Lysyl oxidase propeptide inhibits prostate cancer cell growth by mechanisms that target FGF-2-cell binding and signaling

Lysine Deacetylation Is a Key Function of the Lysyl Oxidase Family of Proteins in Cancer

Mammalian members of the lysyl oxidase (LOX) family of proteins carry a copper-dependent monoamine oxidase domain exclusively within the C-terminal region, which catalyzes ε-amine oxidation of lysine residues of various proteins. However, recent studies have demonstrated that in LOX-like (LOXL) 2-4 the C-terminal canonical catalytic domain and N-terminal scavenger receptor cysteine-rich (SRCR) repeats domain exhibit lysine deacetylation and deacetylimination catalytic activities. Moreover, the N-terminal SRCR repeats domain is more catalytically active than the C-terminal oxidase domain. Thus, LOX is the third family of lysine deacetylases in addition to histone deacetylase and sirtuin families. In this review, we discuss how the LOX family targets different cellular proteins for deacetylation and deacetylimination to control the development and metastasis of cancer.

The apoptotic and anti-proliferative effect of Lysyl oxidase propeptide in Y79 human retinoblastoma cells

Purpose

Retinoblastoma (RB) caused by the mutation of the RB1 gene is one of the most common ocular malignancies in children The propeptide region of lysyl oxidase (LOX), the enzyme involved in the cross-linking of collagen and elastin, has been identified to be anti-tumorigenic in various cancers. However, this role of lysyl oxidase propeptide (LOX-PP) in RB is still elusive. This study aims to identify the anti-tumorigenic effect of LOX-PP in human Y79 RB cells.

Methods

LOX-PP was overexpressed in Y79 RB cells, and differential gene expression was assessed by microarray followed by pathway analysis using transcriptome analysis console (TAC) software. Additionally, cell proliferation was studied by PrestoBlue assay, and DNA content was evaluated by cell cycle and apoptosis assays. The pro-apoptotic and anti-proliferative mechanisms induced by the overexpression of/exogenously added LOX-PP was evaluated by western blotting and real-time PCR.

Results

The expression of the LOX-PP transcript was significantly decreased in Y79 RB cells compared to human retinal endothelial cells. Gene expression analysis in LOX-PP overexpressed Y79 RB cells showed deregulation of pathways involved in apoptosis, cell cycle, focal adhesion-PI3K-AKT signaling, and DNA repair mechanisms. Interestingly, LOX-PP overexpressed Y79 RB cells showed significantly increased apoptosis, decreased proliferation, and cell cycle arrest at S-phase with a concordant reduction of proliferative cell nuclear antigen and Cyclin D1 protein expressions. Moreover, pAKT (S473) was significantly downregulated in Y79 RB cells, which decreased NFκB leading to significantly reduced BCL2 expression.

Conclusions

Our results demonstrate the anti-tumorigenic effect of LOX-PP in Y79 RB cells by inducing apoptosis and decreasing proliferation. This effect was mediated by the downregulation of AKT signaling. These results suggest that LOX-PP can be explored as a therapeutic molecule in RB.

The Lysyl Oxidase G473A Polymorphism Exacerbates Oral Cancer Development in Humans and Mice

Oral cancer is primarily squamous-cell carcinoma with a 5-year survival rate of approximately 50%. Lysyl oxidase (LOX) participates in collagen and elastin maturation. The propeptide of LOX is released as an 18 kDa protein (LOX-PP) in the extracellular environment by procollagen C-proteinases and has tumor-inhibitory properties. A polymorphism in the propeptide region of LOX (rs1800449, G473A) results in a single amino acid substitution of Gln for Arg. Here we investigated the frequency of rs1800449 in OSCC employing TCGA database resources and determined the kinetics and severity of precancerous oral lesion development in wildtype and corresponding knockin mice after exposure to 4-nitroquinoline oxide (4 NQO) in drinking water. Data show that the OSCC is more common in humans carrying the variant compared to the wildtype. Knockin mice are more susceptible to lesion development. The immunohistochemistry of LOX in mouse tissues and in vitro studies point to a negative feedback pathway of wildtype LOX-PP on LOX expression that is deficient in knockin mice. Data further demonstrate modulations of T cell phenotype in knockin mice toward a more tumor-permissive condition. Data provide initial evidence for rs1800449 as an oral cancer susceptibility biomarker and point to opportunities to better understand the functional mechanism of LOX-PP cancer inhibitory activity.

Context Matters: Response Heterogeneity to Collagen-Targeting Approaches in Desmoplastic Cancers

Simple Summary

A common feature of tumor types such as breast cancer, prostate cancer, pancreatic cancer, and soft-tissue sarcoma is the deposition of collagen-rich tissue called desmoplasia. However, efforts to control tumor growth by disrupting desmoplasia, collectively known as “collagen-targeting approaches”, have had mixed and contradictory results, sometimes even within the same cancer type. We believe that this phenomenon may be due—at least partially—to the fact that “collagen” is not a single molecule, but rather a diverse molecular family composed of 28 unique collagen types. Therefore, in this review, we discuss the diversity of collagen molecules in normal and cancer tissue, and explore how collagen heterogeneity relates to the mixed efficacy of collagen-targeting approaches for cancer therapy.

Abstract

The deposition of collagen-rich desmoplastic tissue is a well-documented feature of the solid tumor microenvironment (TME). However, efforts to target the desmoplastic extracellular matrix (ECM) en masse, or collagen molecules more specifically, have been met with mixed and sometimes paradoxical results. In this review, we posit that these discrepancies are due—at least in part—to the incredible diversity of the collagen superfamily. Specifically, whereas studies of “collagen-targeting” approaches frequently refer to “collagen” as a single molecule or relatively homogeneous molecular family, 28 individual collagens have been identified in mammalian tissues, each with a unique structure, supramolecular assembly pattern, tissue distribution, and/or function. Moreover, some collagen species have been shown to exert both pro- and anti-neoplastic effects in the desmoplastic TME, even within the same cancer type. Therefore, herein, we describe the diversity of the collagen family in normal tissues and highlight the context-specific roles of individual collagen molecules in desmoplastic tumors. We further discuss how this heterogeneity relates to the variable efficacy of “collagen-targeting” strategies in this setting and provide guidance for future directions in the field.

Functions and Mechanisms of Pro-Lysyl Oxidase Processing in Cancers and Eye Pathologies with a Focus on Diabetic Retinopathy

Lysyl oxidases are multifunctional proteins derived from five lysyl oxidase paralogues (LOX) and lysyl oxidase-like 1 through lysyl oxidase-like 4 (LOXL1-LOXL4). All participate in the biosynthesis of and maturation of connective tissues by catalyzing the oxidative deamination of lysine residues in collagens and elastin, which ultimately results in the development of cross-links required to function. In addition, the five LOX genes have been linked to fibrosis and cancer when overexpressed, while tumor suppression by the propeptide derived from pro-LOX has been documented. Similarly, in diabetic retinopathy, LOX overexpression, activity, and elevated LOX propeptide have been documented. The proteolytic processing of pro-forms of the respective proteins is beginning to draw attention as the resultant peptides appear to exhibit their own biological activities. In this review we focus on the LOX paralogue, and what is known regarding its extracellular biosynthetic processing and the still incomplete knowledge regarding the activities and mechanisms of the released lysyl oxidase propeptide (LOX-PP). In addition, a summary of the roles of both LOX and LOX-PP in diabetic retinopathy, and brief mentions of the roles for LOX and closely related LOXL1 in glaucoma, and keratoconus, respectively, are included.

