Endocytosis and vesicular trafficking of immune complexes and activation of phospholipase D by the human high-affinity IgG receptor requires distinctphosphoinositide 5-kinase activities

Fc gamma RI, the human high-affinity Ige receptor, is responsible for the i nternalization of immune complexes and their subsequent targetting to the l ysosomes for degradation. We show here that aggregation of Fc gamma RI by s urface immune complexes in interferon-gamma-primed U937 cells causes the tr ansient appearance of swollen vacuolar structures, probably swollen late en dosomes, which disappear as the immune complexes are degraded. Wortmannin a nd LY294002, specific inhibitors of phosphoinositide 3-kinases (PI 3-kinase s), delay the disappearance of these structures and also correspondingly in hibit degradation of Fc gamma RI-mediated immune complexes. In addition the se inhibitors delay the initial phase of Fc gamma RI-mediated endocytosis o f immune complexes and block the activity of Fc gamma RI-stimulated phospho lipase D, an enzyme that has previously been implicated in membrane-traffic king events, p85 is the regulatory subunit of PI 3-kinase. A p85-dependent PI 3-kinase was shown to be involved in the initial phase of Fc gamma RI-me diated endocytosis, but not in the trafficking of immune complexes for degr adation or the activation of phospholipase D. The results presented here sh ow a role for a p85-independent PI 3-kinase in regulating the trafficking o f Fc gamma RI-mediated immune complexes, either directly or as a result of the activation of phospholipase D, and a distinct role for a p85-dependent PI 3-kinase isoform in the initial phases of Fc gamma RI-mediated internali zation of immune complexes.