Peroxidasin protein expression and enzymatic activity in metastatic melanoma cell lines are associated with invasive potential

Peroxidasin is associated with a mesenchymal-like transcriptional phenotype and promotes invasion in metastatic melanoma

Cutaneous melanoma is a highly invasive, heterogeneous and treatment resistant cancer. It's ability to dynamically shift between transcriptional states or phenotypes results in an adaptive cell plasticity that may drive cancer cell invasion or the development of therapy resistance. The expression of peroxidasin (PXDN), an extracellular matrix peroxidase, has been proposed to be associated with the invasive metastatic melanoma phenotype. We have confirmed this association by analysing the transcriptomes of 70 metastatic melanoma cell lines with variable levels of PXDN expression. This analysis highlighted a strong association between high PXDN expression and the undifferentiated invasive melanoma phenotype. To assess the functional role of PXDN in melanoma invasion, we performed a knockout of PXDN in a highly invasive cell line (NZM40). PXDN knockout decreased the invasive potential by ∼50 % and decreased the expression of epithelial-mesenchymal transition and invasive marker genes as determined by RNAseq and substantiated by proteomics analysis. Bioinformatics analysis of differentially expressed genes following PXDN knockout highlighted decreases in genes linked to extracellular matrix formation, organization and degradation as well as signalling pathways such as the WNT pathway. This study provides compelling evidence that PXDN plays a functional role in melanoma invasion by promoting an invasive, mesenchymal-like transcriptional phenotype.

Obesity-driven changes in breast tissue exhibit a pro-angiogenic extracellular matrix signature

Obesity has reached epidemic proportions in the United States, emerging as a risk factor for the onset of breast cancer and a harbinger of unfavorable outcomes [1], [2], [3]. Despite limited understanding of the precise mechanisms, both obesity and breast cancer are associated with extracellular matrix (ECM) rewiring [4], [5], [6]. Utilizing total breast tissue proteomics, we analyzed normal-weight (18.5 to < 25 kg/m2), overweight (25 to < 30 kg/m2), and obese (≥30 kg/m2) individuals to identify potential ECM modifying proteins for cancer development and acceleration. Obese individuals exhibited substantial ECM alterations, marked by increased basement membrane deposition, angiogenic signatures, and ECM-modifying proteins. Notably, the collagen IV crosslinking enzyme peroxidasin (PXDN) emerged as a potential mediator of the ECM changes in individuals with an elevated body mass index (BMI), strongly correlating with angiogenic and basement membrane signatures. Furthermore, glycan-binding proteins galectin-1 (LGALS1) and galectin-3 (LGALS3), which play crucial roles in matrix interactions and angiogenesis, also strongly correlate with ECM modifications. In breast cancer, elevated PXDN, LGALS1, and LGALS3 correlate with reduced relapse-free and distant-metastatic-free survival. These proteins were significantly associated with mesenchymal stromal cell markers, indicating adipocytes and fibroblasts may be the primary contributors of the obesity-related ECM changes. Our findings unveil a pro-angiogenic ECM signature in obese breast tissue, offering potential targets to inhibit breast cancer development and progression.

Exploring mammalian heme peroxidases: A comprehensive review on the structure and function of myeloperoxidase, lactoperoxidase, eosinophil peroxidase, thyroid peroxidase and peroxidasin

The peroxidase family of enzymes is a ubiquitous cluster of enzymes primarily responsible for the oxidation of organic and inorganic substrates. The mammalian heme peroxidase subfamily is characterized by a covalently linked heme prosthetic group which plays a key role in the oxidation of halides and psuedohalides into their respective hypohalous acid and hypothiocyanous acid under the influence of H2O2 as substrate. The members of the heme peroxidase family include Lactoperoxidase (LPO), Eosinophil peroxidase (EPO), Myeloperoxidase (MPO), Thyroid peroxidase (TPO) and Peroxidasin (PXDN). The biological activity of LPO, MPO and EPO pertains to antibacterial, antifungal and antiviral while TPO is involved in the biosynthesis of the thyroid hormone and PXDN helps maintain the ECM. While these enzymes play several immunomodulatory roles, aberrations in their activity have been implicated in diseases such as myocardial infarction, asthma and Alzheimer's amongst others. The sequence and structural similarities amongst the members of the family are strikingly high while the substrate specificities and subcellular locations vary. Hence, it becomes important to provide a consortium of information regarding the members to study their biochemical, pathological and clinical function.

