Urea inhibits hypertonicity-inducible TonEBP expression and action.
Tonicity-responsive genes are regulated by the TonE enhancer element and the tonicity-responsive enhancer binding protein (TonEBP) transcription factor with which it interacts. Urea, a permeant solute coexistent with hypertonic NaCl in the mammalian renal medulla, activates a characteristic set of signaling events that may serve to counteract the effects of NaCl in some contexts. Urea inhibited the ability of hypertonic stressors to increase expression of TonEBP mRNA and also inhibited tonicity-inducible TonE-dependent reporter gene activity. The permeant solute glycerol failed to reproduce these effects, as did cell activators including peptide mitogens and phorbol ester. The inhibitory effect of urea was evident as late as 2 h after the application of hypertonicity. Pharmacological inhibitors of known urea-inducible signaling pathways failed to abolish the inhibitory effect of urea. TonEBP action is incompletely understood, but evidence supports a role for proteasome function and p38 action in regulation; urea failed to inhibit proteasome function or p38 signaling in response to hypertonicity. Consistent with its effect on TonEBP expression and action, urea pretreatment inhibited the effect of hypertonicity on expression of the physiological effector gene, aldose reductase. Taken together, these data 1) define a molecular mechanism of urea-mediated inhibition of tonicity-dependent signaling, and 2) underscore a role for TonEBP abundance in regulating TonE-mediated gene transcription.
Tian
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Division of Nephrology and Molecular Medicine, Oregon Health Sciences University and the Portland Veterans Affairs Medical Center, 3314 S.W. US Veterans Hospital Rd., Portland, OR 97201, USA.
Cohen
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DM
D000449:Aldehyde Reductase / Q000096:biosynthesis / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D003864:Depression, Chemical; D017930:Genes, Reporter / Q000235:genetics; D005990:Glycerol / Q000494:pharmacology; D006801:Humans; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015534:Trans-Activators / Q000096:biosynthesis* / Q000235:genetics; D014157:Transcription Factors; D014508:Urea / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases
C118125:NFAT5 protein, human; C492200:Nfat5 protein, mouse; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D014508:Urea; D000449:Aldehyde Reductase; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D005990:Glycerol