Cisplatin-induced chemoresistance in colon cancer cells involves FXR-dependent and FXR-independent up-regulation of ABC proteins.

Export pumps often limit the usefulness of anticancer drugs. Here we investigated the effect of cisplatin on the expression of ABC proteins in human colon cancer cells. Short-term incubation of Caco-2 and LS174T cells with cisplatin resulted in up-regulation of several ABC pumps, in particular MRP2 and BCRP. In partially cisplatin-resistant cells (LS174T/R) obtained by long-term exposure to cisplatin, MRP2 and BCRP up-regulation was more marked. This was further enhanced when these cells were cultured under maintained stimulation with cisplatin. The MRP2 promoter (MRP2pr) was cloned, and partially deleted constructs linked to reporter genes were generated. Transfection of LS174T and LS174T/R cells with these constructs revealed the ability of cisplatin to activate MRP2pr. The intensity of this response was dependent on the conserved MRP2pr region. Basal MRP2pr activity was higher in LS174T/R cells, in which the expression of the transcription factors c/EBPβ, HNF1α, HNF3β, and HNF4α, but not PXR, p53, c-Myc, AP1, YB-1, NRF2, and RARα was enhanced. Up-regulation was particularly high for FXR (200-fold) and SHP (50-fold). In LS174T/R cells, GW4064 induced the expression of FGF19, SHP, OSTα/β, but not MRP2 and BCRP, although the sensitivity of these cells to cisplatin was further reduced. In LS174T cells, GW4064-induced chemoresistance was seen only after being transfected with FXR+RXR, when BCRP, but not MRP2, was up-regulated. Protection of LS174T cells against cisplatin was mimicked by transfection with BCRP. In conclusion, in colon cancer cells, cisplatin treatment enhances chemoresistance through FXR-dependent and FXR-independent mechanisms involving the expression of BCRP and MRP2, respectively.