Biological effects of ubiquitin-specific peptidase 22 on thyroid papillary cancer cells and its mechanism of action

BACKGROUND: In this study, ubiquitin-specific peptidase 22 (USP22) was detected in both thyroid papillary cancer-1 (TPC-1) and normal thyroid epithelial cell lines (HT-ori3), and its biological function was analyzed. METHOD: Cell culture, resuscitation, and passage, Western blot, and real-time polymerase chain reaction were used. RESULTS: The expression of USP22 was found to be significantly higher in TPC-1 cancer cells than in normal cells. After silencing of the USP22 gene in TPC-1 cells, the levels of USP22 gene and protein expression were significantly decreased. After 6 h with silencing of the USP22 gene, the migration rate was lower and the cells had become smaller than in the control group (P<0.05). At 24 h, the number of invasive cells was significantly lower than in the control group (P<0.05). A cell viability test showed that the differences between the groups increased on days 4 and 5 (P<0.05). The number of colony-forming cells had also decreased significantly after 10 days (P<0.05) in the USP22-siRNA1 group. Compared with the control group, the protein levels of USP22, cyclin D2, and Bmi-1 were significantly decreased (P<0.05). The decrease of USP22 was positively correlated with the decrease of Bmi-1 and cyclin D2. After silencing of the USP22 gene in normal HT-ori3 cells, the USP22 gene and protein expressions decreased significantly (P<0.05). A cell viability test showed that the difference had increased (P<0.01), and the number of cloned cells had significantly decreased than that in negative group (P<0.01). CONCLUSIONS: In conclusion, the USP22 gene plays a key role in the growth, proliferation, invasion, and migration of papillary thyroid cancer cells. USP22 possibly exerts its effect in TPC through the Bmi-1 and cyclin D2 pathways. USP22 also plays a crucial role in the growth of normal thyroid cells.