Characterization of nuclear protein binding sites in the promoter of keratin K17 gene

Promoter Methylation Changes in KRT17: A Novel Epigenetic Marker for Wool Production in Angora Rabbit

Wool production is an important economic trait of Angora rabbits. Exploring molecular markers related to wool production is one of the essentials of Angora rabbits’ breeding. KRT17 (Keratin 17) is an important gene of hair follicle development, which must be explored for genetic/epigenetic variation to assess its effect on wool production. Based on the effective wool production data of 217 Angora rabbits, the high and low yield groups were screened with 1.5 standard deviations of the population mean. The full-length sequence of KRT17 was obtained by rapid amplification of cDNA ends technology, and the polymorphism was analyzed in the promoter, exon, and intron regions by direct sequencing. KRT17, SP1 over-expression plasmids, and siRNA were constructed and transfected into dermal papilla cells. The mRNA expressions of relevant genes were analyzed by RT-qPCR. The methylation level of the KRT17 promoter was determined by Bisulfite Sequencing PCR. Dual-luciferase system, site-directed mutagenesis, and electrophoretic mobility shift assays were used to analyze the binding relationship between SP1 and the promoter of KRT17. The structure map of KRT17 was drawn, and no SNPs were found in the promoter, exon, and intron, indicating a relatively conserved structure of KRT17. Expression of KRT17 was significantly higher in cutaneous tissues than in other tissues and was significantly upregulated in the high-yield group compared to the low-yield group (p < 0.05). Furthermore, the overall high methylation levels of KRT17 CpG I and CpG III showed significant association with low wool yield; the methylation levels of 5 CpG locus (CpG I site 4 and CpG III site 2−5) were significantly different between the high and low yield groups (p < 0.05). The methylation levels of 3 CpG locus (CpG I site 4 and CpG III site 4, 14) showed a significant correlation with KRT17 expression (p < 0.05). Overall, CpG III site 4 significantly affects wool production and KRT17 expressions (p < 0.05). This site promotes SP1 binding to the KRT17 promoter region (CGCTACGCCC) to positively regulate the KRT17 expression. KRT17 CpG III site 4 can be used as candidate epigenetic markers for the breeding of high wool-producing Angora rabbits.

Keratin 17 in psoriasis: Current understanding and future perspectives

Keratin 17 (K17) is a multifaceted cytoskeletal protein that is not commonly expressed in the epidermis under normal physiological conditions. However, in psoriasis, K17 is overexpressed in the suprabasal layer of the epidermis and plays an important role in the pathogenesis of the disease. In this review, we have summarized our findings and those reported in other studies concerning the pathogenic functions of K17, as well as the mechanisms underlying the increase in K17 expression in psoriasis. K17 exerts both pro-proliferative and pro-inflammatory effects on keratinocytes. Moreover, K17 peptides trigger autoreactive T cells and promote psoriasis-related cytokine production. In turn, these cytokines modulate the expression, stability, and protein-protein interactions of K17 through transcriptional and translational regulation and post-translational modification of K17 in keratinocytes. Thus, a K17/T-cell/cytokine autoimmune loop is implicated in the pathogenesis of psoriasis, which is supported by the fact that therapies targeting K17 have achieved good outcomes in psoriasis-like mouse models. Future perspectives of K17 in psoriasis have also been discussed to provide potential directions for further studies.

Keratin 17: a critical player in the pathogenesis of psoriasis

Keratin 17 (K17) is an intermediate filament protein present in the basal cells of complex epithelia, such as nails, hair follicles, sebaceous glands, and eccrine sweat glands. Studies have shown that it is expressed aberrantly in the suprabasal keratinocytes of psoriatic lesions, compared to in normal epidermis. K17 is also closely associated with the immune system and plays an important role in the pathogenesis of psoriasis. In this review, we present our experimental findings concerning the role of K17 in psoriasis, and compare them to results published in the literature. Our results show that cytokines related to Th17 and IL-22-producing (where Th17 is T helper cells, type 17 and IL is interleukin) CD4(+) T cells, including IL-17A and IL-22, upregulate the expression of K17 in keratinocytes. In addition, K17 stimulates autoreactive T cells and promotes the production of psoriasis-associated cytokines. Our findings lend support to the hypothesis that a K17/T-cell/cytokine autoimmune loop is involved in the pathogenesis of psoriasis. We therefore review the current understanding of the K17 immunoregulation, including its expression and direct/indirect effects on immune responses. Pertinent strategies for the treatment of psoriasis are also discussed.

