Macrophage macropinocytosis contributes to wound healing, antigen presentation, and resolution of inflammation. Macropinocytosis also facilitates nutrient uptake and growth in macrophages, T cells, and cancer cells. Here, CRISPR/Cas9 whole-genome screens in murine bone-marrow derived macrophages (BMDM) identified genes regulating unstimulated, PMA-, and CSF1-stimulated uptake of the fluorescent pinocytosis solute tracer, Lucifer yellow. UVRAG and other members of VPS34 complex II (VPS34-II), which catalyze PI(3)P formation from phosphatidylinositol, were identified as positive regulators of macropinocytosis. Targeted gene disruption of Uvrag and Pik3r3 revealed that VPS34-II is required for efficient macropinocytosis with Uvrag-disrupted BMDM having fewer but larger macropinosomes. In contrast, depletion of ATG14, a unique component of VPS34 complex I, increased solute uptake and the number of macropinosomes. Live-cell imagining of macrophages expressing 2xFYVE-fluorescent protein fusions showed PI(3)P present on the plasma membrane, nascent macropinosomes, and endosomes. The presence of PI(3)P on the plasma membrane prior to macropinocytic cup closure, indicates a novel role on the plasma membrane. Quantitative imaging of fixed cells shows a decrease in concentration of PI(3)P in Uvrag-disrupted BMDMs while increase in concentration of PI(3)P in Atg14-disrupted BMDM compared to WT BMDMs. Treatment with the VPS34 inhibitor SAR-405 acutely decreased macropinocytosis but maintained AKT phosphorylation suggesting class I PI3K activity and PI(3,4,5)P3 production are independent of class III PI3K activity. These results suggest that PI(3)P is a key phosphoinositide governing macropinocytosis at the plasma membrane and that it is primarily formed via direct phosphorylation of PI rather than via the sequential dephosphorylation of PIP3.
Neupane, A., Wollman, J. W., Donahoe, J., Pradhan, B., Balster, J. J., Poudel, S., Waniarachchi, K., Hoppe, A. D., Swanson, J. A., Scott, B. L., Thiex, N. W.
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