Quantitative analysis of disturbed cell maturation in dysplastic lesions of the respiratory tract epithelium

VILIP-1 expression in vivo results in decreased mouse skin keratinocyte proliferation and tumor development

VILIP-1, a member of the neuronal Ca²⁺ sensor protein family, is able to act as a tumor suppressor in carcinoma cells by inhibiting cell proliferation and migration. In order to study the role of VILIP-1 in skin carcinogenesis we generated transgenic mice overexpressing VILIP-1 in epidermis under the control of the bovine keratin K5 promoter (K5-VILIP-1). We studied the susceptibility of FVB wild type and VILIP-1 transgenic mice to chemically mediated carcinogenesis. After 30 weeks of treatment with a two-stage carcinogenesis protocol, all animals showed numerous skin tumors. Nevertheless, K5-VILIP-1 mice showed decreased squamous cell carcinoma (SCC) multiplicity of ∼49% (p<0.02) with respect to the corresponding SCC multiplicity observed in wild type (WT) mice. In addition, the relative percentage of low-grade cutaneous SCCs grade I (defined by the differentiation pattern according to the Broders grading scale) increased approximately 50% in the K5-VILIP1 mice when compared with SCCs in WT mice. Similar tendency was observed using a complete carcinogenesis protocol for skin carcinogenesis using benzo(a)pyrene (B(a)P). Further studies of tumors and primary epidermal keratinocyte cultures showed that matrix metalloproteinase 9 (MMP-9) levels and cell proliferation decreased in K5-VILIP-1 mice when compared with their wild counterparts. In addition tissue inhibitor of metalloproteinase 1 (TIMP-1) expression was higher in K5-VILIP-1 keratinocytes. These results show that VILIP-1 overexpression decreases the susceptibility to skin carcinogenesis in experimental mouse cancer models, thus supporting its role as a tumor suppressor gene.

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.

The use of tracheal implants in toxicology and carcinogenesis research

Tracheal implants have served as an important experimental pathology tool with which to study the toxic and/or carcinogenic effects of chemicals upon upper respiratory tract epithelium. Initial studies with this method utilized heterotopic rat tracheal transplants which were exposed to compounds of interest, and assessed for toxic and/or carcinogenic endpoints. Grafts containing rodent tissue have proved useful for studying the cellular and biochemical features of neoplastic progression at different time intervals following in vivo exposure to carcinogens. More recent studies have utilized epithelial denuded tracheal implants inoculated with respiratory cell populations, and xenografted into immunodeficient nu/nu mice. This technique permits the study of airway epithelium from a variety of species, including man. The advent of molecular pathology techniques such as in situ hybridization will further expand the uses of tracheal implant technology for studies with xenografted human tissues. Such implants should prove useful for the examination of species- and tissue-specific characteristics of growth and differentiation by providing a bridge between cell culture and whole animal studies.

Pathological changes induced by formaldehyde in open-ended rat tracheal implants preexposed to benzo(a)pyrene

The promotion effects of 0.1% formaldehyde (HCHO) in phosphate-buffered saline (PBS) were tested in rat tracheal implants preexposed to a minimal carcinogenic dose of 468 micrograms benzo(a)pyrene (BAP) released over one month from 865 micrograms BAP-beeswax pellets. At the time of pellet removal, the tracheas were made into open-ended, flow-through, tracheal implants (FTTI), and exposed twice/week to HCHO for 30 weeks. Morphological alterations in the FTTI were monitored biweekly by collection of exfoliated cells from the luminal washings for cytopathologic diagnosis, and periodically by sacrificing animals for histopathology. FTTI exposed to the BAP followed by 30 weeks of HCHO had extensive squamous metaplasia, a high proliferation index of 7.87 [3H]thymidine-labeled cells/mm basement membrane, and foci of moderate and marked atypia. Clear diagnosis of some of the lesions was difficult because of the acute toxic effects of the repeated exposures to HCHO. These effects were seen in the tissues as well as in the exfoliated cells, which attest to the latter as an efficient, non-destructive, method for determining the responses of the tracheas to exposure to toxic and carcinogenic agents. FTTI exposed to BAP followed by twice weekly PBS, had a mostly flattened epithelium, and a low proliferation index (0.39). FTTI exposed to beeswax pellets, followed by the HCHO had a relatively high proliferation index (4.20) in a mucociliary epithelium exhibiting some basal cell hyperplasia. Control FTTI had a normal mucociliary epithelium with a proliferation index of 1.52 [3H]thymidine labeled cells/mm basement membrane.

Tracheal epithelial cell transformation: a model system for studies on neoplastic progression

Most in vitro transformation studies have been conducted with fibroblast cultures of various origins. The phenotypic changes known to accompany transformation are therefore primarily those that are typical for transformed fibroblasts. Little information exists concerning phenotypic changes occurring during transformation of epithelial cells in vitro. However, recently a number of transformation studies have been reported with tracheal epithelium as a prototype for epithelium from the conducting airways. The initial studies were carried out with organ culture-cell culture systems. These studies reported the qualitative phenotypic changes developing in primary outgrowth cultures after exposure to the direct acting carcinogen N-methyl-N'-nitrosoguanidine. The phenotypic changes observed are all related to changes of in vitro growth characteristics. Several stages can be observed as the cell cultures progress from a "carcinogen altered" to the neoplastic state. While these studies laid the groundwork for the epithelial transformation field, they did not permit quantitation of transformants, since the size of the exposed cell population is unknown. More recently transformation systems with dispersed primary tracheal epithelial cells have been developed which allow quantitation of transformed phenotypes. These systems are being used for clonal analysis of the process of epithelial cell transformation and to study progression and promotion during development of neoplastic transformation.

