Activation of p62/SQSTM1-Keap1-Nuclear Factor Erythroid 2-Related Factor 2 Pathway in Cancer

Nrf2/Keap1/ARE regulation by plant secondary metabolites: a new horizon in brain tumor management

Brain cancer is regarded as one of the most life-threatening forms of cancer worldwide. Oxidative stress acts to derange normal brain homeostasis, thus is involved in carcinogenesis in brain. The Nrf2/Keap1/ARE pathway is an important signaling cascade responsible for the maintenance of redox homeostasis, and regulation of anti-inflammatory and anticancer activities by multiple downstream pathways. Interestingly, Nrf2 plays a somewhat, contradictory role in cancers, including brain cancer. Nrf2 has traditionally been regarded as a tumor suppressor since its cytoprotective functions are considered to be the principle cellular defense mechanism against exogenous and endogenous insults, such as xenobiotics and oxidative stress. However, hyperactivation of the Nrf2 pathway supports the survival of normal as well as malignant cells, protecting them against oxidative stress, and therapeutic agents. Plants possess a pool of secondary metabolites with potential chemotherapeutic/chemopreventive actions. Modulation of Nrf2/ARE and downstream activities in a Keap1-dependant manner, with the aid of plant-derived secondary metabolites exhibits promise in the management of brain tumors. Current article highlights the effects of Nrf2/Keap1/ARE cascade on brain tumors, and the potential role of secondary metabolites regarding the management of the same.

Autophagy and cancer therapy

Autophagy is an intracellular degradation process that sequesters cytoplasmic components in double-membrane vesicles known as autophagosomes, which are degraded upon fusion with lysosomes. This pathway maintains the integrity of proteins and organelles while providing energy and nutrients to cells, particularly under nutrient deprivation. Deregulation of autophagy can cause genomic instability, low protein quality, and DNA damage, all of which can contribute to cancer. Autophagy can also be overactivated in cancer cells to aid in cancer cell survival and drug resistance. Emerging evidence indicates that autophagy has functions beyond cargo degradation, including roles in tumor immunity and cancer stem cell survival. Additionally, autophagy can also influence the tumor microenvironment. This feature warrants further investigation of the role of autophagy in cancer, in which autophagy manipulation can improve cancer therapies, including cancer immunotherapy. This review discusses recent findings on the regulation of autophagy and its role in cancer therapy and drug resistance.

Toward a CRISPR-based mouse model of Vhl-deficient clear cell kidney cancer: Initial experience and lessons learned

CRISPR is revolutionizing the ability to do somatic gene editing in mice for the purpose of creating new cancer models. Inactivation of the VHL tumor suppressor gene is the signature initiating event in the most common form of kidney cancer, clear cell renal cell carcinoma (ccRCC). Such tumors are usually driven by the excessive HIF2 activity that arises when the VHL gene product, pVHL, is defective. Given the pressing need for a robust immunocompetent mouse model of human ccRCC, we directly injected adenovirus-associated viruses (AAVs) encoding sgRNAs against VHL and other known/suspected ccRCC tumor suppressor genes into the kidneys of C57BL/6 mice under conditions where Cas9 was under the control of one of two different kidney-specific promoters (Cdh16 or Pax8) to induce kidney tumors. An AAV targeting Vhl, Pbrm1, Keap1, and Tsc1 reproducibly caused macroscopic ccRCCs that partially resembled human ccRCC tumors with respect to transcriptome and cell of origin and responded to a ccRCC standard-of-care agent, axitinib. Unfortunately, these tumors, like those produced by earlier genetically engineered mouse ccRCCs, are HIF2 independent.

Iron chelators as mitophagy agents: Potential and limitations

Mitochondrial autophagy (mitophagy) is very important process for the maintenance of cellular homeostasis, functionality and survival. Its dysregulation is associated with high risk and progression numerous serious diseases (e.g., oncological, neurodegenerative and cardiovascular ones). Therefore, targeting mitophagy mechanisms is very hot topic in the biological and medicinal research. The interrelationships between the regulation of mitophagy and iron homeostasis are now becoming apparent. In short, mitochondria are central point for the regulation of iron homeostasis, but change in intracellular cheatable iron level can induce/repress mitophagy. In this review, relationships between iron homeostasis and mitophagy are thoroughly discussed and described. Also, therapeutic applicability of mitophagy chelators in the context of individual diseases is comprehensively and critically evaluated.

TRIM44, a Novel Prognostic Marker, Supports the Survival of Proteasome-Resistant Multiple Myeloma Cells

TRIM44, a tripartite motif (TRIM) family member, is pivotal in linking the ubiquitin-proteasome system (UPS) to autophagy in multiple myeloma (MM). However, its prognostic impact and therapeutic potential remain underexplored. Here, we report that TRIM44 overexpression is associated with poor prognosis in a Multiple Myeloma Research Foundation (MMRF) cohort of 858 patients, persisting across primary and recurrent MM cases. TRIM44 expression notably increases in advanced MM stages, indicating its potential role in disease progression. Single-cell RNA sequencing across MM stages showed significant TRIM44 upregulation in smoldering MM (SMM) and MM compared to normal bone marrow, especially in patients with t(4;14) cytogenetic abnormalities. This analysis further identified high TRIM44 expression as predictive of lower responsiveness to proteasome inhibitor (PI) treatments, underscoring its critical function in the unfolded protein response (UPR) in TRIM44-high MM cells. Our findings also demonstrate that TRIM44 facilitates SQSTM1 oligomerization under oxidative stress, essential for its phosphorylation and subsequent autophagic degradation. This process supports the survival of PI-resistant MM cells by activating the NRF2 pathway, which is crucial for oxidative stress response and, potentially, other chemotherapy-induced stressors. Additionally, TRIM44 counters the TRIM21-mediated suppression of the antioxidant response, enhancing MM cell survival under oxidative stress. Collectively, our discoveries highlight TRIM44's significant role in MM progression and resistance to therapy, suggesting its potential value as a therapeutic target.

TRIM44 enhances autophagy via SQSTM1 oligomerization in response to oxidative stress

The deubiquitinase tripartite motif containing 44 (TRIM44) plays a critical role in linking the proteotoxic stress response with autophagic degradation, which is significant in the context of cancer and neurological diseases. Although TRIM44 is recognized as a prognostic marker in various cancers, the complex molecular mechanisms through which it facilitates autophagic degradation, particularly under oxidative stress conditions, have not been fully explored. In this study, we demonstrate that TRIM44 significantly enhances autophagy in response to oxidative stress, reducing cytotoxicity in cancer cells treated with arsenic trioxide. Our research emphasizes the critical role of the posttranslational modification of sequestosome-1 (SQSTM1) and its importance in improving sequestration during autophagic degradation under oxidative stress. We found that TRIM44 notably promotes SQSTM1 oligomerization in both PB1 domain-dependent and oxidation-dependent manners. Furthermore, TRIM44 amplifies the interaction between protein kinase A and oligomerized SQSTM1, leading to enhanced phosphorylation of SQSTM1 at S349. This phosphorylation event activates NFE2L2, a key transcription factor in the oxidative stress response, highlighting the importance of TRIM44 in modulating SQSTM1-mediated autophagy. Our findings support that TRIM44 plays pivotal roles in regulating autophagic sensitivity to oxidative stress, with implications for cancer, aging, aging-associated diseases, and neurodegenerative disorders.

CRHR1 antagonist alleviated depression-like behavior by downregulating p62 in a rat model of post-stroke depression

Post-stroke depression (PSD) is a complication of cerebrovascular disease, which can increase mortality after stroke. CRH is one of the main signaling peptides released after activation of the hypothalamic-pituitary-adrenal (HPA) axis in response to stress. It affects synaptic plasticity by regulating inflammation, oxidative stress and autophagy in the central nervous system. And the loss of spines exacerbates depression-like behavior. Therefore, synaptic deficits induced by CRH may be related to post-stroke depression. However, the underlying mechanism remains unclear. The Keap1-Nrf2 complex is one of the core components of the antioxidant response. As an autophagy associated protein, p62 participates in the Keap1-NrF2 pathway through its Keap1 interaction domain. Oxidative stress is involved in the feedback regulation between Keap1-Nrf2 pathway and p62.However, whether the relationship between CRH and the Keap1-Nrf2-p62 pathway is involved in PSD remains unknown. This study found that serum levels of CRH in 22 patients with PSD were higher than those in healthy subjects. We used MCAO combined with CUMS single-cage SD rats to establish an animal model of PSD. Animal experiments showed that CRHR1 antagonist prevented synaptic loss in the hippocampus of PSD rats and alleviated depression-like behavior. CRH induced p62 accumulation in the prefrontal cortex of PSD rats through CRHR1. CRHR1 antagonist inhibited Keap1-Nrf2-p62 pathway by attenuating oxidative stress. In addition, we found that abnormal accumulation of p62 induces PSD. It alleviates depression-like behavior by inhibiting the expression of p62 and promoting the clearance of p62 in PSD rats. These findings can help explore the pathogenesis of PSD and design targeted treatments for PSD.