Rapid testing of candidate oncogenes and tumour suppressor genes in signal transduction and neoplastic transformation

The COSMIC database (version 94) lists 576 genes in the Cancer Gene Census which have a defined function as drivers of malignancy (oncogenes) or as tumour suppressors (Tier 1). In addition, there are 147 genes with similar functions, but which are less well characterised (Tier 2). Furthermore, next-generation sequencing projects in the context of precision oncology activities are constantly discovering new ones. Since cancer genes differ from their wild-type precursors in numerous molecular and biochemical properties and exert significant differential effects on downstream processes, simple assays that can uncover oncogenic or anti-oncogenic functionality are desirable and may precede more sophisticated analyses. We describe simple functional assays for PTPN11 (protein-tyrosine phosphatase, non-receptor-type 11)/SHP2 mutants, which are typically found in RASopathies and exhibit potential oncogenic activity. We have also designed a functional test for lysyl oxidase (LOX), a prototypical class II tumour suppressor gene whose loss of function may contribute to neoplastic transformation by RAS oncogenes. Moreover, we applied this test to analyse three co-regulated, RAS-responsive genes for transformation-suppressive activity. The integration of these tests into systems biology studies will contribute to a better understanding of cellular networks in cancer.

Lysyl oxidase engineered lipid nanovesicles for the treatment of triple negative breast cancer

In the field of oncology research, a deeper understanding of tumor biology has shed light on the role of environmental conditions surrounding cancer cells. In this regard, targeting the tumor microenvironment has recently emerged as a new way to access this disease. In this work, a novel extracellular matrix (ECM)-targeting nanotherapeutic was engineered using a lipid-based nanoparticle chemically linked to an inhibitor of the ECM-related enzyme, lysyl oxidase 1 (LOX), that inhibits the crosslinking of elastin and collagen fibers. We demonstrated that, when the conjugated vesicles were loaded with the chemotherapeutic epirubicin, superior inhibition of triple negative breast cancer (TNBC) cell growth was observed both in vitro and in vivo. Moreover, in vivo results displayed prolonged survival, minimal cytotoxicity, and enhanced biocompatibility compared to free epirubicin and epirubicin-loaded nanoparticles. This all-in-one nano-based ECM-targeting chemotherapeutic may provide a key-enabling technology for the treatment of TNBC.

Targeting Lysyl Oxidase Family Meditated Matrix Cross-Linking as an Anti-Stromal Therapy in Solid Tumours

Simple Summary

To improve efficacy of solid cancer treatment, efforts have shifted towards targeting both the cancer cells and the surrounding tumour tissue they grow in. The lysyl oxidase (LOX) family of enzymes underpin the fibrotic remodeling of the tumour microenvironment to promote both cancer growth, spread throughout the body and modulate response to therapies. This review examines how the lysyl oxidase family is involved in tumour development, how they can be targeted, and their potential as diagnostic and prognostic biomarkers in solid tumours.

Abstract

The lysyl oxidase (LOX) family of enzymes are a major driver in the biogenesis of desmoplastic matrix at the primary tumour and secondary metastatic sites. With the increasing interest in and development of anti-stromal therapies aimed at improving clinical outcomes of cancer patients, the Lox family has emerged as a potentially powerful clinical target. This review examines how lysyl oxidase family dysregulation in solid cancers contributes to disease progression and poor patient outcomes, as well as an evaluation of the preclinical landscape of LOX family targeting therapeutics. We also discuss the suitability of the LOX family as a diagnostic and/or prognostic marker in solid tumours.

LOXL1 modulates the malignant progression of colorectal cancer by inhibiting the transcriptional activity of YAP

Background

LOX-like 1 (LOXL1) is a lysyl oxidase, and emerging evidence has revealed its effect on malignant cancer progression. However, its role in colorectal cancer (CRC) and the underlying molecular mechanisms have not yet been elucidated.

Methods

LOXL1 expression in colorectal cancer was detected by immunohistochemistry, western blotting and real-time PCR. In vitro, colony formation, wound healing, migration and invasion assays were performed to investigate the effects of LOXL1 on cell proliferation, migration and invasion. In vivo, metastasis models and mouse xenografts were used to assess tumorigenicity and metastasis ability. Molecular biology experiments were utilized to reveal the underlying mechanisms by which LOXL1 modulates the Hippo pathway.

Results

LOXL1 was highly expressed in normal colon tissues compared with cancer tissues. In vitro, silencing LOXL1 in CRC cell lines dramatically enhanced migration, invasion, and colony formation, while overexpression of LOXL1 exerted the opposite effects. The results of the in vivo experiments demonstrated that the overexpression of LOXL1 in CRC cell lines drastically inhibited metastatic progression and tumour growth. Mechanistically, LOXL1 inhibited the transcriptional activity of Yes-associated protein (YAP) by interacting with MST1/2 and increasing the phosphorylation of MST1/2.

Conclusions

LOXL1 may function as an important tumour suppressor in regulating tumour growth, invasion and metastasis via negative regulation of YAP activity.

Fibrosis and cancer: A strained relationship

Tumors are characterized by extracellular matrix (ECM) deposition, remodeling, and cross-linking that drive fibrosis to stiffen the stroma and promote malignancy. The stiffened stroma enhances tumor cell growth, survival and migration and drives a mesenchymal transition. A stiff ECM also induces angiogenesis, hypoxia and compromises anti-tumor immunity. Not surprisingly, tumor aggression and poor patient prognosis correlate with degree of tissue fibrosis and level of stromal stiffness. In this review, we discuss the reciprocal interplay between tumor cells, cancer associated fibroblasts (CAF), immune cells and ECM stiffness in malignant transformation and cancer aggression. We discuss CAF heterogeneity and describe its impact on tumor development and aggression focusing on the role of CAFs in engineering the fibrotic tumor stroma and tuning tumor cell tension and modulating the immune response. To illustrate the role of mechanoreciprocity in tumor evolution we summarize data from breast cancer and pancreatic ductal carcinoma (PDAC) studies, and finish by discussing emerging anti-fibrotic strategies aimed at treating cancer.

YAP/TAZ Related BioMechano Signal Transduction and Cancer Metastasis

Mechanoreciprocity refers to a cell’s ability to maintain tensional homeostasis in response to various types of forces. Physical forces are continually being exerted upon cells of various tissue types, even those considered static, such as the brain. Through mechanoreceptors, cells sense and subsequently respond to these stimuli. These forces and their respective cellular responses are prevalent in regulating everything from embryogenic tissue-specific differentiation, programmed cell death, and disease progression, the last of which being the subject of extensive attention. Abnormal mechanical remodeling of cells can provide clues as to the pathological status of tissues. This becomes particularly important in cancer cells, where cellular stiffness has been recently accepted as a novel biomarker for cancer metastasis. Several studies have also elucidated the importance of cell stiffness in cancer metastasis, with data highlighting that a reversal of tumor stiffness has the capacity to revert the metastatic properties of cancer. In this review, we summarize our current understanding of extracellular matrix (ECM) homeostasis, which plays a prominent role in tissue mechanics. We also describe pathological disruption of the ECM, and the subsequent implications toward cancer and cancer metastasis. In addition, we highlight the most novel approaches toward understanding the mechanisms which generate pathogenic cell stiffness and provide potential new strategies which have the capacity to advance our understanding of one of human-kinds’ most clinically significant medical pathologies. These new strategies include video-based techniques for structural dynamics, which have shown great potential for identifying full-field, high-resolution modal properties, in this case, as a novel application.

