Glycine-induced cytoprotection is mediated by ERK1/2 and AKT in renal cells with ATP depletion

Abstract

Glycine receptor (GlyR) activation by glycine protects cells against ATP depletion. However, the underlying mechanisms remain unclear. To define signaling pathways responsible for the GlyR mediated cytoprotection, we examined the phosphorylation status of key kinases signaling pathways in Madin-Darby canine kidney (MDCK) cells. Our results indicated that growing the ATP-depleted MDCK cells in glycine-containing media increased the level of phosphorylated extracellular signal-regulated kinase 1 and 2 (ERK1/2), Ets-like transcription factor-1 (Elk1), AKT, and Forkhead box O-class 1 (FoxO1), decreased the level of phosphorylated p38 mitogen-activated protein kinase, while having little effect on the phosphorylation status of c-Jun N-terminal kinase 1 and 2. Similar phosphorylation changes in these molecules took place in the GlyRα1 stably expressing HEK-293 cell. We also showed that treating MDCK cells with ERK1/2 inhibitor PD98059 or AKT inhibitor LY294002 diminished cytoprotection against cell death by glycine, as determined by assessment of lactate dehydrogenase release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide activity. In contrast, treatment with p38 inhibitor SB203580 enhanced the glycine-induced cytoprotection. Finally, RNAi-mediated silencing of GlyRα1 abolished the glycine-induced changes in phosphorylation status of the above kinases in ATP-depleted cells. Taken together, our results suggest that the ERK1/2 and AKT signaling pathways are involved in the glycine-GlyR protection of MDCK cells against death induced by ATP depletion.