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

Loss of keratin 13 in oral carcinoma in situ: a comparative study of protein and gene expression levels using paraffin sections

Immunohistochemical loss of keratin (K)13 is one of the most valuable diagnostic criteria for discriminating carcinoma in situ (CIS) from non-malignancies in the oral mucosa while K13 is stably immunolocalized in the prickle cells of normal oral epithelium. To elucidate the molecular mechanism for the loss of K13, we compared the immunohistochemical profiles for K13 and K16 which is not expressed in normal epithelia, but instead enhanced in CIS, with their mRNA levels by in-situ hybridization in formalin-fixed paraffin sections prepared from 23 CIS cases of the tongue, which were surgically removed. Reverse transcriptase-PCR was also performed using RNA samples extracted from laser-microdissected epithelial fragments of the serial paraffin sections in seven of the cases. Although more enhanced expression levels for K16 were confirmed at both the protein and gene levels in CIS in these seven cases, the loss of K13 was associated with repressed mRNA levels in four cases, but not in the other three cases. The results suggest that the loss of K13 is partly due to its gene repression, but may also be due to some unknown post-translational events.

Against the rules: human keratin K80: two functional alternative splice variants, K80 and K80.1, with special cellular localization in a wide range of epithelia

Of the 54 human keratins, five members have, at present, only been characterized at the gene level. In this study we have investigated the expression patterns of keratin K80, whose gene is located at the centromeric end of the type II keratin gene domain. K80 possesses a number of highly unusual properties. Structurally, it is distinctly closer to type II hair keratins than to type II epithelial keratins. Nonetheless, it is found in virtually all types of epithelia (stratified keratinizing/non-keratinizing, hard-keratinizing, as well as non-stratified tissues, and cell cultures thereof). This conspicuously broad expression range implies an unprecedented in vivo promiscuity of K80, which involves more than 20 different type I partners for intermediate filament (IF) formation. Throughout, K80 expression is related to advanced tissue or cell differentiation. However, instead of being part of the cytoplasmic IF network, K80 containing IFs are located at the cell margins close to the desmosomal plaques, where they are tightly interlaced with the cytoplasmic IF bundles abutting there. In contrast, in cells entering terminal differentiation, K80 adopts the "conventional" cytoplasmic distribution. In evolutionary terms, K80 is one of the oldest keratins, demonstrable down to fish. In addition, KRT80 mRNA is subject to alternative splicing. Besides K80, we describe a smaller but fully functional splice variant K80.1, which arose only during mammalian evolution. Remarkably, unlike the widely expressed K80, the expression of K80.1 is restricted to soft and hard keratinizing epithelial structures of the hair follicle and the filiform tongue papilla.

Microarray analysis of cutaneous squamous cell carcinomas reveals enhanced expression of epidermal differentiation complex genes

Gene expression profiles were determined for 12 cutaneous squamous cell carcinomas (SCC) removed from sun-exposed sites on nonimmunosuppressed patients. Gene expression in each SCC was compared to that in sun-exposed skin from the same patient using the Affymetrix HGU133 2.0 PlusGeneChip. We identified 440 genes with increased expression in SCC and 738 with decreased expression; overall we identified a large number of small changes in gene expression rather than a few marked changes that distinguished SCC from sun-exposed skin. Analyzing this robust data set according to biofunctional pathways using DAVID, transcriptional control elements using oPOSSUM, and chromosomal location using GSEA suggested genetic and epigenetic mechanisms of gene expression regulation in SCC. Some altered patterns of gene expression in SCC were consistent with regulation of spatially separated genes by a number of developmentally important transcription factors (forkhead, HMG, and homeo factors) that negatively regulated gene expression and to a few factors that positively regulated expression (Creb-1, NFkappaB, RelA, and Sp-1). We also found that coordinately enhanced expression of epidermal differentiation complex genes on chromosome 1q21 was a hallmark of SCC. A novel finding in our study was enhanced expression of keratin 13 in SCC, a result validated by immunohistochemical staining of an SCC tumor tissue array.

The human keratins: biology and pathology

The keratins are the typical intermediate filament proteins of epithelia, showing an outstanding degree of molecular diversity. Heteropolymeric filaments are formed by pairing of type I and type II molecules. In humans 54 functional keratin genes exist. They are expressed in highly specific patterns related to the epithelial type and stage of cellular differentiation. About half of all keratins—including numerous keratins characterized only recently—are restricted to the various compartments of hair follicles. As part of the epithelial cytoskeleton, keratins are important for the mechanical stability and integrity of epithelial cells and tissues. Moreover, some keratins also have regulatory functions and are involved in intracellular signaling pathways, e.g. protection from stress, wound healing, and apoptosis. Applying the new consensus nomenclature, this article summarizes, for all human keratins, their cell type and tissue distribution and their functional significance in relation to transgenic mouse models and human hereditary keratin diseases. Furthermore, since keratins also exhibit characteristic expression patterns in human tumors, several of them (notably K5, K7, K8/K18, K19, and K20) have great importance in immunohistochemical tumor diagnosis of carcinomas, in particular of unclear metastases and in precise classification and subtyping. Future research might open further fields of clinical application for this remarkable protein family.

