Heterologous desensitization of EGF receptors and PDGF receptors by sequestration in caveolae.

Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) receptors have been reported to signal via caveolin-containing membranes called caveolae. In contrast, others report that EGF and PDGF receptors are exclusively associated with caveolin-devoid membranes called rafts. Our subcellular fractionation and coimmunoprecipitation studies demonstrate that, in the absence of ligand, EGF and PDGF receptors are associated with rafts. However, in the presence of ligand, EGF and PDGF receptors transiently associate with caveolae. Surprisingly, pretreatment of cells with EGF prevents PDGF-dependent phosphorylation of PDGF receptors and extracellular signal-regulated kinase (ERK) 1/2 kinase activation. Furthermore, cells pretreated with PDGF prevent EGF-dependent phosphorylation of EGF receptors and ERK1/2 kinase activation. Radioligand binding studies demonstrate that incubation of cells with EGF or PDGF causes both EGF and PDGF receptors to be reversibly sequestered from the extracellular space. Experiments with methyl-beta-cyclodextrin, filipin, and antisense caveolin-1 demonstrate that sequestration of the receptors is dependent on cholesterol and caveolin-1. We conclude that ligand-induced stimulation of EGF or PDGF receptors can cause the heterologous desensitization of the other receptor by sequestration in cholesterol-rich, caveolin-containing membranes or caveolae.