Profiling and metaanalysis of epidermal keratinocytes responses to epidermal growth factor

BACKGROUND

One challenge of systems biology is the integration of new data into the preexisting, and then re-interpretation of the integrated data. Here we use readily available metaanalysis computational methods to integrate new data on the transcriptomic effects of EGF in primary human epidermal keratinocytes with preexisting transcriptomics data in keratinocytes and in EGF-treated non-epidermal cell types.

RESULTS

We find that EGF promotes keratinocyte proliferation, attachment and motility and, surprisingly, induces DUSPs that attenuate the EGF signal. Our metaanalysis identified overlapping effects of EGF with those of IL-1 and IFNγ, activators of keratinocyte in inflammation and wound healing. We also identified the genes and pathways suppressed by EGF but induced by agents promoting epidermal differentiation. Metaanalysis comparison with the EGF effects in other cell types identified extensive similarities between responses in keratinocytes and in other epithelial cell types, but specific differences with the EGF effects in endothelial cells, and in transformed, oncogenic epithelial cell lines.

CONCLUSIONS

This work defines the specific transcriptional effects of EGF on human epidermal keratinocytes. Our approach can serve as a suitable paradigm for integration of new omics data into preexisting databases and re-analysis of the integrated data sets.

Increased expression of Wnt5a in psoriatic plaques

Psoriasis vulgaris is characterized by hyperproliferation and incomplete terminal differentiation of epidermal keratinocytes. Despite the established role of Wnt pathways in the regulation of stem cell proliferation and differentiation, they have not yet been associated with the pathophysiology of psoriasis. Here, we took biopsies from uninvolved and from lesional skin of 20 patients with plaque-type psoriasis. The biopsies were used for microarray RNA expression profiling. Based on paired samples from 13 patients, we defined 179 genes that were more than 2-fold differentially expressed in lesional skin. This list included 16 genes with known or possible association to the canonical Wnt/beta-catenin or the non-canonical Wnt/Ca2+ pathway. The expression of Wnt5a was 4-fold higher in lesional skin. Other Wnt molecules were largely unchanged (Wnt4 and Wnt16), or tended to be expressed at lower levels (Wnt7b). The mRNA expression levels of two inhibitory factors related to Wnt signaling, frizzled-related protein, and dickkopf homolog 2, were reduced in lesional skin, as was mRNA expression of cyclin D1. These findings were confirmed by quantitative reverse transcription-PCR experiments. We conclude that Wnt5a and other Wnt pathway genes are differentially expressed in psoriatic plaques. Their functional contribution to the pathophysiology of psoriasis needs to be elaborated.

Transcriptional responses of human epidermal keratinocytes to Oncostatin-M

Oncostatin-M (OsM) plays an important role in inflammatory and oncogenic processes in skin, including psoriasis and Kaposi sarcoma. However, the molecular responses to OsM in keratinocytes have not been explored in depth. Here we show the results of transcriptional profiling in OsM-treated primary human epidermal keratinocytes, using high-density DNA microarrays. We find that OsM strongly and specifically affects the expression of many genes, in particular those involved with innate immunity, angiogenesis, adhesion, motility, tissue remodeling, cell cycle and transcription. The timing of the responses to OsM comprises two waves, early at 1h, and late at 48 h, with much fewer genes regulated in the intervening time points. Secreted cytokines and growth factors and their receptors, as well as nuclear transcription factors, are primary targets of OsM regulation, and these, in turn, effect the secondary changes.

Exploiting the keratin 17 gene promoter to visualize live cells in epithelial appendages of mice

Keratin genes afford, given their large number (>50) and differential regulation, a unique opportunity to study the mechanisms underlying specification and differentiation in epithelia of higher metazoans. Moreover, the small size and regulation in cis of many keratin genes enable the use of their regulatory sequence to achieve targeted gene expression in mice. Here we show that 2 kilobases of 5' upstream region from the mouse keratin 17 gene (mK17) confers expression of green fluorescent protein (GFP) in major epithelial appendages of transgenic mice. Like that of mK17, onset of [mK17 5']-GFP reporter expression coincides with the appearance of ectoderm-derived epithelial appendages during embryonic development. In adult mice, [mK17 5']-GFP is appropriately regulated within hair, nail, glands, and oral papilla. Tracking of GFP fluorescence allows for the visualization of growth cycle-related changes in hair follicles, and the defects engendered by the hairless mutation, in live skin tissue. Deletion of an internal 48-bp interval, which encompasses a Gli-responsive element, from this promoter results in loss of GFP fluorescence in most appendages in vivo, suggesting that sonic hedgehog participates in K17 regulation. The compact mK17 gene promoter provides a novel tool for appendage-preferred gene expression and manipulation in transgenic mice.

