3'-untranslated region of SP-B mRNA mediates inhibitory effects of TPA and TNF-alpha on SP-B expression

Surfactant protein-B (SP-B) is a small hydrophobic polypeptide that enhances spreading and stability of surfactant phospholipids in the alveolus of the lung. Decreased expression of SP-B is associated with respiratory 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 stability rather than by decreased rate of SP-B gene transcription. In the present study, a human pulmonary adenocarcinoma cell line, NCI H441-4, was stably transfected with expression vectors consisting of the thymidine 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 human SP-B cDNA [pTKGH(SP-B2.0)] or the 837-bp human SP-B 3'-UTR [pTKGH(SP-B.837)]. The mRNAs and cellular growth hormone protein generated from the chimeric TKGH(SP-B2.0) and TKGH(SP-B.837) genes were each inhibited by approximately 50% by TPA and TNF-alpha. Dexamethasone decreased the inhibitory effects of TPA and TNF-alpha. The inhibition of steady-state hGH-SP-B mRNA by TPA and TNF-alpha was mediated by a cis-active element located in the 3-UTR region of SP-B mRNA.