Cytosolic and endoplasmic reticulum chaperones inhibit wt-p53 to increase cancer cells' survival by refluxing ER-proteins to the cytosol

The endoplasmic reticulum (ER) is an essential sensing organelle responsible for the folding and secretion of almost one-third of eukaryotic cells' total proteins. However, environmental, chemical, and genetic insults often lead to protein misfolding in the ER, accumulating misfolded proteins, and causing ER stress. To solve this, several mechanisms were reported to relieve ER stress by decreasing the ER protein load. Recently, we reported a novel ER surveillance mechanism by which proteins from the secretory pathway are refluxed to the cytosol to relieve the ER of its content. The refluxed proteins gain new prosurvival functions in cancer cells, thereby increasing cancer cell fitness. We termed this phenomenon <u>ER</u> to <u>CY</u>tosol <u>S</u>ignaling (or '<b>ERCYS'</b>). Here, we found that in mammalian cells, ERCYS is regulated by DNAJB12, DNAJB14, and the HSC70 cochaperone SGTA. Mechanistically, DNAJB12 and DNAJB14 bind HSC70 and SGTA - through their cytosolically localized J-domains to facilitate ER-protein reflux. DNAJB12 is necessary and sufficient to drive this phenomenon to increase AGR2 reflux and inhibit wt-p53 during ER stress. Mutations in DNAJB12/14 J-domain prevent the inhibitory interaction between AGR2-wt-p53. Thus, targeting the DNAJB12/14-HSC70/SGTA axis is a promising strategy to inhibit ERCYS and impair cancer cell fitness.