Intracellular localization of the matrix enzyme lysyl oxidase in polarized epithelial cells

Insights into Disease Progression of Translational Preclinical Rat Model of Interstitial Pulmonary Fibrosis through Endpoint Analysis

Idiopathic pulmonary fibrosis (IPF) is a devastating interstitial lung disease characterized by the relentless deposition of extracellular matrix (ECM), causing lung distortions and dysfunction. Animal models of human IPF can provide great insight into the mechanistic pathways underlying disease progression and a means for evaluating novel therapeutic approaches. In this study, we describe the effect of bleomycin concentration on disease progression in the classical rat bleomycin model. In a dose-response study (1.5, 2, 2.5 U/kg i.t), we characterized lung fibrosis at day 14 after bleomycin challenge using endpoints including clinical signs, inflammatory cell infiltration, collagen content, and bronchoalveolar lavage fluid-soluble profibrotic mediators. Furthermore, we investigated fibrotic disease progression after 2 U/kg i.t. bleomycin administration at days 3, 7, and 14 by quantifying the expression of clinically relevant signaling molecules and pathways, epithelial mesenchymal transition (EMT) biomarkers, ECM components, and histopathology of the lung. A single bleomycin challenge resulted in a progressive fibrotic response in rat lung tissue over 14 days based on lung collagen content, histopathological changes, and modified Ashcroft score. The early fibrogenesis phase (days 3 to 7) is associated with an increase in profibrotic mediators including TGFβ1, IL6, TNFα, IL1β, CINC1, WISP1, VEGF, and TIMP1. In the mid and late fibrotic stages, the TGFβ/Smad and PDGF/AKT signaling pathways are involved, and clinically relevant proteins targeting galectin-3, LPA1, transglutaminase-2, and lysyl oxidase 2 are upregulated on days 7 and 14. Between days 7 and 14, the expressions of vimentin and α-SMA proteins increase, which is a sign of EMT activation. We confirmed ECM formation by increased expressions of procollagen-1Aα, procollagen-3Aα, fibronectin, and CTGF in the lung on days 7 and 14. Our data provide insights on a complex network of several soluble mediators, clinically relevant signaling pathways, and target proteins that contribute to drive the progressive fibrotic phenotype from the early to late phase (active) in the rat bleomycin model. The framework of endpoints of our study highlights the translational value for pharmacological interventions and mechanistic studies using this model.

High Glucose Increases Binding of Lysyl Oxidase to Extracellular Matrix Proteins: Implications for Diabetic Retinopathy

Purpose

To determine whether high glucose (HG) compromises internalization of lysyl oxidase (LOX) through excess binding of LOX with extracellular matrix (ECM) proteins.

Methods

To determine whether HG promotes binding of LOX with ECM proteins, fibronectin (FN) and collagen IV (Coll IV), total or ECM-only proteins from rat retinal endothelial cells grown in normal (N; 5 mM) or HG (30 mM) medium were analyzed by coimmunoprecipitation and Western blot (WB). In parallel, coimmunostaining was performed to determine changes in LOX binding to FN or Coll IV. To determine the effect of HG on extracellular LOX levels, medium in which cells were grown for 1, 3, 5, and 7 days were assessed for LOX levels.

Results

WB analysis using total protein showed LOX overexpression and elevated levels of LOX bound to Coll IV or FN in HG condition. Similarly, a significant increase in LOX bound to FN or Coll IV was observed in ECM-only protein. These data were supported by Z-stack confocal microscopy images from coimmunostaining. Furthermore, immunostaining performed on ECM layer revealed increased presence of LOX bound to Coll IV or FN. Additionally, when media from cells grown in HG was monitored, a maximal increase in LOX level was observed by day 3, which declined by day 7.

Conclusions

Findings indicate that HG promotes binding of LOX to FN and Coll IV extracellularly that results in reduced LOX internalization, attenuation of negative feedback, and upregulation of LOX expression associated with diabetic retinopathy.

