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Protein and Vesicle Trafficking, Cytoskeleton

Regulatory interactions of N1303K-CFTR and ENaC in Xenopus oocytes: evidence that chloride transport is not necessary for inhibition of ENaC

¹Division of Pulmonary Medicine, Children's Hospital of Philadelphia and ²Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia; and ³Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania

Submitted 9 February 2006 ; accepted in final form 15 December 2006

Regulatory interactions of the cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial Na⁺ channel (ENaC) are readily apparent in Xenopus oocytes. However, the mechanism underlying these interactions remains controversial. CFTR's first nucleotide binding fold (NBD-1) may be important in these interactions, as dysfunctional CFTRs containing mutations within NBD-1, such as F508 and G551D, lack such functional interactions with murine ENaC (mENaC). We hypothesized that a dysfunctional CFTR containing a non-NBD-1 mutation would retain regulatory interactions with mENaC and tested this hypothesis for N1303K-CFTR, where the mutation is located in CFTR's second nucleotide binding fold (NBD-2). cRNA for -mENaC and N1303K-CFTR was injected separately or together into Xenopus oocytes. ENaC and CFTR functional expression was assessed by two-electrode voltage clamp. Injection of N1303K (class II trafficking mutation) yielded low levels of CFTR function on activation with forskolin and 3-isobutyl-1-methylxanthine (IBMX). In coinjected oocytes, N1303K did not alter mENaC functional expression or surface expression before activation of N1303K. This is similar to our prior observations with F508. However, unlike our observations with F508, activation of N1303K acutely decreased mENaC functional and surface expression, and N1303K currents were enhanced by coinjection of mENaC. Furthermore, genistein only mildly enhanced the functional expression of N1303K-CFTR and did not improve regulation of ENaC by N1303K-CFTR. These data suggest that a structurally and functionally intact CFTR NBD-1 in activated CFTR can regulate mENaC surface expression independent of Cl^– transport in Xenopus oocytes.

cystic fibrosis transmembrane conductance regulator; epithelial Na⁺ channel

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