Functional genetic mouse models: promising tools for investigation of the proteolytic internet

Cancer Susceptibility Models in Protease-Deficient Mice

For decades, proteases have been associated with cancer progression due to the ability of some members of this large group of enzymes to degrade tumor cell surroundings, thereby facilitating cancer invasion and dissemination. However, the generation of mouse models deficient in proteases has revealed the existence of a great variety of functions among proteolytic enzymes in cancer biology, including important tumor-suppressive roles. Therefore, in this chapter, we describe methods to chemically induce different types of cancer (lung adenocarcinoma, hepatocellular carcinoma, oral and esophageal carcinoma, colorectal carcinoma, skin cancer, and fibrosarcoma) in genetically modified mouse models to efficiently evaluate the specific pro- or antitumoral function of proteases in cancer.

Systemic Ablation of MMP-9 Triggers Invasive Growth and Metastasis of Pancreatic Cancer via Deregulation of IL6 Expression in the Bone Marrow

Matrix metalloproteinase 9 (MMP-9/Gelatinase B) is overexpressed in pancreatic ductal adenocarcinoma (PDAC) and plays a central role in tumor cell invasion and metastasis. Here we complemented mechanistic insights in the cancer biology of MMP-9 and investigated the effects of specific long-term loss-of-function, by genetic ablation, of MMP-9 on PDAC initiation and progression in the well-established KPC mouse model of spontaneous PDAC. Tumor growth and progression were analyzed by histopathology and IHC. Invasive growth of PDAC cells was analyzed by both in vitro (proliferation, survival, migration, invasion assays) and in vivo (experimental metastasis assays) methods. Retroviral shRNAi was used to knockdown target genes (MMP-9, IL6R). Gene expression was analyzed by qRT-PCR, immunoblot, ELISA, in situ hybridization, and zymography. PDAC tumors from MMP-9-deficient mice were dramatically larger, more invasive, and contained more stroma. Yet, ablation of MMP-9 in PDAC cells did not directly promote invasive growth. Interestingly, systemic ablation of MMP-9 led to increased IL6 levels resulting from abrogation of MMP-9-dependent SCF signaling in the bone marrow. IL6 levels in MMP-9^-/- mice were sufficient to induce invasive growth and STAT3 activation in PDAC cells via IL6 receptor (IL6R). Interference with IL6R blocked the increased invasion and metastasis of PDAC cells in MMP-9-deficient hosts. In conclusion, ablation of systemic MMP-9 initiated fatal communication between maintenance of physiological functions of MMP-9 in the bone marrow and invasive growth of PDAC via the IL6/IL6R/STAT3 axis.

IMPLICATIONS

Thus, the beneficial effects of host MMP-9 on PDAC are an important caveat for the use of systemic MMP-9 inhibitors in cancer. Mol Cancer Res; 14(11); 1147-58. ©2016 AACR.

Selective Allosteric Inhibition of MMP9 Is Efficacious in Preclinical Models of Ulcerative Colitis and Colorectal Cancer

Expression of matrix metalloproteinase 9 (MMP9) is elevated in a variety of inflammatory and oncology indications, including ulcerative colitis and colorectal cancer. MMP9 is a downstream effector and an upstream mediator of pathways involved in growth and inflammation, and has long been viewed as a promising therapeutic target. However, previous efforts to target matrix metalloproteinases (MMPs), including MMP9, have utilized broad-spectrum or semi-selective inhibitors. While some of these drugs showed signs of efficacy in patients, all MMP-targeted inhibitors have been hampered by dose-limiting toxicity or insufficient clinical benefit, likely due to their lack of specificity. Here, we show that selective inhibition of MMP9 did not induce musculoskeletal syndrome (a characteristic toxicity of pan-MMP inhibitors) in a rat model, but did reduce disease severity in a dextran sodium sulfate-induced mouse model of ulcerative colitis. We also found that MMP9 inhibition decreased tumor growth and metastases incidence in a surgical orthotopic xenograft model of colorectal carcinoma, and that inhibition of either tumor- or stroma-derived MMP9 was sufficient to reduce primary tumor growth. Collectively, these data suggest that selective MMP9 inhibition is a promising therapeutic strategy for treatment of inflammatory and oncology indications in which MMP9 is upregulated and is associated with disease pathology, such as ulcerative colitis and colorectal cancer. In addition, we report the development of a potent and highly selective allosteric MMP9 inhibitor, the humanized monoclonal antibody GS-5745, which can be used to evaluate the therapeutic potential of MMP9 inhibition in patients.

