Molecular mechanisms of retromer-mediated endosome-to-Golgi retrieval

In the cells of your body there are lots of different compartments each with a specific job to do, for example the nucleus of the cell contains your DNA. Other compartments do different jobs and have their own set of proteins that perform these tasks. Proteins are transported to these compartments in tiny carriers that shuttle between the different compartments like trains on a track. For a particular protein to be sent to a specific compartment, the protein must contain a signal that acts like a ticket to direct that protein from one compartment to another. The ?ticket? is read by other proteins that act like ticket inspectors to make sure that the right proteins are sent to the correct destination. If the process goes wrong, either because the ?ticket? is damaged or incorrect, or because the ?ticket inspectors? can?t read the ?ticket? properly then proteins end up in the wrong place and that can cause diseases such as Alzheimer?s disease. We aim to study one of the pathways in the cells to identify all the various ?ticket inspectors? in that pathway and understand what ?tickets? are required in that pathway.

Protein localisation to the compartments that comprise the secretory and endocytic pathways is determined by intrinsic information in proteins (i.e. sorting signals) and extrinsic machinery (i.e. coat proteins) that recognise the sorting signals. Endosome-to-Golgi retrieval is a vital pathway that functions to recycle lysosomal hydrolase receptors, for example the cation-independent mannose 6-phosphate receptor, (CI-MPR) from endosomes to the Golgi and retrieve escaped trans-Golgi network (TGN) resident proteins to maintain the integrity of the TGN. This pathway has been shown to be important in certain genetic diseases including the lysosomal storage disorder, Niemann-Pick C, and more recently has been implicated in the localisation and proteolytic processing of the amyloid precursor protein (APP) and therefore has a role in the development of Alzheimer?s disease (AD).
The main aim of this proposal is to understand the molecular mechanisms of endosome-to-Golgi retrieval. These studies will therefore be of significant importance in determining the underlying causes of complex pathologies such as AD.
Studies in my lab have focused on a conserved protein complex called retromer that is essential for endosome-to-Golgi retrieval in yeast and mammalian cells. Retromer functions to sort cargo proteins such as the CI-MPR into vesicles/tubules for retrieval to the Golgi. Our studies in yeast and mammalian cells have significantly enhanced the understanding of retromer function and provide us with a platform on which we will extend our studies to determine the molecular mechanisms of endosome-to-Golgi retrieval. To understand this pathway, we must identify and characterise the components that function with retromer in endosome-to-Golgi retrieval.
To this end we will investigate the functional significance of the interaction between retromer and the small GTPase rab7. Additionally we have identified three novel proteins, p120, p130 and p190 which interact with retromer. The role of these proteins in retromer function will be explored. To further our understanding of how retromer assembles, we have generated temperature conditional mutants of the yeast Vps26 protein which is a key component of retromer. These mutants will be fully characterised to determine the molecular basis for the assembly of the retromer complex.