Opposing effects of TIGAR- and RAC1-derived ROS on Wnt-driven proliferation in the mouse intestine

Unresolved questions in the regulation of skeletal muscle insulin action by reactive oxygen species

Reactive oxygen species (ROS) are well-established signaling molecules implicated in a wide range of cellular processes, including both oxidative stress and intracellular redox signaling. In the context of insulin action within its target tissues, ROS have been reported to exert both positive and negative regulatory effects. However, the precise molecular mechanisms underlying this duality remain unclear. This Review examines the complex role of ROS in insulin action, with a particular focus on skeletal muscle. We aim to address three critical aspects: (a) the proposed intracellular pro-oxidative redox shift elicited by insulin, (b) the evidence supporting that redox-sensitive cysteine modifications impact insulin signaling and action, and (c) cellular mechanisms underlying how ROS can paradoxically act as both enhancers and inhibitors of insulin action. This Review underscores the urgent need for more systematic research to identify specific reactive species, redox targets, and the physiological significance of redox signaling in maintaining insulin action and metabolic health, with a particular emphasis on human skeletal muscle.

The potential of aryl hydrocarbon receptor as receptors for metabolic changes in tumors

Cancer cells can alter their metabolism to meet energy and molecular requirements due to unfavorable environments with oxygen and nutritional deficiencies. Therefore, metabolic reprogramming is common in a tumor microenvironment (TME). Aryl hydrocarbon receptor (AhR) is a ligand-activated nuclear transcription factor, which can be activated by many exogenous and endogenous ligands. Multiple AhR ligands can be produced by both TME and tumor cells. By attaching to various ligands, AhR regulates cancer metabolic reprogramming by dysregulating various metabolic pathways, including glycolysis, lipid metabolism, and nucleotide metabolism. These regulated pathways greatly contribute to cancer cell growth, metastasis, and evading cancer therapies; however, the underlying mechanisms remain unclear. Herein, we review the relationship between TME and metabolism and describe the important role of AhR in cancer regulation. We also focus on recent findings to discuss the idea that AhR acts as a receptor for metabolic changes in tumors, which may provide new perspectives on the direction of AhR research in tumor metabolic reprogramming and future therapeutic interventions.

WDR12/RAC1 axis promoted proliferation and anti-apoptosis in colorectal cancer cells

BACKGROUND

WD repeat domain 12 (WDR12) plays a crucial role in the ribosome biogenesis pathway. However, its biological function in colorectal cancer (CRC) remains poorly understood. Therefore, this study aims to investigate the roles of WDR12 in the occurrence and progression of CRC, as well as its underlying mechanisms.

METHODS

The expression of WDR12 was assessed through The Cancer Genome Atlas (TCGA) and the Human Protein Atlas (HPA) database. Functional experiments including Celigo assay, MTT assay, and Caspase-3/7 assay were conducted to validate the role of WDR12 in the malignant progression of CRC. Additionally, mRNA chip-sequencing and ingenuity pathway analysis (IPA) were performed to identify the molecular mechanism.

RESULTS

WDR12 expression was significantly upregulated in CRC tissues compared to normal colorectal tissues. Knockdown of WDR12 reduced proliferation and promoted apoptosis of CRC cell lines in vitro and in vivo experiments. Furthermore, WDR12 expression had a significantly inverse association with diseases and functions, including cancer, cell cycle, DNA replication, recombination, cellular growth, proliferation and repair, as revealed by IPA analysis of mRNA chip-sequencing data. Moreover, the activation of cell cycle checkpoint kinases proteins in the cell cycle checkpoint control signaling pathway was enriched in the WDR12 knockdown CRC cell lines. Additionally, downregulation of rac family small GTPase 1 (RAC1) occurred upon WDR12 knockdown, thereby facilitating the proliferation and anti-apoptosis of CRC cells.

CONCLUSION

Our study demonstrates that the WDR12/RAC1 axis promotes tumor progression in CRC. Therefore, WDR12 may serve as a novel oncogene and a potential target for individualized therapy in CRC. These findings provide an experimental foundation for the clinical development of drugs targeting the WDR12/RAC1 axis.

Reactive oxygen species in colorectal cancer adjuvant therapies

Colorectal cancer (CRC), a prevalent global malignancy, often necessitates adjuvant therapies such as chemotherapy, radiotherapy, targeted therapy, and immunotherapy to mitigate tumor burden in advanced stages. The efficacy of these therapies is significantly influenced by reactive oxygen species (ROS). Previous research underscores the pivotal role of ROS in gut pathology, targeted therapy, and drug resistance. ROS-mediated CRC adjuvant therapies encompass a myriad of mechanisms, including cell death and proliferation, survival and cell cycle, DNA damage, metabolic reprogramming, and angiogenesis. Preliminary clinical trials have begun to unveil the potential of ROS-manipulating therapy in enhancing CRC adjuvant therapies. This review aims to provide a comprehensive synthesis of studies exploring the role of ROS in CRC adjuvant therapies.

Tigecycline causes loss of cell viability mediated by mitochondrial OXPHOS and RAC1 in hepatocellular carcinoma cells

BACKGROUND

Despite recent advances in locoregional, systemic, and novel checkpoint inhibitor treatment, hepatocellular carcinoma (HCC) is still associated with poor prognosis. The feasibility of potentially curative liver resection (LR) and transplantation (LT) is limited by the underlying liver disease and a shortage of organ donors. Especially after LR, high recurrence rates present a problem and circulating tumor cells are a major cause of extrahepatic recurrence. Tigecycline, a commonly used glycylcycline antibiotic, has been shown to have antitumorigenic effects and could be used as a perioperative and adjuvant therapeutic strategy to target circulating tumor cells. We aimed to investigate the effect of tigecycline on HCC cell lines and its mechanisms of action.

METHODS

Huh7, HepG2, Hep3B, and immortalized hepatocytes underwent incubation with clinically relevant tigecycline concentrations, and the influence on proliferation, migration, and invasion was assessed in two- and three-dimensional in vitro assays, respectively. Bioinformatic analysis was used to identify specific targets of tigecycline. The expression of RAC1 was detected using western blot, RT-PCR and RNA sequencing. ELISA and flow cytometry were utilized to measure reactive oxygen species (ROS) generation upon tigecycline treatment and flow cytometry to detect alterations in cell cycle. Changes in mitochondrial function were detected via seahorse analysis. RNA sequencing was performed to examine involved pathways.

RESULTS

Tigecycline treatment resulted in a significant reduction of mitochondrial function with concomitantly preserved mitochondrial size, which preceded the observed decrease in HCC cell viability. The sensitivity of HCC cells to tigecycline treatment was higher than that of immortalized non-cancerous THLE-2 hepatocytes. Tigecycline inhibited both migratory and invasive properties. Tigecycline application led to an increase of detected ROS and an S-phase cell cycle arrest. Bioinformatic analysis identified RAC1 as a likely target for tigecycline and the expression of this molecule was increased in HCC cells as a result of tigecycline treatment.

CONCLUSION

Our study provides evidence for the antiproliferative effect of tigecycline in HCC. We show for the first time that this effect, likely to be mediated by reduced mitochondrial function, is associated with increased expression of RAC1. The reported effects of tigecycline with clinically relevant and achievable doses on HCC cells lay the groundwork for a conceivable use of this agent in cancer treatment.

