Misfolded vasopressin V2 receptors caused by extracellular point mutations entail congential nephrogenic diabetes insipidus.

Vasopressin V2 receptor mutants from three different patients with congenital nephrogenic diabetes insipidus phenotypes were investigated after expression in COS cells. The amino acid exchanges within the human V2 receptor are located in the second extracellular loop (T204N, Y205C and V206D). Confocal microscopy showed that all receptor mutants were strongly expressed but mainly located within the cell. Residual binding capacity for the antidiuretic hormone arginine vasopressin (AVP) could only be detected for the T204N mutant and was 10-fold lower than for the wild-type receptor. Stimulation of transfected cells with 1 microM AVP showed that the T204N mutant was able to activate the adenylyl cyclase pathway. In contrast, the Y205C mutant was almost inactive and stimulation of the V206D mutant increased the cAMP accumulation only slightly. Dose dependent stimulation of cells expressing the T204N mutant with AVP and with the therapeutic AVP analogue 1-deamino[D-Arg8]vasopressin (dDAVP) revealed that AVP was 50-fold more potent than dDAVP. This indicates that the ligand binding selectivity of the T204N mutant has changed as compared with the wild-type receptor where AVP is only 2.3-fold more potent than dDAVP. Despite its defects in membrane localization, ligand binding affinity and selectivity, the T204N receptor could be activated with high concentrations of dDAVP. Our results indicate that in cases of congenital nephrogenic diabetes insipidus with residual V2 receptor activities the use of antidiuretic drugs, such as dDAVP, might be beneficial for patients.

An extracellular residue determines the agonist specificity of V2 vasopressin receptors.

The specific V2 agonist 1-deamino [8-D-arginine]-vasopressin (dDAVP), used for treatment of central diabetes insipidus, binds to vasopressin V2 receptors from human, bovine and rat kidney with an affinity that is similar to that of the natural hormone vasopressin. In contrast, the V1 receptors and the porcine V2 receptor do not tolerate a D-arginine in position 8 of vasopressin. By site directed mutagenesis of the cloned bovine and porcine V2 receptors we identified a residue (Asp-103) in the first extracellular loop of vasopressin receptors which is responsible for high affinity binding of dDAVP.