bims-unfpre 2023-04-02 papers

Issue of 2023–04–02
five papers selected by
Susan Logue, University of Manitoba

bioRxiv. 2023 Mar 27. pii: 2023.03.19.533325. [Epub ahead of print]

A beneficial adaptive role for CHOP in driving cell fate selection during ER stress.

Kaihua Liu, Chaoxian Zhao, D Thomas Rutkowski.

Cellular stresses elicit signaling cascades that are capable of both mitigating the inciting dysfunction and initiating cell death when the stress cannot be overcome. During endoplasmic reticulum (ER) stress, the transcription factor CHOP is widely recognized to promote cell death. Yet CHOP carries out this function largely by augmenting protein synthesis, which is an essential component of recovery from stress. In addition, the mechanisms that drive cell fate during ER stress have largely been explored under super-physiological experimental conditions that do not permit cellular adaptation. Thus, it is not clear whether CHOP also has a beneficial role during that adaptation. Here, we have created a new, versatile, genetically modified Chop allele, which we combined with single cell analysis and stresses of physiological intensity, to rigorously examine the contribution of CHOP to cell fate. Surprisingly, we found that, within the cell population, CHOP paradoxically promoted death in some cells but proliferation-and hence recovery-in others. Strikingly, this function of CHOP conferred a stress-specific competitive growth advantage to wild-type cells over cells lacking CHOP. The dynamics of CHOP expression and UPR activation at the single cell level suggested that, by promoting protein synthesis, CHOP maximizes UPR activation which in turn favors stress resolution, subsequent UPR deactivation, and proliferation. Taken together, these findings suggest that CHOP's function can be better described as a "stress test" that drives cells into either of two mutually exclusive fates-adaptation or death-during stress. They point to a previously unappreciated pro-survival function of CHOP during stresses of physiological intensity.

DOI: https://doi.org/10.1101/2023.03.19.533325

Free Radic Biol Med. 2023 Mar 28. pii: S0891-5849(23)00133-8. [Epub ahead of print]

Ferroptosis signaling promotes the release of misfolded proteins via exosomes to rescue ER stress in hepatocellular carcinoma.

Jian Yang, Huanji Xu, Wanlong Wu, Huixi Huang, Chenliang Zhang, Weiping Tang, Qinlin Tang, Feng Bi.

Dysfunction of the ubiquitin‒proteasome system can induce sustained endoplasmic reticulum stress (ERS) and subsequent cell death. However, malignant cells have evolved multiple mechanisms to evade sustained ERS. Therefore, identification of the mechanisms through which tumor cells develop resistance to ERS is important for the therapeutic exploitation of these cells for drug-resistant tumors. Herein, we found that proteasome inhibitors could induce ERS, activate ferroptosis signaling, and thereby induce the adaptive tolerance of tumor cells to ERS. Mechanistically, the activation of ferroptosis signaling was found to promote the formation and secretion of exosomes containing misfolded and unfolded proteins, which resulted in rescuing ERS and promoting tumor cell survival. The inhibition of ferroptosis signaling synergized with bortezomib, a clinically used proteasome inhibitor, to suppress the viability of hepatocellular carcinoma cells in vitro and in vivo. The present findings reveal that ERS resistance can be driven by an ERS-ferroptosis signaling-exosome pathway and have important clinical implications for intracellular signaling, ER homeostasis and drug-resistant cancer therapy.

Keywords: Arachidonic acid; Bortezomib; Endoplasmic reticulum stress; Exosomes; Ferroptosis; Hepatocellular carcinoma

DOI: https://doi.org/10.1016/j.freeradbiomed.2023.03.027

BMC Cancer. 2023 Mar 30. 23(1): 288

RRM2 and CDC6 are novel effectors of XBP1-mediated endocrine resistance and predictive markers of tamoxifen sensitivity.

David Barua, Afrin Sultana, Md Nahidul Islam, Fergus Cox, Ananya Gupta, Sanjeev Gupta.

