Functional roles of MMP14 and MMP15 in early postnatal mammary gland development

Altered mammary gland development and pro-tumorigenic changes in young female mice following prenatal BPAF exposure

Bisphenol A (BPA) is being phased out owing to its endocrine-disrupting effects and is increasingly being replaced by its substitute compounds such as bisphenol AF (BPAF). This study aims to explore the potential adverse outcomes of prenatal BPAF exposure combined with postnatal cross-fostering on the development and long-term health effects of the mammary gland in offspring. The results suggested that prenatal BPAF exposure accelerates the puberty, and induces duct dilatations, angiogenesis, lobular hyperplasia, and enhanced inflammatory cell infiltration in the mammary gland of female offspring. Differentially expressed genes exhibiting time series patterns induced by BPAF exposure were enriched in biological processes related to mammary gland development, epithelial cell proliferation and so on. Notably, 13 breast cancer-related biomarkers including Pgr, Gata3, Egfr and Areg were screened, showing a time-dependent increase in expression. After human homologous gene transformation, TCGA analysis suggested that the human homologues of genes differentially expressed in BPAF-treated mice were associated with increased tumor stages in female patients with breast cancer. Furthermore, postnatal cross-fostering did not completely restore the adverse effects of prenatal BPAF exposure and even showed a reverse tendency. These results imply that prenatal BPAF exposure in utero and postnatally nursing by BPAF exposed dams, have long-term effects on the mammary glands health of female offspring.

Mmp14-dependent remodeling of the pericellular-dermal collagen interface governs fibroblast survival

Dermal fibroblasts deposit type I collagen, the dominant extracellular matrix molecule found in skin, during early postnatal development. Coincident with this biosynthetic program, fibroblasts proteolytically remodel pericellular collagen fibrils by mobilizing the membrane-anchored matrix metalloproteinase, Mmp14. Unexpectedly, dermal fibroblasts in Mmp14-/- mice commit to a large-scale apoptotic program that leaves skin tissues replete with dying cells. A requirement for Mmp14 in dermal fibroblast survival is recapitulated in vitro when cells are embedded within, but not cultured atop, three-dimensional hydrogels of crosslinked type I collagen. In the absence of Mmp14-dependent pericellular proteolysis, dermal fibroblasts fail to trigger β1 integrin activation and instead actuate a TGF-β1/phospho-JNK stress response that leads to apoptotic cell death in vitro as well as in vivo. Taken together, these studies identify Mmp14 as a requisite cell survival factor that maintains dermal fibroblast viability in postnatal dermal tissues.

Cancer cell-derived exosomal miR-425-3p induces white adipocyte atrophy

White adipose tissue wasting plays a critical role in the development and progression of cancer cachexia. However, the mechanism behind the loss of adipose tissue remains ill-defined. In this study, we found that cancer cell-derived exosomes highly expressed miR-425-3p. Administration of cancer cell-derived exosomes significantly inhibited proliferation and differentiation of human preadipocytes-viscereal (HPA-v) cells. In mature adipocytes, cancer cell-derived exosomes activated cAMP/PKA signalling and lipophagy, leading to adipocyte lipolysis and browning of white adipocytes. These exosomes-induced alterations were almost abolished by endocytosis inhibitor cytochalasin D (CytoD) and antagomiR-425-3p, or reproduced by miR-425-3p mimics. In addition, bioinformatics analysis and luciferase reporter assay revealed that miR-425-3p directly targeted proliferation-related genes such as GATA2, IGFBP4, MMP15, differentiation-related gene CEBPA, and phosphodiesterase 4B gene (PDE4B). Depletion of PDE4B enhanced cAMP/PKA signalling and lipophagy, but had no effects on HPA-v proliferation and differentiation. Taken together, these results suggested that cancer cell-derived exosomal miR-425-3p inhibited preadipocyte proliferation and differentiation, increased adipocyte lipolysis, and promoted browning of white adipocytes, all of which might contribute to adipocyte atrophy and ultimately the loss of adipose tissue in cancer cachexia.

