Splicing factor CWC22 prevents tetraploidy formation and mitotic slippage through maintenance of the BubR1 expression and CDK1 activity

Splicing factors play a fundamental role in the process of gene expression. Several splicing factors are highly expressed in cancers and promote the proliferation. Although targeting of splicing factors prolong the duration of G2 phase and mitosis, the involvement of splicing factors in regulation of cell ploidy remains unclear. In this study, we found that knockdown of CWC22, a splicing factor, increased not only the population of G2 phase and mitosis but also tetraploid cells. Notably, CWC22 knockdown induces mitotic slippage, which exhibits rapid mitotic exit without SAC satisfaction after prolonged prometaphase duration. CWC22 knockdown led to cyclin B1 degradation and accumulation of inactive CDK1 having the inhibitory phosphorylation at Tyr15 in mitosis. The cyclin B1 overexpression and Wee1 blockage mitigated the shortage of mitotic duration by CWC22 knockdown. RNA-seq analysis indicated that CWC22 knockdown down-regulated SAC-regulatory genes, including BubR1. The shortage of mitotic duration caused by CWC22 knockdown was also mitigated by both overexpression of BubR1 and Wee1 blockage. Furthermore, CWC22 was highly expressed in pancreatic or cervical cancers, and the higher expression negatively correlated with patients’ prognosis. CWC22 knockdown induced cancer cell death after miotic slippage and prolonged G2 phase due to DNA damage accumulation. These results suggest that CWC22 not only supports proper progression of G2/M phase but also prevents mitotic slippage and tetraploid cell formation via regulation of checkpoint signaling by contributing to the proper expression of BubR1 and the CDK1 activity. These findings reveal a novel splicing factor function in genome stability.