FUNCTIONAL RESCUE OF MUTANT V2 VASOPRESSIN RECEPTORS CAUSING NEPHROGENIC DIABETES-INSIPIDUS BY A COEXPRESSED RECEPTOR POLYPEPTIDE

Inactivating mutations in distinct G protein-coupled receptors (GPCRs) are currently being identified as the cause of a steadily growing num ber of human diseases, Based on previous studies showing that GPCRs ar e assembled from multiple independently stable folding units, we specu lated that such mutant receptors might be functionally rescued by 'sup plying' individual folding domains that are lacking or misfolded in th e mutant receptors, by using a co-expression strategy, To test the fea sibility of this approach, a series of nine mutant V2 vasopressin rece ptors known to be responsible for X-linked nephrogenic diabetes insipi dus were used as model systems, These mutant receptors contained nonse nse, frameshift, deletion or missense mutations in the third intracell ular loop or the last two transmembrane helices, Studies with transfec ted COS-7 cells showed that none of these mutant receptors, in contras t to the wild-type V2 receptor, was able to bind detectable amounts of the radioligand, [H-3]arginine vasopressin, or to activate the G(s)/a denylyl cyclase system, Moreover, immunological studies demonstrated t hat the mutant receptors were not trafficked properly to the cell surf ace, However, several of the nine mutant receptors regained considerab le functional activity upon co-expression with a C-terminal V2 recepto r peptide spanning the sequence where the various mutations occur, In many cases, the restoration of receptor activity by the co-expressed r eceptor peptide was accompanied by a significant increase in cell surf ace receptor density, These findings may lead to the design of novel s trategies in the treatment of diseases caused by inactivating mutation s in distinct GPCRs.