To investigate the mechanism of ubiquitin specific protease 22 (USP22) regulating the occurrence and chemotherapy resistance of colorectal cancer through Wnt/β-catenin pathway.

5-fluorouracil (5-Fu) was used for treating the colorectal cancer cell line HT-29 and establishing the drug-resistant cell line HT-29/5-Fu. The sensitivity of HT-29/5-Fu cells and HT-29 cells to 5-Fu was detected by CCK-8 assay. Western blot was used for detecting the effect of 5-Fu on the protein expression of USP22 in HT-29 colorectal cancer cell lines. Using HT-29 parental cell lines of colorectal cancer, a stable expression cell line of USP22 siRNA was constructed (expressed as HT-29-sh USP22, HT-29/5-Fu-sh USP22). The effect of inhibition of USP22 expression on 5-Fu sensitivity of colorectal cancer cells was investigated by CCK-8 test. Western blotting was used to detect the effects of inhibition of USP22 expression on the proteins expression of USP22, β-catenin through Wnt/β-catenin signaling pathway in HT-29 colorectal cancer cell lines.

(1) The IC₅₀ values of HT-29 and HT-29/5-Fu cells to 5-Fu were (1.58±0.23) mg/L and (14.58±0.94) mg/L, respectively. The sensitivity of HT-29/5-Fu cells to 5-Fu was significantly decreased (n=6, t=8.476, P<0.01). (2) After induction of 0.5, 5.0 mg/L 5-Fu, the expression of USP22 protein (USP22/beta-actin) in HT-29 cells increased significantly (0.5 mg/L vs 0 mg/L: t=7.618, P<0.05; 5.0 mg/L vs 0 mg/L: t=6.992, P<0.05). The expression level of USP22 protein in HT-29/5-Fu group was 0.92±0.11, significantly higher than that in HT-29 group (0.18±0.06) (t=7.618, P<0.05). (3) TheIC₅₀ of 5-Fu in HT-29-sh USP22 group was (0.25±0.23) mg/L, significantly lower than that in HT-29 group (t=6.662, P<0.01). The IC₅₀ of 5-Fu in HT-29/5-Fu-sh USP22 group was (1.36±0.14) mg/L, significantly lower than that in HT-29/5-Fu group (t=7.002, P<0.01), but there was no significant difference between HT-29/5-Fu-sh USP22 group and HT-29 group (t=1.586, P>0.05). Inhibition of USP22 expression could enhance the sensitivity of colorectal cancer cell HT-29 to 5-Fu. (4) The expression of USP22 protein in HT-29-sh USP22 group was (0.07±0.01), which was down-regulated compared with HT-29 group (t=7.105, P<0.01). The expression level of USP22 protein in HT-29/5-Fu-sh USP22 group was 0.33±0.02. Compared with HT-29/5-Fu group, the expression level of USP22 protein was down-regulated (t=6.153, P<0.01). The expression of beta-catenin protein in USP22 siRNA stably expressed cell lines HT-29-sh USP22 and HT-29/5-Fu-sh USP22 was significantly lower than that in the corresponding control group HT-29, HT-29/5-Fu (HT-29-sh USP22 vs HT-29: t=8.823, P<0.01; HT-29/5-Fu-sh USP22 vs HT-29/5-Fu: t=7.656, P<0.01).

5-Fu can increase the protein expression of USP22 in colorectal cancer cells. The inhibition of USP22 expression can increase the drug sensitivity of colorectal cancer cells to 5-Fu, and effectively reverse the resistance of colorectal cancer cells to 5-Fu by mediating the Wnt/β-catenin signaling pathway.