Regulation of growth and differentiation by vitamin A in a cloned fetal lung epithelial cell line cultured on collagen gel in hormone-supplemented medium.

Proliferative and differentiative responses to various doses of vitamin A (VA) were studied in the predifferentiated cells of a fetal Syrian hamster pulmonary epithelial line (M3E3/C3), which were cultured on a collagen gel in a hormone-supplemented medium. These predifferentiated cells possessed well-developed endoplasmic reticulum (ER) and Golgi apparatus. At VA doses higher than 8 micrograms/ml, periodic acid Schiff and slightly alcian blue positive mucuslike granules were produced, which were also detectable electron microscopically. These mucuslike products were rich in sialic acid and resembled quite well those from primary cultures of tracheal epithelial cells of Syrian hamster sucklings when analyzed by column chromatography on various types of gel. At all VA doses studied (2.4, 8, 24 micrograms/ml), cells grew exponentially with an average population doubling time of around 74 h, whereas in the absence of VA they had a linear growth rate and a population doubling time of 158 h between Days 4 and 11. The uptake of [3H]glucosamine into the whole cell homogenates showed a peak at Day 8, irrespective of VA doses (0 to 24 micrograms/ml), and at the highest VA dose (24 micrograms/ml) it exceeded by twofold the control (0 microgram/ml) level. At the same time, [14C]thymidine demonstrated a high peak of uptake on Day 8 at 8 and 24 micrograms/ml VA. There was virtually no difference between 0 and 2.4 micrograms/ml VA, with both doses yielding much lower peaks. Based on the results currently presented and previously reported, three successive stages were hypothesized for the mucous differentiation processes in M3E3/C3. The process from the first undifferentiated stage to the second predifferentiated stage with well-developed ER and Golgi apparatus requires both collagen gels and hormones. Differentiation from the second stage to the third secretory stage with mucous granules is stimulated by VA. These observations indicate that the cell line M3E3/C3 could provide a new system for investigating the mechanisms of mucus differentiation by VA.