Maternal obesity: A potential disruptor of female fertility and current interventions to reduce associated risks

Currently, obesity has achieved epidemic levels in reproductive-aged women with a myriad of consequences. Obesity is susceptible to several reproductive complications that eventually affect fertility rates. These complications originate from the deteriorated quality of oocytes from mothers with obesity, which increases the probability of chromosomal aneuploidy, elevated reactive oxygen species production, compromised embryonic developmental competency, and eventually reduced fertility. Maternal obesity is linked to pregnancy complications such as implantation error, abortion, miscarriage, and early pregnancy loss. This review highlights the adverse effects of maternal obesity on female fertility, with a focus on the mechanistic link between maternal obesity and oocyte quality and discusses possible measures to reduce its associated risks.

Oxygen-consumption based quantification of chemogenetic H2O2 production in live human cells

Reactive Oxygen Species (ROS) in the form of H2O2 can act both as physiological signaling molecules as well as damaging agents, depending on their concentration and localization. The downstream biological effects of H2O2 were often studied making use of exogenously added H2O2, generally as a bolus and at supraphysiological levels. But this does not mimic the continuous, low levels of intracellular H2O2 production by for instance mitochondrial respiration. The enzyme d-Amino Acid Oxidase (DAAO) catalyzes H2O2 formation using d-amino acids, which are absent from culture media, as a substrate. Ectopic expression of DAAO has recently been used in several studies to produce inducible and titratable intracellular H2O2. However, a method to directly quantify the amount of H2O2 produced by DAAO has been lacking, making it difficult to assess whether observed phenotypes are the result of physiological or artificially high levels of H2O2. Here we describe a simple assay to directly quantify DAAO activity by measuring the oxygen consumed during H2O2 production. The oxygen consumption rate (OCR) of DAAO can directly be compared to the basal mitochondrial respiration in the same assay, to estimate whether the ensuing level of H2O2 production is within the range of physiological mitochondrial ROS production. In the tested monoclonal RPE1-hTERT cells, addition of 5 mM d-Ala to the culture media amounts to a DAAO-dependent OCR that surpasses ∼5% of the OCR that stems from basal mitochondrial respiration and hence produces supra-physiological levels of H2O2. We show that the assay can also be used to select clones that express differentially localized DAAO with the same absolute level of H2O2 production to be able to discriminate the effects of H2O2 production at different subcellular locations from differences in total oxidative burden. This method therefore greatly improves the interpretation and applicability of DAAO-based models, thereby moving the redox biology field forward.

Multifaceted role of redox pattern in the tumor immune microenvironment regarding autophagy and apoptosis

The reversible oxidation-reduction homeostasis mechanism functions as a specific signal transduction system, eliciting related physiological responses. Disruptions to redox homeostasis can have negative consequences, including the potential for cancer development and progression, which are closely linked to a series of redox processes, such as adjustment of reactive oxygen species (ROS) levels and species, changes in antioxidant capacity, and differential effects of ROS on downstream cell fate and immune capacity. The tumor microenvironment (TME) exhibits a complex interplay between immunity and regulatory cell death, especially autophagy and apoptosis, which is crucially regulated by ROS. The present study aims to investigate the mechanism by which multi-source ROS affects apoptosis, autophagy, and the anti-tumor immune response in the TME and the mutual crosstalk between these three processes. Given the intricate role of ROS in controlling cell fate and immunity, we will further examine the relationship between traditional cancer therapy and ROS. It is worth noting that we will discuss some potential ROS-related treatment options for further future studies.

Activation of p53-regulated pro-survival signals and hypoxia-independent mitochondrial targeting of TIGAR by human papillomavirus E6 oncoproteins

The high-risk subtype human papillomaviruses (hrHPVs) infect and oncogenically transform basal epidermal stem cells associated with the development of squamous-cell epithelial cancers. The viral E6 oncoprotein destabilizes the p53 tumor suppressor, inhibits p53 K120-acetylation by the Tat-interacting protein of 60 kDa (TIP60, or Kat5), and prevents p53-dependent apoptosis. Intriguingly, the p53 gene is infrequently mutated in HPV + cervical cancer clinical isolates which suggests a possible paradoxical role for this gatekeeper in viral carcinogenesis. Here, we demonstrate that E6 activates the TP53-induced glycolysis and apoptosis regulator (TIGAR) and protects cells against oncogene-induced oxidative genotoxicity. The E6 oncoprotein induces a Warburg-like stress response and activates PI3K/PI5P4K/AKT-signaling that phosphorylates the TIGAR on serine residues and induces its hypoxia-independent mitochondrial targeting in hrHPV-transformed cells. Primary HPV + cervical cancer tissues contain high levels of TIGAR, p53, and c-Myc and our xenograft studies have further shown that lentiviral-siRNA-knockdown of TIGAR expression inhibits hrHPV-induced tumorigenesis in vivo. These findings suggest the modulation of p53 pro-survival signals and the antioxidant functions of TIGAR could have key ancillary roles during HPV carcinogenesis.

NADPH-dependent ROS accumulation contributes to the impaired osteogenic differentiation of periodontal ligament stem cells under high glucose conditions

Diabetes mellitus is an established risk factor for periodontal disease that can aggravate the severity of periodontal inflammation and accelerate periodontal destruction. The chronic high glucose condition is a hallmark of diabetes-related pathogenesis, and has been demonstrated to impair the osteogenic differentiation of periodontal ligament stem cells (PDLSCs), leading to delayed recovery of periodontal defects in diabetic patients. Reactive oxygen species (ROS) are small molecules that can influence cell fate determination and the direction of cell differentiation. Although excessive accumulation of ROS has been found to be associated with high glucose-induced cell damage, the underlying mechanisms remain unclear. Nicotinamide adenine dinucleotide phosphate (NADPH) is an important electron donor and functions as a critical ROS scavenger in antioxidant systems. It has been identified as a key mediator of various biological processes, including energy metabolism and cell differentiation. However, whether NADPH is involved in the dysregulation of ROS and further compromise of PDLSC osteogenic differentiation under high glucose conditions is still not known. In the present study, we found that PDLSCs incubated under high glucose conditions showed impaired osteogenic differentiation, excessive ROS accumulation and increased NADPH production. Furthermore, after inhibiting the synthesis of NADPH, the osteogenic differentiation of PDLSCs was significantly enhanced, accompanied by reduced cellular ROS accumulation. Our findings demonstrated the crucial role of NADPH in regulating cellular osteogenic differentiation under high glucose conditions and suggested a new target for rescuing high glucose-induced cell dysfunction and promoting tissue regeneration in the future.

Sensitization of colon cancer cells to cisplatin by Fbxw7 via negative regulation of the Nox1-mTOR pathway

Colorectal cancer (CRC) is a human malignancy which associates with high mortality rate and poor prognosis. Despite the initial effectiveness in clinical applications of chemotherapeutic agents, a fraction of patients develops chemoresistance. Fbxw7 is an F-box protein serving as a substrate recognition subunit of E3 ubiquitin ligase, leading to degradation of various oncoproteins. In this study, Fbxw7 was significantly downregulated in CRC tumors as well as CRC cells. Fbxw7 suppressed CRC cell proliferation and migration. Moreover, we observed Fbxw7 was positively associated with cisplatin sensitivity. Fbxw7 was significantly downregulated in cisplatin resistant CRC cells. Overexpression of Fbxw7 effectively increased the cisplatin sensitivity of cisplatin resistant CRC cells. Co-immunoprecipitation and GST pull-down assays showed Fbxw7 bond with Nox1 which was a superoxide-generating NADPH oxidase and showed oncogenic roles in colon cancer cells. Interestingly, Fbxw7 downregulated Nox1 through binding it to degrade Nox1 protein. We demonstrated that Fbxw7 negatively regulated mTOR activity through downregulation of Nox1. Finally, overexpression of Fbxw7 effectively increased the cisplatin sensitivity of CRC cells. This process could be further overturned by Nox1 restoration in Fbxw7-overexpressing colon cancer cells. In summary, these results unveiled that Fbxw7 targeted Nox1 for degradation, resulting in blocking the downstream Nox1-mTORC1 signaling to sensitize CRC cells to cisplatin. Our study potentiates that targeting the Fbxw7-Nox1-mTOR pathway could be an effective approach to overcome chemoresistance of colon cancer cells.