Abbreviations: ADPN: adiponectin; aP2: adipocyte protein 2 or fatty acid binding protein 4 (FABP4); BCA: bicinchoninic acid assay; BFA: bafilomycin A1; BMI: body mass index; C/EBP: CCAAT/enhancer binding protein; CEBPA: CCAAT/enhancer-binding protein-alpha; C-Exo: cancer cell-derived exosomes; CNTL: control; CREB: cAMP-response element binding protein; CytoD: cytochalasin D; ECL: chemiluminescence; GATA2: GATA Binding Protein 2; HFD: high fat diet; HSL: hormone-sensitive lipase; IGFBP4: insulin like growth factor binding protein 4; IRS-1: insulin receptor substrate-1; ISO: isoproterenol hydrochloride; KD: knockdown; KO: knock out; LC3: microtubule-associated protein 1A/1B-light chain 3; LMF: lipid mobilizing factor; LPL: lipoprotein lipase; MMP15: matrix metallopeptidase 15; Mir-Inh-C-Exo: cancer cell-derived exosomes with miR-425-3p inhibition; mTOR: mammalian target of rapamycin; Mut: mutant; N-Exo: normal cell-derived exosomes; NSCLC: non-small cell lung cancer; PBS, phosphate buffered saline; PGC-1: peroxisome proliferator-activated receptor-gamma coactivator-1; PDEs: phosphodiesterases; PKI: PKA inhibitor; PKA: cAMP-dependent protein kinase; PLIN1: Perilipin 1; PTHRP: parathyroid hormone-related protein; PVDF: polyvinylidene difluoride; shRNA: short hairpin RNA; UCP1: uncoupling protein 1; WT: wild type.

Matrix Metalloproteinases: From Molecular Mechanisms to Physiology, Pathophysiology, and Pharmacology

The first matrix metalloproteinase (MMP) was discovered in 1962 from the tail of a tadpole by its ability to degrade collagen. As their name suggests, matrix metalloproteinases are proteases capable of remodeling the extracellular matrix. More recently, MMPs have been demonstrated to play numerous additional biologic roles in cell signaling, immune regulation, and transcriptional control, all of which are unrelated to the degradation of the extracellular matrix. In this review, we will present milestones and major discoveries of MMP research, including various clinical trials for the use of MMP inhibitors. We will discuss the reasons behind the failures of most MMP inhibitors for the treatment of cancer and inflammatory diseases. There are still misconceptions about the pathophysiological roles of MMPs and the best strategies to inhibit their detrimental functions. This review aims to discuss MMPs in preclinical models and human pathologies. We will discuss new biochemical tools to track their proteolytic activity in vivo and ex vivo, in addition to future pharmacological alternatives to inhibit their detrimental functions in diseases. SIGNIFICANCE STATEMENT: Matrix metalloproteinases (MMPs) have been implicated in most inflammatory, autoimmune, cancers, and pathogen-mediated diseases. Initially overlooked, MMP contributions can be both beneficial and detrimental in disease progression and resolution. Thousands of MMP substrates have been suggested, and a few hundred have been validated. After more than 60 years of MMP research, there remain intriguing enigmas to solve regarding their biological functions in diseases.

Tiki proteins are substrates of membrane-type matrix metalloproteinases

Tiki proteins represent a new family of Wnt-specific proteases that inhibit Wnt signalling by cleaving and inactivating Wnt proteins. Tiki proteins are glycosylphosphatidylinositol (GPI)-anchored proteases and function in both Wnt-producing and Wnt-responsive cells. However, how Tiki proteins are regulated remains elusive. In this study, we demonstrate that matrix metalloproteinase 15 (MMP15) interacts with TIKI2 and degrades TIKI2 on the cell surface. Functionally, MMP15 relieves the inhibitory effect of TIKI2 on Wnt signalling in Wnt-responsive cells. We further show that Tiki proteins are substrates of MMP14, MMP15 and MMP16 but not MMP3 or MMP13. Our study provides insights into the potential regulation of Tiki family proteins by other proteases.

