Reaction of tonofilament-like intermediate-sized filaments with antibodies raised against isolated defined polypeptides of bovine hoof prekeratin

Immunohistochemical demonstration of cytokeratins in the human prostate

The behaviour of keratins in the human prostate is investigated immunohistochemically by polyclonal rabbit antibodies against keratins from human stratum corneum (kit from ORTHO/Heidelberg) and compared to the behaviour of prostatic acid phosphatase (PAP) and prostate-specific antigen (PSA). In normal glands and cribriform as well as adenomatous hyperplasia only basal cells contain keratin. The secretory epithelium is keratin-negative and in contrast to the basal cells PAP- as well as PSA-positive. In prostatic ducts and utriculus prostaticus keratin is demonstrable in basal cells and urothelium. As in normal glands, the light cylindric epithelium is keratin-negative and PAP- as well as PSA-positive. The cells in atrophic glands and postatrophic hyperplasia may contain keratin as well as PAP and PSA. Urothelial and squamous metaplasia are strongly keratin-positive. PAP and PSA are not found. The cylindric epithelium of the ejaculatory ducts contains keratin at many places. PAP and PSA are not demonstrable. The utriculus does not differ from normal prostatic glands immunohistochemically. This supports the view that the epithelium of the sinus urogenitalis is involved in the embryogenesis of normal prostatic glands and the utriculus as well. Urothelial and squamous metaplasia obviously arise from basal cells which share the same immunohistochemical features. Whether the cells in atrophic glands and postatrophic hyperplasia derive from basal cells or secretory epithelium cannot be decided. The keratin composition of the prostate should be further analyzed by keratin-specific monoclonal antibodies.

Cloning of cDNA and amino acid sequence of a cytokeratin expressed in oocytes of Xenopus laevis

Using a cDNA clone from the ovary of the frog, Xenopus laevis, we have identified the mRNA and determined the complete amino acid sequence of a major cytoskeletal protein expressed in the oocyte. A comparison with other cytoskeletal proteins of Xenopus and mammals identifies this polypeptide Mr 55,700 as a nonepidermal kind of cytokeratin of the basic (type II) subfamily, which represents the amphibian equivalent to cytokeratin no. 8 of simple epithelia of higher mammals. The sequence data demonstrate the high evolutionary stability of this protein. This cytokeratin and its mRNA are present in oocytes, eggs, embryos, liver, and intestinal mucosa of adult frogs, as well as cultured kidney epithelial cells. We suggest that epithelial cell differentiation in early stages of Xenopus embryogenesis differs from other known pathways of cell differentiation in that major cell-type-specific proteins--i.e., cytokeratins of the simple epithelial type--and their mRNAs are maternally provided and distributed to early epithelial cells by special sorting mechanisms.

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.

Identification of two types of keratin polypeptides within the acidic cytokeratin subfamily I

Cytoskeletal filaments of the alpha-keratin type (cytokeratins) are a characteristic of epithelial cells. In diverse mammals (man, cow and rodents) these cytokeratins consist of a family of approximately 20 polypeptides, which may be divided into the more acidic (I) and the more basic (II) subfamilies. These two subfamilies show only limited amino acid sequence homology. In contrast, nucleic acid hybridization experiments and peptide maps have been interpreted to show that polypeptides of the same subfamily share extended sequence homology. We compare two polypeptides of the acidic cytokeratin subfamily, VIb (Mr 54,000) and VII (Mr 50,000), which are co-expressed in large amounts in bovine epidermal keratinocytes. These two epidermal keratins can be distinguished by specific antibodies and show different patterns of expression among several bovine tissues and cultured cells. In addition, they differ in the stability of their complexes with basic keratin polypeptides and in their tryptic peptide maps. The amino acid sequences deduced from the nucleotide sequences of complementary DNA clones containing the 3' ends of the messenger RNAs for these keratins are compared with each other and with available amino acid sequences of human, murine and amphibian epidermal keratins. Bovine keratins VIb and VII share considerable sequence homology in the alpha-helical portion (68% residues identical) but lack significant homology in the extrahelical portion. Bovine keratin VIb shows, in its alpha-helical region, a pronounced sequence homology (88% identity) to the murine epidermal keratin of Mr 59,000. In addition, the non-helical carboxy-terminal regions of both proteins are glycine-rich and contain a canonic sequence GGGSGYGG, which may be repeated several times. Moreover, their mRNAs present a highly conserved stretch of 236 nucleotides containing, in the murine sequence, the end of the coding and all of the non-coding region (81% identical nucleotides). Bovine keratin VII is considerably different from the murine Mr 59,000 keratin but is almost identical to the human cytokeratin number 14 of Mr 50,000, both in the alpha-helical and in the non-alpha-helical regions of the proteins, and the mRNAs of the human and the bovine keratins also display a high homology in their 3' non-coding ends. The results show that in the same species keratins of the same subfamily can differ considerably, whereas equivalent keratin polypeptides of different species are readily identified by characteristic sequence homologies in the alpha-helical and the non-helical regions as well as in the 3' non-coding portions of their mRNAs.(ABSTRACT TRUNCATED AT 400 WORDS)

