The β- and γ-isoforms of type I PIP5K regulate distinct stages of Ca2+ signaling in mast cells

Academic Article

Abstract

  • Crosslinking of IgE receptors by antigen initiates Ca2+ mobilization in mast cells by activating phospholipase-Cγ-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2]. The resulting inositol 1,4,5-trisphosphate-mediated Ca2+ release from the endoplasmic reticulum (ER) activates store-operated Ca2+ entry, which is necessary for exocytotic release of inflammatory mediators. To investigate roles for PtdIns(4,5)P2-synthesizing isozymes of the type I phosphatidylinositol 4-phosphate 5-kinase family (PIP5K-I) in mast cell signaling, we compared the ectopic expression of wild-type and catalytically inactive PIP5K-Iβ in RBL-2H3 mast cells. Surprisingly, both antigen and thapsigargin-stimulated Ca2+ influx were reduced by overexpression of active PIP5K-Iβ, whereas antigen-stimulated Ca2+ release from ER stores was unaffected. Consistent with these results, Ca2+ entry stimulated by antigen or thapsigargin was enhanced by expression of a plasma-membrane-associated inositol polyphosphate 5′-phosphatase, whereas antigen-stimulated Ca2+ release from stores was reduced. To investigate the role of PIP5K-Iγ in antigen-stimulated Ca2+ mobilization, we used bone-marrow-derived mast cells from PIP5K-Iγ–/– mice. Antigen-stimulated Ca2+ release from ER stores was substantially reduced in the absence of PIP5K-Iγ, but thapsigargin-mediated Ca2+ entry was unaffected. In summary, PIP5K-Iγ positively regulates antigen-stimulated Ca2+ release from ER stores, whereas PIP5K-Iβ negatively regulates store-operated Ca2+ entry, suggesting that these different PIP5K-I isoforms synthesize functionally distinct pools of PtdIns(4,5)P2 at the plasma membrane.
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    Digital Object Identifier (doi)

    Author List

  • Vasudevan L; Jeromin A; Volpicelli-Daley L; De Camilli P; Holowka D; Baird B
  • Start Page

  • 2567
  • End Page

  • 2574
  • Volume

  • 122
  • Issue

  • 14