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

Cell lines with extended in vitro growth potential from human renal proximal tubule: characterization, response to inducers, and comparison with established cell lines

Few model systems exist for the study of injury to human renal proximal tubule epithelium. Optimized differentiated human renal epithelial cell lines with extended in vitro growth potential would provide an alternative model system to primary culture or other available non-human mammalian kidney cell lines. For this purpose, human renal tubule epithelial cells were isolated from normal kidney cortex and exposed in culture to a hybrid immortalizing virus, adenovirus 12-SV40. Cell lines were developed by limiting dilution, and three selected cell lines were screened for growth pattern, production of immortalizing virus, tumorigenicity, and ploidy. Cell lines were also monitored for response to inducer agents and matrix factors and were screened for expression of biochemical properties and differentiation markers of renal epithelium. All three are nonproducers of the immortalizing virus and are nontumorigenic. They grow in monolayer, have intermediate growth kinetics, and express markers of renal proximal tubular epithelium by immunohistochemistry. They also express biochemical properties comparable to other widely used proximal tubular cell lines including LLC-RK1, OK, and HK-2 and comparable to human tubular cells in stable culture. Growth medium containing low levels of fetal calf serum, or epidermal growth factor combined with parathyroid hormone, produced optimal growth characteristics, brush border enzyme expression, biochemical properties, and glucose transport in a selected cell line. The addition of dimethyl sulfoxide allows maintenance in morphologically intact monolayers for prolonged periods. These cell lines should be useful model systems for the study of human renal proximal tubular injury or disease.

Quantitative ultrastructural analysis of the relationship between cell growth, shape change, and mucosecretory differentiation in cultured hamster tracheal epithelial cells exposed to retinoic acid

Hamster tracheal epithelial cells in extended (32 degrees C) primary culture with and without supplemental retinoic acid (RA) were studied during the proliferative (5 days) and differentiation phases (11 days) by correlative transmission electron microscopy (EM) and light microscopic (LM) autoradiography to quantify the relationship between cell proliferation, shape change, and mucin granule expression. In retinyl acetate-containing control medium, cell numerical density was higher and [3H]thymidine labeling index (LI) lower at day 11 compared with day 5. The addition of 10(-7) M RA to the medium caused an increase in cell numerical density at both times. LI was increased by RA at 5 days and decreased at 11 days. Measurements of cell shape in ultrathin sections adjacent to LM autoradiographs made in the vertical plane demonstrated an RA-induced change from flat to cuboidal at 5 days and a more columnar phenotype at 11 days. Cells containing mucin granules were of two main types based on their ultrastructure. One type, seen at 5 and 11 days, contained diminutive mucin granules and had an LI of 50% at 11 days. Its LI and frequency (26%) were unaltered by RA. The other type, less frequent (15%) and present only at 11 days, was more columnar and contained mucous granules similar to those found in vivo. RA doubled the frequency of this cell type but did not affect its LI (11%). Cells of this type with more than five mucin granules in EM profile did not incorporate thymidine. The data indicate that RA accelerates and enhances cell shape change toward a more cuboidal phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory differentiation and cell type identification of a human fetal bronchial epithelial cell line (HFBE)

A human fetal bronchial epithelial cell line (HFBE) grew in an undifferentiated pattern under conventional culture conditions. Despite a somewhat fibroblastic shape the cells maintained immunoreactivity to cytokeratin, carcinoembryonic antigen and epithelial membrane antigen. When grown on a collagen gel in a growth-hormone-supplemented medium, their spindle shape became more conspicuous. With an additional supplement of vitamin A (6 micrograms/ml), most of the cells underwent differentiation by producing many bright inclusion bodies which proved to be strongly positive with periodic acid-Schiff and weakly positive with alcian blue staining. Electron microscopy revealed a well-developed rough endoplasmic reticulum, an enlarged Golgi apparatus and many highly electron-dense secretory granules resembling those of Clara cells. Biochemical analysis demonstrated that HFBE cells cultured on collagen gel with vitamin A secreted hyaluronic acid and neutral glycoproteins containing mainly N-linked glycoproteins whose glycans were of a complex type. A monoclonal antibody (SEC-41) generated against the neutral glycoproteins detected a glycoprotein of approximately 52 kDa in the spent culture medium of differentiated HFBE cells. This antibody also reacted with the intracytoplasmic secretory granules in these cells. When tested on frozen sections of lung tissue, the immunohistochemical reactivity of the SEC-41 antibody was confined to Clara cells, some type II pneumocytes in the adult lung, and respiratory epithelial cells in the fetal lung. Moreover, this antibody could detect secretory glycoprotein in broncho-alveolar lavages from two patients. This paper clearly demonstrates that cells derived from human fetal bronchial epithelium can be cultivated in an undifferentiated precursor state and, under appropriate culture conditions, can be stimulated to undergo differentiation into a Clara cell type.