AP-2 transcription factor family member expression, activity, and regulation in human epidermal keratinocytes in vitro

The AP-2 transcription factor family is presumed to play an important role in the regulation of the keratinocyte squamous differentiation program; however, limited functional data are available to support this. In the present study, the activity and regulation of AP-2 were examined in differentiating human epidermal keratinocytes. We report that (1) AP-2 transcriptional activity decreases in differentiated keratinocytes but remains unchanged in differentiation-insensitive squamous cell carcinoma cell lines, (2) diminished AP-2 transcriptional activity is associated with a loss of specific DNA-bound AP-2 complexes, and (3) there is an increase in the ability of cytoplasmic extracts, derived from differentiated keratinocytes, to phosphorylate AP-2 alpha and AP-2 beta when cells differentiate. In contrast, extracts from differentiation-insensitive squamous cell carcinoma cells are unable to phosphorylate AP-2 proteins. Finally, the phosphorylation of recombinant AP-2 alpha by cytosolic extracts from differentiated keratinocytes is associated with decreased AP-2 DNA-binding activity. Combined, these data indicate that AP-2 trans-activation and DNA-binding activity decrease as keratinocytes differentiate, and that this decreased activity is associated with an enhanced ability to phosphorylate AP-2 alpha and beta.

Unique Keratinocyte-Specific Effects of Interferon-γ that Protect Skin from Viruses, Identified Using Transcriptional Profiling

Interferon (IFN)-γ, is a multifunctional, immunomodulatory cytokine with cell type-specific antiviral activities, particularly important in skin, where it is implicated in many diseases ranging from warts to psoriasis and cancer. Since epidermis is our first line of defence against many viruses, we investigated the molecular processes regulated by IFN-γ in keratinocytes using DNA microarrays. We identified the IFN-γ-regulated keratinocyte-specific genes and antiviral processes. Exclusively in keratinocytes, IFN-γ-induced tight junction proteins, presumably to deny viruses paracellular routes of infection. Furthermore, differing from published data, we find that IFN-γ suppressed the expression of keratinocytes differentiation markers including desmosomal proteins, cornified envelope components and suprabasal cytokeratins. Inhibition of differentiation may interfere with the epidermal tropism of viruses that require differentiating cells for growth, for example, papillomaviruses. As in other cell types, IFN-γ induced HLA, cell adhesion and proteasome proteins, facilitating leukocyte attraction and antigen-presentation by keratinocytes. IFN-γ also induced chemokine/cytokines specific for mononuclear cells. IFN-γ suppressed the expression of over 100 genes responsible for cell cycle, DNA replication and RNA metabolism, thereby shutting down many nuclear processes and denying viruses a healthy cell in which to replicate. Thus, uniquely in keratinocytes, IFN-γ initiates a well-organized molecular programme boosting host antiviral defences, obstructing viral entry, suppressing cell proliferation and impeding differentiation.

Interferon-gamma, a strong suppressor of cell proliferation, induces upregulation of keratin K6, one of the inflammatory- and proliferation-associated keratins

