1 and Orai3 are expressed in astrocytes with a large SOCE, whereas TrpC1 is exclusively expressed in astrocytes with a small SOCE. This analytical approach allows us to identify the store operated channel (SOC) subtype in each cell by the degree of SOCE. Our results propose that Stim1 in combination with Orai1 and Orai3 are the major molecular components of astrocytic SOCE under various physiological and pathological conditions.

In vitro aging promotes endoplasmic reticulum (ER)-mitochondria Ca2+ cross talk and loss of store-operated Ca2+ entry (SOCE) in rat hippocampal neurons

Aging is associated to cognitive decline and susceptibility to neuron death, two processes related recently to subcellular Ca²⁺ homeostasis. Memory storage relies on mushroom spines stability that depends on store-operated Ca²⁺ entry (SOCE). In addition, Ca²⁺ transfer from endoplasmic reticulum (ER) to mitochondria sustains energy production but mitochondrial Ca²⁺ overload promotes apoptosis. We have addressed whether SOCE and ER-mitochondria Ca²⁺ transfer are influenced by culture time in long-term cultures of rat hippocampal neurons, a model of neuronal aging. We found that short-term cultured neurons show large SOCE, low Ca²⁺ store content and no functional coupling between ER and mitochondria. In contrast, in long-term cultures reflecting aging neurons, SOCE is essentially lost, Stim1 and Orai1 are downregulated, Ca²⁺ stores become overloaded, Ca²⁺ release is enhanced, expression of the mitochondrial Ca²⁺ uniporter (MCU) increases and most Ca²⁺ released from the ER is transferred to mitochondria. These results suggest that neuronal aging is associated to increased ER-mitochondrial cross talking and loss of SOCE. This subcellular Ca²⁺ remodeling might contribute to cognitive decline and susceptibility to neuron cell death in the elderly.

The ER/PM microdomain, PI(4,5)P₂ and the regulation of STIM1-Orai1 channel function

All forms of cell signaling occur in discreet cellular microdomains in which the ER is the main participant and include microdomains formed by the ER with lysosomes, endosomes, the nucleus, mitochondria and the plasma membrane. In the microdomains the two opposing organelles transfer and exchange constituents including lipids and ions. As is the case for other forms of signaling pathways, many components of the receptor-evoked Ca(2+) signal are clustered at the ER/PM microdomain, including the Orai1-STIM1 complex. This review discusses recent advances in understanding the molecular components that tether the ER and plasma membrane to form the ER/PM microdomains in which PI(4,5)P2 is enriched, and how dynamic targeting of the Orai1-STIM1 complex to PI(4,5)P2-poor and PI(4,5)P2-rich microdomains controls the activity of Orai1 and its regulation by Ca(2+) that is mediated by SARAF.

Store-operated Ca²⁺-entry and adenylyl cyclase

One of the longest-standing effects of SOCE is in its selective regulation of Ca(2+)-sensitive adenylyl cyclase (AC) activity in non-excitable cells. Remarkably it was this source of Ca(2+) (SOCE) rather than the apparent magnitude of the Ca(2+)-rise that conferred AC responsiveness. The molecular basis for this dependence is now resolved in the case of adenylyl cyclase 8 (AC8). Sensors for Ca(2+) and cAMP targeted to ACs have been particularly useful in dissecting the influences upon and composition of what turn out to be signalling microdomains centred on ACs. A number of physiological processes depend on the regulation by SOCE of ACs, but the issue is under-studied. Here I will expand on these topics and point to some immediate unresolved questions.

CRAC channel is inhibited by neomycin in a Ptdlns(4,5)P2-independent manner

Depletion of intracellular Ca(2+) stores evokes store-operated Ca(2+) entry through the Ca(2+) release-activated Ca(2+) (CRAC) channels. In this study, we found that the store-operated Ca(2+) entry was inhibited by neomycin, an aminoglycoside that strongly binds phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). Patch clamp recordings revealed that neomycin blocked the CRAC currents reconstituted by co-expression of Orai1 and Stim1 in HEK293 cells. Using a rapamycin-inducible PtdIns(4,5)P2-specific phosphatase (Inp54p) system to manipulate the PtdIns(4,5)P2 in the plasma membrane, we found that the CRAC current was not altered by PtdIns(4,5)P2 depletion. This result suggests that PtdIns(4,5)P2 is not required for CRAC channel activity, and thereby, neomycin inhibits CRAC channels in a manner that is independent of neomycin-PtdIns(4,5)P2 binding.