Differentiation of Clara cell (distal type) antigen in human fetal bronchial epithelial cell line (HFBE)

A human fetal bronchial cell line (HFBE) grew in an undifferentiated pattern under conventional culture conditions. Despite a somewhat fibroblastic shape, however, they still maintained an immuno-reactivity to cytokeratin, carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA). When grown on a collagen gel in a growth hormone-supplemented medium, their spindle shape became more conspicuous. With the additional supplement of 6 micrograms/ml vitamin A, most of the cells underwent differentiation by producing many bright inclusion bodies which proved to be strongly positive to periodic acid Schiff (PAS) and barely positive to alcian-blue (AB) staining. Electron microscopy revealed well-developed rough endoplasmic reticulum (rER), enlarged Golgi apparatus and many highly electron-dense secretory granules resembling those of Clara cells. Biochemical analysis demonstrated that HFBE cells cultured on collagen gel with vitamin A secreted products containing glycoconjugates of two different molecular weights. The higher molecular weight-product was identified as hyaluronic acid and the lower molecular weight-product as a mixture of neutral glycoproteins containing mainly N-linked glycoproteins whose glycans were of a complex type. While the secretion of hyaluronic acid was inhibited by vitamin A in a dose-dependent manner, that of the neutral glycoproteins was most enhanced by vitamin A in the range from the physiological concentration of 600 ng/ml to 6 micrograms/ml. A monoclonal antibody (SEC-41) generated against the secretory products with the lower molecular weight detected a glycoprotein of approximately 52 kd in the spent culture medium of differentiated HFBE cells. This antibody also reacted with the intra-cytoplasmic secretory granules in these cells. When tested on freeze-sectioned lung tissue, immunohistochemical reactivity of SEC-41 antibody was confined to Clara cells, some type II pneumocytes in the adult lung and respiratory epithelial cells of the fetal lung tissue. Moreover, this antibody could detect the secretory glycoproteins in the broncho-alveolar lavages (BAL) of two human cases. This paper has clearly demonstrated that cells derived from human fetal bronchial epithelium can be cultivated in an undifferentiated precursor state and under appropriate culture conditions they can be stimulated to undergo differentiation into a Clara cell type.

New functional cell-culture approach to pulmonary carcinogenesis and toxicology

Modern pulmonary toxicology (including lung carcinogenesis) has, to assist its rapid development, constantly incorporated the knowledge obtained through cell and tissue-culture studies. While this has been carried out in rather a passive manner until quite recently, the currently necessary multi-disciplinary approach increasingly requires more active involvement of cell/tissue-culture techniques in this area. Our understanding in this regard is that one of such requirements is to establish a cell-culture system consisting of a single population of possible target cells for certain classes of hazardous inhalants. In addition, such target cells in culture should be able to function in a manner as closely resembling the situation in vivo as possible. In view of the culture techniques presently available, this requirement is probably too ideal to be met immediately. Nevertheless, efforts have been made in the last decade to achieve functioning cultures of Clara cells, type II pneumocytes or small mucus granule cells (SMGC), using undifferentiated cells obtained from animal and human fetuses. This attempt forms a sharp contrast to the usual approach, in that while the latter tries to keep the functions of adult cells in an already differentiated state, the former aims at inducing functional differentiation in undifferentiated cells by manipulating culture conditions. In carrying out these efforts, we have shown clear evidence that the type II pneumocytes and Clara cells induced in vitro are closely cognate and share a common precursor cell in culture, and that SMGC are at a pre-stage of differentiation to Clara cells. We have also shown an induced capacity for xenobiotic activation and conjugation in SMGC in culture. Our next plan is to prove similar activity (of mixed-function oxidase) in Clara cells and type II pneumocytes induced to differentiate in culture.