Keratin K6 is known as an inflammatory and hyperproliferative keratin, and is induced by an inflammatory and hyperproliferative agent. In this study, we demonstrated that interferon-gamma, an antiproliferative agent, also induces keratin K6. We used normal human ex vivo skin, normal human cultured keratinocytes, HaCaT keratinocytes, and DJM cells to examine the induction of K6 by interferon-gamma, by immunohistochemical staining, Western blot analysis, promoter chloramphenicol acetyl transferase assay, and reverse transcriptase polymerase chain reaction of mRNA. We succeeded in demonstrating the induction of keratin K6 by interferon-gamma in ex vivo human skin and HaCaT keratinocytes at the protein and message level, and in cultured normal human keratinocytes at the promoter level. The inhibition of the signal transducing activator of transcription 1 pathway by a dominant-negative transfer gene caused the inhibition of K6 induction by interferon-gamma, and the blocking of nuclear factor kappaB using antisense oligonucleotides also inhibited the K6 induction. We also blocked the released interleukin-1alpha from keratinocytes after stimulation with interferon-gamma by neutralizing antibodies, which showed a decrease in the K6 induction. Our results suggest that a small amount of interleukin-1alpha, which cannot induce K6 by itself, is secreted upon stimulation by interferon-gamma, and that the induction of K6 occurs through the synergistic effect of the interferon-gamma/signal transducing activator of transcription 1 and interleukin-1alpha/nuclear factor kappaB pathways. This is the first report to describe K6 induction in epidermal keratinocytes by interferon-gamma and indicate a probable signal transduction pathway, and demonstrates that K6 is a possible partner of K17 in the inflammatory process.

Regulation of keratin expression by ultraviolet radiation: differential and specific effects of ultraviolet B and ultraviolet a exposure

Skin, the most superficial tissue of our body, is the first target of environmental stimuli, among which is solar ultraviolet radiation. Very little is known about the regulation of keratin gene expression by ultraviolet radiation, however, although (i) it is well established that ultraviolet exposure is involved in skin cancers and photoaging and (ii) keratins represent the major epidermal proteins. The aim of this study was to analyze the regulation of human keratin gene expression under ultraviolet B (290-320 nm) or ultraviolet A (320-400 nm) irradiation using a panel of constructs comprising different human keratin promoters cloned upstream of a chloramphenicol acetyl transferase reporter gene and transfected into normal epidermal keratinocytes. By this approach, we demonstrated that ultraviolet B upregulated the transcription of keratin 19 gene and to a lesser extent the keratin 6, keratin 5, and keratin 14 genes. The DNA sequence responsible for keratin 19 induction was localized between -130 and +1. In contrast to ultraviolet B, ultraviolet A irradiation induced only an increase in keratin 17, showing a differential gene regulation between these two ultraviolet ranges. The induction of keratin 19 was confirmed by studying the endogenous protein in keratinocytes in classical cultures as well as in skin reconstructed in vitro and normal human skin. These data show for the first time that keratin gene expression is regulated by ultraviolet radiation at the transcriptional level with a specificity regarding the ultraviolet domain of solar light.

The tissue-dependent keratin 19 gene transcription is regulated by GKLF/KLF4 and Sp1

Keratins play critical roles in cellular differentiation and cytoskeletal organization. Keratin 19 (K19) is unique because it has been implicated as a marker of stem cells in some tissues, such as the hair follicle in the skin. It is also associated with malignant transformation in esophageal and pancreatic cancers. Here, we show that the K19 promoter is active in a subset of gastrointestinal cancer cells derived from esophageal and pancreas but inactive in other contexts. This activity was mapped to a short region containing an overlapping binding site for gut-enriched Krüppel-like factor (GKLF/KLF4) and Sp1. GKLF has a higher binding affinity and is the predominant binding factor in cells with low Sp-1 protein levels. Pancreatic acinar cells normally do not express K19, but overexpression of GKLF and Sp1 in these cells leads to aberrant expression, similar to what is observed in pancreatic cancer. These results demonstrate the functional interaction of ubiquitous and tissue-restricted transcription factors in determining tissue- and neoplasm-specific patterns of gene expression.

Novel mechanism of steroid action in skin through glucocorticoid receptor monomers

Glucocorticoids (GCs), important regulators of epidermal growth, differentiation, and homeostasis, are used extensively in the treatment of skin diseases. Using keratin gene expression as a paradigm of epidermal physiology and pathology, we have developed a model system to study the molecular mechanism of GCs action in skin. Here we describe a novel mechanism of suppression of transcription by the glucocorticoid receptor (GR) that represents an example of customizing a device for transcriptional regulation to target a specific group of genes within the target tissue, in our case, epidermis. We have shown that GCs repress the expression of the basal-cell-specific keratins K5 and K14 and disease-associated keratins K6, K16, and K17 but not the differentiation-specific keratins K3 and K10 or the simple epithelium-specific keratins K8, K18, and K19. We have identified the negative recognition elements (nGREs) in all five regulated keratin gene promoters. Detailed footprinting revealed that the function of nGREs is to instruct the GR to bind as four monomers. Furthermore, using cotransfection and antisense technology we have found that, unlike SRC-1 and GRIP-1, which are not involved in the GR complex that suppresses keratin genes, histone acetyltransferase and CBP are. In addition, we have found that GR, independently from GREs, blocks the induction of keratin gene expression by AP1. We conclude that GR suppresses keratin gene expression through two independent mechanisms: directly, through interactions of keratin nGREs with four GR monomers, as well as indirectly, by blocking the AP1 induction of keratin gene expression.

