Genetic evidence that β-arrestins are dispensable for the initiation of β 2 -adrenergic receptor signaling to ERK.

The β2 -adrenergic receptor (β2 AR) has provided a paradigm to elucidate how G protein-coupled receptors (GPCRs) control intracellular signaling, including the discovery that β-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 β-arrestin 1 (β-arr1) and β-arr2 in β2 AR internalization, trafficking, and signaling to ERK. We found that only β-arr2 was essential for β2 AR internalization. Unexpectedly, β-arr1 and β-arr2 and receptor internalization were dispensable for ERK activation. Instead, β2 AR signaled through Gαs and Gβγ 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 β2 AR signaling through β-arrestin-independent pathways in key physiological functions and under pathological conditions.