Growth inhibition and transformation of a human fetal tracheal epithelial cell line by long-term exposure to diethylnitrosamine

Influence of culture passages on growth kinetics, xenobiotic metabolism, chromosomal stability and transformation in a clonal fetal hamster lung epithelial cell line

M3E3/C3 is a clonal fetal hamster lung epithelial cell line which is used for studies of epithelial differentiation as well as for in vitro toxicologic tests. In this study growth kinetics, xenobiotic metabolism, chromosomal stability and transformation were investigated at increasing culture passage numbers up to 150. Cells of higher passages grew faster and reached higher cell densities than the cells of lower ones. As an indicator of xenobiotic metabolism we measured the activity of 7-ethoxycoumarin-deethylase (ECD), an enzyme belonging to the mixed function oxidase system. Up to passage number 100 the ECD activity strongly increased, followed by a slight decrease in additional passages. The chromosomal stability was assessed by the induction of micronuclei by benzo[a]pyrene (BaP) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). More micronuclei were always detected in cells of higher passages than of lower passages. The capability of cells to be transformed to anchorage independent growth by chemical carcinogens was examined using a soft agar test. After carcinogen exposure with BaP and MNNG, cells of higher passages showed higher transformation frequencies than cells of lower passages. Many cells at passage 150 exhibited an especially high soft agar growth even without carcinogen treatment and were therefore characterized as spontaneously transformed. These results show that metabolic and genetic characteristics of permanently growing cells differ remarkably depending on the culture passage. This has always to be considered when permanently growing cells are used for toxicological studies.

In vitro investigation on proliferative cystic keratinizing squamous lesions in the rat lung

The proliferative cystic squamous cell lesion inducible by inhalation of particulate matter in the rat lung is characterized by the formation of keratin-filled cystic cavities of various sizes bordered by multiple layers of keratinizing squamous epithelial cells. The current investigation is primarily concerned with two points. One is whether the cells participating in this particular cystic configuration can recapitulate their specific in vivo morphogenetic behavior also in the in vitro circumstances. The other is whether these squamous epithelial cells are neoplastic in nature. Although the currently adopted cell culture system was two-dimensional, the specific morphogenetic pattern was reproduced in vitro in a corresponding manner by the squamous cells derived from the aforementioned rat lung lesions. Exposure of these cells to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) at 100 ng/ml induced a marked polymorphism in them and also stimulated their keratinization. In soft agar culture, both TPA-exposed and unexposed cells developed colonies larger than 0.05 mm in diameter with an incidence of 0.73% and 1.12%, respectively. The lower incidence in TPA-exposed cultures can be interpreted in terms of TPA stimulation of keratinization. However, colonies larger than 0.1 mm in diameter were also developed by the TPA-exposed cells, indicating the presence of a cell population responsive to promotional effects of TPA. These results imply that the cells involved in the formation of cystic squamous epithelial cell lesions are already initiated and possess a potential for autonomous benign growth.

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.

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 3H-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 neural glycoproteins was most enhanced by VA in the range from the physiological concentration of 600 ng/ml to 6 micrograms/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.

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.

Secretory differentiation of human fetal bronchial epithelial cells in culture. A study by histochemistry and electron microscopy

Human fetal bronchial epithelial (HFBE) cells at 6-8 passages were cultivated on a collagen gel for 10 days. A basal differentiative medium (BDM), consisting of RPMI 1640 supplemented with hormones and growth factors, was employed. Histochemistry, scanning electron microscopy and transmission electron microscopy revealed that HFBE cells developed secretory granules when cultivated on collagen gel in BDM. They were electron-dense and stained positive for PAS but negative for alcian blue. On additional treatment with 8 micrograms/ml vitamin A (VA), the number of secretory granules was increased. Moreover, the HFBE cells lost their surface microvilli, and dilation of rough endoplasmic reticulum was more marked than in culture without VA.

Chromosome analyses of human mammary epithelial cells at stages of chemical-induced transformation progression to immortality

Benzo(a)pyrene induced extended life (EL) (i.e., a longer than normal proliferative lifespan before senescence) of human breast cells in culture. From many EL cell cultures immortalized cells emerged only once in each of two separate experiments. The original EL cells were mostly normal diploid with only a small percentage of tetraploid cells. The two immortalized cell lines, however, were near diploid, each containing a set of chromosomal aberrations that were present in all the cells analyzed, confirming the clonal origin of both cell lines. For cell line 184A1 the aberrations consisted of deficiencies only, whereas a combination of deficiencies and duplications characterized the 184B5 line. None of the individual aberrations of each set were shared by both cell lines. Both sets of aberrations have remained stable for over 150 population doublings, while some of the other chromosomes showed breakage and reunions. These data are discussed in regard to types of mutations in the sequence of changes from primary to immortalized cells, and it is concluded that the sets of aberrations most likely originated as multiple events in a single cell.

Characterization of human tracheal epithelial cells transformed by an origin-defective simian virus 40

To facilitate understanding of the mechanisms underlying pulmonary diseases, including lung cancer and cystic fibrosis, we have transformed and characterized cultures of human tracheal epithelial cells. Cells were transfected by calcium phosphate precipitation with a plasmid containing a replication-defective simian virus 40 (SV40) genome. Colonies of cells with enhanced growth potential were isolated and analyzed for transformation- and epithelial-specific characteristics. Precrisis cells were observed to express the SV40 large tumor antigen, produce cytokeratins, have microvilli, and form tight junctions. After crisis, cells continued to express the SV40 large tumor antigen as well as epithelial-specific cytokeratins and to display the apical membrane microvilli. Apical membrane Cl channels were opened in postcrisis cells exposed to 50 microM forskolin. These channels showed electrical properties similar to those observed in primary cultures. The postcrisis cells have been in culture for greater than 250 generations and are potentially "immortal." In addition to providing a useful in vitro model for the study of ion transport by human airway epithelial cells, the cells can be used to examine stages of neoplastic progression.

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.

Comparison of chrysene metabolism in epithelial human bronchial and Syrian hamster lung cells

Chrysene is metabolized to 1-, 2-, 3-, and 4-hydroxychrysene and trans-1,2- as well as trans-3,4-dihydroxydihydrochrysene in human and Syrian hamster epithelial lung cells as indicated by GC/MS analysis, whereas K-region oxidation is at most a very minor pathway. Cells of a permanent clonal line of fetal hamster lung metabolized 97% of the chrysene whereas fetal human bronchial epithelial cells converted 24% of the substrate within 8 days incubation. In human cells oxidation at the 3,4-position predominates, whereas oxidation at the 1,2-position is the major pathway in hamster cells. Indication for a bay-region oxidation of chrysene in hamster cells has been obtained.

A fetal Syrian hamster lung epithelial cell line as an in vitro model for respiratory carcinogenesis

A clonal continuous cell line consisting of pre-differentiated lung epithelial cells was established from a Syrian golden hamster fetus on day 15 of gestation. Immunocytological techniques revealed cytoplasmic filaments positive to antikeratin antibody and positive to antivimentin antibody in these cells. Supplementation of the medium with epidermal growth factor, insulin, other types of hormones and vitamin A markedly enhanced cell growth and DNA synthesis. Simultaneously, the cell differentiation characterized by mucus-like glycoprotein production was greatly stimulated. Removal of vitamin A diminished cell growth and this differentiation. The cell system was found to be useful for studying the relationship between in vitro cell transformation and differentiation. Additionally, studies to define general chemical toxicities in this cell system by evaluating several parameters such as cell survival, sialic acid content and enzyme leakage into the medium are in progress.