Signal-driven relocation of GalNAc-transferases (GALNTs) from the Golgi to the ER, termed GALA, promotes tumour growth, but its effects on glycosylation are unclear. Unlike N-glycosylation, which is co-translational, O-glycosylation initiates post-translationally in the Golgi. Here we show that GALA subverts this arrangement in pancreatic ductal adenocarcinomas (PDAC) and in murine pancreatic tumours, where it stimulates growth. Quantitative glycoproteomics on a cellular model reveals a substantial expansion of the O-glycoproteome, consisting in thousands of sites across hundreds of proteins, ER-resident proteins, cell-surface receptors, secreted factors, and extracellular matrix components. Profiling of murine tumours and patient-derived xenografts confirms widespread activation and cross-species conservation of glycosylation patterns. Structural analysis reveals that GALA-specific residues have solvent accessibility as low as N-glycosylation sites, and below Golgi O-glycosylation or phosphorylation sites, indicating that ER O-glycosylation occurs co-translationally. By inverting the normal temporal sequence of folding and glycosylation, cancer cells generate alternative glycoforms that foster tumour growth.
Bennion, R., Lohman, E., Del Rio, G., Rouyer, L., Kowalczewska, M., Le Guezennec, X., Mas, E., Dusetti, N., Chauvin, A., Tomasini, R., Vasseur, S., Guillaumond, F., Chanez, B., Humphries, M. J., Vakhrushev, S. Y., Bard, F. A.
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