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. Author manuscript; available in PMC: 2017 Jul 6.
Published in final edited form as: Trends Mol Med. 2014 Mar 22;20(6):332–342. doi: 10.1016/j.molmed.2014.02.007

Figure 3.

Figure 3

Differences between the glycosylation patterns in normal and tumor-associated MUC1 (TA-MUC1). (A) N-Acetylgalactosamine (GalNAc) is first added to the serine and threonine residues of the MUC1-N VNTR, catalyzed by αGalNAc transferases to generate the Tn antigen. Core 1 β1,3-galactose transferase (Core 1 β1,3-Gal T) catalyzes the addition of galactose to Tn antigen to generate Core 1 O-glycan (also called T antigen). GlcNAc (N-acetyl glucosamine) is then added to the Core 1 O-glycan catalyzed by Core 2 β1,6-N-acetyl glucosamine transferase (Core 2 β1,6-GlcNAc T). The sugar branches of Core 2 glycans undergo further chain elongation followed by termination upon addition of fucose, or sialic acid to the terminal sugar [114]. (B) MUC1 is hypoglycosylated in cancer cells. Tn and T antigens are sialylated to sialyl Tn and sialyl T, respectively, which are catalyzed by the enzyme α2, 6-sialyltransferase and α2, 3-sialyltransferase, respectively. Sialylation causes premature termination of chain elongation. Abbreviations: GalNAc T, N-acetylgalactosamine transferase; GlcNAc T, N-acetyl glucosamine transferase; Gal T, galactose transferase; Sialyl T, sialyl transferase; MUC1, Mucin 1; VNTR, variable number tandem repeat.