MT1-MMP recruits the ER-Golgi SNARE Bet1 for efficient MT1-MMP transport to the plasma membrane

Decoding the MMP14 integrin link: Key player in the secretome landscape

Rapid progress has been made in the exciting field of secretome research in health and disease. The tumor secretome, which is a significant proportion of the tumor proteome, is secreted into the extracellular space to promote intercellular communication and thus tumor progression. Among the many molecules of the secretome, integrins and matrix metalloproteinase 14 (MMP14) stand out as the interplay of adhesion and proteolysis drives invasion. Integrins serve as mechanosensors that mediate the contact of cells with the scaffold of the extracellular matrix and are significantly involved in the precise positioning and activity control of the membrane-bound collagenase MMP14. As a secretome proteinase, MMP14 influences and modifies the secretome itself. While integrins and MT-MMPs are membrane bound, but can be released and are therefore border crossers between the cell surface and the secretome, the extracellular matrix is not constitutively cell-bound, but its binding to integrins and other cell receptors is a stringently regulated process. To understand the mutual interactions in detail, we first summarize the structure and function of MMP14 and how it is regulated at the enzymatic and cellular level. In particular, the mutual interactions between integrins and MMP14 include the proteolytic cleavage of integrins themselves by MMP14. We then review the biochemical, cell biological and physiological effects of MMP14 on the composition and associated functions in the tumor secretome when either bound to the cell membrane, or located on extracellular microvesicles, or as a proteolytically shed non-membrane-bound ectodomain. Novel methods of proteomics, including the analysis of extravesicular vesicles, and new methods for the quantification of MMP14 will provide new research and diagnostic tools. The proteolytic modification of the tumor secretome, especially by MMP14, may bring an additional aspect to tumor secretome studies and will have an impact on the diagnosis and most likely also on the therapy of cancer patients.

SNARE proteins: Core engines of membrane fusion in cancer

Vesicles are loaded with a variety of cargoes, including membrane proteins, secreted proteins, signaling molecules, and various enzymes, etc. Not surprisingly, vesicle transport is essential for proper cellular life activities including growth, division, movement and cellular communication. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) mediate membrane fusion of vesicles with their target compartments that is fundamental for cargo delivery. Recent studies have shown that multiple SNARE family members are aberrantly expressed in human cancers and actively contribute to malignant proliferation, invasion, metastasis, immune evasion and treatment resistance. Here, the localization and function of SNARE proteins in eukaryotic cells are firstly mapped. Then we summarize the expression and regulation of SNAREs in cancer, and describe their contribution to cancer progression and mechanisms, and finally we propose engineering botulinum toxin as a strategy to target SNAREs for cancer treatment.

A MAP1B-cortactin-Tks5 axis regulates TNBC invasion and tumorigenesis

The microtubule-associated protein MAP1B has been implicated in axonal growth and brain development. We found that MAP1B is highly expressed in the most aggressive and deadliest breast cancer subtype, triple-negative breast cancer (TNBC), but not in other subtypes. Expression of MAP1B was found to be highly correlated with poor prognosis. Depletion of MAP1B in TNBC cells impairs cell migration and invasion concomitant with a defect in tumorigenesis. We found that MAP1B interacts with key components for invadopodia formation, cortactin, and Tks5, the latter of which is a PtdIns(3,4)P2-binding and scaffold protein that localizes to invadopodia. We also found that Tks5 associates with microtubules and supports the association between MAP1B and α-tubulin. In accordance with their interaction, depletion of MAP1B leads to Tks5 destabilization, leading to its degradation via the autophagic pathway. Collectively, these findings suggest that MAP1B is a convergence point of the cytoskeleton to promote malignancy in TNBC and thereby a potential diagnostic and therapeutic target for TNBC.

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.

