Differences of expression of cytokeratin polypeptides in various epithelial skin tumors

Keratin and keratinization

A flood of new knowledge and discoveries in the basic science of keratins and keratinization has appeared in the past several years. This review summarizes this recent information with a focus on the epithelial keratin polypeptides, keratin intermediate filaments, keratohyaline granule proteins, cell envelope formation and cell envelope proteins, "soft" keratinization, true disorders of keratinization (i.e., epidermolysis bullosa simplex and epidermolytic hyperkeratosis), and disease and drug effects on keratinization.

Progressive alterations of cytokeratin expressions in the process of chronic arsenism

Recent studies of an endemic occurrence of chronic arsenism in a limited area on the southwest coast of Taiwan are focusing on its cytokeratin analysis in hopes of tracing the disease's biochemical expression. Specimens were obtained from uninvolved skin and arsenical cancers including Bowen's disease, basal cell carcinoma, and squamous cell carcinoma. In this study, we used two-dimensional polyacrylamide gel electrophoresis to analyse cytokeratin expression. Progressive alterations in cytokeratin expression were found in various skin lesions. These include an expression of K16 in the uninvolved skin; K16 and K6 in Bowen's disease; and K16, K6 and K17 in squamous cell carcinoma and basal cell carcinoma. In addition, we found that the K1 isoelectric variants shifted to more acidic forms with the complete absence of K1 in basal cell carcinoma. K16 expression in uninvolved skin indicates that it is nevertheless in a hyperproliferative status. K17 was expressed in squamous cell carcinoma and basal cell carcinoma, but not in Bowen's disease. The progressive impairment of phosphorylation of K1 and K2 in the process of chronic arsenism provides us with a suitable model for studying the biological significance of phosphorylation in intermediate filaments during chemical carcinogenesis.

An immunohistochemical and histochemical study of cytokeratin, involucrin and transglutaminase in seborrhoeic keratosis

The mode of differentiation of seborrhoeic keratoses was investigated by immunohistochemical staining using cytokeratin (CK) polypeptide-specific monoclonal antibodies and an antibody specific for the particulate form of epidermal transglutaminase (ETgase), and by applying an anti-human involucrin serum. The role played by (E)Tgase was further evaluated using an activity assay based on the covalent attachment of monodansylcadaverine. Samples of uninvolved epidermis served as reference tissue. CK reactivities suggested that seborrhoeic keratoses is a hyperproliferative disease with an epidermal CK composition. CK5 and CK14 were prominent markers of basal and basaloid keratinocytes, whereas a decrease in staining occurred in advanced maturation stages and areas of terminal keratinization. In contrast, CK1 and CK10 were prominent markers of suprabasaloid differentiation stages and produced complementary stainings to those of CK5 and 14. Generally, CK10 staining was more impressive than CK1 staining and seemed to start before CK1 staining. In contrast to CK10 staining, cornified areas lost CK1 reactivity. These staining patterns were similar to those observed in uninvolved reference tissues. The epidermal CK subset was further supplemented with the 'hyperproliferative' CK6 and 16 which occur sequentially. Positive staining for CK6 was noted from basal and proximal basaloid cells onwards, whereas distal basaloid cells additionally showed CK16 staining. The presence of other non-epidermal CK polypeptides could not be shown. The competence for other differentiation markers belonging to the group of (E)Tgase and cornifying cell membranes also evolved with a typical epidermal pattern. (E)Tgase activity was restricted to advanced and terminal stages of keratinization and was dual in nature, i.e. a diffuse cytoplasmic staining occurred together with a prominent staining of cornifying cell membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential modulation of epidermal keratinization in immortalized (HaCaT) and tumorigenic human skin keratinocytes (HaCaT-ras) by retinoic acid and extracellular Ca2+

The growth and differentiation response to retinoic acid (RA) was studied in the human keratinocyte line HaCaT and tumorigenic clones transfected with c-Ha-ras oncogene (HaCaT-ras). Differentiation (mainly keratin synthesis) was evaluated and correlated to cell proliferation in vitro but also growth behaviour in vivo (tumorigenicity). Comparable to normal keratinocytes, HaCaT cells and ras clones showed increased expression of the epidermal suprabasal keratins K1 and K10 upon RA depletion of the media (delipidized serum), while simple epithelial type keratins K7, K8 and K18 as well as K19 and K13 (typical of internal stratified epithelia) were almost completely suppressed. The cell density-dependent increase of K1 and K10 at intermediate RA levels (as in regular media with untreated serum) was also observed at Ca2+ levels below 0.1 mM, thus being clearly unrelated to stratification, whereas K13 synthesis was Ca(2+)-dependent and initiated with stratification. The effects on keratins were fully reversed by increasing RA concentrations. There was only mild stimulation of proliferation at RA doses (10(-10) to 10(-8) M) not directly corresponding to suppression of keratinization. Thus, the negative RA influence on K1 and K10, opposed to the effect on simple keratins, substantiates the preserved regulatory capacity rendering these cells appropriate models for biological testing. Among the various tumorigenic HaCaT-ras clones highly and moderately differentiating ones could be distinguished, accordingly induction in vitro led to a comparable spectrum of differentiation markers (K1 and K10 appearing early, and filaggrin late) as growth in vivo. These in vitro results demonstrate that, in spite of some differences in RA sensitivity, virtually all clones possess the epidermal differentiation repertoir which is regulated according to the same principles. Finally, this confirms our in vivo data that differentiation potential is not inversely related to the state of transformation or tumorigenicity.

Induction of epidermal hyperplasia, hyperkeratosis, and papillomas in transgenic mice by a targeted v-Ha-ras oncogene

The regulatory elements of the human keratin K1 gene have been used to target expression of the v-Ha-ras oncogene exclusively in the epidermis of transgenic mice. We developed 12 transgenic mouse lines that express the HK1.ras transgene, producing epidermal hyperplasia in neonates and hyperkeratosis in juveniles. Eventually this skin phenotype diminished but with time adult animals developed papillomas that could persist or regress. The rate and frequency of tumorigenesis appeared to be limited, which suggests that v-Ha-ras requires a second or even third event to elicit and maintain a benign phenotype in transgenic mice. Since in certain transgenic lines papillomas appeared at wound sites, it appears that the promotion stimulus from wounding may be a second event. We envision that such transgenic mice that express v-Ha-ras in the epidermis will become a powerful model for assessing how environmental and molecular factors affect the process of multistage skin carcinogenesis in vivo, as well as a model for evaluating novel therapeutic protocols.

Simple epithelial cytokeratin-expression in seborrheic keratosis

The cytokeratin expression of seborrheic keratosis was studied by means of immunohistochemistry and compared with that of normal human skin. The following findings were obtained in seborrheic keratosis: (1) a partial lack of high molecular weight cytokeratin (#1/68 kD, #10/56.6 kD) in all ten cases examined; (2) the detection of cytokeratin typical for simple epithelia (#8/52.5 kD, #18/45 kD, #19/40 kD) in eight of ten cases; and (3) the detection of cytokeratin #5/58 kD in suprabasal cells in 5 of 10 cases. An immunoelectron-microscopic investigation, using an anti-keratin antibody against cytokeratin #19/40 kD, revealed a whirl-like arrangement of keratin filaments within immunoreactive cells, in contrast to a linear, parallel arrangement in non-immunoreactive cells. Cells known to express cytokeratin typical for simple epithelia, such as sweat gland cells or Merkel cells, were not observed. The altered cytokeratin gene-expression in seborrheic keratosis may be attributable to de-differentiation of tumor cells or potential re-differentiation towards embryonic keratinocytes.

