Journal Article

Dynamic regulation of FGF23 by Fam20C phosphorylation, GalNAc-T3 glycosylation, and furin proteolysis

Dixon, Jack E., Gonzalez, David J., Tagliabracci, Vincent S., Xiao, Junyu, Engel, James L., Wiley, Sandra E., Nidumanda Appaiah, Hitesh, Koller, Antonius, Nizet, Victor, White, Kenneth E.

2014

Overview

The family with sequence similarity 20, member C (Fam20C) has recently been identified as the Golgi casein kinase. Fam20C phosphorylates secreted proteins on Ser-x-Glu/pSer motifs and loss-of-function mutations in the kinase cause Raine syndrome, an often-fatal osteosclerotic bone dysplasia. Fam20C is potentially an upstream regulator of the phosphate-regulating hormone fibroblast growth factor 23 (FGF23), because humans with FAM20C mutations and Fam20C KO mice develop hypophosphatemia due to an increase in full-length, biologically active FGF23. However, the mechanism by which Fam20C regulates FGF23 is unknown. Here we show that Fam20C directly phosphorylates FGF23 on Ser ¹⁸⁰, within the FGF23 R ¹⁷⁶XXR ¹⁷⁹/S ¹⁸⁰AE subtilisin-like proprotein convertase motif. This phosphorylation event inhibits O-glycosylation of FGF23 by polypeptide N -acetylgalactosaminyltransferase 3 (GalNAc-T3), and promotes FGF23 cleavage and inactivation by the subtilisin-like proprotein convertase furin. Collectively, our results provide a molecular mechanism by which FGF23 is dynamically regulated by phosphorylation, glycosylation, and proteolysis. Furthermore, our findings suggest that cross-talk between phosphorylation and O-glycosylation of proteins in the secretory pathway may be an important mechanism by which secreted proteins are regulated.

• Publisher: National Academy of Sciences
• Subject: Amino Acid Sequence / Base Sequence / Biochemistry / Biological Sciences / Casein Kinase I / DNA Primers - genetics / Extracellular Matrix Proteins - immunology / Extracellular Matrix Proteins - metabolism / Fibroblast Growth Factor-23 / fibroblast growth factors / Fibroblast Growth Factors - metabolism / Furin - metabolism / Glycosylation / HEK293 Cells / Humans / Immunoblotting / Immunoprecipitation / Inactivation / Mass Spectrometry / mice / Molecular Sequence Data / Mutation / N-Acetylgalactosaminyltransferases - metabolism / non-specific serine/threonine protein kinase / Phosphates / Phosphorylation / Polypeptide N-acetylgalactosaminyltransferase / Polypeptides / Proteins / Proteolysis / Rodents / Sequence Analysis, DNA / sequence homology / Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Tandem Mass Spectrometry