ABSTRACT
The relative abundance of phosphoinositide (PI) species on the phagosome membrane fluctuates over the course of phagocytosis. PtdIns(3,4,5)P3 and PtdIns(3,4)P2 rapidly increase in the forming of the phagocytic cup, following which they disappear after sealing of the cup. In the present study, we monitored the clearance of these PI species using the enhanced green fluorescent protein-fused pleckstrin homology domain of Akt, a fluorescence probe that binds both PtdIns(3,4,5)P3 and PtdIns(3,4)P2 in Raw 264.7 macrophages. The clearance of PIs was much faster when the phagocytosed particles were coated with IgG. The effect of IgG was not observed in the macrophages deficient in FcγRIIb, an inhibitory IgG receptor. To identify the lipid phosphatases responsible for the FcγRIIb-accelerated PI clearance, we prepared a panel of lipid phosphatase-deficient cells. The lack of a PI 5-phosphatase Src homology 2 domain-containing inositol-5-phosphatase (SHIP)1 or SHIP2 impaired the FcγRIIb-accelerated clearance of PIs. The lack of a PI 4-phosphatase Inpp4a also impaired the accelerated PIs clearance. In the FcγRIIb- and Inpp4a-deficient cells, acidification of the formed phagosome was slowed. These results suggested that FcγRIIb drives the sequential dephosphorylation system comprising SHIPs and Inpp4a, and accelerates phagosome acidification.
Subject(s)
Macrophages/metabolism , Oncogene Protein v-akt/metabolism , Phagocytosis , Phagosomes/metabolism , Phosphoric Monoester Hydrolases/metabolism , Receptors, IgG/metabolism , Animals , Hydrogen-Ion Concentration , Immunoglobulin G/metabolism , Macrophages/immunology , Mice , Oncogene Protein v-akt/genetics , Phosphatidylinositol Phosphates/metabolism , Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases/genetics , Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases/metabolism , Phosphoric Monoester Hydrolases/genetics , Phosphorylation , Protein Binding , RAW 264.7 Cells , RNA, Small Interfering/genetics , Receptors, IgG/geneticsABSTRACT
BACKGROUND: Although lamotrigine may be useful for treating bipolar depressive patients, some lamotrigine-associated adverse effects may prevent the continuation of treatment. The purpose of the present study was to identify risk factors for lamotrigine discontinuation after adjustment for several potential interactive factors. METHODS: We examined tolerability in those who discontinued lamotrigine within 2 months of treatment and those who maintained lamotrigine for more than 2 months. Groups were examined separately because 6-8 weeks are necessary to titrate dose and drug eruptions can often occur within 2 months of treatment commencement. RESULTS: Multiple regression analysis revealed that valproate combination was positively and significantly associated with lamotrigine discontinuation after adjustment for other factors. LIMITATIONS: The limitations of the present study were retrospective observation and a relatively small number of subjects. CONCLUSIONS: The present findings reconfirm that lamotrigine and valproate combination treatment may prevent the continuation of lamotrigine in some patients.
