Efficient cancer cell migration is essential for invasion and metastasis and is driven by cancer cell interaction with their extracellular matrix (ECM). Thus, ECM properties determine the migration phenotype. For example, ECM stiffness can guide cancer cell migration through durotaxis; however, the mechanisms regulating cancer cell durotaxis remain poorly understood. Using in-house stiffness gradient hydrogels, we discovered that MDA-MB-231 breast cancer cell metastatic variants selected for either bone or brain organotropism display impaired durotaxis. Moreover, akin to cells conditioned on soft substrates, these cells have altered mechanoresponses to increasing stiffness, including reduced cell spreading and focal adhesion assembly and signaling. We observed upregulation of the LIM-domain protein leupaxin, a focal adhesion component, in these variants and in soft-conditioned MDA-MB-231 cells compared to parental cells. Leupaxin silencing in brain-tropic metastatic cells restored durotaxis, whereas its overexpression in parental cells impaired durotaxis and mechanosensing, phenocopying the metastatic variants. Mechanistically, leupaxin disrupted paxillin-focal adhesion kinase (FAK) signaling, thereby inhibiting durotaxis. Together, these findings identify leupaxin as a negative regulator of durotaxis in metastatic cells and suggest a mechanism by which tumor cells adapt to mechanical heterogeneity to facilitate metastatic progression. ### Competing Interest Statement The authors have declared no competing interest. European Research Council, 101142305 Research Council of Finland, 346131, 364182, 337530, 357910 Sigrid Jusélius Foundation, https://ror.org/00ckakm23 Jane and Aatos Erkko Foundation, https://ror.org/03vxy9y38 European Molecular Biology Organization, ALTF 798-2021

During tumorigenesis, the extracellular matrix is extensively remodeled. Whereas the impact of such remodeling on tumor growth and invasion is well described, the consequences on immune infiltration are not well understood. Combining tissue imaging and machine learning, we show that immune cell localization in tumors can be predicted by the local topography of fibrillar collagens. Such topographies are dictated by a fibrotic pathway driven by transcription factor 4 (Tcf4) in both cancer and stromal cells, which promotes collagen III deposition and results in intermingled collagen networks that favor intratumor infiltration of T cells and neutrophils. Macrophages inhibit this pathway, highlighting their key structural role in shaping the tumor extracellular matrix. Reanalysis of data from human solid tumors revealed a strong correlation between TCF4, COL3A1, and T cell and neutrophil signatures. Together, our data identify collagen network topographies as a key regulator of tumor-infiltrating immune cells.

The interplay between diverse cell types and their extracellular matrix (ECM) is fundamental for multicellular life. The ECM is a complex meshwork of fibrillar proteins and soluble factors. Cells and their surrounding ECM interact bidirectionally, whereby cells deposit their tissue-specific ECM and remodel it enzymatically and by exerting contractile forces. The ECM in turn modulates cellular functions like gene expression, proliferation, and motility. A careful balance of this interaction is key for homeostasis, and is lost during cancer progression. Different cell types constituting a tumor including cancer and stromal cells, contribute to an imbalanced cell-ECM crosstalk within the tumor. Cumulatively, this leads to a tumor ECM characterized by particular features like increased stiffness and viscoelasticity, altered alignment, bundled fibers, etc. In this review, we discuss the advances in our understanding of the tumor ECM architecture and the multicellular interactions that help achieve it, with a special focus on increasing granularity in disentangling the contributions of individual tumor ECM features in disease progression.

The interplay between diverse cell types and their extracellular matrix (ECM) is fundamental for multicellular life. The ECM is a complex meshwork of fibrillar proteins and soluble factors. Cells and their surrounding ECM interact bidirectionally, whereby cells deposit their tissue-specific ECM and remodel it enzymatically and by exerting contractile forces. The ECM in turn modulates cellular functions like gene expression, proliferation and motility. A careful balance of this interaction is key for homeostasis, and is lost during cancer progression. Different cell types constituting a tumor, including cancer and stromal cells, contribute to an imbalanced cell-ECM crosstalk within the tumor. Cumulatively, this leads to a tumor ECM characterized by particular features like increased stiffness and viscoelasticity, altered alignment, bundled fibers etc. In this review, we discuss the advances in our understanding of the tumor ECM architecture and the multicellular interactions that help achieve it, with a special focus on increasing granularity in disentangling the contributions of individual tumor ECM features in disease progression.