DNA Methylation of PXDN Is Associated with Early-Life Adversity in Adult Mental Disorders

Early-life adversity (ELA) is characterized by exposure to traumatic events during early periods of life, particularly involving emotional, sexual and/or physical adversities during childhood. Mental disorders are strongly influenced by environmental and lifestyle-related risk factors including ELA. However, the molecular link between ELA and the risk of an adult mental disorder is still not fully understood. Evidence is emerging that long-lasting changes in the epigenetic processes regulating gene expression, such as DNA methylation, play an important role in the biological mechanisms linking ELA and mental disorders. Based on a recent study, we analyzed the DNA methylation of a specific CpG site within the gene PXDN-cg10888111-in blood in the context of ELA across a set of psychiatric disorders, namely Borderline Personality Disorder (BPD), Major Depressive Disorder (MDD) and Social Anxiety Disorder (SAD), and its potential contribution to their pathogenesis. We found significant hypermethylation in mentally ill patients with high levels of ELA compared to patients with low levels of ELA, whereas cg10888111 methylation in healthy control individuals was not affected by ELA. Further investigations revealed that this effect was driven by the MDD cohort. Providing a direct comparison of cg10888111 DNA methylation in blood in the context of ELA across three mental disorders, our results indicate the role of PXDN regulation in the response to ELA in the pathogenesis of mental disorders, especially MDD. Further studies will be needed to validate these results and decipher the corresponding biological network that is involved in the transmission of ELA to an adult mental disorder in general.

Melanoma redox biology and the emergence of drug resistance

Melanoma is the deadliest form of skin cancer, with the loss of approximately 60,000 lives world-wide each year. Despite the development of targeted therapeutics, including compounds that have selectivity for mutant oncoproteins expressed only in cancer cells, many patients are either unresponsive to initial therapy or their tumors acquire resistance. This results in five-year survival rates of below 25%. New strategies that either kill drug-resistant melanoma cells or prevent their emergence would be extremely valuable. Melanoma, like other cancers, has long been described as being under increased oxidative stress, resulting in an increased reliance on antioxidant defense systems. Changes in redox homeostasis are most apparent during metastasis and during the metabolic reprogramming associated with the development of treatment resistance. This review discusses oxidative stress in melanoma, with a particular focus on targeting antioxidant pathways to limit the emergence of drug resistant cells.

Identification of tyrosine brominated extracellular matrix proteins in normal and fibrotic lung tissues

Peroxidasin (PXDN) is a secreted heme peroxidase that catalyzes the oxidative crosslinking of collagen IV within the extracellular matrix (ECM) via intermediate hypobromous acid (HOBr) synthesis from hydrogen peroxide and bromide, but recent findings have also suggested alternative ECM protein modifications by PXDN, including incorporation of bromide into tyrosine residues. In this work, we sought to identify the major target proteins for tyrosine bromination by HOBr or by PXDN-mediated oxidation in ECM from mouse teratocarcinoma PFHR9 cells. We detected 61 bromotyrosine (BrY)-containing peptides representing 23 proteins in HOBr-modified ECM from PFHR9 cells, among which laminins displayed the most prominent bromotyrosine incorporation. Moreover, we also found that laminin α1, laminin β1, and tubulointerstitial nephritis antigen-like (TINAGL1) contained BrY in untreated PFHR9 cells, which depended on PXDN. We extended these analyses to lung tissues from both healthy mice and mice with experimental lung fibrosis, and in lung tissues obtained from human subjects. Analysis of ECM-enriched mouse lung tissue extracts showed that 83 ECM proteins were elevated in bleomycin-induced fibrosis, which included various collagens and laminins, and PXDN. Similarly, mRNA and protein expression of PXDN and laminin α/β1 were enhanced in fibrotic mouse lung tissues, and also in mouse bone-marrow-derived macrophages or human fibroblasts stimulated with transforming growth factor β1, a profibrotic growth factor. We identified 11 BrY-containing ECM proteins, including collagen IV α2, collagen VI α1, TINAGL1, and various laminins, in both healthy and mouse fibrotic lung tissues, although the relative extent of tyrosine bromination of laminins was not significantly increased during fibrosis. Finally, we also identified 7 BrY-containing ECM proteins in human lung tissues, again including collagen IV α2, collagen VI α1, and TINAGL1. Altogether, this work demonstrates the presence of several bromotyrosine-modified ECM proteins, likely involving PXDN, even in normal lung tissues, suggesting a potential biological function for these modifications.

