Role of Protein Kinase C in the Activation of Store-operated Ca^(2+) Entry in Airway Smooth Muscle Cells

Store-operated Ca2＋ channels （SOCs） are plasma membrane Ca2＋ permeable channels activated by depletion of intracellular Ca2＋ store. Ca2＋ entry through SOCs is known as store-operated Ca2＋ entry （SOCE）, which plays an important role in the functional regulation of airway smooth muscle cells （ASMCs）. Protein kinase C （PKC） has been shown to have an activating or inhibiting effect on SOCE, depending on cell types and PKC isoforms that are involved. In ASMCs, the effect of PKC on SOCE has not been elucidated so far. In this study, the role of PKC in the activation of SOCE in rat ASMCs was examined by using Ca2＋ fluorescence imaging technique. The results showed that acute application of PKC activators PMA and PDBu did not affect SOCE induced by the sarcoplasmic reticulum Ca2＋-ATPase （SERCA） inhibitor thapsigargin. The non-selective PKC inhibitor chelerythrine significantly inhibited thapsigargin- and bradykinin-induced SOCE. RT-PCR assay identified PKCα, δ and ε isoforms in rat ASMCs. PKCα-selective inhibitor G6976 and PKCε-inhibiting peptide Epsilon-V1-2 had no effect on SOCE; by contrast, PKCδ-selective inhibitor rottlerin attenuated SOCE dramatically, suggesting that PKCδ was the major PKC isoform involved in the activation of SOCE in ASMCs. Moreover, PKC down-regulation by extended exposure to high doses of PMA or PDBu also reduced SOCE, confirming the essential role of PKC in the activation of SOCE in ASMCs. In addition, PKC down-regulation did not influence the expression of stromal interaction molecule 1 （STIM1） and Orai1, two elementary molecules in the regulation and activation of SOCs. These results identified PKCδ as an essential PKC isoform involved in the activation of SOCE, and confirmed that PKC regulates the function of ASMCs in a SOCE-dependent manner.

New insights into store-independent Ca^(2+) entry: secretory pathway calcium ATPase 2 in normal physiology and cancer

Recent studies in secretory pathway calcium ATPases （SPCA） revealed novel functions of SPCA2 in interacting with store-operated Ca2＋ channel Oral I and inducing Ca2＋ influx at the cell surface. Importantly, SPCA2-mediated Ca2＋ signaling is uncoupled from its conventional role of Ca2＋-ATPase and independent of store-operated Ca2＋ signaling pathway. SPCA2-induced store-independent Ca2＋ entry （SICE） plays essential roles in many important physiological processes, while unbalanced SICE leads to enhanced cell proliferation and tumorigenesis. Finally, we have summarized the clinical implication of SICE in oral cancer prognosis and treatment. Inhibition of SICE may be a new target for the development of cancer therapeutics.

Occurrence of cGMP/nitric oxide-sensitive store-operated calcium entry in fibroblasts and its effect on matrix metalloproteinase secretion

AIM： To examine the existence of Nitric oxide/ cGMP sensitive store-operated Ca^2＋ entry in mouse fibroblast NIH/3T3 cells and its influence on matrix metalloproteinase （MMP） production and adhesion ability of fibroblasts. METHODS： NIH/3T3 cells were cultured. Confocal laser scanning microscopy was used to examine the existence of thapsigargin-induced store-operated Ca^2＋ entry in fibroblasts. Gelatin zymography and semiquantitative reverse transcriptase-polymerase chain reaction （RTPCR） were employed to detect the involvement of [Ca^2＋]i and NO/cGMP in MMP secretion. The involvement of NO/ cGMP-sensitive Ca^2＋ entry in adhesion was determined using matrigel-coated culture plates. RESULTS： 8-bromo-cGMP inhibited the thapsigargin-induced Ca^2＋ entry in 3T3 cells. The cGMP-induced inhibition was abolished by an inhibitor of protein kinase G, KT5823 （1μmol/L）. A similar effect on the Ca^2＋ entry was observed in 3T3 cells in response to a NO donor, （±）-S-nitroso-N-acetylpenicillamine （SNAP）. The inhibitory effect of SNAP on the thapsigargin-induced Ca^2＋ entry was also observed, indicating NO/cGMP-regulated Ca^2＋ entry in 3T3 cells. Results of gelatin zymography assay showed that addition of extracellular Ca^2＋ concentration induced MMP release and activation in a dose-dependent manner. RT-PCR also showed that cGMP and SNAP reduced the production of MMP mRNA in 3T3 cells. Experiments investigating adhesion potentials demonstrated that cGMP and SNAP could upgrade 3T3 cell attachment rate to the matrigel-coated culture plates.CONCLUSION： NO/cGMP sensitive store-operated Ca^2＋ entry occurs in fibroblasts, and attenuates their adhesion potentials through its influence on MMP secretion.

