Collagenase expression and activity is modulated by the interaction of collagen types, hypoxia, and nutrition in human lung cells

Phenotype and function of smooth muscle cells derived from the human normal great saphenous vein in response to hypoxia

OBJECTIVE

The contribution of hypoxia to the pathophysiology of vascular smooth muscle cells (VSMCs) has not yet been fully elucidated. This study evaluated the effect of hypoxia on the phenotype and function of SMCs derived from the human normal great saphenous veins (NGSVs).

METHODS

Fifteen NGSV tissue samples were collected. SMCs were isolated and cultured. Proliferation, migration, adhesion, senescence, and the structure of cytoskeletal filaments in SMCs were observed. mRNA and protein expression of Bax, Bcl-2, caspase-3, matrix metalloproteinases (MMP)-2, MMP-9, tissue inhibitor of metalloproteinases (TIMP)-1, and TIMP-2 was detected by fluorescent quantitative polymerase chain reaction and immunoblotting in the cobalt chloride (CoCl2) and the control groups.

RESULTS

A decrease in the number of cytoskeletal filaments was observed. mRNA and protein expression of Bas and caspase-3 was significantly decreased, while the quantity of proliferation, migration, adhesion, senescence, and mRNA and protein expression of Bcl-2, MMP-2, MMP-9, TIMP-1, and TIMP-2 in SMCs in the CoCl2 group were significantly increased compared with the control group.

CONCLUSION

Under hypoxic conditions, the phenotype and function of SMCs derived from the human NGSVs were dysregulated, suggesting that VSMCs switch from the contractile phenotype to the secretory or synthetic phenotype, and more dedifferentiate, resulting in extracellular matrix deposition and apoptotic decrease through the intrinsic pathway.

MMP13 promotes the osteogenic potential of BMP9 by enhancing Wnt/β-catenin signaling via HIF-1α upregulation in mouse embryonic fibroblasts

Bone morphogenetic protein 9 (BMP9) has been validated as one of the most potent osteoinduction factors, but its underlying mechanism remains unclear. As a member of the matrix metalloproteinase (MMP) family, MMP13 may be involved in regulating the lineage-specific differentiation of mouse embryonic fibroblasts (MEFs). The goal of this study was to determine whether MMP13 regulates the osteoinduction potential of BMP9 in MEFs, which are multipotent progenitor cells widely used for stem cell biology research. In vitro and in vivo experiments showed that BMP9-induced osteogenic markers and/or bone were enhanced by exogenous MMP13 in MEFs, but were reduced by MMP13 knockdown or inhibition. The expression of hypoxia inducible factor 1 alpha (HIF-1α) was induced by BMP9, which was enhanced by MMP13. The protein expression of β-catenin and phosphorylation level of glycogen synthase kinase-3 beta (GSK-3β) were increased by BMP9 in MEFs, as was the translocation of β-catenin from the cytoplasm to the nucleus; all these effects of BMP9 were enhanced by MMP13. Furthermore, the MMP13 effects of increasing BMP9-induced β-catenin protein expression and GSK-3β phosphorylation level were partially reversed by HIF-1α knockdown. These results suggest that MMP13 can enhance the osteoinduction potential of BMP9, which may be mediated, at least in part, through the HIF-1α/β-catenin axis. Our findings demonstrate a novel role of MMP13 in the lineage decision of progenitor cells and provide a promising strategy to speed up bone regeneration.

Combined Activation of Guanylate Cyclase and Cyclic AMP in Lung Fibroblasts as a Novel Therapeutic Concept for Lung Fibrosis

