PI3K (phosphoinositide 3-kinase) α 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: p110α, p110β, p110δ and p110γ. Among these cells, only the p110α-deficient cells exhibited lower phagocytosis of opsonized and non-opsonized zymosan. The p110α-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 p110α depletion. None of these processes were impaired in cells lacking p110β, p110δ or p110γ, but were susceptible to a pan-PI3K inhibitor wortmannin. In cells deficient in the enzymes catalysing PtdIns(3,4,5)P3 breakdown [PTEN (phosphatase and tensin homologue deleted on chromosome 10) or SHIP-1 (Src-homology-2-domain-containing inositol phosphatase-1)], uptake of IgG-opsonized particles was enhanced. These results indicated that phagocytosis and fluid-phase pinocytosis of larger molecules are dependent on the lipid kinase activity of p110α, whereas pinocytosis via clathrin-coated and small non-coated vesicles may depend on subtypes of PI3Ks other than class I.

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