Induction of alpha-smooth muscle actin by transforming growth factor-beta 1 in quiescent human breast gland fibroblasts. Implications for myofibroblast generation in breast neoplasia.

BACKGROUND

By using a novel experimental system for the study of reactive fibroblast differentiation at the molecular level, we describe the induction of the alpha-isoform of smooth muscle actin by transforming growth factor-beta (TGF-beta 1) in human normal breast gland fibroblasts.

EXPERIMENTAL DESIGN

The experimental system allowed fibroblasts to plate and remain quiescent and nonreactive but at the same time stay sensitive to environmental cues for more than 2 weeks after explantation. Most important, the biological activity of growth factors and cytokines could be studied without cells entering the cell cycle, thus serving as a model for stromal reactions with little cell turnover.

RESULTS

By use of double-labeling immunocytochemistry, isoelectric focusing, two-dimensional gel electrophoresis, and fluorography, evidence is presented that the effect of TGF-beta 1 is dose-dependent with a maximal response above 80 pg/ml and a course of 6 days. No other growth factor/cytokine tested (platelet-derived growth factor, interleukin-1, insulin-like growth factor-1, acidic fibroblast growth factor, basic fibroblast growth factor, epidermal growth factor, and interferon-gamma) could induce alpha-smooth muscle actin on their own or potentiate the effect of TGF-beta 1. In an inhibitory assay, only basic fibroblast growth factor was found to prevent the action of TGF-beta 1. The relative contribution of TGF-beta 1-like activity to carcinoma cell induced alpha-smooth muscle actin in fibroblasts was deciphered using TGF-beta neutralizing antibodies and medium conditioned by two different breast carcinoma cell lines. Conditioned medium elicited a fibroblast response indistinguishable from that obtained with exogenously added TGF-beta 1, and indeed neutralization attributed the entire response to the sole effect of secreted TGF-beta 1-like activity.

CONCLUSIONS

These results provide a strategy for the molecular characterization of epithelial-stromal interaction in breast neoplasia.