Post-translational proteolytic processing of procollagen C-terminal proteinase enhancer releases a metalloproteinase inhibitor

Netrin-1: Key insights in neural development and disorders

Netrin-1, an essential extracellular protein, has gained significant attention due to its pivotal role in guiding axon and cell migration during embryonic development. The fundamental significance of netrin-1 in developmental biology is reflected in its high conservation across different species as a part of the netrin family. The bifunctional nature of netrin-1 demonstrates its functional versatility, as it can function as either a repellent or an attractant according to the context and the expressed receptors on the target cells including the deleted in colorectal cancer (DCC), the uncoordinated-5 (UNC5), DSCAM, Neogenin-1, Adenosine A2b and Draxin receptors. By directing axonal growth cones toward the appropriate targets, netrin-1 is a critical actor in the formation of the intricate architecture of the nervous system. Netrin-1 is believed to be involved in additional biological and pathological processes in addition to its traditional function in neural development. The behavior of a diverse array of cell types is influenced by controlling cell adhesion and movement, which is impacted by netrin-1. It is a molecule of interest in both developmental biology and clinical research because of its involvement in angiogenesis, tumorigenesis, inflammation, and tissue regeneration, as confirmed by recent studies. The therapeutic capability of netrin-1 in disorders such as cancer, neurodegenerative disorders, and cardiovascular diseases warrants significant attention.

Lineage Plasticity in SCLC Generates Non-Neuroendocrine Cells Primed for Vasculogenic Mimicry

INTRODUCTION

Vasculogenic mimicry (VM), the process of tumor cell transdifferentiation to endow endothelial-like characteristics supporting de novo vessel formation, is associated with poor prognosis in several tumor types, including SCLC. In genetically engineered mouse models (GEMMs) of SCLC, NOTCH, and MYC co-operate to drive a neuroendocrine (NE) to non-NE phenotypic switch, and co-operation between NE and non-NE cells is required for metastasis. Here, we define the phenotype of VM-competent cells and molecular mechanisms underpinning SCLC VM using circulating tumor cell-derived explant (CDX) models and GEMMs.

METHODS

We analyzed perfusion within VM vessels and their association with NE and non-NE phenotypes using multiplex immunohistochemistry in CDX, GEMMs, and patient biopsies. We evaluated their three-dimensional structure and defined collagen-integrin interactions.

RESULTS

We found that VM vessels are present in 23/25 CDX models, 2 GEMMs, and in 20 patient biopsies of SCLC. Perfused VM vessels support tumor growth and only NOTCH-active non-NE cells are VM-competent in vivo and ex vivo, expressing pseudohypoxia, blood vessel development, and extracellular matrix organization signatures. On Matrigel, VM-primed non-NE cells remodel extracellular matrix into hollow tubules in an integrin β1-dependent process.

CONCLUSIONS

We identified VM as an exemplar of functional heterogeneity and plasticity in SCLC and these findings take considerable steps toward understanding the molecular events that enable VM. These results support therapeutic co-targeting of both NE and non-NE cells to curtail SCLC progression and to improve the outcomes of patients with SCLC in the future.

Deficiency of Procollagen C-Proteinase Enhancer 1 in Mice has No Major Impact on Cardiac Collagen and Function Under Basal Conditions

ABSTRACT

Maturation of fibrillar collagen is known to play a crucial role in the pathophysiology of myocardial fibrosis. Procollagen C-proteinase enhancer 1 (PCPE1) has a key role in procollagen maturation and collagen fibril formation. The phenotype of both male and female PCPE1 knock-out mice was investigated under basal conditions to explore the potential of PCPE1 as a therapeutic target in heart failure. Global constitutive PCPE1-/- mice were generated. Serum procollagen I C-terminal propeptide, organ histology, and cutaneous wound healing were assessed in both wild type (WT) and PCPE1-/- mice. In addition, the cardiac expression of genes involved in collagen metabolism was investigated and the total and insoluble cardiac collagen contents determined. Cardiac function was evaluated by echocardiography. No differences in survival, clinical chemistry, or organ histology were observed in PCPE1-/- mice compared with WT. Serum procollagen I C-terminal propeptide was lower in PCPE1-/- mice. Cardiac mRNA expression of Bmp1, Col1a1, Col3a1, and Loxl2 was similar, whereas Tgfb and Loxl1 mRNA levels were decreased in PCPE1-/- mice compared with sex-matched WT. No modification of total or insoluble cardiac collagen content was observed between the 2 strains. Ejection fraction was slightly decreased in PCPE1-/- male mice, but not in females. Finally, wound healing was not altered in PCPE1-/- mice. PCPE1 deficiency does not trigger any major liabilities and does not affect cardiac collagen content nor its function under basal conditions. Further studies are required to evaluate its role under stressed conditions and determine its suitability as a therapeutic target for heart failure.

Procollagen C-proteinase enhancer-1 (PCPE-1), a potential biomarker and therapeutic target for fibrosis

The correct balance between collagen synthesis and degradation is essential for almost every aspect of life, from development to healthy aging, reproduction and wound healing. When this balance is compromised by external or internal stress signals, it very often leads to disease as is the case in fibrotic conditions. Fibrosis occurs in the context of defective tissue repair and is characterized by the excessive, aberrant and debilitating deposition of fibril-forming collagens. Therefore, the numerous proteins involved in the biosynthesis of fibrillar collagens represent a potential and still underexploited source of therapeutic targets to prevent fibrosis. One such target is procollagen C-proteinase enhancer-1 (PCPE-1) which has the unique ability to accelerate procollagen maturation by BMP-1/tolloid-like proteinases (BTPs) and contributes to trigger collagen fibrillogenesis, without interfering with other BTP functions or the activities of other extracellular metalloproteinases. This role is achieved through a fine-tuned mechanism of action that is close to being elucidated and offers promising perspectives for drug design. Finally, the in vivo data accumulated in recent years also confirm that PCPE-1 overexpression is a general feature and early marker of fibrosis. In this review, we describe the results which presently support the driving role of PCPE-1 in fibrosis and discuss the questions that remain to be solved to validate its use as a biomarker or therapeutic target.

Destroy to Rebuild: The Connection Between Bone Tissue Remodeling and Matrix Metalloproteinases

Bone is a dynamic organ that undergoes constant remodeling, an energetically costly process by which old bone is replaced and localized bone defects are repaired to renew the skeleton over time, thereby maintaining skeletal health. This review provides a general overview of bone’s main players (bone lining cells, osteocytes, osteoclasts, reversal cells, and osteoblasts) that participate in bone remodeling. Placing emphasis on the family of extracellular matrix metalloproteinases (MMPs), we describe how: (i) Convergence of multiple protease families (including MMPs and cysteine proteinases) ensures complexity and robustness of the bone remodeling process, (ii) Enzymatic activity of MMPs affects bone physiology at the molecular and cellular levels and (iii) Either overexpression or deficiency/insufficiency of individual MMPs impairs healthy bone remodeling and systemic metabolism. Today, it is generally accepted that proteolytic activity is required for the degradation of bone tissue in osteoarthritis and osteoporosis. However, it is increasingly evident that inactivating mutations in MMP genes can also lead to bone pathology including osteolysis and metabolic abnormalities such as delayed growth. We argue that there remains a need to rethink the role played by proteases in bone physiology and pathology.

