Nuclear factor erythroid 2-related factor 2 (Nrf2), a key
transcription factor regulating
antioxidant, cytoprotective, and metabolic
enzymes, plays important roles in drug resistance and proliferation in
cancer cells. The present study was aimed to examine the expression of Nrf2 in connection with chemotherapeutic drug sensitivity on
cholangiocarcinoma (CCA) cells. The basal levels of Nrf2
protein in cytosol and nuclear fractions of CCA cells were determined using Western blot analysis. Nrf2
mRNA expression of KKU-M156 and KKU-100 cells, representatives of low and high-Nrf2-expressing CCA cells, were silenced using
siRNA. After knockdown of Nrf2, the sensitivity of those cells to the cytotoxicity of
cisplatin (Cis) was enhanced in association with the increased release of AIF and downregulation of Bcl-xl in both cells. Also, knockdown of Nrf2 suppressed the replicative capability of those cells in colony-forming assay and enhanced their sensitivity to antiproliferative activity of Cis and
5-fluorouracil. The chemosensitizing effect was associated with the suppressed expression of Nrf2-regulated and Cis-induced
antioxidant and metabolic genes including NQO1, HO-1, GCLC, TXN, MRP2, TKT, and G6PD. In cell cycle analysis, Nrf2 knockdown cells were arrested at G0/G1 phase and combination with Cis increased the accumulation of cells at S phase. The suppression of KKU-M156 cell proliferation was associated with the downregulation of
cyclin D1 and increased level of p21. Inhibition of Nrf2 could be a novel strategy in enhancing antitumor activity of chemotherapeutic agent in control of resistant
cancer.