Photolabelling the urotensin II receptor reveals distinct agonist- and partial-agonist-binding sites

Urolinin: The First Linear Peptidic Urotensin-II Receptor Agonist

This study investigated the role of individual U-II amino acid positions and side chain characteristics important for U-IIR activation. A complete permutation library of 209 U-II variants was studied in an activity screen that contained single substitution variants of each position with one of the other 19 proteinogenic amino acids. Receptor activation was measured using a cell-based high-throughput fluorescence calcium mobilization assay. We generated the first complete U-II substitution map for U-II receptor activation, resulting in a detailed view into the structural features required for receptor activation, accompanied by complementary information from receptor modeling and ligand docking studies. On the basis of the systematic SAR study of U-II, we created 33 further short and linear U-II variants from eight to three amino acids in length, including d- and other non-natural amino acids. We identified the first high-potency linear U-II analogues. Urolinin, a linear U-II agonist (nWWK-Tyr(3-NO₂)-Abu), shows low nanomolar potency as well as improved metabolic stability.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, urotensin II-related peptide, and their receptor: from structure to function

Urotensin II (UII) is a cyclic neuropeptide that was first isolated from the urophysis of teleost fish on the basis of its ability to contract the hindgut. Subsequently, UII was characterized in tetrapods including humans. Phylogenetic studies and synteny analysis indicate that UII and its paralogous peptide urotensin II-related peptide (URP) belong to the somatostatin/cortistatin superfamily. In mammals, the UII and URP genes are primarily expressed in cholinergic neurons of the brainstem and spinal cord. UII and URP mRNAs are also present in various organs notably in the cardiovascular, renal, and endocrine systems. UII and URP activate a common G protein-coupled receptor, called UT, that exhibits relatively high sequence identity with somatostatin, opioid, and galanin receptors. The UT gene is widely expressed in the central nervous system (CNS) and in peripheral tissues including the retina, heart, vascular bed, lung, kidney, adrenal medulla, and skeletal muscle. Structure-activity relationship studies and NMR conformational analysis have led to the rational design of a number of peptidic and nonpeptidic UT agonists and antagonists. Consistent with the wide distribution of UT, UII has now been shown to exert a large array of biologic activities, in particular in the CNS, the cardiovascular system, and the kidney. Here, we review the current knowledge concerning the pleiotropic actions of UII and discusses the possible use of antagonists for future therapeutic applications.

Biased signaling regulates the pleiotropic effects of the urotensin II receptor to modulate its cellular behaviors

Biased agonism by G-protein-coupled receptor ligands has opened up strategies for targeted physiological or therapeutic actions. We hypothesized that urotensin II (UII)-derived peptides displayed unexpected physiological effects because of such biased signaling on the UII human urotensin (hUT) receptor. We determined the coupling to G proteins and β-arrestins of the UII-activated hUT receptor expressed in HEK293 using bioluminescence resonance energy transfer (BRET) biosensors, as well as the production of IP1-3 and cAMP using homogenous time-resolved Forster resonance energy transfer (FRET) (HTRF)-based assays. The activated receptor coupled to Gi1, GoA, Gq, and G13, excluding Gs, and recruited β-arrestins 1 and 2. Integration of these pathways led to a 2-phase kinetic phosphorylation of ERK1/2 kinases. The tested peptides induced three different profiles: UII, urotensin-related peptide (URP), and UII4-11 displayed the full profile; [Orn(8)]UII and [Orn(5)]URP activated G proteins, although with pEC50s 5-10× higher, and did not or barely recruited β-arrestin; urantide also failed to recruit β-arrestin but displayed a reversed rank order for Gi and Gq vs. Go pEC50s (-8.79±0.20, -8.43±0.21, and -7.86±0.36, respectively, for urantide, -7.87±0.10, -7.23±0.27, and -8.55±0.19, respectively, for [Orn(5)]URP) and was a partial agonist of all G-protein pathways. Interestingly, the peptides differently modulated cell survival but similarly induced cell migration and adhesion. Thus, we demonstrate biased signaling between β-arrestin and G proteins, and between G-protein subtypes, which dictates the receptor's cellular responses.

