Retromer endosome exit domains serve multiple trafficking destinations and regulate local G protein activation by GPCRs

This thesis asks (1) whether the divergent trafficking functions of the endosome-associating coat complex retromer require cargos to exit endosomes separately and (2) if distinct cargo-retromer interaction mechanisms affect signal activation from endosomes. Two retromer cargos that illustrate trafficking to distinct destinations are compared. First, the β-2 adrenergic receptor (B2AR) is a prototypical G protein-coupled receptor that responds to catecholamines and utilizes retromer for its transport from endosomes to the plasma membrane, the recycling pathway. Second, Wntless is a transport receptor for Wnt ligands, which are essential in developmental patterning and are misregulated in cancer, and requires retromer for its transport from endosomes to the trans-Golgi network (TGN), the retrograde transport pathway. Although my studies focus on these two cargos, the assumption is that the mechanistic insight gained is applicable to retromer-dependent transport generally. Chapter one provides an introduction to signaling and G protein-coupled receptors, explains the connection between signaling and membrane trafficking, introduces retromer, describes the model system used, and discusses previous knowledge of GPCR signaling from endosomes. Chapter two describes my findings showing that retromer mediates shared exit of cargos with divergent destinations and exerts a form of kinetic sorting that (1) determines the rate of cargo delivery and (2) controls signal activation by B2AR at endosomes. Finally, chapter three discusses the broader meaning of these new findings, places them into the context of current knowledge, and proposes future directions of this work