Urea signaling in cultured murine inner medullary collecting duct (mIMCD3) cells involves protein kinase C, inositol 1,4,5-trisphosphate (IP3), and a putative receptor tyrosine kinase.
Urea, in concentrations unique to the renal medulla, increases transcription and protein expression of several immediate-early genes (IEGs) including the zinc finger-containing transcription factor, Egr-1. In the present study, the proximal 1.2 kb of the murine Egr-1 5' -flanking sequence conferred urea-responsiveness to a heterologous luciferase reporter gene when transiently transfected into renal medullary mIMCD3 cells,and this effect was comparable with that of the extremely potent immediate-early gene inducer, O-tetradecanoylphorbol 13-acetate (TPA). Urea inducibility of Egr-1 expression was protein kinase C (PKC)-dependent because staurosporine and calphostin C abrogated the urea effect, and down-regulation of PHC through chronic TPa treatment inhibited both urea-inducible Egr-1 protein expression and gene transcription. In addition, hyperosmotic urea increased inositol 1,4,5-trisphosphate (IP3) release from mIMCD3 cells and induced tyrosine phosphorylation of the receptor tyrosine kinase-specific phospholipase C (PLC) isoform, PLC-gamma. Importantly, urea-inducible Egr-1 expression was strongly genistein-sensitive, to a much greater extent than the comparable TPA-inducible Egr-1 expression. These data suggest that urea-inducible Egr-1 expression is a consequence of sequential PLC-gamma activation, IP3 release, and PKC activation. Urea-inducible PLC-gamma activation, in conjunction with the genistein-sensitivity of urea-inducible Egr-1 expression suggest the possibility of a cell surface or cytoplasmic urea-sensing receptor tyrosine kinase.
Cohen
D M
DM
Division of Nephrology, Oregon Health Sciences University, Portland, 97201, USA.
Gullans
S R
SR
Chin
W W
WW
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019833:Genistein; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007529:Isoflavones / Q000494:pharmacology; D007679:Kidney Medulla / Q000166:cytology / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000502:physiology*; D007700:Kinetics; D051379:Mice; D009281:Naphthalenes / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D019311:Staurosporine; D014508:Urea / Q000494:pharmacology*
D000470:Alkaloids; D004791:Enzyme Inhibitors; D007529:Isoflavones; D009281:Naphthalenes; D015544:Inositol 1,4,5-Trisphosphate; D014508:Urea; D019833:Genistein; D020794:Receptor Protein-Tyrosine Kinases; D011493:Protein Kinase C; D017027:Protein Tyrosine Phosphatases; D019311:Staurosporine; C058819:calphostin C