Inside GPCR signalling

Abstract

von Zastrow and colleagues provide direct evidence that G protein-coupled receptor (GPCR) signalling occurs at endosomes, in addition to the plasma membrane. They generated a conformation-specific antibody (nanobody (Nb80)) that functions as a biosensor for activated (that is, agonist-bound) β2 adrenergic receptor (β2AR), a prototypical GPCR. Without agonist, Nb80–GFP localized to the cytoplasm in mammalian cells. After the addition of the agonist isoprenaline, Nb80–GFP was rapidly recruited to the plasma membrane, where it colocalized with β2ARs. β2ARs are known to be internalized after activation. Importantly, the authors observed that internalized β2ARs were not bound to Nb80–GFP; Nb80–GFP was later recruited to activated β2ARs at early endosomes. Use of another nanobody, Nb37, that is specific for activated G proteins, showed that G protein activation occurred at β2AR-containing endosomes, which contributed to the cellular cyclic AMP response. This directly shows that GPCRs signal from endosomes and the plasma membrane.