Monoclonal antibody studies of mammalian epithelial keratins: a review

Appearance of the keratin pair K3/K12 during embryonic and adult corneal epithelial differentiation in the chick and in the rabbit

Sequential expression of the K3/K12 keratin pair was studied during epithelial corneal differentiation, using monoclonal antibodies coupled with electrophoretic analysis. In the chick embryo, K12 appears on day 12, while K3 is present at least from day 11. By contrast, in the rabbit embryo, the expression of K12 (at 17 days) precedes that of K3 (at 21 days). In the adult rabbit, K3 is expressed without K12 in part of the limbus. Thus, within the corneal-type keratin pair, either the acidic or the basic partner appears first, according to the developmental stage or the species.

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.

Altered expression of keratin and vimentin in human retinal pigment epithelial cells in vivo and in vitro

Actively proliferating human retinal pigment epithelial (RPE) cells grown in tissue culture possess keratin-containing intermediate filaments that react with a combination of AE1 and AE3 anti-keratin monoclonal antibodies. Antibody reactivity is lost, however, from RPE cells as the cell population ceases to proliferate when it approaches confluence and attains morphological characteristics more similar to those in vivo. In contrast, clone 8.13 anti-keratin antibody stains all cells in the culture at all stages of the growth cycle and cell densities. These findings were reflected in vivo using retinal pigment epithelium taken directly from the eye. Normal non-proliferating RPE cells bound 8.13 antibody to cytoskeletal structures, as judged by indirect immunofluorescence, but did not bind AE1/AE3 antibodies. However, proliferating dedifferentiated RPE cells from the vitreous humor of patients with proliferative vitreoretinopathy possess filaments that bind both AE1/AE3 and 8.13 antibodies. Thus it appears that structures detected by AE1/AE3 antibodies only occur in actively growing RPE cells in vitro and in vivo. Keratins produced by RPE cells were identified using Western blotting. Species with molecular masses of 54 (keratin 7), 52 (keratin 8), 42 (keratin 18), and 40 (keratin 19) kiloDaltons were the most abundant in proliferating cultured cells, but cells isolated directly from the eye were found to lack keratin 7 and 19. Keratin 19 was, however, observed in proliferating RPE cells from some patients with proliferative vitreoretinopathy. The latter findings explain the differential staining observed with AE1/AE3 antibodies in cells in culture and isolated directly from the eye since these antibodies interact primarily with keratin 19 which is absent from non-proliferating RPE cells. In contrast to the presence of keratin-containing intermediate filaments in human RPE cells in vivo, there are apparently no detectable vimentin-containing cytoskeletal structures. However, all RPE cells cultured in vitro develop filaments composed of vimentin which persist in cells that have reached confluence.

Cystic adenoma of the pigmented ciliary epithelium. Clinical, pathologic, and immunohistopathologic findings

A 51-year-old white man was found to have a deeply pigmented mass in the ciliary body and peripheral choroid of his right eye with an associated vitreous hemorrhage. Although the tumor appeared to be a ciliochoroidal melanoma, a melanocytoma and adenoma of the pigment epithelium also were considered in the differential diagnosis. The tumor was removed by a large partial lamellar sclerocyclochoroidectomy. Results of histopathologic evaluation showed a cystic adenoma of the pigmented ciliary epithelium. To the authors' knowledge, this was the first immunohistopathologic study of this tumor. Results of the study showed marked immunoreactivity for low molecular weight cytokeratins, vimentin, and S-100 protein. These immunohistochemical studies are consistent with the origin of this tumor from pigment epithelial cells.

Disruption of keratin intermediate filaments by ultraviolet radiation in cultured human keratinocytes

Fluorescence microscopy has been utilized to investigate the effects of UV irradiation on the organization of keratin intermediate filaments in normal human epidermal keratinocytes. Sun lamp irradiation induced the condensation of keratin intermediate filaments into the perinuclear region and inhibited the reorganization of keratin filaments normally induced by Ca2+. Exposure to UVC appeared to disrupt keratin filaments similarly, whereas UVA had no discernible effect.

Effect of retinoids on hyperproliferation-associated keratins K6 and K16 in cultured human keratinocytes: a quantitative analysis

The keratin patterns of human epidermal keratinocytes cultured on a 3T3-feeder layer in the presence of 10(-8) M non-aromatic (all-trans retinoic acid and 13-cis retinoic acid) and polyaromatic (arotinoid, arotinoid-sulfone, and free arotinoic-acid) retinoids were analyzed by high resolution one- and two-dimensional gel electrophoresis and immunoblotting. Laser densitometric evaluation of one-dimensional gels allowed to quantitate the changes within the keratin patterns and revealed an increase in the expression of keratins K13, K15, and K19 as induced by both non-aromatic and polyaromatic retinoids, except for the parent compound arotinoid. This would then indicate that such keratinocytes are pursuing a more embryonic type of differentiation. In evaluating the data for the hyperproliferation-associated keratins K6 and K16 we noticed an unexpected result: except for all-trans retinoic acid, these two keratins showed opposite responses. As compared to control cultures, the amount of K6 did generally increase, while K16 was reduced, with arotinoid acid being the most effective retinoid. The apparently uncoupled expression of K6 and K16 appeared also to be concentration dependent when 13-cis retinoic acid at concentrations of 10(-9), 10(-8), and 10(-7) M was analyzed. Considering the overall antiproliferative potency of retinoids, we therefore conclude that K16 alone, rather than the pair K6/K16, should be regarded as a proliferation-related keratin and as such may be used as a sensitive marker to evaluate keratinocyte proliferation.

Serum accelerates the loss of type II cell differentiation in vitro

The differentiated phenotype of the alveolar type II cell is rapidly altered in vitro. To evaluate factors that might influence this process, we isolated and plated rat type II cells in serum-supplemented media to promote adherence and then maintained the cells in a simple nutrient medium in the absence (S- cells) or presence (S+ cells) of serum for 5 to 7 d. The type II S- cells remained metabolically active. Despite protein synthesis that was 50% that of S+ cells, S- cells continued to synthesize a broad spectrum of proteins and to express several features of type II cell differentiation. They synthesized an apical integral membrane glycoprotein, Maclura pomifera agglutinin (MPA)-gp200, and a cytokeratin, No. 19, while S+ cells did not. When supplemented with linoleic acid, S- cells contained lamellar and multivesicular bodies, incorporated cell surface MPA into these structures, and secreted their phosphatidylcholine (PC) in response to mastoparan. Despite the relative synthesis of higher levels of total and saturated PC in S- cells supplemented with linoleic acid, phosphatidylglycerol remained diminished. A surfactant protein (SP-A) was present in S- cells, but synthesis was not detected. These studies demonstrate that serum accelerates the loss of type II cell differentiation in vitro and that the expression of type II cell markers of differentiation is not inherently linked.

