Urea signalling to immediate-early gene transcription in renal medullary cells requires transactivation of the epidermal growth factor receptor.
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.
Zhao
Hongyu
H
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.
Tian
Wei
W
Xu
Hongshi
H
Cohen
David M
DM
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
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