The human type I keratin gene family: characterization of new hair follicle specific members and evaluation of the chromosome 17q21.2 gene domain

In general concurrence with recent studies, bioinformatic analysis of the chromosome 17q21.2 DNA sequence found in the EBI/Genebank database shows the presence of 27 type I keratin genes and five keratin pseudogenes present on 8 contiguous Bacterial Artificial Chromosome (BAC) sequences. This constitutes the 970 kb type I keratin gene domain. Inserted into this domain is a 350 kb region harboring 32 previously characterized keratin-associated protein genes. Of the 27 keratin genes found in this region, six have not been characterized in detail. This study reports the isolation of cDNA sequences for these keratin genes, termed K25irs1-K25irs4, Ka35, and Ka36, as well as cDNA sequences for the previously reported hair keratins hHa3-I, hHa7, and hHa8. RT-PCR analysis of 14 epithelial tissues using primers for the six novel keratins, as well as for keratins 23 and 24, shows that the six novel keratins appear to be hair follicle associated. Previous expression data, coupled with evolutionary analysis studies point to K25irs1-K25irs4 probably being inner root sheath specific keratins. Ka35 and Ka36 are, based on their exon-intron structure and expression characteristics, hair keratins. In contrast, K23 and K24 appear to be epithelial keratins associated with simple/glandular or stratified, non-cornified epithelia, respectively. A literature analysis coupled with the data presented here confirms that all of the 27 keratin genes found on this domain have been characterized at the transcriptional level. Together with K18, a type I keratin gene found on the type II keratin domain, this seems to be the entire complement of functional type I keratins in humans.

Stage-specific expression of the intermediate filament protein cytokeratin 13 in luminal epithelial cells of secretory phase human endometrium and peri-implantation stage rabbit endometrium

In preparation for blastocyst implantation, uterine luminal epithelial cells express new cell adhesion molecules on their apical plasma membrane. Since one mechanism epithelial cells employ to regulate membrane polarity is the establishment of specific membrane-cytoskeletal interactions, this study was undertaken to determine if new cytokeratin (CK) intermediate filament assemblies are expressed in endometrial epithelial cells during developmental stages related to blastocyst implantation. Type-specific CK antibodies were used for immunocytochemical and immunoblot analyses of 1) intermediate filament networks of the endometrial epithelium during embryo implantation in rabbits and 2) proliferative and secretory phases of the human menstrual cycle. CK18, a type I CK found in most simple epithelia, was expressed in all luminal and glandular epithelial cells of both the human and rabbit endometrium at all developmental stages analyzed; it was also strongly expressed in trophectoderm of the implanting rabbit blastocyst. In contrast, CK13, another type I cytokeratin, exhibited a regulated expression pattern in luminal, but not glandular, epithelial cells of secretory phase human and peri-implantation stage rabbit endometrium. Furthermore, in the rabbit implantation chambers, CK13 was predominantly localized at the cell apex of luminal epithelial cells, where it assembled into a dense filamentous network. These data suggest that the stage-specific expression of CK13 and a reorganization of the apical intermediate filament cytoskeleton of uterine luminal epithelial cells may play important functions in preparation for the implantation process.

Cytokeratin expression patterns in jaw cyst linings with metaplastic epithelium

BACKGROUND

Cytokeratin (CK) expression patterns have been studied in numerous intact and diseased oral tissues. However, CK expression in metaplastic squamous cells has not been explored in depth and the origin of metaplastic epithelial linings of the jaw cysts has not been sufficiently investigated.

METHODS

We examined CK expression in 46 postoperative maxillary cysts (POMCs) which were lined with pseudostratified columnar cells only, columnar and squamous cells, and squamous cells only, in 13, 30 and 3 cases, respectively.

RESULTS

The expression of CK8, CK13 and CK18 were observed in 39, 9 and all 43 of the columnar epithelial linings, respectively. Metaplastic squamous epithelia expressed more CK13, and less CK18 and CK8. Of the 33 metaplastic linings, 24 expressed CK8, 23 CK13 and 26 linings expressed CK18. The patterns of expression of CK13 and CK18 observed were CK18(+)-CK13(-) in 10 metaplastic linings, CK18(+)-CK13(+) in 16, and CK18(-)-CK13(+) in 7. The expression of CK13- and CK18-mRNA was generally correlated with level of protein expressed. CK18-mRNA expression was observed by in situ hybridization, not only in the 26 metaplastic linings which were positive for CK18 protein, but also in five of the seven metaplastic linings which did not express CK18 protein. In addition, RT-PCR revealed an expression of CK18-mRNA in all metaplastic squamous linings, although the expression level was weaker than that in the columnar epithelial linings. The CK13-mRNA was expressed inversely to the CK18-mRNA.

CONCLUSIONS

These results indicate that CK18-mRNA is preserved through metaplasia, although the protein expression decreased. Metaplastic squamous cells differentiate with a decrease of CK18 and an increase of CK13 expression.

Expression of cytokeratins (CKs) 8, 13 and 18 and their mRNA in epithelial linings of radicular cysts: implication for the same CK profiles as nasal columnar epithelium in squamous epithelial lining

OBJECTIVE

Our objective was to specify cytokeratin (CK) patterns in lining epithelia of radicular cysts which are sometime lined with ciliated columnar epithelia as seen in the nasal epithelia.

MATERIALS AND METHODS

We examined the CK expression in 52 radicular cysts obtained from 32 maxillary and 20 mandibular lesions and investigated CK-mRNA expression using in situ hybridization in 24 maxillary and 13 mandibular cysts and reverse transcription-polymerase chain reaction (RT-PCR) in 24 maxillary cysts.

RESULTS

Of the maxillary cysts, 20, 29 and 19 squamous epithelial linings were positive for CK8, CK13 and CK18, respectively; of the mandibular cysts, 10, 20 and 11 linings were positive for these CKs, respectively. The expression patterns of CK18(+)-CK13(-), CK18(+)-CK13(+) and CK18(-)-CK13(+) were observed in 3, 16 and 13 linings of the maxillary cysts and 0, 11 and 9 linings of the mandibular cysts, respectively. In situ hybridization revealed the expression of CK18-mRNA in 9 and 4 linings of 24 maxillary and 13 mandibular cysts examined, respectively. With RT-PCR, we explored that both CK18- and CK13-mRNA were expressed not only in the normal nasal and gingival epithelia but also in the examined maxillary cyst linings although their expression levels differed correlating with the difference in CK staining.

