INDUCTION AND CHARACTERIZATION OF SECRETORY DIFFERENTIATION IN HUMAN FETAL BRONCHIAL EPITHELIAL-CELL LINE (HFBE) CULTURED ON COLLAGEN GEL IN GROWTH-HORMONE AND VITAMIN-A-SUPPLEMENTED MEDIUM

A type of secretory differentiation was induced and characterized in a human fetal bronchial epithelial cell line (HFBE), which was grown on a collagen substratum in a basal differentiative medium (BDM) containing growth hormones and with supplementation of various concentrations of vitamin A (VA). HFBE cells grown on a collagen gel in BDM with or without VA assumed a spindle shape with thick cytoplasm arranged in strands running parallel to each other. Under a phase-contrast microscope, cells cultured in the absence of VA possessed a small number of bright inclusion bodies, which proved to be positive to PAS and almost negative to alcian-blue (AB) staining. Electron microscopy revealed well-developed rough endoplasmic reticulum (rER), enlarged Golgi apparatus and a small number of high-density granules resembling serous or Clara cell granules. HFBE cells treated with VA at levels higher than 6-mu/ml showed a remarkable increase of the secretory granules and contained amorphous material in the rER. Addition of a low concentration of VA (6 ng/ml) only stimulated the growth of HFBE cells. In contrast, higher concentrations of VA significantly inhibited the growth and H-3-thymidine incorporation into DNA in a dose-dependent manner. HFBE cells cultured on collagen gel with VA secreted products with 2 different molecular weights into the medium. A high molecular weight-product, consisting of void volume fractions from a Bio-gel A 15-m column, was identified as hyaluronic acid based on the results obtained from the DEAE-ion exchange chromatography and specific enzymatic digestion. A low molecular weight-product fractionated on the A 15-m was tentatively identified as mainly neutral glycoproteins containing N-linked glycans. While the secretion of hyaluronic acid was inhibited by VA in a dose-dependent manner, the secretion of the neutral glycoproteins was most enhanced by VA in the range from the physiological concentration of 600 ng/ml to 6-mu-g/ml. These biochemical data on the secretory products, together with the morphological findings, demonstrate that the HFBE cell line serves as a new model for investigating the cellular differentiation of human lung epithelium.