Multifaceted collagen-DDR1 signaling in cancer

In addition to immune cells and fibroblasts, the tumor microenvironment (TME) comprises an extracellular matrix (ECM) which contains collagens (COLs) whose architecture and remodeling dictate cancer development and progression. COL receptors expressed by cancer cells sense signals generated by microenvironmental alterations in COL state to regulate cell behavior and metabolism. Discoidin domain receptor 1 (DDR1) is a key sensor of COL fiber state and composition that controls tumor cell metabolism and growth, response to therapy, and patient survival. This review focuses on DDR1 to NRF2 signaling, its modulation of autophagy and macropinocytosis (MP), and its role in cancer and other diseases. Elucidating the regulation of DDR1 activity and expression under different pathophysiological conditions will facilitate the discovery of new therapeutics.

EGCG-induced selective death of cancer cells through autophagy-dependent regulation of the p62-mediated antioxidant survival pathway

The effects of EGCG on the selective death of cancer cells by modulating antioxidant pathways through autophagy were explored in various normal and cancer cells. EGCG positively regulated the p62-KEAP1-NRF2-HO-1 pathway in normal cells, while negatively regulating it in cancer cells, leading to selective apoptotic death of cancer cells. In EGCG-treated MRC5 cells (EGCG-MRC5), autophagic flux was blocked, which was accompanied by the formation of p62-positive aggregates. However, EGCG-treated HeLa cells (EGCG-HeLa) showed incomplete autophagic flux and no aggregate formation. The levels of P-ULK1 S556 and S758 increased in EGCG-MRC5 through AMPK-mTOR cooperative interaction. In contrast, EGCG treatment in HeLa cells led to AMPK-induced mTOR inactivation, resulting in abrogation of P-ULK1 S556 and S758 levels. AMPK knockout in EGCG-HeLa restored positive regulation of the p62-mediated pathway, which was accompanied by increased P-mTOR S2448 and P-ULK1 S758 levels. Knockdown of 67LR in EGCG-HeLa abolished AMPK activity but did not restore the p62-mediated pathway. Surprisingly, both AMPK knockout and 67LR knockdown in EGCG-HeLa markedly increased cell viability, despite differential regulation of the antioxidant enzyme HO-1. In conclusion, EGCG induces the selective death of cancer cells through the modulation of at least two autophagy-dependent and independent regulatory pathways: negative regulation involves the mTOR-ULK1 (S556 and S758)-p62-KEAP1-NRF2-HO-1 axis via AMPK activation, whereas positive regulation occurs through the 67LR-AMPK axis.

Proteomic Characterization Identifies Clinically Relevant Subgroups of Gastrointestinal Stromal Tumors

BACKGROUND & AIMS

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract, and it has high metastatic and recurrence rates. We aimed to characterize the proteomic features of GIST to understand biological processes and treatment vulnerabilities.

METHODS

Quantitative proteomics and phosphoproteomics analyses were performed on 193 patients with GIST to reveal the biological characteristics of GIST. Data-driven hypotheses were tested by performing functional experiments using both GIST cell lines and xenograft mouse models.

RESULTS

Proteomic analysis revealed differences in the molecular features of GISTs from different locations or with different histological grades. MAPK7 was identified and functionally proved to be associated with tumor cell proliferation in GIST. Integrative analysis revealed that increased SQSTM1 expression inhibited the patient response to imatinib mesylate. Proteomics subtyping identified 4 clusters of tumors with different clinical and molecular attributes. Functional experiments confirmed the role of SRSF3 in promoting tumor cell proliferation and leading to poor prognosis.

CONCLUSIONS

Our study provides a valuable data resource and highlights potential therapeutic approaches for GIST.

WITHDRAWN: TRIM44 promotes autophagy through SQSTM1 oligomerization in the response to oxidative stress induced by Arsenic Trioxide in cancer cells

The authors have requested that this preprint be removed from Research Square.

miR-128-3p is involved in aluminum-induced cognitive impairment by regulating the Sirt1-Keap1/Nrf2 pathway

Aluminum (Al) is a common neurotoxicant in the environment, but the molecular mechanism of its toxic effects is still unclear. Studies have shown that aluminum exposure causes an increase in neuronal apoptosis. The aim of this study was to investigate the mechanism and signaling pathway of neuronal apoptosis induced by aluminum exposure. The rat model was established by intraperitoneal injection of maltol aluminum for 90 days. The results showed that the escape latency of the three groups exposed to maltol aluminum was higher than that of the control group on the 3rd, 4th and 5th days of the positioning cruise experiment (P < 0.05). On the 6th day of the space exploration experiment, compared with the control group(6.00 ± 0.71,15.33 ± 1.08) and the low-dose group(5.08 ± 1.69,13.67 ± 1.09), the number of times that the high-dose group crossed the platform(2.25 ± 0.76) and the platform quadrant(7.58 ± 1.43) was significantly reduced (P < 0.01). The relative expression levels of Sirt1 and Nrf2 in hippocampal tissues of all groups decreased gradually with increasing maltol aluminum exposure dose the relative expression levels of Sirt1 and Nrf2 in high-dose group (0.261 ± 0.094,0.325 ± 0.108) were significantly lower than those in control group (1.018 ± 0.222,1.009 ± 0.156)(P < 0.05). The relative expression level of Keap1 increased gradually with increasing maltol aluminum exposure dose (P < 0.05). The relative expression level of miR-128-3p in the high-dose group(1.520 ± 0.280) was significantly higher than that in the control group(1.000 ± 0.420) (P < 0.05). The content of GSH-Px in the hippocampus of rats decreased with increasing dose. ROS levels gradually increased. We speculated that subchronic aluminum exposure may lead to the activation of miR-128-3p in rat hippocampus of rats, thereby inhibiting the Sirt1-Keap1/Nrf2 pathway so that the Sirt1-Keap1/Nrf2 pathway could not be activated to exert antioxidant capacity, resulting in an imbalance in the antioxidant system of rats and the apoptosis of neurons, which caused reduced cognitive impairment in rats.

The clarithromycin-binding proteins NIPSNAP1 and 2 regulate cytokine production through mitochondrial quality control

The mechanism underlying the anti-inflammatory effect of macrolide antibiotics, such as clarithromycin (CAM), remains to be clarified. The CAM-binding proteins 4-nitrophenylphosphatase domain and non-neuronal synaptosomal associated protein 25 (SNAP25)-like protein homolog (NIPSNAP) 1 and 2 are involved in the immune response and mitochondrial homeostasis. However, the axis between CAM-NIPSNAP-mitochondria and Toll-like receptor (TLR) and their molecular mechanisms remain unknown. In this study, we sought to elucidate the relationship between mitochondrial homeostasis mediated by NIPSNAP1 and 2 and the immunomodulatory effect of CAM. NIPSNAP1 or 2 knockdown (KD) by RNA interference impaired TLR4-mediated interleukin-8 (IL-8) production. Similar impairment was observed upon treatment with mitochondrial function inhibitors. However, IL-8 secretion was not impaired in NIPSNAP1 and 2 individual knockout (KO) and double KO (DKO) cells. Moreover, the oxygen consumption rate (OCR) in mitochondria measured using a flex analyzer was significantly reduced in NIPSNAP1 or 2 KD cells, but not in DKO cells. CAM also dose-dependently reduced the OCR. These results indicate that CAM suppresses the IL-8 production via the mitochondrial quality control regulated by temporary functional inhibition of NIPSNAP1 and 2. Our findings provide new insight into the mechanisms underlying cytokine production, including the TLR-mitochondria axis, and the immunomodulatory effects of macrolides.