Remodelling of the peripheral lung tissue and fibrotic foci are the main pathologies of idiopathic pulmonary fibrosis (IPF), a disease that is difficult to treat. TGF-β activation of peripheral lung fibroblasts is indicated as the major cause of tissue remodelling in IPF and is resulting in fibroblast hyperplasia and deposition of extracellular matrix. Soluble guanylate cyclase (sGC) stimulators combined with cyclic AMP (cAMP) activators have been reported to reduce proliferation and matrix deposition in other conditions than IPF. Therefore, this drug combination may present a novel therapeutic concept for IPF. This study investigated the effect of BAY 41-2272 and forskolin on remodelling parameters in primary human lung fibroblasts. The study determined TGF-β induced proliferation by direct cell counts after 3 days; and deposition of collagen type-I, type III, and fibronectin. BAY 41-2272 significantly reduced TGF-β induced fibroblast proliferation, but did not reduce viability. This inhibitory effect was further supported by forskolin. Both BAY 41-2272 and forskolin alone reduced TGF-β induced collagen and fibronectin de novo synthesis as well as deposition. This effect was significantly stronger when the two compounds were combined. Furthermore, the TGF-β induced expression of fibrilar α-smooth muscle actin was reduced by BAY 41-2272 and this effect was strengthened by forskolin. In addition, BAY 41-2272 and forskolin reduced TGF-β induced β-catenin. All effects of BAY 41-2272 were concentration dependent. The findings suggest that BAY 41-2272 in combination with cAMP stimulation may present a novel therapeutic strategy to reduce tissue remodelling in IPF.

Extra-cellular matrix proteins induce matrix metalloproteinase-1 (MMP-1) activity and increase airway smooth muscle contraction in asthma

Airway remodelling describes the histopathological changes leading to fixed airway obstruction in patients with asthma and includes extra-cellular matrix (ECM) deposition. Matrix metalloproteinase-1 (MMP-1) is present in remodelled airways but its relationship with ECM proteins and the resulting functional consequences are unknown. We used airway smooth muscle cells (ASM) and bronchial biopsies from control donors and patients with asthma to examine the regulation of MMP-1 by ECM in ASM cells and the effect of MMP-1 on ASM contraction. Collagen-I and tenascin-C induced MMP-1 protein expression, which for tenascin-C, was greater in asthma derived ASM cells. Tenascin-C induced MMP-1 expression was dependent on ERK1/2, JNK and p38 MAPK activation and attenuated by function blocking antibodies against the β1 and β3 integrin subunits. Tenascin-C and MMP-1 were not expressed in normal airways but co-localised in the ASM bundles and reticular basement membrane of patients with asthma. Further, ECM from asthma derived ASM cells stimulated MMP-1 expression to a greater degree than ECM from normal ASM. Bradykinin induced contraction of ASM cells seeded in 3D collagen gels was reduced by the MMP inhibitor ilomastat and by siRNA knockdown of MMP-1. In summary, the induction of MMP-1 in ASM cells by tenascin-C occurs in part via integrin mediated MAPK signalling. MMP-1 and tenascin-C are co-localised in the smooth muscle bundles of patients with asthma where this interaction may contribute to enhanced airway contraction. Our findings suggest that ECM changes in airway remodelling via MMP-1 could contribute to an environment promoting greater airway narrowing in response to broncho-constrictor stimuli and worsening asthma symptoms.

Rabbit model of radiation-induced lung injury

OBJECTIVE

To explore the feasibility of establishing an animal model of chronic radiation-induced lung injury.

METHODS

Twenty-eight New Zealand white rabbits were randomly divided into 3 groups (the right lung irradiation group, the whole lung irradiation group and the control group). Animal model of radiation-induced lung injury was established by high-does radiotherapy in the irradiation groups, then all rabbits underwent CT and pathological examinations at 1, 2, 4, 8, 12, 16 weeks, respectively after radiation.

RESULTS

Within 4 weeks of irradiation, some rabbits in the right lung irradiation group and whole lung irradiation group died. CT and pathological examinations all showed acute radiation pneumonitis. At 8-12 weeks after irradiation, CT scanning showed ground glass samples signs, patchy shadows and fibrotic stripes. Pathological examination showed the fibrosis pulmonary alveolar wall thickened obviously.

CONCLUSIONS

The clinical animal model of chronic radiation-induced lung injury which corresponds to practical conditions in clinic can be successfully established.

Matrix metalloproteinase expression in primary lung fibroblasts of layer type chickens

We attempted to determine the growth characteristics of cultured lung fibroblasts of layer type chickens and to investigate presence of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in these cells in vitro. Lung fibroblasts were isolated, characterized and subcultured from one-day-old layer type chicken lungs. Two different methods, explant culture and enzymatic techniques, were used for culturing and the results were compared. The presence of MMP-2 and TIMP-1 was shown in cultured fibroblasts by immunocytochemical staining, immune blotting and zymography methods. Immune expressions of neither MMP-9 nor TIMP-2 enzymes could be detected.