Effects of High Glucose-Induced Lysyl Oxidase Propeptide on Retinal Endothelial Cell Survival: Implications for Diabetic Retinopathy

Diabetic retinopathy (DR) is characterized by apoptotic cell loss in the retinal vasculature. Lysyl oxidase propeptide (LOX-PP), released during LOX processing, has been implicated in promoting apoptosis in various diseased tissues. However, its role in the development and progression of DR is unknown. We investigated whether high glucose (HG) or diabetes alters LOX-PP expression and thereby influences AKT pathway and affects retinal endothelial cell survival. Rat retinal endothelial cells were grown in normal medium, normal medium and exposed to recombinant LOX-PP (rLOX-PP) or HG medium and examined for LOX-PP expression, AKT and caspase-3 activation. Similarly, rats intravitreally injected with rLOX-PP were examined for changes in retinal LOX-PP levels, AKT phosphorylation, and the number of acellular capillaries and pericyte loss compared with those of control diabetic and nondiabetic rats. Results indicate that HG up-regulates LOX-PP expression and reduces AKT activation. In addition, cells exposed to rLOX-PP alone exhibited increased apoptosis concomitant with decreased AKT phosphorylation. In retinas of diabetic rats, increased LOX-PP level, decreased AKT phosphorylation, and increased number of acellular capillaries and pericyte loss compared with those of nondiabetic rats were observed. Of interest, similar changes were noted in the retinas of rats injected with rLOX-PP. Findings from this study suggest that hyperglycemia-induced LOX-PP overexpression may contribute to retinal vascular cell loss associated with DR.

Involvement of miR-30b in kynurenine-mediated lysyl oxidase expression

Microenvironment components profoundly influence the propensity of cancer metastasis through regulating key molecules controlling metastasis. Lysyl oxidase (LOX) contributes to extracellular matrix (ECM) remodeling, and finally promoting bone metastasis in breast cancer. Kynurenine (Kyn), a microenvironment component, is capable of regulating the biological behaviors of cancer cells, such as promoting node metastasis in vivo. However, it is still unclear whether Kyn controls the generation of LOX. In the current study, a significant increase of migration in the Kyn (30, 50, 100, 200, and 500 μM) group was detected compared with that in the control group in 95D cells in vitro. Subsequently, we demonstrated that 50 μM Kyn not only substantially upregulated the mRNA and secreted levels of LOX rather than cytoplasmic LOX, but also markedly reduced the level of miR-30b at the same time. Furthermore, the direct interaction between LOX mRNA and miR-30b was also confirmed by dual-luciferase assay system. Most importantly, not only was Kyn-induced increase of LOX mRNA significantly attenuated on miR-30b mimics treatment, but also Kyn-mediated the upregulation of the mRNA, and secreted levels of LOX were distinctly strengthened on miR-30b inhibitor treatment. These results suggest that miR-30b is involved in Kyn-mediated LOX expression.

Inhibition of angiogenesis in endothelial cells by Human Lysyl oxidase propeptide

Angiogenesis is a critical process involved in normal physiology. Pathological angiogenesis is observed in vascular diseases and neoplasia. The propeptide domain of LOX (LOX-PP) has been shown to inhibit tumorigenesis in various cancers. In this study, we explored the role of both overexpressed and recombinant LOX-PP in naïve human umbilical vein endothelial cell with the addition of vascular endothelial growth factor (VEGF). Primarily, we observed a significant reduction in the angiogenesis signaling pathways upon LOX-PP overexpression by proteomic analysis. Further functional analysis showed that the VEGF induced cell proliferation, migration, adhesion and tube formation was inhibited by LOX-PP. Moreover, LOX-PP arrested cells at S-phase, reduced F-actin levels and decreased phosphorylation of focal adhesion kinase (FAK) and extracellular signal regulated kinase (ERK). The anti-angiogenic effect of LOX-PP was further confirmed by the reduction in the vascular network formation in chick chorioallantoic membrane (CAM). These results indicate that inhibition of angiogenesis events is not only achieved by overexpressing LOX-PP but also by addition of rLOX-PP. Taken together our findings discovered the anti-angiogenic role of LOX-PP in endothelial cells which suggests that harnessing this potential can be a promising strategy to inhibit angiogenesis.

Lysyl oxidase: A colorectal cancer biomarker of lung and hepatic metastasis

Background

Colorectal cancer (CRC) is a common and lethal disease in which distant metastasis remains the primary cause of death. Paradoxical roles of LOX have been reported in CRC, and the intracellular function of LOX has also recently been determined. Correlations of LOX expression and its intracellular localization with clinicopathological features in CRC patients remain largely unknown. The aim of the present study was to explore the potential roles of LOX in CRC.

Methods

LOX messenger RNA expression was assayed by quantitative PCR in eight paired normal mucosa and tumor tissues. Immunohistochemistry was conducted using tissue arrays to investigate LOX expression in 201 CRC patients. Regulation of LOX by YAP and TEAD4 was explored by YAP or TEAD4 short hairpin RNA interference in a LoVo cell line.

Results

LOX messenger RNA expression was elevated in some CRC specimens, and LOX nuclear localization was detected in CRC tumor tissues. LOX nuclear localization was found to correlate with lung/hepatic metastasis, elevated serum carcinoembryonic antigen concentration, and mucinous tumor type (P < 0.05). Nuclear LOX expression was found to be associated with poor overall and disease‐free survival (P < 0.05), and postoperative lung/hepatic metastasis (P < 0.05). Knockdown of YAP or TEAD4 induced downregulation of LOX expression.

Conclusions

LOX nuclear localization was significantly associated with poor survival in patients with CRC. Nuclear LOX expression was correlated with synchronous or postoperative lung/hepatic metastasis. LOX may prove to be a potential target gene of YAP and TEAD4.

Lysyl oxidase family members in urological tumorigenesis and fibrosis

Lysyl oxidase (LOX) is an extracellular copper-dependent monoamine oxidase that catalyzes crosslinking of soluble collagen and elastin into insoluble, mature fibers. Lysyl oxidase-like proteins (LOXL), LOX isozymes with partial structural homology, exhibit similar catalytic activities. This review summarizes recent findings describing the roles of LOX family members in urological cancers and fibrosis. LOX/LOXL play key roles in extracellular matrix stability and integrity, which is essential for normal female pelvic floor function. LOX/LOXL inhibition may reverse kidney fibrosis and ischemic priapism. LOX and LOXL2 reportedly promote kidney carcinoma tumorigenesis, while LOX, LOXL1 and LOXL4 suppress bladder cancer growth. Multiple studies agree that the LOX propeptide may suppress tumor growth, but the role of LOX in prostate cancer remains controversial. Further studies are needed to clarify the exact effects and mechanism of LOX/LOXL on urological malignancies.

Functional importance of lysyl oxidase family propeptide regions

The lysyl oxidase family of proteins is primarily known for its critical role in catalyzing extracellular oxidative deamination of hydroxylysine and lysine residues in collagens, and lysine residues in elastin required for connective tissue structure and function. Lysyl oxidases have additional important biological functions in health and disease. While the enzyme domains are highly conserved, the propeptide regions are less uniform, and have biological activity, some of which are independent of their respective enzymes. This review summarizes what has been published regarding the functions of the propeptide regions of this family of proteins in the context of extracellular matrix biosynthesis, fibrosis and cancer biology. Although much has been learned, there is a need for greater attention to structure/function relationships and mechanisms to more fully understand these multifunctional proteins.