Discrimination of various epithelia by simple morphometric evaluation of the basal cell layer. A light microscopic analysis of pseudostratified, metaplastic and dysplastic nasal epithelium in nickel workers

This study presents a simple morphometric method for objective classification of pseudostratified, various types of metaplastic, and dysplastic epithelium by evaluation of cellular features in the basal layer only. Fifty-four biopsy specimens were taken for diagnostic reasons from the nasal mucosa of nickel workers, and semithin toluidine-blue-stained sections were analysed. The most sensitive parameters in distinguishing between the various types of epithelium were: (i) the transverse nuclear diameter, (ii) the size of the nucleoli and (iii) the basal cell width expressed as an index weighted towards the cell profiles with the broadest attachment face on the basal lamina. A combination of these three parameters allows a clear separation between dysplastic, metaplastic and pseudostratified epithelium. The sequential increase in these parameters from pseudostratified epithelium through two histologically distinguishable stages of metaplasia (stratified cuboidal and mixed stratified cuboidal/stratified squamous epithelium) to fully developed squamous epithelium supports the concept that metaplasia develops gradually. The continuous increase in these parameters from metaplasia to dysplasia further suggests that metaplasia is a necessary step in the development of nasal epithelial dysplasia. This morphometric model appears especially useful in monitoring small sequential epithelial changes, and might also be used for evaluating other types of epithelia.

Dark epithelial cells in preneoplastic lesions of the human respiratory tract

Dark epithelial cells, previously identified in preneoplastic lesions of rat tracheae induced with chemical carcinogens, were observed in similar lesions in human airways and investigated using plastic-embedded material from the lungs of 21 autopsy cases. The lesion types and the percentage of dark cells in their basal layers were as follows: squamous metaplasia without atypia = 13 +/- 3%, squamous metaplasia with slight atypia = 13 +/- 3%, squamous metaplasia with moderate atypia = 26 +/- 5%, squamous metaplasia with severe atypia = 27 +/- 4%, and carcinoma in situ = 34 +/- 11%. Notwithstanding a technical complication caused by differences in fixation and embedding procedures, it was possible to detect an increase in the number of dark cells in human preneoplastic lesions that was directly proportional to the degree of atypia. This increase points to the importance of these cells in neoplastic development and indicates that, regardless of their nature, the number of dark cells can be used as an indicator of the degree of atypia.

Dark cells in human oral leukoplakias

Dark basal keratinocytes, characterized by a strong affinity for basic dyes and by electron density of cytoplasm and nucleus, could be recognized in eleven oral leukoplakias. The percentage of dark cells was higher in the group comprising leukoplakias verrucosa, and erosiva (28% of the basal cells) than in the leukoplakia simplex group (10%). The presence of these cells is a good indicator of the degree of histological dysplasia and correlates well with the preneoplastic potential of these lesions.

Initiator and promoter induced specific changes in epidermal function and biological potential

Mouse epidermal basal cells can be selectively cultivated in medium with a calcium concentration of 0.01--9.09 mM. Terminal differentiation and sloughing of mature keratinocytes occur when the calcium concentration is increased to 1.2--1.4 mM. When basal cell cultures are exposed to chemical initiators of carcinogenesis, colonies of cells that resist calcium-induced differentiation evolve. Likewise, basal cells derived from mouse skin initiated in vivo yield foci that resist terminal differentiation. This defect in the commitment to terminal differentiation appears to be an essential change in initiated cells in skin and is also characteristic of malignant epidermal cells. This model system has also provided a means to determine if basal cells are more responsive to phorbol esters than other cells in epidermis and to explore the possibility that heterogeneity of response exists within subpopulations of basal cells. The induction of the enzyme ornithine decarboxylase (ODC) was used as a marker for responsiveness to phorbol esters. ODC induction after exposure to 12-0-tetradecanoylphorbol-13-acetate (TPA) in basal cells is enhanced 20-fold over the response of a culture population containing both differentiating and basal cells. When basal cells are induced to differentiate by increased calcium, responsiveness to TPA is lost within several hours. In basal cell cultures, two ODC responses can be distinguished. After exposure to low concentrations of TPA or to weak promoters of the phorbol ester series, ODC activity is maximal at 3 hr. With higher concentrations of TPA, the ODC maximum is at 9 hr. These results are consistent with the presence of subpopulations of basal cells with differing sensitivities to TPA. Other studies that use the enzyme epidermal transglutaminase as a marker for differentiation support this conclusion. In basal cell culture TPA exposure rapidly increases transglutaminase activity and cornified envelope development, reflecting induced differentiation in some cells. As differentiated cells are sloughed from the dish, the remaining basal cells proliferate and become resistant to induced differentiation by 1.2 mM calcium. These data provide additional evidence of basal cell heterogeneity in which TPA induces one subpopulation to differentiate while another is stimulated to proliferate and resists a differentiation signal. Tumor promoters, by their ability to produce heterogeneous responses with regard to terminal differentiation and proliferation, would cause redistribution of subpopulations of epidermal cells in skin. Cells that resist signals for terminal differentiation, such as initiated cells, would be expected to increase in number during remodeling, Clonal expansion of the initiated population could result in a benign tumor with an altered program of differentiation. In skin, benign tumors are the principal product of 2-stage carcinogenesis. Subsequent progression to malignancy may involve an additional step, probably a genetic alteration, that is independent of the tumor promoter.