The beta- and gamma-isoforms of type I PIP5K regulate distinct stages of Ca2+ signaling in mast cells.
Crosslinking of IgE receptors by antigen initiates Ca2+ mobilization in mast cells by activating phospholipase-C gamma-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-I beta in RBL-2H3 mast cells. Surprisingly, both antigen and thapsigargin-stimulated Ca2+ influx were reduced by overexpression of active PIP5K-I beta, 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-I gamma in antigen-stimulated Ca2+ mobilization, we used bone-marrow-derived mast cells from PIP5K-I gamma(-/-) mice. Antigen-stimulated Ca2+ release from ER stores was substantially reduced in the absence of PIP5K-I gamma, but thapsigargin-mediated Ca2+ entry was unaffected. In summary, PIP5K-I gamma positively regulates antigen-stimulated Ca2+ release from ER stores, whereas PIP5K-I beta 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.
Vasudevan
Lavanya
L
Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.
Jeromin
Andreas
A
Volpicelli-Daley
Laura
L
De Camilli
Pietro
P
Holowka
David
D
Baird
Barbara
B
D000818:Animals; D000941:Antigens / Q000378:metabolism; D001854:Bone Marrow Cells / Q000201:enzymology; D020013:Calcium Signaling / Q000187:drug effects; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000072181:Inositol Polyphosphate 5-Phosphatases; D007527:Isoenzymes; D008407:Mast Cells / Q000187:drug effects / Q000201:enzymology*; D051379:Mice; D018345:Mice, Knockout; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D051966:Phospholipase C gamma / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017455:Receptors, IgE / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection
D000941:Antigens; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D019269:Phosphatidylinositol 4,5-Diphosphate; D017455:Receptors, IgE; D011993:Recombinant Fusion Proteins; D019284:Thapsigargin; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases; D051966:Phospholipase C gamma; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases