Regulation of a hair follicle keratin intermediate filament gene promoter

SP1 and KROX20 Regulate the Proliferation of Dermal Papilla Cells and Target the CUX1 Gene

Previous studies have demonstrated that CUX1 could contribute to the proliferation of DPCs in vitro, but the upstream transcriptional regulatory mechanisms of CUX1 remain largely unknown. This study aimed to investigate the upstream transcriptional regulators of CUX1 to enhance our comprehension of the mechanism of action of the CUX1 gene in ovine DPCs. Initially, the JASPAR (2024) software was used to predict the upstream target transcription factors for the CUX1 gene. Subsequently, through RT-qPCR and a double luciferase reporter assay, the interaction between SP1, KROX20, and CUX1 was established, respectively. The results indicated that SP1 and KROX20 were two highly reliable upstream transcription regulators for the CUX1 gene. Additionally, we found that SP1 promoted the proliferation of DPCs by overexpressing SP1 in DPCs, and KROX20 inhibited the proliferation of DPCs by overexpressing KROX20 in DPCs. These findings are also consistent with the transcriptional regulation of CUX1 by SP1 and KROX20, respectively. This study suggests that the effect of DPC proliferation in vitro by CUX1 may regulated by the transcription factors SP1 and KROX20.

A Kaleidoscope of Keratin Gene Expression and the Mosaic of Its Regulatory Mechanisms

Keratins are a family of intermediate filament-forming proteins highly specific to epithelial cells. A combination of expressed keratin genes is a defining property of the epithelium belonging to a certain type, organ/tissue, cell differentiation potential, and at normal or pathological conditions. In a variety of processes such as differentiation and maturation, as well as during acute or chronic injury and malignant transformation, keratin expression undergoes switching: an initial keratin profile changes accordingly to changed cell functions and location within a tissue as well as other parameters of cellular phenotype and physiology. Tight control of keratin expression implies the presence of complex regulatory landscapes within the keratin gene loci. Here, we highlight patterns of keratin expression in different biological conditions and summarize disparate data on mechanisms controlling keratin expression at the level of genomic regulatory elements, transcription factors (TFs), and chromatin spatial structure.

Classification of Widely and Rarely Expressed Genes with Recurrent Neural Network

A tissue-specific gene expression shapes the formation of tissues, while gene expression changes reflect the immune response of the human body to environmental stimulations or pressure, particularly in disease conditions, such as cancers. A few genes are commonly expressed across tissues or various cancers, while others are not. To investigate the functional differences between widely and rarely expressed genes, we defined the genes that were expressed in 32 normal tissues/cancers (i.e., called widely expressed genes; FPKM >1 in all samples) and those that were not detected (i.e., called rarely expressed genes; FPKM <1 in all samples) based on the large gene expression data set provided by Uhlen et al. Each gene was encoded using the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment scores. Minimum redundancy maximum relevance (mRMR) was used to measure and rank these features on the mRMR feature list. Thereafter, we applied the incremental feature selection method with a supervised classifier recurrent neural network (RNN) to select the discriminate features for classifying widely expressed genes from rarely expressed genes and construct an optimum RNN classifier. The Youden's indexes generated by the optimum RNN classifier and evaluated using a 10-fold cross validation were 0.739 for normal tissues and 0.639 for cancers. Furthermore, the underlying mechanisms of the key discriminate GO and KEGG features were analyzed. Results can facilitate the identification of the expression landscape of genes and elucidation of how gene expression shapes tissues and the microenvironment of cancers.

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Some genes are widely expressed across tissues or various cancers.

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A number of genes are rarely expressed across tissues or various cancers.

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The functional differences between widely and rarely expressed genes were studied.

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Several GO terms and KEGG pathways were extracted and analyzed.

Identifying novel strategies for treating human hair loss disorders: Cyclosporine A suppresses the Wnt inhibitor, SFRP1, in the dermal papilla of human scalp hair follicles

Hair growth disorders often carry a major psychological burden. Therefore, more effective human hair growth–modulatory agents urgently need to be developed. Here, we used the hypertrichosis-inducing immunosuppressant, Cyclosporine A (CsA), as a lead compound to identify new hair growth–promoting molecular targets. Through microarray analysis we identified the Wnt inhibitor, secreted frizzled related protein 1 (SFRP1), as being down-regulated in the dermal papilla (DP) of CsA-treated human scalp hair follicles (HFs) ex vivo. Therefore, we further investigated the function of SFRP1 using a pharmacological approach and found that SFRP1 regulates intrafollicular canonical Wnt/β-catenin activity through inhibition of Wnt ligands in the human hair bulb. Conversely, inhibiting SFRP1 activity through the SFRP1 antagonist, WAY-316606, enhanced hair shaft production, hair shaft keratin expression, and inhibited spontaneous HF regression (catagen) ex vivo. Collectively, these data (a) identify Wnt signalling as a novel, non–immune-inhibitory CsA target; (b) introduce SFRP1 as a physiologically important regulator of canonical β-catenin activity in a human (mini-)organ; and (c) demonstrate WAY-316606 to be a promising new promoter of human hair growth. Since inhibiting SFRP1 only facilitates Wnt signalling through ligands that are already present, this ‘ligand-limited’ therapeutic strategy for promoting human hair growth may circumvent potential oncological risks associated with chronic Wnt over-activation.

Hair loss is a common disorder and can lead to psychological distress. Cyclosporine A, a fungal metabolite commonly used as an immunosuppressant, can potently induce hair growth in humans. However, it cannot be effectively used to restore hair growth because of its toxic profile. In this study, we used Cyclosporine A as a lead compound to identify novel therapeutic targets that can aid the development of new hair growth–promoting agents. Through microarray analysis, we found that the level of the secreted Wnt inhibitor, SFRP1, was significantly reduced by Cyclosporine A. This inspired us to design a new pharmacological approach that uses WAY-316606, a reportedly well-tolerated and specific antagonist of SFRP1, to prolong the growth phase of the hair cycle. We show that WAY-316606 enhances human hair growth ex vivo, suggesting that it is a more targeted hair growth promoter with the potential to treat human hair loss disorders.

WNT10A mutation causes ectodermal dysplasia by impairing progenitor cell proliferation and KLF4-mediated differentiation

Human WNT10A mutations are associated with developmental tooth abnormalities and adolescent onset of a broad range of ectodermal defects. Here we show that β-catenin pathway activity and adult epithelial progenitor proliferation are reduced in the absence of WNT10A, and identify Wnt-active self-renewing stem cells in affected tissues including hair follicles, sebaceous glands, taste buds, nails and sweat ducts. Human and mouse WNT10A mutant palmoplantar and tongue epithelia also display specific differentiation defects that are mimicked by loss of the transcription factor KLF4. We find that β-catenin interacts directly with region-specific LEF/TCF factors, and with KLF4 in differentiating, but not proliferating, cells to promote expression of specialized keratins required for normal tissue structure and integrity. Our data identify WNT10A as a critical ligand controlling adult epithelial proliferation and region-specific differentiation, and suggest downstream β-catenin pathway activation as a potential approach to ameliorate regenerative defects in WNT10A patients.

Human WNT10A mutations are associated with dental defects and adult onset ectodermal dysplasia. Xu et al. show that WNT10A-activated ß-catenin plays dual roles in adult epithelial progenitor proliferation and differentiation by complexing with KLF4 in differentiating, but not proliferating, cells.

The expression of KRT2 and its effect on melanogenesis in alpaca skins

In order to investigate the effects of the keratin 2 (KRT2) on alpaca melanocyte in vivo and vitro, the immunohistochemistry (IHC), quantitative real-time PCR (qPCR), Western blot, and alpaca melanocytes transfection methods were used. The results showed that mRNA and protein expression of KRT2 was highly expressed in brown skin in comparison with that in white skin. Moreover, we found that KRT2 was expressed in alpaca melanocytes in vitro by immunocytochemistry. After transfection with KRT2 in alpaca melanocytes, the relative mRNA and protein expression of KRT2, microphthalmia-associtated transcription factor (MITF), tyrosinase (TYR) and tyrosinase-related protein 1 (TYRP1) in alpaca skin melanocytes was increased with significant differences; a further result was the increase of melanin production. The results suggested that KRT2 functions in alpaca hair color formation, which offered an essential theoretical basis for further exploration of the role of melanogenesis.

Characterization of the Promoter Regions of Two Sheep Keratin-Associated Protein Genes for Hair Cortex-Specific Expression

