Immortalized human corneal epithelial cells for ocular toxicity and inflammation studies.

PURPOSE: To develop a metabolically competent, human immortalized corneal epithelial cell line for use in toxicity and inflammation studies. METHODS: Primary corneal epithelial cells (P-CEPI) were immortalized by a recombinant simian virus (SV)40 T antigen retroviral vector defective for viral replication. The cells were grown in serum-free medium with the addition of bovine pituitary extract, cloned at passage 15 and one of the best-growing clones, CEPI-17-CL4, was extensively characterized for differentiation and metabolic characteristics of the human corneal epithelium. Methods used were immunostaining, reverse transcription-polymerase chain reaction (RT-PCR), northern blot analysis, and enzyme assays. RESULTS: The CEPI-17-CL4 cells showed a typical cobblestone morphology, grew to more than 200 passages and expressed the SV40 T antigen in the nucleus of every cell. Immunofluorescence staining for CEPI-17-CL4 cells was strongly positive for keratins (K)8, K18, and K19 and vimentin; weakly positive for K3, K13, and K17; and negative for K4, K7, and K14. Expression of cytokines (interleukin [IL]-1alpha, IL-1beta, IL-6, IL-8, tumor necrosis factor-alpha, and IL-ra), growth factors (transforming growth factor [TGF]-alpha, epidermal growth factors [EGF], EGF receptor [EGFR], TGF-beta1, TGF-beta2, and platelet-derived growth factor-beta) and cytochrome P450 enzymes (1A1, 2C, 2E1, and 3A5) was similar in CEPI-17-CL4 cells and human corneal epithelial samples obtained in biopsy. The CEPI-17-CL4 cells were metabolically competent for enzymes glutathione S-transferase, quinone reductase, aflatoxin aldehyde reductase, glutathione peroxidase, glutathione reductase, superoxide dismutase, and catalase. CONCLUSIONS: The CEPI-17-CL4 cells are truly immortal and express an extensive array of cytokines, growth factors, and metabolic enzymes that resemble the original tissue. These characteristics, which remain stable up to high passage, will allow reproducible, mechanistic studies on toxicity, inflammation, and wound healing.

Human corneal epithelial cell functional responses to inflammatory agents and their antagonists.

PURPOSE: To investigate the epithelial nature of primary and SV40 virus-immortalized human corneal epithelial (CEPI) cells and to study a variety of functional responses to some key inflammatory agents (bradykinin [BK], histamine, and platelet-activating factor [PAF]) and their antagonists in these cells. METHODS: Primary CEPI (P-CEPI) and clone 4 of the SV40 virus-immortalized (CEPI-17-CL4) cells were analyzed for their interaction with several monoclonal antibodies selective for various cytokeratins to define their immunocytochemical characteristics and phenotypic traits. Both cell types were tested for their ability to respond to BK, histamine, and PAF and their antagonists, using the production of [3H]inositol phosphates ([3H]IPs) as an index of receptor activation. The ability of BK, PAF, and histamine to stimulate cytokine release and the induction of mRNA for matrix metalloproteinase-1 (MMP-1) were also studied using enzyme-linked immunosorbent assay and reverse transcriptase-polymerase chain reaction techniques, respectively. RESULTS: P-CEPI and CEPI-17-CL4 cells were both shown to possess the epithelial cell cytokeratins labeled with AE1 and AE3 antibodies. The potencies (EC50s) of BK, histamine, and PAF were similar for stimulating [3H]IPs production in P-CEPI and CEPI-17-CL4 cells: BK = 2.27 to 2.99 nM, PAF = 17.1 to 18.26 nM, and histamine = 1.65 to 5.74 microM (all n = 3 to 6). Both cell types also responded similarly to receptor-selective antagonists for BK, PAF, and histamine (Hoe-140: Ki = 10.1 to 11.9 nM; PCA-4248: Ki = 315 to 421 nM; triprolidine: Ki = 0.8 to 4.76 nM; all n = 5 to 10). Histamine (100 microM) and interleukin-1alpha (IL-1alpha, 10 ng/ml) significantly stimulated IL-6 and granulocyte macrophage colony-stimulating factor release, and histamine, BK, and PAF stimulated the mRNA for MMP-1 in these cells. CONCLUSIONS: These studies have shown that the primary and immortalized human corneal epithelial cells express functional BK (a B2 subtype), histamine (an H1 subtype), and PAF receptors and exhibit very similar immunocytochemical, signal transduction, and pharmacological properties. Therefore, the CEPI-17-CL4 cells (currently at passage 220) appear to provide a useful representative in vitro model system to study the physiological and pathologic aspects of the human corneal epithelium.

Pharmacological analysis of mast cell mediator and neurotransmitter receptors coupled to adenylate cyclase and phospholipase C on immunocytochemically-defined human conjunctival epithelial cells.

