Nuclear localization of active matrix metalloproteinase-2 in cigarette smoke-exposed apoptotic endothelial cells

Novel Roles of MT1-MMP and MMP-2: Beyond the Extracellular Milieu

Matrix metalloproteinases (MMPs) are critical enzymes involved in a variety of cellular processes. MMPs are well known for their ability to degrade the extracellular matrix (ECM) and their extracellular role in cell migration. Recently, more research has been conducted on investigating novel subcellular localizations of MMPs and their intracellular roles at their respective locations. In this review article, we focus on the subcellular localization and novel intracellular roles of two closely related MMPs: membrane-type-1 matrix metalloproteinase (MT1-MMP) and matrix metalloproteinase-2 (MMP-2). Although MT1-MMP is commonly known to localize on the cell surface, the protease also localizes to the cytoplasm, caveolae, Golgi, cytoskeleton, centrosome, and nucleus. At these subcellular locations, MT1-MMP functions in cell migration, macrophage metabolism, invadopodia development, spindle formation and gene expression, respectively. Similar to MT1-MMP, MMP-2 localizes to the caveolae, mitochondria, cytoskeleton, nucleus and nucleolus and functions in calcium regulation, contractile dysfunction, gene expression and ribosomal RNA transcription. Our particular interest lies in the roles MMP-2 and MT1-MMP serve within the nucleus, as they may provide critical insights into cancer epigenetics and tumor migration and invasion. We suggest that targeting nuclear MT1-MMP or MMP-2 to reduce or halt cell proliferation and migration may lead to the development of new therapies for cancer and other diseases.

The effect of surgery on the levels of matrix metalloproteinases in patients with inguinal hernia

Matrix metalloproteinases (MMPs) are associated with the alteration of extracellular matrix. The purpose of this study was to investigate how the levels of matrix metalloproteinases and their inhibitors - TIMPs are influenced by the presence of inguinal hernia as well as by its surgical treatment. The studied group consisted of 25 patients with inguinal hernia and 21 healthy controls for comparison. Two blood samples - before and after the treatment were collected from patients. Serum concentrations of MMPs and TIMPs were analysed by multiplex immunoassays. There was a difference in circulating levels of MMPs in patients before the surgery compared to healthy controls - the concentrations of MMP-2 and MMP-9 were significantly lower (p=0.026, p=0.018, respectively). After the surgery, the levels of MMPs, especially MMP-2 (p<0.0001), were significantly decreased in patients compared to the preoperative values, apart from MMP-9. On the contrary, MMP-9 showed significant increase after the surgery (p<0.0001). Circulation levels of TIMP-2 in patients were significantly decreased in comparison with controls (p=0.004), whereas levels of TIMP-1 were similar to controls. Both tested metalloproteinase inhibitors showed a significant decrease in detected levels (TIMP-1 p=0.0004; TIMP-2 p<0.0001) after the procedure compared to the preoperative values. The levels of MMPs, especially MMP-2 and MMP-9, and their inhibitors TIMP-1 and TIMP-2 are involved by the presence of inguinal hernia as well as are influenced by the surgery.

Diabetes-related intestinal region-specific thickening of ganglionic basement membrane and regionally decreased matrix metalloproteinase 9 expression in myenteric ganglia

BACKGROUND

The importance of the neuronal microenvironment has been recently highlighted in gut region-specific diabetic enteric neuropathy. Regionally distinct thickening of endothelial basement membrane (BM) of intestinal capillaries supplying the myenteric ganglia coincide with neuronal damage in different intestinal segments. Accelerated synthesis of matrix molecules and reduced degradation of matrix components may also contribute to the imbalance of extracellular matrix dynamics resulting in BM thickening. Among the matrix degrading proteinases, matrix metalloproteinase 9 (MMP9) and its tissue inhibitor (TIMP1) are essential in regulating extracellular matrix remodelling.

AIM

To evaluate the intestinal segment-specific effects of diabetes and insulin replacement on ganglionic BM thickness, MMP9 and TIMP1 expression.

METHODS

Ten weeks after the onset of hyperglycaemia gut segments were taken from the duodenum and ileum of streptozotocin-induced diabetic, insulin-treated diabetic and sex- and age-matched control rats. The thickness of BM surrounding myenteric ganglia was measured by electron microscopic morphometry. Whole-mount preparations of myenteric plexus were prepared from the different gut regions for MMP9/TIMP1 double-labelling fluorescent immunohistochemistry. Post-embedding immunogold electron microscopy was applied on ultrathin sections to evaluate the MMP9 and TIMP1 expression in myenteric ganglia and their microenvironment from different gut segments and conditions. The MMP9 and TIMP1 messenger ribonucleic acid (mRNA) level was measured by quantitative polymerase chain reaction.

RESULTS

Ten weeks after the onset of hyperglycaemia, the ganglionic BM was significantly thickened in the diabetic ileum, while it remained intact in the duodenum. The immediate insulin treatment prevented the diabetes-related thickening of the BM surrounding the ileal myenteric ganglia. Quantification of particle density showed an increasing tendency for MMP9 and a decreasing tendency for TIMP1 from the proximal to the distal small intestine under control conditions. In the diabetic ileum, the number of MMP9-indicating gold particles decreased in myenteric ganglia, endothelial cells of capillaries and intestinal smooth muscle cells, however, it remained unchanged in all duodenal compartments. The MMP9/TIMP1 ratio was also decreased in ileal ganglia only. However, a marked segment-specific induction was revealed in MMP9 and TIMP1 at the mRNA levels.

CONCLUSION

These findings support that the regional decrease in MMP9 expression in myenteric ganglia and their microenvironment may contribute to extracellular matrix accumulation, resulting in a region-specific thickening of ganglionic BM.

Impact of cigarette versus electronic cigarette aerosol conditioned media on aortic endothelial cells in a microfluidic cardiovascular model

Atherosclerosis is a complex process involving progressive pathological events, including monocyte adhesion to the luminal endothelial surface. We have developed a functional in vitro adhesion assay using BioFlux microfluidic technology to investigate THP-1 (human acute monocytic leukaemia cell) monocyte adhesion to human aortic endothelial cells (HAECs). The effect of whole smoke conditioned media (WSCM) generated from University of Kentucky reference cigarette 3R4F, electronic cigarette vapour conditioned media (eVCM) from an electronic nicotine delivery system (ENDS) product (Vype ePen) and nicotine on monocyte adhesion to HAECs was evaluated. Endothelial monolayers were grown in microfluidic channels and exposed to 0–1500 ng/mL nicotine or nicotine equivalence of WSCM or eVCM for 24 h. Activated THP-1 cells were perfused through the channels and a perfusion, adhesion period and wash cycle performed four times with increasing adhesion period lengths (10, 20, 30 and 40 min). THP-1 cell adhesion was quantified by counting adherent cells. WSCM induced dose-dependent increases in monocyte adhesion compared to vehicle control. No such increases were observed for eVCM or nicotine. Adhesion regulation was linked to increased ICAM-1 protein expression. Staining of ICAM-1 in HAECs and CD11b (MAC-1) in THP-1 cells demonstrated adhesion molecule co-localisation in BioFlux plates. The ICAM-1 adhesion response to WSCM was downregulated by transfecting HAECs with ICAM-1 siRNA. We conclude that the BioFlux system is able to model human monocyte adhesion to primary human endothelial cells in vitro and WSCM drives the greatest increase in monocyte adhesion via a mechanism involving endothelial ICAM-1 expression.

