E2F1 and cholangiocarcinoma: To test this conjecture, the four very 5-FU-resistant CCA cell lines were treated with a high dose of 100 μM 5-FU (see Fig. 3) over the course of 48 h, and the expression levels of FOXM1, E2F1 and TYMS proteins were examined by western blot analysis (Fig. 3c).