Peripheral membrane associations of matrix metalloproteinases

Extracellular proteolysis in cancer: Proteases, substrates, and mechanisms in tumor progression and metastasis

A vast ensemble of extracellular proteins influences the development and progression of cancer, shaped and reshaped by a complex network of extracellular proteases. These proteases, belonging to the distinct classes of metalloproteases, serine proteases, cysteine proteases, and aspartic proteases, play a critical role in cancer. They often become dysregulated in cancer, with increases in pathological protease activity frequently driven by the loss of normal latency controls, diminished regulation by endogenous protease inhibitors, and changes in localization. Dysregulated proteases accelerate tumor progression and metastasis by degrading protein barriers within the extracellular matrix (ECM), stimulating tumor growth, reactivating dormant tumor cells, facilitating tumor cell escape from immune surveillance, and shifting stromal cells toward cancer-promoting behaviors through the precise proteolysis of specific substrates to alter their functions. These crucial substrates include ECM proteins and proteoglycans, soluble proteins secreted by tumor and stromal cells, and extracellular domains of cell surface proteins, including membrane receptors and adhesion proteins. The complexity of the extracellular protease web presents a significant challenge to untangle. Nevertheless, technological strides in proteomics, chemical biology, and the development of new probes and reagents are enabling progress and advancing our understanding of the pivotal importance of extracellular proteolysis in cancer.

Matrix metalloproteinases at a glance

Matrix metalloproteinases (MMPs) are a family of zinc-dependent proteinases that belong to the group of endopeptidases or matrixins. They are able to cleave a plethora of substrates, including components of the extracellular matrix and cell-surface-associated proteins, as well as intracellular targets. Accordingly, MMPs play key roles in a variety of physiological and pathological processes, such as tissue homeostasis and cancer cell invasion. MMP activity is exquisitely regulated at several levels, including pro-domain removal, association with inhibitors, intracellular trafficking and transport via extracellular vesicles. Moreover, the regulation of MMP activity is currently being rediscovered for the development of respective therapies for the treatment of cancer, as well as infectious, inflammatory and neurological diseases. In this Cell Science at a Glance article and the accompanying poster, we present an overview of the current knowledge regarding the regulation of MMP activity, the intra- and extra-cellular trafficking pathways of these enzymes and their diverse groups of target proteins, as well as their impact on health and disease.

Identification of amino acid residues in the MT-loop of MT1-MMP critical for its ability to cleave low-density lipoprotein receptor

Low-density lipoprotein receptor (LDLR) mediates clearance of plasma LDL cholesterol, preventing the development of atherosclerosis. We previously demonstrated that membrane type 1-matrix metalloproteinase (MT1-MMP) cleaves LDLR and exacerbates the development of atherosclerosis. Here, we investigated determinants in LDLR and MT1-MMP that were critical for MT1-MMP-induced LDLR cleavage. We observed that deletion of various functional domains in LDLR or removal of each of the five predicted cleavage sites of MT1-MMP on LDLR did not affect MT1-MMP-induced cleavage of the receptor. Removal of the hemopexin domain or the C-terminal cytoplasmic tail of MT1-MMP also did not impair its ability to cleave LDLR. On the other hand, mutant MT1-MMP, in which the catalytic domain or the MT-loop was deleted, could not cleave LDLR. Further Ala-scanning analysis revealed an important role for Ile at position 167 of the MT-loop in MT1-MMP’s action on LDLR. Replacement of Ile167 with Ala, Thr, Glu, or Lys resulted in a marked loss of the ability to cleave LDLR, whereas mutation of Ile167 to a non-polar amino acid residue, including Leu, Val, Met, and Phe, had no effect. Therefore, our studies indicate that MT1-MMP does not require a specific cleavage site on LDLR. In contrast, an amino acid residue with a hydrophobic side chain at position 167 in the MT-loop is critical for MT1-MMP-induced LDLR cleavage.

