The antioxidant transcription factor Nrf2 modulates the stress response and phenotype of malignant as well as premalignant pancreatic ductal epithelial cells by inducing expression of the ATF3 splicing variant ΔZip2

The landscape of ATF3 in tumors: Metabolism, expression regulation, therapy approach, and open concerns

Cellular stress response is a pivotal process in tumor development and therapy. Activating transcription factor 3 (ATF3), a representative stress-responsive protein, plays pleiotropic roles in various biological processes. Over the past decade, studies have described not only the general role of ATF3 in tumor metabolism but also the complexity of ATF3 expression regulation and its associated modifications, including phosphorylation, ubiquitination, SUMOylation, and NEDDylation. Interestingly, beyond being a transcription factor, ATF3 can act as a modifier to control the ubiquitination of target molecules, such as p53, to exert its function in tumors. These advances in uncovering ATF3 biological function have yielded new insights into the cellular stress response during tumor development and will be instrumental in developing novel interventions. In this review, we update the role of ATF3 as a nexus in amino acid metabolism, lipid metabolism, glycometabolism, and other metabolic pathways in tumors; delineate the underlying mechanisms involving DNA level regulation, epigenetic regulation, and post-translational modifications of ATF3; and summarize the progression of tumor mono/combination therapies related to ATF3. In particular, we discuss the challenges that need to be addressed to provide a new conceptual framework for further understanding the potential therapeutic value of ATF3 in ongoing clinical trials.

GRP78 as a potential therapeutic target in cancer treatment: an updated review of its role in chemoradiotherapy resistance of cancer cells

GRP78 (Glucose-related protein 78, BiP/HSPA5) is commonly overexpressed in cancer cells. Acting as an activator of endoplasmic reticulum stress, GRP78 is involved in the resistance of cancer cells to injury. Current evidence suggests that GRP78 plays a significant role in the radiotherapy resistance and chemotherapy resistance of cancers, which is accomplished through a variety of complex pathways. These include the promotion of tumor stemness, inhibition of apoptosis, regulation of autophagy, maintenance of tumor microenvironment homeostasis, protection of dormant cells, evasion of senescence, counteraction of autoantibodies against GRP78, facilitation of DNA damage repair, suppression of ferroptosis, and modulation of metabolic reprogramming in tumor cells. Importantly, chemoradiotherapy resistance in cancers are the main reasons for treatment failure in patients, severely affecting their survival. Investigating the mechanisms of GRP78 in tumor therapeutic resistance is essential. In this article, we review the mechanisms by which GRP78 mediates cell survival and chemoradiotherapy resistance in cancers and provide an overview of clinical trials targeting GRP78 therapy.

The molecular mechanism of PLD2-mediated regulation of apoptosis and cell edema in pancreatic cells via the Nrf2/NF-κB pathway

This study aimed to elucidate the molecular mechanisms by which PLD2 controls apoptosis and edema in pancreatic cells via the Nrf2/NF-κB pathway. AR42J rat pancreatic cells were treated with 10 nM mitomycin to create an in vitro pancreatitis model (model group), with a control group receiving phosphate-buffered saline. Cells were transfected with a PLD2 overexpression plasmid using Lipofectamine 3000, forming the PLD2 overexpression group. PLD2 protein expression was assessed by Western blotting, and TNF-α, IL-6, and IL-10 levels were measured by RT-qPCR. Nrf2/NF-κB protein expressions were also analyzed. Apoptosis and necrosis were evaluated using Annexin V-FITC/PI staining and the LDH release test. Cell edema was assessed by cell volume, ion content, and membrane damage. Western blotting was used to analyze pan-apoptosis-related proteins. PLD2 expression was lower in the model group compared to controls (P < 0.05) but higher in the PLD2 overexpression group (P < 0.05). TNF-α, IL-6, and IL-10 levels were elevated in the model group (P < 0.05) and reduced in the PLD2 overexpression group (P < 0.05). Nrf2 expression decreased in the model group but increased with PLD2 overexpression (P < 0.05). NF-κB expression increased in the model group but decreased with PLD2 overexpression (P < 0.05). Apoptosis and necrosis rates were higher in the model group (P < 0.05) but lower in the PLD2 overexpression group (P < 0.05). Cell volume, Na + content, and LDH release increased in the model group (P < 0.05) but decreased with PLD2 overexpression (P < 0.05). RIPK1 expression decreased in the model group (P < 0.05) but increased with PLD2 overexpression (P < 0.05). CASP8, FADD, and ZBP1 levels were higher in the model group (P < 0.05) and reduced with PLD2 overexpression (P < 0.05). PLD2 exerts a protective effect in acute pancreatitis by activating Nrf2 and inhibiting NF-κB, reducing apoptosis, cell swelling, and membrane damage. This highlights potential therapeutic targets for pancreatic inflammation.