The role of vesicle trafficking genes in osteoblast differentiation and function

Using Col2.3GFP transgenic mice expressing GFP in maturing osteoblasts, we isolated Col2.3GFP+ enriched osteoblasts from 3 sources. We performed RNA-sequencing, identified 593 overlapping genes and confirmed these genes are highly enriched in osteoblast differentiation and bone mineralization annotation categories. The top 3 annotations are all associated with endoplasmic reticulum and Golgi vesicle transport. We selected 22 trafficking genes that have not been well characterized in bone for functional validation in MC3T3-E1 pre-osteoblasts. Transient siRNA knockdown of trafficking genes including Sec24d, Gosr2, Rab2a, Stx5a, Bet1, Preb, Arf4, Ramp1, Cog6 and Pacs1 significantly increased mineralized nodule formation and expression of osteoblast markers. Increased mineralized nodule formation was suppressed by concurrent knockdown of P4ha1 and/or P4ha2, encoding collagen prolyl 4-hydroxylase isoenzymes. MC3T3-E1 pre-osteoblasts with knockdown of Cog6, Gosr2, Pacs1 or Arf4 formed more and larger ectopic mineralized bone nodules in vivo, which was attenuated by concurrent knockdown P4ha2. Permanent knockdown of Cog6 and Pacs1 by CRISPR/Cas9 gene editing in MC3T3-E1 pre-osteoblasts recapitulated increased mineralized nodule formation and osteoblast differentiation. In summary, we have identified several vesicle trafficking genes with roles in osteoblast function. Our findings provide potential targets for regulating bone formation.

MT1-MMP as a Key Regulator of Metastasis

Membrane type1-matrix metalloproteinase (MT1-MMP) is a member of metalloproteinases that is tethered to the transmembrane. Its major function in cancer progression is to directly degrade the extracellular matrix components, which are mainly type I-III collagen or indirectly type IV collagen through the activation of MMP-2 with a cooperative function of the tissue inhibitor of metalloproteinase-2 (TIMP-2). MT1-MMP is expressed as an inactive form (zymogen) within the endoplasmic reticulum (ER) and receives truncation processing via furin for its activation. Upon the appropriate trafficking of MT1-MMP from the ER, the Golgi apparatus to the cell surface membrane, MT1-MMP exhibits proteolytic activities to the surrounding molecules such as extracellular matrix components and cell surface molecules. MT1-MMP also retains a non-proteolytic ability to activate hypoxia-inducible factor 1 alpha (HIF-1A) via factors inhibiting the HIF-1 (FIH-1)-Mint3-HIF-1 axis, resulting in the upregulation of glucose metabolism and oxygen-independent ATP production. Through various functions of MT1-MMP, cancer cells gain motility on migration/invasion, thus causing metastasis. Despite the long-time efforts spent on the development of MT1-MMP interventions, none have been accomplished yet due to the side effects caused by off-target effects. Recently, MT1-MMP-specific small molecule inhibitors or an antibody have been reported and these inhibitors could potentially be novel agents for cancer treatment.

Golgi's Role in the Development of Possible New Therapies in Cancer

The Golgi apparatus is an important organelle found in most eukaryotic cells. It plays a vital role in the processing and sorting of proteins, lipids and other cellular components for delivery to their appropriate destinations within the cell or for secretion outside of the cell. The Golgi complex also plays a role in the regulation of protein trafficking, secretion and post-translational modifications, which are significant in the development and progression of cancer. Abnormalities in this organelle have been observed in various types of cancer, although research into chemotherapies that target the Golgi apparatus is still in its early stages. There are a few promising approaches that are being investigated: (1) Targeting the stimulator of interferon genes protein: The STING pathway senses cytosolic DNA and activates several signaling events. It is regulated by numerous post-translational modifications and relies heavily on vesicular trafficking. Based on some observations which state that a decreased STING expression is present in some cancer cells, agonists for the STING pathway have been developed and are currently being tested in clinical trials, showing encouraging results. (2) Targeting glycosylation: Altered glycosylation, which refers to changes in the carbohydrate molecules that are attached to proteins and lipids in cells, is a common feature of cancer cells, and there are several methods that thwart this process. For example, some inhibitors of glycosylation enzymes have been shown to reduce tumor growth and metastasis in preclinical models of cancer. (3) Targeting Golgi trafficking: The Golgi apparatus is responsible for the sorting and trafficking of proteins within the cell, and disrupting this process may be a potential therapeutic approach for cancer. The unconventional protein secretion is a process that occurs in response to stress and does not require the involvement of the Golgi organelles. P53 is the most frequently altered gene in cancer, dysregulating the normal cellular response to DNA damage. The mutant p53 drives indirectly the upregulation of the Golgi reassembly-stacking protein 55kDa (GRASP55). Through the inhibition of this protein in preclinical models, the reduction of the tumoral growth and metastatic capacity have been obtained successfully. This review supports the hypothesis that the Golgi apparatus may be the target of cytostatic treatment, considering its role in the molecular mechanisms of the neoplastic cells.

