Dual role of inactivating Lef1 mutations in epidermis: tumor promotion and specification of tumor type

A TALE/HOX code unlocks WNT signalling response towards paraxial mesoderm

One fundamental yet unresolved question in biology remains how cells interpret the same signalling cues in a context-dependent manner resulting in lineage specification. A key step for decoding signalling cues is the establishment of a permissive chromatin environment at lineage-specific genes triggering transcriptional responses to inductive signals. For instance, bipotent neuromesodermal progenitors (NMPs) are equipped with a WNT-decoding module, which relies on TCFs/LEF activity to sustain both NMP expansion and paraxial mesoderm differentiation. However, how WNT signalling activates lineage specific genes in a temporal manner remains unclear. Here, we demonstrate that paraxial mesoderm induction relies on the TALE/HOX combinatorial activity that simultaneously represses NMP genes and activates the differentiation program. We identify the BRACHYURY-TALE/HOX code that destabilizes the nucleosomes at WNT-responsive regions and establishes the permissive chromatin landscape for de novo recruitment of the WNT-effector LEF1, unlocking the WNT-mediated transcriptional program that drives NMPs towards the paraxial mesodermal fate.

Cells in the developing embryo interpret WNT signalling with context-dependence, but the mechanism decoding these cues is unclear. Here, the authors show that combinatorial TALE/HOX activity destabilizes nucleosomes at WNT-responsive regions to activate paraxial mesodermal genes.

The anti-apoptotic Bcl-2 protein regulates hair follicle stem cell function

Maintaining the architecture, size and composition of an intact stem cell (SC) compartment is crucial for tissue homeostasis and regeneration throughout life. In mammalian skin, elevated expression of the anti‐apoptotic Bcl‐2 protein has been reported in hair follicle (HF) bulge SCs (BSCs), but its impact on SC function is unknown. Here, we show that systemic exposure of mice to the Bcl‐2 antagonist ABT‐199/venetoclax leads to the selective loss of suprabasal BSCs (sbBSCs), thereby disrupting cyclic HF regeneration. RNAseq analysis shows that the pro‐apoptotic BH3‐only proteins BIM and Bmf are upregulated in sbBSCs, explaining their addiction to Bcl‐2 and the marked susceptibility to Bcl‐2 antagonism. In line with these observations, conditional knockout of Bcl‐2 in mouse epidermis elevates apoptosis in BSCs. In contrast, ectopic Bcl‐2 expression blocks apoptosis during HF regression, resulting in the accumulation of quiescent SCs and delaying HF growth in mice. Strikingly, Bcl‐2‐induced changes in size and composition of the HF bulge accelerate tumour formation. Our study identifies a niche‐instructive mechanism of Bcl‐2‐regulated apoptosis response that is required for SC homeostasis and tissue regeneration, and may suppress carcinogenesis.

Stem and progenitor cells in sebaceous gland development, homeostasis and pathologies

Sebaceous glands (SGs), typically associated with hair follicles, are critical for the homeostasis and function of mammalian skin. The main physiological function of SGs is the production and holocrine secretion of sebum to lubricate and protect the skin. Defective SGs have been linked to a variety of skin disorders, including acne, seborrheic dermatitis and formation of sebaceous tumors. Thus, a better understanding how SGs are formed and maintained is important to unravel the underlying molecular and cellular mechanisms of SG pathologies and to find better and effective therapies. Over the last two decades, research has come a long way from the initial identification of skin epithelial stem cells to the isolation and functional characterization of multiple stem cell pools as well as a better understanding of their unique and complex activities that drive skin homeostasis and operate in skin pathologies. Here, we discuss recent progress in unravelling cellular mechanisms underlying SG development, homeostasis and sebaceous tumor formation and assess the role of stem and progenitor cells in controlling SG physiology and disease processes. The development of elegant in vivo imaging as well as various in vitro and ex vivo stem cell and SG tissue models will advance mechanistic studies on SG function and allow drug screening and testing for efficient and successful targeting SG pathologies.

LEF1 Induces DHRS2 Gene Expression in Human Acute Leukemia Jurkat T-Cells

Objective

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disease resulting from the accumulation of genetic changes that affect the development of T-cells. The precise role of lymphoid enhancer-binding factor 1 (LEF1) in T-ALL has been controversial since both overexpression and inactivating LEF1 mutations have been reported to date. Here, we investigate the potential gene targets of LEF1 in the Jurkat human T-cell leukemia cell line.

Materials and Methods

We used small interfering RNA (siRNA) technology to knock down LEF1 in Jurkat cells and then compared the gene expression levels in the LEF1 knockdown cells with non-targeting siRNA-transfected and non-transfected cells by employing microarray analysis.

Results

We identified DHRS2, a tumor suppressor gene, as the most significantly downregulated gene in LEF1 knockdown cells, and we further confirmed its downregulation by real-time quantitative polymerase chain reaction (qRT-PCR) in mRNA and at protein level by western blotting.

Conclusion

Our results revealed that DHRS2 is positively regulated by LEF1 in Jurkat cells, which indicates the capability of LEF1 as a tumor suppressor and, together with previous reports, suggests that LEF1 exhibits a regulatory role in T-ALL via not only its oncogenic targets but also tumor suppressor genes.

Concomitant Orbital Tumours: Small Lymphocytic Lymphoma Involving the Lacrimal Gland of a Patient with Clinical Diagnoses of Muir-Torre Syndrome and Extensive Sebaceous Gland Carcinoma of the Ipsilateral Eyelid

Background/Aims

We present a case of 2 concomitant tumours, i.e., a sebaceous carcinoma (SC) and a small lymphocytic lymphoma (SLL), in the lacrimal gland of a patient with Muir-Torre syndrome.

Methods

Clinical history, orbital examination, diagnostic biopsy, excisional biopsy, and histopathologic analysis were utilized.

Results

An 89-year-old female presented to the eye casualty with corneal ulcer, anterior uveitis, proptosis, and restricted ocular motility. She has a clinical history of breast cancer, colon carcinoma, and SC of the eyelid, which had been resected completely 2 years before. Clinical examination, imaging, and diagnostic biopsy confirmed orbital SC recurrence. Exenteration and subsequent histopathologic analysis of the specimen revealed lymphocytic infiltrates consistent with SLL within the lacrimal gland.

Conclusion

We report for the first time a case of a patient with Muir-Torre syndrome who developed an orbital recurrent SC with an incidental finding of a lacrimal gland B non-Hodgkin lymphoma consistent with SLL. Clinicians should be aware of the possibility of this coexistence of multiple cancer types in patients with sebaceous carcinoma and Muir-Torre syndrome.