Monoclonal antibody analysis of keratin expression in carcinomas of sweat glands

Characteristics of keratins of five carcinomas of sweat gland origin were immunohistochemically investigated with several antikeratin monoclonal antibodies with differing specificities. Specimens were obtained from two cases of mucinous carcinoma of the skin, two cases of classic type of eccrine adenocarcinoma, and a case of eccrine porocarcinoma. The tumor cells of mucinous carcinoma expressed only simple epithelial keratins. In a case of eccrine adenocarcinoma, simple epithelial keratin 19 was diffusely expressed. The expression of the other simple epithelial keratins was confined to the luminal cells, whereas the remaining tumor cells further expressed stratified epithelial keratins. Eccrine porocarcinoma and a second case of eccrine adenocarcinoma did not express simple epithelial keratins, although stratified epithelial keratins were diffusely expressed. These data suggest that carcinomas of sweat glands express various combinations of simple and stratified epithelial keratins. Development of additional data along these lines may help to further define their classification.

Characterization of human cytokeratin 2, an epidermal cytoskeletal protein synthesized late during differentiation

Among the more than 30 different human proteins of the cytokeratin (CK) group of intermediate filament (IF) proteins, the significance of the epidermal polypeptide CK 2 (Moll et al., 1982, Cell 31, 11-24) has been repeatedly questioned in the literature. Here, we show, by in vitro translation and protein gel electrophoresis, that human epidermis from various body sites does indeed contain relatively large amounts of mRNA encoding a distinct polypeptide comigrating with native epidermal CK 2. We also report the isolation of a cDNA clone encoding the complete sequence of CK 2, which is a type II CK different from--but related to--epidermal CKs 1 and 5 on the one hand and corneal CK 3 on the other. The mRNA of approximately 2.6 kb encodes a polypeptide of 645 amino acids and M(r) 65,852, in good agreement with the value of 65.5 kDa previously estimated from gel electrophoresis. This human CK, the largest so far known, displays several features typical of CKs of stratified epithelia, including numerous repeats of glycine-rich tetrapeptides in the head and tail domains. Northern blot and in situ hybridizations have shown that CK 2 is expressed strictly suprabasally, usually starting in the third or fourth cell layer of epidermis, and this was confirmed at the protein level by immunohistochemistry using CK 2-specific antibodies. The protein has been detected as a regular epidermal component in skin samples from different body sites, albeit as a minor CK in "soft skin" (e.g., breast nipple, penile shaft, axilla), but not in foreskin epithelium and in other epithelia, in squamous metaplasias and carcinomas, or in cultured cell lines derived therefrom. We propose that CK 2 is a late cytoskeletal IF addition synthesized during maturation of epidermal keratinocytes which probably contributes to terminal cornification.

Cytokeratin pattern of clinically intact and pathologically changed oral mucosa

The various cytokeratin polypeptides in oral epithelia are expressed in dependence on site and formation of a stratum corneum. Certain cytokeratins occur permanently and others occasionally. In fibrous hyperplasia and Lichen ruber planus, patterns of cytokeratins did not deviate significantly from normal. In some but not all cases of squamous cell carcinoma and leukoplakia studied, marked aberrations of pattern were characterized by (i) appearance of cytokeratin No. 19, (ii) somewhat more frequent occurrence of cytokeratins Nos. 8 and 18, (iii) proteolytic modifications of cytokeratins, and (iv) partial loss of a few site-specific cytokeratins. The aberrations may be taken as additional diagnostic criteria for differentiation between non-aggressive and potentially aggressive leukoplakic lesion, even if they are not correlated with the conventional histological grading of dysplasia.

Effects of Topical Retinoids on Cytoskeletal Proteins: Implications for Retinoid Effects on Epidermal Differentiation

In vivo effects of retinoids on epidermal differentiation were investigated by analyzing cytoskeletal proteins in rhino mice treated topically with all-trans-retinoic acid (RA) and other retinoids (13-cis-retinoic acid, etretinate, TTNPB). Non-disulfide-linked cytoskeletal proteins, including keratins from the epidermal "living layers," were first selectively extracted using 9.5 M urea; subsequently, keratins of the stratum corneum were isolated using 9.5 M urea plus a reducing agent. Gel electrophoresis and immunoblot analysis showed that urea extracts of epidermis from vehicle-treated skin were composed predominantly of four major keratins (analogous to human epidermal keratins K1, K5, K10, and K14), and the keratin filament-associated protein filaggrin. In contrast, extracts of epidermis from retinoid-treated skin contained additional keratins (K6, K16, and K17) and almost no detectable filaggrin. Furthermore, similar analysis of stratum corneum keratins demonstrated that extracts from RA-treated skin did not contain the partially proteolyzed keratins typically observed in stratum corneum extracts of control animals. Hyperplasia-inducing agents (salicylic acid, croton oil) caused an increase in keratins K6, K16, and K17, but they did not effect filaggrin or alter proteolysis of stratum corneum keratins. The result that RA induced expression of keratins K6, K16, and K17, as commonly expressed in hyperproliferative epidermis, is consistent with the notion that retinoids increase epidermal cell proliferation in the basal and/or lower spinous layers. The findings that topical RA decreased filaggrin expression and reduced proteolysis of stratum corneum keratins, despite increased size and number of granular cells and the presence of an anucleate stratum corneum, suggest that topical RA may also modulate a later stage of epidermal differentiation involved in stratum corneum formation.

Keratin expression in basal cell carcinomas

The keratin phenotype of 15 cases of basal cell carcinoma was assayed immunohistochemically using a panel of monospecific antibodies to single keratin polypeptides. Whilst tumour tissue strongly expressed primary keratins 5 and 14 (normally synthesized in basal keratinocytes) no expression of secondary keratins 1 and 10 (characteristic of skin-type differentiation) was detected. Keratin 17, characteristic of the outer hair root sheath, was strongly expressed in all tumours. Keratin 19 was also normally expressed in parts of the hair follicle and was detected in four cases. The 'high cell turnover' keratin 16 was frequently induced in the overlying epidermis, but was rare within tumour tissue. No expression of simple epithelial keratins 8 and 18 was detected. Whilst the keratin phenotype of tumour cells is similar to that of basal cells within part of the hair root sheath, in keeping with suggestions of a follicular origin for basal cell carcinomas, the findings are also compatible with an origin from interfollicular pluripotent stem cells differentiating towards follicular structures.

Cytokeratins as epithelial differentiation markers in premalignant and malignant oral lesions

The keratin expression pattern in oral stratified epithelium is related to the cellular differentiation level. The normal pattern shows the keratin pair K5 and K14 in the stratum basale whereas K1 and K10, or K4 and K13, are the two pairs associated with differentiating suprabasal cells. Monoclonal and polyclonal antibodies to individual keratins (K10, K13 and K14) were used in a two-color immunofluorescence staining method to study their coexpression in single cells. Altered keratin expression in premalignant and malignant lesions indicated abnormal differentiation. Monospecific keratin antibodies were suggested to be useful for evaluation of epithelial differentiation changes in oral dysplasias and oral squamous cell carcinomas.

