Differential modulation of a polymorphism in the COOH terminus of the alpha-subunit of the human epithelial sodium channel by protein kinase Cdelta.

The A663T polymorphism of the alpha-subunit of the human epithelial sodium channel (hENaC) increases the functional and surface expression of alphabetagamma-hENaC in Xenopus laevis oocytes. The context of this residue in the COOH terminus of alpha-hENaC is important for this effect, as a homologous change in murine ENaC (mENaC), A692T, does not alter functional and surface expression of mENaC. Query of a phosphoprotein database suggested that the alpha-T663 residue might be phosphorylated by PKCdelta. General inhibition of PKC with calphostin C decreased the functional and surface expression of alphaT663-hENaC and not alphaA663-hENaC, and was without effect on alphaA692-mENaC, alphaT692-mENaC, and a chimeric m(1-678)/h(650-669)alphaT663, mbetagamma-ENaC. These data suggest that residues outside of the alpha-hENaC COOH terminus are important for modulation of alphaT663-hENaC trafficking by PKC. In contrast, expression of PKCdelta decreased the functional and surface expression of alphaT663-hENaC and the functional expression of m(1-678)/h(650-669)alphaT663, mbetagamma-ENaC, and was without effect on alphaA663-hENaC, alphaA692-mENaC, or alphaT692-mENaC. PKCdelta did not phosphorylate the COOH terminus of either alphaT663-hENaC or alphaA663-hENaC in vitro, suggesting that it acts indirectly to regulate hENaC trafficking. alphaT663-hENaC was retrieved from the oocyte membrane more slowly than alphaA663-hENaC, and calphostin C increased the rate of alphaT663-hENaC removal from the oocyte membrane to a rate similar to that of alphaA663-hENaC. In contrast, PKCdelta did not alter the rate of removal of alphaT663-hENaC from the oocyte membrane, suggesting that PKCdelta altered rates of alphaT663-hENaC biosynthesis and/or delivery to the plasma membrane. These data are consistent with PKC isoform-specific effects on the intracellular trafficking of alphaT663- vs. alphaA663-hENaC.