BACKGROUND: Endocrine-resistant breast cancers have elevated expression of XBP1, where it drives endocrine resistance by controlling the expression of its target genes. Despite the in-depth understanding of the biological functions of XBP1 in ER-positive breast cancer, effectors of endocrine resistance downstream of XBP1 are poorly understood. The aim of this study was to identify the XBP1-regulated genes contributing to endocrine resistance in breast cancer.
METHODS: XBP1 deficient sub-clones in MCF7 cells were generated using the CRISPR-Cas9 gene knockout strategy and were validated using western blot and RT-PCR. Cell viability and cell proliferation were evaluated using the MTS assay and colony formation assay, respectively. Cell death and cell cycle analysis were determined using flow cytometry. Transcriptomic data was analysed to identify XBP1-regulated targets and differential expression of target genes was evaluated using western blot and qRT-PCR. Lentivirus and retrovirus transfection were used to generate RRM2 and CDC6 overexpressing clones, respectively. The prognostic value of the XBP1-gene signature was analysed using Kaplan-Meier survival analysis.
RESULTS: Deletion of XBP1 compromised the upregulation of UPR-target genes during conditions of endoplasmic reticulum (EnR) stress and sensitized cells to EnR stress-induced cell death. Loss of XBP1 in MCF7 cells decreased cell growth, attenuated the induction of estrogen-responsive genes and sensitized them to anti-estrogen agents. The expression of cell cycle associated genes RRM2, CDC6, and TOP2A was significantly reduced upon XBP1 deletion/inhibition in several ER-positive breast cancer cells. Expression of RRM2, CDC6, and TOP2A was increased upon estrogen stimulation and in cells harbouring point-mutants (Y537S, D538G) of ESR1 in steroid free conditions. Ectopic expression of RRM2 and CDC6 increased cell growth and reversed the hypersensitivity of XBP1 KO cells towards tamoxifen conferring endocrine resistance. Importantly, increased expression of XBP1-gene signature was associated with poor outcome and reduced efficacy of tamoxifen treatment in ER-positive breast cancer.
CONCLUSIONS: Our results suggest that RRM2 and CDC6 downstream of XBP1 contribute to endocrine resistance in ER-positive breast cancer. XBP1-gene signature is associated with poor outcome and response to tamoxifen in ER-positive breast cancer.

Keywords: Breast cancer; CDC6; ER stress; Endocrine resistance; RRM2; XBP1

DOI: https://doi.org/10.1186/s12885-023-10745-1

Int J Mol Sci. 2023 Mar 16. pii: 5657. [Epub ahead of print]24(6):

BCL-XL Overexpression Protects Pancreatic β-Cells against Cytokine- and Palmitate-Induced Apoptosis.

Atenea A Perez-Serna, Reinaldo S Dos Santos, Cristina Ripoll, Angel Nadal, Decio L Eizirik, Laura Marroqui.

Diabetes is a chronic disease that affects glucose metabolism, either by autoimmune-driven β-cell loss or by the progressive loss of β-cell function, due to continued metabolic stresses. Although both α- and β-cells are exposed to the same stressors, such as proinflammatory cytokines and saturated free fatty acids (e.g., palmitate), only α-cells survive. We previously reported that the abundant expression of BCL-XL, an anti-apoptotic member of the BCL-2 family of proteins, is part of the α-cell defense mechanism against palmitate-induced cell death. Here, we investigated whether BCL-XL overexpression could protect β-cells against the apoptosis induced by proinflammatory and metabolic insults. For this purpose, BCL-XL was overexpressed in two β-cell lines-namely, rat insulinoma-derived INS-1E and human insulin-producing EndoC-βH1 cells-using adenoviral vectors. We observed that the BCL-XL overexpression in INS-1E cells was slightly reduced in intracellular Ca2+ responses and glucose-stimulated insulin secretion, whereas these effects were not observed in the human EndoC-βH1 cells. In INS-1E cells, BCL-XL overexpression partially decreased cytokine- and palmitate-induced β-cell apoptosis (around 40% protection). On the other hand, the overexpression of BCL-XL markedly protected EndoC-βH1 cells against the apoptosis triggered by these insults (>80% protection). Analysis of the expression of endoplasmic reticulum (ER) stress markers suggests that resistance to the cytokine and palmitate conferred by BCL-XL overexpression might be, at least in part, due to the alleviation of ER stress. Altogether, our data indicate that BCL-XL plays a dual role in β-cells, participating both in cellular processes related to β-cell physiology and in fostering survival against pro-apoptotic insults.

Keywords: BCL-XL; Ca2+ signaling; apoptosis; cytokines; insulin secretion; palmitate; pancreatic β-cells

DOI: https://doi.org/10.3390/ijms24065657

Discov Oncol. 2023 Mar 31. 14(1): 37

NRF2 and STAT3: friends or foes in carcinogenesis?

Andrea Arena, Maria Anele Romeo, Rossella Benedetti, Maria Saveria Gilardini Montani, Roberta Santarelli, Roberta Gonnella, Gabriella D'Orazi, Mara Cirone.

NRF2 is a transcription factor that plays a pivotal role in carcinogenesis, also through the interaction with several pro-survival pathways. NRF2 controls the transcription of detoxification enzymes and a variety of other molecules impinging in several key biological processes. This perspective will focus on the complex interplay of NRF2 with STAT3, another transcription factor often aberrantly activated in cancer and driving tumorigenesis as well as immune suppression. Both NRF2 and STAT3 can be regulated by ER stress/UPR activation and their cross-talk influences and is influenced by autophagy and cytokines, contributing to shape the microenvironment, and both control the execution of DDR, also by regulating the expression of HSPs. Given the importance of these transcription factors, more investigations aimed at better elucidating the outcome of their networking could help to discover new and more efficacious strategies to fight cancer.

Keywords: Cytokines; DDR; NRF2; STAT3; p62/SQSTM1

DOI: https://doi.org/10.1007/s12672-023-00644-z