A new role for LOX and LOXL2 proteins in transcription regulation

Interactions between BRD4S, LOXL2, and MED1 drive cell cycle transcription in triple-negative breast cancer

Triple-negative breast cancer (TNBC) often develops resistance to single-agent treatment, which can be circumvented using targeted combinatorial approaches. Here, we demonstrate that the simultaneous inhibition of LOXL2 and BRD4 synergistically limits TNBC proliferation in vitro and in vivo. Mechanistically, LOXL2 interacts in the nucleus with the short isoform of BRD4 (BRD4S), MED1, and the cell cycle transcriptional regulator B-MyB. These interactions sustain the formation of BRD4 and MED1 nuclear transcriptional foci and control cell cycle progression at the gene expression level. The pharmacological co-inhibition of LOXL2 and BRD4 reduces BRD4 nuclear foci, BRD4-MED1 colocalization, and the transcription of cell cycle genes, thus suppressing TNBC cell proliferation. Targeting the interaction between BRD4S and LOXL2 could be a starting point for the development of new anticancer strategies for the treatment of TNBC.

Lysyl Oxidases as Targets for Cancer Therapy and Diagnostic Imaging

The understanding of the contribution of the tumour microenvironment to cancer progression and metastasis, in particular the interplay between tumour cells, fibroblasts and the extracellular matrix has grown tremendously over the last years. Lysyl oxidases are increasingly recognised as key players in this context, in addition to their function as drivers of fibrotic diseases. These insights have considerably stimulated drug discovery efforts towards lysyl oxidases as targets over the last decade. This review article summarises the biochemical and structural properties of theses enzymes. Their involvement in tumour progression and metastasis is highlighted from a biochemical point of view, taking into consideration both the extracellular and intracellular action of lysyl oxidases. More recently reported inhibitor compounds are discussed with an emphasis on their discovery, structure-activity relationships and the results of their biological characterisation. Molecular probes developed for imaging of lysyl oxidase activity are reviewed from the perspective of their detection principles, performance and biomedical applications.

Involvement of lysyl oxidase in the pathogenesis of arterial stiffness in chronic kidney disease

Patients with chronic kidney disease (CKD) are at increased risk for adverse cardiovascular events. CKD is associated with increases in arterial stiffness, whereas improvements in arterial stiffness correlate with better survival. However, arterial stiffness is increased early in CKD, suggesting that there might be additional factors, unique to kidney disease, that increase arterial stiffness. Lysyl oxidase (LOX) is a key mediator of collagen cross linking and matrix remodeling. LOX is predominantly expressed in the cardiovascular system, and its upregulation has been associated with increased tissue stiffening and extracellular matrix remodeling. Thus, this study was designed to evaluate the role of increased LOX activity in inducing aortic stiffness in CKD and whether β-aminopropionitrile (BAPN), a LOX inhibitor, could prevent aortic stiffness by reducing collagen cross linking. Eight-week-old male C57BL/6 mice were subjected to 5/6 nephrectomy (Nx) or sham surgery. Two weeks after surgery, mice were randomized to BAPN (300 mg/kg/day in water) or vehicle treatment for 4 wk. Aortic stiffness was assessed by pulse wave velocity (PWV) using Doppler ultrasound. Aortic levels of LOX were assessed by ELISA, and cross-linked total collagen levels were analyzed by mass spectrometry and Sircol assay. Nx mice showed increased PWV and aortic wall remodeling compared with control mice. Collagen cross linking was increased in parallel with the increases in total collagen in the aorta of Nx mice. In contrast, Nx mice that received BAPN treatment showed decreased cross-linked collagens and PWV compared with that received vehicle treatment. Our results indicated that LOX might be an early and key mediator of aortic stiffness in CKD.NEW & NOTEWORTHY Arterial stiffness in CKD is associated with adverse cardiovascular outcomes. However, the mechanisms underlying increased aortic stiffness in CKD are unclear. Herein, we demonstrated that 1) increased aortic stiffness in CKD is independent of hypertension and calcification and 2) LOX-mediated changes in extracellular matrix are at least in part responsible for increased aortic stiffness in CKD. Prevention of excess LOX may have therapeutic potential in alleviating increased aortic stiffness and improving cardiovascular disease in CKD.

Enzymatic lysine oxidation as a posttranslational modification

Oxidoreductases catalyze oxidation-reduction reactions and comprise a very large and diverse group of enzymes, which can be subclassified depending on the catalytic mechanisms of the enzymes. One of the most prominent oxidative modifications in proteins is carbonylation, which involves the formation of aldehyde and keto groups in the side chain of lysines. This modification can alter the local macromolecular structure of proteins, thereby regulating their function, stability, and/or localization, as well as the nature of any protein-protein and/or protein-nucleic acid interactions. In this review, we focus on copper-dependent amine oxidases, which catalyze oxidative deamination of amines to aldehydes. In particular, we discuss oxidation reactions that involve lysine residues and that are regulated by members of the lysyl oxidase (LOX) family of proteins. We summarize what is known about the newly identified substrates and how this posttranslational modification regulates protein function in different contexts.

Semicarbazide-Sensitive Amine Oxidase (SSAO) and Lysyl Oxidase (LOX) Association in Rat Aortic Vascular Smooth Muscle Cells

Vascular smooth muscle cells (VSMCs) are the main stromal cells in the medial layer of the vascular wall. These cells produce the extracellular matrix (ECM) and are involved in many pathological changes in the vascular wall. Semicarbazide-sensitive amine oxidase (SSAO) and lysyl oxidase (LOX) are vascular enzymes associated with the development of atherosclerosis. In the vascular smooth muscle cells, increased SSAO activity elevates reactive oxygen species (ROS) and induces VSMCs death; increased LOX induces chemotaxis through hydrogen peroxide dependent mechanisms; and decreased LOX contributes to endothelial dysfunction. This study investigates the relationship between SSAO and LOX in VSMCs by studying their activity, protein, and mRNA levels during VSMCs passaging and after silencing the LOX gene, while using their respective substrates and inhibitors. At the basal level, LOX activity decreased with passage and its protein expression was maintained between passages. βAPN abolished LOX activity (** p < 0.01 for 8 vs. 3 and * p < 0.05 for 5 vs. 8) and had no effect on LOX protein and mRNA levels. MDL72527 reduced LOX activity at passage 3 and 5 (## p < 0.01) and had no effect on LOX protein, and mRNA expression. At the basal level, SSAO activity also decreased with passage, and its protein expression was maintained between passages. MDL72527 abolished SSAO activity (**** p < 0.0001 for 8 vs. 3 and * p < 0.05 for 5 vs. 8), VAP-1 expression at passage 5 (** p < 0.01) and 8 (**** p < 0.0001), and Aoc3 mRNA levels at passage 8 (* p < 0.05). βAPN inhibited SSAO activity (**** p < 0.0001 for 5 vs. 3 and 8 vs. 3 and * p < 0.05 for 5 vs. 8), VAP-1 expression at passage 3 (* p < 0.05), and Aoc3 mRNA levels at passage 3 (* p < 0.05). Knockdown of the LOX gene (**** p < 0.0001 for Si6 vs. Sictrl and *** p < 0.001 for Si8 vs. Sictrl) and LOX protein (** p < 0.01 for Si6 and Si8 vs. Sictrl) in VSMCs at passage 3 resulted in a reduction in Aoc3 mRNA (#### p < 0.0001 for Si6 vs. Sictrl and ### p < 0.001 for Si8 vs. Sictrl) and VAP-1 protein (# p < 0.05 for Si8 vs. Sictrl). These novel findings demonstrate a passage dependent decrease in LOX activity and increase in SSAO activity in rat aortic VSMCs and show an association between both enzymes in early passage rat aortic VSMCs, where LOX was identified as a regulator of SSAO activity, protein, and mRNA expression.

Glioblastoma‐educated mesenchymal stem‐like cells promote glioblastoma infiltration via extracellular matrix remodelling in the tumour microenvironment

Background

The biological function of mesenchymal stem‐like cells (MSLCs), a type of stromal cells, in the regulation of the tumour microenvironment is unclear. Here, we investigated the molecular mechanisms underlying extracellular matrix (ECM) remodelling and crosstalk between MSLCs and glioblastomas (GBMs) in tumour progression.

Methods

In vitro and in vivo co‐culture systems were used to analyze ECM remodelling and GBM infiltration. In addition, clinical databases, samples from patients with GBM and a xenografted mouse model of GBM were used.

Results

Previous studies have shown that the survival of patients with GBM from whom MSLCs could be isolated is substantially shorter than that of patients from whom MSLCs could not be isolated. Therefore, we determined the correlation between changes in ECM‐related gene expression in MSLC‐isolatable patients with that in MSLC non‐isolatable patients using gene set enrichment analysis (GSEA). We found that lysyl oxidase (LOX) and COL1A1 expressions increased in MSLCs via GBM‐derived clusters of differentiation 40 ligand (CD40L). Mechanistically, MSLCs are reprogrammed by the CD40L/CD40/NFκB2 signalling axis to build a tumour infiltrative microenvironment involving collagen crosslinking. Importantly, blocking of CD40L by a neutralizing antibody‐suppressed LOX expression and ECM remodelling, decreasing GBM infiltration in mouse xenograft models. Clinically, high expression of CD40L, clusters of differentiation 40 (CD40) and LOX correlated with poor survival in patients with glioma. This indicated that GBM‐educated MSLCs promote GBM infiltration via ECM remodelling in the tumour microenvironment.

