Platelets favor the outgrowth of established metastases

Despite abundant evidence demonstrating that platelets foster metastasis, anti-platelet agents have low therapeutic potential due to the risk of hemorrhages. In addition, whether platelets can regulate metastasis at the late stages of the disease remains unknown. In this study, we subject syngeneic models of metastasis to various thrombocytopenic regimes to show that platelets provide a biphasic contribution to metastasis. While potent intravascular binding of platelets to tumor cells efficiently promotes metastasis, platelets further support the outgrowth of established metastases via immune suppression. Genetic depletion and pharmacological targeting of the glycoprotein VI (GPVI) platelet-specific receptor in humanized mouse models efficiently reduce the growth of established metastases, independently of active platelet binding to tumor cells in the bloodstream. Our study demonstrates therapeutic efficacy when targeting animals bearing growing metastases. It further identifies GPVI as a molecular target whose inhibition can impair metastasis without inducing collateral hemostatic perturbations.

Blood flow diverts extracellular vesicles from endothelial degradative compartments to promote angiogenesis

Extracellular vesicles released by tumors (tEVs) disseminate via circulatory networks and promote microenvironmental changes in distant organs favoring metastatic seeding. Despite their abundance in the bloodstream, how hemodynamics affect the function of circulating tEVs remains unsolved. We demonstrated that efficient uptake of tEVs occurs in venous endothelial cells that are subjected to hemodynamics. Low flow regimes observed in veins partially reroute internalized tEVs toward non-acidic and non-degradative Rab14-positive endosomes, at the expense of lysosomes, suggesting that endothelial mechanosensing diverts tEVs from degradation. Subsequently, tEVs promote the expression of pro-angiogenic transcription factors in low flow-stimulated endothelial cells and favor vessel sprouting in zebrafish. Altogether, we demonstrate that low flow regimes potentiate the pro-tumoral function of circulating tEVs by promoting their uptake and rerouting their trafficking. We propose that tEVs contribute to pre-metastatic niche formation by exploiting endothelial mechanosensing in specific vascular regions with permissive hemodynamics.

Identification of driver genes for critical forms of COVID-19 in a deeply phenotyped young patient cohort

[Figure: see text].

Impairing flow-mediated endothelial remodeling reduces extravasation of tumor cells

Tumor progression and metastatic dissemination are driven by cell-intrinsic and biomechanical cues that favor the growth of life-threatening secondary tumors. We recently identified pro-metastatic vascular regions with blood flow profiles that are permissive for the arrest of circulating tumor cells. We have further established that such flow profiles also control endothelial remodeling, which favors extravasation of arrested CTCs. Yet, how shear forces control endothelial remodeling is unknown. In the present work, we aimed at dissecting the cellular and molecular mechanisms driving blood flow-dependent endothelial remodeling. Transcriptomic analysis of endothelial cells revealed that blood flow enhanced VEGFR signaling, among others. Using a combination of in vitro microfluidics and intravital imaging in zebrafish embryos, we now demonstrate that the early flow-driven endothelial response can be prevented upon specific inhibition of VEGFR tyrosine kinase and subsequent signaling. Inhibitory targeting of VEGFRs reduced endothelial remodeling and subsequent metastatic extravasation. These results confirm the importance of VEGFR-dependent endothelial remodeling as a driving force of CTC extravasation and metastatic dissemination. Furthermore, the present work suggests that therapies targeting endothelial remodeling might be a relevant clinical strategy in order to impede metastatic progression.

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

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 in vivoand 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.

DNA repair complex licenses acetylation of H2A.Z.1 by KAT2A during transcription

Post-translational modifications of histone variant H2A.Z accompany gene transactivation, but its modifying enzymes still remain elusive. Here, we reveal a hitherto unknown function of human KAT2A (GCN5) as a histone acetyltransferase (HAT) of H2A.Z at the promoters of a set of transactivated genes. Expression of these genes also depends on the DNA repair complex XPC-RAD23-CEN2. We established that XPC-RAD23-CEN2 interacts both with H2A.Z and KAT2A to drive the recruitment of the HAT at promoters and license H2A.Z acetylation. KAT2A selectively acetylates H2A.Z.1 versus H2A.Z.2 in vitro on several well-defined lysines and we unveiled that alanine-14 in H2A.Z.2 is responsible for inhibiting the activity of KAT2A. Notably, the use of a nonacetylable H2A.Z.1 mutant shows that H2A.Z.1ac recruits the epigenetic reader BRD2 to promote RNA polymerase II recruitment. Our studies identify KAT2A as an H2A.Z.1 HAT in mammals and implicate XPC-RAD23-CEN2 as a transcriptional co-activator licensing the reshaping of the promoter epigenetic landscape.