Hairless is a nuclear receptor corepressor essential for skin function

HR Gene Variants Identified in Mexican Patients with Alopecia Areata

Alopecia Areata (AA) is a multifactorial, dermatological disease characterized by non-scarring hair loss. Alterations in candidate genes, such as HR (Hairless), could represent a risk factor for its development. The aim of this study was to search for and analyze variants in exons 3, 15 and 17 of the HR gene in Mexican patients with AA. A total of 30 samples from both AA patients and healthy donors were analyzed in this study. Exons were amplified and sequenced using the Sanger method. Descriptive statistics and χ2 tests were used in the analysis of clinical-demographic characteristics and the comparison of allelic/genotypical frequencies between groups, respectively. The effect on protein function for the non-synonymous variants was determined with three bioinformatics servers. Three gene variants were identified in the HR gene of the evaluated patients. The benign polymorphism c.1010G > A p.(Gly337Asp) (rs12675375) had been previously reported, whereas the variants c.750G > A p.(Gln250Gln) and c.3215T > A (Val1072AGlu) have not been described in other world populations. Both non-synonymous variants proved to be significant (p ≤ 0.05). The variant c.3215T > A p.(Val1072Glu) is of particular interest due to its deleterious effect on the structure and function of the protein; therefore, it could be considered a risk factor for the development of AA.

The Histone Demethylase HR Suppresses Breast Cancer Development through Enhanced CELF2 Tumor Suppressor Activity

The hairless (HR) gene encodes a transcription factor with histone demethylase activity that is essential for development and tissue homeostasis. Previous studies suggest that mutational inactivation of HR promotes tumorigenesis. To investigate HR mutations in breast cancer, we performed targeted next-generation sequencing using DNA isolated from primary breast cancer tissues. We identified HR somatic mutations in approximately 15% of the patient cohort (n = 85), compared with 23% for BRCA2, 13% for GATA3, 7% for BRCA1, and 3% for PTEN in the same patient cohort. We also found an average 23% HR copy number loss in breast cancers. In support of HR's antitumor functions, HR reconstitution in HR-deficient human breast cancer cells significantly suppressed tumor growth in orthotopic xenograft mouse models. We further demonstrated that HR's antitumor activity was at least partly mediated by transcriptional activation of CELF2, a tumor suppressor with RNA-binding activity. Consistent with HR's histone demethylase activity, pharmacologic inhibition of histone methylation suppressed HR-deficient breast cancer cell proliferation, migration and tumor growth. Taken together, we identified HR as a novel tumor suppressor that is frequently mutated in breast cancer. We also showed that pharmacologic inhibition of histone methylation is effective in suppressing HR-deficient breast tumor growth and progression.

Hairless regulates heterochromatin maintenance and muscle stem cell function as a histone demethylase antagonist

Skeletal muscle possesses remarkable regenerative ability because of the resident muscle stem cells (MuSCs). A prominent feature of quiescent MuSCs is a high content of heterochromatin. However, little is known about the mechanisms by which heterochromatin is maintained in MuSCs. By comparing gene-expression profiles from quiescent and activated MuSCs, we found that the mammalian Hairless (Hr) gene is expressed in quiescent MuSCs and rapidly down-regulated upon MuSC activation. Using a mouse model in which Hr can be specifically ablated in MuSCs, we demonstrate that Hr expression is critical for MuSC function and muscle regeneration. In MuSCs, loss of Hr results in reduced trimethylated Histone 3 Lysine 9 (H3K9me3) levels, reduced heterochromatin, increased susceptibility to genotoxic stress, and the accumulation of DNA damage. Deletion of Hr leads to an acceleration of the age-related decline in MuSC numbers. We have also demonstrated that despite the fact that Hr is homologous to a family of histone demethylases and binds to di- and trimethylated H3K9, the expression of Hr does not lead to H3K9 demethylation. In contrast, we show that the expression of Hr leads to the inhibition of the H3K9 demethylase Jmjd1a and an increase in H3K9 methylation. Taking these data together, our study has established that Hr is a H3K9 demethylase antagonist specifically expressed in quiescent MuSCs.

Control of Breast Cancer Pathogenesis by Histone Methylation and the Hairless Histone Demethylase

Breast cancer is a highly heterogeneous disease, encompassing many subtypes that have distinct origins, behaviors, and prognoses. Although traditionally seen as a genetic disease, breast cancer is now also known to involve epigenetic abnormalities. Epigenetic regulators, such as DNA methyltransferases and histone-modifying enzymes, play essential roles in gene regulation and cancer development. Dysregulation of epigenetic regulator activity has been causally linked with breast cancer pathogenesis. Hairless (HR) encodes a 130-kDa transcription factor that is essential for development and tissue homeostasis. Its role in transcription regulation is partly mediated by its interaction with multiple nuclear receptors, including thyroid hormone receptor, retinoic acid receptor-related orphan receptors, and vitamin D receptor. HR has been studied primarily in epidermal development and homeostasis. Hr-mutant mice are highly susceptible to ultraviolet- or carcinogen-induced skin tumors. Besides its putative tumor suppressor function in skin, loss of HR function has also been implicated in increased leukemia susceptibility and promotes the growth of melanoma and brain cancer cells. HR has also been demonstrated to function as a histone H3 lysine 9 demethylase. Recent genomics studies have identified HR mutations in a variety of human cancers, including breast cancer. The anticancer function and mechanism of action by HR in mammary tissue remains to be investigated. Here, we review the emerging role of HR, its histone demethylase activity and histone methylation in breast cancer development, and potential for epigenetic therapy.

Vitamin D-vitamin D receptor system down-regulates expression of uncoupling proteins in brown adipocyte through interaction with Hairless protein

Our previous study showed that feeding mice with vitamin D deficiency diet markedly alleviated high-fat-diet-induced overweight, hyperinsulinemia, and hepatic lipid accumulation. Moreover, vitamin D deficiency up-regulated the expression of uncoupling protein 3 (Ucp3) in white adipose tissue (WAT) and brown adipose tissue (BAT). The present study aimed to further investigate the effects of vitamin D and vitamin D receptor (Vdr) on Ucp1–3 (Ucps) expression in brown adipocyte and the mechanism involved in it. Rat primary brown adipocytes were separated and purified. The effects of the 1,25(OH)₂D₃ (1,25-dihydroxyvitamin D3; the hormonal form of vitamin D) and Vdr system on Ucps expression in brown adipocytes were investigated in basal condition and activated condition by isoproterenol (ISO) and triiodothyronine (T3). Ucps expression levels were significantly down-regulated by 1,25(OH)₂D₃ in the activated brown adipocyte. Vdr silencing reversed the down-regulation of Ucps by 1,25(OH)₂D₃, whereas Vdr overexpression strengthened the down-regulation effects. Hairless protein did express in brown adipocyte and was localized in cell nuclei. 1,25(OH)₂D₃ increased Hairless protein expression in the cell nuclei. Hairless (Hr) silencing notably elevated Ucps expression in activated condition induced by ISO and T3. Moreover, immunoprecipitation results revealed that Vdr could interact with Hairless, which might contribute to decreasing expression of Vdr target gene Ucps. These data suggest that vitamin D suppresses expression of Ucps in brown adipocyte in a Vdr-dependent manner and the corepressor Hairless protein probably plays a role in the down-regulation.

Transgenic mice display hair loss and regrowth overexpressing mutant Hr gene

Mutations in the hairless (Hr) gene in both mice and humans have been implicated in the development of congenital atrichia, but the role of Hr in skin and hair follicle (HF) biology remains unknown. Here, we established transgenic mice (TG) overexpressing mutant Hr to investigate its specific role in the development of HF. Three transgenic lines were successfully constructed, and two of them (TG3 and TG8) displayed a pattern of hair loss and regrowth with alternation in the expression of HR protein. The mutant Hr gene inhibited the expression of the endogenous gene in transgenic individuals, which led to the development of alopecia. Interestingly, the hair regrew with the increase in the endogenous expression levels resulting from decreased mutant Hr expression. The findings of our study indicate that the changes in the expression of Hr result in hair loss or regrowth.

Hairless controls hair fate decision via Wnt/β-catenin signaling

The hairless (Hr) gene plays a central role in the hair cycle, considering that mutations in the gene result in hair loss with the exception of a few vibrissae after the first hair growth cycle in both mice and humans. This study examinedthe uncommon phenotype and using microarray analyses and functional studies, we found that β-catenin was mediated by Hr. Progenitor keratinocytes from the bulge region differentiate into both epidermis and sebaceous glands, and fail to adopt the hair keratinocytes fate in the mutant scalp, due to the decreased Wnt/β-catenin signaling in the absence of the hairless protein. This may be attributed to the dysfunction of normal epithelial-mesenchymal interactions in the hair follicle (HF).

The Mammalian Hairless Protein as a DNA Binding Phosphoprotein

The mammalian hairless (Hr) protein plays critical roles in skin and brain tissues, but how it interacts with DNA and partner protein is only now being defined. Our initial tests of four consensus response elements, revealed that rat Hr can specifically bind to a consensus p53 response element (p53RE), 5'-AGACATGCCTAGACATGCCT-3', but not to response elements for NF-κB, TCF4 or Sp1. We then employed ChIP assays which verified that human HR binds to a p53RE of the GADD45A gene in both HEK293 (embryonic kidney) and U87 (glioblastoma) cells. Further, HR was shown to interact directly with the p53 protein in a co-immunoprecipitation assay. Cotransfections with p53RE reporter gene constructs revealed that rat Hr can boost p53-mediated transactivation of a reporter gene linked to the GADD45A p53RE, but blunts p53-mediated transactivation when the reporter gene is linked to a p21 promoter fragment containing a p53RE, with implications for the regulation of these two cell cycle control genes. Finally, our investigations of HR phosphorylation revealed that rat Hr is a substrate for PKC, but not PKA, and that human HR is phosphorylated in intact U87 cells at Ser-416, located in a highly conserved region which partially fulfills the criteria of a PKC site. We propose that mammalian Hr is a phosphoprotein which can exert cross-talk with the p53 pathway with important implications for the regulation of cell proliferation and differentiation in tissues such as skin and brain where Hr is highly expressed. J. Cell. Biochem. 118: 341-350, 2017. © 2016 Wiley Periodicals, Inc.

Naked but not Hairless: the pitfalls of analyses of molecular adaptation based on few genome sequence comparisons

The naked mole-rat (Heterocephalus glaber) is the only rodent species that naturally lacks fur. Genome sequencing of this atypical rodent species recently shed light on a number of its morphological and physiological adaptations. More specifically, its hairless phenotype has been traced back to a single amino acid change (C397W) in the hair growth associated (HR) protein (or Hairless). By considering the available species diversity, we show that this specific position is in fact variable across mammals, including in the horse that was misleadingly reported to have the ancestral Cysteine. Moreover, by sequencing the corresponding HR exon in additional rodent species, we demonstrate that the C397W substitution is actually not a peculiarity of the naked mole-rat. Instead, this specific amino acid substitution is present in all hystricognath rodents investigated, which are all fully furred, including the naked mole-rat closest relative, the Damaraland mole-rat (Fukomys damarensis). Overall, we found no statistical correlation between amino acid changes at position 397 of the HR protein and reduced pilosity across the mammalian phylogeny. This demonstrates that this single amino acid change does not explain the naked mole-rat hairless phenotype. Our case study calls for caution before making strong claims regarding the molecular basis of phenotypic adaptation based on the screening of specific amino acid substitutions using only few model species in genome sequence comparisons. It also exposes the more general problem of the dilution of essential information in the supplementary material of genome papers thereby increasing the probability that misleading results will escape the scrutiny of editors, reviewers, and ultimately readers.

Commentary on: Hairless and the polyamine putrescine form a negative regulatory loop in the epidermis

Polyamines are cationic amines essential for cellular proliferation. Recently, their role in hair follicle (HF) growth has started to be explored, but their exact function is still obscure. In the October issue of Experimental Dermatology, Luke et al. follow the observation that putrescine overproducing mice and hairless (HR) mutant mice show a similar clinical phenotype of hair loss and dermal cyst formation. They show that HR and putrescine form a negative regulatory feedback mechanism, which might regulate hair cycling and therefore control hair growth. This study clearly demonstrates that a strong connection exists between HR and polyamines although there are probably additional molecular pathways involved in the polyamine regulation of hair growth which remain to be discovered.

Hair follicle disruption facilitates pathogenesis to UVB-induced cutaneous inflammation and basal cell carcinoma development in Ptch(+/-) mice

Hairless mice carrying homozygous mutations in hairless gene manifest rudimentary hair follicles (HFs), epidermal cysts, hairless phenotype, and enhanced susceptibility to squamous cell carcinomas. However, their susceptibility to basal cell carcinomas (BCCs), a neoplasm considered originated from HF-localized stem cells, is unknown. To demonstrate the role of HFs in BCC development, we bred Ptch(+/-)/C57BL6 with SKH-1 hairless mice, followed by brother-sister cross to get F2 homozygous mutant (hairless) or wild-type (haired) mice. UVB-induced inflammation was less pronounced in shaved haired than in hairless mice. In hairless mice, inflammatory infiltrate was found around the rudimentary HFs and epidermal cysts. Expression of epidermal IL1f6, S100a8, vitamin D receptor, repetin, and major histocompatibility complex II, biomarkers depicting susceptibility to cutaneous inflammation, was also higher. In these animals, HF disruption altered susceptibility to UVB-induced BCCs. Tumor onset in hairless mice was 10 weeks earlier than in haired littermates. The incidence of BCCs was significantly higher in hairless than in haired animals; however, the magnitude of sonic hedgehog signaling did not differ significantly. Overall, 100% of hairless mice developed >12 tumors per mouse after 32 weeks of UVB therapy, whereas haired mice developed fewer than three tumors per mouse after 44 weeks of long-term UVB irradiation. Tumors in hairless mice were more aggressive than in haired littermates and manifested decreased E-cadherin and enhanced mesenchymal proteins. These data provide novel evidence that disruption of HFs in Ptch(+/-) mice enhances cutaneous susceptibility to inflammation and BCCs.

Hairless is a histone H3K9 demethylase

The hairless (HR) protein contains a Jumonji C (JmjC) domain that is conserved among a family of proteins with histone demethylase (HDM) activity. To test whether HR possesses HDM activity, we performed a series of in vitro demethylation assays, which demonstrated that HR can demethylate monomethylated or dimethylated histone H3 lysine 9 (H3K9me1 or me2). Moreover, ectopic expression of wild-type HR, but not JmjC-mutant HR, led to pronounced demethylation of H3K9 in cultured human HeLa cells. We also show that two missense mutations in HR, which we and others described in patients with atrichia with papular lesions, abolished the demethylase activity of HR, demonstrating the role of HR demethylase activity in human disease. By ChIP-Seq analysis, we identified multiple new HR target genes, many of which play important roles in epidermal development, neural function, and transcriptional regulation, consistent with the predicted biological functions of HR. Our findings demonstrate for the first time that HR is a H3K9 demethylase that regulates epidermal homeostasis via direct control of its target genes.

Characterization of hairless (Hr) and FGF5 genes provides insights into the molecular basis of hair loss in cetaceans

Background

Hair is one of the main distinguishing characteristics of mammals and it has many important biological functions. Cetaceans originated from terrestrial mammals and they have evolved a series of adaptations to aquatic environments, which are of evolutionary significance. However, the molecular mechanisms underlying their aquatic adaptations have not been well explored. This study provided insights into the evolution of hair loss during the transition from land to water by investigating and comparing two essential regulators of hair follicle development and hair follicle cycling, i.e., the Hairless (Hr) and FGF5 genes, in representative cetaceans and their terrestrial relatives.

Results

The full open reading frame sequences of the Hr and FGF5 genes were characterized in seven cetaceans. The sequence characteristics and evolutionary analyses suggested the functional loss of the Hr gene in cetaceans, which supports the loss of hair during their full adaptation to aquatic habitats. By contrast, positive selection for the FGF5 gene was found in cetaceans where a series of positively selected amino acid residues were identified.

Conclusions

This is the first study to investigate the molecular basis of the hair loss in cetaceans. Our investigation of Hr and FGF5, two indispensable regulators of the hair cycle, provide some new insights into the molecular basis of hair loss in cetaceans. The results suggest that positive selection for the FGF5 gene might have promoted the termination of hair growth and early entry into the catagen stage of hair follicle cycling. Consequently, the hair follicle cycle was disrupted and the hair was lost completely due to the loss of the Hr gene function in cetaceans. This suggests that cetaceans have evolved an effective and complex mechanism for hair loss.

