Keratins K14 Research Articles

Nkx-2.3 gene in mouse epidermal maturation.

In higher vertebrates, from amphibians to humans, epidemial maturation is a conserved developmental process. Using adult epidemial tissue and an established keratinocyte cell line, the mouse Nkx-2.3 homeobox gene was demonstrated, for the first time, to be expressed in mouse epidermal keratinocytes. Under the normal culture condition, the spontaneous aggregation phenomenon, a common initiation step of ES cell differentiation, and the induction of mouse adult K1 keratin, a marker of mature epidermal keratinocytes, were both observed in vitro when the Xenopus Nkx-2.3 gene was stably transfected into a mouse pluripotent P19 EC cell line. The induction of mouse K1 keratin by using its Xenopus orthologous gene in the mouse P19 cell implies that Nkx-2.3 may play a conserved role in the epidermal maturation of the mouse, as it does in that of the frog (Ma, 2004). However, the CAT assay study on frog adult keratin promoter could not find the induction of adult keratin. This implies there might not be a direct activation of its promoter.

Treasure or artifact: a decade of p63 research speaks for itself

Treasure or artifact: a decade of p63 research speaks for itself

Defining the complex epithelia that comprise the canine claw with molecular markers of differentiation

Canine claws are complex epithelial structures resembling the mammalian hair fibre, and human nail plate, in terms of tissue-specific differentiation. They are composed of several distinct epithelial cell lineages undergoing either hard or soft keratinization. The claw plate has three distinct regions: stratum externum, stratum medium (SM) and stratum internum and the underside and tip are cushioned by a soft keratinizing epithelium, the sole. We have examined keratin expression in the canine claw and associated epithelia. Digits from German shepherd dogs were decalcified, processed and sectioned by sledge microtome. Sections were stained with haematoxylin and eosin or treated with specific antibodies to various keratins (immunohistochemistry). Proteins were extracted from claw components and analysed by SDS-PAGE and Western blotting. The keratinized canine claw plate expressed hair-specific keratins (type I, K25-K38 and type II, K71-K86) but only the inner region of the SM contained K6- and K16-positive tubules, soft epithelia running through the hard keratinized claw plate. The soft keratinaceous sole epithelium expressed keratins K5, K6, K14, K16 and K17 and contained cells with abundant envelopes. The canine claw had two slippage zones, the inner claw bed, between the claw plate and ungula process, which expressed K17 and the region between the inner and outer claw sheath, equivalent to the hair follicle companion layer, which expressed K6, K77, K16 and K17. In conclusion, several different cell types have been defined in the canine claw presenting a complex mechanism of cellular differentiation.

Barrier Function of Cultivated Limbal and Oral Mucosal Epithelial Cell Sheets

To investigate barrier function of cultivated limbal and oral mucosal epithelial sheets. Human and rabbit cultivated limbal epithelial sheets (CLES) and cultivated oral mucosal epithelial sheets (COMES) were subjected to immunohistochemistry for keratin K3, K4, K13, ZO-1, and occludin. Results were compared with those obtained from normal cornea and oral mucosa. Prepared under various culture conditions, the in vitro barrier function of these sheets was evaluated by biotin assay and transepithelial electrical resistance measurement. The CLES and COMES were transplanted to rabbit eyes with limbal deficiency, and fluorophotometry was performed before and after surgery. Transplanted corneas were subjected to immunohistochemistry after surgery. Both normal corneal epithelium and CLES were positive for K3 but negative for K13. Both CLES and COMES showed positive expression of ZO-1 and occludin in the apical epithelium. Both CLES and COMES demonstrated tight junction-like structures in the apical portion of the superficial epithelium by electron microscopy. Although rabbit COMES showed better barrier function than CLES, as evaluated by biotin assay and transepithelial electrical resistance, no such differences were noted in human sheets. Whereas epithelial barrier function was significantly improved after transplantation of CLES in the rabbit limbal deficiency models, recovery was not remarkable after COMES transplantation. Immunohistochemical study revealed that transplanted COMES had an irregular epithelial thickness with decreased expression of ZO-1 in some areas. Epithelial barrier function was influenced by various factors such as culture condition and local environment after transplantation. CLES appears to offer better barrier function than COMES.

