Effect of cigarette smoke condensate and vitamin A depletion on keratin expression patterns in cultured hamster tracheal epithelium. An immunohistomorphological study using monoclonal antibodies to keratins

A Review of In Vitro Modelling Approaches to the Identification and Modulation of Squamous Metaplasia in the Human Tracheobronchial Epithelium

Squamous metaplasia in the tracheobronchial epithelium (TBE) involves the replacement of the normal pseudostratified mucociliary epithelium with a stratified squamous epithelium. Squamous metaplasia is considered to be an adaptive response that protects the lumen from the effects of inhaled airborne pollutants, but which might also feature as a pre-neoplastic lesion preceding squamous cell carcinoma. With the exception of transglutaminase I, involucrin, and cytokeratins 5, 6 and 13, few markers that contribute to the squamous phenotype have been identified in human TBE that can be used in diagnosis or to monitor its development in laboratory investigations, and current models are inadequate to provide statistically meaningful data. Therefore, new predictive markers have been identified, and new techniques established, in epithelial in vitro models capable of expressing squamous characteristics, which will be used to identify hazardous exposures and elucidate the mechanisms by which they induce their effects. A protocol for the quantitative detection of transglutaminase activity has been standardised in keratinocytes, based on the enzymatic incorporation of fluorescein–cadaverine (FC) into bis(γ-glutamyl) polyamine cross-links. The specificity of this compound as a transglutaminase substrate was demonstrated by using a range of competitive transglutaminase inhibitors, and by modulation of the squamous pathway. FC incorporation was localised to the cell membrane of terminally differentiating cells, and was not visible in basal, proliferating cells. High calcium-containing medium, nicotine and cigarette smoke condensates (CSC) induced an increase in FC incorporation, providing evidence of their role in enhancing the squamous pathway. Analysis by flow cytometry was used to provide a quantitative assessment of a range of optimised squamous differentiation markers, identified in normal human bronchial epithelia and in a bronchial cell line. Transglutaminase I was induced in a time-dependent manner, in post-confluent cells induced to differentiate down the squamous pathway, whereas involucrin was ubiquitously expressed and the levels of cytokeratins 5, 6 and 18 were reduced. The response of these and other differentiation markers to squamous-inducing conditions is being explored.

The use of an in vitro submerged keratinocyte model to predict induction of squamous metaplasia

An in vitro submerged keratinocyte model of squamous metaplasia (SQ) in epithelia is being developed to assess the risk associated with exposure to certain environmental agents. Tracheobronchial epithelium (TBE) in vivo can respond to airborne environmental insult by becoming squamous. Epidemiological evidence suggests that cigarette smoke is capable of inducing this change. Retinoic acid has been shown to maintain cells in the mucociliary state. SQ is considered protective and adaptive but potentially preneoplastic if unrelenting and is used histologically in the diagnosis of squamous cell carcinoma. SQ is characterised by upregulation of the expression of transglutaminase I (TGI), TGI activity leading to the formation of isopeptide cross-linked envelopes and replacement of the mucociliary cell type with non-polar squamous cells out of contact with the basal lamina. The ability of the in vitro keratinocyte submerged model to predict the squamous metaplastic response in vivo has been investigated in vitro using TG catalysed fluorescein cadaverine incorporation as a measure of cross-linked envelope formation, Alamar blue conversion to measure viability and Coomassie blue incorporation to measure total cellular protein. The modulation of the squamous condition by retinoic acid (RA), cigarette smoke condensate (CSC) and nicotine has been assessed in keratinocytes cultured in Green's medium. RA inhibited FC incorporation by 95% at 1 x 10(-5) M and simultaneously increased cell viability providing evidence to support its role in the regulation of the non-differentiated state. Nicotine (0-1 mg/ml) induced a dose-dependent increase in viability at 6 days, a response that was accompanied by an increase in FC incorporation at 12 days. CSC (0-5 microg/ml) increased FC incorporation after 12 days. Hence, nicotine modulated the squamous condition by up-regulating TGI activity following a period of hyperactivity. CSC induced a gradual change to the differentiated state and RA served to maintain the cells in an undifferentiated state.

