Remodeling of keratin-coupled cell adhesion complexes

International audienceEpithelial cells constitute the main barrier between the inside and outside of organs, acting as gatekeepers of their structure and integrity. Hemidesmosomes and desmosomes are respectively cell-matrix and cell-cell adhesions coupled to the intermediate filament cytoskeleton. These adhesions ensure mechanical integrity of the epithelial barrier. Although desmosomes and hemidesmosomes are essential in maintaining strong cell-cell and cell-matrix adhesions, there is an emerging view that they should be remodeled in order to maintain epithelial homeostasis. Here we review the adhesion properties of desmosomes and hemidesmosomes, as well as the mechanisms driving their remodeling. We also discuss recent data suggesting that keratin-coupled adhesion complexes can sense the biomechanical cellular environment and participate in the cellular response to such external cues

Deciphering circulating tumor cells binding in a microfluidic system thanks to a parameterized mathematical model

Metastatic spread is a crucial process in which some questions remain unanswered. In this work, we focus on tumor cells circulating in the bloodstream, so-called Circulating Tumor Cells (CTCs). We aim to characterize their trajectories under the influence of hemodynamic forces and adhesion forces resulting from interaction with an endothelial layer using in vitro measurements performed with a microfluidic device. This essential step in tumor spread precedes intravascular arrest and metastatic extravasation. Our strategy is based on a differential equation model - a Poiseuille model for the fluid velocity and an ODE system for the cell adhesion model - and allows us to separate the two phenomena underlying cell motion: transport of the cell through the fluid and adhesion to the endothelial layer. A robust calibration procedure enables us to characterize the dynamics. Our strategy reveals the expected role of the glycoprotein CD44 compared to the integrin ITGB1 in the deceleration of CTCs and quantifies the strong impact of the fluid velocity in the protein binding

An Arf6- and caveolae-dependent pathway links hemidesmosome remodeling and mechanoresponse

International audienceHemidesmosomes (HDs) are epithelial-specific cell-matrix adhesions that stably anchor the intracellular keratin network to the extracellular matrix. Although their main role is to protect the epithelial sheet from external mechanical strain, how HDs respond to mechanical stress remains poorly understood. Here we identify a pathway essential for HD remodeling and outline its role with respect to α6β4 integrin recycling. We find that α6β4 integrin chains localize to the plasma membrane, caveolae, and ADP-ribosylation factor-6+ (Arf6+) endocytic compartments. Based on fluorescence recovery after photobleaching and endocytosis assays, integrin recycling between both sites requires the small GTPase Arf6 but neither caveolin1 (Cav1) nor Cavin1. Strikingly, when keratinocytes are stretched or hypo-osmotically shocked, α6β4 integrin accumulates at cell edges, whereas Cav1 disappears from it. This process, which is isotropic relative to the orientation of stretch, depends on Arf6, Cav1, and Cavin1. We propose that mechanically induced HD growth involves the isotropic flattening of caveolae (known for their mechanical buffering role) associated with integrin diffusion and turnover

Fluids and their mechanics in tumour transit: shaping metastasis

International audienceThe Greek phrase 'Panta Rhei' , which literally translates as 'everything flows' , is a philosophical concept that is often attributed to the presocratic Greek philosopher Heraclitus (circa 500 bc) and was an attempt to explain the ever-changing nature of life. Work over the past decades has shown that this notion might also apply to tumour metastasis, a complex multistep process whereby malignant tumours shed invasive cells with metastatic capacity that need to overcome many obstacles (for example, immune surveillance) for successful outgrowth at secondary sites 1. However, in addition to the multiple molecular pathways driving metastasis, a plethora of studies conducted over the past two decades strongly suggest that mechanical forces are also responsible for tumour progression and response to classical therapies 2-4. Among these forces, fluid-based mechanics have progressively entered the scene. Indeed, on their way to forming a metastasis, tumour cells and tumour-secreted factors use and exploit three main bodily fluids-blood, lymph and interstitial fluid 5-7 (Fig. 1a). Circulating tumour cells (CTCs) and their associated material, including soluble factors and extracellular vesicles (EVs), can directly travel through the haematogenous system 1,8 or sequentially use both the lymphatic and blood vasculature to colonize distant organs 9-11 (Fig. 1b). This notion that fluid-based mechanics can shape metastasis originated from an early pivotal study that coined the 'hemodynamic theory' , which showed that arterial blood flow in certain organs can be positively correlated with the frequency and patterns of metasta-sis 12 , supporting a link between flow mechanics and the secondary site of metastasis. When transported in fluids, CTCs are subjected to and exploit various mechanical forces, which can influence their fate in many ways. For instance, high shear forces exerted on CTCs can induce mechanical stress, leading to cell fragmentation and death 13 , whereas intermediate shear forces have been shown to favour CTC intravascular arrest and extravasation 14. Thus, an improved understanding of the mechanical forces encountered by CTCs and tumour-associated material in fluids is crucial for fully elucidating the metastatic cascade and delineating vulnerable CTC states for therapeutic intervention. In this Review, we describe how circulating tumour-derived material (cells and associated factors) use bodily fluids, their underlying forces and the resultant stresses they impose as a natural means to escape from primary tumours, travel throughout the body, prime pre-metastatic niches (PMNs) and successfully seed distant metastases. We briefly discuss key flow-related aspects of tumour growth and invasion that have received considerable attention 2,6,7 and discuss how these modes of flow are essential means of transport Fluids and their mechanics in tumour transit: shaping metastasis Abstract | 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

Ral GTPases promote breast cancer metastasis by controlling biogenesis and organ targeting of exosomes

International audienceCancer 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 in vivo 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

Hemodynamic forces tune the arrest, adhesion and extravasation of circulating tumor cells

International audienc

Hemodynamic forces tune the arrest, adhesion and extravasation of circulating tumor cells

International audienc