In vivo assessment of protease dynamics in cutaneous wound healing by degradomics analysis of porcine wound exudates

Proteases control complex tissue responses by modulating inflammation, cell proliferation and migration, and matrix remodeling. All these processes are orchestrated in cutaneous wound healing to restore the skin's barrier function upon injury. Altered protease activity has been implicated in the pathogenesis of healing impairments, and proteases are important targets in diagnosis and therapy of this pathology. Global assessment of proteolysis at critical turning points after injury will define crucial events in acute healing that might be disturbed in healing disorders. As optimal biospecimens, wound exudates contain an ideal proteome to detect extracellular proteolytic events, are noninvasively accessible, and can be collected at multiple time points along the healing process from the same wound in the clinics. In this study, we applied multiplexed Terminal Amine Isotopic Labeling of Substrates (TAILS) to globally assess proteolysis in early phases of cutaneous wound healing. By quantitative analysis of proteins and protein N termini in wound fluids from a clinically relevant pig wound model, we identified more than 650 proteins and discerned major healing phases through distinctive abundance clustering of markers of inflammation, granulation tissue formation, and re-epithelialization. TAILS revealed a high degree of proteolysis at all time points after injury by detecting almost 1300 N-terminal peptides in ∼450 proteins. Quantitative positional proteomics mapped pivotal interdependent processing events in the blood coagulation and complement cascades, temporally discerned clotting and fibrinolysis during the healing process, and detected processing of complement C3 at distinct time points after wounding and by different proteases. Exploiting data on primary cleavage specificities, we related candidate proteases to cleavage events and revealed processing of the integrin adapter protein kindlin-3 by caspase-3, generating new hypotheses for protease-substrate relations in the healing skin wound in vivo. The data have been deposited to the ProteomeXchange Consortium with identifier PXD001198.

Tetraspanin CD63 acts as a pro-metastatic factor via β-catenin stabilization

The tetraspanin CD63 is implicated in pro-metastatic signaling pathways but, so far, it is unclear, how CD63 levels affect the tumor cell phenotype. Here, we investigated the effect of CD63 modulation in different metastatic tumor cell lines. In vitro, knock down of CD63 induced a more epithelial-like phenotype concomitant with increased E-cadherin expression, downregulation of its repressors Slug and Zeb1, and decreased N-cadherin. In addition, β-catenin protein was markedly reduced, negatively affecting expression of the target genes MMP-2 and PAI-1. β-catenin inhibitors mimicked the epithelial phenotype induced by CD63 knock down. Inhibition of β-catenin upstream regulators PI3K/AKT or GSK3β could rescue the mesenchymal phenotype underlining the importance of the β-catenin pathway in CD63-regulated cell plasticity. CD63 knock down-induced phenotypical changes correlated with a decrease of experimental metastasis whereas CD63 overexpression enhanced the tumor cell-intrinsic metastatic potential. Taken together, our data show that CD63 is a crucial player in the regulation of the tumor cell-intrinsic metastatic potential by affecting cell plasticity.

Network analyses reveal pervasive functional regulation between proteases in the human protease web

Network modeling of interactions between proteases and their inhibitors reveals a network of new protein connections and cascades in the protease web.

Proteolytic processing is an irreversible posttranslational modification affecting a large portion of the proteome. Protease-cleaved mediators frequently exhibit altered activity, and biological pathways are often regulated by proteolytic processing. Many of these mechanisms have not been appreciated as being protease-dependent, and the potential in unraveling a complex new dimension of biological control is increasingly recognized. Proteases are currently believed to act individually or in isolated cascades. However, conclusive but scattered biochemical evidence indicates broader regulation of proteases by protease and inhibitor interactions. Therefore, to systematically study such interactions, we assembled curated protease cleavage and inhibition data into a global, computational representation, termed the protease web. This revealed that proteases pervasively influence the activity of other proteases directly or by cleaving intermediate proteases or protease inhibitors. The protease web spans four classes of proteases and inhibitors and so links both recently and classically described protease groups and cascades, which can no longer be viewed as operating in isolation in vivo. We demonstrated that this observation, termed reachability, is robust to alterations in the data and will only increase in the future as additional data are added. We further show how subnetworks of the web are operational in 23 different tissues reflecting different phenotypes. We applied our network to develop novel insights into biologically relevant protease interactions using cell-specific proteases of the polymorphonuclear leukocyte as a system. Predictions from the protease web on the activity of matrix metalloproteinase 8 (MMP8) and neutrophil elastase being linked by an inactivating cleavage of serpinA1 by MMP8 were validated and explain perplexing Mmp8^−/− versus wild-type polymorphonuclear chemokine cleavages in vivo. Our findings supply systematically derived and validated evidence for the existence of the protease web, a network that affects the activity of most proteases and thereby influences the functional state of the proteome and cell activity.