Oncogenic Mutant p53 Sensitizes Non-Small Cell Lung Cancer Cells to Proteasome Inhibition via Oxidative Stress-Dependent Induction of Mitochondrial Apoptosis

SIGNIFICANCE

NSCLC is the leading cause of cancer death due, in part, to a lack of active therapies in advanced disease. We demonstrate that combination therapy with a proteasome inhibitor, BH3-mimetic, and chemotherapy is an active precision therapy in NSCLC cells and tumors expressing Onc-p53 alleles.

The Role of Nrf2 in the Regulation of Mitochondrial Function and Ferroptosis in Pancreatic Cancer

The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) represents the master regulator of the cellular antioxidant response and plays a critical role in tumorigenesis. This includes a preventive effect of Nrf2 on cell death through ferroptosis, which represents an essential mechanism of therapy resistance in malignant tumors, such as pancreatic ductal adenocarcinoma (PDAC) as one of the most aggressive and still incurable tumors. Addressing this issue, we provide an overview on Nrf2 mediated antioxidant response with particular emphasis on its effect on mitochondria as the organelle responsible for the execution of ferroptosis. We further outline how deregulated Nrf2 adds to the progression and therapy resistance of PDAC, especially with respect to the role of ferroptosis in anti-cancer drug mediated cell killing and how this is impaired by Nrf2 as an essential mechanism of drug resistance. Our review further discusses recent approaches for Nrf2 inhibition by natural and synthetic compounds to overcome drug resistance based on enhanced ferroptosis. Finally, we provide an outlook on therapeutic strategies based on Nrf2 inhibition combined with ferroptosis inducing drugs.

The bacterial metabolite, lithocholic acid, has antineoplastic effects in pancreatic adenocarcinoma

Lithocholic acid (LCA) is a secondary bile acid. LCA enters the circulation after bacterial synthesis in the gastrointestinal tract, reaches distantly located cancer cells, and influences their behavior. LCA was considered carcinogenic, but recent studies demonstrated that LCA has antitumor effects. We assessed the possible role of LCA in pancreatic adenocarcinoma. At the serum reference concentration, LCA induced a multi-pronged antineoplastic program in pancreatic adenocarcinoma cells. LCA inhibited cancer cell proliferation and induced mesenchymal-to-epithelial (MET) transition that reduced cell invasion capacity. LCA induced oxidative/nitrosative stress by decreasing the expression of nuclear factor, erythroid 2-like 2 (NRF2) and inducing inducible nitric oxide synthase (iNOS). The oxidative/nitrosative stress increased protein nitration and lipid peroxidation. Suppression of oxidative stress by glutathione (GSH) or pegylated catalase (pegCAT) blunted LCA-induced MET. Antioxidant genes were overexpressed in pancreatic adenocarcinoma and decreased antioxidant levels correlated with better survival of pancreatic adenocarcinoma patients. Furthermore, LCA treatment decreased the proportions of cancer stem cells. Finally, LCA induced total and ATP-linked mitochondrial oxidation and fatty acid oxidation. LCA exerted effects through the farnesoid X receptor (FXR), vitamin D receptor (VDR), and constitutive androstane receptor (CAR). LCA did not interfere with cytostatic agents used in the chemotherapy of pancreatic adenocarcinoma. Taken together, LCA is a non-toxic compound and has antineoplastic effects in pancreatic adenocarcinoma.

Survivin Splice Variant 2β Enhances Pancreatic Ductal Adenocarcinoma Resistance to Gemcitabine

Background

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal disease with poor prognosis, as it is difficult to predict or circumvent, and it develops chemoresistance quickly. One cellular mechanism associated with chemoresistance is alternative splicing dysfunction, a process through which nascent mRNA is spliced into different isoforms. Survivin (Baculoviral IAP Repeat-Containing Protein 5 (BIRC5)), a member of the inhibitor of apoptosis (IAP) protein family and a cell cycle-associated oncoprotein, is overexpressed in most cancers and undergoes alternative splicing (AS) to generate six different splicing isoforms.

Methods

To determine if survivin splice variants (SSV) could be involved in PDAC chemoresistance, a Gemcitabine (Gem) resistant (GR) cell line, MIA PaCa-2 GR, was created and assessed for its SSV levels and their potential association with GR. Cross-resistance was assessed in MIA-PaCa-2 GR cells to FIRINOX (5-fluorouracil (5-FU), irinotecan, and oxaliplatin). Once chemoresistance was confirmed, RT-qPCR was used to assess the expression of survivin splice variants (SSVs) in PDAC cell lines. To confirm the effect of SSVs on chemoresistance, we used siRNA to knockdown all SSVs or SSV 2β.