An Active Role of the ΔN Isoform of p63 in Regulating Basal Keratin Genes K5 and K14 and Directing Epidermal Cell Fate

BackgroundOne major defining characteristic of the basal keratinocytes of the stratified epithelium is the expression of the keratin genes K5 and K14. The temporal and spatial expression of these two genes is usually tightly and coordinately regulated at the transcriptional level. This ensures the obligate pairing of K5 and K14 proteins to generate an intermediate filament (IF) network that is essential for the structure and function of the proliferative keratinocytes. Our previous studies have shown that the basal-keratinocyte restricted transcription factor p63 is a direct regulator of K14 gene.Methodology/Principal FindingsHere we provide evidence that p63, specifically the ΔN isoform also regulates the expression of the K5 gene by binding to a conserved enhancer within the 5′ upstream region. By using specific antibodies against ΔNp63, we show a concordance in the expression between basal keratins and ΔNp63 proteins but not the TAp63 isoforms during early embryonic skin development. We demonstrate, that contrary to a previous report, transgenic mice expressing ΔNp63 in lung epithelium exhibit squamous metaplasia with de novo induction of K5 and K14 as well as transdifferentiation to the epidermal cell lineage. Interestingly, the in vivo epidermal inductive properties of ΔNp63 do not require the C-terminal SAM domain. Finally, we show that ΔNp63 alone can restore the expression of the basal keratins and reinitiate the failed epidermal differentiation program in the skin of p63 null animals.SignificanceΔNp63 is a critical mediator of keratinocyte stratification program and directly regulates the basal keratin genes.

Human Female Hair Follicles Are a Direct, Nonclassical Target for Thyroid-Stimulating Hormone

Pituitary thyroid-stimulating hormone (TSH) regulates thyroid hormone synthesis via receptors (TSH-R) expressed on thyroid epithelial cells. As the hair follicle (HF) is uniquely hormone-sensitive and, hypothyroidism with its associated, increased TSH serum levels clinically can lead to hair loss, we asked whether human HFs are a direct target for TSH. Here, we report that normal human scalp skin and microdissected human HFs express TSH-R mRNA. TSH-R-like immunoreactivity is limited to the mesenchymal skin compartments in situ. TSH may alter HF mesenchymal functions, as it upregulates alpha-smooth muscle actin expression in HF fibroblasts. TSH-R stimulation by its natural ligand in organ culture changes the expression of several genes of human scalp HFs (for example keratin K5), upregulates the transcription of classical TSH target genes and enhances cAMP production. Although the functional role of TSH in human HF biology awaits further dissection, these findings document that intracutaneous TSH-Rs are fully functional in situ and that HFs of female individuals are direct targets for nonclassical, extrathyroidal TSH bioregulation. This suggests that organ-cultured scalp HFs provide an instructive and physiologically relevant human model for exploring nonclassical functions of TSH, in and beyond the skin.

Immunoexpression of keratins in the calcifying cystic odontogenic tumor epithelium

Ameloblastomatous epithelium containing clusters of ghost cells is the typical histopathology of calcifying cystic odontogenic tumor (CCOT). This paper aimed to assess keratins AE1-AE3, K7, K10/13, K14, K18, K19, vimentin, laminin, and collagen IV in 08 CCOTs to discuss their histopathogenesis. Similarity to the immunoprofile of the stratified squamous epithelium was seen in the with the basal layer expressing K14 and the upper cells expressing K10/13. When compared to the immunoprofile of the normal odontogenic epithelium, of odontogenic tumor epithelia and of the ghost cells described in the literature, it was possible to suggest that the CCOT epithelium differentiates towards squamous type.

