Phenotypic plasticity of extracellular matrix gene expression in cultured hamster lung fibroblasts. Regulation of type I procollagen and fibronectin synthesis.

Abstract Enhanced synthesis and accumulation of interstitial collagens in the lungs of bleomycin-treated animals have been ascribed to drug-induced alterations in the cellular phenotype as judged by preferentially elevated rates of transcription of collagen and fibronectin genes (Raghow, R., Lurie, S., Seyer, J. M., and Kang, A. H. (1985) J. Clin. Invest. 76, 1733-1739). To explore the biosynthetic contribution of mesenchymal cells to the fibrotic process we cultured hamster lung fibroblasts from animals at 0, 1, 2, and 4 weeks after bleomycin treatment and compared their ability to synthesize type I collagen and fibronectin. Our analyses involved (i) measurements of the rates of procollagen and fibronectin synthesis in relation to the total protein synthesis, (ii) quantitative analyses of the steady-state levels of mRNAs coding for type I procollagen chains and fibronectin by Northern hybridization, and finally (iii) a semiquantitative comparison of the steady-state levels of type I procollagen transcripts by in situ hybridization to recombinant cDNA probes. We show that in the earliest stages of the growth in vitro, the patterns of type I procollagen and fibronectin biosynthesis by cells in primary culture closely corresponded with those found in the intact lung. With increasing duration in culture, the distinctive phenotypes of cells from control as well as fibrotic lungs changed steadily; the biosynthetic profiles of fibroblasts cultured for 10 days from untreated or bleomycin-treated lungs were nearly identical. Based on these data, we conclude that the biosynthetic phenotype of fibroblasts, as judged by the parameters of collagen and fibronectin synthesis, appears to be reversible. The characteristic biosynthetic phenotype of fibroblasts, in the interactive milieu of the intact lung (both control and bleomycin-treated), is maintained by cellular and/or humoral factor(s) which are removed or inactivated by the procedures used for isolation and in vitro culture of fibroblasts.