Nephrogenic Diabetes Insipidus. A V2 Vasopressin Receptor Unable to Stimulate Adenylyl Cyclase
|Title:||Nephrogenic Diabetes Insipidus. A V2 Vasopressin Receptor Unable to Stimulate Adenylyl Cyclase|
|Authors:||Birnbaumer, Mariel; Rosenthal, Walter; Antaramian, Anaid; Gilbert, Stephanie|
|Publisher:||Journal of Biological Chemistry|
|Date Published:||June 25, 1993|
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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)
Normally, the antidiuretic hormone, arginine vasopressin (AVP), binds with V2R in the principal cell of the kidney collecting duct. When this binding occurs the G-protein to which the V2R is coupled is activated. The adenylyl cyclase system is then stimulated, which increases the level of cAMP. This stimulates aquaporin-2s (AQP2s), water-transporting proteins, to insert themselves in the apex of the kidney collecting duct cells. The water permeability of these cells is then increased, which allows them to reabsorb water and concentrate urine.
The authors cloned one of the V2R mutations associated with NDI. (To date, there are 116 known V2R mutations associated with NDI.) The mutations they chose, called the Q2 mutation, resulted in the amino acid histidine taking the place of the amino acid, arginine, in the V2R.
The researchers sought to determine whether this structural alteration of the V2R due to the Q2 mutation impaired the V2R's ability to function, and if so, how. They expressed the mutated V2Rs in laboratory cell cultures and compared their ability to transport to the cell surfaces (in order to bind with AVP) to cell cultures with normal V2Rs. The researchers found that the mutant V2R binds with AVP with an affinity close to normal, but that, once bound, it could not stimulate adenylyl cyclase as normal V2Rs can. If adenylyl cyclase cannot be stimulated, then the molecular sequence which leads to kidney collecting duct water reabsorption and urine concentration does not occur. This research provides biochemical proof that the Q2 mutant V2R is a cause of NDI.
The authors reason that the structural alteration of the V2R produced by the Q2 mutation interferes with the proper folding of the V2R so that it is misshapen. This makes it difficult for the V2R to contact the G-protein or to stimulate adenylyl cyclase, as well as to transport across the endoplasmic reticulum (ER) and the Golgi apparatus. The altered V2Rs may also not be able to insert themselves into the cell membrane efficiently or, more likely, they may degrade more quickly in the ER or Golgi.
The authors state a more definite case for the defective V2Rs being structured so as to lack the ability to contact the G-protein.