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Autosomal-dominant hypophosphatemic rickets (ADHR) mutations stabilize FGF-23
K E White1, G Carn, B Lorenz-Depiereux
1Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA.
Kidney International
|December 12, 2001
Summary
Autosomal-dominant hypophosphatemic rickets (ADHR) mutations in FGF23 confer protease resistance. This resistance may increase FGF23 levels, leading to phosphate wasting in patients.
Area of Science:
- Biochemistry
- Genetics
- Molecular Biology
Background:
- Autosomal-dominant hypophosphatemic rickets (ADHR) is a renal phosphate wasting disorder.
- The gene responsible for ADHR is FGF23, encoding a secreted protein.
- Missense mutations R176Q, R179W, and R179Q in FGF23 were previously identified in ADHR kindreds.
Purpose of the Study:
- To investigate whether ADHR mutations in FGF23 affect its susceptibility to protease cleavage.
- To determine if mutations within the subtilisin-like proprotein convertase (SPC) cleavage site impact FGF23 processing.
Main Methods:
- Site-directed mutagenesis was used to introduce ADHR mutations into FGF23 cDNA.
- Mutated and wild-type FGF23 were expressed in HEK293 cells.
- Western blot analyses with C-terminal and FLAG antibodies were employed to assess protein expression and cleavage.
Main Results:
- Wild-type FGF23 was detected as 32 kD and 12 kD species, indicating cleavage.
- Mutated FGF23 proteins were primarily detected as the 32 kD species, suggesting reduced cleavage.
- FLAG-tagged wild-type FGF23 showed 36 kD and 26 kD bands, while the R176Q mutant predominantly appeared as the 36 kD species.
Conclusions:
- FGF23 proteins with ADHR mutations are secreted and exhibit reduced sensitivity to protease cleavage.
- ADHR mutations likely protect FGF23 from proteolysis.
- This protection may lead to elevated circulating FGF23 concentrations, causing phosphate wasting in ADHR patients.