1999 European Regional Conference Proceeding

May 12 - 16, 1999

Conference: 1999 European Regional Conference
Title: Binding properties and cAMP production study of 7 mutant V2 receptors related to cNDI
Authors: Morin, Denis; Mouillac, Bernard; Knoers, Nine; Bichet, Daniel G.; Manning, Ph.D., D.Sc., Maurice; Barberis, Claude
Institutions: INSERM U469, INSERM U401, CCIPE, University Medical Centre Nijmegen, Hopital du Sacre-Coeur de Montreal, Medical College of Ohio

After identification of mutations of the V2 receptor gene in patients with congenital nephrogenic diabetes insipidus, we performed the functional studies of the mutant V2 receptors by reproducing the mutations using site-directed mutagenesis and expressing the mutated receptors in COS-7 and CHO cells. Using immunoflurorescence microscopy of transfected cells, we showed that most of the mutant V2 receptors responsible for X-linked NDI are not transported to the cell surface. Nevertheless, in some cases, the mutant proteins are expressed on the plasma membrane and are still able to induce cAMP production. We had the opportunity to study 7 V2 mutant receptors, all of them having the ability to induce cAMP production. Binding studies using [3H]-AVP and a cyclic-peptide antagonist ligand: [125I]-d(CH2)5[D-Tyr(Et)2, Val4, Tyr-NH29] AVP, showed that all the mutants' receptors studied yielded a reduced binding affinity for AVP, while only five of them had a reduced affinity for the antagonist. cAMP production studies showed clearly that those mutant V2 receptors are able to respond to AVP and different V2 receptors agonists by inducing a significant cAMP increase. Our results gave us some new data concerning the study of the V2 receptor agonist and antagonist binding sites. It also suggested that, at least theoretically, V2 receptor agonists may be useful in patients with cNDI having those mutations in their V2 receptor gene.

Supported by Réseau INSERM de Recherche Clinique (N° 4R011A).

Most of the mutant vasopressin-2 receptors (AVPR2s) responsible for X-linked nephrogenic diabetes insipidus (X-NDI) are unable to travel to the cell surface, where they must be if they are to bind vasopressin (VP). Morin, et al., studied seven AVPR2 mutants responsible for X-NDI that were able to travel to the cell surface. Though all these mutant AVPR2s had a reduced binding affinity for VP -- a functional impairment resulting in NDI -- they still could respond to VP by inducing a significant increase in the metabolic regulator, cAMP.

The researchers' study also generated data concerning AVPR2 agonist and antagonist binding sites. (An agonist is a drug that has an affinity for AVPR2 and, once bound to it, the drug stimulates physiologic activity normally stimulated by VP. An antagonist is a drug that binds with AVP2R, but does not elicit a biological response.) The data suggest that, in some cases, AVPR2 agonists may be useful in treating patients with X-NDI.