Selective membrane exclusion in phagocytic and macropinocytic cups.
Specialized eukaryotic cells can ingest large particles and sequester them within membrane-delimited phagosomes. Many studies have described the delivery of lysosomal proteins to the phagosome, but little is known about membrane sorting during the early stages of phagosome formation. Here we used Dictyostelium discoideum amoebae to analyze the membrane composition of newly formed phagosomes. The membrane delimiting the closing phagocytic cup was essentially derived from the plasma membrane, but a subgroup of proteins was specifically excluded. Interestingly the same phenomenon was observed during the formation of macropinosomes, suggesting that the same sorting mechanisms are at play during phagocytosis and macropinocytosis. Analysis of mutant strains revealed that clathrin-associated adaptor complexes AP-1, -2 and -3 were not necessary for this selective exclusion and, accordingly, ultrastructural analysis revealed no evidence for vesicular transport around phagocytic cups. Our results suggest the existence of a new, as yet uncharacterized, sorting mechanism in phagocytic and macropinocytic cups.
Mercanti
Valentina
V
Université de Genève, Centre Médical Universitaire, Département de Physiologie Cellulaire et Métabolisme, 1 rue Michel Servet, CH-1211 Genève 4, Switzerland.
Charette
Steve J
SJ
Bennett
Nelly
N
Ryckewaert
Jean-Jeacques
JJ
Letourneur
François
F
Cosson
Pierre
P
D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology*; D002478:Cells, Cultured; D004023:Dictyostelium / Q000502:physiology; D007425:Intracellular Membranes / Q000502:physiology; D008954:Models, Biological; D009218:Myosins / Q000502:physiology; D010587:Phagocytosis / Q000502:physiology*; D010588:Phagosomes / Q000737:chemistry / Q000502:physiology; D010873:Pinocytosis / Q000502:physiology*; D021381:Protein Transport / Q000502:physiology
D033942:Adaptor Proteins, Vesicular Transport; D009218:Myosins