Intermediate-size filaments in a germ cell: Expression of cytokeratins in oocytes and eggs of the frog Xenopus

Vitellogenic oocytes and eggs of the frog Xenopus laevis contain intermediate-size filaments that are resistant to extractions in high-salt buffers and Triton X-100 and are specifically stained with antibodies to cytokeratins. Gel electrophoresis of cytoskeletal proteins from Xenopus oocytes shows a specific enrichment of three polypeptides designated components 1 [Mr, 56,000; IEP (pI obtained by two-dimensional gel electrophoresis in the presence of 9.5 M urea), ca. 5.9], 2 (Mr, 46,000; IEP, 5.38), and 3 (Mr, 42,000; IEP, ca. 5.3). The same three cytoskeletal polypeptides are found in eggs and early embryos, in intestinal mucosa of adult frogs, and in cultured kidney epithelial cells. They are different from amphibian vimentin and desmin and from the keratins present in the epidermis of adult frogs. Peptide mapping and immunoblotting experiments indicate that Xenopus cytokeratin component 1 is related to cytokeratin A of higher vertebrates but is different from the two smaller cytoskeletal polypeptides 2 and 3. Incorporation of [35 S]methionine shows that all three polypeptides are synthesized in both oocytes and embryos. Our observations show that maternal storage is not only restricted to proteins serving basic cellular functions but also can extend to proteins related to a specific form of cell differentiation (i.e., epithelial formation) in the early embryo. The data suggest that mechanisms of epithelial differentiation in Xenopus embryogenesis are different from those of early mammalian embryos in which no such intermediate-size-filament storage pool has been detected.

Intermediate filaments of the vimentin and prekeratin type in human epidermis

Monospecific antibodies to intermediate filaments of mesenchymally derived vimentin, applied to frozen sections of human skin, specifically stained dendritic basal and suprabasal cells. Cellular morphology, distribution, reaction pattern with anti-HLA-DR in serial sections, and OKT6 in double-staining procedures identified these cells as melanocytes and Langerhans cells. As shown previously in animals keratinocytes stained with antiprekeratin exclusively. Thus, vimentin is an intracellular marker for Langerhans cells and melanocytes, differentiating them from keratinocytes.

Differential immunological crossreactivity of HeLa keratin antibodies with human epidermal keratins

HeLa cells contain four keratin-like proteins having molecular weights of 50,000 (IEF 31), 48,500 (IEF 36), 44,000 (IEF 44), and 43,500 (IEF 46), respectively. Mouse polyclonal antibodies prepared against two of these keratins (IEF 31 and 46) have been used in this study to identify human epidermal keratins with common antigenic determinants. Using a sensitive immunoprecipitation procedure we show that the IEF 31 antibody crossreacts with three human acidic epidermal keratins, termed K1, K2, and K3, having molecular weights of 44,000, 47,500, and 54,000, respectively. One of these keratins (K1) comigrated with HeLa keratin IEF 44 and exhibited an identical one-dimensional peptide map. This protein is also abundant in basaliomas. In contrast to these results, the IEF 46 antibody showed no crossreactivity with any of the human acidic or basic [35S]methionine-labeled epidermal proteins. The lack of crossreactivity of this antibody was further confirmed by indirect immunofluorescence staining of cryostat sections from human split skin. These results emphasize both the similarity and diversity of antigenic determinants among HeLa and epidermal keratins.

