A novel pathway of epithelial sodium channel activation involves a serum- and glucocorticoid-inducible kinase consensus motif in the C terminus of the channel's alpha-subunit.
Aldosterone-induced serum- and glucocorticoid-inducible kinase isoform 1 (SGK1) contributes to the regulation of the epithelial sodium channel (ENaC), the activity of which is critical for long term blood pressure control. Aldosterone-induced SGK1 is thought to enhance ENaC surface expression by phosphorylating Nedd4-2 and thereby preventing ENaC retrieval and degradation. In outside-out membrane patches of Xenopus laevis oocytes heterologously expressing ENaC, amiloride-sensitive ENaC currents were enhanced by phosphatase inhibitors and were dependent on cytosolic Mg(2+). This indicates that a kinase is involved in channel regulation. Indeed, recombinant constitutively active SGK1, included in the pipette solution, caused a sustained 2- to 3-fold increase of ENaC currents. Deletion of the C terminus of alphaENaC largely reduced the stimulatory effect of SGK1, whereas stimulation by SGK1 did not require the presence of the C termini of the beta- or gamma-subunits. Replacing the serine residue Ser(621) of the SGK1 consensus motif in the C terminus of the alpha-subunit by an alanine specifically abolished the stimulatory effect of SGK. Our findings indicate that SGK1 can stimulate ENaC activity independently of an inhibition of Nedd4-2-mediated channel retrieval. This defines a novel regulatory pathway likely to be relevant for aldosterone-induced stimulation of ENaC in vivo.
Diakov
Alexei
A
Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Waldstrasse 6, 91054 Erlangen, Germany.
Korbmacher
Christoph
C
D000409:Alanine / Q000737:chemistry; D000584:Amiloride / Q000494:pharmacology; D020816:Amino Acid Motifs; D000818:Animals; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004789:Enzyme Activation; D053503:Epithelial Sodium Channels; D017353:Gene Deletion; D017874:Immediate-Early Proteins; D008274:Magnesium / Q000737:chemistry; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D018075:RNA, Complementary / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D015222:Sodium Channels / Q000378:metabolism*; D013997:Time Factors; D014981:Xenopus; D014982:Xenopus laevis; D000099184:Serum-Glucocorticoid Regulated Kinases
D000409:Alanine; D000584:Amiloride; D018076:DNA, Complementary; D053503:Epithelial Sodium Channels; D017874:Immediate-Early Proteins; D008274:Magnesium; D009687:Nuclear Proteins; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases; D018075:RNA, Complementary; D011994:Recombinant Proteins; D012694:Serine; D015222:Sodium Channels; D000099184:Serum-Glucocorticoid Regulated Kinases