DUOX2-mediated production of reactive oxygen species induces epithelial mesenchymal transition in 5-fluorouracil resistant human colon cancer cells

Particulate matter stimulates the NADPH oxidase system via AhR-mediated epigenetic modifications

Stimulation of human keratinocytes with particulate matter 2.5 (PM2.5) elicits complex signaling events, including a rise in the generation of reactive oxygen species (ROS). However, the mechanisms underlying PM2.5-induced ROS production remain unknown. Here, we show that PM2.5-induced ROS production in human keratinocytes is mediated via the NADPH oxidase (NOXs) system and the Ca2+ signaling pathway. PM2.5 treatment increased the expression of NOX1, NOX4, and a calcium-sensitive NOX, dual oxidase 1 (DUOX1), in human epidermal keratinocyte cell line. PM2.5 bound to aryl hydrocarbon receptor (AhR), and this complex bound to promoter regions of NOX1 and DUOX1, suggesting that AhR acted as a transcription factor of NOX1 and DUOX1. PM2.5 increased the transcription of DUOX1 via epigenetic modification. Moreover, a link between DNA demethylase and histone methyltransferase with the promoter regions of DUOX1 led to an elevation in the expression of DUOX1 mRNA. Interestingly, PM2.5 increased NOX4 expression and promoted the interaction of NOX4 and Ca2+ channels within the cytoplasmic membrane or endoplasmic reticulum, leading to Ca2+ release. The increase in intracellular Ca2+ concentration activated DUOX1, responsible for ROS production. Our findings provide evidence for a PM2.5-mediated ROS-generating system network, in which increased NOX1, NOX4, and DUOX1 expression serves as a ROS signal through AhR and Ca2+ activation.

The regulation of plasma gelsolin by DNA methylation in ovarian cancer chemo-resistance

BACKGROUND

Ovarian cancer (OVCA) is the most lethal gynecologic cancer and chemoresistance remains a major hurdle to successful therapy and survival of OVCA patients. Plasma gelsolin (pGSN) is highly expressed in chemoresistant OVCA compared with their chemosensitive counterparts, although the mechanism underlying the differential expression is not known. Also, its overexpression significantly correlates with shortened survival of OVCA patients. In this study, we investigated the methylation role of Ten eleven translocation isoform-1 (TET1) in the regulation of differential pGSN expression and chemosensitivity in OVCA cells.

METHODS

Chemosensitive and resistant OVCA cell lines of different histological subtypes were used in this study to measure pGSN and TET1 mRNA abundance (qPCR) as well as protein contents (Western blotting). To investigate the role of DNA methylation specifically in pGSN regulation and pGSN-induced chemoresistance, DNMTs and TETs were pharmacologically inhibited in sensitive and resistant OVCA cells using specific inhibitors. DNA methylation was quantified using EpiTYPER MassARRAY system. Gain-and-loss-of-function assays were used to investigate the relationship between TET1 and pGSN in OVCA chemoresponsiveness.

RESULTS

We observed differential protein and mRNA expressions of pGSN and TET1 between sensitive and resistant OVCA cells and cisplatin reduced their expression in sensitive but not in resistant cells. We observed hypomethylation at pGSN promoter upstream region in resistant cells compared to sensitive cells. Pharmacological inhibition of DNMTs increased pGSN protein levels in sensitive OVCA cells and decreased their responsiveness to cisplatin, however we did not observe any difference in methylation level at pGSN promoter region. TETs inhibition resulted in hypermethylation at multiple CpG sites and decreased pGSN protein level in resistant OVCA cells which was also associated with enhanced response to cisplatin, findings that suggested the methylation role of TETs in the regulation of pGSN expression in OVCA cells. Further, we found that TET1 is inversely related to pGSN but positively related to chemoresponsiveness of OVCA cells.

CONCLUSION

Our findings broaden our knowledge about the epigenetic regulation of pGSN in OVCA chemoresistance and reveal a novel potential target to re-sensitize resistant OVCA cells. This may provide a future therapeutic strategy to improve the overall OVCA patient survival.

Targeting proteasomal deubiquitinases USP14 and UCHL5 with b-AP15 reduces 5-fluorouracil resistance in colorectal cancer cells

5-Fluorouracil (5-FU) is the first-line treatment for colorectal cancer (CRC) patients, but the development of acquired resistance to 5-FU remains a big challenge. Deubiquitinases play a key role in the protein degradation pathway, which is involved in cancer development and chemotherapy resistance. In this study, we investigated the effects of targeted inhibition of the proteasomal deubiquitinases USP14 and UCHL5 on the development of CRC and resistance to 5-FU. By analyzing GEO datasets, we found that the mRNA expression levels of USP14 and UCHL5 in CRC tissues were significantly increased, and negatively correlated with the survival of CRC patients. Knockdown of both USP14 and UCHL5 led to increased 5-FU sensitivity in 5-FU-resistant CRC cell lines (RKO-R and HCT-15R), whereas overexpression of USP14 and UCHL5 in 5-FU-sensitive CRC cells decreased 5-FU sensitivity. B-AP15, a specific inhibitor of USP14 and UCHL5, (1-5 μM) dose-dependently inhibited the viability of RKO, RKO-R, HCT-15, and HCT-15R cells. Furthermore, treatment with b-AP15 reduced the malignant phenotype of CRC cells including cell proliferation and migration, and induced cell death in both 5-FU-sensitive and 5-FU-resistant CRC cells by impairing proteasome function and increasing reactive oxygen species (ROS) production. In addition, b-AP15 inhibited the activation of NF-κB pathway, suppressing cell proliferation. In 5-FU-sensitive and 5-FU-resistant CRC xenografts nude mice, administration of b-AP15 (8 mg·kg-1·d-1, intraperitoneal injection) effectively suppressed the growth of both types of tumors. These results demonstrate that USP14 and UCHL5 play an important role in the development of CRC and resistance to 5-FU. Targeting USP14 and UCHL5 with b-AP15 may represent a promising therapeutic strategy for the treatment of CRC.

TRPV1 inhibition overcomes cisplatin resistance by blocking autophagy-mediated hyperactivation of EGFR signaling pathway

Cisplatin resistance along with chemotherapy-induced neuropathic pain is an important cause of treatment failure for many cancer types and represents an unmet clinical need. Therefore, future studies should provide evidence regarding the mechanisms of potential targets that can overcome the resistance as well as alleviate pain. Here, we show that the emergence of cisplatin resistance is highly associated with EGFR hyperactivation, and that EGFR hyperactivation is arisen by a transcriptional increase in the pain-generating channel, TRPV1, via NANOG. Furthermore, TRPV1 promotes autophagy-mediated EGF secretion via Ca²⁺ influx, which activates the EGFR-AKT signaling and, consequentially, the acquisition of cisplatin resistance. Importantly, TRPV1 inhibition renders tumors susceptible to cisplatin. Thus, our findings indicate a link among cisplatin resistance, EGFR hyperactivation, and TRPV1-mediated autophagic secretion, and implicate that TRPV1 could be a crucial drug target that could not only overcome cisplatin resistance but also alleviate pain in NANOG⁺ cisplatin-resistant cancer.

