Autosomal-dominant hypophosphatemic rickets (ADHR) mutations stabilize FGF-23

Kidney Int. 2001 Dec;60(6):2079-86. doi: 10.1046/j.1523-1755.2001.00064.x.

Abstract

Background: The gene for the renal phosphate wasting disorder autosomal-dominant hypophosphatemic rickets (ADHR) is FGF23, which encodes a secreted protein related to the fibroblast growth factors (FGFs). We previously detected missense mutations R176Q, R179W, and R179Q in FGF23 from ADHR kindreds. The mutations replace R residues within a subtilisin-like proprotein convertase (SPC) cleavage site 176RHTR-179 (RXXR motif). The goal of these studies was to determine if the ADHR mutations lead to protease resistance of FGF-23.

Methods: The ADHR mutations were introduced into human FGF-23 cDNA clones with or without an N-terminal FLAG tag by site-directed mutagenesis and were transiently transfected into HEK293 cells. Protein expression was determined by Western analyses.

Results: Antibodies directed toward the C-terminal portion of FGF-23 revealed that the native FGF-23 protein resolved as 32 kD and 12 kD species in HEK293 conditioned media; however, the three mutated proteins were detected only as the 32 kD band. An N-terminal FLAG-tagged native FGF-23 resolved as two bands of 36 kD and 26 kD when detected with a FLAG antibody, whereas the R176Q mutant resolved primarily as the 36 kD protein species. Cleavage of FGF-23 was not enhanced by extracellular incubation of FGF-23 with HEK293 cells. Native and mutant FGF-23s bound heparin.

Conclusions: FGF-23 proteins containing the ADHR mutations are secreted, and produce polypeptides less sensitive to protease cleavage than wild-type FGF-23. Therefore, the ADHR mutations may protect FGF-23 from proteolysis, thereby potentially elevating circulating concentrations of FGF-23 and leading to phosphate wasting in ADHR patients.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cell Line
  • Drug Stability
  • Extracellular Space / metabolism
  • Fibroblast Growth Factors / chemistry
  • Fibroblast Growth Factors / genetics
  • Fibroblast Growth Factors / metabolism*
  • Gene Expression
  • Genes, Dominant*
  • Heparin / metabolism
  • Humans
  • Hypophosphatemia, Familial / genetics*
  • Intracellular Membranes / metabolism
  • Mutation, Missense / physiology*

Substances

  • Fibroblast Growth Factors
  • fibroblast growth factor 23
  • Heparin