70-kDa-heat shock protein presents an adjustable lectinic activity towards O-linked N-acetylglucosamine

Numerous works demonstrated that the dynamic O-GlcNAc glycosylation could protect against the proteasomal degradation by modifying the target proteins and the proteasome itself. Considering that Hsp70 is a crucial component in the quality control of protein conformation in the proteasomal pathway, we investigated the possibility that Hsp70 physically interacts with O-GlcNAc proteins through a lectinic activity. First, we demonstrate that in HepG2 cells, Hsp70 can specifically bind to O-GlcNAc residues but also is itself modified by O-GlcNAc. Second, when cells were deprived of glucose (nutrient stress), Hsp70 lectinic activity markedly increased whereas its glycosylation dramatically decreased. On the other hand, a 42 degrees C thermic stress did not affect any of these features. Lastly, the nature of O-GlcNAc modified proteins co-immunoprecipitating with Hsp70 was similar for cells submitted to the thermic and to nutrient stress. These results strongly suggest that O-GlcNAc influences protein stability through specific interaction with 70-kDa-heat shock protein members.