Targeting the splicing factor CWC22 induces mitotic slippage through repression of BubR1 expression and CDK1 activity...

Splicing factors play a fundamental role in gene expression. Several splicing factors are highly expressed in cancers and promote cell proliferation. Although targeting splicing factors prolongs the duration of G2/M phase, the involvement of splicing factors in the regulation of mitotic checkpoint signaling remains unclear. In this study, we found that knockdown of the splicing factor CWC22 increased not only the population of G2 phase and mitotic cells but also that of tetraploid cells. Notably, CWC22 knockdown induced mitotic slippage, which exhibited premature mitotic exit without spindle assembly checkpoint (SAC) satisfaction following prolonged prometaphase duration. CWC22 knockdown led to cyclin B1 degradation and accumulation of inactive cyclin-dependent kinase 1 with inhibitory phosphorylation at Tyr15 in mitosis. Simultaneous cyclin B1 overexpression and Wee1 blockade mitigated the shortened mitotic duration caused by CWC22 knockdown. RNA-Seq analysis indicated that CWC22 knockdown downregulated SAC-regulatory genes, including BubR1. The shortened mitotic duration caused by CWC22 knockdown was also mitigated by both overexpression of BubR1 and Wee1 blockade. Public datasets showed that CWC22 was highly expressed in pancreatic or cervical cancers, and higher expression negatively correlated with patient prognosis. Targeting CWC22 induced cancer cell death following mitotic slippage and a prolonged G2 phase because of DNA damage accumulation. These results suggest that highly expressed CWC22 contributes to the progression of G2/M phase and prevents mitotic slippage-caused whole-genome doubling by maintaining the SAC function and cyclin-dependent kinase 1 activity in cancer cells. These findings reveal a novel splicing factor function in mitotic checkpoint signaling, which enables uncontrolled cell proliferation in CWC22-overexpressing cancer cells.