Plk1 bound to Bub1 contributes to spindle assembly checkpoint activity during mitosis

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Faithful chromosome segregation relies on kinetochore-microtubule attachment and spindle assembly checkpoint (SAC) monitoring.
• The precise mechanisms coordinating these processes remain incompletely understood.

Purpose of the Study:

• To investigate the role of polo-like kinase 1 (Plk1) in regulating SAC activity and kinetochore-microtubule attachment.
• To elucidate the molecular interactions and pathways through which Plk1 influences SAC function.

Main Methods:

• Co-immunoprecipitation assays to study protein interactions.
• Western blotting and immunofluorescence microscopy to assess protein localization and phosphorylation.
• Analysis of kinetochore-microtubule attachments and SAC activity in Plk1-depleted cells.

Main Results:

• Plk1 directly binds to Bub1, contributing to SAC maintenance, but not to CLASP2 or CLIP-170.
• Plk1 phosphorylates Mps1 and the MELT repeats of Knl1, crucial steps for SAC activation.
• Bub1 serves as a scaffold for SAC components on phosphorylated MELT repeats, with Plk1 supporting Bub1 kinetochore localization.

Conclusions:

• Plk1 plays a critical role in maintaining SAC activity during prometaphase by ensuring Bub1 localization to kinetochores.
• This function of Plk1 is essential for coordinating stable kinetochore-microtubule attachment with SAC signaling, ensuring accurate chromosome segregation.