CONCLUSION

It is concluded that CK13- and CK18-mRNA are constitutively expressed in columnar and squamous epithelial cells, respectively, and that the variant CK expression patterns with CK18-mRNA expression in maxillary radicular cysts are indicative of the possibility of phenotypic transformation in the cyst linings.

Detection of cytokeratin dynamics by time-lapse fluorescence microscopy in living cells

To monitor the desmosome-anchored cytokeratin network in living cells fusion protein HK13-EGFP consisting of human cytokeratin 13 and the enhanced green fluorescent protein was stably expressed in vulvar carcinoma-derived A-431 cells. It is shown for A-431 subclone AK13-1 that HK13-EGFP emits strong fluorescence in fixed and living cells, being part of an extended cytoplasmic intermediate filament network that is indistinguishable from that of parent A-431 cells. Biochemical, immunological and ultrastructural analyses demonstrate that HK13-EGFP behaves identically to the endogenous cytokeratin 13 and is therefore a reliable in vivo tag for this polypeptide and the structures formed by it. Time-lapse fluorescence microscopy reveals that the cytokeratin 13-containing network is in constant motion, resulting in continuous restructuring occurring in single and migratory cells, as well as in desmosome-anchored cells. Two major types of movement are distinguished: (i) oscillations of mostly long filaments, and (ii) an inward-directed flow of fluorescence originating as diffuse material at the cell periphery and moving in the form of dots and thin filaments toward the deeper cytoplasm where it coalesces with other filaments and filament bundles. Both movements are energy dependent and can be inhibited by nocodazole, but not by cytochalasin D. Finally, disassembly and reformation of cytokeratin filament networks are documented in dividing cells revealing distinct and rapidly occurring stages of cytokeratin organisation and distribution.

Modulation of cell proliferation by cytokeratins K10 and K16

The members of the large keratin family of cytoskeletal proteins are expressed in a carefully regulated tissue- and differentiation-specific manner. Although these proteins are thought to be involved in imparting mechanical integrity to epithelial cells, the functional significance of their complex differential expression is still unclear. Here we provide new data suggesting that the expression of particular keratins may influence cell proliferation. Specifically, we demonstrate that the ectopic expression of K10 inhibits the proliferation of human keratinocytes in culture, while K16 expression appears to promote the proliferation of these cells. Other keratins, such as K13 or K14, do not significantly alter this parameter. K10-induced inhibition is reversed by the coexpression of K16 but not that of K14. These results are coherent with the observed expression pattern of these proteins in the epidermis: basal, proliferative keratinocytes express K14; when they terminally differentiate, keratinocytes switch off K14 and start K10 expression, whereas in response to hyperproliferative stimuli, K16 replaces K10. The characteristics of this process indicate that K10 and K16 act on the retinoblastoma (Rb) pathway, as (i) K10-induced inhibition is hampered by cotransfection with viral oncoproteins which interfere with pRb but not with p53; (ii) K10-mediated cell growth arrest is rescued by the coexpression of specific cyclins, cyclin-dependent kinases (CDKs), or cyclin-CDK complexes; (iii) K10-induced inhibition does not take place in Rb-deficient cells but is restored in these cells by cotransfection with pRb or p107 but not p130; (iv) K16 efficiently rescues the cell growth arrest induced by pRb in HaCaT cells but not that induced by p107 or p130; and (v) pRb phosphorylation and cyclin D1 expression are reduced in K10-transfected cells and increased in K16-transfected cells. Finally, using K10 deletion mutants, we map this inhibitory function to the nonhelical terminal domains of K10, hypervariable regions in which keratin-specific functions are thought to reside, and demonstrate that the presence of one of these domains is sufficient to promote cell growth arrest.

Isolation, sequence and expression of the gene encoding human keratin 13

Keratins are a family of highly homologous proteins expressed as pairs of acidic and basic forms which make intermediate filaments in epithelial cells. Keratin 13 (K13) is the major acidic keratin, which together with K4, its basic partner, is expressed in the suprabasal layers of non-cornified stratified epithelia. The mechanism which allows mucosal-specific expression of this keratin remains unknown. To provide insight into the tissue-specific expression, we have isolated the human K13 gene by screening a chromosome 17 library with a specific K13 cRNA probe. Sequence analysis of unidirectional deletions produced by transposon Tn3 has revealed that the gene is 4601 nucleotides long and contains seven introns and eight exons. When driven by the CMV promoter, the gene produced K13 protein in MCF-7 cells, which normally do not express this protein. Two transcription-start sites were identified, the major being at 61 and the minor at 63 nucleotides upstream of ATG. The upstream sequence contained a TATA box and several other putative transcription factor binding sites. A single copy of the K13 gene was detected in the human genome by Southern hybridisation and polymerase chain reaction. K13 mRNA shows differential expression in cultured keratinocytes, and in A431 cells the RNA levels remained independent of calcium concentrations in the culture medium. Characterisation of the human K13 gene will facilitate elucidation of the molecular mechanism regulating K13 expression in mucosal tissues.