Conclusion

Our findings provide mechanistic insights into the pro‐infiltrative tumour microenvironment produced by GBM‐educated MSLCs and highlight a potential therapeutic target that can be used for suppressing GBM infiltration.

Diagnostic Value, Prognostic Value, and Immune Infiltration of LOX Family Members in Liver Cancer: Bioinformatic Analysis

Background

Liver cancer (LC) is well known for its prevalence as well as its poor prognosis. The aberrant expression of lysyl oxidase (LOX) family is associated with liver cancer, but their function and prognostic value in LC remain largely unclear. This study aimed to explore the function and prognostic value of LOX family in LC through bioinformatics analysis and meta-analysis.

Results

The expression levels of all LOX family members were significantly increased in LC. Area under the receiver operating characteristic curve (AUC) of LOXL2 was 0.946 with positive predictive value (PPV) of 0.994. LOX and LOXL3 were correlated with worse prognosis. Meta-analysis also validated effect of LOX on prognosis. Nomogram of these two genes and other predictors was also plotted. There was insufficient data from original studies to conduct meta-analysis on LOXL3. The functions of LOX family members in LC were mostly involved in extracellular and functions and structures. The expressions of LOX family members strongly correlated with various immune infiltrating cells and immunomodulators in LC.

Conclusions

For LC patients, LOXL2 may be a potential diagnostic biomarker, while LOX and LOXL3 have potential prognostic and therapeutic values. Positive correlation between LOX family and infiltration of various immune cells and immunomodulators suggests the need for exploration of their roles in the tumor microenvironment and for potential immunotherapeutic to target LOX family proteins.

Minerals and Cancer: Overview of the Possible Diagnostic Value

Simple Summary

Minerals are important but often overlooked compounds that are required for a variety of cellular biochemical processes and pathways that regulate cell proliferation. Their dietary imbalance, which is becoming more common in the diets of industrialized countries, is linked to an increased risk of cancer. The current review will present some of the most important minerals for human physiology and evaluate their potential application as cancer biomarkers.

Abstract

Cancer is the second leading cause of death worldwide and is expected to increase by one-third over the next two decades, in parallel with the growing proportion of the elderly population. Treatment and control of cancer incidence is a global issue. Since there is no clear way to prevent or cure this deadly malignancy, diagnostic, predictive, and prognostic markers for oncological diseases are of great therapeutic value. Minerals and trace elements are important micronutrients for normal physiological function of the body. They are abundant in natural food sources and are regularly included in dietary supplements whereas highly processed industrial food often contains reduced or altered amounts of them. In modern society, the daily intake, storage pools, and homeostasis of these micronutrients are dependent on certain dietary habits and can be thrown out of balance by malignancies. The current work summarizes the data on minerals and trace elements associated with abnormal accumulation or depletion states in tumor patients and discusses their value as potential tumor-associated biomarkers that could be introduced into cancer therapy.

Loxl3 Promotes Melanoma Progression and Dissemination Influencing Cell Plasticity and Survival

Simple Summary

Malignant melanoma is the most lethal skin cancer due to its aggressive clinical behavior and therapeutic resistance. A comprehensive knowledge of the molecular mechanisms underlying melanoma progression is urgently needed to improve the survival of melanoma patients. Phenotypic plasticity of melanoma cells has emerged as a key process in melanomagenesis and therapy resistance. This phenotypic plasticity is sustained by an epithelial-to-mesenchymal (EMT)-like program that favors multiple intermediate states and allows adaptation to changing microenvironments along melanoma progression. Given the essential role of lysyl oxidase-like 3 (LOXL3) in human melanoma cell survival and its contribution to EMT, we generated mice with conditional melanocyte-specific targeting of Loxl3, concomitant to Braf activation and Pten deletion. Our results supported a key role of Loxl3 for melanoma progression, metastatic dissemination, and genomic stability, and supported its contribution to melanoma phenotypic plasticity by modulating the expression of several EMT transcription factors (EMT-TFs).

Abstract

Malignant melanoma is a highly aggressive tumor causing most skin cancer-related deaths. Understanding the fundamental mechanisms responsible for melanoma progression and therapeutic evasion is still an unmet need for melanoma patients. Progression of skin melanoma and its dissemination to local or distant organs relies on phenotypic plasticity of melanoma cells, orchestrated by EMT-TFs and microphthalmia-associated TF (MITF). Recently, melanoma phenotypic switching has been proposed to uphold context-dependent intermediate cell states benefitting malignancy. LOXL3 (lysyl oxidase-like 3) promotes EMT and has a key role in human melanoma cell survival and maintenance of genomic integrity. To further understand the role of Loxl3 in melanoma, we generated a conditional Loxl3-knockout (KO) melanoma mouse model in the context of BrafV600E-activating mutation and Pten loss. Melanocyte-Loxl3 deletion increased melanoma latency, decreased tumor growth, and reduced lymph node metastatic dissemination. Complementary in vitro and in vivo studies in mouse melanoma cells confirmed Loxl3’s contribution to melanoma progression and metastasis, in part by modulating phenotypic switching through Snail1 and Prrx1 EMT-TFs. Importantly, a novel LOXL3-SNAIL1-PRRX1 axis was identified in human melanoma, plausibly relevant to melanoma cellular plasticity. These data reinforced the value of LOXL3 as a therapeutic target in melanoma.

Fibrosis in Mesothelioma: Potential Role of Lysyl Oxidases

Immunotherapies (such as checkpoint inhibitors) and standard chemotherapies (such as cisplatin) have limitations in the successful treatment of malignant pleural mesothelioma (MPM). Fibrosis is the accumulation of collagen in the extracellular matrix (ECM) of tissues, making them denser than that of healthy tissues and thereby affecting drug delivery and immune cell infiltration. Moreover, fibrosis severely affects the patient's breathing and quality of life. The production of collagen and its assembly is highly regulated by various enzymes such as lysyl oxidases. Many solid tumors aberrantly express the family of lysyl oxidases (LOX/LOXL). This review examines how LOX/LOXLs were found to be dysregulated in noncancerous and cancerous settings, discusses their roles in solid tumor fibrosis and pathogenesis and explores the role of fibrosis in the development and poor clinical outcomes of patients with MPM. We examine the current preclinical status of drugs targeting LOX/LOXLs and how the incorporation of such drugs may have therapeutic benefits in the treatment and management of patients with MPM.

Lysyl oxidase regulation and protein aldehydes in the injured newborn lung

During newborn lung injury, excessive activity of lysyl oxidases (LOXs) disrupts extracellular matrix (ECM) formation. Previous studies indicate that TGFβ activation in the O₂-injured mouse pup lung increases lysyl oxidase (LOX) expression. But how TGFβ regulates this, and whether the LOXs generate excess pulmonary aldehydes are unknown. First, we determined that O₂-mediated lung injury increases LOX protein expression in TGFβ-stimulated pup lung interstitial fibroblasts. This regulation appeared to be direct; this is because TGFβ treatment also increased LOX protein expression in isolated pup lung fibroblasts. Then using a fibroblast cell line, we determined that TGFβ stimulates LOX expression at a transcriptional level via Smad2/3-dependent signaling. LOX is translated as a pro-protein that requires secretion and extracellular cleavage before assuming amine oxidase activity and, in some cells, reuptake with nuclear localization. We found that pro-LOX is processed in the newborn mouse pup lung. Also, O₂-mediated injury was determined to increase pro-LOX secretion and nuclear LOX immunoreactivity particularly in areas populated with interstitial fibroblasts and exhibiting malformed ECM. Then, using molecular probes, we detected increased aldehyde levels in vivo in O₂-injured pup lungs, which mapped to areas of increased pro-LOX secretion in lung sections. Increased activity of LOXs plays a critical role in the aldehyde generation; an inhibitor of LOXs prevented the elevation of aldehydes in the O₂-injured pup lung. These results reveal new mechanisms of TGFβ and LOX in newborn lung disease and suggest that aldehyde-reactive probes might have utility in sensing the activation of LOXs in vivo during lung injury.

Lysyl oxidase-like 2 is increased in asthma and contributes to asthmatic airway remodelling

Background

Airway smooth muscle (ASM) cells are fundamental to asthma pathogenesis, influencing bronchoconstriction, airway hyperresponsiveness and airway remodelling. The extracellular matrix (ECM) can influence tissue remodelling pathways; however, to date no study has investigated the effect of ASM ECM stiffness and cross-linking on the development of asthmatic airway remodelling. We hypothesised that transforming growth factor-β (TGF-β) activation by ASM cells is influenced by ECM in asthma and sought to investigate the mechanisms involved.

Methods

This study combines in vitro and in vivo approaches: human ASM cells were used in vitro to investigate basal TGF-β activation and expression of ECM cross-linking enzymes. Human bronchial biopsies from asthmatic and nonasthmatic donors were used to confirm lysyl oxidase like 2 (LOXL2) expression in ASM. A chronic ovalbumin (OVA) model of asthma was used to study the effect of LOXL2 inhibition on airway remodelling.

Results

We found that asthmatic ASM cells activated more TGF-β basally than nonasthmatic controls and that diseased cell-derived ECM influences levels of TGF-β activated. Our data demonstrate that the ECM cross-linking enzyme LOXL2 is increased in asthmatic ASM cells and in bronchial biopsies. Crucially, we show that LOXL2 inhibition reduces ECM stiffness and TGF-β activation in vitro, and can reduce subepithelial collagen deposition and ASM thickness, two features of airway remodelling, in an OVA mouse model of asthma.