Increased extracellular matrix deposition and stiffness promotes solid tumour progression. Yet, the precise mechanotransduction pathways, especially in less-studied mechanically responsive cancers, remain poorly understood. Here we address this gap using patient-derived tumour cells from early (mobile, T1) and advanced (immobile, T3) stages of vocal fold cancer, the most common squamous cell carcinoma severely impacting the voice box. We reveal that vocal fold cancer progression is linked to cell surface receptor heterogeneity, a loss of laminin-binding integrins in cell–cell junctions and a flocking mode of collective cell motility. Mimicking the physiological movement of healthy vocal fold tissue with stretching or vibrations decreases oncogenic β-catenin and Yes-associated protein (YAP) nuclear levels in vocal fold cancer. Multiplex immunohistochemistry of vocal fold cancer tumours shows a correlation between the extracellular matrix composition, nuclear YAP and patient survival, concordant with vocal fold cancer sensitivity to oncogenic YAP-TEAD Hippo pathway inhibitors both in vitro and in vivo. Overall, our findings suggest that vocal fold cancer is a mechanically sensitive malignancy, and that the restoration of tumour mechanophenotype or YAP/TAZ targeting represents a tractable anti-oncogenic therapeutic avenue for vocal fold cancer.

Constitutive integrin endocytosis and recycling control cell movement and morphology. In contrast, the role of newly synthesized integrins delivered via the biosynthetic pathway has been largely overlooked. We used the retention using selective hooks system to monitor the localization of new integrins exiting the endoplasmic reticulum in space and time. We discovered that new integrin delivery to the plasma membrane is polarized and enhances cell protrusion and focal adhesion growth in an extracellular matrix-ligand-dependent manner. Motor-clutch modeling explained the increased adhesion as higher integrin availability driving recruitment of additional receptors. Unexpectedly, live-cell imaging revealed a small subset of fast-emerging integrin vesicles rapidly transported to the cell surface to facilitate localized spreading. This unconventional secretion depended on cell adhesion and correlated with increased surface levels of immature, high-mannose glycosylated integrin, indicating bypass of the canonical Golgi-dependent secretory pathway. Thus, spatial plasma membrane-targeting of new integrins rapidly alters adhesion receptor availability, providing cells with added plasticity to respond to their environment.

During tumorigenesis, the extracellular matrix (ECM), which constitutes the structural scaffold of tissues, is profoundly remodeled. While the impact of such remodeling on tumor growth and invasion has been extensively investigated, much less is known on the consequences of ECM remodeling on tumor infiltration by immune cells. By combining tissue imaging and machine-learning, we here show that the localization of T lymphocytes and neutrophils, which orchestrate antitumor immune responses, can be predicted by defined topographical features of fibrillar collagen networks. We further show that these collagen topographies result from the activation of a fibrotic pathway controlled by the transcription factor Tcf4 upon depletion of tumor-associated macrophages at late tumor stages. This pathway promotes the deposition of collagen 3 by both tumor and stromal cells, resulting in intermingled collagen networks that favor intra-tumoral T cell and neutrophil localization. Importantly, analysis of human colorectal cancer public bulk RNAseq databases showed a strong correlation between Tcf4 and collagen 3, as well as between the expression of these genes and tumor infiltration by T lymphocytes and neutrophils, attesting the clinical relevance of our findings. This study highlights the key structural role of macrophages on the tumor extracellular matrix and identifies collagen network topographies as a major regulator of tumor infiltration by immune cells. ### Competing Interest Statement The authors have declared no competing interest.

ABSTRACT Cell migration is controlled by the coordinated action of cell adhesion, cytoskeletal dynamics, contractility and cell extrinsic cues. Integrins are the main adhesion receptors to ligands of the extracellular matrix (ECM), linking the actin cytoskeleton to the ECM and enabling cells to sense matrix rigidity and mount a directional cell migration response to stiffness gradients. Most models studied show preferred migration of single cells or cell clusters towards increasing rigidity. This is referred to as durotaxis, and since its initial discovery in 2000, technical advances and elegant computational models have provided molecular level details of stiffness sensing in cell migration. However, modeling has long predicted that, depending on cell intrinsic factors, such as the balance of cell adhesion molecules (clutches) and the motor proteins pulling on them, cells might also prefer adhesion to intermediate rigidity. Recently, experimental evidence has supported this notion and demonstrated the ability of cells to migrate towards lower rigidity, in a process called negative durotaxis. In this Review, we discuss the significant conceptual advances that have been made in our appreciation of cell plasticity and context dependency in stiffness-guided directional cell migration.

