Akt signaling dynamics in plasma membrane microdomains visualized by FRET-based reporters.

Human kinase Akt has been shown to be activated at the plasma membrane upon generation of the cell membrane bound second messenger phosphatidylinositol (3,4,5)-trisphosphate through phosphatidylinositol 3-kinase (PI3K). Several components in the PI3K/Akt signaling pathway have been found in the detergent-resistant plasma membrane compartments, lipid rafts. Increasing evidence also suggests crucial roles of lipid rafts in the activation of Akt in different cell types. However, the regulatory mechanisms of Akt activation at different microdomains of the plasma membrane are not clear. Using a newly developed genetically encodable fluorescent kinase reporter based on fluorescence resonance energy transfer (FRET), AktAR, we studied spatio-temporal dynamics of Akt activity within plasma membrane microdomains in live-cell context. Our studies suggest that Akt activity is turned on more rapidly in lipid rafts upon growth factor stimulation, and platelet-derived growth factor (PDGF) or insulin-like Growth Factor-1 (IGF-1) stimulated Akt activity is differentially regulated between raft and non-raft regions of the plasma membrane.