Abnormal Epithelial Differentiation and Tear Film Alteration in Pinguecula

To investigate the differentiation of conjunctival epithelium and tear film function in pingueculae. Twelve patients (12 eyes) who underwent simple excision for pingueculae were enrolled in the study. Immunostaining for K14, K19, K10, MUC5AC, Pax6, P63, Ki67, and K16 was performed on the pinguecula epithelium and normal conjunctival epithelium. Schirmer I test results and tear film break-up time (TFBUT) were evaluated just before and 1 month after surgery. Abnormal epidermal differentiation of pinguecula tissue, as evidenced by a decline in or absence of Pax6 expression, was accompanied by a decline in or absence of K19 keratin and MUC5AC, and an increase in K10 and K14 keratin. Furthermore, the pinguecula epithelium was actively proliferating, as evidenced by positive expression of Ki67, P63, and K16 keratin. The Schirmer I test results did not indicate any significant differences before and after surgery. However, the TFBUT was significantly prolonged 1 month after surgery compared with before surgery. Pinguecula is a condition of abnormal epithelial differentiation. It is characterized by squamous proliferation and metaplasia, resulting in instability of tear film with normal basic tear secretion.

E7 Oncoprotein of Novel Human Papillomavirus Type 108 Lacking the E6 Gene Induces Dysplasia in Organotypic Keratinocyte Cultures

The genome organization of the novel human papillomavirus type 108 (HPV108), isolated from a low-grade cervical lesion, deviates from those of other HPVs in lacking an E6 gene. The three related HPV types HPV103, HPV108, and HPV101 were isolated from cervicovaginal cells taken from normal genital mucosa (HPV103) and low-grade (HPV108) and high-grade cervical (HPV101) intraepithelial neoplasia (Z. Chen, M. Schiffman, R. Herrero, R. DeSalle, and R. D. Burk, Virology 360:447-453, 2007, and this report). Their unusual genome organization, against the background of considerable phylogenetic distance from the other HPV types usually associated with lesions of the genital tract, prompted us to investigate whether HPV108 E7 per se is sufficient to induce the above-mentioned clinical lesions. Expression of HPV108 E7 in organotypic keratinocyte cultures increases proliferation and apoptosis, focal nuclear polymorphism, and polychromasia. This is associated with irregular intra- and extracellular lipid accumulation and loss of the epithelial barrier. These alterations are linked to HPV108 E7 binding to pRb and inducing its decrease, an increase in PCNA expression, and BrdU incorporation, as well as increased p53 and p21(CIP1) protein levels. A delay in keratin K10 expression, increased expression of keratins K14 and K16, and loss of the corneal proteins involucrin and loricrin have also been noted. These modifications are suggestive of infection by a high-risk papillomavirus.

Nkx-2.3 gene in mouse epidemial maturation

In higher vertebrates, from amphibians to humans, epidemial maturation is a conserved developmental process. Using adult epidemial tissue and an established keratinocyte cell line, the mouse Nkx-2.3 homeobox gene was demonstrated, for the first time, to be expressed in mouse epidermal keratinocytes. Under the normal culture condition, the spontaneous aggregation phenomenon, a common initiation step of ES cell differentiation, and the induction of mouse adult K1 keratin, a marker of mature epidermal keratinocytes, were both observed in vitro when the Xenopus Nkx-2.3 gene was stably transfected into a mouse pluripotent P19 EC cell line. The induction of mouse K1 keratin by using its Xenopus orthologous gene in the mouse P19 cell implies that Nkx-2.3 may play a conserved role in the epidermal maturation of the mouse, as it does in that of the frog (Ma, 2004). However, the CAT assay study on frog adult keratin promoter could not find the induction of adult keratin. This implies there might not be a direct activation of its promoter.

