Different patterns of cytokeratin expression in the normal epithelia of the upper respiratory tract

Cell-penetrating peptides for transmucosal delivery of proteins

Enabling non-invasive delivery of proteins across the mucosal barriers promises improved patient compliance and therapeutic efficacies. Cell-penetrating peptides (CPPs) are emerging as a promising and versatile tool to enhance protein and peptide permeation across various mucosal barriers. This review examines the structural and physicochemical attributes of the nasal, buccal, sublingual, and oral mucosa that hamper macromolecular delivery. Recent development of CPPs for overcoming those mucosal barriers for protein delivery is summarized and analyzed. Perspectives regarding current challenges and future research directions towards improving non-invasive transmucosal delivery of macromolecules for ultimate clinical translation are discussed.

Expanded Basal Compartment and Disrupted Barrier in Vocal Fold Epithelium Infected with Mouse Papillomavirus MmuPV1

Laryngeal infection with low-risk human papillomaviruses can cause recurrent respiratory papillomatosis (RRP), a disease with severe effects on vocal fold epithelium resulting in impaired voice function and communication. RRP research has been stymied by limited preclinical models. We recently reported a murine model of laryngeal MmuPV1 infection and disease in immunodeficient mice. In the current study, we compare quantitative and qualitative measures of epithelial proliferation, apoptosis, differentiation, and barrier between mice with MmuPV1-induced disease of the larynx and surrounding tissues and equal numbers of uninfected controls. Findings supported our hypothesis that laryngeal MmuPV1 infection recapitulates many features of RRP. Like RRP, MmuPV1 increased proliferation in infected vocal fold epithelium, expanded the basal compartment of cells, decreased differentiated cells, and altered cell–cell junctions and basement membrane. Effects of MmuPV1 on apoptosis were equivocal, as with RRP. Barrier markers resembled human neoplastic disease in severe MmuPV1-induced disease. We conclude that MmuPV1 infection of the mouse larynx provides a useful, if imperfect, preclinical model for RRP that will facilitate further study and treatment development for this intractable and devastating disease.

A Novel In Vivo Model of Laryngeal Papillomavirus-Associated Disease Using Mus musculus Papillomavirus

Recurrent respiratory papillomatosis (RRP), caused by laryngeal infection with low-risk human papillomaviruses, has devastating effects on vocal communication and quality of life. Factors in RRP onset, other than viral presence in the airway, are poorly understood. RRP research has been stalled by limited preclinical models. The only known papillomavirus able to infect laboratory mice, Mus musculus papillomavirus (MmuPV1), induces disease in a variety of tissues. We hypothesized that MmuPV1 could infect the larynx as a foundation for a preclinical model of RRP. We further hypothesized that epithelial injury would enhance the ability of MmuPV1 to cause laryngeal disease, because injury is a potential factor in RRP and promotes MmuPV1 infection in other tissues. In this report, we infected larynges of NOD scid gamma mice with MmuPV1 with and without vocal fold abrasion and measured infection and disease pathogenesis over 12 weeks. Laryngeal disease incidence and severity increased earlier in mice that underwent injury in addition to infection. However, laryngeal disease emerged in all infected mice by week 12, with or without injury. Secondary laryngeal infections and disease arose in nude mice after MmuPV1 skin infections, confirming that experimentally induced injury is dispensable for laryngeal MmuPV1 infection and disease in immunocompromised mice. Unlike RRP, lesions were relatively flat dysplasias and they could progress to cancer. Similar to RRP, MmuPV1 transcript was detected in all laryngeal disease and in clinically normal larynges. MmuPV1 capsid protein was largely absent from the larynx, but productive infection arose in a case of squamous metaplasia at the level of the cricoid cartilage. Similar to RRP, disease spread beyond the larynx to the trachea and bronchi. This first report of laryngeal MmuPV1 infection provides a foundation for a preclinical model of RRP.

The pharyngeal mucosa is not involved in eosinophilic oesophagitis

BACKGROUND

Eosinophilic oesophagitis is thought to be an isolated oesophageal disease associated with biopsy-verified eosinophilia of the squamous cell epithelium of the oesophagus. Food- or aeroallergens have been suggested to be the cause of eosinophilic oesophagitis; however, as these allergens pass through the pharynx sharing the same squamous cell epithelium, eosinophilic infiltration could be expected also here. Whether this is true or not has hitherto not been clarified.

AIM

To find out whether eosinophilia is present also within the pharyngeal epithelium in patients with eosinophilic oesophagitis.

METHODS

In all, 10 patients (median age 34, range 15-70) with biopsy-verified eosinophilic oesophagitis [peak count >20 eosinophils per high power field (hpf)] were biopsied also in the pharynx. The biopsies underwent histopathological examination and at each level, the peak number of eosinophils per hpf was counted.

RESULTS

None of the patients examined was found to have eosinophilia within the squamous cell epithelium of the pharynx (median peak count 0, range 0-1).

CONCLUSIONS

The pronounced eosinophilic infiltration in eosinophilic oesophagitis appears to be an isolated oesophageal phenomenon not shared by the adjoining organ sites and in particular, not by the pharynx. This may have implications for future research.

Cytokeratin fragments in the serum: their utility for the management of oral cancer

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy and is a major cause of cancer morbidity and mortality worldwide. Oral cancer is the most predominant malignancy in the Indian subcontinent due to the widespread habits of chewing tobacco and related products. Patients with oral tumours have a high risk of early locoregional relapse. Early detection of disease progression remains a challenging task mainly due to the lack of adequate early prognostic markers. CEA, SCC Ag, CA-125, serum cytokeratin (CK) fragments, Cyfra 21-1 (CK 19), TPS (CK 18), TPA (CK 8, 18, and 19) etc. are being used as serum markers for the prediction of prognosis of various malignancies. This review presents the available literature on serum CK markers in different malignancies evaluates their utility in the management of oral cancer, and identifies the lacunae which need to be addressed to develop sensitive and specific assays for early detection of recurrence, prognosis, and treatment monitoring.

Lutheran blood group antigen as a receptor for alpha5 laminins in gingival epithelia

BACKGROUND

Lutheran blood group glycoprotein (Lu) is a transmembrane receptor of the immunoglobulin superfamily. Lu serves as a receptor for alpha5 laminins (Lm). The Lm alpha5 chain is a constituent of Lms-511 and -521. Lm-511 is found in most human basement membranes (BMs) and also is detected in BM of gingival epithelia. Recent studies indicated that Lu mediates cell adhesion to Lms-511/521 independently or in concert with integrins. This study focused on the expression of Lu in gingival epithelia and on cultured immortalized gingival keratinocytes. The role of Lu and alpha(3) and beta(1) integrin subunits in the adhesion of oral epithelial cells to Lms-511/521 was also studied.

METHODS

Immunofluorescence microscopy was used to study the expression of Lu in gingival tissues and in cultured gingival keratinocytes. Immunoprecipitation of radioactively metabolically labeled cells was used to detect Lu. Cell adhesion to Lm-511/521 preparation and to pure Lm-511 was studied in quantitative cell adhesion experiments. Morphological adhesion assays were carried out for visualization of the morphology and adhesion structure formation of the adhering cells.