Thiol oxidative stress-dependent degradation of transglutaminase2 via protein S-glutathionylation sensitizes 5-fluorouracil therapy in 5-fluorouracil-resistant colorectal cancer cells

5-Fluorouracil (5-Fu) is a first-line drug for colorectal cancer (CRC) therapy. However, the development of 5-Fu resistance limits its chemotherapeutic effectiveness and often leads to poor prognoses of CRC. Transglutaminase 2 (TGM2), a member of the transglutaminase family, is considered to be associated with chemoresistance through apoptotic prevention in various cancers including CRC. TGM2 was found to be overexpressed in two 5-Fu-resistant CRC cell lines and down-regulated by increased thiol oxidative stress induced by inhibition of glutathione reductase (GR). The present study aimed to explore the role of TGM2 in 5-Fu-resistant CRC and the mechanism of action by which the elevated thiol oxidative stress down-regulates TGM2 protein level. The results revealed that 5-Fu-resistance induced by overexpression of TGM2 in CRC cells was reversed through up-regulation of thiol oxidative stress. Knockdown of TGM2 increased the chemosensitivity of CRC cells to 5-Fu. Thiol oxidative stress potentially enhanced the therapeutic effect of 5-Fu in the resistant CRC cells by promotion of 5-Fu-induced apoptosis through down-regulation of TGM2. The elevated thiol oxidative stress increased the S-glutathionylation of TGM2 and led to proteasomal degradation of TGM2. Furthermore, Cys193 was identified as the S-glutathionylation site in TGM2, and its mutation resulted in thiol oxidative stress-mediated CRC cell apoptotic resistance. TGM2-induced EMT was also suppressed by the elevated thiol oxidative stress. A xenograft tumor model confirmed the effect of thiol oxidative stress in the reversal of 5-Fu resistance in CRC cells in vivo. TGM2 protein expression level was found to be significantly higher in human CRC specimens than in non-cancerous colorectal tissues. Taken together, the present data suggest an important role of TGM2 in 5-Fu resistance in CRC cells. Up-regulation of thiol oxidative stress could be a potential therapeutic approach for treating 5-Fu-resistant CRC and TGM2 may serve as a potential therapeutic target of thiol oxidative stress.

Redox signaling in drug-tolerant persister cells as an emerging therapeutic target

Drug-tolerant persister (DTP) cells have attracted significant interest, given their predominant role in treatment failure. In this respect, DTP cells reportedly survive after anticancer drug exposure, and their DNA repair mechanisms are altered to enhance adaptive mutation, accounting for the emergence of drug-resistant mutations. DTP cells resume proliferation upon treatment withdrawal and are responsible for cancer relapse. Current evidence suggests that DTP cells mediate redox signaling-mediated cellular homeostasis by developing various adaptive mechanisms, especially metabolic reprogramming that promotes mitochondrial oxidative respiration and a robust antioxidant process. There is an increasing consensus that disrupting redox homeostasis by intervening with redox signaling is theoretically a promising therapeutic strategy for targeting these sinister cells. In this review, we provide a comprehensive overview of the characteristics of DTP cells and the underlying mechanisms involved in redox signaling, aiming to provide a unique perspective on potential therapeutic applications based on their vulnerabilities to redox regulation.

Metastasis prevention: How to catch metastatic seeds

Despite considerable advances in the evolution of anticancer therapies, metastasis still remains the main cause of cancer mortality. Therefore, current strategies for cancer cure should be redirected towards prevention of metastasis. Targeting metastatic pathways represents a promising therapeutic opportunity aimed at obstructing tumor cell dissemination and metastatic colonization. In this review, we focus on preclinical studies and clinical trials over the last five years that showed high efficacy in suppressing metastasis through targeting lymph node dissemination, tumor cell extravasation, reactive oxygen species, pre-metastatic niche, exosome machinery, and dormancy.

Targeting epigenetic regulators to overcome drug resistance in cancers

Drug resistance is mainly responsible for cancer recurrence and poor prognosis. Epigenetic regulation is a heritable change in gene expressions independent of nucleotide sequence changes. As the common epigenetic regulation mechanisms, DNA methylation, histone modification, and non-coding RNA regulation have been well studied. Increasing evidence has shown that aberrant epigenetic regulations contribute to tumor resistance. Therefore, targeting epigenetic regulators represents an effective strategy to reverse drug resistance. In this review, we mainly summarize the roles of epigenetic regulation in tumor resistance. In addition, as the essential factors for epigenetic modifications, histone demethylases mediate the histone or genomic DNA modifications. Herein, we comprehensively describe the functions of the histone demethylase family including the lysine-specific demethylase family, the Jumonji C-domain-containing demethylase family, and the histone arginine demethylase family, and fully discuss their regulatory mechanisms related to cancer drug resistance. In addition, therapeutic strategies, including small-molecule inhibitors and small interfering RNA targeting histone demethylases to overcome drug resistance, are also described.

Reactive oxygen species as mediators of disease progression and therapeutic response in colorectal cancer

Significance Reactive oxygen species (ROS) are critical to normal cellular function with redox homeostasis achieved by balancing ROS production with removal through detoxification mechanisms. Many of the conventional chemotherapies used to treat colorectal cancer (CRC) derive a proportion of their cytotoxicity from ROS generation and resistance to chemotherapy is associated with elevated detoxification mechanisms. Furthermore, cancer stem cells demonstrate elevated detoxification mechanisms making definitive treatment with existing chemotherapy challenging. In this article we review the roles of ROS in normal and malignant colonic cell biology and how existing and emerging therapies might harness ROS for therapeutic benefit. Recent advances Recent publications have elucidated the contribution of ROS to the cytotoxicity of conventional chemotherapy alongside the emerging approaches of photodynamic therapy (PDT), sonodynamic therapy (SDT) and radiodynamic therapy (RDT) in which ROS are generated in response to excitatory light, sound or X-ray stimuli to promote cancer cell apoptosis. Critical issues The majority of patients with metastatic CRC have a very poor prognosis with 5-year survival of approximately 13% making the need for new or more effective treatments an imperative. Future Directions Modulation of ROS through a combination of new and emerging therapies may improve the efficacy of current chemotherapy providing novel approaches to treat otherwise resistant disease.

