FGF23 signaling activity of Klotho mutants.

A. Western Blot showing differences in ERK phosphorylation compared to total expression of ERK after transfection of the V5-tagged FGF receptor and KL WT or KLΔ9L4b. Cells were treated with 10 ng/mL FGF23 for 30 minutes. bFGF is used as positive control for ERK phosphorylation. Arrow marks the reduction in the pERK doublet by KLΔ9L4b relative to KL WT. B. High concentrations of FGF23 increases ERK phosphorylation in mouse and human KL mutants. Western Blot of HEK-293 cells transfected with human and mouse Klotho mutants with different doses of FGF23 for 15 minutes. Western Blotting was performed with either pERK or total ERK antibodies.