J. Neurochem. (2011) 116, 396–405.

Injury‐induced expression of p75 neurotrophin receptor (p75NTR) in the CNS induces neuronal apoptosis and prevents neuronal regrowth. The mechanisms regulating injury‐induced p75NTR expression are poorly characterized but previous studies have established that reductions in extracellular osmolarity which mimic cytotoxic edema induce p75NTR gene expression through pathways that activate the Sp1 transcription factor. In this report, we examined how extracellular osmolarity converges on Sp1 to regulate p75NTR expression. We report that levels of O‐linked N‐acetylglucosamine (O‐GlcNAc) transferase (OGT), the enzyme that mediates O‐linked attachment of GlcNAc, are reduced by extracellular hypo‐osmolarity and that global levels of protein O‐GlcNAcylation and of Sp1 show a corresponding decline. We demonstrate that chemical and RNAi‐based treatments that reduce cellular O‐GlcNAcylation facilitate p75NTR induction by hypo‐osmolarity, directly linking protein O‐GlcNAcylation to p75NTR induction. To determine if Sp1 O‐GlcNAc content regulates p75NTR expression, we replaced endogenous Sp1 with a Sp1 mutated at O‐GlcNAc target residues. This O‐GlcNAc‐deficient form of Sp1‐enhanced p75NTR expression, demonstrating that O‐GlcNAcylation of Sp1 negatively regulates p75NTR expression. We conclude that a stress‐induced decline in the O‐GlcNAc content of Sp1 drives expression of p75NTR.