Regulation of Epidermal Growth Factor Receptor Internalization by G Protein-Coupled Receptors

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Abstract
The epidermal growth factor (EGF) receptor (EGFR) plays a central role in regulating cell proliferation, differentiation, and migration. Cellular responses to EGF are dependent upon the amount of EGFR present on the cell surface. Stimulation with EGF induces sequestration of the receptor from the plasma membrane and its subsequent downregulation. Recently, internalization of the EGFR was also shown to be required for mitogenic signaling via the activation of MAP kinases. Therefore, mechanisms regulating internalization of the EGFR represent an important facet for the control of cellular response. Here, we demonstrate that EGFR is removed from the cell surface not only following stimulation with EGF, but also in response to stimulation of G protein-coupled lysophosphatidic acid (LPA) and β2 adrenergic (β2AR) receptors. Using a FLAG epitope-tagged EGFR to quantitate receptor internalization, we show that incubation with EGF, LPA, or isoproterenol (ISO) causes the time-dependent loss of cell surface EGFR. Internalization of EGFR by these ligands involves the tyrosine kinase activity of the receptor itself and c-Src, as well as the GTPase activity of dynamin. Unexpectedly, we find that internalization of the EGFR by EGF is dependent upon Gβγ and β-arrestin proteins; expression of minigenes encoding the carboxyl terminii of the G protein-coupled receptor kinase 2, or β-arrestin1, attenuates LPA-, ISO-, and EGF-mediated internalization of EGFR. Thus, G protein-coupled receptors can control the function of the EGFR by regulating its endocytosis.