Determination of cell uptake pathways for tumor inhibitor lysyl oxidase propeptide

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.

Regulating the properties of XQ-2d for targeted delivery of therapeutic agents to pancreatic cancers

Enhanced recognition ability, cell uptake capacity, and biostability are characteristics attributed to aptamer-based targeted anticancer agents, and are possibly associated with increased accumulation at the tumor site, improved therapeutic efficacy and reduced negative side effects. Herein, a phosphorothioate backbone modification strategy was applied to regulate the biomedical properties of pancreatic cancer cell-targeting aptamer for efficient in vivo drug delivery. Specifically, the CD71- targeting aptamer XQ-2d was modified into a fully thio-substituted aptamer S-XQ-2d, improving the plasma stability of S-XQ-2d and mitomycin C (MMC)-functionalized S-XQ-2d (MFSX), thus considerably prolonging their half-life in mice. Moreover, the binding and uptake capacities of S-XQ-2d were significantly enhanced. MFSX showed the same level of cytotoxicity as that of MMC against targeted cancer cells, but lower toxicity to non-targeted cells, highlighting its specificity and biosafety. Brief mechanistic studies demonstrated that XQ-2d and S-XQ-2d had different interaction modes and internalization pathways with the targeted cells.

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.

Targeting the lysyl oxidases in tumour desmoplasia

The extracellular matrix (ECM) is a fundamental component of tissue microenvironments and its dysregulation has been implicated in a number of diseases, in particular cancer. Tumour desmoplasia (fibrosis) accompanies the progression of many solid cancers, and is also often induced as a result of many frontline chemotherapies. This has recently led to an increased interest in targeting the underlying processes. The major structural components of the ECM contributing to desmoplasia are the fibrillar collagens, whose key assembly mechanism is the enzymatic stabilisation of procollagen monomers by the lysyl oxidases. The lysyl oxidase family of copper-dependent amine oxidase enzymes are required for covalent cross-linking of collagen (as well as elastin) molecules into the mature ECM. This key step in the assembly of collagens is of particular interest in the cancer field since it is essential to the tumour desmoplastic response. LOX family members are dysregulated in many cancers and consequently the development of small molecule inhibitors targeting their enzymatic activity has been initiated by many groups. Development of specific small molecule inhibitors however has been hindered by the lack of crystal structures of the active sites, and therefore alternate indirect approaches to target LOX have also been explored. In this review, we introduce the importance of, and assembly steps of the ECM in the tumour desmoplastic response focussing on the role of the lysyl oxidases. We also discuss recent progress in targeting this family of enzymes as a potential therapeutic approach.

Development of an AAV-Based MicroRNA Gene Therapy to Treat Machado-Joseph Disease

Spinocerebellar ataxia type 3 (SCA3), or Machado-Joseph disease (MJD), is a progressive neurodegenerative disorder caused by a CAG expansion in the ATXN3 gene. The expanded CAG repeat is translated into a prolonged polyglutamine repeat in the ataxin-3 protein and accumulates within inclusions, acquiring toxic properties, which results in degeneration of the cerebellum and brain stem. In the current study, a non-allele-specific ATXN3 silencing approach was investigated using artificial microRNAs engineered to target various regions of the ATXN3 gene (miATXN3). The miATXN3 candidates were screened in vitro based on their silencing efficacy on a luciferase (Luc) reporter co-expressing ATXN3. The three best miATXN3 candidates were further tested for target engagement and potential off-target activity in induced pluripotent stem cells (iPSCs) differentiated into frontal brain-like neurons and in a SCA3 knockin mouse model. Besides a strong reduction of ATXN3 mRNA and protein, small RNA sequencing revealed efficient guide strand processing without passenger strands being produced. We used different methods to predict alteration of off-target genes upon AAV5-miATXN3 treatment and found no evidence for unwanted effects. Furthermore, we demonstrated in a large animal model, the minipig, that intrathecal delivery of AAV5 can transduce the main areas affected in SCA3 patients. These results proved a strong basis to move forward to investigate distribution, efficacy, and safety of AAV5-miATXN3 in large animals.

