Critical role of PIP5KIγ87 in InsP3-mediated Ca2+ signaling

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Abstract
Phosphatidylinositol 4,5-bisphosphate (PIP2) is the obligatory precursor of inositol 1,4,5-trisphosphate (InsP3 or IP3) and is therefore critical to intracellular Ca2+ signaling. Using RNA interference (RNAi), we identified the short splice variant of type I phosphatidylinositol 4-phosphate 5-kinase γ (PIP5KIγ87) as the major contributor of the PIP2 pool that supports G protein–coupled receptor (GPCR)-mediated IP3 generation. PIP5KIγ87 RNAi decreases the histamine-induced IP3 response and Ca2+ flux by 70%. Strikingly, RNAi of other PIP5KI isoforms has minimal effect, even though some of these isoforms account for a larger percent of total PIP2 mass and have previously been implicated in receptor mediated endocytosis or focal adhesion formation. Therefore, PIP5KIγ879s PIP2 pool that supports GPCR-mediated Ca2+ signaling is functionally compartmentalized from those generated by the other PIP5KIs.