Ching T T, Hsu A L, Johnson A J, Chen C S
Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, Kentucky 40536-0082, USA.
J Biol Chem. 2001 May 4;276(18):14814-20. doi: 10.1074/jbc.M009851200. Epub 2001 Feb 5.
This study presents evidence that phosphoinositide 3-kinase (PI3K) plays a concerted role with phospholipase Cgamma 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. Moreover, inhibition of PI3K by LY294002 or by overexpression of the dominant negative inhibitor Deltap85 suppresses the Ca(2+) response to the cross-linking of the high affinity receptor for IgE (FcepsilonRI). Concomitant treatment of RBL-2H3 cells with LY294002 or Deltap85 and 2-aminoethyl diphenylborate, a cell-permeant antagonist of D-myo-inositol 1,4,5-trisphosphate receptors, abrogates antigen-induced Ca(2+) signals, whereas either treatment alone gives rise to partial inhibition. Conceivably, PI(3,4,5)P(3)-sensitive Ca(2+) entry and capacitative Ca(2+) entry represent major Ca(2+) influx pathways that sustain elevated [Ca(2+)]i to achieve optimal physiological responses. This study also refutes the second messenger role of D-myo-inositol 1,3,4,5-tetrakisphosphate in regulating FcepsilonRI-mediated Ca(2+) response. Considering the underlying mechanism, our data suggest that PI(3,4,5)P(3) directly stimulates a Ca(2+) transport system in plasma membranes. Together, these data provide a molecular basis to account for the role of PI3K in the regulation of FcepsilonRI-mediated degranulation in mast cells.
本研究表明，磷脂酰肌醇3激酶（PI3K）与磷脂酶Cγ协同作用，通过磷脂酰肌醇3,4,5-三磷酸（PI(3,4,5)P(3)）敏感的Ca(2+)内流途径，启动肥大细胞中抗原介导的Ca(2+)信号传导。接近其生理水平浓度的外源性PI(3,4,5)P(3)可诱导Ca(2+)瞬间流入RBL-2H3细胞。这种PI(3,4,5)P(3)诱导的细胞内Ca(2+)增加与磷脂酶C活性或内部储存的耗尽无关。此外，LY294002或显性负性抑制剂Deltap85的过表达对PI3K的抑制作用，抑制了Ca(2+)对IgE高亲和力受体（FcepsilonRI）交联的反应。用LY294002或Deltap85与2-氨基乙基二苯基硼酸盐（一种D-肌醇1,4,5-三磷酸受体的细胞渗透性拮抗剂）同时处理RBL-2H3细胞，可消除抗原诱导的Ca(2+)信号，而单独任何一种处理只会产生部分抑制作用。可以想象，PI(3,4,5)P(3)敏感的Ca(2+)内流和容量性Ca(2+)内流代表了维持[Ca(2+)]i升高以实现最佳生理反应的主要Ca(2+)内流途径。本研究还反驳了D-肌醇1,3,4,5-四磷酸在调节FcepsilonRI介导的Ca(2+)反应中的第二信使作用。考虑到潜在机制，我们的数据表明PI(3,4,5)P(3)直接刺激质膜中的Ca(2+)转运系统。总之，这些数据为解释PI3K在肥大细胞中调节FcepsilonRI介导的脱颗粒作用提供了分子基础。