Natural Marine and Terrestrial Compounds as Modulators of Matrix Metalloproteinases-2 (MMP-2) and MMP-9 in Alzheimer's Disease

Several studies have reported neuroprotective effects by natural products. A wide range of natural compounds have been investigated, and some of these may play a beneficial role in Alzheimer's disease (AD) progression. Matrix metalloproteinases (MMPs), a family of zinc-dependent endopeptidases, have been implicated in AD. In particular, MMP-2 and MMP-9 are able to trigger several neuroinflammatory and neurodegenerative pathways. In this review, we summarize and discuss existing literature on natural marine and terrestrial compounds, as well as their ability to modulate MMP-2 and MMP-9, and we evaluate their potential as therapeutic compounds for neurodegenerative and neuroinflammatory diseases, with a focus on Alzheimer's disease.

Multifunctional intracellular matrix metalloproteinases: implications in disease

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that were first discovered as proteases, which target and cleave extracellular proteins. During the past 20 years, however, intracellular roles of MMPs were uncovered and research on this new aspect of their biology expanded. MMP-2 is the first of this protease family to be reported to play a crucial intracellular role where it cleaves several sarcomeric proteins inside cardiac myocytes during oxidative stress-induced injury. Beyond MMP-2, currently at least eleven other MMPs are known to function intracellularly including MMP-1, MMP-3, MMP-7, MMP-8, MMP-9, MMP-10, MMP-11, MMP-12, MMP-14, MMP-23 and MMP-26. These intracellular MMPs are localized to different compartments inside the cell including the cytosol, sarcomere, mitochondria, and the nucleus. Intracellular MMPs contribute to the pathogenesis of various diseases. Cardiovascular renal disorders, inflammation, and malignancy are some examples. They also exert antiviral and bactericidal effects. Interestingly, MMPs can act intracellularly through both protease-dependent and protease-independent mechanisms. In this review, we will highlight the intracellular mechanisms of MMPs activation, their numerous subcellular locales, substrates, and roles in different pathological conditions. We will also discuss the future direction of MMP research and the necessity to exploit the knowledge of their intracellular targets and actions for the design of targeted inhibitors.

Unravelling the Network of Nuclear Matrix Metalloproteinases for Targeted Drug Design

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that are responsible for the degradation of a wide range of extracellular matrix proteins, which are involved in many cellular processes to ensure the normal development of tissues and organs. Overexpression of MMPs has been observed to facilitate cellular growth, migration, and metastasis of tumor cells during cancer progression. A growing number of these proteins are being found to exist in the nuclei of both healthy and tumor cells, thus highlighting their localization as having a genuine purpose in cellular homeostasis. The mechanism underlying nuclear transport and the effects of MMP nuclear translocation have not yet been fully elucidated. To date, nuclear MMPs appear to have a unique impact on cellular apoptosis and gene regulation, which can have effects on immune response and tumor progression, and thus present themselves as potential therapeutic targets in certain types of cancer or disease. Herein, we highlight and evaluate what progress has been made in this area of research, which clearly has some value as a specific and unique way of targeting the activity of nuclear matrix metalloproteinases within various cell types.

Extracellular Matrix Remodeling of Adipose Tissue in Obesity and Metabolic Diseases

The extracellular matrix (ECM) is a network of different proteins and proteoglycans that controls differentiation, migration, repair, survival, and development, and it seems that its remodeling is required for healthy adipose tissue expansion. Obesity drives an excessive lipid accumulation in adipocytes, which provokes immune cells infiltration, fibrosis (an excess of deposition of ECM components such as collagens, elastin, and fibronectin) and inflammation, considered a consequence of local hypoxia, and ultimately insulin resistance. To understand the mechanism of this process is a challenge to treat the metabolic diseases. This review is focused at identifying the putative role of ECM in adipose tissue, describing its structure and components, its main tissue receptors, and how it is affected in obesity, and subsequently the importance of an appropriate ECM remodeling in adipose tissue expansion to prevent metabolic diseases.

Mechanisms of whole smoke conditioned media induced cytotoxicity to human aortic endothelial cells

Chronic exposure to cigarette smoke can lead to endothelial dysfunction and potentially endothelial cell death. Here, we exposed Human Aortic Endothelial Cells (HAECs) to whole smoke conditioned media (WSCM) over a range of nicotine equivalence (n.e.) concentrations (0-8000 ng/mL n.e.). After 24 h, Neutral Red Uptake (NRU) and reduction of 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) to formazan was determined for each exposure concentration and compared to control. IC₅₀ values in the NRU assay were: 4582 ng/mL n.e. ± 1074, 4587 ng/mL n.e. ± 951, 4993 ng/mL n.e. ± 1239 and 4691 ng/mL n.e. ± 402 for four HAEC donors. IC₅₀ values in the MTT assay were: 4885 ng/mL n.e. ± 1341, 4584 ng/mL n.e. ± 806, 5749 ng/mL n.e. ± 783 and 5228 ng/mL n.e. ± 593 for the four donors. To examine the mechanism responsible for WSCM-induced cytotoxicity in HAECs, flow cytometry using necrosis (Propidium Iodide) and apoptosis (Annexin V) markers were used. Annexin V-positive cell populations increased in a dose dependent manner while increases in PI-positive cell populations occurred at the highest doses of WSCM (5000-8000 ng/mL n.e.). Western blotting for cleaved caspase-3 confirmed that apoptosis occurs at >5000 ng/mL n.e. WSCM, coinciding with reduced HAEC survival.

Matrix metalloproteinases participation in the metastatic process and their diagnostic and therapeutic applications in cancer

Matrix metalloproteinases (MMPs) participate from the initial phases of cancer onset to the settlement of a metastatic niche in a second organ. Their role in cancer progression is related to their involvement in the extracellular matrix (ECM) degradation and in the regulation and processing of adhesion and cytoskeletal proteins, growth factors, chemokines and cytokines. MMPs participation in cancer progression makes them an attractive target for cancer therapy. MMPs have also been used for theranostic purposes in the detection of primary tumor and metastatic tissue in which a particular MMP is overexpressed, to follow up on therapy responses, and in the activation of cancer cytotoxic pro-drugs as part of nano-delivery-systems that increase drug concentration in a specific tumor target. Herein, we review MMPs molecular characteristics, their synthesis regulation and enzymatic activity, their participation in the metastatic process, and how their functions have been used to improve cancer treatment.

