Low expression of the PPARγ-regulated gene thioredoxin-interacting protein accompanies human melanoma progression and promotes experimental lung metastases

Peroxisome proliferator-activated receptors: Key regulators of tumor progression and growth

One of the main causes of death on the globe is cancer. Peroxisome-proliferator-activated receptors (PPARs) are nuclear hormone receptors, including PPARα, PPARδ and PPARγ, which are important in regulating cancer cell proliferation, survival, apoptosis, and tumor growth. Activation of PPARs by endogenous or synthetic compounds regulates tumor progression in various tissues. Although each PPAR isotype suppresses or promotes tumor development depending on the specific tissues or ligands, the mechanism is still unclear. PPARs are receiving interest as possible therapeutic targets for a number of disorders. Numerous clinical studies are being conducted on PPARs as possible therapeutic targets for cancer. Therefore, this review will focus on the existing and future uses of PPARs agonists and antagonists in treating malignancies. PubMed, Science Direct, and Scopus databases were searched regarding the effect of PPARs on various types of cancers until the end of May 2023. The results of the review articles showed the therapeutic influence of PPARs on a wide range of cancer on in vitro, in vivo and clinical studies. However, further experimental and clinical studies are needed to be conducted on the influence of PPARs on various cancers.

MiR-455-3p mediates PPARα through UBN2 to promote apoptosis and autophagy in acute myeloid leukemia cells

Acute myeloid leukemia (AML) is one of the deadliest hematologic malignancies, and its targeted therapy has developed slowly. The molecular mechanism of the pathophysiology of the disease remains to be clarified. The aim of our study was to probe the specific regulatory mechanism of miR-455-3p in AML. This study measured the levels of miR-455-3p and ubinuclein-2 (UBN2) in AML cell lines, evaluated cell viability with CCK-8, used flow cytometry to estimate the cell cycle and apoptosis, detected cell apoptosis and autophagy-related protein levels by Western blotting, and added 50 μM chloroquine (CQ) to evaluate the relationship between autophagy and AML. In animal experiments, HL-60 cells were injected into male non-obese diabetic/severe combined immunodeficiency disease (NOD/SCID) mice through the tail vein to determine survival time and observe the degree of liver and spleen damage in the mice. miR-455-3p was prominently reduced in the peripheral blood and AML cell lines, and UBN2 showed high expression. The transfected miR-455-3p mimic effectively restrained the activity of AML cells, whereas overexpression of UBN2 or the addition of the autophagy inhibitor CQ reversed the effect of miR-455-3p. The interaction between UBN2 and peroxisome proliferator-activated receptor alpha (PPARα) was confirmed by coimmunoprecipitation, and overexpression of PPARα reversed the promoting effect of UBN2 knockdown on apoptosis and autophagy in AML cells. In conclusion, miR-455-3p mediates PPARα protein expression through UBN2, exacerbating AML cell apoptosis and autophagy. This study found that miR-455-3p plays an important role in AML cell apoptosis and autophagy, which may provide novel insights for the treatment of AML diseases.

Comparative analyses of transcriptome sequencing and carcinogenic exposure toxicity of nicotine and 6-methyl nicotine in human bronchial epithelial cells

Electronic cigarettes have become a purported safer alternative to the conventional cigarettes in recent years. Nicotine is the main component of electronic cigarettes, and other nicotinic compounds are synthesized as alternatives to nicotine. However, scientific data on the potential health effects of electronic cigarettes are scarce. Herein, we evaluated the cytotoxicity of nicotine and its analog 6-methyl nicotine (6-MN) on human bronchial epithelial cells (BEAS-2B cells) in vitro. Furthermore, we performed transcriptome sequencing to systematically assess the effects of nicotine and 6-MN on BEAS-2B cells. The cytotoxicity assay revealed that BEAS-2B cells were more sensitive to 6-MN than to nicotine. Transcriptome sequencing revealed 1208 differentially expressed cancer-related proteins (CRP) in the 6-MN groups relative to that with CRP in the control group. In addition, 6-MN had a greater negative effect on the CRP expression than nicotine. Bioinformatic analysis revealed that the differentially expressed genes and proteins in the 6-MN group were significantly enriched in the cancer-related pathways, unlike those in the nicotine group. Further validations of some lung cancer-related proteins, such as NF-κB p65, EGFR, and MET, were conducted by immunoblotting and real-time PCR, which revealed that 6-MN may have a greater negative effect on tumor development and metastasis than nicotine. Taken together, our findings suggest that new electronic cigarettes with 6-MN might offer some advantages over conventional electronic cigarettes containing nicotine.