Fibrillar fibronectin plays a key role as nucleator of collagen I polymerization during macromolecular crowding-enhanced matrix assembly

Macromolecular crowding is used by tissue engineers to accelerate extracellular matrix assembly in vitro, however, most mechanistic studies focus on the impact of crowding on collagen fiber assembly and largely ignore the highly abundant provisional matrix protein fibronectin. We show that the accelerated collagen I assembly as induced by the neutral crowding molecule Ficoll is regulated by cell access to fibronectin. Ficoll treatment leads to significant increases in the amount of surface adherent fibronectin, which can readily be harvested by cells to speed up fibrillogenesis. FRET studies reveal that Ficoll crowding also upregulates the total amount of fibronectin fibers in a low-tension state through upregulating fibronectin assembly. Since un-stretched fibronectin fibers have more collagen binding sites to nucleate the onset of collagen fibrillogenesis, our data suggest that the Ficoll-induced upregulation of low-tension fibronectin fibers contributes to enhanced collagen assembly in crowded conditions. In contrast, chemical cross-linking of fibronectin to the glass substrate prior to cell seeding prevents early force mediated fibronectin harvesting from the substrate and suppresses upregulation of collagen I assembly in the presence of Ficoll, even though the crowded environment is known to drive enzymatic cleavage of procollagen and collagen fiber formation. To show that our findings can be exploited for tissue engineering applications, we demonstrate that the addition of supplemental fibronectin in the form of an adsorbed coating markedly improves the speed of tissue formation under crowding conditions.

Pathologies of matrix metalloproteinase-2 underactivity: a perspective on a neglected condition 1

A member of the matrix metalloproteinase family, matrix metalloproteinase-2 (MMP-2, gelatinase A), has been extensively studied for its role in both normal physiology and pathological processes. Whereas most research efforts in recent years have investigated the pathologies associated with MMP-2 overactivity, the pathological mechanisms elicited by MMP-2 underactivity are less well understood. Here, we distinguish between 2 states and describe their causes: (i) MMP-2 deficiency (complete loss of MMP-2 activity) and (ii) MMP-2 insufficiency (defined as MMP-2 activity below baseline levels). Further, we review the biology of MMP-2, summarizing the current literature on MMP-2 underactivity in both mice and humans, and describe research being conducted by our lab towards improving our understanding of the pathological mechanisms elicited by MMP-2 deficiency/insufficiency. We think that this research could stimulate the discovery of new therapeutic approaches for managing pathologies associated with MMP-2 underactivity. Moreover, similar concepts could apply to other members of the matrix metalloproteinase family.

Strategies to Target Matrix Metalloproteinases as Therapeutic Approach in Cancer

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that are capable of degrading numerous extracellular matrix (ECM) components thus participating in physiological and pathological processes. Apart from the remodeling of ECM, they affect cell-cell and cell-matrix interactions and are implicated in the development and progression of various diseases such as cancer. Numerous studies have demonstrated that MMPs evoke epithelial to mesenchymal transition (EMT) of cancer cells and affect their signaling, adhesion, migration and invasion to promote cancer cell aggressiveness. Various studies have suggested MMPs as suitable targets for treatment of malignancies, and several MMP inhibitors (MMPIs) have been developed. Although initial trials have failed to establish MMPIs as anticancer agents due to lack of specificity and side effects, new MMPIs have been developed with improved action that are currently being investigated. Furthermore, novel strategies that target MMPs for improving drug delivery and regulating their activity in tumors are presented. This review summarizes the implication of MMPs in cancer progression and discusses the advancements in their targeting.

Current diagnostics and treatment of fibrosarcoma -perspectives for future therapeutic targets and strategies

Adult-type fibrosarcoma is a rare and highly aggressive subtype of soft tissue sarcomas. Due to the existence of other spindle-cell shaped sarcomas, its diagnosis is always one of exclusion. The likelihood of misdiagnoses between similar tumour entities is high, and often leads to inappropriate tumour treatment. We summarize here the main features of fibrosarcoma. When fibrosarcoma is appropriately diagnosed, the patient`s overall prognosis is generally quite poor. Fibrosarcoma is characterized by its low sensitivity towards radio- and chemotherapy as well as by its high rate of tumour recurrences. Thus it is important to identify new methods to improve treatment of this tumour entity. We discuss some promising new directions in fibrosarcoma research, specifically focusing on more effective targeting of the tumour microenvironment. Communication between tumour cells and their surrounding stromal tissue play a crucial role in cancer progression, invasion, metastasis and chemosensitivity. The therapeutic potential of targeting the tumour microenvironment is addressed.

Matrix Metalloproteinases: A challenging paradigm of cancer management

Matrix metalloproteinases (MMPs) are members of zinc-dependent endopeptidases implicated in a variety of physiological and pathological processes. Over the decades, MMPs have been studied for their role in cancer progression, migration, and metastasis. As a result, accumulated evidence of MMPs incriminating role has made them an attractive therapeutic target. Early generations of broad-spectrum MMP inhibitors exhibited potent inhibitory activities, which subsequently led to clinical trials. Unexpectedly, these trials failed to meet the desired goals, mainly due to the lack of efficacy, poor oral bioavailability, and toxicity. In this review, we discuss the regulatory role of MMPs in cancer progression, current strategies in targeting MMPs for cancer treatment including prodrug design and tumor imaging, and therapeutic value of MMPs as biomarkers in breast, lung, and prostate cancers.

Proteases decode the extracellular matrix cryptome

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

Multilevel regulation of matrix metalloproteinases in tissue homeostasis indicates their molecular specificity in vivo

The matrix metalloproteinases (MMPs) play a crucial role in irreversible remodeling of the extracellular matrix (ECM) in normal homeostasis and pathological states. Accumulating data from various studies strongly suggest that MMPs are tightly regulated, starting from the level of gene expression all the way to zymogen activation and endogenous inhibition, with each level controlled by multiple factors. Recent in vivo findings indicate that cell-ECM and cell-cell interactions, as well as ECM bio-active products, contribute an additional layer of regulation at all levels, indicating that individual MMP expression and activity in vivo are highly coordinated and tissue specific processes.

Matrix metalloproteinases in biologic samples

Matrix metalloproteinases (MMPs) are an important class of endopeptidases, having a role in a diverse range of physiological and pathological processes. This chapter provides an overview of the key regulatory processes in MMP production and activation. The common techniques used to assess MMP activity are discussed and their various strengths and weaknesses presented. This comparison of methodologies is specifically intended to aid any investigator who wishes to determine the most appropriate analytical method for their future studies because any investigation of MMPs in biological samples should be cognizant of the key mechanisms influencing the expression and activity of these proteinases. The endogenous, preanalytic and analytic chemistry of MMP activation influences the interpretation of the various techniques widely employed throughout the literature. Therefore, the ability to accurately evaluate the true endogenous activity of MMPs is heavily dependent on a clear understanding of these processes.

The NTR domain of procollagen C-proteinase enhancer-1 (PCPE-1) mediates PCPE-1 binding to syndecans-1, -2 and -4 as well as fibronectin

Procollagen C-proteinase enhancer 1 (PCPE-1) is an extracellular matrix glycoprotein that can stimulate procollagen processing by procollagen C-proteinases (PCPs) such as bone morphogenetic protein-1 (BMP-1). PCPE-1 consists of two CUB domains that bind to the procollagen C-propeptide and are responsible for enhancing activity and a netrin-like (NTR) domain that binds to BMP-1 as well as heparin and heparan sulfate. The NTR domain also mediates binding of PCPE-1 to cells, an interaction inhibited by heparin, thus suggesting involvement of cell membrane heparan-sulfate proteoglycans (HSPGs). Using pull-down experiments and an ELISA type binding assay we show here that PCPE-1 binds to three cell membrane HSPGs, syndecans-1, -2 and -4. We also demonstrate that this binding is mediated by the NTR domain and depends on the glycosaminoglycan chains of the syndecans. Using co-immunoprecipitation and an ELISA type binding assay we show that PCPE-1 can also bind fibronectin (an established binding partner of BMP-1), another interaction involving the NTR domain. Consistently, fibronectin inhibits cell attachment to PCPE-1 although it does not affect PCPE-1 enhancing activity. PCPE-1 is not an adhesive protein since cell attachment to PCPE-1 is not associated with cell spreading and/or actin filaments formation. The results suggest that PCPE-1 binding to syndecans and/or fibronectin may control collagen fibril assembly on the cell surface. Further characterization of these interactions may pave the way for future design of new means to modulate collagen deposition in pathological conditions such as fibrosis.