Molecular and cellular biomarkers for field cancerization and multistep process in head and neck tumorigenesis

One way to explain the development of head and neck cancer is through the theories of field cancerization, i.e., the exposure of an entire field of tissue to repeated carcinogenic insult, and multistep process, i.e., development of multiple cancers in a predisposed filed through a series of recognizable stages. Recent molecular genetic studies of histologically normal and premalignant epithelia of high-risk subjects and studies of malignant tumors in aerodigestive tract epithelia have identified a continuum of accumulated specific genetic alterations that possibly occur during the clonal evolution of tumors, namely, during the multistep process. Second primary or multiple primary tumors arise in the same fields as independent clones, with similar but unique molecular genetic and/or cellular alterations. Consequently, the assessment of these genetic and phenotypic alterations has been integrated into clinical chemoprevention trials in an effort to identify biomarkers that are also risk predictors and intermediate end points. This review covers candidate biomarkers of the processes of field cancerization and multistep tumor development in aerodigestive tract epithelia, including general and specific genetic markers, proliferation markers, and squamous differentiation markers.

Expression of markers of differentiation in normal bronchial epithelium and bronchial dysplasia

Bronchial epithelial dysplasia is a non-invasive cellular change often associated with physical or chemical injury and considered a pre-neoplastic lesion in the formation of lung cancer. A series of 39 bronchial dysplasias associated with both neoplastic and non-neoplastic lesions were assessed for expression of markers of differentiation by immunocytochemistry and compared with samples of normal bronchial epithelium. The normal bronchial epithelium studied expressed cytokeratins (CKs) 4, 6, 7, 8, 18, and 19 in all cases; CK 13 in 13 cases; and peanut agglutinin (PNA) in seven cases. Involucrin, CK 10, and CK 14 were not observed in the normal bronchial samples. In the dysplastic bronchial biopsies, epithelial staining was observed with epithelial CKs 7, 8, 18, and 19 in all cases; CK 13 was seen in 26 cases; CK 14 in 13 cases; CK 6 in 11 cases; and CK 10 in five cases. In 13 cases of dysplasia, only simple epithelial antigens were identified. Involucrin expression was observed in 17 dysplastic biopsies and PNA in 12. By Fisher's exact test, a significant association between non-severe histological grade of dysplasia and CK 6 expression (P = 0.018) was found. Comparison of the results using the same analysis showed significant correlations between the loss of CK 6 expression (P < 0.001) and the expression of CK 14 (P = 0.008) and involucrin (P = 0.0018) with bronchial dysplasia. These data show that the pattern of differentiation antigen expression in bronchial dysplasia is significantly different from that of the normal bronchial epithelium, but the phenotypic heterogeneity of these lesions is similar to that of bronchial carcinomas.

An approach for treating the hepatobiliary disease of cystic fibrosis by somatic gene transfer

Cystic fibrosis (CF) is an inherited disease of epithelial cell ion transport that is associated with pathology in multiple organ systems, including lung, pancreas, and liver. As treatment of the pulmonary manifestations of CF has improved, management of CF liver disease has become increasingly important in adult patients. This report describes an approach for treating CF liver disease by somatic gene transfer. In situ hybridization and immunocytochemistry analysis of rat liver sections indicated that the endogenous CFTR (cystic fibrosis transmembrane conductance regulator) gene is primarily expressed in the intrahepatic biliary epithelial cells. To specifically target recombinant genes to the biliary epithelium in vivo, recombinant adenoviruses expressing lacZ or human CFTR were infused retrograde into the biliary tract through the common bile duct. Conditions were established for achieving recombinant gene expression in virtually all cells of the intrahepatic bile ducts in vivo. Expression persisted in the smaller bile ducts for the duration of the experiment, which was 21 days. These studies suggest that it may be feasible to prevent CF liver disease by genetically reconstituting CFTR expression in the biliary tract, using an approach that is clinically feasible.