Expression of fetal cytokeratins in epidermal cells and colloid bodies in lichen planus

Clusters of immunoglobulin (Ig)-coated colloid bodies (CBs) in the dermo-epidermal zone are a typical immunohistochemical feature in lichen planus (LP)-lesions. They are considered to represent dyskeratotic basal keratinocytes, yet their composition has not been completely elucidated. In the present study, skin biopsies of 10 LP-lesions, 3 other dermatoses, and 10 biopsies of normal skin were studied immunohistochemically using monoclonal antibodies (MAbs) against fetal and differentiated epidermal antigens. CBs were identified by FITC-anti-Ig. Binding of MAb was visualized by double staining technique. Cytokeratin (CK) 10/11, a marker of epidermal differentiation, was consistently detected in suprabasal keratinocytes and also in up to 95% of Ig-positive CBs in LP. CK10/11 was additionally detected in basal keratinocytes in 9 LP-lesions, but not in normal skin. The basal cell-specific MAb BL7 stained basal layer keratinocytes in all biopsies. In contrast to normal skin, in LP scattered suprabasal keratinocytes and CBs were also positive for BL7 in 10 and 7 cases, respectively. While fetal cytokeratins (CK13 and CK8/18) were completely absent in control skin specimens, both cytokeratins were detected in various numbers of keratinocytes and CBs in all LP-lesions. Our results support the hypothesis of an epidermal origin of CBs. The cytokeratin profile seems to be severely disturbed in LP. This includes both accelerated differentiation by the expression of suprabasal CK10/11 in basal keratinocytes and dedifferentiation by the expression of fetal epidermal antigens (CK13 and CK8/18). It is tempting to speculate that the observed alterations may trigger T-cell activation and inflammatory onset in LP.

Cytokeratin and vimentin expression in normal epithelium and squamous cell carcinomas of the larynx

The immunohistochemical expression patterns of cytokeratin polypeptides and vimentin were investigated in normal epithelia and squamous cell carcinomas of the larynx with special emphasis on tumor grading. During malignant transformation of epithelial cells, the cytokeratin expression patterns changed, depending on the differentiation grade of the carcinomas. In low-grade carcinomas, the expression patterns were close to those of the normal epithelium. With increasing tumor grade, there was decreased expression of stratification cytokeratins and increased expression of basal cell, simple cell and hyperproliferation-related cytokeratins. Increasing tumor grade was also associated with the expression of vimentin, a cytoskeletal protein of mesenchymal cells. No relationship was found between vimentin expression and the presence of lymph-node metastases.

Sequences and differential expression of three novel human type-II hair keratins

As part of a program designed to characterize human hair keratin genes and their expression, we present the cDNA sequences and deduced amino acid sequences of three type-II hair keratins hHb3, hHb5, and hHb6, which by virtue of their amino acid homologies are the orthologs of the previously described sheep wool keratins, K2.10, K2.12, and K.211 [29]. Amino acid sequences comparisons of these keratins, including the previously characterized human K2.9 ortholog hHb1, show extreme conservation not only in the alpha-helices but also in the aminoterminal and proximal carboxyterminal domains. They also demonstrate higher sequence relationships between hHb1, hHb3, and hHb6 as compared to hHb5, which exhibits chain-specific sequences in both the head and tail domains. In situ hybridization studies using specific 3'-probes for the four type-II hair keratins reveal sequential patterns of gene expression in human anagen follicles. Remarkably the onset of hHb5 mRNA synthesis occurs immediately above a small population of matrix cells at the base of the hair bulb and the trichocytes lining the dermal papilla. hHb5 mRNA synthesis extends upward through the matrix and ends in the lower part of the cortex of the hair shaft. In contrast, both hHb1 and hHb3 mRNA synthesis begins simultaneously in the cortex 10-15 cell layers above the apex of the dermal papilla, thus partially overlapping that of hHb5 but continuing to a point well beyond hHb5 in the upper cortex. Synthesis of hHb6 mRNA starts slightly higher than either hHb1 or hHb3 mRNA and proceeds much farther up into the keratogenous zone of the hair shaft. Our study demonstrates that the differentiation of human hair in terms of hair keratin expression begins much earlier than previously assumed, i.e. in lower matrix cells of the hair bulb. This early phase of hair differentiation is followed by a late cortical phase of terminal differentiation which comprises at least three type-II hair keratins in the zone of elongation and the keratogenous zone of the hair shaft.

Dynamic O-linked glycosylation of nuclear and cytoskeletal proteins

Modification of Ser and Thr residues by attachment of O-linked N-acetylglucos-amine [Ser(Thr)-O-GlcNAcylation] to eukaryotic nuclear and cytosolic proteins is as dynamic and possibly as abundant as Ser(Thr) phosphorylation. Known O-GlcNAcylated proteins include cytoskeletal proteins and their regulatory proteins; viral proteins; nuclear-pore, heat-shock, tumor-suppressor, and nuclearoncogene proteins; RNA polymerase II catalytic subunit; and a multitude of transcription factors. Although functionally diverse, all of these proteins are also phosphoproteins. Most O-GlcNAcylated proteins form highly regulated multimeric associations that are dependent upon their posttranslational modifications. Evidence is mounting that O-GlcNAcylation is an important regulatory modification that may have a reciprocal relationship with O-phosphorylation and may modulate many biological processes in eukaryotes.

Coordinate control of growth and cytokeratin 13 expression by retinoic acid

Retinoic acid (RA) modulates the growth and differentiation of various normal and malignant cells. These effects are most likely mediated by changes in gene expression. Genes whose expression is modulated by RA may be useful as markers of growth responsiveness to retinoids. Using differential cDNA cloning we identified 10 genes regulated by RA in the head and neck squamous cell carcinoma cell line MDA886Ln. Keratin (K) 13 gene expression was the gene expression most related to the degree of sensitivity of growth to RA, as K13 was not expressed in a series of RA-resistant cell lines. Our data suggest that low K13 expression may be mechanistically related to resistance to RA-induced growth inhibition.

