Phenotypic consequences of transforming growth factor beta1 gene ablation in murine embryonic fibroblasts: autocrine control of cell proliferation and extracellular matrix biosynthesis.

The profound effects of transforming growth factor beta1 (TGF-beta1) on the immune system, cardiogenesis, in yolk sac hematopoeisis and in differentiation of endothelium have been demonstrated by detailed analyses of TGF-beta1 knockout mice during embryogenesis. We have systematically examined the autocrine and paracrine roles of TGF-beta1 in cell proliferation and in its ability to modulate the gene expression of selected components of extracellular matrix (ECM) using embryonic fibroblasts from TGF-beta1 null mice (TGF-beta-1(-/-)). The rates of cell proliferation of embryonic fibroblasts from normal mice (TGF-beta1(+/+)) and TGF-beta1 null mice were compared by cell counting, by 3H thymidine incorporation, and by measuring the fraction of cells in the G1, S, and G2/M phases of the cell cycle by fluorescent activated cell sorting (FACS). Concurrently, the expression of pro-alpha1(I) collagen, fibronectin, and plasminogen activator inhibitor-1 (PAI-1) was also quantified by hybridization of total mRNA from TGF-beta1(+/+) and TGF-beta1(-/-) embryonic fibroblasts. We report that TGF-beta1(-/-) cells proliferated at about twice the rate of TGF-beta1(+/+) cells. Further, TGF-beta1 null fibroblasts accumulated and synthesized lower constitutive levels of pro-alpha1(I) collagen, fibronectin, and PAI-1 mRNA. The quantitative differences in the rates of cell proliferation and ECM gene expression between TGF-beta1(+/-) and TGF-beta1(-/-) cells could be eliminated by treatment of TGF-beta1(+/+) cells with a neutralizing antibody of TGF-beta1. Thus, our results are consistent with the hypothesis that TGF-beta1 acts as a negative autocrine regulator of growth and a positive autocrine regulator of ECM biosynthesis in embryonic fibroblasts.