Expression of simple epithelial keratins 8 and 18 in epidermal neoplasia

A systematic study of keratin expression in epidermal lesions (six actinic keratoses, 10 Bowen's disease, seven squamous cell carcinomas) has been undertaken by using a large panel of monospecific monoclonal antibodies to individual keratins. Expression of differentiation-specific keratins was frequently delayed or lost from dysplastic regions. Novel expression of the embryonic, or simple epithelial, keratins 8 and 18 was widely observed in intradermal areas of poorly differentiated squamous cell carcinomas. In addition, the most proliferative of in situ malignancies (Bowen's disease) also contained small numbers of cells expressing simple epithelial keratins. These observations suggest that the expression of simple epithelial keratins may be of functional importance in malignancy of keratinocytes and could be related to tumor invasion and/or to changes in epithelial-mesenchymal interactions.

Normal psoriatic epidermis expression of hyperproliferation-associated keratins

Keratin expression in lesional, marginal and uninvolved psoriatic epidermis was analysed by one- and two-dimensional gel electrophoresis and immunoblotting. Keratins K1, K5, K6, K10, K14, and K16 were identified in lesional epidermis. Keratins K6 and K16 were found in all epidermis probes of uninvolved skin, but never occurred in normal epidermis of control skin samples. By means of laser-densitometric evaluation of one-dimensional gels a downregulation of K1 and K10 and an upregulation of K6 and K16 was found in psoriatic epidermis. Unexpectedly, the level of K5 was considerably lower and the level of K14 considerably higher in lesional skin than in normal epidermis. These results demonstrate that not only basal keratinocytes in lesional epidermis but also suprabasal keratinocytes in uninvolved psoriatic epidermis express an altered differentiation pattern. The latter phenomenon could be very important in understanding the development of the so-called "Köbner effect" in psoriatic epidermis.

Biology of basal cell carcinoma (Part I)

Basal cell carcinoma is the most common malignancy in humans. Although rarely metastatic, it is capable of significant local destruction and disfigurement. This two-part article reviews the current understanding of basal cell carcinoma biology. Part I examines significant clinical, histologic, and ultrastructural features that relate to invasive potential. Genetic characteristics, including tumor growth rate, chromosomal abnormalities, and oncogene presence, are discussed, and expression of important cell and matrix proteins, including keratin, fibronectin, and HLA antigens, are reviewed. Further topics to be explored in Part II include host immunologic responses, theories of pathogenesis, and valuable second-line therapeutic regimens for treatment of multiple cancers.

The cytokeratin expression of cultured human foetal keratinocytes

Skin samples taken from foetuses of 15-19 weeks gestational age and keratinocytes were cultured by the 3T3 feeder method or in serum-free MCDB 153 medium on 16 mm coverslips. Keratinocytes taken from paediatric circumcisions and patients undergoing plastic surgery were also cultured using the 3T3 feeder method. A panel of monoclonal antibodies against a number of cytokeratins and differentiation markers were used in the PAP technique to analyse the cells. Cryostat sections taken from the donor skin samples were stained simultaneously. Foetal skin expressed the cytokeratins 7, 13 and 19 that were not observed postnatally. This cytokeratin expression as maintained in both culture conditions and also observe in paediatric and adult keratinocytes. Cytokeratin 7 was expressed on a greater proportion of foetal cells than in vivo, whereas the expression of 13 and 19 decreased. All keratinocytes expressed vimentin, transferrin receptor and Ki67 (proliferating cell antigen), while a small proportion expressed involucrin throughout culture, indicating their high level of differentiation and proliferation. No differences were observed between low and high density cultures. Foetal keratinocytes cultured in MCDB 153 did not reach confluence and stronger staining of differentiation markers was observed in these cells. These results show that the in vivo differences in cytokeratin expression of foetal and adult keratinocytes disappear in the culture.

Monoclonal antibodies to two different epitopes in a 30-kD CNBr peptide of the K1 and K2 keratins

Two anti-keratin monoclonal antibodies, Kab-2 and Kab-3, with specificities for different epitopes of type II (basic) human epidermal keratins, were produced. These antibodies had different immunofluorescent staining patterns on human fetal epidermis. Western blots and solid phase RIA showed both antibodies bound to 65-67-kD basic keratins (K1 and K2) extracted from foreskin epidermis. Competitive binding studies with the two Kab antibodies and other anti-keratin monoclonal antibodies showed that Kab-2 and Kab-3 recognized related epitopes, distinct from the epitopes recognized by other anti-keratin antibodies AE-1, 2, and 3. Kab-2 and Kab-3 epitopes were distinguished by differences in their reactivity with peptides generated by Staphylococcus aureus V8 protease digestion of the K1 keratin; the antibodies recognized both common and unique peptides. Western blots of cyanogen bromide digests of the K1 keratin showed that both Kab antibodies reacted with a 30-kD fragment of the molecule presumed to be the N-terminal CNBr peptide. We interpret these data to indicate that in tissues, portions of the N-terminal region of the K1 keratin are differentially available for reaction with these monoclonal antibodies and that morphologic differences in staining with monoclonal antibodies to the same molecule can reflect epitope specificity or epitope availability related to supramolecular organization.

Cytokeratin expression in human tongue epithelium

The epithelium of the human tongue shows diverse morphological variations from one site to another and even within the epithelium of the same papilla. This complexity has led to confusion regarding tongue epithelium as being orthokeratinized, parakeratinized, or nonkeratinized. Cytokeratins have been shown to characterize different epithelia. The present paper describes cytokeratin expression by adult tongue epithelia and relates their distribution to morphology. Six healthy human tongue specimens were obtained after plastic surgery and cytokeratin expression was investigated immunohistochemically, using a panel of 15 antibodies for cytoskeletal proteins, and biochemically using two-dimensional gel electrophoresis. The results showed that the ventral and lateral surfaces of the tongue are related to the nonkeratinizing stratified squamous epithelia, esophageal type, whereas the dorsal surface showed mixed expression of cytokeratins. In the tip of filiform and on the surface of fungiform papillae, cytokeratins of terminal differentiation are expressed as skin type; and in the rest of the papillae as well as in interpapillary areas, the epithelium expresses esophageal type cytokeratins. Certain simple epithelial cytokeratins were found in taste buds. Cytokeratin 19 was also detected in the basal cell layer of all esophageal type epithelia in the tongue. The present results provide basis for studies on the biological events in epithelial differentiation during development and in pathology.

Immunocytochemical demonstration of intermediate filament proteins, S-100 protein and CEA in apocrine sweat glands and apocrine gland derived lesions of the dog

The presence of carcinoembryonic antigen (CEA), intermediate filament proteins and S-100 protein in normal and pathological canine apocrine sweat glands was investigated, using a standard immunoperoxidase technique. The normal apocrine sweat glands showed a constant immunoreactivity in all the cases studied. The cells of the acini and of the ducts only reacted with the antikeratin antibody. The myoepithelial cells reacted positively with the antisera antikeratin and anti protein S-100. Epithelial cells of apocrine cysts, sweat gland adenomas and sweat gland carcinomas showed the same immunoreaction than normal apocrine cells. Proliferating myoepithelial cells were also positive for vimentin. In two out of three adenocarcinomas a positive reaction with the anti CEA could be detected in the glandular cells. This can be due to the presence in glandular cells of CEA or of Nonspecific Crossreacting Antigen (NCA). These findings indicate that demonstration of keratin is a useful aid in the detection of apocrine gland derived lesions in the dog. Similarly, S-100 protein is a marker for myoepithelial cells. Further research is necessary to investigate the expression of CEA in canine tumours.

