Hepatocyte growth factor inhibits amiloride-sensitive Na⁺ channel function in cystic fibrosis airway epithelium in vitro

Cystic fibrosis (CF) airway epithelial cells have a reduced cAMP-dependent Cl^- conductance channel (CFTR) function but an increased level of amiloride-sensitive Na⁺ channel (ENaC) activity. Recently expression of the α-subunit of the ENaC protein complex was shown to be down-regulated by activation of the extracellular signal-regulated protein kinase (ERK) pathway. In the present study we have examined the actions of a potent regulator of the ERK pathway, recombinant human hepatocyte growth factor (rhHGF), on the function of ENaC in confluent, polarized monolayers of both primary cultures of CF airway cells and an SV40-transformed CF nasal epithelial cell line (JME CF/15). Treatment of JME/CF 15 cells with rhHGF at concentrations of 100 ng/ml and above was found to dramatically decrease the activity of amiloride-sensitive Na⁺ transport. This effect required basolateral exposure of the cytokine. Addition of 100 ng/ml rhHGF to JME/CF 15 cells decreased I(eq) with a t(1/2) of ~ 18 h, with a maximal inhibition of ~ 90% by 36 h. By 48 h, stimulation with rhHGF induced a down-regulation of its receptor, c-met, expressed in these cells. The decrease in I(eq) of JME/CF 15 monolayers was not immediatelly reversed upon removal of rhHGF. Treatment with rhHGF did not appear to affect monolayer resistances nor Cl^- currents induced by mediators such as isoproterenol, histamine or bradykinin. Studies with primary cultures of CF airway cell sheets demonstrated comparable sensitivity and time-course properties for the inhibition of amiloride-sensitive currents following rhHGF addition. These observations are consistent with the possible application of an extracellular signalling molecule, such as the cytokine HGF, to reduce the abnormally high activity of amiloride-sensitive Na⁺ ion channels observed in CF airway cells.