Immuno-electron microscopic study of keratin distribution in the cochlea using monoclonal antibody

Keratin distribution in the cochlea has been studied immuno-electron microscopically by both pre-embedding and postembedding methods. Keratin immunoreactivity in the guinea pig cochlea was clearly demonstrated in Hensen's cells, the reticular lamina surrounding both outer and inner hair cells, outer and inner pillar cells, Claudius' cells, inner and external sulcus cells, interdental cells of the spiral limbus, Reissner's membrane, border cells, inner phalangeal cells, Deiters' cells, and spiral prominence cells. Keratin expression at the ultrastructural level showed a nonfilamentous keratin system in the cytoplasm of cochlear supporting cells.

Modulation of differentiation and proliferation in human colon carcinoma cells by transforming growth factor beta 1 and beta 2

We have previously characterized the diversity of cellular responses to transforming growth factor (TGF)-beta 1 from human colon carcinoma cells. We now show that morphological alteration and part of the growth-inhibitory responses elicited by growth factor (GF) are associated with the secondary effect of the induction of synthesis of extracellular matrix (ECM) glycoproteins. Specifically, morphological alteration is associated with the ECM glycoprotein laminin, and growth inhibition is associated with both laminin and fibronectin. Both TGF-beta 1 and TGF-beta 2 down-modulate the expression of nucleolar protein B23 (also known as numatrin or nucleophosmin, a positive regulator of cell proliferation). With one exception, the biological effects of both TGF-beta 1 and TGF-beta 2 on these human colon carcinoma cell lines are identical. Both GFs up-modulate the expression of carcinoembryonic antigen (CEA) and CEA-related gene products. However, some of these products are differentially regulated by TGF-beta 1 and TGF-beta 2. The differences in the profile of the induction of these CEA and CEA-related gene products, in the responsive cells, functionally distinguish TGF-beta 1 from TGF-beta 2. Finally, we identified and characterized some of the cellular proteins, the expression of which is up-modulated by GF. These proteins are epithelium-associated, differentiation-related cytokeratins. Both TGF-beta 1 and TGF-beta 2 up-modulate expression of the acidic and basic subtypes of human keratins in the responsive human colon carcinoma cells. Both the responsive and unresponsive cells, however, possess receptors for GFs.

Epithelial cysts in the central nervous system, characteristic expression of cytokeratins in an immunohistochemical study

Nineteen epithelial cysts in the central nervous system including six colloid cysts of the third ventricle, seven Rathke's cleft cysts in the sella, two enterogenous cysts in the posterior fossa, two epithelial cysts in the spinal canal and two neuroectodermal cysts in the cerebrum were examined immunohistochemically for expression of intermediate filament proteins-simple type, stratified type and skin type cytokeratins and GFAP. Colloid cysts of the third ventricle, Rathke's cleft cysts in the sella and epithelial cysts in the spinal canal expressed complex type cytokeratins while enterogenous cysts and neuro-ectodermal cysts showed only simple type cytokeratins. In addition, Rathke's cleft cysts expressed GFAP in occasional lining cells. The characteristic composition and distribution of cytokeratins in various kinds of epithelial cysts in the central nervous system are demonstrated and discussed with regard to their origins.

Cultured epidermal autografts and allografts: a study of differentiation and allograft survival

Cultured epidermal sheets were examined before and at various times after grafting on skin ulcer beds. Before grafting, the sheet consisted of four to five layers of keratinocytes with incomplete differentiation. Ten days after grafting, graft recipient sites showed compact hyperkeratosis, a normal-appearing epidermis, and a flat dermoepidermal junction. At 6 months, the stratum corneum had a basket-weave appearance but the dermoepidermal junction remained flat. Monoclonal antibodies to keratins 14 and 10 showed normal basal and suprabasal localization, respectively. Electron microscopy showed a normal basement membrane with anchoring fibrils. LH7:2, a monoclonal antibody that binds to the type VII collagen molecule, stained the dermoepidermal junction in all biopsy specimens. AE-1, an antibody that stains suprabasal cells in hyperproliferative skin, was expressed suprabasally for up to 12 weeks after healing (16 weeks after grafting), but expression was confined to the basal layer at 18 weeks after healing (6 months after grafting). Anti-involucrin staining was found in the deeper layers of the epidermis up to 12 weeks after healing (16 weeks after grafting) but had receded to a normal distribution in upper spinous and granular layers at 18 weeks (6 months after grafting). Overall, the histologic patterns observed in recipient sites during the first 4 months after grafting resembled those observed for 10 to 14 days in newly healed epidermis and in hyperproliferative states such as psoriasis. In four sex-mismatched graft sites, specimens were reacted with a biotinylated probe to the Y chromosome by in situ hybridization. Lack of Y chromosome-positive cells suggested that host keratinocytes had replaced the allografts. Multilocus DNA analysis in one patient confirmed this observation. Our data suggest that an altered state of epithelial maturation persists for several months after culture grafting, with restoration of the normal pattern by 6 months. No differences were detected between autografted and allografted sites.

New approaches and concepts in the study of differentiation of oral epithelia

Epithelial structural proteins, the keratins and keratin-associated proteins, are useful as markers of differentiation because their expression is both region-specific and differentiation-specific. In general, basal cells in all stratified oral epithelia express similar keratins, while the suprabasal cells express a specific set of markers indicating commitment to a distinct program of differentiation. Critical factors in the regulation of epithelial protein expression are now under investigation. The promoter regions of keratin genes are being characterized to determine what sequences within the genes are responsible for differential expression. One important extracellular factor that influences epithelial protein expression is retinol (vitamin A), which exerts its effects via a group of nuclear receptor proteins that may also be expressed in a region-specific manner. These molecular biological approaches enhance our understanding of the mechanisms regulating differentiation of oral epithelia and its regional complexity.

