1998 Global Conference Proceeding

March 02 - 04, 1998

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Conference: 1998 Global Conference
Title: Functional studies of twelve mutant V2 vasopressin receptors related to nephrogenic diabetes insipidus: molecular basis of a mild clinical phenotype.
Authors: Morin, Denis; Ala, Youssef; Sabatier, Nancy; Vargas-Poussou, Rosa; Alonso, Gerard; Hibert, Marcel; Turaner, M.S.; Barberis, Claude; Bichet, Daniel G.; Jard, Serge
Institutions: INSERM U469, INSERM 469 & 336, INSERM 469 and 336, Hopital Necker-Enfants Malades Tour Lavoisier, Marion Merrell Dow Research Institute, Hopital du Sacre-Coeur de Montreal, Unite INSERM 469, Unit? INSERM
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Abstract • Translation
X-linked nephrogenic diabetes insipidus is a rare disease with defective renal and extrarenal arginine-vasopressin V2 receptor responses due to mutations in the AVPR2 gene in Xq28. To study the cause of loss of function of mutant V2 receptors, we expressed twelve mutant receptors (N55H, L59P, L83Q, V88M, 497CC->GG, AR202, I209F, 700delC, 908insT, A294P, P322H, P322S) in COS-7 cells. Eleven of these including P322H, were characterized by a complete loss of function, but the mutation P322S demonstrated a mild clinical and in vitro phenotype. This was characterized by a late diagnosis without any growth or developmental delay and a significant increase in urine osmolality after intravenous dDAVP administration. In vitro the P322S mutant was able to partially activate the Gs/adenylyl cyclase system in contrast to the other mutants including P322H which were completely inactive in this regard. This showed not only that Pro 322 is important for proper V2R coupling, but also that the degree of impairment is strongly dependent on the identity of the substituting aminoacid. Three dimensional modeling of the P322H and P322S mutant receptors suggested that 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 the carboxyl group of Asp 85, which does not occur in the P322 receptor.

X-linked nephrogenic diabetes insipidus (NDI) occurs when mutations in the arginine-vasopressin receptor (AVPR2) cause the receptor to be unresponsive to the action of the antidiuretic hormone, vasopressin. Morin, et. al., studying the loss of function of mutant receptors found in different patients, created 12 mutant receptors and studied their function in laboratory conditions. Eleven of the mutant receptors were completely dysfunctional, but one, P322S, was able to function to a degree. The patient with this mutation did not have any developmental delay, his NDI expressed itself late, and he showed an increased ability to concentrate urine after injection of synthetic arginine-vasopressin.

In its non-mutated form, V2 receptor P322 plays an important role in receiving the antidiuretic message. In one of its mutated forms - P322H - the receptor is completely dysfunctional. As Morin, et. al's., work shows, however, another one of its mutated forms - P322S - exhibits only mild dysfunction. This illustrates how even slight changes (mutations) in genetic sequencing (in this case a single amino acid switch) can determine both impairment and degrees of impairment in receptor function.