Effects of mesenchymal stem cells on matrix metalloproteinase synthesis in cardiac fibroblasts

Mesenchymal stem cell (MSC) transplantation has been known to decrease matrix metalloproteinase (MMP) synthesis in myocardium after myocardial infarction (MI) and improve ventricular remodeling; however, the underlying mechanisms are unclear. This study investigated the effects of MSC on MMP synthesis in cardiac fibroblasts (CFs) through paracrine actions. CFs were cultured under hypoxic (0.5% pO(2)) conditions for 24 h before co-culture with MSCs or hypoxia-preconditioned MSCs (H-MSCs) in transwell plates. CFs and MSCs/H-MSCs shared a medium with or without erythropoietin (EPO) neutralizing antibody (EPOAb) or EPO-soluble receptor (EPOsR). The results showed that protein expression and activity of MMP-2 and membrane type 1-MMP, but not MMP-9, in CFs were significantly increased in response to hypoxia and decreased after co-culture with MSCs or H-MSCs. Hypoxia up-regulated phosphorylation of extracellular signal-regulated kinase (ERK)1/2 of CFs which was down-regulated after CFs' co-culture with MSCs. Tissue inhibitors of metalloproteinases-1 (TIMP-1) in CFs was decreased after hypoxia and increased when co-cultured with MSCs or H-MSCs. Exogenous EPOAb or EPOsR partially inhibited MSCs' effect on MMP-2 expression and activity in CFs. The present findings suggested that MSCs influence MMP/TIMP expression in CFs via the ERK1/2 pathway and EPO acts as a key factor in the paracrine actions of MSCs.

Pheochromocytomas: the (pseudo)-hypoxia hypothesis

Hypoxia and pheochromocytoma/paraganglioma have a long common history. Since the description, almost 40 years ago, of an increased incidence of head and neck paragangliomas in chronic hypoxia, discoveries on oxygen-sensing and on hereditary paraganglioma in the beginning of years 2000 provided the proof of concept of a strong link between these neuroendocrine tumors and the hypoxic pathway. It was demonstrated that both SDH and VHL genes mutations lead to the abnormal stabilization and activation of hypoxia-inducible factors, and to the subsequent regulation of multiple target genes, the products of which are implicated in proliferation, apoptosis, angiogenesis, energy metabolism or invasiveness and metastases. Altogether, physiological, genetic, cellular and molecular data collected over years all point to a central role of the hypoxic or pseudohypoxic pathway in pheochromocytoma and paraganglioma tumorigenesis.

Hypoxia-induced phenotypic switch of fibroblasts to myofibroblasts through a matrix metalloproteinase 2/tissue inhibitor of metalloproteinase-mediated pathway: implications for venous neointimal hyperplasia in hemodialysis access

PURPOSE

Hemodialysis grafts fail because of venous neointimal hyperplasia formation caused by adventitial fibroblasts that have become myofibroblasts (ie, alpha-smooth muscle actin [SMA]-positive cells) and migrate to the neointima. There is increased expression of hypoxia-inducible factor (HIF)-1alpha in venous neointimal hyperplasia formation in experimental animal models and clinical samples. It was hypothesized that, under hypoxic stimulus (ie, HIF-1alpha), fibroblasts will convert to myofibroblasts through a matrix metalloproteinase (MMP)-2-mediated pathway.

MATERIALS AND METHODS

Murine AKR-2B fibroblasts were made hypoxic or normoxic for 24, 48, and 72 hours. Protein expression for HIF-1alpha, alpha-SMA, MMP-2, MMP-9, tissue inhibitor of metalloproteinase (TIMP)-1, and TIMP-2 was performed to determine the kinetic changes of these proteins. Immunostaining for alpha-SMA, collagen, and fibronectin was performed.

RESULTS

At all time points, there was significantly increased expression of HIF-1alpha in the hypoxic fibroblasts compared with normoxic fibroblasts (P < .05). There was significantly increased expression of alpha-SMA at all time points, which peaked by 48 hours in hypoxic fibroblasts compared with normoxic fibroblasts (P < .05). There was a significant increase in the expression of active MMP-2 by 48-72 hours and a significant increase in TIMP-1 by 48-72 hours by hypoxic fibroblasts (P < .05). By 72 hours, there was significant increase in TIMP-2 expression (P < .05). Immunohistochemical analysis demonstrated increased expression of alpha-SMA, collagen, and fibronectin as the duration of hypoxia increased.