Lysyl oxidase propeptide promotes adipogenesis through inhibition of FGF-2 signaling

Lysyl oxidase (LOX) catalyzes the oxidative deamination of lysine residues in collagen and elastin, key components of connective tissue. LOX is synthesized as an inactive 50 kD pre-proenzyme, and secreted to the extracellular matrix where it is cleaved into an active 32 kD LOX, and an 18kD free propeptide (LOX-PP), purportedly an inhibitor of fibroblast growth factor-2 (FGF-2) signaling. Given that adipocytes are distributed inside the connective tissue, it is likely that LOX-PP has an important regulatory role in adipogenesis, which has not been studied. Using NIH 3T3-L1 cells, we observed that FGF-2 inhibited adipogenesis, and LOX-PP promoted adipogenesis of 3T3-L1 cells in the presence of FGF-2; the expression of peroxisome proliferator-activated receptor (PPAR) γ and CCAAT-enhancer binding protein (C/EBP) α, two markers of adipogenesis, were enhanced in the presence of LOX-PP. We further observed that LOX-PP down-regulated AKT and ERK1/2, two proliferative signaling proteins down-stream of FGF-2 signaling. Similarly, inhibition of FGF-2 receptor signaling by canofin, a competitive inhibitor of FGF-2 receptor, promoted adipogenesis albeit less effective compared to LOX-PP. To further explore whether LOX-PP promoted adipogenesis through inhibition of FGF-2 signaling, site directed mutagenesis of LOX-PP, resulting in an Arg158 to Gln158 mutation which abolishes the inhibitory activity of LOX-PP to FGF-2 receptor, attenuated the adipogenic promoting properties of LOX-PP. In summary, for the first time, our data show that LOX-PP enhances adipogenesis at least partially through inhibition of FGF-2 receptor signaling. Our data suggest that LOX-PP may serve as a bona fide therapeutic target for regulating adipogenesis and adipose tissue development.

Major Action of Endogenous Lysyl Oxidase in Clear Cell Renal Cell Carcinoma Progression and Collagen Stiffness Revealed by Primary Cell Cultures

Human clear cell renal cell carcinoma (ccRCC) is therapy resistant; therefore, it is worthwhile studying in depth the molecular aspects of its progression. In ccRCC the biallelic inactivation of the VHL gene leads to stabilization of hypoxia-inducible factors (HIFs). Among the targets of HIF-1α transcriptional activity is the LOX gene, which codes for the inactive proenzyme (Pro-Lox) from which, after extracellular secretion and proteolysis, derives the active enzyme (Lox) and the propeptide (Lox-PP). By increasing stiffness of extracellular matrix by collagen crosslinking, Lox promotes tumor progression and metastasis. Lox and Lox-PP can reenter the cells where Lox promotes cell proliferation and invasion, whereas Lox-PP acts as tumor suppressor because of its Ras recision and apoptotic activity. Few data are available concerning LOX in ccRCC. Using an in vitro model of ccRCC primary cell cultures, we performed, for the first time in ccRCC, a detailed study of endogenous LOX and also investigated their transcriptomic profile. We found that endogenous LOX is overexpressed in ccRCC, is involved in a positive-regulative loop with HIF-1α, and has a major action on ccRCC progression through cellular adhesion, migration, and collagen matrix stiffness increment; however, the oncosuppressive action of Lox-PP was not found to prevail. These findings may suggest translational approaches for new therapeutic strategies in ccRCC.

Nuclear expression of lysyl oxidase enzyme is an independent prognostic factor in rectal cancer patients

Emerging evidence has implicated a pivotal role for lysyl oxidase (LOX) in cancer progression and metastasis. Whilst the majority of work has focused on the extracellular matrix cross-linking role of LOX, the exact function of intracellular LOX localisation remains unclear. In this study, we analysed the LOX expression patterns in the nuclei of rectal cancer patient samples and determined the clinical significance of this expression. Nuclear LOX expression was significantly increased in patient lymph node metastases compared to their primary tumours. High nuclear LOX expression in tumours was correlated with a high rate of distant metastasis and increased recurrence. Multivariable analysis showed that high nuclear LOX expression was also correlated with poor overall survival and disease free survival. Furthermore, we are the first to identify LOX enzyme isoforms (50 kDa and 32 kDa) within the nucleus of colon cancer cell lines by confocal microscopy and Western blot. Our results show a powerful link between nuclear LOX expression in tumours and patient survival, and offer a promising prognostic biomarker for rectal cancer patients.

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.

Sex-Linked Skeletal Phenotype of Lysyl Oxidase Like-1 Mutant Mice

Lysyl oxidases are required for collagen and elastin cross-linking and extracellular matrix maturation including in bone. The lysyl oxidase family consists of lysyl oxidase (LOX) and 4 isoforms (LOXL1-4). Here we investigate whether deletion of LOXL1, which has been linked primarily to elastin maturation, leads to skeletal abnormalities. Left femurs (n = 8), L5 vertebrae (n = 8), and tibiae (n = 8) were analyzed by micro-computed tomography in 13-week-old wild-type (WT) and LOXL1-/- male and female mice. Right femurs (n = 8) were subjected to immunohistochemistry for LOXL1, and histochemical/histology analyses of osteoclasts and growth plates. Sera from all mice were analyzed for bone turnover markers. Results indicate strong expression of LOXL1 in wild-type growth plates in femurs. Significant deterioration of trabecular bone structure in long bones and vertebrae from female was observed but not from male, mutant mice compared with WT. Decreases in BV/TV, Conn.D, trabecular thickness, and number in the femoral distal metaphysis were observed in female, but not in male, mutant mice. Trabecular spacing was increased significantly in femurs of female mutant mice. Findings were similar in trabeculae of L5 vertebrae from female mutant mice. The number of TRAP positive osteoclasts at the trabecular bone surface was increased in female mutant mice compared with WT females, consistent with increased serum RANKL and decreased OPG levels. Analysis of bone turnover markers confirmed increased bone resorption as indicated by significantly elevated CTX-1 in the serum of female LOXL1-/- mice compared to their wild-type counterparts, as well as decreased bone formation as measured by decreased serum levels of PINP. Picrosirius red staining revealed a loss of heterogeneity in collagen organization in female LOXL1-/- mice only, with little to no yellow and orange birefringence. Organization was also impaired in chondrocyte columns in both female and male LOXL1-/- mice, but to a greater extent in females. Data indicate that LOXL1-/- mutant mice develop appendicular and axial skeletal phenotypes characterized by decreased bone volume fraction and compromised trabecular microstructure, predominantly in females.

Inhibition of Lysyl Oxidase and Lysyl Oxidase-Like Enzymes Has Tumour-Promoting and Tumour-Suppressing Roles in Experimental Prostate Cancer

Lysyl oxidase (LOX) and LOX-like (LOXL) enzymes are key players in extracellular matrix deposition and maturation. LOX promote tumour progression and metastasis, but it may also have tumour-inhibitory effects. Here we show that orthotopic implantation of rat prostate AT-1 tumour cells increased LOX and LOXLs mRNA expressions in the tumour and in the surrounding non-malignant prostate tissue. Inhibition of LOX enzymes, using Beta-aminopropionitrile (BAPN), initiated before implantation of AT-1 cells, reduced tumour growth. Conversely, treatment that was started after the tumours were established resulted in unaffected or increased tumour growth. Moreover, treatment with BAPN did not suppress the formation of spontaneous lymph node metastases, or lung tumour burden, when tumour cells were injected intravenously. A temporal decrease in collagen fibre content, which is a target for LOX, was observed in tumours and in the tumour-adjacent prostate tissue. This may explain why early BAPN treatment is more effective in inhibiting tumour growth compared to treatment initiated later. Our data suggest that the enzymatic function of the LOX family is context-dependent, with both tumour-suppressing and tumour-promoting properties in prostate cancer. Further investigations are needed to understand the circumstances under which LOX inhibition may be used as a therapeutic target for cancer patients.

