Mechanisms of cell surface recycling pathways (360G-Wellcome-204636_Z_16_Z)

Cell surface proteins continually recycle through endosomes, where trafficking decisions control protein levels and activity. Yet, we have limited understanding of the mechanisms that regulate this recycling. I have identified a direct trafficking pathway from endosomes back to the plasma membrane in yeast, and have used genetic approaches to identify machinery that controls this. The majority of candidates identified are highly conserved; I now plan to define the fundamental mechanisms used by these molecules to control recycling. My key goal is to understand three specific regulatory units that I hypothesize are required for endosomes to create recycling tubules, into which cargoes are packaged and delivered back to the plasma membrane. I propose experiments to test three specific hypotheses: 1) Nhx1 elevates osmotic pressure in endosomes to drive recycling tubule formation, 2) Rag GTPases catalyse recycling tubule morphogenesis and drive selective cargo sorting, and 3) Ist1 polymerises on endosomes to drive scission of the recycling tubule. These yeast proteins all have clear human orthologues, and a series of experiments is aimed at testing these human versions in recycling. Importantly, I plan to extend these studies in human cells, to validate conserved recycling mechanisms identified in yeast and reveal additional mechanisms.