Immunostaining images from CRC patients stained with AGR2 and SGTA antibodies

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 ER to CYtosol
Signaling (or "ERCYS"). 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.

内质网（Endoplasmic Reticulum, ER）是一类至关重要的感知细胞器，负责折叠并分泌几乎占真核细胞总蛋白三分之一的蛋白质。然而，环境、化学及遗传刺激常诱导内质网内蛋白质错误折叠，引发错误折叠蛋白累积，进而诱发内质网应激。为缓解这一病理状态，已有多项研究报道了多种可通过降低内质网蛋白负荷以减轻内质网应激的机制。近期本团队报道了一种新型内质网监测机制：分泌途径中的蛋白质被逆向转运至细胞质基质，以减轻内质网的内容物负担。这类被逆向转运的蛋白质在癌细胞中可获得新的促存活功能，从而提升癌细胞的生存适合度。我们将这一现象命名为内质网-细胞质信号通路（ER to CYtosol Signaling, 简称ERCYS）。本研究发现，在哺乳动物细胞中，ERCYS的活性受DNAJB12、DNAJB14以及热休克蛋白70同源物（HSC70）的辅助伴侣蛋白SGTA调控。从分子机制层面来看，DNAJB12与DNAJB14可通过其定位于细胞质的J结构域，分别结合HSC70与SGTA，进而促进内质网蛋白的逆向转运过程。DNAJB12既是驱动该现象的必需因子，也是充分因子：其可增强AGR2的逆向转运，并在内质网应激条件下抑制野生型p53（wt-p53）的活性。若DNAJB12/14的J结构域发生突变，则会阻断AGR2与野生型p53之间的抑制性相互作用。因此，靶向DNAJB12/14-HSC70/SGTA信号轴是抑制ERCYS活性、削弱癌细胞生存适合度的极具潜力的治疗策略。