FUNCTIONAL-STUDIES OF 12 MUTANT V-2 VASOPRESSIN RECEPTORS RELATED TO NEPHROGENIC DIABETES-INSIPIDUS - MOLECULAR-BASIS OF A MILD CLINICAL PHENOTYPE

X-linked nephrogenic diabetes insipidus (NDI) is a rare disease with d efective renal and extrarenal arginine vasopressin V2 receptor respons es due to mutations in the AVPR2 gene in Xq28. To study the cause of l oss of function of mutant V2 receptors, we expressed 12 mutations (N55 H, L59P, L83Q, V88M, 497CC --> GG, Delta R202, I209F, 700delC, 908insT , A294P, P322H, P322S) in COS-7 cells. Eleven of these, including P322 H, were characterized by a complete loss of function, but the mutation P322S demonstrated a mild clinical and in vitro phenotype. This was c haracterized by a late diagnosis without any growth or developmental d elay and a significant increase in urine osmolality after intravenous 1-deamino[D-Arg(8)]AVP administration. In vitro, the P322S mutant was able to partially activate the Gs/adenylyl cyclase system in contrast to the other V2R mutants including P322H, which were completely inacti ve in this regard. This showed not only that Pro 322 is important for proper V2R coupling, but also that the degree of impairment is strongl y dependent on the identity of the substituting amino acid. Three-dime nsional modeling of the P322H and P322S mutant receptors suggested tha t the complete loss of function of the P322H receptor could be due, in part, to hydrogen bond formation between the His 322 side chain and t he carboxyl group of Asp 85, which does not occur in the P322S recepto r.