Changes in cytokeratin expression in gingiva during inflammation

Cytokeratins represent specific markers of certain pathways of epithelial differentiation. The purpose of this study was to describe the alterations of cytokeratin pattern and topographical distribution of individual cytokeratins in inflamed gingiva. Five healthy and 15 inflammatory samples of human gingiva were studied. From each biopsy, cryostat sections allowed histological staining, immunofluorescence microscopy using a battery of monoclonal antibodies to cytokeratins, and gel electrophoresis. The results show marked differences in cytokeratin expression by healthy epithelia as compared with inflamed gingiva: in suprabasal cell layers there were reductions or disappearance of cytokeratins 1, 2 and 10, 11--specific for terminal differentiation--and increased expression of cytokeratins 4 and 13, as well as--in basal and parabasal cell layers--expression of cytokeratin 19. These alterations might represent an adaptation of involved epithelia to the alterations brought about by the inflammatory process.

Human squamous cell carcinoma from skin: establishment and characterization of a new cell line (HSC-5)

A new cell line, designated as HSC-5 and derived from human skin squamous cell carcinoma (SCC), has been established in vitro and maintained proliferative in continuous tissue culture for over two years. The cells grow in a monolayer in vitro and have anaplastic epithelioid features. The doubling time was about 35 hr at the 30th passage. Chromosome analysis showed hypotetraploidy with a modal number of 76. A trial of transplantation of the cultured cells into nude mice was not successful. Analysis of cytokeratins from HSC-5 by two-dimensional gel electrophoresis revealed polypeptides No. 5, 8, 13, 18 and 19. The cell line is available to other investigators.

Flow cytometric quantification of human epidermal cells expressing keratin 16 in vivo after standardized trauma

The intermediate filament protein keratin 16 is expressed in hyperproliferative epidermis. The present study aims to clarify the relationship between the expression of this keratin type, hyperproliferation (percentage of cells in SG2M phases), and keratinization (keratin 10 expression). These three parameters were quantified in biopsy material taken at different time intervals following sellotape stripping--this being a dynamic in vivo model for the induction of hyperproliferation. From the biopsy specimens cell suspensions were prepared, labeled with antibodies KS8.12 (specially directed against keratin 16) and RKSE60 (directed against keratin 10), and analyzed using flow cytometry. Percentages of cells in SG2M phases were assessed by measuring the relative DNA content after propidium iodide staining. Keratin 16 expression in the suprabasal layer anticipated epidermal proliferation, suggesting a role of the suprabasal compartment in the induction of epidermal growth. Keratin 10 expression decreased about 1 day after the onset of keratin 16 expression, indicating that these processes do not depend directly upon each other.

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.

Transient synthesis of K6 and K16 keratins in regenerating rabbit corneal epithelium: keratin markers for an alternative pathway of keratinocyte differentiation

Cultured rabbit corneal epithelial cells undergo three distinct stages of growth and differentiation characterized by the sequential appearance of K5/K14 keratin markers for basal keratinocytes, K6/K16 keratin markers for "hyperproliferative" keratinocytes, and K3/K12 keratin markers for corneal-type differentiation. Analyses of [35S]methionine-labeled, newly synthesized keratins revealed that K6/K16 are synthesized only briefly when the cells undergo exponential growth, and their synthesis is suppressed when the cells reach confluence and switch to synthesizing K3/K12. Transient synthesis of K6/K16 was also observed in vivo during corneal epithelial regeneration. Although K6/K16 expression in general correlates well with cellular growth, drug-induced inhibition of corneal epithelial growth and related data on human epidermal keratinocytes indicate that these two events are dissociable. These results establish clearly for the first time a reciprocal relationship, on a protein level, between the synthesis of K6/K16 and a differentiation-related keratin pair, K3/K12. Such a relationship strongly suggests a competitive mechanism controlling the synthesis of these two major classes of keratins in the suprabasal compartment. Our results also indicate that although hyperproliferation is usually accompanied by K6/K16 expression, the reverse is not always true. Taken together, the data suggest that K6/K16 are synthesized, perhaps by default, as an alternative suprabasal keratin pair under conditions that are nonpermissive for keratinocytes to express their normal, differentiation-related keratin pairs.

Absence of differentiation-related expression of keratin 10 in early stages of vulvar squamous carcinoma

Using specific monoclonal antibodies (DE-K10 and DE-SCK respectively), the expression of some differentiation-related epidermal keratins was studied in 38 human vulvar squamous carcinomas. In the epidermis, expression of keratin 10 (K10) strictly paralleled the extent of differentiation; it was absent in the basal layer, appeared in the first suprabasal layers and increased in concentration towards the granular layer. However, K10 was rarely detected (1 case out of 12) in early stages of vulvar squamous carcinomas (tumours less than 2 cm, clinical stage I) regardless of the tumour grade. In larger and more advanced tumours (greater than 2 cm, clinical stages II and III), K10 was detected in 21 out of 26 cases. Its expression appeared to be related to maturation of malignant keratinocytes, being preferentially detected in more-differentiated parts. Occasionally however, cells that did not show histological signs of keratinisation were also K10-positive. Modified stratum corneum keratins (recognized specifically by monoclonal antibody DE-SCK) were detected in the most keratinized areas (horn pearls and their close vicinity) of some K10-positive tumours, i.e., in a pattern close to their normal expression in terminally differentiated epidermal cells. These data suggest differences in the regulation of K10 expression during the differentiation processes in the normal keratinising squamous epithelium and in squamous carcinomas. While the normal pattern of vulvar epithelial differentiation is accompanied by an increasing expression of K10, malignant keratinocytes, also when these are histologically moderately or well differentiated, cease expressing this keratin in the early stages of tumour development.

Filaggrin expression in cutaneous and mucosal human papillomavirus induced lesions

A series of 32 human papillomavirus induced lesions derived from epidermis and mucosa was studied for the modulation of filaggrin-profilaggrin (F-PF) expression according to the degree of virus infection as compared to normal skin and mucosa biopsies. This investigation was carried out on frozen sections using indirect immunofluorescence for filaggrin detection and group specific viral antigen and by in situ hybridization with biotinylated probes for viral DNA detection and typing. The 9 cutaneous warts showed an increase of F-PF expression in upper layer cells as compared to normal epidermis, which could be related to the high production of virus (viral antigen and HPV types 1 or 2). The 5 condyloma acuminata displayed also an enhanced expression of these components which was located in several upper layers but virus infection was confirmed in 2 of them with HPV types 6, 11 or 16. The 6 laryngeal papillomas exhibited a granular reactivity pattern for F-PF in suprabasal cell layers with an increase in the upper layers; viral antigen was found in 4 cases and HPV DNA types 6, 11 or 16 were detected in 4 specimens. Conversely among 12 cervical intraepithelial neoplasia, F-PF was expressed only in very superficial layers in few cases, without any correlation with the DNA detection (6, 11 or 16, 18). Taken together these data are suggestive of an intense expression of F-PF in benign lesions which can replicate the virus and a discrete or an absent expression of these components in premalignant or malignant lesions.