Interplay Between LOX Enzymes and Integrins in the Tumor Microenvironment

Members of the lysyl oxidase (LOX) family are secreted copper-dependent amine oxidases that catalyze the covalent crosslinking of collagens and elastin in the extracellular matrix (ECM), an essential process for the structural integrity of all tissues. LOX enzymes can also remodel the tumor microenvironment and have been implicated in all stages of tumor initiation and progression of many cancer types. Changes in the ECM can influence several cancer cell phenotypes. Integrin adhesion complexes (IACs) physically connect cells with their microenvironment. This review article summarizes the main findings on the role of LOX proteins in modulating the tumor microenvironment, with a particular focus on how ECM changes are integrated by IACs to modulate cells behavior. Finally, we discuss how the development of selective LOX inhibitors may lead to novel and effective therapies in cancer treatment.

Biophysics of Tumor Microenvironment and Cancer Metastasis - A Mini Review

The role of tumor microenvironment in cancer progression is gaining significant attention. It is realized that cancer cells and the corresponding stroma co-evolve with time. Cancer cells recruit and transform the stromal cells, which in turn remodel the extra cellular matrix of the stroma. This complex interaction between the stroma and the cancer cells results in a dynamic feed-forward/feed-back loop with biochemical and biophysical cues that assist metastatic transition of the cancer cells. Although biochemistry has long been studied for the understanding of cancer progression, biophysical signaling is emerging as a critical paradigm determining cancer metastasis. In this mini review, we discuss the role of one of the biophysical cues, mostly the mechanical stiffness of tumor microenvironment, in cancer progression and its clinical implications.

Lysyl oxidase promotes epithelial-to-mesenchymal transition during paraquat-induced pulmonary fibrosis

Lysyl oxidase (LOX) is a copper-dependent amine oxidase that plays a critical role in pulmonary fibrosis. Our previous study demonstrated that epithelial-to-mesenchymal transition (EMT) was strongly associated with paraquat (PQ) induced pulmonary fibrosis. This present study was aimed to evaluate the potential involvement of LOX on EMT in the process of pulmonary fibrosis induced by PQ. We established an in vivo rat model and an in vitro cell model induced by PQ treatment and found that LOX protein expression was significantly up-regulated and collagen deposition was enhanced in rats. The EMT process was strongly found in A549 and RLE-6TN cells after PQ exposure. After inactivating LOX with an inhibitor, pulmonary fibrosis was significantly reduced and EMT was also suppressed. Additionally, small interfering RNA (siRNA) targeting LOX was used to silence LOX expression to observe EMT in A549 cells. As a result, LOX could promote the progress of EMT, and inactivating LOX alleviated the EMT process in PQ-induced pulmonary fibrosis and mesenchymal-to-epithelial transition (MET) occurred after inactivating LOX in vitro and in vivo. In conclusion, LOX could promote the progress of EMT and inactivating LOX alleviated EMT in PQ-induced pulmonary fibrosis. Therefore, LOX could potentially be a new candidate therapeutic target for pulmonary fibrosis induced by PQ by regulating the balance between EMT and MET.

Cooperative Effect of miR-141-3p and miR-145-5p in the Regulation of Targets in Clear Cell Renal Cell Carcinoma

Background

Due to the poor prognosis for advanced renal cell carcinoma (RCC), there is an urgent need for new therapeutic targets and for prognostic markers to identify high risk tumors. MicroRNAs (miRNAs) are frequently dysregulated in tumors, play a crucial role during carcinogenesis and therefore might be promising new biomarkers. In previous studies, we identified miR-141-3p and miR-145-5p to be downregulated in clear cell RCC (ccRCC). Our objective was to investigate the functional association of these miRNAs, focusing on the cooperative regulation of new specific targets and their role in ccRCC progression.

Methods

The effect of miR-141-3p and miR-145-5p on cell migration was examined by overexpression in 786-O cells. New targets of both miRNAs were identified by miRWalk, validated in 786-O and ACHN cells and additionally characterized in ccRCC tissue on mRNA and protein level.

