Fibroblast growth factor 23 leads to endolysosomal routing of the renal phosphate cotransporters NaPi-IIa and NaPi-IIc in vivo.

Na-dependent phosphate cotransporters NaPi-IIa and NaPi-IIc, located at the brush-border membrane of renal proximal tubules, are regulated by numerous factors, including fibroblast growth factor 23 (FGF23). FGF23 downregulates NaPi-IIa and NaPi-IIc abundance after activating a signaling pathway involving phosphorylation of ERK1/2 (phospho-ERK1/2). FGF23 also downregulates expression of renal 1-α-hydroxylase () and upregulates 24-hydroxylase (), thus reducing plasma calcitriol levels.