Dual Oxidase 2 (DUOX2) as a Proteomic Biomarker for Predicting Treatment Response to Chemoradiation Therapy for Locally Advanced Rectal Cancer: Using High-Throughput Proteomic Analysis and Machine Learning Algorithm

High-throughput mass-spectrometry-based quantitative proteomic analysis was performed using formalin-fixed, paraffin-embedded (FFPE) biopsy samples obtained before treatment from 13 patients with locally advanced rectal cancer (LARC), who were treated with concurrent chemoradiation therapy (CCRT) followed by surgery. Patients were divided into complete responder (CR) and non-complete responder (nCR) groups. Immunohistochemical (IHC) staining of 79 independent FFPE tissue samples was performed to validate the predictive ability of proteomic biomarker candidates. A total of 3637 proteins were identified, and the expression of 498 proteins was confirmed at significantly different levels (differentially expressed proteins—DEPs) between two groups. In Gene Ontology enrichment analyses, DEPs enriched in biological processes in the CR group included proteins linked to cytoskeletal organization, immune response processes, and vesicle-associated protein transport processes, whereas DEPs in the nCR group were associated with biosynthesis, transcription, and translation processes. Dual oxidase 2 (DUOX2) was selected as the most predictive biomarker in machine learning algorithm analysis. Further IHC validation ultimately confirmed DUOX2 as a potential biomarker for predicting the response of nCR to CCRT. In conclusion, this study suggests that the treatment response to RT may be affected by the pre-treatment tumor microenvironment. DUOX2 is a potential biomarker for the early prediction of nCR after CCRT.

Harnessing redox signaling to overcome therapeutic-resistant cancer dormancy

Dormancy occurs when cells preserve viability but stop proliferating, which is considered an important cause of tumor relapse, which may occur many years after clinical remission. Since the life cycle of dormant cancer cells is affected by both intracellular and extracellular factors, gene mutation or epigenetic regulation of tumor cells may not fully explain the mechanisms involved. Recent studies have indicated that redox signaling regulates the formation, maintenance, and reactivation of dormant cancer cells by modulating intracellular signaling pathways and the extracellular environment, which provides a molecular explanation for the life cycle of dormant tumor cells. Indeed, redox signaling regulates the onset of dormancy by balancing the intrinsic pathways, the extrinsic environment, and the response to therapy. In addition, redox signaling sustains dormancy by managing stress homeostasis, maintaining stemness and immunogenic equilibrium. However, studies on dormancy reactivation are still limited, partly explained by redox-mediated activation of lipid metabolism and the transition from the tumor microenvironment to inflammation. Encouragingly, several drug combination strategies based on redox biology are currently under clinical evaluation. Continuing to gain an in-depth understanding of redox regulation and develop specific methods targeting redox modification holds the promise to accelerate the development of strategies to treat dormant tumors and benefit cancer patients.

Fangchinoline inhibits non-small cell lung cancer metastasis by reversing epithelial-mesenchymal transition and suppressing the cytosolic ROS-related Akt-mTOR signaling pathway

Few drugs alleviate non-small cell lung cancer (NSCLC) metastasis effectively. Small molecular screening demonstrated that fangchinoline (Fan) reversed epithelial-mesenchymal transition (EMT) in NSCLC cells, inhibiting cell invasion and migration. RNA sequencing (RNA-seq) of Fan-treated NSCLC cells revealed that Fan potently quenched the NADP⁺ metabolic process. Molecular docking analysis revealed that Fan directly and specifically targeted NOX4. NOX4 was associated with poor prognosis in NSCLC in both The Cancer Genome Atlas (TCGA) and Hong Kong cohorts. In mitochondrial DNA-depleted ρ⁰ NSCLC cells, Fan decreased cytosolic reactive oxygen species (ROS) to inhibit the Akt-mTOR signaling pathway by directly promoting NOX4 degradation. In TCGA and Hong Kong cohorts, NOX4 upregulation acted as a driver event as it positively correlated with metastasis and oxidative stress. Single-cell RNA-seq indicated that NOX4 was overexpressed, especially in cancer cells, cancer stem cells, and endothelial cells. In mice, Fan significantly impeded subcutaneous xenograft formation and reduced metastatic nodule numbers in mouse lung and liver. Drug sensitivity testing demonstrated that Fan suppressed patient-derived organoid growth dose-dependently. Fan is a potent small molecule for alleviating NSCLC metastasis by directly targeting NOX4 and is a potential novel therapeutic agent.

Psychological stress disrupts intestinal epithelial cell function and mucosal integrity through microbe and host-directed processes

Psychological stress alters the gut microbiota and predisposes individuals to increased risk for enteric infections and chronic bowel conditions. Intestinal epithelial cells (IECs) are responsible for maintaining homeostatic interactions between the gut microbiota and its host. In this study, we hypothesized that disruption to colonic IECs is a key factor underlying stress-induced disturbances to intestinal homeostasis. Conventionally raised (CONV-R) and germ-free (GF) mice were exposed to a social disruption stressor (Str) to ascertain how stress modifies colonic IECs, the mucosal layer, and the gut microbiota. RNA sequencing of IECs isolated from CONV-R mice revealed a robust pro-inflammatory (Saa1, Il18), pro-oxidative (Duox2, Nos2), and antimicrobial (Reg3b/g) transcriptional profile as a result of Str. This response occurred concomitant to mucus layer thinning and signs of microbial translocation. In contrast to their CONV-R counterparts, IECs from GF mice or mice treated with broad spectrum antibiotics exhibited no detectable transcriptional changes in response to Str. Nevertheless, IECs from Str-exposed GF mice exhibited an altered response to ex vivo bacterial challenge (increased dual Oxidase-2 [Duox2] and nitric oxide synthase-2 (Nos2)), indicating that STR primes host IEC pro-oxidative responses. In CONV-R mice stress-induced increases in colonic Duox2 and Nos2 (ROS generating enzymes) strongly paralleled changes to microbiome composition and function, evidencing Str-mediated ROS production as a primary factor mediating gut-microbiota dysbiosis. In conclusion, a mouse model of social stress disrupts colonic epithelial and mucosal integrity, a response dependent on an intact microbiota and host stress signals. Together these preclinical findings may provide new insight into mechanisms of stress-associated bowel pathologies in humans.