The keratin-associated proteins (KAPs) are the structural proteins of hair fibers and are thought to play an important role in determining the physical properties of hair fibers. These proteins are activated in a striking sequential and spatial pattern in the keratinocytes of hair fibers. Thus, it is important to elucidate the mechanism that underlies the specific transcriptional activity of these genes. In this study, sheep KRTAP 3–3 and KRTAP11-1 genes were found to be highly expressed in wool follicles in a tissue-specific manner. Subsequently, the promoter regions of the two genes that contained the 5′ flanking/5′ untranslated regions and the coding regions were cloned. Using an in vivo transgenic approach, we found that the promoter regions from the two genes exhibited transcriptional activity in hair fibers. A much stronger and more uniformly expressed green fluorescent signal was observed in the KRTAP11-1-ZsGreen1 transgenic mice. In situ hybridization revealed the symmetrical expression of sheep KRTAP11-1 in the entire wool cortex. Consistently, immunohistochemical analysis demonstrated that the pattern of ZsGreen1 expression in the hair cortex of transgenic mice matches that of the endogenous KRTAP11-1 gene, indicating that the cloned promoter region contains elements that are sufficient to govern the wool cortex-specific transcription of KRTAP11-1. Furthermore, regulatory regions in the 5′ upstream sequence of the sheep KRTAP11-1 gene that may regulate the observed hair keratinocyte specificity were identified using in vivo reporter assays.

Transcriptional regulation analysis and the potential transcription regulator site in the extended KAP6.1 promoter in sheep

The high glycine/tyrosine type II keratin protein 6.1 (KAP6.1) is a member of the keratin-associated protein family, which is restricted to cells in hair follicles and is associated with fiber diameter and fiber curvature in Merino sheep. In this study, we obtained a series of progressive 5'-deletion fragments of the KAP6.1 gene promoter from ovine genomic DNA. The KAP6.1 5'-upstream region was fused to luciferase and transfected into sheep fetal fibroblast cells (sFFCs). We demonstrated that the sequence from -1,523 to -1 bp (taking the A of the initiator methionine ATG as the +1 nt position) gave rise to a higher luciferase activity comparing to the published region from -1,042 to -1 bp. Whereas, decreased transcriptional activity of the KAP6.1 promoter was observed when the sequence extended to -3,699 bp. To identify the DNA elements that are important for transcriptional activity, we performed structural analysis and electrophoretic mobility shift assay (EMSA). Structural analysis of the KAP6.1 promoter showed that transcription factors NF-kappa-B, AP-1, and C/EBP-alpha synergistically activate KAP6.1 promoter, while POU2F1 might function as a strong negative regulator. The EMSA showed that NF-kappa-B element bound to the nuclear protein extracted from sFFCs. We conclude that NF-kappa-B binding site is an enhancer element of KAP6.1 promoter in vitro. The results are potentially useful for elucidating the regulator mechanisms of KAP6.1.

Beta-catenin/LEF-1 signalling in breast cancer--central players activated by a plethora of inputs

Although the role of Wnt signalling in breast cancer is far from being fully understood, in the last years its importance has been reported frequently. Besides stimulation by canonical Wnt signalling, the downstream effectors beta-catenin and the transcriptional modulators of the T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) family can also be activated by other inputs including the TGF-beta pathway. Wnt and TGF-beta signalling are both major signal transduction pathways, which provide important cues during development and tumor progression. However, particularly TGF-beta has a complicated influence on oncogenesis, which ranges from suppressive to promoting activity. Signalling pathways activated in parallel with TGF-beta might determine the oncogenic influence, and therefore place signals cooperating with TGF-beta into the limelight. During early development Wnt and TGF-beta signalling collaborate extensively. Here we provide an overview of the known interactions of Wnt with TGF-beta signalling in development and metastasis, particularly in breast cancer. We want to focus on the Wnt-activated transcription factor complex beta-catenin/LEF-1, its upstream activators, its downstream targets and consequences on the cellular level in response to beta-catenin/LEF-1 activation.

Keratins of the Human Hair Follicle

Substantial progress has been made regarding the elucidation of differentiation processes of the human hair follicle. This review first describes the genomic organization of the human hair keratin gene family and the complex expression characteristics of hair keratins in the hair-forming compartment. Sections describe the role and fate of hair keratins in the diseased hair follicle, particularly hereditary disorders and hair follicle-derived tumors. Also included is a report on the actual state of knowledge concerning the regulation of hair keratin expression. In the second part of this review, essentially the same principles are applied to outline more recent and, thus, occasionally fewer data on specialized epithelial keratins expressed in various tissue constituents of the external sheaths and the companion layer of the follicle. A closing outlook highlights issues that need to be explored further to deepen our insight into the biology and genetics of the hair follicle.

