Melanoma Glycome Regulates the Pro-Oncogenic Properties of Extracellular Galectin-3.

Metastatic melanoma is an aggressive skin cancer with a five-year survival rate of only 35%. Despite recent advances in immunotherapy, there is still an urgent need for the development of innovative therapeutic approaches to improve clinical outcomes of patients with metastatic melanoma. Prior research from our laboratory revealed that loss of the I-branching enzyme β1,6 N-acetylglucosaminyltransferase 2 (GCNT2), with consequent substitution of melanoma surface I-branched poly-N-acetyllactosamines (poly-LacNAcs) with i-linear poly-LacNAcs, is implicated in driving melanoma metastasis. In the current study, we explored the role of galectin-3 (Gal-3), a lectin that avidly binds surface poly-LacNAcs, in dictating melanoma aggressive behavior. Our results show that Gal-3 favors binding to i-linear poly-LacNAcs, while enforced GCNT2/I-branching disrupts this interaction, thereby suppressing Gal-3-dependent malignant characteristics, including extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway activation, expression, cell proliferation, and migration. This report establishes the crucial role of extracellular Gal-3 interactions with i-linear glycans in promoting melanoma cell aggressiveness, placing GCNT2 as a tumor suppressor protein and suggesting both extracellular Gal-3 and i-linear glycans as potential therapeutic targets for metastatic melanoma.