Proteases modify the structure and activity of all proteins by peptide bond hydrolysis and are increasingly recognized as integral regulatory components of numerous biological mechanisms. Deregulated protease activity is a common characteristic of many diseases. However, protease drug development is complicated by an incomplete understanding of protease biology. One missing piece in this puzzle is the interplay between proteases: Some proteases activate other proteases, whereas some proteases inactivate inhibitors, leading to currently unpredictable cleavage of additional proteins. Using database annotations we mathematically modeled protease interactions. Our model includes 1,230 proteins and shows connections between 141,523 pairs of proteases, substrates, and inhibitors. Thus, proteases interact on a large scale to form the protease web, which links most studied groups of proteases and their inhibitors, indicating that the potential of regulation through this network is very large. We found that this interplay is robust to targeted or untargeted pruning of the protease web and that protease inhibitors are central to network connectivity. Our model was used to decipher proteolytic pathways that drive inflammatory processes in vivo. Consequently, protease regulatory interactions should be recognized and explored further to understand in vivo roles and to select better drug targets that avoid side effects arising from inhibition of unexpected activities.

Matrix metalloproteinases contribute to kidney fibrosis in chronic kidney diseases

Matrix metalloproteinases (MMPs) are members of the neutral proteinase family. They were previously thought to be anti-fibrotic because of their ability to degrade and remodel of extracellular matrix. However, recent studies have shown that MMPs are implicated in initiation and progression of kidney fibrosis through tubular cell epithelial–mesenchymal transition (EMT) as well as activation of resident fibroblasts, endothelial-mesenchymal transition (EndoMT) and pericyte-myofibroblast transdifferentiation. Interstitial macrophage infiltration has also been shown to correlate with the severity of kidney fibrosis in various chronic kidney diseases. MMPs secreted by macrophages, especially MMP-9, has been shown by us to be profibrotic by induction of tubular cells EMT. EMT is mainly induced by transforming growth factor-β (TGF-β). However, MMP-9 was found by us and others to be up-regulated by TGF-β1 in kidney tubular epithelial cells and secreted by activated macrophages, resulting in EMT and ultimately kidney fibrosis. Therefore, MMP-9 may serve as a potential therapeutic target to prevent kidney fibrosis in chronic kidney disease. This review, by a particular focus on EMT, seeks to provide a comprehensive understanding of MMPs, especially MMP-9, in kidney fibrosis.

Matrix metalloproteinase-9 of tubular and macrophage origin contributes to the pathogenesis of renal fibrosis via macrophage recruitment through osteopontin cleavage

A pro-fibrotic role of matrix metalloproteinase-9 (MMP-9) in tubular cell epithelial-mesenchymal transition (EMT) is well established in renal fibrosis; however studies from our group and others have demonstrated some previously unrecognized complexity of MMP-9 that has been overlooked in renal fibrosis. Therefore, the aim of this study was to determine the expression pattern, origin and the exact mechanism underlying the contribution of MMP-9 to unilateral ureteral obstruction (UUO), a well-established model of renal fibrosis via MMP-9 inhibition. Renal MMP-9 expression in BALB/c mice with UUO was examined on day 1, 3, 5, 7, 9, 11 and 14. To inhibit MMP-9 activity, MMP-2/9 inhibitor or MMP-9-neutralizing antibody was administered daily for 4 consecutive days from day 0-3, 6-9 or 10-13 and tissues harvested at day 14. In UUO, there was a bi-phasic early- and late-stage upregulation of MMP-9 activity. Interestingly, tubular epithelial cells (TECs) were the predominant source of MMP-9 during early stage, whereas TECs, macrophages and myofibroblasts produced MMP-9 during late-stage UUO. Early- and late-stage inhibition of MMP-9 in UUO mice significantly reduced tubular cell EMT and renal fibrosis. Moreover, MMP-9 inhibition caused a significant reduction in MMP-9-cleaved osteopontin and macrophage infiltration in UUO kidney. Our in vitro study showed MMP-9-cleaved osteopontin enhanced macrophage transwell migration and MMP-9 of both primary TEC and macrophage induced tubular cell EMT. In summary, our result suggests that MMP-9 of both TEC and macrophage origin may directly or indirectly contribute to the pathogenesis of renal fibrosis via osteopontin cleavage, which, in turn further recruit macrophage and induce tubular cell EMT. Our study also highlights the time dependency of its expression and the potential of stage-specific inhibition strategy against renal fibrosis.