Bi-allelic null variant in matrix metalloproteinase-15, causes congenital cardiac defect, cholestasis jaundice, and failure to thrive

Here, we delineate the phenotype of two siblings with a bi-allelic frameshift variant in MMP15 gene with congenital cardiac defects, cholestasis, and dysmorphism. Genome sequencing analysis revealed a recently reported homozygous frameshift variant (c.1058delC, p.Pro353Glnfs*102) in MMP15 gene that co-segregates with the phenotype in the family in a recessive mode of inheritance. Relative quantification of MMP15 mRNA showed evidence of degradation of the mutated transcript, presumably by nonsense mediated decay. Likewise, MMP15: p.Gly231Arg, a concurrently reported homozygous missense variant in another patient exhibiting a similar phenotype, was predicted to disrupt zinc ion binding to the MMP-15 enzyme catalytic domain, which is essential for substrate proteolysis, by structural modeling. Previous animal models and cellular findings suggested that MMP15 plays a crucial role in the formation of endocardial cushions. These findings confirm that MMP15 is an important gene in human development, particularly cardiac, and that its loss of function is likely to cause a severe disorder phenotype.

Dynamic Expression of Membrane Type 1-Matrix Metalloproteinase (Mt1-mmp/Mmp14) in the Mouse Embryo

MT1-MMP/MMP14 belongs to a subgroup of the matrix metalloproteinases family that presents a transmembrane domain, with a cytosolic tail and the catalytic site exposed to the extracellular space. Deficient mice for this enzyme result in early postnatal death and display severe defects in skeletal, muscle and lung development. By using a transgenic line expressing the LacZ reporter under the control of the endogenous Mt1-mmp promoter, we reported a dynamic spatiotemporal expression pattern for Mt1-mmp from early embryonic to perinatal stages during cardiovascular development and brain formation. Thus, Mt1-mmp shows expression in the endocardium of the heart and the truncus arteriosus by E8.5, and is also strongly detected during vascular system development as well as in endothelial cells. In the brain, LacZ reporter expression was detected in the olfactory bulb, the rostral cerebral cortex and the caudal mesencephalic tectum. LacZ-positive cells were observed in neural progenitors of the spinal cord, neural crest cells and the intersomitic region. In the limb, Mt1-mmp expression was restricted to blood vessels, cartilage primordium and muscles. Detection of the enzyme was confirmed by Western blot and immunohistochemical analysis. We suggest novel functions for this metalloproteinase in angiogenesis, endocardial formation and vascularization during organogenesis. Moreover, Mt1-mmp expression revealed that the enzyme may contribute to heart, muscle and brain throughout development.

EFA6B regulates a stop signal for collective invasion in breast cancer

Cancer is initiated by somatic mutations in oncogenes or tumor suppressor genes. However, additional alterations provide selective advantages to the tumor cells to resist treatment and develop metastases. Their identification is of paramount importance. Reduced expression of EFA6B (Exchange Factor for ARF6, B) is associated with breast cancer of poor prognosis. Here, we report that loss of EFA6B triggers a transcriptional reprogramming of the cell-to-ECM interaction machinery and unleashes CDC42-dependent collective invasion in collagen. In xenograft experiments, MCF10 DCIS.com cells, a DCIS-to-IDC transition model, invades faster when knocked-out for EFA6B. In addition, invasive and metastatic tumors isolated from patients have lower expression of EFA6B and display gene ontology signatures identical to those of EFA6B knock-out cells. Thus, we reveal an EFA6B-regulated molecular mechanism that controls the invasive potential of mammary cells; this finding opens up avenues for the treatment of invasive breast cancer.

Fabrication of Adipose-Derived Stem Cell-Based Self-Assembled Scaffold under Hypoxia and Mechanical Stimulation for Urethral Tissue Engineering

Long urethral strictures are often treated with autologous genital skin and buccal mucosa grafts; however, risk of hair ingrowth and donor site morbidity, restrict their application. To overcome this, we introduced a tissue-engineered human urethra comprising adipose-derived stem cell (ASC)-based self-assembled scaffold, human urothelial cells (UCs) and smooth muscle cells (SMCs). ASCs were cultured with ascorbic acid to stimulate extracellular matrix (ECM) production. The scaffold (ECM) was stained with collagen type-I antibody and the thickness was measured under a confocal microscope. Results showed that the thickest scaffold (28.06 ± 0.59 μm) was achieved with 3 × 10⁴ cells/cm² seeding density, 100 μg/mL ascorbic acid concentration under hypoxic and dynamic culture condition. The biocompatibility assessment showed that UCs and SMCs seeded on the scaffold could proliferate and maintain the expression of their markers (CK7, CK20, UPIa, and UPII) and (α-SMA, MHC and Smootheline), respectively, after 14 days of in vitro culture. ECM gene expression analysis showed that the ASC and dermal fibroblast-based scaffolds (control) were comparable. The ASC-based scaffold can be handled and removed from the plate. This suggests that multiple layers of scaffold can be stacked to form the urothelium (seeded with UCs), submucosal layer (ASCs only), and smooth muscle layer (seeded with SMCs) and has the potential to be developed into a fully functional human urethra for urethral reconstructive surgeries.

