Molecular Mechanism of GPCR‐mediated ERK Pathway in Cancer

Abstract

G protein-coupled receptors (GPCRs) are known to activate extracellular-signal-regulated kinase (ERK), a master regulator of cell proliferation and survival and a key oncogenic component. The co-occurrence of KRAS and GNAS (which encodes Gsa) mutations has been reported in several cancers including pancreatic ductal adenocarcinoma (PDAC), hinting at synergistic roles of these two pathways in activating pro-tumorigenic ERK. However, the precise mechanisms and the role underlying GPCR-mediated ERK regulation are not clearly understood. Here we investigated how the spatially organized β2-adrenergic receptor (b2AR) signaling controls ERK using FRET-based ERK activity biosensors targeted to various subcellular regions, which enable us to interrogate spatial and temporal regulation of ERK activity in living cells. In b2AR expressing HEK293 cells, epinephrine induces ERK activity at the endosome and in the nucleus, but not at the plasma membrane. This pool of ERK activity depends on endosome-localized active Gsa and requires ligand-stimulated b2AR endocytosis. The inhibition of endosomal b2AR and Gsa signaling using endosome-targeted nanobody and peptide inhibitor decreased basal nuclear ERK activity and proliferation in AsPC-1 cells, a PDAC cell line. The discovery of endosomal Gsa-mediated ERK activation could add the missing spatiotemporal information of GPCR regulation of ERK and also fill in the gap in our knowledge of GPCR signaling in cancer development, providing the basis for new therapeutic strategies for PDAC.