Abstract 546: β1 Adrenergic Receptor-Mediated Epidermal Growth Factor Receptor Transactivation Induces Differential Extracellular-Regulated Kinase Activation
The epidermal growth factor receptor (EGFR) contributes to cardiac growth, in part through the nuclear translocation of phosphorylated extracellular-regulated kinase (pERK) to activate transcription factors such as Elk1. Recently, we have shown that β1 adrenergic receptors (β1AR) transactivate EGFRs to induce ERK signaling. We hypothesized that ERK activated via β1AR-mediated EGFR transactivation behaves differently than ERK activated by growth factor stimulation of EGFR. HEK 293 cells stably expressing β1AR and transfected with FLAG- or GFP-EGFR and RFP-ERK were treated with dobutamine (Dob; β1AR agonist) or EGF (EGFR ligand). EGF and Dob each induced FLAG-EGFR phosphorylation and EGFR-GFP internalization, as detected by immunoblotting and confocal microscopy (see figure⇓ arrowheads), respectively, which were abolished by the EGFR antagonist AG 1478. Remarkably, only EGF stimulation induced translocation of cytosolic ERK-RFP to the nucleus, whereas Dob-activated ERK was restricted to the cytoplasm (see figure⇓ arrows). EGF and Dob both stimulated ERK (figure⇓, lower panel), resulting in phosphorylation of the cytosolic pERK substrates p70 and p85 S6K, confirming activation of ERK via both signaling pathways. Using an Elk1-driven luciferase reporter system, where nuclear pERK-mediated Elk1 activation induces luciferase expression, increased luciferase levels were detected only in response to treatment with EGF and not Dob. These data reveal a new signaling paradigm in which β1AR-mediated transactivation of EGFR differs from growth factor stimulation by restricting activated ERK to the cytoplasm, resulting in differential effects on gene regulation.