CONCLUSIONS

Under hypoxic conditions, fibroblasts will convert to myofibroblasts through an MMP-2-mediated pathway, which may provide insight into the mechanism of venous neointimal hyperplasia.

COMMD1 disrupts HIF-1alpha/beta dimerization and inhibits human tumor cell invasion

The gene encoding COMM domain-containing 1 (COMMD1) is a prototypical member of the COMMD gene family that has been shown to inhibit both NF-kappaB- and HIF-mediated gene expression. NF-kappaB and HIF are transcription factors that have been shown to play a role in promoting tumor growth, survival, and invasion. In this study, we demonstrate that COMMD1 expression is frequently suppressed in human cancer and that decreased COMMD1 expression correlates with a more invasive tumor phenotype. We found that direct repression of COMMD1 in human cell lines led to increased tumor invasion in a chick xenograft model, while increased COMMD1 expression in mouse melanoma cells led to decreased lung metastasis in a mouse model. Decreased COMMD1 expression also correlated with increased expression of genes known to promote cancer cell invasiveness, including direct targets of HIF. Mechanistically, our studies show that COMMD1 inhibits HIF-mediated gene expression by binding directly to the amino terminus of HIF-1alpha, preventing its dimerization with HIF-1beta and subsequent DNA binding and transcriptional activation. Altogether, our findings demonstrate a role for COMMD1 in tumor invasion and provide a detailed mechanism of how this factor regulates the HIF pathway in cancer cells.

CIGARETTE SMOKE-INDUCED HYPERCAPNIC EMPHYSEMA IN C3H MICE IS ASSOCIATED WITH INCREASES OF MACROPHAGE METALLOELASTASE AND SUBSTANCE P IN THE LUNGS

The authors tested whether macrophage metalloelastase (MMP-12) and substance P (SP) were increased in the cigarette smoke (CS)-exposed female C3H/HeN mice with hypercapnic emphysema. The authors found that as compared to control (filtered air), 16 weeks of CS exposure significantly up-regulated mRNA and protein levels of MMP-12, the ratio of MMP-12/tissue inhibitor of matrix metalloproteinase-1, and SP/preprotachykinin-A (a precursor to SP) in the lungs. Importantly, a significant correlation was found between MMP-12 and SP, and between MMP-12/SP and the degrees of hypoxemia/hypercapnia denoted in CS-exposed mice. These data suggest a possible involvement of SP and MMP-12 in the pathogenesis of severe COPD.

mTOR in renal cell cancer: modulator of tumor biology and therapeutic target

Elucidation of the crucial role of the PI3K/Akt/mTOR pathway in the pathogenesis of cancer has led to the development of various drugs targeting this signaling cascade at distinct levels. mTOR, a serine/threonine kinase plays a pivotal role in coupling growth stimuli to cell cycle progression. There are two distinct macromolecular complexes of mTOR: mTORC1, which is rapamycin-sensitive and contains raptor; and mTORC2, which is rapamycin-insensitive and contains rictor. However, in recent preclinical studies a sustained exposure of cancer cells to rapamycin has been shown to inhibit the function of both mTORC1 and mTORC2 complexes. Downstream targets of these complexes, which involve HIF-1alpha and HIF-2alpha, cyclin D1 and PKC-alpha, are responsible for the activation of various intracellular processes leading to the activation of cell proliferation, and induction of angiogenesis, metastasis or chemoresistance. Since the biology of renal cell cancer (RCC) is tightly controlled by mTOR, targeted inhibition of mTOR function appeared to be a promising therapeutic approach for RCC patients. To date, results of two, large, Phase III clinical trials evaluating the efficacy of rapamycin derivatives (i.e., temsirolimus and everolimus) in the treatment of RCC have been published. First-line temsirolimus (CCI-779) administered to metastatic, poor-prognosis RCC patients significantly prolonged overall and progression-free survival when compared with IFN-alpha. Treatment of metastatic RCC patients refractory to tyrosine kinase inhibitors with everolimus (RAD-001) significantly prolonged progression-free survival when compared with placebo. Therapeutic strategies based on mTOR inhibition in RCC demonstrated a significant clinical activity. However, there are still patients refractory to mTOR inhibitors. Various molecular mechanisms of resistance to rapalogues have been identified and will have to be targeted simultaneously with mTOR in order to achieve a complete inhibition of signaling pathways crucial for the pathogenesis of RCC. Such clinical trials evaluating a combination of mTOR inhibitors with other targeted therapies are ongoing.