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.

Reprint of "The complex dynamics of myocardial interstitial fibrosis in heart failure. Focus on collagen cross-linking"

Myocardial interstitial fibrosis (MIF) is a common finding in heart failure (HF) patients, both with preserved and reduced ejection fraction, as well as in HF animal models. MIF is associated with impaired cardiac function and worse clinical outcome. The impact of MIF is influenced not only by the quantity but also by changes in the quality of collagen fibers and in the extracellular matrix components, such as a shift in collagen types proportion, increased fibronectin polymerization and increased degree of collagen cross-linking (CCL). In particular, CCL, a process that renders collagen fibers stiffer and more resistant to degradation, is increased both in patients and animal models of HF. Importantly, in HF patients increased cardiac CCL is directly associated with increased left ventricular stiffness and a higher risk of hospitalization for HF. The aim of this review is to address the complexity of MIF in HF, focusing on CCL.

The complex dynamics of myocardial interstitial fibrosis in heart failure. Focus on collagen cross-linking

Myocardial interstitial fibrosis (MIF) is a common finding in heart failure (HF) patients, both with preserved and reduced ejection fraction, as well as in HF animal models. MIF is associated with impaired cardiac function and worse clinical outcome. The impact of MIF is influenced not only by the quantity but also by changes in the quality of collagen fibers and in the extracellular matrix components, such as a shift in collagen types proportion, increased fibronectin polymerization and increased degree of collagen cross-linking (CCL). In particular, CCL, a process that renders collagen fibers stiffer and more resistant to degradation, is increased both in patients and animal models of HF. Importantly, in HF patients increased cardiac CCL is directly associated with increased left ventricular stiffness and a higher risk of hospitalization for HF. The aim of this review is to address the complexity of MIF in HF, focusing on CCL.

Impact of Epigenetic Regulation on Head and Neck Squamous Cell Carcinoma

The most common type of head and neck cancer, head and neck squamous cell carcinoma (HNSCC), can develop therapeutic resistance that complicates its treatment. The 5-y survival rate for HNSCC remains at ~50%, and improving these outcomes requires a better understanding of the pathogenesis of HNSCC. Studies of HNSCC using in vitro, ex vivo, and in vivo approaches provide a novel conceptual framework based on epigenetic mechanisms for developing future clinical applications. Normal oral tissues are influenced by environmental factors that induce pathological changes affecting the network of epigenetic enzymes and signaling pathways to induce HNSCC growth and metastasis. Although various epigenetic regulator families, such as DNA methyltransferases, ten-eleven translocation proteins, histone acetyltransferases, histone deacetylases, BET bromodomain proteins, protein arginine methyltransferases, histone lysine methyltransferases, and histone lysine demethylases, have a role in diverse cancers, specific members have a function in HNSCC. Recently, lysine-specific demethylases have been identified as a potential, attractive, and novel target of HNSCC. Lysine-specific demethylase 1 (LSD1) expression is inappropriately upregulated in HNSCC and an orthotopic HNSCC mouse model. LSD1 can demethylate lysine at specific histone positions to repress gene expression or stimulate transcription, indicating a dual and context-dependent role in transcriptional regulation. Our study showed that LSD1 promotes HNSCC growth and metastasis. Pharmacological attenuation of LSD1 inhibits orthotopic and patient-derived HNSCC xenograft growth-specific target genes and signaling pathways. This review provides recent evidence demonstrating the function of epigenetic regulator enzymes in HNSCC progression, including potential therapeutic applications for such enzymes in combination and immunotherapy.

