Potential regulation of nuclear UDP-N-acetylglucosaminyl transferase (OGT) by substrate availability: ability of chromatin protein to bind UDP-N-acetylglucosamine and reduce OGT-mediated O-Linked glycosylation.

UDP-N-acetylglucosaminyl transferase (OGT) resides in both cytosolic and nuclear compartments and catalyzes O-linked glycosylation of various proteins. In the current study, we have extracted protein from nuclear DNA (chromatin protein) using 0.2% NP-40 detergent. Addition of chromatin protein to either cytosolic or nuclear preparations (containing abundant OGT) resulted in a dose-dependent loss of OGT activity. Since chromatin-mediated loss of OGT activity could be restored by immunopurification of OGT, we conclude that loss of enzyme activity is not due to direct inactivation of OGT. Addition of UDP-galactose (to saturate potential UDP binding proteins) effectively restored OGT activity in cytosol containing chromatin protein. This indicates that chromatin protein inhibits OGT activity by binding UDP-GlcNAc. These studies suggest that nuclear substrate availability may comprise one of the in vivo mechanisms regulating OGT activity and O-linked glycosylation of nuclear proteins. This is potentially significant, since most transcription factors are O-linked glycosylated and such post-translational modifications can alter gene expression.