Neuroendocrinology and neurobiology of sebaceous glands

The nervous system communicates with peripheral tissues through nerve fibres and the systemic release of hypothalamic and pituitary neurohormones. Communication between the nervous system and the largest human organ, skin, has traditionally received little attention. In particular, the neuro-regulation of sebaceous glands (SGs), a major skin appendage, is rarely considered. Yet, it is clear that the SG is under stringent pituitary control, and forms a fascinating, clinically relevant peripheral target organ in which to study the neuroendocrine and neural regulation of epithelia. Sebum, the major secretory product of the SG, is composed of a complex mixture of lipids resulting from the holocrine secretion of specialised epithelial cells (sebocytes). It is indicative of a role of the neuroendocrine system in SG function that excess circulating levels of growth hormone, thyroxine or prolactin result in increased sebum production (seborrhoea). Conversely, growth hormone deficiency, hypothyroidism, and adrenal insufficiency result in reduced sebum production and dry skin. Furthermore, the androgen sensitivity of SGs appears to be under neuroendocrine control, as hypophysectomy (removal of the pituitary) renders SGs largely insensitive to stimulation by testosterone, which is crucial for maintaining SG homeostasis. However, several neurohormones, such as adrenocorticotropic hormone and α-melanocyte-stimulating hormone, can stimulate sebum production independently of either the testes or the adrenal glands, further underscoring the importance of neuroendocrine control in SG biology. Moreover, sebocytes synthesise several neurohormones and express their receptors, suggestive of the presence of neuro-autocrine mechanisms of sebocyte modulation. Aside from the neuroendocrine system, it is conceivable that secretion of neuropeptides and neurotransmitters from cutaneous nerve endings may also act on sebocytes or their progenitors, given that the skin is richly innervated. However, to date, the neural controls of SG development and function remain poorly investigated and incompletely understood. Botulinum toxin-mediated or facial paresis-associated reduction of human sebum secretion suggests that cutaneous nerve-derived substances modulate lipid and inflammatory cytokine synthesis by sebocytes, possibly implicating the nervous system in acne pathogenesis. Additionally, evidence suggests that cutaneous denervation in mice alters the expression of key regulators of SG homeostasis. In this review, we examine the current evidence regarding neuroendocrine and neurobiological regulation of human SG function in physiology and pathology. We further call attention to this line of research as an instructive model for probing and therapeutically manipulating the mechanistic links between the nervous system and mammalian skin.

Wnt Signaling Pathways in Keratinocyte Carcinomas

The skin functions as a barrier between the organism and the surrounding environment. Direct exposure to external stimuli and the accumulation of genetic mutations may lead to abnormal cell growth, irreversible tissue damage and potentially favor skin malignancy. Skin homeostasis is coordinated by an intricate signaling network, and its dysregulation has been implicated in the development of skin cancers. Wnt signaling is one such regulatory pathway orchestrating skin development, homeostasis, and stem cell activation. Aberrant regulation of Wnt signaling cascades not only gives rise to tumor initiation, progression and invasion, but also maintains cancer stem cells which contribute to tumor recurrence. In this review, we summarize recent studies highlighting functional evidence of Wnt-related oncology in keratinocyte carcinomas, as well as discussing preclinical and clinical approaches that target oncogenic Wnt signaling to treat cancers. Our review provides valuable insight into the significance of Wnt signaling for future interventions against keratinocyte carcinomas.

Magnifying glass on spiradenoma and cylindroma histogenesis and tumorigenesis using systematic transcriptome analysis

Spiradenoma and cylindroma are related sweat gland tumors. To delineate their histogenesis, gene profiles, and their potential drivers, we performed a whole-transcriptome sequencing analysis of fourteen samples of spiradenoma/cylindroma in comparison to normal samples. A total of 12 spiradenomas, 5 cylindromas, 3 hybrid spiradenomas/cylindromas and 2 adnexal carcinomas were included in this study. 1335 characteristic genes and transcripts expressed over all 14 spiradenoma/cylindroma tumors were identified, and two groups of expression profiles were observed. Highest upregulated top 7 gene signatures characterized benign tumors with developmental and differentiation related genes, and carcinomas with top 7 genes mainly related to signaling, reorganization and metabolism of membranes. Immunohistochemistry of protein expressions validated 4 upregulated genes (ODAM, HOXB13, MYB and SOX10) considered important and as potential biomarkers for spiradenomas and cylindromas. We further compared the transcriptome of eccrine adnexal tumors with the transcriptome of adenoid cystic carcinoma (ACC) to identify the overlapping genes that may indicate histogenesis. There were 36 specific genes overlapping between adnexal carcinomas and the epithelial-dominant subtype of ACC, and 27 specific genes overlapping benign adnexal tumors with the myoepithelial-dominant subtype of ACC, At this point there is no known specific biomarker to aid in the diagnosis of eccrine spiradenoma and cylindroma in small samples or biopsies within the context of morphological overlap with ACC. In conclusion, spiradenomas and cylindromas are characterized by overexpressed developmental genes, where LHX2 and activated WNT signaling possibly drive associated carcinomas.

Mutant Lef1 controls Gata6 in sebaceous gland development and cancer

Mutations in Lef1 occur in human and mouse sebaceous gland (SG) tumors, but their contribution to carcinogenesis remains unclear. Since Gata6 controls lineage identity in SG, we investigated the link between these two transcription factors. Here, we show that Gata6 is a β‐catenin‐independent transcriptional target of mutant Lef1. During epidermal development, Gata6 is expressed in a subset of Sox9‐positive Lef1‐negative hair follicle progenitors that give rise to the upper SG. Overexpression of Gata6 by in utero lentiviral injection is sufficient to induce ectopic sebaceous gland elements. In mice overexpressing mutant Lef1, Gata6 ablation increases the total number of skin tumors yet decreases the proportion of SG tumors. The increased tumor burden correlates with impaired DNA mismatch repair and decreased expression of Mlh1 and Msh2 genes, defects frequently observed in human sebaceous neoplasia. Gata6 specifically marks human SG tumors and also defines tumors with elements of sebaceous differentiation, including a subset of basal cell carcinomas. Our findings reveal that Gata6 controls sebaceous gland development and cancer.

