Caspases-dependent cleavage of mitotic checkpoint proteins in response to microtubule inhibitor

Area of Science:

• Cell Biology
• Molecular Biology
• Cancer Research

Background:

• The mitotic checkpoint ensures accurate chromosome segregation, preventing aneuploidy.
• Cells exiting mitosis without checkpoint silencing undergo apoptosis, crucial for tumor suppression.
• The biochemical link between mitotic checkpoint function and apoptosis remains unclear.

Purpose of the Study:

• To investigate the biochemical mechanisms linking the mitotic checkpoint to apoptosis.
• To identify how prolonged mitotic arrest impacts checkpoint protein stability.

Main Methods:

• Inducing prolonged spindle damage to trigger mitotic arrest.
• Analyzing the cleavage of mitotic checkpoint kinases (Bub1, BubR1) using caspase inhibitors.
• Expressing caspase-resistant mutants of Bub1 and BubR1 to assess their impact on apoptosis and polyploidy.

Main Results:

• Prolonged spindle damage led to caspase-dependent cleavage of Bub1 and BubR1.
• Expression of caspase-resistant Bub1 and BubR1 mutants increased apoptosis after mitotic arrest.
• Caspase-resistant mutants enhanced the elimination of polyploid cells compared to wild-type proteins.

Conclusions:

• Mitotic checkpoint proteins (Bub1, BubR1) are cleaved by caspases during prolonged mitotic arrest.
• This caspase-mediated cleavage is a novel biochemical property of these checkpoint proteins.
• The cleavage promotes apoptosis and reduces polyploidy, contributing to genomic stability.