Mad2 Overexpression Uncovers a Critical Role for TRIP13 in Mitotic Exit

Summary

The mitotic checkpoint ensures proper segregation of chromosomes by delaying anaphase until all kinetochores are bound to microtubules. This inhibitory signal is composed of a complex containing Mad2, which inhibits anaphase progression. The complex can be disassembled by p31comet and TRIP13; however, TRIP13 knockdown has been shown to cause only a mild mitotic delay. Overexpression of checkpoint genes, as well as TRIP13, is correlated with chromosomal instability (CIN) in cancer, but the initial effects of Mad2 overexpression are prolonged mitosis and decreased proliferation. Here we show that TRIP13 overexpression significantly reduced, and TRIP13 reduction significantly exacerbated, the mitotic delay associated with Mad2 overexpression but not that induced by microtubule depolymerization. The combination of Mad2 overexpression and TRIP13 loss reduced the ability of checkpoint complexes to disassemble and significantly inhibited the proliferation of cells in culture and tumor xenografts. These results identify an unexpected dependency on TRIP13 in cells overexpressing Mad2.

Graphical abstract

TRIP13 is a putative mitotic checkpoint silencing protein. However, depletion of TRIP13 causes only mild mitotic exit phenotypes. Marks et al. find that TRIP13 becomes critical for mitotic exit in Mad2-overexpressing cells. Both proteins are co-overexpressed in cancer, and TRIP13 may be a therapeutic target in Mad2-overexpressing tumors.