Endosomes function in the uptake, recycling, and degradation of nutrients, receptors, and cell signaling molecules. Previously, we have characterized phosphatidylinositol (PI) 4-kinase type II-based protein modules at endosomes that differentially regulate Wnt signaling. During the forthcoming funding period we will dissect the molecular basis underlying complex formation between PI3KC2β with Raptor and HOPS and of PI4KIIα/β and exocyst. We will analyze how these PI kinase modules are organized in time and space, how they contribute to endolysosomal membrane homeostasis, and how they regulate cell signaling.