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

To study the potential influence of cystic fibrosis conductance regulator ( CFTR) on intracellular pH regulation during apoptosis induction, we used PS 120 Chinese hamster lung fibroblasts devoid of the Na+/H+ exchanger (NHE1 i soform) transfected with constructs, allowing the expression of CFTR and/or NHE1. Kinetics of lovastatin-induced apoptosis were measured by orcein sta ining, double staining with Hoechst-33258, propidium. iodide, DNA fragmenta tion, and annexin V labeling. En PS120 control cells, the percentage of apo ptotic cells after 40 h of lovastatin treatment was 23 +/- 3%, whereas in P S120 CFTR-transfected cells, this percentage was 40 +/- 4%. In PS120 NHE1 c ells, the transfection. with CFTR did not modify the percentage of apoptoti c cells after 40 h (control: 19 +/- 3%, n = 8; CFTR: 17 +/- 1%, n = 8), ind icating that blocking intracellular acidification by overexpressing the Na/H+ exchanger inhibited the enhancement of apoptosis induced by CFTR. In al l cell lines, the initial pH values were identical (pH = 7.46 +/- 0.04, n = 9), and treatment with lovastatin led to intracellular acidification. Howe ver, the pH value after 40 h was lower in PS120 CFTR-transfectecl 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 this increased intracellular acidific ation observed in CFT-R-transfected cells, the activity of the DIDS-inhibit able Cl-/HCO3- exchanger was studied. 8-Bromoadenosine 3',5'-cyclic monopho sphate incubation resulted in Cl-/HCO3- exchanger activation in PS120 CFTR- transfected cells but had no effect on PS120 cells. Together, our results s uggest that CFTR can enhance apoptosis in Chinese hamster lung fibroblasts, probably due to the modulation of the Cl-/HCO3- exchanger, resulting in a more efficient intracellular acidification.