Cytoplasmic Tail of MT1-MMP: A Hub of MT1-MMP Regulation and Function

MT1-MMP (MMP-14) is a multifunctional protease that regulates ECM degradation, activation of other proteases, and a variety of cellular processes, including migration and viability in physiological and pathological contexts. Both the localization and signal transduction capabilities of MT1-MMP are dependent on its cytoplasmic domain that constitutes the final 20 C-terminal amino acids, while the rest of the protease is extracellular. In this review, we summarize the ways in which the cytoplasmic tail is involved in regulating and enacting the functions of MT1-MMP. We also provide an overview of known interactors of the MT1-MMP cytoplasmic tail and the functional significance of these interactions, as well as further insight into the mechanisms of cellular adhesion and invasion that are regulated by the cytoplasmic tail.

SEC22B inhibition attenuates colorectal cancer aggressiveness and autophagic flux under unfavorable environment

Autophagy has bidirectional functions in cancer by facilitating cell survival and death in a context-dependent manner. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a large family of proteins essential for numerous biological processes, including autophagy; nevertheless, their potential function in cancer malignancy remains unclear. Here, we explored the gene expression patterns of SNAREs in tissues of patients with colorectal cancer (CRC) and discovered that SEC22B expression, a vesicle SNARE, was higher in tumor tissues than in normal tissues, with a more significant increase in metastatic tissues. Interestingly, SEC22B knockdown dramatically decreased CRC cell survival and growth, especially under stressful conditions, such as hypoxia and serum starvation, and decreased the number of stress-induced autophagic vacuoles. Moreover, SEC22B knockdown successfully attenuated liver metastasis in a CRC cell xenograft mouse model, with histological signs of decreased autophagic flux and proliferation within cancer cells. Together, this study posits that SEC22B plays a crucial role in enhancing the aggressiveness of CRC cells, suggesting that SEC22B might be an attractive therapeutic target for CRC.

Mechanisms and roles of podosomes and invadopodia

Cell invasion into the surrounding extracellular matrix or across tissue boundaries and endothelial barriers occurs in both physiological and pathological scenarios such as immune surveillance or cancer metastasis. Podosomes and invadopodia, collectively called 'invadosomes', are actin-based structures that drive the proteolytic invasion of cells, by forming highly regulated platforms for the localized release of lytic enzymes that degrade the matrix. Recent advances in high-resolution microscopy techniques, in vivo imaging and high-throughput analyses have led to considerable progress in understanding mechanisms of invadosomes, revealing the intricate inner architecture of these structures, as well as their growing repertoire of functions that extends well beyond matrix degradation. In this Review, we discuss the known functions, architecture and regulatory mechanisms of podosomes and invadopodia. In particular, we describe the molecular mechanisms of localized actin turnover and microtubule-based cargo delivery, with a special focus on matrix-lytic enzymes that enable proteolytic invasion. Finally, we point out topics that should become important in the invadosome field in the future.

Syntaxin 7 contributes to breast cancer cell invasion by promoting invadopodia formation

Invasion in various cancer cells requires coordinated delivery of signaling proteins, adhesion proteins, actin-remodeling proteins and proteases to matrix-degrading structures called invadopodia. Vesicular trafficking involving SNAREs plays a crucial role in the delivery of cargo to the target membrane. Screening of 13 SNAREs from the endocytic and recycling route using a gene silencing approach coupled with functional assays identified syntaxin 7 (STX7) as an important player in MDA-MB-231 cell invasion. Total internal reflection fluorescence microscopy (TIRF-M) studies revealed that STX7 resides near invadopodia and co-traffics with MT1-MMP (also known as MMP14), indicating a possible role for this SNARE in protease trafficking. STX7 depletion reduced the number of invadopodia and their associated degradative activity. Immunoprecipitation studies revealed that STX7 forms distinct SNARE complexes with VAMP2, VAMP3, VAMP7, STX4 and SNAP23. Depletion of VAMP2, VAMP3 or STX4 abrogated invadopodia formation, phenocopying what was seen upon lack of STX7. Whereas depletion of STX4 reduced MT1-MMP level at the cell surfaces, STX7 silencing significantly reduced the invadopodia-associated MT1-MMP pool and increased the non-invadosomal pool. This study highlights STX7 as a major contributor towards the invadopodia formation during cancer cell invasion. This article has an associated First Person interview with the first author of the paper.