Lymphoid Enhancer Factor 1 Contributes to Hepatocellular Carcinoma Progression Through Transcriptional Regulation of Epithelial-Mesenchymal Transition Regulators and Stemness Genes

Lymphoid enhancer factor 1 (LEF1) activity is associated with progression of several types of cancers. The role of LEF1 in progression of hepatocellular carcinoma (HCC) remains poorly known. We investigated LEF1 expression in HCC and its interactions with epithelial-mesenchymal transition (EMT) regulators (e.g., Snail, Slug, Twist) and stemness genes (e.g., octamer-binding transcription factor 4 [Oct4], sex determining region Y-box 2 [Sox2], Nanog homeobox [Nanog]). Microarray analysis was performed on resected tumor samples from patients with HCC with or without postoperative recurrence. LEF1 expression was associated with postoperative recurrence as validated by immunohistochemical staining in another HCC cohort. Among 74 patients, 44 displayed a relatively high percentage of LEF1 staining (>30% of HCC cells), which was associated with a reduced recurrence-free interval (P < 0.001) and overall survival (P = 0.009). In multivariate analysis, a high percentage of LEF1 staining was significantly associated with low albumin level (P = 0.035), Twist overexpression (P = 0.018), Snail overexpression (P = 0.064), co-expression of Twist and Snail (P = 0.054), and multinodular tumors (P = 0.025). Down-regulation of LEF1 by short hairpin RNA decreased tumor sphere formation, soft agar colony formation, and transwell invasiveness of HCC cell lines Mahlavu and PLC. Xenotransplant and tail vein injection experiments revealed that LEF1 down-regulation in Mahlavu reduced tumor size and metastasis. LEF1 up-regulation in Huh7 increased sphere formation, soft agar colony formation, and transwell invasiveness. LEF1 was shown to physically interact with and transcriptionally activate promoter regions of Oct4, Snail, Slug, and Twist. Furthermore, Oct4, Snail, and Twist transactivated LEF1 to form a regulatory positive-feedback loop. Conclusion: LEF1 plays a pivotal role in HCC progression through transcriptional regulation of Oct4 and EMT regulators.

The epithelial-mesenchymal transition induced by transcription factor LEF-1 is independent of β-catenin

Transcription factor lymphoid-enhancer-binding factor 1 (LEF-1) is a key molecule in the Wnt/β-catenin signaling pathway. Slug is one of the Wnt/β-catenin target genes and can induce epithelial-mesenchymal transition (EMT). Previously, we have shown that not only wild-type LEF-1 but also LEF-1 lacking the amino-terminal β-catenin-binding region can induce EMT, suggesting that LEF-1 acts independently of β-catenin. Because it has been reported that LEF-1 interacts with β-catenin outside the amino-terminal domain, namely, in the middle part of the molecule, the possible participation of β-catenin has not been formally ruled out. To determine the involvement of β-catenin in the LEF-1-induced EMT, we produced MDCK cells with a deletion of the β-catenin gene and then expressed LEF-1 in the cells. We found that LEF-1 induced EMT in those cells. In the absence of β-catenin, γ-catenin has been shown to take over the role of β-catenin. To examine this possibility, we first established MDCK cells with a double knockout of β-catenin and γ-catenin genes and then expressed LEF-1 in these cells. We found that LEF-1 can induce EMT in these cells; therefore, we conclude that neither β-catenin nor γ-catenin expression is necessary for the LEF-1-mediated induction of EMT.

Wnt Signaling in Adult Epithelial Stem Cells and Cancer

Wnt/β-catenin signaling is integral to the homeostasis and regeneration of many epithelial tissues due to its critical role in adult stem cell regulation. It is also implicated in many epithelial cancers, with mutations in core pathway components frequently present in patient tumors. In this chapter, we discuss the roles of Wnt/β-catenin signaling and Wnt-regulated stem cells in homeostatic, regenerative and cancer contexts of the intestines, stomach, skin, and liver. We also examine the sources of Wnt ligands that form part of the stem cell niche. Despite the diversity in characteristics of various tissue stem cells, the role(s) of Wnt/β-catenin signaling is generally coherent in maintaining stem cell fate and/or promoting proliferation. It is also likely to play similar roles in cancer stem cells, making the pathway a salient therapeutic target for cancer. While promising progress is being made in the field, deeper understanding of the functions and signaling mechanisms of the pathway in individual epithelial tissues will expedite efforts to modulate Wnt/β-catenin signaling in cancer treatment and tissue regeneration.

Therapeutic targeting of oncogenic transcription factors by natural products in eye cancer

Carcinogenesis has a multifactorial etiology, and the underlying molecular pathogenesis is still not entirely understood, especially for eye cancers. Primary malignant intraocular neoplasms are relatively rare, but delayed detection and inappropriate management contribute to poor outcomes. Conventional treatment, such as orbital exenteration, chemotherapy, or radiotherapy, alone results in high mortality for many of these malignancies. Recent sequential multimodal therapy with a combination of high-dose chemotherapy, followed by appropriate surgery, radiotherapy, and additional adjuvant chemotherapy has helped dramatically improve management. Transcription factors are proteins that regulate gene expression by modulating the synthesis of mRNA. Since transcription is a dominant control point in the production of many proteins, transcription factors represent key regulators for numerous cellular functions, including proliferation, differentiation, and apoptosis, making them compelling targets for drug development. Natural compounds have been studied for their potential to be potent yet safe chemotherapeutic drugs. Since the ancient times, plant-derived bioactive molecules have been used to treat dreadful diseases like cancer, and several refined pharmaceutics have been developed from these compounds. Understanding targeting mechanisms of oncogenic transcription factors by natural products can add to our oncologic management toolbox. This review summarizes the current findings of natural products in targeting specific oncogenic transcription factors in various types of eye cancer.

Genetically modified laboratory mice with sebaceous glands abnormalities

Sebaceous glands (SG) are exocrine glands that release their product by holocrine secretion, meaning that the whole cell becomes a secretion following disruption of the membrane. SG may be found in association with a hair follicle, forming the pilosebaceous unit, or as modified SG at different body sites such as the eyelids (Meibomian glands) or the preputial glands. Depending on their location, SG fulfill a number of functions, including protection of the skin and fur, thermoregulation, formation of the tear lipid film, and pheromone-based communication. Accordingly, SG abnormalities are associated with several diseases such as acne, cicatricial alopecia, and dry eye disease. An increasing number of genetically modified laboratory mouse lines develop SG abnormalities, and their study may provide important clues regarding the molecular pathways regulating SG development, physiology, and pathology. Here, we summarize in tabulated form the available mouse lines with SG abnormalities and, focusing on selected examples, discuss the insights they provide into SG biology and pathology. We hope this survey will become a helpful information source for researchers with a primary interest in SG but also as for researchers from unrelated fields that are unexpectedly confronted with a SG phenotype in newly generated mouse lines.