Antioxidative Sirt1 and the Keap1-Nrf2 Signaling Pathway Impair Inflammation and Positively Regulate Autophagy in Murine Mammary Epithelial Cells or Mammary Glands Infected with Streptococcus uberis

Streptococcus uberis mastitis in cattle infects mammary epithelial cells. Although oxidative responses often remove intracellular microbes, S. uberis survives, but the mechanisms are not well understood. Herein, we aimed to elucidate antioxidative mechanisms during pathogenesis of S. uberis after isolation from clinical bovine mastitis milk samples. S. uberis's in vitro pathomorphology, oxidative stress biological activities, transcription of antioxidative factors, inflammatory response cytokines, autophagosome and autophagy functions were evaluated, and in vivo S. uberis was injected into the fourth mammary gland nipple of each mouse to assess the infectiousness of S. uberis potential molecular mechanisms. The results showed that infection with S. uberis induced early oxidative stress and increased reactive oxygen species (ROS). However, over time, ROS concentrations decreased due to increased antioxidative activity, including total superoxide dismutase (T-SOD) and malondialdehyde (MDA) enzymes, plus transcription of antioxidative factors (Sirt1, Keap1, Nrf2, HO-1). Treatment with a ROS scavenger (N-acetyl cysteine, NAC) before infection with S. uberis reduced antioxidative responses and the inflammatory response, including the cytokines IL-6 and TNF-α, and the formation of the Atg5-LC3II/LC3I autophagosome. Synthesis of antioxidants determined autophagy functions, with Sirt1/Nrf2 activating autophagy in the presence of S. uberis. This study demonstrated the evasive mechanisms of S. uberis in mastitis, including suppressing inflammatory and ROS defenses by stimulating antioxidative pathways.

Immunological dimensions of neuroinflammation and microglial activation: exploring innovative immunomodulatory approaches to mitigate neuroinflammatory progression

The increasing life expectancy has led to a higher incidence of age-related neurodegenerative conditions. Within this framework, neuroinflammation emerges as a significant contributing factor. It involves the activation of microglia and astrocytes, leading to the release of pro-inflammatory cytokines and chemokines and the infiltration of peripheral leukocytes into the central nervous system (CNS). These instances result in neuronal damage and neurodegeneration through activated nucleotide-binding domain and leucine-rich repeat containing (NLR) family pyrin domain containing protein 3 (NLRP3) and nuclear factor kappa B (NF-kB) pathways and decreased nuclear factor erythroid 2-related factor 2 (Nrf2) activity. Due to limited effectiveness regarding the inhibition of neuroinflammatory targets using conventional drugs, there is challenging growth in the search for innovative therapies for alleviating neuroinflammation in CNS diseases or even before their onset. Our results indicate that interventions focusing on Interleukin-Driven Immunomodulation, Chemokine (CXC) Receptor Signaling and Expression, Cold Exposure, and Fibrin-Targeted strategies significantly promise to mitigate neuroinflammatory processes. These approaches demonstrate potential anti-neuroinflammatory effects, addressing conditions such as Multiple Sclerosis, Experimental autoimmune encephalomyelitis, Parkinson's Disease, and Alzheimer's Disease. While the findings are promising, immunomodulatory therapies often face limitations due to Immune-Related Adverse Events. Therefore, the conduction of randomized clinical trials in this matter is mandatory, and will pave the way for a promising future in the development of new medicines with specific therapeutic targets.

Integrating Network Pharmacology and Experimental Validation to Decipher the Anti-Inflammatory Effects of Magnolol on LPS-induced RAW264.7 Cells

INTRODUCTION

Magnolol is beneficial against inflammation-mediated damage. However, the underlying mechanisms by which magnolol exerts anti-inflammatory effects on macrophages remain unclear.

OBJECTIVE

In this study, network pharmacology and experimental validation were used to assess the effect of magnolol on inflammation caused by lipopolysaccharide (LPS) in RAW264.7 cells.

MATERIALS AND METHODS

Genes related to magnolol were identified in the PubChem and Swiss Target Prediction databases, and gene information about macrophage polarization was retrieved from the GeneCards, OMIM, and PharmGKB databases. Analysis of protein-protein interactions was performed with STRING, and Cytoscape was used to construct a component-target-disease network. GO and KEGG enrichment analyses were performed to ascertain significant molecular biological processes and signaling pathways. LPS was used to construct the inflammatory cell model. ELISA and qRT.PCR were used to examine the expression levels of inflammationassociated factors, immunofluorescence was used to examine macrophage markers (CD86 and CD206), and western blotting was used to examine protein expression levels.

RESULTS

The hub target genes of magnolol that act on macrophage polarization were MDM2, MMP9, IL-6, TNF, EGFR, AKT1, and ERBB2. The experimental validation results showed that magnolol treatment decreased the levels of proinflammatory factors (TNF-α, IL-1β, and IL-6). Moreover, the levels of anti-inflammatory factors (IL-10 and IL-4) were increased. In addition, magnolol upregulated the expression of M2 markers (Agr-1, Fizzl, and CD206) and downregulated M1 markers (CD86). The cell experiment results supported the network pharmacological results and demonstrated that magnolol alleviated inflammation by modulating the PI3k-Akt and P62/keap1/Nrf2 signaling pathways.

CONCLUSION

According to network pharmacology and experimental validation, magnolol attenuated inflammation in LPS-induced RAW264.7 cells mainly by inhibiting M1 polarization and enhancing M2 polarization by activating the PI3K/Akt and P62/keap1/Nrf2 signaling pathways.

The master antioxidant defense is activated during EBV latent infection

IMPORTANCE

To our knowledge, this is the first report delineating the activation of the master antioxidant defense during EBV latency. We show that EBV-triggered reactive oxygen species production activates the Keap1-NRF2 pathway in EBV-transformed cells, and LMP1 plays a major role in this event, and the stress-related kinase TBK1 is required for NRF2 activation. Moreover, we show that the Keap1-NRF2 pathway is important for cell proliferation and EBV latency maintenance. Our findings disclose how EBV controls the balance between oxidative stress and antioxidant defense, which greatly improve our understanding of EBV latency and pathogenesis and may be leveraged to opportunities toward the improvement of therapeutic outcomes in EBV-associated diseases.

Anti-inflammatory activity of 2-methoxy-4-vinylphenol involves inhibition of lipopolysaccharide-induced inducible nitric oxidase synthase by heme oxygenase-1

BACKGROUND

2-Methoxy-4-vinylphenol (2M4VP) is a natural anti-inflammatory compound derived from red wine, but its underlying mechanism remains unclear. Heme oxygenase-1 (HO-1), an anti-inflammatory enzyme, inhibits NO gene expression, while nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor involved in HO-1 production, binds to the antioxidant response element (ARE) in the nucleus and promotes HO-1 transcription. Based on the hypothesis that the inhibitory effect of 2M4VP on NO production is mediated by HO-1, we examined the possible mechanism of the anti-inflammatory activity of 2M4VP in this study.

MATERIALS AND METHODS

The anti-inflammatory activity of 2M4VP was analyzed by Griess method, ELISA, qPCR, and Western blotting using LPS-treated macrophage lineage RAW264.7 cells. The impact of 2M4VP on the Nrf2/ARE pathway was also analyzed using immunocytochemistry and an ARE luciferase reporter using HEK293 cells.

RESULTS

The results showed that 2M4VP reduced the production of LPS-induced NO and inducible nitric oxidase synthase (iNOS). In addition, 2M4VP increased the expression of HO-1, while pretreatment with the Nrf2 inhibitor ML385 downregulated HO-1 expression. 2M4VP induced Kelch-like ECH-associated protein 1 (Keap1) degradation. Furthermore, it promoted Nrf2 nuclear translocation and increased luciferase activity by binding to the ARE.

CONCLUSIONS

2M4VP induces Keap1 degradation and promotes Nrf2 nuclear translocation. Activation of Nrf2/ARE pathway enhances HO-1 expression and leads to iNOS inhibition for anti-inflammatory function.

