The Two CaenorhabditiselegansUDP-Glucose:glycoproteinGlucosyltransferase Homologues Have Distinct Biological Functions

LUCILA I. BUZZI, SERGIO H. SIMONETTA, ARMANDO J. PARODI AND OLGA A. CASTRO

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2011 vol. 6 p. 27025 - 27039

1932-6203

The UDP-Glc:glycoproteinglucosyltransferase (UGGT) is the sensor of glycoprotein conformations in the glycoprotein folding quality control as it exclusively glucosylates glycoproteins not displaying their native conformations. Monoglucosylated glycoproteins thus formed may interact with the lectin-chaperones calnexin (CNX) and calreticulin (CRT). This interaction prevents premature exit of folding intermediates to the Golgi and enhances folding efficiency. Bioinformatic analysis showed that in Caenorhabditis. elegansthere are two open reading frames (F48E3.3 and F26H9.8 to be referred as uggt-1 and uggt-2, respectively) coding for UGGT homologues. Expression of codon-optimized versions of both genes in Schizosaccharomycespombe mutants devoid of UGGT activity showed that uggt-1 codes for an active UGGT protein (CeUGGT-1). On the other hand, uggt-2 coded for a protein (CeUGGT-2) apparently not displaying a canonical UGGT activity. We constructed transgenic worms carrying the uggt-1 promoter linked to the GFP coding sequence and found that the corresponding protein is expressed in cells of the nervous system and is upregulated under ER stress. No such upregulation was found for uggt-2. Real-time PCR analysis showed that both uggt-1 and uggt-2 genes are expressed during the entire C. eleganslife cycle but the expression of the latter was at most 3 % of that of the former. RNAi-mediated depletion of CeUGGT-1 but not of CeUGGT-2 resulted in a reduced lifespan and that of CeUGGT-1 and CeUGGT-2 in a developmental delay. We found that both CeUGGT1 and CeUGGT2 play a protective role under ER stress conditions, since 10 ìg/ml tunicamycin arrested development at the L2/L3 stage of both uggt-1(RNAi) and uggt-2(RNAi) but not of control worms. Furthermore, we found that the role of CeUGGT-2 but not CeUGGT-1 is significant in relieving low ER stress levels in the absence of the ire-1 unfolding protein response signaling pathway. Our results indicate that both C. elegansUGGT homologues have  distinct biological functions.