Metabolism and Colorectal Cancer

Reprogrammed metabolism is a hallmark of colorectal cancer (CRC). CRC cells are geared toward rapid proliferation, requiring nutrients and the removal of cellular waste in nutrient-poor environments. Intestinal stem cells (ISCs), the primary cell of origin for CRCs, must adapt their metabolism along the adenoma-carcinoma sequence to the unique features of their complex microenvironment that include interactions with intestinal epithelial cells, immune cells, stromal cells, commensal microbes, and dietary components. Emerging evidence implicates modifiable risk factors related to the environment, such as diet, as important in CRC pathogenesis. Here, we focus on describing the metabolism of ISCs, diets that influence CRC initiation, CRC genetics and metabolism, and the tumor microenvironment. The mechanistic links between environmental factors, metabolic adaptations, and the tumor microenvironment in enhancing or supporting CRC tumorigenesis are becoming better understood. Thus, greater knowledge of CRC metabolism holds promise for improved prevention and treatment.

Harnessing Redox Disruption to Treat Human Herpesvirus 8 (HHV-8) Related Malignancies

Reprogrammed metabolism is regarded as a hallmark of cancer and offers a selective advantage to tumor cells during carcinogenesis. The redox equilibrium is necessary for growth, spread and the antioxidant pathways are boosted following Reactive Oxygen Species (ROS) production to prevent cell damage in tumor cells. Human herpesvirus 8 (HHV-8), the etiologic agent of Kaposi sarcoma KS and primary effusion lymphoma (PEL), is an oncogenic virus that disrupts cell survival-related molecular signaling pathways leading to immune host evasion, cells growths, angiogenesis and inflammatory tumor-environment. We recently reported that primaquine diphosphate causes cell death by apoptosis in HHV-8 infected PEL cell lines in vivo and exhibits therapeutic anti-tumor activity in mice models and advanced KS. Our findings also suggest that the primaquine-induced apoptosis in PEL cells is mostly influenced by ROS production and targeting the redox balance could be a new approach to treat HHV-8 related diseases. In this review, we summarized the knowledge about the influence of ROS in cancer development; more specifically, the proof of evidence from our work and from the literature that redox pathways are important for the development of HHV-8 pathologies.

Tracing the electron flow in redox metabolism: The appropriate distribution of electrons is essential to maintain redox balance in cancer cells

Cancer cells are characterized by sustained proliferation, which requires a huge demand of fuels to support energy production and biosynthesis. Energy is produced by the oxidation of the fuels during catabolism, and biosynthesis is achieved by the reduction of smaller units or precursors. Therefore, the oxidation-reduction (redox) reactions in cancer cells are more active compared to those in the normal counterparts. The higher activity of redox metabolism also induces a more severe oxidative stress, raising the question of how cancer cells maintain the redox balance. In this review, we overview the redox metabolism of cancer cells in an electron-tracing view. The electrons are derived from the nutrients in the tumor microenvironment and released during catabolism. Most of the electrons are transferred to NAD(P) system and then directed to four destinations: energy production, ROS generation, reductive biosynthesis and antioxidant system. The appropriate distribution of these electrons achieved by the function of redox regulation network is essential to maintain redox homeostasis in cancer cells. Interfering with the electron distribution and disrupting redox balance by targeting the redox regulation network may provide therapeutic implications for cancer treatment.

Extrinsic cell death pathway plasticity: a driver of clonal evolution in cancer?

Human cancers are known to adhere to basic evolutionary principles. During their journey from early transformation to metastatic disease, cancer cell populations have proven to be remarkably adaptive to different forms of intra- and extracellular selective pressure, including nutrient scarcity, oxidative stress, and anti-cancer immunity. Adaption may be achieved via the expansion of clones bearing driver mutations that optimize cellular fitness in response to the specific selective scenario, e.g., mutations facilitating evasion of cell death, immune evasion or increased proliferation despite growth suppression, all of which constitute well-established hallmarks of cancer. While great progress concerning the prevention, diagnosis and treatment of clinically apparent disease has been made over the last 50 years, the mechanisms underlying cellular adaption under selective pressure via the immune system during early carcinogenesis and its influence on cancer cell fate or disease severity remain to be clarified. For instance, evasion of cell death is generally accepted as a hallmark of cancer, yet recent decades have revealed that the extrinsic cell death machinery triggered by immune effector cells is composed of an astonishingly complex network of interacting—and sometimes compensating—modes of cell death, whose role in selective processes during early carcinogenesis remains obscure. Based upon recent advances in cell death research, here we propose a concept of cell death pathway plasticity in time shaping cancer evolution prior to treatment in an effort to offer new perspectives on how cancer cell fate may be determined by cell death pathway plasticity during early carcinogenesis.

The role of TIGAR in nervous system diseases

TP53-induced glycolysis and apoptosis regulator (TIGAR) mainly regulates pentose phosphate pathway by inhibiting glycolysis, so as to synthesize ribose required by DNA, promote DNA damage repair and cell proliferation, maintain cell homeostasis and avoid body injury. Its physiological functions include anti-oxidative stress, reducing inflammation, maintaining mitochondrial function, inhibiting apoptosis, reducing autophagy etc. This paper reviews the research of TIGAR in neurological diseases, including stroke, Parkinson’s disease (PD), Alzheimer’s disease (AD), seizures and brain tumors, aiming to provide reference for the development of new therapeutic targets.

Non-enzymatic role of SOD1 in intestinal stem cell growth

Superoxide dismutase 1 (SOD1) modulates intestinal barrier integrity and intestinal homeostasis as an antioxidant enzyme. Intestinal homeostasis is maintained by the intestinal stem cells (ISCs). However, whether and how SOD1 regulates ISCs is unknown. In this study, we established intestinal organoids from tamoxifen-inducible intestinal epithelial cell-specific Sod1 knockout (Sod1^f/f; Vil-creERT2) mice. We found that loss of Sod1 in organoids suppressed the proliferation and survival of cells and Lgr5 gene expression. SOD1 is known for nearly half a century for its canonical role as an antioxidant enzyme. We identified its enzyme-independent function in ISC: inhibition of SOD1 enzymatic activity had no impact on organoid growth, and enzymatically inactive Sod1 mutants could completely rescue the growth defects of Sod1 deficient organoids, suggesting that SOD1-mediated ISC growth is independent of its enzymatic activity. Moreover, Sod1 deficiency did not affect the ROS levels of the organoid, but induced the elevated WNT signaling and excessive Paneth cell differentiation, which mediates the occurrence of growth defects in Sod1 deficient organoids. In vivo, epithelial Sod1 loss induced a higher incidence of apoptosis in the stem cell regions and increased Paneth cell numbers, accompanied by enhanced expression of EGFR ligand Epiregulin (EREG) in the stromal tissue, which may compensate for Sod1 loss and maintain intestinal structure in vivo. Totally, our results show a novel enzyme-independent function of SOD1 in ISC growth under homeostasis.

