NF-κB regulates protein quality control after heat stress through modulation of the BAG3-HspB8 complex

We previously found that the NF-kappa B transcription factor is activated during the recovery period after heat shock; moreover, we demonstrated that NF-kappa B is essential for cell survival after heat shock by activating autophagy, a mechanism that probably helps the cell to cope with hyperthermic stress through clearance of damaged proteins. In this study, we analyze the involvement of NF-kappa B in basal and heat-stress-induced protein quality control, by comparing the level of multiubiquitylated and/or aggregated proteins, and proteasome and autophagic activity in NF-kappa B-competent and NF-kappa B-incompetent cells. We show that NF-kappa B has only a minor role in basal protein quality control, where it modulates autophagosome maturation. By contrast, NF-kappa B is shown to be a key player in protein quality control after hyperthermia. Indeed, NF-kappa B-incompetent cells show highly increased levels of multiubiquitylated and/or aggregated proteins and aggresome clearance defects; a phenotype that disappears when NF-kappa B activity is restored to normal. We demonstrate that during heat shock recovery NF-kappa B activates selective removal of misfolded or aggregated proteins a process also called 'aggrephagy' by controlling the expression of BAG3 and HSPB8 and by modulating the level of the BAG3-HspB8 complex. Thus NF-kappa B-mediated increase in the level of the BAG3-HspB8 complex leads to upregulation of aggrephagy and clearance of irreversibly damaged proteins and might increase cell survival in conditions of hyperthermia.