An engineering strategy to target activated EGFR with CAR T cells

Chimeric antigen receptor (CAR) T cells have shown remarkable response rates in hematological malignancies. In contrast, CAR T cell treatment of solid tumors is associated with several challenges, in particular the expression of most tumor-associated antigens at lower levels in vital organs, resulting in on-target/off-tumor toxicities. Thus, innovative approaches to improve the tumor specificity of CAR T cells are urgently needed. Based on the observation that many human solid tumors activate epidermal growth factor receptor (EGFR) on their surface through secretion of EGFR ligands, we developed an engineering strategy for CAR-binding domains specifically directed against the ligand-activated conformation of EGFR. We show, in several experimental systems, that the generated binding domains indeed enable CAR T cells to distinguish between active and inactive EGFR. We anticipate that this engineering concept will be an important step forward to improve the tumor specificity of CAR T cells directed against EGFR-positive solid cancers.

Reactive Halogen Species: Role in Living Systems and Current Research Approaches

Reactive halogen species (RHS) are highly reactive compounds that are normally required for regulation of immune response, inflammatory reactions, enzyme function, etc. At the same time, hyperproduction of highly reactive compounds leads to the development of various socially significant diseases - asthma, pulmonary hypertension, oncological and neurodegenerative diseases, retinopathy, and many others. The main sources of (pseudo)hypohalous acids are enzymes from the family of heme peroxidases - myeloperoxidase, lactoperoxidase, eosinophil peroxidase, and thyroid peroxidase. Main targets of these compounds are proteins and peptides, primarily methionine and cysteine residues. Due to the short lifetime, detection of RHS can be difficult. The most common approach is detection of myeloperoxidase, which is thought to reflect the amount of RHS produced, but these methods are indirect, and the results are often contradictory. The most promising approaches seem to be those that provide direct registration of highly reactive compounds themselves or products of their interaction with components of living cells, such as fluorescent dyes. However, even such methods have a number of limitations and can often be applied mainly for in vitro studies with cell culture. Detection of reactive halogen species in living organisms in real time is a particularly acute issue. The present review is devoted to RHS, their characteristics, chemical properties, peculiarities of interaction with components of living cells, and methods of their detection in living systems. Special attention is paid to the genetically encoded tools, which have been introduced recently and allow avoiding a number of difficulties when working with living systems.

Inflammation-Associated Cytotoxic Agents in Tumorigenesis

Chronic inflammatory processes are related to all stages of tumorigenesis. As inflammation is closely associated with the activation and release of different cytotoxic agents, the interplay between cytotoxic agents and antagonizing principles is highlighted in this review to address the question of how tumor cells overcome the enhanced values of cytotoxic agents in tumors. In tumor cells, the enhanced formation of mitochondrial-derived reactive species and elevated values of iron ions and free heme are antagonized by an overexpression of enzymes and proteins, contributing to the antioxidative defense and maintenance of redox homeostasis. Through these mechanisms, tumor cells can even survive additional stress caused by radio- and chemotherapy. Through the secretion of active agents from tumor cells, immune cells are suppressed in the tumor microenvironment and an enhanced formation of extracellular matrix components is induced. Different oxidant- and protease-based cytotoxic agents are involved in tumor-mediated immunosuppression, tumor growth, tumor cell invasion, and metastasis. Considering the special metabolic conditions in tumors, the main focus here was directed on the disturbed balance between the cytotoxic agents and protective mechanisms in late-stage tumors. This knowledge is mandatory for the implementation of novel anti-cancerous therapeutic approaches.

Peroxidasin Inhibition by Phloroglucinol and Other Peroxidase Inhibitors

Human peroxidasin (PXDN) is a ubiquitous peroxidase enzyme expressed in most tissues in the body. PXDN represents an interesting therapeutic target for inhibition, as it plays a role in numerous pathologies, including cardiovascular disease, cancer and fibrosis. Like other peroxidases, PXDN generates hypohalous acids and free radical species, thereby facilitating oxidative modifications of numerous biomolecules. We have studied the inhibition of PXDN halogenation and peroxidase activity by phloroglucinol and 14 other peroxidase inhibitors. Although a number of compounds on their own potently inhibited PXDN halogenation activity, only five were effective in the presence of a peroxidase substrate with IC50 values in the low μM range. Using sequential stopped-flow spectrophotometry, we examined the mechanisms of inhibition for several compounds. Phloroglucinol was the most potent inhibitor with a nanomolar IC50 for purified PXDN and IC50 values of 0.95 μM and 1.6 μM for the inhibition of hypobromous acid (HOBr)-mediated collagen IV cross-linking in a decellularized extracellular matrix and a cell culture model. Other compounds were less effective in these models. Most interestingly, phloroglucinol was identified to irreversibly inhibit PXDN, either by mechanism-based inhibition or tight binding. Our work has highlighted phloroglucinol as a promising lead compound for the design of highly specific PXDN inhibitors and the assays used in this study provide a suitable approach for high-throughput screening of PXDN inhibitors.