Conclusion

These data are the first to highlight a role for LOXL2 in the development of asthmatic airway remodelling and suggest that LOXL2 inhibition warrants further investigation as a potential therapy to reduce remodelling of the airways in severe asthma.

Novel role for matrix cross-linking enzyme LOXL2 in asthmatic airway remodelling: LOXL2 is increased in #asthma but LOXL2 inhibition reduces matrix stiffness in airway smooth muscle cells and reduces remodelling in vivohttps://bit.ly/3FnzGb3

Reciprocal regulation of LOXL2 and HIF1α drives the Warburg effect to support pancreatic cancer aggressiveness

Hypoxic microenvironment is common in solid tumors, particularly in pancreatic ductal adenocarcinoma (PDAC). The Warburg effect is known to facilitate cancer aggressiveness and has long been linked to hypoxia, yet the underlying mechanism remains largely unknown. In this study, we identify that lysyl oxidase-like 2 (LOXL2) is a hypoxia-responsive gene and is essential for the Warburg effect in PDAC. LOXL2 stabilizes hypoxia-inducible factor 1α (HIF1α) from prolyl hydroxylase (PHD)-dependent hydroxylation via hydrogen peroxide generation, thereby facilitating the transcription of multiple glycolytic genes. Therefore, a positive feedback loop exists between LOXL2 and HIF1α that facilitates glycolytic metabolism under hypoxia. Moreover, LOXL2 couples the Warburg effect to tumor growth and metastasis in PDAC. Hijacking glycolysis largely compromises LOXL2-induced oncogenic activities. Collectively, our results identify a hitherto unknown hypoxia-LOXL2-HIF1α axis in regulating the Warburg effect and provide an intriguing drug target for PDAC therapy.

LOXL2 Inhibitor Attenuates Angiotensin II-Induced Atrial Fibrosis and Vulnerability to Atrial Fibrillation through Inhibition of Transforming Growth Factor Beta-1 Smad2/3 Pathway

OBJECTIVES

Angiotensin II (Ang II)-induced atrial fibrosis plays a vital role in the development of atrial fibrillation (AF). Lysyl oxidase-like 2 (LOXL2) plays an essential role in matrix remodeling and fibrogenesis, indicating it may involve fibrosis-associated diseases. This study aims to elucidate the role of LOXL2 in AF, and its specific inhibitor can suppress Ang II-induced inflammatory atrial fibrosis and attenuate the enhanced vulnerability to AF.

METHODS

Male mice C57BL/6 were subcutaneously infused with either saline or Ang II (2 mg/kg/day) for 4 weeks. DMSO or LOXL2 inhibitor LOXL2-IN-1 hydrochloride (LOXL2-IN-1) at a dose of 100 μg/kg/day were intraperitoneally injected once daily for 4 weeks. Morphological, histological, and biochemical analyses were performed. AF was induced by transesophageal burst pacing in vivo.

RESULTS

Expression of LOXL2 was increased in serum of AF patients and Ang II-treated mice. LOXL2-IN-1 significantly attenuated Ang II-induced AF vulnerability, cardiac hypertrophy, atrial inflammation, and fibrosis. LOXL2-IN-1 suppressed Ang II-induced expression of transforming growth factor beta-1 (TGF-β1) and collagen I and phosphorylation of Smad2/3 in atrial tissue.

CONCLUSIONS

LOXL2 is a target of AF, and its inhibitor prevents atrial fibrosis and attenuated enhanced vulnerability to AF potentially through the TGF-β/Smad pathway.

The Interactome of Cancer-Related Lysyl Oxidase and Lysyl Oxidase-Like Proteins

The members of the lysyl oxidase (LOX) family are amine oxidases, which initiate the covalent cross-linking of the extracellular matrix (ECM), regulate ECM stiffness, and contribute to cancer progression. The aim of this study was to build the first draft of the interactome of the five members of the LOX family in order to determine its molecular functions, the biological and signaling pathways mediating these functions, the biological processes it is involved in, and if and how it is rewired in cancer. In vitro binding assays, based on surface plasmon resonance and bio-layer interferometry, combined with queries of interaction databases and interaction datasets, were used to retrieve interaction data. The interactome was then analyzed using computational tools. We identified 31 new interactions and 14 new partners of LOXL2, including the α5β1 integrin, and built an interactome comprising 320 proteins, 5 glycosaminoglycans, and 399 interactions. This network participates in ECM organization, degradation and cross-linking, cell-ECM interactions mediated by non-integrin and integrin receptors, protein folding and chaperone activity, organ and blood vessel development, cellular response to stress, and signal transduction. We showed that this network is rewired in colorectal carcinoma, leading to a switch from ECM organization to protein folding and chaperone activity.

LOXL2 Upregulation in Gliomas Drives Tumorigenicity by Activating Autophagy to Promote TMZ Resistance and Trigger EMT

Glioma is the most prevalent primary brain tumor in adults and has an extremely unfavorable prognosis. As a member of the lysyl oxidase (LOX) family, lysyl-oxidase-like-2 (LOXL2) is known to play different roles in different tumors. However, the role of LOXL2 in glioma has not yet been fully elucidated. In the present study, we detected that LOXL2 was considerably upregulated in glioma and that LOXL2 upregulation was evidently related to glioma WHO grade, malignant molecular subtypes, and poor prognosis in glioma patients. Additionally, we found that LOXL2 not only promoted glioma cells proliferation, migration, invasion, and induced the epithelial-to-mesenchymal transition (EMT) process, but also reduced the sensitivity of glioma cells to temozolomide (TMZ). Furthermore, we identified that LOXL2 reduced TMZ sensitivity and induced EMT in glioma via the activation of autophagy. Mechanistically, LOXL2 enhanced Atg7 expression by promoting the phosphorylation of Erk1/2, leading to the activation of autophagy and regulation of EMT process and TMZ sensitivity through autophagy. Our study describes an LOXL2-Erk1/2-Atg7 signaling axis that influences glioma EMT and chemosensitivity through autophagy; moreover, LOXL2 may serve as a promising therapeutic target in the treatment of glioma.

Lysyl oxidase directly contributes to extracellular matrix production and fibrosis in systemic sclerosis

Pulmonary fibrosis is one of the important causes of morbidity and mortality in fibroproliferative disorders such as systemic sclerosis (SSc) and idiopathic pulmonary fibrosis (IPF). Lysyl oxidase (LOX) is a copper-dependent amine oxidase whose primary function is the covalent crosslinking of collagens in the extracellular matrix (ECM). We investigated the role of LOX in the pathophysiology of SSc. LOX mRNA and protein levels were increased in lung fibroblasts of SSc patients compared with healthy controls and IPF patients. In vivo, bleomycin induced LOX mRNA expression in lung tissues, and LOX activity increased in the circulation of mice with pulmonary fibrosis, suggesting that circulating LOX parallels levels in lung tissues. Circulating levels of LOX were reduced upon amelioration of fibrosis with an antifibrotic peptide. LOX induced ECM production at the transcriptional level in lung fibroblasts, human lungs, and human skin maintained in organ culture. In vivo, LOX synergistically exacerbated fibrosis in bleomycin-treated mice. Further, LOX increased the production of interleukin (IL)-6, and the increase was mediated by LOX-induced c-Fos expression, the nuclear localization of c-Fos, and its engagement with the IL-6 promoter region. Our findings demonstrate that LOX expression and activity correlate with fibrosis in vitro, ex vivo, and in vivo. LOX induced ECM production via upregulation of IL-6 and nuclear localization of c-Fos. Thus, LOX has a direct pathogenic role in SSc-associated fibrosis that is independent of its crosslinking function. Our findings also suggest that measuring circulating LOX levels and activity can be used for monitoring response to antifibrotic therapy.

Lysyl Oxidase (LOX): Functional Contributions to Signaling Pathways

Cu-dependent lysyl oxidase (LOX) plays a catalytic activity-related, primary role in the assembly of the extracellular matrix (ECM), a dynamic structural and regulatory framework which is essential for cell fate, differentiation and communication during development, tissue maintenance and repair. LOX, additionally, plays both activity-dependent and independent extracellular, intracellular and nuclear roles that fulfill significant functions in normal tissues, and contribute to vascular, cardiac, pulmonary, dermal, placenta, diaphragm, kidney and pelvic floor disorders. LOX activities have also been recognized in glioblastoma, diabetic neovascularization, osteogenic differentiation, bone matrix formation, ligament remodeling, polycystic ovary syndrome, fetal membrane rupture and tumor progression and metastasis. In an inflammatory context, LOX plays a role in diminishing pluripotent mesenchymal cell pools which are relevant to the pathology of diabetes, osteoporosis and rheumatoid arthritis. Most of these conditions involve mechanisms with complex cell and tissue type-specific interactions of LOX with signaling pathways, not only as a regulatory target, but also as an active player, including LOX-mediated alterations of cell surface receptor functions and mutual regulatory activities within signaling loops. In this review, we aim to provide insight into the diverse ways in which LOX participates in signaling events, and explore the mechanistic details and functional significance of the regulatory and cross-regulatory interactions of LOX with the EGFR, PDGF, VEGF, TGF-β, mechano-transduction, inflammatory and steroid signaling pathways.