Isolation and characterization of sulfur globule proteins from Chromatium vinosum and Thiocapsa roseopersicina

Purple sulfur bacteria store sulfur as intracellular globules enclosed by a protein envelope. The proteins associated with sulfur globules of Chromatium vinosum and Thiocapsa roseopersicina were isolated by extraction into 50% aqueous acetonitrile containing 1% trifluoroacetic acid and 10 mM dithiothreitol. The extracted proteins were separated by reversed-phase HPLC, revealing three major proteins from C. vinosum and two from T. roseopersicina. All of these proteins have similar, rather unusual amino acid compositions, being rich in glycine and aromatic amino acids, particularly tyrosine. The molecular masses of the C. vinosum proteins were determined to be 10,498, 10,651, and 8,479 Da, while those from T. roseopersicina were found to be 10,661 and 8,759 Da by laser desorption time-of-flight mass spectrometry. The larger T. roseopersicina protein is N-terminally blocked, probably by acetylation, but small amounts of the unblocked form (mass = 10,619) were also isolated by HPLC. Protein sequencing showed that the two larger C. vinosum proteins are homologous to each other and to the large T. roseopersicina protein. The 8,479 Da C. vinosum and 8,759 Da T. roseopersicina proteins are also homologous, indicating that sulfur globule proteins are conserved between different species of purple sulfur bacteria.

Expression of the synaptophysin gene family is not restricted to neuronal and neuroendocrine differentiation in rat and human

The integral membrane protein synaptophysin is one of the major polypeptide components of the small, electron-translucent, transmitter-containing vesicles in neurons and of similar vesicles in neuroendocrine (NE) cells. In an attempt to identify synaptophysin-related molecules, such as synaptoporin, it was noticed in polymerase chain reaction (PCR) experiments that products having the expected size could be amplified not only from neuronal and NE cells, but also from non-NE cells. Northern blot hybridization analyses demonstrated that certain non-NE cells express low amounts of synaptophysin mRNA although the encoded polypeptide could not be detected. These observations, however, did not explain the consistent amplification of cDNA fragments regardless of cell type. PCR products were therefore cloned and a novel type of cDNA was identified in rat and human. The partial human cDNA was completed by isolation of phage cDNA clones constructed from a human keratinocyte cell line (HaCaT) and by PCR. When used in hybridization experiments with genomic DNA, this clone recognized a single gene. The 2106 bp cDNA contains an open reading frame coding for a polypeptide of calculated molecular weight 28,565 and having an isoelectric point of 8.45. This polypeptide is very similar to synaptophysin in the four transmembrane domains and the connecting loop regions but lacks the characteristic cytoplasmic tail. Extensive PCR analyses and Northern blot hybridization experiments demonstrated that the synaptophysin-related gene is ubiquitously expressed in vitro and in vivo. To stress the ubiquity of expression in contrast to the restricted distribution of synaptophysin and synaptoporin, I propose to refer to the encoded polypeptide as pantophysin.

Expression of cytokeratins 13 and 16 in middle ear cholesteatoma

The accumulation of keratinizing epithelium in the middle ear cavity is a crucial factor in the pathogenesis of cholesteatoma. We hypothesize that keratinocytes from the skin of the ear canal migrate and hyperproliferate in response to inflammation in the middle ear cavity to cause accumulation of keratin debris. In the present study, we investigated the expression of specific cytokeratins (CKs) in the cholesteatoma matrix to determine whether cholesteatoma is a hyperproliferative disease. Cytokeratin expression was examined in cholesteatoma, meatal skin, and tympanic membrane with two monoclonal antibodies, one for both cytokeratins 13 and 16 (antibody K8.12), and another for cytokeratin 13 only (antibody KS-1A3). CK 13 (MW 51 KD) is a marker of differentiation and CK 16 (MW 48 KD) is a marker of hyperproliferation of keratinocytes. The use of immunoblot probes showed that CKs 13 and 16 were present in cholesteatoma. Immunofluorescent staining showed the presence of CK 16 in the suprabasal layer of cholesteatoma, which was located near the external ear canal. CK 13 was localized in the suprabasal layer of meatal skin and tympanic membrane. CK 13 was localized in the basal layer of the cholesteatoma, distal to the external ear canal, but not in the meatal skin and tympanic membrane. Taken together, the present data suggest that cholesteatoma is a hyperproliferative disease and that cholesteatoma expresses CK 16 near the external ear canal and transforms to express CK 13 during growth distally.

The large type II 70-kDa keratin of mouse epidermis is the ortholog of human keratin K2e

The basic keratin pattern of mammalian epidermis consists of the basal keratin pair K5/K14 and the differentiation-specific keratin pair K1/K10. Distinct skin sites of the adult mouse, i.e., ear, sole of the foot, and interscale regions of tail skin, express an additional, type II 70-kilodalton (kDa) keratin without a defined new type I partner in suprabasal epidermal cells. Until now, the question whether this large keratin is specific for the mouse (or related small rodents) or whether orthologous keratins exist in other species has not yet been answered. In the present study, we have determined the full-length amino acid sequence of the 70-kDa keratin. The keratin comprises 707 amino acid residues and has a calculated molecular weight of 70,976.70 Da. From the structural point of view, the 70-kDa keratin is remarkable in that more than half of both the V1 and V2 subdomains of its non alpha-helical head and tail portions consist of different glycine-rich peptide motifs that are configured consecutively at least two times and as much as seven times in tandem. By means of sequence comparisons and phylogenetic investigations, we show that the 70-kDa keratin represents the murine ortholog of the human 65-kDa keratin K2e, whose nature as a genuine keratin has recently been demonstrated. The unusually large size difference of 5 kDa between MK2e and HK2e is due mainly to a different duplication rate of the glycine-rich peptide motifs in the respective V subdomains of the orthologous keratins. We discuss the properties of these highly specialized keratins, which in both species define locally restricted epidermal keratin phenotypes, and compare them with other orthologous keratins that belong to the basic epidermal keratin pattern.

