Transformed Human Bronchial Epithelial Cells (BEAS-2B) Alter the Growth and Morphology of Normal Human Bronchial Epithelial Cells in Vitro

Normal human bronchial epithelial cells (BE) and adenovirus-12 SV40 hybrid virus transformed, non-tumorigenic human bronchial epithelial cells (BEAS-2B) were cultured for 7 days in a serum-free hormone supplemented medium. BE cells after 3 days in culture were exposed to conditioned medium (CMt) from confluent BEAS-2B cells. By day 7, CMt-treated BE cells exhibited a lower colony forming efficiency (CFE), fewer cells per colony, and a reduced mitotic index (MI) and BrdU (bromodeoxyuridine) labeling index. CMt also enhanced the expression of a terminally differentiated squamous phenotype in BE cells. Cell free lysates from BEAS-2B cells (CFLt) had effects similar to CMt on the MI and morphology of BE cells. In contrast, CMt and CFLt did not inhibit the growth, or alter the morphology of BEAS-2B cells. Conditioned medium from BE cells (CMn) did not reduce the growth of BEAS-2B cells, and had little effect on the morphology of BE cells. In co-cultures, BE cells in direct contact with BEAS-2B cells had a lower MI (0.4-0.7 vs. 1.6%) compared with colonies of BE cells in these cocultures. The concentration of transforming growth factor beta (TGF-beta) in conditioned media from BEAS-2B cells (CMt) was increased 10-fold over that in CMn. TGF-beta is known to induce terminal differentiation in epithelial cells. These results suggest that the selective growth advantage of transformed cells over normal cells during human bronchial carcinogenesis may be related to the release of autocrine/paracrine factors (e.g., TGF-beta) from transformed cells, which down-regulates and terminally differentiates the normal cells.