ROS Promote Hypoxia-Induced Keratinocyte Epithelial-Mesenchymal Transition by Inducing SOX2 Expression and Subsequent Activation of Wnt/β-Catenin

We previously showed that wound-induced hypoxia is related to keratinocyte migration. The ability of keratinocytes within wound healing to undergo epithelial to mesenchymal transition (EMT) contributes significantly to the acquisition of migratory properties. However, the effect of hypoxia on keratinocyte EMT on wound healing and the potential mechanism are poorly documented. This study first demonstrated that reactive oxygen species (ROS) appear to be an essential signalling mediator in keratinocytes with increased EMT and migration subjected to hypoxic conditions. Next, we showed that the expression of sex-determining region Y-box 2 (SOX2), a stemness-associated molecule, is ROS-dependent under hypoxia and that SOX2 inhibition in keratinocytes dramatically prevented hypoxia-induced EMT and migration. In addition, β-catenin was found to be a potential molecular target of SOX2, and the activation of Wnt/β-catenin was required for hypoxia-induced EMT and migration. Using an in vitro skin culture model and an in vivo skin wound model, our study further reinforced the critical role of ROS in inducing EMT through SOX2 expression and subsequent activation of Wnt/β-catenin, allowing for rapid reepithelialization of the wound area. Taken together, our findings reveal a previously unknown mechanism by which hypoxia promotes wound healing by promoting reepithelialization through the production of ROS, inducing keratinocyte EMT and migration via the enhancement of SOX2 and activation of Wnt/β-catenin.

Macrophages play a role in inflammatory transformation of colorectal cancer

Colorectal cancer (CRC) is one of the most common and fatal cancers worldwide, and it is also a typical inflammatory cancer. The function of macrophages is very important in the tissue immune microenvironment during inflammatory and carcinogenic transformation. Here, we evaluated the function and mechanism of macrophages in intestinal physiology and in different pathological stages. Furthermore, the role of macrophages in the immune microenvironment of CRC and the influence of the intestinal population and hypoxic environment on macrophage function are summarized. In addition, in the era of tumor immunotherapy, CRC currently has a limited response rate to immune checkpoint inhibitors, and we summarize potential therapeutic strategies for targeting tumor-associated macrophages.

Prediction of Biochemical Recurrence-Free Survival of Prostate Cancer Patients Leveraging Multiple Gene Expression Profiles in Tumor Microenvironment

Tumor-adjacent normal (TAN) tissues, which constitute tumor microenvironment and are different from healthy tissues, provide critical information at molecular levels that can be used to differentiate aggressive tumors from indolent tumors. In this study, we analyzed 52 TAN samples from the Cancer Genome Atlas (TCGA) prostate cancer patients and developed a 10-gene prognostic model that can accurately predict biochemical recurrence-free survival based on the profiles of these genes in TAN tissues. The predictive ability was validated using TAN samples from an independent cohort. These 10 prognostic genes in tumor microenvironment are different from the prognostic genes detected in tumor tissues, indicating distinct progression-related mechanisms in two tissue types. Bioinformatics analysis showed that the prognostic genes in tumor microenvironment were significantly enriched by p53 signaling pathway, which may represent the crosstalk tunnels between tumor and its microenvironment and pathways involving cell-to-cell contact and paracrine/endocrine signaling. The insight acquired by this study has advanced our knowledge of the potential role of tumor microenvironment in prostate cancer progression.

Natural Compound Shikonin Induces Apoptosis and Attenuates Epithelial to Mesenchymal Transition in Radiation-Resistant Human Colon Cancer Cells

Radiation resistance represents an imperative obstacle in the treatment of patients with colorectal cancer, which remains difficult to overcome. Here, we explored the anti-proliferative and migration-inhibiting properties of the natural product shikonin on a radiation-resistant human colon carcinoma cell line (SNU-C5RR). Shikonin reduced the viability of these cells in a dose-dependent manner; 38 μM of shikonin was determined as the half-maximal inhibitory concentration. Shikonin induced apoptotic cell death, as demonstrated by increased apoptotic body formation and the number of TUNEL-positive cells. Moreover, shikonin enhanced mitochondrial membrane depolarization and Bax expression and also decreased Bcl-2 expression with translocation of cytochrome c from mitochondria into the cytosol. In addition, shikonin activated mitogen-activated protein kinases, and their specific inhibitors reduced the cytotoxic effects of shikonin. Additionally, shikonin decreased the migration of SNU-C5RR cells via the upregulation of E-cadherin and downregulation of N-cadherin. Taken together, these results suggest that shikonin induces mitochondria-mediated apoptosis and attenuates epithelial-mesenchymal transition in SNU-C5RR cells.

Cancer chemopreventive role of fisetin: Regulation of cell signaling pathways in different cancers

It is becoming progressively more understandable that pharmaceutical targeting of drug-resistant cancers is challenging because of intra- and inter-tumor heterogeneity. Interestingly, naturally derived bioactive compounds have unique ability to modulate wide-ranging deregulated oncogenic cell signaling pathways. In this review, we have focused on the available evidence related to regulation of PI3K/AKT/mTOR, Wnt/β-catenin, NF-κB and TRAIL/TRAIL-R by fisetin in different cancers. Fisetin has also been shown to inhibit the metastatic spread of cancer cells in tumor-bearing mice. We have also summarized how fisetin regulated autophagy in different cancers. In addition, this review also covers fisetin-mediated regulation of VEGF/VEGFR, EGFR, necroptosis and Hippo pathway. Fisetin has entered into clinical trials particularly in context of COVID19-associated inflammations. Furthermore, fisetin mediated effects are also being tested in clinical trials with reference to osteoarthritis and senescence. These developments will surely pave the way for full-fledge and well-designed clinical trials of fisetin in different cancers. However, we still have to comprehensively analyze and fully unlock pharmacological potential of fisetin against different oncogenic signaling cascades and non-coding RNAs. Fisetin has remarkable potential as chemopreventive agent and future studies must converge on the identification of additional regulatory roles of fisetin for inhibition and prevention of cancers.

Epithelial-mesenchymal transition: When tumor cells meet myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous myeloid cell population characterized by protumoral functions in the tumor immune network. An increasing number of studies have focused on the biological functions of MDSCs in tumor immunity. Epithelial-mesenchymal transition (EMT) is a cellular plasticity process accompanied by a loss of epithelial phenotypes and an acquisition of mesenchymal phenotypes. In general, tumor cells that undergo EMT are more likely to invade and metastasize. Recently, extensive evidence suggests that EMT is closely related to a highly immunosuppressive environment. This review will summarize the immunosuppressive capacities of MDSC subsets and their distinct role in tumor EMT and further discuss immunotherapy for tumor EMT by targeting MDSCs.