RESULTS

Immunofluorescence studies on gingiva showed complete coalignment of Lu on basal epithelial cells with the BM Lm alpha5 chain. A surface-confined, punctate immunoreaction for Lu was detected throughout cell surfaces on cultured gingival cells. Immunoprecipitation showed a broad polypeptide with molecular weight 85,000. In quantitative cell adhesion assays, the adhesion of cells to both Lm alpha5 preparations was diminished with monoclonal antibodies (MAbs) against integrin alpha(3) and even more effectively with MAbs against the beta(1) subunit. When the adhesion sites were blocked with soluble recombinant Lu (sol-Lu), the adhesion of gingival epithelial cells to Lms-511/521 was reduced significantly, and sol-Lu increased the inhibition with integrin alpha(3) antibody. Lm-511 did not induce lamellipodia or focal contacts in cultured gingival keratinocytes.

CONCLUSIONS

Lu was in coalignment with Lm alpha5 chain in gingival epithelia. Lu also seemed to have a role in gingival epithelial cell adhesion together with integrin alpha(3)beta(1).

Burkholderia cenocepacia ET12 strain activates TNFR1 signalling in cystic fibrosis airway epithelial cells

Burkholderia cenocepacia is an important pulmonary pathogen in individuals with cystic fibrosis (CF). Infection is often associated with severe pulmonary inflammation, and some patients develop a fatal necrotizing pneumonia and sepsis ('cepacia syndrome'). The mechanisms by which this species causes severe pulmonary inflammation are poorly understood. Here, we demonstrate that B. cenocepacia BC7, a potentially virulent representative of the epidemic ET12 lineage, binds to tumour necrosis factor receptor 1 (TNFR1) and activates TNFR1-related signalling pathway similar to TNF-alpha, a natural ligand for TNFR1. This interaction participates in stimulating a robust IL-8 production from CF airway epithelial cells. In contrast, BC45, a less virulent ET12 representative, and ATCC 25416, an environmental B. cepacia strain, do not bind to TNFR1 and stimulate only minimal IL-8 production from CF cells. Further, TNFR1 expression is increased in CF airway epithelial cells compared with non-CF cells. We also show that B. cenocepacia ET12 strain colocaizes with TNFR1 in vitro and in the lungs of CF patients who died due to infection with B. cenocepacia, ET12 strain. Together, these results suggest that interaction of B. cenocepacia, ET12 strain with TNFR1 may contribute to robust inflammatory responses elicited by this organism.

Cytokeratin expression in palatal and marginal mucosa of cleft palate patients

OBJECTIVE

The margin of a palatal cleft is a unique anatomical site since the palatal mucosa is continuous with the nasal or nasopharyngeal mucosa. The aim of this study was to compare the expression patterns of cytokeratins and basal membrane components of the mucosa in the area of the cleft.

DESIGN

Biopsies from the mucosa of the hard palate and from the cleft margin in the soft palate were obtained from five patients during the primary surgical closure of the cleft. The tissues were processed for haematoxylin-eosin staining and for immunohistochemistry. Antibodies against the cytokeratins (CK) 4, 7, 8, 10, 13, 16 and 18, and the basal membrane components heparan sulphate (HS) and collagen type IV (CIV) were used for immunostaining.

RESULTS

The nasopharyngeal epithelium was thinner than the epithelium of the soft palatal mucosa, and showed less interpapillary ridges. The nasopharyngeal epithelium was stratified but expressed the keratins of a simple epithelium (CK 7, 8 and 18). The expression pattern abruptly changed into that of a typical non-keratinized stratified epithelium (CK 4, 13) at the transition to the soft palatal epithelium. The epithelium of the hard palate was a fully differentiated, keratinized and stratified epithelium (CK 10, 16). The basal membrane was thinner in the nasopharyngeal epithelium, which might be related to the presence of abundant inflammatory cells.

CONCLUSION

The area around the palatal cleft showed three different types of epithelium. There was an abrupt transition in phenotype of the epithelium from the oral side to the nasopharyngeal side.

Laminin-5-mediated gene expression in human prostate carcinoma cells

Interactions between extracellular matrix (ECM) proteins and prostate carcinoma cells provide a dynamic model of prostate tumor progression. Previous work in our laboratory showed that laminin-5, an important member of a family of ECM glycoproteins expressed in the basal lamina, is lost in prostate carcinoma. Moreover, we showed that the receptor for laminin-5, the alpha6beta4 integrin, is altered in prostate tumors. However, the genes that laminin-5 potentially regulates and the significance of its loss of expression in prostate cancer are not known. We selected cDNA microarray as a comprehensive and systematic method for surveying and examining gene expression induced by laminin-5. To establish a definitive role for laminin-5 in prostate tumor progression and understand the significance of its loss of expression, we used a cDNA microarray containing 5289 human genes to detect perturbations of gene expression when DU145 prostate carcinoma cells interacted with purified laminin-5 after 0.5, 6, and 24 h. Triplicate experiments showed modulations of four, 61, and 14 genes at 0.5, 6, and 24 h, respectively. Genes associated with signal transduction, cell adhesion, the cell cycle, and cell structure were identified and validated by northern blot analysis. Protein expression was further assessed by immunohistochemistry. Mol. Carcinog. 30:119-129, 2001.

Cable-piliated Burkholderia cepacia binds to cytokeratin 13 of epithelial cells

Although the Burkholderia cepacia complex consists of several genomovars, one highly transmissible strain of B. cepacia has been isolated from the sputa of cystic fibrosis (CF) patients throughout the United Kingdom and Canada. This strain expresses surface cable (Cbl) pili and is thought to be the major strain associated with the fatal "cepacia syndrome." In the present report we characterize the specific 55-kDa buccal epithelial cell (BEC) protein that binds cable pilus-positive B. cepacia. N-terminal sequences of CNBr-generated internal peptides identified the protein as cytokeratin 13 (CK13). Western blots of BEC extracts probed with a specific monoclonal antibody to CK13 confirmed the identification. Mixed epidermal cytokeratins (which contain CK13), cytokeratin extract from BEC (which consists essentially of CK13 and CK4), and a polyclonal antibody to mixed cytokeratins inhibited B. cepacia binding to CK13 blots and to normal human bronchial epithelial (NHBE) cells. Preabsorption of the antikeratin antibody with the BEC cytokeratin fraction reversed the inhibitory effect of the antibody. A cytokeratin mixture lacking CK13 was ineffective as an inhibitor of binding. Colocalization of CK13 and B. cepacia by confocal microscopy demonstrated that intact nonpermeabilized NHBE cells express small amounts of surface CK13 and bind Cbl-positive B. cepacia in the same location. Binding to intact NHBE cells was dependent on bacterial concentration and was saturable, whereas a Cbl-negative isolate exhibited negligible binding. These findings raise the possibility that surface-accessible CK13 in respiratory epithelia may be a biologically relevant target for the binding of cable piliated B. cepacia.

