Chaperone Complexes from the Endoplasmic Reticulum (ER) and the Cytosol Inhibit Wild-Type p53 by Activating the ER-to-Cytosol Signaling Pathway

Alapfogalmak

Chaperone complexes from the ER and cytosol, specifically DNAJB12 and DNAJB14, regulate the reflux of ER proteins to the cytosol, which inhibits the activity of wild-type p53 in cancer cells.

Kivonat

The study investigates the mechanism by which proteins are refluxed from the endoplasmic reticulum (ER) to the cytosol, a process known as ER-to-Cytosol Signaling (ERCYS). The authors found that mammalian cells have five putative orthologs of the yeast HLJ1 protein, which was previously shown to be essential for this reflux process. Among these, DNAJB12 and DNAJB14 appear to be the most significant.

Mechanistically, DNAJB12 and DNAJB14 bind to the cytosolic HSC70 chaperone and its cochaperone SGTA through their cytosol-facing J-domains, facilitating the reflux of ER proteins to the cytosol. This reflux process targets a wide range of ER-resident and secretory proteins, including the anterior gradient 2 (AGR2) protein, which can then interact with and inhibit the activity of the pro-apoptotic protein p53 in the cytosol.

Silencing DNAJB12 and DNAJB14 impairs the reflux of ER proteins and restores p53 activity during ER stress. Overexpression of DNAJB12, but not DNAJB14, is sufficient to induce the reflux of ER proteins and inhibit p53 activity. This effect requires the functional J-domain of DNAJB12, which is necessary for recruiting the cytosolic chaperone machinery.

The authors propose that targeting the DNAJB12/14-HSC70/SGTA axis is a promising strategy to inhibit ERCYS and restore p53 activity, thereby impairing cancer cell fitness.

Statisztikák

The cytosolic enrichment of AGR2, DNAJB11, and HYOU1 was significantly increased in wild-type A549 cells treated with the ER stress inducers tunicamycin and thapsigargin.
Silencing both DNAJB12 and DNAJB14 in A549 cells highly affected the cytosolic accumulation of AGR2, DNAJB11, and HYOU1 during ER stress.
Overexpression of DNAJB12, but not DNAJB14, was sufficient to cause the reflux of AGR2, DNAJB11, and HYOU1 to the cytosol in the absence of ER stress.

Idézetek

"DNAJB12 and DNAJB14 are necessary and sufficient to drive this phenomenon to increase AGR2 reflux and inhibit wt-p53 during ER stress."
"Downregulation of DNAJB12 and DNAJB14 increases cell toxicity and wt-p53 activity during etoposide treatment."
"Overexpressing DNAJB12 in A549 cells was sufficient to cause reflux of AGR2, DNAJB11, and HYOU1 at 12 and 24 hours post-induction."

Főbb Kivonatok

Chaperone Complexes From The Endoplasmic Reticulum (ER) And The Cytosol Inhibit wt-p53 By Activation The ER To Cytosol Signaling

by Dabsan,S., Z... : www.biorxiv.org 08-03-2023

https://www.biorxiv.org/content/10.1101/2023.08.01.551134v1

Mélyebb kérdések

How might the different DNAJ proteins (DNAJB12, DNAJB14, DNAJC14, DNAJC18, DNAJC30) have specialized functions in regulating the reflux of distinct sets of ER proteins to the cytosol?

The different DNAJ proteins, including DNAJB12, DNAJB14, DNAJC14, DNAJC18, and DNAJC30, may have specialized functions in regulating the reflux of distinct sets of ER proteins to the cytosol due to their unique structural and functional characteristics. Each DNAJ protein likely interacts with specific client proteins in the ER and facilitates their reflux to the cytosol through interactions with chaperones and cochaperones.

DNAJB12 and DNAJB14: These proteins are highly homologous and may have overlapping functions in promoting ER protein reflux. They have been shown to be essential for the reflux of ER-resident proteins, such as AGR2, to the cytosol. DNAJB12 and DNAJB14 may have specific binding affinities for certain client proteins, leading to the selective reflux of these proteins during ER stress.

DNAJC14, DNAJC18, and DNAJC30: These DNAJ proteins are putative orthologs of the yeast HLJ1 and share a similar topology with a J-domain facing the cytosol. While they may have lower similarity scores to DNAJB12 and DNAJB14, they could still play crucial roles in regulating the reflux of specific subsets of ER proteins. The differences in their sequences and structures may determine their specificity in interacting with distinct client proteins and facilitating their reflux to the cytosol.