DUOX2 promotes the progression of colorectal cancer cells by regulating the AKT pathway and interacting with RPL3

Dual oxidase 2 (DUOX2) is an important regulatory protein in the organic process of thyroid hormone iodine. Mounting evidence suggests that DUOX2 plays a crucial role in the occurrence and development of cancers. However, the function and mechanism of DUOX2 in colorectal cancer (CRC) have not been fully clarified. In the present study, the relationship between the expression of DUOX2 and the clinicopathological features and prognosis of CRC patients was analyzed. Furthermore, the effects of DUOX2 on proliferation and invasion in vitro and in vivo were examined. DUOX2-associated proteins were identified by immunoprecipitation (IP). Next-generation sequencing detection was performed to illustrate the mechanism of DUOX2 in CRC cells. It was found that the expression levels of DUOX2 in metastatic sites were significantly higher than those in primary tumor tissues, and this was demonstrated to be associated with poor prognosis. The knockdown of DUOX2 inhibited the invasion and migration of CRC cells. Furthermore, DUOX2 regulated the stability of ribosomal protein uL3 (RPL3) by affecting the ubiquitination status of RPL3, and the invasion and migration ability of DUOX2 can be reversed by the overexpression of RPL3. The downregulation of DUOX2 can affect the expression level of a large number of genes, and a number of these are enriched in the PI3K-AKT pathway. Some of the changes caused by DUOX2 can be reversed by RPL3. In summary, DUOX2 exhibits a significantly higher expression in CRC tumor samples, and facilitates the invasion and metastasis ability of CRC cells by interacting with RPL3.

Re-expression of REG family and DUOXs genes in CRC organoids by co-culturing with CAFs

Organoids derived from epithelial tumors have recently been utilized as a preclinical model in basic and translational studies. This model is considered to represent the original tumor in terms of 3D structure, genetic and cellular heterogeneity, but not tumor microenvironment. In this study, we established organoids and paired cancer-associated fibroblasts (CAFs) from surgical specimens of colorectal carcinomas (CRCs), and evaluated gene expression profiles in organoids with and without co-culture with CAFs to assess interactions between tumor cells and CAFs in tumor tissues. We found that the expression levels of several genes, which are highly expressed in original CRC tissues, were downregulated in organoids but re-expressed in organoids by co-culturing with CAFs. They comprised immune response- and external stimulus-related genes, e.g., REG family and dual oxidases (DUOXs), which are known to have malignant functions, leading tumor cells to proliferative and/or anti-apoptotic states and drug resistant phenotypes. In addition, the degree of differential induction of REG1 and DUOX2 in the co-culture system varied depending on CAFs from each CRC case. In conclusion, the co-culture system of CRC organoids with paired CAFs was able to partially reproduce the tumor microenvironment.

A truncated protein product of the germline variant of the DUOX2 gene leads to adenomatous polyposis

Objective:

In some patients with adenomatous polyposis, an identifiable pathogenic variant of known associated genes cannot be found. Researchers have studied this for decades; however, few new genes have been identified.

Methods:

Adenomatous polyposis coli (APC) negative polyposis patients were identified through next-generation sequencing and multiplex ligation-dependent probe amplification. Then, whole-exome sequencing (WES) was used to determine candidate genes harboring pathogenic variants. Functional experiments were performed to explore their effects. Subsequently, using Sanger sequencing, we found other polyposis patients carrying variants of the DUOX2 gene, encoding dual oxidase 2, and analyzed them.

Results:

From 88 patients with suspected familial adenomatous polyposis, 25 unrelated APC negative polyposis patients were identified. Based on the WES results of 3 patients and 2 healthy relatives from a family, the germline nonsense variant (c.1588A>T; p.K530X) of the DUOX2 gene was speculated to play a decisive role in the pedigree in relation to adenomatous polyposis. During functional experiments, we observed that the truncated protein, hDuox2 K530, was overexpressed in the adenoma in a carrier of the DUOX2 nonsense variant, causing abnormal cell proliferation through endoplasmic reticulum (ER) retention. In addition, we found two unrelated APC negative patients carrying DUOX2 missense variants (c.3329G>A, p.R1110Q; c.4027C>T, p.L1343F). Given the results of the in silico analysis, these two missense variants might exert a negative influence on the function of hDuox2.

Conclusions:

To our knowledge, this is the first study that reports the possible association of DUOX2 germline variants with adenomatous polyposis. With an autosomal dominant inheritance, it causes ER retention, inducing an unfolded protein response.

L-fucose ameliorates the carcinogenic properties of Fusobacterium nucleatum in colorectal cancer

Fusobacterium nucleatum (Fn) is considered a promoting factor in colorectal cancer (CRC); however, only a few studies have investigated therapies against Fn. L-fucose is a natural monosaccharide that has prebiotic potential. The present study aimed to investigate the effect of L-fucose on the carcinogenic properties of Fn. The HCT116 and SW480 colon cancer cell lines were treated with Fn and Fn+L-fucose (Fnf), respectively. The Cell Counting Kit-8 (CCK-8), colony formation, Transwell migration and invasion and wound healing assays were performed to assess the proliferative, migratory and invasive abilities of the cells, respectively. Western blot was performed to detect the protein levels of jak/stat3 pathway components and EMT. The results of the CCK-8, colony formation, Transwell and wound healing assays demonstrated that treatment with Fn significantly enhanced the proliferative, migratory and invasive abilities of HCT116 and SW480 colon cancer cells. Notably, these effects were significantly reversed following addition of L-fucose. Furthermore, L-fucose inhibited the carcinogenic properties of Fn to activate the stat3 pathway and epithelial-to-mesenchymal transition. Taken together, the results of the present study suggest that L-fucose ameliorates the carcinogenic properties of Fn in vitro, and thus may serve as a novel therapeutic target for flora-related colon cancer.

