Reactive oxygen and nitrogen intermediates increase transforming growth factor-beta 1 release from human epithelial alveolar cells through two different mechanisms

Transforming growth factor (TGF)-beta 1 is a growth factor involved in the mechanisms of lung repair and fibrosis that follow inflammatory processes. We sought to examine the link between the generation of reactive oxygen int ermediates (ROI) or reactive nitrogen intermediates (RNI) by inflammatory c ells and the expression of TGF-beta 1 by alveolar epithelial cells. Exposur e of the A549 lung epithelial cell line to either an ROI generating system (xanthine and xanthine oxidase) or an RNI donor (S-nitroso-N-acetyl-penicil lamine [SNAP]) promoted a time- and dose-dependent increase in TGF-beta 1 r elease, as measured by a specific enzyme-linked immunosorbant assay. At the peak, the levels of TGF-beta 1 were twice the control values. The inductio n of TGF-beta 1 release by ROI was blunted by catalase and unaffected by su peroxide dismutase, indicating the involvement of hydrogen peroxide. The re sponse was also blunted by 5,6-dichloro- 1-beta-D-ribofuranosyl benzimidazo le (DRB), a specific RNA polymerase II inhibitor, and accompanied by a corr esponding increase in TGF-beta 1 messenger RNA, as measured by quantitative /competitive reverse transcription polymerase chain reaction, suggesting th e involvement of transcriptional mechanisms and possibly other downstream m echanisms. In contrast, RNI-induced TGF-beta 1 release was unaffected by DR B and blunted by the protein synthesis inhibitor cycloheximide, suggesting the involvement of translational and post-translational mechanisms. This re sponse required cyclic guanosine monophosphate (cGMP)-mediated processes be cause (I) immunoreactive cGMP accumulated in the culture medium of SNAP-tre ated cells: (2) SNAP-induced TGF-beta 1 release was blunted by KT 5823, an inhibitor of sGMP-dependent protein kinase; and (3) similar increase in TGF -beta 1 release was obtained by cell exposure to membrane-pennneable dibuty ryl-cGMP or to atrial natriuretic factor, a known agonist of particulate gu anylate cyclase. These data suggest that in vitro exposure of human alveola r epithelial cells to ROI and RNI enhances TGF-beta 1 release through diffe rent mechanisms. In vivo, this control may constitute a molecular link; bet ween inflammatory and fibrotic processes.