Intermediate filaments and their interaction with membranes. The desmosome-cytokeratin filament complex and epithelial differentiation

Intermediate-sized filaments represent a class of morphologically similar but biochemically and immunologically distinguishable cytoplasmic protein polymer structures. Five major filament types have been identified (cytokeratin, vimentin, desmin, neurofilament protein, glia filament protein) and antibodies to these proteins have been used for distinguishing different cell types and tumors derived therefrom. Epithelial and carcinoma cells are characterized by the presence of cytokeratin filaments and desmosomal elements identified by antibodies to certain high molecular weight proteins of desmosomal plaques. However, the specific pattern of cytokeratin polypeptides is different in different epithelia. The potential value of cell type identification by immunological reactions with antibodies to cytoskeletal proteins in tumor diagnosis is discussed.

Keratin-like proteins in normal and neoplastic cells of human and rat mammary gland as revealed by immunofluorescence microscopy

Normal and neoplastic human breast tissue as well as lactating and nonlactating rat mammary glands and 7,12-dimethylbenz(alpha)-anthracene-induced mammary adenocarcinomas of rat, were examined by indirect immunofluorescence microscopy using guinea pig antibodies to human and bovine epidermal prekeratin and to cytokeratin polypeptide D from mouse hepatocytes. In normal mammary glands of both species, lactating rats included, the antibodies raised against human and bovine epidermal prekeratins strongly stained ductal and myoepithelial cells, whereas antibodies to hepatic cytokeratin D revealed, in addition, fibrillar staining in cells of the alveolus-like terminal lobular units and in milk secreting cells of the rat. The presence of some finely dispersed intermediate-sized filaments of the cytokeratin type in lactating alveolar cells of rat mammary gland was also demonstrated by electron microscopy. In human intraductal mammary carcinomas the antibodies to epidermal prekeratins showed staining in myoepithelial cells and intralumenal papillary protrusions of the tumor, whereas the antibodies to hepatic cytokeratin D presented an almost complementary pattern in that they showed strongest staining in the more basally located layers of tumor cells. Intraductal adenocarcinomas of rats showed strong staining with all keratin antibodies examined. In contrast to previous studies using exclusively antisera raised against epidermal prekeratin, out results show that all types of neoplastic and non-neoplastic epithelial cells of mammary gland of both species contain-at least some-filaments of the cytokeratin type identifiable by immunologic reaction, if antibodies are used that recognize a broad range of epidermal and nonepidermal cytokeratins. Consequently, such broad range antibodies to keratin-like proteins provide adequate tools to identify and characterize neoplastic and non-neoplastic epithelial cells and to eliminate false negative immunocytochemical findings in tumor diagnosis. In addition, our observation that in the same human carcinoma two cell types can be distinguished by their reaction with two different antibodies to cytokeratins from epidermis and liver, respectively, indicates that the cells of a given carcinoma can differ in their cytoskeletal composition, thus presenting further criteria for diagnostic differentiation.

Mallory body-like abnormalities in carcinomas induced by cultured transformed rat liver cells

