The cochaperone BAG3 promotes the stabilization of p53 under heat stress conditions.

Bcl-2-associated athanogene 3 (BAG3) is the only member of the BAG cochaperone family that is induced by stressful stimuli such as heat shock and heavy metals. In the present study, bag3 knockout (KO) HeLa cells were generated via the CRISPR-Cas9 system, and the role of BAG3 in relation to p53 under heat stress conditions was investigated. Normally, the levels of p53 were low in both wild-type (WT) and KO cells, while heat shock increased the levels of nuclear p53 in both cell lines. However, the increased level of p53 was much greater in WT cells than in KO cells, which suggested that BAG3 played a role in controlling the level of p53 under heat stress conditions. The mRNA level of p53 did not increase in either WT or KO cells during the heat stress period, which suggested that the differences in the levels of p53 were not due to transcriptional regulation. Both treatment with the proteasome inhibitor MG132 and heat shock drastically increased p53 levels to a similar extent in WT cells. Interestingly, both BAG3 and Hsp70 rapidly translocated to the nucleus and formed a complex with p53 upon heat stress. During a 1-h recovery period from heat stress, the transcriptional activity of p53 increased up to 4-fold in WT cells, but only 1.69-fold in KO cells. These results demonstrate that Hsp70 and BAG3 are involved in the quality control of p53 under heat stress conditions and suggest a role for BAG3 as a cochaperone protein.