On the regulation of hair keratin expression: lessons from studies in pilomatricomas

Human hair follicles exhibit a complex pattern of sequential hair keratin expression in the hair matrix, cuticle, and cortex. In pilomatricomas, that is, benign skin tumors thought to arise from germinative matrix cells of the hair follicle and retaining morphological signs of cortical differentiation, this differential hair keratin pattern has been shown to be faithfully preserved in the lower and upper transitional cell compartments of the tumors. Here we show that also the co-expression of hair keratin hHa5 with its regulatory nuclear homeoprotein HOXC13 in matrix cells of the hair follicle is maintained in lower transitional cells of pilomatricomas. In contrast, the nuclear co-expression of LEF1 and beta-catenin, which in the hair follicle has been postulated to initiate cortex cell differentiation through the induction of hair keratin hHa1 expression (Merill et al, Genes Dev 15:1688-1705, 2001), is not preserved in upper transitional cells of pilomatricomas. Although these cells correctly express hHa1, they are completely devoid of LEF1 and nuclear LEF1/beta-catenin co-expression is shifted to a subpopulation of hair keratin-free basaloid cells of the tumors. These data imply that unlike the normal hair follicle, cortical differentiation in pilomatricomas is not under the control of the canonical Wnt signaling pathway.

Beta-catenin expression in benign and malignant pilomatrix neoplasms

BACKGROUND

Beta-catenin is a 92-kDa protein, initially identified as a coprecipitating species with the E-cadherin cell-cell adhesive complex. It plays a role in signal transduction in the Wnt signalling pathway and has been identified as an oncogene in colon cancer and melanoma. Exon 3 beta-catenin-activating mutations were found in 75% of cases of pilomatricoma (PM). Previous studies have shown that nuclear and/or cytoplasmic staining may correlate with beta-catenin gene mutation.

OBJECTIVES

Because the immunohistochemical expression of beta-catenin in the nucleus or the cytoplasm correlates with beta-catenin mutation, we studied the immunohistochemical profile of beta-catenin expression in normal scalp hair follicles and in PM and pilomatrix carcinoma (PC).

METHODS

We reviewed 21 cases of PM and five cases of PC using immunohistochemical staining with commercially available antibody in a standard fashion on formalin-fixed paraffin-embedded tissue samples.

RESULTS

All 26 tumours displayed both nuclear and cytoplasmic staining in the basaloid cells with focal membranous staining. Shadow cells were negative in all tumours. Normal control sections from the scalp displayed nuclear reactivity of the matrical cells, mostly concentrated in the supramatrical zone of hair follicles. Membranous staining was present along the intercellular junctions of the epidermis and along the outer and inner root sheaths of hair follicles. We have found similar patterns of beta-catenin nuclear and cytoplasmic expression in both PM and PC.

CONCLUSIONS

Despite the shared beta-catenin expression, the biological behaviour of PM and PC is markedly different. These two tumours probably share the activation of a common cellular pathway that could be related to their shared method of keratinization or a shared dysfunction of the cellular adhesion complex and consequently tumorigenesis. To the best of our knowledge, this is the first report on the beta-catenin immunohistochemical expression profile in PC.

Type II epithelial keratin 6hf (K6hf) is expressed in the companion layer, matrix, and medulla in anagen-stage hair follicles

More than half of the known keratin genes (n approximately 50) are expressed in the hair follicle. An in-depth knowledge of their differential expression in this organ will help us to understand the mechanisms of its formation and cycling, and the etiology of inherited hair disorders. Keratin 6hf is a type II keratin recently shown to occur in the companion layer. We cloned the mouse ortholog and characterized its expression in skin and oral mucosa. The mK6hf gene is 9.1 kb long and located in the cluster of type II keratin genes on mouse chromosome 15, between the keratin 6 (mK6alpha/mK6beta) and hair keratin genes. In situ hybridization and protein immunolocalization showed that, in addition to the companion layer, mK6hf is expressed in the upper matrix and medulla of the anagen-stage hair. This distribution is seen for all types of mouse hairs and medullated human hairs. The distribution of keratin 6hf protein in the hair shaft mirrors that of keratin 17, and the observation of reduced levels of keratin 6hf in keratin 17 null hair argues for a direct interaction between them. mK6hf is also expressed in the nail bed epithelium and fungiform papillae of dorsal tongue epithelium. Our findings provide an additional marker for the hair matrix and medulla, and suggest that the cellular precursors for the medulla, cortex, and cuticle compartments are already spatially segregated within the hair matrix. They also have obvious implications for the epithelial alterations associated with defects in keratin 6 genes.

