bims-ershed 2023-06-11 papers

J Cancer. 2023 ;14(8): 1336-1349

PERK/ATF3-Reduced ER Stress on high potassium environment in the suppression of tumor ferroptosis.

Xufeng Pu, Li Li, Zhenhui Chen, Aihua Gong, Jiao Lei, Lirong Zhang, Hsiang-I Tsai.

Potassium (K+) is a vital intracellular cation. In the human body, it regulates membrane potential, electrical excitation, protein synthesis, and cell death. Recent studies revealed that dying cancer cells release potassium into the tumor microenvironment (TME), thereby influencing cell survival-related events. Several investigations reported that potassium channels and high potassium levels influence apoptosis. Increasing extracellular potassium and inhibiting K+ efflux channels significantly block the apoptotic machinery. However, it is unknown whether a high-potassium environment also affects other types of cell death such as ferroptosis. In the present study, cell counting kit (CCK-8), colony formation ability, and 5-ethynyl-2'-deoxyuridine (EdU) assays demonstrated that a high-potassium environment reverses erastin-induced ferroptosis. RNA sequencing (RNA-Seq) and Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene ontology (GO) analyses indicated that high potassium levels attenuated the unfolded protein response that is characteristic of endoplasmic reticulum (ER) stress. The ER transmembrane proteins PRKR-like ER kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6) are recognized as ER stress sensors. Here, the PERK blocker GSK2606414 significantly rescued ferroptosis. The present work also disclosed that the ER-related gene activating transcription factor 3 (ATF3) played a vital role in regulating ferroptosis in a high-potassium environment. The foregoing results revealed the roles of potassium and the TME in cancer cell ferroptosis and provided a potential clinical therapeutic strategy for cancer.

DOI: https://doi.org/10.7150/jca.83556

bioRxiv. 2023 May 22. pii: 2023.05.22.541645. [Epub ahead of print]

Rescue of proteotoxic stress and neurodegeneration by the Zn 2+ transporter ZIP7.

Xiaoran Guo, Morgan Mutch, Alba Yurani Torres, Maddalena Nano, Drew McDonald, Zijing Chen, Craig Montell, Wei Dai, Denise J Montell.

Proteotoxic stress drives numerous degenerative diseases. In response to misfolded proteins, cells adapt by activating the unfolded protein response (UPR), including endoplasmic reticulum-associated protein degradation (ERAD). However persistent stress triggers apoptosis. Enhancing ERAD is a promising therapeutic approach for protein misfolding diseases. From plants to humans, loss of the Zn 2+ transporter ZIP7 causes ER stress, however the mechanism is unknown. Here we show that ZIP7 enhances ERAD and that cytosolic Zn 2+ is limiting for deubiquitination of client proteins by the Rpn11 Zn 2+ metalloproteinase as they enter the proteasome in Drosophila and human cells. ZIP7 overexpression rescues defective vision caused by misfolded rhodopsin in Drosophila. Thus ZIP7 overexpression may prevent diseases caused by proteotoxic stress, and existing ZIP inhibitors may be effective against proteasome-dependent cancers.
One-Sentence Summary: Zn 2+ transport from the ER to the cytosol promotes deubiquitination and proteasomal degradation of misfolded proteins and prevents blindness in a fly neurodegeneration model.

DOI: https://doi.org/10.1101/2023.05.22.541645

bioRxiv. 2023 May 24. pii: 2023.05.23.541973. [Epub ahead of print]

Early and late chaperone intervention therapy boosts XBP1s and ADAM10, restores proteostasis, and rescues learning in Alzheimer's Disease mice.

Jennifer M Hafycz, Ewa Strus, Nirinjini N Naidoo.

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder that is pervasive among the aging population. Two distinct phenotypes of AD are deficits in cognition and proteostasis, including chronic activation of the unfolded protein response (UPR) and aberrant Aβ production. It is unknown if restoring proteostasis by reducing chronic and aberrant UPR activation in AD can improve pathology and cognition. Here, we present data using an APP knock-in mouse model of AD and several protein chaperone supplementation paradigms, including a late-stage intervention. We show that supplementing protein chaperones systemically and locally in the hippocampus reduces PERK signaling and increases XBP1s, which is associated with increased ADAM10 and decreased Aβ42. Importantly, chaperone treatment improves cognition which is correlated with increased CREB phosphorylation and BDNF. Together, this data suggests that chaperone treatment restores proteostasis in a mouse model of AD and that this restoration is associated with improved cognition and reduced pathology.
One-sentence summary: Chaperone therapy in a mouse model of Alzheimer's disease improves cognition by reducing chronic UPR activity.

DOI: https://doi.org/10.1101/2023.05.23.541973

Trends Mol Med. 2023 Jun 01. pii: S1471-4914(23)00094-1. [Epub ahead of print]

PERK inhibition in hearts: angel or devil?

Lintong Men, Li Lin, Junyi Guo.

Keywords: PERK; cardiomyocytes; heart failure; unfolded protein response

DOI: https://doi.org/10.1016/j.molmed.2023.05.004

Nature. 2023 Jun 07.

A cytosolic surveillance mechanism activates the mitochondrial UPR.

F X Reymond Sutandy, Ines Gößner, Georg Tascher, Christian Münch.

The mitochondrial unfolded protein response (UPRmt) is essential to safeguard mitochondria from proteotoxic damage by activating a dedicated transcriptional response in the nucleus to restore proteostasis1,2. Yet, it remains unclear how the information on mitochondria misfolding stress (MMS) is signalled to the nucleus as part of the human UPRmt (refs. 3,4). Here, we show that UPRmt signalling is driven by the release of two individual signals in the cytosol-mitochondrial reactive oxygen species (mtROS) and accumulation of mitochondrial protein precursors in the cytosol (c-mtProt). Combining proteomics and genetic approaches, we identified that MMS causes the release of mtROS into the cytosol. In parallel, MMS leads to mitochondrial protein import defects causing c-mtProt accumulation. Both signals integrate to activate the UPRmt; released mtROS oxidize the cytosolic HSP40 protein DNAJA1, which leads to enhanced recruitment of cytosolic HSP70 to c-mtProt. Consequently, HSP70 releases HSF1, which translocates to the nucleus and activates transcription of UPRmt genes. Together, we identify a highly controlled cytosolic surveillance mechanism that integrates independent mitochondrial stress signals to initiate the UPRmt. These observations reveal a link between mitochondrial and cytosolic proteostasis and provide molecular insight into UPRmt signalling in human cells.

DOI: https://doi.org/10.1038/s41586-023-06142-0