Molecular characterization of the body site-specific human epidermal cytokeratin 9: cDNA cloning, amino acid sequence, and tissue specificity of gene expression

Differentiation of human plantar and palmar epidermis is characterized by the suprabasal synthesis of a major special intermediate-sized filament (IF) protein, the type I (acidic) cytokeratin 9 (CK 9). Using partial amino acid (aa) sequence information obtained by direct Edman sequencing of peptides resulting from proteolytic digestion of purified CK 9, we synthesized several redundant primers by 'back-translation'. Amplification by polymerase chain reaction (PCR) of cDNAs obtained by reverse transcription of mRNAs from human foot sole epidermis, including 5'-primer extension, resulted in multiple overlapping cDNA clones, from which the complete cDNA (2353 bp) could be constructed. This cDNA encoded the CK 9 polypeptide with a calculated molecular weight of 61,987 and an isoelectric point at about pH 5.0. The aa sequence deduced from cDNA was verified in several parts by comparison with the peptide sequences and showed the typical structure of type I CKs, with a head (153 aa), and alpha-helical coiled-coil-forming rod (306 aa), and a tail (163 aa) domain. The protein displayed the highest homology to human CK 10, not only in the highly conserved rod domain but also in large parts of the head and the tail domains. On the other hand, the aa sequence revealed some remarkable differences from CK 10 and other CKs, even in the most conserved segments of the rod domain. The nuclease digestion pattern seen on Southern blot analysis of human genomic DNA indicated the existence of a unique CK 9 gene. Using CK 9-specific riboprobes for hybridization on Northern blots of RNAs from various epithelia, a mRNA of about 2.4 kb in length could be identified only in foot sole epidermis, and a weaker cross-hybridization signal was seen in RNA from bovine heel pad epidermis at about 2.0 kb. A large number of tissues and cell cultures were examined by PCR of mRNA-derived cDNAs, using CK 9-specific primers. But even with this very sensitive signal amplification, only palmar/plantar epidermis was found positive. By in situ hybridization and immunolocalization we further showed that CK 9 is only expressed in the suprabasal cell layers of this special epidermal tissue. We discuss the molecular properties of CK 9 and its cell type- and body site-specific expression in relation to the special differentiation of palmar/plantar epidermis and to diseases specific for this body site.

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.

Intermediate filaments as differentiation markers of exocrine pancreas. II. Expression of cytokeratins of complex and stratified epithelia in normal pancreas and in pancreas cancer

Cytokeratin (CK) expression in tumors generally reflects the CK pattern of the corresponding normal epithelium. Pancreas cancers express CK of simple epithelia 7, 8, 18 and 19, as normal ductal cells. To analyze whether CK of complex or stratified epithelia are abnormally expressed in pancreas cancers, we have used polypeptide-specific mouse monoclonal antibodies (MAbs) detecting CK 5, CK 10, CK 13, CK 14 and CK 17, and an antibody detecting CK 13, CK 15 and CK 16. The streptavidin-peroxidase technique was applied on sections of fresh-frozen specimens of normal pancreas and of pancreas cancer. None of these polypeptides were expressed by normal acinar and centro-acinar cells. CK 5, CK 14 and CK 17 were expressed by less than 5% of cells in normal ducts, whereas CK 10, CK 13, CK 15 and CK 16 were not expressed at all. In tumors, CK 14, CK 15/16 and CK 17 were detected in the majority of cases studied; CK 5, CK 10 and CK 13 were present in a sub-population of pancreas cancers. CK of complex/stratified epithelia were detected in areas of glandular differentiation, but expression was more intense in areas of squamous differentiation. In pancreatitis adjacent to cancer, CK of complex/stratified epithelia were weakly detected or undetectable. These results suggest that up-regulation of these CK takes place in pancreas cancer. The CK phenotype may be of help in the differential diagnosis of this tumor.

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

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

Low frequency of codon 61 Ha-ras mutations and lack of keratin 13 expression in 7,12-dimethylbenz[a]-anthracene-induced hamster skin tumors

Alterations in the pattern of keratin expression are a common feature of skin-tumor development. In this study, we investigated whether the loss of epidermal keratin 1 (K1) and its replacement by mucosal keratin 13 (K13) is unique to mouse skin tumors induced by 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA), since it has been reported that human epidermal tumors do not exhibit aberrant expression of K13. With that purpose, we analyzed the keratin profiles of 16 DMBA-induced hamster skin tumors using monospecific antibodies against K1 and K13. Although all the tumors expressed K1, they also showed an overall tendency towards loss of this keratin; furthermore, none of the tumors expressed K13. Previous studies have suggested that the induction of K13 in mouse skin is related to the mutation of the Ha-ras gene by the initiating agent DMBA, a mutation consistently found in murine DMBA/TPA-induced tumors and rarely found in human skin tumors. Therefore, we also evaluated the tumors for the presence of codon-61 mutations by direct sequencing of DNA extracted from paraffin-embedded tissue sections. Only three tumors showed an A-->T transversion in the second nucleotide of Ha-ras codon 61. However, presence of the mutation did not correlate with K1 staining. Although hamster skin tumors were induced by the same initiator as were mouse skin tumors, hamster skin tumors did not show the same keratin profile. Moreover, their immunohistochemical expression of K1 and K13 and their codon 61 sequences resembled that of their human counterparts. These results suggest that the aberrant expression of K13 may be unique to murine skin. Furthermore, although codon 61 Ha-ras mutation appears to be related to keratin alterations in the mouse model, this mutation is not sufficient to produce the same biochemical changes in other species.

