Regulation of fibronectin biosynthesis by dexamethasone, transforming growth factor β, and cAMP in human cell lines

Abstract

The regulation of fibronectin (FN) biosynthesis by dexamethasone (a synthetic glucocorticoid), forskolin (an activator of adenylate cyclase), and transforming growth factor β (TGF-β) was examined in six human cell lines. Dexamethasone treatment produced the largest increase in FN biosynthesis in the fibrosarcoma cell line, HT-1080 (~45-fold). This seems to result from a dexamethasone-mediated increase in FN mRNA stability which increases the message half-life from ~11 to 26 h. The relative instability of FN mRNA in the fibrosarcoma (t( 1/2 ) 11 h) compared to normal fibroblasts (70 h) appears to result from the particular transformed phenotype of the HT-1080 cells. Forskolin and TGF-β increase the rate of FN gene transcription in most of the cell lines. These effects (four- to six-fold) occur rapidly and do not require protein synthesis in the responsive cell lines which include normal fibroblasts. However, in the fibrosarcoma (HT-1080), a surprisingly large induction (20-30-fold) is observed and this induction is different from that in the normal fibroblasts and the other cell lines in that both protein synthesis and a lag period are required. Synergism is seen with dexamethasone and either forskolin or TGF-β in HT-1080 cells increasing the rate of FN biosynthesis ~200-fold to a level similar to normal fibroblasts. This seems to result from a combination of FN mRNA stabilization (dexamethasone) and increased transcription (forskolin and TGF-β).