Dioscin ameliorates cisplatin-induced intestinal toxicity by mitigating oxidative stress and inflammation

Cisplatin is the most widely prescribed drug in chemotherapy, but its gastrointestinal toxicity reduces therapeutic efficacy. Oxidative stress and inflammation are considered to be the main pathogenesis of cisplatin-induced intestinal toxicity. Dioscin is a steroidal saponin with potential anti-cancer, antioxidant, and anti-inflammatory activities. In this study, we established a rat model of intestinal injury by tail vein injection of cisplatin, and intragastrically administered dioscin to evaluate its effect on intestinal injury. Biochemical markers, western blotting, qRT-PCR and histopathological staining were used to analyze intestinal injury according to various molecular mechanisms. The results revealed that dioscin significantly inhibited cisplatin-induced intestinal mucosal damage and decreased DAO levels in rats. Furthermore, dioscin activated the Nrf2/HO-1 pathway to increase the level of antioxidant enzymes and reduce the levels of MDA and H₂O₂. In addition, dioscin pretreatment significantly reduced ileum epithelial NLRP3 inflammasome formation and decreased the levels of inflammatory factors compared with the cisplatin group. In parallel, Nrf2 inhibitor ML385 blocked the therapeutic effect of dioscin in rat with cisplatin-induced intestinal toxicity. In terms of mechanisms, dioscin reversed cisplatin-induced up-regulation of MAPKs and up-regulated p-PI3K and p-AKT levels. Meanwhile, dioscin potently promoted Wnt3A/β-catenin signaling to relieve cisplatin-induced proliferation inhibition. In conclusion, our study suggests that dioscin could ameliorate the cisplatin-induced intestinal toxicity by reducing oxidative stress and inflammation.

The crosstalk of the human microbiome in breast and colon cancer: A metabolomics analysis

The human microbiome's role in colon and breast cancer is described in this review. Understanding how the human microbiome and metabolomics interact with breast and colon cancer is the chief area of this study. First, the role of the gut and distal microbiome in breast and colon cancer is investigated, and the direct relationship between microbial dysbiosis and breast and colon cancer is highlighted. This work also focuses on the many metabolomic techniques used to locate prospective biomarkers, make an accurate diagnosis, and research new therapeutic targets for cancer treatment. This review clarifies the influence of anti-tumor medications on the microbiota and the proactive measures that can be taken to treat cancer using a variety of therapies, including radiotherapy, chemotherapy, next-generation biotherapeutics, gene-based therapy, integrated omics technology, and machine learning.

The role of ROS in tumour development and progression

Eukaryotic cells have developed complex systems to regulate the production and response to reactive oxygen species (ROS). Different ROS control diverse aspects of cell behaviour from signalling to death, and deregulation of ROS production and ROS limitation pathways are common features of cancer cells. ROS also function to modulate the tumour environment, affecting the various stromal cells that provide metabolic support, a blood supply and immune responses to the tumour. Although it is clear that ROS play important roles during tumorigenesis, it has been difficult to reliably predict the effect of ROS modulating therapies. We now understand that the responses to ROS are highly complex and dependent on multiple factors, including the types, levels, localization and persistence of ROS, as well as the origin, environment and stage of the tumours themselves. This increasing understanding of the complexity of ROS in malignancies will be key to unlocking the potential of ROS-targeting therapies for cancer treatment.

Balancing reactive oxygen species generation by rebooting gut microbiota

Reactive oxygen species (ROS; free radical form O₂ ^•‾ , superoxide radical; OH^• , hydroxyl radical; ROO^• , peroxyl; RO^• , alkoxyl and non-radical form ¹ O₂ , singlet oxygen; H₂ O₂ , hydrogen peroxide) are inevitable companions of aerobic life with crucial role in gut health. But, overwhelming production of ROS can cause serious damage to biomolecules. In this review, we have discussed several sources of ROS production that can be beneficial or dangerous to the human gut. Microorganisms, organelles and enzymes play crucial role in ROS generation, where, NOX1 is the main intestinal enzyme, which produce ROS in the intestine epithelial cells. Previous studies have reported that probiotics play significant role in gut homeostasis by checking the ROS generation, maintaining the antioxidant level, immune system and barrier protection. With current knowledge, we have critically analyzed the available literature and presented the outcome in the form of bubble maps to suggest the probiotics that help in controlling the ROS-specific intestinal diseases, such as inflammatory bowel disease (IBD) and colon cancer. Finally, it has been concluded that rebooting of the gut microbiota with probiotics, postbiotics or fecal microbiota transplantation (FMT) can have crucial implications in the structuring of gut communities for the personalized management of the gastrointestinal (GI) diseases.

Redox Regulation in Cancer Cells during Metastasis

Metastasis is an inefficient process in which the vast majority of cancer cells are fated to die, partly because they experience oxidative stress. Metastasizing cancer cells migrate through diverse environments that differ dramatically from their tumor of origin, leading to redox imbalances. The rare metastasizing cells that survive undergo reversible metabolic changes that confer oxidative stress resistance. We review the changes in redox regulation that cancer cells undergo during metastasis. By better understanding these mechanisms, it may be possible to develop pro-oxidant therapies that block disease progression by exacerbating oxidative stress in cancer cells. SIGNIFICANCE: Oxidative stress often limits cancer cell survival during metastasis, raising the possibility of inhibiting cancer progression with pro-oxidant therapies. This is the opposite strategy of treating patients with antioxidants, an approach that worsened outcomes in large clinical trials.

Inhibition of ribosomal RNA processing 15 Homolog (RRP15), which is overexpressed in hepatocellular carcinoma, suppresses tumour growth via induction of senescence and apoptosis

Recent studies suggest that RRP15 (Ribosomal RNA Processing 15 Homolog) might be a potential target for cancer therapy. However, the role of RRP15 in hepatocarcinogenesis remains poorly delineated. In this study, we aimed to evaluate the expression and biological function of RRP15 in human hepatocellular carcinoma (HCC). We show that RRP15 was up regulated in HCC cell lines and tumours. Up-regulation of RRP15 in HCC tumours was also correlated with unfavorable prognosis. We further show that the frequent up-regulation of RRP15 in HCCs is at least partly driven by recurrent gene copy gain at chromosome 1q41. Functional studies indicated that RRP15 knockdown suppresses HCC proliferation and growth both in vitro and in vivo. Mechanistically, RRP15 depletion in p53-wild-type HepG2 cells induced senescence via activation of the p53-p21 signalling pathway through enhanced interaction of RPL11 with MDM2, as well as inhibition of SIRT1-mediated p53 deacetylation. Moreover, RRP15 depletion in p53-mutant PLC5 and p53-deleted Hep3B cells induced metabolic shift from the glycolytic pentose-phosphate to mitochondrial oxidative phosphorylation via regulating a series of key genes such as HK2 and TIGAR, and thus, promoted the generation of ROS and apoptosis. Taken together, our findings provide evidence for an important role of the RRP15 gene in hepatocarcinogenesis through regulation of HCC proliferation and growth, raising the possibility that targeting RRP15 may represent a potential therapeutic strategy for HCC treatment.

Role of reactive oxygen species in tumors based on the 'seed and soil' theory: A complex interaction (Review)

Tumor microenvironment (TME) can serve as the 'soil' for the growth and survival of tumor cells and function synergically with tumor cells to mediate tumor progression and therapeutic resistance. Reactive oxygen species (ROS) is somewhat of a double‑edged sword for tumors. Accumulating evidence has reported that regulating ROS levels can serve an anti‑tumor role in the TME, including the promotion of cancer cell apoptosis, inhibition of angiogenesis, preventing immune escape, manipulating tumor metabolic reorganization and improving drug resistance. In the present review, the potential role of ROS in anti‑tumor therapy was summarized, including the possibility of directly or indirectly targeting the TME.