The challenges of oral drug delivery via nanocarriers

The oral application of pharmaceuticals is unarguably the most convenient method of application. Especially for protein- or peptide-based drugs, however, the effectiveness is significantly reduced due to enzymatic digestion in the stomach as well as a poor bioavailability in the small intestine. For these difficult formulations, the encapsulation into nanocarriers would protect the sensitive drug and thus could considerably improve the efficiency of oral drug delivery. In the last years, many candidate biodegradable nanomaterials for such carrier systems have been published. However, before the cargo can be released, the nanocarrier needs to cross multiple barriers of the human body, including a layer of intestinal mucus and epithelial as well as endothelial cells. For overcoming these cellular barriers, transcytosis is favored over a paracellular transport for most nanomaterials as paracellular transport routes lack selectivity of transported molecules once opened up. The exact mechanisms behind the transcellular translocations are up to now still not completely understood. For the vast majority of nanocarriers, the rate of transcellular transport is not sufficient to realize their application in oral drug delivery. Especially trafficking into the endolysosomal pathway often marks a key problem. In this review, we focus on the molecular mechanisms of overcoming cellular barriers, especially transcytosis, and highlight difficulties of oral drug delivery via nanocarriers.

Macropinocytosis activated by oncogenic Dbl enables specific targeted delivery of Tat/pDNA nano-complexes into ovarian cancer cells

BACKGROUND

Successful implementation of gene therapy heavily relies on efficiently delivering genetic materials and specific targeting into cells. Oncogene-driven endocytosis stimulates nutrient uptake and also develops an endocytosis-mediated defense against therapeutic agents. Cell-penetrating peptides, typically HIV-Tat, are well known for efficient delivery of nucleic acid drugs but lack targeting specificity. Various passive targeting strategies were pursued to enhance the tumor targeting efficiency; however, they are still limited by complicated cellular endocytosis routes and the heterogeneity of cancer types.

METHODS

Tat/pDNA complexes were noncovalently compacted and their physiochemical properties were determined. The siRNA pool and pLV-RNAi-GFP lentivirus were used to knock down dbl oncogene (originally isolated from diffuse B-cell lymphoma) expression, and its overexpression was performed by plasmid transient transfection. The cellular uptake of fluorescent ligands was quantified by confocal imaging and flow cytometry analysis. The transgene efficiency was determined by the Luciferase expression assay. Rho GTPase activation was checked by the GST-Rho GTPase-binding domain pull-down assay.

RESULTS

pGL3 plasmid DNA was noncovalently compacted with the Tat peptide into nano-size complexes at high N/P ratios. Macropinocytosis, a clathrin- and caveolin-independent endocytosis process, was shown to contribute to the uptake of middle-sized (∼600 nm) Tat/pGL3 complexes. Cell-type-specific variation in macropinocytosis was essentially controlled by the action of the Dbl oncogene. Onco-Dbl presentation constantly induced a high level of macropinocytosis activity in ovarian cancer cells. Onco-Dbl overexpression hyperstimulated macropinocytosis enhancement in cells mainly through actin cytoskeleton reorganization mediated by the PH domain and Rac1 activation. The Dbl-driven Rho GTPase signaling collectively determined the cell-type-specific macropinocytosis phenotype.

CONCLUSION

Such an aspect can be exploited to selectively confer targeted delivery of Tat/pDNA nano-complexes into ovarian cancer cells. Our work provides a novel alternative for targeted delivery of cell-penetrating peptide-based nucleic acid drugs into certain tumor types if specific endocytosis pathways are used.

Insights into the structure and dynamics of lysyl oxidase propeptide, a flexible protein with numerous partners

Lysyl oxidase (LOX) catalyzes the oxidative deamination of lysine and hydroxylysine residues in collagens and elastin, which is the first step of the cross-linking of these extracellular matrix proteins. It is secreted as a proenzyme activated by bone morphogenetic protein-1, which releases the LOX catalytic domain and its bioactive N-terminal propeptide. We characterized the recombinant human propeptide by circular dichroism, dynamic light scattering, and small-angle X-ray scattering (SAXS), and showed that it is elongated, monomeric, disordered and flexible (D_max: 11.7 nm, R_g: 3.7 nm). We generated 3D models of the propeptide by coarse-grained molecular dynamics simulations restrained by SAXS data, which were used for docking experiments. Furthermore, we have identified 17 new binding partners of the propeptide by label-free assays. They include four glycosaminoglycans (hyaluronan, chondroitin, dermatan and heparan sulfate), collagen I, cross-linking and proteolytic enzymes (lysyl oxidase-like 2, transglutaminase-2, matrix metalloproteinase-2), a proteoglycan (fibromodulin), one growth factor (Epidermal Growth Factor, EGF), and one membrane protein (tumor endothelial marker-8). This suggests new roles for the propeptide in EGF signaling pathway.