Regulation of phagocytosis and cytokine secretion by store-operated calcium entry in primary isolated murine microglia

Microglia are immune effector cells in the central nervous system that participate in tissue repair, inflammatory responses, and neuronal degeneration. The most important signaling factor in the differentiation of immune-active cells after stimulation is the sustained high calcium concentration in the cytosol, which is called store-operated calcium entry (SOCE). Recently, the molecular identity of the store-operated channel (SOC) has revealed that Orai1, Orai2, Orai3, Stim1, and Stim2 constitute the most of SOC. In this study, we demonstrate that Orai1- and Stim1-mediated SOC regulated the phagocytic activity and cytokine release of primary isolated murine microglia. RT-PCR analysis revealed that primary cultured microglia from neonatal ICR mouse brains had Orai1, Orai2, Orai3, and Stim1. To elucidate the role of SOCE in the immune functions of microglia, pharmacological inhibitors or knockdown with Orai1 or Stim1 siRNA was applied, and UDP-induced phagocytic activity and LPS-induced cytokine secretion activity were compared. The pharmacological inhibition and siRNA effect was verified by measuring thapsigargin (TG)-, ATP-, or UDP-activated SOCE Ca2+ influx and proper siRNA-mediated knockdown was verified by western blot analysis. UDP-induced phagocytic activity was inhibited by pharmacological inhibitors of SOCE, such as SKF96365 or 2-APB, and knockdown of Orai1 and Stim1. Cytokine secretion of TNF-α and IL-6 by LPS treatment was also inhibited by SKF96365 and knockdown of Orai1 and Stim1. Meanwhile, LPS stimulation-induced NF-κB activation was not altered, but NFAT1 activity was attenuated with Stim1 knockdown. These results indicate that SOCE, which was composed of Orais and Stim1, regulates UDP-induced phagocytosis and LPS-stimulated cytokine secretion in microglia.

May the remodeling of the Ca²⁺ toolkit in endothelial progenitor cells derived from cancer patients suggest alternative targets for anti-angiogenic treatment?

Endothelial progenitor cells (EPCs) may be recruited from bone marrow to sustain the metastatic switch in a number of solid cancers, including breast cancer (BC) and renal cellular carcinoma (RCC). Preventing EPC mobilization causes tumor shrinkage. Novel anti-angiogenic treatments have been introduced in therapy to inhibit VEGFR-2 signaling; unfortunately, these drugs blocked tumor angiogenesis in pre-clinical murine models, but resulted far less effective in human patients. Understanding the molecular mechanisms driving EPC proliferation and tubulogenesis in cancer patients could outline novel targets for alternative anti-angiogenic treatments. Store-operated Ca²⁺ entry (SOCE) regulates the growth of human EPCs, and it is mediated by the interaction between the endoplasmic reticulum Ca²⁺-sensor, Stim1, and the plasmalemmal Ca²⁺ channels, Orai1 and TRPC1. EPCs do not belong to the neoplastic clone: thus, unlike tumor endothelium and neoplastic cells, they should not remodel their Ca²⁺ toolkit in response to tumor microenvironment. However, our recent work demonstrated that EPCs isolated from naïve RCC patients (RCC-EPCs) undergo a dramatic remodeling of their Ca²⁺ toolkit by displaying a remarkable drop in the endoplasmic reticulum Ca²⁺ content, by down-regulating the expression of inositol-1,4,5-receptors (InsP3Rs), and by up-regulating Stim1, Orai1 and TRPC1. Moreover, EPCs are dramatically less sensitive to VEGF stimulation both in terms of Ca²⁺ signaling and of gene expression when isolated from tumor patients. Conversely, the pharmacological abolition of SOCE suppresses proliferation in these cells. These results question the suitability of VEGFR-2 as a therapeutically relevant target for anti-angiogenic treatments and hint at Orai1 and TRPC1 as more promising alternatives. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

Ca2+ signaling in taste bud cells and spontaneous preference for fat: unresolved roles of CD36 and GPR120

Recent compelling evidences from rodent and human studies raise the possibility for an additional sixth taste modality devoted to oro-gustatory perception of dietary lipids. Understanding the mechanisms underlying oro-gustatory detection of dietary fat is critical for the prevention and treatment of obesity. A number of studies have suggested that lingual CD36, a glycoprotein, highly expressed by circumvallate papillae of the tongue, is implicated in the perception of dietary fat taste. G protein-coupled receptors (GPCRs) are important signaling molecules for many aspects of cellular functions. It has been shown that these receptors, particularly GPR120, are also involved in lipid taste perception. We have shown that dietary long-chain fatty acids (LCFAs), in CD36-positive taste bud cells (TBC), induce increases in free intracellular Ca(2+) concentrations, [Ca(2+)]i, by recruiting Ca(2+) from endoplasmic reticulum (ER) pool via inositol 1,4,5-triphosphate production, followed by Ca(2+) influx via opening of store-operated Ca(2+) (SOC) channels. GPR120 is also coupled to increases in [Ca(2+)]i by dietary fatty acids. We observed that stromal interaction molecule 1 (STIM1), a sensor of Ca(2+) depletion in the ER, mediated fatty acid-induced Ca(2+) signaling and spontaneous preference for fat in the mouse. In this review article, we discuss the recent advances and unresolved roles of CD36 and GPR120 in lipid taste signaling in taste bud cells.