ST6GAL1-MEDIATED SILALYLATION IS CRITICAL FOR GLIOBLASTOMA GROWTH

Abstract Although altered cell surface glycosylation was one of the earliest modifications observed in neoplastic progression, this facet of cancer cell biology has received meager attention, particularly in brain tumors. Among the various glycosyltransferases present in human cells, golgi sialyltransferase ST6Gal1 [beta-galactoside alpha-2,6-sialyltransferase 1] adds sialic acid residues in α2-6 linkage to membrane-bound and secreted N-glycans. ST6Gal1 is known to be pro-tumorigenic in epithelial cancers where it can promote epithelial to mesenchymal transformation, tumor-initiating cell (TIC) phenotypes, and survival of cells exposed to stressors such as chemo- and radiotherapy, hypoxia, or serum starvation. However, roles for this potent TIC regulator have not been well explored in GBM as experiments in standard cell lines suggested ST6Gal1 was epigenetically silenced. To explore our hypothesis that ST6Gal1-mediated α2,6 sialylation is elevated in Brain Tumor Initiating Cells (BTICs) and promotes GBM growth, we utilized GBM patient-derived xenografts (PDXs). ST6Gal1 is expressed in GBM PDX tissue sections and elevated in stem-like BTICs in comparison to differentiated GBM cells or astrocytes. Knockdown of ST6Gal1 in BTICs decreased growth and neurosphere formation capacity in vitro, suggesting that ST6Gal1 regulates BTIC maintenance. Similarly, cells isolated directly from PDXs that were sorted for high and low expression of α2,6 sialylation showed that α2,6 sialylationhigh GBM PDX have elevated neurosphere formation capacity and growth. Further, immunocompromised mice injected with sorted α2,6 sialylationhigh PDX cells had significantly lower survival compared to mice injected with α2,6 sialylationlow cells. Using proteomic analysis of ST6Gal1 KD vs NT PDX, we identified novel regulators of cancer stem cell biology directly modulated by ST6Gal1. As we identified a small subset of IDHwt GBMs with ST6Gal1 and SOX2 amplification, we are generating a novel gliomagenesis model with conditional ST6Gal1 overexpression. Together, our data strongly implicates ST6Gal1 as a regulator of GBM BTIC maintenance and GBM growth.