A431 cells express approximately 10e6 epidermal growth factor (EGF) receptors at the cell surface. Upon stimulation with EGF, A431 cells exhibit a dramatic increase in phosphorylation of EGF receptors followed by activation of major cell signaling pathways, such as PKB/Akt and MAP kinase pathways. Downstream of these cell signaling pathways, a variety of cytoskeletal, cytoplasmic, and nuclear proteins become phosphorylated at different time points after EGF stimulation.