Behavior of Metalloproteinases in Adipose Tissue, Liver and Arterial Wall: An Update of Extracellular Matrix Remodeling

Extracellular matrix (ECM) remodeling is required for many physiological and pathological processes. Metalloproteinases (MMPs) are endopeptidases which are able to degrade different components of the ECM and nucleus matrix and to cleave numerous non-ECM proteins. Among pathological processes, MMPs are involved in adipose tissue expansion, liver fibrosis, and atherosclerotic plaque development and vulnerability. The expression and the activity of these enzymes are regulated by different hormones and growth factors, such as insulin, leptin, and adiponectin. The controversial results reported up to this moment regarding MMPs behavior in ECM biology could be consequence of the different expression patterns among species and the stage of the studied pathology. The aim of the present review was to update the knowledge of the role of MMPs and its inhibitors in ECM remodeling in high incidence pathologies such as obesity, liver fibrosis, and cardiovascular disease.

The roles of microRNAs in the pathogenesis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by a progressive and irreversible airflow obstruction, with an abnormal lung function. The etiology of COPD correlates with complex interactions between environmental and genetic determinants. However, the exact pathogenesis of COPD is obscure although it involves multiple aspects including oxidative stress, imbalance between proteolytic and anti-proteolytic activity, immunity and inflammation, apoptosis, and repair and destruction in both airways and lungs. Many genes have been demonstrated to be involved in those pathogenic processes of this disease in patients exposed to harmful environmental factors. Previous reports have investigated promising microRNAs (miRNAs) to disclose the molecular mechanisms for COPD development induced by different environmental exposure and genetic predisposition encounter, and find some potential miRNA biomarkers for early diagnosis and treatment targets of COPD. In this review, we summarized the expression profiles of the reported miRNAs from studies of COPD associated with environmental risk factors including cigarette smoking and air pollution exposures, and provided an overview of roles of those miRNAs in the pathogenesis of the disease. We also highlighted the potential utility and limitations of miRNAs serving as diagnostic biomarkers and therapeutic targets for COPD.

Identification of genes and genetic networks associated with BAG3‑dependent cell proliferation and cell survival in human cervical cancer HeLa cells

Bcl‑2‑associated athanogene (BAG) 3, is a member of the BAG protein family and a known co‑chaperone of heat shock protein (HSP) 70. BAG3 serves a role in regulating a variety of cellular functions, including cell growth, proliferation and cell death including apoptosis. BAG3 is a stress‑inducible protein, however the constitutive expression level of BAG3 is increased in cancer cells compared with healthy cells. Recent proteomics technology combined with bioinformatics has revealed that BAG3 participates in an interactome with a number of proteins other than its typical partner HSP70. The functional types represented in the interactome included nucleic acid binding proteins and transcription factors, as well as chaperones, which indicated that overexpression of BAG3 may contribute to proliferation and cell survival through the alteration of gene transcription. While an increasing number of studies have addressed the function of BAG3 as a co‑chaperone protein, BAG3‑dependent alteration of gene transcription has not been studied extensively. The present study established two BAG3 knockout human cervical cancer HeLa cell clones and addressed the role of BAG3 in cell proliferation and survival through gene transcription, using DNA microarray‑based transcriptome analysis and bioinformatics. The present study also identified two genetic networks associated with 'cellular growth and proliferation' and 'cell death and survival', which are dysregulated in the absence of BAG3, and may therefore be linked to BAG3 overexpression in cancer. These findings provide a molecular basis for understanding of BAG3‑dependent cell proliferation and survival from the aspect of alteration of gene expression.

Sub-Cellular Localization of Metalloproteinases in Megakaryocytes

Metalloproteinases (MMPs) are zinc-dependent endopeptidases that play essential roles as the mediator of matrix degradation and remodeling during organogenesis, wound healing and angiogenesis. Although MMPs were originally identified as matrixin proteases that act in the extracellular matrix, more recent research has identified members of the MMP family in unusual locations within the cells, exerting distinct functions in addition to their established role as extracellular proteases. During thrombopoiesis, megakaryocytes (Mks) sort MMPs to nascent platelets through pseudopodial-like structure known as proplatelets. Previous studies identified gelatinases, MMP-2 and MMP-9, as a novel regulator system of Mks and the platelet function. In this work we have exploited a sensitive immunoassay to detect and quantify multiple MMP proteins and their localization, in conditioned medium and sub-cellular fractions of primary human CD34⁺-derived Mks. We provide evidence that Mks express other MMPs in addition to gelatinases MMP-2 and MMP-9, peculiar isoforms of MMP-9 and MMPs with a novel nuclear compartmentalization.

Adenosine diphosphate regulates MMP2 and MMP9 activity in malignant mesothelioma cells

Although an association between cancer progression and matrix metalloproteinase (MMP) 2 and MPP9 expression has been known, the expression, nuclear localization, and physiologically controlled activation of these two MMPs have not been investigated in malignant mesothelioma cells. We examined the expression and intracellular localization of MMP2/9 in ZL55 malignant mesothelioma cells, as well as their regulation by ADP. Using real-time PCR, we showed that activation of the P2Y1 receptor by ADP increased the expression of MMP2/9 mRNAs; MMP2/9 collected from conditioned media also showed an increase in activity; and ADP induced the nuclear localization of MMP2/9. The effects of ADP on transcription of the MMPs were due to activation of c-Src, Akt, and NF-κB, while ERK1/2 phosphorylation was needed for the increase in enzymatic activity and the regulation of nuclear import. We also showed that the nuclear localization of MMP2/9 induced by ADP causes the cleavage and inactivation of poly-ADP-ribose polymerase-1. These findings may help to elucidate the mechanisms regulating MMP2/9 activation in ZL55 human epithelioid mesothelioma cells, and perhaps other cells. Therapeutic approaches that promote ADP accumulation in a tumor environment may constitute an effective means to induce anticancer activity.

miR-34a is involved in CSE-induced apoptosis of human pulmonary microvascular endothelial cells by targeting Notch-1 receptor protein

Background

Abnormal apoptosis of lung endothelial cells has been observed in emphysematous lung tissue and has been suggested to be an important upstream event in the pathogenesis of chronic obstructive pulmonary disease (COPD). Studies have shown that microRNAs (miRNAs) contribute to the pathogenesis of pulmonary diseases by regulating cell apoptosis. The present study was designed to investigate the expression of microRNA-34a (miR-34a) in human pulmonary microvascular endothelial cells (HPMECs) exposed to cigarette smoke extract (CSE), and the potential regulatory role of miR-34a in endothelial cell apoptosis.