Nitric oxide-matrix metaloproteinase-9 interactions: biological and pharmacological significance--NO and MMP-9 interactions

Nitric oxide (NO) and matrix metalloproteinase 9 (MMP-9) levels are found to increase in inflammation states and in cancer, and their levels may be reciprocally modulated. Understanding interactions between NO and MMP-9 is of biological and pharmacological relevance and may prove crucial in designing new therapeutics. The reciprocal interaction between NO and MMP-9 have been studied for nearly twenty years but to our knowledge, are yet to be the subject of a review. This review provides a summary of published data regarding the complex and sometimes contradictory effects of NO on MMP-9. We also analyse molecular mechanisms modulating and mediating NO-MMP-9 interactions. Finally, a potential therapeutic relevance of these interactions is presented.

Extended interaction network of procollagen C-proteinase enhancer-1 in the extracellular matrix

PCPE-1 (procollagen C-proteinase enhancer-1) is an extracellular matrix glycoprotein that can stimulate procollagen processing by procollagen C-proteinases such as BMP-1 (bone morphogenetic protein 1). PCPE-1 interacts with several proteins in addition to procollagens and BMP-1, suggesting that it could be involved in biological processes other than collagen maturation. We thus searched for additional partners of PCPE-1 in the extracellular matrix, which could provide new insights into its biological roles. We identified 17 new partners of PCPE-1 by SPR (surface plasmon resonance) imaging. PCPE-1 forms a transient complex with the β-amyloid peptide, whereas it forms high or very high affinity complexes with laminin-111 (KD=58.8 pM), collagen VI (KD=9.5 nM), TSP-1 (thrombospondin-1) (KD1=19.9 pM, KD2=14.5 nM), collagen IV (KD=49.4 nM) and endostatin, a fragment of collagen XVIII (KD1=0.30 nM, KD2=1.1 nM). Endostatin binds to the NTR (netrin-like) domain of PCPE-1 and decreases the degree of superstimulation of PCPE-1 enhancing activity by heparin. The analysis of the PCPE-1 interaction network based on Gene Ontology terms suggests that, besides its role in collagen deposition, PCPE-1 might be involved in tumour growth, neurodegenerative diseases and angiogenesis. In vitro assays have indeed shown that the CUB1CUB2 (where CUB is complement protein subcomponents C1r/C1s, urchin embryonic growth factor and BMP-1) fragment of PCPE-1 inhibits angiogenesis.

Quantitative proteomics reveals regulatory differences in the chondrocyte secretome from human medial and lateral femoral condyles in osteoarthritic patients

Background

Osteoarthritis (OA) is a destructive joint disease and there are no known biomarkers available for an early diagnosis. To identify potential disease biomarkers and gain further insight into the disease mechanisms of OA we applied quantitative proteomics with SILAC technology on the secretomes from chondrocytes of OA knees, designated as high Mankin (HM) scored secretome. A quantitative comparison was made between the secretomes of the medial and lateral femur condyle chondrocytes in the same knee since the medial femur condyle is usually more affected in OA than the lateral condyle, which was confirmed by Mankin scoring. The medial/lateral comparison was also made on the secretomes from chondrocytes taken from one individual with no clinically apparent joint-disease, designated as low Mankin (LM) scored secretome.

Results

We identified 825 proteins in the HM secretome and 69 of these showed differential expression when comparing the medial and lateral femoral compartment. The LM scored femoral condyle showed early signs of OA in the medial compartment as assessed by Mankin score. We here report the identification and relative quantification of several proteins of interest for the OA disease mechanism e.g. CYTL1, DMD and STAB1 together with putative early disease markers e.g. TIMP1, PPP2CA and B2M.

Conclusions

The present study reveals differences in protein abundance between medial/lateral femur condyles in OA patients. These regulatory differences expand the knowledge regarding OA disease markers and mechanisms.

Potential clinical applications of matrix metalloproteinase inhibitors and their future prospects

Matrix metalloproteinases (MMPs) are endopeptidases that are involved in extracellular matrix degradation. They are also implicated in a number of abnormal bioprocesses, such as tumor growth, invasion, and metastasis. Therefore, controlling MMP activities has generated considerable interest as a possible therapeutic target. The tissue inhibitors of metalloproteinases (TIMPs) are the major naturally occurring proteins that specifically inhibit MMPs and assist in maintaining the balance between extracellular matrix destruction and formation. However, TIMPs are probably not suitable for pharmacological applications due to their short half-lives in vivo. During the last few decades, synthetic MMP inhibitors (MMPIs) have undergone rapid clinical development in attempts to control MMP enzymatic activities in abnormal bioprocesses. Although studies with these agents have met with limited clinical success, the field of MMPIs is still expanding, and generation of highly effective and selective MMPIs might be a promising direction of this research area.

Matrix metalloproteinase inhibitors as investigative tools in the pathogenesis and management of vascular disease

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade various components of the extracellular matrix (ECM). MMPs could also regulate the activity of several non-ECM bioactive substrates and consequently affect different cellular functions. Members of the MMPs family include collagenases, gelatinases, stromelysins, matrilysins, membrane-type MMPs, and others. Pro-MMPs are cleaved into active MMPs, which in turn act on various substrates in the ECM and on the cell surface. MMPs play an important role in the regulation of numerous physiological processes including vascular remodeling and angiogenesis. MMPs may also be involved in vascular diseases such as hypertension, atherosclerosis, aortic aneurysm, and varicose veins. MMPs also play a role in the hemodynamic and vascular changes associated with pregnancy and preeclampsia. The role of MMPs is commonly assessed by measuring their gene expression, protein amount, and proteolytic activity using gel zymography. Because there are no specific activators of MMPs, MMP inhibitors are often used to investigate the role of MMPs in different physiologic processes and in the pathogenesis of specific diseases. MMP inhibitors include endogenous tissue inhibitors (TIMPs) and pharmacological inhibitors such as zinc chelators, doxycycline, and marimastat. MMP inhibitors have been evaluated as diagnostic and therapeutic tools in cancer, autoimmune disease, and cardiovascular disease. Although several MMP inhibitors have been synthesized and tested both experimentally and clinically, only one MMP inhibitor, i.e., doxycycline, is currently approved by the Food and Drug Administration. This is mainly due to the undesirable side effects of MMP inhibitors especially on the musculoskeletal system. While most experimental and clinical trials of MMP inhibitors have not demonstrated significant benefits, some trials still showed promising results. With the advent of new genetic and pharmacological tools, disease-specific MMP inhibitors with fewer undesirable effects are being developed and could be useful in the management of vascular disease.

Neu1 sialidase and matrix metalloproteinase-9 cross-talk is essential for Toll-like receptor activation and cellular signaling

The signaling pathways of mammalian Toll-like receptors (TLRs) are well characterized, but the precise mechanism(s) by which TLRs are activated upon ligand binding remains poorly defined. Recently, we reported a novel membrane sialidase-controlling mechanism that depends on ligand binding to its TLR to induce mammalian neuraminidase-1 (Neu1) activity, to influence receptor desialylation, and subsequently to induce TLR receptor activation and the production of nitric oxide and proinflammatory cytokines in dendritic and macrophage cells. The α-2,3-sialyl residue of TLR was identified as the specific target for hydrolysis by Neu1. Here, we report a membrane signaling paradigm initiated by endotoxin lipopolysaccharide (LPS) binding to TLR4 to potentiate G protein-coupled receptor (GPCR) signaling via membrane Gα(i) subunit proteins and matrix metalloproteinase-9 (MMP9) activation to induce Neu1. Central to this process is that a Neu1-MMP9 complex is bound to TLR4 on the cell surface of naive macrophage cells. Specific inhibition of MMP9 and GPCR Gα(i)-signaling proteins blocks LPS-induced Neu1 activity and NFκB activation. Silencing MMP9 mRNA using lentivirus MMP9 shRNA transduction or siRNA transfection of macrophage cells and MMP9 knock-out primary macrophage cells significantly reduced Neu1 activity and NFκB activation associated with LPS-treated cells. These findings uncover a molecular organizational signaling platform of a novel Neu1 and MMP9 cross-talk in alliance with TLR4 on the cell surface that is essential for ligand activation of TLRs and subsequent cellular signaling.

Applying macromolecular crowding to enhance extracellular matrix deposition and its remodeling in vitro for tissue engineering and cell-based therapies

With the advent of multicellular organisms, the exterior of the cells evolved dramatically from highly aqueous surroundings into an extracellular matrix and space crowded with macromolecules. Cell-based therapies require removal of cells from their crowded physiological context and propagating them in dilute culture medium to attain therapeutically relevant numbers whilst preserving their phenotype. However, bereft of their microenvironment, cells under perform and lose functionality. Major efforts currently aim to modify cell culture surfaces and build three dimensional scaffolds to improve this situation. We discuss here alternative strategies that enable cells to re-create their own microenvironment in vitro, using carbohydrate-based macromolecules as culture media additives that create an excluded volume effect at defined fraction volume occupancies. This biophysical approach dramatically enhances extracellular matrix deposition by differentiated cells and stem cells, and boosts progenitor cell differentiation and proliferation. We begin to understand how well cells really can perform ex vivo if given the chance.

SFRPs act as negative modulators of ADAM10 to regulate retinal neurogenesis

It is well established that retinal neurogenesis in mouse embryos requires the activation of Notch signaling, but is independent of the Wnt signaling pathway. We found that genetic inactivation of Sfrp1 and Sfrp2, two postulated Wnt antagonists, perturbs retinal neurogenesis. In retinas from Sfrp1(-/-); Sfrp2(-/-) embryos, Notch signaling was transiently upregulated because Sfrps bind ADAM10 metalloprotease and downregulate its activity, an important step in Notch activation. The proteolysis of other ADAM10 substrates, including APP, was consistently altered in Sfrp mutants, whereas pharmacological inhibition of ADAM10 partially rescued the Sfrp1(-/-); Sfrp2(-/-) retinal phenotype. Conversely, ectopic Sfrp1 expression in the Drosophila wing imaginal disc prevented the expression of Notch targets, and this was restored by the coexpression of Kuzbanian, the Drosophila ADAM10 homolog. Together, these data indicate that Sfrps inhibit the ADAM10 metalloprotease, which might have important implications in pathological events, including cancer and Alzheimer's disease.

Binding of procollagen C-proteinase enhancer-1 (PCPE-1) to heparin/heparan sulfate: properties and role in PCPE-1 interaction with cells

Procollagen C-proteinase enhancer-1 (PCPE-1) is an extracellular matrix (ECM) glycoprotein that can stimulate procollagen processing by procollagen C-proteinases (PCPs) such as bone morphogenetic protein-1 (BMP-1). The PCPs can process additional extracellular protein precursors and play fundamental roles in developmental processes and assembly of the ECM. The stimulatory activity of PCPE-1 is restricted to the processing of fibrillar procollagens, suggesting PCPE-1 is a specific regulator of collagen deposition. PCPE-1 consists of two CUB domains that bind to the procollagen C-propeptides and are required for PCP enhancing activity, and one NTR domain that binds heparin. To understand the biological role of the NTR domain, we performed surface plasmon resonance (SPR) binding assays, cell attachment assays as well as immunofluorescence and activity assays, all indicating that the NTR domain can mediate PCPE-1 binding to cell surface heparan sulfate proteoglycans (HSPGs). The SPR data revealed binding affinities to heparin/HSPGs in the high nanomolar range and dependence on calcium. Both 3T3 mouse fibroblasts and human embryonic kidney cells (HEK-293) attached to PCPE-1, an interaction that was inhibited by heparin. Cell attachment was also inhibited by an NTR-specific antibody and the NTR fragment. Immunofluorescence analysis revealed that PCPE-Flag binds to mouse fibroblasts and heparin competes for this binding. Cell-associated PCPE-Flag stimulated procollagen processing by BMP-1 several fold. Our data suggest that through interaction with cell surface HSPGs, the NTR domain can anchor PCPE-1 to the cell membrane, permitting pericellular enhancement of PCP activity. This points to the cell surface as a physiological site of PCPE-1 action.

Role of the netrin-like domain of procollagen C-proteinase enhancer-1 in the control of metalloproteinase activity

The netrin-like (NTR) domain is a feature of several extracellular proteins, most notably the N-terminal domain of tissue inhibitors of metalloproteinases (TIMPs), where it functions as a strong inhibitor of matrix metalloproteinases and some other members of the metzincin superfamily. The presence of a C-terminal NTR domain in procollagen C-proteinase enhancers (PCPEs), proteins that stimulate the activity of astacin-like tolloid proteinases, raises the possibility that this might also have inhibitory activity. Here we show that both long and short forms of the PCPE-1 NTR domain, the latter beginning at the N-terminal cysteine known to be critical for TIMP activity, show no inhibition, at micromolar concentrations, of several members of the metzincin superfamily, including matrix metalloproteinase-2, bone morphogenetic protein-1 (a tolloid proteinase), and different ADAMTS (a disintegrin and a metalloproteinase with thrombospondin motifs) proteinases from the adamalysin family. In contrast, we report that the NTR domain within PCPE-1 leads to superstimulation of bone morphogenetic protein-1 activity in the presence of heparin and heparan sulfate. These observations point to a new mechanism whereby binding to cell surface-associated or extracellular heparin-like sulfated glycosaminoglycans might provide a means to accelerate procollagen processing in specific cellular and extracellular microenvironments.

Metalloproteases and the degradome

Metalloproteases comprise a heterogeneous group of proteolytic enzymes whose main characteristic is the utilization of a metal ion to polarize a water molecule and perform hydrolytic reactions. These enzymes represent the most densely populated catalytic class of proteases in many organisms and play essential roles in multiple biological processes. In this chapter, we will first present a general description of the complexity of metalloproteases in the context of the degradome, which is defined as the complete set of protease genes encoded by the genome of a certain organism. We will also discuss the functional relevance of these enzymes in a large variety of biological and pathological conditions. Finally, we will analyze in more detail three families of metalloproteases: ADAMs (a disintegrin and metalloproteinase), ADAMTSs (ADAMs with thrombospondin domains), and MMPs (matrix metalloproteinases) which have a growing relevance in a number of human pathologies including cancer, arthritis, neurodegenerative disorders, and cardiovascular diseases.

The netrin protein family

The netrins are a family of extracellular proteins that direct cell and axon migration during embryogenesis.

