Lithium Induces ER Stress and N-Glycan Modification in Galactose-Grown Jurkat Cells

Abstract

We previously reported that lithium had a significant impact on Ca2+ regulation and induced unfolded protein response (UPR) in yeast cells grown on galactose due to inhibition of phosphoglucomutase (PGM), however the exact mechanism has not been established yet. In this study, we analysed lithium's effect in galactose-fed cells to clarify whether these ER-related changes are the result of a relative hypoglycemic state. Furthermore, we investigated whether the alterations in galactose metabolism impact protein post-translational modifications. Thus, Jurkat cells were incubated in glucose or galactose containing media with or without lithium treatment. We found that galactose-fed and lithium treated cells showed better survivability than fasting cells. We also found higher UDP-Hexose and glycogen levels in these cells compared to fasting cells. On the other hand, the UPR (X-box binding protein 1 mRNA levels) of galactose-fed and lithium treated cells was even greater than in fasting cells. We also found increased amount of proteins that contained N-linked N-acetyl-glucosamine, similar to what was reported in fasting cells by a recent study. Our results demonstrate that lithium treatment of galactose-fed cells can induce stress responses similar to hypoglycemia, however cell survival is still secured by alternative pathways. We propose that clarifying this process might be an important addition toward the better understanding of the molecular mechanisms that regulate ER-associated stress response.

The unfolded protein response has a protective role in yeast models of classic galactosemia

“…We have also observed in microarray experiments that the ERO1 gene is also induced under this condition ( Bro et al, 2003 ). Recently, Nagy and co-workers showed that lithium induced UPR in galactose-grown Jurkat cells ( Nagy et al, 2013 ). Despite all of this evidence of UPR activation in classic galactosemia models, none of these works carefully characterized this response nor did they probe the importance of UPR activation under these circumstances.…”

A Genome-Wide Screen in Saccharomyces cerevisiae Reveals a Critical Role for Oxidative Phosphorylation in Cellular Tolerance to Lithium Hexafluorophosphate

“…Additionally, lithium can replace other cations (Na + , K + , Ca + ), and specifically competes with magnesium ions (Mg 2+ ), thus interrupting ion channel activity, Na + /K + homeostasis, and the activity of magnesium-containing enzymes [ 15 , 16 , 17 ]. Other studies have indicated that lithium in high concentrations alters nucleic acid and protein biosynthesis [ 17 ], as well as introduces endoplasmic reticulum stress and N-glycan modification in certain conditions [ 18 ]. Likewise, fluorine is also toxic to cells, and hexafluorophosphates quaternary ammonium salts has been reported to lead to oxidative stress [ 19 ].…”

The yeast protein Ubx4p contributes to mitochondrial respiration and lithium–galactose–mediated activation of the unfolded protein response

“…Lithium is also capable of inhibiting the activity of the enzyme phosphoglucomutase because it competes with its cofactor magnesium (2). Because of this inhibition, cells treated with lithium in the presence of galactose accumulate toxic metabolites of the Leloir pathway in yeast (2)(3)(4) and human cells (5). Accumulation of intermediate metabolites of galactose metabolism such as galactose-1-phosphate also occurs in patients with classic galactosemia, an inborn error of metabolism caused by mutations in the GALT gene (6,7).…”

“…Yeast cells treated with lithium in the presence of galactose exhibit modifications in cellular homeostasis such as changes in glycogen, calcium, and phosphate levels and a metabolic shift from fermentation to respiration (3,(9)(10)(11). Another important feature of lithium/galactose treatment is the increase in endoplasmic reticulum (ER) 3 stress and unfolded protein response (UPR), both in yeast and in human cells (3,5). This UPR activation depends on the synthesis of galactose-1-phosphate and also occurs in genetic models of classic galactosemia (3,12,13).…”