Quantitative imaging of lateral ErbB1 receptor signal propagation in the plasma membrane

Evidence for a new signaling mechanism consisting of ligand-independent lat eral propagation of receptor activation in the plasma membrane is presented . We visualized the phosphorylation of green fluorescent protein (GFP)-tagg ed ErbB1 (ErbB1-GFP) receptors in cells focally stimulated with epidermal g rowth factor (EGF) covalently attached to beads. This was achieved by quant itative imaging of protein reaction states in cells by fluorescence resonan ce energy transfer (FRET) with global analysis of fluorescence lifetime ima ging microscopy (FLIM) data. The rapid and extensive propagation of recepto r phosphorylation over the entire cell after focal stimulation demonstrates a signaling wave at the plasma membrane resulting in full activation of al l receptors.