The third intracellular loop and carboxyl tail of neurokinin 1 and 3 receptors determine interactions with β-arrestins

Tachykinins interact with three neurokinin receptors (NKRs) that are often coexpressed by the same cell. Cellular responses to tachykinins depend on the NKR subtype that is activated. We compared the colocalization of NK1R and NK3R with β-arrestins 1 and 2, which play major roles in receptor desensitization, endocytosis, and signaling. In cells expressing NK1R, the selective agonist Sar-Met-substance P induced rapid translocation of β-arrestins 1 and 2 from the cytosol to the plasma membrane and then endosomes, indicative of interaction with both isoforms. In contrast, the NK3R interacted transiently with only β-arrestin 2 at the plasma membrane. Despite these differences, both NK1R and NK3R similarly desensitized, internalized, and activated MAP kinases. Because interactions with β-arrestins can explain differences in the rate of receptor resensitization, we compared resensitization of agonist-induced Ca²⁺ mobilization. The NK1R resensitized greater than two-fold more slowly than the NK3R. Replacement of intracellular loop 3 and the COOH tail of the NK1R with comparable domains of the NK3R diminished colocalization of the NK1R with β-arrestin 1 and accelerated resensitization to that of the NK3R. Thus loop 3 and the COOH tail specify colocalization of the NK1R with β-arrestin 1 and determine the rate of resensitization.