Moderate exercise-induced dynamics on key sepsis-associated signaling pathways in the liver

BACKGROUND

There is a clear relationship between quantitative measures of fitness (e.g., VO₂ max) and outcomes after surgical procedures. Whether or not fitness is a modifiable risk factor and what underlying biological processes drive these changes are not known. The purpose of this study was to evaluate the moderate exercise training effect on sepsis outcomes (survival) as well as the hepatic biological response. We chose to study the liver because it plays a central role in the regulation of immune defense during systemic infection and receives blood flow directly from the origin of infection (gut) in the cecal ligation and puncture (CLP) model.

METHODS

We randomized 50 male (♂) and female (♀) Sprague-Dawley rats (10 weeks, 340 g) to 3 weeks of treadmill exercise training, performed CLP to induce polymicrobial "sepsis," and monitored survival for five days (Part I). In parallel (Part II), we randomized 60 rats to control/sedentary (G1), exercise (G2), exercise + sham surgery (G3), CLP/sepsis (G4), exercise + CLP [12 h (G5) and 24 h (G6)], euthanized at 12 or 24 h, and explored molecular pathways related to exercise and sepsis survival in hepatic tissue and serum.

RESULTS

Three weeks of exercise training significantly increased rat survival following CLP (polymicrobial sepsis). CLP increased inflammatory markers (e.g., TNF-a, IL-6), which were attenuated by exercise. Sepsis suppressed the SOD and Nrf2 expression, and exercise before sepsis restored SOD and Nrf2 levels near the baseline. CLP led to increased HIF1a expression and oxidative and nitrosative stress, the latter of which were attenuated by exercise. Haptoglobin expression levels were increased in CLP animals, which was significantly amplified in exercise + CLP (24 h) rats.

CONCLUSIONS

Moderate exercise training (3 weeks) increased the survival in rats exposed to CLP, which was associated with less inflammation, less oxidative and nitrosative stress, and activation of antioxidant defense pathways.

Autophagy: A Cellular Guardian against Hepatic Lipotoxicity

Lipotoxicity is a phenomenon of lipid-induced cellular injury in nonadipose tissue. Excess of free saturated fatty acids (SFAs) contributes to hepatic injury in nonalcoholic fatty liver disease (NAFLD), which has been growing at an unprecedented rate in recent years. SFAs and their derivatives such as ceramides and membrane phospholipids have been shown to induce intrahepatic oxidative damage and ER stress. Autophagy represents a cellular housekeeping mechanism to counter the perturbation in organelle function and activation of stress signals within the cell. Several aspects of autophagy, including lipid droplet assembly, lipophagy, mitophagy, redox signaling and ER-phagy, play a critical role in mounting a strong defense against lipotoxic lipid species within the hepatic cells. This review provides a succinct overview of our current understanding of autophagy-lipotoxicity interaction and its pharmacological and nonpharmacological modulation in treating NAFLD.

P62/SQSTM1 upregulates NQO1 transcription via Nrf2/Keap1a signaling pathway to resist microcystins-induced oxidative stress in freshwater mussel Cristaria plicata

Microcystins (MCs) are the most frequent and widely distributed type of cyanotoxin in aquatic systems, and they cause an imbalance of the body's oxidative system. In a previous experiment, we demonstrated that the mollusk Cristaria plicata can protect against MC-induced oxidative damage through the nuclear factor erythroid 2-related factor 2(Nrf2)/Kelch-like epichlorohydrin-related protein-1 (Keap1) pathway. Here, we evaluated whether selective autophagy affects the Nrf2/Keap1a anti-oxidative stress pathway in C. plicata. Full-length cDNA sequences of p62/SQSTM1 from C. plicata (Cpp62) were divided into 2484 bp fragments. From N-terminal to C-terminal, the amino acid sequence of Cpp62 contained PB1 (Phox and Bem1p domain), ZNF (zinc finger domain) chain, LIR (LC3 interacting region) and UBA (ubiquitin-associated domain) domains, but not the KIR (Keap1 interacting region) domain. We confirmed that Cpp62 did not bind to CpKeap1a in vitro, and the relative level of Cpp62 was the highest in the hepatopancreas. Moreover, MCs significantly upregulated the mRNA and protein levels of Cpp62 in the hepatopancreas after CpKeap1a knockdown, whereas Nrf2 upregulated the transcription levels of Cpp62, suggesting that MCs increased Cpp62 expression via the Nrf2/Keap1a signaling pathway. Moreover, Cpp62 and CpNrf2 proteins have a strong affinity for the NQO1 promoter, but MCs inhibited the ability of CpNrf2 and Cpp62 to upregulate luciferase activity. The results show that Nrf2 and the p62 protein induced p62 expression by binding to ARE (antioxidant response element) sequences in the p62 promoter of C. plicata, thereby promoting p62 to resist MC-induced oxidative stress. Therefore, we speculate that MCs induce p62-dependent autophagy in C. plicata, resulting in the inhibition of Nrf2 transcription and Cpp62 promoter activity. These findings help to reveal the mechanism by which the p62-Nrf2/Keap1 pathway mitigates MC-induced oxidative damage in mussels.

Blockage of Nrf2 and autophagy by L-selenocystine induces selective death in Nrf2-addicted colorectal cancer cells through p62-Keap-1-Nrf2 axis

Persistent Nrf2 activation is typically noted in many cancers, including colorectal cancer (CRC), aiding cancer cells in overcoming growth stress and promoting cancer progression. Sustained Nrf2 activation, which is beneficial for cancer cells, is called "Nrf2 addiction"; it is closely associated with malignancy and poor prognosis in patients with cancer. However, Nrf2 inhibitors may have adverse effects on normal cells. Here, we found that the selenocompound L-selenocystine (SeC) is selectively cytotoxic in the Nrf2-addicted CRC cell line WiDr cells, but not in non-Nrf2-addicted mesenchymal stem cells (MSCs) and normal human colon cells. Another CRC cell line, C₂BBe₁, which harbored lower levels of Nrf2 and its downstream proteins were less sensitive to SeC, compared with the WiDr cells. We further demonstrated that SeC inhibited Nrf2 and autophagy activation in the CRC cells. Antioxidant GSH pretreatment partially rescued the CRC cells from SeC-induced cytotoxicity and Nrf2 and autophagy pathway inhibition. By contrast, SeC activated Nrf2 and autophagy pathway in non-Nrf2-addicted MSCs. Transfecting WiDr cells with Nrf2-targeting siRNA decreased persistent Nrf2 activation and alleviated SeC cytotoxicity. In KEAP1-knockdown C₂BBe₁ cells, Nrf2 pathway activation increased SeC sensitivity and cytotoxicity. In conclusion, SeC selectively attacks cancer cells with constitutively activated Nrf2 by reducing Nrf2 and autophagy pathway protein expression through the P62-Nrf2-antioxidant response element axis and eventually trigger cell death.

NEAT1 Confers Radioresistance to Hepatocellular Carcinoma Cells by Inducing PINK1/Parkin-Mediated Mitophagy

A long noncoding RNA, nuclear paraspeckle assembly transcript 1 (NEAT1) variant 1 (NEAT1v1), confers radioresistance to hepatocellular carcinoma (HCC) cells by inducing autophagy via γ-aminobutyric acid A receptor-associated protein (GABARAP). Radiation induces oxidative stress to damage cellular components and organelles, but it remains unclear how NEAT1v1 protects HCC cells from radiation-induced oxidative stress via autophagy. To address this, we precisely investigated NEAT1v1-induced autophagy in irradiated HCC cell lines. X-ray irradiation significantly increased cellular and mitochondrial oxidative stress and mitochondrial DNA content in HCC cells while NEAT1v1 suppressed them. NEAT1v1 concomitantly induced the phosphatase and tensin homolog-induced kinase 1 (PINK1)/parkin-mediated mitophagy. Interestingly, parkin expression was constitutively upregulated in NEAT1v1-overexpressing HCC cells, leading to increased mitochondrial parkin levels. Superoxide dismutase 2 (SOD2) was also upregulated by NEAT1v1, and GABARAP or SOD2 knockdown in NEAT1v1-overexpressing cells increased mitochondrial oxidative stress and mitochondrial DNA content after irradiation. Moreover, it was suggested that SOD2 was involved in NEAT1v1-induced parkin expression, and that GABARAP promoted parkin degradation via mitophagy. This study highlights the unprecedented roles of NEAT1v1 in connecting radioresistance and mitophagy in HCC.