There and back again: Intracellular trafficking, release and recycling of matrix metalloproteinases

Matrix metalloproteinases are a family of zinc-dependent endopeptidases that are involved in a large variety of proteolytic processes in physiological and pathological scenarios, including immune cell surveillance, tissue homeostasis, or tumor cell metastasis. This is based on their ability to cleave a plethora of substrates that include components of the extracellular matrix, but also cell surface-associated and intracellular proteins. Accordingly, a tight regulatory web has evolved that closely regulates spatiotemporal activity of specific MMPs. An often underappreciated mechanism of MMP regulation involves their trafficking to and from specific subcellular sites that require MMP activity only for a certain period. In this review, we focus on the current knowledge of MMP intracellular trafficking, their secretion or surface exposure, as well as their recycling back from the cell surface. We discuss molecular mechanisms that enable these steps, in particular microtubule-dependent motility of vesicles that is driven by molecular motors and directed by vesicle regulatory proteins. Finally, we also point out open questions in the field of MMP motility that may become important in the future.

Membrane-type I matrix metalloproteinase (MT1-MMP), lipid metabolism and therapeutic implications

Lipids exert many essential physiological functions, such as serving as a structural component of biological membranes, storing energy, and regulating cell signal transduction. Dysregulation of lipid metabolism can lead to dyslipidemia related to various human diseases, such as obesity, diabetes, and cardiovascular disease. Therefore, lipid metabolism is strictly regulated through multiple mechanisms at different levels, including the extracellular matrix. Membrane-type I matrix metalloproteinase (MT1-MMP), a zinc-dependent endopeptidase, proteolytically cleaves extracellular matrix components, and non-matrix proteins, thereby regulating many physiological and pathophysiological processes. Emerging evidence supports the vital role of MT1-MMP in lipid metabolism. For example, MT1-MMP mediates ectodomain shedding of low-density lipoprotein receptor and increases plasma low-density lipoprotein cholesterol levels and the development of atherosclerosis. It also increases the vulnerability of atherosclerotic plaque by promoting collagen cleavage. Furthermore, it can cleave the extracellular matrix of adipocytes, affecting adipogenesis and the development of obesity. Therefore, the activity of MT1-MMP is strictly regulated by multiple mechanisms, such as autocatalytic cleavage, endocytosis and exocytosis, and post-translational modifications. Here, we summarize the latest advances in MT1-MMP, mainly focusing on its role in lipid metabolism, the molecular mechanisms regulating the function and expression of MT1-MMP, and their pharmacotherapeutic implications.

Maternal Immune System and State of Inflammation Dictate the Fate and Severity of Disease in Preeclampsia

Preeclampsia, a multisystem disorder in pregnant women, is diagnosed by onset of new hypertension, proteinuria, or organ damage. Antiangiogenic factors, such as soluble fms-like tyrosine kinase 1 (sFlt1) and soluble endoglin (sEng), are long known to be involved in preeclampsia. However, the role of maternal immune system and inflammation in promotion of preeclampsia has lately been a subject of immense interest. Link between maternal inflammation and preeclampsia is not well established. Furthermore, whether cigarette smoke promotes inflammation and also promotes severity of preeclampsia remains an open question. We herein investigated correlation of established inflammation signatures in the plasma and placental tissue from cohorts of preterm preeclampsia (PPE) and preterm pregnancies (control) with or without smoking history. Besides confirming increased levels of Flt1 and Eng in preeclampsia, we also observed an increase in various mediators of maternal inflammation in women with PPE compared to preterm cohort. Increased IL-6, IL-35, and TNF-α and reduced IL-10 in serum and higher MMP-12, TLR4, HMGB-1, and iNOS and lower Foxp3, CD56 transcripts in placental tissues of PPE compared to preterm pregnancies indicate an association of preterm preeclampsia with stark imbalance in maternal immune system and signatures of inflammation. Smoker PPE cohorts showed highest inflammatory signatures including statistically significant increase for many signatures compared to other cohorts. Together, these results provide evidence for association of inflammation with PPE and strong correlation of smoking with inflammatory signatures in PPE.