The name netrin is derived from the Sanskrit Netr, meaning 'guide'. Netrins are a family of extracellular proteins that direct cell and axon migration during embryogenesis. Three secreted netrins (netrins 1, 3 and 4), and two glycosylphosphatidylinositol (GPI)-anchored membrane proteins, netrins G1 and G2, have been identified in mammals. The secreted netrins are bifunctional, acting as attractants for some cell types and repellents for others. Receptors for the secreted netrins include the Deleted in Colorectal Cancer (DCC) family, the Down's syndrome cell adhesion molecule (DSCAM), and the UNC-5 homolog family: Unc5A, B, C and D in mammals. Netrin Gs do not appear to interact with these receptors, but regulate synaptic interactions between neurons by binding to the transmembrane netrin G ligands NGL1 and 2. The chemotropic function of secreted netrins has been best characterized with regard to axon guidance during the development of the nervous system. Extending axons are tipped by a flattened, membranous structure called the growth cone. Multiple extracellular guidance cues direct axonal growth cones to their ultimate targets where synapses form. Such cues can be locally derived (short-range), or can be secreted diffusible cues that allow target cells to signal axons from a distance (long-range). The secreted netrins function as short-range and long-range guidance cues in different circumstances. In addition to directing cell migration, functional roles for netrins have been identified in the regulation of cell adhesion, the maturation of cell morphology, cell survival and tumorigenesis.

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.

The role of matrix metalloproteinases in the pathophysiology and progression of human nervous system malignancies: a chance for the development of targeted therapeutic approaches?

BACKGROUND

Matrix metalloproteinases (MMPs) are a group of zinc- dependent endopeptidases involved in the degradation of extracellular matrix components. MMPs have been implicated in a wide variety of physiological processes, such as angiogenesis, wound healing and tissue remodeling. However, recent studies have revealed a significant role for MMPs in tumorigenesis pathophysiology and prediction of patients' clinical outcome. Alterations in the regulation of MMP expression are thought to play an important role in the development and progression of central nervous system (CNS) malignancies.

OBJECTIVE/METHODS

This study provides an up-to-date review of the literature on the pathophysiologic involvement of MMPs in the development and progression of human CNS malignancies, as well as the potential use of natural and/or synthetic MMP-inhibitors (MMPIs) as a targeted therapeutic approach to this group of neoplasms.

RESULTS/CONCLUSIONS

The currently available data provide clear evidence for the involvement of MMPs in the pathophysiology of astrocytomas, glioblastomas, meningiomas, medulloblastomas/primitive neuroectodermal tumors and pituitary tumors. The use of MMPIs in the treatment of CNS malignancies has, until now, reached controversial (but mainly disappointing) results that can nevertheless provide the basis for further investigation. The co-administration of other agents, the use of surgery and/or radiation, and elimination of the MMPIs-induced adverse effects, as well as the use of antisense technology, might be the tools by which the natural and synthetic MMPIs could find their place in everyday clinical practice for the management of CNS malignancies.

Different patterns of human serum procollagen C-proteinase enhancer1 (PCPE1)

BACKGROUND

Procollagen C-proteinase (PCP) enhancer 1 (PCPE1) specifically stimulates the PCP activity of bone morphogenic protein 1 (BMP1), a multisubstrate enzyme essential to the formation of extracellular matrix, via direct interaction with its substrate procollagen. Thus, in this study we sought to determine if serum PCPE1 (sPCPE1), a regulator of collagen formation, can be used as a diagnostic marker of collagen metabolism/remodeling.

METHODS

We developed a method to track sPCPE1, and the findings were applied to evaluate the association of sPCPE1 glycopatterns with growth and presence of bone complication.

RESULTS

Isoelectric focusing revealed that sPCPE1 has a multi-band appearance and that sPCPE1 glycopatterns are due to an N-linked oligosaccharide decorated with sialic acid. Evaluation of PCPE1 glycopatterns in different groups of subjects revealed a significant difference among preterm babies, term babies, and adults. Furthermore, in adults with breast cancer, the glycopattern intensity correlated with the presence of bone metastasis.

CONCLUSIONS

The sPCPE1 glycopattern appears to be associated with the physiological and pathological states of bone. This study shows for the first time sPCPE1 glycopattern and suggest that changes in glycosylation of the protein may be in correlation with collagen metabolism. Studies are currently underway to determine its appearance in the serum of normal population on one hand and its appearance during growth and metabolic bone diseases on the other hand.

Lymphocyte/macrophage interactions: biomaterial surface-dependent cytokine, chemokine, and matrix protein production

The role of lymphocytes in the biological response to synthetic polymers is poorly understood despite the transient appearance of lymphocytes at the biomaterial implant site. To investigate cytokines, chemokines, and extracellular matrix (ECM) proteins produced by lymphocytes and macrophages in response to biomaterial surfaces, human peripheral blood monocytes and lymphocytes were co-cultured on polyethylene terephthalate (PET)-based material surfaces displaying distinct hydrophobic, hydrophilic/neutral, hydrophilic/anionic, and hydrophilic/cationic chemistries. Antibody array screening showed the majority of detected proteins are inflammatory mediators that guide the early inflammatory phases of wound healing. Proteomic ELISA quantification and adherent cell analysis were performed after 3, 7, and 10 days of culture. IL-2 and IFN-gamma were not detected in any co-cultures suggesting lack of lymphocyte activation. The hydrophilic/neutral surfaces increased IL-8 relative to the hydrophobic PET surface (p < 0.05). The hydrophilic/anionic surfaces promoted increased TNF-alpha over hydrophobic and cationic surfaces and increased MIP-1beta compared to hydrophobic surfaces (p < 0.05). Since enhanced macrophage fusion was observed on hydrophilic/anionic surfaces, the production of these cytokines likely plays an important role in the fusion process. The hydrophilic/cationic surface promoted IL-10 production and increased matrix metalloproteinase (MMP)-9/tissue inhibitor of MMP (TIMP) relative to hydrophilic/neutral and anionic surfaces (p < 0.05). These results suggest hydrophilic/neutral and anionic surfaces promote pro-inflammatory responses and reduced degradation of the ECM, whereas the hydrophilic/cationic surfaces induce an anti-inflammatory response and greater MMP-9/TIMP with an enhanced potential for ECM breakdown. The study also underscores the usefulness of protein arrays in assessing the role of soluble mediators in the inflammatory response to biomaterials.

Mutations in mammalian tolloid-like 1 gene detected in adult patients with ASD

Atrial septal defect (ASD) is an incomplete septation of atria in human heart causing circulatory problems. Its frequency is estimated at one per 10 000. Actions of numerous genes have been linked to heart development. However, no single gene defect causing ASD has yet been identified. Incomplete heart septation similar to ASD was reported in transgenic mice with both inactive alleles of gene encoding mammalian zinc metalloprotease a mammalian tolloid-like 1 (tll1). Here, we have screened 19 ASD patients and 15 healthy age-matched individuals for mutations in TLL1 gene. All 22 exons were analyzed exon by exon for heteroduplex formation. Subsequently, DNA fragments forming heteroduplexes were sequenced. In four nonrelated patients, three missense mutations in coding sequence, and one single base change in the 5'UTR have been detected. Two mutations (Met182Leu, and Ala238Val) were detected in ASD patients with the same clinical phenotype. As the second mutation locates immediately upstream of the catalytic zinc-binding signature, it might change the enzyme substrate specificity. The third change, Leu627Val in the CUB3 domain, has been found in an ASD patient with interatrial septum aneurysm in addition to ASD. The CUB3 domain is important for substrate-specific recognition. In the remaining 15 patients as well as in 15 reference samples numerous base substitutions, deletions, and insertions have been detected, but no mutations changing the coding sequence have been found. Lack of mutations in relation to ASD of these patients could possibly be because of genetic heterogeneity of the syndrome.