Pyrogallol enhances therapeutic effect of human umbilical cord mesenchymal stem cells against LPS-mediated inflammation and lung injury via activation of Nrf2/HO-1 signaling

The main challenges in clinical applications of mesenchymal stem cells (MSCs) are attributed to their heterogeneity. It is believed that preconditioning of MSCs with active compounds may enhance the expression of potentially therapeutic molecules and thus achieve stable and effective therapeutic outcomes. In the present study, we investigated the mechanism by which pyrogallol increased the therapeutic efficacy of human umbilical cord mesenchymal stem cells (hUCMSCs) against LPS-induced acute lung injury (ALI). hUCMSCs with pyrogallol treatment increased expression of HO-1 at both mRNA and protein levels, accompanied by Kelch-Like ECH-Associated Protein 1 (Keap1) degradation, and upregulation of the Nrf2 protein levels as well as nuclear translocation of Nrf2. Moreover, the modulation of Keap1 and Nrf2 as well as HO-1 upregulation by pyrogallol was reversed by pretreatment with N-acetylcysteine (NAC) and a P38 kinase inhibitor (SB203580). Whereas, NAC pretreatment abrogated pyrogallol-mediated activation of P38 kinase, indicating that pyrogallol-derived ROS led to P38 kinase activation, thus promoting Nrf2/HO-1 signaling. Additionally, we found that the induction of p62 by the pyrogallol-mediated ROS/P38/Nrf2 axis interacted with Keap1 and resulted in autophagic degradation of Keap1, which created a positive feedback loop to further release of Nrf2. Furthermore, the increased expression of HO-1 in pyrogallol-pretreated hUCMSCs led to enhanced inhibitory effects on LPS-mediated TLR4/P-P65 signaling in BEAS-2B cells, resulting in increasing suppression of LPS-indued expression of a series of pro-inflammatory mediators. Compared to untreated hUCMSCs, Sprague-Dawley (SD) rats with pyrogallol-primed hUCMSCs transplantation showed enhanced improvements in LPS-mediated lung pathological alterations, the increased lung index (lung/body ratio), apoptosis of epithelial cells, the activation of TLR4/NF-κB signaling as well as the release of pro-inflammatory mediators. Together, these results suggested that hUCMSCs with pyrogallol pretreatment enhanced the therapeutic efficacy of hUCMSCs, which may provide a promising therapeutic strategy to maximize the therapeutic efficacy of hUCMSC-based therapy for treating LPS-associated ALI.

Perspectives and mechanisms for targeting ferroptosis in the treatment of hepatocellular carcinoma

Ferroptosis is a novel process of regulated cell death discovered in recent years, mainly caused by intracellular lipid peroxidation. It is morphologically manifested as shrinking of mitochondria, swelling of cytoplasm and organelles, rupture of plasma membrane, and formation of double-membrane vesicles. Work done in the past 5 years indicates that induction of ferroptosis is a promising strategy in the treatment of hepatocellular carcinoma (HCC). System xc^-/GSH/GPX4, iron metabolism, p53 and lipid peroxidation pathways are the main focus areas in ferroptosis research. In this paper, we analyze the ferroptosis-inducing drugs and experimental agents that have been used in the last 5 years in the treatment of HCC. We summarize four different key molecular mechanisms that induce ferroptosis, i.e., system xc^-/GSH/GPX4, iron metabolism, p53 and lipid peroxidation. Finally, we outline the prognostic analysis associated with ferroptosis in HCC. The findings summarized suggest that ferroptosis induction can serve as a promising new therapeutic approach for HCC and can provide a basis for clinical diagnosis and prevention of this disease.

The functions and effects of CUL3-E3 ligases mediated non-degradative ubiquitination

Ubiquitination of substrates usually have two fates: one is degraded by 26S proteasome, and the other is non-degradative ubiquitination modification which is associated with cell cycle regulation, chromosome inactivation, protein transportation, tumorigenesis, achondroplasia, and neurological diseases. Cullin3 (CUL3), a scaffold protein, binding with the Bric-a-Brac-Tramtrack-Broad-complex (BTB) domain of substrates recognition adaptor and RING-finger protein 1 (RBX1) form ubiquitin ligases (E3). Based on the current researches, this review has summarized the functions and effects of CUL3-E3 ligases mediated non-degradative ubiquitination.

tert-Butylhydroquinone-induced formation of high-molecular-weight p62: A novel mechanism in the activation of Nrf2-Keap1

The respiratory system is always exposed to air and is most vulnerable to attack by environmental free radicals. The nuclear factor E2-related factor 2-Kelch-like ECH-associated protein 1-antioxidant response element (Nrf2-Keap1-ARE) pathway and p62 are both involved in the oxidative stress response. However, the interplay between these two systems remains largely unknown. This study shows that treatment of L2 cells with tert-Butylhydroquinone (tBHQ) generates a high-molecular-weight (HMW) form of p62, leading to activation of the Nrf2-Keap1-ARE pathway. The levels of HMW-p62 increased as the tBHQ concentration increased, with concomitant decreases seen in the classical form of p62. Moreover, small interfering RNA targeting p62 increases Keap1 protein levels and inactivates the Nrf2-Keap1-ARE pathway. These results demonstrate that the Nrf2-Keap1 pathway is partially regulated by p62. tBHQ-induced HMW-p62 production may be a novel mechanism in the activation of the Nrf2-Keap1-ARE pathway.

Activation of the P62-Keap1-NRF2 Pathway Protects against Ferroptosis in Radiation-Induced Lung Injury

Radiation-induced lung injury (RILI) is one of the most common, serious, and dose-limiting toxicities of thoracic radiotherapy. A primary cause for this is the radiation-induced cell death. Ferroptosis is a recently recognized form of regulated cell death, characterized by the accumulation of lipid peroxidation products and lethal reactive oxygen species (ROS). The ROS generated by irradiation might be the original trigger of ferroptosis in RILI. In addition, activation of the P62-Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (NRF2) pathway has been shown to blunt ferroptosis and thus acts as a protective factor. Therefore, this study aimed to explore the protective effect of the P62-Keap1-NRF2 pathway against radiation-induced ferroptosis in alveolar epithelial cells. First, we found that radiation induced ferroptosis in vitro using a RILI cell model, which could be significantly reduced by ferrostatin-1 (Fer-1), a specific ferroptosis inhibitor. Additionally, overexpression of P62 interacted with Keap1 to facilitate the translocation of NRF2 into the nucleus and promote the expression of its target proteins, including quinone oxidoreductase 1 (NQO1), heme oxygenase 1 (HO1), and ferritin heavy chain 1 (FTH1). In summary, our results demonstrated that the activation of the P62-Keap1-NRF2 pathway prevents radiation-induced ferroptosis in RILI cells, providing a theoretical basis of finding a potential therapeutic approach for RILI.

Signal amplification in the KEAP1-NRF2-ARE antioxidant response pathway

The KEAP1-NRF2-ARE signaling pathway plays a central role in mediating the adaptive cellular stress response to oxidative and electrophilic chemicals. This canonical pathway has been extensively studied and reviewed in the past two decades, but rarely was it looked at from a quantitative signaling perspective. Signal amplification, i.e., ultrasensitivity, is crucially important for robust induction of antioxidant genes to appropriate levels that can adequately counteract the stresses. In this review article, we examined a number of well-known molecular events in the KEAP1-NRF2-ARE pathway from a quantitative perspective with a focus on how signal amplification can be achieved. We illustrated, by using a series of mathematical models, that redox-regulated protein sequestration, stabilization, translation, nuclear trafficking, DNA promoter binding, and transcriptional induction - which are embedded in the molecular network comprising KEAP1, NRF2, sMaf, p62, and BACH1 - may generate highly ultrasensitive NRF2 activation and antioxidant gene induction. The emergence and degree of ultrasensitivity depend on the strengths of protein-protein and protein-DNA interaction and protein abundances. A unique, quantitative understanding of signal amplification in the KEAP1-NRF2-ARE pathway will help to identify sensitive targets for the prevention and therapeutics of oxidative stress-related diseases and develop quantitative adverse outcome pathway models to facilitate the health risk assessment of oxidative chemicals.