Peroxisome proliferator-activated receptors as therapeutic target for cancer

Peroxisome proliferator-activated receptors (PPARs) are transcription factors belonging to the nuclear receptor family. There are three subtypes of PPARs, including PPAR-α, PPAR-β/δ and PPAR-γ. They are expressed in different tissues and act by regulating the expression of target genes in the form of binding to ligands. Various subtypes of PPAR have been shown to have significant roles in a wide range of biological processes including lipid metabolism, body energy homeostasis, cell proliferation and differentiation, bone formation, tissue repair and remodelling. Recent studies have found that PPARs are closely related to tumours. They are involved in cancer cell growth, angiogenesis and tumour immune response, and are essential components in tumour progression and metastasis. As such, they have become a target for cancer therapy research. In this review, we discussed the current state of knowledge on the involvement of PPARs in cancer, including their role in tumourigenesis, the impact of PPARs in tumour microenvironment and the potential of using PPARs combinational therapy to treat cancer by targeting essential signal pathways, or as adjuvants to boost the effects of current chemo and immunotherapies. Our review highlights the complexity of PPARs in cancer and the need for a better understanding of the mechanism in order to design effective cancer therapies.

The role of peroxisome proliferator-activated receptors in the tumor microenvironment, tumor cell metabolism, and anticancer therapy

Peroxisome proliferator-activated receptors (PPARs) have been extensively studied for over 3 decades and consist of three isotypes, including PPARα, γ, and β/δ, that were originally considered key metabolic regulators controlling energy homeostasis in the body. Cancer has become a leading cause of human mortality worldwide, and the role of peroxisome proliferator-activated receptors in cancer is increasingly being investigated, especially the deep molecular mechanisms and effective cancer therapies. Peroxisome proliferator-activated receptors are an important class of lipid sensors and are involved in the regulation of multiple metabolic pathways and cell fate. They can regulate cancer progression in different tissues by activating endogenous or synthetic compounds. This review emphasizes the significance and knowledge of peroxisome proliferator-activated receptors in the tumor microenvironment, tumor cell metabolism, and anti-cancer treatment by summarizing recent research on peroxisome proliferator-activated receptors. In general, peroxisome proliferator-activated receptors either promote or suppress cancer in different types of tumor microenvironments. The emergence of this difference depends on various factors, including peroxisome proliferator-activated receptor type, cancer type, and tumor stage. Simultaneously, the effect of anti-cancer therapy based on drug-targeted PPARs differs or even opposes among the three peroxisome proliferator-activated receptor homotypes and different cancer types. Therefore, the current status and challenges of the use of peroxisome proliferator-activated receptors agonists and antagonists in cancer treatment are further explored in this review.

High TXNIP expression accelerates the migration and invasion of the GDM placenta trophoblast

INTRODUCTION

Our previous study has proofed the glucose sensitive gene-thioredoxin-interacting protein (TXNIP) expression was up in the placenta of the patients with gestational diabetes mellitus (GDM), but the pathological mechanisms underlying abnormal TXNIP expression in the placenta of patients with GDM is completely unclear and additional investigations are required to explain the findings we have observed. In the present study, we simulated the high TXNIP expression via introducing the Tet-On "switch" in vitro, approximate to its expression level in the real world, to explore the following consequence of the abnormal TXNIP.

METHODS

The expression and localization of TXNIP in the placenta of GDM patients and the health control was investigated via immunofluorescent staining, western blot and RT-qPCR. Overexpression of TXNIP was achieved through transfecting Tet-on system to the human trophoblastic cell line-HTR-8/Svneo cell. TXNIP knockout was obtained via CRISPR-Cas9 method. The cell phenotype was observed via IncuCyte Imaging System and flow cytometry. The mechanism was explored via western blot and RT-qPCR.

RESULTS

The expression level of TXNIP in the GDM placenta was nearly 2-3 times higher than that in the control. The TXNIP located at trophoblastic cells of the placenta. When the expression of TXNIP was upregulated, the migration and invasion of the cells accelerated, but cell apoptosis and proliferation did not changed compared with the control group. Furthermore, the size of the TetTXNIP cells became larger, and the expression level of Vimentin and p-STAT3 increased in the TetTXNIP cells. All the changes mentioned above were opposite in the TXNIP-KO cells.