Cytokeratin patterns of tissues related to cholesteatoma pathogenesis

Specimens of cholesteatoma matrix, meatal epidermis, and middle ear epithelium were removed during surgery, and immunohistochemical techniques were used to investigate cytokeratin expression. The use of five chain-specific anticytokeratin monoclonal antibodies and one broad specific anticytokeratin monoclonal antibody showed the divergent behavior of middle ear epithelium compared with the cytokeratin expression of the other two types of epithelium. Middle ear epithelium was characterized by the presence of cytokeratins 4, 8, 18, and 19, whereas in both cholesteatoma and meatal epidermis cytokeratin 10 predominated. Furthermore, cholesteatoma showed an infrequent focal presence of cytokeratins 4, 18, and 19. The similarity between cholesteatoma and meatal epidermis with respect to morphology, and the presence of cytokeratin 10 support an epidermal origin of cholesteatoma. However, a metaplastic origin cannot be excluded, because of the infrequent occurrence of a small amount of cytokeratins 4, 18, and 19 in cholesteatoma matrix that was not found in meatal epidermis but was a component of the cytokeratin pattern of middle ear epithelium.

Comparison of cytokeratin, filaggrin and involucrin profiles in oral leukoplakias and squamous carcinomas

As the distribution pattern of cytokeratin (CK), filaggrin and involucrin has recently been suggested to discriminate between benign and malignant epithelial growths, biopsies of healthy oral mucosa, leukoplakias without and with dysplasia and squamous cell carcinomas were examined immunohistochemically using a panel of 4 monoclonal antibodies (AB) against different cytokeratin polypeptides (34 beta E12, KL1 and Pkk1) and filaggrin as well as a polyclonal AB to involucrin. Major and statistically significant differences were observed in the profiles of CKs (except Pkk1), filaggrin and involucrin between leukoplakias without and with epithelial dysplasia. However, the alteration in the expression of CKs, filaggrin and involucrin proved to be not a constant feature in leukoplakias with dysplasia as a considerable portion (20-25%) of them revealed the profiles of CKs, filaggrin and involucrin similar to those of benign leukoplakias, and vice versa. Immunostaining of these antigens did not define the diagnosis of dysplasia in leukoplakias more precisely than grading in conventional histology can do so far. However, immunohistochemical sensitivity in detecting a broad range of variation in the abnormal maturation patterns of keratinocytes in leukoplakias with dysplasia can be used to divide these lesions into subgroups to elucidate their prognosis in follow-up studies.

The use of retinoic acid to probe the relation between hyperproliferation-associated keratins and cell proliferation in normal and malignant epidermal cells

When cells from normal human epidermis and from the human squamous cell carcinoma line SCC-13 were seeded on floating rafts of collagen and fibroblasts, they stratified and underwent terminal differentiation. Although the program of differentiation in SCC-13 cells was morphologically abnormal, the cultures resembled normal epidermal raft cultures by expressing the terminal differentiation-specific keratins, K1/K10, and by restricting their proliferative capacity to the basal-like cells of the population. In addition, the differentiating cells of both normal and SCC-13 raft cultures expressed keratins K6 and K16, which are not normally expressed in epidermis, but are synthesized suprabasally during wound-healing and in various epidermal diseases associated with hyperproliferation. While the behavior of normal and SCC-13 rafts was quite similar when they were cultured over normal medium, significant biochemical differences began to emerge when the cultures were exposed to retinoic acid. Most notably, while the SCC-13 cultures still stratified extensively, they showed a marked inhibition of both abnormal (K6/K16) and normal (K1/K10) differentiation-associated keratins, concomitantly with an overall disappearance of differentiated phenotype. Surprisingly, the reduction in K6/K16 in retinoid-treated SCC-13 cultures was not accompanied by a decrease in cell proliferation. Using immunohistochemistry combined with [3H]thymidine labeling, we demonstrate that while the expression of K6 and K16 are often associated with hyperproliferation, these keratins are only produced in the nondividing, differentiating populations of proliferating cultures. Moreover, since their expression can be suppressed without a corresponding decrease in proliferation, the expression of these keratins cannot be essential to the nature of the hyperproliferative epidermal cell.

Expression of EGF receptor, involucrin, and cytokeratins in basal cell carcinomas and squamous cell carcinomas of the skin

The distribution of several markers of keratinocyte differentiation was studied in normal epidermis, basal cell carcinomas (BCCs), and squamous cell carcinomas (SCCs) using the immunoperoxidase technique on frozen sections of punch biopsy specimens. As markers a panel of chain-specific monoclonal antibodies (MoAbs) directed against cytokeratin (CK) 4, 8, 10, 13, 18 and 19, a polyclonal antiserum against involucrin, as well as a MoAb against the epidermal growth factor (EGF) receptor were used. In 15 out of 19 BCCs tested, expression of CK 8 was seen. Only a few individual cells in a limited number of BCCs showed positive staining for CK 4, 18, or 19. No expression of CK 10 was seen except for some foci of cell keratinization. Involucrin was not found in BCCs except for some squamous horn cysts. In all BCC cells expression of EGF receptor was found. In the suprabasal layers of normal epidermis from SCC patients, positive staining for CK 10 was seen. A few individual cells in a limited number of SCCs showed positive staining for CK 4, 8, or 18. Involucrin was expressed in the center of SCCs and in the upper layers of normal epidermis. Expression of EGF receptor was found in all SCC cells. These results demonstrate differences in cellular origin and differentiation between BCC and SCC.

Expression of hair-related keratins in a soft epithelium: subpopulations of human and mouse dorsal tongue keratinocytes express keratin markers for hair-, skin- and esophageal-types of differentiation

The dorsal surfaces of mammalian tongues are covered with numerous projections known as filiform papillae whose morphology varies in different species. Using a panel of monoclonal antibodies to keratins as probes, we have established that, in both human and mouse, the interpapillary epithelia express mainly the "esophageal-type" keratins, while the papillary epithelia express "skin-type" keratins as well as some keratins reacting with a monoclonal antibody (AE13) to hair keratins. The AE13-reactive proteins of the mouse were found to be very similar to those of authentic mouse hair keratins. However, the corresponding protein of human tongue appears to be different from all known human keratins. This protein has a MW of 51K; it is relatively acidic; it is sulfhydryl-rich, as revealed by iodoacetic acid-induced charge and apparent size shift; it shares an epitope with all the known acidic human hair keratins; and it is associated with keratin fibrils in vivo. This protein may therefore be regarded as a novel type I "hard" keratin. These data establish that mammalian dorsal tongue epithelia can be divided into at least three compartments that undergo mainly "esophageal-", "skin-" and "hair"-types of differentiation. Different keratin filaments, e.g., those of the esophageal- and hair-types, exhibit strikingly different degrees of lateral aggregation, which can potentially account for the different physical strength and rigidity of various cellular compartments. Our data also suggest the possibility that variations in papillary structure in human and mouse may arise from different spatial arrangements of specific keratinocytes, and/or from the expression of specialized hair-related keratins.

