Campbell Krusemark

The neurotensin receptor 1 (NTSR1) is a G protein-coupled receptor (GPCR) with diverse central and peripheral activities, including the regulation of brain dopamine signaling, body temperature, and blood pressure. NTSR1 predominantly couples to the Gq family of heterotrimeric G proteins. Agonist binding stimulates GDP-to-GTP exchange and dissociation of the Gq Gα subunit from the βγ subunits. Balanced agonism of the NSTR1 results in Gq signaling as well as the recruitment of β-arrestin, which mediates receptor internalization and a spatially and temporally distinct pattern of kinase activation. We recently developed β-arrestin-biased allosteric modulators of the NTSR1. Typified by compound SBI-553, these modulators stimulate NTSR1-β-arrestin recruitment in the absence of Gq signaling. These modulators appear to maintain the ability of balanced agonists to modulate brain dopamine and attenuate addiction-associated behaviors in animal models, but they lack the thermal and hemodynamic regulatory properties of balanced agonists. Compounds of this class are promising candidates for anti-addiction drug development, but their mechanism of action has yet to be fully elucidated. Critically, it is unclear what role G protein-coupled receptor kinases (GRKs) and receptor phosphorylation play in the NTSR1-β-arrestin engagement stimulated by these biased allosteric modulators. Canonically, GPCR recruitment of β-arrestin is preceded by the recruitment of the kinase GRK2, which phosphorylates residues on the receptor’s C-terminal tail. Recruitment of the kinase GRK2 is preceded, in turn, by G protein activation and the binding of dissociated βγ to GRK2. It is unknown whether SBI-553-induced β-arrestin recruitment is preceded by GRK2 recruitment and receptor phosphorylation.