An Extracellular Congenital Nephrogenic Diabetes Insipidus Mutation of the Vasopressin Receptor Reduces Cell Surface Expression, Affinity for Ligand, and Coupling to the Gs/adenylyl Cyclase System

Title: An Extracellular Congenital Nephrogenic Diabetes Insipidus Mutation of the Vasopressin Receptor Reduces Cell Surface Expression, Affinity for Ligand, and Coupling to the Gs/adenylyl Cyclase System
Authors: Birnbaumer, Mariel; Gilbert, Stephanie; Rosenthal, Walter
Publisher: Molecular Endocrinology
Date Published: July 01, 1994
Reference Number: 99
The mutation of the type-2 vasopressin receptor (V2R) apparently responsible for X-linked congenital nephrogenic diabetes insipidus (CNDI) in the Q3 family consists of a T to C transition in codon 113, causing the change of Arg-113 to Trp. Arg-113 is located in the putative first extracellular loop of the V2R next to a frequently conserved Cys thought to interact via a disulfide bridge with a Cys of the second extracellular loop. The present study explored whether this mutation may account for the CNDI phenotype. The mutation was excised from the genomic DNA of a Q3 patient and introduced into the V2R cDNA, which was then placed into an expression plasmid and transfected into COS cells for transient expression and murine L cells for stable expression. Studies with L cells expressing similar levels of wild type and Q3 receptors showed that the mutant receptor has a 20-fold reduced affinity for arginine vasopressin (AVP) and stimulates adenylyl cyclase with an EC50 that is increased by a factor of about 60-fold. The same shift in the EC50 for adenylyl cyclase stimulation was obtained when deamino [8-D-Arg] vasopressin was substituted for AVP. Studies with COS cells revealed that at equal levels of transfected DNA, the mutant receptor is expressed at lower levels (about 20%) than the wild type receptor, indicating that the mutation hinders the transport of the receptor to the cell membrane. (ABSTRACT TRUNCATED AT 250 WORDS)
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This translation by the NDI Foundation is to assist the lay reader. To provide a clear, accessible interpretation of the original article, we eliminated or simplified some technical detail and complicated scientific language. We concentrated our translation on those aspects of the article dealing directly with NDI. The NDI Foundation thanks the researchers for their work toward understanding and more effectively treating this disorder.
© Copyright NDI Foundation 2007 (JC)

The antidiuretic hormone, arginine vasopressin (AVP), promotes urine concentration in the kidney collecting duct. It does this by binding with the vasopressin-2 receptor (V2R). This binding initiates the following molecular sequence:
Mutations of the V2R gene can result in V2Rs which are unable to bind with AVP. Since the binding cannot take place, neither can the molecular sequence that results in water reabsorption and urine concentration. The result is the disorder known as nephrogenic diabetes insipidus (NDI), the primary symptoms of which are polyuria (chronic passage of large volumes of urine) and polydipsia (chronic, excessive thirst).

Birnbaumer, et al., studied one V2R gene mutation found in an NDI patient, analyzing its structural alterations and functional characteristics. The mutation expressed itself in the first extracellular loop of the V2R (V2Rs have three extracellular loops. You can look at a diagram of the V2R for a clearer understanding.) The mutation resulted in the amino acid, tryptophan, being in the position the amino acid, arginine, should have occupied.

The effects this structural change had on the mutated V2Rs' functional capabilities were:
  1. the mutated V2Rs had a 20-fold reduced affinity for AVP,
  2. they were expressed on the cell surface, the place they must be if they are to bind with AVP, at one-fifth the level of normal V2Rs,
  3. and their ability to stimulate adenylyl cyclase activity was significantly reduced.
Thus, the mutation of the V2R gene partially reduces all three functions that are critical for normal behavior of V2Rs.

The authors believe this is the first extracellular V2R mutation to be reported in the literature that combines all these functional defects. They conclude this mutation is the molecular basis for their patient's NDI.