Direct gene transfer of human CFTR into human bronchial epithelia of xenografts with E1-deleted adenoviruses

We describe the use of a human bronchial xenograft model for studying the efficiency and biology of in vivo gene transfer into human bronchial epithelia with recombinant E1 deleted adenoviruses. All cell types in the surface epithelium except basal cells efficiently expressed the adenoviral transduced recombinant genes, lacZ and CFTR, for 3-5 weeks. Stable transgene expression was associated with high level expression of the early adenoviral gene, E2a, in a subset of transgene expressing cells and virtually undetectable expression of the late adenoviral genes encoding the structural proteins, hexon and fiber. These studies begin to address important issues that relate to safety and in vivo efficacy of recombinant adenoviruses for gene delivery into the human airway.

In vivo retroviral gene transfer into human bronchial epithelia of xenografts

Cystic fibrosis (CF) is the most common lethal inherited disease in the Caucasian population with an incidence of approximately 1 in 2,500 live births. Pulmonary complications of CF, which are the most morbid aspects of the disease, are caused by primary abnormalities in epithelial cells that lead to impaired mucociliary clearance. One potential therapeutic strategy is to reconstitute expression of the CF gene in airway epithelia by somatic gene transfer. To this end, we have developed an animal model of the human airway using bronchial xenografts and have tested the efficiency of in vivo retroviral gene transfer. Using the LacZ reporter gene, we find the efficiency of in vivo retroviral gene transfer to be dramatically dependent on the regenerative and mitotic state of the epithelium. Within an undifferentiated regenerating epithelium in which 40% of nuclei labeled with BrdU, 5-10% retroviral gene transfer was obtained. In contrast, no gene transfer was noted in a fully differentiated epithelium in which 1% of nuclei labeled with BrdU. These findings suggest that retroviral mediated gene transfer to the airway in vivo may be feasible if the proper regenerative state can be induced.

Squamous cell metaplasia in the human lung: molecular characteristics of epithelial stratification

Squamous cell metaplasia (SCM) is a frequent epithelial alteration of the human tracheobronchial mucosa. This review pays particular attention to the fact that SCM can mimic esophageal, and in some instances even skin-type differentiation, showing striking similarities not only in morphology but also in terms of gene expression. Therefore, characterization of this dynamic process lends insight into the process of stratification, squamous cell formation, and "keratinization" in a pathologically relevant in vivo situation in man. First, the concept of metaplasia is presented with certain historical viewpoints on histogenesis. Then, the morphological characteristics of normal bronchial epithelium are compared with the altered phenotype of cells in SCM. These changes are described as a disturbance of the finely tuned balance of differentiation and proliferation through the action of a variety of extrinsic and intrinsic factors. Molecular aspects of altered cell/cell and cell/extracellular matrix interactions in stratified compared with single-layered epithelia are discussed with reference to SCM in the lung. Intracellular organizational and compositional changes are then summarized with special emphasis on the differential distribution of the cytokeratin (CK) polypeptides. Finally, the still unresolved problems of the histogenetic relationships between normal bronchial mucosa, SCM, and pulmonary neoplasms are addressed. As these questions remain open, examples for detection of well defined "markers" are provided that may be employed as objective criteria for determining clinically important cellular differentiation features.

Submucosal glands are the predominant site of CFTR expression in the human bronchus

We have used in situ hybridization and immunocytochemistry to characterize the cellular distribution of cystic fibrosis (CF) gene expression in human bronchus. The cystic fibrosis transmembrane conductance regular (CFTR) was primarily localized to cells of submucosal glands in bronchial tissues from non-CF individuals notably in the serous component of the secretory tubules as well as a subpopulation of cells in ducts. Normal distribution of CFTR mRNA was found in CF tissues while expression of CFTR protein was genotype specific, with delta F508 homozygotes demonstrating no detectable protein and compound heterozygotes expressing decreased levels of normally distributed protein. Our data suggest mechanisms whereby defects in CFTR expression could lead to abnormal production of mucus in human lung.

