Figure 4. EGFR contributes to 5-FU resistance in colon cancer cells. (A) The 5-FU IC50 values were determined in HT29 and HT29R cells cultured in the presence of various concentrations of 5-FU (n=3). (B) Colony formation assays revealed that HT29-R was insensitive to 5-FU treatment (n=3). (C) EGFR protein levels were increased in HT29-R cells compared with parental HT29 cells. (D) EGFR siRNA successfully suppressed EGFR expression in HT29-R cells (n=3). (E) EGFR silencing sensitized HT29-R cells to 5-FU treatment (n=3. (F) Colony formation assays showed that HT29-R was sensitive to 5-FU treatment upon EGFR siRNA transfection (n=3).