Variable keratin polypeptide profile in human stratum corneum

Stratum corneum samples obtained from 46 members in three generations of seven families were analyzed for keratin pattern by gel electrophoresis. All these samples of apparently normal upper arm skin expressed the 55 kDa, 56.5 kDa, and 65 kDa keratin proteins; while only 28%, 20% and 48% of the samples expressed the 50 kDa, 58 kDa, and 67 kDa proteins, respectively. The keratin phenotype was identical in all members of two families (9 individuals) and variable in members of five other families (37 individuals), in whom the patterns were consistent with autosomal dominant inheritance. These results demonstrate inter-individual variations in stratum corneum keratin pattern and may reflect either polymorphism of genes coding for the various keratin polypeptides or a post transcriptional modification of mature keratins by proteolytic digestion.

Alveolar epithelial cell keratin expression during lung development

Defining the expression and organization of keratins has provided insight into epithelial cell differentiation during tissue development and remodeling. We have used monoclonal antibodies to examine keratin distribution in lung epithelial cells in the rat from the preglandular phase of gestation to the adult. Of particular interest were the distributions of keratin No. 18 and keratin No. 19, since previous results have suggested these keratins may be important in alveolar epithelial cell transitions occurring in adult remodeling lung and in cultured type II cells. The epithelial tubes at 15 days of gestation do not react with 24A3 monoclonal antibody to keratin No. 18, nor is this antigen apparent by gel or immunoblot analysis. Staining is apparent at day 16, however, showing a light punctate pattern at the basal edge of the cells, and becomes prominent by day 17, with intensity greatest in the larger airway tubes. The intensity and number of cells in the parenchyma staining with 24A3 peaks at postnatal days 5 to 10, when proliferation and cytodifferentiation of type I and type II cells is most active. In the adult, staining of type II cells is present mainly at the cell periphery, and occasional reactive attenuated type I-like cells can be observed. Keratin No. 19 immunoreactivity is not present in the primitive epithelial tube until 19 days' gestation but predominantly stains type II pneumocytes in the adult rat lung throughout the entire cell. AE3 antibody to basic keratins stains similarly to keratin No. 19. We conclude that keratin No. 18 is expressed at high levels in type II cells during development in periods of intense proliferation and alveolarization. This correlates with our previous observations on keratin expression following bleomycin lung injury.

Human oral epithelial cell culture. II. Keratin expression in fetal and adult gingival cells

Epithelial cells from human fetal and adult gingiva were cultured in keratinocyte growth medium (KGM), a serum-free medium. The expression of keratin proteins in these cells was evaluated using immunohistochemistry and SDS-PAGE-immunoblot analysis and compared with expression in the tissue. Keratins 5, 6, 14, 16, and 19 were identified in cells cultured from both fetal and adult tissues. K19 was localized in basal cells of fetal oral tissue but was not seen in adult gingiva (except for scattered Merkel cells). K1 and K10 were expressed in tissue, but not in cultured cells. The keratin profiles of cultured epithelial cells from several adult donors were similar and were identical in cultures from primary through Passage 5. K13, a differentiation-specific keratin, was expressed in all suprabasal cells of fetal oral epithelium, but shows only spotty expression in adult gingival tissue. K13 was expressed in cultures of fetal cells, but very weakly or not at all in cultures of adult cells. K13 expression was greater in cultures grown with physiologic calcium concentrations (1.2 mM) than in those grown at 0.15 mM or less. Our findings are consistent with basal-like characters of these cells in 0.15 mM calcium growth conditions. Differentiation of fetal oral cells in culture to the suprabasal basal cell stage in 1.2 mM Ca2+ is shown by the expression of K13.

Differential extraction of keratin subunits and filaments from normal human epidermis

We have investigated keratin interactions in vivo by sequentially extracting water-insoluble proteins from normal human epidermis with increasing concentrations of urea (2, 4, 6, and 9.5 M) and examining each extract by one- and two-dimensional gel electrophoresis, immunoblot analysis using monoclonal anti-keratin antibodies, and EM. The viable layers of normal human epidermis contain keratins K1, K2, K5, K10/11, K14, and K15, which are sequentially expressed during the course of epidermal differentiation. Only keratins K5, K14, and K15, which are synthesized by epidermal basal cells, were solubilized in 2 M urea. Extraction of keratins K1, K2, and K10/11, which are expressed only in differentiating suprabasal cells, required 4-6 M urea. Negative staining of the 2-M urea extract revealed predominantly keratin filament subunits, whereas abundant intermediate-sized filaments were observed in the 4-urea and 6-M urea extracts. These results indicate that in normal human epidermis, keratins K5, K14, and K15 are more soluble than the differentiation-specific keratins K1, K2, and K10/11. This finding suggests that native keratin filaments of different polypeptide composition have differing properties, despite their similar morphology. Furthermore, the observation of stable filaments in 4 and 6 M urea suggests that epidermal keratins K1, K2, and K10/11, which ultimately form the bulk of the protective, nonviable stratum corneum, may comprise filaments that are unusually resistant to denaturation.

Keratin filaments of epithelial and taste-bud cells in the circumvallate papillae of adult and developing mice

Keratin filaments of epithelial- and taste-bud cells in the circumvallate papillae of adult and developing mice were studied by immunocytochemistry using monoclonal antikeratin antibodies (PKK2 and PKK3) and by conventional electron microscopy. Elongated cells (type-I, -II, and -III cells) of the taste buds were stained by PKK3 antibody, which reacts with 45-kdalton keratin, whereas basal cells of the taste buds and surrounding epithelial cells showed negative staining with PKK3. Such PKK3-reactive cells occurred at 0 day after birth, when taste-buds first appeared in the dorsal surface epithelium of the papillae. Thus 45-kdalton keratin seems to be an excellent immunocytochemical marker for identifying taste-bud cells. Epithelial cells in all layers of the trench wall and basal layer cells of the dorsal surface contained densely aggregated bundles of keratin filaments that reacted with PKK2 antibody, but not with PKK3. In contrast, taste-bud cells and spinous and granular layer cells of the dorsal surface possessed loose aggregated bundles of filaments that reacted with PKK3, but not with PKK2. These results suggest that the aggregation and distribution pattern of keratin filaments may reflect differences in the keratin subtypes that comprise these filaments.

