emergent (emergency?)， ask for revision， thanks

Objective: Colon cancer is currently the third leading cause of cancer death throughout the world. Recent studies indicated that over-expression of microRNA-21 (miR-21) and down regulation of Fas ligand are both associated with the improved chemo-resistance of 5-fluorouracil and cell apoptosis in colon cancer cells. The This study was conducted to uncover the relationship between miR-21 and FasL in colon cancer progression.

Materials and methods: In this research, various a variety of software and q-RT-PCR were used to predict the target genes of mir-21. Luciferase report assay was conducted to verify whether FasL was a target gene of miR-21. Colon cancer cells RKO were treated in there three different groups: pre-mir-21 transfected group, FasL siRNA transfected group and a negative control group. For each group, MTT assays were carried out to detect the cell viability; q-RT-PCR and western blot were used to measure the expression level of miR-21 in both mRNA and protein level (this makes no sense). Expression level of caspase-3 was detected by western blot.

Results: miR-21 inhibited the Fas ligand mRNA by targeting its 3'-UTR—thus further inhibiting its expression at protein level in colon cancer cell line RKO. Moreover, transfected RKO cells with pre-miR-21 suppressed the expression of FasL effectively, which promoted proliferation and reduced apoptosis of RKO. After being treated with 5-FU, the amount of FasL at mRNA and protein levels were both elevated. Furthermore, miR-21 over-expression and FasL down-regulation significantly reduced the therapeutic efficacy of 5-FU.

Conclusion: Taken together, this study showed that miR-21 over-expression repressed decreased the sensitivity of 5-FU and cell apoptosis by down-regulation of FasL. and Both miR-21 and FasL might be a may represent pivotal clinical targets of therapeutic efficacy in colorectal cancer.