Saffron anti-metastatic properties, ancient spice novel application

Crocus sativus L. (saffron), was applied as a spice, food colorant and medicine since four millennia ago and has been used as a remedy for various maladies. In the last three decades, the anti-primary tumor properties of saffron and its main carotenoids, crocin and crocetin, have been well explored. Despite the fact that metastasis is the leading cause of death in cancer patients, the anti-metastatic potential of saffron and its carotenoids has been surveyed only this decade. This review aims to provide an unprecedented overview of the anti-metastatic effects of saffron, crocin and crocetin, and the mechanisms underlying these effects. Investigations on various cancers demonstrated the anti-migratory, anti-invasion, anti-angiogenic potentials of saffron and its carotenoids, as well as their effects suppressing cell-ECM adhesion and enhancing cell-cell attachment. Saffron and its carotenoids exert their impact through different mechanisms such as reduction of CD34 and suppression of Wnt/β-catenin, Ras/ERK, P38, DCLK1, EMT, matrix metalloproteinases and urokinases. Crocin displayed more effective anti-metastatic potency, in comparison with saffron extract and crocetin. The bioaccessibility/bioavailability, nontoxicity on normal cells, confirmed anti-tumor efficiency and the recent evidence on the anti-metastatic potential of saffron and its carotenoids, recommends them as a propitious multipotent dietary agent and herbal medicine.

Membrane-type 1 Matrix Metalloproteinase Modulates Tissue Homeostasis by a Non-proteolytic Mechanism

Membrane-type 1 matrix metalloproteinase (MT1-MMP, MMP-14), a transmembrane proteinase with a short cytoplasmic tail, is a major effector of extracellular matrix remodeling. Genetic silencing of MT1-MMP in mouse (Mmp14 ^-/- ) and man causes dwarfism, osteopenia, arthritis, and lipodystrophy, abnormalities ascribed to defective collagen turnover. We have previously shown non-proteolytic functions of MT1-MMP mediated by its cytoplasmic tail, where the unique tyrosine (Y573) controls intracellular signaling. The Y573D mutation blocks TIMP-2/MT1-MMP-induced Erk1/2 and Akt signaling without affecting proteolytic activity. Here, we report that a mouse with the MT1-MMP Y573D mutation (Mmp14 ^Y573D/Y573D ) shows abnormalities similar to but also different from those of Mmp14 ^-/- mice. Skeletal stem cells (SSC) of Mmp14 ^Y573D/Y573D mice show defective differentiation consistent with the mouse phenotype, which is rescued by wild-type SSC transplant. These results provide the first in vivo demonstration that MT1-MMP modulates bone, cartilage, and fat homeostasis by controlling SSC differentiation through a mechanism independent of proteolysis.

Understanding seasonal weight loss tolerance in dairy goats: a transcriptomics approach

Background

Seasonal weight loss (SWL) is a very important limitation to the production of ruminants in the Mediterranean and Tropical regions. In these areas, long dry seasons lead to poor pastures with low nutritional value. During the dry season, ruminants, particularly those raised in extensive production systems, lose around 30% of their body weight. Seasonal weight loss has important consequences on animal productive performance and health. In this study, RNA sequencing was used to characterize feed restriction effects in dairy goat of 2 breeds with different SWL tolerance: Majorera (tolerant) and Palmera (susceptible). Nine Majorera and ten Palmera goats were randomly distributed in a control and a restricted group: Majorera Control (adequately fed; MC; n = 4), Palmera Control (adequately fed; PC; n = 6), Majorera Restricted (feed restricted; ME; n = 5) and Palmera Restricted (feed restricted; PE; n = 4). On day 22 of the trial, mammary gland biopsies were collected for transcriptomics analysis.