Progress in matrix metalloproteinase research

Matrix metalloproteinases (MMPs) are now acknowledged as key players in the regulation of both cell-cell and cell-extracellular matrix interactions. They are involved in modifying matrix structure, growth factor availability and the function of cell surface signalling systems, with consequent effects on cellular differentiation, proliferation and apoptosis. They play central roles in morphogenesis, wound healing, tissue repair and remodelling in response to injury and in the progression of diseases such as arthritis, cancer and cardiovascular disease. Because of their wide spectrum of activities and expression sites, the elucidation of their potential as drug targets in disease or as important features of the repair process will be dependent upon careful analysis of their role in different cellular locations and at different disease stages. Novel approaches to the specific regulation of individual MMPs in different contexts are also being developed.

Dynamic characterisation of the netrin-like domain of human type 1 procollagen C-proteinase enhancer and comparison to the N-terminal domain of tissue inhibitor of metalloproteinases (TIMP)

The backbone mobility of the C-terminal domain of procollagen C-proteinase enhancer (NTR PCOLCE1), part of a connective tissue glycoprotein, was determined using 15N NMR spectroscopy. NTR PCOLCE1 has been shown to be a netrin-like domain and adopts an OB-fold such as that found in the N-terminal domain of tissue inhibitors of metalloproteinases-1 (N-TIMP-1), N-TIMP-2, the laminin-binding domain of agrin and the C-terminal domain of complement protein C5. NMR relaxation dynamics of NTR PCOLCE1 highlight conformational flexibility in the N-terminus, strand A and the proximal CD loop. This region in N-TIMP is known to be essential for inhibitory activity against the matrix metalloproteinases and suggests that this region is of equal importance for NTR PCOLCE1, although the specific functional activity of the NTR PCOLCE1 domain is still unknown. Dynamics observed within the structural core of NTR PCOLCE1 that are not observed in N-TIMP molecules suggest that although the two domains have a similar architecture, the NTR PCOLCE1 domain will show different thermodynamic properties on binding and hence the target molecule could be somewhat different from that observed for the TIMPs. ModelFree order parameters show that NTR PCOLCE1 has more flexibility than both N-TIMP-1 and N-TIMP-2.

Matrix metalloproteinases and their inhibitors in vascular remodeling and vascular disease

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that degrade various components of the extracellular matrix (ECM). Members of the MMP family include collagenases, gelatinases, stromelysins, matrilysins and membrane-type MMPs. ProMMPs are cleaved into active forms that promote degradation of ECM proteins. Also, recent evidence suggests direct or indirect effects of MMPs on ion channels in the endothelium and vascular smooth muscle, and on other mechanisms of vascular relaxation/contraction. Endogenous tissue inhibitors of metalloproteinases (TIMPs) reduce excessive proteolytic ECM degradation by MMPs. The balance between MMPs and TIMPs plays a major role in vascular remodeling, angiogenesis, and the uterine and systemic vasodilation during normal pregnancy. An imbalance in the MMPs/TIMPs activity ratio may underlie the pathogenesis of vascular diseases such as abdominal aortic aneurysm, varicose veins, hypertension and preeclampsia. Downregulation of MMPs using genetic manipulations of endogenous TIMPs, or synthetic pharmacological inhibitors such as BB-94 (Batimastat) and doxycycline, and Ro-28-2653, a more specific inhibitor of gelatinases and membrane type 1-MMP, could be beneficial in reducing the MMP-mediated vascular dysfunction and the progressive vessel wall damage associated with vascular disease.

Atrial extracellular matrix remodelling in patients with atrial fibrillation

Atrial fibrillation (AF) is the most frequent clinical arrhythmia. Atrial fibrosis is an important factor in initiating and maintaining AF. However, the collagen turnover and its regulation in AF has not been completely elucidated. We tested the hypothesis that the extracellular matrix changes are more severe in patients with permanent AF in comparison with those in patients in sinus rhythm (SR). Intraoperative biopsies from the right atrial appendages (RAA) and free walls (RFW) from 24 patients with AF undergoing a mini-Maze procedure and 24 patients in SR were investigated with qualitative and quantitative immunofluorescent and Western blot analyses. As compared with SR, all patients with AF exhibited dysregulations in collagen type I and type III synthesis/degradation. Tissue inhibitors of metalloproteinases (TIMP2) was significantly enhanced only in RAA-AF. As compared with SR, collagen VI, matrix metalloproteinases MMP2, MMP9 and TIMP1 were significantly increased while TIMP3 and TIMP4 remained unchanged in all AF groups. Reversion-inducing cysteine-rich protein with Kazal motifs (RECK), a newly discovered MMPs inhibitor, was elevated in RFW as compared to RAA-AF (P<0.05) and RFW-SR (P<0.05). The level of transforming growth factor (TGF)-β1 was higher in AF than SR. Smad2 and phosphorylated Smad2 showed an elevation in RFW-AF as compared to RFW-SR, RAA-AF, and RAA-SR groups (P<0.05). Conclusions: Atrial fibrosis in AF is characterized by severe alterations in collagen I and III synthesis/degradation associated with disturbed MMP/TIMP systems and increased levels of RECK. TGF-β1 contributes to atrial fibrosis via TGF-β1-Smad pathway by phospho-rylating Smad2. These processes culminate in accumulations of fibrillar and non-fibrillar collagens leading to excessive atrial fibrosis and maintainance of AF.

Procollagen C-proteinase enhancer-1 (PCPE-1) interacts with beta2-microglobulin (beta2-m) and may help initiate beta2-m amyloid fibril formation in connective tissues

Dialysis related amyloidosis (DRA) is a progressive and serious complication in patients under long-term hemodialysis and mainly leads to osteo-articular diseases. Although beta(2)-microglobulin (beta2-m) is the major structural component of beta2-m amyloid fibrils, the initiation of amyloid formation is not clearly understood. Here, we have identified procollagen C-proteinase enhancer-1 (PCPE-1) as a new interacting protein with beta2-m by screening a human synovium cDNA library. The interaction of beta2-m with full-length PCPE-1 was confirmed by immunoprecipitation, solid-phase binding and pull-down assays. By yeast two-hybrid analysis and pull-down assay, beta2-m appeared to interact with PCPE-1 via the NTR (netrin-like) domain and not via the CUB (C1r/C1s, Uegf and BMP-1) domain region. In synovial tissues derived from hemodialysis patients with DRA, beta2-m co-localized and formed a complex with PCPE-1. beta2-m did not alter the basal activity of bone morphogenetic protein-1/procollagen C-proteinase (BMP-1/PCP) nor BMP-1/PCP activity enhanced by PCPE-1. PCPE-1 did not stimulate beta2-m amyloid fibril formation from monomeric beta2-m in vitro under acidic and neutral conditions as revealed by thioflavin T fluorescence spectroscopy and electron microscopy. Since PCPE-1 is abundantly expressed in connective tissues rich in type I collagen, it may be involved in the initial accumulation of beta2-m in selected tissues such as tendon, synovium and bone. Furthermore, since such preferential deposition of beta2-m may be linked to subsequent beta2-m amyloid fibril formation, the disruption of the interaction between beta2-m and PCPE-1 may prevent beta2-m amyloid fibril formation and therefore PCPE-1 could be a new target for the treatment of DRA.

