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Abstract:
Lipids affect the membrane properties determining essential biological processes. Earlier studies have suggested a role of switch-activated protein 70 (SWAP-70) in lipid raft formation of dendritic cells. We used lipidomics combined with genetic and biochemical assays to analyze the role of SWAP-70 in lipid dynamics. TLR activation using LPS as a ligand represented a pathogenic immunogenic stimulus, physical disruption of cell-cell contacts a tolerogenic stimulus. Physical disruption, but not LPS, caused an increase of phosphatidylcholine ether and cholesteryl esters in CD11c(+) immune cells. An increase of ceramide (Cer) was a hallmark for LPS activation. SWAP-70 was required for regulating the increase and localization of Cers in the cell membrane. SWAP-70 controls Cer accumulation through the regulation of pH-dependent acid-sphingomyelinase activity and of RhoA-dependent transport of endosomal contents to the plasma membrane. Poor accumulation of Cers in Swap70(-/-) cells caused decreased apoptosis. This shows that two different pathways of activation, immunogenic and tolerogenic, induce different changes in the lipid composition of cultured CD11c(+) cells, and highlights the important role of SWAP-70 in Cer dynamics in dendritic cells.
