This study presents evidence that phosphoinositide (PI) 3-kinase is involved in T cell Ca2+ signaling via a phosphatidylinositol 3,4,5-trisphosphate PI(3,4,5)P3-sensitive Ca2+entry pathway. First, exogenous PI(3,4,5)P3 at concentrations close to its physiological levels induces Ca2+ influx in T cells, whereas PI(3,4)P2, PI(4,5)P2, and PI(3)P have no effect on [Ca2+]i. This Ca2+ entry mechanism is cell type-specific as B cells and a number of cell lines examined do not respond to PI(3,4,5)P3 stimulation. Second, inhibition of PI 3-kinase by wortmannin and by overexpression of the dominant negative inhibitor Δp85 suppresses anti-CD3-induced Ca2+response, which could be reversed by subsequent exposure to PI(3,4,5)P3. Third, PI(3,4,5)P3 is capable of stimulating Ca2+ efflux from Ca2+-loaded plasma membrane vesicles prepared from Jurkat T cells, suggesting that PI(3,4,5)P3 interacts with a Ca2+ entry system directly or via a membrane-bound protein. Fourth, although D-myo-inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) mimics PI(3,4,5)P3 in many aspects of biochemical functions such as membrane binding and Ca2+ transport, we raise evidence that Ins(1,3,4,5)P4 does not play a role in anti-CD3- or PI(3,4,5)P3-mediated Ca2+ entry. This PI(3,4,5)P3-stimulated Ca2+ influx connotes physiological significance, considering the pivotal role of PI 3-kinase in the regulation of T cell function. Given that PI 3-kinase and phospholipase C-γ form multifunctional complexes downstream of many receptor signaling pathways, we hypothesize that PI(3,4,5)P3-induced Ca2+ entry acts concertedly with Ins(1,4,5)P3-induced Ca2+ release in initiating T cell Ca2+ signaling. By using a biotinylated analog of PI(3,4,5)P3 as the affinity probe, we have detected several putative PI(3,4,5)P3-binding proteins in T cell plasma membranes.
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This work was supported by National Institutes of Health GrantsGM53448 (to C.-S. C.) and AI21490 (to S. B.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Hsu, Ao-Lin; Ching, Tsui-Ting; Sen, Goutam; Wan, Da-Sheng; Bondada, Subbarao; Authi, Kalwant S.; and Chen, Ching-Shih, "Novel Function of Phosphoinositide 3-Kinase in T Cell Ca2+ Signaling" (2000). Pharmaceutical Sciences Faculty Publications. 106.