Differential expression of cytokeratin after orthotopic implantation of newly established human tongue cancer cell lines of defined metastatic ability

Two human tongue squamous cell carcinoma cell lines, SQUU-A and SQUU-B, were established from the same patient. Cervical lymph node metastasis was detected in the mice orthotopically implanted with SQUU-B (86.7%, 13/15), but not in those with SQUU-A (0/13). Histologically, SQUU-B showed invasive growth and intravasation in the tongue, whereas SQUU-A simply demonstrated expansive growth without intravasation. By Western blot analysis, nonmetastatic clone SQUU-A expressed cytokeratin (CK)13/4, 14, 16/6, 18/8, and 19, whereas a high metastatic clone SQUU-B expressed CK18/8 and 19. The reverse transcription-polymerase chain reaction technique showed that CK13/4 mRNA was expressed in both cell lines, but CK14 and 16 mRNA was expressed only in SQUU-A. CK13 was immunohistochemically expressed in both SQUU-A and SQUU-B transplanted into the tongues of nude mice; CK14 and 16 were detected in SQUU-A of the tongues, but not in SQUU-B. As seen in SQUU-B cell line, SQUU-B of the cervical lymph node metastasis did not exhibit CK13, 14, or 16. These results suggest that the loss or down-regulation of CK13, 14, or 16 is related to the invasive and metastatic ability of cancer. The cytoskeletal system is thus considered to be closely related to the malignant phenotype.

Three-dimensional xenograft model of dysplastic human laryngeal mucosa

OBJECTIVE

Development of new therapeutic interventions in head and neck squamous cell carcinoma (HNSCC) will be facilitated by a model system that incorporates the ease of manipulation found in current tissue culture systems while retaining the three dimensional architecture that defines these malignancies.

STUDY DESIGN

Original scientific investigation.

METHODS

We describe a modification of a normal respiratory mucosa model system which recreates premalignant mucosal histology. Grossly normal appearing human mucosa is harvested from laryngectomy specimens, the mucosal epithelium selectively removed by protease treatment and placed in conventional tissue culture. After 7 days, the cells are seeded into denuded rat tracheas, which are in turn implanted in flank pockets of athymic nu/nu mice. The tracheas are incubated for three weeks, removed and the mucosa examined histologically.

RESULTS

As originally described, normal pseudostratified squamous epithelium can be re-established in this system. Using human dysplastic mucosa as a starting material, mucosal histologies of respiratory dysplasia, squamous metaplasia, squamous dysplasia and squamous carcinoma in situ can be established.

CONCLUSION

This system will provide a paradigm for future therapeutic interventions to modify the progression of squamous metaplasia to dysplasia, carcinoma in situ and invasive squamous cell carcinoma.

Effect of snuff on cytokeratin expression in oral vestibular sulcus epithelium

Differences in the expression of cytokeratins (CK) in specimens obtained from snuff-affected oral epithelium of the maxillary vestibular sulcus and clinically normal sulcular epithelium were studied by indirect immunofluorescence staining with a panel of monoclonal antibodies (MAbs). CK 14, a marker of stratified squamous epithelium was not seen expressed in 3/11 of the snuff user's specimens. Terminal differentiation markers, typical of cornified epithelia (CK 1, 9, 10 and 11), were detected suprabasally in the snuff user's keratosis but not in the normal control epithelium. The use of snuff seemed to change the CK staining pattern of the mucosa so that it resembles more that of a cornified type of epithelium. Simple epithelial-type CK were included in the study in order to establish the CK profile of the snuff-induced keratosis, for comparison with normal and dysplastic lesions. MAb to CK 7 and 19 showed reactivity in the basal cells and suprabasally whereas the monospecific MAb anti-CK 7 showed suprabasal staining both in the control and affected epithelia. By using MAbs, we found no immunoreactivity against CK 18 either in normal or affected epithelia, whereas we found suprabasal reaction (5/11) against CK 8 in the snuff user's epithelia. The two MAbs demonstrating the expression of CK 19, normally confined to the basal cells of the stratified squamous epithelium, showed variable patterns of expression both in basal cells and suprabasally in the snuff lesions. The results show that use of oral snuff causes some alterations in the CK expression pattern of the affected epithelium. Whether the alterations are indicative of a premalignant change is, however, uncertain. The results encourage further studies on the subject.

The interpretation of leukoplakia in laryngeal pathology

Leukoplakia is only a descriptive clinical term designating a white patch or plaque of the mucosa and must be complemented by histology. On the other hand, keratosis is an exclusively histological term denoting pathological production and accumulation of keratin on the surface of the laryngeal epithelium. Leukoplakia is usually keratosis, but not always. Keratosis can mask various epithelial changes, from simple hyperplasia to invasive squamous carcinoma and is only the superficially visible manifestation of an underlying pathological process. Keratosis means total replacement of superficial epithelial cells by keratin filaments, and dissolution of the nuclei. When nuclei are retained in keratinized cells, the process is termed parakeratosis. Therefore, keratosis can be classified as a separate entity only when histopathological examination reveals superficial keratotic changes accompanying a normal squamous epithelium. To identify the presence of keratosis in various benign laryngeal entities divided according to severity of epithelial abnormalities, and to determine whether keratosis has any prognostic value, we performed a retrospective analysis on bioptic material on 4,291 tissue specimens over a period of 15 years. Our results suggest that keratosis must be considered as only one sign of the disorder within the complex of other pathological changes and not as a distinct pathological entity. For this very reason, keratinization of the epithelial surface was not included among significant parameters used for the grading of epithelial changes into the particular group according to Kambic-Lenart classification.

Cytokeratin profile suggests metaplastic epithelial transformation in Barrett's oesophagus

Cytokeratins are subunit proteins of epithelial cell intermediate filaments, which are genetically determined. Because epithelia have their own characteristic cytokeratin profile, this may reveal the origin of the epithelium. The cytokeratin profile of Barrett's oesophagus, complicating severe gastro-oesophageal reflux disease, was determined in 35 consecutive patients and in 10 normal controls in order to provide insight into the origin of Barrett's epithelium. Immunostaining of frozen sections showed abundant immunoactivity for cytokeratin (CK) 13, which is characteristic of squamous epithelia, including that of the oesophagus, but is not present in the simple columnar epithelium of the cardia. On the other hand, the latter epithelium expresses mainly CK 8, 18 and 19, also found in Barrett's epithelium. The presence of CK 13 in Barrett's epithelium may indicate its origin from the squamous oesophageal epithelium and not from the proximal migration of columnar epithelial cells of the gastric cardia.

Epitope mapping of monoclonal antibodies to keratin 19 using keratin fragments, synthetic peptides and phage peptide libraries

To generate tools for monitoring processing and folding in keratin intermediate filaments, a group of monoclonal antibodies reacting with the intermediate filament protein keratin 19 were studied using different approaches to define the structure and localization of their epitopes. The binding pattern to bacterially expressed human keratin 19 fragments allowed the definition of minimal amino acid sequences required for antibody binding. The screening of overlapping 15-residue peptides confirmed and further specified the epitope locations for a subset of the tested antibodies. In addition, the epitope of an antibody with apparent species-restricted specificity (LE64) was revealed by isolating and characterizing a full-length keratin 19 clone from a PtK2 cDNA library. Taken together with species cross-reactivity of individual antibodies and sequence information obtained by probing a phage display library, specific amino acid residues could be highlighted as likely to be involved in the antibody binding.

