Abnormal expression of the mitotic checkpoint protein BubR1 contributes to the anti-microtubule drug resistance of esophageal squamous cell carcinoma cells.

Esophageal cancer is a common malignancy with a high mortality rate. The lack of effective chemotherapy and a means to overcome drug resistance leads to the predictable failure of esophageal cancer treatment. Mitotic checkpoint proteins play a critical role in regulating the cell cycle and proliferation. Abnormal expression of the mitotic checkpoint protein BubR1 has been reported in several types of cancers. In this study, we investigated the role of BubR1 in conferring resistance of esophageal cancer cells to anti-microtubule drugs. Using quantitative real-time PCR analysis on 50 samples of paired esophageal squamous cell cancer (ESC) tissues and adjacent non-cancerous tissues, we found that 72% (36 of 50) of the analyzed ESC samples exhibited high expression levels of BubR1, which was also confirmed in ESC cell lines. ESC cells with high levels of BubR1 were less sensitive to the anti-microtubule drugs paclitaxel and nocodazole. Recombinant adenovirus-mediated enforced expression of BubR1 in relatively sensitive ESC cell lines resulted in increased resistance to paclitaxel. Conversely, RNAi-mediated knockdown of BubR1 restored ESC cell sensitivity to paclitaxel. Cell cycle analysis indicated that the sub-G1 population increased in the ESC cells with reduced BubR1 levels. Taken together, our results suggest that upregulation of BubR1 expression may be associated with ESC resistance to paclitaxel treatment. Thus, BubR1 may serve as a potential chemosensitizing target to overcome chemoresistance.