Abstract 295 Cytokines: Intracellular Signaling Platform, Tuesday, 5/4

Transforming growth factor β (TGF-β) regulates proliferation and differentiation of many cell types and is implicated in the pathogenesis of chronic lung disease in premature infants. Previously, we found that treatment of cultured human fetal lung with TGF-β1 decreased content of surfactant proteins (SP), acting at the level of gene transcription. We also observed that TGF-β1 added to H441 cells decreased SP-B expression and was correlated with decreased nuclear thyroid transcription factor-1 (TTF-1) and increased cytoplasmic TTF-1, a transcription factor important for expression of all SP genes. In the current study we examined human fetal lung explants and fetal type II cells for production of TGF-β and its effects on SP mRNAs and TTF-1. Treatment of explants with TGF-β1 (30 ng/ml) caused a loss of TTF-1 from the nucleus and accumulation in the cytoplasm of type II cells using both electromobility shift assay and immunofluorescent techniques. We isolated type II cells from hormone-treated lung explants and found that the cells maintained expression of SP-A, SP-B, SP-C, and SP-D mRNAs for several days in the presence of dexamethasone (10 mM) + 8-Br-cAMP (0.1 mM) + isobutylmethylxanthine (IBMX, 0.1 mM). Exposure of hormone-treated cells to TGF-β1 for 4 days reduced the content of both SP-A and SP-B mRNAs (12±4 and 19±6% of control, p<0.05, respectively) and caused a shift in TTF-1 immunoreactivity from nucleus to cytoplasm. Production of endogenous TGF-β was determined in a bioassay using a stably transfected TGF-β responsive cell line. Type II cells cultured in hormone-free medium accumulated TGF-β1 in the culture medium (1-20 ng/ml) in a time-dependent manner. Treatment of the cells with dexamethasone + cAMP caused a time-dependent decrease in TGF-β in medium and cells to 22±6% and 39±8% of control, respectively, after 3 days. In separate experiments, treatment of cells with cAMP alone had no effect on levels of TGF-β, whereas dexamethasone alone decreased the concentration. We conclude that TGF-β acts directly in fetal type II cells to decrease SP gene expression, in part secondary to cytoplasmic trapping of TTF-1, and that glucocorticoid decreases production of endogenous TGF-β. We speculate that glucocorticoid down-regulation of endogenous TGF-β may contribute to the stimulation of SP gene expression.