The role of peroxidasin in solid cancer progression

Peroxidasin is a heme-containing peroxidase enzyme that plays a vital role in the cross-linking of collagen IV molecules in basement membranes. Collagen IV cross-links are essential for providing structure and mechanical stability throughout tissue development, homeostasis, and wound healing. During cancer progression, the basement membrane is degraded, and proteins typically found in the basement membrane, including peroxidasin and collagen IV, can be found spread throughout the tumour microenvironment where they interact with cancer cells and alter cell behaviour. Whilst peroxidasin is reported to be up-regulated in a number of different cancers, the role that it plays in disease progression and metastasis has only recently begun to be studied. This review highlights the current literature exploring the known roles of peroxidasin in normal tissues and cancer progression, regulators of peroxidasin expression, and the reported relationships between peroxidasin expression and patient outcome in cancer.

Acidic Growth Conditions Promote Epithelial-to-Mesenchymal Transition to Select More Aggressive PDAC Cell Phenotypes In Vitro

Pancreatic Ductal Adenocarcinoma (PDAC) is characterized by an acidic microenvironment, which contributes to therapeutic failure. So far there is a lack of knowledge with respect to the role of the acidic microenvironment in the invasive process. This work aimed to study the phenotypic and genetic response of PDAC cells to acidic stress along the different stages of selection. To this end, we subjected the cells to short- and long-term acidic pressure and recovery to pH_e 7.4. This treatment aimed at mimicking PDAC edges and consequent cancer cell escape from the tumor. The impact of acidosis was assessed for cell morphology, proliferation, adhesion, migration, invasion, and epithelial-mesenchymal transition (EMT) via functional in vitro assays and RNA sequencing. Our results indicate that short acidic treatment limits growth, adhesion, invasion, and viability of PDAC cells. As the acid treatment progresses, it selects cancer cells with enhanced migration and invasion abilities induced by EMT, potentiating their metastatic potential when re-exposed to pH_e 7.4. The RNA-seq analysis of PANC-1 cells exposed to short-term acidosis and pH_e-selected recovered to pH_e 7.4 revealed distinct transcriptome rewiring. We describe an enrichment of genes relevant to proliferation, migration, EMT, and invasion in acid-selected cells. Our work clearly demonstrates that upon acidosis stress, PDAC cells acquire more invasive cell phenotypes by promoting EMT and thus paving the way for more aggressive cell phenotypes.

Extracellular matrix remodeling in tumor progression and immune escape: from mechanisms to treatments

The malignant tumor is a multi-etiological, systemic and complex disease characterized by uncontrolled cell proliferation and distant metastasis. Anticancer treatments including adjuvant therapies and targeted therapies are effective in eliminating cancer cells but in a limited number of patients. Increasing evidence suggests that the extracellular matrix (ECM) plays an important role in tumor development through changes in macromolecule components, degradation enzymes and stiffness. These variations are under the control of cellular components in tumor tissue via the aberrant activation of signaling pathways, the interaction of the ECM components to multiple surface receptors, and mechanical impact. Additionally, the ECM shaped by cancer regulates immune cells which results in an immune suppressive microenvironment and hinders the efficacy of immunotherapies. Thus, the ECM acts as a barrier to protect cancer from treatments and supports tumor progression. Nevertheless, the profound regulatory network of the ECM remodeling hampers the design of individualized antitumor treatment. Here, we elaborate on the composition of the malignant ECM, and discuss the specific mechanisms of the ECM remodeling. Precisely, we highlight the impact of the ECM remodeling on tumor development, including proliferation, anoikis, metastasis, angiogenesis, lymphangiogenesis, and immune escape. Finally, we emphasize ECM "normalization" as a potential strategy for anti-malignant treatment.

