FGF23 is processed by proprotein convertases but not by PHEX.
X-linked hypophosphatemia (XLH) and autosomal dominant hypophosphatemic rickets (ADHR) are characterized by renal phosphate wasting, rickets, and osteomalacia. ADHR is caused by gain of function mutations in the fibroblast growth factor 23 gene (FGF23). During secretion, FGF23 is processed at the C-terminus between amino acids 179 and 180. The cleavage site is mutated in ADHR, preventing processing of FGF23. Here, we show that FGF23 is likely to be cleaved by subtilisin-like proprotein convertases (SPC) as cleavage can be inhibited by a specific SPC inhibitor in HEK293 cells. SPCs, which are widely expressed, were demonstrated to be also present in HEK293 cells as well as in osteoblasts. XLH is caused by loss of function mutations in the putative endopeptidase PHEX. It was tempting to speculate that FGF23 is a substrate of PHEX, but studies have been inconclusive so far. Here, we used a secreted form of PHEX (secPHEX) and tagged and untagged FGF23 constructs for co-incubation experiments. These experiments provided evidence against cleavage of intact FGF23(25-251) as well as of N-terminal (FGF23(25-179)) and C-terminal (FGF23(180-251)) fragments by the endopeptidase PHEX.
Benet-Pagès
Anna
A
Institute of Human Genetics, GSF National Research Center, 85764 München-Neuherberg, Germany.
Lorenz-Depiereux
Bettina
B
Zischka
Hans
H
White
Kenneth E
KE
Econs
Michael J
MJ
Strom
Tim M
TM
D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D006801:Humans; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; D043484:Proprotein Convertases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000378:metabolism*
D017931:DNA Primers; C000717427:FGF23 protein, human; D011506:Proteins; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D043484:Proprotein Convertases; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506231:PHEX protein, human