Hairless promotes PPARγ expression and is required for white adipogenesis

Adipose tissue is the largest compartment in the mammalian body for storing energy as fat, providing an important reservoir of fuel for maintaining whole body energy homeostasis. Herein, we identify the transcriptional cofactor hairless (HR) to be required for white adipogenesis. Moreover, forced expression of HR in non-adipogenic precursor cells induces adipogenic gene expression and enhances adipocyte formation under permissive conditions. HR exerts its proadipogenic effects by regulating the expression of PPARγ, one of the central adipogenic transcription factors. In conclusion, our data provide a new mechanism required for white adipogenesis.

Loss of hairless confers susceptibility to UVB-induced tumorigenesis via disruption of NF-kappaB signaling

In order to model squamous cell carcinoma development in vivo, researchers have long preferred hairless mouse models such as SKH-1 mice that have traditionally been classified as ‘wild-type’ mice irrespective of the genetic factors underlying their hairless phenotype. The work presented here shows that mutations in the Hairless (Hr) gene not only result in the hairless phenotype of the SKH-1 and Hr^−/− mouse lines but also cause aberrant activation of NFκB and its downstream effectors. We show that in the epidermis, Hr is an early UVB response gene that regulates NFκB activation and thereby controls cellular responses to irradiation. Therefore, when Hr expression is decreased in Hr mutant animals there is a corresponding increase in NFκB activity that is augmented by UVB irradiation. This constitutive activation of NFκB in the Hr mutant epidermis leads to the stimulation a large variety of downstream effectors including the cell cycle regulators cyclin D1 and cyclin E, the anti-apoptosis protein Bcl-2, and the pro-inflammatory protein Cox-2. Therefore, Hr loss results in a state of uncontrolled epidermal proliferation that promotes tumor development, and Hr mutant mice should no longer be considered merely hairless 'wild-type' mice. Instead, Hr is a crucial UVB response gene and its loss creates a permissive environment that potentiates increased tumorigenesis.

Hairless and NFκB form a positive feedback loop after UVB and TNFα stimulation

Hairless (HR) is a nuclear protein with corepressor activity whose exact function in the skin remains to be determined. Mutations in both human and mouse Hairless lead to hair loss accompanied by the appearance of papules, a disorder called atrichia with papular lesions. Furthermore, mice with mutations in HR are known to have a higher susceptibility to ultraviolet radiation-induced tumorigenesis, suggesting that HR plays a crucial role in the epidermal UVB response. Using normal human keratinocytes (NHKs) and keratinocytes containing a mutation in HR, we found that HR is an early UVB response gene that negatively regulates NFκB mRNA expression. HR mutant keratinocytes have a dysregulated UVB response that includes increased proliferation and the aberrant activation of NFκB effector genes. Additionally, we show that another UVB response gene, TNFα, negatively regulates HR mRNA expression. TNFα-induced negative regulation of HR occurs through a direct interaction of the p65 subunit with a single NFκB-binding domain located in the HR promoter region. Therefore, we show for the first time that HR and NFκB participate in a positive feedback loop that can be initiated either by UVB or TNFα.

Chromatin as an oxygen sensor and active player in the hypoxia response

Changes in the availability or demand for oxygen induce dramatic changes at the cellular level. Primarily, activation of a family of oxygen labile transcription factors, Hypoxia Inducible Factor (HIF), initiates a variety of cellular processes required to re-instate oxygen homeostasis. Oxygen is sensed by molecular dioxygenases in cells, such as the prolyl-hydroxylases (PHDs), enzymes which are responsible for the oxygen-dependent regulation of HIF. As HIF is a transcription factor it must bind DNA sequences of its target genes possibly in the context of a complex chromatin structure. How chromatin structure changes in response to hypoxia is currently unknown. However, the identification of a novel class of histone demethylases as true dioxygenases suggests that chromatin can act as an oxygen sensor and plays an active role in the coordination of the cellular response to hypoxia. This review will discuss the current knowledge on how hypoxia engages with different proteins involved in chromatin organisation and dynamics.