Results

Our results showed that the expression of miR-34a was significantly increased in CSE-treated HPMECs, and inhibiting miR-34a attenuated CSE-induced HPMEC apoptosis. Furthermore, expression of Notch-1, a receptor protein in the Notch signalling pathway, was decreased and was inversely correlated with miR-34a expression in HPMECs treated with CSE. Computational miRNA target prediction confirmed that Notch-1 is a target of miR-34a. Luciferase reporter assay further confirmed the direct interaction between miR-34a and the 3’-untranslated region (UTR) of Notch-1. Restoration of Notch-1 pathway was able to partially block the effect of miR-34a on HPMEC apoptosis. These results indicate that Notch-1 is a critical downstream target of miR-34a in regulating the CSE-induced HPMEC apoptosis.

Conclusions

Our results suggest that miR-34a plays a key role in CSE-induced endothelial cell apoptosis by directly regulating its target gene Notch-1 in endothelial cells.

Nuclear matrix metalloproteinases: functions resemble the evolution from the intracellular to the extracellular compartment

Matrix metalloproteinase (MMP) is defined as an endopeptidase in the extracellular matrix (ECM), which plays essential roles in physiological processes such as organogenesis, wound healing, angiogenesis, apoptosis and motility. MMPs are produced and assembled in the cytoplasm as proenzymes with a cytoplasmic domain and require extracellular activation. MMPs can degrade receptors, extracellular matrix proteins, PARPs and release apoptotic substances. MMPs have been found in the cytosol, organelles and extracellular compartments and recently many types of MMPs have been found in the nucleus. However, the mechanisms and roles of MMPs inside the cell nucleus are still poorly understood. Here we summarized the nuclear localization mechanisms of MMPs and their functions in the nucleus such as apoptosis, tissue remodeling upon injury and cancer progression. Most importantly, we found that nuclear MMPs have evolved to translocate to membrane and target ECM possibly through evolution of nuclear localization signal (NLS), natural selection and anti-apoptotic survival. Thus, the knowledge about the evolution and regulation of nuclear MMPs appears to be essential in understanding a variety of cellular processes along with the development of MMP-targeted therapeutic drugs against the progression of certain diseases.

New intracellular activities of matrix metalloproteinases shine in the moonlight

Adaption of a single protein to perform multiple independent functions facilitates functional plasticity of the proteome allowing a limited number of protein-coding genes to perform a multitude of cellular processes. Multifunctionality is achievable by post-translational modifications and by modulating subcellular localization. Matrix metalloproteinases (MMPs), classically viewed as degraders of the extracellular matrix (ECM) responsible for matrix protein turnover, are more recently recognized as regulators of a range of extracellular bioactive molecules including chemokines, cytokines, and their binders. However, growing evidence has convincingly identified select MMPs in intracellular compartments with unexpected physiological and pathological roles. Intracellular MMPs have both proteolytic and non-proteolytic functions, including signal transduction and transcription factor activity thereby challenging their traditional designation as extracellular proteases. This review highlights current knowledge of subcellular location and activity of these "moonlighting" MMPs. Intracellular roles herald a new era of MMP research, rejuvenating interest in targeting these proteases in therapeutic strategies. This article is part of a Special Issue entitled: Matrix Metalloproteinases edited by Rafael Fridman.

Matrix-metalloproteinases as targets for controlled delivery in cancer: An analysis of upregulation and expression

While commonly known for degradation of the extracellular matrix, matrix metalloproteinases (MMPs) exhibit broad potential for use in targeting of bioactive and imaging agents in cancer treatment. MMPs are upregulated at all stages of expression in cancers. A comprehensive analysis of published literature on expression of all MMP subtypes at the genetic, protein, and activity levels in normal and diseased tissues indicate targeting applicability in a variety of cancers. This expression significantly increases at advanced cancer stages, providing an improved opportunity for controlled release in higher-stage patients. Since MMPs are integral at every stage of metastasis, MMP roles in cancer are discussed with a focus on MMP distribution and mobility within cells and tumors for cancer targeting applications. Several strategies for MMP utilization in targeting - such as matrix degradation, MMP cleavage, MMP binding, and MMP-induced environmental changes - are addressed.

The role of cyclooxygenase-2 in the protection against apoptosis in vascular endothelial cells induced by cigarette smoking

BACKGROUND

Apoptosis has been demonstrated to be an important upstream event in the pathogenesis of chronic obstructive pulmonary disease (COPD). Cyclooxygenase-2 (COX-2) seems to be biologically relevant in COPD. However, the role of COX-2 in the apoptosis in vascular endothelial cells induced by cigarette smoke extract (CSE) remains to be elucidated. Our recent study found that the prostacyclin, one of the COX products in the microvascular endothelium, inhibited apoptosis in the emphysematous lungs of rats induced by CSE. In order to clarify the role of COX-2 in the apoptosis of vascular endothelial cells induced by CSE, we performed the present experiment to elucidate it.

METHODS

Twenty surgical lung specimens were obtained from 6 patients with COPD, 7 smoking controls and seven nonsmoking controls. The apoptotic index (AI) and COX-2 protein expression were detected in lung tissues. To further investigate the effects of CSE on the apoptosis and COX-2 expression in a human vascular endothelial cell line, the apoptosis rate and COX-2 expression were examined in human umbilical vein endothelial cells (ECV304) under exposure to varied concentrations of CSE as well as under exposure to 5.0% CSE for varied durations. Repeatedly, the apoptosis rate and COX-2 expression in ECV304 cells under 5.0% CSE were examined after exposing to varied concentrations of celecoxib, a highly selective COX-2 inhibitor.

RESULTS

Significantly increased AI and expression of COX-2 were found both in the lungs of patients with COPD and smoking controls compared with nonsmoking controls. The CSE induced apoptosis in ECV304 cells in means of both dose-dependent and time-dependent manners. The COX-2 was slightly expressed in the cells after exposing to 5% CSE for 3 and 6 h, and markedly expressed after the exposure time for 9 and 12 h, but vanished after 24 h of the exposure. Of interest, with the completely block of the COX-2 expression by celecoxib at 50.0 µmol/L, the apoptosis rate was markedly increased again in ECV304 cells under exposure to 5.0% CSE.

CONCLUSIONS

Endothelial cell apoptosis and the expression of COX-2 protein were increased in both COPD patients and CSE-induced vascular endothelial cells. Of interest, it seems that the COX-2 probably had a protective role against the apoptosis in the vascular endothelial cells induced by cigarette smoking.

