Hypoxia controls the glycome signature and galectin-8 – ligand axis to promote pro-tumorigenic properties of metastatic melanoma.
The prognosis for patients with metastatic melanoma (MM) involving distant organs is grim, and treatment resistance is potentiated by tumor-initiating cells (TIC) that thrive under hypoxia. MM cells, including TICs, express a unique glycome featuring i-linear poly-N-acetyllactosamines (poly-LacNAc) via loss of I-branching enzyme, β1,6 N-acetylglucosaminyltransferase 2 (GCNT2). Whether hypoxia instructs MM TIC development by modulating the glycome signature remains unknown. Here, we explored hypoxia-dependent alterations in MM glycome-associated genes and found that GCNT2 was downregulated and a galectin (Gal)-8 – ligand axis, involving both extracellular and cell-intrinsic Gal-8, was induced. Low GCNT2 levels correlated with poor patient outcome and patient serum samples were elevated for Gal-8. Depressed GCNT2 in MM cells upregulated TIC marker, nerve growth factor receptor (NGFR)/CD271, whereas loss of MM cell-intrinsic Gal-8 markedly lowered NGFR and reduced TIC activity in vivo. Extracellular Gal-8 bound preferentially to i-linear poly-LacNAcs on N-glycans of the TIC marker and pro-metastatic molecule CD44, among other receptors and activated pro-survival factor AKT. This study reveals the importance of hypoxia governing the MM glycome by enforcing i-linear poly-LacNAc and Gal-8 expression. This mechanistic investigation also uncovers glycome-dependent regulation of pro-MM factor, NGFR, implicating i-linear poly-LacNAcs and Gal-8 as biomarkers and therapeutic targets of MM.