TGF-β1 Stimulation of Fibronectin Transcription in Cultured Human Lung Fibroblasts Requires Active Geranylgeranyl Transferase I, Phosphatidylcholine-Specific Phospholipase C, Protein Kinase C-δ, and p38, But Not erk1/erk2

Abstract The cytokine transforming growth factor-β (TGF-β) has multiple effects on a variety of cell types, modulating cell growth and differentiation as well as extracellular matrix deposition and degradation. In the present work, we demonstrate that TGF-β1 produces a fourfold increase in transcription of the fibronectin gene in cultured human fetal lung fibroblasts with only a small increase in mRNA stability resulting in a significant increase in fibronectin mRNA steady state level. A corresponding increase in production of fibronectin protein accompanied the increase in mRNA. Through the use of specific inhibitors, we demonstrate that geranylgeranylated, but not farnesylated or acylated protein(s), protein kinase C-δ, phosphatidylcholine-specific phospholipse C, tyrosine kinase activity, and stress-activated protein kinase p38 are required for this TGF-β1 effect. Trimeric G proteins and mitogen-activated protein kinases erk1 and erk2 do not appear to be involved. While these results emphasize the complexities involved in the control of extracellular matrix synthesis by TGF-β, they also identify reaction sites that may be amenable to pharmacologic modulation. Such modulation could be of great advantage in the treatment of a wide variety of undesirable fibrotic reactions.