Proteomic analysis ofChlamydia pneumoniae-infected HL cells reveals extensive degradation of cytoskeletal proteins

Cytoskeletal proteins of HL cells, following Chlamydia pneumoniae infection, were studied by two-dimensional gel electrophoresis and two-dimensional difference gel electrophoresis. Proteome analyses of HL cells at 48 and 72 h postinfection revealed significant changes in important constituents of the intermediate filament and microtubulin networks. These cytoskeletal proteins, identified as keratin K8, keratin K18, vimentin and beta-tubulin, were represented by several distinct spots with different pI and molecular weight values, implying that they have undergone posttranslational modifications stimulated by the infection. According to MS analyses, these proteins appeared to be N- and/or C-terminally truncated. Additional immunoblot analyses suggested that inhibiting the activity of the chlamydial protease-like activity factor (CPAF) by lactacystin results in increased stability of keratin K18, vimentin and beta-tubulin in infected HL cells. Interestingly, primary amino acid sequence analyses revealed potential recognition/cleavage sites for CPAF in each of these cytoskeletal proteins. These results provide an insight into the pathogenic mechanisms exploited by chlamydia, and suggest that proteolytic modification of the indicated proteins may be involved in establishing a productive infection.

Heparanase 1: a key participant of inner root sheath differentiation program and hair follicle homeostasis

Heparanase is a heparan sulphate endo-glycosidase which was previously detected in the outer root sheath of murine hair follicles. Heparanase overexpression was reported to improve mouse hair (re)growth. In this study, we investigated its involvement in human hair biology. Immunofluorescence detection was used to explore heparanase distribution in both anagen and catagen hair follicles. Heparanase functionality was assessed in in vitro cultured hair follicles, in the presence of a heparanase activity inhibitor. Our results showed that heparanase expression was (i) primarily located in the inner root sheath (IRS) of human hair follicle, and there (ii) restricted to anagen phase. Furthermore, inhibition of heparanase in in vitro cultured hair follicles induced a catagen-like process. Hair shaft retreat upward was accompanied by a decrease in Ki67-positive cells, the formation of an epithelial strand as evidenced by K14 keratin expression, and the loss of IRS as assessed by transglutaminase 1 and desmoglein labelling. IRS distribution of heparanase and the induction of catagen-like involution of hair follicles when a potent heparanase inhibitor is added suggest that heparanase is a key actor of IRS differentiation and hair homeostasis.

Long-term alteration in the expression of keratins 6 and 16 in the epidermis of mice after chronic UVB exposure

The influences of chronic UVB exposure on epidermal differentiation have been poorly studied compared to dermal photo-aging although those effects are very important in terms of photo-damage to the skin. The purpose of this study was to investigate the effects of chronic UVB exposure on keratin expression in the epidermis. The effects on murine skin of chronic exposure to weak UVB (below 1 MED) was examined by immunoblotting for keratins K10, K5, K6, and K16, by immunohistochemistry using antibodies to K6, K16, and Ki67 as well as by conventional HE staining of skin sections. Alterations of keratin expression induced by the chronic UVB exposure were distinct from those elicited by a single acute UVB exposure. The expression of keratins K6 and K16 was quite long-lasting, continuing for 7 weeks after 6 weeks of chronic UVB exposure and for 6 weeks after 9 weeks of chronic UVB exposure. In contrast, K6 and K16 expression induced by a single UVB exposure at 0.5 MED or 3 MED almost ceased within 2 weeks after that exposure. Furthermore, the expression of the constructive keratins, K5 and K10, remained almost unchanged by chronic UVB exposure. Epidermal thickness was increased significantly immediately after the 9 weeks of chronic UVB exposure; however, it had returned to normal level 6 weeks later. The alterations in keratin expression accompanied the marked disruption of the ordered ultrastructure of keratin intermediate filaments, which were observed by TEM. Thus, chronic exposure to UVB has a deep impact on the biosynthetic regulation of different keratins in the epidermis, thereby interfering with the ordered ultrastructure of keratin intermediate filaments. Those events could have relevance to the mechanism of photo-damage, such as fine wrinkles observed in chronically UV-exposed skin in addition to dermal photo-aging.

