Urea-associated oxidative stress and Gadd153/CHOP induction

Urea treatment (100-300 mM) increased expression of the oxidative stress-re sponsive transcription factor, Gadd153/CHOP, at the mRNA and protein levels (at greater than or equal to 4 h) in renal medullary mIMCD3 cells in cultu re, whereas other solutes did not. Expression of the related protein, CCAAT / enhancer-binding protein (C/EBP-beta), was not affected, nor was expressi on of the sensor of endoplasmic reticulum stress, grp78. Urea modestly incr eased Gadd153 transcription by reporter gene analysis but failed to influen ce Gadd153 mRNA stability. Importantly, upregulation of Gadd153 mRNA and pr otein expression by urea was antioxidant sensitive. Accordingly, urea treat ment was associated with oxidative stress, as quantitated by intracellular reduced glutathione content in mIMCD3 cells. In addition, antioxidant treat ment partially inhibited the ability of urea to activate transcription of a n Egr-1 luciferase reporter gene. Therefore oxidative stress represents a n ovel solute-signaling pathway in the kidney medulla and, potentially, in ot her tissues.