CDK1-Mediated Phosphorylation of BAG3 Promotes Mitotic Cell Shape Remodeling and the Molecular Assembly of Mitotic p62 Bodies

Abstract

The cochaperone BCL2-associated athanogene 3 (BAG3), in complex with the heat shock protein HSPB8, facilitates mitotic rounding, spindle orientation, and proper abscission of daughter cells. BAG3 and HSPB8 mitotic functions implicate the sequestosome p62/SQSTM1, suggesting a role for protein quality control. However, the interplay between this chaperone-assisted pathway and the mitotic machinery is not known. Here, we show that BAG3 phosphorylation at the conserved T285 is regulated by CDK1 and activates its function in mitotic cell shape remodeling. BAG3 phosphorylation exhibited a high dynamic at mitotic entry and both a non-phosphorylatable BAG3T285A and a phosphomimetic BAG3T285D protein were unable to correct the mitotic defects in BAG3-depleted HeLa cells. We also demonstrate that BAG3 phosphorylation, HSPB8, and CDK1 activity modulate the molecular assembly of p62/SQSTM1 into mitotic bodies containing K63 polyubiquitinated chains. These findings suggest the existence of a mitotically regulated spatial quality control mechanism for the fidelity of cell shape remodeling in highly dividing cells.

Genetics of BAG3: A Paradigm for Developing Precision Therapies for Dilated Cardiomyopathies

“… 35 , 45 Subsequently, BAG3 interacts directly with the macroautophagy receptor protein p62 (also known as sequestosome‐1) and induces selective macroautophagy while lysosomes uptake and degrade protein aggregates. 35 , 46 BAG3‐mediated selective macroautophagy plays critical roles in the cellular protein quality control system. 35 Antiapoptosis: With BAG3 as an athanogene, the Hsp70‐BAG3 complex protects antiapoptotic Bcl‐2 proteins from proteasomal degradation and activates the antiapoptotic nuclear factor kappa B (NF‐κB) pathway.…”

“… 35 , 45 Subsequently, BAG3 interacts directly with the macroautophagy receptor protein p62 (also known as sequestosome‐1) and induces selective macroautophagy while lysosomes uptake and degrade protein aggregates. 35 , 46 BAG3‐mediated selective macroautophagy plays critical roles in the cellular protein quality control system. 35 …”

The Role of Small Heat Shock Proteins in Protein Misfolding Associated Motoneuron Diseases

“…Finally, HSPB8 and BAG3 together are involved in the control of the cell cycle during mitosis and cytokinesis, where they maintain proper actin structure homeostasis and dynamics [ 166 , 250 , 297 , 298 ]. HSPB8 is also involved in RNA metabolism, thanks to its ability to bind DDX20, an RNA helicase involved in the activity of the SMN protein; notably, some HSPB8 mutants show alteration of DDX20 binding [ 299 ].…”