Specific role of phosphoinositide 3-kinase p110α in the regulation of phagocytosis and pinocytosis in macrophages

PI3K (phosphoinositide 3-kinase) alpha has been implicated in phagocytosis and fluid-phase pinocytosis in macrophages. The subtype-specific role of PI3K in these processes is poorly understood. To elucidate this issue, we made Raw 264.7 cells (a mouse leukaemic monocyte-macrophage cell line) deficient in each of the class-I PI3K catalytic subunits: p110 alpha, p110 beta, p110 delta and p110 gamma. Among these cells, only the p110 alpha-deficient cells exhibited lower phagocytosis of opsonized and non-opsonized zymosan. The p11 alpha-deficient cells also showed the impaired phagocytosis of IgG-opsonized erythrocytes and the impaired fluid-phase pinocytosis of dextran (molecular mass of 40 kDa). Receptor-mediated pinocytosis of DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate)-labelled acetylated low-density lipoprotein and fluid-phase pinocytosis of Lucifer Yellow (molecular mass of 500 Da) were resistant to p110 alpha depletion. None of these processes were impaired in cells lacking p110 beta, p110 delta or p110 gamma, but were Susceptible to a pan-PI3K inhibitor wortmannin. In cells deficient in the enzymes catalysing PtdIns(3,4,5)P-3 breakdown [PTEN (phosphatase and tensin homologue deleted oil chromosome 10) or SHIP-1 (Src-homology-2-domain-containing inositol phosphatase-1)], uptake of IgG-opsonized particles wits enhanced. These results indicated that phagocytosis and fluid-phase pinocytosis of larger molecules are dependent oil the lipid kinase activity of p110 alpha, whereas pinocytosis via clathrin-coated and small non-coated vesicles may depend oil subtypes of PI3Ks other than class I.