Intracellular trafficking of a polymorphism in the COOH terminus of the α-subunit of the human epithelial sodium channel is modulated by casein kinase 1

Intracellular trafficking of a polymorphism in the COOH terminus of the alpha-subunit of the human epithelial sodium channel is modulated by casein kinase 1. Am J Physiol Renal Physiol 293: F868-F876, 2007. First published June 27, 2007; doi: 10.1152/ajprenal.00194.2007. -The A663T polymorphism of the alpha-subunit of the human epithelial sodium channel (hENaC) increases the functional and surface expression of alpha beta gamma-hENaC in Xenopus laevis oocytes, and the context of this residue in the COOH terminus of alpha-hENaC is important for this effect. Query of a phosphoprotein database suggested that the alpha-T663 residue of hENaC might be a substrate for phosphorylation by casein kinase 1 (CK1). We tested the hypotheses that phosphorylation of alpha-T663-hENaC by CK1 would regulate the increased functional and surface expression of alpha-T663hENaC vs. alpha-A663-hENaC in oocytes. General inhibition of CK1 with IC261 decreased the functional and surface expression of alpha-T663-hENaC, but not alpha-A663-hENaC. This decrease in alpha-T663hENaC functional expression resulted from reduced delivery of alpha-T663-hENaC to the oocyte membrane. IC261 also inhibited the functional expression of alpha- T692-mENaC and a chimeric m(1-678)/h( 650- 669) alpha-T663, m beta gamma ENaC, but not alpha-A692-mENaC or m( 1678)/h( 650- 669) alpha-A663, m beta gamma ENaC. These data suggest that additional residues outside of the alpha- hENaC COOH terminus are important for modulation of alpha-T663-hENaC trafficking by CK1. Overexpression of CK1 alpha did not alter functional expression of alpha-T663-hENaC. In contrast, modest overexpression of CK1 delta enhanced, whereas higher levels of CK1 delta overexpression inhibited alpha-T663-hENaC functional expression. CK1 did not phosphorylate the COOH terminus of either alpha-T663-hENaC or alpha-A663-hENaC in vitro. These data suggest that CK1, and perhaps specifically CK1 delta, regulates the intracellular trafficking of the alpha- A663T functional polymorphism of hENaC indirectly by altering the rate of alpha-T663-hENaC biosynthesis and/or delivery to the plasma membrane.