Monoclonal antibody (Mab) markers for subpopulations of rat tracheal epithelial (RTE) cells

We sought monoclonal antibodies (Mabs) that would recognize distinct subsets of rat tracheal epithelial (RTE) cells. Mice were immunized with pronase-dissociated RTE cells and hybridomas whose supernatants immunocytochemically stained subpopulations of tracheal cells were selected. We report the immunohistochemical staining properties of the antibodies and give the results of preliminary biochemical characterization of the antigens. Four different types of antibodies were produced. Antibody RTE 1 stained most RTE cells. Three antibodies (RTE 2, 7, and 13) recognized a subpopulation of nonciliated cells, both columnar and basal cells. Antibody RTE 3 intensely labeled the surface of ciliated cells. Three antibodies reacted with granule components of secretory cells; antibodies RTE 9 and 11 reacted with mucous-type secretory cells and antibody RTE 12 stained all tracheal surface secretory cells. As described in detail, some antibodies were RTE cell specific while others also reacted with cells and secretions in other organs; the antibodies did not cross react with guinea pig or rabbit tissues. Periodate sensitivity of the antigens suggested that some antibodies recognized carbohydrate moieties while others detected peptide epitopes. In some cases, Western blotting revealed the molecular weights of the antigens, but some antigens were denatured by sodium dodecyl sulfate (SDS) and heat treatment. These antibody probes provide a useful means to immunochemically study changes in cell type distribution and/or epitope expression during development, injury, and regeneration.

Changes in cytokeratin expression accompany squamous metaplasia of the human respiratory epithelium

To determine the characteristics of metaplastic changes of the nasal respiratory epithelium, the distribution of individual cytokeratins (CKs) was studied immunohistochemically and by two-dimensional gel electrophoresis. The authors define four types of changes of the normal pseudostratified columnar epithelium: (1) transitional pseudostratified epithelium (first unusual CK.: no. 13); (2) stratified columnar epithelium (increased expression of CKs 4 and 13; CKs 7, 8, 18 and 19 reduced); (3) stratified squamous epithelium, nonkeratinized (appearance of CK 16); and (4) stratified squamous epithelium, keratinized (expression of CKs 1 and 10, variable CK5 and 14 patterns in basal cells). These phenotypes were found simultaneously within single specimens, resulting in apparent overall variability in the immunohistochemical staining patterns. Spatially, changes in CK expression towards "normal" parts were not abrupt but rather gradual. Biochemical data confirmed the immunohistochemical findings and added CK 6 to the pattern of altered nasal mucosa. The findings of this study suggest a stem cell metaplasia in the nasal epithelium which is based on its inherent bimodal developmental programme. A gradual loss of normal respiratory epithelial differentiation, as seen by the loss of CKs 7, 8, and 18, was paralleled by the appearance of squamous epithelial type CKs, e.g. the expression of CKs 1, 10 and 13. Basal cell types CKs 5, 14, 17 and 19 were maintained during this process. Implications of these results for general concepts of CK expression in the metaplastic process are discussed.

Complexity of expression of intermediate filament proteins, including glial filament protein, in endometrial and ovarian adenocarcinomas