Contrasting Expression of Keratins in Mouse and Human Embryonic Stem Cells

RNA expression data reveals that human embryonic stem (hES) cells differ from mouse ES (mES) cells in the expression of RNAs for keratin intermediate filament proteins. These differences were confirmed at the cellular and protein level and may reflect a fundamental difference in the epithelial nature of embryonic stem cells derived from mouse and human blastocysts. Mouse ES cells express very low levels of the simple epithelial keratins K8, K18 and K19. By contrast hES cells express moderate levels of the RNAs for these intermediate filament proteins as do mouse stem cells derived from the mouse epiblast. Expression of K8 and K18 RNAs are correlated with increased c-Jun RNA expression in both mouse and human ES cell cultures. However, decreasing K8 and K18 expression associated with differentiation to neuronal progenitor cells is correlated with increasing expression of the Snai2 (Slug) transcriptional repression and not decreased Jun expression. Increasing K7 expression is correlated with increased CDX2 and decreased Oct4 RNA expression associated with the formation of trophoblast derivatives by hES cells. Our study supports the view that hES cells are more similar to mouse epiblast cells than mouse ES cells and is consistent with the epithelial nature of hES cells. Keratin intermediate filament expression in hES cells may modulate sensitivity to death receptor mediated apoptosis and stress.

BALB/c and C57BL6 mouse strains vary in their ability to heal corneal epithelial debridement wounds

Genetically engineered mice are usually produced on a mixed genetic background and can be derived from several mouse strains including 129SvJ, C57BL6, and BALB/c. To determine whether differences in recurrent corneal epithelial erosions (RCEEs), corneal epithelial stem cell deficiency (CESCD), and cell migration rate vary between two different mouse strains (BALB/c and C57BL6), 8-week mice were subjected to 1.5 (small) or 2.8 mm (large) manual debridement wounds and allowed to heal for 4 weeks. Syndecan-1 (sdc-1) null mice backcrossed seven generations onto a BALB/c genetic background were also included in the RCEE and CESCD studies to permit comparisons between genotypes within a single strain. After sacrifice, corneas were assessed for the presence of recurrent erosions; no fewer than 15 corneas were used for each strain or genotype studied. Data show that the frequency of recurrent erosions after small wounds was 81 +/− 9% in the C57BL6 mice, 73 +/− 2% in the BALB/c mice, and 32 +/− 6% in sdc-1 null mice. Neither strain developed CESCD after small wounds. The frequency of erosions after large wounds was greater (88 +/− 8%) in the C57BL6 mice compared to BALB/c (60 +/− 2%), and sdc-1 null mice (32 +/− 5%). Four weeks after the large wounds, fixed, flat mounted corneas were assessed for evidence of CESCD with antibodies against the conjunctival keratin K8 and the goblet cell marker, the mucin Muc5AC. The frequency of CESCD 4 weeks after the large wounds was significantly greater in the C57BL6 mice than in the BALB/c or sdc-1 null mice. To assess cell migration rates, corneas were subjected to 1.5 mm wounds and allowed to heal for 12, 15, 18, 21, and 24 h. After sacrifice, corneas were stained with Richardson stain (BALB/c) or propidium iodide (C57BL6) to assess reepithelialization rates. While reepithelialization rates were similar for the early times after wounding, by 24 h the C57BL6 corneas had healed faster: 16 of 30 corneas from the C57BL6 mice were closed compared to 9 of 30 of the BALB/c wounds. BALB/c corneas appeared larger overall compared to C57BL6 corneas; measurements of the overall mass of the enucleated eyes and diameters of the flat-mounted corneas confirmed that C57BL6 eyes and corneas were 6.8% and 4.4% smaller respectively than those of BALB/c mice even though the masses of the two mouse strains at 8 weeks of age were identical. Using BrdU to label dividing cells, we found that 18 h after wounding, C57BL6 and BALB/c corneal epithelia showed similar numbers of proliferating cells. To determine if the enhanced corneal epithelial cell migration rate seen in the C57BL6 mice was specific to the cornea, we conducted time-lapse studies to assess random cell migration rates in vitro using primary cultures of mouse epidermal keratinocytes. Consistent with the in vivo data, epidermal keratinocytes derived from BALB/c mice migrated 60% slower than C57BL6 cells. These data prove that strain-specific differences in cell migration rate in vivo are present in the cornea and are accompanied by differences in the frequencies of recurrent erosions and corneal epithelial stem cell deficiency.