Hepatoma cells isolated from rats after administration of a carcinogen, diethylnitrosamine, and propagated in culture, contained a genetically stable cytoskeletal abnormality resembling Mallory bodies. These juxtanuclear aggregates of intermediate-sized filaments were maintained in carcinomas produced in nude mice after inoculation of uncloned mass cultures and a cloned subculture. Paraffin and frozen sections of these tumors revealed acentric nuclei and a glassy hyalin-type cytoplasmic lesion which stained pink with hematoxylin-eosin and blue with Mallory's aniline blue stain. The cells in culture and in the tumor sections were strongly positive for gamma-glutamyl transpeptidase. Cryostat sections examined by indirect immunofluorescence microscopy with antisera to purified bovine hoof prekeratin, desmosome-associated tonofilaments from bovine muzzle, and murine vimentin, as well as transmission electron microscopy revealed the presence of juxtanuclear aggregates of intermediate-sized filaments. All characteristics previously reported for the tissue culture cell line were stably maintained in the tumor tissue. These results suggest that the Mallory body-containing cells frequently observed in man in alcoholic hepatitis and other degenerative liver diseases could, under appropriate environmental "promoting" conditions, be precursor cells in focal hepatocellular carcinoma formation.

Isolation and characterization of desmosome-associated tonofilaments from rat intestinal brush border

Epithelial cells of the small intestine, like those of other internal organs, contain intermediate-sized filaments immunologically related to epidermal prekeratin which are especially concentrated in the cell apex. Brush-order fractions were isolated from rat small intestine, and apical tonofilaments attached to desmosomal plaques and terminal web residues were prepared therefrom by extraction in high salt (1.5 M KCl) buffer and Triton X-100. The structure of these filaments was indistinguishable from that of epidermal tonofilaments and, as with epidermal prekeratin, filaments could be reconstituted from solubilized, denatured intestinal tonofilament protein. On SDS polyacrylamide gel electrophoresis of proteins of the extracted desmosome-tonofilament fractions, a number of typical brush-border proteins were absent or reduced, and enrichment of three major polypeptides of Mr 55,000, 48,000, and 40,000 was noted. On two-dimensional gel electrophoresis, the three enriched major polypeptides usually appeared as pairs of isoelectric variants, and the two smaller components (Mr 48,000, and 40,000) were relatively acidic (isoelectric pH values of 5.40 and below), compared to the Mr 55,000 protein which focused at pH values higher than 6.4. The tonofilament proteins were shown to be immunologically related to epidermal prekeratin by immunoreplica and blotting techniques using antibodies to bovine epidermal prekeratins. Similar major polypeptides were found in desmosome-attached tonofilaments from small intestine of mouse and cow. However, comparisons with epidermal tissues of cow and rat showed that all major polypeptides of intestinal tonofilaments were different from the major prekeratin polypeptides of epidermal tonofilaments. The results present the first analysis of a defined fraction of tonofilaments from a nonepidermal cell. The data indicate that structurally identical tonofilaments can be formed, in different types of cells, by different polypeptides of the cytokeratin family of proteins and that tonofilaments of various epithelia display tissue-specific patterns of their protein subunits.

Intermediate-sized filaments of the prekeratin type in myoepithelial cells

Myoepithelial cells from mammary glands, the modified sweat glands of bovine muzzle, and salivary glands have been studied by electron microscopy and by immunofluorescence microscopy in frozen sections in an attempt to further characterize the type of intermediate-sized filaments present in these cells. Electron microscopy has shown that all myoepithelial cells contain extensive meshworks of intermediate-sized (7--11-nm) filaments, many of which are anchored at typical desmosomes or hemidesmosomes. The intermediate-sized filaments are also intimately associated with masses of contractile elements, identified as bundles of typical 5--6-nm microfilaments and with characteristically spaced dense bodies. This organization resembles that described for various smooth muscle cells. In immunofluorescence microscopy, using antibodies specific for the various classes of intermediate-sized filaments, the myoepithelial cells are strongly decorated by antibodies to prekeratin. They are not specifically stained by antibodies to vimentin, which stain mesenchymal cells, nor by antibodies to chick gizzard desmin, which decorate fibrils in smooth muscle Z bands and intercalated disks in skeletal and cardiac muscle of mammals. Myoepithelial cells are also strongly stained by antibodies to actin. The observations show (a) that the epithelial character, as indicated by the presence of intermediate-sized filaments of the prekeratin type, is maintained in the differentiated contractile myoepithelial cell, and (b) that desmin and desmin-containing filaments are not generally associated with musclelike cell specialization for contraction but are specific to myogenic differentiation. The data also suggest that in myoepithelial cells prekeratin filaments are arranged--and might function--in a manner similar to the desmin filaments in smooth muscle cells.