Hypoxia regulates human lung fibroblast proliferation via p53-dependent and -independent pathways

Background

Hypoxia induces the proliferation of lung fibroblasts in vivo and in vitro. However, the subcellular interactions between hypoxia and expression of tumor suppressor p53 and cyclin-dependent kinase inhibitors p21 and p27 remain unclear.

Methods

Normal human lung fibroblasts (NHLF) were cultured in a hypoxic chamber or exposed to desferroxamine (DFX). DNA synthesis was measured using bromodeoxyuridine incorporation, and expression of p53, p21 and p27 was measured using real-time RT-PCR and Western blot analysis.

Results

DNA synthesis was increased by moderate hypoxia (2% oxygen) but was decreased by severe hypoxia (0.1% oxygen) and DFX. Moderate hypoxia decreased p21 synthesis without affecting p53 synthesis, whereas severe hypoxia and DFX increased synthesis of both p21 and p53. p27 protein expression was decreased by severe hypoxia and DFX. Gene silencing of p21 and p27 promoted DNA synthesis at ambient oxygen concentrations. p21 and p53 gene silencing lessened the decrease in DNA synthesis due to severe hypoxia or DFX exposure. p21 gene silencing prevented increased DNA synthesis in moderate hypoxia. p27 protein expression was significantly increased by p53 gene silencing, and was decreased by wild-type p53 gene transfection.

Conclusion

These results indicate that in NHLF, severe hypoxia leads to cell cycle arrest via the p53-p21 pathway, but that moderate hypoxia enhances cell proliferation via the p21 pathway in a p53-independent manner. In addition, our results suggest that p27 may be involved in compensating for p53 in cultured NHLF proliferation.

Role of hypoxia in inflammatory upper airway disease

PURPOSE OF REVIEW

Hypoxia is a potent stimulus for inflammation and remodeling. Hypoxia develops in chronic sinusitis as shown via tissue oxygen concentrations and colonization with obligate anaerobes. This hypoxia reflects occlusion of the sinus ostia and thereby failure of transepithelial oxygenation, nonvascularized exudates, and the tendency of inflammatory hyperplasia to exceed neovascularization.

RECENT FINDINGS

Hypoxia-induced transcription factors are responsible for transcription of numerous inflammatory cytokines and growth factors, including vascular endothelial growth factor, CXCL8, CCL11, transforming growth factor-beta, inducible nitric oxide synthase, as well as matrix remodeling proteins such as procollagen and matrix metalloproteinases.

SUMMARY

Many diseases, such as asthma, share the tendency to afflict respiratory epithelium of the lower (bronchi) and upper (sinus) airway. Although the histopathology and inflammation of asthma and its associated sinusitis share many features, aggressive fibrosis, polyp formation and intense hyperplasia are not features of asthma, a disease seldom associated with significant chronic hypoxia. In contrast, fibrosis is a cardinal feature of hypoxic diseases of the lungs such as interstitial lung diseases and primary pulmonary hypertension. Arguably, chronic sinusitis can be viewed as reflecting both 'asthma' and 'primary pulmonary hypertension' of the upper airway.

Hypoxia-inducible factors: central regulators of the tumor phenotype

Low oxygen levels are a defining characteristic of solid tumors, and responses to hypoxia contribute substantially to the malignant phenotype. Hypoxia-induced gene transcription promotes characteristic tumor behaviors, including angiogenesis, invasion, metastasis, de-differentiation and enhanced glycolytic metabolism. These effects are mediated, at least in part, by targets of the hypoxia-inducible factors (HIFs). The HIFs function as heterodimers comprising an oxygen-labile alpha-subunit and a stable beta-subunit also referred to as ARNT. HIF-1alpha and HIF-2alpha stimulate the expression of overlapping as well as unique transcriptional targets, and their induction can have distinct biological effects. New targets and novel mechanisms of dysregulation place the HIFs in an ever more central role in tumor biology and have led to development of pharmacological inhibitors of their activity.