The epidermis: genes on - genes off

The epidermal keratinocyte stem cell is distinguished by a relatively undifferentiated phenotype and an ability to proliferate. As part of a carefully orchestrated process, the offspring of these stem cells lose the ability to proliferate and begin a process of morphologic and biochemical transformation that results in their conversion into corneocytes. This process requires the coordinated expression of a host of cellular genes. The mechanisms responsible for regulation of these genes is an area of intense interest. In keratinocytes, as in other cell types, the expression of most genes is regulated at the transcriptional level by a class of proteins called transcription factors. Transcription factors are nuclear proteins that regulate transcription by mediating the final steps in the relay of information from the cell surface to the nucleus and the gene. These factors bind to specific DNA sequence elements located within the target gene. In this brief review we summarize evidence implicating activator protein 1 (AP1), AP2, Sp1, POU domain, CCAAT enhancer binding protein, and several other transcription factors as regulators of expression of keratinocyte genes.

Regulation of gene expression in developing epidermal epithelia

Skin is one of the most thoroughly studied epithelia and can be used as a model for transcriptional control of epithelial differentiation. In particular, the stages of epidermal development and differentiation from a simple epithelium are well characterized. Temporal gene expression during development can be used to assign roles for transcription factors in epidermal differentiation. Approaches to understanding transcriptional regulation in epidermis include extensive promoter analysis and expression studies, in some cases coupled to functional studies. This work has not produced any consensus about the importance of any particular factor or class of factors in epidermal specification. There is, as yet, nothing similar to the myo D family of tissue-specific and cell-type determining factors in epidermis. These studies, however, have revealed much about control of the differentiation process in epidermis. Most recently, there has been a suggestion that epithelial transcription can be influenced directly by the status of the adhesion complexes at the cell surface, providing a direct link between one of the distinguishing features of the epithelial state and gene transcription.

Regulation of epidermal expression of keratin K17 in inflammatory skin diseases

Keratin K17, the myoepithelial keratin, is expressed in psoriasis but is not present in healthy skin. Psoriasis is associated with production of gamma interferon (IFN gamma), which induces the expression of keratin K17 by activating transcription factor STAT1. Our hypothesis states that the induction of K17 is specific for the inflammatory reactions associated with high levels of IFN gamma and activation of STAT1. One of the corollaries of the hypothesis is that the STAT1-activating cytokines should induce the expression of keratin K17, whereas those cytokines that work through other mechanisms should not. Furthermore, because the STAT activation pathway is dependent upon protein phosphorylation events, phosphorylation inhibitors should attenuate the induction of keratin K17, whereas protein phosphatase inhibitors should augment it. To test this hypothesis, we analyzed lesional samples of inflammatory diseases using immunofluorescence, transfected keratinocytes with K17 gene promoter DNAs in the presence of various cytokines, and followed nuclear translocation of STAT1 in keratinocytes using specific antibodies. Confirming the hypothesis, we found that K17 is induced in psoriasis and dermatitis caused by delayed type hypersensitivity, which are associated with high levels of IFN gamma, but not in samples of atopic dermatitis, which is not. Two cytokines, interleukin-6 and leukemia inhibitory factor, which can induce phosphorylation of STAT1, can also induce K17 expression, whereas interleukin-3, interleukin-4, interleukin-10, and granulocyte macrophage colony stimulating factor have no effect on K17 expression. As expected, staurosporine and genistein inhibited, whereas okadaic acid augmented, the induction of K17 by IFN gamma. Our data indicate that in inflammatory skin diseases, lymphocytes, through the cytokines they produce, differently regulate not only each other, but also keratin gene expression in epidermis one of their target tissues.