Gene expression network analyses in response to air pollution exposures in the trucking industry

BACKGROUND

Exposure to air pollution, including traffic-related pollutants, has been associated with a variety of adverse health outcomes, including increased cardiopulmonary morbidity and mortality, and increased lung cancer risk.

METHODS

To better understand the cellular responses induced by air pollution exposures, we performed genome-wide gene expression microarray analysis using whole blood RNA sampled at three time-points across the work weeks of 63 non-smoking employees at 10 trucking terminals in the northeastern US. We defined genes and gene networks that were differentially activated in response to PM_2.5 (particulate matter ≤ 2.5 microns in diameter) and elemental carbon (EC) and organic carbon (OC).

RESULTS

Multiple transcripts were strongly associated (p_adj < 0.001) with pollutant levels (48, 260, and 49 transcripts for EC, OC, and PM_2.5, respectively), including 63 that were statistically significantly correlated with at least two out of the three exposures. These genes included many that have been implicated in ischemic heart disease, chronic obstructive pulmonary disease (COPD), lung cancer, and other pollution-related illnesses. Through the combination of Gene Set Enrichment Analysis and network analysis (using GeneMANIA), we identified a core set of 25 interrelated genes that were common to all three exposure measures and were differentially expressed in two previous studies assessing gene expression attributable to air pollution. Many of these are members of fundamental cancer-related pathways, including those related to DNA and metal binding, and regulation of apoptosis and also but include genes implicated in chronic heart and lung diseases.

CONCLUSIONS

These data provide a molecular link between the associations of air pollution exposures with health effects.

Circumscribed sebaceous neoplasms: a morphological, immunohistochemical and molecular analysis

Sebaceous neoplasms encompass a range of lesions, including benign entities such as sebaceous adenoma and sebaceoma, as well as sebaceous carcinoma. The distinction of sebaceous carcinoma from benign lesions relies on histological identification of architectural or cytological features of malignancy. In this study we have assessed the diagnostic discriminatory ability of mitotic rate and immunohistochemical markers (p53, bcl-2 and p16) in a selected group of well circumscribed sebaceous neoplasms, incorporating examples of sebaceous adenoma, sebaceoma and sebaceous carcinoma. We found that mitotic rate was significantly higher in malignant lesions as compared to benign lesions, but none of the immunohistochemical markers showed a discriminatory expression pattern. In addition, we performed a mutational analysis on the same group of lesions using next generation sequencing (NGS) technology. The most commonly mutated gene was TP53, although there was no correlation between the p53 immunohistochemical results and number or type of TP53 mutation detected. CDKN2A, EGFR, CTNNB1 and KRAS were also commonly mutated across all lesions. No particular gene, mutation profile or individual mutation could be identified which directly correlated with the consensus histological diagnosis. In conclusion, within this diagnostically challenging group of lesions, mitotic activity, but not immunohistochemical labelling for p16 or bcl-2, correlates with diagnostic category. While a number of genes potentially involved in the genesis of sebaceous neoplasia were uncovered, any molecular differences between the histological diagnostic categories remain unclear.

Compartmentalized Epidermal Activation of β-Catenin Differentially Affects Lineage Reprogramming and Underlies Tumor Heterogeneity

Wnt/β-catenin activation in adult epidermis can induce new hair follicle formation and tumor development. We used lineage tracing to uncover the relative contribution of different stem cell populations. LGR6(+) and LRIG1(+) stem cells contributed to ectopic hair follicles formed in the sebaceous gland upon β-catenin activation, whereas LGR5(+) cells did not. Lgr6, but not Lrig1 or Lgr5, was expressed in a subpopulation of interfollicular epidermal cells that were competent to form new hair follicles. Oncogenic β-catenin expression in LGR5(+) cells led to formation of pilomatricomas, while LRIG1(+) cells formed trichoadenomas and LGR6(+) cells formed dermatofibromas. Tumor formation was always accompanied by a local increase in dermal fibroblast density and transient extracellular matrix remodeling. However, each tumor had a distinct stromal signature in terms of immune cell infiltrate and expression of CD26 and CD44. We conclude that compartmentalization of epidermal stem cells underlies different responses to β-catenin and skin tumor heterogeneity.

Loss of Rad51c accelerates tumourigenesis in sebaceous glands of Trp53-mutant mice

Germline mutations in RAD51C predispose to breast and ovarian cancers. However, the mechanism of RAD51C-mediated carcinogenesis is poorly understood. We previously reported a first-generation Rad51c-knock-out mouse model, in which a spontaneous loss of both Rad51c and Trp53 together resulted in a high incidence of sebaceous carcinomas, particularly in preputial glands. Here we describe a second-generation mouse model, in which Rad51c is deleted, alone or together with Trp53, in sebaceous glands, using Cre-mediated recombination. We demonstrate that deletion of Rad51c alone is not sufficient to drive tumourigenesis and may only cause keratinization of preputial sebocytes. However, deletion of Rad51c together with Trp53 leads to tumour development at around 6 months of age, compared to 11 months for single Trp53-mutant mice. Preputial glands of double-mutant mice are also characterized by increased levels of cell proliferation and DNA damage and form multiple hyperplasias, detectable as early as 2 months of age. Our results reveal a critical synergy between Rad51c and Trp53 in tumour progression and provide a predictable in vivo model system for studying mechanisms of Rad51c-mediated carcinogenesis.

Interfering with stem cell-specific gatekeeper functions controls tumour initiation and malignant progression of skin tumours

Epithelial cancer constitutes a major clinical challenge and molecular mechanisms underlying the process of tumour initiation are not well understood. Here we demonstrate that hair follicle bulge stem cells (SCs) give rise to well-differentiated sebaceous tumours and show that SCs are not only crucial in tumour initiation, but are also involved in tumour plasticity and heterogeneity. Our findings reveal that SC-specific expression of mutant Lef1, which mimics mutations found in human sebaceous tumours, drives sebaceous tumour formation. Mechanistically, we demonstrate that mutant Lef1 abolishes p53 activity in SCs. Intriguingly, mutant Lef1 induces DNA damage and interferes with SC-specific gatekeeper functions normally protecting against accumulations of DNA lesions and cell loss. Thus, normal control of SC proliferation is disrupted by mutant Lef1, thereby allowing uncontrolled propagation of tumour-initiating SCs. Collectively, these findings identify underlying molecular and cellular mechanisms of tumour-initiating events in tissue SCs providing a potential target for future therapeutic strategies.