Results

In functional analysis, a tumor suppressive effect of miR-141-3p and miR-145-5p by decreasing migration and invasion of RCC cells could be shown. Furthermore, co-overexpression of the miRNAs seemed to result in an increased inhibition of cell migration. Both miRNAs were recognized as post-transcriptional regulators of the targets EAPP, HS6ST2, LOX, TGFB2 and VRK2. Additionally, they showed a cooperative effect again as demonstrated by a significantly increased inhibition of HS6ST2 and LOX expression after simultaneous overexpression of both miRNAs. In ccRCC tissue, LOX mRNA expression was strongly increased compared to normal tissue, allowing also to distinguish between non-metastatic and already metastasized primary tumors. Finally, in subsequent tissue microarray analysis LOX protein expression showed a prognostic relevance for the overall survival of ccRCC patients.

Conclusion

These results illustrate a jointly strengthening effect of the dysregulated miR-141-3p and miR-145-5p in various tumor associated processes. Focusing on the cooperative effect of miRNAs provides new opportunities for the development of therapeutic strategies and offers novel prognostic and diagnostic capabilities.

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.

New frontiers in fibrotic disease therapies: The focus of the Joan and Joel Rosenbloom Center for Fibrotic Diseases at Thomas Jefferson University

Fibrotic diseases constitute a world-wide major health problem, but research support remains inadequate in comparison to the need. Although considerable understanding of the pathogenesis of fibrotic reactions has been attained, no completely effective therapies exist. Although fibrotic disorders are diverse, it is universally appreciated that a particular cell type with unique characteristics, the myofibroblast, is responsible for replacement of functioning tissue with non-functional scar tissue. Understanding the cellular and molecular mechanisms responsible for the creation of myofibroblasts and their activities is central to the development of therapies. Critical signaling cascades, initiated primarily by TGF-β, but also involving other cytokines which stimulate pro-fibrotic reactions in the myofibroblast, offer potential therapeutic targets. However, because of the multiplicity and complex interactions of these signaling pathways, it is very unlikely that any single drug will be successful in modifying a major fibrotic disease. Therefore, we have chosen to examine the effectiveness of administration of several drug combinations in a mouse pneumoconiosis model. Such treatment proved to be effective. Because fibrotic diseases that tend to be chronic, are difficult to monitor, and are patient variable, implementation of clinical trials is difficult and expensive. Therefore, we have made efforts to identify and validate non-invasive biomarkers found in urine and blood. We describe the potential utility of five such markers: (i) the EDA form of fibronectin (Fn(EDA)), (ii) lysyl oxidase (LOX), (iii) lysyl oxidase-like protein 2 (LoxL2), (iv) connective tissue growth factor (CTGF, CCNII), and (v) the N-terminal propeptide of type III procollagen (PIIINP).

Screening of lysyl oxidase (LOX) and lysyl oxidase like (LOXL) enzyme expression and activity in preterm prelabor rupture of fetal membranes

OBJECTIVE

Lysyl oxidase (LOX) and LOX like enzymes (LOXL1-4) physiologically remodel extracellular matrix and pathologically contribute to cellular senescence under oxidative stress (OS). We characterized LOX and LOXL expressions and activity in human fetal membranes.

METHODS

Human fetal membranes from women with uncomplicated pregnancies at term, preterm birth with intact membranes (PTB) or preterm prelabor rupture of membranes (pPROM), and in vitro fetal membranes stimulated with water-soluble cigarette smoke extract (CSE), an OS inducer, were analyzed by real-time PCR and immunohistochemistry for LOX and LOXL (1-4) expression and localization. LOX activity was measured by fluorometric assay.

RESULTS

LOX gene expression was ∼2.5-fold higher in fetal membranes from pPROM compared to PTB and term (P=0.02). LOX and LOXL1, 2 and 4 were localized to both amniotic and chorionic cells, whereas LOXL3 was limited to chorion. LOX and LOXL isoform expressions were not different between CSE treated and untreated groups, while LOX activity was increased in the presence of an antioxidant (P=0.02).