Sphingosine kinase 1 downregulation is required for adaptation to serine deprivation

It has been well-established that cancer cells often display altered metabolic profiles, and recent work has concentrated on how cancer cells adapt to serine removal. Serine can be either taken exogenously or synthesized from glucose, and its regulation forms an important mechanism for nutrient integration. One of the several important metabolic roles for serine is in the generation of bioactive sphingolipids since it is the main substrate for serine palmitoyltransferase, the initial and rate-limiting enzyme in the synthesis of sphingolipids. Previously, serine deprivation has been connected to the action of the tumor suppressor p53, and we have previously published on a role for p53 regulating sphingosine kinase 1 (SK1), an enzyme that phosphorylates sphingosine to form sphingosine-1-phosphate (S1P). SK1 is a key enzyme in sphingolipid synthesis that functions in pro-survival and tumor-promoting pathways and whose expression is also often elevated in cancers. Here we show that SK1 was degraded during serine starvation in a time and dose-dependent manner, which led to sphingosine accumulation. This was independent of effects on p53 but required the action of the proteasome. Furthermore, we show that overexpression of SK1, to compensate for SK1 loss, was detrimental to cell growth under conditions of serine starvation, demonstrating that the suppression of SK1 under these conditions is adaptive. Mitochondrial oxygen consumption decreased in response to SK1 degradation, and this was accompanied by an increase in intracellular reactive oxygen species (ROS). Suppression of ROS with N-acteylcysteine resulted in suppression of the metabolic adaptations and in decreased cell growth under serine deprivation. The effects of SK1 suppression on ROS were mimicked by D-erythro-sphingosine, whereas S1P was ineffective, suggesting that the effects of loss of SK1 were due to the accumulation of its substrate sphingosine. This study reveals a new mechanism for regulating SK1 levels and a link of SK1 to serine starvation as well as mitochondrial function.

VHL regulates the sensitivity of clear cell renal cell carcinoma to SIRT4-mediated metabolic stress via HIF-1α/HO-1 pathway

Clear cell renal cell carcinomas (ccRCC) reprogram carbon metabolism responses to hypoxia, thereby promoting utilization of glutamine. Recently, sirtuin 4 (SIRT4), a novel molecular has turned out to be related to alternating glutamine metabolism and modulating the tumor microenvironment. However, the role of SIRT4 in ccRCC remains poorly understood. Here, we illustrated that the expression of SIRT4 is markedly reduced in cancerous tissues, and closely associated with malignancy stage, grade, and prognosis. In ccRCC cells, SIRT4 exerted its proapoptotic activity through enhancing intracellular reactive oxygen species (ROS). Heme oxygenase-1 (HO-1) is part of an endogenous defense system against oxidative stress. Nevertheless, overexpression of SIRT4 hindered the upregulation of HO-1 in von Hippel-Lindau (VHL)-proficient cells and repressed its expression in VHL-deficient cells. This discrepancy indicated that competent VHL withstands the inhibitory role of SIRT4 on HIF-1α/HO-1. Functionally, overexpression of HO-1 counteracted the promotional effects of SIRT4 on ROS accumulation and apoptosis. Mechanistically, SIRT4 modulates ROS and HO-1 expression via accommodating p38-MAPK phosphorylation. By contrast, downregulation of p38-MAPK by SB203580 decreased intracellular ROS level and enhanced the expression of HO-1. Collectively, this work revealed a potential role for SIRT4 in the stimulation of ROS and the modulation of apoptosis. SIRT4/HO-1 may act as a potential therapeutic target, especially in VHL-deficient ccRCCs.

Interplay Between Reactive Oxygen/Reactive Nitrogen Species and Metabolism in Vascular Biology and Disease

Reactive oxygen species (ROS; e.g., superoxide [O₂^•-] and hydrogen peroxide [H₂O₂]) and reactive nitrogen species (RNS; e.g., nitric oxide [NO^•]) at the physiological level function as signaling molecules that mediate many biological responses, including cell proliferation, migration, differentiation, and gene expression. By contrast, excess ROS/RNS, a consequence of dysregulated redox homeostasis, is a hallmark of cardiovascular disease. Accumulating evidence suggests that both ROS and RNS regulate various metabolic pathways and enzymes. Recent studies indicate that cells have mechanisms that fine-tune ROS/RNS levels by tight regulation of metabolic pathways, such as glycolysis and oxidative phosphorylation. The ROS/RNS-mediated inhibition of glycolytic pathways promotes metabolic reprogramming away from glycolytic flux toward the oxidative pentose phosphate pathway to generate nicotinamide adenine dinucleotide phosphate (NADPH) for antioxidant defense. This review summarizes our current knowledge of the mechanisms by which ROS/RNS regulate metabolic enzymes and cellular metabolism and how cellular metabolism influences redox homeostasis and the pathogenesis of disease. A full understanding of these mechanisms will be important for the development of new therapeutic strategies to treat diseases associated with dysregulated redox homeostasis and metabolism. Antioxid. Redox Signal. 34, 1319-1354.

NOX1-dependent redox signaling potentiates colonic stem cell proliferation to adapt to the intestinal microbiota by linking EGFR and TLR activation

The colon epithelium is a primary point of interaction with the microbiome and is regenerated by a few rapidly cycling colonic stem cells (CSCs). CSC self-renewal and proliferation are regulated by growth factors and the presence of bacteria. However, the molecular link connecting the diverse inputs that maintain CSC homeostasis remains largely unknown. We report that CSC proliferation is mediated by redox-dependent activation of epidermal growth factor receptor (EGFR) signaling via NADPH oxidase 1 (NOX1). NOX1 expression is CSC specific and is restricted to proliferative CSCs. In the absence of NOX1, CSCs fail to generate ROS and have a reduced proliferation rate. NOX1 expression is regulated by Toll-like receptor activation in response to the microbiota and serves to link CSC proliferation with the presence of bacterial components in the crypt. The TLR-NOX1-EGFR axis is therefore a critical redox signaling node in CSCs facilitating the quiescent-proliferation transition and responds to the microbiome to maintain colon homeostasis.

Glutathione and its precursors in cancer

Buffering oxidative stress is as a crucial requirement for tumorigenesis. Antioxidant is a term reserved for molecules that quench reactive oxygen species (ROS) and alleviate oxidative stress. The details regarding antioxidant synthesis, their utilization to eliminate ROS, and their ability to promote different stages of tumorigenesis are unclear. Here, we focus on glutathione (GSH), the most abundant antioxidant in the cell, and its precursor amino acids (cysteine, glutamate, and glycine). Even though GSH was discovered more than a century ago, continued research into this antioxidant has provided answers to longstanding questions while also posing new ones.

Reactive Oxygen Species in intestinal stem cell metabolism, fate and function

Long dismissed as merely harmful respiratory by-products, Reactive Oxygen Species (ROS) have emerged as critical intracellular messengers during cell growth and differentiation. ROS's signaling roles are particularly prominent within the intestine, whose high regenerative capacity is maintained by Intestinal Stem Cells (ISCs). In this review, we outline roles for ROS in ISCs as revealed by studies using Drosophila and mouse model systems. We focus particularly on recent studies highlighting how ROS ties to metabolic adaptations, which ensure energy supply matches demand during ISC activation and differentiation. We describe how declines in these adaptive mechanisms, through aging or pathology, promote reciprocal changes in ISC metabolism and ROS signaling. These changes ultimately contribute to aberrant ISC function, a loss of tissue homeostasis, and a shortened lifespan.