Interaction of two functional genetic variants LOXL1 rs1048661 and VEGFA rs3025039 on the risk of age-related macular degeneration in Chinese women

Background

Cumulative evidence indicates that LOXL1 and VEGF-a play important roles in extracellular matrix formation and angiogenesis, respectively. The disorder of extracellular matrix and angiogenesis are the key factors of pathogenesis of age-related macular degeneration (AMD). We hypothesized that rs1048661 (T>G) in the LOXL1 gene and rs3025039 (C>T) in the VEGFA gene might be associated with risk of AMD.

Methods

A total of 533 unrelated Chinese subjects, 286 cases (247 with early AMD and 39 with late neovascular AMD) and 247 controls, were included in the study. The gene sequences of LOXL1 rs1048661 and VEGFA rs3025039 were amplified by polymerase chain reaction and genotyped. Interaction between rs1048661 and rs3025039 on AMD risk was also assessed.

Results

LOXL1 rs1048661 but not VEGFA rs3025039 was associated with a significantly increased risk of AMD. The adjusted odds ratio was 1.6 (95% CI, 1.1-2.5) for rs1048661 TT + GT genotype compared with GG homozygotes in the dominant model analysis. Moreover, there was a significant gene-gene interaction between these two polymorphic loci. In VEGFA rs3025039 CC + CT genotype which indicated sufficient expression of VEGF-a, LOXL1 rs1048661 had odds ratios of 1.7 (95% CI, 1.1-2.7) for early AMD and 3.6 (95% CI, 1.1-12.3) for late neovascular AMD in the dominant model analysis. However, LOXL1 rs1048661 did not confer the risk of AMD in subjects harboring VEGFA rs3025039 TT genotype which indicated decreased expression of VEGF-a.

Conclusions

Our findings suggest that LOXL1 rs1048661 (T>G) may be involved in the risk of AMD. In addition, LOXL1 rs1048661 and VEGFA rs3025039 interacted to confer the development of AMD, especially for late-stage neovascular AMD. Our data need to be further validated.

LOX gene polymorphisms are associated with osteoporotic vertebral compression fracture in postmenopausal Chinese women

INTRODUCTION

Collagen cross-linking, which is regulated by lysyl oxidase (LOX), plays critical roles in bone mechanical strength. LOX can influence bone remodeling by modulating osteoblast and osteoclast activity. This study aimed to explore the effect of LOX gene polymorphisms on osteoporotic fractures susceptibility in postmenopausal Chinese women.

METHODS

This was a prospective study of postmenopausal women who visited the outpatient and community clinics of the local Hospital. Five tagging single nucleotide polymorphisms (SNPs) in the LOX gene were determined. Bone mineral density (BMD) was measured at the lumbar spine, femoral neck, and hip using dual-energy X-ray absorptiometry. Fractures were confirmed by X-ray and divided into: vertebral compression fracture (OVCF) and non-OVCF (all other fractures).

RESULTS

This study included 602 patients with non-traumatic fractures and 1343 healthy volunteers. The rs1800449 was significantly associated with vertebral compression fracture (OVCF) after adjusting for age and BMI (P = 0.012). Compared with subjects with the GG genotype, the risk of having OVCF was 1.28 and 1.74, respectively for subjects with the GA and AA genotypes (P = 0.043 and P = 0.018). A recessive genetic model showed that carriers of the AA genotype had higher fracture risk compared to G carriers (GA and GG genotypes) (P = 0.015). The rs2288393 SNP exhibited marginally significant association with OVCF (P = 0.051). Haplotype analyses corroborated our single SNP results: both haplotype CGA and CCG contained rs10519694, rs2288393, and rs1800449, and were significant associated with OVCF (P = 0.048 and P = 0.032, respectively). On the other hand, we found no evidence of an association of LOX gene allelic variants with either BMD or non-OVCF (all P > 0.05).

CONCLUSION

The results suggest that genetic polymorphisms in LOX may contribute to susceptibility to OVCF in Chinese postmenopausal women.

Amelioration of Cavernosal Fibrosis and Erectile Function by Lysyl Oxidase Inhibition in a Rat Model of Cavernous Nerve Injury

BACKGROUND

Cavernous nerve injury (CNI) causes fibrosis and loss of smooth muscle cells (SMCs) in the corpus cavernosum and leads to erectile dysfunction, and lysyl oxidase (LOX) activation has been found to play an important role in fibrotic diseases.

AIM

To evaluate the role of LOX in penile fibrosis after bilateral CNI (BCNI).

METHODS

Rats underwent BCNI or a sham operation and were treated with vehicle or β-aminopropionitrile, a specific LOX activity inhibitor. 30 days after BCNI, rats were tested for erectile function before penile tissue harvest. LOX and extracellular matrix component expression levels in the corpus cavernosum, including matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), fibronectin (FN), collagen (COL) I, and COL IV, were evaluated by real-time quantitative polymerase chain reaction and western blot. Corporal fibrosis was evaluated by Masson trichrome staining. Localization of LOX and SMC content in the corpus cavernosum were assessed by immunohistochemistry.

OUTCOMES

Ratio of intracavernous pressure to mean arterial blood pressure; LOX, MMPs, TIMPs, COL I, COL IV, and FN expression; penile fibrosis; penile SMC content.

RESULTS

After BCNI, there was an increase in penile LOX expression and activity, increased penile fibrosis, decreased SMC content, and impaired erectile function. TIMP1, TIMP2, COL I, COL IV, and FN expression was markedly upregulated, whereas the enzyme activity of MMPs was decreased after BCNI. β-Aminopropionitrile treatment, at least in part, prevented a decrease in the ratio of intracavernous pressure to mean arterial blood pressure, decreased penile expression of TIMP1, TIMP2, COL I, COL IV, and FN, increased MMP activity, prevented corporal fibrosis, and preserved SMC content.

CLINICAL TRANSLATION

LOX over-activation contributes to penile fibrosis and LOX inhibition could be a promising strategy in preventing the progression of CNI-induced erectile dysfunction.

STRENGTHS AND LIMITATIONS

This is the 1st study to demonstrate the role of LOX activation in penile fibrosis. However, the exact mechanism of how LOX influences extracellular matrix protein synthesis and SMC content preservation awaits further investigation.

CONCLUSION

CNI induced LOX over-activation in cavernous tissue, and inhibition of LOX preserved penile morphology and improved erectile function in a rat model of BCNI. Wan Z-H, Li G-H, Guo Y-L, et al. Amelioration of Cavernosal Fibrosis and Erectile Function by Lysyl Oxidase Inhibition in a Rat Model of Cavernous Nerve Injury. J Sex Med 2018;15:304-313.

Lysyl oxidases: from enzyme activity to extracellular matrix cross-links

The lysyl oxidase family comprises five members in mammals, lysyl oxidase (LOX) and four lysyl oxidase like proteins (LOXL1-4). They are copper amine oxidases with a highly conserved catalytic domain, a lysine tyrosylquinone cofactor, and a conserved copper-binding site. They catalyze the first step of the covalent cross-linking of the extracellular matrix (ECM) proteins collagens and elastin, which contribute to ECM stiffness and mechanical properties. The role of LOX and LOXL2 in fibrosis, tumorigenesis, and metastasis, including changes in their expression level and their regulation of cell signaling pathways, have been extensively reviewed, and both enzymes have been identified as therapeutic targets. We review here the molecular features and three-dimensional structure/models of LOX and LOXLs, their role in ECM cross-linking, and the regulation of their cross-linking activity by ECM proteins, proteoglycans, and by inhibitors. We also make an overview of the major ECM cross-links, because they are the ultimate molecular readouts of LOX/LOXL activity in tissues. The recent 3D model of LOX, which recapitulates its known structural and biochemical features, will be useful to decipher the molecular mechanisms of LOX interaction with its various substrates, and to design substrate-specific inhibitors, which are potential antifibrotic and antitumor drugs.

LOXL2-mediated H3K4 oxidation reduces chromatin accessibility in triple-negative breast cancer cells

Oxidation of H3 at lysine 4 (H3K4ox) by lysyl oxidase-like 2 (LOXL2) generates an H3 modification with an unknown physiological function. We find that LOXL2 and H3K4ox are higher in triple-negative breast cancer (TNBC) cell lines and patient-derived xenografts (PDXs) than those from other breast cancer subtypes. ChIP-seq revealed that H3K4ox is located primarily in heterochromatin, where it is involved in chromatin compaction. Knocking down LOXL2 reduces H3K4ox levels and causes chromatin decompaction, resulting in a sustained activation of the DNA damage response (DDR) and increased susceptibility to anticancer agents. This critical role that LOXL2 and oxidized H3 play in chromatin compaction and DDR suggests that functionally targeting LOXL2 could be a way to sensitize TNBC cells to conventional therapy.

Elevated exosomal lysyl oxidase like 2 is a potential biomarker for head and neck squamous cell carcinoma

OBJECTIVES

The secretory enzyme lysyl oxidase like 2 (LOXL2) is speculated to contribute to tumor progression through its functions in the remodeling of extracellular matrix and epithelial-mesenchymal transition. We previously identified elevated expression of LOXL2 in metastatic human head and neck squamous cell carcinoma (HNSCC) cells in a mouse lymph node metastases model. Here we performed a case series study examining LOXL2 expression levels in human serum from HNSCC patients to evaluate whether LOXL2 is worth evaluation in a large cohort study.