Results

The MIA PaCa-2 GR cell line was 40 times more resistant to Gem and revealed increased resistance to FIRINOX (5-fluorouracil (5-FU), irinotecan, and oxaliplatin); when compared to the parental MIA-PaCa-2 cells. RT-qPCR studies revealed an 8-fold relative expression increase in SSV 2β and a 2- to 8-fold increase in the other five SSVs in the GR cells. Knockdown of all SSV or SSV 2β only, using small inhibitory RNA (siRNA), sensitized the GR cells to Gem, indicating that these SSVs play a role in PDAC chemoresistance.

Conclusion

These findings provide evidence for the potential role of SSV 2β and other SSVs in innate and acquired PDAC chemoresistance. We also show that the expression of SSVs is not affected by the type of chemoresistance, therefore targeting survivin splice variants in combination with chemotherapy could benefit a wide range of patients.

The Orexin-A/OX1R System Induces Cell Death in Pancreatic Cancer Cells Resistant to Gemcitabine and Nab-Paclitaxel Treatment

Pancreatic ductal adenocarcinoma (PDAC) represents the fourth cause of cancer-associated death in the West. This type of cancer has a very poor prognosis notably due to the development of chemoresistance when treatments including gemcitabine and Abraxane (Nab-paclitaxel) were prescribed. The identification of new treatment circumventing this chemoresistance represents a key challenge. Previous studies demonstrated that the activation of orexin receptor type 1 (OX1R), which was ectopically expressed in PDAC, by its natural ligand named orexin-A (OxA), led to anti-tumoral effect resulting in the activation of mitochondrial pro-apoptotic mechanism. Here, we demonstrated that OxA inhibited the pancreatic cancer cell (AsPC-1) growth and inhibited the tumor volume in preclinical models as effectively as gemcitabine and Nab-paclitaxel. Moreover, the combination therapy including OxA plus gemcitabine or OxA plus Nab-paclitaxel was additive on the inhibition of cancer cell growth and tumor development. More importantly, the treatment by OxA of chemoresistant tumors to gemcitabine or Nab-paclitaxel obtained by successive xenografts in mice revealed that OxA was able to induce a strong inhibition of tumor development, whereas no OxA resistance was identified in tumors. The OX1R/OxA system might be an innovative and powerful alternative treatment of chemoresistant PDAC.

NRF2/HO-1 pathway activation by ATF3 in a noise-induced hearing loss murine model

BACKGROUND

Excessive oxidative stress of the inner ear as a result of high, intense noise exposure is regarded as a major mechanism underlying the development of noise-induced hearing loss (NIHL). The present study was designed to explore the effect and mechanism of activated transcription factor 3 (ATF3) in reduction/oxidation homeostasis of NIHL.

METHOD

In vitro and in vivo assays were performed to investigate the functional role of ATF3 in the inner ear. Mice hearing was measured using auditory brainstem response. ATF3 short hairpin RNA (shRNA) was transfected into House Ear Institute-Organ of Corti 1 (HEI-OC1) cells to decrease ATF3 expression. Western blotting and quantitative real-time polymerase chain reaction (RT-qPCR) were performed to quantify ATF3, NRF2, HO-1 and NQO1 expression. Glutathione (GSH) assay was performed to detect intracellular GSH levels. ATF3 immunofluorescence analysis was carried out in cochlear cryosectioned samples and HEI-OC1 cells to localize ATF3 expression. Cell counting kit 8 assay and flow cytometry were performed to analyze cell viability.

RESULT

ATF3 was upregulated in noise-exposed cochleae and HEI-OC1 cells treated with H₂O₂. NRF2 is a key factor regulated by ATF3. NRF2, HO-1, NQO1, and GSH expression was significantly downregulated in shATF3 HEI-OC1 cells. ATF3 silencing promoted reactive oxygen species accumulation and increased apoptosis and necrosis with H₂O₂ stimulus.

CONCLUSION

ATF3 functions as an antioxidative factor by activating the NRF2/HO-1 pathway.