Cell type-specific effect of hypoxia and platelet-derived growth factor-BB on extracellular matrix turnover and its consequences for lung remodeling

Hypoxia is associated with extracellular matrix remodeling in several inflammatory lung diseases, such as fibrosis, chronic obstructive pulmonary disease, and asthma. In a human cell culture model, we assessed whether extracellular matrix modification by hypoxia and platelet-derived growth factor (PDGF) involves the action of matrix metalloproteinases (MMPs) and thereby affects cell proliferation. Expression of MMP and its activity were assessed by zymography and enzyme-linked immunosorbent assay in human lung fibroblasts and pulmonary vascular smooth muscle cells (VSMCs), and synthesis of soluble collagen type I was assessed by enzyme-linked immunosorbent assay. In both cell types, hypoxia up-regulated the expression of MMP-1, -2, and -9 precursors without subsequent activation. MMP-13 was increased by hypoxia only in fibroblasts. PDGF-BB inhibited the synthesis and secretion of all hypoxia-dependent MMP via Erk1/2 mitogen-activated protein (MAP) kinase activation. Hypoxia and PDGF-BB induced synthesis of soluble collagen type I via Erk1/2 and p38 MAP kinase. Hypoxia-induced cell proliferation was blocked by antibodies to PDGF-BB or by inhibition of Erk1/2 but not by the inhibition of MMP or p38 MAP kinase in fibroblasts. In VSMCs, hypoxia-induced proliferation involved Erk1/2 and p38 MAP kinases and was further increased by fibroblast-conditioned medium or soluble collagen type I via Erk1/2. In conclusion, hypoxia controls tissue remodeling and proliferation in a cell type-specific manner. Furthermore, fibroblasts may affect proliferation of VSMC indirectly by inducing the synthesis of soluble collagen type I.

Physiological oxygenation status is required for fully differentiated phenotype in kidney cortex proximal tubules

Hypoxia has been suspected to trigger transdifferentiation of renal tubular cells into myofibroblasts in an epithelial-to-mesenchymal transition (EMT) process. To determine the functional networks potentially altered by hypoxia, rat renal tubule suspensions were incubated under three conditions of oxygenation ranging from normoxia (lactate uptake) to severe hypoxia (lactate production). Transcriptome changes after 4 h were analyzed on a high scale by restriction fragment differential display. Among 1,533 transcripts found, 42% were maximally expressed under severe hypoxia and 8% under mild hypoxia (Po2 = 48 mmHg), suggesting two different levels of oxygen sensing. Normoxia was required for full expression of the proximal tubule-specific transcripts 25-hydroxyvitamin D 1-hydroxylase ( Cyp27b1) and l-pyruvate kinase ( Pklr), transcripts involved in tissue cohesion such as fibronectin ( Fn1) and N-cadherin ( Cdh2), and non-muscle-type myosin transcripts. Mild hypoxia increased myogenin transcript level. Conversely, severe hypoxia increased transcripts involved in extracellular matrix remodeling, those of muscle-type myosins, and others involved in creatine phosphate synthesis and lactate transport ( Slc16a7). Accordingly, microscopy showed loss of tubule aggregation under hypoxia, without tubular disruption. Hypoxia also increased the levels of kidney-specific transcripts normally restricted to the less oxygenated medullary zone and others specific for the distal part of the nephron. We conclude that extensive oxygen supply to the kidney tubule favors expression of its differentiated functions specifically in the proximal tubule, whose embryonic origin is mesenchymal. The phenotype changes could potentially permit transient adaptation to hypoxia but also favor pathological processes such as tissue invasion.