Immunohistochemical expression of keratin proteins in urinary bladder carcinoma

Transitional carcinomas of the urinary bladder were examined immunohistochemically for keratin proteins with the use of polyclonal antiserum (TK, 41-65 kDa) and 3 monoclonal antibodies (KL 1, 55-57 kDa; PKK 1, nos. 19, 18, 8; and K 8.12, nos. 16, 13). Umbrella cells gave particularly strong staining for TK, KL 1 and PKK 1, whereas they were negative for K 8.12. Basal- and intermediate-layer cells in urothelial epithelium were moderately positive for all keratins. Brunn's nests cells showed comparatively slight or moderate keratin staining, and K 8.12 staining of Brunn's nests was higher than in urothelial epithelial cells. Transitional carcinoma (grades I and II) indicated uniform keratin distribution, and staining was strong with TK, while that of KL 1, PKK 1 and K 8.12 varied, and grade III tumors showed the lowest intensity of staining. K 8.12 staining in papillary transitional carcinomas was strongly positive in basal located tumor cells, as compared with apical tumor cells. Squamous cell carcinoma was varying positive to keratin reactions dependent on the degree of keratinization. Heterogenity of keratin distribution in papillary transitional carcinomas was given between basal tumor cells and well differentiated tumor cells including umbrella-like cells.

Epidermal hyperproliferation assessed by the monoclonal antibody Ks8.12 on frozen sections

Using the monoclonal antibody Ks8.12 directed against keratins 13 and 16, we have studied psoriatic and trauma-induced hyperproliferation. In normal skin 40 and 64 h after sellotape stripping and in psoriatic lesions, a pronounced suprabasal staining by Ks8.12 was observed. In unstripped normal skin and in the clinically uninvolved skin of psoriatic patients some patchy staining limited to the basal layer was seen. The clear distinction between normal and hyperproliferative skin in keratin expression as detected by Ks8.12 indicates that this antibody may serve as a marker for epidermal proliferation in psoriasis.

Identification of an orthologous mammalian cytokeratin gene. High degree of intron sequence conservation during evolution of human cytokeratin 10

Among the human acidic (type I) cytokeratins, components 10 and 11 are especially interesting, as they are under various kinds of expression control. They are synthesized in the suprabasal cell layers of certain stratified epithelia, notably epidermis, in an endogenous differentiation program; they are expressed in certain epithelial tumours but not in others; they can appear de novo in certain pathological situations such as in squamous metaplasias; and their expression in vivo and in vitro is under positive influence of extracellular calcium concentrations and is reduced in the presence of vitamin A or other retinoids. To provide a basis for studies of the various regulatory elements, we have isolated the human gene encoding cytokeratin 10, using a cDNA probe derived from the corresponding bovine gene, and have sequenced the mRNA coding region as well as adjacent regions approximately 1500 bases 5' upstream and 1000 bases 3' downstream. The eight exons encode a polypeptide 59,535 Mr, i.e. somewhat larger than the corresponding bovine and murine proteins. The deduced amino acid sequences display a high degree of homology, which is not restricted to the exons and the 5' and 3' adjacent regions but, surprisingly, is also evident in the seven introns, some of which contain extended sequence elements with 70% identical nucleotides and more, i.e. similar to the homology in the adjacent exons. This exceptionally high level of conservation of intron sequences is discussed in relation to the recently accumulating evidence of the occurrence of intron sequences important in the regulation of the expression of members of other multigene families during development.

Use of monospecific antisera and cRNA probes to localize the major changes in keratin expression during normal and abnormal epidermal differentiation

We report here the isolation and characterization of three antisera, each of which is specific for a single keratin from one of the three different pairs (K1/K10, K14/K5, K16/K6) that are differentially expressed in normal human epidermis and in epidermal diseases of hyperproliferation. We have used these antisera in conjunction with monospecific cRNA probes for epidermal keratin mRNAs to investigate pathways of differentiation in human epidermis and epidermal diseases in vivo and in epidermal cells cultured from normal skin and from squamous cell carcinomas in vitro. Specifically, our results suggest that: (a) the basal-specific keratin mRNAs are down-regulated upon commitment to terminal differentiation, but their encoded proteins are stable, and can be detected throughout the spinous layers; (b) the hyperproliferation-associated keratin mRNAs are expressed at a low level throughout normal epidermis when their encoded proteins are not expressed, but are synthesized at high levels in the suprabasal layers of hyperproliferating epidermis, coincident with the induced expression of the hyperproliferation-associated keratins in these cells; and (c) concomitantly with the induction of the hyperproliferation-associated keratins in the suprabasal layers of the epidermis is the down-regulation of the expression of the terminal differentiation-specific keratins. These data have important implications for our understanding of normal epidermal differentiation and the deviations from this process in the course of epidermal diseases of hyperproliferation.

Keratin polypeptide expression in mouse epidermis and cultured epidermal cells

Adult mouse epidermis contains up to 11 distinct keratin polypeptides, as resolved by two-dimensional gel electrophoresis. These include both basic (Type II; 67-, 65-, 63-, 62-, and 60-kDa) and acidic (Type I; 61- to 59-, 54-, 52-, 49-, and 48-kDa) keratins that exhibit multiple isoelectric forms. Several, but not all, of these keratins, identified by immunoblotting, were found to be actively synthesized in the skin when assayed in short-term pulse-labeling experiments. When compared to the adult, newborn mouse epidermis expresses fewer keratin subunits. However, greater amounts of keratins associated with differentiated suprabasal cells and stratum corneum, which is more pronounced morphologically in the newborn, were identified. We also observed strain-specific differences in the expression of a Type I acidic keratin. This 61-kDa (pI, approx. 5.3) keratin was produced exclusively by the CF-1 mouse and, based on peptide mapping, appeared to be related to the acidic 59-kDa keratin that was identified in this strain as well as all other mouse strains. The 61-kDa keratin was not expressed in vitamin A-deficient animals, suggesting that its appearance may be related to a retinoid-dependent posttranslational modification. In comparison to keratin expression in vivo, primary mouse keratinocyte monolayer cultures maintained in low Ca2+ (less than 0.08 mM) did not express the terminal differentiation keratins of 67-kDa (basic) or 59-kDa (acidic), although enhanced synthesis of the 60-kDa (basic) and the 52-kDa and 59-kDa (acidic) keratins associated with proliferation were observed. In addition, a subpopulation of nonadherent cells was continuously produced by the primary keratinocyte cultures that expressed the 67-kDa (basic) keratin specific for terminal differentiation. When the keratinocyte cultures were induced to terminally differentiate with Ca2+, the overall pattern of keratin expression was not changed significantly. Taken together, these results provide further evidence for the variable nature of keratin expression in mouse epidermal keratinocytes under different growth conditions.

Immunohistochemical staining patterns of sweat glands and their neoplasms using two monoclonal antibodies to keratins

The staining patterns of normal sweat glands and sweat gland-derived neoplasms using 2 monoclonal antibodies to keratins (Dako-CK1, Cam 5.2) has been assessed. Based on findings in normal glands, the differentiation of these benign neoplasms is considered, with positive evidence for apocrine and eccrine differentiation, and in the latter, differentiation to ductal or secretory type epithelia. This easily applied technique (indirect immunoperoxidase) is suitable for use in routinely processed tissue and employs 2 commercially available monoclonal antibodies. The findings may be of assistance in general surgical reporting of problematic cases.

