Mutant FGF-23 responsible for autosomal dominant hypophosphatemic rickets is resistant to proteolytic cleavage and causes hypophosphatemia in vivo

• Published in: Endocrinology (Philadelphia) 2002-08, Vol.143 (8), p.3179-3179
• Main Authors: Shimada, Takashi, Muto, Takanori, Urakawa, Itaru, Yoneya, Takashi, Yamazaki, Yuji, Okawa, Katsuya, Takeuchi, Yasuhiro, Fujita, Toshiro, Fukumoto, Seiji, Yamashita, Takeyoshi
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; CHO Cells; Cricetinae; Fibroblast Growth Factors - chemistry; Fibroblast Growth Factors - genetics; Fibroblast Growth Factors - metabolism; Hypophosphatemia, Familial - etiology; Hypophosphatemia, Familial - genetics; Male; Mice; Mice, Inbred BALB C; Molecular Sequence Data; Mutation, Missense; Recombinant Proteins - metabolism; Structure-Activity Relationship
• ISSN: 0013-7227
• DOI: 10.1210/en.143.8.3179

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).