CONCLUSIONS

Abnormal expression of TXNIP might be related to the impairment of the GDM placental function, affecting the migration and invasion of the placental trophoblast cells through STAT3 and Vimentin related pathway; thus, TXNIP might be the potential therapeutic target for repairing the placental dysfunction deficient in GDM patients.

Melatonin inhibits bladder tumorigenesis by suppressing PPARγ/ENO1-mediated glycolysis

Melatonin is a well-known natural hormone, which shows a potential anticancer effect in many human cancers. Bladder cancer (BLCA) is one of the most malignant human cancers in the world. Chemoresistance is an increasingly prominent phenomenon that presents an obstacle to the clinical treatment of BLCA. There is an urgent need to investigate novel drugs to improve the current clinical status. In our study, we comprehensively explored the inhibitory effect of melatonin on BLCA and found that it could suppress glycolysis process. Moreover, we discovered that ENO1, a glycolytic enzyme involved in the ninth step of glycolysis, was the downstream effector of melatonin and could be a predictive biomarker of BLCA. We also proved that enhanced glycolysis simulated by adding exogenous pyruvate could induce gemcitabine resistance, and melatonin treatment or silencing of ENO1 could intensify the cytotoxic effect of gemcitabine on BLCA cells. Excessive accumulation of reactive oxygen species (ROS) mediated the inhibitory effect of melatonin on BLCA cells. Additionally, we uncovered that PPARγ was a novel upstream regulator of ENO1, which mediated the downregulation of ENO1 caused by melatonin. Our study offers a fresh perspective on the anticancer effect of melatonin and encourages further studies on clinical chemoresistance.

PPARs and the Kynurenine Pathway in Melanoma-Potential Biological Interactions

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors involved in various physiological and pathological processes within the skin. PPARs regulate several processes in one of the most aggressive skin cancers, melanoma, including proliferation, cell cycle, metabolic homeostasis, cell death, and metastasis. In this review, we focused not only on the biological activity of PPAR isoforms in melanoma initiation, progression, and metastasis but also on potential biological interactions between the PPAR signaling and the kynurenine pathways. The kynurenine pathway is a major pathway of tryptophan metabolism leading to nicotinamide adenine dinucleotide (NAD+) production. Importantly, various tryptophan metabolites exert biological activity toward cancer cells, including melanoma. Previous studies confirmed the functional relationship between PPAR and the kynurenine pathway in skeletal muscles. Despite the fact this interaction has not been reported in melanoma to date, some bioinformatics data and biological activity of PPAR ligands and tryptophan metabolites may suggest a potential involvement of these metabolic and signaling pathways in melanoma initiation, progression, and metastasis. Importantly, the possible relationship between the PPAR signaling pathway and the kynurenine pathway may relate not only to the direct biological effect on melanoma cells but also to the tumor microenvironment and the immune system.

Physiological and Pathophysiological Roles of Thioredoxin Interacting Protein: A Perspective on Redox Inflammation and Metabolism

Significance: Thioredoxin interacting protein (TXNIP) is a member of the arrestin fold superfamily with important cellular functions, including cellular transport, mitochondrial energy generation, and protein cycling. It is the only arrestin-domain protein known to covalently bind to thioredoxin and plays roles in glucose metabolism, inflammation, apoptosis, and cancer. Recent Advances: The crystal structure of the TXNIP-thioredoxin complex provided details about this fascinating interaction. Recent studies showed that TXNIP is induced by endoplasmic reticulum (ER) stress, activates NLR family pyrin domain containing 3 (NLRP3) inflammasomes, and can regulate glucose transport into cells. The tumor suppressor role of TXNIP in various cancer types and the role of TXNIP in fructose absorption are now described. Critical Issues: The influence of TXNIP on redox state is more complex than its interaction with thioredoxin. Future Directions: It is incompletely understood which functions of TXNIP are thioredoxin-dependent. It is also unclear whether TXNIP binding can inhibit glucose transporters without endocytosis. TXNIP-regulated control of ER stress should also be investigated further. Antioxid. Redox Signal. 38, 442-460.