Sequence analysis of murine cytokeratin endo A (no. 8) cDNA. Evidence for mRNA species initiated upstream of the normal 5' end in PCC4 cells

Keratin 8 (Endo A) is expressed in simple epithelia, together with keratin 18 (Endo B). Filaments formed by this keratin pair are the first cytoskeletal elements induced during mouse embryogenesis. We have isolated Endo A cDNA clones from lambda gt11 libraries prepared with mRNA isolated from PCC4 embryonal carcinoma (EC) cells. Sequencing of three overlapping cDNAs and of a genomic clone allowed us to determine the complete sequence of the Endo A message. Analysis of the protein sequence deduced showed that the Endo A protein presented all the characteristics of intermediate filaments, including an alpha-helical central rod domain and nonhelical N- and C-termini. In the rod domain, the degree of similarity to the other members of the basic keratin family was high. A high degree of homology to keratin 8 of other species was observed, even in the non-helical domains. During these analyses, we found clones extending upstream of the normal 5' end of the mRNA. Sequence comparison between these cDNAs and the 5' upstream region of the Endo A gene suggested that they corresponded to transcripts initiated at an upstream alternative promoter. These observations supported previous results showing the presence of Endo A transcripts initiated upstream of the normal 5' end in mouse morulae and blastocysts.

Aberrant expression during two-stage mouse skin carcinogenesis of a type I 47-kDa keratin, K13, normally associated with terminal differentiation of internal stratified epithelia

Specific keratin cDNA probes and monospecific antikeratin antisera were used to analyze mouse epidermis and epidermal tumors for the expression of a type I 47-kDa keratin, K13, normally associated with terminal differentiation of internal stratified epithelia. We demonstrated that this keratin was virtually absent from the entire body epidermis at various stages of development. Also, it was not detected in various forms of acute and chronic epidermal hyperproliferation or in epidermal cells cultured under conditions that favored either cell proliferation or in vitro differentiation. In contrast, K13 was consistently expressed in squamous cell carcinomas of the skin induced by 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate (TPA), whereas papillomas obtained by the same two-stage protocol were distinctly heterogeneous with regard to the expression of this keratin. These findings were true for two different strains of mice (NMRI and Sencar). Papillomas collected from Sencar mice after 12 wk or from NMRI mice after 15 wk of promotion with TPA were either negative for K13 or elicited variable amounts of this keratin. In all cases of positive expression of K13 in tumors, as in normal stratified internal epithelia, both the keratin protein and its mRNA invariably occurred in the differentiating cell compartments. In contrast to what we found in internal stratified epithelia, however, K13 was expressed without its commonly encountered type II 57-kDa partner, K4. Papillomas negative for the K13 protein were also devoid of K13 transcripts. This indicates that the aberrant K13 expression in tumors is regulated at the level of transcription. Our results suggest that K13 may provide a marker for malignant conversion in the mouse two-stage skin carcinogenesis model and may be especially suited for studies of gene expression regulation.

Keratins of the human hair follicle: "hyperproliferative" keratins consistently expressed in outer root sheath cells in vivo and in vitro

Keratins produced by morphologically distinct compartments of the human hair folicle (hHF) were analysed and compared to those produced by cultured hHF and interfollicular keratinocytes. Five of the major keratins, the basic keratins nos. 5 and 6 (apparent mol. mass 60 and 58 kDa) and the acidic keratins nos. 14, 16, and 17 (51, 49 and 48 kDa), could be labelled in intact hHF and were found in all fractions of the outer root sheath (ORS). The other major keratins, which were not labelled under these conditions (basic-neutral hHbI and -II; 60-62 kDa and acidic hHaI and -II; 40-42 kDa) were associated with hair shaft (hHS) both in the follicle and, virtually unchanged, in the distal part of the hair. Another, previously undescribed, group of proteins with keratin-like properties exhibiting a broad pI-spectrum (basic to slightly acidic: hIC-I, -II, -III, 64-67 kDa; distinctly acidic: hIC-IV, about 54 kDa) was detected in isolated inner root sheath (IRS), in the cuticular material shed from denuded hHS, and also in nail plates. In our experiments only ORS cells grew readily in culture irrespective of their origin from peripheral (mesenchyme-adjacent) or more central ORS-cell layers. In contrast to keratinocytes from interfollicular epidermis (IFE) the cultured ORS cells expressed a keratin set virtually identical to that expressed in vivo. This set also closely resembled that expressed by IFE keratinocyte cultures. The identity of the respective keratins (nos. 5, 6, 14, 16, and 17) present in all these cells in vivo and in vitro was confirmed by tryptic peptide mapping. The data indicated that the microenvironment (in situ) directs the differentiation of ORS cells in a manner comparable to the way it is directed by conventional culture conditions, with consistent expression of the "basal" and "hyperproliferative" set of keratins. This, however, does not exclude the possibility that other types of environmentally induced response may occur, as seen for example during the reepithelialization of superficial skin wounds by ORS cells.

Regulated expression of differentiation-associated keratins in cultured epidermal cells detected by monospecific antibodies to unique peptides of mouse epidermal keratins

Monospecific antibodies to mouse epidermal keratins were generated in rabbits and guinea pigs by injecting synthetic peptides of unique keratin sequences. The sequences were deduced from nucleotide sequences of cDNA clones representing basal (K14) and suprabasal (K1 and K10) cell-specific and hyperproliferative (K6) keratins of both the type-I and type-II subclasses. By applying single-and double-label immunofluorescence analysis, the expression of keratin peptides was analyzed in cultured keratinocytes maintained in the basal or suprabasal cell phenotypes. These cell types were selected by growth in medium containing 0.05 mM Ca2+ (basal cell) or 1.4 mM Ca2+ (suprabasal cell). The cultured basal cells expressed K6 and K14, but less than 1% expressed K1 and K10. Within a few hours after being placed in 1.4 mM Ca2+, K1 expression was observed, and by 24 h, 10%-17% of the cells expressed K1. K10 expression appeared to lag behind K1 expression, with only 5%-10% of cells in 1.4 mM Ca2+ exhibiting K10 immunoreactivity. Double-labeling studies indicated that virtually all K10-positive cells also expressed K1, while only about one-half of the K1-positive cells expressed K10. The treatment of basal cells with retinoic acid at pharmacological concentrations prevented the expression of K1 and K10 when cells were challenged by 1.4 mM Ca2+. Similarly, the introduction of the v-rasH oncogene into basal cells by a defective retroviral vector prevented the expression of suprabasal keratins in 1.4 mM Ca2+ medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Retinoids as important regulators of terminal differentiation: examining keratin expression in individual epidermal cells at various stages of keratinization

When human epidermal cells were seeded on floating rafts of collagen and fibroblasts, they stratified at the air-liquid interface. The suprabasal cells synthesized the large type II (K1) and type I (K10/K11) keratins characteristic of terminal differentiation in skin. At earlier times in culture, expression of the large type II keratins appeared to precede the expression of their type I partners. At later times, all suprabasal cells expressed both types, suggesting that the accumulation of a critical level of K1 keratin may be a necessary stimulus for K10 and K11 expression. Expression of the terminal differentiation-specific keratins was completely suppressed by adding retinoic acid to the culture medium, or by submerging the cultures in normal medium. In submerged cultures, removal of vitamin A by delipidization of the serum restored the keratinization process. In contrast, calcium and transforming growth factor-beta did not influence the expression of the large keratins in keratinocytes grown in the presence of retinoids, even though they are known to induce certain morphological features of terminal differentiation. Retinoic acid in the raft medium not only suppressed the expression of the large keratins, but, in addition, induced the synthesis of two new keratins not normally expressed in epidermis in vivo. Immunofluorescence localized one of these keratins, K19, to a few isolated cells of the stratifying culture. In contrast, the other keratin, K13, appeared uniformly in a few outer layers of the culture. Interestingly, K13 expression correlated well with the gradient of retinoid-mediated disruptions of intercellular interactions in the culture. These data suggest that K13 induction may in some way relate to the reduction in either the number or the strength of desmosomal contacts between suprabasal cells of stratified squamous epithelial tissues.

