| Summary: | The importance of elucidating the cell biological mechanisms of migration is underlined by the fundamental roles this process plays in tissue development, immunology, neurobiology, and the invasion and metastasis phases of oncogenesis. Members of the Rho family of small g-proteins have been shown to be master regulators of cell migration. Here it is shown that the Rho GAP domain-containing protein GRAF1 defines and regulates a major clathrin-independent endocytic pathway responsible for the internalisation of bacterial exotoxins, GPI linked proteins, and extracellular fluid. This endocytic pathway is independent of Clathrin, Caveolin and Flotillin, but can be further defined by the presence of Rab8. Since GRAF1 is a multidomain protein, biochemical dissection of this endocytic route could then be performed. GRAF1 localises to highly dynamic PtdIns(4,5)P<sub>2</sub>-enriched membranes via N-terminal BAR and PH domains, and interacts with proteins including Dynamin, GIT1, FAK, and PAK2. Since these latter proteins promote the disassembly of focal adhesions, this places GRAF1 in a position whereby it may coordinate cell migratory events through coupling membrane redistribution and focal adhesion turnover. Indeed, GRAF1 is necessary for turnover of focal complexes/adhesions, and GRAF1-dependent endocytosis occurs from these sites in a small G-protein dependent manner. Further, GRAF1 is necessary for cell migration. The studies presented in this thesis thereby provide the first markers for this prevalent endocytic pathway and reveal dynamic cellular anatomy responsible for the coupling of endocytosis and cell migration.
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