The expression patterns of intermediate filament proteins of primary and metastatic endometrial (n = 18) and ovarian (n = 24) adenocarcinomas were analyzed by immunocytochemistry using a panel of specific antibodies and by gel electrophoresis of cytoskeletal preparations, followed by immunoblotting. All cells of all endometrial adenocarcinomas studied contained the "simple epithelial"-type cytokeratins (CKs) 8, 18, and (mostly) 19, with variable numbers of cells also positive for CK 7 and vimentin. In addition, most of these tumors contained individual cells or groups of cells that were positive for the stratification-related CKs 4, 5, 6, 13, 14, and 17. The latter CKs were often associated with squamous cell foci, but were also found in some single (nonsquamous) tumor cells, indicative of early stages of squamous cell differentiation. Ovarian carcinomas of various histologic types and grades contained predominantly CKs 7, 8, 18, and 19. Serous, endometrioid, and anaplastic tumors, but not mucinous and clear cell tumors, also contained minor amounts of stratification-related CKs in variable combinations, mostly including CK 4. In all tumor types except mucinous tumors, vimentin was consistently detected in variable proportions of tumor cells which, however, were rather low in anaplastic carcinomas. Surprisingly, glial filament protein was detected in a minor proportion (< or = 20%) of tumor cells in seven of 14 serous and endometrioid ovarian carcinomas and in three of 18 endometrial carcinomas. These different intermediate filament expression patterns of müllerian duct-type carcinomas, only partly related to the morphologic appearance of the specific type of tumor, might reflect the multipotentiality of differentiation of müllerian duct-derived epithelia. Cytoskeletal features of potential diagnostic value, especially in metastatic carcinomas, are discussed.

Keratin 13 expression is linked to squamous differentiation in rabbit tracheal epithelial cells and down-regulated by retinoic acid

Rabbit tracheal epithelial (RbTE) cells in primary culture undergo at confluence a multistep program of squamous differentiation. This study examines the expression of keratins in RbTE cells in relation to this differentiation process. During the exponential growth phase RbTE cells are undifferentiated and express three major keratins, K5, K14, and K19, and two minor keratins, K6 and K16. Squamous differentiation is accompanied by increased expression of keratins K6, K16, and K19, and in particular of keratin K13, which reacts specifically with the monoclonal antibody AE8. These changes in keratin synthesis coincide with the commitment to terminal differentiation. Retinoic acid, an inhibitor of the expression of the squamous differentiated phenotype, inhibits the increase in the expression of K6, K16, and K13 and reduces the expression of K5 and K14; however, retinoic acid treatment results in increased levels of keratin K19 and K18. Retinoic acid inhibits the expression of K16 and K13 at concentrations as low as 10(-9)-10(-10) M. At least some of these changes in keratins appear to be related to alterations in the cellular levels of the respective mRNAs. Our results indicate that specific changes in keratin expression, in particular keratin K13, correlate with the onset of squamous differentiation in RbTE cells. Induction of the expression of keratin K13 may function as a marker of squamous differentiation in tracheobronchial epithelial cells.

Intermediate filament expression in normal and vitamin A depleted cultured hamster tracheal epithelium as detected by monoclonal antibodies. A study with emphasis on histological changes

Using immunohistochemical techniques, the keratin expression patterns in basal and columnar cells (mucus-producing and ciliated cells) were investigated in tracheal organ cultures. Tracheas were from either hamsters fed a control diet or from hamsters fed a vitamin A-deficient diet; tracheas from the latter group were treated in vitro with all-trans retinol. In tracheas from hamsters fed a control diet, basal cells generally reacted with the RCK102 antibody and columnar cells with the RGE53 and the HCK19 antibodies, and both basal and columnar cells were recognized by the RCK105 antibody. The squamous cell cytokeratin 10 (detected by the RKSE60 antibody) was not expressed in cultured tracheas from hamsters fed a normal or a vitamin A-deficient diet. In the course of the in vitro period a number of keratins were "switched on" or "switched off" in both basal and columnar cells. In tracheas from vitamin A-deprived hamsters the RCK102 antibody clearly recognized basal cells and cigarette smoke condensate-induced proliferating basal cells, whereas the RGE53 antibody reacted with mucus-producing and ciliated cells. During organ culture foci of columnar epithelial cells expressed basal cell properties (detected with the RCK102 antibody) after all-trans retinol treatment and were found negative for the RGE53 antibody. Furthermore, it appeared that the RGE53-negative columnar cells contained periodic acid-Schiff-positive mucous granules. These findings indicate that basal cells may differentiate into columnar cells. Tracheal epithelium did not appear to co-express vimentin next to keratins during organ culture, which may be due to the intact three-dimensional organization present in these organ cultures.