Epithelial cells are characterised by a tight intercellular adhesion. Disassembly of E-cadherin-mediated cell-cell adhesion can induce a transition from a benign epithelial phenotype to an invasive mesenchymal phenotype. Therefore, understanding the underlying mechanisms leading to adherens junction disruption will provide insights into potential therapeutic agents to prevent tumour metastasis. The small GTPases Arf6 and Rac can each disassemble E-cadherin-based junctions, upon which epithelial cells scatter. Preliminary results in our lab showed that Rae requires PAK function during junction disassembly and that Arf6 disrupts keratinocyte junctions in a process dependent on Rac signalling. Crosstalk between Arf6 and Rac has been described previously, but.the exact molecular mechanisms involved during Arf6-induced junction disassembly are not known. A good candidate molecule to provide the link between Arf6 and Rac is GIT1. GIT1 interacts with active Arf6 by an Arf6GAP domain and induces Rac activation via binding to the RacGEF 0PIX. Rac regulates many cellular. processes in which no effector proteins have been yet identified, inclUding perturbation of cell-cell contacts. Using a keratinocyte eDNA library screen with active Rac as bait, a new Rac binding protein named Armus has been isolated previously.. This protein is interesting as in addition to binding specifically to active Rac, it contains a TBC/RabGAP domain at its C-terminus, which is predicted to inactivate Rab small GTPases. Armus function is currently unknown. The aim of my PhD project was to test the involvement of GIT1, PAK and Armus in the disassembly of E-cadherin junctions induced by active Arf6 and Rac. I found that GIT1 and D-PIX might provide the link towards Rac signalling during Arf6induced junction disassembly. Furthermore, expression of the TBC/RabGAP domain of Armus can block Arf6-induced junction disruption by inactivating Rab7. In contrast, the Rac effector PAK1 does not playa role in Arf6-dependent junction disassembly. Moreover, I found that Armus and GIT1 are distributed on similar vesicular structures, suggesting that these proteins are spatially and functionally linked.Imperial Users onl