Enhancement of pituitary adenoma cell invasion and adhesion is mediated by discoidin domain receptor-1

The discoidin domain receptor-1 (DDR1) tyrosine kinases are a family of cell surface receptors that bind to several types of collagen and facilitate cell adhesion that is known association with several cancers. However, no previous study has examined the expression and function of DDR1 in pituitary adenoma. Tissue microarray analysis of DDR1 expression levels in 52 pituitary adenoma tissues revealed that DDR1 expression was significantly related to hormonal background (Kruskal-Wallis test; P < 0.0001). To further elucidate the function of DDR1 in pituitary adenoma, we developed DDR1 over- and under-expressing cell lines using DDR1 clone transfection and short interfering ribonucleic acids (siRNA)-based DDR1 gene silencing, respectively, in a human pituitary adenoma cell line (HP-75). Real-time reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting confirmed that expression of both DDR1 isoforms (DDR1a and DDR1b) was elevated by clone transfection and diminished by siRNA. Matrigel invasion assays revealed that cell invasion was increased in HP-75 cells over-expressing DDR1 and decreased in cells under-expressing DDR1. Consistent with this, zymography revealed that the activation levels of matrix metalloproteinase (MMP)-2 and -9 were increased and decreased in cells over- and under-expressing DDR1, respectively. Examination of in vitro cell adhesion to collagen types I, II, III, and IV with respect to MMP-2 and -9 expression revealed that DDR1 regulated cell adhesion to collagen type I, which was responsible for accelerating secretion of MMP-2 and -9 in DDR1 over-expressing cells. Taken together, these results strongly suggest that DDR1 mediates cell invasion-related signaling between collagen type I and MMP-2 and -9 in pituitary adenoma cells.

Hypoxia stimulates breast carcinoma cell invasion through MT1-MMP and MMP-2 activation

The process of cancer cell invasion involves degradation of the extracellular matrix (ECM) by proteases, integrin adhesion and cell motility. The role of ECM degrading proteases on the hypoxia-induced invasion of breast carcinoma cells was investigated. Hypoxia markedly increased the invasion capacity of MDA-MB-231 and MDA-MB-435 breast carcinoma cell lines. Matrix metalloproteinase (MMP) inhibitors blocked the hypoxia-induced invasion, whereas other protease inhibitors had no effect. Antibodies or siRNAs blocking either membrane type-1 MMP (MT1-MMP) or MMP-2 were effective in reducing the hypoxia-induced invasion. Serum-free reconstitution experiments confirmed the involvement of the MT1-MMP/MMP-2/tissue inhibitor of metalloproteinase-2 complex in this hypoxia-induced response. Overexpression of MT1-MMP in a poorly invasive breast cancer cell line, T47-D, promoted hypoxia-induced invasion and MMP-2 activation. Cell surface accumulation and activation of MT1-MMP without apparent regulation at the mRNA or protein levels indicated a post-translational adaptive response to hypoxia. Inhibition of the small GTPase RhoA eliminated the hypoxia-induced invasion and blocked the localization of MT1-MMP to the plasma membrane. Zymographic and molecular analysis of human breast tumors showed a strong correlation between hypoxic microenvironments and MMP-2 activation without changes in MT1-MMP expression. Our studies suggest that hypoxic tumor microenvironments promote breast cancer invasion through an MT1-MMP-dependent mechanism.

Lysyl oxidase is essential for hypoxia-induced metastasis

Metastasis is a multistep process responsible for most cancer deaths, and it can be influenced by both the immediate microenvironment (cell-cell or cell-matrix interactions) and the extended tumour microenvironment (for example vascularization). Hypoxia (low oxygen) is clinically associated with metastasis and poor patient outcome, although the underlying processes remain unclear. Microarray studies have shown the expression of lysyl oxidase (LOX) to be elevated in hypoxic human tumour cells. Paradoxically, LOX expression is associated with both tumour suppression and tumour progression, and its role in tumorigenesis seems dependent on cellular location, cell type and transformation status. Here we show that LOX expression is regulated by hypoxia-inducible factor (HIF) and is associated with hypoxia in human breast and head and neck tumours. Patients with high LOX-expressing tumours have poor distant metastasis-free and overall survivals. Inhibition of LOX eliminates metastasis in mice with orthotopically grown breast cancer tumours. Mechanistically, secreted LOX is responsible for the invasive properties of hypoxic human cancer cells through focal adhesion kinase activity and cell to matrix adhesion. Furthermore, LOX may be required to create a niche permissive for metastatic growth. Our findings indicate that LOX is essential for hypoxia-induced metastasis and is a good therapeutic target for preventing and treating metastases.