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.

More than a syllable in fib-ROS-is: The role of ROS on the fibrotic extracellular matrix and on cellular contacts

Fibrosis is characterized by excess deposition of extracellular matrix (ECM). However, the ECM changes during fibrosis not only quantitatively but also qualitatively. Thus, the composition is altered as the expression of various ECM proteins changes. Moreover, also posttranslational modifications, secretion, deposition and crosslinkage as well as the proteolytic degradation of ECM components run differently during fibrosis. As several of these processes involve redox reactions and some of them are even redox-regulated, reactive oxygen species (ROS) influence fibrotic diseases. Redox regulation of the ECM has not been studied intensively, although evidences exist that the alteration of the ECM, including the redox-relevant processes of its formation and degradation, may be of key importance not only as a cause but also as a consequence of fibrotic diseases. Myofibroblasts, which have differentiated from fibroblasts during fibrosis, produce most of the ECM components and in return obtain important environmental cues of the ECM, including their redox-dependent fibrotic alterations. Thus, myofibroblast differentiation and fibrotic changes of the ECM are interdependent processes and linked with each other via cell-matrix contacts, which are mediated by integrins and other cell adhesion molecules. These cell-matrix contacts are also regulated by redox processes and by ROS. However, most of the redox-catalyzing enzymes are localized within cells. Little is known about redox-regulating enzymes, especially the ones that control the formation and cleavage of redox-sensitive disulfide bridges within the extracellular space. They are also important players in the redox-regulative crosstalk between ECM and cells during fibrosis.

Fragments generated upon extracellular matrix remodeling: Biological regulators and potential drugs

The remodeling of the extracellular matrix (ECM) by several protease families releases a number of bioactive fragments, which regulate numerous biological processes such as autophagy, angiogenesis, adipogenesis, fibrosis, tumor growth, metastasis and wound healing. We review here the proteases which generate bioactive ECM fragments, their ECM substrates, the major bioactive ECM fragments, together with their biological properties and their receptors. The translation of ECM fragments into drugs is challenging and would take advantage of an integrative approach to optimize the design of pre-clinical and clinical studies. This could be done by building the contextualized interaction network of the ECM fragment repertoire including their parent proteins, remodeling proteinases, and their receptors, and by using mathematical disease models.

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.

Excess α-synuclein compromises phagocytosis in iPSC-derived macrophages

To examine the pathogenic role of α-synuclein (αS) in Parkinson's Disease, we have generated induced Pluripotent Stem Cell lines from early onset Parkinson's Disease patients with SNCA A53T and SNCA Triplication mutations, and in this study have differentiated them to PSC-macrophages (pMac), which recapitulate many features of their brain-resident cousins, microglia. We show that SNCA Triplication pMac, but not A53T pMac, have significantly increased intracellular αS versus controls and release significantly more αS to the medium. SNCA Triplication pMac, but not A53T pMac, show significantly reduced phagocytosis capability and this can be phenocopied by adding monomeric αS to the cell culture medium of control pMac. Fibrillar αS is taken up by pMac by actin-rearrangement-dependent pathways, and monomeric αS by actin-independent pathways. Finally, pMac degrade αS and this can be arrested by blocking lysosomal and proteasomal pathways. Together, these results show that macrophages are capable of clearing αS, but that high levels of exogenous or endogenous αS compromise this ability, likely a vicious cycle scenario faced by microglia in Parkinson's disease.