Overall, the diversity of DNAJ proteins in the ER membrane suggests a complex regulatory network for the reflux of ER proteins to the cytosol. Each DNAJ protein may have unique client preferences and interactions with chaperones, contributing to the selective reflux of different sets of ER proteins based on cellular needs and stress conditions.

What are the potential compensatory mechanisms or alternative pathways that could be activated when the DNAJB12/14-HSC70/SGTA axis is disrupted, and how might these impact cancer cell fitness?

When the DNAJB12/14-HSC70/SGTA axis is disrupted, leading to impaired reflux of ER proteins to the cytosol, cancer cells may activate compensatory mechanisms or alternative pathways to maintain cellular homeostasis and survival. These compensatory mechanisms could impact cancer cell fitness in several ways:

Upregulation of other chaperones: In response to the disruption of the DNAJB12/14-HSC70/SGTA axis, cancer cells may upregulate other chaperones and cochaperones to assist in protein folding, trafficking, and degradation. This compensatory mechanism aims to alleviate ER stress and maintain protein homeostasis in the absence of efficient ER protein reflux.

Activation of the unfolded protein response (UPR): The UPR is a stress response pathway activated in the presence of misfolded proteins in the ER. When the DNAJB12/14-HSC70/SGTA axis is disrupted, cancer cells may enhance UPR signaling to cope with ER stress and restore protein folding capacity. However, prolonged UPR activation can lead to cell death or adaptation to ER stress conditions.

Alterations in protein degradation pathways: Disruption of the DNAJB12/14-HSC70/SGTA axis may affect the efficiency of ER-associated degradation (ERAD) and proteasomal degradation pathways. Cancer cells may modulate these pathways to degrade misfolded proteins accumulated in the ER and prevent cytotoxicity.

Changes in signaling pathways: The disruption of the DNAJB12/14-HSC70/SGTA axis could impact signaling pathways involved in cell survival, proliferation, and apoptosis. Cancer cells may activate alternative survival pathways or inhibit proapoptotic signals to counteract the effects of ER stress and protein misfolding.

Overall, the activation of compensatory mechanisms and alternative pathways in response to the disruption of the DNAJB12/14-HSC70/SGTA axis reflects the adaptability of cancer cells to maintain their fitness and survival under stressful conditions. However, these compensatory mechanisms may also present vulnerabilities that could be targeted for therapeutic intervention.

Given the role of ER stress and ERCYS in various diseases beyond cancer, could targeting this pathway have broader therapeutic implications for other pathologies?

Targeting the ER stress pathway and ERCYS could indeed have broader therapeutic implications for various diseases beyond cancer. The involvement of ER stress in the pathogenesis of numerous disorders, including neurodegenerative diseases, metabolic disorders, and inflammatory conditions, highlights the potential of targeting this pathway for therapeutic interventions. Here are some ways in which targeting the ER stress pathway and ERCYS could benefit other pathologies:

Neurodegenerative diseases: ER stress has been implicated in the pathogenesis of neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases. Modulating ER stress responses and promoting proper protein folding and degradation could mitigate neuronal damage and protein aggregation associated with these conditions.

Metabolic disorders: Conditions like diabetes, obesity, and fatty liver disease are characterized by ER stress in metabolic tissues. Targeting the ERCYS pathway to enhance protein folding and alleviate ER stress could improve metabolic function and insulin sensitivity in these disorders.

Inflammatory conditions: ER stress plays a role in the pathogenesis of inflammatory diseases such as inflammatory bowel disease, rheumatoid arthritis, and atherosclerosis. By targeting the ER stress response and promoting efficient protein handling, it may be possible to reduce inflammation and tissue damage in these conditions.

Rare genetic disorders: Many rare genetic disorders are caused by mutations in genes encoding ER-resident proteins, leading to protein misfolding and ER stress. Modulating the ERCYS pathway could help in managing these disorders by promoting the proper folding and trafficking of mutant proteins.

Overall, targeting the ER stress pathway and ERCYS holds promise for a wide range of diseases beyond cancer, offering potential therapeutic strategies to alleviate cellular stress, restore protein homeostasis, and improve disease outcomes. Further research into the specific mechanisms and targets within the ER stress pathway could uncover novel therapeutic avenues for diverse pathologies.