Deconvoluting the Complexity of Reactive Oxygen Species (ROS) in Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are becoming a serious public health concern as the world’s population continues to age, demanding the discovery of more effective therapies. Excessive formation of reactive oxygen species (ROS) can result in oxidative stress (OS), which can be regarded as one of the common causes of neurodegenerative diseases (NDs). Thus, in this review, we focus on summarizing the consequences of ROS NDs, while taking the four prevalent NDs as examples, including Alzheimer’s disease (AD), Parkinson’s disease (PD), Amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD), to illustrate the key signaling pathways and relevant drugs. Together, these findings may shed new light on a field in which ROS-related pathways play a key role; thereby setting the groundwork for the future therapeutic development of neurodegenerative diseases.

The role of autophagy and mitophagy in cancers

Autophagy is an important life phenomenon in eukaryotic cells. Its main role is to remove and degrade its damaged organelles and excess biological macromolecules, and use degradation products to provide energy and rebuild the cell structure, playing an important role in maintaining cell homeostasis and cell life activities. Mitophagy is a form of macroautophagy. It has the beneficial effect of eliminating damaged mitochondria, thereby maintaining the integrity of the mitochondrial pool. Autophagy and mitophagy have a dual role in the development of cancer. On one hand, autophagy and mitophagy can maintain the normal physiological function of cells. On the other hand, excessive autophagy and mitophagy can lead to diseases. The present review introduces the mechanisms of autophagy and mitophagy, and the main related proteins, and introduce the correlation with cancers, providing a basis for the treatment of cancers through the understanding of these proteins.

High expression of p62/SQSTM1 predicts shorter survival for patients with pancreatic cancer

BACKGROUND

Accumulation of the signal adaptor protein p62 has been demonstrated in many forms of cancer, including pancreatic ductal adenocarcinoma (PDAC). Although data from experimental studies suggest that p62 accumulation accelerates the development of PDAC, the association between p62 protein expression and survival in PDAC patients is unclear.

METHODS

Thirty-three tumor specimens from PDAC patients treated by primary surgery were obtained. Immunohistochemical expression of p62, microtubule-associated protein 1A/1B-light chain 3 (LC3), and nuclear factor-erythroid factor 2-related factor 2 (NRF2) in tumor tissue was examined for associations with clinicopathological characteristics and disease-specific survival (DSS).

RESULTS

There was no association between p62 expression and any of the clinicopathological variables. However, high p62 protein expression in tumor cells was significantly associated with shorter DSS (7 months vs. 29 months, p = 0.017). The hazard ratio for death in patients with high p62 protein expression in tumor cells was 2.88 (95% confidence interval: 1.17-7.11, p = 0.022). In multivariable analysis, high p62 expression was an independent prognostic factor for shorter DSS (p = 0.020) when follow up time was more than 5 years. LC3 and NRF2 staining was not associated with survival or other clinicopathological parameters.

CONCLUSION

Our results show that high p62 protein expression in tumor cells is associated with shorter survival following pancreatic tumor resection. This association supports a role for p62 as a prognostic marker in patients with PDAC treated by primary surgery.

ULK1 Signaling in the Liver: Autophagy Dependent and Independent Actions

Liver is the primary organ for energy metabolism and detoxification in the human body. Not surprisingly, a derangement in liver function leads to several metabolic diseases. Autophagy is a cellular process, which primarily deals with providing molecules for energy production, and maintains cellular health. Autophagy in the liver has been implicated in several hepatic metabolic processes, such as, lipolysis, glycogenolysis, and gluconeogenesis. Autophagy also provides protection against drugs and pathogens. Deregulation of autophagy is associated with the development of non-alcoholic fatty liver disease (NAFLD) acute-liver injury, and cancer. The process of autophagy is synchronized by the action of autophagy family genes or autophagy (Atg) genes that perform key functions at different steps. The uncoordinated-51-like kinases 1 (ULK1) is a proximal kinase member of the Atg family that plays a crucial role in autophagy. Interestingly, ULK1 actions on hepatic cells may also involve some autophagy-independent signaling. In this review, we provide a comprehensive update of ULK1 mediated hepatic action involving lipotoxicity, acute liver injury, cholesterol synthesis, and hepatocellular carcinoma, including both its autophagic and non-autophagic functions.

NEAT1 Confers Radioresistance to Hepatocellular Carcinoma Cells by Inducing Autophagy through GABARAP

A long noncoding RNA (lncRNA), nuclear enriched abundant transcript 1 (NEAT1) variant 1 (NEAT1v1), is involved in the maintenance of cancer stem cells (CSCs) in hepatocellular carcinoma (HCC). CSCs are suggested to play important roles in therapeutic resistance. Therefore, we investigated whether NEAT1v1 is involved in the sensitivity to radiation therapy in HCC. Gene knockdown was performed using short hairpin RNAs, and NEAT1v1-overexpressing HCC cell lines were generated by stable transfection with a NEAT1v1-expressing plasmid DNA. Cells were irradiated using an X-ray generator. We found that NEAT1 knockdown enhanced the radiosensitivity of HCC cell lines and concomitantly inhibited autophagy. NEAT1v1 overexpression enhanced autophagy in the irradiated cells and conferred radioresistance. Gamma-aminobutyric acid receptor-associated protein (GABARAP) expression was downregulated by NEAT1 knockdown, whereas it was upregulated in NEAT1v1-overexpressing cells. Moreover, GABARAP was required for NEAT1v1-induced autophagy and radioresistance as its knockdown significantly inhibited autophagy and sensitized the cells to radiation. Since GABARAP is a crucial protein for the autophagosome-lysosome fusion, our results suggest that NEAT1v1 confers radioresistance to HCC by promoting autophagy through GABARAP.

Melatonin and verteporfin synergistically suppress the growth and stemness of head and neck squamous cell carcinoma through the regulation of mitochondrial dynamics

The prevalence of head and neck squamous cell carcinoma (HNSCC) has continued to rise for decades. However, drug resistance to chemotherapeutics and relapse, mediated by cancer stem cells (CSCs), remains a significant impediment in clinical oncology to achieve successful treatment. Therefore, we focused on analyzing CSCs in HNSCC and demonstrated the effect of melatonin (Mel) and verteporfin (VP) on SCC-25 cells. HNSCC CSCs were enriched in the reactive oxygen species-low state and in sphere-forming cultures. Combination treatment with Mel and VP decreased HNSCC viability and increased apoptosis without causing significant damage to normal cells. Sphere-forming ability and stem cell population were reduced by co-treatment with Mel and VP, while mitochondrial ROS level was increased by the treatment. Furthermore, the expression of mitophagy markers, parkin and PINK1, was significantly decreased in the co-treated cells. Mel and VP induced mitochondrial depolarization and inhibited mitochondrial function. Parkin/TOM20 was localized near the nucleus and formed clusters of mitochondria in the cells after treatment. Moreover, Mel and VP downregulated the expression of markers involved in epithelial-mesenchymal transition and metastasis. The migration capacity of cells was significantly decreased by co-treatment with Mel and VP, accompanied by the down-regulation of MMP-2 and MMP-9 expression. Taken together, these results indicate that co-treatment with Mel and VP induces mitochondrial dysfunction, resulting in the apoptosis of CSCs. Mel and VP could thus be further investigated as potential therapies for HNSCC through their action on CSCs.

USP10 inhibits the dopamine-induced reactive oxygen species-dependent apoptosis of neuronal cells by stimulating the antioxidant Nrf2 activity

Nrf2 is an antioxidant transcriptional activator in many types of cells, and its dysfunction plays key roles in a variety of human disorders, including Parkinson's disease (PD). PD is characterized by the selective loss of dopaminergic neurons in PD-affected brain regions. Dopamine treatment of neuronal cells stimulates the production of reactive oxygen species (ROS) and increases ROS-dependent neuronal apoptosis. In this study, we found that the ubiquitin-specific protease 10 (USP10) protein reduces dopamine-induced ROS production of neuronal cells and ROS-dependent apoptosis by stimulating the antioxidant activity of Nrf2. USP10 interacted with the Nrf2 activator p62, increased the phosphorylation of p62, increased the interaction of p62 with the Nrf2 inhibitor Keap1, and stimulated Nrf2 antioxidant transcriptional activity. In addition, USP10 augmented dopamine-induced Nrf2 translation. Taken together, these results indicate that USP10 is a key regulator of Nrf2 antioxidant activity in neuronal cells and suggest that USP10 activators are promising therapeutic agents for oxidative stress–related diseases, including PD.

