THE FAK-ABCA1 SYSTEM

Population context-dependent regulation of membrane lipid composition and downstream activities in mammalian cells: the FAK-ABCA1 system

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 Obiettivo del progetto (Objective)

'The aim of this project is to uncover a novel regulatory mechanism that explains how cells change their membrane lipid composition and trafficking as a function of population context, and how that is used to adapt the cell’s physiology to its microenvironment. To do so, I will use single cell microscopy over large populations, lipidomic, phosphoproteomic and microarray analysis of mice cells deleted from Focal Adhesion Kinase (FAK).

When cells grow at low local cell density or at the edges of cell islets, FAK becomes activated. This event activates signalling and gene regulation. Interestingly, silencing of FAK strongly impairs sphingolipid GM1 amount at the plasma membrane and fate through clathrin-independent endocytosis, leading to drastic diminution of Simian Virus 40 (SV40) infection. Microarray analysis of FAK-KO cells and Wild Type, in dense and sparse contexts, shows that lysosomal, Golgi apparatus and trafficking genes are controlled by activated Focal Adhesion Kinase. ABCA1, a membrane scrambler and cholesterol efflux mediator, is the second overall strongest hit and the only membrane protein amongst the top hits. Strikingly the loss-of-FAK phenotype in cell spreading and growth can be reversed by inhibiting ABCA1, suggesting that FAK act on membranes by controlling ABCA1 production.

I would like to characterise the actors and dynamics of the FAK-ABCA1 system to understand how it couples membrane composition and clathrin-independent trafficking to local environments. I will apply i)phosphoproteomic approach and chromatin Immunoprecipitation for finding key signalling axis from FAK activation to gene regulation, ii)lipidomic for characterizing FAK effect on membrane composition, and iii)leading edge single cell microscopy over large populations both in live or fixed conditions in order to characterise the FAK-ABCA1 system effect on membrane ordering and sphingolipid endocytosis to the Golgi apparatus or lysosome, as a function of cell density'