DUOX2 participates in skin aging induced by UVB in HSF2 cells by activating NF-κB signaling

Skin and in particular photoaging or premature aging, are caused by a variety of factors, including hormone imbalance and exposure to ultraviolet radiation. The aim of the present study was to explore the roles of Dual oxidase 2 (DUOX2) and related NF-κB signals in skin photoaging. Cell models of photoaging were constructed by irradiating human skin fibroblast lines (HSF2) with ultraviolet B (UVB) of different doses (0, 15, 30 and 60 mj/cm²). The cell counting kit-8 (CCK8) was used to determine cell proliferation. Flow cytometry was used to determine the production of reactive oxygen species (ROS). A biochemical method was to determine the content of hydrogen peroxide, and the quantitative PCR (qPCR) was used to determine the expression of matrix metalloproteinase 2 (MMP2), matrix metalloproteinase 9 (MMP9), Col-Ⅰ and α-SMA in the cells. Enzyme-linked immunosorbent assay (ELISA) was used to determine the expression of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Western blot analysis was performed to determine the expression of DUOX2, p65 and p-p65. The results showed that,UVB irradiation dose- and time-dependently inhibited the proliferation of HSF2 cells. Cellular inflammatory response, ROS production and hydrogen peroxide increase was promoted. Col-Ⅰ and α-SMA were downregulated, MMP2 and MMP9 were upregulated, and the phosphorylation of NF-κB p65 was promoted. The above indicators were all reversed by interference with DUOX2. Overexpression of DUOX2 has an effect that is similar to UVB irradiation, but the effects can be significantly weakened by NF-κB inhibitor, NAC. Upregulation of DUOX2 expression plays a crucial role in UVB-induced aging of HSF2 cells. The specific mechanism is related to the promotion of ROS production and cellular inflammatory response and activation of NF-κB signals.

The Role of Oxidative Stress and Its Counteractive Utility in Colorectal Cancer (CRC)

An altered redox status accompanied by an elevated generation of reactive oxygen/nitrogen species (ROS/RNS) has been implicated in a number of diseases including colorectal cancer (CRC). CRC, being one of the most common cancers worldwide, has been reported to be associated with multiple environmental and lifestyle factors (e.g., dietary habits, obesity, and physical inactivity) and harboring heightened oxidative stress that results in genomic instability. Although under normal condition ROS regulate many signal transduction pathways including cell proliferation and survival, overwhelming of the antioxidant capacity due to metabolic abnormalities and oncogenic signaling leads to a redox adaptation response that imparts drug resistance. Nevertheless, excessive reliance on elevated production of ROS makes the tumor cells increasingly vulnerable to further ROS insults, and the abolition of such drug resistance through redox perturbation could be instrumental to preferentially eliminate them. The goal of this review is to demonstrate the evidence that links redox stress to the development of CRC and assimilate the most up-to-date information that would facilitate future investigation on CRC-associated redox biology. Concomitantly, we argue that the exploitation of this distinct biochemical property of CRC cells might offer a fresh avenue to effectively eradicate these cells.

Malic enzyme 1 (ME1) in the biology of cancer: it is not just intermediary metabolism

Malic enzyme 1 (ME1) is a cytosolic protein that catalyzes the conversion of malate to pyruvate while concomitantly generating NADPH from NADP. Early studies identified ME1 as a mediator of intermediary metabolism primarily through its participatory roles in lipid and cholesterol biosynthesis. ME1 was one of the first identified insulin-regulated genes in liver and adipose and is a transcriptional target of thyroxine. Multiple studies have since documented that ME1 is pro-oncogenic in numerous epithelial cancers. In tumor cells, the reduction of ME1 gene expression or the inhibition of its activity resulted in decreases in proliferation, epithelial-to-mesenchymal transition and in vitro migration, and conversely, in promotion of oxidative stress, apoptosis and/or cellular senescence. Here, we integrate recent findings to highlight ME1's role in oncogenesis, provide a rationale for its nexus with metabolic syndrome and diabetes, and raise the prospects of targeting the cytosolic NADPH network to improve therapeutic approaches against multiple cancers.

Emerging role of NRF2 in ROS-mediated tumor chemoresistance

Chemoresistance is a central cause for the tumor management failure. Cancer cells disrupt the redox homeostasis through reactive oxygen species (ROS) regulatory mechanisms, leading to tumor progression and chemoresistance. The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of neutralizing cellular ROS and restoring redox balance. Understanding the role of NRF2 in ROS-mediated chemoresistance can be helpful in the development of chemotherapy strategies with better efficiency. In this review, we sum up the roles of ROS in the development of chemoresistance to classical chemotherapy agents including cisplatin, 5-fluorouracil, gemcitabine, oxaliplatin, paclitaxel, and doxorubicin, and how to overcome ROS-mediated tumor chemoresistance by targeting NRF2. Finally, we propose that targeting NRF2 might be a promising strategy to resist ROS-driven chemoresistance and acquire better efficacy in cancer treatment.

PERK controls bone homeostasis through the regulation of osteoclast differentiation and function

Osteoclasts are multinucleated giant cells with the ability to degrade bone tissue, and are closely related to abnormal bone metabolic diseases. Endoplasmic reticulum (ER) is an organelle responsible for protein modification, quality control, and transportation. The accumulation of unfolded or misfolded proteins in ER cavity induces ER stress. Double-stranded RNA-dependent protein kinase-like ER kinase (PERK) is an ER stress-sensing protein, which is ubiquitous in eukaryotic cells. Systemic PERK knockout mice show severe bone loss, suggesting that PERK is of great significance for maintaining the normal growth and development of bone tissue, but the role of PERK in osteoclastogenesis is still unclear. In this study, we found that PERK was significantly activated during RANKL-induced osteoclast differentiation; knockdown of PERK by siRNA and inhibition of PERK by GSK2606414, respectively, had significant negative regulatory effects on the formation and bone resorption of osteoclasts. PERK inhibitor GSK2606414 down-regulated the mRNA levels and protein expression of osteoclast differentiation marker genes, and inhibited RANKL-induced activation of Mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways. Treatment with PERK inhibitor GSK2606414 in ovariectomized mouse model significantly suppressed bone loss and osteoclast formation. Thapsigargin activated ER stress to enhance autophagy, while GSK2606414 had a significant inhibitory effect on autophagy flux and autophagosome formation. Antioxidant N-acetylcysteine (NAC) could inhibit the expression of PERK phosphorylation, osteoclast-related proteins and autophagy-related proteins, but the use of PERK activator CCT020312 can reverse inhibition effect of NAC. Our findings demonstrate a key role for PERK in osteoclast differentiation and suggest its therapeutic potential.