New Look of EBV LMP1 Signaling Landscape

Simple Summary

Epstein-Barr Virus (EBV) infection is associated with various lymphomas and carcinomas as well as other diseases in humans. The transmembrane protein LMP1 plays versatile roles in EBV life cycle and pathogenesis, by perturbing, reprograming, and regulating a large range of host cellular mechanisms and functions, which have been increasingly disclosed but not fully understood so far. We summarize recent research progress on LMP1 signaling, including the novel components LIMD1, p62, and LUBAC in LMP1 signalosome and LMP1 novel functions, such as its induction of p62-mediated selective autophagy, regulation of metabolism, induction of extracellular vehicles, and activation of NRF2-mediated antioxidative defense. A comprehensive understanding of LMP1 signal transduction and functions may allow us to leverage these LMP1-regulated cellular mechanisms for clinical purposes.

Abstract

The Epstein–Barr Virus (EBV) principal oncoprotein Latent Membrane Protein 1 (LMP1) is a member of the Tumor Necrosis Factor Receptor (TNFR) superfamily with constitutive activity. LMP1 shares many features with Pathogen Recognition Receptors (PRRs), including the use of TRAFs, adaptors, and kinase cascades, for signal transduction leading to the activation of NFκB, AP1, and Akt, as well as a subset of IRFs and likely the master antioxidative transcription factor NRF2, which we have gradually added to the list. In recent years, we have discovered the Linear UBiquitin Assembly Complex (LUBAC), the adaptor protein LIMD1, and the ubiquitin sensor and signaling hub p62, as novel components of LMP1 signalosome. Functionally, LMP1 is a pleiotropic factor that reprograms, balances, and perturbs a large spectrum of cellular mechanisms, including the ubiquitin machinery, metabolism, epigenetics, DNA damage response, extracellular vehicles, immune defenses, and telomere elongation, to promote oncogenic transformation, cell proliferation and survival, anchorage-independent cell growth, angiogenesis, and metastasis and invasion, as well as the development of the tumor microenvironment. We have recently shown that LMP1 induces p62-mediated selective autophagy in EBV latency, at least by contributing to the induction of p62 expression, and Reactive Oxygen Species (ROS) production. We have also been collecting evidence supporting the hypothesis that LMP1 activates the Keap1-NRF2 pathway, which serves as the key antioxidative defense mechanism. Last but not least, our preliminary data shows that LMP1 is associated with the deregulation of cGAS-STING DNA sensing pathway in EBV latency. A comprehensive understanding of the LMP1 signaling landscape is essential for identifying potential targets for the development of novel strategies towards targeted therapeutic applications.

GPR30 Activation by 17β-Estradiol Promotes p62 Phosphorylation and Increases Estrogen Receptor α Protein Expression by Inducing Its Release from a Complex Formed with KEAP1

Estrogens can elicit rapid cellular responses via the G-protein-coupled receptor 30 (GPR30), followed by estrogen receptor α (ERα/ESR1)-mediated genomic effects. Here, we investigated whether rapid estrogen signaling via GRP30 may affect ESR1 expression, and we examined the underlying molecular mechanisms. The exposure of human endometrial cancer cells to 17β-estradiol promoted p62 phosphorylation and increased ESR1 protein expression. However, both a GPR30 antagonist and GPR30 silencing abrogated this phenomenon. GPR30 activation by 17β-estradiol elicited the SRC/EGFR/PI3K/Akt/mTOR signaling pathway. Intriguingly, unphosphorylated p62 and ESR1 were found to form an intracellular complex with the substrate adaptor protein KEAP1. Upon phosphorylation, p62 promoted ESR1 release from the complex, to increase its protein expression. Given the critical role played by p62 in autophagy, we also examined how this process affected ESR1 expression. The activation of autophagy by everolimus decreased ESR1 by promoting p62 degradation, whereas autophagy inhibition with chloroquine increased ESR1 expression. The treatment of female C57BL/6 mice with the autophagy inhibitor hydroxychloroquine—which promotes p62 expression—increased both phosphorylated p62 and ESR1 expression in uterine epithelial cells. Collectively, our results indicate that 17β-estradiol-mediated GPR30 activation elicits the SRC/EGFR/PI3K/Akt/mTOR signaling pathway and promotes p62 phosphorylation. In turn, phosphorylated p62 increased ESR1 expression by inducing its release from complexes that included KEAP1. Our findings may lead to novel pharmacological strategies aimed at decreasing ESR1 expression in estrogen-sensitive cells.

Targeting NRF2 and Its Downstream Processes: Opportunities and Challenges

The transcription factor NRF2 coordinates the expression of a vast array of cytoprotective and metabolic genes in response to various stress inputs to restore cellular homeostasis. Transient activation of NRF2 in healthy tissues has been long recognized as a cellular defense mechanism and is critical to prevent cancer initiation by carcinogens. However, cancer cells frequently hijack the protective capability of NRF2 to sustain the redox balance and meet their metabolic requirements for proliferation. Further, aberrant activation of NRF2 in cancer cells confers resistance to commonly used chemotherapeutic agents and radiotherapy. During the last decade, many research groups have attempted to block NRF2 activity in tumors to counteract the survival and proliferative advantage of cancer cells and reverse resistance to treatment. In this review, we highlight the role of NRF2 in cancer progression and discuss the past and current approaches to disable NRF2 signaling in tumors. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Apatinib triggers autophagic and apoptotic cell death via VEGFR2/STAT3/PD-L1 and ROS/Nrf2/p62 signaling in lung cancer

Background

Recently, a variety of clinical trials have shown that apatinib, a small-molecule anti-angiogenic drug, exerts promising inhibitory effects on multiple solid tumors, including non-small cell lung cancer (NSCLC). However, the underlying molecular mechanism of apatinib on NSCLC remains unclear.

Methods

MTT, EdU, AO/EB staining, TUNEL staining, flow cytometry, colony formation assays were performed to investigate the effects of apatinib on cell proliferation, cell cycle distribution, apoptosis and cancer stem like properties. Wound healing and transwell assays were conducted to explore the role of apatinib on migration and invasion. The regulation of apatinib on VEGFR2/STAT3/PD-L1 and ROS/Nrf2/p62 signaling were detected. Furthermore, we collected conditioned medium (CM) from A549 and H1299 cells to stimulate phorbol myristate acetate (PMA)-activated THP-1 cells, and examined the effect of apatinib on PD-L1 expression in macrophages. The Jurkat T cells and NSCLC cells co-culture model was used to assess the effect of apatinib on T cells activation. Subcutaneous tumor formation models were established to evaluate the effects of apatinib in vivo. Histochemical, immunohistochemical staining and ELISA assay were used to examine the levels of signaling molecules in tumors.

Results

We showed that apatinib inhibited cell proliferation and promoted apoptosis in NSCLC cells in vitro. Apatinib induced cell cycle arrest at G1 phase and suppressed the expression of Cyclin D1 and CDK4. Moreover, apatinib upregulated Cleaved Caspase 3, Cleaved Caspase 9 and Bax, and downregulated Bcl-2 in NSCLC cells. The colony formation ability and the number of CD133 positive cells were significantly decreased by apatinib, suggesting that apatinib inhibited the malignant and stem-like features of NSCLC cells. Mechanistically, apatinib inhibited PD-L1 and c-Myc expression by targeting VEGFR2/STAT3 signaling. Apatinib also inhibited PD-L1 expression in THP-1 derived macrophages stimulated by CM from NSCLC cells. Furthermore, apatinib pretreatment increased CD69 expression and IFN-γ secretion in stimulated Jurkat T cells co-cultured with NSCLC cells. Apatinib also promoted ROS production and inhibited Nrf2 and p62 expression, leading to the autophagic and apoptotic cell death in NSCLC. Moreover, apatinib significantly inhibited tumor growth in vivo.

Conclusion

Our data indicated that apatinib induced autophagy and apoptosis in NSCLC via regulating VEGFR2/STAT3/PD-L1 and ROS/Nrf2/p62 signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02069-4.