Repurposing econazole as a pharmacological autophagy inhibitor to treat pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is characterized by the highest mortality among carcinomas. The pathogenesis of PDAC requires elevated autophagy, inhibition of which using hydroxychloroquine has shown promise. However, current realization is impeded by its suboptimal use and unpredictable toxicity. Attempts to identify novel autophagy-modulating agents from already approved drugs offer a rapid and accessible approach. Here, using a patient-derived organoid model, we performed a comparative analysis of therapeutic responses among various antimalarial/fungal/parasitic/viral agents, through which econazole (ECON), an antifungal compound, emerged as the top candidate. Further testing in cell-line and xenograft models of PDAC validated this activity, which occurred as a direct consequence of dysfunctional autophagy. More specifically, ECON boosted autophagy initiation but blocked lysosome biogenesis. RNA sequencing analysis revealed that this autophagic induction was largely attributed to the altered expression of activation transcription factor 3 (ATF3). Increased nuclear import of ATF3 and its transcriptional repression of inhibitor of differentiation-1 (ID-1) led to inactivation of the AKT/mammalian target of rapamycin (mTOR) pathway, thus giving rise to autophagosome accumulation in PDAC cells. The magnitude of the increase in autophagosomes was sufficient to elicit ER stress-mediated apoptosis. Furthermore, ECON, as an autophagy inhibitor, exhibited synergistic effects with trametinib on PDAC. This study provides direct preclinical and experimental evidence for the therapeutic efficacy of ECON in PDAC treatment and reveals a mechanism whereby ECON inhibits PDAC growth.

Role of Nrf2 in Pancreatic Cancer

Pancreatic tumors are a serious health problem with a 7% mortality rate worldwide. Inflammatory processes and oxidative stress play important roles in the development of pancreatic diseases/cancer. To maintain homeostasis, a balance between free radicals and the antioxidant system is essential. Nuclear Factor Erythroid 2-Related Factor 2/NFE2L2 (Nrf2) and its negative regulator Kelch-Like ECH-Associated Protein 1 (Keap1) provide substantial protection against damage induced by oxidative stress, and a growing body of evidence points to the canonical and noncanonical Nrf2 signaling pathway as a pharmacological target in the treatment of pancreatic diseases. In this review, we present updated evidence on the activation of the Nrf2 signaling pathway and its importance in pancreatic cancer. Our review covers potential modulators of canonical and noncanonical pathway modulation mechanisms that may have a positive effect on the therapeutic response. Finally, we describe some interesting recent discoveries of novel treatments related to the antioxidant system for pancreatic cancer, including natural or synthetic compounds with therapeutic properties.

New Discoveries and Ambiguities of Nrf2 and ATF3 Signaling in Environmental Arsenic-Induced Carcinogenesis

Environment exposure to arsenic had been linked to increased incidents of human cancers. In cellular and animal experimental systems, arsenic has been shown to be highly capable of activating several signaling pathways that play critical roles in cell growth regulation, malignant transformation and the stemness of cancer stem-like cells. Emerging evidence indicates certain oncogenic properties of the Nrf2 transcription factor that can be activated by arsenic and many other environmental hazards. In human bronchial epithelial cells, our most recent data suggested that arsenic-activated Nrf2 signaling fosters metabolic reprogramming of the cells through shifting mitochondrial TCA cycle to cytosolic glycolysis, and some of the metabolites in glycolysis shunt the hexosamine biosynthesis and serine-glycine pathways important for the energy metabolism of the cancer cells. In the current report, we further demonstrated direct regulation of oncogenic signals by arsenic-activated Nrf2 and connection of Nrf2 with ATF3 stress transcription factor. Meanwhile, we also highlighted some unanswered questions on the molecular characteristics of the Nrf2 protein, which warrants further collaborative efforts among scientists for understanding the important role of Nrf2 in human cancers either associated or not to environmental arsenic exposure.

Dual roles and therapeutic potential of Keap1-Nrf2 pathway in pancreatic cancer: a systematic review

Pancreatic cancer (PC) is one of the most fatal diseases with a very high rate of metastasis and low rate of survival. Despite the advances in understanding this devastating disease, PC still accounts for 3% of all cancers and causes almost 7% of death of cancer patients. Recent studies have demonstrated that the transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf2) and its key negative regulator Kelch-like ECH-associated protein 1 (Keap1) are dysregulated in PC and the Keap1-Nrf2 pathway is an emerging target for PC prevention and therapy. Indeed, Nrf2 plays an either tumor-suppressive or promoting function in PC, which depends on the developmental stages of the disease and the cellular context. Several natural-product Nrf2 activators have been developed to prevent pancreatic carcinogenesis, while the Nrf2 inhibitors have been examined for their efficacy in inhibiting PC growth and metastasis and reversing chemoresistance. However, further preclinical and clinical studies for determining the effectiveness and safety of targeting the Keap1-Nrf2 pathway for PC prevention and therapy are warranted. In this review, we comprehensively discuss the dual roles of the Keap1-Nrf2 signaling pathway in PC as well as the current targeting strategies and known activators and inhibitors of Nrf2. We also propose new strategies that may be used to address the current issues and develop more specific and more effective Nrf2 activator/inhibitors for PC prevention and therapy.