Agonist-induced inhibition of phosphatidylserine synthesis is secondary to the emptying of intracellular Ca2+ stores in Jurkat T-cells.
The biosynthesis of phosphatidylserine (PtdSer) by the serine base-exchange enzyme system, in Jurkat T-lymphocytes, was inhibited in intact cells maintained in low-Ca(2+)-containing buffer (< 10 microM-Ca2+) by using Ca2+ ionophores (A23187 or ionomycin). The rise in cytosolic Ca2+ concentration under these experimental conditions was only due to the release of Ca2+ from intracellular compartments, suggesting that the inhibition of PtdSer synthesis was correlated with the emptying of intracellular Ca2+ pools. This was further studied in saponin-permeabilized cells, in which PtdSer synthesis was found to be inhibited by EGTA, Ca2+ ionophores (A23187 or ionomycin) and Ca(2+)-ATPase inhibitors [thapsigargin or 2,5-di-(t-butyl)-benzohydroquinone]. Since Ca(2+)-ATPase inhibitors impaired refilling of the Ca2+ stores with Ca2+, and since in CD3-activated Jurkat T-cells the Ca2+ stores remained empty after 1 h of treatment with anti-CD3 monoclonal antibodies, we suggest that PtdSer synthesis is mainly regulated by the level of Ca2+ in the intracellular compartments and that the Ca(2+)-dependent serine base-exchange system responsible for PtdSer synthesis is probably located within or close to a Ca(2+)-storage organelle.
Pelassy
C
C
Interactions Cellulaires en Immunologie, INSERM U343, Faculté de Médecine, Nice, France.
Breittmayer
J P
JP
Aussel
C
C
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017252:CD3 Complex / Q000276:immunology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects; D010718:Phosphatidylserines / Q000096:biosynthesis*; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D000911:Antibodies, Monoclonal; D017252:CD3 Complex; D006873:Hydroquinones; D010718:Phosphatidylserines; D013729:Terpenes; C019359:2,5-di-tert-butylhydroquinone; D000001:Calcimycin; D015759:Ionomycin; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium