5-Fluorouracil upregulates the activity of Wnt signaling pathway in CD133-positive colon cancer stem-like cells

Background and Objective:CD133-positive colon cancer stem like cells (CSLCs) are resistant to the conventional cytotoxic drug 5-fluorouracil (5-FU).Wnt signaling pathway plays important roles in colon cancer carcinogenesis and metastasis, and regulates the self-renewal capacity of CSLCs.In the present study, we explored the impact of 5-FU on Wnt signaling pathway of CD133-positive colon CSLCs, and the relation between Wnt signaling pathway and drug resistance of CD133-positive colon CSLCs.Methods:Magnetic activation cell separation was used to collect CD133-positive cells from colon cancer cell line DLD1, which was transfected with luciferase reporter for Wnt signaling activity.The activity of Wnt signaling pathway was compared between CD133-positive and CD133-negative cells.After the treatment with 1 μg/mL of 5-FU, the cell proliferation rates of DLD1 cells, CD133-positive cells, and CD133-negative cells were compared.After the treatment with 1 μg/mL and 10 μg/mL of 5-FU for 48 h, Wnt activity was compared between CD133-positive and CD133-negative cells.The expression of CD133 and cell apoptosis of CD133-positive cells was detected after exposure to 50 ng/mL of dickkopf (DKK)-1, a Wnt pathway inhibitor.Results:After the treatment with 5-FU, the cell proliferation rate of CD133-positive cells was higher than that of CD133-negative cells and the sensitivity of CD133-positive cells to 5-FU decreased.Wnt activity was higher in CD133-positive cells than in CD133-negative cells [(46.3±0.3)% vs.(33.9±2.7)%, P=0.009].After the treatment with 1 μg/mL and 10 μg/mL of 5-FU, Wnt activity of CD133-positive cells was (90.1±10.0)% (P=0.012) and (52.9±2.5)% (P=0.047), respectively, whereas that of CD133-negative cells was (35.5±3.3)% (P=0.434) and (26.5±0.4)% (P=0.046), respectively.CD133 expression in CD133-positive cells decreased from (87.2±5.3)% to (60.6±3.1)% (P=0.022) after treatment with DKK-1, whereas the cell apoptosis rate increased from (11.8±0.2)% to (28.3±0.6)% (P=0.013).Conclusions:Wnt activity is higher in CD133-positive DLD1 cells than in CD133-negative DLD1 cells.5-FU can upregulate Wnt activity of CD133-positive colon CSLCs.Blocking Wnt activity may reverse drug sensitivity of CD133-positive cells to 5-FU.