CONCLUSIONS

Increase of LOX expression in pPROM, an OS-related disease, and the apparent inhibition of LOX activity by CSE restored by antioxidant treatment suggest that reactive oxygen species might influence LOX-mediated tissue remodeling in fetal membranes. Balanced antioxidant supplementation during pregnancy may reduce the risk of pPROM by increasing LOX activity.

Transcriptome analysis of PPARγ target genes reveals the involvement of lysyl oxidase in human placental cytotrophoblast invasion

Human placental development is characterized by invasion of extravillous cytotrophoblasts (EVCTs) into the uterine wall during the first trimester of pregnancy. Peroxisome proliferator-activated receptor γ (PPARγ) plays a major role in placental development, and activation of PPARγ by its agonists results in inhibition of EVCT invasion in vitro. To identify PPARγ target genes, microarray analysis was performed using GeneChip technology on EVCT primary cultures obtained from first-trimester human placentas. Gene expression was compared in EVCTs treated with the PPARγ agonist rosiglitazone versus control. A total of 139 differentially regulated genes were identified, and changes in the expression of the following 8 genes were confirmed by reverse transcription-quantitative polymerase chain reaction: a disintegrin and metalloproteinase domain12 (ADAM12), connexin 43 (CX43), deleted in liver cancer 1 (DLC1), dipeptidyl peptidase 4 (DPP4), heme oxygenase 1 (HMOX-1), lysyl oxidase (LOX), plasminogen activator inhibitor 1 (PAI-1) and PPARγ. Among the upregulated genes, lysyl oxidase (LOX) was further analyzed. In the LOX family, only LOX, LOXL1 and LOXL2 mRNA expression was significantly upregulated in rosiglitazone-treated EVCTs. RNA and protein expression of the subfamily members LOX, LOXL1 and LOXL2 were analyzed by absolute RT-qPCR and western blotting, and localized by immunohistochemistry and immunofluorescence-confocal microscopy. LOX protein was immunodetected in the EVCT cytoplasm, while LOXL1 was found in the nucleus and nucleolus. No signal was detected for LOXL2 protein. Specific inhibition of LOX activity by β-aminopropionitrile in cell invasion assays led to an increase in EVCT invasiveness. These results suggest that LOX, LOXL1 and LOXL2 are downstream PPARγ targets and that LOX activity is a negative regulator of trophoblastic cell invasion.

High glucose induced differential expression of lysyl oxidase and its isoform in ARPE-19 cells

PURPOSE

Lysyl oxidase (LOX) stabilizes the extracellular matrix (ECM) by cross-linking collagen and elastin molecules. In proliferative diabetic retinopathy (PDR), there is ECM remodeling with neovascularization and basement membrane changes. While protease activities are well reported, the role of LOX in the pathogenesis of diabetic retinopathy is less studied. This study was done to see the effect of high glucose on the activity and expression of LOX and its isoforms in ARPE-19 cells.

MATERIALS AND METHODS

ARPE-19 cells were exposed to high glucose up to 48 h, and LOX activity was determined by N-acetyl-3,7-dihydroxyphenoxazine assay. The mRNA expression of LOX and its isoforms was done by real-time PCR and the protein expression by ELISA. Immunohistochemistry for LOX was done in epiretinal membrane from PDR.

RESULTS

With an increase in glucose concentration LOX activity and protein was reduced significantly at 30 mM glucose at 48 h. mRNA expression of LOX, LOXL1, and LOXL2 varied with time and concentration of glucose. Vascular endothelial growth factor (VEGF) increased the LOX activity as well as the mRNA expression. Pigment epithelium-derived factor (PEDF) downregulated the mRNA expression of LOX, LOXL1, and LOXL2. The matrix metalloprotease (MMP) activity increased significantly with the increase in glucose concentration. The diabetic neovascular membrane showed increased immunostaining of LOX.

CONCLUSIONS

This study suggests that although the LOX activity, which is composite of all the isoforms, was reduced under high glucose conditions, there was a differential mRNA expression with increased LOX and LOXL1 and decreased LOXL2 expression.

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.

