BLEOMYCIN STIMULATES PRO-ALPHA-1(I) COLLAGEN PROMOTER THROUGH TRANSFORMING GROWTH-FACTOR-BETA RESPONSE ELEMENT BY INTRACELLULAR AND EXTRACELLULAR SIGNALING

The role of transforming growth factor beta as a mediator of the fibro genic effect of bleomycin in lung has been investigated at the transcr iptional level. Several constructs containing the rat pro-alpha 1(I) c ollagen promoter fused to the chloramphenicol acetyltransferase gene w ere transfected into rat lung fibroblasts. Both bleomycin and transfor ming growth factor beta 1 increased promoter activity in fibroblasts t ransfected with constructs containing the transforming growth factor b eta response element. Fibroblasts transfected with a deletion construc t that lacks this response element did not respond to either bleomycin or transforming growth factor beta 1. Anti-transforming growth factor beta 1-neutralizing antibodies did not block the increase in promoter activity induced by bleomycin, suggesting intracellular signaling. Mu tation of the transforming growth factor beta response element greatly reduced the bleomycin effect, which also infers intracellular signali ng. In addition, plasmin added to the media greatly enhanced bleomycin stimulation of promoter activity demonstrating that transforming grow th factor beta mediates the bleomycin effect through extracellular sig naling.