N-acetylglucosaminyltransferase III (GnT-III) is known to catalyze N-glycan "bisection" and thereby modulate the formation of highly branched complex structures within the Golgi apparatus. While active, it inhibits the action of other GlcNAc transferases such as GnT-IV and GnT-V. Moreover, GnT-III is considered as an inhibitor of the metastatic potential of cancer cells both in vitro and in vivo. However, the effects of GnT-III may be more diverse and depend on the cellular context. We describe the detailed glycomic analysis of the effect of GnT-III overexpression in WM266-4-GnT-III metastatic melanoma cells. We used MALDI-TOF and ESI-ion-trap-MS/MS together with HILIC-HPLC of 2-AA labeled N-glycans to study the N-glycome of membrane-attached and secreted proteins. We found that the overexpression of GnT-III in melanoma leads to the modification of a broad range of N-glycan types by the introduction of the "bisecting" GlcNAc residue with highly branched complex structures among them. The presence of these unusual complex N-glycans resulted in stronger interactions of cellular glycoproteins with the PHA-L. Based on the data presented here we conclude that elevated activity of GnT-III in cancer cells does not necessarily lead to a total abrogation of the formation of highly branched glycans. In addition, the modification of pre-existing N-glycans by the introduction of "bisecting" GlcNAc can modulate their capacity to interact with carbohydrate-binding proteins such as plant lectins. Our results suggest further studies on the biological function of "bisected" oligosaccharides in cancer cell biology and their interactions with carbohydrate-binding proteins.
Keywords: Cancer; Glycome; Glycosylation; Melanoma; N-acetylglucosaminyltransferase III.