Role for engagement of-arrestin2 by the transactivated EGFR in agonist-specific regulation of receptor activation of ERK1/2

Background and Purpose-Arrestins function as signal transducers linking GPCRs to ERK1/2 signalling either by scaffolding members of ERK1/2s cascades or by transactivating receptor tyrosine kinases through Src-mediated release of transactivating factor. Recruitment of -arrestins to the activated GPCRs is required for ERK1/2 activation. Our previous studies showed that receptors activate ERK1/2 through a -arrestin-dependent mechanism without inducing -arrestin binding to the receptors. However, the precise mechanisms involved remain to be established. Experimental ApproachERK1/2 activation by receptor ligands was assessed using HEK293 cells in vitro and male Sprague Dawley rats in vivo. Immunoprecipitation, immunoblotting, siRNA transfection, intracerebroventricular injection and immunohistochemistry were used to elucidate the underlying mechanism. Key ResultsWe identified a new signalling pathway in which recruitment of -arrestin2 to the EGFR rather than receptor was required for its role in receptor-mediated ERK1/2 activation in response to H-Tyr-Tic-Phe-Phe-OH (TIPP) or morphine stimulation. Stimulation of the receptor with ligands leads to the phosphorylation of PKC, which acts upstream of EGFR transactivation and is needed for the release of the EGFR-activating factor, whereas -arrestin2 was found to act downstream of the EGFR transactivation. Moreover, we demonstrated that coupling of the PKC/EGFR/-arrestin2 transactivation pathway to receptor-mediated ERK1/2 activation was ligand-specific and the Ser(363) of receptors was crucial for ligand-specific implementation of this ERK1/2 activation pathway. Conclusions and ImplicationsThe receptor-mediated activation of ERK1/2 is via ligand-specific transactivation of EGFR. This study adds new insights into the mechanism by which receptors activate ERK1/2.