Novel paracrine modulation of Notch-DLL4 signaling by fibulin-3 promotes angiogenesis in high-grade gliomas

• Published in: Cancer research (Chicago, Ill.) Vol. 74; no. 19; pp. 5435 - 5448
• Main Authors: Nandhu, Mohan S, Hu, Bin, Cole, Susan E, Erdreich-Epstein, Anat, Rodriguez-Gil, Diego J, Viapiano, Mariano S
• Format: Journal Article
• Language: English
• Published: United States 01.10.2014
• Subjects: Animals; Brain Neoplasms - blood supply; Brain Neoplasms - metabolism; Cell Line, Tumor; Disease Models, Animal; Extracellular Matrix Proteins - metabolism; Glioma - blood supply; Glioma - metabolism; Humans; Intercellular Signaling Peptides and Proteins - metabolism; Neovascularization, Pathologic; Rats; Receptors, Notch - metabolism; Signal Transduction
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.can-14-0685

High-grade gliomas are characterized by exuberant vascularization, diffuse invasion, and significant chemoresistance, resulting in a recurrent phenotype that makes them impossible to eradicate in the long term. Targeting protumoral signals in the glioma microenvironment could have significant impact against tumor cells and the supporting niche that facilitates their growth. Fibulin-3 is a protein secreted by glioma cells, but absent in normal brain, that promotes tumor invasion and survival. We show here that fibulin-3 is a paracrine activator of Notch signaling in endothelial cells and promotes glioma angiogenesis. Fibulin-3 overexpression increased tumor VEGF levels, microvascular density, and vessel permeability, whereas fibulin-3 knockdown reduced vessel density in xenograft models of glioma. Fibulin-3 localization in human glioblastomas showed dense fiber-like condensations around tumor blood vessels, which were absent in normal brain, suggesting a remarkable association of this protein with tumor endothelium. At the cellular level, fibulin-3 enhanced endothelial cell motility and association to glioma cells, reduced endothelial cell sprouting, and increased formation of endothelial tubules in a VEGF-independent and Notch-dependent manner. Fibulin-3 increased ADAM10/17 activity in endothelial cells by inhibiting the metalloprotease inhibitor TIMP3; this resulted in increased Notch cleavage and increased expression of DLL4 independently of VEGF signaling. Inhibition of ADAM10/17 or knockdown of DLL4 reduced the proangiogenic effects of fibulin-3 in culture. Taken together, these results reveal a novel, proangiogenic role of fibulin-3 in gliomas, highlighting the relevance of this protein as an important molecular target in the tumor microenvironment.