The bone morphogenetic protein 1/Tolloid-like metalloproteinases

A decade ago, bone morphogenetic protein 1 (BMP1) was shown to provide the activity necessary for proteolytic removal of the C-propeptides of procollagens I-III: precursors of the major fibrillar collagens. Subsequent studies have shown BMP1 to be the prototype of a small group of extracellular metalloproteinases that play manifold roles in regulating formation of the extracellular matrix (ECM). Soon after initial cloning of BMP1, genetic studies showed the related Drosophila proteinase Tolloid (TLD) to be necessary for the formation of the dorsal-ventral axis in early embryogenesis. It is now clear that the BMP1/TLD-like proteinases, conserved in species ranging from Drosophila to humans, act in dorsal-ventral patterning via activation of transforming growth factor beta (TGFbeta)-like proteins BMP2, BMP4 (vertebrates) and decapentaplegic (arthropods). More recently, it has become apparent that the BMP1/TLD-like proteinases are activators of a broader subset of the TGFbeta superfamily of proteins, with implications that these proteinases may be key in orchestrating the formation of ECM with growth factor activation and BMP signaling in morphogenetic processes.

Collagen matrix deposition is dramatically enhancedin vitrowhen crowded with charged macromolecules: The biological relevance of the excluded volume effect

The excluded volume effect (EVE) rules all life processes. It is created by macromolecules that occupy a given volume thereby confining other molecules to the remaining space with large consequences on reaction kinetics and molecular assembly. Implementing EVE in fibroblast culture accelerated conversion of procollagen to collagen by procollagen C-proteinase (PCP/BMP-1) and proteolytic modification of its allosteric regulator, PCOLCE1. This led to a 20-30- and 3-6-fold increased collagen deposition in two- and three-dimensional cultures, respectively, and creation of crosslinked collagen footprints beneath cells. Important parameters correlating with accelerated deposition were hydrodynamic radius of macromolecules and their negative charge density.

Imaging probes targeting matrix metalloproteinases

During the past few years, several imaging probes targeting matrix metalloproteinases (MMPs) have been developed. Most of these probes have been validated in animal models. Overall, results derived from most of these studies have been disappointing. Whether or not this relates to shortcomings of the imaging probes used or to the set-up of the reported studies is currently unclear. Firstly, MMPs targeted in these studies, MMP-1, -2 and -9, are cell secreted and their expression is known to vary extensively within one tumor type, depending on the stage of development of the tumor and on the presence of naturally occurring TIMPs. Given the lack of data on the levels of MMP expression by incoculated tumor tissue at the time of imaging in most studies reported, it cannot be excluded that the negative results reported are, in fact, false-negative imaging results. Secondly, given that most of the agents used for imaging are intrinsically broad-spectrum agents, their higher affinity for specific subsets of MMPs does not necessarily imply that a positive imaging result also corresponds to overexpression of specific subsets of MMPs, as suggested in some papers published. Accordingly, well-characterized tumor models need to be developed for the purpose of validating currently available, as well as future, MMP-imaging probes. So far, only 111In-DTPA-N-TIMP-2 has been injected in patients, respectively suffering from Kaposi Sarcoma. Imaging results obtained with this agent proved disappointing. Imaging results obtained with other MMP-targeting probes in patients are awaited.

Proteomics discovery of metalloproteinase substrates in the cellular context by iTRAQ labeling reveals a diverse MMP-2 substrate degradome

Elucidation of protease substrate degradomes is essential for understanding the function of proteolytic pathways in the protease web and how proteases regulate cell function. We identified matrix metalloproteinase-2 (MMP-2) cleaved proteins, solubilized pericellular matrix, and shed cellular ectodomains in the cellular context using a new multiplex proteomics approach. Tryptic peptides of intact and cleaved proteins, collected from conditioned culture medium of Mmp2(-/-) fibroblasts expressing low levels of transfected active human MMP-2 at different time points, were amine-labeled with iTRAQ mass tags. Peptide identification and relative quantitation between active and inactive protease transfectants were achieved following tag fragmentation during tandem MS. Known substrates of MMP-2 were identified thereby validating this technique with many novel MMP-2 substrates including the CX(3)CL1 chemokine fractalkine, osteopontin, galectin-1, and HSP90alpha also being identified and biochemically confirmed. In comparison with ICAT-labeling and quantitation, 8-9-fold more proteins and substrates were identified by iTRAQ. "Peptide mapping," the location of multiple peptides identified within a particular protein by iTRAQ in combination with their relative abundance ratios, enabled the domain shed and general location of the cleavage site to be identified in the native cellular substrate. Hence this advance in degradomics cell-based screens for native protein substrates casts new light on the roles for proteases in cell function.

Matrix metalloproteinases in lung: multiple, multifarious, and multifaceted

The matrix metalloproteinases (MMPs), a family of 25 secreted and cell surface-bound neutral proteinases, process a large array of extracellular and cell surface proteins under normal and pathological conditions. MMPs play critical roles in lung organogenesis, but their expression, for the most part, is downregulated after generation of the alveoli. Our knowledge about the resurgence of the MMPs that occurs in most inflammatory diseases of the lung is rapidly expanding. Although not all members of the MMP family are found within the lung tissue, many are upregulated during the acute and chronic phases of these diseases. Furthermore, potential MMP targets in the lung include all structural proteins in the extracellular matrix (ECM), cell adhesion molecules, growth factors, cytokines, and chemokines. However, what is less known is the role of MMP proteolysis in modulating the function of these substrates in vivo. Because of their multiplicity and substantial substrate overlap, MMPs are thought to have redundant functions. However, as we explore in this review, such redundancy most likely evolved as a necessary compensatory mechanism given the critical regulatory importance of MMPs. While inhibition of MMPs has been proposed as a therapeutic option in a variety of inflammatory lung conditions, a complete understanding of the biology of these complex enzymes is needed before we can reasonably consider them as therapeutic targets.

Procollagen C proteinase enhancer 1 genes are important determinants of the mechanical properties and geometry of bone and the ultrastructure of connective tissues

Procollagen C proteinases (pCPs) cleave type I to III procollagen C propeptides as a necessary step in assembling the major fibrous components of vertebrate extracellular matrix. The protein PCOLCE1 (procollagen C proteinase enhancer 1) is not a proteinase but can enhance the activity of pCPs approximately 10-fold in vitro and has reported roles in inhibiting other proteinases and in growth control. Here we have generated mice with null alleles of the PCOLCE1 gene, Pcolce, to ascertain in vivo roles. Although Pcolce-/- mice are viable and fertile, Pcolce-/- male, but not female, long bones are more massive and have altered geometries that increase resistance to loading, compared to wild type. Mechanical testing indicated inferior material properties of Pcolce-/- male long bone, apparently compensated for by the adaptive changes in bone geometry. Male and female Pcolce-/- vertebrae both appeared to compensate for inferior material properties with thickened and more numerous trabeculae and had a uniquely altered morphology in deposited mineral. Ultrastructurally, Pcolce-/- mice had profoundly abnormal collagen fibrils in both mineralized and nonmineralized tissues. In Pcolce-/- tendon, 100% of collagen fibrils had deranged morphologies, indicating marked functional effects in this tissue. Thus, PCOLCE1 is an important determinant of bone mechanical properties and geometry and of collagen fibril morphology in mammals, and the human PCOLCE1 gene is identified as a candidate for phenotypes with defects in such attributes in humans.

