Two vasopressin type 2 receptor gene mutations R143P and delta V278 in patients with nephrogenic diabetes insipidus impair ligand binding of the receptor.

We recently identified vasopressin type 2 receptor gene mutations in two unrelated Japanese families with X-linked nephrogenic diabetes insipidus, which were a missense mutation from Arg143 to Pro (R143P) and a single amino acid deletion of Val278 or 279 (delta V278). To investigate the mechanism by which the mutations cause arginine vasopressin (AVP) resistance in this disorder, we expressed them in mammalian cells and analyzed their functional properties. Stable expression study with Chinese hamster ovary (CHO) cells demonstrated that the R143P mutation reduced receptor binding capacity to 10% of normal. However, the R143P mutant itself had a normal affinity for AVP and stimulated adenylyl cyclase production at up to 50% of the wild-type level, suggesting that the mutant receptors could function normally despite their reduced surface expression. In contrast, the delta V278 mutation totally abolished receptor-ligand binding and subsequent adenylyl cyclase stimulation, indicating that delta V278 mutant is virtually nonfunctional receptor. Northern blotting revealed that mutant CHO cell lines produced levels of receptor mRNA similar to the wild-type cell line. Our results suggest that the two mutations impair binding activity of the receptor without affecting mRNA accumulation, thereby causing AVP resistance through a posttranscriptional mechanism.