Macropinocytosis is an actin-driven process of large-scale and non-specific 
fluid uptake used for feeding by some cancer cells and the macropinocytosis 
model organism Dictyostelium discoideum In Dictyostelium, macropinocytic cups 
are organized by 'macropinocytic patches' in the plasma membrane. These contain 
activated Ras, Rac and phospholipid PIP3, and direct actin polymerization to 
their periphery. We show that a Dictyostelium Akt (PkbA) and an SGK (PkbR1) 
protein kinase act downstream of PIP3 and, together, are nearly essential for 
fluid uptake. This pathway enables the formation of larger macropinocytic 
patches and macropinosomes, thereby dramatically increasing fluid uptake. 
Through phosphoproteomics, we identify a RhoGAP, GacG, as a PkbA and PkbR1 
target, and show that it is required for efficient macropinocytosis and 
expansion of macropinocytic patches. The function of Akt and SGK in cell feeding 
through control of macropinosome size has implications for cancer cell biology.