The gain-of-function GLI1 transcription factor TGLI1 enhances expression of VEGF-C and TEM7 to promote glioblastoma angiogenesis

// Richard L. Carpenter 1 , Ivy Paw 1 , Hu Zhu 4 , Sherona Sirkisoon 1 , Fei Xing 1 , Kounosuke Watabe 1, 3 , Waldemar Debinski 1, 2, 3 , Hui-Wen Lo 1, 2, 3 1 Department of Cancer Biology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA 2 Brain Tumor Center of Excellence, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA 3 Comprehensive Cancer Center, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA 4 Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA Correspondence to: Hui-Wen Lo, e-mail: hlo@wakehealth.edu Keywords: glioblastoma, TGLI1, GLI1, angiogenesis, VEGF-C Received: March 23, 2015      Accepted: May 21, 2015      Published: June 04, 2015 ABSTRACT We recently discovered that truncated glioma-associated oncogene homolog 1 (TGLI1) is highly expressed in glioblastoma (GBM) and linked to increased GBM vascularity. The mechanisms underlying TGLI1-mediated angiogenesis are unclear. In this study, we compared TGLI1- with GLI1-expressing GBM xenografts for the expression profile of 84 angiogenesis-associated genes. The results showed that expression of six genes were upregulated and five were down-regulated in TGLI1-carrying tumors compared to those with GLI1. Vascular endothelial growth factor-C (VEGF-C) and tumor endothelial marker 7 (TEM7) were selected for further investigations because of their significant correlations with high vascularity in 135 patient GBMs. TGLI1 bound to both VEGF-C and TEM7 gene promoters. Conditioned medium from TGLI1-expressing GBM cells strongly induced tubule formation of brain microvascular endothelial cells, and the induction was prevented by VEGF-C/TEM7 knockdown. Immunohistochemical analysis of 122 gliomas showed that TGLI1 expression was positively correlated with VEGF-C, TEM7 and microvessel density. Analysis of NCBI Gene Expression Omnibus datasets with 161 malignant gliomas showed an inverse relationship between tumoral VEGF-C, TEM7 or microvessel density and patient survival. Together, our findings support an important role that TGLI1 plays in GBM angiogenesis and identify VEGF-C and TEM7 as novel TGLI1 target genes of importance to GBM vascularity.