Antiparallel microtubule bundling supports KIF15-driven mitotic spindle assembly

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• The mitotic spindle is essential for accurate chromosome segregation, with Eg5 kinesin driving its bipolar assembly.
• Eg5 inhibitors (K5Is) lead to K5I-resistant cells (KIRCs) where KIF15 promotes spindle assembly, but KIF15 is less potent than Eg5.
• Protein Regulator of Cytokinesis 1 (PRC1) bundles antiparallel microtubules and enhances KIF15-microtubule binding.

Purpose of the Study:

• To investigate the role of PRC1 in enhancing KIF15 activity for spindle assembly in K5I-resistant cells (KIRCs).
• To determine if PRC1 can confer resistance to Eg5 inhibitors in normal cells.

Main Methods:

• Studied the effects of PRC1 loss and overexpression on spindle bipolarity in KIRCs.
• Assessed the impact of PRC1 overexpression on K5I-naïve cells treated with S-trityl-L-cysteine (STLC).
• Compared PRC1 effects with those of TPX2, another microtubule bundler.

Main Results:

• Loss of PRC1 in KIRCs decreased spindle bipolarity.
• Overexpression of PRC1 increased spindle formation efficiency in KIRCs.
• PRC1 overexpression protected K5I-naïve cells from STLC and promoted K5I resistance.
• TPX2 did not fully replicate these PRC1-mediated effects.

Conclusions:

• PRC1-mediated microtubule bundling creates a favorable architecture for KIF15-driven spindle assembly when Eg5 is inhibited.
• PRC1 plays a critical role in establishing resistance to Eg5 inhibitors by enhancing KIF15 function.