Peroxidase is a novel potential marker in glioblastoma through bioinformatics method and experimental validation

Peroxidase (PXDN), a specific extracellular matrix (ECM)-associated protein, has been determined as a tumor indicator and therapeutic target in various tumors. However, the effects of PXDN in prognostic performance and clinical implications in glioblastoma multiforme (GBM) remains unknown. Here, we assessed PXDN expression pattern and its performance on prognosis among GBM cases from TCGA and CGGA databases. PXDN was up-regulated within GBM samples in comparison with normal control. High PXDN expression was a dismal prognostic indicator in GBM. Single cell RNA analysis was conducted to detect the cell localization of PXDN. We also set up a PPI network to explore the interacting protein associated with PXDN, including TSKU, COL4A1 and COL5A1. Consistently, functional enrichment analysis revealed that several cancer hallmarks were enriched in the GBM cases with high PXDN expression, such as epithelial-mesenchymal transition (EMT), fatty acid metabolism, glycolysis, hypoxia, inflammatory response, and Wnt/beta-catenin signaling pathway. Next, this study analyzed the association of PXDN expression and immunocyte infiltration. PXDN expression was in direct proportion to the infiltrating degrees of NK cells resting, T cells regulatory, M0 macrophage, monocytes and eosinophils. The roles of PXDN on immunity were further estimated by PXDN-associated immunomodulators. In addition, four prognosis-related lncRNAs co-expressed with PXDN were identified. Finally, we observed that PXDN depletion inhibits GBM cell proliferation and migration by in vitro experiments. Our data suggested that PXDN has the potential to be a powerful prognostic biomarker, which might offer a basis for developing therapeutic targets for GBM.

Measuring peroxidasin activity in live cells using bromide addition for signal amplification

Peroxidasin (PXDN) is involved in the crosslinking of collagen IV, a major constituent of basement membranes. Disruption of basement membrane integrity as observed in genetic alterations of collagen IV or PXDN can result in developmental defects and diverse pathologies. Hence, the study of PXDN activity in (patho)physiological contexts is highly relevant. So far, measurements of PXDN activity have been reported from purified proteins, cell lysates and de-cellularized extracellular matrix. Here, for the first time we report the measurement of PXDN activity in live cells using the Amplex Red assay with a signal amplifying modification. We observe that bromide addition enhances the obtained signal, most likely due to formation of HOBr. Abrogation of signal amplification by the HOBr scavenger carnosine supports this hypothesis. Both, pharmacological inhibition as well as complementary genetic approaches confirm that the obtained signal is indeed related to PXDN activity. We validate the modified assay by investigating the effect of Brefeldin A, to inhibit the secretory pathway and thus the access of PXDN to the extracellular Amplex Red dye. Our method opens up new possibilities to investigate the activity of PXDN in (patho)physiological contexts.

Uric Acid Reacts with Peroxidasin, Decreases Collagen IV Crosslink, Impairs Human Endothelial Cell Migration and Adhesion

Uric acid is considered the main substrate for peroxidases in plasma. The oxidation of uric acid by human peroxidases generates urate free radical and urate hydroperoxide, which might affect endothelial function and explain, at least in part, the harmful effects of uric acid on the vascular system. Peroxidasin (PXDN), the most recent heme-peroxidase described in humans, catalyzes the formation of hypobromous acid, which mediates collagen IV crosslinks in the extracellular matrix. This enzyme has gained increasing scientific interest since it is associated with cardiovascular disease, cancer, and renal fibrosis. The main objective here was to investigate whether uric acid would react with PXDN and compromise the function of the enzyme in human endothelial cells. Urate decreased Amplex Red oxidation and brominating activity in the extracellular matrix (ECM) from HEK293/PXDN overexpressing cells and in the secretome of HUVECs. Parallelly, urate was oxidized to 5-hydroxyisourate. It also decreased collagen IV crosslink in isolated ECM from PFHR9 cells. Urate, the PXDN inhibitor phloroglucinol, and the PXDN knockdown impaired migration and adhesion of HUVECs. These results demonstrated that uric acid can affect extracellular matrix formation by competing for PXDN. The oxidation of uric acid by PXDN is likely a relevant mechanism in the endothelial dysfunction related to this metabolite.

Mammalian peroxidasin (PXDN): From physiology to pathology

Heme-containing peroxidases catalyze the oxidation of a variety of substrates by consuming hydrogen peroxide (H2O2), and play diversified roles in physiology and pathology including innate immunity, the synthesis of thyroid hormone and the extracellular matrix, as well as the pathogenesis of several inflammatory diseases. Peroxidasin (PXDN), also known as Vascular Peroxidase-1 (VPO1), is a newly identified peroxidase and expresses in multiple cells and tissues including cardiovascular system and the lung. Recent studies imply its roles in the innate immunity, cardiovascular physiology and diseases, and extracellular matrix formation. Studies on the role of PXDN in human diseases are entering a new and exciting stage, and this review provides the insights into this emerging field of PXDN.