Transcriptional regulation of the lung fatty acid synthase gene by glucocorticoid, thyroid hormone and transforming growth factor-β1

Fatty acid synthase (FAS) is a key enzyme in the biosynthesis of lung surfactant. FAS expression in fetal lungs is increased by glucocorticoids and this effect is largely due to increased transcription. The stimulatory effect of glucocorticoid on FAS expression is antagonized by thyroid hormone and transforming growth factor-β1 (TGF-β1). To determine the glucocorticoid responsive regions of the FAS gene we employed deletion analysis and reporter gene assays. A549 cells were transfected with various FAS gene constructs ligated to the firefly luciferase gene and cultured with dexamethasone (Dex) for 24 h after which luciferase activity was measured. Dex increased luciferase expression in response to a fragment in the promoter and 5′-flanking region of the FAS gene, from −1592 to +65 bp. This increase was antagonized by triiodothyronine (T3) and TGF-β1. Serial deletions showed that the full response to Dex and T3 were retained in the 89 bp −33/+56 bp fragment whereas the response to TGF was mediated by the immediately upstream −104/−34 bp sequence. The Dex responsive region of the FAS gene could not be separated from the minimal promoter showing that they are intimately associated. The extents of Dex stimulation and antagonism by T3 and TGF in A549 cells were similar to those noted on parameters of FAS expression in fetal lung explants. These data show that the effects of Dex, T3 and TGF on FAS expression are mediated by DNA sequences in the promoter region of the gene.