Key Matrix Remodeling Enzymes: Functions and Targeting in Cancer

Tissue functionality and integrity demand continuous changes in distribution of major components in the extracellular matrices (ECMs) under normal conditions aiming tissue homeostasis. Major matrix degrading proteolytic enzymes are matrix metalloproteinases (MMPs), plasminogen activators, atypical proteases such as intracellular cathepsins and glycolytic enzymes including heparanase and hyaluronidases. Matrix proteases evoke epithelial-to-mesenchymal transition (EMT) and regulate ECM turnover under normal procedures as well as cancer cell phenotype, motility, invasion, autophagy, angiogenesis and exosome formation through vital signaling cascades. ECM remodeling is also achieved by glycolytic enzymes that are essential for cancer cell survival, proliferation and tumor progression. In this article, the types of major matrix remodeling enzymes, their effects in cancer initiation, propagation and progression as well as their pharmacological targeting and ongoing clinical trials are presented and critically discussed.

A guide to the composition and functions of the extracellular matrix

Extracellular matrix (ECM) is a dynamic 3-dimensional network of macromolecules that provides structural support for the cells and tissues. Accumulated knowledge clearly demonstrated over the last decade that ECM plays key regulatory roles since it orchestrates cell signaling, functions, properties and morphology. Extracellularly secreted as well as cell-bound factors are among the major members of the ECM family. Proteins/glycoproteins, such as collagens, elastin, laminins and tenascins, proteoglycans and glycosaminoglycans, hyaluronan, and their cell receptors such as CD44 and integrins, responsible for cell adhesion, comprise a well-organized functional network with significant roles in health and disease. On the other hand, enzymes such as matrix metalloproteinases and specific glycosidases including heparanase and hyaluronidases contribute to matrix remodeling and affect human health. Several cell processes and functions, among them cell proliferation and survival, migration, differentiation, autophagy, angiogenesis, and immunity regulation are affected by certain matrix components. Structural alterations have been also well associated with disease progression. This guide on the composition and functions of the ECM gives a broad overview of the matrisome, the major ECM macromolecules, and their interaction networks within the ECM and with the cell surface, summarizes their main structural features and their roles in tissue organization and cell functions, and emphasizes the importance of specific ECM constituents in disease development and progression as well as the advances in molecular targeting of ECM to design new therapeutic strategies.

Heparan Sulfate Proteoglycan Signaling in Tumor Microenvironment

In the last few decades, heparan sulfate (HS) proteoglycans (HSPGs) have been an intriguing subject of study for their complex structural characteristics, their finely regulated biosynthetic machinery, and the wide range of functions they perform in living organisms from development to adulthood. From these studies, key roles of HSPGs in tumor initiation and progression have emerged, so that they are currently being explored as potential biomarkers and therapeutic targets for cancers. The multifaceted nature of HSPG structure/activity translates in their capacity to act either as inhibitors or promoters of tumor growth and invasion depending on the tumor type. Deregulation of HSPGs resulting in malignancy may be due to either their abnormal expression levels or changes in their structure and functions as a result of the altered activity of their biosynthetic or remodeling enzymes. Indeed, in the tumor microenvironment, HSPGs undergo structural alterations, through the shedding of proteoglycan ectodomain from the cell surface or the fragmentation and/or desulfation of HS chains, affecting HSPG function with significant impact on the molecular interactions between cancer cells and their microenvironment, and tumor cell behavior. Here, we overview the structural and functional features of HSPGs and their signaling in the tumor environment which contributes to tumorigenesis and cancer progression.