GDF15 Repression Contributes to 5-Fluorouracil Resistance in Human Colon Cancer by Regulating Epithelial-Mesenchymal Transition and Apoptosis

Chemotherapy based on 5-fluorouracil (5-FU) is the standard approach for colon cancer treatment, and resistance to 5-FU is a significant obstacle in the clinical treatment of colon cancer. However, the mechanisms underlying 5-FU resistance in colon cancer cells remain largely unknown. This study aimed at determining whether 5-FU-resistant colon cancer cells undergo epithelial-mesenchymal transition (EMT) and apoptosis and the role of GDF15—a member of the transforming growth factor β/bone morphogenetic protein super family and a protein known to be involved in cancer progression—in the regulation of EMT and apoptosis of these cells, along with the underlying mechanisms. In vitro apoptosis detection assay, growth inhibition assay, transwell, and wound healing experiments revealed that 5-FU-resistant colon cancer cells possessed enhanced EMT and antiapoptotic ability. These cells also showed a stronger tendency to proliferate and metastasize in vivo. Quantitative reverse transcription-PCR and western blotting revealed that 5-FU-resistant colon cancer cells expressed lower levels of growth differentiation factor 15 (GDF15) than did 5-FU-sensitive colon cancer cells. Moreover, the transient GDF15 overexpression resensitized 5-FU-resistant colon cells to 5-FU. Collectively, these findings indicate the mechanism underlying the 5-FU resistance of colon cancer cells and provide new therapeutic targets for improving the prognosis of colon cancer patients.

Inhibiting the Activity of NADPH Oxidase in Cancer

Significance: The primary function of NADPH oxidases (NOX1-5 and dual oxidases DUOX1/2) is to produce reactive oxygen species (ROS). If inadequately regulated, NOX-associated ROS can promote oxidative stress, aberrant signaling, and genomic instability. Correspondingly, NOX isoforms are known to be overexpressed in multiple malignancies, thus constituting potential therapeutic targets in cancer. Recent Advances: Multiple genetic studies aimed at suppressing the expression of NOX proteins in cellular and animal models of cancer have provided support for the notion that NOXs play a pro-tumorigenic role. Further, large drug screens and rational design efforts have yielded inhibitor compounds, such as the diphenylene iodonium (DPI) analog series developed by our group, with increased selectivity and potency over "first generation" NOX inhibitors such as apocynin and DPI. Critical Issues: The precise role of NOX enzymes in tumor biology remains poorly defined. The tumorigenic properties of NOXs vary with cancer type, and precise tools, such as selective inhibitors, are needed to deconvolute NOX contribution to cancer development. Most NOX inhibitors developed to date are unspecific, and/or their mechanistic and pharmacological characteristics are not well defined. A lack of high-resolution crystal structures for NOX functional domains has hindered the development of potent and selective inhibitors. Future Directions: In-depth studies of NOX interactions with the tumor microenvironment (e.g., cytokines, cell-surface antigens) will help identify new approaches for NOX inhibition in cancer.

New CXCR4 Antagonist Peptide R (Pep R) Improves Standard Therapy in Colorectal Cancer

The chemokine receptor CXCR4 is overexpressed and functional in colorectal cancer. To investigate the role of CXCR4 antagonism in potentiating colon cancer standard therapy, the new peptide CXCR4 antagonist Peptide R (Pep R) was employed. Human colon cancer HCT116 xenograft-bearing mice were treated with chemotherapeutic agents (CT) 5-Fluorouracil (5FU) and oxaliplatin (OX) or 5FU and radio chemotherapy (RT-CT) in the presence of Pep R. After two weeks, CT plus Pep R reduced by 4-fold the relative tumor volume (RTV) as compared to 2- and 1.6-fold reductions induced, respectively, by CT and Pep R. In vitro Pep R addition to CT/RT-CT impaired HCT116 cell growth and further reduced HCT116 and HT29 clonal capability. Thus, the hypothesis that Pep R could target the epithelial mesenchyme transition (EMT) process was evaluated. While CT decreased ECAD and increased ZEB-1 and CD90 expression, the addition of Pep R restored the pretreatment expression. In HCT116 and HT29 cells, CT/RT-CT induced a population of CD133+CXCR4+ cells, supposedly a stem-resistant cancer cell population, while Pep R reduced it. Taken together, the results showed that targeting CXCR4 ameliorates the effect of treatment in colon cancer through inhibition of cell growth and reversal of EMT treatment-induced markers, supporting further clinical studies.

The role of dual oxidases in physiology and cancer

NOX/DUOX enzymes are transmembrane proteins that carry electrons through biological membranes generating reactive oxygen species. The NOX family is composed of seven members, which are NOX1 to NOX5 and DUOX1 and 2. DUOX enzymes were initially called thyroid oxidases, based on their high expression level in the thyroid tissue. However, DUOX expression has been documented in several extrathyroid tissues, mostly at the apical membrane of the salivary glands, the airways, and the intestinal tract, revealing additional cellular functions associated with DUOX-related H2O2 generation. In this review, we will briefly summarize the current knowledge regarding DUOX structure and physiological functions, as well as their possible role in cancer biology.

Redox Imbalance in Idiopathic Pulmonary Fibrosis: A Role for Oxidant Cross-Talk Between NADPH Oxidase Enzymes and Mitochondria

Significance: Idiopathic pulmonary fibrosis (IPF) is a progressive age-related lung disease with a median survival of only 3 years after diagnosis. The pathogenic mechanisms behind IPF are not clearly understood, and current therapeutic approaches have not been successful in improving disease outcomes. Recent Advances: IPF is characterized by increased production of reactive oxygen species (ROS), primarily by NADPH oxidases (NOXes) and mitochondria, as well as altered antioxidant defenses. Recent studies have identified the NOX isoform NOX4 as a key player in various important aspects of IPF pathology. In addition, mitochondrial dysfunction is thought to enhance pathological features of IPF, in part by increasing mitochondrial ROS (mtROS) production and altering cellular metabolism. Recent findings indicate reciprocal interactions between NOX enzymes and mitochondria, which affect regulation of NOX activity as well as mitochondrial function and mtROS production, and collectively promote epithelial injury and profibrotic signaling. Critical Issues and Future Directions: The precise molecular mechanisms by which ROS from NOX or mitochondria contribute to IPF pathology are not known. This review summarizes the current knowledge with respect to the various aspects of ROS imbalance in the context of IPF and its proposed roles in disease development, with specific emphasis on the importance of inappropriate NOX activation, mitochondrial dysfunction, and the emerging evidence of NOX-mitochondria cross-talk as important drivers in IPF pathobiology.

The Yin-Yang Regulation of Reactive Oxygen Species and MicroRNAs in Cancer

Reactive oxygen species (ROS) are highly reactive oxygen-containing chemical species formed as a by-product of normal aerobic respiration and also from a number of other cellular enzymatic reactions. ROS function as key mediators of cellular signaling pathways involved in proliferation, survival, apoptosis, and immune response. However, elevated and sustained ROS production promotes tumor initiation by inducing DNA damage or mutation and activates oncogenic signaling pathways to promote cancer progression. Recent studies have shown that ROS can facilitate carcinogenesis by controlling microRNA (miRNA) expression through regulating miRNA biogenesis, transcription, and epigenetic modifications. Likewise, miRNAs have been shown to control cellular ROS homeostasis by regulating the expression of proteins involved in ROS production and elimination. In this review, we summarized the significance of ROS in cancer initiation, progression, and the regulatory crosstalk between ROS and miRNAs in cancer.

