Mutational analysis of the conserved Asp2.50 and ERY motif reveals signaling bias of the urotensin II receptor.

Class A (rhodopsin-like) G protein-coupled receptors possess conserved residues and motifs that are important for their specific activity. In the present study, we examined the role of residue Asp97(2.50) as well as residues Glu147(3.49), Arg148(3.50), and Tyr149(3.51) of the ERY motif on the functionality of the urotensin II receptor (UT). Mutations D97(2.50)A, R148(3.50)A, and R148(3.50)H abolished the ability of UT to activate phospholipase C, whereas mutations E147(3.49)A and Y149(3.51)A reduced the ability to activate PLC by 50%. None of the mutants exhibited constitutive activity. However, R148(3.50)A and R148(3.50)H promoted ERK1/2 activation, which was abolished by 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG1478), an inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase activity. Both these mutants were capable of directly activating EGFR, which confirmed that they activated the mitogen-activated protein kinase (MAPK) pathway by a Galpha(q/11)-independent transactivation of EGFR. The D97(2.50)A, R148(3.50)A, and R148(3.50)H mutants did not readily internalize and did not promote translocation or colocalize with beta-arrestin2-GFP. Finally, the agonist-induced internalization of the E147(3.49)A mutant receptor was significantly increased compared with wild-type receptor. This study highlights the major contribution of the conserved Asp(2.50) residue to the functionality of the UT receptor. The Arg residue in the ERY motif of UT is an important structural element in signaling crossroads that determine whether Galpha(q/11)-dependent and -independent events can occur.