Effects of TNF-alpha and phorbol ester on human surfactant protein and MnSOD gene transcription in vitro.

Tumor necrosis factor-alpha (TNF-alpha) and the phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) decrease the synthesis of surfactant proteins association with decreased SP-A and SP-B mRNA. Nuclear run-on assays were utilized to test whether the inhibitory effects of TNF-alpha and TPA were associated with changes in surfactant protein gene transcription. SP-A gene transcription was inhibited by both TNF-alpha and TPA as assessed by nuclear run-on assays. Inhibitory effects of both agents on SP-A gene transcription were readily detected within 6 h after exposure and persisted for 24 h. While TNF-alpha and TPA decreased cellular SP-B mRNA content, transcription of the SP-B gene was not influenced by these agents. In contrast to the inhibitory effects of TPA and TNF-alpha on SP-A and SP-B mRNAs, steady-state mRNA and rate of transcription of human manganese superoxide dismutase (MnSOD) were increased by both agents. The time course and extent of increased MnSOD gene transcription by TNF-alpha and TPA were distinct. Transcription of the human beta-actin gene was not altered by either agent. The inhibitory effects of TPA and TNF-alpha on SP-A expression in pulmonary adenocarcinoma cells are associated with the inhibition of SP-A gene transcription. Loss of SP-B mRNA was not accompanied by decreased SP-B gene transcription. Actinomycin D blocked the inhibitory effects of TNF-alpha and TPA on SP-A and SP-B mRNA, supporting a role for posttranscriptional events in the modulation of the expression of the surfactant proteins SP-A and SP-B.