N-acetylglucosaminyltransferase V modifies the signaling pathway of epidermal growth factor receptor

Abstract

Transfection of sense cDNA of N-acetylglucosamyltransferase V (GnTV-S) into human H7721 hepatocarcinoma cells resulted in an increase in the N-acetylglucosaminebeta1,6mannosealpha1,3- branch (GnT-V product) on the N-glycans of epidermal growth factor (EGF) receptor (EGFR), and promotion of its EGF binding and tyrosine autophosphorylation, but showed little effect on the expression of EGFR protein. The phosphorylation at T308, S473 and tyrosine residue(s) and the activity of protein kinase B (Akt/PKB) as well as the phosphorylation of p42/44 mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK) before and after EGF stimulation were concomitantly increased. Conversely, in the antisense GnT-V (GnTV-AS)-transfected H7721 cells, all the results were the reverse of those with GnTV-S-transfected cells. After the cells were treated with 1-deoxymannojirimycin, an inhibitor of N-glycan processing at high mannose, or antibody against the extracellular glycan domain of EGFR, the differences in PKB activity, p42/44 MAPK and MEK phosphorylation among GnTV-S-, GnTV-AS- and mock-transfected cells were significantly attenuated. These findings indicate that the altered expression of GnT-V will change the glycan structure and function of EGFR, which may modify downstream signal transduction.

Blocking of N-acetylglucosaminyltransferase V induces cellular endoplasmic reticulum stress in human hepatocarcinoma 7721 cells

“…The result indicated that the structure of N-glycans in intracellular glycoproteins was altered generally due to the repression of GnT-V. It was consistent with the change of structure of N-glycans on GnT-V-AS/7721 cell surface in the previous studies [11][12][13].…”

“…The previous studies also found that the fuction of the glycoproteins on cell surfaces was changed for abnormal quantity of GnT-V products, which influenced the pathways or mechanisms associated with cancer progress and metastasis potential [8,9,12,13]. However the effects of altering GnT-V expression or activity on glycans structures as well as functions of intracellular N-glycoproteins have not been reported.…”

“…The consequence of GnT-V suppression was confirmed opposing to that in the enzyme overexpressed carcinoma cells. The decreased β-1,6-GlcNAc branch on the receptor of some growth factors, such as EGFR on 7721 cells surface, reduced their binding affinity and tyrosine autophosphorylation, and the phosphorylation and/or activity of some key signal molecules in both Ras/Raf/MEK/MAPK and PI-3-K/PKB pathway was sequentially reduced [12]. Besides these, the amount of β-1,6-GlcNAc branch on integrin β1 subunit was decreased after blocking GnT-V in 7721, which conduced to adhesion [13].…”

“…In previous studies, GnT-V biofunction was extensively studied with the GnT-V-AS/7721 cell line obtained by stably transfecting 7721 human hepatocarcinoma cell line with antisense GnT-V cDNA [11][12][13][14]. In this paper, gene expression profile of GnT-V-AS/7721 cells was studied by cDNA array analysis, and the expression pattern consistent with ER stress was found.…”

High expression of N-acetylglucosaminyltransferase V in mucinous tumors of the ovary

“…L 4 -PHA lectin blotting revealed that the major target glycoproteins of GnT-V in mucinous ovarian carcinoma were 60-200 kDa in molecular size. Previous reports indicated several specific substrates for GnT-V glycosylation and changes in the biological characteristics of cancer cells; matriptase (21), lamp-1 (22), N-cadherin (23), ·5ß1-integrin (14,16), and epidermal growth factor receptor (EGFR) (24). In these substrates, ·5ß1-integrin is a protein heterodimer of 150 and 130 kDa, and is associated with migration.…”