Changes in lung-specific molecular expression during differentiation of hamster embryonic M3E3/C3 cell line

To clarify the differentiation mechanisms of bronchiolar epithelial cells, changes at the transcription level of epithelial cell-specific proteins were examined using M3E3/C3, a cell line derived from hamster fetal lung. During a 9-day incubation period with 24 mug/mL of retinol, the cells became attached to each other and formed large bud-like structures which could be detected with periodic acid-Schiff staining. During the incubation period, the mRNA level of surfactant-associated protein-B significantly increased 2.6- and 5.4-fold higher than cells incubated without retinol on days 3 and 9, respectively. The Clara cell-specific secretory protein mRNA level also increased and peaked at 5.1-fold (P < 0.05) on day 5 compared with control cells. In contrast, mRNA for surfactant-associated protein-C, an alveolar type II cell-specific protein, decreased. Moreover, the expression of the gene for hepatocyte nuclear factor 3 alpha, a putative transactivating factor for lung-related genes, was up-regulated resulting in consistently higher levels (2.4- to 5.6-fold) compared with controls, while those for transmembrane-type mucin-1 and glyceraldehyde-3-phosphate dehydrogenase were constantly expressed during the incubation. The present study confirms that at the gene transcription level M3E3/C3 cells differentiate into Clara-like cells with mucus granules in the presence of retinol.