Fibroblast growth factor-2-induced signaling through lipid raft-associated fibroblast growth factor receptor...

The plasma membrane is not homogeneous but contains specific subcompartments characterized by their unique lipid and protein composition. Based on their enrichment in various signaling molecules, these membrane microdomains are recognized to be sites of localized signal transduction for a number of extracellular stimuli. We have previously shown that fibroblast growth factor-2 (FGF2) induced a specific signaling response within a lipid raft membrane microdomain in human neuroblastoma cells characterized by the tyrosine phosphorylation of a p80 phosphoprotein. Herein, we show that this protein is the signaling adaptor FRS2 and that it is localized exclusively to lipid rafts in vitro and in vivo. We have examined how the tyrosine phosphorylation and serine-threonine phosphorylation of FRS2 within lipid rafts affect the response of cells to FGF2 signaling. Our data suggest that activation of protein kinase C, Src family kinases, and MEK1/2 are involved in regulating serine-threonine phosphorylation of FRS2, which can indirectly affect FRS2 phosphotyrosine levels. We also show that Grb2 is recruited to lipid rafts during signaling events and that activation of MEK1/2 by different mechanisms within lipid rafts may lead to different cellular responses. This work suggests that compartmentalized signaling within lipid rafts may provide a level of specificity for growth factor signaling.