NRF2 and Key Transcriptional Targets in Melanoma Redox Manipulation

Melanocytes are dendritic, pigment-producing cells located in the skin and are responsible for its protection against the deleterious effects of solar ultraviolet radiation (UVR), which include DNA damage and elevated reactive oxygen species (ROS). They do so by synthesizing photoprotective melanin pigments and distributing them to adjacent skin cells (e.g., keratinocytes). However, melanocytes encounter a large burden of oxidative stress during this process, due to both exogenous and endogenous sources. Therefore, melanocytes employ numerous antioxidant defenses to protect themselves; these are largely regulated by the master stress response transcription factor, nuclear factor erythroid 2-related factor 2 (NRF2). Key effector transcriptional targets of NRF2 include the components of the glutathione and thioredoxin antioxidant systems. Despite these defenses, melanocyte DNA often is subject to mutations that result in the dysregulation of the proliferative mitogen-activated protein kinase (MAPK) pathway and the cell cycle. Following tumor initiation, endogenous antioxidant systems are co-opted, a consequence of elevated oxidative stress caused by metabolic reprogramming, to establish an altered redox homeostasis. This altered redox homeostasis contributes to tumor progression and metastasis, while also complicating the application of exogenous antioxidant treatments. Further understanding of melanocyte redox homeostasis, in the presence or absence of disease, would contribute to the development of novel therapies to aid in the prevention and treatment of melanomas and other skin diseases.

Potential Therapeutic Effects of PPAR Ligands in Glioblastoma

Glioblastoma (GB), also known as grade IV astrocytoma, represents the most aggressive form of brain tumor, characterized by extraordinary heterogeneity and high invasiveness and mortality. Thus, a great deal of interest is currently being directed to investigate a new therapeutic strategy and in recent years, the research has focused its attention on the evaluation of the anticancer effects of some drugs already in use for other diseases. This is the case of peroxisome proliferator-activated receptors (PPARs) ligands, which over the years have been revealed to possess anticancer properties. PPARs belong to the nuclear receptor superfamily and are divided into three main subtypes: PPAR-α, PPAR-β/δ, and PPAR-γ. These receptors, once activated by specific natural or synthetic ligands, translocate to the nucleus and dimerize with the retinoid X receptors (RXR), starting the signal transduction of numerous genes involved in many physiological processes. PPARs receptors are activated by specific ligands and participate principally in the preservation of homeostasis and in lipid and glucose metabolism. In fact, synthetic PPAR-α agonists, such as fibrates, are drugs currently in use for the clinical treatment of hypertriglyceridemia, while PPAR-γ agonists, including thiazolidinediones (TZDs), are known as insulin-sensitizing drugs. In this review, we will analyze the role of PPARs receptors in the progression of tumorigenesis and the action of PPARs agonists in promoting, or not, the induction of cell death in GB cells, highlighting the conflicting opinions present in the literature.

PPARs and Tumor Microenvironment: The Emerging Roles of the Metabolic Master Regulators in Tumor Stromal-Epithelial Crosstalk and Carcinogenesis

Peroxisome proliferator-activated receptors (PPARs) have been extensively studied for more than three decades. Consisting of three isotypes, PPARα, γ, and β/δ, these nuclear receptors are regarded as the master metabolic regulators which govern many aspects of the body energy homeostasis and cell fate. Their roles in malignancy are also increasingly recognized. With the growing interest in crosstalk between tumor stroma and epithelium, this review aims to highlight the current knowledge on the implications of PPARs in the tumor microenvironment. PPARγ plays a crucial role in the metabolic reprogramming of cancer-associated fibroblasts and adipocytes, coercing the two stromal cells to become substrate donors for cancer growth. Fibroblast PPARβ/δ can modify the risk of tumor initiation and cancer susceptibility. In endothelial cells, PPARβ/δ and PPARα are pro- and anti-angiogenic, respectively. Although the angiogenic role of PPARγ remains ambiguous, it is a crucial regulator in autocrine and paracrine signaling of cancer-associated fibroblasts and tumor-associated macrophages/immune cells. Of note, angiopoietin-like 4 (ANGPTL4), a secretory protein encoded by a target gene of PPARs, triggers critical oncogenic processes such as inflammatory signaling, extracellular matrix derangement, anoikis resistance and metastasis, making it a potential drug target for cancer treatment. To conclude, PPARs in the tumor microenvironment exhibit oncogenic activities which are highly controversial and dependent on many factors such as stromal cell types, cancer types, and oncogenesis stages. Thus, the success of PPAR-based anticancer treatment potentially relies on innovative strategies to modulate PPAR activity in a cell type-specific manner.