REGULATION OF EXTRACELLULAR MATRIX PROTEINS BY TRANSFORMING GROWTH FACTOR β1IN CULTURED PULMONARY ENDOTHELIAL CELLS

Abstract

Transforming growth factor beta-1 (TGF-β1), which is present in lung tissue, has been suggested to play a role in modulating vascular cell function in vivo. The action of TGF-β1in vivo, especially at the local site of application to connective tissue, is anabolic and leads to pulmonary fibrosis and angiogenesis, strongly indicating that TGF-β may have practical applications in repair of tissue injury caused by burns, trauma, or surgery. In the present study, we have used cultured bovine pulmonary artery endothelial (BPAE) cells as a model system. Expression of various proteins, including SPARC (secreted protein acidic and rich in cysteines), type IV procollagen and fibronectin (FN) was examined by radiolabeling the cells with [3H]proline, immunoprecipitation with specific antibodies, and Northern blot analyses by using specific cDNA probes. Cultured cells were labeled with [3H]proline for 24h in either the absence or in the presence of TGF-β1(0–20ng/ml). Incorporation of radioactivity was observed in a concentration-dependent manner, maximal at 5ng/ml. Northern blot hybridization demonstrated that TGF-β1(5ng/ml) treatment of BPAE cells caused an increase in steady-state levels of mRNA for SPARC (75%) and FN, thus, indicating a positive modulation. To determine whether TGF-β1has an effect on cell proliferation in the cultures, the incorporation of [3H]thymidine into cellular nuclei was used to measure DNA replication; 5ng/ml had an inhibitory effect (42%) on cell proliferation. Protein production by TGF-β1, surprisingly, showed decrease in SPARC levels (42%) and in contrast increased levels of FN (86%) and type IV procollagen (334%). Our results indicate that on exposure to TGF-β1, cultured BPAE cells differentially change expression of extracellular matrix proteins which may be important in remodeling of tissue and healing at sites of injury.