Estrogen deficiency promotes cigarette smoke-induced changes in the extracellular matrix in the lungs of aging female mice

Female smokers have a faster decline in lung function with increasing age and overall develop a greater loss of lung function than male smokers. This raises the question of whether estrogen status in women affects susceptibility to cigarette smoke (CS)-induced lung disease. Mouse models suggest that female mice are more susceptible than males to CS-induced lung disease. Moreover, young CS-exposed female mice develop emphysema earlier than male mice. The purpose of this study was to characterize the relationship of estrogen status on the pattern and severity of CS-induced lung disease. In this study, 15-month-old female C57BL/6J mice were ovariectomized and administered either placebo (pla) or 17β-estradiol (E₂, 0.025 mg) 2 weeks after ovariectomy. They were further divided into those that were exposed to CS and no-smoke controls (NSC). Mice were exposed to CS in stainless steel inhalation chambers 3 hours a day, 5 days a week for 6 months, and sacrificed after 24 weeks of CS exposure. Blood and urine were collected at sacrifice to measure estrogen and cotinine levels, a metabolite of nicotine. Uterine weight was recorded as an indicator of estrogen status. Results showed that CS in the absence of E₂ induced a decrease in hydroxyproline content, macrophage number, and respiratory chain complex-1 protein. CS without E₂ also resulted in an increase in matrix metalloproteinase-2 activity and apoptosis and a change in the ratio of estrogen receptor subtype. These findings were abrogated with administration of E_2, suggesting that estrogen deficiency increases susceptibility to CS-induced lung disease.

Nuclear matrix metalloproteinase-2 in the cardiomyocyte and the ischemic-reperfused heart

Matrix metalloproteinases (MMPs) are zinc-dependent proteases involved in intra- and extra-cellular matrix remodeling resulting from oxidative stress injury to the heart. MMP-2 was the first MMP to be localized to the nucleus; however, its biological functions there are unclear. We hypothesized that MMP-2 is present in the nucleus under normal physiological conditions but increases during myocardial ischemia-reperfusion (I/R) injury-induced oxidative stress, proteolyzing nuclear structural proteins. Lamins are intermediate filament proteins that provide structural support to the nucleus and are putative targets of MMP-2. To identify lamin susceptibility to MMP-2 proteolysis, purified lamin A or B was incubated with MMP-2 in vitro. Lamin A, but not lamin B, was proteolysed by MMP-2 into an approximately 50kDa fragment, which was also predicted by in silico cleavage site analysis. Immunofluorescent confocal microscopy and subcellular fractionation showed MMP-2 both in the cytosol and nuclei of neonatal rat ventricular myocytes. Rat hearts were isolated and perfused by the Langendorff method aerobically, or subjected to I/R injury in the presence or absence of o-phenanthroline, an MMP inhibitor. Nuclear fractions extracted from I/R hearts showed increased MMP-2 activity, but not protein level. The level of troponin I, a known sarcomeric target of MMP-2, was rescued in I/R hearts treated with o-phenanthroline, demonstrating the efficacy of MMP inhibition. However, lamin A or B levels remained unchanged in I/R hearts. MMP-2 has a widespread subcellular distribution in cardiomyocytes, including a significant presence in the nucleus. The increase in nuclear MMP-2 activity seen during stunning injury here, indicates yet unknown biological actions, other than lamin proteolysis, which may require more severe ischemia to effect.

Intracellular MMP-2 activity in skeletal muscle is associated with type II fibers

Matrix metalloproteinase 2 (MMP-2) is a proteolytic enzyme implicated in motility, differentiation, and regeneration of skeletal muscle fibers through processing of extracellular substrates. Although MMP-2 has been found to be localized intracellularly in cardiomyocytes where the enzyme is thought to contribute to post-ischemic loss of contractility, little is known about intracellular MMP-2 activity in skeletal muscle fibers. In the present study we demonstrate intracellular MMP-2 in normal skeletal muscle by immunohistochemical staining. Immunogold electron microscopic analyses indicated that the enzyme was concentrated in Z-lines of the sarcomers, in the nuclear membrane, and in mitochondria. By use of in situ zymography, we found that gelatinolytic activity in muscle fibers was co-localized with immunofluorecent staining for MMP-2. Staining for MMP-9, the other member of the gelatinase group of the MMPs, was negative. The broad-spectrum metalloprotease inhibitor EDTA and the selective gelatinase inhibitor CTT2, but not the cysteine inhibitor E64, strongly reduced the gelatinolytic activity. The intracellular gelatinolytic activity was much more prominent in fast twitch type II fibers than in slow twitch type I fibers, and there was a decrease in intracellular gelatinolytic activity and MMP-2 expression in muscles from mice exposed to high intensity interval training. Together our results indicate that MMP-2 is part of the intracellular proteolytic network in normal skeletal muscle, especially in fast twitch type II fibers. Further, the results suggest that intracellular MMP-2 in skeletal muscle fibers is active during normal homeostasis, and affected by the level of physical activity.

Matrix metalloproteinases, new insights into the understanding of neurodegenerative disorders

Matrix metalloproteinases (MMPs) are a subfamily of zinc-dependent proteases that are responsible for degradation and remodeling of extracellular matrix proteins. The activity of MMPs is tightly regulated at several levels including cleavage of prodomain, allosteric activation, compartmentalization and complex formation with tissue inhibitor of metalloproteinases (TIMPs). In the central nervous system (CNS), MMPs play a wide variety of roles ranging from brain development, synaptic plasticity and repair after injury to the pathogenesis of various brain disorders. Following general discussion on the domain structure and the regulation of activity of MMPs, we emphasize their implication in various brain disorder conditions such as Alzheimer’s disease, multiple sclerosis, ischemia/reperfusion and Parkinson’s disease. We further highlight accumulating evidence that MMPs might be the culprit in Parkinson’s disease (PD). Among them, MMP-3 appears to be involved in a range of pathogenesis processes in PD including neuroinflammation, apoptosis and degradation of α-synuclein and DJ-1. MMP inhibitors could represent potential novel therapeutic strategies for treatments of neurodegenerative diseases.

Features of matrix metalloproteinase-2 expression in the nuclei of tumor cells of a skin melanoma

Goal of the study. To compare expression of matrix metalloproteinase-2 (MMP-2) in the nuclei and cytoplasm of tumor cells and assess the mutual relation between the localization of MMP-2 expression and different clinical and morphologic criteria in patients with a skin melanoma. Materials and methods. Tumor samples obtained from paraffin blocks taken from patients suffering from a skin melanoma and treated at the Krasnoyarsk Territorial Oncologic Dispensary served as the object of the study. Skin tissue samples taken from patients suffering from a skin melanoma (n = 44) were obtained from the Krasnoyarsk Territorial Pathological Anatomy Bureau. Immunohistochemistry was performed based on a standard technique using primary anti-matrix metalloproteinase-2 antibodies. Results. MMP-2 expression was revealed in the nuclei of tumor cells of a skin melanoma in 43.1% of cases and in the cytoplasm in 56.9% of cases. No significant differences in MMP-2 expression in the nuclei and cytoplasm were revealed (p = 0.33). Patients with nuclear expression in tumor cells are characterized by a more favorable prognosis than patients with cytoplasmic enzyme expression in tumor complexes. No dependence of the intracellular localization of MMP-2 expression on the patient sex or age, tumor localization, Clark level of invasion, Breslow’s thickness, particular features of tumor lymphocyte infiltration, tumor growth phase, histological subtype, pigmentation, tumor ulceration and tumor stage according to AJCC (American Joint Committee on Cancer) was revealed. Conclusion. MMP-2 located in the nuclei can be related to hypoxia in the tumor tissue as well as increased peroxynitrite level, which, in its turn, can have an effect on the function and regulation of matrix metalloproteinases. Moreover, MMP-2 with an atypical localization can be related to tumor cells with different biological characteristics within the same tumor, which characterize the intratumoral heterogeneity of neoplasms. The biological and clinical role of changes in the intracellular localization of the enzyme needs further explanation.

