Regulation of transforming growth factor beta 1 by nitric oxide

Many tumor cells or their secreted products suppress the function of tumor- infiltrating macrophages, Tumor cells often produce abundant transforming g rowth factor beta 1 (TGF-beta 1), which in addition to other immunosuppress ive actions suppresses the inducible isoform of NO synthase, TGF-beta 1 is secreted in a latent form, which consists of TGF-beta 1 noncovalently assoc iated with latency-associated peptide (LAP) and which can be activated effi ciently by exposure to reactive oxygen species, Coculture of the human lung adenocarcinoma cell line A549 and ANA-1 macrophages activated with IFN-gam ma plus lipopolysaccharide resulted in increased synthesis and activation o f latent TGF-beta 1 protein by both A549 and ANA-1 cells, whereas unstimula ted cultures of either cell type alone expressed only latent TGF-beta 1, We investigated whether exposure of tumor cells to NO influences the producti on, activation, or activity of TGF-beta 1. A549 human lung adenocarcinoma c ells exposed to the chemical NO donor diethylamine-NONOate showed increased immunoreactivity of cell-associated latent and active TGF-beta 1 in a time - and dose-dependent fashion at 24-48 h after treatment. Exposure of latent TGF-beta 1 to solution sources of NO neither led to recombinant latent TGF -beta 1 activation nor modified recombinant TGF-beta 1 activity. A novel me chanism was observed, however: treatment of recombinant LAP with NO resulte d in its nitrosylation and interfered with its ability to neutralize active TGF-beta 1, These results provide the first evidence that nitrosative stre ss influences the regulation of TGF-beta 1 and raise the possibility that N O production may augment TGP-beta 1 activity by modifying a naturally occur ring neutralizing peptide.