Systems-level analysis of proteolytic events in increased vascular permeability and complement activation in skin inflammation

During inflammation, vascular permeability is increased by various proteolytic events, such as the generation of bradykinin, that augment local tissue responses by enabling tissue penetration of serum proteins, including complement and acute-phase proteins. Proteases also govern inflammatory responses by processing extracellular matrix proteins and soluble bioactive mediators. We quantified changes in the proteome and the nature of protein amino termini (the N-terminome) and the altered abundance of murine proteases and inhibitors during skin inflammation. Through analysis of the N-terminome by iTRAQ-TAILS, we identified cotranslational and posttranslational αN-acetylation motifs, quantitative increases in protein abundance, and qualitative changes in the proteolytic signature during inflammation. Of the proteins identified in normal skin, about half were cleaved, and phorbol ester-induced inflammation increased the proportion of cleaved proteins, including chemokines and complement proteins, that were processed at previously uncharacterized sites. In response to phorbol ester-induced inflammation, mice deficient in matrix metalloproteinase 2 (MMP2) showed reduced accumulation of serum proteins in the skin and exhibited different proteolytic networks from those of wild-type mice. We found that the complement 1 (C1) inhibitor attenuated the increase in serum protein accumulation in inflamed skin. Cleavage and inactivation of the C1 inhibitor by MMP2 increased complement activation and bradykinin generation in wild-type mice, leading to increased vessel permeability during inflammation, which was diminished in Mmp2(-/-) mice. Thus, our systems-level analysis of proteolysis dissected cleavage events associated with skin inflammation and demonstrated that loss of a single protease could perturb the proteolytic signaling network and enhance inflammation.

The substrate degradome of meprin metalloproteases reveals an unexpected proteolytic link between meprin β and ADAM10

The in vivo roles of meprin metalloproteases in pathophysiological conditions remain elusive. Substrates define protease roles. Therefore, to identify natural substrates for human meprin α and β we employed TAILS (terminal amine isotopic labeling of substrates), a proteomics approach that enriches for N-terminal peptides of proteins and cleavage fragments. Of the 151 new extracellular substrates we identified, it was notable that ADAM10 (a disintegrin and metalloprotease domain-containing protein 10)-the constitutive α-secretase-is activated by meprin β through cleavage of the propeptide. To validate this cleavage event, we expressed recombinant proADAM10 and after preincubation with meprin β, this resulted in significantly elevated ADAM10 activity. Cellular expression in murine primary fibroblasts confirmed activation. Other novel substrates including extracellular matrix proteins, growth factors and inhibitors were validated by western analyses and enzyme activity assays with Edman sequencing confirming the exact cleavage sites identified by TAILS. Cleavages in vivo were confirmed by comparing wild-type and meprin(-/-) mice. Our finding of cystatin C, elafin and fetuin-A as substrates and natural inhibitors for meprins reveal new mechanisms in the regulation of protease activity important for understanding pathophysiological processes.