Redox-Mediated Mechanism of Chemoresistance in Cancer Cells

Cellular reactive oxygen species (ROS) status is stabilized by a balance of ROS generation and elimination called redox homeostasis. ROS is increased by activation of endoplasmic reticulum stress, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family members and adenosine triphosphate (ATP) synthesis of mitochondria. Increased ROS is detoxified by superoxide dismutase, catalase, and peroxiredoxins. ROS has a role as a secondary messenger in signal transduction. Cancer cells induce fluctuations of redox homeostasis by variation of ROS regulated machinery, leading to increased tumorigenesis and chemoresistance. Redox-mediated mechanisms of chemoresistance include endoplasmic reticulum stress-mediated autophagy, increased cell cycle progression, and increased conversion to metastasis or cancer stem-like cells. This review discusses changes of the redox state in tumorigenesis and redox-mediated mechanisms involved in tolerance to chemotherapeutic drugs in cancer.

Hydrogen peroxide-producing NADPH oxidases and the promotion of migratory phenotypes in cancer

The cellular microenvironment plays a critical role in cancer initiation and progression. Exposure to oxidative stress, specifically hydrogen peroxide (H₂O₂), has been linked to aberrant cellular signaling through which the development of cancer may be promoted. Three members of the NADPH oxidase family (NOX4, DUOX1 and DUOX2) explicitly generate this non-radical oxidant in a wide range of tissues, often in support of the inflammatory response. This review summarizes the contributions of each H₂O₂-producing NOX to the invasive behaviors of tumors and/or the epithelial-mesenchymal transition (EMT) in cancer that plays an essential role in metastasis. Tissue localization in tumorigenesis is also highlighted, with patient-derived TCGA microarray data profiled across 31 cancer cohorts to provide a comprehensive guide to the relevance of NOX4/DUOX1/DUOX2 in cancer studies.

Reactive oxygen species induce epithelial‑mesenchymal transition, glycolytic switch, and mitochondrial repression through the Dlx‑2/Snail signaling pathways in MCF‑7 cells

Reactive oxygen species (ROS) are important cellular second messengers involved in various aspects of cell signaling. ROS are elevated in multiple types of cancer cells, and this elevation is known to be involved in pathological processes of cancer. Although high levels of ROS exert cytotoxic effects on cancer cells, low levels of ROS stimulate cell proliferation and survival by inducing several pro‑survival signaling pathways. In addition, ROS have been shown to induce epithelial‑mesenchymal transition (EMT), which is essential for the initiation of metastasis. However, the precise mechanism of ROS‑induced EMT remains to be elucidated. In the present study, it was indicated that ROS induce EMT by activating Snail expression, which then represses E‑cadherin expression in MCF‑7 cells. It was further indicated that distal‑less homeobox‑2 (Dlx‑2), one of the human Dlx gene family proteins involved in embryonic development, acts as an upstream regulator of ROS‑induced Snail expression. It was also revealed that ROS treatment induces the glycolytic switch, a phenomenon whereby cancer cells primarily rely on glycolysis instead of mitochondrial oxidative phosphorylation for ATP production, even in the presence of oxygen. In addition, ROS inhibited oxidative phosphorylation and caused cytochrome c oxidase inhibition via the Dlx‑2/Snail cascade. These results suggest that ROS induce EMT, the glycolytic switch and mitochondrial repression by activating the Dlx‑2/Snail axis, thereby playing crucial roles in MCF‑7 cancer cell progression.

Targeting the cell signaling pathway Keap1-Nrf2 as a therapeutic strategy for adenocarcinomas of the lung

INTRODUCTION

Kelch-like ECH associated protein 1/Nuclear factor erythroid 2-like factor 2 (Keap1-Nrf2) signaling plays a pivotal role in response to oxidative stress in lung cancer. Mutations in KEAP1/NFE2L2 genes always cause persistent Nrf2 activation in lung cancer cells that confer therapeutic resistance and aggressive tumorigenic activity, dictating either poor prognosis or short duration of response to chemotherapy in clinical observations. Areas covered: We provide a review of the mechanisms underlying the regulation of Keap1-Nrf2 at different stages, including genetic mutations, epigenetic modifications, translational/post-translational alterations, and protein-protein interactions. Based on the current knowledge, we discuss the possibilities of intervening Keap1-Nrf2 in lung adenocarcinoma as a therapeutic target. Expert opinion: It is prevalently conceived that Keap1-Nrf2 signaling plays different roles at diverse stages of cancer. Although various Nrf2 or Keap1 inhibitors have been reported during the last decades, none of these inhibitors are currently under clinical studies or in clinical applications, suggesting that sole inhibition of Nrf2 might not be sufficient to suppress tumor growth. On the basis of current studies, we suggest that the rational combination of Nrf2 suppression with chemical agents which cause enhanced oxidative imbalance or abnormal metabolism would be promising in the treatment of lung adenocarcinoma.

Targeting ROR1 inhibits epithelial to mesenchymal transition in human lung adenocarcinoma via mTOR signaling pathway

The receptor tyrosine kinase-like orphan receptor 1 (ROR1) is a type I surface transmembrane protein that contributes to progression of tumor-cell growth and metastasis. We and others have shown that the roles of ROR1 include inhibiting apoptosis, potentiating EGFR signaling, and inducing proliferation in lung cancer, but the roles and mechanisms of ROR1 in lung adenocarcinoma metastasis have not been elucidated. Here we chose four lung adenocarcinoma cell lines, PC9 (erlotinib-sensitive), PC9erlo (acquired erlotinib-resistant), NCI-H358 (partial erlotinib-resistant), and NCI-H1975 (erlotinib-resistant) as cell models to simulate the clinical situation. We found that ROR1 prompted epithelial to mesenchymal transition (EMT) by increasing the expression level of a key epithelial gene, E-cadherin, while decreasing the expression level of the key mesenchymal gene vimentin. Silencing ROR1 by siRNA significantly reduced the migration and invasion of lung adenocarcinoma cells in vitro and also significantly inhibited the phosphorylation of Akt (Ser473), mTOR (Ser2448), Raptor (Ser792) and p70S6K (Thr389) in all four cell lines. This strongly supports our proposal that ROR1 may play a central role in tumor progression and metastasis in lung adenocarcinoma through mTOR signaling, regardless of its EGFR-TKI sensitivity status.