Lack of effect of hormonal treatment and smoking on cytokeratin expression in buccal mucosa

Differences in cytokeratin expression of clinically normal buccal mucosa were studied in 50 healthy women by indirect immunofluorescence staining with monoclonal antibodies. The subjects were divided into four groups: control group (N = 18), smokers (N = 8), oral contraceptive users (N = 8) and smokers receiving oral contraceptives (N = 16). Our findings indicate that cytokeratin expression in noncornified stratified epithelium is not influenced by smoking or oestradiol/progesterone treatment. Only cytokeratin No. 19 showed variable patterns of expression but the differences could not be ascribed to smoking or contraceptives. Cytokeratin No. 19 gave a positive reaction in the basal and suprabasal layers in 34 subjects (68%). In 9 (18%) specimens, the staining was positive in the basal cells and showed a positive heterogeneous cytoplasmic reaction in the suprabasal cells. Interestingly, cytokeratin No. 7 was recognized in all epithelial cells except the basal cells. Our results suggest that changes in the serum oestradiol levels do not affect the cytokeratin pattern in buccal mucosa.

Retinoic acid provokes metaplasia of epithelium formed in vitro by adult human epidermal keratinocytes

A striking effect of retinoids is their ability to alter cell fate during development. The mucous metaplasia produced by treating chick embryo skin in organ culture with retinoic acid is a classical example of this property. It has been impossible so far to demonstrate that retinoids are able to provoke metaplasia of adult keratinocytes grown in vitro, although these agents have been shown to block terminal epidermal differentiation, to induce increased synthesis of mucopolysaccharides, and to induce the ectopic expression of K19 and K13 keratins. Our previous work showed that adult human epidermal keratinocytes grown on dermal equivalents at the surface of a culture medium containing physiological amounts of retinoids form a normal keratinized epidermis, while when excess retinoic acid is added to the culture medium, keratinization is prevented but stratification is not. Here we show that the distribution of tissue- and differentiation-stage-specific markers in retinoic acid-treated epithelium is similar to that of the oral mucosa. Moreover, when the excess retinoic acid is removed, a new epithelium is formed beneath the "old" one and this epithelium displays an epidermal orthokeratinized phenotype, whereas the "old" epithelium remains unchanged. This phenomenon of "partial reversibility", as well as the mutually exclusive distribution of the markers of the two alternative routes of differentiation, demonstrate that retinoic acid is indeed able to provoke metaplasia of adult epidermal keratinocytes.

CYFRA 21-1 as a tumor marker used in measuring the serum fragment of cytokeratin subunit 19 by immunoradiometric assay

Serum levels of cytokeratin subunit 19 (CYFRA 21-1) were measured in 42 healthy volunteers, 104 cases of malignant diseases, 30 patients with chronic renal failure and 13 patients with nonmalignant and infectious diseases. The reliability of the method was demonstrated after dilution of serum samples and intra- and inter-assay reproducibility. Serum CYFRA-21-1 concentrations were less than 2.00 ng/ml in all healthy controls and 86% of the malignant cases had high serum CYFRA 21-1 levels. However slightly elevated values of CYFRA 21-1 were observed in most chronic renal failure patients. High correlation was observed between serum CYFRA 21-1 and Tissue Polypeptide Antigen (TPA) values (r = 0.90, n = 10) but not with serum alpha-feto protein (AFP) concentrations. Furthermore, cross binding tests with the CYFRA 21-1 tracer/CYFRA 21-1 antibody-coated beads and CYFRA 21-1 tracer/TPA antibody-coated beads also gave an almost linear graph. These results indicate that CYFRA 21-1 and TPA share similar type of antigens.

Biology and chemoprevention of head and neck cancer

Head and neck cancer remains a common cause of mortality and morbidity in the United States and throughout the world. In spite of advances in the management of patients with advanced disease, overall survival in this group remains poor. Furthermore, although cancer mortality is lower in patients with early-stage disease, treatment results in significant morbidity, and these patients also face the risk of developing a second primary tumor. Chemoprevention is an innovative approach to decrease overall cancer morbidity and mortality using substances that are capable of preventing cancer progression. Head and neck cancer is an excellent model for chemoprevention, as its biology is consistent with the two concepts important for the development of chemoprevention strategies: field cancerization and multistep carcinogenesis. Several classes of compounds have been evaluated in chemoprevention trials. The most frequently studied agents, the retinoids, were found frequently to induce remissions in patients with oral leukoplakia. Furthermore, retinoids prevented progression to malignancy in one randomized maintenance study. Other agents, including beta-carotene and vitamin E, have been found also to have activity in the management of oral leukoplakia. However, the clinical role of chemopreventive agents in reducing cancer mortality remains to be defined. Two studies, one in head and neck cancer and one in lung cancer, have shown the ability of retinoids to prevent the development of second primary tumors. Current large randomized trials are defining the effectiveness of these agents in reducing the mortality of aerodigestive tract tumors in individuals at high risk.

Cytokeratin expression in normal and (pre)malignant head and neck epithelia: an overview

Intermediate filament proteins (IFPs) are important markers of tissue differentiation and have been receiving increasing interest, in particular, through their applicability in the characterization of malignant tumors. Cytokeratins (Cks) are a family of IFPs that are typically specific for epithelial cells. They are expressed in certain combinations depending on the type of epithelium and the degree of differentiation. This review presents a critical analysis of the available data on Ck expression in normal and (pre) neoplastic epithelia of the head and neck region. Special attention is paid to technical and cell biologic pitfalls, which can lead to false-negative or false-positive data. It appears that only a limited fraction of the reported data contributes substantially to our knowledge of IFP expression in head and neck cancer because of the use of ill-defined, often formalin-fixed and paraffin-embedded, tissue specimens, and the application of limited panels of monoclonal antibodies. It is concluded that the use of immunocytohistochemistry is promising for the differential diagnosis of head and neck tumors and contributes to our knowledge on their biologic behavior. However, documentations of more complete Ck expression patterns of normal and (pre)malignant epithelium are required, together with their correlation to clinical parameters.

A panel of biomarkers of carcinogenesis of the upper aerodigestive tract as potential intermediate endpoints in chemoprevention trials

BACKGROUND

Patients with squamous cell carcinoma of the head and neck have a 10-30% risk of developing a second primary tumor. The concept of "field cancerization" assumes that the whole upper aerodigestive tract is affected and prone to malignant transformation. This study was undertaken to investigate the value of a panel of monoclonal antibodies to identify biomarkers in oral mucosa associated with cancer risk. Such biomarkers may be suitable candidates to serve as intermediate endpoints in cancer chemoprevention trials.

METHODS

As a model, the expression of antigens was assessed in cytologic preparations obtained from macroscopically normal oral mucosa of patients with tongue carcinoma and of controls. The panel consisted of antibodies against cytokeratin 8, 10, 13, and 19 and the monoclonal antibodies designated K931, K984, E48, Ki-67, and UM-A9.

RESULTS

Oral mucosa of cancer patients had a more than threefold increased expression of cytokeratin 19 as compared with controls (36.0 versus 11.3%; P < 0.01).

CONCLUSION

Cytokeratin 19 is a potential intermediate endpoint in head and neck cancer chemopreventive trials.

