The phosphorylation of endogenous Nedd4-2 In Na+-absorbing human airway epithelial cells

Noor A. S. Ismail, Deborah L. Baines, Stuart M. Wilson (Lead / Corresponding author)

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    Abstract

    Neural precursor cell expressed, developmentally down-regulated protein 4-2 (Nedd4-2) mediates the internalisation / degradation of epithelial Na(+) channel subunits (a-, ß- and ?-ENaC). Serum / glucocorticoid inducible kinase 1 (SGK1) and protein kinase A (PKA) both appear to inhibit this process by phosphorylating Nedd4-2-Ser221, -Ser327 and -Thr246. This Nedd4-2 inactivation process is thought to be central to the hormonal control of Na+ absorption. The present study of H441 human airway epithelial cells therefore explores the effects of SGK1 and / or PKA upon the phosphorylation / abundance of endogenous Nedd4-2; the surface expression of ENaC subunits, and electrogenic Na+ transport. Effects on Nedd4-2 phosphorylation/abundance and the surface expression of ENaC were monitored by western analysis, whilst Na+ absorption was quantified electrometrically. Acutely (20min) activating PKA in glucocorticoid-deprived (24h) cells increased the abundance of Ser221-phosphorylated, Ser327-phosphorylated and total Nedd4-2 without altering the abundance of Thr246-phosphorylated Nedd4-2. Activating PKA under these conditions did not cause a co-ordinated increase in the surface abundance of a-, ß- and ?-ENaC and had only a very small effect upon electrogenic Na+absorption. Activating PKA (20min) in glucocorticoid-treated (0.2µM dexamethasone, 24h) cells, on the other hand, increased the abundance of Ser221-, Ser327- and Thr246-phosphorylated and total Nedd4-2; increased the surface abundance of a-, ß- and ?-ENaC and evoked a clear stimulation of Na+ transport. Chronic glucocorticoid stimulation therefore appears to allow cAMP-dependent control of Na+ absorption by facilitating the effects of PKA upon the Nedd4-2 and ENaC subunits.

    Original languageEnglish
    Pages (from-to)32-42
    Number of pages11
    JournalEuropean Journal of Pharmacology
    Volume732
    DOIs
    Publication statusPublished - 5 Jun 2014

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