(A) The expression of the Slc15a family of genes, which encodes peptide transporters, in osteoblastic cells is assayed using RT-PCR. (B) The untransfected MC3T3-E1 cells treated with PBS, glycine, or histidine, MC3T3-E1 cells transfected with Control siRNA, and MC3T3-E1 with knocked down Slc15a4 were treated with uranine (upper panel) (green) or FITC-labeled-Pro-Hyp (lower panel) (green) for 48 h. After incubation, the nuclei were stained with PI (red). The images were captured using a KEYENCE fluorescent microscope. Scale bar, 100 µm. The data are representative of three independent experiments. (C) Slc15a4 was knocked down in MC3T3-E1 cells. Cell lysates were collected and expression levels of Slc15a4 was analyzed via Western blotting.