The β2-adrenergic receptor mediates extracellular signal-regulated kinase activation via assembly of a multi-receptor complex with the epidermal growth factor receptor
Many G protein-coupled receptors (GPCRs) activate MAP kinases by stimulating tyrosine kinase signaling cascades. In some systems, GPCRs stimulate tyrosine phosphorylation by inducing the 'transactivation' of a receptor tyrosine kinase (RTK). The mechanisms underlying GPCR-induced RTK transactivation have not been clearly defined. Here we report that GPCR activation mimics growth factor-mediated stimulation of the epidermal growth factor receptor (EGFR) with respect to many facets of RTK function. β2- Adrenergic receptor (β2AR) stimulation of COS-7 cells induces EGFR dimerization, tyrosine autophosphorylation, and EGFR internalization. Coincident with EGFR transactivation, isoproterenol exposure induces the formation of a multireceptor complex containing both the β2AR and the 'transactivated' EGFR. β2AR-mediated EGFR phosphorylation and subsequent β2AR stimulation of extracellular signal-regulated kinase (ERK) 1/2 are sensitive to selective inhibitors of both EGFR and Src kinases, indicating that both kinases are required for EGFR transactivation. β2AR-dependent signaling to ERK1/2, like direct EGF stimulation of ERK1/2 activity, is sensitive to inhibitors of clathrin-mediated endocytosis, suggesting that signaling downstream of both the EGF-activated and the GPCR-transactivated EGFRs requires a productive engagement of the complex with the cellular endocytic machinery. Thus, RTK transactivation is revealed to be a process involving both association of receptors of distinct classes and the interaction of the transactivated RTK with the cells endocytic machinery.
Maudsley, S; Pierce, KL; Zamah, AM; Miller, WE; Ahn, S; Daaka, Y; Lefkowitz, RJ; Luttrell, LM
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