Epithelial sodium channel regulated by differential composition of a signaling complex

Abstract

Hormonal control of transepithelial sodium (Na ؉ ) transport utilizes phosphatidylinositide 3 -kinase (PI3K) and Raf-MAPK/ERK kinase (MEK)-ERK-dependent signaling pathways, which impact numerous cell functions. How signals transmitted by these pathways are sorted and appropriately transmitted to alter Na ؉ transport without altering other physiologic processes is not well understood. Here, we report the identification of a signaling complex that selectively modulates the cell surface expression of the epithelial sodium channel (ENaC), an ion channel that is essential for fluid and electrolyte balance in mammals. Raf-1 and the ubiquitin ligase, Nedd4-2, are constitutively-expressed inhibitory components of this ENaC regulatory complex, which interact with, and decrease the expression of, cell surface ENaC. The activities of Nedd4-2 and Raf-1 are inhibited cooperatively by the PI3K-dependent kinase serum-and glucocorticoid-induced kinase 1 (SGK1), and the Raf-1-interacting protein glucocorticoid-induced leucine zipper (GILZ1), which are aldosterone-stimulated components of the complex. Together, SGK1 and GILZ1 synergistically stimulate ENaC cell surface expression. Interestingly, GILZ1 and SGK1 do not have synergistic, and in fact have opposite, effects on an unrelated activity, FKHRL1-driven gene transcription. Together, these data suggest that GILZ1 and SGK1 provide a physical and functional link between the PI3K-and Raf-1-dependent signaling modules and represent a unique mechanism for specifically controlling Na ؉ transport without inappropriately activating other cell functions.glucocorticoid-induced leucine zipper protein ͉ Nedd4-2 ͉ Raf-1 ͉ serum-and glucocorticoid-induced kinase 1

Novel Mechanism of Impaired Function of Organic Anion-Transporting Polypeptide 1B3 in Human Hepatocytes: Post-Translational Regulation of OATP1B3 by Protein Kinase C Activation

“…5, after PMA treatment (0.1 mM, 30 minutes), the surface and total protein levels of FLAG-OATP1B3 were 0.9 6 0.1-fold and 1.1 6 0.1-fold of control, respectively, suggesting that PKC activation did not affect either the surface or the total FLAG-Myc-OATP1B3 protein levels. GAPDH, a marker for intracellular protein (Soundararajan et al, 2009), was only detected in the total protein but not in the surface fraction, suggesting that the surface fraction was not contaminated with intracellular protein.…”

Glioma-specific Cation Conductance Regulates Migration and Cell Cycle Progression

“…Activation of this pathway is generally attributed to ligand binding to EGFR and related receptors, initiating a classical tyrosine kinase signaling cascade. In epithelial cells, ERK activation is associated with decreased surface expression of ENaC sodium channels (11,12), exerting effects on mechanisms of channel retrieval from the membrane.…”

mTOR Complex-2 Activates ENaC by Phosphorylating SGK1

“…The phosphorylated HM then provides a docking site for PDK1, which phosphorylates T256 within the activation loop 37 ; the fully activated kinase is recruited by GILZ1 to substrates that are themselves associated with ENaC. 38 These substrates, including Nedd4-2 and cRaf, are phosphorylated and inhibited, and thus ENaC residence at the plasma membrane is increased,. 19,38,39 Through this mechanism, SGK1 activation and physiologic effects are selectively controlled by mTORC2 in the absence of mTORC1-dependent changes in protein synthesis and cellular proliferation.…”

“…38 These substrates, including Nedd4-2 and cRaf, are phosphorylated and inhibited, and thus ENaC residence at the plasma membrane is increased,. 19,38,39 Through this mechanism, SGK1 activation and physiologic effects are selectively controlled by mTORC2 in the absence of mTORC1-dependent changes in protein synthesis and cellular proliferation. These data provide further insight into the molecular mechanism(s) underlying Na ϩ balance and BP regulation and suggest a mechanism for the regulation of a specific physiologic process through selective recruitment of pleiotropic signaling molecules.…”