Synthesis of Mucin Glycoproteins by Epithelial Cells Isolated from Swine Trachea by Specific Proteolysis

Mucus-producing cells were isolated from swine trachea mucosa by a method that included enzymatic digestion of the epithelial surface with Dispase, a neutral protease from Bacillus polymyxa, and differential attachment of the washed cells to culture flasks coated with collagen. Epithelial cells were the major cell type isolated by these procedures. Ciliated cells that did not attach to the flasks were removed by decantation , and fibroblasts were destroyed by the bacterial protease. The isolated cells synthesized respiratory mucins and the rate of secretion was increased about threefold when tracheas were exposed to sulfur dioxide. The cultured cells incorporated both [35S]O4 and [I-14C]N-acetylglucosamine into secreted mucin glycoproteins. The secretion of glycoprotein increased for about 3 d until the cells became confluent, and then a constant rate was observed for a period of at least 7 d. This increase in the output of mucin glycoprotein during the initial 3 d of culture was accompanied by a corresponding increase in the number of mucus-producing cells in the flasks. The results obtained in these and subsequent studies suggest that the rate of formation of mucus-producing cells may be a rate limiting step in the regulation of mucin glycoprotein synthesis in tracheal epithelium. The chemical, physical, and immunological properties of the glycoprotein secreted by isolated tracheal epithelial cells were very similar to the mucin glycoprotein purified from washes of swine trachea epithelium. The purified mucin glycoproteins showed complete cross-reaction with antibodies to trachea mucin glycoprotein. They were eluted near the void volume during gel filtration of Sepharose CL-6B columns. The glycoprotein isolated from culture media under the standard assay conditions had nearly the same carbohydrate composition as samples purified from washes of trachea epithelium. Reduced oligosaccharides released by beta-elimination with dilute alkaline borohydride showed similar elution profiles during chromatography on Bio Gel P-6 columns. Taken collectively, these results suggest that the isolated epithelial cells secreted mucin glycoproteins that were very similar to those synthesized by the intact trachea epithelium under standard incubation conditions.