Hsp70-GlcNAc-binding activity is released by stress, proteasome inhibition, and protein misfolding

Numerous recent works strengthen the idea that the nuclear and cytosolic-specific O-GIcNAc glycosylation protects cells against injuries. We have first investigated O-G1cNAc level and Hsp70-GIcNAc-binding activity (HGBA) behaviour after exposure of HeLa and HepG(2) cells to a wide variety of stresses. O-GIcNAc and HGBA responses were different according to the stress and according to the cell. HGBA was released for almost all stresses, while O-GIcNAc level was modified either upwards or downwards, depending to the stress. Against all expectations, we demonstrated that energy charge did not significantly vary with stress whereas UDP-GIcNAc pools were more dramatically affected even if differences in UDP-GlcNAc contents were not correlated with O-G1cNAc variations suggesting that O-GIcNAc transferase is itself finely regulated during cell injury. Finally, HGBA could be triggered by proteasome inhibition and by L-azetidine-2-carboxylic acid (a proline analogue) incorporation demonstrating that protein misfolding is one of the key-activator of this Hsp70 property. (c) 2007 Elsevier Inc. All rights reserved.