Cystic Fibrosis Transmembrane Conductance Regulator Differentially Regulates Human and Mouse Epithelial Sodium Channels in Xenopus Oocytes

Abstract

The cystic fibrosis transmembrane conductance regulator (CFTR), in addition to its well defined Cl ؊ channel properties, regulates other ion channels. CFTR inhibits murine or rat epithelial Na ؉ channel (mENaC or rENaC) currents in many epithelial and non-epithelial cells, whereas murine or rat ENaC increases CFTR functional expression. These regulatory interactions are reproduced in Xenopus oocytes where both the open probability and surface expression of wild type CFTR Cl ؊ channels are increased when CFTR is co-expressed with ␣␤␥ mENaC, and conversely the activity of mENaC is inhibited after wild type CFTR activation. Using the Xenopus oocyte expression system, differences in functional regulatory interactions were observed when CFTR was co-expressed with either ␣␤␥ mENaC or ␣␤␥ human ENaC (hENaC). Co-expression of CFTR and ␣␤␥ mENaC or hENaC resulted in an ϳ3-fold increase in CFTR Cl ؊ current compared with oocytes expressing CFTR alone. Oocytes co-injected with both CFTR and mENaC or hENaC expressed an amiloride-sensitive whole cell current that was decreased compared with that observed with the injection of mENaC or hENaC alone before CFTR activation with forskolin/3-isobutyl-1-methylxanthine. CFTR activation resulted in a further 50% decrease in mENaC-mediated currents, an ϳ20% decrease in ␣-T663-hENaC-mediated currents, and essentially no change in ␣-A663-hENaC-mediated currents. Changes in ENaC functional expression correlated with ENaC surface expression by oocyte surface biotinylation experiments. Assessment of regulatory interactions between CFTR and chimeric mouse/human ENaCs suggest that the 20 C-terminal amino acid residues of ␣ ENaC confer species specificity regarding ENaC inhibition by activated CFTR.

Interregulation of Proton-gated Na+ Channel 3 and Cystic Fibrosis Transmembrane Conductance Regulator

“…Amiloride inhibits these apically located Na ϩ channels with varying efficacies. CFTR down-regulates amiloridesensitive ␣␤␥ ENaC activity in Xenopus oocytes (3)(4)(5)(6)(7)(8)(9)(10)(11). These results are in agreement with observations from normal and CF tissues (12)(13)(14)(15)(16)(17).…”

“…Also, amiloride sensitivity, ion selectivity, and single channel conductance are different from native epithelial Na ϩ channels (23). In addition, the putative CFTR channels in Calu-3 cells (but not heterologously expressed CFTR in oocytes) exhibit a basal, glibenclamide-inhibitable Cl Ϫ current before the addition of cAMP (4,7,8,38). The mechanisms for the differences between cloned and native epithelial cation and anion channels are not clear.…”

“…A reciprocal interaction between homomeric CFTR and ENaC has been reported (4,7,8); CFTR down-regulates ␣␤␥ ENaC, whereas ␣␤␥ ENaC up-regulates CFTR. In contrast, CFTR up-regulates heteromeric ASIC1a/2a channels (39).…”

Impact of αENaC Polymorphisms on the Risk of Ischemic Cerebrovascular Events: A Multicenter Case–Control Study

“…The frequent Thr663Ala variant is situated in the COOH terminus of the protein, which shows considerable interspecies variability (15 ). These interspecies differences in the 20 C-terminal amino acid residues also seem to explain species differences for regulatory proteins such as cystic fibrosis transmembrane conductance regulator.…”

Expression of CFTR from a ciliated cell-specific promoter is ineffective at correcting nasal potential difference in CF mice

“…36 It has also been reported that the interaction of mouse and human CFTR with ENaC is species specific. 37 Thus it is possible that the human CFTR, due to sequence differences, does not function properly in mouse cells under all conditions. This could be the result of altered glycosylation, mis-localization as a result of altered binding to other proteins, or a failure to be activated by the murine signaling (kinase) pathways.…”