METHODS

LOXL2 protein levels in three serum samples from HNSCC patients were assessed by immunoblotting and LOXL2 tissue expression was examined in one human tongue squamous cell carcinoma (SCC) tissue by immunohistochemistry as a representative of HNSCC tissue. Serum samples were further fractionated in exosomes and supernatants by ultracentrifugation, which were then subjected to immunoblot and in vitro LOX activity analyses. Exosomal LOXL2 levels of 36 serum samples from HNSCC patients and seven healthy volunteers were measured using polymer sedimentation exosome preparation followed by ELISA measurement and subjected to statistical analyses.

RESULTS

Immunoblot analyses revealed that LOXL2 was present in serum exosomal fractions from three HNSCC patients, and we observed approximately threefold higher levels of LOXL2 in HNSCC patients compared with three healthy volunteers. Immunohistochemical LOXL2 staining was detected in HNSCC cells in addition to non-cancerous lipid tissues and some muscles in human tongue HNSCC tissue. Further measurements of exosomal LOXL2 by ELISA showed over ninefold higher mean LOXL2 levels in patients compared with controls. Statistical analysis revealed a correlation between elevated serum exosomal LOXL2 levels and low-grade, but not high-grade, HNSCC.

CONCLUSIONS

Our case series study that elevated serum exosomal LOXL2 levels exhibited a correlation with low-grade HNSCCs. A follow-up large cohort clinical study will be required to determine the potential clinical utility of LOXL2 as a new biomarker and/or therapy target for HNSCCs.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:E327-E334, 2020.

LOXL1 Is Regulated by Integrin α11 and Promotes Non-Small Cell Lung Cancer Tumorigenicity

Integrin α11, a stromal collagen receptor, promotes tumor growth and metastasis of non-small cell lung cancer (NSCLC) and is associated with the regulation of collagen stiffness in the tumor stroma. We have previously reported that lysyl oxidase like-1 (LOXL1), a matrix cross-linking enzyme, is down-regulated in integrin α11-deficient mice. In the present study, we investigated the relationship between LOXL1 and integrin α11, and the role of LOXL1 in NSCLC tumorigenicity. Our results show that the expression of LOXL1 and integrin α11 was correlated in three lung adenocarcinoma patient datasets and that integrin α11 indeed regulated LOXL1 expression in stromal cells. Using cancer-associated fibroblast (CAF) with either a knockdown or overexpression of LOXL1, we demonstrated a role for LOXL1 in collagen matrix remodeling and collagen fiber alignment in vitro and in vivo in a NSCLC xenograft model. As a consequence of collagen reorganization in NSCLC tumor stroma, we showed that LOXL1 supported tumor growth and progression. Our findings demonstrate that stromal LOXL1, under regulation of integrin α11, is a determinant factor of NSCLC tumorigenesis and may be an interesting target in this disease.

Mechanism for oral tumor cell lysyl oxidase like-2 in cancer development: synergy with PDGF-AB

Extracellular lysyl oxidases (LOX and LOXL1–LOXL4) are critical for collagen biosynthesis. LOXL2 is a marker of poor survival in oral squamous cell cancer. We investigated mechanisms by which tumor cell secreted LOXL2 targets proximal mesenchymal cells to enhance tumor growth and metastasis. This study identified the first molecular mechanism for LOXL2 in the promotion of cancer via its enzymatic modification of a non-collagenous substrate in the context of paracrine signaling between tumor cells and resident fibroblasts. The role and mechanism of active LOXL2 in promoting oral cancer was evaluated and employed a novel LOXL2 small molecule inhibitor, PSX-S1C, administered to immunodeficient, and syngeneic immunocompetent orthotopic oral cancer mouse models. Tumor growth, histopathology, and metastases were monitored. In vitro mechanistic studies with conditioned tumor cell medium treatment of normal human oral fibroblasts were carried out in the presence and absence of the LOXL2 inhibitor to identify signaling mechanisms promoted by LOXL2 activity. Inhibition of LOXL2 attenuated cancer growth and lymph node metastases in the orthotopic tongue mouse models. Immunohistochemistry data indicated that LOXL2 expression in and around tumors was decreased in mice treated with the inhibitor. Inhibition of LOXL2 activity by administration of PXS-S1C to mice reduced tumor cell proliferation, accompanied by changes in morphology and in the expression of epithelial to mesenchymal transition markers. In vitro studies identified PDGFRβ as a direct substrate for LOXL2, and indicated that LOXL2 and PDGF-AB together secreted by tumor cells optimally activated PDGFRβ in fibroblasts to promote proliferation and the tendency toward fibrosis via ERK activation, but not AKT. Optimal fibroblast proliferation in vitro required LOXL2 activity, while tumor cell proliferation did not. Thus, tumor cell-derived LOXL2 in the microenvironment directly targets neighboring resident cells to promote a permissive local niche, in addition to its known role in collagen maturation.

Prognostic and clinicopathological significance of LOXL2 in cancers: A systematic review and meta-analysis

BACKGROUND

Lysyl oxidase-like 2 (LOXL2) is an extracellular matrix (ECM)-modifying enzyme which can regulate the tensile strength of connective tissues by crosslink of collagen and elastin. Numerous studies have claimed correlations between LOXL2 expression and prognosis or clinicopathological characteristics in various cancers. However, the validities of these claims are still in question. To address these experimental results, a meta-analysis was done to assess the prognostic and clinicopathological significance of LOXL2 expression in various cancers.

METHODS

The keywords were used for searching systematically in PubMed, Web of Science, Embase, Wanfang database, and CNKI. Stata SE15.0 was used for meta-analysis. The hazard ratio (HR) and odds ratios (ORs) were pooled to assess the relationship between LOXL2 expression and overall survival (OS), disease-free survival (DFS), and clinicopathological parameters.

RESULTS

Seventeen studies with 3,881 patients were considered as valid studies. The results indicated that the patients who had a positive LOXL2 expression had a shorter OS (HR 1.60, 95% CI 1.26-1.94, p < 0.001) or DFS (HR 1.46, 95% CI 1.14-1.78, p < 0.001). For clinicopathological parameters, statistical significances were presented in age (OR 1.34, 95% CI 1.13-1.58, p = 0.001), lymph node metastasis (OR 2.20, 95% CI 1.37-3.53, p < 0.001), tumor size (OR 1.46, 95% CI 1.15-1.85, p = 0.002), and vascular invasion (OR 1.82, 95% CI 1.33-2.48, p < 0.001).

CONCLUSIONS

The results demonstrate that positive LOXL2 expression presents poorer OS and worse clinicopathological parameters. LOXL2 may be an effective biomarker to evaluate the prognosis in different type of cancers.

Megakaryocytic leukemia 1 (MKL1) mediates high glucose induced epithelial-mesenchymal transition by activating LOX transcription

Diabetic retinopathy (DR) is one of the most devastating complications of diabetes mellitus. When exposed to high glucose (HG), retinal epithelial cells undergo profound alterations both morphologically and functionally in a well-conserved process known as epithelial-to-mesenchymal transition (EMT). The mechanism governing HG-induced EMT in retinal epithelial cells is not completely understood. Here we report that treatment with 25 mM glucose led to EMT in retinal pigmented epithelial cells (RPE) characterized by a simultaneous down-regulation of E-Cadherin (encoded by CDH1) and up-regulation of alpha smooth muscle actin (encoded by ACTA2). HG-induced EMT in RPEs was accompanied by augmented expression and enhanced nuclear enrichment of MKL1, a transcriptional modulator. In contrast, MKL1 knockdown by siRNA or inhibition by CCG-1423 abrogated HG-induced EMT in RPEs. Of interest, MKL1 mediated the transcriptional activation of LOX, a mesenchymal marker, in RPEs in response to HG stimulation. Mechanistically, MKL1 interacted with and was recruited by AP-1 to the proximal LOX promoter to promote LOX trans-activation likely through altering the chromatin structure. Finally, LOX depletion by siRNA or inhibition by aminopropionitrile in RPEs abolished HG-induced EMT. In conclusion, our data support a role for MKL1 in mediating HG-induced EMT in retinal epithelial cells via epigenetic activation of LOX transcription.

GINS2 promotes cell proliferation and inhibits cell apoptosis in thyroid cancer by regulating CITED2 and LOXL2

To explore the mechanisms of GINS2 on cell proliferation and apoptosis in thyroid cancer (TC) cells. Expressions of GINS2 were inhibited in K1 and SW579 cells using gene interference technology. The abilities of proliferation and apoptosis, and cell cycle were determined by MTT assay and flow cytometric assay. The downstream molecules of GINS2 were searched by microarray and bioinformatics and validated by qRT-PCR and western blotting. In the in vivo study, the tumor growth was compared and the whole-body fluorescent imaging was analyzed. After GINS2 was interfered, cell proliferation was significantly inhibited (P < 0.01) and apoptosis rate increased (P < 0.01) in both K1 and SW579 cells. Cell cycle changed significantly in K1 cells, but not in SW579 cells. With bioinformatics upstream analysis, TGF-β1 was found as the most significantly upstream regulator. Expressions of TGF-β1 and its downstream target molecules CITED2 and LOXL2 were validated and found downregulated significantly in mRNA and protein levels (P < 0.05). The results of the nude mouse xenograft assay suggested that the volume and weight of tumor in ones infected with shGINS2 were statistically smaller than controls (P < 0.05). GINS2 plays an important role in cell proliferation and apoptosis of thyroid cancer by regulating the expressions of CITED2 and LOXL2, which may be a potential biomarker for diagnosis or prognosis and a drug target for therapy.