ras gene activation and aberrant expression of keratin K13 in ultraviolet B radiation-induced epidermal neoplasias of mouse skin

Both papillomas and squamous cell carcinomas (SCC) induced in mouse epidermis by initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA) exhibit aberrant expression of a type I keratin, K13, that is normally characteristic of terminal differentiation of internal stratified epithelia. There is evidence that the aberrant expression of K13 depends on the presence of an activated ras gene in mouse epidermal keratinocytes (Sutter et al., Mol Carcinog 4:467-476, 1991). To assess the general validity of this hypothesis, we investigated both aberrant K13 expression and activation of each of the three members of the ras gene family in epidermal tumors induced in four different mouse strains (SKH-1 hr, SENCAR, BALB/c, and C3H/He) by chronic irradiation with ultraviolet (UV) B. The tumor collection comprised nine papillomas and 30 well or poorly differentiated SCC. Aberrant K13 expression occurred in only five of 39 tumors and was restricted to SCC of both types. This indicates that aberrant K13 expression in UV-induced epidermal tumors was intrinsically different from that in chemically induced tumors. Polymerase chain reaction analysis of the tumors for different point mutations in codons 12, 13, and 61 of the Ha-ras and Ki-ras genes and in codon 61 of the N-ras gene revealed that only one of the well differentiated tumors from a SKH-1 hr mouse exhibited a GGA-->GAA mutation in codon 12 of the Ha-ras gene. Although this tumor was also positive for aberrant K13 expression, such a correlation could not be made for the remaining K13-expressing tumors. This indicates that the activation of one of the members of the ras gene family is not a general prerequisite for the aberrant expression of K13 in mouse epidermal keratinocytes.

Squamous cell metaplasia in the human lung: molecular characteristics of epithelial stratification

Squamous cell metaplasia (SCM) is a frequent epithelial alteration of the human tracheobronchial mucosa. This review pays particular attention to the fact that SCM can mimic esophageal, and in some instances even skin-type differentiation, showing striking similarities not only in morphology but also in terms of gene expression. Therefore, characterization of this dynamic process lends insight into the process of stratification, squamous cell formation, and "keratinization" in a pathologically relevant in vivo situation in man. First, the concept of metaplasia is presented with certain historical viewpoints on histogenesis. Then, the morphological characteristics of normal bronchial epithelium are compared with the altered phenotype of cells in SCM. These changes are described as a disturbance of the finely tuned balance of differentiation and proliferation through the action of a variety of extrinsic and intrinsic factors. Molecular aspects of altered cell/cell and cell/extracellular matrix interactions in stratified compared with single-layered epithelia are discussed with reference to SCM in the lung. Intracellular organizational and compositional changes are then summarized with special emphasis on the differential distribution of the cytokeratin (CK) polypeptides. Finally, the still unresolved problems of the histogenetic relationships between normal bronchial mucosa, SCM, and pulmonary neoplasms are addressed. As these questions remain open, examples for detection of well defined "markers" are provided that may be employed as objective criteria for determining clinically important cellular differentiation features.

Chromosomal mapping of human cytokeratin 13 gene (KRT13)

In the present study the human cytokeratin 13 gene (KRT13), encoding a polypeptide characteristic of internal stratified epithelia, has been mapped with the help of the polymerase chain reaction and somatic cell hybrids to chromosome 17. In situ hybridization of a KRT13 cDNA probe to metaphase chromosomes allowed the assignment of the KRT13 gene within the q12-q21.2 region of chromosome 17.

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

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

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.

Changes of expression of intermediate filament proteins during ontogenesis of eccrine sweat glands

The intermediate filament expression in fetal and adult human eccrine sweat glands was studied by immunoperoxidase microscopy performed on cryostat sections using monoclonal antibodies against various cytokeratins (CK), vimentin, and actin. In palmar skin of 14-week-old fetuses, the early dermal cords showed a primitive CK pattern similar to that of epidermal basal cells. From week 15 on (distal finger skin), inner cells of the proximal (ductal) portion of the glandular anlagen expressed CK 1/10/11 and 19 (markers of adult eccrine ductal luminal cells). In addition, CK 4 was expressed in ductal luminal cells mainly in the fetal period. In the distal portion of the sweat gland anlagen the increased or new expression of the simple-epithelium-type CK 7, 8, 18, and 19 was detected at week 15, indicating the onset of the secretory differentiation pathway. Two subsegments of the prospective secretory portion could be distinguished (elongated part and end bud). Interestingly, in fetuses, most secretory portion cells co-expressed vimentin in addition to CK. From week 22 on, peripheral cells of the secretory portion were stained for CK 17 and smooth-muscle-type actin, suggesting myoepithelial differentiation. In newborn and adult eccrine glands, secretory cells expressed mainly CK 7, 8, 18, and 19, whereas myoepithelial cells were conspicuous by their co-expression of certain CK (including CK 5 and 17), vimentin, and smooth-muscle-type actin and sometimes even glial filament protein (GFP), similar to myoepithelial cells of other glands. These results throw further light onto the complex processes of fetal development of eccrine sweat glands and their cellular diversification. The possible biologic significance of the differential CK expression in the various glandular cell types is discussed.