Lysyl oxidase propeptide stimulates osteoblast and osteoclast differentiation and enhances PC3 and DU145 prostate cancer cell effects on bone in vivo

Lysyl oxidase pro-enzyme is secreted by tumor cells and normal cells as a 50 kDa pro-enzyme into the extracellular environment where it is cleaved into the ~30 kDa mature enzyme (LOX) and 18 kDa pro-peptide (LOX-PP). Extracellular LOX enzyme activity is required for normal collagen and elastin extracellular cross-linking and maturation of the extracellular matrix. Extracellular LOX-PP acts as a tumor suppressor and can re-enter cells from the extracellular environment to induce its effects. The underlying hypothesis is that LOX-PP has the potential to promote bone cell differentiation, while inhibiting cancer cell effects in bone. Here we investigate the effect of LOX-PP on bone marrow cell proliferation and differentiation towards osteoblasts or osteoclasts, and LOX-PP modulation of prostate cancer cell conditioned media-induced alterations of proliferation and differentiation of bone marrow cells in vitro. Effects of overexpression of rLOX-PP in DU145 and PC3 prostate cancer cell lines on bone structure in vivo after intramedullary injections were determined. Data show that prostate cancer cell conditioned media inhibited osteoblast differentiation in bone marrow-derived cells, which was reversed by rLOX-PP treatment. Prostate cancer conditioned media stimulated osteoclast differentiation which was further enhanced by rLOX-PP treatment. rLOX-PP stimulated osteoclast differentiation by inhibiting OPG expression, up-regulating CCN2 expression, and increasing osteoclast fusion. In vivo studies indicate that rLOX-PP expression by PC3 cells implanted into the tibia of mice further enhanced PC3 cell ability to resorb bone, while rLOX-PP expression in DU145 cells resulted in non-significant increases in net bone formation. rLOX-PP enhances both osteoclast and osteoblast differentiation. rLOX-PP may serve to enhance coupling interactions between osteoclasts and osteoblasts helping to maintain a normal bone turnover in health, while contributing to bone abnormalities in disease.

Lysyl oxidase mediates hypoxia-induced radioresistance in non-small cell lung cancer A549 cells

Hypoxia-induced radioresistance has been well known as the main obstacle in cancer radiotherapy. Lysyl oxidase (LOX) was previously demonstrated to play an important role in hypoxia-induced biological behaviors, such as metastasis and angiogenesis, through hypoxia-inducible factor-1α (HIF-1α), which is an important contributing factor to radioresistance in tumor cells. However, how LOX plays a role in hypoxia-induced radioresistance has yet to be determined. Here, we found that LOX expression was in accordance with HIF-1α expression, and LOX expression at the mRNA and protein level, and enzymatic activity were remarkably upregulated in the hypoxic A549 cells, compared with normoxic A549 cells. Inhibition of LOX resulted in the reduction of the ability to repair double-stranded breaks (DSBs), promotion of apoptosis, relief of G2/M cycle arrest, and eventually reduction of hypoxia-induced radioresistance in the hypoxic A549 cells. This suggests that LOX may play an important role in hypoxia-induced radioresistance. Together, our results might suggest a novel potential therapeutic target in the management of non-small cell lung cancer (NSCLC).

High Lysyl Oxidase (LOX) in the Non-Malignant Prostate Epithelium Predicts a Poor Outcome in Prostate Cancer Patient Managed by Watchful Waiting

Lysyl oxidase (LOX) has been shown to both promote and suppress tumor progression, but its role in prostate cancer is largely unknown. LOX immunoreactivity was scored in prostate tumor epithelium, tumor stroma and in the tumor-adjacent non-malignant prostate epithelium and stroma. LOX scores in tumor and non-malignant prostate tissues were then examined for possible associations with clinical characteristics and survival in a historical cohort of men that were diagnosed with prostate cancer at transurethral resection and followed by watchful waiting. Men with a low LOX score in the non-malignant prostate epithelium had significantly longer cancer specific survival than men with a high score. Furthermore, LOX score in non-malignant prostate epithelium remained prognostic in a multivariable analysis including Gleason score. LOX score in prostate tumor epithelium positively correlated to Gleason score and metastases but was not associated with cancer survival. LOX score in tumor and non-malignant prostate stroma appeared unrelated to these tumor characteristics. In radical prostatectomy specimens, LOX immune-staining corresponded to LOX in-situ hybridization and LOX mRNA levels were found to be similar between tumor and adjacent non-malignant areas, but significantly increased in bone metastases samples. LOX levels both in tumors and in the surrounding tumor-bearing organ are apparently related to prostate cancer aggressiveness.

Proteases decode the extracellular matrix cryptome

The extracellular matrix is comprised of 1100 core-matrisome and matrisome-associated proteins and of glycosaminoglycans. This structural scaffold contributes to the organization and mechanical properties of tissues and modulates cell behavior. The extracellular matrix is dynamic and undergoes constant remodeling, which leads to diseases if uncontrolled. Bioactive fragments, called matricryptins, are released from the extracellular proteins by limited proteolysis and have biological activities on their own. They regulate numerous physiological and pathological processes such as angiogenesis, cancer, diabetes, wound healing, fibrosis and infectious diseases and either improve or worsen the course of diseases depending on the matricryptins and on the molecular and biological contexts. Several protease families release matricryptins from core-matrisome and matrisome-associated proteins both in vitro and in vivo. The major proteases, which decrypt the extracellular matrix, are zinc metalloproteinases of the metzincin superfamily (matrixins, adamalysins and astacins), cysteine proteinases and serine proteases. Some matricryptins act as enzyme inhibitors, further connecting protease and matricryptin fates and providing intricate regulation of major physiopathological processes such as angiogenesis and tumorigenesis. They strengthen the role of the extracellular matrix as a key player in tissue failure and core-matrisome and matrisome-associated proteins as important therapeutic targets.

Determination of cell uptake pathways for tumor inhibitor lysyl oxidase propeptide

The lysyl oxidase propeptide (LOX-PP) is derived from pro-lysyl oxidase (Pro-LOX) by extracellular biosynthetic proteolysis. LOX-PP inhibits breast and prostate cancer xenograft tumor growth and has tumor suppressor activity. Although, several intracellular targets and molecular mechanisms of action of LOX-PP have been identified, LOX-PP uptake pathways have not been reported. Here we demonstrate that the major uptake pathway for recombinant LOX-PP (rLOX-PP) is PI3K-dependent macropinocytosis in PWR-1E, PC3, SCC9, MDA-MB-231 cell lines. A secondary pathway appears to be dynamin- and caveola dependent. The ionic properties of highly basic rLOX-PP provide buffering capacity at both high and low pHs. We suggest that the buffering capacity of rLOX-PP, which serves to limit endosomal acidification, sustains PI3K-dependent macropinocytosis in endosomes which in turn is likely to facilitate LOX-PP endosomal escape into the cytoplasm and its observed interactions with cytoplasmic targets and nuclear uptake.

EWS/FLI1 Target Genes and Therapeutic Opportunities in Ewing Sarcoma

Ewing sarcoma is an aggressive bone malignancy that affect children and young adults. Ewing sarcoma is the second most common primary bone malignancy in pediatric patients. Although significant progress has been made in the treatment of Ewing sarcoma since it was first described in the 1920s, in the last decade survival rates have remained unacceptably invariable, thus pointing to the need for new approaches centered in the molecular basis of the disease. Ewing sarcoma driving mutation, EWS–FLI1, which results from a chromosomal translocation, encodes an aberrant transcription factor. Since its first characterization in 1990s, many molecular targets have been described to be regulated by this chimeric transcription factor. Their contribution to orchestrate Ewing sarcoma phenotype has been reported over the last decades. In this work, we will focus on the description of a selection of EWS/FLI1 targets, their functional role, and their potential clinical relevance. We will also discuss their role in other types of cancer as well as the need for further studies to be performed in order to achieve a broader understanding of their particular contribution to Ewing sarcoma development.