Expression of the histone H3 gene in benign, semi-malignant and malignant lesions of the head and neck: a reliable proliferation marker

To search for a reliable proliferation marker in epithelial head and neck lesions, we have analysed the expression of the histone H3 gene by in situ hybridisation and compared this with the immunoreactivity of the widely used monoclonal antibody Ki-67. In many lesions, the Ki-67 staining failed to delineate proliferation. In contrast, the H3 hybridisation signals were in accordance with the histopathology of the biopsies: in hyperplastic epithelia, significant H3 mRNA levels were only seen in areas with inflammation. Dysplastic cells showed distinctly elevated H3 expression. Benign and semi-malignant tumours, i.e. basal cell carcinomas, showed moderate H3 signals at the periphery. In squamous cell carcinomas, H3 expression was always high at the expanding zone of the tumour and was most extensive in undifferentiated carcinomas. Thus, the expression of the histone H3 gene closely reflected the dynamics of neoplastic growth within and around head and neck tumours.

Squamous cell differentiation markers in normal, premalignant, and malignant epithelium: effects of retinoids

Vitamin A and some of its analogs (retinoids) maintain normal differentiation of epithelial tissues by preventing aberrant squamous differentiation of cells in nonkeratinizing epithelia. They can also reverse squamous metaplasia, which develops in vivo during vitamin A deficiency. These effects are the result of the ability of retinoids to suppress the expression of genes associated with squamous differentiation (e.g., transglutaminase type I, loricrin, involucrin, filaggrin, and keratin K1). In addition, retinoids reverse keratinizing premalignant lesions in the oral cavity, and inhibit the growth and squamous differentiation of head and neck squamous cell carcinomas (HNSCCs) in vitro. Nuclear retinoic acid receptors, which function as DNA-binding, trans-acting, transcription-modulating factors, are considered to be the proximate mediators of the effects of retinoids on gene expression and may mediate the re-regulation of aberrant differentiation and growth of premalignant and some malignant cells, thereby suppressing the development of head and neck cancer.

Laryngeal hyperplastic lesions, follow-up study and application of lectins and anticytokeratins for their evaluation

A retrospective study of 878 biopsy specimens from 692 patients with laryngeal hyperplastic aberrations was performed according to the Kambic-Lenart classification. Special attention was focused on 88 patients with persistent or recurring disease. In these carcinoma developed in 17 (2.4%) patients, 12 (1.7%) of whom had had atypical hyperplasia. We therefore propose that the term precancerosis, which so definitely implies cancer, should be replaced with the expression risky epithelium where nothing is determined in advance, but a careful follow-up of the patients is imperative. In particular cases of laryngeal hyperplastic lesions, mainly in abnormal and in atypical hyperplasias when the tissue specimens are cut tangentially, the exact identification and position of individual epithelial cells is essential. In such cases histochemical and immunohistochemical methods yield more precise evaluation. Lectins and cytokeratins provide good markers of epithelial maturation. These results contribute to a more useful evaluation of laryngeal hyperplastic lesions, crucial for the choice of adequate therapy.

Suprabasal marker proteins distinguishing keratinizing squamous epithelia: cytokeratin 2 polypeptides of oral masticatory epithelium and epidermis are different

Terminal differentiation of squamous epithelia is usually characterized by the synthesis of a subset of cytokeratins (CKs) in suprabasal cell layers which become major components of the intermediate filament (IF) bundle cytoskeleton of the maturing cells. We have examined the significance, molecular nature and pattern of synthesis of the elusive human CK 2 by analyzing mRNAs from certain stratified epithelia, using in vitro translation, cDNA cloning. Northern blotting and in situ hybridization. We show that genuine polypeptides with the typical gel electrophoretic mobility of CK 2 exist but that the CK 2 present in the masticatory epithelia of hard palate and gingiva (CK 2p) differs from that found in epidermis (CK 2e) by its amino acid sequence and is encoded by a different gene. The two CKs 2 show only limited sequence homology (71% identical amino acid positions in the rod domain), and the oral CK 2p is more closely related to the corneal CK 3 (86%), as is also indicated by the cross-reaction of monoclonal antibody AE5. By in situ hybridization and immunocytochemistry, we further show that both CK 2e and CK 2p are expressed only in suprabasal cell layers of the specific epithelia where they can accumulate to represent major cytoskeletal proteins. We discuss this tissue-type specificity of CK 2 synthesis in otherwise morphologically and biochemically similar epithelia in relation to differences of IF appearance and packing in upper strata between epidermal and masticatory epithelia as well as to tissue formation and differentiation during development.

Nuclear proteins involved in transcription of the human K5 keratin gene

Keratin K5 is expressed in the basal layer of stratified epithelia in mammals and its synthesis is regulated by hormones and vitamins such as retinoic acid. The molecular mechanisms that regulate K5 expression are not known. To initiate analysis of the protein factors that interact with the human K5 keratin gene upstream region, we have used gel-retardation and DNA-mediated cell-transfection assays. We found five DNA sites that specifically bind nuclear proteins. DNA-protein interactions at two of the sites apparently increase transcription levels, at one decrease it. The importance of the remaining two sites is, at present, unclear. In addition, the location of the retinoic acid and thyroid hormone nuclear receptor action site has been determined, and we suggest that it involves a cluster of five sites similar to the consensus recognition elements. The complex constellation of protein binding sites upstream from the K5 gene probably reflects the complex regulatory circuits that govern the expression of the K5 keratin in mammalian tissues.

Morphologic correlation between liver epithelium and mesenchyme allows insight into histogenesis of focal nodular hyperplasia (FNH) of the liver

The microanatomic organization of focal nodular hyperplasia (FNH) of the liver was analyzed to obtain information about the histogenesis of this tumor-like lesion. All of the 11 examples of FNH studied showed subdivision into multiple pseudolobules, which were characterized by fibrovascular and ductular areas radiating from perilobular septa, and an expanding periphery of normal appearing hepatocytes. Immunohistochemical analysis showed continuous transitions from normal hepatocytes in the periphery of the pseudolobules, which expressed only the keratins 8 and 18, to small hepatocytes and ductular aggregates in the center of the pseudolobules, both of which also expressed the keratins 7 and 19. Ductular metaplasia of hepatocytes was always accompanied by sinusoidal endothelial cells stained by the endothelial markers BMA 120, M 616, and by an increase in collagenous fibers especially of type III. Further development of this fibrovascular and ductular transformation lead to subdivision of the involved pseudolobules. The pseudolobules had similar mean sizes, irrespective of their site in the periphery or the center of the FNHs, showing that proliferation, fibrovascular and ductular transformation and subdivision of these micronodules are a basic histogenetic phenomenon in FNH. The findings indicate that local changes in the interrelations between liver epithelial and mesenchymal cells influence substantially the abnormal but nevertheless regulated growth of liver parenchyma which gives rise to FNH.

Patterns of cytokeratin expression in human gingival epithelia

Specimens of human gingiva were collected from teenage and adult subjects and frozen sections were stained with an extensive panel of monoclonal antibodies with defined specificities for individual cytokeratins. The results indicated different and distinctive patterns of keratin expression by the oral gingival, oral sulcular and the junctional epithelia. It was observed that epithelium with staining characteristics of sulcular epithelium extended over the gingival crest onto the oral surface of the gingiva. Junctional epithelium showed the unusual pattern of co-expression of keratins typical of the stratifying and of the simple epithelial phenotypes. The patterns of gingival keratin expression are compared with those of other mucosal epithelia. The findings are discussed in relation to mechanisms that may determine or influence the junctional epithelial phenotype.