Domain structure and function of matrix metalloprotease 23 (MMP23): role in potassium channel trafficking

MMP23 is a member of the matrix metalloprotease family of zinc- and calcium-dependent endopeptidases, which are involved in a wide variety of cellular functions. Its catalytic domain displays a high degree of structural homology with those of other metalloproteases, but its atypical domain architecture suggests that it may possess unique functional properties. The N-terminal MMP23 pro-domain contains a type-II transmembrane domain that anchors the protein to the plasma membrane and lacks the cysteine-switch motif that is required to maintain other MMPs in a latent state during passage to the cell surface. Instead of the C-terminal hemopexin domain common to other MMPs, MMP23 contains a small toxin-like domain (TxD) and an immunoglobulin-like cell adhesion molecule (IgCAM) domain. The MMP23 pro-domain can trap Kv1.3 but not closely-related Kv1.2 channels in the endoplasmic reticulum, preventing their passage to the cell surface, while the TxD can bind to the channel pore and block the passage of potassium ions. The MMP23 C-terminal IgCAM domain displays some similarity to Ig-like C2-type domains found in IgCAMs of the immunoglobulin superfamily, which are known to mediate protein-protein and protein-lipid interactions. MMP23 and Kv1.3 are co-expressed in a variety of tissues and together are implicated in diseases including cancer and inflammatory disorders. Further studies are required to elucidate the mechanism of action of this unique member of the MMP family.

Matrix metalloproteinase 3 promotes cellular anti-dengue virus response via interaction with transcription factor NFκB in cell nucleus

Dengue virus (DENV), the causative agent of human Dengue hemorrhagic fever, is a mosquito-borne virus of immense global health importance. Characterization of cellular factors promoting or inhibiting DENV infection is important for understanding the mechanism of DENV infection. In this report, MMP3 (stromelysin-1), a secretory endopeptidase that degrades extracellular matrices, has been shown promoting cellular antiviral response against DENV infection. Quantitative RT-PCR and Western Blot showed that the expression of MMP3 was upregulated in DENV-infected RAW264.7 cells. The intracellular viral loads were significantly higher in MMP3 silenced cells compared with controls. The expression level of selective anti-viral cytokines were decreased in MMP3 siRNA treated cells, and the transcription factor activity of NFκB was significantly impaired upon MMP3 silencing during DENV infection. Further, we found that MMP3 moved to cell nucleus upon DENV infection and colocalized with NFκB P65 in nucleus. Co-immunoprecipitation analysis suggested that MMP3 directly interacted with NFκB in nucleus during DENV infection and the C-terminal hemopexin-like domain of MMP3 was required for the interaction. This study suggested a novel role of MMP3 in nucleus during viral infection and provided new evidence for MMPs in immunomodulation.

Epithelial expression of extracellular matrix metalloproteinase inducer/CD147 and matrix metalloproteinase-2 in neoplasms and precursor lesions derived from cutaneous squamous cells: An immunohistochemical study

Extracellular matrix metalloproteinase inducer (CD147) is a transmembrane glycoprotein involved in the regulation of matrix metalloproteinases (MMPs). The study investigated CD147 and MMP-2 expression in epidermis of cutaneous squamous lesions. CD147 and MMP-2 expressions were evaluated immunohistochemically in 44 specimens: 18 actinic keratoses (AK), 6 squamous cell carcinomas in situ (SCCIS), 13 squamous cell carcinomas (SCC; peritumoral and invasive portions assessed), and 7 normal skins. Patterns of expression were assessed, with MMP-2 in nuclei (MMP-2n) and cytoplasm (MMP-2c) evaluated separately. The expression of each marker was quantified using a calculated immunohistochemical/histologic score (H-score). Correlations were analyzed for the marker H-scores in each study group. Associations between H-scores and histopathologic parameters were also evaluated. CD147 H-score was the highest in SCC (invasive islands), followed by AK, SCCIS, and control specimens, respectively. MMP-2n and MMP-2c H-scores were the highest in AK, followed by SCCIS, SCC, and control specimens, respectively. MMP-2c and MMP-2n H-scores were significantly higher in peritumoral epidermis than in invasive islands of SCC. MMP-2c and CD147 H-scores were positively correlated in the peritumoral SCCs. CD147 H-score was positively correlated with tumor differentiation in SCC. The findings suggest that overexpression of CD147 plays a role in the development of SCC.

Hydrogen peroxide-induced necrotic cell death in cardiomyocytes is independent of matrix metalloproteinase-2

Matrix metalloproteinase-2 (MMP-2) is well known to proteolyse both extracellular and intracellular proteins. Reactive oxygen species activate MMP-2 at both transcriptional and post-translational levels, thus MMP-2 activation is considered an early event in oxidative stress injury. Although hydrogen peroxide is widely used to trigger oxidative stress-induced cell death, the type of cell death (apoptosis vs. necrosis) in cardiomyocytes is still controversial depending on the concentration used and the exposure time. We carefully investigated the mode of cell death in neonatal rat cardiomyocytes induced by different concentrations (50-500 μM) of hydrogen peroxide at various time intervals after exposure and determined whether MMP-2 is implicated in hydrogen peroxide-induced cardiomyocyte death. Treating cardiomyocytes with hydrogen peroxide led to elevated MMP-2 level/activity with maximal effects seen at 200 μM. Hydrogen peroxide caused necrotic cell death by disrupting the plasmalemma as evidenced by the release of lactate dehydrogenase in a concentration- and time-dependent manner as well as the necrotic cleavage of PARP-1. The absence of both caspase-3 cleavage/activation and apoptotic cleavage of PARP-1 illustrated the weak contribution of apoptosis. Pre-treatment with selective MMP inhibitors did not protect against hydrogen peroxide-induced necrosis. In conclusion hydrogen peroxide increases MMP-2 level/activity in cardiomyocytes and induces necrotic cell death, however, the later effect is MMP-2 independent.