Differential location of different types of intermediate-sized filaments in various tissues of the chicken embryo

The location of constitutive proteins of different types of intermediate-sized (about 10 mm) filaments (cytokeratin, vimentin, desmin, brain filament protein) was examined in various tissues of 11--20 day chick embryos, using specific antibodies against the isolated proteins and immunofluorescence microscopy on frozen sections and on isolated serous membrane. The tissues studied which contained epithelia were small intestine, gizzard, esophagus, crop, liver, kidney, thymus, mesenteries, and epidermis. The results show that the different intermediate filament proteins, as seen in the same organ, are characteristic of specific lines of differentiation: Cytokeratin filaments are restricted to--and specific for--epithelial cells; vimentin filaments are seen--at this stage of embryogenesis--only in mesenchymal cells, including connective tissue, endothelial and blood cells, and chondrocytes; filaments containing protein(s) related to the subunit protein prepared from gizzard 10 nm filaments (i.e., desmin) are significant only in muscle cells; and intermediate filament protein of brain, most probably neurofilament protein, is present only in nerve cells. We conclude that for most tissues the expression of filaments of cytokeratin, vimentin, desmin, and neurofilament protein is mutually exclusive, and that these protein structurees provide useful markers for histochemical and cytochemical differentiation of cells of epithelial, mesenchymal, myogenic, and neurogenic differentiation.

Simultaneous expression of two different types of intermediate sized filaments in mouse keratinocytes proliferating in vitro

The intermediate-sized filaments present in epidermal keratinocytes derived from mouse skin and in an established cell line (HEL) derived from spontaneous transformation of murine keratinocytes grown in vitro, have been examined by immunofluorescence microscopy, using antibodies directed against subunit proteins of different classes of intermediate-sized filaments, as well as by electron microscopy and gel electrophoresis of cytoskeletal preparations highly enriched in intermediate-sized filaments. The keratinocytes derived from neonatal skin, which are capable of only limited replication in vitro, show only a single type of intermediate-sized filaments, i.e., the tonofibril-like arrays of filaments containing prekeratin. HEL cells, which proliferate indefinitely in vitro, retain the tonofilament-like structures typical of differentiated epidermal cells but in addition display intermediate-sized filaments of the vimentin type, i.e., the filament system typically found in mesenchymal and mesenchyme-derived cells. We discuss the possibility that (i) the advent of vimentin-type filaments in epidermal cells in culture is related either to the transformed state or the in vitro growth conditions as such and (ii) other differentiated epithelial cells proliferating in vitro may have more than one system of intermediate-sized filaments.

Identification and characterization of epithelial cells in mammalian tissues by immunofluorescence microscopy using antibodies to prekeratin

The occurrence of intermediate-sized filaments containing prekeratin-like proteins ('cytokeratins') has been examined in various organs of rat and cow by electron microscopy and by immunofluorescence microscopy on frozen sections using antibodies to defined constitutive proteins of various types of intermediate-sized filaments (prekeratin, vimentin, desmin). Positive cytokeratin reaction and tonofilament-like structures have been observed in the following epithelia: epidermis; ductal, secretory, and myoepithelial cells of sweat glands; mammary gland duct; myoepithelial cells of lactating mammary gland; milk secreting cells of cow; ductal, secretory, and myoepithelial cells of various salivary glands; tongue mucosa; bile duct; excretory duct of pancreas; intestinal mucosa; urothelium; trachea; bronchi; thymus reticulum, including Hassall corpuscles; mesothelium; uterus; and ciliated cells of oviduct. None of the epithelial cells mentioned has shown significant reaction with antibodies to vimentin, the major component of the type of intermediate-sized filaments predominant in mesenchymal cells. The widespread, if not general occurrence of cytokeratin filaments in epithelial cells is emphasized, and it is proposed to use this specific structure as a criterion for true epithelial character or origin.