Essential roles of BMPR-IA signaling in differentiation and growth of hair follicles and in skin tumorigenesis

Hair differentiation and growth are controlled by complex reciprocal signaling between epithelial and mesenchymal cells. To better understand the requirement and molecular mechanism of BMP signaling in hair follicle development, we performed genetic analyses of bone morphogenetic protein receptor 1A (BMPR-IA) function during hair follicle development by using a conditional knockout approach. The conditional mutation of Bmpr1a in ventral limb ectoderm and its derivatives (epidermis and hair follicles) resulted in a lack of hair outgrowth from the affected skin regions. Mutant hair follicles exhibited abnormal morphology and lacked hair formation and pigment deposition during anagen. The timing of the hair cycle and the proliferation of hair matrix cells were also affected in the mutant follicles. We demonstrate that signaling via epithelial BMPR-IA is required for differentiation of both hair shaft and inner root sheath from hair matrix precursor cells in anagen hair follicles but is dispensable for embryonic hair follicle induction. Surprisingly, aberrant de novo hair follicle morphogenesis together with hair matrix cell hyperplasia was observed in the absence of BMPR-IA signaling within the affected skin of adult mutants. They developed hair follicle tumors from 3 months of age, indicating that inactivation of epidermal BMPR-IA signaling can lead to hair tumor formation. Taken together, our data provide genetic evidence that BMPR-IA signaling plays critical and multiple roles in controlling cell fate decisions or maintenance, proliferation, and differentiation during hair morphogenesis and growth, and implicate Bmpr1a as a tumor suppressor in skin tumorigenesis.

beta-Catenin is expressed aberrantly in tumors expressing shadow cells. Pilomatricoma, craniopharyngioma, and calcifying odontogenic cyst

We studied the beta-catenin immunohistochemical profile in tumors expressing shadow cells: pilomatricoma, 10 cases; calcifying odontogenic cyst, 6 cases; and craniopharyngioma, 9 cases. There was strong membranous, cytoplasmic, and nuclear staining of the immature basaloid cells in all of these tumors. Shadow cells were negative in all tumors. It has been documented that rising levels of free beta-catenin drive the formation of complexes with T-cell factor/lymphoid enhancer factor (TCF-Lef) and up-regulate the wingless-Wnt cell-cell signals. The end result is an abnormality of beta-catenin degradation and, thus, a buildup of free beta-catenin in the cytoplasm and/or nucleus, resulting in the stimulation of cellular proliferation and/or inhibition of cell death. beta-Catenin seems to have an important role in the oncogenesis of these tumors. The similar pattern of keratinization in these tumors and the similar pattern of beta-catenin immunoreactivity in the cytoplasm and the nucleus are important findings. It seems that the activation of a common cellular pathway, namely Wnt-beta-catenin-TCF-Lef, has a role in the pathogenesis of these tumors. The latter could be related to their shared method of keratinization or shared dysfunction of the cellular adhesion complex leading to tumorigenesis.

The LEF1/beta -catenin complex activates movo1, a mouse homolog of Drosophila ovo required for epidermal appendage differentiation

Drosophila ovo/svb (dovo) is required for epidermal cuticle/denticle differentiation and is genetically downstream of the wg signaling pathway. Similarly, a mouse homolog of dovo, movo1, is required for the proper formation of hair, a mammalian epidermal appendage. Here, we provide biochemical evidence that movo1 encodes a nuclear DNA binding protein (mOvo1a) that binds to DNA sequences similar to those that dOvo binds to, further supporting the notion that mOvo1a and dOvo are genetically and biochemically homologous proteins. Additionally, we show that the movo1 promoter is activated by the lymphoid enhancer factor 1 (LEF1)/beta-catenin complex, a transducer of wnt signaling. Collectively, our findings suggest that movo1 is a developmental target of wnt signaling during hair morphogenesis in mice, and that the wg/wnt-ovo link in epidermal appendage regulatory pathways has been conserved between mice and flies.

Improved detection of lacZ reporter gene expression in transgenic epithelia by immunofluorescence microscopy

The bacterial lacZ gene is commonly used as a reporter for the in vivo analysis of gene regulation in transgenic mice. However, several laboratories have reported poor detection of beta-galactosidase (the lacZ gene product) using histochemical techniques, particularly in skin. Here we report the difficulties we encountered in assessing lacZ expression in transgenic keratinocytes using classic X-gal histochemical protocols in tissues shown to express the transgene by mRNA in situ hybridization. We found that lacZ reporter gene expression could be reliably detected in frozen tissue sections by immunofluorescence analysis using a beta-galactosidase-specific antibody. Moreover, we were able to localize both transgene and endogenous gene products simultaneously using double-label immunofluorescence. Our results suggest that antibody detection of beta-galactosidase should be used to verify other assays of lacZ expression, particularly where low expression levels are suspected or patchy expression is observed.