Differential cytokeratin expression in normal, hyperplastic and malignant epithelial cells from human prostate

Studies were undertaken to define the expression of cytokeratins in normal, hyperplastic and malignant epithelial cells from human prostate. Cytokeratin (CK) polypeptides, separated by two-dimensional electrophoresis, were identified by immunoblotting with CK-specific monoclonal antibodies. CK polypeptides 5, 7, 8, 15, 18 and 19 were identified in fresh normal and hyperplastic prostate. Expression of CK 15 has not been previously reported in human prostate. Analysis of central and peripheral zone tissues from human prostate did not reveal qualitative differences in CK expression between these areas. Epithelial cells harvested from fresh BPH tissue by percoll gradient centrifugation and propagated in vitro using selective culture techniques showed alterations in CK expression compared to intact human prostate. Specifically, CKs 6, 14, 16 and 17 were noted in cultured BPH epithelial cells but not fresh normal prostate or BPH tissue. Immunoblot analysis of the established prostate cancer cell lines PC3, DU145 and LNCAP showed expression of CKs 8 and 18 but not CKs 5, 7 and 15 which were observed in benign prostate. These studies further characterize CK expression in benign and malignant human prostate and provide insights which may be useful in differentiating normal, hyperplastic and malignant epithelial cells in the human prostate gland.

Stratum corneum antibodies detected by hemagglutination are not directed against keratin intermediate filaments

Autoantibodies to stratum corneum (SC) occur in virtually all normal adult human sera. These antibodies may be directed against various antigens of the SC. They have been detected by indirect immunofluorescence, passive hemagglutination (HA), immune adherence, and most recently by enzyme immunoassay and immunoblot methods. The purpose of our study was to examine whether antibodies to SC antigens as detected by passive HA are similar to the keratin intermediate filament (KIF) reactive antibodies. SC antigen preparation was prepared from psoriatic scales by the trypsin-phenol-water (TPW) extraction method. KIFs were prepared by 8 M urea extraction of normal callus or psoriatic scales. The anti-SC antibody titers of normal human sera were determined by passive HA before and after absorption with TPW-SC antigen preparation and upon absorption with KIFs. Similarly, titers of anti-KIF antibodies were determined on absorbed and unabsorbed sera by immunoblot assay. The results of this study indicate that the absorption of the sera with KIFs did not affect the titer of antibodies to TPW-extractable SC antigens whereas the titer of KIF antibodies dropped. KIF-reactive antibodies, on the other hand, were not affected by absorption with TPW-SC antigen, whereas the latter absorbed out the corresponding reactive antibodies. These results indicate that antibodies directed against SC antigen are different from the KIF-reactive antibodies.

Immunohistochemical characterization of epithelial cells in human lacrimal glands. I. Normal major and accessory lacrimal glands

Expression patterns of cytokeratins (CKs), actin, lactoferrin (Lf), lysozyme (Ly), vimentin, and S-100 protein were immunohistochemically examined in paraffin sections from eight normal major and accessory lacrimal glands (LGs). Luminal duct cells and a number of secretory cells stained with the antibodies (ABs) KL1 and Pkk1 (CK 7, 8, 17, 18), while basal duct and myoepithelial cells reacted with the AB 34 beta E12 (CK 5). Myoepithelial cells expressing CK 5 and actin were restricted to acini and intralobular ducts, and their number was greater in major LGs than accessory ones. Lf and Ly were found in 50%-75% of acini and intralobular ducts. Vimentin was absent in parenchyma of LGs. S-100 protein reaction was observed in a number of acinar and luminal duct cells of major LGs whereas epithelia of accessory LGs remained negative. Distribution patterns of CKs, Lf, and Ly in major and accessory LGs are identical. The difference with respect to the number of myoepithelial cells as well as S-100 protein reactivity between major and accessory LGs reactivity appeared to be relevant to the differences in their secretory mechanisms and local environment.

Heterogeneity in harlequin ichthyosis, an inborn error of epidermal keratinization: variable morphology and structural protein expression and a defect in lamellar granules

Skin biopsies and scale samples from nine infants and one fetus affected with harlequin ichthyosis (HI) were obtained from eight families. Epidermal differentiation was examined by morphologic and biochemical criteria and cell culture studies. Two striking abnormalities were identified; first, keratin and filaggrin expression were abnormal and varied between cases, and, second, in all cases lamellar granules were absent or abnormal, and intercellular lamellae within the stratum corneum were absent. Three HI phenotypes were distinguished by variable expression of epidermal structural proteins. Cases were classified by the absence (type 1) or presence (types 2 and 3) of keratins K6 and K16 ("hyperproliferative" keratins) and by the presence of profilaggrin in the interfollicular epidermis (types 1 and 2 only). Profilaggrin is apparently not converted to filaggrin, but it is retained in the scale. The block in profilaggrin processing may be due to an inactive phosphatase. Siblings in two families (presenting with types 1 and 2) showed the same type classification suggesting that expression of the phenotype is consistent within families but differs between families. Cultured HI keratinocytes were normal by phase microscopy, but abnormal by electron microscopy with no lamellar granules and extensive stacking of the upper layers. We conclude that harlequin ichthyosis is a genetically heterogeneous group of disorders with altered lamellar granules, intercellular lipids, and variation in expression and/or processing of structural protein markers of normal epidermal keratinization. Furthermore, the lamellar granule and structural protein defects may be indirectly related via a mechanism involving phosphorylation/dephosphorylation.

