Fibronectin synthesis by human tubular epithelial cells in culture: Effects of PDGF and TGF-β on synthesis and splicing

Fibronectin synthesis by human tubular epithelial cells in culture: Effects of PDGF and TGF-β on synthesis and splicing. Background Enhanced synthesis of extracellular matrix proteins including fibronectin (FN) is associated with the development of sclerosis. In this context we studied FN synthesis by tubular epithelial cells in response to transforming growth factor-β (TGF-β) and platelet-derived growth factor (PDGF). Methods FN protein synthesis by human tubular epithelial cells in culture (TEC) was measured by biosynthetic labeling and ELISA. Splicing of FN was assessed by RT-PCR and by Northern blotting. Results Cultivated TEC synthesized and released FN, the majority of which was deposited as an unsoluble protein and a minor portion (10 to 15%) was released into the supernatant. TGF-β and, to a lesser degree, PDGF, up-regulated FN synthesis. All three FN splice variants (EDA, EDB, and IIICS) were produced. PDGF did not influence the splicing. TGF-β preferentially up-regulated the EDA splice variant, but had no effect on the splicing of the other domains. Conclusions PDGF and TGF-β both up-regulate FN synthesis of TEC. TGF-β, but not PDGF, also changed the quality of the de novo synthesized FN, and thus has a different role in the development of sclerosis.