Mitotic kinases regulate MT-polymerizing/MT-bundling activity of DDA3.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Mitotic kinases are key regulators of cell cycle progression through phosphorylation of target proteins.
• DDA3 is a spindle-associated phosphoprotein involved in chromosome segregation and microtubule dynamics.
• Understanding DDA3 regulation is crucial for comprehending cell cycle control.

Purpose of the Study:

• To identify and characterize the phosphorylation sites on endogenous DDA3.
• To investigate the impact of DDA3 phosphorylation on its microtubule-binding and bundling activities.
• To elucidate the roles of specific mitotic kinases (Cdk1, Aurora A, Plk1) in DDA3 regulation.

Main Methods:

• Mass spectrometry was employed to identify phosphorylation sites on DDA3.
• Biochemical assays were used to assess microtubule (MT) polymerizing, bundling, and binding activities.
• In vitro kinase assays were performed using purified DDA3 and specific mitotic kinases.

Main Results:

• Four key phosphorylation sites (Ser22, Ser65, Ser70, Ser223) were identified on DDA3.
• Phosphorylation converts DDA3 from a state with MT polymerizing/bundling activity to one with only MT-binding activity.
• Cdk1 and Aurora A negatively regulate MT-polymerizing and bundling activities, while Plk1 does not.
• Aurora A and Plk1-mediated phosphorylation inhibit subsequent phosphorylation by other kinases, highlighting sequential phosphorylation.

Conclusions:

• Mitotic kinases regulate DDA3 function during the cell cycle via sequential phosphorylation.
• This phosphorylation cascade modulates DDA3's microtubule-associated activities, impacting chromosome movement and spindle dynamics.
• DDA3 serves as a critical node integrating signals from multiple mitotic kinases to control cell division.