Non-canonical β-adrenergic activation of ERK at endosomes

G protein-coupled receptors (GPCRs), the largest family of signaling receptors, as well as important drug targets, are known to activate extracellular-signal-regulated kinase (ERK), a master regulator of cell proliferation and survival(1). However, the precise mechanisms underlying GPCR-mediated ERK activation are not clearly understood(2–4). Here we investigated how spatially organized β(2)-adrenergic receptor (β(2)AR) signaling controls ERK. Using subcellularly targeted ERK activity biosensors(5), we show that β(2)AR signaling induces ERK activity at endosomes, but not at the plasma membrane. This pool of ERK activity depends on active, endosome-localized Gα(s) and requires ligand-stimulated β(2)AR endocytosis. We further identify an endosomally localized non-canonical signaling axis consisting of Gα(s), Raf and mitogen-activated protein kinase kinase (MEK), resulting in endosomal ERK activity that propagates into the nucleus. Selective inhibition of endosomal β(2)AR and Gα(s) signaling blunted nuclear ERK activity, c-Myc gene expression and cell proliferation. These results uncover a non-canonical mechanism for the spatial regulation of ERK via GPCR signaling and identify a functionally important endosomal signaling axis.