Dance of The Golgi: Understanding Golgi Dynamics in Cancer Metastasis

The Golgi apparatus is at the center of protein processing and trafficking in normal cells. Under pathological conditions, such as in cancer, aberrant Golgi dynamics alter the tumor microenvironment and the immune landscape, which enhances the invasive and metastatic potential of cancer cells. Among these changes in the Golgi in cancer include altered Golgi orientation and morphology that contribute to atypical Golgi function in protein trafficking, post-translational modification, and exocytosis. Golgi-associated gene mutations are ubiquitous across most cancers and are responsible for modifying Golgi function to become pro-metastatic. The pharmacological targeting of the Golgi or its associated genes has been difficult in the clinic; thus, studying the Golgi and its role in cancer is critical to developing novel therapeutic agents that limit cancer progression and metastasis. In this review, we aim to discuss how disrupted Golgi function in cancer cells promotes invasion and metastasis.

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.

The trans-SNARE complex VAMP4/Stx6/Stx7/Vti1b is a key regulator of Golgi to late endosome MT1-MMP transport in macrophages

The activity of the matrix metalloproteinase (MMP) MT1-MMP is strictly regulated by expression and cellular location. In macrophages LPS activation leads to the up-regulation of MT1-MMP and this need to be at the cell surface for them to degrade the dense extracellular matrix (ECM) components to create a path to migrate into injured and infected tissues. Fixed and live imaging shows newly made MT1-MMP is packaged into vesicles that traffic to and fuse with LBPA⁺ LAMP1⁺ late endosomes en route to the surface. The R-SNARE VAMP4, found on Golgi-derived vesicles that traffic to late endosomes, forms a trans-SNARE complex with the Q-SNARE complex Stx6/Stx7/Vti1b. The Stx6/Stx7/Vti1b complex has been shown to be up-regulated in lipopolysaccharide (LPS)-activated cells to increase trafficking of key cytokines through the classical pathway and now we show here it is up-regulation also plays a role in the late endosomal pathway of MT1-MMP trafficking. Depletion of any of the SNAREs in this complex reduces surface MT1-MMP and gelatin degradation. Conversely, overexpression of the Stx6/Stx7/Vti1b components increases surface MT1-MMP levels. This suggests that Stx6/Stx7/Vti1b is a key Q-SNARE complex in macrophages during an immune response and in partnership with VAMP4 it regulates transport of newly made MT1-MMP.

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.

Role of Extracellular Vesicles in Autoimmune Pathogenesis

Autoimmune diseases are conditions that emerge from abnormal immune responses to natural parts of the body. Extracellular vesicles (EVs) are membranous structures found in almost all types of cells. Because EVs often transport “cargo” between cells, their ability to crosstalk may be an important communication pathway within the body. The pathophysiological role of EVs is increasingly recognized in autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, Sjogren's syndrome, Type 1 diabetes, and autoimmune thyroid disease. EVs are considered as biomarkers of these diseases. This article outlines existing knowledge on the biogenesis of EVs, their role as messegers in cellular communication and the function in T/B cell differentiation and maturation, and focusing on their potential application in autoimmune diseases.

Regulation of MT1-MMP Activity through Its Association with ERMs

Membrane-bound proteases play a key role in biology by degrading matrix proteins or shedding adhesion receptors. MT1-MMP metalloproteinase is critical during cancer invasion, angiogenesis, and development. MT1-MMP activity is strictly regulated by internalization, recycling, autoprocessing but also through its incorporation into tetraspanin-enriched microdomains (TEMs), into invadopodia, or by its secretion on extracellular vesicles (EVs). We identified a juxtamembrane positively charged cluster responsible for the interaction of MT1-MMP with ERM (ezrin/radixin/moesin) cytoskeletal connectors in breast carcinoma cells. Linkage to ERMs regulates MT1-MMP subcellular distribution and internalization, but not its incorporation into extracellular vesicles. MT1-MMP association to ERMs and insertion into TEMs are independent phenomena, so that mutation of the ERM-binding motif in the cytoplasmic region of MT1-MMP does not preclude its association with the tetraspanin CD151, but impairs the accumulation and coalescence of CD151/MT1-MMP complexes at actin-rich structures. Conversely, gene deletion of CD151 does not impact on MT1-MMP colocalization with ERM molecules. At the plasma membrane MT1-MMP autoprocessing is severely dependent on ERM association and seems to be the dominant regulator of the enzyme collagenolytic activity. This newly characterized MT1-MMP/ERM association can thus be of relevance for tumor cell invasion.