We sought to establish and immunocytochemically characterize primary cultures of human conjunctival epithelial (HCE) cells, and to determine the types of receptors coupled to adenylate cyclase (AC) and phospholipase C (PLC) present on them which may be stimulated following allergic or inflammatory provocation of the tissue. HCE cells possessed the key epithelial cell surface cytokeratins AE1, AE3 and AE5. Signal transduction studies (n > or = 3), using agonists and antagonists, revealed the presence of beta 2-adrenergic (isoproterenol EC50 = 5.2 nM), prostaglandin E2 (EC50 = 168 nM) and vasoactive intestinal peptide (EC50 = 0.69 nM) receptors positively coupled to AC in HCE cells. Bradykinin (EC50 = 0.83 nM), platelet activating factor (EC50 = 4.5 nM), leukotriene C4 (EC50 = 300 nM) and histamine1 (EC50 = 3.1 microM) receptors were coupled to PLC (n = 3 for each). These data suggest that HCE cells in vivo may represent target cells for mast cell mediators and certain neurotransmitters which are released into the tear-film upon allergic provocation of the conjunctiva.

Comparison of SEM processing methods for cultured human lens epithelial cells grown on flat and microcarrier bead substrates.

The increasing importance of in vitro models has presented new challenges in SEM processing techniques. The present study has evaluated the quality of preservation of cultured human lens epithelial cells processed by critical point, Peldri II, and tert-butyl alcohol drying. Specimens processed by critical point drying produced specimens with severe cracking of cell processes and microcracks across cell membrane surfaces. Peldri II and tert-butyl alcohol drying eliminated breakage of the filopodia and lamellipodia as well as eliminating the microcracks across the apical membrane surface. The morphology of lens epithelial cells grown on Cytodex 3 beads appeared rounded with convoluted membrane surfaces. These morphological features were present for cells processed by all three methods. Cytodex 3 beads were subsequently shown to shrink 52% in diameter during dehydration, which results in an 89% reduction in volume for the bead. Cells grown on Biosilon beads, which do not shrink, had a morphology similar to the cells grown on a flat substrate. These results indicate that Peldri II and tert-butyl alcohol drying offer an attractive alternative to critical point drying when preparing cultured cells for SEM. Interpretation of cultured cell morphology must consider shrinkage of the substrate material as a possible contributor to artifact.

Macular corneal dystrophy: immunochemical characterization using monoclonal antibodies.

Macular corneal dystrophy is an inherited corneal disease characterized by corneal opacities resulting from intra- and extracellular deposits within the corneal stroma. Several monoclonal antibodies developed against antigens of corneal fibroblasts were screened for their reactivity with these abnormal deposits in corneas with macular dystrophy using an indirect peroxidase-conjugated immunostaining technique. One of these monoclonal antibodies (designated 8F1-3) reacted very strongly with these abnormal deposits. Although the antigen recognized by this monoclonal antibody was present in the normal corneal stromal and endothelial cells, its concentration in the cells in the corneas with macular dystrophy appeared to be considerably higher, based on the intensity of the immunostaining reaction. Corneal fibroblasts grown in tissue culture were employed for further characterization of the antigen. After fixing with paraformaldehyde and permeabilizing with Triton X-100, immunofluorescent staining of the corneal fibroblasts using these monoclonal antibodies revealed a filamentous pattern of staining which resembled that seen for vimentin filaments. On treatment of corneal fibroblasts with colchicine, the filaments recognized by this antibody were withdrawn from their cytoplasmic array to form a perinuclear cap as also observed for vimentin-containing intermediate filaments. Immunoelectron microscopic studies using colloidal gold-conjugated antimouse IgG indicated that this monoclonal antibody recognized an antigen associated with intermediate-type filament. However, antivimentin antibody did not react with the abnormal deposits in the corneas with macular dystrophy, indicating that the antigen identified in the present study, although associated with intermediate filaments, was not vimentin. Analyses of cytoskeletal antigens by the immunoblotting technique further revealed that this monoclonal antibody recognized two polypeptides with Mr48,000 and 45,000, while antivimentin antibody reacted with 58,000 Mr polypeptide (vimentin).

Murine endodermal cytokeratins Endo A and Endo B are localized in the same intermediate filament.

The intracellular distribution of extra-embryonic endodermal, cytoskeletal proteins A (Endo A) and B (Endo B) was investigated by double-label immunofluorescent microscopy and double-label immunoelectron microscopy. In parietal endodermal cells, the immunofluorescent distribution of Endo B was always coincident with that of Endo A and could be distinguished from vimentin, particularly at the periphery of the cell. At the electron microscopic level, antibodies against both Endo A and Endo B recognized both bundles and individual intermediate filaments. Double-label immunoelectron microscopy was achieved by use of two sizes of colloidal gold particles (5 nm and 20 nm) that were stabilized with secondary antibodies. These results show that Endo A and B are found in the same intermediate filament and probably co-polymerize to form such structures.