Mechanism of JmjC-containing protein Hairless in the regulation of vitamin D receptor function

The JmjC-domain-containing protein Hairless (HR) and the vitamin D receptor (VDR) play a critical role in the maintenance of hair growth. Mutations in HR or VDR cause alopecia in humans and mice. Here we show that HR interacts with VDR and induces VDR relocalization in the nuclei. HR associates and colocalizes with nuclear receptor co-repressor (N-CoR) which is localized to subnuclear structures termed matrix-associated deacetylase (MAD) bodies. It is found that the HR mutants (C622G, N970S, D1012N, V1136D), associated with alopecia universalis congenita (AUC) or atrichia with papular lesions (APL), exhibit an abnormal subcellular distribution in addition to the impaired co-repressor activity with VDR. Studies on deletion mutants of HR indicate that the JmjC domain contributes to the co-repressor activity of HR. Our work provides new clues and evidence for the understanding on the role of HR in hair growth.

TNIP1 is a corepressor of agonist-bound PPARs

Nuclear receptor (NR) coregulators include coactivators, contributing to holoreceptor transcriptional activity, and corepressors, mediating NR target gene silencing in the absence of hormone. We identified an atypical NR coregulator, TNFα-induced protein 3-interacting protein 1 (TNIP1), from a peroxisome proliferator activated receptor (PPAR) α screen of a human keratinocyte cDNA library. TNIP1's complex nomenclature parallels its additional function as an NF-κB inhibitor. Here we show TNIP1 is an atypical NR corepressor using two-hybrid systems, biochemical studies, and receptor activity assays. The requirements for TNIP1-PPAR interaction are characteristic for coactivators; however, TNIP1 partially decreases PPAR activity. TNIP1 has separable transcriptional activation and repression domains suggesting a modular nature to its overall effect. It may provide a means of lowering receptor activity in the presence of ligand without total loss of receptor function. TNIP1's multiple roles and expression in several cell types suggest its regulatory effect depends on its expression level and the expression of other regulators in NR and/or NF-κB signaling pathways. As a NR coregulator, TNIP1 targeting agonist-bound PPAR and reducing transcriptional activity offers control of receptor signaling not available from typical corepressors and may contribute to combinatorial regulation of transcription.

Molecular evolution of HR, a gene that regulates the postnatal cycle of the hair follicle

Hair is a unique mammalian trait that is absent in all other animal forms. Hairlessness is rare in mammals and humans are exceptional among primates in lacking dense layer of hair covering. HR was the first gene identified to be implicated in hair-cycle regulation. Point mutations in HR lead to congenital human hair loss, which results in the complete loss of body and scalp hairs. HR functions are indispensable for initiation of postnatal hair follicular cycling. This study investigates the phylogenetic history and analyzes the protein evolutionary rate to provide useful insight into the molecular evolution of HR. The data demonstrates an acceleration of HR sequence evolution in human branch and suggests that the ability of HR protein to mediate postnatal hair-cycling has been altered in the course of human evolution. In particular those residues were pinpointed which should be regarded as target of positive Darwinian selection during human evolution.

Metabolic changes in skin caused by Scd1 deficiency: a focus on retinol metabolism

We previously reported that mice with skin-specific deletion of stearoyl-CoA desaturase-1 (Scd1) recapitulated the skin phenotype and hypermetabolism observed in mice with a whole-body deletion of Scd1. In this study, we first performed a diet-induced obesity experiment at thermoneutral temperature (33°C) and found that skin-specific Scd1 knockout (SKO) mice still remain resistant to obesity. To elucidate the metabolic changes in the skin that contribute to the obesity resistance and skin phenotype, we performed microarray analysis of skin gene expression in male SKO and control mice fed a standard rodent diet. We identified an extraordinary number of differentially expressed genes that support the previously documented histological observations of sebaceous gland hypoplasia, inflammation and epidermal hyperplasia in SKO mice. Additionally, transcript levels were reduced in skin of SKO mice for genes involved in fatty acid synthesis, elongation and desaturation, which may be attributed to decreased abundance of key transcription factors including SREBP1c, ChREBP and LXRα. Conversely, genes involved in cholesterol synthesis were increased, suggesting an imbalance between skin fatty acid and cholesterol synthesis. Unexpectedly, we observed a robust elevation in skin retinol, retinoic acid and retinoic acid-induced genes in SKO mice. Furthermore, SEB-1 sebocytes treated with retinol and SCD inhibitor also display an elevation in retinoic acid-induced genes. These results highlight the importance of monounsaturated fatty acid synthesis for maintaining retinol homeostasis and point to disturbed retinol metabolism as a novel contributor to the Scd1 deficiency-induced skin phenotype.