Association between keratin staining patterns and the structural and functional aspects of palatine tonsil epithelium

The keratin composition of stratified squamous epithelia has a complex pattern, which varies in different regions and as a result of pathological developments. The exact factors responsible for the characteristic keratin composition in a given epithelium are unknown. However, the environment, including factors from the connective tissue, is known to influence epithelial morphology and keratin composition. We here report that the reticulated squamous epithelium of the crypts of palatine tonsils shows an extensive staining for keratins 5 and 19 in basal as well as suprabasal cells, in contrast to neighbouring non-reticulated crypt epithelium and the epithelium at the tonsillar surface, in which staining is restricted to basal cells. The reticulation of the crypt epithelium is thought to be initiated by infiltration of immune-related cells in a preexistent non-reticulated epithelium. The extensive staining for keratins 5 and 19 in reticulated crypt epithelium correlates with the presence of numerous immune system-related cells and marked expression of intercellular adhesion molecule-1 (ICAM-1), thought to be involved in inflammatory and immunological responses. The results suggest that the massive lymphocytic traffic in the reticulated crypt epithelium and the overall distinct immune environment are responsible for the unique keratin staining pattern observed.

Expression of different cytokeratin subclasses in human chordoma

A detailed immunohistochemical characterization of different cytokeratin subclasses was performed on frozen tumour tissue from three classical chordomas. Simple epithelium cytokeratins Nos 8, 18, and 19 were detected in all tumour cells while cytokeratin No. 7 was not found. Cytokeratins characteristic of squamous differentiation, including keratinization, were generally lacking, with the exception of the varying expression of cytokeratin No. 4. Vimentin was found in all the tumours, while they lacked desmin immunoreactivity. The present study indicates the co-expression of vimentin and cytokeratins, predominantly of the simple epithelium type. In addition, chordoma cells have the ability to express cytokeratins characteristic of squamous differentiation. This finding corresponds well to the electron microscopic findings of tonofilament bundles ending in well-developed desmosomes.

Expression of keratin 13 in human epithelial neoplasms

The distribution of the 52 kDa keratin 13 was evaluated immunohistochemically, using the AE8 monoclonal antibody. Various squamous and transitional cell epithelial lesions and representative control tissues were studied. This antibody performed adequately in formalin-fixed and paraffin-embedded tissue, but like keratin immunohistochemistry in general, required protease pretreatment. Keratin 13 was found consistently in the suprabasal layers of squamous epithelia of oral cavity, tonsils, larynx, esophagus, lower female genital tract, and transitional urothelium, but it was absent in the epidermis. Generally, various forms of squamous metaplasia were AE8-positive. In dysplasia, AE8 reactivity was considerably decreased or even absent despite the presence of apparent suprabasal maturation. In differentiated squamous cell carcinomas, AE8 immunoreactivity was usually limited to a few cells in the center of the keratinized foci. However, in 10% of squamous cell carcinomas, a significant number of tumor cells was positive. Only well-differentiated urothelial carcinomas showed AE8 immunoreactivity, while poorly differentiated tumors were negative. Interestingly, a Brenner's tumor showed a high number of AE8-positive epithelial cells. Our results show that the expression of keratin 13, as immunohistochemically determined by AE8 antibody, is significantly down-regulated in squamous cell malignancies. Its possible value as an adjunct to diagnosis of dysplasia should be investigated further.

Quantitative immunohistochemical analysis of keratins and desmoplakins in human gingiva and peri-implant mucosa

Quantitative immunohistochemistry was used to compare the distributions of keratins and desmoplakins in human gingiva and peri-implant mucosa (three specimens each). In gingiva, keratin 1 (a marker of cornification) and desmoplakins I & II (markers of desmosomes) stained most heavily in granular strata followed by corneal strata; keratin 13, a marker of non-cornifying stratified squamous cells, stained most heavily in suprabasal strata of oral sulcular epithelium. Keratin 19, a marker for junctional epithelium, stained the basal stratum of oral sulcular epithelium most heavily. In peri-implant mucosa, the patterns of staining were similar, except that staining for desmoplakins I & II was generally significantly reduced compared with gingiva, and junctional epithelium co-expressed keratins 13 and 19. Peri-implant junctional epithelial cells attached to titanium implant abutments were removed by trypsin/EDTA digestion, and also exhibited co-expression of keratins 13 and 19. Inflammatory cell infiltration was associated with reduction of keratin 1 staining in gingiva. The data indicate that the epithelia of gingiva and peri-implant mucosa are not composed of identical cell populations.

Mutant keratin expression in transgenic mice causes marked abnormalities resembling a human genetic skin disease

To explore the relationship between keratin gene mutations and genetic disease, we made transgenic mice expressing a mutant keratin in the basal layer of their stratified squamous epithelia. These mice exhibited abnormalities in epidermal architecture and often died prematurely. Blistering occurred easily, and basal cell cytolysis was evidence at the light and electron microscopy levels. Keratin filament formation was markedly altered, with keratin aggregates in basal cells. In contrast, terminally differentiating cells made keratin filaments and formed a stratum corneum. Recovery of outer layer cells was attributed to down-regulation of mutant keratin expression and concomitant induction of differentiation-specific keratins as cells terminally differentiate, and the fact that these cells arose from basal cells developing at a time when keratin expression was relatively low. Collectively, the pathobiology and biochemistry of the transgenic mice and their cultured keratinocytes bore a resemblance to a group of genetic disorders known as epidermolysis bullosa simplex.

Immunohistochemical study of cytokeratin expression in normal and pathologic middle ear mucosa of the rat

The expression of cytokeratins in the epithelium of the middle ear and external auditory meatus of the rat was studied on cryosections of ethylenediaminetetraacetic acid-decalcified specimens by use of a panel of monoclonal antibodies. The normal middle ear epithelium revealed a complex cytokeratin profile, including regional differences. The induction of sterile middle ear effusions resulted in increased cytokeratin expression. Infective effusions were accompanied by both quantitative and qualitative changes in the cytokeratin expression patterns. The differences observed between the cytokeratin profiles of external meatal skin and those of middle ear epithelium may form a useful tool for research into cholesteatoma development.

Immunohistochemical interpretation of early epithelial disorders of pyriform sinus

Expression of cytokeratins (CKs) was investigated immunohistochemically by use of monospecific monoclonal anti-CK antibodies in normal epithelia of pyriform sinus and epithelial lesions such as simple hyperplasia, different degrees of dysplasia, in situ carcinoma, and invasive carcinoma. In normal epithelium, strong expression of CK-19 was consistently observed only in the basal layer as basic CK, while expression of CK-13 showed a completely reverse pattern, being expressed only in suprabasal layers as stratification-related CK. Characteristic changes in expression pattern of these two CKs were observed in accordance with the degree of epithelial disorders and differentiation of carcinoma. Cytokeratin 1, as keratinization-associated CK, was observed only in keratinized cells of hyperplastic epithelia and well-differentiated carcinomas. These findings may be useful in evaluating epithelial disorders and classifying carcinomas more objectively, and may assist earlier detection of carcinoma when used with standard histologic techniques.

