β1,4-Galactosyltransferase V activates Notch1 signaling in glioma stem-like cells and promotes their transdifferentiation into endothelial cells

Malignant glioblastoma multiforme is one of the most aggressive human cancers, with very low survival rates. Recent studies have reported that glioma stem-like cells transdifferentiate into endothelial cells, indicating a new mechanism for tumor angiogenesis and potentially providing new therapeutic options for glioblastoma treatment. Glioma malignancy is strongly associated with altered expression of N-linked oligosaccharide structures on the cell surface. We have previously reported that 1,4-galactosyltransferase V (1,4GalTV), which galactosylates the GlcNAc1-6Man arm of the branched N-glycans, is highly expressed in glioma and promotes glioma cell growth in vitro and in vivo. However, the mechanism by which 1,4GalTV stimulates glioma growth is unknown. Here we demonstrate that short hairpin RNA-mediated 1,4GalTV knockdown inhibits the tumorigenesis of glioma stem-like cells and reduces their transdifferentiation into endothelial cells. We also found that 1,4GalTV overexpression increased glioma stem-like cell transdifferentiation into endothelial cells and that this effect required 1,4GalTV galactosylation activity. Moreover, 1,4GalTV promoted 1,4-galactosylation of Notch1 and increased Notch1 protein levels. Of note, ectopic expression of activated Notch1 rescued the inhibitory effect of 1,4GalTV depletion on glioma stem-like cell transdifferentiation. In summary, our findings indicate that 1,4GalTV stimulates transdifferentiation of glioma stem-like cells into endothelial cells by activating Notch1 signaling. These detailed insights shed important light on the mechanisms regulating glioma angiogenesis.