PDF(Pubmed)
Abstract：
FGF23 is an O-glycosylated circulating peptide hormone with a critical role in phosphate homeostasis; it is inactivated by cellular proprotein convertases in a pre-release degradative pathway. We have here examined the metabolism of FGF23 in a model bone cell line, IDG-SW3, prior to and following differentiation, as well as in regulated secretory cells. Labeling experiments showed that the majority of (35)S-labeled FGF23 was cleaved to smaller fragments which were constitutively secreted by all cell types. Intact FGF23 was much more efficiently stored in differentiated than in undifferentiated IDG-SW3 cells. The prohormone convertase PC2 has recently been implicated in FGF23 degradation; however, FGF23 was not targeted to forskolin-stimulatable secretory vesicles in a regulated cell line, suggesting that it lacks a targeting signal to PC2-containing compartments. In vitro, PC1/3 and PC2, but not furin, efficiently cleaved glycosylated FGF23; surprisingly, PC5/6 accomplished a small amount of conversion. FGF23 has recently been shown to be phosphorylated by the kinase FAM20C, a process which was shown to reduce FGF23 glycosylation and promote its cleavage; our in vitro data, however, show that phosphorylation does not directly impact cleavage, as both PC5/6 and furin were able to efficiently cleave unglycosylated, phosphorylated FGF23. Using qPCR, we found that the expression of FGF23 and PC5/6, but not PC2 or furin, increased substantially following osteoblast to osteocyte differentiation. Western blotting confirmed the large increase in PC5/6 expression upon differentiation. FGF23 has been linked to a variety of bone disorders ranging from autosomal dominant hypophosphatemic rickets to chronic kidney disease. A better understanding of the biosynthetic pathway of this hormone may lead to new treatments for these diseases.
摘要：
FGF23是一种O-糖基化的循环肽激素，在磷酸盐稳态中起关键作用；它在释放前降解途径中被细胞前蛋白转化酶灭活。我们在这里检查了模型骨细胞系中FGF23的代谢，IDG-SW3，在分化之前和之后，以及受调节的分泌细胞。标记实验表明,(35)S-标记的FGF23的大部分被切割为由所有细胞类型组成型分泌的较小片段。完整的FGF23在分化的IDG-SW3细胞中比在未分化的IDG-SW3细胞中更有效地储存。激素原转化酶PC2最近与FGF23降解有关；然而，FGF23在受调节的细胞系中不靶向毛喉素可刺激的分泌囊泡，这表明它缺乏对含PC2区室的靶向信号。体外，PC1/3和PC2，但不是弗林，有效切割的糖基化FGF23；令人惊讶的是，PC5/6完成了少量的转换。FGF23最近被证明被激酶FAM20C磷酸化，一个被证明可以减少FGF23糖基化并促进其切割的过程；我们的体外数据，然而,表明磷酸化不会直接影响切割，因为PC5/6和弗林蛋白酶都能够有效地切割未糖基化的，磷酸化FGF23。使用qPCR，我们发现FGF23和PC5/6的表达，而不是PC2或弗林蛋白酶，成骨细胞向骨细胞分化后显著增加。Western印迹证实了分化后PC5/6表达的大幅增加。FGF23与多种骨疾病有关，从常染色体显性遗传低磷酸盐血症病到慢性肾脏疾病。更好地了解这种激素的生物合成途径可能会导致这些疾病的新疗法。