Altered keratin expression in ichthyosis hystrix Curth-Macklin. A light and electron microscopic study

The pathogenesis of a rare form of the ichthyotic diseases, ichthyosis hystrix Curth-Macklin, was investigated by immunohistochemistry and electron microscopy. Monoclonal antibodies (Mabs) against keratins expressed in normal basal cells (PKK2 and KA1), Mabs against keratins only present in normal fetal skin (PKK1), and Mabs against keratins 1, 2, 10, and 11 (KA5 and K8.60) were used. The Mabs reacting with normal basel cells showed an increased reaction with many cell layers. The Mab PKK1 distinctly reacted with the basal cell layer, suggesting an expression of fetal keratins. Electron microscopic study of both normal-looking and involved skin revealed the keratinization disorder characterized by tonofilament shells, perinuclear vacuoles, and binuclear keratinocytes. The results suggest that there is no prematurity of keratinization, but rather a pathological expression of specific keratin genes leading to expression of fetal keratins in this form of ichthyosis hystrix.

Extensive changes in cytokeratin expression patterns in pathologically affected human gingiva

The stratified squamous epithelium of the oral gingiva and the hard palate is characterized by a tissue architecture and a cytoskeletal composition similar to, although not identical with, that of the epidermis and fundamentally different from that of the adjacent non-masticatory oral mucosa. Using immunocytochemistry with antibodies specific for individual cytokeratins, in situ hybridization and Northern blots of RNA with riboprobes specific for individual cytokeratin mRNAs, and gel electrophoresis of cytoskeletal proteins of microdissected biopsy tissue samples, we show changes in the pattern of expression of cytokeratins and their corresponding mRNAs in pathologically altered oral gingiva. Besides a frequently, although not consistently, observed increase in the number of cells producing cytokeratins 4 and 13 (which are normally found as abundant components in the sulcular epithelium and the alveolar mucosa but not in the oral gingiva) and a reduction in the number of cells producing cytokeratins 1, 10 and 11, the most extensive change was noted for cytokeratin 19, a frequent cytokeratin in diverse one-layered and complex epithelia. While in normal oral gingiva cytokeratin 19 is restricted to certain, sparsely scattered cells of --or near--the basal cell layer, probably neuroendocrine (Merkel) cells, in altered tissue of inflamed samples it can appear in larger regions of the basal cell layer(s) and, in apparently more advanced stages, also in a variable number of suprabasal cells. Specifically, our in situ hybridization experiments show that this altered suprabasal cytokeratin 19 expression is more extended at the mRNA than at the protein level, indicating that cytokeratin 19 mRNA synthesis may be a relatively early event during the alteration. These changes in cytokeratin expression under an external pathological influence are discussed in relation to other factors known to contribute to the expression of certain cytokeratins and with respect to changes occurring during dysplasia and malignant transformation of oral epithelia.

Expression of keratin 5 as a distinctive feature of epithelial and biphasic mesotheliomas. An immunohistochemical study using monoclonal antibody AE14

In previous biochemical analyses, keratin 5 (Mr 58,000) has been detected in most mesotheliomas with epithelial component but not in pulmonary adenocarcinomas (Blobel et al., Am J Pathol 121: 235-247, 1985). In the present study, we have characterized a monoclonal antibody, AE14, as being selectively specific for keratin 5 (apart from the reactivity with certain hair proteins) as shown by immunoblotting of gel-electrophoretically separated proteins from various tissues. Immunohistochemical screening of a variety of normal human tissues, using immunoperoxidase microscopy on cryostat sections, revealed the binding of this antibody to the basal, immature cells of stratified squamous epithelia, to basal cells of pseudostratified epithelia, to some myoepithelial cells, thymic reticulum cells, certain pancreatic duct cells, as well as a variable subpopulation of mesothelial cells of the pleura and the peritoneum. In 12/13 epithelial and biphasic mesotheliomas of the pleura, heterogeneous but extended staining with antibody AE14 was seen whereas 21 pulmonary adenocarcinomas were negative or, in six of these cases, showed staining of only a few cells. Among carcinomas from other sites, colonic adenocarcinomas and renal cell carcinomas were negative whereas limited staining was found in some pancreatic adenocarcinomas. It is suggested that antibody AE14 may be useful, as a defined polypeptide-specific reagent, in the histologic distinction between mesotheliomas and most adenocarcinomas. Furthermore, the expression patterns of keratin 5 as detected by antibody AE14 in various normal and malignant epithelial tissues are discussed, particularly their relation to processes of squamous metaplasia and their indication of phenotypic tumor heterogeneity.

Synthesis of cytokeratin 13, a component characteristic of internal stratified epithelia, is not induced in human epidermal tumors

Human cytokeratin 13 is one of the most abundant intermediate filament (IF) proteins of many internal stratified epithelia and occurs, at least in certain cell cultures, in an O-glycosylated form binding the lectin, wheat germ agglutinin (WGA). As other groups have reported that, in the mouse, the synthesis of mRNA encoding the 47-kDa cytokeratin corresponding to human cytokeratin 13 is induced in epidermal keratinocytes during malignant transformation, we have examined the synthesis of cytokeratin 13 mRNA and protein in human epidermis and epidermal tumors, using specific cDNA probes and cytokeratin 13 antibodies. We isolated two different cDNA clones from the vulvar carcinoma cell line A-431, in which this protein is abundant: One clone seems to represent the entire mRNA, whereas the other is only a minor component and encodes a truncated cytokeratin 13 lacking most of the carboxy-terminal tail domain, probably a product of alternative, "incorrect" splicing. Comparison of the amino acid sequences with those of other cytokeratins revealed a high degree of conservation with respect to several other human type I cytokeratins, notably cytokeratin 15, and to the murine 47-kDa cytokeratin. When human epidermis and a series of benign and malignant epidermal tumors were examined with these cDNA probes and cytokeratin-13-specific antibodies we did not find an induction of expression in keratinocytes, normal or malignantly transformed, except for some scattered, sparse cytokeratin-13-positive cells and very low levels of cytokeratin 13 mRNA, detectable only with the highly sensitive polymerase chain reaction (PCR). We conclude that the gene(s) encoding cytokeratin 13 are not induced in human keratinocytes during epidermal carcinogenesis, in apparent contrast to reports of murine epidermal tumors, and we discuss possible explanations for this interspecies difference.

Immunohistochemical analysis of stratum corneum components in oral squamous epithelia

The generation of a stratum corneum in squamous epithelia involves marked changes in morphology and in the expression of cell products. We have examined the expression of some of the components involved in this process in oral squamous epithelia with different terminal differentiation patterns by use of immunofluorescent techniques. Involucrin and transglutaminase are involved in formation of cornified envelopes consistently seen in the stratum corneum. Both components were present in keratinized oral epithelia (palatal epithelium and hyperkeratinized buccal epithelium). The nonkeratinized normal buccal epithelium stained positive as well. Filaggrin, a protein derived from a precursor present in keratohyalin granules, is proposed to aggregate keratin filaments in the cornified layer. Although the staining differed markedly in quantity, this component was likewise detected in both keratinized and nonkeratinized epithelia. The staining patterns for different keratin polypeptides, however, showed qualitative differences between the different epithelia. Thus, it seems that the keratin composition shows differentiation-specific characteristics, whereas the presence of other important components needed to generate a stratum corneum is not as closely related to the terminal differentiation pattern of oral epithelia.