FGFR3 Down-Regulation is Involved in bacillus Calmette-Guérin Induced Bladder Tumor Growth Inhibition

PURPOSE

Bacillus Calmette-Guérin is the standard treatment for patients with nonmuscle invasive high histological grade bladder cancer. Previously we found that bacillus Calmette-Guérin induces murine bladder cancer MB49 cell death in vitro and in vivo, generating tissue remodeling, which involves the release of fibroblast growth factor (FGF)-2.

MATERIALS AND METHODS

We studied the effect of bacillus Calmette-Guérin treatment on FGF-2 and FGF receptor (FGFR) expression in bladder cancer.

RESULTS

In vitro FGF-2 increased MB49 cell proliferation but did not reverse bacillus Calmette-Guérin induced cell death. Increased FGF-2 expression was detected after bacillus Calmette-Guérin treatment. Moreover MB49 cells expressed high FGFR3 levels, which decreased after treatment. Similar results were observed in human T24 bladder cancer cells. In vivo MB49 tumors expressed higher FGFR3 levels than normal urothelium. Tumor FGFR3 decreased after treatment and correlated with tumor growth inhibition in response to bacillus Calmette-Guérin. In a pilot bioassay using 11 human bladder tumors treated ex vivo with bacillus Calmette-Guérin we found a subgroup of 41% of patients in whom FGFR3 was decreased after treatment.

CONCLUSIONS

Based on bladder cancer murine model results we infer that down-regulation of FGFR3 is a predictive marker of a good response to bacillus Calmette-Guérin therapy. The decrease in FGFR3 in response to bacillus Calmette-Guérin occurred not only in a murine model but also in a human bladder cancer cell line and in some patient samples. More patients and increased followup are needed to establish the predictive role of FGFR3 as a marker in human bladder cancer.

Effects of tumor-suppressor lysyl oxidase propeptide on prostate cancer xenograft growth and its direct interactions with DNA repair pathways

Lysyl oxidase (LOX) is a multifunctional protein required for normal collagen and elastin biosynthesis and maturation. In addition, LOX has complex roles in cancer in which the lysyl oxidase propeptide (LOX-PP) domain of secreted pro-LOX has tumor-suppressor activity, while the active enzyme promotes metastasis. In prostate cancer cell lines, recombinant LOX-PP (rLOX-PP) inhibits the growth of PC3 cells in vitro by mechanisms that were not characterized, while in DU145 cells rLOX-PP targeted fibroblast growth factor signaling. Because rLOX-PP can enhance effects of a genotoxic chemotherapeutic on breast cancer cell apoptosis, we reasoned that rLOX-PP could target DNA repair pathways typically elevated in cancer. Here we demonstrate for the first time that rLOX-PP inhibits prostate xenograft growth in vivo and that activating phosphorylations of the key DNA repair molecules ataxia-telangiectasia mutated (ATM) and checkpoint kinase 2 (CHK2) are inhibited by rLOX-PP expression in vivo. In addition, in vitro studies showed that rLOX-PP inhibits radiation-induced activating phosphorylations of ATM and CHK2 and that exogenously added rLOX-PP protein can localize to the nucleus in both DU145 and PC3 cells. rLOX-PP pull-down studies resulted in detection of a protein complex with the nuclear DNA repair regulator MRE11 in both cell lines, and rLOX-PP localized to radiation-induced nuclear DNA repair foci. Finally, rLOX-PP was shown to sensitize both DU145 and PC3 cells to radiation-induced cell death determined in colony-formation assays. These data provide evidence that rLOX-PP has a nuclear mechanism of action in which it directly interacts with DNA repair proteins to sensitize prostate cancer cells to the effects of ionizing radiation.

Hypoxia and Prostate Cancer Aggressiveness: A Tale With Many Endings

Angiogenesis, increased glycolysis, and cellular adaptation to hypoxic microenvironment are characteristic of solid tumors, including prostate cancer. These representative features are the cornerstone of cancer biology, which are well correlated with invasion, metastasis, and lethality, as well as likely with the success of prostate cancer treatment (eg, tumor hypoxia has been associated with resistance to chemotherapy and radiotherapy). It is well established that prostate cancer cells also metabolically depend on enhanced glucose transport and glycolysis for expansion, whereas growth is contingent with neovascularization to permit diffusion of oxygen and glucose. While hypoxia inducible factor 1 alpha (HIF-1α) remains the central player, the succeeding activated molecules and pathways track distinct branches, all positively correlated with the degree of intratumoral hypoxia. Among these, the vascular endothelial growth factor axis as well as the lysyl oxidase and carbonic anhydrase IX activities are notable in prostate cancer and merit further study. Here, we demonstrate their linkage with HIF-1α as a tentative explanatory mechanism of prostate cancer aggressiveness. Hypoxia drives a tale where HIF-1α-dependent effects lead to many influences in distinct key cancer biology features, rendering targeted therapies toward targets at the endings less efficient. The most appropriate approach will be to inhibit the upstream common driver (HIF-1α) activity. Additional translational and clinical research initiatives in prostate cancer are required to prove its usefulness.

Tumor microenvironment and metabolism in prostate cancer

Prostate cancer is no longer viewed mostly as a disease of abnormally proliferating epithelial cells, but rather as a disease affecting the complex interactions between the cells of the prostate epithelial compartment and the surrounding stromal compartment in which they live. Indeed, the microenvironment in which tumor cells evolve towards an aggressive phenotype is highly heterogeneous, as it is composed of different cell populations such as endothelial cells, fibroblasts, macrophages, and lymphocytes, either resident or trans-differentiated by bone marrow-derived mesenchymal stem cells recruited at the tumor site. Cancer-associated fibroblasts, the most abundant population within this microenvironment, exert a mandatory role in prostate cancer progression as they metabolically sustain cancer cell survival and growth, recruit inflammatory and immune cells, and promote cancer cells stemness and epithelial mesenchymal transition, thereby favoring metastatic dissemination of aggressive cancers. The interruption of this two-compartment crosstalk, together with the idea that stromal cells are mostly vulnerable, being drug-sensitive, could lead to the development of anticancer therapies that target tumor stromal elements.