The presence of multiple stem and progenitor cells in the skin has a major impact on the formation of different epidermal tumours. Here the authors identify bulge stem cells as the cells of origin of sebaceous tumours through genetic lineage tracing and molecular studies in a mouse model.

Benzo pyrene-induced DNA adducts and gene expression profiles in target and non-target organs for carcinogenesis in mice

BACKGROUND

Gene expression changes induced by carcinogens may identify differences in molecular function between target and non-target organs. Target organs for benzo[a]pyrene (BaP) carcinogenicity in mice (lung, spleen and forestomach) and three non-target organs (liver, colon and glandular stomach) were investigated for DNA adducts by 32P-postlabelling, for gene expression changes by cDNA microarray and for miRNA expression changes by miRNA microarray after exposure of animals to BaP.

RESULTS

BaP-DNA adduct formation occurred in all six organs at levels that did not distinguish between target and non-target. cDNA microarray analysis showed a variety of genes modulated significantly by BaP in the six organs and the overall gene expression patterns were tissue specific. Gene ontology analysis also revealed that BaP-induced bioactivities were tissue specific; eight genes (Tubb5, Fos, Cdh1, Cyp1a1, Apc, Myc, Ctnnb1 and Cav) showed significant expression difference between three target and three non-target organs. Additionally, several gene expression changes, such as in Trp53 activation and Stat3 activity suggested some similarities in molecular mechanisms in two target organs (lung and spleen), which were not found in the other four organs. Changes in miRNA expression were generally tissue specific, involving, in total, 21/54 miRNAs significantly up- or down-regulated.

CONCLUSIONS

Altogether, these findings showed that DNA adduct levels and early gene expression changes did not fully distinguish target from non-target organs. However, mechanisms related to early changes in p53, Stat3 and Wnt/β-catenin pathways may play roles in defining BaP organotropism.

Epidermal barrier defects link atopic dermatitis with altered skin cancer susceptibility

Atopic dermatitis can result from loss of structural proteins in the outermost epidermal layers, leading to a defective epidermal barrier. To test whether this influences tumour formation, we chemically induced tumours in EPI−/− mice, which lack three barrier proteins—Envoplakin, Periplakin, and Involucrin. EPI−/− mice were highly resistant to developing benign tumours when treated with 7,12-dimethylbenz(a)anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). The DMBA response was normal, but EPI−/− skin exhibited an exaggerated atopic response to TPA, characterised by abnormal epidermal differentiation, a complex immune infiltrate and elevated serum thymic stromal lymphopoietin (TSLP). The exacerbated TPA response could be normalised by blocking TSLP or the immunoreceptor NKG2D but not CD4+ T cells. We conclude that atopy is protective against skin cancer in our experimental model and that the mechanism involves keratinocytes communicating with cells of the immune system via signalling elements that normally protect against environmental assaults.

DOI:http://dx.doi.org/10.7554/eLife.01888.001

Skin cancer is a common and growing problem—according to the World Health Organization, skin cancers account for one in every three cancers diagnosed world wide. There is some evidence from epidemiological studies that patients with certain allergies might be protected against cancer and, in particular, that the allergic skin condition atopic dermatitis is associated with reduced levels of various skin cancers. However, it is difficult to know if this reduction is due to the atopic dermatitis itself or to the drugs used to treat this allergy.

Genetically engineered mice that are lacking three proteins that are involved in the formation of the cornified envelope—the protective layer that replaces the normal plasma membrane in the cells of the outermost skin layers—can be used to study atopic dermatitis. These ‘triple knockout mice’ have a defective epidermal barrier and altered levels of immune T-cells in the skin.

Now Cipolat et al. have investigated whether defects in the epidermal barrier protect against skin cancer. Knockout mice and wild-type mice were treated with two chemicals: DMBA, which causes mutations in a gene called HRas, and TPA, which promotes the formation of tumours from cells that contain HRas mutations. After about 16 weeks almost all of the wild-type mice had at least one benign tumour, whereas half of the knockout mice had no tumours. Overall, the average number of benign tumours per mouse was six times higher in the wild-type mice. This shows that the mutations that cause the epidermal barrier defects in knockout mice also protect them against the tumours caused by the combined effects of DMBA and TPA.

Cipolat et al. then compared how the mice responded to DMBA or TPA alone. The knockout mice and the wild-type mice responded to DMBA in the same way; however, the knockout mice showed an exaggerated response to TPA, including a strong inflammatory reaction. This response comprised the production of higher levels of various proteins that are involved in communications between skin cells and the immune system. Cipolat et al. propose that the immune reaction caused by this exaggerated response could help to prevent tumour formation by eliminating tumour-forming cells in the skin.

DOI:http://dx.doi.org/10.7554/eLife.01888.002

MicroRNA-26b represses colon cancer cell proliferation by inhibiting lymphoid enhancer factor 1 expression

microRNAs (miR) can act as oncogenes and tumor suppressors and several miRs are associated with cancer development and progression through the modulation of multiple cellular processes. miR26b is downregulated in several cancers and tumors and miR26b directly targets the lymphoid enhancer factor 1 (Lef1)3'UTR and inhibits endogenous Lef1 expression. We report that miR26b expression is associated with human colon cancer through the regulation of LEF1 expression in colon cancer cells. Analyses of multiple colon cancer cell lines revealed an inverse correlation between miR26b and LEF1 expression. Normal human colon cells express low levels of LEF1 and high levels of miR26b; however, human colon cancer cells have decreased miR26b expression and increased LEF1 expression. We demonstrate that miR26b expression is a potent inhibitor of colon cancer cell proliferation and significantly decreases LEF1 expression. The LEF1-regulated genes cyclin D1 and c-Myc were indirectly repressed by miR26b and this was consistent with decreased proliferation. miR26b overexpression in SW480 colon cancer cells also inhibited tumor growth in nude mice and this was due to decreased tumor growth and not apoptosis. Analyses of human colon cancer databases also demonstrated a link between miR26b and LEF1 expression. c-Myc expression is associated with multiple cancers and we propose that miR26b may act as a potential therapeutic agent in reducing cancer cell proliferation through repressing LEF1 activation of c-Myc and cyclin D1 expression.

Epithelial stem cells in adult skin

The skin is the first line of defense against dehydration and external environmental aggressions. It constantly renews itself throughout adult life mainly due to the activity of tissue-specific stem cells. In this review, we discuss fundamental characteristics of different stem cell populations within the skin and how they are able to contribute to normal skin homeostasis. We also examine the most recent results regarding the cell-intrinsic and -extrinsic components of the stem cell niche within the adult skin epithelium. Finally, we address the recent efforts to understand how abnormal regulation of stem cell activity contributes to the initiation and progression of skin-associated cancers.