Aberrant in vitro expression of keratin K13 induced by Ca2+ and vitamin A acid in mouse epidermal cell lines

Normally the expression of the murine type I keratin K13 is restricted to differentiating cells of internal squamous epithelia which line the oral cavity and the upper digestive tract. Recently, however, we were able to show that K13 is aberrantly but constitutively expressed without its normal type II partner K4 also in differentiating parts of 7,12-dimethylbenz(a)anthracene (DMBA/TPA) 12-O-tetradecanoylphorbol-13-acetate-induced squamous cell carcinomas of mouse back skin, whereas its likewise suprabasal expression in papillomas is variable (Nischt et al., Mol. Carcinogenesis 1, 96-108, 1988). In an attempt to reproduce the aberrant expression of K13 in a mouse in vitro system, we have investigated eight established murine epidermal cell lines for their putative ability to express K13. The cell lines differed distinctly in their derivation and comprised cell lines originating from DMBA/TPA induced papillomas (line SP1) or DMBA-treated adult mouse epidermis (line 308) as well as cell lines derived from DMBA or DMBA/TPA-treated primary epidermal keratinocytes (lines PDV and MCA 3D) and cell lines which arose spontaneously by long-term culture of normal epidermal keratinocytes (lines HEL 30 degrees HEL 37 degrees, HELP I and HELP III). We show that, independent of their derivation, all cell lines possess the intrinsic property to aberrantly express K13. Invariably the K13 gene is not expressed when the lines are cultured under low Ca2+ conditions (0.05 mM) and thus prevented from differentiation. Its expression can, however, be induced either by increasing the extracellular Ca2+ concentration or by the addition of physiological concentrations of vitamin A acid to low Ca2+ medium. Whereas in the latter case, K13 expression occurs without concomitant induction of morphological differentiation of the cells, Ca2+ elevation in the culture medium induces squamous differentiation and K13 expression occurs only in differentiating cells, thus reflecting the situation observed in in vivo tumors. All cell lines exhibit a concentration optimum for the stimulatory agents; however, the degree of maximal K13 expression varies considerably among the individual cell lines and shows a striking correlation with the reported tumorigenicity of the lines after transplantation to animals. In contrast, a tentatively suggested correlation between the activation of the Ha-ras gene and the aberrant expression of K13 (Nischt et al., Mol. Carcinogenesis 1, 96-108, 1988) could not definitely be confirmed since we observed K13 expression also in three cell lines which did not carry a mutation in codon 61 of the Ha-ras gene.(ABSTRACT TRUNCATED AT 400 WORDS)

The synaptophysin-encoding gene in rat and man is specifically transcribed in neuroendocrine cells

Synaptophysin (SY) is an integral membrane protein of presynaptic small (30-80-nm) translucent vesicles also present in dispersed neuroendocrine cells. As the occurrence of this type of vesicle is specific for two major pathways of differentiation, the neuronal and neuroendocrine-epithelial information on the regulation of SY synthesis should contribute to an understanding of regulatory principles common to both pathways. Isolation and comparison of the complete rat and human single-copy genes showed that despite the difference in size (16 kb in rat vs. 13 kb in man) intron/exon boundaries are precisely conserved. Surprisingly, intron VI is located in the 3'-noncoding region in both species. The major transcriptional start point, as determined by primer extension and S1-nuclease protection analyses in rat pheochromocytoma-derived PC12 cells and rat brain, mapped to a site 27 nt 5' of the first methionine codon. Unexpectedly, the 5' upstream region is devoid of any TATA or CAAT boxes, but shows instead typical features of 'housekeeping' genes, i.e., G + C-rich islands and four Sp1-binding motifs. Using 'nuclear run-on' assays, we have identified examples in which SY synthesis is regulated at the transcriptional level. Reporter gene constructs showed that approx. 1.2 kb of the immediate upstream region contains promoter enhancer elements that were, however, insufficient to confer cell-type specific expression, whereas sequences farther upstream were able to suppress thymidine kinase promoter activity in a cell-type-dependent fashion.

v-Ha-ras-induced mouse skin papillomas exhibit aberrant expression of keratin K13 as do their 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate -induced analogues

Introduction of the v-Ha-ras gene into primary epidermal keratinocytes, followed by grafting of these cells to animals, leads to the formation of benign epidermal tumors that resemble papillomas induced chemically by a two-stage carcinogenesis protocol. In this study, we investigated v-Ha-ras-induced papillomas for aberrant expression of type I keratin K13, previously described in 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13- acetate (DMBA/TPA)-induced mouse epidermal tumors. Papillomas produced from three independent infection series were removed 3 wk after grafting concomitant with control grafts originating from mock-, neo-, and v-fos-infected primary keratinocytes. Combined analysis of the grafts by western blotting of extracted keratins and immunofluorescence studies of frozen sections with a K13-monospecific antibody revealed K13 expression in all v-Ha-ras-induced papillomas and absence of this keratin in all control grafts. K13-positive cells in papillomas were restricted to the suprabasal cell layers of the lesions and, at this stage of papilloma development, occurred as foci of varying extensions. Analysis of genomic DNA from v-Ha-ras-induced papillomas for the methylation state of a CpG dinucleotide in the distant promoter region of the K13 gene revealed the occurrence of unmethylated DNA copies that were generated at the expense of methylated DNA copies ubiquitously present in normal epidermis. The ratio of unmethylated to methylated DNA copies correlated with the extent of suprabasal K13 protein expression. Thus, all features of aberrant K13 expression previously described in DMBA/TPA-induced papillomas were shared by v-Ha-ras-induced papillomas.