Distribution of a special subset of keratinocytes characterized by the expression of cytokeratin 9 in adult and fetal human epidermis of various body sites

Biochemical analyses have previously shown that palmar and plantar epidermis, unlike the epidermis of other body sites, contain cytokeratin 9 (Mr 64,000), an unusually large acidic (type I) cytokeratin. Guinea-pig antibodies that specifically and selectively react with bovine and human cytokeratin 9 were used for the immunocytochemical identification of cytokeratin 9 in adult and fetal human epidermis from various body sites. In the epidermis of palms and soles, antibodies against cytokeratin 9 stained a high proportion of the keratinocytes in suprabasal locations. These suprabasal cytokeratin-9-positive keratinocytes were often arranged in vertical columns and concentrated around intraepidermal sweat-gland ducts, but they sometimes also formed extended continuous sheets. In contrast, another type-I component, cytokeratin(s) 10/11, was uniformly distributed among suprabasal keratinocytes. By double-labeling immunofluorescence microscopy using a monoclonal antibody against cytokeratin(s) 10/11, we found that cytokeratin 9 usually appears in cells located one or two layers above the cells in which cytokeratin(s) 10/11 is detected, indicating that most keratinocytes expressing cytokeratin 9 also express cytokeratin(s) 10/11. At other body sites, cytokeratin 9 was only detected in sparsely distributed keratinocytes localized in upper epidermal layers; these cells were scattered or formed small clusters, and often exhibited a conspicuous association with the epidermal portion of eccrine sweat-gland ducts. During human fetal development, cytokeratin 9 was first detected at week 15 of gestation in some suprabasal cells of the foot-sole epidermis and, occasionally, in basal cells. At later fetal stages, most of the cytokeratin-9-positive cells appeared in clusters that were mainly concentrated in glandular ridges and interridges. Our results show that two major types of terminally differentiating keratinocytes can be distinguished in human epidermis, i.e. those that do and those that do not express cytokeratin 9. This special program of keratinocyte differentiation identified by the presence of cytokeratin 9 appears to be related to the morphogenesis of palm and sole epidermis, where this protein is expressed early in fetal life. Possible biological functions of this subset of cytokeratin-9-positive keratinocytes are discussed.

Expression of cytokeratins and vimentin in epithelial cells of normal and pathologic thyroid tissue

The presence of intermediate filament proteins of the cytokeratin and vimentin type was evaluated in normal and pathologically changed thyroid tissue specimens. Using the indirect immunoperoxidase technique with 4 different cytokeratin monoclonal antibodies: RCK114 (broad spectred), K2080 (broad spectred), RGE53 (directed against component 18, present in simple epithelium) and RKSE60 (directed against component 10, associated with keratinization). Co-expression of cytokeratin and vimentin was evaluated with a double immunoenzyme staining technique. The results indicate that normal and transformed cells express cytokeratins of the non-epidermal type. Cytokeratins of the epidermal type are sometimes present in carcinomas. They do not differentiate in tumour type (i.e. papillary, follicular, anaplastic or medullary carcinoma). The co-expression of cytokeratins and vimentin is not restricted to carcinomas: in a small percentage of cases it is also present in normal epithelial cells of the thyroid gland. Moreover, the distribution pattern of cytokeratins and vimentin within the cell is changed in malignant transformed epithelial cells of the gland and seems to be inversely related to the degree of differentiation of these cells. The implications of our findings for the possible use of cytokeratins and vimentin in diagnostic pathology are discussed.

Immunohistochemical study of structural proteins in developing junctional epithelium

The objective of this study was to investigate structural proteins of ameloblasts, reduced enamel epithelium and junctional epithelium using antikeratin antibodies to determine if keratin expression changes as ameloblasts differentiate to cells of junctional epithelium. Block sections of fully erupted, partially erupted and unerupted molar and incisor teeth were removed at necropsy from monkeys age 2, 5, 6 and 7 years. Tissues were fixed in Carnoy's fixative, decalcified in Kristensen's solution for 4 to 8 weeks, embedded in paraffin and sectioned at 5 mu. Representative sections were stained with hematoxylin and eosin. Remaining sections were stained with antikeratin antibodies AE1, AE3, 34 beta E12, 35 beta H11 and anti-40kD using the avidin-biotin-conjugated immunoperoxidase method. Results were analyzed qualitatively for presence or absence of staining products. Antibody 35 beta H11 reacted with ameloblasts and reduced enamel epithelium during the early maturation phase of tooth development but not with the reduced enamel epithelium of erupting teeth or with junctional epithelium. The anti-40kD antibody stained ameloblasts and reduced enamel epithelium of unerupted teeth and teeth erupting through oral epithelium; however, junctional epithelium of partially erupted and fully erupted teeth were unstained. Antibodies AE1, AE3 and 34 beta E12 stained ameloblasts and all layers of reduced enamel epithelium and junctional epithelium in all stages of development. These results suggest a relationship between expression of structural proteins and changes during development and differentiation of ameloblasts to junctional epithelial cells.

Cytokeratin No. 9, an epidermal type I keratin characteristic of a special program of keratinocyte differentiation displaying body site specificity

Plantar epidermis of the bovine heel pad as well as human plantar and palmar epidermis contain large amounts of an acidic (type I) keratin polypeptide (No. 9) of Mr 64,000 which so far has not been found in epidermis of other sites of the body. We present evidence for the keratinous nature of this protein, including its ability to form cytokeratin complexes and intermediate-sized filaments in vitro. We have isolated RNA from plantar epidermis of both species and show, using translation in vitro, that these polypeptides are genuine products of distinct mRNAs. Using immunofluorescence microscopy with specific antibodies against this protein, we demonstrate its location in most cells of suprabasal layers of plantar epidermis as well as in sparse keratinocytes which occur, individually or in small clusters, in upper layers of epidermis of other body locations. We conclude that cytokeratin No. 9 is characteristic of a special program of keratinocyte differentiation which during morphogenesis is expressed in most epidermal keratinocytes of soles and palms but only in a few keratinocytes at other body sites. This example of cell type-specific expression of a member of a multigene family in relation to a body site-related program of tissue differentiation raises important biological questions concerning the regulation of keratinocyte differentiation and morphogenesis as well as the function of such topological heterogeneity within a given type of tissue.