Expression of the lysyl oxidase propeptide in hepatocellular carcinoma and its clinical relevance

Lysyl oxidase is an important extracellular matrix remodeling enzyme and plays critical roles in tumor progression and development. Its tumor-suppressor activity has been shown to depend on the propeptide region. Previous studies have reported that the expression levels of lysyl oxidase propeptide (LOX-PP) are associated with cancer of the breast, pancreas, lung, prostate and gastrointestinal system. However, to date, the exact effects and molecular mechanisms of LOX-PP in hepatocellular carcinoma progression are still unclear. The present study aimed to investigate the expression and clinical significance of LOX-PP in human hepatocellular carcinoma. First, 42 cases of hepatocellular carcinoma and corresponding adjacent non-cancerous tissues (ANCTs) were collected, and the expression of LOX-PP in these samples was assessed by immunohistochemistry (IHC). The clinicopathological characteristics of all patients were recorded. Next, in in vitro studies, recombinant adenovirus LOX (ad-LOX-PP) was used to infect hepatocellular carcinoma cell lines to determine the function of LOX-PP. To determine whether ad-LOX-PP affects hepatocellular carcinoma cell survival, cell viability was examined by CCK-8 assay, and cell cycle progression was assessed by flow cytometry. We also investigated the effects of LOX-PP on the expression of cell cycle regulators (cyclin D1 and cyclin E) by western blot analysis. The migration and invasion capacities of hepatocellular carcinoma cells were observed by wound-healing and tranwell invasion assays. To further investigate how LOX-PP affects migration levels of matrix metallopeptidase (MMP)-2 and MMP-9 were assessed by western blot analysis. Additionally, markers of the PI3K and MAPK signaling pathway were detected to further confirm the mechanisms of LOX-PP. As a result, reduced expression of LOX-PP was found in hepatocellular carcinoma tissues, when compared with that in the ANCTs (15 vs. 83%, P<0.01), and its expression was associated with tumor stage and distant metastasis (each P<0.05). Proliferation in hepatocellular carcinoma cells was significantly decreased in the ad-LOX-PP group as indicated by CCK-8 assay. LOX-PP significantly reduced the expression of Ki-67, while prominent increases in the rate of apoptosis and cell cycle arrest were observed. Similarly, cell migration was significantly inhibited in the ad-LOX-PP group as evidenced by transwell invasion and wound-healing assays. The expression levels of MMP-2 and MMP-9 were attenuated in the ad-LOX-PP group, suggesting that LOX-PP inhibits hepatocellular carcinoma cell migration via down-regulation of MMPs expression. When LOX-PP expression was potentiated by an adenovirus containing LOX-PP, the expression of p-ERK was significantly downregulated, indicating that LOX-PP inhibits hepatocellular carcinoma cell proliferation and induces its apoptosis probably through downregulation of the MAPK/ERK pathway.

Human copper-dependent amine oxidases

Copper amine oxidases (CAOs) are a class of enzymes that contain Cu(2+) and a tyrosine-derived quinone cofactor, catalyze the conversion of a primary amine functional group to an aldehyde, and generate hydrogen peroxide and ammonia as byproducts. These enzymes can be classified into two non-homologous families: 2,4,5-trihydroxyphenylalanine quinone (TPQ)-dependent CAOs and the lysine tyrosylquinone (LTQ)-dependent lysyl oxidase (LOX) family of proteins. In this review, we will focus on recent developments in the field of research concerning human CAOs and the LOX family of proteins. The aberrant expression of these enzymes is linked to inflammation, fibrosis, tumor metastasis/invasion and other diseases. Consequently, there is a critical need to understand the functions of these proteins at the molecular level, so that strategies targeting these enzymes can be developed to combat human diseases.

Lysyl oxidase in colorectal cancer

Colorectal cancer is the third most prevalent form of cancer worldwide and fourth-leading cause of cancer-related mortality, leading to ~600,000 deaths annually, predominantly affecting the developed world. Lysyl oxidase is a secreted, extracellular matrix-modifying enzyme previously suggested to act as a tumor suppressor in colorectal cancer. However, emerging evidence has rapidly implicated lysyl oxidase in promoting metastasis of solid tumors and in particular colorectal cancer at multiple stages, affecting tumor cell proliferation, invasion, and angiogenesis. This emerging research has stimulated significant interest in lysyl oxidase as a strong candidate for developing and deploying inhibitors as functional efficacious cancer therapeutics. In this review, we discuss the rapidly expanding body of knowledge concerning lysyl oxidase in solid tumor progression, highlighting recent advancements in the field of colorectal cancer.

Current strategies for inhibiting FGFR activities in clinical applications: opportunities, challenges and toxicological considerations

Aberrations in fibroblast growth factor receptor (FGFR) signaling are instrumental to the pathophysiology of several malignancies and disorders. Hence, FGFR inhibitors are explored in therapeutics with early candidates developed as competitors for the ATP-binding pocket in the kinase domain. More recent programs yielded compounds of diverse scaffolds with alternative binding modes. Concurrently, monoclonal antibodies and peptide-based agents provide independent options for clinical development. Notwithstanding this rapid progress, we contemplate the toxicological impact of FGFR inhibition based on the defined role of FGFR family members in physiology and homeostasis. The high homology among FGFR1-4 and also with other kinase subfamilies creates an additional challenge in developing selective inhibitors. It orchestrates an ongoing conundrum of moderating a balance between synergism through multitargeting kinase inhibition and minimizing off-target toxicities.

Lysyl oxidase is downregulated by the EWS/FLI1 oncoprotein and its propeptide domain displays tumor supressor activities in Ewing sarcoma cells

Ewing sarcoma is the second most common bone malignancy in children and young adults. It is driven by oncogenic fusion proteins (i.e. EWS/FLI1) acting as aberrant transcription factors that upregulate and downregulate target genes, leading to cellular transformation. Thus, identificating these target genes and understanding their contribution to Ewing sarcoma tumorigenesis are key for the development of new therapeutic strategies. In this study we show that lysyl oxidase (LOX), an enzyme involved in maintaining structural integrity of the extracellular matrix, is downregulated by the EWS/FLI1 oncoprotein and in consequence it is not expressed in Ewing sarcoma cells and primary tumors. Using a doxycycline inducible system to restore LOX expression in an Ewing sarcoma derived cell line, we showed that LOX displays tumor suppressor activities. Interestingly, we showed that the tumor suppressor activity resides in the propeptide domain of LOX (LOX-PP), an N-terminal domain produced by proteolytic cleavage during the physiological processing of LOX. Expression of LOX-PP reduced cell proliferation, cell migration, anchorage-independent growth in soft agar and formation of tumors in immunodeficient mice. By contrast, the C-terminal domain of LOX, which contains the enzymatic activity, had the opposite effects, corroborating that the tumor suppressor activity of LOX is mediated exclusively by its propeptide domain. Finally, we showed that LOX-PP inhibits ERK/MAPK signalling pathway, and that many pathways involved in cell cycle progression were significantly deregulated by LOX-PP, providing a mechanistic explanation to the cell proliferation inhibition observed upon LOX-PP expression. In summary, our observations indicate that deregulation of the LOX gene participates in Ewing sarcoma development and identify LOX-PP as a new therapeutic target for one of the most aggressive paediatric malignancies. These findings suggest that therapeutic strategies based on the administration of LOX propeptide or functional analogues could be useful for the treatment of this devastating paediatric cancer.

Megakaryocyte polyploidy is inhibited by lysyl oxidase propeptide

Megakaryocytes (MKs), the platelet precursors, undergo an endomitotic cell cycle that leads to polyploidy. Lysyl oxidase propeptide (LOX-PP) is generated from lysyl oxidase (LOX) pro-enzyme after proteolytical cleavage. We recently reported that LOX, a known matrix cross-linking enzyme, contributes to MK lineage expansion. In addition, LOX expression levels are ploidy-dependent, with polyploidy MKs having minimal levels. This led us to test the effects of LOX-PP on the number and ploidy of primary MKs. LOX-PP significantly decreases mouse bone marrow MK ploidy coupled with a reduction in MK size. MK number is unchanged upon LOX-PP treatment. Analysis of LOX-PP- or vehicle-treated MKs by western blotting revealed a reduction in ERK1/2 phosphorylation and in the levels of its downstream targets, cyclin D3 and cyclin E, which are known to play a central role in MK endomitosis. Pull-down assays and immunochemistry staining indicated that LOX-PP interacts with α-tubulin and the mictotubules, which can contribute to decreased MK ploidy. Thus, our findings defined a role for LOX-PP in reducing MK ploidy. This suggests that high-level expression of LOX in aberrantly proliferating MKs could play a part in inhibiting their polyploidization via LOX-PP.