The transcription factor LEF-1 induces an epithelial-mesenchymal transition in MDCK cells independent of β-catenin

The epithelial-mesenchymal transition (EMT), a key process in the tumor metastatic cascade, is characterized by the loss of cell-cell junctions and cell polarity, as well as the acquisition of migratory and invasive properties. LEF-1 is a member of the lymphoid enhancer-binding factor/T-cell factor (LEF/TCF) family of DNA-binding transcription factors, which interact with nuclear β-catenin and act as central transcriptional mediators of Wnt signaling. To investigate the role of LEF-1 in EMT, we generated stable LEF-1 transfectants using MDCK cells. The transfectants had a spindle-shaped mesenchymal morphology, and enhanced migration and invasiveness relative to control cells. These EMT changes were accompanied by the downregulation of an epithelial marker protein, E-cadherin, and the upregulation of mesenchymal marker proteins, vimentin and N-cadherin. Consistent with these observations, the mRNA levels of Slug, ZEB1, and ZEB2-EMT-related transcription factors-increased significantly. Although the N-terminally deleted mutant LEF-1 cannot interact with β-catenin, it retained the ability to induce EMT. Consistent with these observations, neither the expression of a dominant negative β-catenin/engrailed chimera, nor the expression of a cytoplasmic domain of E-cadherin that sequesters β-catenin from binding to LEF/TCF, reversed LEF-1-induced EMT. Together, these data indicated that the nuclear function of β-catenin was not necessary for the induction of Slug, ZEB1, and ZEB2 expression leading to EMT.

Indian hedgehog controls proliferation and differentiation in skin tumorigenesis and protects against malignant progression

Mutations in the hedgehog pathway drive the formation of tumors in many different organs, including the development of basal cell carcinoma in the skin. However, little is known about the role of epidermal Indian hedgehog (Ihh) in skin physiology. Using mouse genetics, we identified overlapping and distinct functions of Ihh in different models of epidermal tumorigenesis. Epidermal deletion of Ihh resulted in increased formation of benign squamous papilloma. Strikingly, Ihh-deficient mice showed an increase in malignant squamous cell carcinoma and developed lung and lymph node metastases. In a sebaceous gland tumor model, Ihh deficiency inhibited tumor cell differentiation. More mechanistically, IHH stimulated cell proliferation by activating the transcription factor GLI2 in human keratinocytes and human tumors. Thus, our results uncover important functions for Ihh signaling in controlling proliferation, differentiation, malignant progression, and metastasis of epithelial cancer, establishing Ihh as a gatekeeper for controlling the grade of tumor malignancy.

Selective ablation of glucocorticoid receptor in mouse keratinocytes increases susceptibility to skin tumorigenesis

We recently demonstrated that mice lacking the epidermal glucocorticoid (GC) receptor (GR) (GR epidermal knockout (GR(EKO)) mice) have developmental defects and sensitivity to epidermal challenge in adulthood. We examined the susceptibility of GR(EKO) mice to skin chemical carcinogenesis. GR(EKO) mice treated with a low dose of 12-dimethylbenz(a) anthracene (DMBA) followed by phorbol 12-myristate 13-acetate (PMA) promotion exhibited earlier papilloma formation with higher incidence and multiplicity relative to control littermates (CO). Augmented proliferation and inflammation and defective differentiation of GR(EKO) keratinocytes contributed to the phenotype, likely through increased AKT and STAT3 (signal transducer and activator of transcription 3) activities. GR(EKO) tumors exhibited signs of early malignization, including delocalized expression of laminin A, dermal invasion of keratin 5 (K5)-positive cells, K13 expression, and focal loss of E-cadherin. Cultured GR(EKO) keratinocytes were spindle like, with loss of E-cadherin and upregulation of smooth muscle actin (SMA) and Snail, suggesting partial epithelial-mesenchymal transition. A high DMBA dose followed by PMA promotion generated sebaceous adenomas and melanocytic foci in GR(EKO) and CO. Importantly, the number, growth kinetics, and extent of both tumor types increased in GR(EKO) mice, suggesting that in addition to regulating tumorigenesis from epidermal lineages, GR in keratinocytes is important for cross-talk with other skin cells. Altogether, our data reinforce the importance of GR in the pathogenesis of skin cancer.

Wnt signaling in skin development, homeostasis, and disease

The skin and its appendages constitute the largest organ of the body. Its stratified epithelia offer protection from environmental stresses such as dehydration, irradiation, mechanical trauma, and pathogenic infection, whereas its appendages, like hair and sebaceous glands, help regulate body temperature as well as influence animal interaction and social behavior through camouflage and sexual signaling. To respond to and function effectively in a dynamic external environment, the skin and its appendages possess a remarkable ability to regenerate in a carefully controlled fashion. When this finely tuned homeostatic process is disrupted, skin diseases such as cancers may result. At present, the molecular signals that orchestrate cell proliferation, differentiation, and patterning in the skin remain incompletely understood. It is increasingly apparent that many morphogenetic pathways with key roles in development are also important in regulating skin biology. Of these, Wnt signaling has emerged as the dominant pathway controlling the patterning of skin and influencing the decisions of embryonic and adult stem cells to adopt the various cell lineages of the skin and its appendages, as well as subsequently controlling the function of differentiated skin cells. Here we will review established concepts and present recent advances in our understanding of the diverse roles that Wnt signaling plays in skin development, homeostasis, and disease.

Wnt signaling in skin organogenesis

While serving as the interface between an organism and its environment, the skin also can elaborate a wide range of skin appendages to service specific purposes in a region-specific fashion. As in other organs, Wnt signaling plays a key role in regulating the proliferation, differentiation and motility of skin cells during their morphogenesis. Here I will review some of the recent work that has been done on skin organogenesis. I will cover dermis formation, the development of skin appendages, cycling of appendages in the adult, stem cell regulation, patterning, orientation, regional specificity and modulation by sex hormone nuclear receptors. I will also cover their roles in wound healing, hair regeneration and skin related diseases. It appears that Wnt signaling plays essential but distinct roles in different hierarchical levels of morphogenesis and organogenesis. Many of these areas have not yet been fully explored but are certainly promising areas of future research.

