Mast cells impair melanoma cell homing and metastasis by inhibiting HMGA1 secretion.

Metastatic disease is the major cause of death from cancer. From the primary tumour, cells remotely prepare the environment of the future metastatic sites by secreted factors and extracellular vesicles. During this process, known as pre-metastatic niche formation, immune cells play a crucial role. Mast cells are haematopoietic bone marrow-derived innate immune cells whose function in lung immune response to invading tumours remains to be defined. We found reduced melanoma lung metastasis in mast cell-deficient mouse models (Wsh and MCTP5-Cre-RDTR), supporting a pro-metastatic role for mast cells in vivo. However, due to evidence pointing to their antitumorigenic role, we studied the impact of mast cells in melanoma cell function in vitro. Surprisingly, in vitro co-culture of bone-marrow-derived mast cells with melanoma cells showed that they have an intrinsic anti-metastatic activity. Mass spectrometry analysis of melanoma-mast cell co-cultures secretome showed that HMGA1 secretion by melanoma cells was significantly impaired. Consistently, HMGA1 knockdown in B16-F10 cells reduced their metastatic capacity in vivo. Importantly, analysis of HMGA1 expression in human melanoma tumours showed that metastatic tumours with high HMGA1 expression are associated with reduced overall and disease-free survival. Moreover, we show that HMGA1 is reduced in the nuclei and enriched in the cytoplasm of melanoma metastatic lesions when compared to primary tumours. These data suggest that high HMGA1 expression and secretion from melanoma cells promote metastatic behaviour. Targeting HMGA1 expression intrinsically or extrinsically by mast cells actions reduce melanoma metastasis. Our results pave the way to the use of HMGA1 as anti-metastatic target in melanoma as previously suggested in other cancer types.US NIH (R01-CA169416); Children's Cancer and Blood Foundation; Feldestein Foundation; Melanoma Research Alliance; Nancy C. and Daniel P. Paduano Foundation; Starr Foundation;Translational NeTwork for the CLinical application of Extracellular VesicleSS

Tumour exosomal CEMIP protein promotes cancer cell colonization in brain metastasis

The development of effective therapies against brain metastasis is currently hindered by limitations in our understanding of the molecular mechanisms driving it. Here we define the contributions of tumour-secreted exosomes to brain metastatic colonization and demonstrate that pre-conditioning the brain microenvironment with exosomes from brain metastatic cells enhances cancer cell outgrowth. Proteomic analysis identified cell migration-inducing and hyaluronan-binding protein (CEMIP) as elevated in exosomes from brain metastatic but not lung or bone metastatic cells. CEMIP depletion in tumour cells impaired brain metastasis, disrupting invasion and tumour cell association with the brain vasculature, phenotypes rescued by pre-conditioning the brain microenvironment with CEMIP exosomes. Moreover, uptake of CEMIP+ exosomes by brain endothelial and microglial cells induced endothelial cell branching and inflammation in the perivascular niche by upregulating the pro-inflammatory cytokines encoded by Ptgs2, Tnf and Ccl/Cxcl, known to promote brain vascular remodelling and metastasis. CEMIP was elevated in tumour tissues and exosomes from patients with brain metastasis and predicted brain metastasis progression and patient survival. Collectively, our findings suggest that targeting exosomal CEMIP could constitute a future avenue for the prevention and treatment of brain metastasis

Identification of distinct nanoparticles and subsets of extracellular vesicles by asymmetric flow field-flow fractionation

The heterogeneity of exosomal populations has hindered our understanding of their biogenesis, molecular composition, biodistribution and functions. By employing asymmetric flow field-flow fractionation (AF4), we identified two exosome subpopulations (large exosome vesicles, Exo-L, 90-120 nm; small exosome vesicles, Exo-S, 60-80 nm) and discovered an abundant population of non-membranous nanoparticles termed 'exomeres' (~35 nm). Exomere proteomic profiling revealed an enrichment in metabolic enzymes and hypoxia, microtubule and coagulation proteins as well as specific pathways, such as glycolysis and mTOR signalling. Exo-S and Exo-L contained proteins involved in endosomal function and secretion pathways, and mitotic spindle and IL-2/STAT5 signalling pathways, respectively. Exo-S, Exo-L and exomeres each had unique N-glycosylation, protein, lipid, DNA and RNA profiles and biophysical properties. These three nanoparticle subsets demonstrated diverse organ biodistribution patterns, suggesting distinct biological functions. This study demonstrates that AF4 can serve as an improved analytical tool for isolating extracellular vesicles and addressing the complexities of heterogeneous nanoparticle subpopulations.The authors also acknowledge the Genomics Resource Core facility (WCM) for their high-quality service. The authors thank C. Ghajar and J. Weiss for feedback on the manuscript and members of the Lyden laboratory for discussions. Our study was supported by the National Cancer Institute (U01-CA169538 to D.L.), the National Institutes of Health (NIH; R01-CA169416 to D.L. and H.P.; R01-CA218513 to D.L. and H.Z.), the US Department of Defense (W81XWH-13-10249 to D.L.), W81XWH-13-1-0425 (to D.L., J.Br.), the Sohn Conference Foundation (D.L., I.M., H.P. and H.Z.), the Children’s Cancer and Blood Foundation (D.L.), The Manning Foundation (A.H. and D.L.), The Hartwell Foundation (D.L.), The Nancy C. and Daniel P. Paduano Foundation (D.L.), The Starr Cancer Consortium (H.P. and D.L.; D.L. and H.Z.), the Pediatric Oncology Experimental Therapeutic Investigator Consortium (POETIC; D.L.), the James Paduano Foundation (D.L. and H.P.), the NIH/WCM CTSC (NIH/NCATS: UL1TR00457 to H.M. and H.Z.; UL1TR002384 to D.L., H.M. and H.Z.), the Malcolm Hewitt Wiener Foundation (D.L.), the Champalimaud Foundation (D.L.), the Thompson Family Foundation (D.L., R.S.), U01-CA210240 (D.L.), the Beth Tortolani Foundation (J.Br.), the Charles and Marjorie Holloway Foundation (J.Br.), the Sussman Family Fund (J.Br.), the Lerner Foundation (J.Br.), the Breast Cancer Alliance (J.Br.), the Manhasset Women’s Coalition Against Breast Cancer (J.Br.), the National Institute on Minority Health and Health Disparities (NIMHD) of the NIH (MD007599 to H.M.), NIH/NCATS (UL1TR00457 to H.M.). C.R., A.M., D.F., A.F., A.S. and H.O. acknowledge FEDER (Fundo Europeu de Desenvolvimento Regional funds through COMPETE 2020) POCI, Portugal 2020 (NORTE-01-0145-FEDER-000029) and FCT – Fundação para a Ciência e a Tecnologia in the framework of the project ‘Institute for Research and Innovation in Health Sciences’ (POCI-01-0145-FEDER-007274) and the FCT project POCI-01-0145-FEDER-016585 (PTDC/BBB-EBI/0567/2014). The authors acknowledge FCT for grants to A.M. (SFRH/BPD/75871/2011) and A.F. (SFRH/BPD/111048/2015). D.F. acknowledges FCT (SFRH/BD/110636/2015), the BiotechHealth PhD Programme (PD/0016/2012) and the American Portuguese Biomedical Research Fund.S