Elucidating the underlying molecular pathogenesis of NR3C2 mutants causing autosomal dominant pseudohypoaldosteronism type 1.
BACKGROUND
Pseudohypoaldosteronism type 1 (PHA1) is a rare salt-wasting syndrome. Mutations in the NR3C2 gene coding for the mineralocorticoid receptor (MR) cause autosomal dominant PHA1.


OBJECTIVE
Our objective was to reveal the cause of renal salt loss in six PHA1 patients and analyze the mutants' functional impact on MR function.


METHODS
Our study included the following: clinical and hormonal characterization of the patients' phenotype, analysis of the NR3C2 gene, determination of receptor affinities to aldosterone and the transcriptional activation abilities of the MR mutants, investigation of subcellular translocation using fluorescence-labeled MR, and studying changes in mutant receptor conformation with proteolysis experiments and three-dimensional modeling.


RESULTS
Six heterozygous NR3C2 mutations were detected. One frameshift mutation (c.1131dupT) has been reported previously. The second frameshift mutation (c.2871dupC), which has only recently been reported by our group, showed no aldosterone binding and no transactivation because of a major change in receptor conformation. Two novel nonsense mutations generate a truncated receptor protein. Two missense mutations differently affect MR function. S818L was reported recently without complete in vitro data. S818L does not bind aldosterone or activate transcription or translocate into the nucleus. A major displacement of several residues involved in aldosterone binding was PHA1 causing. The novel E972G mutation showed a significantly lower ligand-binding affinity and only 9% of wild-type transcriptional activity caused by major changes in receptor conformation.


CONCLUSIONS
Our data on six mutations extend the spectrum of PHA1-causing NR3C2 gene mutations. Studying naturally occurring mutants helps to clarify their pathogenicity and to identify crucial residues for MR structure and function.
Riepe
Felix G
FG
Division of Pediatric Endocrinology, Department of Pediatrics, University Hospital Schleswig-Holstein, Schwanenweg 20, D-24105 Kiel, Germany. friepe@pediatrics.uni-kiel.de
Finkeldei
Johannes
J
de Sanctis
Luisa
L
Einaudi
Silvia
S
Testa
Alberto
A
Karges
Beate
B
Peter
Michael
M
Viemann
Matthias
M
Grötzinger
Joachim
J
Sippell
Wolfgang G
WG
Fejes-Toth
Geza
G
Krone
Nils
N
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D005260:Female; D015870:Gene Expression; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000032:analysis / Q000378:metabolism; D009154:Mutation; D010375:Pedigree; D017433:Protein Structure, Secondary; D021381:Protein Transport; D011546:Pseudohypoaldosteronism / Q000209:etiology* / Q000235:genetics* / Q000378:metabolism; D011817:Rabbits; D018161:Receptors, Mineralocorticoid / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D015533:Transcriptional Activation; D014162:Transfection
D050505:Mutant Proteins; D018161:Receptors, Mineralocorticoid