2004 Global Researcher Conference Proceeding
April 09 - 11, 2004
|Conference:||2004 Global Researcher Conference|
|Title:||Lack of AVP-induced phosphorylation of the Aquaporin-2 mutants AQP2-R254L and AQP2-R254Q explains dominant Nephrogenic Diabetes Insipidus|
|Authors:||de Mattia, Fabrizio; Savelkoul, Paul J.M.; Oksche, Alexander; Robertson, Gary; Deen, Peter M.T.|
|Institutions:||University of Nijmegen, NHGRI, Institut Fuer Pharmakologie, Northwestern University Medical School|
Phosphorylation is the process wherein a phosphate group is added onto an organic molecule. On the aquaporin 2 (AQP2) protein, phosphorylation occurs at Ser256, a serine amino acid that is the 256th amino acid on the chain of amino acids that makes up the AQP2. When phosphorylation occurs at Ser256, it induces the AQP2 to translocate from the cell interior to the cell membrane, a movement necessary for the kidney to concentrate urine. This phosphorylation process is accomplished by protein kinase A (PKA), which recognizes a PKA consensus site located in the section of the AQP2 called the C-tail.
Here, De Mattia, et al., identified two families, in which dominant NDI was caused by R254L and R254Q mutations in AQP2, which destroy the PKA consensus site. These AQP2 mutants are functional water channels, but are unable to travel to the cell membrane. Instead, they are retained in intracellular vesicles in a distribution pattern that was similar to that of non-phosphorylated normal AQP2 (wt-AQP2). Although these AQP2 mutants were phosphorylated at a low basal level at Ser256, their level of phosphorylation was not increased upon forskolin treatment, and the forskolin did not induce the mutant AQP2s to move to the cell membrane. Upon co-expression, both mutants interacted with and retained wt-AQP2 in intracellular vesicles.
These data indicated that in these families, dominant NDI is caused by the inability to phosphorylate the mutants at S256 by PKA and, as such, they represent the first AQP2 mutants in which dominant NDI is caused by a loss of function instead of a gain of function.