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 gro wth and secretory cell differentiation of hamster tracheal epithelial (HTE) cells in culture. In this study, we tested the hypothesis that o ne way by which retinoic acid (RA) stimulates growth is by decreasing transforming growth factor beta (TGF beta) expression or activity or b oth. HTE cells were very sensitive to TGF beta-induced growth inhibiti on. 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 b eta 1 transcript of 2.4 kb was expressed in HTE cells, and the amount increased by fourfold as cell proliferation decreased and differentiat ion increased. No TGF beta 2 mRNA could be detected in proliferating u ndifferentiated HTE cells, but two distinct mRNAs (5.1 and 3.5 kb) wer e observed to be induced in a transient fashion in RA-treated cells wh ich correlated with the onset of differentiation. The amount of biolog ically active TGF beta in conditioned media from HTE cells at differen t stages of growth and differentiation in primary culture was determin ed by the mink lung epithelial cell growth inhibition assay and the us e of neutralizing antibodies. These assays indicated a large increase in the total amount of TGF beta at the time the cells slowed their gro wth and started to differentiate. The activity was due primarily to TG F beta 1. Interestingly, cells treated with RA had a major component o f ''preactivated'' (non-latent) TGF beta 1 compared to control cells. Addition of TGF beta 1 neutralizing antibodies directly to HTE culture s delayed the onset of both growth arrest and differentiation. These r esults do not support the hypothesis that RA stimulates HTE cell growt h by decreasing TGF beta; rather they suggest that endogenously produc ed TGF beta may play a role in the initiation of growth arrest which p recedes differentiation.