Mitochondrial Reactive Oxygen Species and Mitophagy: A Complex and Nuanced Relationship

Significance: Mitochondria represent a major source of intracellular reactive oxygen species (ROS) generation. This is often a consequence of oxidative phosphorylation, which can produce ROS as a result of leakage from the electron transport chain. In addition, quality control mechanisms exist to protect cells from cytotoxic ROS production. One such mechanism is selective autophagic degradation of ROS-producing mitochondria, termed mitophagy, that ultimately results in elimination of mitochondria in the lysosome. Recent Advances: However, while the relationship between mitophagy and ROS production is clearly interwoven, it is yet to be fully untangled. In some circumstances, mitochondrial ROS (mtROS) are elevated as a consequence of mitophagy induction. Critical Issues: In this review, we discuss mtROS generation and their detrimental effects on cellular viability. In addition, we consider the cellular defense mechanisms that the eukaryotic cell uses to abrogate superfluous oxidative stress. In particular, we delve into the prominent mechanisms governing mitophagy induction that bear on oxidative stress. Future Directions: Finally, we examine the pathological conditions associated with defective mitophagy, where additional research may help to facilitate understanding.

Antioxidants Promote Intestinal Tumor Progression in Mice

Dietary antioxidants and supplements are widely used to protect against cancer, even though it is now clear that antioxidants can promote tumor progression by helping cancer cells to overcome barriers of oxidative stress. Although recent studies have, in great detail, explored the role of antioxidants in lung and skin tumors driven by RAS and RAF mutations, little is known about the impact of antioxidant supplementation on other cancers, including Wnt-driven tumors originating from the gut. Here, we show that supplementation with the antioxidants N-acetylcysteine (NAC) and vitamin E promotes intestinal tumor progression in the ApcMin mouse model for familial adenomatous polyposis, a hereditary form of colorectal cancer, driven by Wnt signaling. Both antioxidants increased tumor size in early neoplasias and tumor grades in more advanced lesions without any impact on tumor initiation. Importantly, NAC treatment accelerated tumor progression at plasma concentrations comparable to those obtained in human subjects after prescription doses of the drug. These results demonstrate that antioxidants play an important role in the progression of intestinal tumors, which may have implications for patients with or predisposed to colorectal cancer.

A RAC-GEF network critical for early intestinal tumourigenesis

RAC1 activity is critical for intestinal homeostasis, and is required for hyperproliferation driven by loss of the tumour suppressor gene Apc in the murine intestine. To avoid the impact of direct targeting upon homeostasis, we reasoned that indirect targeting of RAC1 via RAC-GEFs might be effective. Transcriptional profiling of Apc deficient intestinal tissue identified Vav3 and Tiam1 as key targets. Deletion of these indicated that while TIAM1 deficiency could suppress Apc-driven hyperproliferation, it had no impact upon tumourigenesis, while VAV3 deficiency had no effect. Intriguingly, deletion of either gene resulted in upregulation of Vav2, with subsequent targeting of all three (Vav2-/- Vav3-/- Tiam1-/-), profoundly suppressing hyperproliferation, tumourigenesis and RAC1 activity, without impacting normal homeostasis. Critically, the observed RAC-GEF dependency was negated by oncogenic KRAS mutation. Together, these data demonstrate that while targeting RAC-GEF molecules may have therapeutic impact at early stages, this benefit may be lost in late stage disease.

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.

Metabolic determinants of cellular fitness dependent on mitochondrial reactive oxygen species

Mitochondria-derived reactive oxygen species (mROS) are required for the survival, proliferation, and metastasis of cancer cells. The mechanism by which mitochondrial metabolism regulates mROS levels to support cancer cells is not fully understood. To address this, we conducted a metabolism-focused CRISPR-Cas9 genetic screen and uncovered that loss of genes encoding subunits of mitochondrial complex I was deleterious in the presence of the mitochondria-targeted antioxidant mito-vitamin E (MVE). Genetic or pharmacologic inhibition of mitochondrial complex I in combination with the mitochondria-targeted antioxidants, MVE or MitoTEMPO, induced a robust integrated stress response (ISR) and markedly diminished cell survival and proliferation in vitro. This was not observed following inhibition of mitochondrial complex III. Administration of MitoTEMPO in combination with the mitochondrial complex I inhibitor phenformin decreased the leukemic burden in a mouse model of T cell acute lymphoblastic leukemia. Thus, mitochondrial complex I is a dominant metabolic determinant of mROS-dependent cellular fitness.

Metformin and oxyphotodynamic therapy as a novel treatment approach for triple-negative breast cancer

Background

Treatment for triple-negative breast cancer (TNBC) remains a significant challenge due to a lack of targeted therapies. While photodynamic therapy (PDT) has been utilized as a treatment approach for several types of cancer, oxyphotodynamic therapy (OPDT) is a novel method that improves treatment efficacy by increasing local oxygen concentration. Metformin (MET) has been demonstrated utility as an anti-tumor agent by acting through the adenosine monophosphate-activated protein kinase (AMPK) pathway. We hypothesized that MET in combination with heme, a byproduct of 5-aminolevulinic acid (ALA), may increase cytotoxicity for cancer treatment. This study aimed to investigate the synergistic effect of MET and ALA with PDT or OPDT on TNBC tumorigenic cells.

Methods

The treatment efficacy and phototoxicity of PDT or OPDT were determined using a cell viability assay. PDT/OPDT experiments were carried out in nine groups based on different combinations and concentrations of ALA and/or MET. To calculate the synergistic effect by compuSyn soft for different groups, cells were incubated with ALA and/or MET at the following concentrations (0, 0.25, 0.5,1, 2, 4, 8, 16, 24, and 32 mM). The fluorescence of ALA-induced protoporphyrin IX (PpIX) and MitoTracker Green were observed under a confocal microscope.

Results

The optimized therapeutic concentration ratio of ALA and MET was determined to be 1:1. The inhibition of cancer growth (IC₅₀) for each group was 14.03, 10.62, 7.71, 18.27, 22.09, 23.96, 4.57, 10.20, and 8.18 mM, respectively. The combination index (CI) values (fa =0.5) of the last three combination groups (groups 7, 8, and 9) were 0.44, 1.70, and 1.47, respectively. PpIX fluorescence intensity of group 9 (ALA-MET-OPDT group) remained the highest among all groups, indicating an enhanced therapeutic effect.

Conclusions

This study introduces OPDT as a novel anti-tumor therapy for TNBC. Furthermore, the combined use of ALA and MET had a synergistic anti-tumor effect in TNBC cells when combined with OPDT.

Role of Glutathione Depletion and Reactive Oxygen Species Generation on Caspase-3 Activation: A Study With the Kinase Inhibitor Staurosporine

Oxidative stress is known to contribute to the progression of apoptosis. Staurosporine is a broad-spectrum inducer of apoptosis, but its mechanism of action is not well understood. The goal of the present work was to elucidate the role of glutathione and reactive oxygen species (ROS) in the execution of staurosporine-induced apoptosis. HeLa cells were treated with staurosporine at 1 μM for up to 4 h. The concentration of glutathione, generation of ROS, and activation of caspase-3 were measured. The introduction of staurosporine significantly decreased the concentration of cellular glutathione and increased the presence of ROS after 3 h. These findings were concurrent with the activation of caspase-3. Interestingly, pre-treatment of cells with N-acetylcysteine, a precursor of glutathione, and a thiol antioxidant failed to block the depletion of glutathione, generation of ROS, and activation of caspase-3. Collectively, these results suggest that the cellular redox status may be one of the critical factors of the apoptotic pathway leading to caspase-3 activation by staurosporine.

