CFTR modulates programmed cell death by decreasing intracellular pH in Chinese hamster lung fibroblasts

To study the potentialinfluence of cystic fibrosis conductance regulator (CFTR) onintracellular pH regulation during apoptosis induction, we usedPS120 Chinese hamster lung fibroblasts devoid of theNa⁺/H⁺ exchanger (NHE1 isoform) transfectedwith constructs, allowing the expression of CFTR and/or NHE1. Kineticsof lovastatin-induced apoptosis were measured by orceinstaining, double staining with Hoechst-33258, propidium iodide, DNAfragmentation, and annexin V labeling. In PS120 control cells, thepercentage of apoptotic cells after 40 h of lovastatintreatment was 23 ± 3%, whereas in PS120 CFTR-transfected cells,this percentage was 40 ± 4%. In PS120 NHE1 cells, thetransfection with CFTR did not modify the percentage of apoptoticcells after 40 h (control: 19 ± 3%, n = 8;CFTR: 17 ± 1%, n = 8), indicating that blockingintracellular acidification by overexpressing theNa⁺/H⁺ exchanger inhibited the enhancement ofapoptosis induced by CFTR. In all cell lines, the initial pHvalues were identical (pH = 7.46 ± 0.04, n = 9), and treatment with lovastatin led to intracellular acidification.However, the pH value after 40 h was lower in PS120 CFTR-transfected cells (pH = 6.85 ± 0.02, n = 10) than in PS120 cells (pH = 7.15 ± 0.03, n = 10). To further investigate the origin of thisincreased intracellular acidification observed in CFTR-transfected cells, the activity of the DIDS-inhibitableCl/HCO exchanger was studied.8-Bromoadenosine 3',5'-cyclic monophosphate incubation resulted inCl/HCO exchanger activation in PS120 CFTR-transfected cells but had no effect on PS120 cells. Together, ourresults suggest that CFTR can enhance apoptosis in Chinese hamster lung fibroblasts, probably due to the modulation of the Cl/HCO exchanger, resulting in a more efficient intracellular acidification.