The lysyl oxidases LOX and LOXL2 are necessary and sufficient to repress E-cadherin in hypoxia: insights into cellular transformation processes mediated by HIF-1

Hypoxia has been shown to promote tumor metastasis and lead to therapy resistance. Recent work has demonstrated that hypoxia represses E-cadherin expression, a hallmark of epithelial to mesenchymal transition, which is believed to amplify tumor aggressiveness. The molecular mechanism of E-cadherin repression is unknown, yet lysyl oxidases have been implicated to be involved. Gene expression of lysyl oxidase (LOX) and the related LOX-like 2 (LOXL2) is strongly induced by hypoxia. In addition to the previously demonstrated LOX, we characterize LOXL2 as a direct transcriptional target of HIF-1. We demonstrate that activation of lysyl oxidases is required and sufficient for hypoxic repression of E-cadherin, which mediates cellular transformation and takes effect in cellular invasion assays. Our data support a molecular pathway from hypoxia to cellular transformation. It includes up-regulation of HIF and subsequent transcriptional induction of LOX and LOXL2, which repress E-cadherin and induce epithelial to mesenchymal transition. Lysyl oxidases could be an attractive molecular target for cancers of epithelial origin, in particular because they are partly extracellular.

Tumor suppressive effect of lysyl oxidase proenzyme

Lysyl oxidase acts as both a matrix modifying enzyme and an oncogene suppressor. It is synthesized as a 50-kDa proenzyme, secreted, and processed into an approximately 30 kDa mature, active enzyme and an 18-kDa propeptide. The tumor suppressive effect of lysyl oxidase appears to be exerted within the cell, so the subcellular localization of protein forms was investigated. Propeptide-specific antibody detected 50-kDa proenzyme in cytoplasmic and nuclear extracts of non-transformed mouse fibroblasts, but free 18-kDa propeptide was not detected in any extract. Antibody to epitope near the N-terminus of mature lysyl oxidase detected the proenzyme product in non-transformed cells, and a 30-kDa cytoplasmic protein in both non-transformed and transformed cells. RNA interference reduced the expression of lysyl oxidase mRNA and 50-kDa proenzyme in non-transformed cells, but had no effect on 30-kDa protein, indicating that although this protein displays a lysyl oxidase epitope, it is not derived from lysyl oxidase message. The absence of both free 18-kDa propeptide and mature lysyl oxidase within non-transformed cells suggests that cellular reversion after restoration of lysyl oxidase gene expression is mediated by the 50-kDa proenzyme within cells.

Evolutionary conservation of vertebrate notochord genes in the ascidian Ciona intestinalis

To reconstruct a minimum complement of notochord genes evolutionarily conserved across chordates, we scanned the Ciona intestinalis genome using the sequences of 182 genes reported to be expressed in the notochord of different vertebrates and identified 139 candidate notochord genes. For 66 of these Ciona genes expression data were already available, hence we analyzed the expression of the remaining 73 genes and found notochord expression for 20. The predicted products of the newly identified notochord genes range from the transcription factors Ci-XBPa and Ci-miER1 to extracellular matrix proteins. We examined the expression of the newly identified notochord genes in embryos ectopically expressing Ciona Brachyury (Ci-Bra) and in embryos expressing a repressor form of this transcription factor in the notochord, and we found that while a subset of the genes examined are clearly responsive to Ci-Bra, other genes are not affected by alterations in its levels. We provide a first description of notochord genes that are not evidently influenced by the ectopic expression of Ci-Bra and we propose alternative regulatory mechanisms that might control their transcription.

Hypoxia/reoxygenation: a dynamic regulator of lysyl oxidase-facilitated breast cancer migration