Human nasal epithelium: characterization and effects of in vitro exposure to sulfur dioxide

Human nasal turbinate tissue from surgical specimens was dissected free of connective tissue, and primary epithelial cultures were established by explant techniques. Transmission electron microscopy revealed that cultured cells retained homogeneous cytoplasmic granules, tonofilaments, and desmosomes and formed a homogeneous monolayer. The epithelial cells stained positively with cytokeratin antibodies AE1, AE3, and 35BH11 but failed to stain with two other cytokeratin antibodies, AE2 and 34BE12. Staining was also positive with anti-desmoplakin I and II but negative with antivimentin (43BE8), anti-desmin, and anti-human factor VIII antibodies. Cultured cells were exposed to filtered air or sulfur dioxide at 1-5 ppm for 30-60 min. Although there was no increase in cell lysis as measured by chromium-51 release, SO2 exposure significantly inhibited [3H]leucine incorporation compared to air exposure. This effect was dependent on both SO2 concentration and exposure duration. Control experiments revealed that these SO2 effects were not caused by the [H+] load produced by SO2 exposure. Electron microscopy of cells exposed to air or SO2 did not show any significant morphological differences.

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.

Cytokeratins and cytokeratin filaments in subpopulations of cultured human and rodent cells of nonepithelial origin: modes and patterns of formation

Using immunofluorescence microscopy, we observed that in several established cell culture lines derived from different nonepithelial tissues and species, cells spontaneously emerge, usually at low frequencies, which contain cytoplasmic structures decorated by antibodies specific for cytokeratins 8 and 18. This phenomenon was further examined at both the protein (gel electrophoreses of cytoskeletal proteins, followed by immunoblotting) and the RNA (Northern blots, "nuclear run-on" analysis, in situ hybridization) level. Positive cell lines included simian virus (SV40)-transformed human fibroblasts (HF-SV80, WI-38 VA13), human astrocytic glioma cells (U333 CG/343MG), rat (RVF-SMC) and hamster (BHK-21/13) cells derived from vascular smooth muscle and murine sarcoma MS-180 cells. In two cell lines (HF-SV80 and BHK-21/13), the frequency of the cytokeratin-containing cells and of the cytokeratin fibril arrays per cell was drastically increased upon treatment with 5-azacytidine. The structural appearance of the cytokeratins was variable in the different cell lines but could also differ among cells of the same culture: While small granular or comma-shaped structures or bizarrely shaped filament arrays prevailed in WI-38, RVF and normally grown BHK-21 cells, most of the other lines revealed extended normal-looking, fibrillar arrays. In one line (MS-180), the appearance of cytokeratins was associated with a morphological change, as it was only found in a subpopulation of cells that had lost their typical elongated and spindle-shaped phenotype and assumed a rounded ("coccoid") shape. Our results show that the expression of the genes encoding cytokeratins 8 and 18 is not necessarily restricted to programs of epithelial differentiation and that factors stochastically effective appear in cultured cell lines that allow the synthesis of these cytoskeletal components. Mechanisms possibly involved in this spontaneous and selective advent of cytokeratins 8 and 18 and implications for tumor diagnosis are discussed.

Spontaneous losses of control of cytokeratin gene expression in transformed, non-epithelial human cells occurring at different levels of regulation

Intermediate filaments (IFs) of the cytokeratin (CK) type are cytoskeletal elements typical for epithelial differentiation. However, in diverse transformed culture lines of non-epithelial origin, rare cells emerge spontaneously, which synthesize, in addition to their vimentin IFs, CKs 8 and 18. We enriched such cells by cloning and studied the level(s) of regulation at which these changes occur. We found that in SV40-transformed fibroblasts the CK 18 gene is constitutively transcribed into translatable mRNA but that the protein is rapidly degraded in the absence of its complex partner, CK 8. In contrast, cells immunocytochemically positive for CK IFs contained both CKs 8 and 18, which apparently stabilized in heterotypic complexes. These findings and related observations of active genes for CKs 8 and/or 18 in several other transformed non-epithelial cell lines indicate that the genes for CKs 18 and, less frequently, 8 can be active in diverse different non-epithelial cell lines; synthesis of type I and type II CK pair partners can be uncoupled; control of CK IF formation can take place at different levels. We suggest that the intrinsic instability of the inactive state of these genes is responsible for the occurrence of CKs 8 and 18 in certain non-epithelial tissues and tumors, a caveat in tumor diagnosis.

Isolation of subpopulations of murine epidermal cells using monoclonal antibodies against differentiation-related cell surface molecules

Monoclonal antibodies (mAbs) against epithelial cells were prepared by immunization of rats with lyophilized murine epithelia. Screening against tissue sections and epithelial cell suspensions permitted identification of mAbs against surface molecules that are expressed early in cell differentiation. Staining with these mAbs followed by fluorescence-activated cell sorting enabled isolation of subpopulations of basal epithelial cells. Staining these subpopulations with antibodies against known differentiation markers (cytokeratins and bullous pemphigoid antigen) and measurements of cell size indicated that they represented fractions of the basal cell population in sequential stages of early differentiation. Labeling mice with bromodeoxyuridine at various times prior to cell isolation showed that the least-differentiated basal cells cycle more slowly than those at later stages, data which support the concept of a differentiation-related, hierarchical pattern of organization of the proliferative compartment.

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.

Keratin protein expression during the development of conducting airway epithelium in nonhuman primates

Keratin protein expression during the development of Rhesus monkey conducting airway epithelium was investigated by both biochemical and immunohistochemical methods. Keratin proteins were extracted from tracheal and intrapulmonary airway tissues of fetal (at 80- and 140-day gestational ages), neonatal, and adult animals. Using immunoblot analyses and immunohistochemistry with various monoclonal (AE1, AE3, AE8, 6.01 and 6.11) and monospecific antibodies (anti-50/55 and anti-40 kDa), the presence of keratins 5, 6, 8, 13, 14, and 19 in adult airway epithelium were demonstrated. Except for keratin 13 (51 kDa), the remaining keratins could be immunologically detected in fetal and neonatal tissues. To further understand the nature of the synthesis of keratin 13 during development, airway epithelial cells from different ages were isolated and cultured in vitro. Cultured cells were labeled with 35S-methionine, and the patterns of keratin protein were analyzed by one- and two-dimensional sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Results indicated that the cultured airway cells synthesized additional keratins including 7, 15, 16, 17, and 18. However, consistent with the in vivo finding, fetal cells synthesized less or no keratin 13. These in vivo and in vitro studies strongly suggest that the synthesis of the keratin 13 in monkey conducting airway epithelium is developmentally regulated.

