Fine-tuning of actin dynamics by the HSPB8-BAG3 chaperone complex facilitates cytokinesis and contributes to its impact on cell division

Abstract

The small heat shock protein HSPB8 and its cochaperone BAG3 are proposed to regulate cytoskeletal proteostasis in response to mechanical signaling in muscle cells. Here, we show that in dividing cells, the HSPB8-BAG3 complex is instrumental to the accurate disassembly of the actin-based contractile ring during cytokinesis, a process required to allow abscission of daughter cells. Silencing of HSPB8 markedly decreased the mitotic levels of BAG3 in HeLa cells, supporting its crucial role in BAG3 mitotic functions. Cells depleted of HSPB8 were delayed in cytokinesis, remained connected via a disorganized intercellular bridge, and exhibited increased incidence of nuclear abnormalities that result from failed cytokinesis (i.e., bi-and multi-nucleation). Such phenotypes were associated with abnormal accumulation of F-actin at the intercellular bridge of daughter cells at telophase. Remarkably, the actin sequestering drug latrunculin A, like the inhibitor of branched actin polymerization CK666, normalized F-actin during cytokinesis and restored proper cell division in HSPB8-depleted cells, implicating deregulated actin dynamics as a cause of abscission failure. Moreover, this HSPB8-dependent phenotype could be corrected by rapamycin, an autophagy-promoting drug, whereas it was mimicked by drugs impairing lysosomal function. Together, the results further support a role for the HSPB8-BAG3 chaperone complex in quality control of actin-based structure dynamics that are put under high tension, notably during cell cytokinesis. They expand a so-far underappreciated connection between selective autophagy and cellular morphodynamics that guide cell division.

BAG3 and SYNPO (synaptopodin) facilitate phospho-MAPT/Tau degradation via autophagy in neuronal processes

“…promotes the disassembly of actin-based contractile ring and actin turnover in order to assist proper cell division [37]. SYNPO also participates in the organization of the actin cytoskeleton.…”

HSPB8 and BAG3 cooperate to promote spatial sequestration of ubiquitinated proteins and coordinate the cellular adaptive response to proteasome insufficiency

“…HSPB8 and BAG3 form a stoichiometric complex with functional implications in selective autophagy and mitotic progression (46,47,56). Nonetheless, accumulating ; 1-16 h), showing the levels of phosphorylated-p62 (pS349, pS403) or total p62 levels.…”

“…Recent evidence further indicates that HSPB8 may also have independent chaperone activities during proteotoxic stress (45). In contrast, we have recently shown that during mitotic cell division, BAG3-related activities and stability would depend on its interaction with HSPB8 (46,47). Thus, whether and how HSPB8 contributes to BAG3-related functions during proteotoxic stress remain unclear.…”

“…To characterize the impact of HSPB8 in this pathway, HeLa-RFP-H2B cells were treated with control siRNA or HSPB8-or BAG3specific siRNAs, which achieved .75% depletion of the proteins in these cells ( Fig. 1A) (46,47). Cells were then incubated with the proteasome inhibitor MG132, and aggresome formation was analyzed microscopically after Ub immunostaining ( Fig.…”

Viruses go modular

“…Recently, BAG3 and the CASA machinery were reported to regulate both the synthesis and degradation of filamin, a key actin-cross-linking protein at the plasma membrane that modulates cell adhesion and migration (106 -110). BAG3 is also involved in regulating the disassembly of the actin-based contractile ring during cytokinesis (cell-cell separation) (111,112). Cytokinesis is topologically equivalent to a virion budding from the cell surface (virus-cell separation), and both processes involve some of the same host pathways (113)(114)(115)(116)(117)(118)(119)(120)(121).…”