Protein ubiquitination is modulated by O-GlcNAc glycosylation.
During the past two decades, O-GlcNAc modification of cytosolic and nuclear proteins has been intensively studied. Nevertheless, the function of this post-translational modification remains unclear. It has been recently speculated that O-GlcNAc could act as a protective signal against proteasomal degradation, both by modifying target substrates and/or by inhibiting the proteasome itself. In this work, we have investigated the putative relation between O-GlcNAc and the ubiquitin pathway. First, we showed that the level of both modifications increased rapidly after thermal stress but, unlike ubiquitinated proteins, O-GlcNAc-modified proteins failed to be stabilized by inhibiting proteasome function. Increasing O-GlcNAc levels, using glucosamine or PUGNAc, enhanced ubiquitination. Inversely, when O-GlcNAc levels were reduced, using forskolin or glucose deprivation, ubiquitination decreased. Targeted-RNA interference of O-GlcNAc transferase also reduced ubiquitination and moreover halved cell thermotolerance. Finally, we demonstrated that the ubiquitin-activating enzyme E1 was O-GlcNAc modified and that its glycosylation and its interaction with Hsp70 varied according to the conditions of cell culture. Altogether, these results show that O-GlcNAc and ubiquitin are not strictly antagonistic post-translational modifications, but rather that the former might regulate the latter, and also suggest that E1 could be one of the common links between the two pathways.
Guinez
Céline
C
UMR USTL/CNRS 8576, Laboratoire de Glycobiologie Structurale et Fonctionnelle, IFR 147, 59655 Villeneuve d'Ascq, France.
Mir
Anne-Marie
AM
Dehennaut
Vanessa
V
Cacan
René
R
Harduin-Lepers
Anne
A
Michalski
Jean-Claude
JC
Lefebvre
Tony
T
D000117:Acetylglucosamine / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D002470:Cell Survival; D006031:Glycosylation; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006367:HeLa Cells; D018869:Heat-Shock Response; D006801:Humans; D017351:N-Acetylglucosaminyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D044764:Ubiquitin-Activating Enzymes / Q000378:metabolism; D054875:Ubiquitination
D018840:HSP70 Heat-Shock Proteins; D011506:Proteins; D034741:RNA, Small Interfering; D017351:N-Acetylglucosaminyltransferases; C449880:O-GlcNAc transferase; D046988:Proteasome Endopeptidase Complex; D044764:Ubiquitin-Activating Enzymes; D000117:Acetylglucosamine