Hsp90 Inhibition Leads to the Degradation of O‐Linked N‐Acetylglucosamine Transferase and to the Reduction of O‐GlcNAcylation

Abstract

O‐linked N‐acetylglucosamine (O‐GlcNAc), which is increased in conditions such as hyperglycemia, has been implicated in many major human diseases such as diabetes and cardiovascular diseases. O‐GlcNAc transferase (OGT) catalyzes the addition of O‐GlcNAc to the serine/threonine residues of the protein substrates. Recently, we found that O‐GlcNAcylation inhibits proteasome function by the modification of Rpt2. In this study, we found a novel mechanism to modulate O‐GlcNAcylation in the cell. Exposure of bovine aortic endothelial (BAE) cells and human lung microvascular endothelial (HLMVE) cells to Hsp90 inhibitors, radicicol or 17‐AAG, resulted in significant reduction of OGT expression, and consequently, the reduction of O‐GlcNAcylation, suggesting that OGT might be a client protein of Hsp90. Hsp90 inhibition attenuated the increased O‐GlcNAcylation in cells exposed to high glucose, glucosamine or O‐GlcNAcase inhibitor, PUGNAc. The half‐life of OGT was reduced dramatically by Hsp90 inhibition. The degradation of OGT was proteasome‐dependent. Inhibition of proteasome by MG132, epoxomycin or Bortezomib, in conjunction with Hsp90 inhibition, led to the accumulation of OGT in the detergent‐insoluble fraction of the cell lysates, but not in the supernatant. These results strongly suggest that Hsp90 inhibitors might be administered to reverse the adverse effects of O‐GlcNAcylation in human diseases.