In Vivo Expansion of Cancer Stemness Affords Novel Cancer Stem Cell Targets: Malignant Rhabdoid Tumor as an Example

Cancer stem cell (CSC) identification relies on transplantation assays of cell subpopulations sorted from fresh tumor samples. Here, we attempt to bypass limitations of abundant tumor source and predetermined immune selection by in vivo propagating patient-derived xenografts (PDX) from human malignant rhabdoid tumor (MRT), a rare and lethal pediatric neoplasm, to an advanced state in which most cells behave as CSCs. Stemness is then probed by comparative transcriptomics of serial PDXs generating a gene signature of epithelial to mesenchymal transition, invasion/motility, metastasis, and self-renewal, pinpointing putative MRT CSC markers. The relevance of these putative CSC molecules is analyzed by sorting tumorigenic fractions from early-passaged PDX according to one such molecule, deciphering expression in archived primary tumors, and testing the effects of CSC molecule inhibition on MRT growth. Using this platform, we identify ALDH1 and lysyl oxidase (LOX) as relevant targets and provide a larger framework for target and drug discovery in rare pediatric cancers.

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Human malignant rhabdoid tumor (MRT) can be propagated in vivo as tumor xenografts

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Long-term propagated PDX enrich for CSC frequency with no need for immune selection

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Distinct gene signature in stem-like MRT xenografts reveals putative CSC biomarkers

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Screening of putative CSC biomarkers allows identification of therapeutic targets

Loxl2 is dispensable for dermal development, homeostasis and tumour stroma formation

Lysyl oxidase-like 2 (LOXL2) is a copper-dependent monoamine oxidase that contributes to the remodelling of the extracellular matrix (ECM) by cross linkage of collagen and elastin fibres and has emerged as a potential therapeutic target in cancer and fibrosis. In the skin, LOXL2 is essential for epidermal cell polarity and differentiation. However, its role in the dermis has not been evaluated. We found that Loxl2 is dispensable for mouse dermal development, maturation and homeostasis, yet affects dermal stiffness. Neither loss of Loxl2 nor increased Loxl2 expression affected dermal architecture following treatment with the phorbol ester TPA. Furthermore, Loxl2 expression did not alter the stroma of DMBA-TPA-induced tumours. We conclude that, although Loxl2 is expressed in both dermis and epidermis, its function appears largely confined to the epidermis.

Lysyl oxidase like-2 contributes to renal fibrosis in Col4α3/Alport mice

Lysyl oxidase like-2 (LOXL2) is an amine oxidase with both intracellular and extracellular functions. Extracellularly, LOXL2 promotes collagen and elastin crosslinking, whereas intracellularly, LOXL2 has been reported to modify histone H3, stabilize SNAIL, and reduce cell polarity. Although LOXL2 promotes liver and lung fibrosis, little is known regarding its role in renal fibrosis. Here we determine whether LOXL2 influences kidney disease in COL4A3 (-/-) Alport mice. These mice were treated with a small molecule inhibitor selective for LOXL2 or with vehicle and assessed for glomerular sclerosis and fibrosis, albuminuria, blood urea nitrogen, lifespan, pro-fibrotic gene expression and ultrastructure of the glomerular basement membrane. Laminin α2 deposition in the glomerular basement membrane and mesangial filopodial invasion of the glomerular capillaries were also assessed. LOXL2 inhibition significantly reduced interstitial fibrosis and mRNA expression of MMP-2, MMP-9, TGF-β1, and TNF-α. LOXL2 inhibitor treatment also reduced glomerulosclerosis, expression of MMP-10, MMP-12, and MCP-1 mRNA in glomeruli, and decreased albuminuria and blood urea nitrogen. Mesangial filopodial invasion of the capillary tufts was blunted, as was laminin α2 deposition in the glomerular basement membrane, and glomerular basement membrane ultrastructure was normalized. There was no effect on lifespan. Thus, LOXL2 plays an important role in promoting both glomerular and interstitial pathogenesis associated with Alport syndrome in mice. Other etiologies of chronic kidney disease are implicated with our observations.

Evaluation of Fluorine-18-Labeled α1(I)-N-Telopeptide Analogs as Substrate-Based Radiotracers for PET Imaging of Melanoma-Associated Lysyl Oxidase

Accumulating evidence suggests an unequivocal role of lysyl oxidases as key players of tumor progression and metastasis, which renders this enzyme family highly attractive for targeted non-invasive functional imaging of tumors. Considering their function in matrix remodeling, malignant melanoma appears as particularly interesting neoplasia in this respect. For the development of radiotracers that enable PET imaging of the melanoma-associated lysyl oxidase activity, substrates derived from the type I collagen α1 N-telopeptide were labeled with fluorine-18 using N-succinimidyl 4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB) as prosthetic reagent. With regards to potential crosslinking to tumor-associated collagen in vivo, their interaction with triple-helical type I collagen was studied by SPR. A mouse model of human melanoma was established on the basis of the A375 cell line, for which the expression of the oncologically relevant lysyl oxidase isoforms LOX and LOXL2 was demonstrated in Western blot and immunohistochemical experiments. The radiopharmacological profiles of the peptidic radiotracers were evaluated in normal rats and A375 melanoma-bearing mice by ex vivo metabolite analysis, whole-body biodistribution studies and dynamic PET imaging. Out of three ¹⁸F-labeled telopeptide analogs, the one with the most favorable substrate properties has shown favorable tumor uptake and tumor-to-muscle ratio. Lysyl oxidase-mediated tumor uptake was proven by pharmacological inhibition using β-aminopropionitrile and by employing negative-control analogs of impeded or abolished targeting capability. The latter were obtained by substituting the lysine residue by ornithine and norleucine, respectively. Comparing the tumor uptake of the lysine-containing peptide with that of the non-functional analogs indicate the feasibility of lysyl oxidase imaging in melanoma using substrate-based radiotracers.

The apparent competitive action of ECM proteases and cross-linking enzymes during fibrosis: Applications to drug discovery

Progressive loss of organ function in most organs is associated with fibrosis, a tissue state associated with abnormal matrix buildup. If highly progressive, the fibrotic process eventually leads to organ failure and death. Fibrosis is a basic connective tissue lesion defined by the increase in the amount of fibrillar extracellular matrix (ECM) components in a tissue or organ. In addition, intrinsic changes in important structural cells can induce the fibrotic response by regulating the differentiation, recruitment, proliferation and activation of extracellular matrix-producing myofibroblasts. ECM enzymes belonging to the family of matrix metalloproteinases (MMPs) and lysyl oxidases (LOXs) play a crucial role in ECM remodeling and regeneration. MMPs have a catalytic role in degradation of ECM, whereas LOX/LOXLs mediate ECM, especially collagen, cross-linking and stiffening. Importantly, enzymes from both families are elevated during the fibrotic response to tissue injury and its resolution. Yet, the apparent molecular competition or antagonistic activities of these enzyme families during the various stages of fibrosis is often overlooked. In this review, we discuss the diverse roles of MMPs and LOX/LOXL2 in chronic organ fibrosis. Finally, we review contemporary therapeutic strategies for fibrosis treatment, based on neutralization of MMP and LOX activity, as well as the development of novel drug delivery approaches.

Protein-Derived Cofactors Revisited: Empowering Amino Acid Residues with New Functions

A protein-derived cofactor is a catalytic or redox-active site in a protein that is formed by post-translational modification of one or more amino acid residues. These post-translational modifications are irreversible and endow the modified amino acid residues with new functional properties. This Perspective focuses on the following advances in this area that have occurred during recent years. The biosynthesis of the tryptophan tryptophylquinone cofactor is catalyzed by a diheme enzyme, MauG. A bis-Fe^IV redox state of the hemes performs three two-electron oxidations of specific Trp residues via long-range electron transfer. In contrast, a flavoenzyme catalyzes the biosynthesis of the cysteine tryptophylquinone (CTQ) cofactor present in a newly discovered family of CTQ-dependent oxidases. Another carbonyl cofactor, the pyruvoyl cofactor found in classes of decarboxylases and reductases, is formed during an apparently autocatalytic cleavage of a precursor protein at the N-terminus of the cleavage product. It has been shown that in at least some cases, the cleavage is facilitated by binding to an accessory protein. Tyrosylquinonine cofactors, topaquinone and lysine tyrosylquinone, are found in copper-containing amine oxidases and lysyl oxidases, respectively. The physiological roles of different families of these enzymes in humans have been more clearly defined and shown to have significant implications with respect to human health. There has also been continued characterization of the roles of covalently cross-linked amino acid side chains that influence the reactivity of redox-active metal centers in proteins. These include Cys-Tyr species in galactose oxidase and cysteine dioxygenase and the Met-Tyr-Trp species in the catalase-peroxidase KatG.

The lncRNA GATA6-AS epigenetically regulates endothelial gene expression via interaction with LOXL2

Impaired or excessive growth of endothelial cells contributes to several diseases. However, the functional involvement of regulatory long non-coding RNAs in these processes is not well defined. Here, we show that the long non-coding antisense transcript of GATA6 (GATA6-AS) interacts with the epigenetic regulator LOXL2 to regulate endothelial gene expression via changes in histone methylation. Using RNA deep sequencing, we find that GATA6-AS is upregulated in endothelial cells during hypoxia. Silencing of GATA6-AS diminishes TGF-β2-induced endothelial-mesenchymal transition in vitro and promotes formation of blood vessels in mice. We identify LOXL2, known to remove activating H3K4me3 chromatin marks, as a GATA6-AS-associated protein, and reveal a set of angiogenesis-related genes that are inversely regulated by LOXL2 and GATA6-AS silencing. As GATA6-AS silencing reduces H3K4me3 methylation of two of these genes, periostin and cyclooxygenase-2, we conclude that GATA6-AS acts as negative regulator of nuclear LOXL2 function.