Transgenic expression of S100A2 in hairless mouse skin enhances Cxcl13 mRNA in response to solar-simulated radiation

S100A2 is a homodimeric protein that undergoes oxidative cross-linking and translocation from the nucleus to the cytosol in the context of oxidative stress. Suggestive of a role for S100A2 in the cutaneous response to ultraviolet light, we found altered S100A2 immunostaining in photodamaged human skin, and crosslinking of S100A2 after ultraviolet A (UVA) irradiation of normal human keratinocytes (NHK). Skin from mice, rats, and rabbits did not contain S100A2 protein, whereas skin samples from pigs, frogs and humans were strongly positive. Survival after UVA irradiation was significantly greater in NHK compared to mouse keratinocytes, suggesting a protective role for S100A2. To test this hypothesis in vivo, we expressed S100A2 in SKH2/J hairless mice under the control of a bovine keratin 5 promoter, and compared responses of TG and WT mice from 1 to 7 days after a single dose (0.5-1 MED) of solar-simulated radiation (SSR) from UVA-340 bulbs. WT and TG mice manifested a similarly robust response to SSR, characterized by epidermal hyperplasia, marked induction of p21(WAF), and a twofold increase in p53. Thymine dimers (TD) were markedly increased in the epidermis and the dermis, but while over 95% of the epidermal TD were removed by 5-6 days, elevated dermal TD persisted nearly unchanged for 7 days. Global transcriptional profiling of WT and TG mice revealed strong induction of multiple transcripts, including keratins K6 and K16, defensin beta 3, S100A8, S100A9, Sprr2i and Sprr2f. However, the only S100A2-dependent difference we observed was an induction of Cxcl13 transcripts in TG, but not WT mice (4.4-fold vs. 0.7-fold, n = 3, P = 0.022). This finding was confirmed in an independent set of mice analyzed by quantitative RT-PCR (8.8-fold vs. 1.2-fold, n = 4, P = 0.001). The finding of persistent dermal DNA damage after suberythemal doses of SSR merits further study.

Keratin down-regulation in vimentin-positive cancer cells is reversible by vimentin RNA interference, which inhibits growth and motility

At later stages of tumor progression, epithelial carcinogenesis is associated with transition to a mesenchymal phenotype, which may contribute to the more aggressive properties of cancer cells and may be stimulated by growth factors such as epidermal growth factor and transforming growth factor-beta. Previously, we found that cells derived from a nodal metastatic squamous cell carcinoma are highly proliferative and motile in vitro and tumorigenic in vivo. In the current study, we have investigated the role of vimentin in proliferation and motility. Cells derived from nodal metastasis express high levels of vimentin, which is undetectable in tumor cells derived from a synchronous primary lesion of tongue. Vimentin expression was enhanced by epidermal growth factor and transforming growth factor-beta both independently and in combination. Use of RNA interference resulted in the generation of stable cell lines that express constitutively low levels of vimentin. RNA interference-mediated vimentin knockdown reduced cellular proliferation, migration, and invasion through a basement membrane substitute by 3-fold compared with nontargeting controls. In addition, cells with reduced vimentin reexpressed differentiation-specific keratins K13, K14, and K15 as a result of increased gene transcription as judged by quantitative PCR and promoter-reporter assays. Furthermore, cells in which vimentin expression was reduced showed a greatly decreased tumorigenic potential, as tumors developing from these cells were 70% smaller than those from control cells. The data suggest that reversal of the mesenchymal phenotype by inhibiting vimentin expression results in reexpression of epithelial characteristics and reduced tumor aggressiveness.

