Abstract
Glioma is the world's commonest primary brain malignancy with much of its biology relating to translational and post-translational events still unknown. In this study, we investigated the clinicopathological significance of N-linked β1-6-GlcNAc branches and GnT-V enzyme in the development and progression of astrocytic glioma. Expression of GnT-V and its GlcNAc-β1-6 oligosaccharides by-product together with Con-A binding sugars were assessed immunohistochemically on tissue microarrays of 16 normal brain and 159 tissue samples of astrocytomas of variable grades and histology. Although tissues of both grade I astrocytomas and normal brain showed considerably higher GnT-V expression, GlcNAc-β1-6 expression was significantly high only in tissues of grade I astrocytomas (p < 0.001), which is attributable to elevated levels of the precursor Con-A binding sugar moieties (p < 0.001). The activity of GnT-V enzyme was found to be dependent on the degree of glioma pathogenesis, as the GlcNAc-β1-6 branched expression diminished with every progressive grade of glioma, reaching minimum in glioblastoma (p < 0.001). Having biphasic activity in gliomagenesis, the role of GnT-V in glioma was deciphered by generating different ectopic GnT-V expressions in U-87 cells, which showed the highest GnT-V expression among selected glioma cell lines. Transient GnT-V rescue was achieved in knockdown clones by transfection with GnT-V expression vector. Suppression of GnT-V in U-87 cells slowed cell proliferation with G0/G1 cell cycle phase arrest. Reduced tumorigenicity, invasiveness and cell-ECM interactions were also associated with suppressed in vitro GnT-V activity suggesting GnT-V may act as an oncoprotein. We report for the first time that GnT-V products are involved in early gliomagenesis but their reduced expression, correlating with low Con-A binding sugars level found in high tumor grades predicts the loss of total N-glycosylation in glioma development and may be of potential diagnostic and/or prognostic value in astrocytoma.