Cells sense and respond to the extracellular matrix (ECM) milieu through integrin proteins. Integrin availability on the plasma membrane, regulated by endosomal receptor uptake and recycling, has been extensively studied and regulates cell dynamics in various normal and pathological contexts1–5. In contrast, the role of integrin transport through the biosynthetic pathway has been considered primarily as a mechanism to replenish the receptor pool and too slow to influence cell dynamics6. Here, we adopted the RUSH (Retention Using Selective Hooks) assay to synchronize integrin anterograde transport from the endoplasmic reticulum (ER), allowing spatial and temporal analysis of newly synthesized receptor traffic. We observe that the delivery of new integrins to the plasma membrane is polarized in response to specific ECM ligands, facilitates integrin recruitment specifically to the membrane-proximal tip of focal adhesions (FA) and contributes to cell protrusion and FA growth. We explain the augmented adhesion growth using a computational molecular clutch model7, where increased integrin availability drives recruitment of additional integrins. Notably, a subset of newly synthesized integrins undergo rapid traffic from the ER to the cell surface to facilitate localized cell spreading, seemingly bypassing the Golgi. This unconventional secretion is dependent on cell adhesion and mediated by Golgi reassembling stacking proteins (GRASPs) association with the PDZ-binding motif in the integrin α5 cytoplasmic tail. This spatially targeted delivery of integrins through the biosynthetic pathway may propel cell dynamics by rapidly altering adhesion receptor availability, providing cells with an additional degree of plasticity to respond to their environment.

How cells sense tissue stiffness to guide cell migration is a fundamental question in development, fibrosis and cancer. Although durotaxis—cell migration towards increasing substrate stiffness—is well established, it remains unknown whether individual cells can migrate towards softer environments. Here, using microfabricated stiffness gradients, we describe the directed migration of U-251MG glioma cells towards less stiff regions. This ‘negative durotaxis’ does not coincide with changes in canonical mechanosensitive signalling or actomyosin contractility. Instead, as predicted by the motor–clutch-based model, migration occurs towards areas of ‘optimal stiffness’, where cells can generate maximal traction. In agreement with this model, negative durotaxis is selectively disrupted and even reversed by the partial inhibition of actomyosin contractility. Conversely, positive durotaxis can be switched to negative by lowering the optimal stiffness by the downregulation of talin—a key clutch component. Our results identify the molecular mechanism driving context-dependent positive or negative durotaxis, determined by a cell’s contractile and adhesive machinery.

Despite their roles in intercellular communications, the different populations of extracellular vesicles (EVs) and their secretion mechanisms are not fully characterized: how and to what extent EVs form as intraluminal vesicles of endocytic compartments (exosomes), or at the plasma membrane (PM) (ectosomes) remains unclear. Here we follow intracellular trafficking of the EV markers CD9 and CD63 from the endoplasmic reticulum to their residency compartment, respectively PM and late endosomes. We observe transient co-localization at both places, before they finally segregate. CD9 and a mutant CD63 stabilized at the PM are more abundantly released in EVs than CD63. Thus, in HeLa cells, ectosomes are more prominent than exosomes. By comparative proteomic analysis and differential response to neutralization of endosomal pH, we identify a few surface proteins likely specific of either exosomes (LAMP1) or ectosomes (BSG, SLC3A2). Our work sets the path for molecular and functional discrimination of exosomes and small ectosomes in any cell type.

ABSTRACT Despite their important and multiple roles in intercellular communications, the different populations of extracellular vesicles (EVs) and their secretion mechanisms are not fully characterized yet. In particular, how and to what extent EVs form either as intraluminal vesicles of endocytic compartments (exosomes), or at the plasma membrane (ectosomes) remains unclear. We followed in HeLa cells the intracellular trafficking of the EV markers CD9 and CD63 from the endoplasmic reticulum to their residency compartment and identified transient co-localization both at the plasma membrane (PM) and in endosomes, before they finally segregate. CD9 was more abundantly released in EVs than CD63. However, when forcing expression of CD63 at the PM, by mutating its lysosome-addressing motive, its secretion in EVs was increased. Thus, in HeLa cells, small ectosomes are more prominently released than exosomes. By comparative proteomic analysis, we identified a few surface proteins likely specific of either exosomes (e.g. LAMP1) or ectosomes (e.g. BSG, SLC3A2), based on their known intracellular location in lysosomes or the PM, and on the different effects on their release of Bafilomycin A1, a drug that neutralizes endosomal pH. Our work sets the path for molecular and functional discrimination of exosomes and small ectosomes in any cell type.

Cells release a variety of extracellular vesicles (EVs; including exosomes, microvesicles, and many others) into their environment. EVs can bud in endosomes or directly at the plasma membrane, carrying a selection of components from the cell and displaying various functional properties. Different techniques can be used to separate EV subtypes and EVs from co-isolated components, resulting in preparations of different abundance and purity.

The ability of exosomes to transfer cargo from donor to acceptor cells, thereby triggering phenotypic changes in the latter, has generated substantial interest in the scientific community. However, the extent to which exosomes differ from other extracellular vesicles in terms of their biogenesis and functions remains ill-defined. Here, we discuss the current knowledge on the specificities of exosomes and other types of extracellular vesicles, and their roles as important agents of cell-to-cell communication.

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles (“MISEV”) guidelines for the field in 2014. We now update these “MISEV2014” guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points. ARTICLE HISTORY Received 20 September 2018 Accepted 25 September 2018

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.