Inhibition of LSD1 epigenetically attenuates oral cancer growth and metastasis

Lysine-specific demethylase 1 (LSD1) is a nuclear histone demethylase and a member of the amine oxidase (AO) family. LSD1 is a flavin-containing AO that specifically catalyzes the demethylation of mono- and di-methylated histone H3 lysine 4 through an FAD-dependent oxidative reaction. LSD1 is inappropriately upregulated in lung, liver, brain and esophageal cancers, where it promotes cancer initiation, progression, and metastasis. However, unlike other lysine-specific demethylases, the role and specific targets of LSD1 in oral squamous cell carcinoma (OSCC) pathogenesis remain unknown. We show that LSD1 protein expression was increased in malignant OSCC tissues in a clinical tissue microarray, and its expression correlated with progressive tumor stages. In an orthotopic oral cancer mouse model, LSD1 overexpression in aggressive HSC-3 cells promoted metastasis whereas knockdown of LSD1 inhibited tumor spread, suggesting that LSD1 is a key regulator of OSCC metastasis. Pharmacological inhibition of LSD1 using a specific small molecule inhibitor, GSK-LSD1, down-regulated EGF signaling pathway. Further, GSK-LSD1 attenuates CTGF/CCN2, MMP13, LOXL4 and vimentin expression but increased E-cadherin expression in pre-existing, patient-derived tonsillar OSCC xenografts. Similarly, GSK-LSD1 inhibited proliferation and CTGF expression in mesenchymal cells, including myoepithelial cells and osteosarcoma cells. In addition, gene set enrichment analysis revealed that GSK-LSD1 increased p53 expression and apoptosis while inhibiting c-myc, β-catenin and YAP-induced oncogenic transcriptional networks. These data reveal that aberrant LSD1 activation regulates key OSCC microenvironment and EMT promoting factors, including CTGF, LOXL4 and MMP13.

Lysyl Oxidase and the Tumor Microenvironment

The lysyl oxidase (LOX) family of oxidases contains a group of extracellular copper-dependent enzymes that catalyze the cross-linking of collagen and elastin by oxidation, thus maintaining the rigidity and structural stability of the extracellular matrix (ECM). Aberrant expression or activation of LOX alters the cellular microenvironment, leading to many diseases, including atherosclerosis, tissue fibrosis, and cancer. Recently, a number of studies have shown that LOX is overexpressed in most cancers and that it is involved in the regulation of tumor progression and metastasis. In contrast, a few reports have also indicated the tumor-suppressing role of LOX. In this short review, we discuss recent research on the correlations between LOX and cancer. Further, the role of LOX in tumor microenvironment remodeling, tumorigenesis, and metastasis and the underlying mechanisms have also been elucidated.

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.

Matricryptins Network with Matricellular Receptors at the Surface of Endothelial and Tumor Cells

The extracellular matrix (ECM) is a source of bioactive fragments called matricryptins or matrikines resulting from the proteolytic cleavage of extracellular proteins (e.g., collagens, elastin, and laminins) and proteoglycans (e.g., perlecan). Matrix metalloproteinases (MMPs), cathepsins, and bone-morphogenetic protein-1 release fragments, which regulate physiopathological processes including tumor growth, metastasis, and angiogenesis, a pre-requisite for tumor growth. A number of matricryptins, and/or synthetic peptides derived from them, are currently investigated as potential anti-cancer drugs both in vitro and in animal models. Modifications aiming at improving their efficiency and their delivery to their target cells are studied. However, their use as drugs is not straightforward. The biological activities of these fragments are mediated by several receptor families. Several matricryptins may bind to the same matricellular receptor, and a single matricryptin may bind to two different receptors belonging or not to the same family such as integrins and growth factor receptors. Furthermore, some matricryptins interact with each other, integrins and growth factor receptors crosstalk and a signaling pathway may be regulated by several matricryptins. This forms an intricate 3D interaction network at the surface of tumor and endothelial cells, which is tightly associated with other cell-surface associated molecules such as heparan sulfate, caveolin, and nucleolin. Deciphering the molecular mechanisms underlying the behavior of this network is required in order to optimize the development of matricryptins as anti-cancer agents.

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.

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.