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Glycobiology. 2015 Feb;25(2):225-40. doi: 10.1093/glycob/cwu105. Epub 2014 Oct 1.

Golgi N-glycan branching N-acetylglucosaminyltransferases I, V and VI promote nutrient uptake and metabolism.

Author information

1
Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 600 University Avenue, Room #988, Toronto, ON, Canada M5G1X5.
2
Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 600 University Avenue, Room #988, Toronto, ON, Canada M5G1X5 Department of Molecular Genetics.
3
Disease Glycomics Team, Systems Glycobiology Research Group, Chemical Biology Department, RIKEN-Max Planck Joint Research Center, RIKEN Global Research Cluster, Wako, Saitama 351-0198, Japan Graduate School of Advanced Sciences of Matter, Hiroshima University, Hiroshima 739-8530, Japan.
4
Disease Glycomics Team, Systems Glycobiology Research Group, Chemical Biology Department, RIKEN-Max Planck Joint Research Center, RIKEN Global Research Cluster, Wako, Saitama 351-0198, Japan.
5
Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 600 University Avenue, Room #988, Toronto, ON, Canada M5G1X5 Department of Molecular Genetics Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada M5G1X5 dennis@lunenfeld.ca.

Abstract

Nutrient transporters are critical gate-keepers of extracellular metabolite entry into the cell. As integral membrane proteins, most transporters are N-glycosylated, and the N-glycans are remodeled in the Golgi apparatus. The Golgi branching enzymes N-acetylglucosaminyltransferases I, II, IV, V and avian VI (encoded by Mgat1, Mgat2, Mgat4a/b/c Mgat5 and Mgat6), each catalyze the addition of N-acetylglucosamine (GlcNAc) in N-glycans. Here, we asked whether N-glycan branching promotes nutrient transport and metabolism in immortal human HeLa carcinoma and non-malignant HEK293 embryonic kidney cells. Mgat6 is absent in mammals, but ectopic expression can be expected to add an additional β1,4-linked branch to N-glycans, and may provide evidence for functional redundancy of the N-glycan branches. Tetracycline (tet)-induced overexpression of Mgat1, Mgat5 and Mgat6 resulted in increased enzyme activity and increased N-glycan branching concordant with the known specificities of these enzymes. Tet-induced Mgat1, Mgat5 and Mgat6 combined with stimulation of hexosamine biosynthesis pathway (HBP) to UDP-GlcNAc, increased cellular metabolite levels, lactate and oxidative metabolism in an additive manner. We then tested the hypothesis that N-glycan branching alone might promote nutrient uptake when glucose (Glc) and glutamine are limiting. In low glutamine and Glc medium, tet-induced Mgat5 alone increased amino acids uptake, intracellular levels of glycolytic and TCA intermediates, as well as HEK293 cell growth. More specifically, tet-induced Mgat5 and HBP elevated the import rate of glutamine, although transport of other metabolites may be regulated in parallel. Our results suggest that N-glycan branching cooperates with HBP to regulate metabolite import in a cell autonomous manner, and can enhance cell growth in low-nutrient environments.

KEYWORDS:

Golgi N-glycan branching; N-acetylglucosaminyltransferase enzymes; hexosamine biosynthetic pathway; metabolism; nutrient uptake

PMID:
25395405
PMCID:
PMC4276413
DOI:
10.1093/glycob/cwu105
[Indexed for MEDLINE]
Free PMC Article

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