Intermediate filament protein synthesis in preimplantation murine embryos.

The synthesis of two extraembryonic endodermal cytoskeletal proteins (Endo B, Mr = 50,000; Endo A, Mr = 55,000) was detected by immunoprecipitation at the 4- to 8-cell stage of preimplantation mouse development. The first detectable synthesis of both proteins occurs at about the same time as the earliest allocation of cells to the trophectodermal lineage. Both Endo A and B were identified in the two-dimensional gel pattern of blastocyst cytoskeletal proteins prepared by nonionic detergent and high-salt extraction. Endo A and B were identified as the y and x blastocyst cytoskeletal proteins, respectively, previously described by other investigators. Antibodies to Endo B are shown to react with intermediate filaments at the electron microscopic level, confirming that Endo B is an authentic intermediate filament protein. Previously, the TROMA 1 monoclonal antibody prepared by other investigators was shown to react specifically with Endo A and to decorate trophoblast cytoskeletons but did not react with the inner cell mass of blastocysts. Endo B antibodies are now also shown to decorate trophoblast cytoskeletons.

Coordinate expression of parietal endodermal functions in hybrids of embryonal carcinoma and endodermal cells.

A derivative, FOT5, of the F9 murine embryonal carcinoma cell line which is resistant to ouabain and thioguanine was fused with a near diploid parietal endodermal cell line, PFHR9, Hybrid clones (ENEC1 to ENEC5) were isolated in HAT Medium containing ouabain at a frequency of approximately 2 x 10(-4). The DNA contents and chromosome number of the ENEC hybrids were approximately the sum of those of the parents. Five hybrid cell lines examined in detail expressed the following parietal endodermal functions: plasminogen activator activity, basement membrane proteins, and endodermal cytoskeletal proteins. Embryonal carcinoma characteristic functions (tumorigenicity, a stage specific embryonic antigen, and high alkaline phosphatase activity) were extinguished in the hybrids. No hybrid clones with embryonal carcinoma morphology were observed among 1,358 hybrid clones examined. Hybrids, propagated for over 100 generations, continued to express endodermal functions and not embryonal carcinoma functions. The coordinate expression of endodermal functions and the extinction of embryonal carcinoma functions in the ENEC hybrids suggest that the parietal endodermal cells contain diffusible activities which extinguish embryonal carcinoma functions and possibly cause the embryonal carcinoma genome to express parietal endodermal characteristics.

Distribution of cell lengths in cultures of a lexA mutant of Escherichia coli K-12.

Distributions of cell lengths in lexA+ and lexA mutant cultures during normal growth and under thymidine starvation conditions are presented. During normal growth lexA mutant cells were slightly shorter, on the average, than were lexA+ cells. lexA mutant cells were also shorter in comparison with lexA+ cells after a period of thymidine starvation. These results are consistent with the hypothesis that the lexA gene is involved in the coordination of cell division with DNA repair.

Analysis of cell division in single clones of the Escherichia coli K-12 lexA mutant.

The growth of clones of lexA mutant and lexA+ cells was analyzed. During normal growth lexA mutant clones frequently divided early, producing smaller newborn cells than the lexA+ clones. Some newborn cells in the lexA clones did not elongate or divide at all, a response that was never observed in the lexA+ clones. When starved for thymidine, most of the lexA mutant clones elongated and subsequently divided. The majority of lexA+ clones also elongated but did not divide. The above results suggest that one of the functions of the lexA+ gene is coordination of DNA repair with cell division.

Production of cells without deoxyribonucleic acid during thymidine starvation of lexA- cultures of Escherichia coli K-12.

When thymidine-requiring lexA- strains were starved for thymidine, the kinetics of survival were similar to those of a nearly isogenic lexA+ strain. The size distribution of cells in the lexA- and lexA+ cultures were, however, quite different. Whereas most of the cells in the starved lexA+ cultures grew into long filamentous forms (longer than 4.0 mum), many of the lexA- cells were found to have a normal rod shape (4.0 mum or shorter). It was shown that lexA- cells undergo more divisions during thymidine starvation than lexA+ cells. Furthermore, using an autoradiographic method to analyze deoxyribonucleic acid (DNA) distribution in the starved cells, we demonstrated that cells without DNA are produced in both normal and starved lexA- cultures at a much higher frequency than in lexA+ cultures. Some of these cells may be produced by breakdown of DNA, but we favor the hypothesis that they result from an abnormal cell division process. Since lexA mutations are dominant, we conclude that a diffusible product decreases the synthesis or activity of an inhibitor of cell division in lexA- strains when DNA synthesis is blocked by thymidine starvation.