Muscarinic receptor regulates extracellular signal regulated kinase by two modes of arrestin binding

Significance G-protein–coupled receptors (GPCRs) can transmit external signals into the cytoplasm via the activation of G proteins. They also mediate G-protein–independent signaling that uses arrestin to activate an extracellular signal-regulated kinase (ERK) cascade. Using real-time optical measurements, we show that arrestin binds in two modes. Stable binding of arrestin to phosphorylated amino acids in the third intracellular loop of the muscarinic receptor upregulates ERK. Transient binding of arrestin to the unphosphorylated receptor downregulates ERK. Thus, the signaling bias of ERK can be determined by binding modes of arrestin to the receptors. Our results suggest a molecular mechanism for GPCR-arrestin-ERK coupling and pave the way for the development of new therapeutic approaches.