On the Pro-Metastatic Stress Response to Cancer Therapies: Evidence for a Positive Co-Operation between TIMP-1, HIF-1α, and miR-210

In contrast to expectations in the past that tumor starvation or unselective inhibition of proteolytic activity would cure cancer, there is accumulating evidence that microenvironmental stress, such as hypoxia or broad-spectrum inhibition of metalloproteinases can promote metastasis. In fact, malignant tumor cells, due to their genetic and epigenetic instability, are predisposed to react to stress by adaptation and, if the stress persists, by escape and formation of metastasis. Recent recognition of the concepts of dynamic evolution as well as population and systems biology is extremely helpful to understand the disappointments of clinical trials with new drugs and may lead to paradigm-shifts in therapy strategies. This must be complemented by an increased understanding of molecular mechanism involved in stress response. Here, we review new roles of Hypoxia-inducible factor-1 (HIF-1), one transcription factor regulating stress response-related gene expression: HIF-1 is crucial for invasion and metastasis, independent from its pro-survival function. In addition, HIF-1 mediates pro-metastatic microenvironmental changes of the proteolytic balance as triggered by high systemic levels of tissue inhibitor of metalloproteinases-1 (TIMP-1), typical for many aggressive cancers, and regulates the metabolic switch to glycolysis, notably via activation of the microRNA miR-210. There is preliminary evidence that TIMP-1 also induces miR-210. Such positive-regulatory co-operation of HIF-1α, miR-210, and TIMP-1, all described to correlate with bad prognosis of cancer patients, opens new perspectives of gaining insight into molecular mechanisms of metastasis-inducing evasion of tumor cells from stress.

Differential Impact of Cysteine Cathepsins on Genetic Mouse Models of De novo Carcinogenesis: Cathepsin B as Emerging Therapeutic Target

Lysosomal cysteine cathepsins belong to a family of 11 human proteolytic enzymes. Some of them correlate with progression in a variety of cancers and therefore are considered as potential therapeutic targets. Until recently, the contribution of individual cathepsins to tumorigenesis and tumor progression remained unknown. By crossing various types of mouse cancer models with mice where specific cathepsins have been ablated, we contributed to this gap of knowledge and will summarize the results in this report. The employed models are the Rip1-Tag2 model for pancreatic neuroendocrine tumors, the K14-HPV16 model for squamous skin and cervical cancers, and the MMTV-PyMT model for metastasizing breast cancer, the KPC model for pancreatic ductal adenocarcinoma, and the APC(min) mice developing early stages of intestinal neoplasia. All models harbor mutations in relevant tumor suppressors and/or cell-type specific expression of potent oncogenes, which initiate de novo carcinogenesis in the targeted tissues. In all these models deletion of cathepsin B led to suppression of the aggressiveness of the respective cancer phenotype. Cathepsin B is networking with other proteases as it was shown for cathepsin X/Z. In contrast, deletion of cathepsin L was beneficial in the RiP1-Tag2 model, but enhanced tumorigenesis in the APC(min), and the K14-HPV16 mice. A logical consequence of these results would be to further pursue selective inhibition of cathepsin B. Moreover, it became clear that cathepsins B and S derived from cells of the tumor microenvironment support cancer growth. Strikingly, delivery of broad spectrum cysteine cathepsin inhibitors in the tumor microenvironment disrupts the permissive ecosystem of the cancer and results in impaired growth or even in regression of the tumor. In addition, combination of cysteine cathepsin inhibition and standard chemotherapy improves the therapeutic response of the latter. Taken together, the next preclinical challenges for developing cathepsin inhibition as cancer therapy might be the improvement of inhibitor selectivity and targeted delivery to the tumor microenvironment and investigation of the biological context of the individual factors within the complex proteolytic network.

Protease signalling: the cutting edge

Protease research has undergone a major expansion in the last decade, largely due to the extremely rapid development of new technologies, such as quantitative proteomics and in-vivo imaging, as well as an extensive use of in-vivo models. These have led to identification of physiological substrates and resulted in a paradigm shift from the concept of proteases as protein-degrading enzymes to proteases as key signalling molecules. However, we are still at the beginning of an understanding of protease signalling pathways. We have only identified a minor subset of true physiological substrates for a limited number of proteases, and their physiological regulation is still not well understood. Similarly, links with other signalling systems are not well established. Herein, we will highlight current challenges in protease research.

Wound degradomics - current status and future perspectives

Proteases are pivotal modulators of extracellular matrix components and bioactive proteins at all phases of cutaneous wound healing and thereby essentially contribute to the successful reestablishment of skin integrity upon injury. As a consequence, disturbance of proteolytic activity at the wound site is a major factor in the pathology of chronic wounds. A large body of data acquired in many years of research provide a good understanding of how individual proteases may influence the repair process. The next challenge will be to integrate these findings and to elucidate the complex interactions of proteolytic enzymes, their inhibitors and substrates on a system-wide level. Here, we present novel approaches that might help to achieve this ambitious goal in cutaneous wound healing research.

