title: Ca2+ Influx through Store-operated Calcium Channels Replenishes the Functional Phosphatidylinositol 4,5-Bisphosphate Pool Used by Cysteinyl Leukotriene Type I Receptors.
abstract: Oscillations in cytoplasmic Ca(2+) concentration are a universal mode of signaling following physiological levels of stimulation with agonists that engage the phospholipase C pathway. Sustained cytoplasmic Ca(2+) oscillations require replenishment of the membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2), the source of the Ca(2+)-releasing second messenger inositol trisphosphate. Here we show that cytoplasmic Ca(2+) oscillations induced by cysteinyl leukotriene type I receptor activation run down when cells are pretreated with Li(+), an inhibitor of inositol monophosphatases that prevents PIP2 resynthesis. In Li(+)-treated cells, cytoplasmic Ca(2+) signals evoked by an agonist were rescued by addition of exogenous inositol or phosphatidylinositol 4-phosphate (PI4P). Knockdown of the phosphatidylinositol 4-phosphate 5 (PIP5) kinases α and γ resulted in rapid loss of the intracellular Ca(2+) oscillations and also prevented rescue by PI4P. Knockdown of talin1, a protein that helps regulate PIP5 kinases, accelerated rundown of cytoplasmic Ca(2+) oscillations, and these could not be rescued by inositol or PI4P. In Li(+)-treated cells, recovery of the cytoplasmic Ca(2+) oscillations in the presence of inositol or PI4P was suppressed when Ca(2+) influx through store-operated Ca(2+) channels was inhibited. After rundown of the Ca(2+) signals following leukotriene receptor activation, stimulation of P2Y receptors evoked prominent inositol trisphosphate-dependent Ca(2+) release. Therefore, leukotriene and P2Y receptors utilize distinct membrane PIP2 pools. Our findings show that store-operated Ca(2+) entry is needed to sustain cytoplasmic Ca(2+) signaling following leukotriene receptor activation both by refilling the Ca(2+) stores and by helping to replenish the PIP2 pool accessible to leukotriene receptors, ostensibly through control of PIP5 kinase activity.
authors.affiliation: From the Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, United Kingdom.
authors.forename: Abdullah
authors.initials: A
authors.lastname: Alswied
authors.affiliation: From the Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford OX1 3PT, United Kingdom anant.parekh@dpag.ox.ac.uk.
authors.forename: Anant B
authors.initials: AB
authors.lastname: Parekh
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling; D045744:Cell Line, Tumor; D003470:Culture Media; D003593:Cytoplasm / Q000378:metabolism; D017997:Leukotriene C4 / Q000378:metabolism; D015289:Leukotrienes / Q000378:metabolism; D008094:Lithium / Q000737:chemistry; D000071740:ORAI1 Protein; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000737:chemistry*; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D018077:Receptors, Leukotriene / Q000378:metabolism*; D015398:Signal Transduction; D016608:Talin / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D003470:Culture Media; D015289:Leukotrienes; D000071740:ORAI1 Protein; C532493:Orai1 protein, rat; D019269:Phosphatidylinositol 4,5-Diphosphate; D034741:RNA, Small Interfering; D018077:Receptors, Leukotriene; D016608:Talin; D017997:Leukotriene C4; D008094:Lithium; D010738:Type C Phospholipases; D002118:Calcium
keywords: calcium channel; calcium intracellular release; calcium release-activated calcium channel protein 1 (ORAI1); phosphatidylinositol kinase (PI kinase); phosphatidylinositol signaling