PKM2 compensates for proteasome dysfunction by mediating the formation of the CHIP‐HSP70‐BAG3 complex and the aggregation of ubiquitinated proteins

Abstract Protein aggregation and degradation via autophagy (aggrephagy) are major strategies adopted by cells to remove misfolded polypeptides when there is proteasome dysfunction. The functional protein complex consisting of heat shock protein 70 (Hsp70), cochaperone ubiquitin ligase carboxyl‐terminal of Hsp70/Hsp90 interacting protein (CHIP), and co‐chaperone Bcl‐2‐associated athanogene 3 (BAG3) has been associated with the activation of protein aggregation. However, data on the mechanisms of action of the complex in the protein degradation remains scant. Here, we report that upon proteasome stress, the M2 isoform of pyruvate kinase (PKM2) promotes the aggregation of ubiquitinated proteins and its knockout or knockdown aggravates the sensitivity of cells to proteasome inhibitors. Besides, following proteasome inhibition, PKM2 promotes the interaction of BAG3 with CHIP and HSP70. Interestingly, re‐expression of loss‐of‐function mutants in PKM2‐knockout cells showed that the regulatory function of PKM2 in this progress does not depend on the activity of glycolytic enzymes or protein kinases. Taken together, these findings demonstrate that PKM2 mediates the formation of the CHIP‐HSP70‐BAG3 protein complex and promotes the aggregation of ubiquitinated misfolded proteins, thus compensating for proteasome stress in cells.