Results

From these samples, 24,260 unique transcripts were identified. From those, 82 transcripts were differentially expressed between MC and ME, 99 between PC and PE, twelve between both control groups and twenty-nine between both restricted groups.

Conclusions

Feed restriction affected several biochemical pathways in both breeds such as: carbohydrate and lipid transport; intracellular trafficking, RNA processing and signal transduction. This research also highlights the importance or involvement of the genes in tolerance (ENPP1, S-LZ, MT2A and GPNB) and susceptibility (GPD1, CTPS1, ELOVL6 and NR4A1) to SWL with respectively higher expression in the Majorera restriced group and the Palmera restricted group in comparison to the control groups. In addition, results from the study may be extrapolated to other dairy ruminant species.

MMP14 is required for delamination of chick neural crest cells independently of its catalytic activity

Matrix metalloproteinases have a broad spectrum of substrates ranging from extracellular matrix components and adhesion molecules to chemokines and growth factors. Despite being mostly secreted, MMPs have been detected in the cytosol, the mitochondria or the nucleus. Although most of the attention is focused on their role in matrix remodeling, the diversity of their substrates and their complex trafficking open the possibility for non-canonical functions. Yet in vivo examples and experimental demonstration of the physiological relevance of such activities are rare. Here, we have used chick neural crest (NC) cells, a highly migratory stem cell population likened to invasive cancer cells, as a model for physiological epithelial-mesenchymal transition (EMT). We demonstrate that MMP14 is required for NC delamination. Interestingly, this role is independent of its cytoplasmic tail and of its catalytic activity. Our in vivo data indicate that, in addition to being a late pro-invasive factor, MMP14 is also likely to be an early player, owing to its role in EMT.

Long non-coding RNAs: How to regulate the metastasis of non-small-cell lung cancer

Non–small‐cell lung cancer (NSCLC) has become the most lethal human cancer because of the high rate of metastasis. Hence, clarifying the molecular mechanism underlying NSCLC metastasis is very important to improve the prognosis of patients with NSCLC. Long non‐coding RNAs (LncRNAs) are a class of RNA molecules longer than 200 nucleotides, which can participate in diverse biological processes. About 18% of human LncRNAs were recently found to be associated with tumours. Many studies indicated that aberrant expression of LncRNAs played key roles in the progression and metastasis of NSCLC. According to the function in tumours, LncRNAs can be divided into two classes: oncogenic LncRNAs and tumour‐suppressor LncRNAs. In this review, we summarized the main molecular mechanism of LncRNAs regulating NSCLC metastasis, including three aspects: (a) LncRNAs interact with miRNAs as ceRNAs; (b) LncRNAs bind with target proteins; and (c) LncRNAs participate in the transduction of different signal pathways. Then, LncRNAs can exert their function to regulate the metastasis of NSCLC through influencing the progression of epithelial‐mesenchymal transition (EMT) and the properties of cancer stem cell (CSC). But, it is necessary to do some further research to demonstrate the LncRNAs particular regulatory mechanism of inhibiting the metastasis of NSCLC and explore new drugs targeting LncRNAs.

LncRNA MAFG-AS1 facilitates the migration and invasion of NSCLC cell via sponging miR-339-5p from MMP15

Non-small-cell carcinoma (NSCLC) is the most common cancer along with high mortality rate worldwide. In the present study, our data showed that lncRNA MAF BZIP Transcription Factor G Antisense RNA 1 (MAFG-AS1) was over-expressed in NSCLC tissues and cell lines. Overexpression of MAFG-AS1 promoted the migration, invasion and enhanced epithelial-mesenchymal transition (EMT) of NSCLC cell. In addition, miR-339-5p was predicted to be a target of MAFG-AS1 and the level of miR-339-5p was down-regulated in NSCLC. Over-expression of MAFG-AS1 significantly decreased the level of miR-339-5p in NSCLC cell. Moreover, the matrix metalloproteinase 15 (MMP15) was identified to be a target of miR-339-5p. The level of MMP15 was negatively regulated by miR-339-5p whereas positively controlled by MAFG-AS1. In addition, up-regulation of miR-339-5p neutralized the promoting impact of MAFG-AS1 on the migration, invasion and EMT of NSCLC cell. Finally, the xenograft model suggested that MAFG-AS1 promoted the metastasis of NSCLC cell in vivo. Altogether, we proved that MAFG-AS1-miR-339-5p-MMP15 axis might be a promising therapeutic target for the treatment of patients with NSCLC.

