Integrin-mediated adhesion controls the transmission of many signals downstream of growth factor and cytokine receptors. These effects modulate cell growth, differentiation and many other functions. Our previous work identified an integrin-regulated membrane trafficking pathway that mediates a number of these effects. Detachment of anchorage- dependent cells from their extracellular matrix triggers internalization of lipid raft components via caveolae. The resultant clearance of these domains from the plasma membrane inhibits growth factor activation of Rho family GTPases, Erk and Akt. Replating cells on extracellular matrix triggers exocytosis of these components to promote cell spreading and restore signaling. During the last grant period, we identified Arf6 as the key determinant of the first step of exocytosis: exit of raft components from the recycling endosomes. We then showed that RalA mediates the next step, docking of exocytic vesicles at the plasma membrane through its interaction with the exocyst. RalA has been implicated as a specific regulator of anchorage-dependence of growth and cancer metastasis in many systems, thus, our data link integrin regulation of membrane trafficking with tumor growth and metastasis. We now propose to investigate the mechanisms by which integrins control the exocytosis pathway and investigate its role in cell motility. Specifically, we will elucidate the mechanism by which integrins regulate RalA during lipid raft exocytosis by identifying the relevant guanine nucleotide exchange factor that mediates integrin activation of RalA and further define the mechanism of activation. We will similarly identify the exchange factors that mediate Arf6 activation and investigate mechanism. Lastly, we will elucidate the role of integrin-regulated lipid raft transport in cell motility, specifically whether there is spatially restricted regulation of lipid raft trafficking via the same pathway and how it contributes to directed cell movement. This work will contribute to our understanding of a pathway that is fundamental to cell behavior as well as crucial in regulating cancer metastasis.
Integrin signaling is one of the basic cellular regulatory mechanisms that governs cell growth, migration, tissue organization and morphogenesis. Defects in these pathways lead to immune deficiencies, autoimmune diseases, birth defects and cancer to name but a few. Integrin signaling mediates anchorage dependence of cell growth, a fundamental mechanism that serves as a safeguard against cancer metastasis. This project aims to elucidate the pathways by which integrins regulate lipid raft vesicular transport and subsequent effects on cell migration and signaling. Our previous work on this pathway has shown that it is regulated by gene products that are highly linked to cancer metastasis. This project therefore has direct relevance for understanding and potentially treating cancer metastasis, as well as important implications for a wide range of morphogenetic and migratory processes in humans.
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