Matrix metalloproteinases cleave membrane-bound PD-L1 on CD90+ (myo-)fibroblasts in Crohn's disease and regulate Th1/Th17 cell responses

Increased T helper (Th)1/Th17 immune responses are a hallmark of Crohn's disease (CD) immunopathogenesis. CD90+ (myo-)fibroblasts (MFs) are abundant cells in the normal (N) intestinal mucosa contributing to mucosal tolerance via suppression of Th1 cell activity through cell surface membrane-bound PD-L1 (mPD-L1). CD-MFs have a decreased level of mPD-L1. Consequently, mPD-L1-mediated suppression of Th1 cells by CD-MFs is decreased, yet the mechanism responsible for the reduction in mPDL-1 is unknown. Increased expression of matrix metalloproteinases (MMPs) has been reported in CD. Herein we observed that when compared to N- and ulcerative colitis (UC)-MFs, CD-MFs increase in LPS-inducible levels of MMP-7 and -9 with a significant increase in both basal and inducible MMP-10. A similar pattern of MMP expression was observed in the CD-inflamed mucosa. Treatment of N-MFs with a combination of recombinant human MMP-7, -9 and -10 significantly decreased mPD-L1. In contrast, inhibition of MMP activity with MMP inhibitors or anti-MMP-10 neutralizing antibodies restores mPD-L1 on CD-MFs. CD-MFs demonstrated reduced capacity to suppress Th1 and Th17 responses from activated CD4+ T cells. By contrast, supplementation of the CD-MF:T-cell co-cultures with MMP inhibitors or anti-MMP neutralizing antibodies restored the CD-MF-mediated suppression. Our data suggest that (i) increased MMP-10 expression by CD-MFs and concomitant cleavage of PD-L1 from the surface of CD-MFs are likely to be one of the factors contributing to the decrease of mPD-L1-mediated suppression of Th1/Th17 cells in CD; and (ii) MMPs are likely to have a significant role in the intestinal mucosal immune responses.

Mechanism and Inhibition of Matrix Metalloproteinases

Matrix metalloproteinases hydrolyze proteins and glycoproteins forming the extracellular matrix, cytokines and growth factors released in the extracellular space, and membrane-bound receptors on the outer cell membrane. The pathological relevance of MMPs has prompted the structural and functional characterization of these enzymes and the development of synthetic inhibitors as possible drug candidates. Recent studies have provided a better understanding of the substrate preference of the different members of the family, and structural data on the mechanism by which these enzymes hydrolyze the substrates. Here, we report the recent advancements in the understanding of the mechanism of collagenolysis and elastolysis, and we discuss the perspectives of new therapeutic strategies for targeting MMPs.

MT1-MMP Binds Membranes by Opposite Tips of Its β Propeller to Position It for Pericellular Proteolysis

Critical to migration of tumor cells and endothelial cells is the proteolytic attack of membrane type 1 matrix metalloproteinase (MT1-MMP) upon collagen, growth factors, and receptors at cell surfaces. Lipid bilayer interactions of the substrate-binding hemopexin-like (HPX) domain of MT1-MMP were investigated by paramagnetic nuclear magnetic resonance relaxation enhancements (PREs), fluorescence, and mutagenesis. The HPX domain binds bilayers by blades II and IV on opposite sides of its β propeller fold. The EPGYPK sequence protruding from both blades inserts among phospholipid head groups in PRE-restrained molecular dynamics simulations. Bilayer binding to either blade II or IV exposes the CD44 binding site in blade I. Bilayer association with blade IV allows the collagen triple helix to bind without obstruction. Indeed, vesicles enhance proteolysis of collagen triple-helical substrates by the ectodomain of MT1-MMP. Hypothesized side-by-side MT1-MMP homodimerization would allow binding of bilayers, collagen, CD44, and head-to-tail oligomerization.

Estrogen Effects on Wound Healing

Wound healing is a physiological process, involving three successive and overlapping phases—hemostasis/inflammation, proliferation, and remodeling—to maintain the integrity of skin after trauma, either by accident or by procedure. Any disruption or unbalanced distribution of these processes might result in abnormal wound healing. Many molecular and clinical data support the effects of estrogen on normal skin homeostasis and wound healing. Estrogen deficiency, for example in postmenopausal women, is detrimental to wound healing processes, notably inflammation and re-granulation, while exogenous estrogen treatment may reverse these effects. Understanding the role of estrogen on skin might provide further opportunities to develop estrogen-related therapy for assistance in wound healing.