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A more recent version of this article appeared on July 1, 2007
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Submitted on January 26, 2007
Revised on March 29, 2007
Accepted on April 5, 2007
*Department of Microbiology and Immunology and Program in Immunology, University of Michigan Medical School, Ann Arbor, MI 48109-0620
Monitoring Editor: Yu-li Wang
In macrophages, enzymes that synthesize or hydrolyze phosphatidylinositol (3,4,5)-trisphosphate (PI(3,4,5)P3) regulate Fc
receptor-mediated phagocytosis. Inhibition of phosphatidylinositol 3-kinase (PI3K) or overexpression of the lipid phosphatases PTEN and SHIP-1, which hydrolyze PI(3,4,5)P3 to PI(4,5)P2 and PI(3,4)P2, respectively, inhibit phagocytosis in macrophages. To examine how these enzymes regulate phagosome formation, the distributions of YFP chimeras of enzymes and PH domains specific for their substrates and products were analyzed quantitatively. PTEN-YFP did not localize to phagosomes, suggesting that PTEN regulates phagocytosis globally within the macrophage. SHIP1-YFP and p85-YFP were recruited to forming phagosomes. SHIP1-YFP sequestered to the leading edge and dissociated from phagocytic cups earlier than did p85-CFP, indicating that SHIP-1 inhibitory activities are restricted to the early stages of phagocytosis. PH domain chimeras indicated that early during phagocytosis, PI(3,4,5)P3 was slightly more abundant than PI(3,4)P2 at the leading edge of the forming cup. These results support a model in which phagosomal PI3K generates PI(3,4,5)P3 necessary for later stages of phagocytosis, PTEN determines if those late stages can occur and SHIP-1 regulates when and where they occur by transiently suppressing PI(3,4,5)P3-dependent activities necessary for completion of phagocytosis.
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