Decreased UDP-GlcNAc levels abrogate proliferation control in EMeg32-deficient cells

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Abstract
The hexosamine pathway provides UDP‐N‐acetylhexosamine donor substrates used in cytosolic and Golgi‐mediated glycosylation of proteins and for formation of glycosylphosphatidylinositol (GPI) anchors, which tether proteins to the outer plasma membrane. We have recently identified the murine glucosamine‐6‐phosphate (GlcN6P) acetyltransferase, EMeg32, as a developmentally regulated enzyme on the route to UDP‐N‐acetylglucosamine (UDP‐GlcNAc). Here we describe embryos and cells that have the EMeg32 gene inactivated by homologous recombination. Homozygous mutant embryos die at around embryonic day (E) 7.5 with a general proliferative delay of development. In vitro differentiated EMeg32−/− ES cells show reduced proliferation. Mouse embryonic fibroblasts (MEFs) deficient for EMeg32 exhibit defects in proliferation and adhesiveness, which could be complemented by stable re‐expression of EMeg32 or by nutritional restoration of intracellular UDP‐GlcNAc levels. Reduced UDP‐GlcNAc levels predominantly translated into decreased O‐GlcNAc modifications of cytosolic and nuclear proteins. Interestingly, growth‐impaired EMeg32−/− MEFs withstand a number of apoptotic stimuli and express activated PKB/AKT. Thus, EMeg32‐dependent UDP‐GlcNAc levels influence cell cycle progression and susceptibility to apoptotic stimuli.