Phosphorylation of eIF2α via the general control kinase, GCN2, modulates the ability of renal medullary cells to survive high urea stress

Cai Q, Brooks HL. Phosphorylation of eIF2 alpha via the general control kinase, GCN2, modulates the ability of renal medullary cells to survive high urea stress. Am J Physiol Renal Physiol 301: F1202-F1207, 2011. First published August 31, 2011; doi:10.1152/ajprenal.00272.2011.-The phosphorylation of the alpha-subunit of the eukaryotic translation initiation factor 2 (eIF2 alpha) occurs under many stress conditions in mammalian cells and is mediated by one of four eIF2 alpha kinases: PERK, PKR, GCN2, and HRI. Cells of the renal medulla are regularly exposed to fluctuating concentrations of urea and sodium, the extracellular solutes responsible for the high osmolality in the renal medulla, and thus the kidneys ability to concentrate the urine in times of dehydration. Urea stress is known to initiate molecular responses that diverge from those seen in response to hypertonic stress (NaCl). We show that urea-inducible GCN2 activation initiates the phosphorylation of eIF2 alpha and the downstream increase of activating transcription factor 3 (ATF3). Loss of GCN2 sensitized cells to urea stress, increasing the expression of activated caspase-3 and decreasing cell survival. Loss of GCN2 ablated urea-induced phosphorylation of eIF2 alpha and reduced the expression of ATF3.