Glycoprotein secretion by cultured hamster trachea epithelial cells: A model system for in vitro studies of mucus synthesis

To characterize the biological functions of cultured hamster tracheal cells, a microassay has been developed utilizing [³H]N-acetyl-d-galactosamine and [¹⁴C] serine as a double label for glycoprotein synthesis. After a 24-hr incubation of cell monolayers with these radioactive precursors, the cell culture supernatant was precipitated with trichloroacetic acid and electrophoresed on polyacrylamide gels. A single radioactive peak was detected containing both radioisotopes with a migration corresponding to a molecular weight of approximately 18,500 daltons. Under similar culture conditions, tracheal explants produced a nearly identical gel profile; in contrast, three established cell lines lacked most of this biosynthetic capability. Collagenase and hyaluronidase did not degrade the secreted macromolecule, and its sensitivity to weak alkali treatment revealed that it is a glycoprotein with O-glycosidic linkages. Vitamin A significantly enhanced its secretion, directly correlating with previous in vivo studies demonstrating a vitamin A prerequisite for normal mucus-secreting epithelium. Histochemical staining indicated the presence of acidic mucins within secretory packets on the cell. We have therefore concluded that this epithelial cell cultured from the hamster trachea has the specialized capacity for mucus secretion, and it may serve as a versatile model system for studying the synthesis and nature of mucus glycoproteins.