Cholesterol is important in control of EGF receptor kinase activity but EGF receptors are not concentrated in caveolae

We have investigated the localization and function of the epidermal growth factor receptor (EGFR) in normal cells, in cholesterol-depleted cells and in cholesterol enriched cells. Using immunoelectron microscopy we find that the EGFR is randomly distributed at the plasma membrane and not enriched in caveolae. Binding of EGF at 4°C does not change the localization of EGFR,and by immunoelectron microscopy we find that only small amounts of bound EGF localize to caveolae. However, upon patching of lipid rafts, we find that a significant amount of the EGFR is localized within rafts. Depletion of the plasma membrane cholesterol causes increased binding of EGF, increased dimerization of the EGFR, and hyperphosphorylation of the EGFR. Addition of cholesterol was found to reduce EGF binding and reduce EGF-induced EGFR activation. Our results suggest that the plasma membrane cholesterol content directly controls EGFR activation.