Metastasis is a dynamic succession of events involving the dissemination of tumour cells to distant sites within the body, ultimately reducing the survival of patients with cancer. To colonize ...distant organs and, therefore, systemically disseminate within the organism, cancer cells and associated factors exploit several bodily fluid systems, which provide a natural transportation route. Indeed, the flow mechanics of the blood and lymphatic circulatory systems can be co-opted to improve the efficiency of cancer cell transit from the primary tumour, extravasation and metastatic seeding. Flow rates, vessel size and shear stress can all influence the survival of cancer cells in the circulation and control organotropic seeding patterns. Thus, in addition to using these fluids as a means to travel throughout the body, cancer cells exploit the underlying physical forces within these fluids to successfully seed distant metastases. In this Review, we describe how circulating tumour cells and tumour-associated factors leverage bodily fluids, their underlying forces and imposed stresses during metastasis. As the contribution of bodily fluids and their mechanics raises interesting questions about the biology of the metastatic cascade, an improved understanding of this process might provide a new avenue for targeting cancer cells in transit.
Cancer extracellular vesicles (EVs) shuttle at distance and fertilize pre-metastatic niches facilitating subsequent seeding by tumor cells. However, the link between EV secretion mechanisms and their ...capacity to form pre-metastatic niches remains obscure. Using mouse models, we show that GTPases of the Ral family control, through the phospholipase D1, multi-vesicular bodies homeostasis and tune the biogenesis and secretion of pro-metastatic EVs. Importantly, EVs from RalA or RalB depleted cells have limited organotropic capacities
and are less efficient in promoting metastasis. RalA and RalB reduce the EV levels of the adhesion molecule MCAM/CD146, which favors EV-mediated metastasis by allowing EVs targeting to the lungs. Finally, RalA, RalB, and MCAM/CD146, are factors of poor prognosis in breast cancer patients. Altogether, our study identifies RalGTPases as central molecules linking the mechanisms of EVs secretion and cargo loading to their capacity to disseminate and induce pre-metastatic niches in a CD146-dependent manner.
Studying key biological events within complex model systems relies on dynamic and functional imaging at optimum spatial and temporal resolutions. Intravital correlative light and electron microscopy ...(intravital CLEM) combines imaging living multicellular model systems with electron microscopy, and offers full ultrastructural details of dynamic or transient events in vivo . However, routine use of intravital CLEM is hindered by multiple technological challenges faced when targeting a micron-size object (e.g., single cells or organelles) in a complex living organism. Recently, various approaches have been developed to overcome these limitations. In this review we outline the current methods and present the power of intravital CLEM in different fields of research. Finally, we describe approaches that will make intravital CLEM a routine, quantitative method for high-resolution cell biology in vivo.
Exosomes are secreted vesicles arising from the fusion of multivesicular bodies (MVBs) with the plasma membrane. Despite their importance in various processes, the molecular mechanisms controlling ...their formation and release remain unclear. Using nematodes and mammary tumor cells, we show that Ral GTPases are involved in exosome biogenesis. In Caenorhabditis elegans, RAL-1 localizes at the surface of secretory MVBs. A quantitative electron microscopy analysis of RAL-1-deficient animals revealed that RAL-1 is involved in both MVB formation and their fusion with the plasma membrane. These functions do not involve the exocyst complex, a common Ral guanosine triphosphatase (GTPase) effector. Furthermore, we show that the target membrane SNARE protein SYX-5 colocalizes with a constitutively active form of RAL-1 at the plasma membrane, and MVBs accumulate under the plasma membrane when SYX-5 is absent. In mammals, RalA and RalB are both required for the secretion of exosome-like vesicles in cultured cells. Therefore, Ral GTPases represent new regulators of MVB formation and exosome release.
Tumor extracellular vesicles (EVs) mediate the communication between tumor and stromal cells mostly to the benefit of tumor progression. Notably, tumor EVs travel in the bloodstream, reach distant ...organs, and locally modify the microenvironment. However, visualizing these events in vivo still faces major hurdles. Here, we describe an approach for tracking circulating tumor EVs in a living organism: we combine chemical and genetically encoded probes with the zebrafish embryo as an animal model. We provide a first description of tumor EVs’ hemodynamic behavior and document their intravascular arrest. We show that circulating tumor EVs are rapidly taken up by endothelial cells and blood patrolling macrophages and subsequently stored in degradative compartments. Finally, we demonstrate that tumor EVs activate macrophages and promote metastatic outgrowth. Overall, our study proves the usefulness and prospects of zebrafish embryo to track tumor EVs and dissect their role in metastatic niches formation in vivo.
