UC San Diego

G-protein-coupled receptors (GPCRs), the largest family of signalling receptors, as well as important drug targets, are known to activate extracellular-signal-regulated kinase (ERK)-a master regulator of cell proliferation and survival¹. However, the precise mechanisms that underlie GPCR-mediated ERK activation are not clearly understood^2-4. Here we investigated how spatially organized β₂-adrenergic receptor (β₂AR) signalling controls ERK. Using subcellularly targeted ERK activity biosensors⁵, we show that β₂AR signalling 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 β₂AR endocytosis. We further identify an endosomally localized non-canonical signalling axis comprising Gα_s, RAF and mitogen-activated protein kinase kinase, resulting in endosomal ERK activity that propagates into the nucleus. Selective inhibition of endosomal β₂AR and Gα_s signalling blunted nuclear ERK activity, MYC gene expression and cell proliferation. These results reveal a non-canonical mechanism for the spatial regulation of ERK through GPCR signalling and identify a functionally important endosomal signalling axis.