Lysyl oxidase-like 3 is required for melanoma cell survival by maintaining genomic stability

Lysyl oxidase-like 3 (LOXL3) is a member of the lysyl oxidase family comprising multifunctional enzymes with depicted roles in extracellular matrix maturation, tumorigenesis, and metastasis. In silico expression analyses followed by experimental validation in a comprehensive cohort of human cell lines revealed a significant upregulation of LOXL3 in human melanoma. We show that LOXL3 silencing impairs cell proliferation and triggers apoptosis in various melanoma cell lines. Further supporting a pro-oncogenic role in melanoma, LOXL3 favors tumor growth in vivo and cooperates with oncogenic BRAF in melanocyte transformation. Upon LOXL3 depletion, melanoma cells display a faulty DNA damage response (DDR), characterized by ATM checkpoint activation and inefficient ATR activation leading to the accumulation of double-strand breaks (DSBs) and aberrant mitosis. Consistent with these findings, LOXL3 binds to proteins involved in the maintenance of genome integrity, in particular BRCA2 and MSH2, whose levels dramatically decrease upon LOXL3 depletion. Moreover, LOXL3 is required for efficient DSB repair in melanoma cells. Our results reveal an unexpected role for LOXL3 in the control of genome stability and melanoma progression, exposing its potential as a novel therapeutic target in malignant melanoma, a very aggressive condition yet in need for more effective treatment options.

Increased serum lysyl oxidase-like 2 levels correlate with the degree of left atrial fibrosis in patients with atrial fibrillation

Atrial fibrillation (AF) progression is generally accompanied by increased atrial fibrosis and atrial structural remodeling. Lysyl oxidase-like 2 (LOXL2) is known to play an important role in many fibrotic conditions, including cardiac fibrosis. The present study aimed to explore the relationship between serum LOXL2 levels and AF. Fifty-four AF patients and 32 control subjects were enrolled in the study. High-density three-dimensional electroanatomic mapping was performed, and mean bipolar voltage was assessed in AF patients. LOXL2 levels were measured by enzyme-linked immunosorbent assay. All patients underwent echocardiography to assess left atrium size and left ventricle function. Serum LOXL2 levels were significantly elevated in AF patients compared with the control group (526.81 ± 316.82 vs 240.94 ± 92.51 pg/ml, P<0.01). In addition, serum LOXL2 level was significantly correlated with the size of the left atrium (LAD) (r² = 0.38, P<0.01). Furthermore, the serum LOXL2 levels were significantly higher in AF patients with LAD ≥ 40 mm compared with those with LAD < 40 mm (664.34 ± 346.50 vs 354.90 ± 156.23 pg/ml, P<0.01). And the Spearman's correlation analysis further revealed that the mean bipolar left atrial voltage was inversely correlated with the LOXL2 (r² = -0.49, P<0.01) in AF patients. Multivariate regression analysis further demonstrated that serum LOXL2 [odds ratio (OR) 1.013, 95% confidence interval (CI) 1.002-1.024, P<0.05] and LAD (OR 1.704, 95% CI 1.131-2.568, P<0.01) were independent predictors of AF. In conclusion, serum LOXL2 levels were significantly elevated and were correlated with the degree of left atrial fibrosis in AF patients.

Anabolic role of lysyl oxidase like-2 in cartilage of knee and temporomandibular joints with osteoarthritis

Background

Lysyl oxidase like-2 (LOXL2) is a copper-dependent amine oxidase. Our previous studies showed that LOXL2 is elevated during mouse fracture healing. The goal of this study was to evaluate the potential of LOXL2 to act as an anabolic agent in cartilage affected by osteoarthritis (OA).

Methods

LOXL2 was visualized in tissues from human knee and hip joints and temporomandibular joints (TMJ) by immunofluorescence. The activity of LOXL2 in human articular and TMJ chondrocytes was assessed by cell-based assays, microarray analysis, and RT-qPCR, and LOXL2-mediated activation of NF-κB and extracellular signal-related kinase (ERK) signaling pathways was measured by western blotting. To examine LOXL2-induced effect in vivo, we implanted Matrigel-imbedded human chondrocytes into nude mice and exposed them to exogenous LOXL2 for 6 weeks. Finally, LOXL2-induced effects on collagen type 2 α1 (COL2A1) and phospho-SMAD2/3 were evaluated by immunofluorescence analysis.

Results

LOXL2 staining was detected in damaged regions of human TMJ, hip and knee joints affected by OA. Stimulation with transforming growth factor (TGF)-β1 upregulated LOXL2 expression, while pro-inflammatory cytokines IL-1β and TNF-α downregulated LOXL2, in human chondrocytes. Viral transduction of LOXL2 in OA chondrocytes increased the mRNA levels of chondroitin sulfate proteoglycan (CSPG4), aggrecan (ACAN), sex determining region Y-box containing gene 9 (SOX9), and COL2A1 but reduced the levels of extracellular matrix (ECM)-degrading enzymes matrix metalloproteinase (MMP)1, MMP3, and MMP13. Further, forced expression of LOXL2 promoted chondrogenic lineage-specific gene expression, increased the expression of COL2A1 in the presence of TNF-α, and inhibited chondrocyte apoptosis. LOXL2 expression also inhibited IL-1β-induced phospho-NF-κB/p65 and TGF-β1-induced ERK1/2 phosphorylation. Matrigel constructs of human chondrocytes from the knee joint and TMJ implanted in nude mice showed anabolic responses after LOXL2 transduction, including increased expression of SOX9, ACAN, and COL2A1. Finally, immunofluorescence staining revealed co-localization of LOXL2 with SOX9 in the nuclei of cells in the implants, decreased phospho-SMAD2/3, and increased COL2A1 staining.

Conclusion

Our results suggest that although LOXL2 is upregulated in cartilage affected by OA, this may be a protective response that promotes anabolism while inhibiting specific catabolic responses in the pathophysiology of OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1388-8) contains supplementary material, which is available to authorized users.

Perturbations to lysyl oxidase expression broadly influence the transcriptome of lung fibroblasts

Lysyl oxidases are credited with pathogenic roles in lung diseases, including cancer, fibrosis, pulmonary hypertension, congenital diaphragmatic hernia, and bronchopulmonary dysplasia (BPD). Lysyl oxidases facilitate the covalent intra- and intermolecular cross-linking of collagen and elastin fibers, thereby imparting tensile strength to the extracellular matrix (ECM). Alternative ECM-independent roles have recently been proposed for lysyl oxidases, including regulation of growth factor signaling, chromatin remodeling, and transcriptional regulation, all of which impact cell phenotype. We demonstrate here that three of the five lysyl oxidase family members, Lox, Loxl1, and Loxl2, are highly expressed in primary mouse lung fibroblasts compared with other constituent cell types of the lung. Microarray analyses revealed that small interfering RNA knockdown of Lox, Loxl1, and Loxl2 was associated with apparent changes in the expression of 134, 3,761, and 3,554 genes, respectively, in primary mouse lung fibroblasts. The impact of lysyl oxidase expression on steady-state Mmp3, Mmp9, Eln, Rarres1, Gdf10, Ifnb1, Csf2, and Cxcl9 mRNA levels was validated, which is interesting, since the corresponding gene products are relevant to lung development and BPD, where lysyl oxidases play a functional role. In vivo, the expression of these genes broadly correlated with Lox, Loxl1, and Loxl2 expression in a mouse model of BPD. Furthermore, β-aminopropionitrile (BAPN), a selective lysyl oxidase inhibitor, did not affect the steady-state mRNA levels of lysyl oxidase target genes, in vitro in lung fibroblasts or in vivo in BAPN-treated mice. This study is the first to report that lysyl oxidases broadly influence the cell transcriptome.

Global Mapping of the Macrophage-HIV-1 Transcriptome Reveals that Productive Infection Induces Remodeling of Host Cell DNA and Chromatin

It has been proposed that macrophages could serve as long-lived compartments for HIV-1 infection under in vivo situations because these cells are resistant to the virus-mediated cytopathic effect, produce progeny virus over extended periods of time and are localized in tissues that are often less accessible by treatment. Comprehensive experimental studies are thus needed to characterize the HIV-1-induced modulation of host genes in these myeloid lineage cells. To shed light on this important issue, we performed comparative analyses of mRNA expression levels of host genes in uninfected bystander and HIV-1-infected human macrophages using an infectious reporter virus construct coupled with a large-scale RNA sequencing approach. We observed a rapid differential expression of several host factors in the productively infected macrophage population including genes regulating DNA replication factors and chromatin remodeling. A siRNA-mediated screening study to functionally identify host determinants involved in HIV-1 biology has provided new information on the virus molecular regulation in macrophages.

