title: H-Ras mediates the inhibitory effect of epidermal growth factor on the epithelial Na+ channel.
abstract: The present study investigates the role of small G-proteins of the Ras family in the epidermal growth factor (EGF)-activated cellular signalling pathway that downregulates activity of the epithelial Na+ channel (ENaC). We found that H-Ras is a key component of this EGF-activated cellular signalling mechanism in M1 mouse collecting duct cells. Expression of a constitutively active H-Ras mutant inhibited the amiloride-sensitive current. The H-Ras-mediated signalling pathway that inhibits activity of ENaC involves c-Raf, and that the inhibitory effect of H-Ras on ENaC is abolished by the MEK1/2 inhibitor, PD98059. The inhibitory effect of H-Ras is not mediated by Nedd4-2, a ubiquitin protein ligase that regulates the abundance of ENaC at the cell surface membrane, or by a negative effect of H-Ras on proteolytic activation of the channel. The inhibitory effects of EGF and H-Ras on ENaC, however, were not observed in cells in which expression of caveolin-1 (Cav-1) had been knocked down by siRNA. These findings suggest that the inhibitory effect of EGF on ENaC-dependent Na+ absorption is mediated via the H-Ras/c-Raf, MEK/ERK signalling pathway, and that Cav-1 is an essential component of this EGF-activated signalling mechanism. Taken together with reports that mice expressing a constitutive mutant of H-Ras develop renal cysts, our findings suggest that H-Ras may play a key role in the regulation of renal ion transport and renal development.
authors.affiliation: Discipline of Physiology, The Bosch Institute, School of Medical Sciences, The University of Sydney, New South Wales, 2006, Australia.
authors.forename: Il-Ha
authors.initials: IH
authors.lastname: Lee
authors.affiliation: Discipline of Physiology, The Bosch Institute, School of Medical Sciences, The University of Sydney, New South Wales, 2006, Australia.
authors.forename: Sung-Hee
authors.initials: SH
authors.lastname: Song
authors.affiliation: Discipline of Physiology, The Bosch Institute, School of Medical Sciences, The University of Sydney, New South Wales, 2006, Australia.
authors.forename: David I
authors.initials: DI
authors.lastname: Cook
authors.affiliation: Discipline of Physiology, The Bosch Institute, School of Medical Sciences, The University of Sydney, New South Wales, 2006, Australia.
authors.forename: Anuwat
authors.initials: A
authors.lastname: Dinudom
mesh_terms: D000818:Animals; D015536:Down-Regulation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D062686:Epithelial Sodium Channel Blockers / Q000494:pharmacology*; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009154:Mutation; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D051381:Rats; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels; C528429:Hras protein, rat; D015513:Oncogene Proteins; D004815:Epidermal Growth Factor; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1; D018631:ras Proteins