title: Breast cancer cells promote a notch-dependent mesenchymal phenotype in endothelial cells participating to a pro-tumoral niche.
abstract: BACKGROUND
  Endothelial cells (ECs) are responsible for creating a tumor vascular niche as well as producing angiocrine factors. ECs demonstrate functional and phenotypic heterogeneity when located under different microenvironments. Here, we describe a tumor-stimulated mesenchymal phenotype in ECs and investigate its impact on tumor growth, stemness, and invasiveness.
  
  
  METHODS
  Xenograft tumor assay in NOD/SCID mice and confocal imaging were conducted to show the acquisition of mesenchymal phenotype in tumor-associated ECs in vivo. Immunocytochemistry, qPCR and flow cytometry techniques showed the appearance of mesenchymal traits in ECs after contact with breast tumor cell lines MDA-MB231 or MCF-7. Cell proliferation, cell migration, and sphere formation assays were applied to display the functional advantages of mesenchymal ECs in tumor growth, invasiveness, and enrichment of tumor initiating cells. qPCR and western blotting were used to investigate the mechanisms underlying EC mesenchymal transition.
  
  
  RESULTS
  Our results showed that co-injection of ECs and tumor cells in NOD/SCID mice significantly enhanced tumor growth in vivo with tumor-associated ECs expressing mesenchymal markers while maintaining their intrinsic endothelial trait. We also showed that a mesenchymal phenotype is possibly detectable in human neoplastic breast biopsies as well as ECs pre-exposed to tumor cells (ECs(Mes)) in vitro. The ECs(Mes) acquired prolonged survival, increased migratory behavior and enhanced angiogenic properties. In return, ECs(Mes) were capable of enhancing tumor survival and invasiveness. The mesenchymal phenotypes in ECs(Mes) were the result of a contact-dependent transient phenomenon and reversed upon removal of the neoplastic contexture. We showed a synergistic role for TGFβ and notch pathways in this phenotypic change, as simultaneous inhibition of notch and TGFβ down-regulated Smad1/5 phosphorylation and Jag1(KD) tumor cells were unable to initiate the process.
  
  
  CONCLUSIONS
  Overall, our data proposed a crosstalk mechanism between tumor and microenvironment where tumor-stimulated mesenchymal modulation of ECs enhanced the constitution of a transient mesenchymal/endothelial niche leading to significant increase in tumor proliferation, stemness, and invasiveness. The possible involvement of notch and TGFβ pathways in the initiation of mesenchymal phenotype may propose new stromal targets.
authors.affiliation: Stem Cell and Microenvironment Laboratory, Weill Cornell Medical College in Qatar, Education City, Qatar Foundation, P.O. Box 24144, Doha, Qatar. Peg2006@qatar-med.cornell.edu.
authors.forename: Pegah
authors.initials: P
authors.lastname: Ghiabi
authors.affiliation: Department of Genetic Medicine, Weill Cornell Medical College, New york city, NY, USA. Jij2007@med.cornell.edu.
authors.forename: Jie
authors.initials: J
authors.lastname: Jiang
authors.affiliation: Stem Cell and Microenvironment Laboratory, Weill Cornell Medical College in Qatar, Education City, Qatar Foundation, P.O. Box 24144, Doha, Qatar. Jep2026@qatar-med.cornell.edu.|Department of Genetic Medicine, Weill Cornell Medical College, New york city, NY, USA. Jep2026@qatar-med.cornell.edu.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Pasquier
authors.affiliation: Stem Cell and Microenvironment Laboratory, Weill Cornell Medical College in Qatar, Education City, Qatar Foundation, P.O. Box 24144, Doha, Qatar. Mam2116@qatar-med.cornell.edu.
authors.forename: Mahtab
authors.initials: M
authors.lastname: Maleki
authors.affiliation: Stem Cell and Microenvironment Laboratory, Weill Cornell Medical College in Qatar, Education City, Qatar Foundation, P.O. Box 24144, Doha, Qatar. Naa2037@qatar-med.cornell.edu.
authors.forename: Nadine
authors.initials: N
authors.lastname: Abu-Kaoud
authors.affiliation: Stem Cell and Microenvironment Laboratory, Weill Cornell Medical College in Qatar, Education City, Qatar Foundation, P.O. Box 24144, Doha, Qatar. Nah2024@qatar-med.cornell.edu.|Department of Genetic Medicine, Weill Cornell Medical College, New york city, NY, USA. Nah2024@qatar-med.cornell.edu.
authors.forename: Najeeb
authors.initials: N
authors.lastname: Halabi
authors.affiliation: Stem Cell and Microenvironment Laboratory, Weill Cornell Medical College in Qatar, Education City, Qatar Foundation, P.O. Box 24144, Doha, Qatar. Bsg2004@qatar-med.cornell.edu.|Department of Genetic Medicine, Weill Cornell Medical College, New york city, NY, USA. Bsg2004@qatar-med.cornell.edu.
authors.forename: Bella S
authors.initials: BS
authors.lastname: Guerrouahen
authors.affiliation: Department of Genetic Medicine, Weill Cornell Medical College, New york city, NY, USA. srafii@med.cornell.edu.
authors.forename: Shahin
authors.initials: S
authors.lastname: Rafii
authors.affiliation: Stem Cell and Microenvironment Laboratory, Weill Cornell Medical College in Qatar, Education City, Qatar Foundation, P.O. Box 24144, Doha, Qatar. Jat2021@qatar-med.cornell.edu.|Department of Genetic Medicine, Weill Cornell Medical College, New york city, NY, USA. Jat2021@qatar-med.cornell.edu.
authors.forename: Arash
authors.initials: A
authors.lastname: Rafii
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D061307:Human Umbilical Vein Endothelial Cells / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008648:Mesoderm / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D010641:Phenotype; D051880:Receptors, Notch / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D059467:Transcriptome / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000378:metabolism; D059016:Tumor Microenvironment; D023041:Xenograft Model Antitumor Assays
chemical_list: D051880:Receptors, Notch; D016212:Transforming Growth Factor beta