Apatinib suppressed proliferation, induced cell cycle arrest and apoptosis, and inhibited malignancy in NSCLC in vitro and in vivo.

Apatinib downregulated PD-L1 and c-Myc in NSCLC through VEGFR2/STAT3 pathway.

Apatinib inhibited PD-L1 expression in THP-1 derived macrophages stimulated by the conditioned medium from NSCLC cells and partially restored the activation of Jurkat T cells co-cultured with NSCLC cells.

Apatinib induced ROS generation and inhibited Nrf2 and p62 expression, leading to the autophagic and apoptotic cell death in NSCLC.

Plasma Rich in Growth Factors Promotes Autophagy in ARPE19 Cells in Response to Oxidative Stress Induced by Blue Light

Age-related macular degeneration (AMD) causes the degeneration of photoreceptors and retinal cells leading to vision loss in older subjects. Among possible exogenous risk factors, it has been recently proposed that long-term exposure to blue light could aggravate the course of AMD. In the search for therapeutic options, plasma rich in growth factors (PRGF) has been shown to enhance cell antioxidant pathways and protect photoreceptors against the harm produced by blue light, although its mechanism of action remains unknown. One possible mechanism, autophagy, is one of the most conservative cell renewal systems used in eukaryotes to destroy cellular components that have been damaged by some kind of insult. The oxidative stress of exposure to blue light is known to induce cell autophagy. In this study, we examined the combined effects on autophagy of blue light and PRGF in a retinal cell line, ARPE19. In response to treatment with both PRGF and blue light, we detected the modulated expression of autophagy markers such as NF-kB, p62/sqstm1, Atg5, LC3 and Beclin1, and inflammatory markers such as IL1B and IL18. Our findings suggest that PRGF promotes cell autophagy in response to exposure to blue light.

The Pathways Underlying the Multiple Roles of p62 in Inflammation and Cancer

p62 is a highly conserved, multi-domain, and multi-functional adaptor protein critically involved in several important cellular processes. Via its pronounced domain architecture, p62 binds to numerous interaction partners, thereby influencing key pathways that regulate tissue homeostasis, inflammation, and several common diseases including cancer. Via binding of ubiquitin chains, p62 acts in an anti-inflammatory manner as an adaptor for the auto-, xeno-, and mitophagy-dependent degradation of proteins, pathogens, and mitochondria. Furthermore, p62 is a negative regulator of inflammasome complexes. The transcription factor Nrf2 regulates expression of a bundle of ROS detoxifying genes. p62 activates Nrf2 by interaction with and autophagosomal degradation of the Nrf2 inhibitor Keap1. Moreover, p62 activates mTOR, the central kinase of the mTORC1 sensor complex that controls cell proliferation and differentiation. Through different mechanisms, p62 acts as a positive regulator of the transcription factor NF-κB, a central player in inflammation and cancer development. Therefore, p62 represents not only a cargo receptor for autophagy, but also a central signaling hub, linking several important pro- and anti-inflammatory pathways. This review aims to summarize knowledge about the molecular mechanisms underlying the roles of p62 in health and disease. In particular, different types of tumors are characterized by deregulated levels of p62. The elucidation of how p62 contributes to inflammation and cancer progression at the molecular level might promote the development of novel therapeutic strategies.

Molecular basis for the disruption of Keap1-Nrf2 interaction via Hinge & Latch mechanism

The Keap1-Nrf2 system is central for mammalian cytoprotection against various stresses and a drug target for disease prevention and treatment. One model for the molecular mechanisms leading to Nrf2 activation is the Hinge-Latch model, where the DLGex-binding motif of Nrf2 dissociates from Keap1 as a latch, while the ETGE motif remains attached to Keap1 as a hinge. To overcome the technical difficulties in examining the binding status of the two motifs during protein-protein interaction (PPI) simultaneously, we utilized NMR spectroscopy titration experiments. Our results revealed that latch dissociation is triggered by low-molecular-weight Keap1-Nrf2 PPI inhibitors and occurs during p62-mediated Nrf2 activation, but not by electrophilic Nrf2 inducers_. This study demonstrates that Keap1 utilizes a unique Hinge-Latch mechanism for Nrf2 activation upon challenge by non-electrophilic PPI-inhibiting stimuli, and provides critical insight for the pharmacological development of next-generation Nrf2 activators targeting the Keap1-Nrf2 PPI.

Using NMR spectroscopy, Horie, Suzuki, Inoue et al. show that the dissociation of Keap1 from Nrf2, or the Hinge-Latch mechanism, is triggered by Keap1-Nrf2 inhibitors and occurs during p62- mediated Nrf2 activation, but not by electrophilic Nrf2 inducers. This study provides insights into the design of Nrf2 activators targeting the Keap1-Nrf2 interaction.

Cancer cells escape autophagy inhibition via NRF2-induced macropinocytosis

Many cancers, including pancreatic ductal adenocarcinoma (PDAC), depend on autophagy-mediated scavenging and recycling of intracellular macromolecules, suggesting that autophagy blockade should cause tumor starvation and regression. However, until now autophagy-inhibiting monotherapies have not demonstrated potent anti-cancer activity. We now show that autophagy blockade prompts established PDAC to upregulate and utilize an alternative nutrient procurement pathway: macropinocytosis (MP) that allows tumor cells to extract nutrients from extracellular sources and use them for energy generation. The autophagy to MP switch, which may be evolutionarily conserved and not cancer cell restricted, depends on activation of transcription factor NRF2 by the autophagy adaptor p62/SQSTM1. NRF2 activation by oncogenic mutations, hypoxia, and oxidative stress also results in MP upregulation. Inhibition of MP in autophagy-compromised PDAC elicits dramatic metabolic decline and regression of transplanted and autochthonous tumors, suggesting the therapeutic promise of combining autophagy and MP inhibitors in the clinic.

NRF2 activates macropinocytosis upon autophagy inhibition

Su et al. demonstrate that upon inhibiting autophagy, an intracellular nutrient recycling pathway, pancreatic ductal adenocarcinoma cells upregulate NRF2-mediated transcription of macropinocytosis pathway components, thereby triggering an alternate route for tumors to scavenge nutrients from extracellular sources. Accordingly, the combined inhibition of autophagy and macropinocytosis may improve cancer treatment.

Amino acid metabolism and autophagy in skeletal development and homeostasis

Bone is an active organ that is continuously remodeled throughout life via formation and resorption; therefore, a fine-tuned bone (re)modeling is crucial for bone homeostasis and is closely connected with energy metabolism. Amino acids are essential for various cellular functions as well as an energy source, and their synthesis and catabolism (e.g., metabolism of carbohydrates and fatty acids) are regulated through numerous enzymatic cascades. In addition, the intracellular levels of amino acids are maintained by autophagy, a cellular recycling system for proteins and organelles; under nutrient deprivation conditions, autophagy is strongly induced to compensate for cellular demands and to restore the amino acid pool. Metabolites derived from amino acids are known to be precursors of bioactive molecules such as second messengers and neurotransmitters, which control various cellular processes, including cell proliferation, differentiation, and homeostasis. Thus, amino acid metabolism and autophagy are tightly and reciprocally regulated in our bodies. This review discusses the current knowledge and potential links between bone diseases and deficiencies in amino acid metabolism and autophagy.

Coordinate regulation of the senescent state by selective autophagy

Cellular senescence is a complex stress response implicated in aging. Autophagy can suppress senescence but is counterintuitively necessary for full senescence. Although its anti-senescence role is well described, to what extent autophagy contributes to senescence establishment and the underlying mechanisms is poorly understood. Here, we show that selective autophagy of multiple regulatory components coordinates the homeostatic state of senescence. We combined a proteomic analysis of autophagy components with protein stability profiling, identifying autophagy substrate proteins involved in several senescence-related processes. Selective autophagy of KEAP1 promoted redox homeostasis during senescence. Furthermore, selective autophagy limited translational machinery components to ameliorate senescence-associated proteotoxic stress. Lastly, selective autophagy of TNIP1 enhanced senescence-associated inflammation. These selective autophagy networks appear to operate in vivo senescence during human osteoarthritis. Our data highlight a caretaker role of autophagy in the stress support network of senescence through regulated protein stability and unravel the intertwined relationship between two important age-related processes.