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•MemBright allows for bright and specific staining of EVs•The zebrafish embryo allows tracking of tumor EVs at high spatiotemporal resolution•Circulating tumor EVs are mostly taken up by endothelial cells and patrolling macrophages•Zebrafish melanoma EVs favor metastatic outgrowth in zebrafish embryos
Tumor extracellular vesicles (EVs) promote tumor progression. However, their behavior in body fluids remains mysterious. Hyenne et al. show that the zebrafish embryo can be used to track and assess the function of circulating tumor EVs in vivo and provide a high-resolution description of their dissemination and uptake.
The mechanisms regulating the extension of small unicellular tubes remain poorly defined. Here we identify several steps in Caenorhabditis elegans excretory canal growth, and propose a model for ...lumen extension. Our results suggest that the basal and apical excretory membranes grow sequentially: the former extends first like an axon growth cone; the latter extends next as a result of an osmoregulatory activity triggering peri-apical vesicles (a membrane reservoir) to fuse with the lumen. An apical cytoskeletal web including intermediate filaments and actin crosslinking proteins ensures straight regular lumen growth. Expression of several genes encoding proteins mediating excretory lumen extension, such as the osmoregulatory STE20-like kinase GCK-3 and the intermediate filament IFB-1, is regulated by ceh-26 (here referred to as pros-1), which we found essential for excretory canal formation. Interestingly, PROS-1 is homologous to vertebrate Prox1, a transcription factor controlling lymphatic vessel growth. Our findings have potential evolutionary implications for the origin of fluid-collecting organs, and provide a reference for lymphangiogenesis.
Among a plethora of functions, extracellular vesicles released by primary tumors spread in the organism and reach distant organs where they can induce the formation of a premetastatic niche. This ...constitutes a favorable microenvironment for circulating tumor cells which facilitates their seeding and colonization. In this review, we describe the journey of extracellular vesicles (EVs) from the primary tumor to the future metastatic organ, with a focus on the mechanisms used by EVs to target organs with a specific tropism (i.e., organotropism). We then highlight important tumor EV cargos in the context of premetastatic niche formation and summarize their known effects on extracellular matrix remodeling, angiogenesis, vessel permeabilization, resident cell activation, recruitment of foreign cells, and ultimately the formation of a pro‐inflammatory and immuno‐tolerant microenvironment. Finally, we discuss current experimental limitations and remaining opened questions in light of metastatic diagnosis and potential therapies targeting PMN formation.
C. elegans embryonic elongation is a morphogenetic event driven by actomyosin contractility and muscle-induced tension transmitted through hemidesmosomes. A role for the microtubule cytoskeleton has ...also been proposed, but its contribution remains poorly characterized. Here, we investigate the organization of the non-centrosomal microtubule arrays present in the epidermis and assess their function in elongation. We show that the microtubule regulators γ-tubulin and NOCA-1 are recruited to hemidesmosomes and adherens junctions early in elongation. Several parallel approaches suggest that microtubule nucleation occurs from these sites. Disrupting the epidermal microtubule array by overexpressing the microtubule-severing protein Spastin or by inhibiting the C. elegans ninein homolog NOCA-1 in the epidermis mildly affected elongation. However, microtubules were essential for elongation when hemidesmosomes or the activity of the Rho kinase LET-502/ROCK were partially compromised. Imaging of junctional components and genetic analyses suggest that epidermal microtubules function together with Rho kinase to promote the transport of E-cadherin to adherens junctions and myotactin to hemidesmosomes. Our results indicate that the role of LET-502 in junctional remodeling is likely to be independent of its established function as a myosin II activator, but requires a microtubule-dependent pathway involving the syntaxin SYX-5. Hence, we propose that non-centrosomal microtubules organized by epidermal junctions contribute to elongation by transporting junction remodeling factors, rather than having a mechanical role.
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