Tissue- and cell-specific co-localization of intracellular gelatinolytic activity and matrix metalloproteinase 2

Matrix metalloproteinase 2 (MMP-2) is a proteolytic enzyme that degrades extracellular matrix proteins. Recent studies indicate that MMP-2 also has a role in intracellular proteolysis during various pathological conditions, such as ischemic injuries in heart and brain and in tumor growth. The present study was performed to map the distribution of intracellular MMP-2 activity in various mouse tissues and cells under physiological conditions. Samples from normal brain, heart, lung, liver, spleen, pancreas, kidney, adrenal gland, thyroid gland, gonads, oral mucosa, salivary glands, esophagus, intestines, and skin were subjected to high-resolution in situ gelatin zymography and immunohistochemical staining. In hepatocytes, cardiac myocytes, kidney tubuli cells, epithelial cells in the oral mucosa as well as in excretory ducts of salivary glands, and adrenal cortical cells, we found strong intracellular gelatinolytic activity that was significantly reduced by the metalloprotease inhibitor EDTA but not by the cysteine protease inhibitor E-64. Furthermore, the gelatinolytic activity was co-localized with MMP-2. Western blotting and electron microscopy combined with immunogold labeling revealed the presence of MMP-2 in different intracellular compartments of isolated hepatocytes. Our results indicate that MMP-2 takes part in intracellular proteolysis in specific tissues and cells during physiological conditions.

Site-specific expression of gelatinolytic activity during morphogenesis of the secondary palate in the mouse embryo

Morphogenesis of the secondary palate in mammalian embryos involves two major events: first, reorientation of the two vertically oriented palatal shelves into a horizontal position above the tongue, and second, fusion of the two shelves at the midline. Genetic evidence in humans and mice indicates the involvement of matrix metalloproteinases (MMPs). As MMP expression patterns might differ from sites of activity, we used a recently developed highly sensitive in situ zymography technique to map gelatinolytic MMP activity in the developing mouse palate. At embryonic day 14.5 (E14.5), we detected strong gelatinolytic activity around the lateral epithelial folds of the nasopharyngeal cavity, which is generated as a consequence of palatal shelf elevation. Activity was concentrated in the basement membrane of the epithelial fold but extended into the adjacent mesenchyme, and increased in intensity with lateral outgrowth of the cavity at E15.5. Gelatinolytic activity at this site was not the consequence of epithelial fold formation, as it was also observed in Bmp7-deficient embryos where shelf elevation is delayed. In this case, gelatinolytic activity appeared in vertical shelves at the exact position where the epithelial fold will form during elevation. Mmp2 and Mmp14 (MT1-MMP), but not Mmp9 and Mmp13, mRNAs were expressed in the mesenchyme around the epithelial folds of the elevated palatal shelves; this was confirmed by immunostaining for MMP-2 and MT1-MMP. Weak gelatinolytic activity was also found at the midline of E14.5 palatal shelves, which increased during fusion at E15.5. Whereas MMPs have been implicated in palatal fusion before, this is the first report showing that gelatinases might contribute to tissue remodeling during early stages of palatal shelf elevation and formation of the nasopharynx.

Hypoxia-induced endothelial CX3CL1 triggers lung smooth muscle cell phenotypic switching and proliferative expansion

Distal arterioles with limited smooth muscles help maintain the high blood flow and low pressure in the lung circulation. Chronic hypoxia induces lung distal vessel muscularization. However, the molecular events that trigger alveolar hypoxia-induced peripheral endothelium modulation of vessel wall smooth muscle cell (SMC) proliferation and filling of nonmuscular areas are unclear. Here, we investigated the role of CX3CL1/CX3CR1 system in endothelial-SMC cross talk in response to hypoxia. Human lung microvascular endothelial cells responded to alveolar oxygen deficiency by overproduction of the chemokine CX3CL1. The CX3CL1 receptor CX3CR1 is expressed by SMCs that are adjacent to the distal endothelium. Hypoxic release of endothelial CX3CL1 induced SMC phenotypic switching from the contractile to the proliferative state. Inhibition of CX3CR1 prevented CX3CL1 stimulation of SMC proliferation and monolayer expansion. Furthermore, CX3CR1 deficiency attenuated spiral muscle expansion, distal vessel muscularization, and pressure elevation in response to hypoxia. Our findings indicate that the capillary endothelium relies on the CX3CL1-CX3CR1 axis to sense alveolar hypoxia and promote peripheral vessel muscularization. These results have clinical significance in the development of novel therapeutics that target mechanisms of distal arterial remodeling associated with pulmonary hypertension induced by oxygen deficiency that is present in people living at high altitudes and patients with obstructive lung diseases.

Nuclear localization of matrix metalloproteinases

Matrix metalloproteinases (MMPs) were originally identified as matrixin proteases that act in the extracellular matrix. Recent works have uncovered nontraditional roles for MMPs in the extracellular space as well as in the cytosol and nucleus. There is strong evidence that subspecialized and compartmentalized matrixins participate in many physiological and pathological cellular processes, in which they can act as both degradative and regulatory proteases. In this review, we discuss the transcriptional and translational control of matrixin expression, their regulation of intracellular sorting, and the structural basis of activation and inhibition. In particular, we highlight the emerging roles of various matrixin forms in diseases. The activity of matrix metalloproteinases is regulated at several levels, including enzyme activation, inhibition, complex formation and compartmentalization. Most MMPs are secreted and have their function in the extracellular environment. MMPs are also found inside cells, both in the nucleus, cytosol and organelles. The role of intracellular located MMPs is still poorly understood, although recent studies have unraveled some of their functions. The localization, activation and activity of MMPs are regulated by their interactions with other proteins, proteoglycan core proteins and / or their glycosaminoglycan chains, as well as other molecules. Complexes formed between MMPs and various molecules may also include interactions with noncatalytic sites. Such exosites are regions involved in substrate processing, localized outside the active site, and are potential binding sites of specific MMP inhibitors. Knowledge about regulation of MMP activity is essential for understanding various physiological processes and pathogenesis of diseases, as well as for the development of new MMP targeting drugs.

Fluticasone propionate and Salmeterol combination induces SOCS-3 expression in airway epithelial cells

Fluticasone propionate (FP) and Salmeterol (SAL) are commonly used in combination therapy for patients with Chronic obstructive pulmonary disease (COPD). Clinical studies show that FP/SAL used in combination therapy was found to inhibit airway inflammation in COPD patients. However, the mechanisms associated with FP/SAL induced anti-inflammatory effects were not clear. We have evaluated the effect of FP/SAL and tobacco smoke (TS) on SOCS-3 and interleukine-6 expression in bronchial airway epithelial cells (BAEpCs). Human BAEpCs were exposed to TS and subsequently treated with FP or SAL alone or in combinations in the presence and absence of mitogen activated protein kinase (MAPK) inhibitors for either Erk1/Erk2, or p38 or PI3 kinase. In BAEpCs, TS induced IL-6 expression via ERK1/ERK2 MAPK pathway and FP/SAL inhibited TS mediated IL-6 expression. TS down regulated the SOCS-3 expression via activation of Erk1/Erk2, and p38 MAPK signaling. When TS exposed BAEpCs were treated with FP/SAL SOCS-3 expression was restored. FP/SAL combinations induced significantly higher expression of SOCS-3 in BAEpCs when compared to individual drug. Pretreatment with Ly294002 a PI3 MAPK inhibitor significantly attenuated FP/SAL induced SOCS-3 expression in BAEpCs. Furthermore, FP/SAL blunted TS induced phosphorylation of Erk1/Erk2 and p38 MAPK in BAEpCs. Our study suggests that TS inhibits SOCS-3, combination of FP/SAL has a profound synergistic effect on SOCS-3 induction in BAEpCs and it is dependent on PI3 kinase signaling pathway. SOCS-3 may represent a potential biomarker for understanding the efficacy and a novel anti-inflammatory mechanism of FP/SAL combination therapy in the treatment of COPD.