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

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

A rat liver 57-kDa protein is identified to share antigenic determinants with statin, a marker for nonproliferating cells

The nuclear protein statin, found uniquely in nonproliferating cells, has been previously identified by mouse monoclonal antibodies designated as S-30 and S-44. We report here the screening of various rat tissues for proteins cross-reacting with these antibodies. As revealed by immunoblotting, two polypeptides (mol wt 80 and 57 kDa) and a group of lower-molecular-weight proteins migrating between 34 and 38 kDa were found to react with the anti-statin antibodies. The most prominent immunoreactivity was observed with a 57-kDa protein present in rat liver. Upon further fractionation of the liver protein extract with ammonium sulfate [(NH4)2SO4] the 57-kDa protein, designated as rat liver protein 57 or RLp57, was detected independently with both anti-statin antibodies in the 30 to 60% (NH4)2SO4 fraction. In order to determine whether rat liver protein 57 is indeed specifically recognized by anti-statin antibody S-44, we used RLp57 transferred onto nitrocellulose paper as a specific substrate for the adsorption of the S-44 antibody from ascites fluid. As shown by indirect immunofluorescence microscopy the solution remaining after adsorption failed to stain human fibroblasts. The adsorbed immunoglobulin, however, upon elution revealed statin-specific nuclear staining activity on senescent fibroblasts. These findings suggest that rat liver protein 57 and the human fibroblast statin share similar antigenic determinants recognized by the statin-specific S-44 antibody. Our results indicate furthermore that the statin previously identified in fibroblasts may represent one member of a group of several antigenically related proteins detectable with specific anti-statin antibodies.

Immunoenzyme techniques in dermatopathology

The advantages and disadvantages of the immunofluorescence and immunoperoxidase techniques and an introductory description of the major variations of the basic immunoperoxidase method are discussed. The ability to identify intermediate filaments, T and B lymphocyte cell markers, S-100 proteins, myelin basic protein, and carcinoembryonic antigen in tissue sections can assist the dermatopathologist in classifying undifferentiated or histologically similar-appearing tumors. A systematic approach to the diagnosis of a majority of these tumors with the use of immunoenzyme staining is provided.

Two type II keratin genes are localized on human chromosome 12

Human genomic DNA containing two type II keratin genes, one coding for keratin 1 (K1, a 68-kD basic protein) and another closely linked type II gene 10-15 kb upstream (K?, gene product unknown), was isolated on a single cosmid clone. EcoRI restriction fragments of the cosmid were subcloned into pGEM-3Z, and specific probes comprising the C-terminal coding and 3' noncoding regions of the two genes were constructed. The type II keratin genes were localized by in situ hybridization of the subcloned probes to normal human lymphocyte chromosomes. In a total of 70 chromosome spreads hybridized with the K? probe (gHK?-3', PstI, 800 bp), 36 of the 105 grains observed were on chromosome 12, and 32 of these were clustered on the long arm near the centromere (12q11-13). In 100 labeled metaphases hybridized with the K1 probe (gHK1-3', BamHI-PstI, 2100 bp), 53 grains localized to chromosome 12 and 46 of these were found in the same region (q11-13). Therefore, both the gene for human keratin 1, a specific marker for terminal differentiation in mammalian epidermis, and another closely linked unknown type II keratin gene (K?, 10-15 kb upstream of K1) are on the long arm (q11-13) of human chromosome 12.

Immunohistochemical distribution of keratin proteins in clinically healthy human gingival epithelia

In clinically healthy/subclinically inflamed biopsies of marginal gingiva, the immunohistochemical distribution of keratin proteins was studied in junctional (JE), sulcular (SE), oral gingival (OGE) and in a few samples of alveolar mucosal epithelium (AE) by means of various mouse monoclonal anti-keratin antibodies in an indirect fluorescence technique. All regions stained in a nearly similar way with AE3 (keratins 1-8, all cells) and BE14 (keratin 5, basal and supra/parabasal cells). AE8-staining (keratin 13, supra/parabasal and spinous cells) was primarily confined to the stratified, nonkeratinized epithelia SE and AE, but also a variable part of JE and less frequently OGE were positive. The parakeratinized OGE was distinct in showing a homogeneous staining with AE2 (keratins 1/2, 10) and AE5 (keratin 3) throughout spinous cell layers. These antibodies did not stain JE and AE whereas SE stained in a scattered way with AE5 and sometimes also with AE2. The latter finding might indicate initial keratinization at molecular level. The JE was distinct in retaining basal characteristics throughout the epithelium with PKK2 (keratin 7, 16, 17, 19) and BE14 (keratin 5) although some initial suprabasal maturation, as observed with AE8, cannot be excluded. Differences in keratin staining of gingival epithelia and the AE was found with respect to AE1-reactivity (keratins 10, 14-16, 19) which was suprabasal in JE, SE and OGE but basal in AE.

Distribution of cytokeratin polypeptides in epithelia of the adult human urinary tract

Cytokeratin expression was studied in the epithelia lining the normal human urine conducting system using immunohistochemistry on frozen sections employing a panel of 14 monoclonal antibodies. Eleven of these anticytokeratin antibodies reacted specifically with one of the 19 human cytokeratin polypeptides. Profound differences were found in the cytokeratin expression patterns between the different types of epithelium in the male and female urinary tract. In the areas showing morphological transitions of transitional epithelium to columnar epithelium and of nonkeratinizing squamous epithelium to keratinizing squamous epithelium gradual shifts of cytokeratin expression patterns were observed, often anticipating the morphological changes. However, also within one type of epithelium, i.e. the transitional epithelium, two different patterns of cytokeratin expression were found. Expression of cytokeratin 7 was homogeneous in the transitional epithelium of renal pelvis and ureter but heterogeneous in the transitional epithelium of the bladder. Furthermore, intraepithelial differences in cytokeratin expression could be shown to be differentiation related. Using a panel of chain-specific monoclonal antibodies to cytokeratins 8 and 18 conformational and/or biochemical changes in the organization of these intermediate filaments were demonstrated upon differentiation in columnar and transitional epithelium.