Keratin 19: predicted amino acid sequence and broad tissue distribution suggest it evolved from keratinocyte keratins

The type I keratin 19 is unusual in its tissue distribution in that under normal circumstances it does not seem to be restricted, as the other keratins are, to expression in either stratified or simple epithelia. In addition to the previously reported distribution of keratin 19 in human tissues, we have observed keratin 19 in epidermal basal cells, in a defined region of the hair follicle, and in nipple epidermis. We noticed that expression of keratin 19 appears to be especially characteristic of regions of labile or variable cellular differentiation as indicated by the presence of multiple keratin phenotypes in close proximity to each other. Using a monoclonal antibody recognizing keratin 19 (LP2K) to screen a human placenta cDNA expression library, we have isolated, cloned, and sequenced cDNA coding for full-length human keratin 19, as confirmed by its reactivity with several other known anti-keratin 19 monoclonal antibodies and by the near identity of its sequence with that of the bovine keratin 19 homologue. This similarity extends to both proteins being truncated at the C-terminal end to only 13 amino acids beyond the rod domain. Although the amino acid homology over the N-terminal and helical rod domains is particularly high, the human and bovine proteins diverge substantially over the short C-terminal domain, which suggests that this region has no conserved function. Comparison with other type I keratins indicates that the closest evolutionary neighbors of keratin 19 are keratinocyte keratins, probably 13 and 14, and not the simple epithelial keratin 18. Assessing the histochemistry and sequence data together, we propose that the cell may use this apparently deficient keratin as a "neutral" keratin. While unimpaired in its ability to polymerize (keeping the cell integrated into the epithelial sheet via filament-desmosome networks), keratin 19 expression does not irrevocably commit a cell to any one of the local differentiation options. Such predicted differentiational flexibility may also imply vulnerability to transformation.

Patterns of expression of intermediate filaments in ameloblastoma and human fetal tooth germ

Monoclonal antibodies (Mab) were used to study the expression of cytokeratins and vimentin in various histological types of ameloblastoma and in human fetal tooth germ. The ameloblastoma and the tooth germ epithelia showed characteristics of both simple glandular and stratified squamous epithelial cells. Cytokeratin No. 18 was detected focally in most ameloblastomas studied but not in fetal odontogenic epithelia. Cytokeratins Nos. 8 and 19 were expressed in all epithelial elements of ameloblastomas and tooth germs. Only two tumors showed focally characteristics of keratinizing epithelia also seen in dental lamina but not in the enamel organ. All tumors except the granular cell ameloblastoma showed a variable coexpression of vimentin and cytokeratins in their neoplastic epithelia. A similar coexpression was detected in the stellate reticulum cells of the developing tooth. Ameloblastoma and human tooth germ epithelia share complex pattern of cytokeratin polypeptides together with coexpression of vimentin. The results strongly support the theory that ameloblastomas are of odontogenic origin and not direct derivatives of basal cells of oral epithelium or epidermis.

Expression of intermediate filament proteins in fetal and adult human lung tissues

The expression patterns of intermediate filament proteins in fetal and normal or nonpathological adult human lung tissues are described using (chain-specific) monoclonal antibodies. In early stages of development (9-10 weeks and 25 weeks of gestation) only so-called simple cytokeratins such as cytokeratins 7 (minor amounts). 8, 18 and 19 are detected in bronchial epithelial cells. At later stages of development, the cytokeratin expression patterns become more complex. The number of bronchial cells positive for cytokeratin 7 increases, but basal cells in the bronchial epithelium remain negative. These latter cells show, however, expression of cytokeratin 14 in the third trimester of gestation. Developing alveolar epithelial cells express cytokeratins 7, 8, 18 and 19. In adult human bronchial epithelium cytokeratins 4 (varying amounts), 7, 8, 13 (minor amounts), 14, 18 and 19 can be detected, with the main expression of cytokeratins 7, 8, and 18 in columnar cells and the main expression of cytokeratin 14 in basal cells. Vimentin is detected in all mesenchymal tissues. In addition, fetal lung expresses vimentin in bronchial epithelium, however, to a lesser extent with increasing age, resulting in the expression of vimentin in only few scattered bronchial cells at birth. Also in adult bronchial epithelium the expression of vimentin is noticed in part of the basal and columnar epithelial cells. Desmin filaments, present in smooth muscle cells of the lung, appear to alter their protein structure with age. In early stages of development smooth muscle cells surrounding blood vessels are partly reactive with some cytokeratin antibodies and with a polyclonal desmin antibody. At week 9-10 and week 25 of gestation a monoclonal antibody to desmin, however, is not reactive with blood vessel smooth muscle cells but is only reactive with smooth muscle cells surrounding bronchi. With increasing age the reactivity of cytokeratin antibodies with smooth muscle cells in blood vessels decreases, while the reactivity with the monoclonal desmin antibody increases. Our results show that during differentiation profound changes in the intermediate filament expression patterns occur in the different cell types of the developing lung.

Ultrastructural and immunocytochemical characterization of the cellular phenotype in primary adenoid liver tumours of the rat

The cellular phenotype of 34 primary adenoid liver tumours induced in rats with N-nitrosomorpholine was studied by immunocytochemical and electron microscopical methods in order to elucidate the histo- and cytogenesis of these tumours. Three types of ducts were distinguished in the adenoid liver tumours at the ultrastructural level being characterized as of hepatocellular, transitional and cholangiocellular phenotype. The transitional cells took an intermediate position between the hepatocellular and the cholangiocellular phenotype. Frequent features of the hepatocyte-like differentiation were large round nuclei with a dispersed chromatin, glycogen-associated ER complexes, peroxisomes and the formation of bile canaliculi. Evidence for the relationship to bile ductular cells was provided by the regular association with a basement membrane, the (inconstant) positive immunohistochemical reaction for cytokeratin polypeptide KA-4, a poorly developed ER and small mitochondria. An additional finding in the ducts with a transitional cellular phenotype was the selective accumulation of mast cells integrated into the epithelium. Intimate associations between cells of the hepatocellular, transitional and cholangiocellular phenotype were observed at the light and electron microscopic level. The results suggest that a transdifferentiation (metaplasia) from cells with a hepatocellular to those with a transitional or cholangiocellular phenotype takes place in many liver tumours.

Evidence for a hepatocellular lineage in a combined hepatocellular-cholangiocarcinoma of transitional type

A combined hepatocellular-cholangiocarcinoma (CHC) of transitional subtype and the surrounding cirrhotic liver tissue were investigated immunocytochemically by monoclonal antibodies specific for each of the keratin polypeptides 7, 8, 18 and 19. Different keratin subsets were found in different parts of the tumour. The hepatocellular component reveals keratins 8 and 18, with the bordering cells of trabecular formations additionally expressing keratins 7 and 19. The same keratins i.e. 7, 8, 18, 19 were found in normal bile duct epithelium as well as in cholangiocarcinomatous and transitional areas of hepatocellular and cholangiocellular differentiation. Normal hepatocytes express only keratin 8 and 18. In cirrhotic liver some modified hepatocytes additionally express keratin 7. When ductal transformation is observed in the marginal parts of portal tracts and fibrous septa the keratin polypeptide pattern mimics that of bile duct epithelium. The cholangiocellular metaplasia of hepatocytes observed here correlates well with findings in hepato-organogenesis and hepatocarcinogenesis and suggests that the transitional subtype of combined hepatocellular-cholangiocarcinoma is a variant of hepatocellular carcinoma.