Matrix metalloproteinases in cancer: comparison of known and novel aspects of their inhibition as a therapeutic approach

Matrix dissolution is a crucial step during tumor progression that converts a premalignant cell to an overtly malignant one. Main players in this step are the various matrix metalloproteinases (MMPs), which differ in substrate specificity and tissue distribution, and thereby also differ in presence and function during various stages of initial and systemic tumor spread. Accordingly, the inhibition of MMP synthesis and/or activity represents novel potential therapeutic strategies for the treatment of cancer patients. Considerable work has already been carried out on synthetic inhibitors of MMP activity, but with little or even adverse effects in recent clinical studies. The reasons may be inappropriate patient populations in too advanced tumor stages, or inappropriate enzymes as targets for inhibition. Upregulation of endogenous tissue inhibitors of MMP (TIMPs) also provided ambiguous results, since TIMPs possess biologic functions in addition to MMP inhibition, for example, TIMP-2 is a main player in the MMP-2 activation cascade. This may explain, at least in part, the adverse effects of TIMP application/upregulation. Other strategies have been sought in order to overcome these problems. These include the downregulation of MMP transcription by cytokines. However, the effects of cytokines (other than MMP inhibition) may also limit the use of this approach. Finally, empiric evidence for control and modulation of MMP transcription and/or activation by several naturally occurring substances, such as flavonoids, green tea polyphenols and curcumin, represent novel options for the control of MMP activity even in early tumor stages. Additionally, these substances have little or no toxic side effects and good bioavailability, and therefore their continuing analysis provides intriguing insight into tumor pathophysiology and possibly new therapeutic options.

Targeting matrix metalloproteases to improve cutaneous wound healing

Wound repair is a physiological event in which tissue injury initiates a repair process leading to restoration of structure and function of the tissue. Cutaneous wound repair can be divided into a series of overlapping phases including formation of fibrin clot, inflammatory response, granulation tissue formation incorporating re-epithelialisation and angiogenesis and finally, matrix formation and remodelling. Matrix metalloproteases (MMPs) are a family of neutral proteases that play a vital role throughout the entire wound healing process. They regulate inflammation, degrade the extracellular matrix (ECM) to facilitate the migration of cells and remodel the new ECM. However, excessive MMP activity contributes to the development of chronic wounds. Selective control of MMP activity may prove to be a valuable therapeutic approach to promote healing of chronic ulcers. Recent evidence indicates that the anticoagulant, activated protein C may be useful in the treatment of non-healing wounds by preventing excessive protease activity through inhibition of inflammation and selectively increasing MMP-2 activity to enhance angiogenesis and re-epithelialisation.

Developmental roles of the BMP1/TLD metalloproteinases

The astacin family (M12A) of the metzincin subclan MA(M) of metalloproteinases has been detected in developing and mature individuals of species that range from hydra to humans. Functions of this family of metalloproteinase vary from digestive degradation of polypeptides, to biosynthetic processing of extracellular proteins, to activation of growth factors. This review will focus on a small subgroup of the astacin family; the bone morphogenetic protein 1 (BMP1)/Tolloid (TLD)-like metalloproteinases. In vertebrates, the BMP1/TLD-like metalloproteinases play key roles in regulating formation of the extracellular matrix (ECM) via biosynthetic processing of various precursor proteins into mature functional enzymes, structural proteins, and proteins involved in initiating mineralization of the ECM of hard tissues. Roles in ECM formation include: processing of the C-propeptides of procollagens types I-III, to yield the major fibrous components of vertebrate ECM; proteolytic activation of the enzyme lysyl oxidase, necessary to formation of covalent cross-links in collagen and elastic fibers; processing of NH2-terminal globular domains and C-propeptides of types V and XI procollagen chains to yield monomers that are incorporated into and control the diameters of collagen type I and II fibrils, respectively; processing of precursors for laminin 5 and collagen type VII, both of which are involved in securing epidermis to underlying dermis; and maturation of small leucine-rich proteoglycans. The BMP1/TLD-related metalloproteinases are also capable of activating the vertebrate transforming growth factor-beta (TGF-beta)-like "chalones" growth differentiation factor 8 (GDF8, also known as myostatin), and GDF11 (also known as BMP11), involved in negative feedback inhibition of muscle and neural tissue growth, respectively; by freeing them from noncovalent latent complexes with their cleaved prodomains. BMP1/TLD-like proteinases also liberate the vertebrate TGF-beta-like morphogens BMP2 and 4 and their invertebrate ortholog decapentaplegic, from latent complexes with the vertebrate extracellular antagonist chordin and its invertebrate ortholog short gastrulation (SOG), respectively. The result is formation of the BMP signaling gradients that form the dorsal-ventral axis in embryogenesis. Thus, BMP1/TLD-like proteinases appear to be key to regulating and orchestrating formation of the ECM and signaling by various TGF-beta-like proteins in morphogenetic and homeostatic events.

Diverse biological functions of extracellular collagen processing enzymes

Collagens are abundant proteins in higher organisms, and are formed by a complex biosynthetic pathway involving intracellular and extracellular post-translational modifications. Starting from simple soluble precursors, this interesting pathway produces insoluble functional fibrillar and non-fibrillar elements of the extracellular matrix. The present review highlights recent progress and new insights into biological regulation of extracellular procollagen processing, and some novel functions of byproducts of these extracellular enzymatic transformations. These findings underscore the notion that released propeptides and other proteolytic products of extracellular matrix proteins have important biological functions, and that structural proteins are multifunctional. An emerging concept is that a dynamic interplay exists between extracellular products and byproducts with cells that helps to maintain normal cellular phenotypes and tissue integrity.

Melanocyte and keratinocyte carcinogenesis: p53 family protein activities and intersecting mRNA expression profiles

Melanocytes and keratinocytes were analyzed for potential roles of p53, p73, and p63 tumor suppressor family proteins and of malignancy-specific gene expression changes in the etiology of multi-step cancer. Melanocytes expressed deltaNp73alpha, two p63 isoforms and p53. Although p21 and Noxa mRNA levels increased following DNA damage, p53 family member binding to p21 and Noxa DNA probes was undetectable, suggesting p53 family-independent responses. In contrast, keratinocytes expressed multiple isoforms each of p73 and p63 that were induced to bind p21 and Noxa DNA probes after ionizing (IR) or after ultraviolet B (UVB) irradiation, correlating with p21 and Noxa mRNA induction and with apoptosis. Interestingly, IR-resistant malignant melanocytes and keratinocytes both exhibited Noxa mRNA induction after UVB treatment, correlating with DNA binding of p53 family proteins to the Noxa probe only in keratinocytes. To uncover other malignancy-specific events, we queried mouse initiated keratinocyte clones for early changes that were exacerbated in malignant derivatives and also differentially expressed in human advanced melanoma versus normal melanocytes. Using a new method for ranking and normalization of microarray data for 5000 probe sets, 27 upregulated and 13 downregulated genes satisfied our query. Of these, the majority was associated with late-stage human cancers and six were novel genes. Thus, clonal lineage mouse models representing early through late cancer progression stages may inform the focus on early, potentially causal events from microarray studies of human cancers, facilitating prognosis and molecular therapy.

Intracellular reactive oxygen species activate Src tyrosine kinase during cell adhesion and anchorage-dependent cell growth

Src tyrosine kinases are central components of adhesive responses and are required for cell spreading onto the extracellular matrix. Among other intracellular messengers elicited by integrin ligation are reactive oxygen species, which act as synergistic mediators of cytoskeleton rearrangement and cell spreading. We report that after integrin ligation, the tyrosine kinase Src is oxidized and activated. Src displays an early activation phase, concurrent with focal adhesion formation and driven mainly by Tyr527 dephosphorylation, and a late phase, concomitant with reactive oxygen species production, cell spreading, and integrin-elicited kinase oxidation. In addition, our results suggest that reactive oxygen species are key mediators of in vitro and in vivo v-Src tumorigenic properties, as both antioxidant treatments and the oxidant-insensitive C245A and C487A Src mutants greatly decrease invasivity, serum-independent and anchorage-independent growth, and tumor onset. Therefore we propose that, in addition to the known phosphorylation/dephosphorylation circuitry, redox regulation of Src activity is required during both cell attachment to the extracellular matrix and tumorigenesis.