Fluctuating oxygen levels characterize the microenvironment of many cancers and tumor hypoxia is associated with increased invasion and metastatic potential concomitant with a poor prognosis. Similarly, the expression of lysyl oxidase (LOX) in breast cancer facilitates tumor cell migration and is associated with estrogen receptor negative status and reduced patient survival. Here we demonstrate that hypoxia/reoxygenation drives poorly invasive breast cancer cells toward a more aggressive phenotype by up-regulating LOX expression and catalytic activity. Specifically, hypoxia markedly increased LOX protein expression; however, catalytic activity (beta-aminopropionitrile inhibitable hydrogen peroxide production) was significantly reduced under hypoxic conditions. Moreover, poorly invasive breast cancer cells displayed a marked increase in LOX-dependent FAK/Src activation and cell migration following hypoxia/reoxygenation, but not in response to hypoxia alone. Furthermore, LOX expression is only partially dependent on hypoxia inducible factor-1 (HIF-1alpha) in poorly invasive breast cancer cells, as hypoxia mimetics and overexpression of HIF-1alpha could not up-regulate LOX expression to the levels observed under hypoxia. Clinically, LOX expression positively correlates with tumor progression and co-localization with hypoxic regions (defined by HIF-1alpha expression) in ductal carcinoma in situ and invasive ductal carcinoma primary tumors. However, positive correlation is lost in metastatic tumors, suggesting that LOX expression is independent of a hypoxic environment at later stages of tumor progression. This work demonstrates that both hypoxia and reoxygenation are necessary for LOX catalytic activity which facilitates breast cancer cell migration through a hydrogen peroxide-mediated mechanism; thereby illuminating a potentially novel mechanism by which poorly invasive cancer cells can obtain metastatic competency.

Evidence for the epithelial to mesenchymal transition in biliary atresia fibrosis

The epithelial to mesenchymal transition has recently been implicated as a source of fibrogenic myofibroblasts in organ fibrosis, particularly in the kidney. There is as yet minimal evidence for the epithelial to mesenchymal transition in the liver. We hypothesized that this process in biliary epithelial cells plays an important role in biliary fibrosis and might be found in patients with especially rapid forms, such as is seen in biliary atresia. We therefore obtained liver tissue from patients with biliary atresia as well as a variety of other pediatric and adult liver diseases. Tissues were immunostained with antibodies against the biliary epithelial cell marker CK19 as well as with antibodies against proteins characteristically expressed by cells undergoing the epithelial to mesenchymal transition, including fibroblast-specific protein 1, the collagen chaperone heat shock protein 47, the intermediate filament protein vimentin, and the transcription factor Snail. The degree of colocalization was quantified using a multispectral imaging system. We observed significant colocalization between CK19 and other markers of the epithelial to mesenchymal transition in biliary atresia as well as other liver diseases associated with significant bile ductular proliferation, including primary biliary cirrhosis. There was minimal colocalization seen in healthy adult and pediatric livers, or in livers not also demonstrating bile ductular proliferation. Multispectral imaging confirmed significant colocalization of the different markers in biliary atresia. In conclusion, we present significant histologic evidence suggesting that the epithelial to mesenchymal transition occurs in human liver fibrosis, particularly in diseases such as biliary atresia and primary biliary cirrhosis with prominent bile ductular proliferation.

Paradoxical roles for lysyl oxidases in cancer—A prospect

Lysyl oxidase (LOX) is an extracellular matrix (ECM) enzyme that catalyzes the cross-linking of collagens or elastin in the extracellular compartment, thereby regulating the tensile strength of tissues. However, recent reports have demonstrated novel roles for LOX, including the ability to regulate gene transcription, motility/migration, and cell adhesion. These diverse functions have led researchers to hypothesize that LOX may have multiple roles affecting both extra- and intracellular cell function(s). Particularly noteworthy is aberrant LOX expression and activity that have been observed in various cancerous tissues and neoplastic cell lines. Both down and upregulation of LOX in tumor tissues and cancer cell lines have been described, suggesting a dual role for LOX as a tumor suppressor, as well as a metastasis promoter gene--creating a conundrum within the LOX research field. Here, we review the body of evidence on LOX gene expression, regulation, and function(s) in various cancer cell types and tissues, as well as stromal-tumor cell interactions. Lastly, we will examine putative mechanisms in which LOX facilitates breast cancer invasion and metastasis. Taken together, the literature demonstrates the increasingly important role(s) that LOX may play in regulating tumor progression and the necessity to elucidate its myriad mechanisms of action in order to identify potentially novel therapeutics.