Development and homeostasis of the sebaceous gland

The important role of epidermal appendages especially the sebaceous gland has only recently been recognized. In particular, it has been convincingly shown that normal development and maintenance of the sebaceous gland are required for skin homeostasis since atrophic sebaceous glands and disturbances in sebaceous lipid composition result in major defects of the physiological barrier and maintenance of the skin. Consequently, it is important to unravel the signaling network controlling proper sebaceous lineage differentiation in mammalian skin and to understand the underlying mechanisms leading to severe skin diseases, including abnormal proliferation and differentiation of the gland, defects of the lipid metabolism and barrier, as well as sebaceous tumor formation. Over the last years, results from transgenic and knock out mouse models manipulating distinct signaling pathways in the skin as well as the detailed analysis of human sebaceous gland-derived cell lines provided new insights into crucial mediators balancing proliferation and differentiation of the sebaceous gland. Here, we discuss our current knowledge of in vivo mechanisms of sebaceous gland development, maintenance and disorders and highlight recent contributions to the field of sebaceous gland biology.

Embryonic stem cell markers

Embryonic stem cell (ESC) markers are molecules specifically expressed in ES cells. Understanding of the functions of these markers is critical for characterization and elucidation for the mechanism of ESC pluripotent maintenance and self-renewal, therefore helping to accelerate the clinical application of ES cells. Unfortunately, different cell types can share single or sometimes multiple markers; thus the main obstacle in the clinical application of ESC is to purify ES cells from other types of cells, especially tumor cells. Currently, the marker-based flow cytometry (FCM) technique and magnetic cell sorting (MACS) are the most effective cell isolating methods, and a detailed maker list will help to initially identify, as well as isolate ESCs using these methods. In the current review, we discuss a wide range of cell surface and generic molecular markers that are indicative of the undifferentiated ESCs. Other types of molecules, such as lectins and peptides, which bind to ESC via affinity and specificity, are also summarized. In addition, we review several markers that overlap with tumor stem cells (TSCs), which suggest that uncertainty still exists regarding the benefits of using these markers alone or in various combinations when identifying and isolating cells.

Adult mammalian stem cells: the role of Wnt, Lgr5 and R-spondins

After its discovery as oncogen and morphogen, studies on Wnt focused initially on its role in animal development. With the finding that the colorectal tumour suppressor gene APC is a negative regulator of the Wnt pathway in (colorectal) cancer, attention gradually shifted to the study of the role of Wnt signalling in the adult. The first indication that adult Wnt signalling controls stem cells came from a Tcf4 knockout experiment: mutant mice failed to build crypt stem cell compartments. This observation was followed by similar findings in multiple other tissues. Recent studies have indicated that Wnt agonists of the R-spondin family provide potent growth stimuli for crypts in vivo and in vitro. Independently, Lgr5 was found as an exquisite marker for these crypt stem cells. The story has come full circle with the finding that the stem cell marker Lgr5 constitutes the receptor for R-spondins and occurs in complex with Frizzled/Lrp.

Mechanisms regulating epidermal stem cells

The skin epidermis contains different appendages such as the hair follicle and the sebaceous glands. Recent studies demonstrated that several types of stem cells (SCs) exist in different niches within the epidermis and maintain discrete epidermal compartments, but the exact contribution of each SC populations under physiological conditions is still unclear. In addition, the precise mechanisms controlling the balance between proliferation and differentiation of epidermal SC still remain elusive. Recent studies provide new insights into these important questions by showing the contribution of hair follicle SC to the sebaceous lineage and the importance of chromatin modifications and micro-RNAs (miRs) in regulating epidermal SCs renewal and differentiation. In this review, we will discuss the importance of these papers to our understanding of the mechanisms that control epidermal SC functions.

Epithelial stem cells, wound healing and cancer

It is well established that tissue repair depends on stem cells and that chronic wounds predispose to tumour formation. However, the association between stem cells, wound healing and cancer is poorly understood. Lineage tracing has now shown how stem cells are mobilized to repair skin wounds and how they contribute to skin tumour development. The signalling pathways, including WNT and Hedgehog, that control stem cell behaviour during wound healing are also implicated in tumour formation. Furthermore, tumorigenesis and wound repair both depend on communication between epithelial cells, mesenchymal cells and bone marrow-derived cells. These studies suggest ways to harness stem cells for wound repair while minimizing cancer risk.

Differentiation of the sebaceous gland

The sebaceous gland is renewed throughout adult life and homeostasis of this particular organ is controlled by a precise interplay of hormones, cytokines, signalling molecules and mediators of the lipid metabolism. Although the true function of sebaceous glands has yet to be fully determined, recent evidence demonstrates that normal homeostasis of the sebaceous gland and functional lipid metabolism of sebocytes is crucial for maintenance of the skin barrier. In addition, analysis of mutant mouse models revealed a close interdependency of the sebaceous gland with hair follicles because abnormal morphogenesis of sebaceous glands often results in degeneration of hair follicle structures. Anomalous regulation of sebaceous glands is involved in the pathogenesis of acne, one of the most prevalent human diseases, or could lead to formation of sebaceous hyperplasia and tumours. This review highlights some of the recent findings on the importance of signalling pathways controlling morphogenesis and differentiation of the sebaceous gland in vivo.

TCF/Lef1 activity controls establishment of diverse stem and progenitor cell compartments in mouse epidermis

This work investigates cell fate and lineages of hair follicles and sebaceous glands (SG) in the mouse epidermis. The combination of transgenic models with complementary tracing techniques provides unequivocal evidence for a direct contribution of bulge stem cells to the SG units as well as stem cell niches within the isthmus region.

Mammalian epidermis consists of the interfollicular epidermis, hair follicles (HFs) and associated sebaceous glands (SGs). It is constantly renewed by stem and progenitor cell populations that have been identified and each compartment features a distinct mechanism of cellular turnover during renewal. The functional relationship between the diverse stem cell (SC) pools is not known and molecular signals regulating the establishment and maintenance of SC compartments are not well understood. Here, we performed lineage tracing experiments to demonstrate that progeny of HF bulge SCs transit through other SC compartments, suggesting a hierarchy of competent multipotent keratinocytes contributing to tissue renewal. The bulge was identified as a bipotent SC compartment that drives both cyclic regeneration of HFs and continuous renewal of SGs. Our data demonstrate that aberrant signalling by TCF/Lef1, transcription factors crucial for bulge SC activation and hair differentiation, results in development of ectopic SGs originating from bulge cells. This process of de novo SG formation is accompanied by the establishment of new progenitor niches. Detailed molecular analysis suggests the recapitulation of steps of tissue morphogenesis.

Reporting the Implementation of the Three Rs in European Primate and Mouse Research Papers: Are We Making Progress?

