Mutant FGF-23 responsible for autosomal dominant hypophosphatemic rickets is resistant to proteolytic cleavage and causes hypophosphatemia in vivo.
FGF-23 is involved in the pathogenesis of two similar hypophosphatemic diseases, autosomal dominant hypophosphatemic rickets/osteomalacia (ADHR) and tumor-induced osteomalacia (TIO). We have shown that the overproduction of FGF-23 by tumors causes TIO. In contrast, ADHR derives from missense mutations in FGF-23 gene. However, it has been unclear how those mutations affect phosphate metabolism. Therefore, we produced mutant as well as wild-type FGF-23 proteins and examined their biological activity. Western blot analysis using site-specific antibodies showed that wild-type FGF-23 secreted into conditioned media was partially cleaved between Arg(179) and Ser(180). In addition, further processing of the cleaved N-terminal portion was observed. In constrast, mutant FGF-23 proteins found in ADHR were resistant to the cleavage. In order to clarify which molecule has the biological activity to induce hypophosphatemia, we separated full-length protein, the N-terminal and C-terminal fragments of wild-type FGF-23. When the activity of each fraction was examined in vivo, only the full-length FGF-23 decreased serum phosphate. Mutant FGF-23 protein that was resistant to the cleavage also retained the activity to induce hypophosphatemia. The extent of hypophosphatemia induced by the single administration of either wild-type or the mutant full-length FGF-23 protein was similar. In addition, implantation of CHO cells expressing the mutant FGF-23 protein caused hypophosphatemia and the decrease of bone mineral content. We conclude that ADHR is caused by hypophosphatemic action of mutant full-length FGF-23 proteins that are resistant to the cleavage between Arg(179) and Ser(180).
Shimada
Takashi
T
Pharmaceutical Research Labs, KIRIN Brewery Co. Ltd., Japan.
Muto
Takanori
T
Urakawa
Itaru
I
Yoneya
Takashi
T
Yamazaki
Yuji
Y
Okawa
Katsuya
K
Takeuchi
Yasuhiro
Y
Fujita
Toshiro
T
Fukumoto
Seiji
S
Yamashita
Takeyoshi
T
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007015:Hypophosphatemia, Familial / Q000209:etiology* / Q000235:genetics; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D011994:Recombinant Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship
C000717428:Fgf23 protein, mouse; D011994:Recombinant Proteins; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23