Amelogenesis Imperfecta and Other Biomineralization Defects in <i>Fam20a</i> and <i>Fam20c</i> Null Mice

Vogel, Peter; Hansen, Gwenn M.; Read, Robert W.; Vance, R. B.; Thiel, Manfred; Liu, J.; Wronski, Thomas J.; Smith, Deon; Jeter-Jones, Sabrina; Brommage, Robert

doi:10.1177/0300985812453177

Cited by 113 publications

(132 citation statements)

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“…S9). This model is consistent with the marked elevation of intact, biologically active FGF23 observed in humans with the Fam20C T268M mutation (12) and in Fam20C KO mice (13,14).…”

Section: Discussionsupporting

confidence: 87%

“…Nonlethal cases have also been reported, and these patients develop hypophosphatemia as a result of elevated levels of the phosphate-regulating hormone fibroblast growth factor 23 (FGF23) (12). Additionally, Fam20C knockout (KO) mice develop renal phosphate wasting due to an increase in circulating bioactive FGF23 as well as severe hypophosphatemic rickets (13,14). Thus, Fam20C has been proposed to be a regulator of FGF23; however, the molecular mechanisms underlying the control of this hormone by Fam20C are unclear.…”

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confidence: 99%

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

Tagliabracci¹,

Engel²,

Wiley³

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

265

252

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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 176 XXR 179 /S 180 AE 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.phosphate homeostasis | rickets | Fam20 | familial tumoral calcinosis | chronic kidney disease P rotein kinases are evolutionarily conserved enzymes that regulate numerous cellular processes by transferring a molecule of phosphate from ATP to target substrates (1, 2). The vast majority of theses enzymes function within the nucleus and cytosol. In contrast, there are several examples of phosphorylated proteins that are secreted from the cell, which raises the question: What are the kinases that phosphorylate these secreted phosphoproteins? We recently identified a small family of secretory pathway kinases that phosphorylate secreted proteins and proteoglycans (3). These enzymes have N-terminal signal sequences that direct them to the lumen of the endoplasmic reticulum, where they encounter the proteins or proteoglycans that they phosphorylate. One member of this atypical kinase family is the family with sequence similarity 20, member C (Fam20C), which phosphorylates secreted proteins on Ser(S)-xGlu(E)/pSer(pS) (S-x-E/pS) motifs (3, 4). Because Fam20C localizes within the secretory pathway and the vast majority of secreted phosphoproteins are phosphorylated on S-x-E/pS motifs, Fam20C has been proposed to play a major role in the generation of the secreted phosphoproteome (5-7). For example, ∼75% of human serum and cerebrospinal fluid phosphoproteins are phosphorylated on S-x-E/pS motifs (8, 9). This includes proteins important for tooth and bone formation, as well as numerous hormones. In most cases, the functional importance of these phosphorylation events is unknown.Loss-of-function mutations in the human FAM20C gene cause Raine syndrome, an often-fatal osteosclerotic bone dysplasia (10, 11)....

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“…S9). This model is consistent with the marked elevation of intact, biologically active FGF23 observed in humans with the Fam20C T268M mutation (12) and in Fam20C KO mice (13,14).…”

Section: Discussionsupporting

confidence: 87%

mentioning

confidence: 99%

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

Tagliabracci¹,

Engel²,

Wiley³

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

265

252

View full text Add to dashboard Cite

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“…Most individuals with Raine syndrome die within a few weeks after birth; however, nonlethal cases with dental abnormalities and clinical features of hypophosphatemia have been reported (17,18). Loss of Fam20C in mice also results in severe bone and tooth anomalies, as well as hypophosphatemia (19)(20)(21).Two other closely related Fam20C paralogs, Fam20A and Fam20B, are present in humans (22). Fam20B is ubiquitously expressed and phosphorylates xylose within the tetrasaccharide linkage region of proteoglycans (23).…”

mentioning

confidence: 99%

“…This phosphorylation event may influence glycosaminoglycan biosynthesis (24). Genetic deletion of Fam20B in mice results in embryonic lethality at E13.5, and mutations in Danio rerio result in reduced cartilage matrix production and skeletal defects (19,25). The substrates for Fam20A are unknown; however, mutations in FAM20A are known to cause amelogenesis imperfecta (AI) and enamel renal syndrome (ERS) in humans (26)(27)(28)(29).…”

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confidence: 99%

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Crystal structure of the Golgi casein kinase

Xiao

Tagliabracci

Wen

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The family with sequence similarity 20 (Fam20) kinases phosphorylate extracellular substrates and play important roles in biomineralization. Fam20C is the Golgi casein kinase that phosphorylates secretory pathway proteins within Ser-x-Glu/pSer motifs. Mutations in Fam20C cause Raine syndrome, an osteosclerotic bone dysplasia. Here we report the crystal structure of the Fam20C ortholog from Caenorhabditis elegans. The nucleotide-free and Mn/ ADP-bound structures unveil an atypical protein kinase-like fold and highlight residues critical for activity. The position of the regulatory αC helix and the lack of an activation loop indicate an architecture primed for efficient catalysis. Furthermore, several distinct elements, including the presence of disulfide bonds, suggest that the Fam20 family diverged early in the evolution of the protein kinase superfamily. Our results reinforce the structural diversity of protein kinases and have important implications for patients with disorders of biomineralization.P rotein phosphorylation is a fundamental mechanism that regulates numerous physiological processes (1, 2). Protein kinases have evolved to function as dynamic switches relaying signals in response to various stimuli by transferring a phosphate from ATP to target proteins (3-5). Most phosphoproteins are found within the cell, residing in the nuclei and cytosol; however, secreted proteins, including casein and other members of the secretory calciumbinding phosphoprotein family, are phosphorylated as well (6). We recently identified a family of kinases that reside in the secretory pathway and function to phosphorylate extracellular substrates (7,8). One member of this family, Fam20C (family with sequence similarity 20, member C), is the physiological casein kinase that phosphorylates multiple secreted proteins within a Ser-x-Glu/pSer motif (7, 9, 10). The importance of this discovery is underscored by the fact that some 75% of the phosphoproteins identified in human serum and cerebrospinal fluid contain phosphate within this motif (11-13). Furthermore, mutations in FAM20C cause Raine syndrome, a deadly osteosclerotic bone dysplasia characterized by generalized osteosclerosis, ectopic calcifications, and characteristic facial features (14-16). Most individuals with Raine syndrome die within a few weeks after birth; however, nonlethal cases with dental abnormalities and clinical features of hypophosphatemia have been reported (17,18). Loss of Fam20C in mice also results in severe bone and tooth anomalies, as well as hypophosphatemia (19)(20)(21).Two other closely related Fam20C paralogs, Fam20A and Fam20B, are present in humans (22). Fam20B is ubiquitously expressed and phosphorylates xylose within the tetrasaccharide linkage region of proteoglycans (23). This phosphorylation event may influence glycosaminoglycan biosynthesis (24). Genetic deletion of Fam20B in mice results in embryonic lethality at E13.5, and mutations in Danio rerio result in reduced cartilage matrix production and skeletal defects (19,25). The substra...

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