New insights into the activation mechanism of store-operated calcium channels:roles of STIM and Orai

The activation of Ca2+ entry through store-operated channels by agonists that deplete Ca2+ from the endoplasmic reticulum (ER) is a ubiquitous signaling mechanism, the molecular basis of which has remained elusive for the past two decades. Store-operated Ca2+-release-activated Ca2+ (CRAC) channels constitute the sole pathway for Ca2+ entry following antigen-receptor engagement. In a set of breakthrough studies over the past two years, stromal interaction molecule 1 (STIM1, the ER Ca2+ sensor) and Orai1 (a pore-forming subunit of the CRAC channel) have been identified. Here we review these recent studies and the insights they provide into the mechanism of store-operated Ca2+ channels (SOCCs).

Effects of total flavonoids of Rhododendra simsii on ameliorating brain injury via G protein-coupled SOCE pathway mediated by STIM and Orai in subacute phase of ischemia/reperfusion

OBJECTIVE To explore the effect of total flavonoids of Rhododendra simsii(TFR)on improving cerebral ischemia/reperfusion injury(CIRI)and its relationship with STIM/Orai-regulated operational Ca^(2+)influx(SOCE)pathway.METHODS Oxygen-glucose deprivation/reoxygenation(OGD/R)PC12 cells were used to simulate CIRI in vitro,and the intracellular Ca^(2+)concentration and apoptosis rate of PC12 cells were detected by laser confocal microscope and flow cytometry,respectively.The regulation of STIM/Orai on SOCE was analyzed by STIM/Orai gene silencing and STIM/O rai gene overexpression.The CIRI model was established by MCAO in SD rats.The activities of inflammatory cytokines IL^(-1),IL-6 and TNF-αin serum were detected by ELISA.The pathological changes of ischemic brain tissue and the infarction of rat brain tissue were detected by HE staining and TTC staining.The protein and mRNA expression levels of STIM1,STIM2,Orai1,caspase-3 and PKB in brain tissue were detected by Western blotting and RT-qPCR,respectively.RESULTS The results of in vitro experiment showed that the fluorescence intensity of Ca^(2+)and apoptosis rate in PC12 cells treated with TFR were significantly lower than those in OGD/R group,and this trend was enhanced by SOCE antagonist 2-APB.STIM1/STIM2/Orai1 gene silencing significantly reduced apoptosis and Ca^(2+)overload in OGD/R model,while TFR combined with overexpression of STIM1/STIM2/Orai1 aggravated apoptosis and Ca2+overload.In the in vivo experiment,TFR significantly reduced the brain histopathological damage,infarction of brain tissue,the contents of IL^(-1),IL-6 and TNF-αin the serum in MCAO rats and down-regulated the expression of STIM1,STIM2,Orai1 and caspase-3 protein and mRNA in the brain tissue,and up-regulated the expression of PKB.The above effects were enhanced by the addition of 2-APB.CONCLUSION The above results indicate that TFR may reduce the contents of inflammatory factors and apoptosis,decrease Ca2+overload and ameliorate brain injury by inhibiting SOCE pathway mediated by STIM and Orai,suggesting that it has a protective effect against subacute CIRI.

Targeting calcium signaling in cancer therapy

The intracellular calcium ions(Ca^(2+)) act as second messenger to regulate gene transcription,cell proliferation, migration and death. Accumulating evidences have demonstrated that intracellular Ca^(2+)homeostasis is altered in cancer cells and the alteration is involved in tumor initiation, angiogenesis,progression and metastasis. Targeting derailed Ca^(2+)signaling for cancer therapy has become an emerging research area. This review summarizes some important Ca^(2+)channels, transporters and Ca^(2+)-ATPases,which have been reported to be altered in human cancer patients. It discusses the current research effort toward evaluation of the blockers, inhibitors or regulators for Ca^(2+)channels/transporters or Ca^(2+)-ATPase pumps as anti-cancer drugs. This review is also aimed to stimulate interest in, and support for researchinto the understanding of cellular mechanisms underlying the regulation of Ca^(2+)signaling in different cancer cells, and to search for novel therapies to cure these malignancies by targeting Ca^(2+)channels or transporters.