TMIC-27. CONTACT-INDUCED BI-DIRECTIONAL PRO-SURVIVAL SIGNALING BETWEEN ENDOTHELIAL CELLS AND CANCER STEM-LIKE CELLS IN GLIOBLASTOMA

Abstract

We have demonstrated previously that direct contact between brain endothelial cells (ECs) and cancer stem-like cells (CSCs) from glioblastoma (GBM) significantly enhances endothelial cell migration and angiogenesis through a distinct signaling pathway (Burgett et al, Oncotarget 2016; doi: 10.18632/oncotarget.9700). To determine whether this contact promotes bi-directional signaling that regulates survival, we co-cultured ECs with CSCs on laminin in neurobasal media (NBM) without growth factors (3 hrs) and analyzed the mRNA expression of genes regulating survival and apoptosis with comparison to the mRNA levels found for ECs or CSCs cultured in the conditioned media from EC-CSC co-culture on laminin in NBM without growth factors (CM/EC+CSC). ECs or CSCs from co-culture or from culture in CM/EC+CSCs were harvested with accutase, sorted for expression or not of the EC marker CD31, and stained for the EC marker vWf or for the CSC marker Sox2. We found that the direct contact of ECs and CSCs significantly increased the mRNA levels of the anti-apoptotic proteins Bcl2 and survivin by 58- and 5.2-fold, respectively in ECs, compared to the mRNA levels of these genes in ECs cultured in CM/EC+CSCs. We also found that the direct contact of ECs and CSCs significantly increased the mRNA levels of Bcl2 and survivin by 2.3- and 3.5-fold in CSCs as well as significantly decreased the mRNA level of the apoptosis-inducing Fas ligand in CSCs by 3.5-fold, as compared to CSCs cultured in CM/EC+CSC. In contrast, there was no change in the mRNA levels of MCL1 and TRAF1 genes in ECs or CSCs that were in direct contact. These data suggest that direct contact between ECs and CSCs promotes bi-directional pro-survival signaling in the perivascular niche in GBM that is not due to secreted factors from ECs or CSCs.