Molecular mechanisms regulating hair follicle development

Clinical conditions causing hair loss, such as androgenetic alopecia, alopecia areata, and scarring alopecia, can be psychologically devastating to individuals and are the target of a multimillion dollar pharmaceutical industry. The importance of the hair follicle in skin biology, however, does not rest solely with its ability to produce hair. Hair follicles are self-renewing and contain reservoirs of multipotent stem cells that are capable of regenerating the epidermis and are thought to be utilized in wound healing. Hair follicles are also the sites of origin of many neoplasias, including some basal cell carcinomas and pilomatricoma. These diseases result from inappropriate activation of signaling pathways that regulate hair follicle morphogenesis. Identification of the signaling molecules and pathways operating in developing and postnatal, cycling, hair follicles is therefore vital to our understanding of pathogenic states in the skin and may ultimately permit the development of novel therapies for skin tumors as well as for hair loss disease. The purpose of this review is to summarize recent progress in our understanding of the molecular mechanisms regulating hair follicle formation, and to discuss ways in which this information may eventually be utilized in the clinic.

Expression of ΔNLef1 in mouse epidermis results in differentiation of hair follicles into squamous epidermal cysts and formation of skin tumours

To examine the consequences of repressing β-catenin/Lef1 signalling in mouse epidermis, we expressed a ΔNLef1 transgene, which lacks the β-catenin binding site, under the control of the keratin 14 promoter. No skin abnormalities were detected before the first postnatal hair cycle. However, from 6 weeks of age, mice underwent progressive hair loss which correlated with the development of dermal cysts. The cysts were derived from the base of the hair follicles and expressed morphological and molecular markers of interfollicular epidermis. Adult mice developed spontaneous skin tumours, most of which exhibited sebaceous differentiation, which could be indicative of an origin in the upper part of the hair follicle. The transgene continued to be expressed in the tumours and β-catenin signalling was still inhibited, as evidenced by absence of cyclin D1 expression. However, patched mRNA expression was upregulated, suggesting that the sonic hedgehog pathway might play a role in tumour formation. Based on our results and previous data on the consequences of activating β-catenin/Lef1 signalling in postnatal keratinocytes, we conclude that the level of β-catenin signalling determines whether keratinocytes differentiate into hair or interfollicular epidermis, and that perturbation of the pathway by overexpression of ΔNLef1 can lead to skin tumour formation.

beta-catenin expression in pilomatrixomas. Relationship with beta-catenin gene mutations and comparison with beta-catenin expression in normal hair follicles

BACKGROUND

beta-catenin functions in signal transduction in the Wnt signalling pathway, which has recently been implicated in hair follicle (HF) morphogenesis. beta-catenin gene mutations affecting exon 3 have been reported in a high percentage of human pilomatrixomas. However, the expression pattern of beta-catenin in human HFs and pilomatrixomas has not been reported.

OBJECTIVES

To analyse immunohistochemically the expression pattern of beta-catenin in normal anagen HFs and in 40 human pilomatrixomas.

METHODS

In 11 of these tumours we also studied exon 3 beta-catenin gene mutations by polymerase chain reaction and direct sequencing. As these mutations have been related to a replication error (RER) phenotype in other tumour types, we explored whether or not this association also occurs in pilomatrixomas.

RESULTS

beta-catenin was expressed in the cell membranes of the outer and inner root sheaths and in matrix cells located at the base and periphery of the HF bulb. However, central matrix cells that differentiate into cortical cells, cortical and cuticular cells expressed beta-catenin in the nucleus, suggesting a role in signal transduction. In addition, some fibroblasts of the dermal papilla also showed nuclear expression of beta-catenin. All 40 analysed pilomatrixomas showed intense nuclear and cytoplasmic beta-catenin expression in proliferating matrix (basaloid) cells. In areas of maturation, transitional cells mainly showed cytoplasmic and membranous expression of beta-catenin, while only a few cells retained nuclear expression. Shadow or ghost cells did not show beta-catenin expression. Three of 11 tumours (26%) had beta-catenin mutations. All three had the same heterozygote mis-sense mutation: a G to T change affecting the first nucleotide at codon 32 (D32Y). None of the 11 tumours studied had a positive RER phenotype.

CONCLUSIONS

Present and previous studies suggest that the Wnt/beta-catenin/Tcf-Lef pathway is activated in normal matrix cells of the HF to induce differentiation to the hair shaft. Additionally, the beta-catenin mutation in matrix cells of the HF stabilizes beta-catenin protein, which translocates into the nucleus, where it activates of gene transcription together with lymphoid enhancer factor-1 producing pilomatrixoma. These mutations occur without an underlying defect in DNA mismatch repair.