Hijacking a Morphogenesis Proteinase for Cancer Cell Invasion

A long-standing question in biology is whether cancer cells exploit developmental processes to invade the surrounding stroma. In this issue of Developmental Cell, Feinberg et al. (2018) identify the matrix metalloproteinase Mmp14 as a key driver of mammary invasion common to both development and cancer but expose an underlying twist.

Divergent Matrix-Remodeling Strategies Distinguish Developmental from Neoplastic Mammary Epithelial Cell Invasion Programs

Metastasizing breast carcinoma cells have been hypothesized to mobilize tissue-invasive activity by co-opting the proteolytic systems employed by normal mammary epithelial cells undergoing branching morphogenesis. However, the critical effectors underlying morphogenesis remain unidentified, and their relationship to breast cancer invasion programs is yet to be established. Here, we identify the membrane-anchored matrix metalloproteinase, Mmp14/MT1-MMP, but not the closely related proteinase Mmp15/MT2-MMP, as the dominant proteolytic effector of both branching morphogenesis and carcinoma cell invasion in vivo. Unexpectedly, however, epithelial cell-specific targeting of Mmp14/MT1-MMP in the normal mammary gland fails to impair branching, whereas deleting the proteinase in carcinoma cells abrogates invasion, preserves matrix architecture, and completely blocks metastasis. By contrast, in the normal mammary gland, extracellular matrix remodeling and morphogenesis are ablated only when Mmp14/MT1-MMP expression is specifically deleted from the periductal stroma. Together, these findings uncover the overlapping but divergent strategies that underlie developmental versus neoplastic matrix remodeling programs.

Genetic and scRNA-seq Analysis Reveals Distinct Cell Populations that Contribute to Salivary Gland Development and Maintenance

Stem and progenitor cells of the submandibular salivary gland (SMG) give rise to, maintain, and regenerate the multiple lineages of mature epithelial cells including those belonging to the ductal, acinar, basal and myoepithelial subtypes. Here we have exploited single cell RNA-sequencing and in vivo genetic lineage tracing technologies to generate a detailed map of the cell fate trajectories and branch points of the basal and myoepithelial cell populations of the mouse SMG during embryonic development and in adults. Our studies show that the transcription factor p63 and alpha-smooth muscle actin (SMA) serve as faithful markers of the basal and myoepithelial cell lineages, respectively and that both cell types are endowed with progenitor cell properties. However, p63⁺ basal and SMA⁺ myoepithelial cells exhibit distinct cell fates by virtue of maintaining different cellular lineages during morphogenesis and in adults. Collectively, our results reveal the dynamic and complex nature of the diverse SMG cell populations and highlight the distinct differentiation potential of the p63 and SMA expressing subtypes in the stem and progenitor cell hierarchy. Long term these findings have profound implications towards a better understanding of the molecular mechanisms that dictate lineage commitment and differentiation programs during development and adult gland maintenance.

A Potential Role for MMPs during the Formation of Non-Neurogenic Placodes

The formation of non-neurogenic placodes is critical prior to the development of several epithelial derivatives (e.g., feathers, teeth, etc.) and their development frequently involves morphogenetic proteins (or morphogens). Matrix metalloproteinases (MMPs) are important enzymes involved in extracellular matrix remodeling, and recent research has shown that the extracellular matrix (ECM) can modulate morphogen diffusion and cell behaviors. This review summarizes the known roles of MMPs during the development of non-neurogenic structures that involve a placodal stage. Specifically, we discuss feather, hair, tooth, mammary gland and lens development. This review highlights the potential critical role MMPs may play during placode formation in these systems.

