[Studies on the regulation of normal bronchial epithelial cell proliferation and proto-oncogene expression].

The regulatory mechanisms of proliferation and differentiation of normal airway epithelial cells seem important for the better understanding of lung carcinogenesis. We isolated bovine and human bronchial epithelial cells by enzymatic digestion of bronchi, and cultured them in serum-free growth factor-supplemented medium. To determine the role of growth factors in the proliferation of bovine bronchial epithelial cells, the effect of each of these additives was evaluated. Of these, fetal calf serum (FCS), bovine pituitary extract (BPE), insulin and insulin-like growth factor-1 (IGF-1) showed a significant stimulatory effect on cell growth. These four additives induced transient increases in c-fos, c-jun and c-myc proto-oncogene mRNA levels. Transforming growth factor beta (TGF beta) inhibited growth factor-induced cell proliferation, and also showed selective inhibition of c-myc induction. We also studied the effect of interleukin 6 (IL-6) on human bronchial epithelial cell proliferation. IL-6 showed a significant inhibitory effect on cell growth. These cells were capable of expressing and releasing IL-6 and had specific receptors for IL-6, suggesting an autocrine mechanism. These results suggest that TGF beta and IL-6 may play roles in the regulation of airway epithelial cell growth as inhibitory growth factors.