TCF4 silencing sensitizes the colon cancer cell line to oxaliplatin as a common chemotherapeutic drug

Abstract

Colon cancer is among the most prevalent cancers worldwide. Although the main modality of treatment is surgery, resistance to chemoradiotherapy raises concerns. Hence, we aimed to determine the effect of RNA-mediated silencing of tcf4, the downstream effector of the wnt signaling pathway, on the response of the SW480 cell line to oxaliplatin, a common chemotherapeutic drug. For this, two different silencing sequences against TCF4 mRNA were selected and cloned into pSilencer neo2.1. The SW480 cell line was stably transfected with the silencing constructs (namely p1396, p1874, and p silencer containing a scrambled sequence) and labeled SW1396, SW1874, and SW-Sc, respectively. Subsequently, the effect of oxaliplatin (from 0 to 11.25 μmol/l) on these cells was studied using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide proliferation assay. Suppression of tcf4 expression in stable transfected cells with p1396 and p1874 was confirmed by quantitative reverse transcription-PCR and western blot analysis. Although oxaliplatin was not toxic to SW480 and SW-sc in the range tested, in SW1396 and SW1874 cells, a toxic effect was evident at 3.75 and 4.375 μmol/l. Also, SW1396 and SW1874 cells appeared to have a round shape in comparison with SW480 and SW-Sc cells. Only for SW1396, the number of apoptotic cells was significantly different before and after the addition of oxaliplatin (LC50 of oxaliplatin). The proliferating cells in SW480, SW1874, and SW-Sc increased after treatment with oxaliplatin; however, this was not observed in SW1396. Although silencing the tcf4 gene would confer sensitivity to oxaliplatin in SW1874 and especially SW1396, in SW480 and SW-Sc, the lethal effect of oxaliplatin was compensated by its effect in increasing the proliferation of cells. This sensitization effect may be because of different mechanisms including TCF4 motifs in the ABCB1 promoter or defects in nucleotide excision repair or double-strand break repair systems after tcf4 silencing.