Association between lysyl oxidase G473A polymorphism and ovarian cancer in the Han Chinese population

OBJECTIVE

Lysyl oxidase (LOX) is an extracellular enzyme critical for the cross-linking of collagens and elastin. A single-nucleotide polymorphism of LOX G473A is associated with various diseases. This retrospective study investigated the association between LOX G473A polymorphism and susceptibility to ovarian cancer in the Han Chinese population.

METHODS

The LOX variant G473A was detected by polymerase chain reaction-restriction fragment length polymorphism in patients with ovarian cancer and healthy control subjects.

RESULTS

The frequencies of the LOX 473AA genotype and the A allele were significantly higher in patients with ovarian cancer (n = 318) than in control subjects (n = 406) (odds ratio [OR] 2.30, 95% confidence interval [CI] 1.36, 3.87; OR 1.57, 95% CI 1.23, 2.00; respectively). The prevalence of the GA genotype, AA genotype and A allele were significantly higher in patients with more advanced stages of ovarian cancer compared with those with primary stage disease.

CONCLUSIONS

This study suggests that LOX G473A polymorphism is a new risk factor for ovarian cancer and that LOX protein might be a possible therapeutic target in ovarian cancer.

The rationale for targeting the LOX family in cancer

The therapeutic targeting of extracellular proteins is becoming hugely attractive in light of evidence implicating the tumour microenvironment as pivotal in all aspects of tumour initiation and progression. Members of the lysyl oxidase (LOX) family of proteins are secreted by tumours and are the subject of much effort to understand their roles in cancer. In this Review we discuss the roles of members of this family in the remodelling of the tumour microenvironment and their paradoxical roles in tumorigenesis and metastasis. We also discuss how targeting this family of proteins might lead to a new avenue of cancer therapeutics.

Lysyl oxidase, extracellular matrix remodeling and cancer metastasis

Lysyl oxidase (LOX) family oxidases, LOX and LOXL1-4, oxidize lysine residues in collagens and elastin, resulting in the covalent crosslinking and stabilization of these extracellular matrix (ECM) structural components, thus provide collagen and elastic fibers much of their tensile strength and structural integrity. Abnormality in LOX expression and/or activity results in connective tissue disorders and fibrotic diseases. Despite LOX family oxidases have been reported to function as tumor suppressors, recent studies have highlighted the roles of LOX family oxidases in promoting cancer metastasis. LOX family oxidases are highly expressed in invasive tumors, and are closely associated with metastasis and poor patient outcome. Consistent to their roles in connective tissue homeostasis, LOX family oxidases expedite tumorigenesis and metastasis through active remodeling of tumor microenvironment. LOX family oxidases are also actively involved in the process of epithelial-mesenchymal transition (EMT), an event critical in cancer cell invasion and metastasis. In this review, we will summarize the recent progress on LOX family oxidases, with much of the focus on the roles and mechanism of LOX in tumor progression and metastasis.

Human breast cancer cell metastasis is attenuated by lysyl oxidase inhibitors through down-regulation of focal adhesion kinase and the paxillin-signaling pathway

The extracellular matrix (ECM) plays a critical role in the development and invasion of primary breast tumors. Lysyl oxidase (LOX), which is an ECM remodeling enzyme, appears to play roles in promoting cancer cell motility and invasion. To ascertain whether LOX overexpression in breast tumor tissues from Asian patients is associated with decreases in metastasis-free and overall survival in breast cancer patients, the mRNA levels of LOX were examined in paired tumor/normal tissue samples using real-time RT-PCR analysis (n = 246 pair-matched samples). To test whether specifically targeting LOX by inhibiting its activity (using beta-aminopropionitrile (β-APN), a LOX inhibitor), mRNA expression (using siRNA), or protein expression (using 25 μM magnolol) attenuates the invasion of MDA-MB-231 breast cancer cells, a cancer cell migration assay was performed. Interestingly, only 78.5% (n = 193) of the breast cancer tumors displayed detectable LOX expression. Nearly 60% (n = 120) of the cases fell into Group 1 (tumor > normal, T > N); in this group, the mean LOX expression in the tumor cells was 20.2-fold greater than in normal cells. However, in Group 2 (normal > tumor, N > T), the LOX expression level in most of the normal tissues examined (80%, 59/73) was less than fivefold greater than in the tumor tissues. The increased level of active LOX in the invasive breast cancer cell line MDA-MB-231 was accompanied by the increased phosphorylation of focal adhesion kinase at Tyr-576 and of paxillin at Tyr-118. We also found that the addition of β-APN (300 μM) and magnolol (25 μM), synergistically inhibited the migration and invasion of MDA-MB-231 cells. In this article, we describe, for the first time, higher expression of a LOX protein in breast tumors compared with normal tissues from Asian patients. Moreover, the results indicate that the inhibition of LOX using magnolol may represent a more desirable strategy for breast cancer therapy than the use of β-APN.

Inflammasomes in carcinogenesis and anticancer immune responses

In the complex interplay between malignant cells and their microenvironment, caspase-1 activation complexes (inflammasomes) have contrasting roles. Inflammasomes may operate at the cell-autonomous level to eliminate malignant precursors through programmed cell death or, conversely, may stimulate the production of trophic factors for cancer cells and their stroma. In inflammatory cells, caspase-1 activation can fuel a cycle that leads to sterile inflammation and carcinogenesis, whereas in antigen-presenting cells, inflammasomes can stimulate anticancer immune responses. The inhibition of inflammasomes or neutralization of their products, mainly interleukin 1β (IL-1β) and IL-18, has profound effects on carcinogenesis and tumor progression. Thus, inflammasomes are promising therapeutic targets in cancer-related clinical conditions. Here we discuss present and future indications for the clinical use of inflammasome inhibitors.

Blimp1 activation by AP-1 in human lung cancer cells promotes a migratory phenotype and is inhibited by the lysyl oxidase propeptide

B lymphocyte-induced maturation protein 1 (Blimp1) is a master regulator of B cell differentiation, and controls migration of primordial germ cells. Recently we observed aberrant Blimp1 expression in breast cancer cells resulting from an NF-κB RelB to Ras signaling pathway. In order to address the question of whether the unexpected expression of Blimp1 is seen in other epithelial-derived tumors, we selected lung cancers as they are frequently driven by Ras signaling. Blimp1 was detected in all five lung cancer cell lines examined and shown to promote lung cancer cell migration and invasion. Interrogation of microarray datasets demonstrated elevated BLIMP1 RNA expression in lung adenocarcinoma, pancreatic ductal carcinomas, head and neck tumors as well as in glioblastomas. Involvement of Ras and its downstream kinase c-Raf was confirmed using mutant and siRNA strategies. We next addressed the issue of mechanism of Blimp1 activation in lung cancer. Using knockdown and ectopic expression, the role of the Activator Protein (AP)-1 family of transcription factors was demonstrated. Further, chromatin immunoprecipitation assays confirmed binding to identified AP-1 elements in the BLIMP1 promoter of ectopically expressed c-Jun and of endogenous AP-1 subunits following serum stimulation. The propeptide domain of lysyl oxidase (LOX-PP) was identified as a tumor suppressor, with ability to reduce Ras signaling in lung cancer cells. LOX-PP reduced expression of Blimp1 by binding to c-Raf and inhibiting activation of AP-1, thereby attenuating the migratory phenotype of lung cancer cells. Thus, Blimp1 is a mediator of Ras/Raf/AP-1 signaling that promotes cell migration, and is repressed by LOX-PP in lung cancer.