3'-UNTRANSLATED REGION OF SP-B MESSENGER-RNA MEDIATES INHIBITORY EFFECTS OF TPA AND TNF-ALPHA ON SP-B EXPRESSION

Surfactant protein-B (SP-B) is a small hydrophobic polypeptide that en hances spreading and stability of surfactant phospholipids in the alve olus of the lung. Decreased expression of SP-B is associated with resp iratory failure in premature infants and in adult patients with acute respiratory distress syndrome (ARDS). Tumor necrosis factor-alpha (TNF -alpha) and 12-O-tetradecanoylphorbol-13 acetate (TPA) cause ARDS-like lung injury in vivo. Inhibitory effects of TPA and TNF-alpha on SP-B mRNA expression in vitro were mediated by decreased SP-B mRNA stabilit y rather than by decreased rate of SP-B gene transcription. In the pre sent study, a human pulmonary adenocarcinoma cell line, NCI H441-4, wa s stably transfected with expression vectors consisting of the thymidi ne kinase (TK) promotor and human growth hormone (hGH) gene, in which the hGH 3'-untranslated region (3'-UTR) was replaced by the 2.0-kb hum an SP-B cDNA [pTKGH(SP-B2.0)] or the 837-bp human SP-B 3'-UTR [pTKGH(S P-B.837)]. The mRNAs and cellular growth hormone protein generated fro m the chimeric TKGH(SP-B2.0) and TKGH(SP-B.837) genes were each inhibi ted by similar to 50% by TPA and TNF-alpha, Dexamethasone decreased th e inhibitory effects of TPA and TNF-alpha. The inhibition of steady-st ate hGH-SP-B mRNA by TPA and TNF-alpha was mediated by a cis-active el ement located in the 3-UTR region of SP-B mRNA.