Overexpression of Man2C1 leads to protein underglycosylation and upregulation of endoplasmic reticulum-associated degradation pathway.
Unfolded glycoproteins retained in the endoplasmic reticulum (ER) are degraded via the ER-associated degradation (ERAD) pathway. These proteins are subsequently transported to the cytosol and degraded by the proteasomal complex. Although the sequential events of ERAD are well described, its regulation remains poorly understood. The cytosolic mannosidase, Man2C1, plays an essential role in the catabolism of cytosolic free oligomannosides, which are released from the degraded proteins. We have investigated the impact of Man2C1 overexpression on protein glycosylation and the ERAD process. We demonstrated that overexpression of Man2C1 led to modifications of the cytosolic pool of free oligomannosides and resulted in accumulation of small Man(2-4)GlcNAc(1) glycans in the cytosol. We further correlated this accumulation with incomplete protein glycosylation and truncated lipid-linked glycosylation precursors, which yields an increase in N-glycoprotein en route to the ERAD. We propose a model in which high mannose levels in the cytosol interfere with glucose metabolism and compromise N-glycan synthesis in the ER. Our results show a clear link between the intracellular mannose-6-phosphate level and synthesis of the lipid-linked precursors for protein glycosylation. Disturbance in these pathways interferes with protein glycosylation and upregulated ERAD. Our findings support a new concept that regulation of Man2C1 expression is essential for maintaining efficient protein N-glycosylation.
Unité de Glycobiologie Structurale et Fonctionnelle, UMR CNRS 8576, IFR 147, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France.
Coralie
C
Bernon
Yoann
Y
Carré
Elina
E
Kuokkanen
Marie-Christine
MC
Slomianny
Anne-Marie
AM
Mir
Frédéric
F
Krzewinski
René
R
Cacan
Pirkko
P
Heikinheimo
Willy
W
Morelle
Jean-Claude
JC
Michalski
François
F
Foulquier
Sandrine
S
Duvet
D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006031:Glycosylation; D006367:HeLa Cells; D006801:Humans; D008360:Mannosephosphates / Q000378:metabolism; D008361:Mannosidases / Q000096:biosynthesis* / Q000737:chemistry; D009844:Oligosaccharides / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D014162:Transfection; D015854:Up-Regulation; D014532:Uridine Diphosphate Glucose / Q000378:metabolism; D043323:alpha-Mannosidase
D008360:Mannosephosphates; D009844:Oligosaccharides; C028569:oligomannoside; C027693:mannose-6-phosphate; D008361:Mannosidases; C511245:MAN2C1 protein, human; D043323:alpha-Mannosidase; D046988:Proteasome Endopeptidase Complex; D014532:Uridine Diphosphate Glucose