scholarly journals Two Pathways for Importing GDP-fucose into the Endoplasmic Reticulum Lumen Function Redundantly in theO-Fucosylation of Notch inDrosophila

2009 ◽  
Vol 285 (6) ◽  
pp. 4122-4129 ◽  
Author(s):  
Hiroyuki O. Ishikawa ◽  
Tomonori Ayukawa ◽  
Minoru Nakayama ◽  
Shunsuke Higashi ◽  
Shin Kamiyama ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Endoplasmic Reticulum Lumen

scholarly journals Inhibition of adipogenesis: a new job for the ER Ca2+ pool

2008 ◽  
Vol 182 (1) ◽  
pp. 11-13 ◽  
Author(s):  
Jacopo Meldolesi
Keyword(s):  
Endoplasmic Reticulum ◽  
Binding Protein ◽  
Endoplasmic Reticulum Lumen ◽  
Cell Biol ◽  
Multipotent Cells

Adipogenesis is the process of differentiation of adipocytes from mesenchymal multipotent cells through adipocyte precursors. In this issue, a study by the groups of Opas and Michalak (Szabo, E., Y. Qiu, S. Baksh, M. Michalak, and M. Opas. 2008. J. Cell. Biol. 182:103–116) demonstrates that this process is repressed by increasing intracellular Ca2+, which, in turn, is dependent on the expression of calreticulin, the major Ca2+-binding protein of the endoplasmic reticulum lumen.

scholarly journals Association of the Golgi UDP-Galactose Transporter with UDP-Galactose:Ceramide Galactosyltransferase Allows UDP-Galactose Import in the Endoplasmic Reticulum

2003 ◽  
Vol 14 (8) ◽  
pp. 3482-3493 ◽  
Author(s):  
Hein Sprong ◽  
Sophie Degroote ◽  
Tommy Nilsson ◽  
Masao Kawakita ◽  
Nobuhiro Ishida ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Molecular Complex ◽  
Immunofluorescence Microscopy ◽  
Subcellular Fractionation ◽  
Intestinal Cells ◽  
Endoplasmic Reticulum Lumen ◽  
Double Label ◽  
Sizeable Fraction ◽  
Human Intestinal Cells

UDP-galactose reaches the Golgi lumen through the UDP-galactose transporter (UGT) and is used for the galactosylation of proteins and lipids. Ceramides and diglycerides are galactosylated within the endoplasmic reticulum by the UDP-galactose:ceramide galactosyltransferase. It is not known how UDP-galactose is transported from the cytosol into the endoplasmic reticulum. We transfected ceramide galactosyltransferase cDNA into CHOlec8 cells, which have a defective UGT and no endogenous ceramide galactosyltransferase. Cotransfection with the human UGT1 greatly stimulated synthesis of lactosylceramide in the Golgi and of galactosylceramide in the endoplasmic reticulum. UDP-galactose was directly imported into the endoplasmic reticulum because transfection with UGT significantly enhanced synthesis of galactosylceramide in endoplasmic reticulum membranes. Subcellular fractionation and double label immunofluorescence microscopy showed that a sizeable fraction of ectopically expressed UGT and ceramide galactosyltransferase resided in the endoplasmic reticulum of CHOlec8 cells. The same was observed when UGT was expressed in human intestinal cells that have an endogenous ceramide galactosyltransferase. In contrast, in CHOlec8 singly transfected with UGT 1, the transporter localized exclusively to the Golgi complex. UGT and ceramide galactosyltransferase were entirely detergent soluble and form a complex because they could be coimmunoprecipitated. We conclude that the ceramide galactosyltransferase ensures a supply of UDP-galactose in the endoplasmic reticulum lumen by retaining UGT in a molecular complex.

scholarly journals Adaptation of enterocytic Caco-2 cells to glucose modulates triacylglycerol-rich lipoprotein secretion through triacylglycerol targeting into the endoplasmic reticulum lumen

2006 ◽  
Vol 395 (2) ◽  
pp. 393-403 ◽  
Author(s):  
Thomas Pauquai ◽  
Julien Bouchoux ◽  
Danielle Chateau ◽  
Romain Vidal ◽  
Monique Rousset ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Subcellular Fractionation ◽  
Dietary Lipids ◽  
Protein Activity ◽  
Transfer Protein ◽  
Endoplasmic Reticulum Lumen ◽  
Mean Size ◽  
Low Glucose ◽  
Lipoprotein Assembly ◽  
Glucose Supply

Enterocytes are responsible for the absorption of dietary lipids, which involves TRL [TG (triacylglycerol)-rich lipoprotein] assembly and secretion. In the present study, we analysed the effect on TRL secretion of Caco-2 enterocyte adaptation to a differential glucose supply. We showed that TG secretion in cells adapted to a low glucose supply for 2 weeks after confluence was double that of control cells maintained in high-glucose-containing medium, whereas the level of TG synthesis remained similar in both conditions. This increased secretion resulted mainly from an enlargement of the mean size of the secreted TRL. The increased TG availability for TRL assembly and secretion was not due to an increase in the MTP (microsomal TG transfer protein) activity that is required for lipid droplet biogenesis in the ER (endoplasmic reticulum) lumen, or to the channelling of absorbed fatty acids towards the monoacylglycerol pathway for TG synthesis. Interestingly, by electron microscopy and subcellular fractionation studies, we observed, in the low glucose condition, an increase in the TG content available for lipoprotein assembly in the ER lumen, with the cytosolic/microsomal TG levels being verapamil-sensitive. Overall, we demonstrate that Caco-2 enterocytes modulate TRL secretion through TG partitioning between the cytosol and the ER lumen according to the glucose supply. Our model will help in identifying the proteins involved in the control of the balance between TRL assembly and cytosolic lipid storage. This mechanism may be a way for enterocytes to regulate TRL secretion after a meal, and thus impact on our understanding of post-prandial hypertriglyceridaemia.

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