title: Annexin-mediated membrane fusion of human neutrophil plasma membranes and phospholipid vesicles.
abstract: Membrane fusion was studied using human neutrophil plasma membrane preparations and phospholipid vesicles approximately 0.15 microns in diameter and composed of phosphatidylserine and phosphatidylethanolamine in a ratio of 1 to 3. Liposomes were labeled with N-(7-nitrobenzo-2-oxa-1,3-diazol-4-yl (NBD) and lissamine rhodamine B derivatives of phospholipids. Apparent fusion was detected as an increase in fluorescence of the resonance energy transfer donor, NBD, after dilution of the probes into unlabeled membranes. 0.5 mM Ca2+ alone was sufficient to cause substantial fusion of liposomes with a plasma membrane preparation but not with other liposomes. Both annexin I and des(1-9)annexin I caused a substantial increase in the rate of fusion under these conditions while annexin V inhibited fusion. Fusion mediated by des(1-9)annexin I was observed at Ca2+ concentrations as low as approximately 5 microM, suggesting that the truncated form of this protein may be active at physiologically low Ca2+ concentrations. Trypsin treated plasma membranes were incapable of fusion with liposomes, suggesting that plasma membrane proteins may mediate fusion. Liposomes did not fuse with whole cells at any Ca2+ concentration, indicating that the cytoplasmic side of the membrane is involved. These results suggest that annexin I and unidentified plasma membrane proteins may play a role in Ca(2+)-dependent degranulation of human neutrophils.
authors.affiliation: William B Castle Hematology Laboratory, Boston City Hospital, Department of Medicine, Boston University School of Medicine, MA 02118.
authors.forename: L
authors.initials: L
authors.lastname: Oshry
authors.forename: P
authors.initials: P
authors.lastname: Meers
authors.forename: T
authors.initials: T
authors.lastname: Mealy
authors.forename: A I
authors.initials: AI
authors.lastname: Tauber
mesh_terms: D017304:Annexin A5; D017302:Annexins; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000502:physiology*; D015550:Cell Degranulation; D002462:Cell Membrane / Q000502:physiology; D005453:Fluorescence; D006801:Humans; D008081:Liposomes / Q000378:metabolism*; D008561:Membrane Fusion / Q000502:physiology*; D009504:Neutrophils / Q000502:physiology*; D010714:Phosphatidylethanolamines / Q000032:analysis; D010718:Phosphatidylserines / Q000032:analysis; D011257:Pregnancy Proteins / Q000502:physiology*; D012235:Rhodamines; D014357:Trypsin / Q000378:metabolism
chemical_list: D017304:Annexin A5; D017302:Annexins; D002135:Calcium-Binding Proteins; D008081:Liposomes; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D011257:Pregnancy Proteins; D012235:Rhodamines; C022027:lissamine rhodamine B; D014357:Trypsin; D002118:Calcium