Inhibition of endosome fusion by phospholipase A2 (PLA2) inhibitors points to a role for PLA2 in endocytosis.
Fusion of intracellular membrane-bound compartments is a common step in the transport of macromolecules along the endocytic and secretory pathways. A large number of factors active in the fusion process or its regulation have been identified; however, the actual sequence of events leading to membrane fusion is still unknown. In this study, we have assessed a possible role for PLA2 in endosome fusion by using an in vitro reconstitution assay and by examining endocytosis in intact cells. Several PLA2 inhibitors blocked endosome fusion in a broken-cell preparation. Inhibition was reversed by addition of arachidonic acid. At the electron microscope level, endosome clusters were observed even in the presence of inhibitors; however, actual fusion between endosomes was largely reduced. Fusion frequency increased upon the addition of arachidonic acid. A membrane-permeable PLA2 inhibitor blocked mixing of ligands internalized sequentially but did not affect internalization. The results indicate that vesicle fusion along the endocytic pathway requires a PLA2 activity. The effect of this activity would be, at least in part, mediated by arachidonic acid release.
Mayorga
L S
LS
Department of Cell Biology & Physiology, Washington University School of Medicine, St. Louis, MO 63110.
Colombo
M I
MI
Lennartz
M
M
Brown
E J
EJ
Rahman
K H
KH
Weiss
R
R
Lennon
P J
PJ
Stahl
P D
PD
D000818:Animals; D000911:Antibodies, Monoclonal; D016718:Arachidonic Acid / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D004705:Endocytosis / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007700:Kinetics; D008264:Macrophages; D008561:Membrane Fusion / Q000187:drug effects; D008854:Microscopy, Electron; D015388:Organelles / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2
D000911:Antibodies, Monoclonal; D004791:Enzyme Inhibitors; D016718:Arachidonic Acid; D010741:Phospholipases A; D054467:Phospholipases A2