An immunocytochemical study of cytokeratin expression in human middle ear cholesteatoma

An indirect immunofluorescent method with monoclonal anti-cytokeratin antibodies was used to localize various cytokeratins in human middle ear cholesteatoma. The 50 K/58 K and 56.5 K/65-67 K paired cytokeratins are markers of skin type and were found in the specimens of human middle ear cholesteatomas studied. In contrast, the 40 K and 45 K cytokeratins (markers of simple epithelia), the 48 K cytokeratin (marker of hyperproliferative epidermal disease) and the 51 K cytokeratin (marker of internal organ epithelia) were absent in human middle ear cholesteatoma. These findings indicate that the pattern of cytokeratins in human middle ear cholesteatoma is similar to that of skin but is different from those of simple epithelium, internal organ epithelia, and hyperproliferative epidermal disease. These findings also support the skin type epithelial origin of cholesteatoma and strongly favor the migration theory in the genesis of cholesteatomas.

Abnormal organization of keratin intermediate filaments in cultured keratinocytes of epidermolysis bullosa simplex

Distinctive abnormality in the organization of keratin intermediate filaments (KIFs) was found for the first time in cultured epidermal keratinocytes from two patients with hereditary epidermolysis bullosa simplex (EBS), which showed cleavages above the basement membrane zone due to the fragility of basal cells. KIFs in EBS keratinocytes revealed an irregular radial arrangement composed of sparse but thick KIF bundles. Furthermore, these KIF bundles in many cells changed into numerous ball-like keratin aggregates and disappeared beyond these keratin aggregates in the peripheral cytoplasm. Electron microscopy of cultured EBS keratinocytes showed that many ball-like structures consisting of fine filaments or granules or homogeneous substances were scattered in the peripheral regions of the cell attaching to the dish, and intermediate filaments appeared to be emanating from or surrounding the structures. These ball-like keratin aggregates have never been observed in normal human keratinocytes.

Relationship between tektins and intermediate filament proteins: an immunological study

Affinity-purified antibodies raised against three flagellar tektins (tektin A, B, and C) from each of two sea urchin species (Lytechinus pictus and Strongylocentrotus purpuratus) were used to study the immunological relationship between tektins and intermediate filament proteins. By immunofluorescence microscopy, several antitektins revealed a staining of intermediate filament-like arrays in three vertebrate cell lines tested. Immunoelectron microscopy substantiated the cross reaction of antitektins with intermediate filaments. When the cells were treated with cytochalasin B, the arrangement of the filaments recognized by anti-(Lp)-tektin B was altered; the alteration observed is typical for keratin filaments. By immunoblot, it was found that anti-(Lp)-tektin B cross reacted with two isoforms or different proteins of approximately 54 kD with pIs of 6.1 and 6.2 in human carcinoma epithelia (HeLa) cells and with two isoforms or different proteins of approximately 55 kD with pIs of 6.1 and 6.3 in pig kidney epithelia (LLC-PK1) cells. Furthermore, when antitektin antibodies were affinity purified with the 54 kD HeLa keratin, these keratin-specific antibodies again restained the original tektins on immunoblots. From these observations, it can be concluded that tektins and keratins are to a certain extent immunologically related. To determine the degree of the immunological relationship, tektin filaments and purified intermediate filaments from HeLa cells were cleaved with alpha-chymotrypsin and examined by quantitative immunoblot analysis. On immunoblots of digested tektins from L. pictus, anti-(Lp)-tektin B recognized several cleavage products in the range of 20 kD to 46 kD. However, when immunoblots of digested intermediate filaments from HeLa cells were probed, the cross reaction of anti-(Lp)-tektin B with HeLa keratins was eliminated by more than 98% within 2 min, suggesting that tektins have epitopes in common with the end domains of certain keratins.

Immunohistochemistry of cytokeratin proteins in squamous and transitional cell lesions of the urinary tract

Expression of low and high molecular weight cytokeratin proteins was investigated immunohistochemically in a variety of transitional and squamous epithelial lesions of the urinary tract with and without schistosomiasis. The monoclonal antibodies used were CAM 5.2 and NCL5D3 for low, PK 63 and 121 for high, and MAK 6 for a broad range of intermediate molecular weight cytokeratins. On staining with CAM 5.2 and NCL5D3, urothelial hyperplasias (n = 12) and grades 1 (n = 5) and 2 (n = 10) papillary transitional cell carcinomas showed labelling patterns quite distinct from carcinoma in situ (n = 4) and non-papillary grades 2 (n = 6) and 3 tumours (n = 3). Among squamous lesions only focal positivity was obtained in 14 of 22 moderate to poorly differentiated squamous cell carcinomas. By contrast, PK 63 and 121 stained squamous lesions exclusively. MAK 6 stained the whole range of urothelial and squamous lesions with the exception of squamous metaplasias. Polyclonal antikeratin adequately labelled spindle cell areas of high grade tumours. The distinctive staining patterns given by these or similar antibodies may help in the identification of squamous metaplasia and in diagnosing tumours of the urothelium.

The pattern of cytokeratin synthesis is a marker of type 2 cell differentiation in adult and maturing fetal lung alveolar cells

During the last stages of fetal life, the immature epithelial cells of the rat lung alveolus develop the properties of mature type 2 cells. Adult type 2 cells rapidly lose these same properties when isolated and maintained in cell culture. We have examined the synthesis of cytokeratin proteins by adult type 2 cells as they lose their differentiated characteristics during 1 week in culture, and of immature fetal alveolar epithelial cells as they differentiate either in utero or when cultured on an extracellular matrix. Freshly isolated adult type 2 cells synthesize four cytokeratins which by electrophoretic mobilities and Western blot analysis correspond to human cytokeratins Nos. 7, 8, 18, and 19. During 7 days in culture synthesis of cytokeratin No. 19 is dramatically decreased and cytokeratin No. 18 becomes the predominant acidic cytokeratin produced. Fetal lung epithelial cells at 18 days gestation lack most characteristics of mature type 2 cells. When freshly isolated, these cells synthesize cytokeratins Nos. 7, 8, and 18 but make only minimal amounts of cytokeratin No. 19. When these cells are allowed to mature either in utero or in culture on a whole basement membrane extract, they develop both the morphological characteristics and the pattern of cytokeratin synthesis of fully developed type 2 cells, with cytokeratins No. 19 being the major acidic cytokeratin produced.