Role of urotensin II in health and disease

Urotensin II (UII) is an 11 amino acid cyclic peptide originally isolated from the goby fish. The amino acid sequence of UII is exceptionally conserved across most vertebrate taxa, sharing structural similarity to somatostatin. UII binds to a class of G protein-coupled receptor known as GPR14 or the urotensin receptor (UT). UII and its receptor, UT, are widely expressed throughout the cardiovascular, pulmonary, central nervous, renal, and metabolic systems. UII is generally agreed to be the most potent endogenous vasoconstrictor discovered to date. Its physiological mechanisms are similar in some ways to other potent mediators, such as endothelin-1. For example, both compounds elicit a strong vascular smooth muscle-dependent vasoconstriction via Ca2+ release. UII also exerts a wide range of actions in other systems, such as proliferation of vascular smooth muscle cells, fibroblasts, and cancer cells. It also 1) enhances foam cell formation, chemotaxis of inflammatory cells, and inotropic and hypertrophic effects on heart muscle; 2) inhibits insulin release, modulates glomerular filtration, and release of catecholamines; and 3) may help regulate food intake and the sleep cycle. Elevated plasma levels of UII and increased levels of UII and UT expression have been demonstrated in numerous diseased conditions, including hypertension, atherosclerosis, heart failure, pulmonary hypertension, diabetes, renal failure, and the metabolic syndrome. Indeed, some of these reports suggest that UII is a marker of disease activity. As such, the UT receptor is emerging as a promising target for therapeutic intervention. Here, a concise review is given on the vast physiologic and pathologic roles of UII.

Characterization of the insulinostatic effect of urotensin II: a study in the perfused rat pancreas

We have investigated the effect of urotensin II (UII) on insulin secretion at normal and high glucose concentrations as well as induced by secretagogues acting on the B cell via different mechanisms. The study was performed in the perfused rat pancreas. UII, at 1 nM, blocked the insulin response to an increase in perfusate glucose concentration from 5.5 to 9 mM while failed to significantly modify insulin secretion at higher glucose levels (from 9 to 13 mM). The insulinotropic effect of this glucose challenge was reduced by 10 nM UII. UII, at 1 nM, inhibited tolbutamide-induced insulin secretion, whereas, it did not affect KCl-induced insulin release. UII inhibited exendin-4-induced insulin secretion, an effect not observed in pertussis toxin-treated rats.

CONCLUSION

1) B cells are less sensitive to UII at a high glucose level than at a low glucose. 2) The inhibitory effect of UII on both glucose and tolbutamide-induced insulin release, suggests the implication of ATP-dependent K(+) channels. The insulinostatic effect of UII was not observed during KCl stimulation, a condition in which these channels are overridden. 3) The insulinostatic effect of UII can also be mediated by its inhibitory action on the adenylate cyclase/cAMP system via a pertussis toxin-sensitive G(i) protein.

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.

Solution structure of urotensin-II receptor extracellular loop III and characterization of its interaction with urotensin-II

Urotensin-II (U-II) is a vasoactive hormone that acts through a G-protein-coupled receptor named UT. Recently, we have shown, using the surface plasmon resonance technology that human U-II (hU-II) interacts with the hUT(281-300) fragment, a segment containing the extracellular loop III (EC-III) and short extensions of the transmembrane domains VI and VII (TM-VI and TM-VII). To further investigate the interaction of UT receptor with U-II, we have determined the solution structure of hUT(281-300) by high-resolution NMR and molecular modeling and we have examined, also using NMR, the binding with hU-II at residue level. In the presence of dodecylphosphocholine micelles, hUT(281-300) exhibited a type III beta-turn (Q285-L288), followed by an -helical structure (A289-L299), the latter including a stretch of transmembrane helix VII. Upon addition of hU-II, significant chemical shift perturbations were observed for residues located just on the N-terminal side of the beta-turn (end of TM-VI/beginning of EC-III) and on one face of the -helix (end of EC-III/beginning of TM-VII). These data, in conjunction with intermolecular NOEs, suggest that the initiation site of EC-III, as well as the upstream portion of helix VII, would be involved in agonist binding and allow to propose points of interaction in the ligand-receptor complex.

Biological properties and functional determinants of the urotensin II receptor

The urotensin II receptor (UT) is a member of the G protein-coupled receptor (GPCR) family and binds the cyclic undecapeptide urotensin II (U-II) as well as the octapeptide urotensin II-related peptide (URP). The active UT mediates pleiotropic effects through various signal transduction pathways, including coupling to G proteins and activating the mitogen-activated protein kinase pathway. Several highly conserved residues and motifs of class A GPCRs that are important for activity are found in UT. This review highlights some of the putative roles of these motifs in the binding, activation and desensitization of UT.