Tumor cell-derived Timp-1 is necessary for maintaining metastasis-promoting Met-signaling via inhibition of Adam-10

In many different tumor entities, increased expression of tissue inhibitor of metalloproteinases-1 (Timp-1) is associated with poor prognosis. We previously reported in mouse models that elevated systemic levels of Timp-1 induce a gene expression signature in the liver microenvironment increasing the susceptibility of this organ to tumor cells. This host effect was dependent on increased activity of the hepatocyte growth factor (Hgf)/hepatocyte growth factor receptor (Met) signaling pathway. In a recent study we showed that Met signaling is regulated by Timp-1 as it inhibits the Met sheddase A disintegrin and metalloproteinase-10 (Adam-10). The aim of the present study was to elucidate whether the metastatic potential of tumor cells benefits from autocrine Timp-1 as well and involves Adam-10 and Met signaling. In a syngeneic murine model of experimental liver metastasis Timp-1 expression and Met signaling were localized within metastatic colonies and expressed by tumor cells. Knock down of tumor cell Timp-1 suppressed Met signaling in metastases and inhibited metastasis formation and tumor cell-scattering in the liver. In vitro, knock down of tumor cell Timp-1 prevented Hgf-induced Met phosphorylation. Consequently, knock down of Met sheddase Adam-10 triggered auto-phosphorylation and responsiveness to Hgf. Accordingly, Adam-10 knock down increased Met phosphorylation in metastatic foci and induced tumor cell scattering into the surrounding liver parenchyma. In conclusion, these findings show that tumor cell-derived Timp-1 acts as a positive regulator of the metastatic potential and support the concept that proteases and their natural inhibitors, as members of the protease web, are major players of signaling during normal homeostasis and disease.

New opportunities in drug design of metalloproteinase inhibitors: combination between structure-function experimental approaches and systems biology

INTRODUCTION

MMPs (matrix metalloproteinases) and ADAMs (a disintegrin and metalloproteinases) are endopeptidases central to the degradation and remodeling of the extracellular matrix. These proteases also exhibit regulatory activity in cell signaling pathways and thus tissue homeostasis under normal conditions and in many diseases. Consequently, individual members of the MMP and ADAM protein families were identified as important therapeutic targets. However, designing effective inhibitors in vivo for this class of enzymes appears to be extremely challenging. This is attributed to the broad structural similarity of their active sites and to the dynamic functional interconnectivity of MMPs with other proteases, their inhibitors, and substrates (the so-called degradome) in healthy and disease tissues.

AREAS COVERED

The article covers the progress in designing metalloproteinase inhibitors, based on recent advancements in our understanding of enzyme structures and their function as master regulators. It also discusses the potential of utilizing structure-based drug design strategies in conjunction with systems biology experimental approaches for designing potent and therapeutically effective metalloproteinase inhibitors.

EXPERT OPINION

We highlight the use of protein-based drug design strategies, for example, antibodies and protein scaffolds, targeting extracatalytic domains, which are central to proteolytic and non-proteolytic enzyme functions. Such rationally designed function-blocking inhibitors may create new opportunities in disease management and in emerging therapies that require control of dysregulated MMP activity without causing severe side effects. Importantly, the lessons learned from studying these protein-based inhibitors can be implemented to design new and effective small or medium sized synthetic antagonists.

Identification of a survival-independent metastasis-enhancing role of hypoxia-inducible factor-1alpha with a hypoxia-tolerant tumor cell line

During tumor progression, malignant cells must repeatedly survive microenvironmental stress. Hypoxia-inducible factor-1 (HIF-1) signaling has emerged as one major pathway allowing cellular adaptation to stress. Recent findings led to the hypothesis that HIF-1alpha may enhance the metastatic potential of tumor cells by a survival-independent mechanism. So far it has not been shown that HIF-1alpha also directly regulates invasive processes during metastasis in addition to conferring a survival advantage to metastasizing tumor cells. In a hypoxia-tolerant tumor cell line (L-CI.5s), which did not rely on HIF-1 signaling for viability in vitro and in vivo, knockdown of Hif-1alpha reduced invasiveness of the tumor cells in vitro as well as extravasation and secondary infiltration in vivo. Liver metastases associated induction of proinvasive receptor tyrosine kinase Met phosphorylation as well as gelatinolytic activity were Hif-1alpha-dependent. Indeed, promoter activity of the matrix metalloproteinase-9 (mmp-9) was shown to be Hif-1alpha-dependent. This study uncovers a new survival-independent biological function of HIF-1alpha contributing to the efficacy of metastases formation.

