Figure 3. PTBP1 facilitates chemoresistance of osteosarcoma cells to DXR in vitro. DXR-resistant osteosarcoma cell lines (U2OS/DXR, MG63/DXR, HOS/DXR) were treated with expression vector containing PTBP1 gene and their parental cells with siRNA targeting PTBP1. (A) The knockdown efficiency of si-PTBP1 was verified using RT-qPCR in U2OS/DXR cells. (B) Western blot analysis determined the protein level of PTBP1 (normalized to GAPDH) in DXR-resistant osteosarcoma cells and their parental cells. CCK-8 assays were performed to examine cell viability and IC50 of DXR in U2OS/DXR cells (C) and their parental cells (D). (E) EdU labeling assays were used to reflect the proliferation of DXR-resistant U2OS and MG63 cells and their parental cells. Values obtained from three independent experiments in triplicate are analyzed by unpaired t test between two groups and by ANOVA with Tukey's test among three or more groups. Values at different time points were tested by repeated measurement ANOVA followed by Bonferroni test. *p < 0.05 compared with parental cells treated with oe-NC or DXR-resistant osteosarcoma cells treated with si-NC.