Lung endothelial cell platelet-activating factor production and inflammatory cell adherence are increased in response to cigarette smoke component exposure

An early event in the pathogenesis of emphysema is the development of inflammation associated with accumulation of polymorphonuclear leukocytes (PMN) in small airways, and inflammatory cell recruitment from the circulation involves migration across endothelial and epithelial cell barriers. Platelet-activating factor (PAF) promotes transendothelial migration in several vascular beds, and we postulated that increased PAF production in the airways of smokers might enhance inflammatory cell recruitment and exacerbate inflammation. To examine this possibility, we incubated human lung microvascular endothelial cells (HMVEC-L) with cigarette smoke extract (CSE) and found that CSE inhibits PAF-acetylhydrolase (PAF-AH) activity. This enhances HMVEC-L PAF production and PMN adherence, and adherence is blocked by PAF receptor antagonists (CV3988 or ginkgolide B). CSE also inhibited PAF-AH activity of lung endothelial cells isolated from wild-type (WT) and iPLA(2)β knockout mice, and with WT cells, CSE enhanced PAF production and RAW 264.7 cell adherence. In contrast, CSE did not affect PAF production or RAW 264.7 cell adherence to iPLA(2)β-null cells, suggesting that iPLA(2)β plays an important role in PAF production by lung endothelial cells. These findings suggest that inhibition of PAF-AH by components of cigarette smoke may initiate or exacerbate inflammatory lung disease by enhancing PAF production and promoting accumulation of inflammatory cells in small airways. In addition, iPLA(2)β is identified as a potential target for therapeutic interventions to reduce airway inflammation and the progression of chronic lung disease.

What does matrix metalloproteinase-1 expression in patients with breast cancer really tell us?

Molecular and biochemical expressions of matrix metalloproteinases in breast cancer tissue and cells offers promise in helping us understand the breast cancer microenvironment, and also in the future it is hoped this will improve its detection, treatment and prognosis. In a retrospective study recently published in BMC Cancer, microenvironment predisposing to breast cancer progression, metastatic behavior and the expression of matrix metalloproteinase-1 (MMP-1) and its correlation with well-known biochemical, molecular and clinicopathologic factors in breast cancer cells and cancer-associated stromal cells was examined; this study also analyzed patient survival in different breast cancer subtypes. The positive correlation in breast tumor and stromal cells between MMP-1 expression and several markers of tumor grade and stage provide us with some useful new insights into important questions about the molecular profiling of the stromal microenvironment in metastatic breast cancer. The study showed that MMP-1 expression is strongly associated with poor clinical outcome, so now we look forward to future larger studies in breast cancer patients in which we can relate wider MMP molecular profiling to identify lethal tumor and stromal microenvironments predisposing to breast cancer progression, metastatic behavior and poor prognosis. Please see related article http://www.biomedcentral.com/1471-2407/11/348.

Regulation of matrix metalloproteinase activity in health and disease

The activity of matrix metalloproteinases (MMPs) is regulated at several levels, including enzyme activation, inhibition, complex formation and compartmentalization. Regulation at the transcriptional level is also important, although this is not a subject of the present minireview. Most MMPs are secreted and have their function in the extracellular environment. This is also the case for the membrane-type MMPs (MT-MMPs). MMPs are also found inside cells, both in the nucleus, cytosol and organelles. The role of intracellular located MMPs is still poorly understood, although recent studies have unraveled some of their functions. The localization, activation and activity of MMPs are regulated by their interactions with other proteins, proteoglycan core proteins and/or their glycosaminoglycan chains, as well as other molecules. Complexes formed between MMPs and various molecules may also include interactions with noncatalytic sites. Such exosites are regions involved in substrate processing, localized outside the active site, and are potential binding sites of specific MMP inhibitors. Knowledge about regulation of MMP activity is essential for understanding various physiological processes and pathogenesis of diseases, as well as for the development of new MMP targeting drugs.

Gelatin in situ zymography on fixed, paraffin-embedded tissue: zinc and ethanol fixation preserve enzyme activity

In situ zymography is a method for the detection and localization of enzymatic activity in tissue sections. This method is used with frozen sections because routine fixation of tissue in neutral-buffered formalin inhibits enzyme activity. However, frozen sections present with poor tissue morphology, making precise localization of enzymatic activity difficult to determine. Ethanol- and zinc-buffered fixative (ZBF) are known to preserve both morphological and functional properties of the tissue well, but it has not previously been shown that these fixatives preserve enzyme activity. In the present study, we show that in situ zymography can be performed on ethanol- and ZBF-fixed paraffin-embedded tissue. Compared with snap-frozen tissue, ethanol- and ZBF-fixed tissue showed stronger signals and superior morphology, allowing for a much more precise detection of gelatinolytic activity. Gelatinolytic enzymes could also be extracted from both ethanol- and ZBF-fixed tissue. The yield, as analyzed by SDS-PAGE gelatin zymography and Western blotting, was influenced by the composition of the extraction buffer, but was generally lower than that obtained from unfixed tissue.

Matrix metalloproteinase-2 and myocardial oxidative stress injury: beyond the matrix

Matrix metalloproteinase (MMP)-2 belongs to a family of zinc-dependent proteases which are best known for their ability to proteolyse extracellular matrix proteins throughout the body, including the cardiovascular system. Increased MMP-2 activity has been demonstrated in myocardial ischaemia and reperfusion injury and the progression to congestive heart failure, with most evidence to date for its role in cardiac remodelling. Recent evidence, however, shows that MMP-2 also co-localizes with and proteolyses specific protein targets within the cardiomyocyte to cause acute, reversible contractile dysfunction, challenging the conventional wisdom on the 'extracellular matrix only' actions of this enzyme. In this review, we discuss the recent upsurge in MMP-2 research with regards to its activation by non-proteolytic pathways in the setting of enhanced oxidative stress in the heart. We will focus on the consequences of intracellular actions of MMP-2 within the cardiomyocyte and its regulation at several levels including its expression, post-translational modifications, and regulation by endogenous tissue inhibitors of metalloproteinases, caveolin, and small molecule MMP inhibitors. MMP-2 is emerging as an important signalling protease implicated in the proteolytic regulation of various intracellular proteins in myocardial oxidative stress injury.