title: Urea signalling to immediate-early gene transcription in renal medullary cells requires transactivation of the epidermal growth factor receptor.
abstract: Signalling by physiological levels of urea (e.g. 200 mM) in cells of the mammalian renal medulla is reminiscent of activation of a receptor tyrosine kinase. The epidermal growth factor (EGF) receptor may be transactivated by a variety of G-protein-coupled receptors, primarily through metalloproteinase-dependent cleavage of a membrane-anchored EGF precursor. In the murine inner medullary collecting duct (mIMCD3) cell line, urea (200 mM) induced prompt (1-5 min) tyrosine phosphorylation of the EGF receptor. Pharmacological inhibition of EGF receptor kinase activity with AG1478 or PD153035 blocked urea-inducible transcription and expression of the immediate-early gene, Egr-1. AG1478 blocked, either fully or partially, other hallmarks of urea signalling including Elk-1 activation and extracellular signal-regulated kinase phosphorylation. EGF receptor kinase inhibition also blocked the cytoprotective effect of urea observed in the context of hypertonicity-inducible apoptosis. EGF receptor transactivation was likely to be attributable to metalloproteinase-dependent ectodomain shedding of an EGF receptor agonist because both specific and non-specific inhibitors of metalloproteinases blocked the urea effect. Heparin-binding EGF (HB-EGF), in particular, was implicated because the diphtheria toxin analogue and highly specific antagonist of HB-EGF, CRM197, also blocked urea-inducible transcription. In aggregate, these data indicate that signalling in response to urea in renal medullary cells requires EGF receptor transactivation, probably through autocrine action of HB-EGF.
authors.affiliation: Division of Nephrology, Department of Medicine, Oregon Health & Science University and the Portland Veterans Affairs Medical Center, 3314 S.W. US Veterans Hospital Road, Portland, OR 97201, USA.
authors.forename: Hongyu
authors.initials: H
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Tian
authors.forename: Hongshi
authors.initials: H
authors.lastname: Xu
authors.forename: David M
authors.initials: DM
authors.lastname: Cohen
mesh_terms: D000818:Animals; D003451:Cryoprotective Agents / Q000378:metabolism; D004268:DNA-Binding Proteins; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D007668:Kidney / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000502:physiology; D015533:Transcriptional Activation; D014508:Urea / Q000378:metabolism*; D050807:ets-Domain Protein Elk-1
chemical_list: D003451:Cryoprotective Agents; D004268:DNA-Binding Proteins; C494113:Elk1 protein, mouse; C587884:Hbegf protein, mouse; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D004815:Epidermal Growth Factor; D014508:Urea; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases; D008666:Metalloendopeptidases