The catalog of human hair keratins. II. Expression of the six type II members in the hair follicle and the combined catalog of human type I and II keratins

The human type II hair keratin subfamily consists of six individual members and can be divided into two groups. The group A members hHb1, hHb3, and hHb6 are structurally related, whereas group C members hHb2, hHb4, and hHb5 are rather distinct. Specific antisera against the individual hair keratins were used to establish the two-dimensional catalog of human type II hair keratins. In this catalog, hHb5 showed up as a series of isoelectric variants, well separated from a lower, more acidic, and complex protein streak containing isoelectric variants of hair keratins hHb1, hHb2, hHb3, and hHb6. Both in situ hybridization and immunohistochemistry on anagen hair follicles showed that hHb5 and hHb2 defined early stages of hair differentiation in the matrix (hHb5) and cuticle (hHb5 and hHb2), respectively. Although cuticular differentiation proceeded without the expression of further type II hair keratins, cortex cells simultaneously expressed hHb1, hHb3, and hHb6 at an advanced stage of differentiation. In contrast, hHb4, which is undetectable in hair follicle extracts and sections, could be identified as the largest and most alkaline member of this subfamily in cytoskeletal extracts of dorsal tongue. This hair keratin was localized in the posterior compartment of the tongue filiform papillae. Comparative analysis of type II with the previously published type I hair keratin expression profiles suggested specific, but more likely, random keratin-pairing principles during trichocyte differentiation. Finally, by combining the previously published type I hair keratin catalog with the type II hair keratin catalog and integrating both into the existing catalog of human epithelial keratins, we present a two-dimensional compilation of the presently known human keratins.

Analysis of mouse keratin 6a regulatory sequences in transgenic mice reveals constitutive, tissue-specific expression by a keratin 6a minigene

The analysis of keratin 6 expression is complicated by the presence of multiple isoforms that are expressed constitutively in a number of internal stratified epithelia, in palmoplantar epidermis, and in the companion cell layer of the hair follicle. In addition, keratin 6 expression is inducible in interfollicular epidermis and the outer root sheath of the follicle, in response to wounding stimuli, phorbol esters, or retinoic acid. In order to establish the critical regions involved in the regulation of keratin 6a (the dominant isoform in mice), we generated transgenic mice with two different-sized mouse keratin 6a constructs containing either 1.3 kb or 0.12 kb of 5' flanking sequence linked to the lacZ reporter gene. Both constructs also contained the first intron and the 3' flanking sequence of mouse keratin 6a. Ectopic expression of either transgene was not observed. Double-label immunofluorescence analyses demonstrated expression of the reporter gene in keratin 6 expressing tissues, including the hair follicle, tongue, footpad, and nail bed, showing that both transgenes retained keratinocyte-specific expression. Quantitative analysis of beta-galactosidase activity verified that both the 1.3 and 0.12 kb keratin 6a promoter constructs produced similar levels of the reporter. Notably, both constructs were constitutively expressed in the outer root sheath and interfollicular epidermis in the absence of any activating stimulus, suggesting that they lack the regulatory elements that normally silence transcription in these cells. This study has revealed that a keratin 6a minigene contains critical cis elements that mediate tissue-specific expression and that the elements regulating keratin 6 induction lie distal to the 1.3 kb promoter region.

Forkhead/winged-helix transcription factor Whn regulates hair keratin gene expression: molecular analysis of the nude skin phenotype

The molecular characteristics of the nude phenotype (alopecia and thymic aplasia) in humans and rodents are unknown. The nude locus encodes Whn, a transcription factor of the forkhead/winged-helix class. Expression of Whn in HeLa cells induced expression of human hair keratin genes Ha3-II and Hb5. Correspondingly, in nude mice, which are homozygous for a loss-of-function mutation of Whn, expression of mouse mHa3 and mHb5 hair keratin genes is severely reduced. Characterization of a previously identified nude allele, nu(Y), revealed a mis-sense mutation (R320C) in the DNA binding domain of Whn. This mutant protein is unable to activate hair keratin gene expression in HeLa cells. When the Whn transcription factor was expressed in two parts, one containing the N-terminal DNA binding domain and the other the C-terminal activation domain, no activation of hair keratin genes in HeLa cells was observed. However, when these two proteins were noncovalently linked by means of synthetic dimerizers, hair keratin gene expression was induced. This finding suggests that target gene activation by Whn depends on the structural integrity and physical proximity of DNA binding and activation domains, providing a molecular framework to explain the loss-of-function phenotypes of all previously characterized nude mutations. Our results implicate Whn as a transcriptional regulator of hair keratin genes and reveal the nude phenotype as the first example of an inherited skin disorder that is caused by loss of expression rather than mutation of keratin genes.