Roles of Copper-Binding Proteins in Breast Cancer

Copper ions are needed in several steps of cancer progression. However, the underlying mechanisms, and involved copper-binding proteins, are mainly elusive. Since most copper ions in the body (in and outside cells) are protein-bound, it is important to investigate what copper-binding proteins participate and, for these, how they are loaded with copper by copper transport proteins. Mechanistic information for how some copper-binding proteins, such as extracellular lysyl oxidase (LOX), play roles in cancer have been elucidated but there is still much to learn from a biophysical molecular viewpoint. Here we provide a summary of copper-binding proteins and discuss ones reported to have roles in cancer. We specifically focus on how copper-binding proteins such as mediator of cell motility 1 (MEMO1), LOX, LOX-like proteins, and secreted protein acidic and rich in cysteine (SPARC) modulate breast cancer from molecular and clinical aspects. Because of the importance of copper for invasion/migration processes, which are key components of cancer metastasis, further insights into the actions of copper-binding proteins may provide new targets to combat cancer.

Small Molecule Lysyl Oxidase-like 2 (LOXL2) Inhibitors: The Identification of an Inhibitor Selective for LOXL2 over LOX

Two series of novel LOXL2 enzyme inhibitors are described: benzylamines substituted with electron withdrawing groups at the para-position and 2-substituted pyridine-4-ylmethanamines. The most potent compound, (2-chloropyridin-4-yl)methanamine 20 (hLOXL2 IC₅₀ = 126 nM), was shown to be selective for LOXL2 over LOX and three other amine oxidases (MAO-A, MAO-B, and SSAO). Compound 20 is the first published small molecule inhibitor selective for LOXL2 over LOX.

Comparative analysis of lysyl oxidase (like) family members in pulmonary fibrosis

Extracellular matrix (ECM) composition and stiffness are major driving forces for the development and persistence of fibrotic diseases. Lysyl oxidase (LOX) and LOX-like (LOXL) proteins play crucial roles in ECM remodeling due to their collagen crosslinking and intracellular functions. Here, we systematically investigated LOX/L expression in primary fibroblasts and epithelial cells under fibrotic conditions, Bleomycin (BLM) induced lung fibrosis and in human IPF tissue. Basal expression of all LOX/L family members was detected in epithelial cells and at higher levels in fibroblasts. Various pro-fibrotic stimuli broadly induced LOX/L expression in fibroblasts, whereas specific induction of LOXL2 and partially LOX was observed in epithelial cells. Immunohistochemical analysis of lung tissue from 14 IPF patients and healthy donors revealed strong induction of LOX and LOXL2 in bronchial and alveolar epithelium as well as fibroblastic foci. Using siRNA experiments we observed that LOXL2 and LOXL3 were crucial for fibroblast-to-myofibroblast transition (FMT). As FMT could only be reconstituted with an enzymatically active LOXL2 variant, we conclude that LOXL2 enzymatic function is crucial for fibroblast transdifferentiation. In summary, our study provides a comprehensive analysis of the LOX/L family in fibrotic lung disease and indicates prominent roles for LOXL2/3 in fibroblast activation and LOX/LOXL2 in IPF.

Time-resolved Global and Chromatin Proteomics during Herpes Simplex Virus Type 1 (HSV-1) Infection

Herpes simplex virus (HSV-1) lytic infection results in global changes to the host cell proteome and the proteins associated with host chromatin. We present a system level characterization of proteome dynamics during infection by performing a multi-dimensional analysis during HSV-1 lytic infection of human foreskin fibroblast (HFF) cells. Our study includes identification and quantification of the host and viral proteomes, phosphoproteomes, chromatin bound proteomes and post-translational modifications (PTMs) on cellular histones during infection. We analyzed proteomes across six time points of virus infection (0, 3, 6, 9, 12 and 15 h post-infection) and clustered trends in abundance using fuzzy c-means. Globally, we accurately quantified more than 4000 proteins, 200 differently modified histone peptides and 9000 phosphorylation sites on cellular proteins. In addition, we identified 67 viral proteins and quantified 571 phosphorylation events (465 with high confidence site localization) on viral proteins, which is currently the most comprehensive map of HSV-1 phosphoproteome. We investigated chromatin bound proteins by proteomic analysis of the high-salt chromatin fraction and identified 510 proteins that were significantly different in abundance during infection. We found 53 histone marks significantly regulated during virus infection, including a steady increase of histone H3 acetylation (H3K9ac and H3K14ac). Our data provide a resource of unprecedented depth for human and viral proteome dynamics during infection. Collectively, our results indicate that the proteome composition of the chromatin of HFF cells is highly affected during HSV-1 infection, and that phosphorylation events are abundant on viral proteins. We propose that our epi-proteomics approach will prove to be important in the characterization of other model infectious systems that involve changes to chromatin composition.

Induction of altered gene expression profiles in cultured bovine granulosa cells at high cell density

BACKGROUND

In previous studies it has been shown that bovine granulosa cells (GC) cultured at a high plating density dramatically change their physiological and molecular characteristics, thus resembling an early stage of luteinization. During the present study, these specific effects on the GC transcriptome were comprehensively analysed to clarify the underlying mechanisms.

METHODS

GC were cultured in serum free medium with FSH and IGF-1 stimulation at different initial plating density. The estradiol and progesterone production was determined by radioimmunoassays and the gene expression profiles were analysed by mRNA microarray analysis after 9 days. The data were statistically analysed and the abundance of selected, differentially expressed transcripts was re-evaluated by qPCR. Bioinformatic pathway analysis of density affected transcripts was done using Ingenuity Pathway Analysis.

RESULTS

The data showed that at high plating density the expression of 1510 annotated genes, represented by 1575 transcript clusters, showed highly altered expression levels. Nearly two-thirds were up- and one third down-regulated. Within the top up-regulated genes VNN2, RGS2 and PTX3 could be identified, as well as HBA or LOXL2. Down-regulated genes included important key genes of folliculogenesis like CYP19A1 and FSHR. Ingenuity pathway analysis identified "AMPK signaling" as well as "cAMP-mediated signaling" as major pathways affected by the alteration of the expression profile. Main putative upstream regulators were TGFB1 and VEGF, thus indicating a connection with cell differentiation and angiogenesis. A detailed cluster analysis revealed one single cluster that was highly associated with the upstream regulator beta-estradiol. Within this cluster key genes of steroid biosynthesis were not included, but instead, other genes importantly involved in follicular development, like OXT and VEGFA as well as the three most down-regulated genes TXNIP, PAG11 and ARRDC4 were identified.

CONCLUSIONS

From these data we hypothesize that high density conditions induce a stage of differentiation in cultured GC that is similar to early post-LH conditions in vivo. Furthermore we hypothesize that specific cell-cell-interactions led to this differentiation including transformations necessary to promote angiogenesis.

Heparanase 2 Attenuates Head and Neck Tumor Vascularity and Growth

The endoglycosidase heparanase specifically cleaves the heparan sulfate (HS) side chains on proteoglycans, an activity that has been implicated strongly in tumor metastasis and angiogenesis. Heparanase-2 (Hpa2) is a close homolog of heparanase that lacks intrinsic HS-degrading activity but retains the capacity to bind HS with high affinity. In head and neck cancer patients, Hpa2 expression was markedly elevated, correlating with prolonged time to disease recurrence and inversely correlating with tumor cell dissemination to regional lymph nodes, suggesting that Hpa2 functions as a tumor suppressor. The molecular mechanism associated with favorable prognosis following Hpa2 induction is unclear. Here we provide evidence that Hpa2 overexpression in head and neck cancer cells markedly reduces tumor growth. Restrained tumor growth was associated with a prominent decrease in tumor vascularity (blood and lymph vessels), likely due to reduced Id1 expression, a transcription factor highly implicated in VEGF-A and VEGF-C gene regulation. We also noted that tumors produced by Hpa2-overexpressing cells are abundantly decorated with stromal cells and collagen deposition, correlating with a marked increase in lysyl oxidase expression. Notably, heparanase enzymatic activity was unimpaired in cells overexpressing Hpa2, suggesting that reduced tumor growth is not caused by heparanase regulation. Moreover, growth of tumor xenografts by Hpa2-overexpressing cells was unaffected by administration of a mAb that targets the heparin-binding domain of Hpa2, implying that Hpa2 function does not rely on heparanase or heparan sulfate. Cancer Res; 76(9); 2791-801. ©2016 AACR.

Lysyl Oxidase Isoforms and Potential Therapeutic Opportunities for Fibrosis and Cancer

INTRODUCTION

The lysyl oxidase family of enzymes is classically known as being required for connective tissue maturation by oxidizing lysine residues in elastin and lysine and hydroxylysine residues in collagen precursors. The resulting aldehydes then participate in cross-link formation, which is required for normal connective tissue integrity. These enzymes have biological functions that extend beyond this fundamental biosynthetic role, with contributions to angiogenesis, cell proliferation, and cell differentiation. Dysregulation of lysyl oxidases occurs in multiple pathologies including fibrosis, primary and metastatic cancers, and complications of diabetes in a variety of tissues.

AREAS COVERED

This review summarizes the major findings of novel roles for lysyl oxidases in pathologies, and highlights some of the potential therapeutic approaches that are in development and which stem from these new findings.

EXPERT OPINION

Fundamental questions remain regarding the mechanisms of novel biological functions of this family of proteins, and regarding functions that are independent of their catalytic enzyme activity. However, progress is underway in the development of isoform-specific pharmacologic inhibitors, potential therapeutic antibodies and gaining an increased understanding of both tumor suppressor and metastasis promotion activities. Ultimately, this is likely to lead to novel therapeutic agents.