Roles of class III phosphatidylinositol 3-kinase, Vps34, in phagocytosis, autophagy, and endocytosis in retinal pigmented epithelium

Phosphatidylinositol-3-phosphate (PI(3)P) is important for multiple functions of retinal pigmented epithelial (RPE) cells, but its functions in RPE have not been studied. In RPE from mouse eyes and in cultured human RPE cells, PI(3)P-enriched membranes include endosomes, the trans-Golgi network, phagosomes, and autophagophores. Mouse RPE cells lacking activity of the PI-3 kinase, Vps34, lack detectable PI(3)P and die prematurely. Phagosomes containing rod discs accumulate, as do membrane aggregates positive for autophagosome markers. These autophagy-related membranes recruit LC3/Atg8 without Vps34, but phagosomes do not. Vps34 loss leads to accumulation of lysosomes which do not fuse with phagosomes or membranes with autophagy markers. Thus, Vps34-derived PI(3)P is not needed for initiation of phagocytosis or endocytosis, nor for formation of membranes containing autophagy markers. In contrast, Vps34 and PI(3)P are essential for intermediate and later stages, including membrane fusion with lysosomes.