Intracellular activation of vasopressin V2 receptor mutants in nephrogenic diabetes insipidus by nonpeptide agonists

Binding of the peptide hormone vasopressin to its type-2 receptor (V2R) in kidney triggers a cAMP-mediated translocation of Aquaporin-2 water channels to the apical membrane, resulting in water reabsorption and thereby preventing dehydration. Mutations in the V2R gene lead to Nephrogenic Diabetes Insipidus (NDI), a disorder in which this process is disturbed, because the encoded, often intrinsically functional mutant V2 receptors are misfolded and retained in the endoplasmic reticulum (ER). Since plasma membrane expression is thought to be essential for V2R activation, cell permeable V2R antagonists have been used to induce maturation and rescue cell surface expression of V2R mutants, after which they need to be displaced by vasopressin for activation. Here, however, we show that 3 novel nonpeptide V2R agonists, but not vasopressin, activate NDI-causing V2R mutants at their intracellular location, without changing their maturation and at a sufficient level to induce the translocation of aquaporin-2 to the apical membrane. Moreover, in contrast to plasma membrane V2R, degradation of intracellular V2R mutants is not increased by their activation. Our data reveal that G protein-coupled receptors (GPCRs) normally active at the plasma membrane can be activated intracellularly and that intracellular activation does not induce their degradation; the data also indicate that nonpeptide agonists constitute highly promising therapeutics for diseases caused by misfolded GPCRs in general, and NDI in particular.