Genetic evidence that b-arrestins are dispensable for the initiation of b2-adrenergic receptor signaling to ERK

Abstract

The b2-adrenergic receptor (b2AR) has provided a paradigm to elucidate how G protein-coupled receptors (GPCRs) control intracellular signaling, including the discovery that b-arrestins, which bind to ligand-activated GPCRs, are central for GPCR function. We used genome editing, conditional gene deletion, and small interfering RNAs (siRNAs) to determine the roles of b-arrestin 1 (b-arr1) and b-arr2 in b2AR internalization, trafficking, and signaling to ERK. We found that only b-arr2 was essential for b2AR internalization. Unexpectedly, b-arr1 and b-arr2 and receptor internalization were dispensable for ERK activation. Instead, b2AR signaled through Gas and Gbg subunits through a pathway that involved the tyrosine kinase SRC, the adaptor protein SHC, the guanine nucleotide exchange factor SOS, the small GTPase RAS, and the kinases RAF and MEK, which led to ERK activation. These findings provide a molecular framework for b2AR signaling through b-arrestin-independent pathways in key physiological functions and under pathological conditions.