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Annexin A7‐Mediated Membrane Fusion during Surfactant Secretion is increased with Diacylglycerol Enrichment of Lamellar Bodies
Author(s) -
Chander Avinash,
Chen XiaoLiang,
Callender Delon
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a550-a
Subject(s) - phosphatidylinositol , diacylglycerol kinase , phospholipid , chemistry , lipid bilayer fusion , phosphatidylcholine , biochemistry , phosphatidylserine , vesicle , phosphatidylethanolamine , secretion , biophysics , diglyceride , pulmonary surfactant , membrane , biology , protein kinase c , fatty acid , signal transduction
Annexin A7 (A7) increases lung surfactant secretion in permeabilized alveolar type II cells, possibly by increasing fusion between lamellar bodies (LB) and plasma membrane as shown in vitro. Stimulation of type II cells with ATP increases the phospholipase C‐mediated hydrolysis of phosphatidylinositol bisphosphate (PIP 2 ), elevates cell diacylglycerol (DAG), and augments surfactant secretion. For this study, we hypothesized that the presence of DAG or PIP 2 would alter protein‐membrane interaction and the Ca 2+ ‐dependent fusion activity of A7. The Ca 2+ ‐dependent increase in A7 fluorescence was higher in the presence of 5% PIP 2 containing phospholipid vesicles (PLV) in comparison to that with PLV without PIP 2 , indicating that PIP 2 altered the protein‐membrane interaction. Fluorescence quenching studies also indicated change in molecular organization since 5% dansyl phosphatidylethanolamine‐PLV quenched the A7 fluorescence in presence of PIP 2 ‐PLV or 5% DAG‐PLV, but not in presence of PLV without PIP 2 or DAG. These results suggest that PIP 2 hydrolysis to DAG does not further affect the mode of protein‐membrane interaction. Membrane fusion was measured by Ca 2+ ‐dependent change in transfer efficiency of resonance energy as reflected in increased fluorescence. Incubation of isolated lung LB with DAG and 10μM Ca 2+ caused LB enrichment with DAG. The A7‐mediated fusion of DAG‐enriched LB was higher in comparison to that of untreated LB. Thus, ATP treatment of type II cells could increase the DAG content of LB and facilitate A7‐mediated membrane fusion activity during surfactant secretion. Supported by HL 49959