NOX1-Dependent mTORC1 Activation via S100A9 Oxidation in Cancer Stem-like Cells Leads to Colon Cancer Progression

Cancer stem cells (CSCs) are associated with the refractory nature of cancer, and elucidating the targetable pathways for CSCs is crucial for devising innovative antitumor therapies. We find that the proliferation of CSC-enriched colon spheroids from clinical specimen is dependent on mTORC1 kinase, which is activated by reactive oxygen species (ROS) produced by NOX1, an NADPH oxidase. In the spheroid-derived xenograft tumors, NOX1 is preferentially expressed in LGR5-positive cells. Dependence on NOX1 expression or mTOR kinase activity is corroborated in the xenograft tumors and mouse colon cancer-derived organoids. NOX1 co-localizes with mTORC1 in VPS41-/VPS39-positive lysosomes, where mTORC1 binds to S100A9, a member of S100 calcium binding proteins, in a NOX1-produced ROS-dependent manner. S100A9 is oxidized by NOX1-produced ROS, which facilitates binding to mTORC1 and its activation. We propose that NOX1-dependent mTORC1 activation via S100A9 oxidation in VPS41-/VPS39-positive lysosomes is crucial for colon CSC proliferation and colon cancer progression.

TIGAR/AP-1 axis accelerates the division of Lgr5- reserve intestinal stem cells to reestablish intestinal architecture after lethal radiation

During radiologic or nuclear accidents, high-dose ionizing radiation (IR) can cause gastrointestinal syndrome (GIS), a deadly disorder that urgently needs effective therapy. Unfortunately, current treatments based on natural products and antioxidants have shown very limited effects in alleviating deadly GIS. Reserve intestinal stem cells (ISCs) and secretory progenitor cells are both reported to replenish damaged cells and contribute to crypt regeneration. However, the suppressed β-catenin/c-MYC axis within these slow-cycling cells leads to limited regenerative response to restore intestinal integrity during fatal accidental injury. Current study demonstrates that post-IR overexpression of TIGAR, a critical downstream target of c-MYC in mouse intestine, mounts a hyperplastic response in Bmi1-creERT⁺ reserve ISCs, and thus rescues mice from lethal IR exposure. Critically, by eliminating damaging reactive oxygen species (ROS) yet retaining the proliferative ROS signals, TIGAR-overexpression enhances the activity of activator protein 1, which is indispensable for initiating reserve-ISC division after lethal radiation. In addition, it is identified that TIGAR-induction exclusively gears the Lgr5⁻ subpopulation of reserve ISCs to regenerate crypts, and intestinal TIGAR-overexpression displays equivalent intestinal reconstruction to reserve-ISC-restricted TIGAR-induction. Our findings imply that precise administrations toward Lgr5⁻ reserve ISCs are promising strategies for unpredictable lethal injury, and TIGAR can be employed as a therapeutic target for unexpected radiation-induced GIS.

The Complex Interplay between Antioxidants and ROS in Cancer

Reactive oxygen species (ROS) play important roles in tissue homeostasis, cellular signaling, differentiation, and survival. In this review, we discuss the types ofROS, their impact on cellular processes, and their pro- and antitumorigenic effects. Further, we discuss recent advances in our understanding of both endogenous and exogenous antioxidants in tumorigenic processes. Finally, wediscuss how aberrant activation of antioxidant programs by the transcription factor NFE2-related factor 2 (NRF2) influences tumorigenesis and metastasis, and where the current gaps in our knowledge remain.

Rac1 Signaling: From Intestinal Homeostasis to Colorectal Cancer Metastasis

The small GTPase Rac1 has been implicated in a variety of dynamic cell biological processes, including cell proliferation, cell survival, cell-cell contacts, epithelial mesenchymal transition (EMT), cell motility, and invasiveness. These processes are orchestrated through the fine tuning of Rac1 activity by upstream cell surface receptors and effectors that regulate the cycling Rac1-GDP (off state)/Rac1-GTP (on state), but also through the tuning of Rac1 accumulation, activity, and subcellular localization by post translational modifications or recruitment into molecular scaffolds. Another level of regulation involves Rac1 transcripts stability and splicing. Downstream, Rac1 initiates a series of signaling networks, including regulatory complex of actin cytoskeleton remodeling, activation of protein kinases (PAKs, MAPKs) and transcription factors (NFkB, Wnt/β-catenin/TCF, STAT3, Snail), production of reactive oxygen species (NADPH oxidase holoenzymes, mitochondrial ROS). Thus, this GTPase, its regulators, and effector systems might be involved at different steps of the neoplastic progression from dysplasia to the metastatic cascade. After briefly placing Rac1 and its effector systems in the more general context of intestinal homeostasis and in wound healing after intestinal injury, the present review mainly focuses on the several levels of Rac1 signaling pathway dysregulation in colorectal carcinogenesis, their biological significance, and their clinical impact.

Dynamic ROS Control by TIGAR Regulates the Initiation and Progression of Pancreatic Cancer

The TIGAR protein has antioxidant activity that supports intestinal tissue repair and adenoma development. Using a pancreatic ductal adenocarcinoma (PDAC) model, we show that reactive oxygen species (ROS) regulation by TIGAR supports premalignant tumor initiation while restricting metastasis. Increased ROS in PDAC cells drives a phenotypic switch that increases migration, invasion, and metastatic capacity. This switch is dependent on increased activation of MAPK signaling and can be reverted by antioxidant treatment. In mouse and human, TIGAR expression is modulated during PDAC development, with higher TIGAR levels in premalignant lesions and lower TIGAR levels in metastasizing tumors. Our study indicates that temporal, dynamic control of ROS underpins full malignant progression and helps to rationalize conflicting reports of pro- and anti-tumor effects of antioxidant treatment.

A deeper understanding of intestinal organoid metabolism revealed by combining fluorescence lifetime imaging microscopy (FLIM) and extracellular flux analyses

Stem cells and the niche in which they reside feature a complex microenvironment with tightly regulated homeostasis, cell-cell interactions and dynamic regulation of metabolism. A significant number of organoid models has been described over the last decade, yet few methodologies can enable single cell level resolution analysis of the stem cell niche metabolic demands, in real-time and without perturbing integrity. Here, we studied the redox metabolism of Lgr5-GFP intestinal organoids by two emerging microscopy approaches based on luminescence lifetime measurement - fluorescence-based FLIM for NAD(P)H, and phosphorescence-based PLIM for real-time oxygenation. We found that exposure of stem (Lgr5-GFP) and differentiated (no GFP) cells to high and low glucose concentrations resulted in measurable shifts in oxygenation and redox status. NAD(P)H-FLIM and O2-PLIM both indicated that at high 'basal' glucose conditions, Lgr5-GFP cells had lower activity of oxidative phosphorylation when compared with cells lacking Lgr5. However, when exposed to low (0.5 mM) glucose, stem cells utilized oxidative metabolism more dynamically than non-stem cells. The high heterogeneity of complex 3D architecture and energy production pathways of Lgr5-GFP organoids were also confirmed by the extracellular flux (XF) analysis. Our data reveals that combined analysis of NAD(P)H-FLIM and organoid oxygenation by PLIM represents promising approach for studying stem cell niche metabolism in a live readout.

