TMET-44. ST6Gal1 Mediated α2,6 Sialylation Regulates Glioblastoma Metabolism and GLUT3 Dynamics

Unlike other post translational modifications like phosphorylation, glycosylation has often been overlooked as a critical regulator of cell signaling in cancers, including brain tumors. One form of glycosylation is sialylation, or the addition of sialic acid to glycoproteins. We recently published that brain tumor initiating cells (BTICs) express high levels of the glycosyltransferase beta-galactoside α2,6-sialytransferase 1 (ST6Gal1). ST6Gal1-mediated α2,6 sialylation in BTICs was critical for glioblastoma growth in vivo. To further identify the molecular targets of ST6Gal1 in BTICs, we performed proteomic profiling of α2,6 sialylated proteins in cell lysates with and without ST6Gal1. When the proteins that were pulled down in non-targeting controls but depleted with ST6Gal1knockdown were evaluated in pathways analysis, there was enrichment for metabolic pathways. Untargeted metabolomics of GBM cells with ST6Gal1 knockdown further confirmed shifts in metabolism with ST6Gal1 loss, notably changes in glycolysis. α2,6 sialylation high GBM cells had increased glucose uptake in comparison to α2,6 sialylation low GBM cells: knockdown of ST6Gal1 with two different shRNAs in BTICs also decreased glucose uptake in comparison to non-targeting control shRNA cells. Knowing that a major regulator of glucose uptake in BTICs is the N-glycoprotein GLUT3, we investigated whether GLUT3 could be a target for ST6Gal1-α2,6 mediated sialylation. Based on its sequence, GLUT3 has a single, potential N-glycan target for α2,6 sialylation. While the biological consequence of GLUT3 α2,6 sialylation remained unknown, ST6Gal1-mediated α2,6 sialylation regulates protein conformation, cell-surface retention, and interactions. Thus, we used high resolution imaging to investigate ST6Gal1 impacts on GLUT3 cell-surface dynamics. We determined that ST6Gal1 knockdown decreased cell surface levels of GLUT3 but did not decrease intracellular levels of GLUT3. Overall, we demonstrate a critical role for ST6Gal1 and α2,6 sialylation in GBM metabolism and define GLUT3 as a novel target of ST6Gal1-mediated α2,6 sialylation.