Phosphoinositide 3-Kinase Facilitates Antigen-stimulated Ca2+ Influx in RBL-2H3 Mast Cells via a Phosphatidylinositol 3,4,5-Trisphosphate-sensitive Ca2+Entry Mechanism

Abstract

This study presents evidence that phosphoinositide 3-kinase (PI3K) plays a concerted role with phospholipase C␥ in initiating antigen-mediated Ca 2؉ signaling in mast cells via a phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P 3 )-sensitive Ca 2؉ entry pathway. Exogenous PI(3,4,5)P 3 at concentrations close to its physiological level induces instantaneous Ca 2؉ influx into RBL-2H3 cells. This PI(3,4,5)P 3 -induced intracellular Ca 2؉ increase is independent of phospholipase C activity or the depletion of internal stores. ) and diacylglycerol, which induce the release of Ca 2ϩ from intracellular stores and the activation of protein kinase C, respectively. On the other hand, stimulation of PI3K results in transient accumulation of micromolar levels of phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P 3 ) and phosphatidylinositol 3,4-bisphosphate (PI(3,4)P 2 ). Although the involvement of PI3K in antigen-induced degranulation is established (7-11), a clear consensus regarding how lipid products derived from the action of PI3K mediate the cellular responses has yet to emerge. Putative downstream targets for PI(3,4,5)P 3 and PI(3,4)P 2 include SH2-or pleckstrin homology (PH) domain-containing signaling enzymes such as PLC-␥, Akt, and Bruton's tyrosine kinase (Btk) (12, 13), which transduce the signal to the respective signaling pathways. In addition, data from several laboratories suggest a role of PI3K in the regulation of intracellular Ca 2ϩ ([Ca 2ϩ ] i ) increase in mast cells (9,11,14). Evidence suggests that PI3K may mediate [Ca 2ϩ ] i elevation in mast cells via two distinct mechanisms. First, in vitro data indicate that PI(3,4,5)P 3 stimulates Ins(1,4,5)P 3 production by activating PLC␥ isozymes (15,16). This PLC␥ activation may be attained directly by facilitating membrane translocation (15, 16) or indirectly via Btk (14, 17). Second, PI3K may increase [Ca 2ϩ ] i by facilitating Ca 2ϩ mobilization across plasma membranes (11). This premise was prompted by data showing the inhibitory effect of PI3K inhibitors on antigen-induced Ca 2ϩ response (9,11,14), and is in * This work was supported by National Institutes of Health Grant GM53448. 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.‡ To whom correspondence should be addressed: College of Pharmacy, The Ohio State University, 500 West 12th Ave., Columbus, OH 43210-1291. Tel.: 614-688-4008; Fax: 614-688-8556; E-mail: chen@ dendrite.pharmacy.ohio-state.edu.1 The abbreviations used are: Fc⑀RI, the high affinity receptor for IgE; PI3K, phosphoinositide 3-kinase; PLC, phospholipase C; PI(3,4,5)P 3 , phosphatidylinositol 3,4,5-trisphosphate; PI(3,4)P 2 , phosphatidylinositol 3,4-bisphosphate; PI(4,5)P 2 , phosphatidylinositol 4,5-bisphosphate; PI(3)P, phosphatidylinositol 3-monophosphate; Ins(1,4,5)P 3 , D-myo-inositol 1,4,5-trisphosphate; Ins(1,3,4,5)P 4 , Dmyo-inositol 1,3,4...

Requirement of Ca2+and CaMKII for Stat1 Ser-727 phosphorylation in response to IFN-γ

“…It was reported recently that the phosphatidylinositol 3-kinase (PI3K)͞Akt pathway could be involved also in the IFN-␥-induced phosphorylation of Stat1 S727 in human tumor cell lines or mouse embryonic fibroblasts (15). PI3K has been shown to facilitate antigen-stimulated Ca 2ϩ flux in Jurkat T cells and mast cells (44,45), which could result in activation of Ca 2ϩ -dependent serine kinases. It seems likely that in different cellular contexts, more than one serine kinase pathway can converge on Stat1 during or after its activation through tyrosine phosphorylation on the cell surface.…”

The PI3-K/Akt pathway: roles related to alterations in vasomotor responses in diabetic models

“…Indeed, PI3-K has been proposed to exert an indirect modulating effect on inositol 1,4,5,-triphosphate (IP3) receptors and Ca 2+ releaseactivated Ca 2+ channels in nonexcitable cells (Scharenberg and Kinet, 1998). A noncapacitative Ca 2+ influx is also regulated by PIP3 in RBL-2H3 cells (Ching et al, 2001). In excitable cells, PI3-K stimulates voltage-gated Ca 2+ channels (Blair and Marshall, 1997;Viard et al, 1999).…”

Phospholipase Cγ negatively regulates Rac/Cdc42 activation in antigen‐stimulated mast cells

“…These two second messengers lead to increases in cytoplasmic calcium and activation of calcium/diacylglycerol-regulated isoforms of protein kinase C (PKC) which culminate in granule margination and exocytosis [7]. PI3K plays an important regulatory role as an upstream activator of PLCc1, as well as a regulator of calcium flux during mast cell degranulation [8][9][10][11][12][13].…”

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