Metabolic reprogramming by tobacco-specific nitrosamines (TSNAs) in cancer

Metabolic reprogramming is a hallmark of cancer and the link between oncogenes activation, tumor supressors inactivation and bioenergetics modulation is well established. However, numerous carcinogenic environmental factors are responsible for early cancer initiation and their impact on metabolic reprogramming just starts to be deciphered. For instance, it was recently shown that UVB irradiation triggers metabolic reprogramming at the pre-cancer stage with implication for skin cancer detection and therapy. These observations foster the need to study the early changes in tissue metabolism following exposure to other carcinogenic events. According to the International Agency for Research on Cancer (IARC), tobacco smoke is a major class I-carcinogenic environmental factor that contains different carcinogens, but little is known on the impact of tobacco smoke on tissue metabolism and its participation to cancer initiation. In particular, tobacco-specific nitrosamines (TSNAs) play a central role in tobacco-smoke mediated cancer initiation. Here we describe the recent advances that have led to a new hypothesis regarding the link between nitrosamines signaling and metabolic reprogramming in cancer.

A bidirectional effect of Rac1 inhibition-Protects radiation-induced intestinal injury while inhibits tumor

AIMS

To investigate whether Rac1 inhibition can alleviate radiation-induced intestinal injury (RIII), meanwhile exist no protection on tumors.

MATERIALS AND METHODS

Rac1 inhibition was achieved by its specific inhibitor, NSC23766. Mice were pretreated with different intraperitoneal injections, which were normal saline for NS group (N = 9), and 2.5 mg/kg and 5 mg/kg of NSC23766 for Low-Dose group (N = 9) and High-Dose group (N = 9), respectively. After total body irritation (10Gy), small intestinal tissues were collected for Hematoxylin-Eosin (H&E) staining and Terminal-deoxynucleotidyl Transferase Mediated dUTP Nick End Labeling (TUNEL). Intestinal epithelial and tumor cell lines, namely MODE-k and CT-26, were used to further study the role of Rac1 inhibition on radiation damage. Flow cytometry was used to detect changes in reactive oxygen species production, cell cycles and mitochondrial membrane potential, the latter was also checked by fluorescence microscope. Changes of protein-expression associated with apoptosis and cell cycles were detected by Western blotting to explain the possible molecular mechanism.

KEY FINDINGS

Height of intestine villi and depth of crypt were higher (P < 0.01) and apoptosis ratio lower (P < 0.01) in High-Dose group compared with those in NS group. After radiation, Rac1 inhibition pre-treatment improved the vitality (P < 0.01) and reduced the apoptosis (P < 0.01) in MODE-k while yielded opposite results in CT-26, and reduced ROS production of MODE-k (P < 0.01) while had little effect on that of CT-26. Rac1 inhibition differently affected the cell cycles of normal cells and that of tumor cells.

SIGNIFICANCE

Inhibition of Rac1 could alleviate RIII, meanwhile assist the killing effect of radiation on tumor cells.

Cell Clustering Promotes a Metabolic Switch that Supports Metastatic Colonization

Cancer metastasis depends on cell survival following loss of extracellular matrix attachment and dissemination through the circulation. The metastatic spread can be enhanced by the clustering of detached cancer cells and increased antioxidant defense. Here, we link these responses by describing how cell clustering limits reactive oxygen species (ROS). Loss of attachment causes mitochondrial perturbations and increased ROS production. The formation of cell clusters induces a hypoxic environment that drives hypoxia-inducible factor 1-alpha (Hif1α)-mediated mitophagy, clearing damaged mitochondria and limiting ROS. However, hypoxia and reduced mitochondrial capacity promote dependence on glycolysis for ATP production that is supported by cytosolic reductive metabolism. Preventing this metabolic adaptation or disruption of cell clusters results in ROS accumulation, cell death, and a reduction of metastatic capacity in vivo. Our results provide a mechanistic explanation for the role of cell clustering in supporting survival during extracellular matrix detachment and metastatic spread and may point to targetable vulnerabilities.

TIGAR impedes compression-induced intervertebral disc degeneration by suppressing nucleus pulposus cell apoptosis and autophagy

To investigate whether TP53-induced glycolysis and apoptosis regulator (TIGAR) participates in compression-induced intervertebral disc (IVD) degeneration, and to determine the regulatory effect of TIGAR on nucleus pulposus (NP) cell autophagy and apoptosis following compression-induced injuries. IVD tissues were collected from human patients undergoing surgery (n = 20) and skeletally mature Sprague-Dawley rats (n = 15). Initially, the effect of compression on the expression of TIGAR was evaluated with in vivo and in vitro models. In addition, TIGAR was silenced to investigate the regulatory effect of TIGAR on compression-induced intracellular reactive oxygen species (ROS) levels, autophagy, and apoptosis in rat NP cells. Furthermore, the P53 inhibitor pifithrin-α (PFTα) and SP1 inhibitor mithramycin A were employed to detect expression level changes of TIGAR and autophagy-associated target molecules. TIGAR expression of NP cells increased gradually in human degenerative IVDs and in rat NP cells under compression both in vivo and in vitro. TIGAR knockdown enhanced compression-induced intracellular ROS generation and the NADPH/NADP⁺ and GSH/GSSG ratios. Moreover, TIGAR knockdown amplified the compression-induced caspase-3 activation and the apoptosis rate of rat NP cells. Likewise, knockdown of TIGAR significantly accelerated LC3B expression and autophagosome formation in rat NP cells during compression-induced injuries. The results also established that mithramycin A could inhibit TIGAR expression and autophagy levels in NP cells under compression conditions, while PFTα had no similar effect. Our data demonstrated that TIGAR acted as an important endogenous negative regulator of ROS levels, which might inhibit compression-induced apoptosis and autophagy through SP1-dependent mechanisms.

The role of Wnt signaling pathway in tumor metabolic reprogramming

The occurrence and development of tumors is a complex process involving long-term multi-factor participation. In this process, tumor cells from a set of abnormal metabolic patterns that are different from normal cells. This abnormal metabolic change is called metabolic reprogramming of tumors. Wnt signaling pathway is one of the critical signaling pathways regulating cell proliferation and differentiation. In recent years, it has been found that Wnt signaling participates in the occurrence and development of malignant tumors by affecting metabolic reprogramming. This paper reviews the role of Wnt signaling in tumor metabolic reprogramming to provide crucial theoretical guidance for targeted therapy and drug response of tumors.

Metabolic pathways regulating colorectal cancer initiation and progression

Colorectal cancer (CRC) is one of the most common types of cancer worldwide. Despite recent advances in the molecular genetics of CRC, poor treatment outcomes highlight the need for a better understanding of the underlying mechanisms accounting for tumor initiation and progression. Recently, deregulation of cellular metabolism has emerged as a key hallmark of cancer. Reprogramming of core cellular metabolic pathways by cancer cells provides energy, anaplerotic precursors and reducing equivalents required to support tumor growth. Here, we review key findings implicating cancer metabolism as a major contributor of tumor initiation, growth and metastatic dissemination in CRC. We summarize the metabolic pathways governing stem cell fate in the intestine, the metabolic adaptations of proliferating colon cancer cells and their crosstalk with oncogenic signaling, and how they fulfill the energetic demands imposed by the metastatic cascade. Lastly, we discuss how some of these metabolic pathways could represent new vulnerabilities of CRC cells with the potential to be targeted.