Avoiding spam in the proteolytic internet: future strategies for anti-metastatic MMP inhibition

Phase III clinical trials with cancer patients with the first generation of synthetic MMP inhibitors (MMPIs) failed due to inefficacy and adverse side effects. These results were unexpected, given the wealth of pre-clinical data implicating MMPs as cancer targets, but are attributable to the broad-spectrum activity of these early MMPIs and the limited knowledge of the variety of biological functions of MMPs at the time they were deployed. These experiences stimulated the development of a variety of highly specific synthetic MMPIs. However, the bottle-neck is the identification of true target-MMPs. Functional genetic approaches are being complicated by the existence of the 'protease web,' i.e., the dynamic interconnectivity of MMPs and other proteases, their inhibitors, and substrates that collectively establish homeostasis in signaling in healthy and disease-afflicted tissue. Therefore, even specific MMP inhibition can result in seemingly unpredictable induction of systemic protease web-associated modulations (spam), which can comprise metastasis-promoting molecules such as other proteases and cytokines. Such undesired information in local proteolytic networks or relayed systemically in the organism via the proteolytic internet needs to be understood and defined in order to design specific metastasis therapies employing highly specific MMPIs in combination with spam-filtering agents.

Matrix metalloproteinases: what do they not do? New substrates and biological roles identified by murine models and proteomics

The biological roles of the matrix metalloproteinases (MMPs) have been traditionally associated with the degradation and turnover of most of the components of the extracellular matrix (ECM). This functional misconception has been used for years to explain the involvement of the MMP family in developmental processes, cell homeostasis and disease, and led to clinical trials of MMP inhibitors for the treatment of cancer that failed to meet their endpoints and cast a shadow on MMPs as druggable targets. Accumulated evidence from a great variety of post-trial MMP degradomics studies, ranging from transgenic models to recent state-of-the-art proteomics screens, is changing the dogma about MMP functions. MMPs regulate cell behavior through finely tuned and tightly controlled proteolytic processing of a large variety of signaling molecules that can also have beneficial effects in disease resolution. Moreover, net proteolytic activity relies upon direct interactions between the different protease and protease inhibitor families, interconnected in a complex protease web, with MMPs acting as key nodal components. Such complexity renders simple interpretation of Mmp knockout mice very difficult. Indeed, the phenotype of these models reveals the response of a complex system to the loss of one protease rather than necessarily a direct effect of the lack of functional activity of a protease. Such a shift in the MMP functional paradigm, together with the difficulties associated with current methods of studying proteases this highlights the need for new high content degradomics approaches to uncover and annotate MMP activities in vivo and identify novel interactions within the protease web. Integration of these techniques with specifically designed animal models for final validation should lay the foundations for the development of new inhibitors that specifically target disease-related MMPs and/or their upstream effectors that cause deleterious effects in disease, while sparing MMP functions that are protective.

Matrix metalloproteinase proteomics: substrates, targets, and therapy

Proteomics encompasses powerful techniques termed 'degradomics' for unbiased high-throughput protease substrate discovery screens that have been applied to an important family of extracellular proteases, the matrix metalloproteinases (MMPs). Together with the data generated from genetic deletion and transgenic mouse models and genomic profiling, these screens can uncover the diverse range of MMP functions, reveal which MMPs and MMP-mediated pathways exacerbate pathology, and which are involved in protection and the resolution of disease. This information can be used to identify and validate candidate drug targets and antitargets, and is critical for the development of new inhibitors of MMP function. Such inhibitors may target either the MMP directly in a specific manner or pathways upstream and downstream of MMP activity that are mediating deleterious effects in disease. Since MMPs do not operate alone but are part of the 'protease web', it is necessary to use system-wide approaches to understand MMP proteolysis in vivo, to discover new biological roles and their potential for therapeutic modification.