Stratified epithelial sheets engineered from a single adult murine corneal/limbal progenitor cell

The limbal region of the adult cornea contains stem cells which are ultimately responsible for regeneration of the corneal epithelium during wound repair. However, primarily-isolated murine corneal/limbal epithelial cells rapidly senesce on plastic in a serum-free low [Ca2+] medium, suggesting only transit amplifying cells are promoted. We developed a novel expansion method by seeding at a low cell density (<500 cells/cm2) and prolonging each culture time beyond the lifespan of transit amplifying cells (4 weeks). Expanded cells were uniformly small, negative to K12 keratin, but positive for p63 nuclear staining, and could be subcultured beyond 100 passages. After limiting dilution, one clone (TKE2) was selected that exhibited single cell clonal expansion with a doubling time of 34.2 hrs, and had normal karyotyping, but no anchorage-independent growth. A single cell could be continually expanded to a confluent monolayer on denuded amniotic membrane and became stratified by exposing to the air-medium interface. The resultant stratified epithelium expressed K14 keratin, involucrin, connexin 43 and p63, but not K12 keratin or Pax 6. However, expression of K12 could be up-regulated by increasing extracellular calcium concentration and addition of foetal bovine serum (FBS) at P12, but less so at P85. Therefore, this murine lim-bal/corneal epithelium-derived progenitor cell line still retained the plasticity for adopting corneal lineage differentiation, could be useful for investigating limbal niche cues that may promote corneal epithelial fate decision.

New concepts on the histogenesis of eccrine neoplasia from keratin expression in the normal eccrine gland, syringoma and poroma

Peripheral and luminal layers of eccrine sweat gland ducts are self-renewing structures. Proliferation is restricted to the lowermost luminal layer, but randomly scattered in the peripheral layer. Each layer exhibits differential expression of keratins K5/K14 and K6/K16. Keratin K1 occurs only in peripheral cells and the novel keratin K77 is specific for luminal cells. To investigate the expression of luminal (K77), peripheral (K1) and further discriminatory keratins in two eccrine sweat gland tumours: syringoma, thought to show differentiation towards luminal cells of intraepidermal sweat ducts and eccrine poroma, considered to arise from poroid cells, i.e. peripheral duct cells; and keratinocytes of the lower acrosyringium/sweat duct ridge differentiating towards cells of intradermal/intraepidermal duct segments. Paraffin-embedded sections were examined by immunohistochemistry using several keratin, smooth muscle actin and Ki-67 antibodies. We confirmed the ductal nature of syringomas. Despite drastic morphological alterations in both layers, their keratin patterns remained almost undisturbed compared with normal ducts. In eccrine poroma epidermal keratins K5/K14 were ubiquitously expressed in all poroid cells. Cell islands deviating morphologically from poroid cells contained epidermal keratins K1/K10. K77 expression was limited to luminal cells of intact duct structures within the tumours. Syringomas are benign tumours of luminal cells of the lowermost intraglandular sweat duct. Poroid precursor cells of poromas do not comprise peripheral duct cells nor do poromas differentiate towards peripheral or luminal duct cells. Instead, poroid cells consist only of keratinocytes of the lowermost acrosyringium and the sweat duct ridge and poromas tend to differentiate towards the cells of the upper acrosyringium.

IKKα enhances human keratinocyte differentiation and determines the histological variant of epidermal squamous cell carcinomas

Squamous cell carcinomas (SCCs) of the skin display different clinical features according to their epithelial differentiation grade and histological variant. Understanding the causes of these divergences might increase the curability of SCCs. Therefore, it is important to study the mechanisms of differentiation in keratinocytes. IKK (IκB kinase) α is an important protein for epidermal morphogenesis, although the pathways through which it exerts its function are unknown and controversy exists about its role in cancer development. We show that enhanced IKKα expression increases both early and terminal differentiation of human keratinocytes through an E-cadherin-dependent mechanism. Increased expression of IKKα in mouse tumorigenic epidermal cells leads to changes in the differentiation pattern of the resulting SCCs, originating a distinct histological variant that resembles the human acantholytic SCC (ASCC) variant. Although human ASCCs have an aggressive clinical course and high risk of metastasis, nothing is known about their etiology. We show that human ASCCs, as observed in the counterpart IKKα murine tumors, express high levels of both IKKα and E-cadherin, with absence of keratins K1 and K10, usually co-expressed with IKKα and E-cadherin. The tight correlation between the properties of both murine and human ASCC variants strongly suggests that IKKα is responsible for the development of this human SCC variant.