E-cadherin cleavage by MT2-MMP regulates apical junctional signaling and epithelial homeostasis in the intestine

Cadherin-based intercellular adhesions are essential players in epithelial homeostasis, but their dynamic regulation during tissue morphogenesis and remodeling remain largely undefined. Here, we characterize an unexpected role for the membrane-anchored metalloproteinase MT2-MMP in regulating epithelial cell quiescence. Following co-immunoprecipitation and mass spectrometry, the MT2-MMP cytosolic tail was found to interact with the zonula occludens protein-1 (ZO-1) at the apical junctions of polarized epithelial cells. Functionally, MT2-MMP localizes in the apical domain of epithelial cells where it cleaves E-cadherin and promotes epithelial cell accumulation, a phenotype observed in 2D polarized cells as well as 3D cysts. MT2-MMP-mediated cleavage subsequently disrupts apical E-cadherin-mediated cell quiescence resulting in relaxed apical cortical tension favoring cell extrusion and re-sorting of Src kinase activity to junctional complexes, thereby promoting proliferation. Physiologically, MT2-MMP loss of function alters E-cadherin distribution, leading to impaired 3D organoid formation by mouse colonic epithelial cells ex vivo and reduction of cell proliferation within intestinal crypts in vivo Taken together, these studies identify an MT2-MMP-E-cadherin axis that functions as a novel regulator of epithelial cell homeostasis in vivo.

Leaders in collective migration: are front cells really endowed with a particular set of skills?

Collective cell migration is the coordinated movement emerging from the interaction of at least two cells. In multicellular organisms, collective cell migration is ubiquitous. During development, embryonic cells often travel in numbers, whereas in adults, epithelial cells close wounds collectively. There is often a division of labour and two categories of cells have been proposed: leaders and followers. These two terms imply that followers are subordinated to leaders whose proposed broad range of actions significantly biases the direction of the group of cells towards a specific target. These two terms are also tied to topology. Leaders are at the front while followers are located behind them. Here, we review recent work on some of the main experimental models for collective cell migration, concluding that leader-follower terminology may not be the most appropriate. It appears that not all collectively migrating groups are driven by cells located at the front. Moreover, the qualities that define leaders (pathfinding, traction forces and matrix remodelling) are not specific to front cells. These observations indicate that the terms leaders and followers are not suited to every case. We think that it would be more accurate to dissociate the function of a cell from its position in the group. The position of cells can be precisely defined with respect to the direction of movement by purely topological terms such as "front" or "rear" cells. In addition, we propose the more ample and strictly functional definition of "steering cells" which are able to determine the directionality of movement for the entire group. In this context, a leader cell represents only a specific case in which a steering cell is positioned at the front of the group.

Membrane-type matrix metalloproteases as diverse effectors of cancer progression

Membrane-type matrix metalloproteases (MT-MMP) are pivotal regulators of cell invasion, growth and survival. Tethered to the cell membranes by a transmembrane domain or GPI-anchor, the six MT-MMPs can exert these functions via cell surface-associated extracellular matrix degradation or proteolytic protein processing, including shedding or release of signaling receptors, adhesion molecules, growth factors and other pericellular proteins. By interactions with signaling scaffold or cytoskeleton, the C-terminal cytoplasmic tail of the transmembrane MT-MMPs further extends their functionality to signaling or structural relay. MT-MMPs are differentially expressed in cancer. The most extensively studied MMP14/MT1-MMP is induced in various cancers along malignant transformation via pathways activated by mutations in tumor suppressors or proto-oncogenes and changes in tumor microenvironment including cellular heterogeneity, extracellular matrix composition, tissue oxygenation, and inflammation. Classically such induction involves transcriptional programs related to epithelial-to-mesenchymal transition. Besides inhibition by endogenous tissue inhibitors, MT-MMP activities are spatially and timely regulated at multiple levels by microtubular vesicular trafficking, dimerization/oligomerization, other interactions and localization in the actin-based invadosomes, in both tumor and the stroma. The functions of MT-MMPs are multifaceted within reciprocal cellular responses in the evolving tumor microenvironment, which poses the importance of these proteases beyond the central function as matrix scissors, and necessitates us to rethink MT-MMPs as dynamic signaling proteases of cancer. This article is part of a Special Issue entitled: Matrix Metalloproteinases edited by Rafael Fridman.