Expression of TGF-beta during in vitro differentiation of hamster tracheal epithelial cells.

The control of growth and differentiation of tracheal epithelial cells is poorly understood. Retinoic acid seems to be essential for the growth and secretory cell differentiation of hamster tracheal epithelial (HTE) cells in culture. In this study, we tested the hypothesis that one way by which retinoic acid (RA) stimulates growth is by decreasing transforming growth factor beta (TGF beta) expression or activity or both. HTE cells were very sensitive to TGF beta-induced growth inhibition. TGF beta 1 was more potent than TGF beta 2 with 50% inhibition of growth achieved at a concentration less than 0.1 ng/ml. A single TGF beta 1 transcript of 2.4 kb was expressed in HTE cells, and the amount increased by fourfold as cell proliferation decreased and differentiation increased. No TGF beta 2 mRNA could be detected in proliferating undifferentiated HTE cells, but two distinct mRNAs (5.1 and 3.5 kb) were observed to be induced in a transient fashion in RA-treated cells which correlated with the onset of differentiation. The amount of biologically active TGF beta in conditioned media from HTE cells at different stages of growth and differentiation in primary culture was determined by the mink lung epithelial cell growth inhibition assay and the use of neutralizing antibodies. These assays indicated a large increase in the total amount of TGF beta at the time the cells slowed their growth and started to differentiate. The activity was due primarily to TGF beta 1. Interestingly, cells treated with RA had a major component of "preactivated" (non-latent) TGF beta 1 compared to control cells.(ABSTRACT TRUNCATED AT 250 WORDS)