The pulmonary neuroendocrine cell (PNEC) system consists of fibrosis transmembrane conductance regulator (CFTR) and solitary cells and distinctive cell clusters termed neuroepithelial Cl Ϫ conductances during the neonatal period corresponding bodies (NEB) localized in the airway epithelium. PNEC/NEB to peak NEB numbers and the transition to air breathing express a variety of bioactive substances, including amine (sero- (2, 5). It is now known that CFTR regulates other ion tonin, 5HT) and

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... ptides. We have previously shown that channels including pulmonary epithelial cell Na ϩ channels NEB cells are O 2 sensors expressing nicotinamide adenine di-(6-13). Since the O 2 sensing complex in NEB involves O 2phosphate oxidase complex and O 2 sensitive K ؉ channel. Resensitive K ϩ channels (1, 14, 15), we have postulated that the cently, we demonstrated expression of functional cystic fibrosis function of CFTR in PNEC/NEB could be physiologically transmembrane conductance regulator (CFTR) and Cl Ϫ conducimportant. However, a significant limitation to more detances in NEB cells of rabbit neonatal lung. Because PNEC/NEB tailed biochemical and molecular investigations of this relaare sparsely distributed and difficult to study in native lung, tionship is the relative paucity of PNEC/NEB cells, which we investigated small-cell lung carcinoma (SCLC) and carcinoid represent Ͻ 1% of the lung parenchyma. tumor cell lines (tumor counterparts of normal PNEC/NEB) as An alternate model to native PNEC/NEB are immortalmodels for PNEC/NEB. SCLC (H146, H345) and carcinoid (H727) ized cell lines of small-cell lung carcinomas (SCLC) or varicell lines express neuroendocrine cell markers, including chroant carcinoid tumor which represent the tumor cell countermogranin A, neural cell adhesion molecule (N-CAM), 5HT, and part to PNEC/NEB. Although not entirely representative, tryptophan hydroxylase. We report that H146, H345, and H727 express CFTR messenger RNA (reverse transcription polymerase these tumor lines recapitulate neuroendocrine cell phenochain reaction) and protein (immunoblotting) and possess type, including the ability to synthesize bioactive amine functional CFTR Cl Ϫ conductance, demonstrated by an iodide (serotonin, 5HT) and a variety of neuropeptides (16-19), efflux assay inhibitable by transfection with antisense CFTR. as wells as O 2 sensing properties (20). In this study, we Using an immunoassay to quantitate 5HT secretion, we also analyzed SCLC cell lines H146 and H345 and carcinoid cell show that downregulation of CFTR abolishes hypoxia-induced line H727 for coordinate expression of CFTR and neuroen-5HT release, and reduces secretory response to high potassium. docrine cell markers. These cell lines have been previously Our findings suggest that CFTR may modulate neurosecretory characterized and shown to be representative models of the activity of PNEC/NEB possessing O 2 sensor function. We pro-PNEC system (21, 22). Similar to the O 2 sensory function pose that these tumor cell lines may be useful models for investipresent in NEB (1), the H146 cell line has been shown gating the role of CFTR in PNEC/NEB functions in health and to express a functional nicotinamide adenine diphosphate disease. used a sensitive competitive ELISA for 5HT. Our studies