The retinal pigment epithelium and other tissues immunocytochemical studies using hybridoma supernatants

We describe the production of hybridomas producing antibody reactive with retinal pigment epithelium. The patterns of reactivity obtained when supernatants from these hybrids were used to immuno-stain ocular and non-ocular tissues are described. From the patterns of reactivity obtained we suggest that the RPE shares common features with simple and glandular epithelia as well as myoepithelial cells. These findings may lend support to the hypotheses of RPE cell migration and contraction in the formation of epiretinal membranes and retinal detachment.

Monoclonal antibody mapping of keratins 8 and 17 and of vimentin in normal human mammary gland, benign tumors, dysplasias and breast cancer

The distribution of keratins 8 and 17 and of vimentin in 28 normal human mammary tissue samples, 16 benign tumors, 26 fibrocytic diseases and 52 malignant breast tumors have been studied using monoclonal antibodies HI, E3 and NT30, respectively. Three cell populations in normal mammary epithelium have been identified: luminal epithelium containing keratin 8, myoepithelium of the lobular structures positive for vimentin, and myoepithelium of extralobular ducts positive for keratin 17. In different kinds of benign tumor and dysplastic proliferation a mosaic of cells with all normal phenotypes has been observed. The majority of cells co-expressed keratins 8 and 17 or vimentin. In the overwhelming majority of carcinomas, cells did not contain myoepithelial markers (keratin 17 and vimentin) but expressed only keratin 8 specific to normal luminal epithelium.

The sequence of the human epidermal 58-kD (#5) type II keratin reveals an absence of 5' upstream sequence conservation between coexpressed epidermal keratins

We report the isolation and sequencing of cDNA and genomic clones encoding the complete sequence of the human 58-kD epidermal keratin (#5). The sequence specifies a protein of 62,471 daltons that contains a central alpha-helical segment capable of forming a coiled-coil structure flanked by regions that are not alpha-helical. A comparison of the primary sequence with the known sequences of other intermediate filament proteins reveals many common motifs. The 58-kD keratin is highly similar to other type II keratins and less similar to type I keratins and other intermediate filament proteins. The 58-kD keratin is regulated by retinoids in several tissues and is one of four keratins abundantly expressed in epidermal keratinocytes, where it may be important in maintaining structural integrity of the integument. A comparison of the keratin 5 sequence with coexpressed keratin 14 reveals an absence of sequence conservation in regulatory regions and suggests that common sequence elements may not be necessary for coordinate expression of type I and type II keratin partners. Interestingly, keratin 5 contains only one region weakly resembling the SV40 enhancer-like sequence found in some other keratins indicating that this sequence motif may not be necessary for regulation or abundant expression of all epidermal keratins.

Expression of simple epithelial type cytokeratins in stratified epithelia as detected by immunolocalization and hybridization in situ

Multi-layered ("stratified") epithelia differ from one-layered ("simple") polar epithelia by various architectural and functional properties as well as by their cytoskeletal complements, notably a set of cytokeratins characteristic of stratified tissue. The simple epithelial cytokeratins 8 and 18 have so far not been detected in any stratified epithelium. Using specific monoclonal antibodies we have noted, in several but not all samples of stratified epithelia, including esophagus, tongue, exocervix, and vagina, positive immunocytochemical reactions for cytokeratins 8, 18, and 19 which in some regions were selective for the basal cell layer(s) but extended into suprabasal layers in others. In situ hybridization with different probes (riboprobes, synthetic oligonucleotides) for mRNAs of cytokeratin 8 on esophageal epithelium has shown, in extended regions, relatively strong reactivity for cytokeratin 8 mRNA in the basal cell layer. In contrast, probes to cytokeratin 18 have shown much weaker hybridization which, however, was rather evenly spread over basal and suprabasal strata. These results, which emphasize the importance of in situ hybridization in studies of gene expression in complex tissues, show that the genes encoding simple epithelial cytokeratins can be expressed in stratified epithelia. This suggests that continual expression of genes coding for simple epithelial cytokeratins is compatible with the formation of squamous stratified tissues and can occur, at least in basal cell layers, simultaneously with the synthesis of certain stratification-related cytokeratins. We also emphasize differences of expression and immunoreactivity of these cytokeratins between different samples and in different regions of the same stratified epithelium and discuss the results in relation to changes of cytokeratin expression during fetal development of stratified epithelia, in response to environmental factors and during the formation of squamous cell carcinomas.

Molecular characterization and expression of the stratification-related cytokeratins 4 and 15

A number of human cytokeratins are expressed during the development of stratified epithelia from one-layered polar epithelia and continue to be expressed in several adult epithelial tissues. For studies of the regulation of the synthesis of stratification-related cytokeratins in internal tissues, we have prepared cDNA and genomic clones encoding cytokeratin 4, as a representative of the basic (type II) cytokeratin subfamily and cytokeratin 15, as representative of the acidic (type I) subfamily, and determined their nucleotide sequences. The specific expression of mRNAs encoding these two polypeptides in certain stratified tissues and cultured cell lines is demonstrated by Northern blot hybridization. Hybridization in situ with antisense riboprobes and/or synthetic oligonucleotides shows the presence of cytokeratin 15 mRNA in all layers of esophagus, whereas cytokeratin 4 mRNA tends to be suprabasally enriched, although to degrees varying in different regions. We conclude that the expression of the genes encoding these stratification-related cytokeratins starts already in the basal cell layer and does not depend on vertical differentiation and detachment from the basal lamina. Our results also show that simple epithelial and stratification-related cytokeratins can be coexpressed in basal cell layers of certain stratified epithelia such as esophagus. Implications of these findings for epithelial differentiation and the formation of squamous cell carcinomas are discussed.

Developmental-specific expression and immunoreactivity of keratins during odontogenesis in rat embryos

The enamel organ of the mammalian dental primordium undergoes a precise sequence of differentiation. To correlate this differentiation with tissue-specific markers we analysed the keratin protein composition and immunoreactivity of incisor primordia from the earliest stage of odontogenesis to the neonatal period. Throughout the enamel organ synthesized a characteristic subset of keratin proteins, and the expression of one specific keratin marked the onset of the cap stage. Interestingly, the immunoreactivity of the ameloblastic keratins against polyclonal antibodies increased with progressive odontogenesis, suggesting that cytokeratin filaments may undergo post-translational or conformational alterations during assembly within differentiating enamel-organ cells.