Characterization of a 300 kbp region of human DNA containing the type II hair keratin gene domain

Screening of an arrayed human genomic P1 artificial chromosome DNA library by means of the polymerase chain reaction with a specific primer pair from the human type II hair keratin hHb5 yielded two P1 artificial chromosome clones covering approximately 300 kb of genomic DNA. The contig contained six type II hair keratin genes, hHb1-hHb6, and four keratin pseudogenes psihHbA-psihHbD. This hair keratin gene domain was flanked by type II epithelial keratins K6b/K6hf and K7, respectively. The keratin genes/pseudogene are 5-14 kbp in size with intergenic distances of 5-19 kbp of DNA and do not exhibit a single direction of transcription. With one exception, type II hair keratin genes are organized into nine exons and eight introns, with strictly conserved exon-intron boundaries. The functional hair keratin genes are grouped into two distinct subclusters near the extremities of the hair keratin gene domain. One subcluster encodes the highly related hair keratins hHb1, hHb3, and hHb6; The second cluster encodes the structurally less related hair keratins hHb2, hHb4, and hHb5. Reverse transcription-polymerase chain reaction shows that all hair keratin genes are expressed in the hair follicle. Pseudogene psihHbD is also transcriptionally expressed, albeit with alterations in splicing and frameshift mutations, leading to premature stop codons in the splice forms analyzed. Evolutionary tree analysis revealed a divergence of the type II hair keratin genes from the epithelial keratins, followed by their segregation into the members of the two subclusters over time. We assume that the approximately 200 kbp DNA domain contains the entire complement of human type II hair keratin genes.

Submucosal gland development in the airway is controlled by lymphoid enhancer binding factor 1 (LEF1)

Previous studies have demonstrated that transcription of the lymphoid enhancer binding factor 1 (Lef1) gene is upregulated in submucosal gland progenitor cells just prior to gland bud formation in the developing ferret trachea. In the current report, several animal models were utilized to functionally investigate the role of LEF1 in initiating and supporting gland development in the airway. Studies on Lef1-deficient mice and antisense oligonucleotides in a ferret xenograft model demonstrate that LEF1 is functionally required for submucosal gland formation in the nasal and tracheal mucosa. To determine whether LEF1 expression was sufficient for the induction of airway submucosal glands, two additional model systems were utilized. In the first, recombinant adeno-associated virus was used to overexpress the human LEF1 gene in a human bronchial xenograft model of regenerative gland development in the adult airway. In a second model, the LEF1 gene was ectopically overexpressed under the direction of the proximal airway-specific CC10 promoter in transgenic mice. In both of these models, morphometric analyses revealed no increase in the number or size of airway submucosal glands, indicating that ectopic LEF1 expression alone is insufficient to induce submucosal gland development. In summary, these studies demonstrate that LEF1 expression is required, but in and of itself is insufficient, for the initiation and continued morphogenesis of submucosal glands in the airway.

Multiple roles for activated LEF/TCF transcription complexes during hair follicle development and differentiation

LEF/TCF DNA-binding proteins act in concert with activated beta -catenin, the product of Wnt signaling, to transactivate downstream target genes. To probe the role of activated LEF/TCF transcription factor complexes in hair follicle morphogenesis and differentiation, we engineered mice harboring TOPGAL, a beta -galactosidase gene under the control of a LEF/TCF and beta -catenin inducible promoter. In mice, TOPGAL expression was directly stimulated by a stabilized form of beta -catenin, but was also dependent upon LEF1/TCF3 in skin. During embryogenesis, TOPGAL activation occurred transiently in a subset of LEF1-positive cells of pluripotent ectoderm and underlying mesenchyme. Downgrowth of initiated follicles proceeded in the absence of detectable TOPGAL expression, even though LEF1 was still expressed. While proliferative matrix cells expressed the highest levels of Lef1 mRNAs, LEF1 concentrated in the precursor cells to the hair shaft, where TOPGAL expression was co-induced with hair-specific keratin genes containing LEF/TCF-binding motifs. LEF1 and TOPGAL expression ceased during catagen and telogen, but reappeared at the start of the postnatal hair cycle, concomitant with precortex formation. In contrast to hair shaft precursor cells, postnatal outer root sheath expressed TCF3, but not TOPGAL. TCF3 was also expressed in the putative follicle stem cells, and while TOPGAL was generally silent in this compartment, it was stimulated at the start of the hair cycle in a fashion that appeared to be dependent upon stabilization of beta -catenin. Taken together, our findings demonstrate that LEF1/TCF3 is necessary but not sufficient for TOPGAL activation, revealing the existence of positive and negative regulators of these factors in the skin. Furthermore, our findings unveil the importance of activated LEF/TCF complexes at distinct times in hair development and cycling when changes in cell fate and differentiation commitments take place.