It is now more than 20 years since both Council of Europe Convention ETS123 and EU Directive 86/609?EEC were introduced, to promote the implementation of the Three Rs in animal experimentation and to provide guidance on animal housing and care. It might therefore be expected that reports of the implementation of the Three Rs in animal research papers would have increased during this period. In order to test this hypothesis, a literature survey of animal-based research was conducted. A randomly-selected sample from 16 high-profile medical journals, of original research papers arising from European institutions that featured experiments which involved either mice or primates, were identified for the years 1986 and 2006 (Total sample = 250 papers). Each paper was scored out of 10 for the incidence of reporting on the implementation of Three Rs-related factors corresponding to Replacement (justification of non-use of non-animal methods), Reduction (statistical analysis of the number of animals needed) and Refinement (housing aspects, i.e. increased cage size, social housing, enrichment of cage environment and food; and procedural aspects, i.e. the use of anaesthesia, analgesia, humane endpoints, and training for procedures with positive reinforcement). There was no significant increase in overall reporting score over time, for either mouse or primate research. By 2006, mouse research papers scored an average of 0 out of a possible 10, and primate research papers scored an average of 1.5. This review provides systematic evidence that animal research is still not properly reported, and supports the call within the scientific community for action to be taken by journals to update their policies.

Tumor formation initiated by nondividing epidermal cells via an inflammatory infiltrate

In mammalian epidermis, integrin expression is normally confined to the basal proliferative layer that contains stem cells. However, in epidermal hyperproliferative disorders and tumors, integrins are also expressed by suprabasal cells, with concomitant up-regulation of Erk mitogen-activated protein kinase (MAPK) signaling. In transgenic mice, expression of activated MAPK kinase 1 (MEK1) in the suprabasal, nondividing, differentiated cell layers (InvEE transgenics) results in epidermal hyperproliferation and skin inflammation. We now demonstrate that wounding induces benign tumors (papillomas and keratoacanthomas) in InvEE mice. By generating chimeras between InvEE mice and mice that lack the MEK1 transgene, we demonstrate that differentiating, nondividing cells that express MEK1 stimulate adjacent transgene-negative cells to divide and become incorporated into the tumor mass. Dexamethasone treatment inhibits tumor formation, suggesting that inflammation is involved. InvEE skin and tumors express high levels of IL1α; treatment with an IL1 receptor antagonist delays tumor onset and reduces incidence. Depletion of γδ T cells and macrophages also reduces tumor incidence. Because a hallmark of cancer is uncontrolled proliferation, it is widely assumed that tumors arise only from dividing cells. In contrast, our studies show that differentiated epidermal cells can initiate tumor formation without reacquiring the ability to divide and that they do so by triggering an inflammatory infiltrate.

The effect of c-myc on stem cell fate influences skin tumor phenotype

Nonmelanoma skin cancers (NMSCs) consist of a variety of tumor types including basal cell carcinoma, squamous cell carcinoma, a variety of hair follicle tumors, and sebaceous gland tumors. Genetic alterations that alter the fate of multipotent stem cells are believed to influence NMSC phenotype. We previously generated a transgenic mouse line which constitutively expressed c-myc under the control of the K14 promoter (K14.MYC2). These mice exhibited an increase in size and number of sebaceous glands, suggesting that c-myc diverted multipotential stem cells to a sebaceous lineage. Our goal in the current study was to determine if alterations in the commitment of multipotent stem cells to different cell fates would influence tumor phenotype. To this end, we exposed K14.MYC2 mice to a chemical carcinogenesis protocol and discovered that these mice were predisposed to develop sebaceous adenomas. Our data demonstrate that genetic alterations that alter the fate of multipotent stem cells during embryonic development can markedly influence the phenotype of NMSC that develop following exposure to carcinogens.

Sebaceous neoplasia and the Muir-Torre syndrome: important connections with clinical implications

Sebaceous neoplasia comprises a spectrum ranging from benign to malignant. Proper histological identification is important for treatment, prognosis and potential association with the Muir-Torre syndrome (MTS). Our increased understanding of the significance and pathogenesis of these tumours has led to improved risk stratification, screening recommendations, and treatment of patients with an initial presentation of a sebaceous tumour. This review focuses on the diagnostic and histological features of sebaceous lesions, the MTS, and recent insights into the molecular pathogenesis of sebaceous tumours.

Sebaceous carcinoma: the great masquerader: emgerging concepts in diagnosis and treatment

Sebaceous carcinoma (SC) is a rare tumor with a high rate of local recurrence and metastasis to lymph nodes and organs. The majority of SCs occur in the periocular region frequently presenting as painless, round subcutaneous nodules with a high tendency of diffuse and invasive growth in the eyelid and conjunctiva. It frequently masquerades as inflammatory conditions or as other tumors leading to delay in diagnosis, inappropriate treatment and increased morbidity and mortality. Sebaceous carcinoma is associated with Muir-Torre syndrome, a genetic condition presenting with sebaceous skin tumors associated with internal malignancy. Therefore, SC patients must be carefully evaluated and referred to an internist or gastroenterologist when indicated. Surgery is the definitive therapy for SC. In recent years, less radical surgical strategies are being used with improved outcomes. Current studies demonstrate that Mohs micrographic surgery (MMS) provides maximal tissue conservation and lower recurrence rates. Greater awareness and understanding of SC and its behavior has led to earlier diagnosis and appropriate treatment.

Loss of Rad51c leads to embryonic lethality and modulation of Trp53-dependent tumorigenesis in mice

RecA/Rad51 protein family members (Rad51, Rad51b, Rad51c, Rad51d, Xrcc2, and Xrcc3) are essential for DNA repair by homologous recombination, and their role in cancers has been anticipated. Here we provide the first direct evidence for a tumor suppressor function for a member of the Rad51 family. We show that Rad51c deficiency leads to early embryonic lethality, which can be delayed on a Trp53-null background. To uncover the role of Rad51c in tumorigenesis, we have exploited the fact that Rad51c and Trp53 are both closely located on the mouse chromosome 11. We have generated double heterozygous (DH) mice carrying mutant alleles of both genes either on different (DH-trans) or on the same chromosome (DH-cis), the latter allowing for a deletion of wild-type alleles of both genes by loss of heterozygosity. DH-trans mice, in contrast to DH-cis, developed tumors with latency and spectrum similar to Trp53 heterozygous mice. Strikingly, Rad51c mutation in DH-cis mice promoted the development of tumors of specialized sebaceous glands and suppressed tumors characteristic of Trp53 mutation. In addition, DH-cis females developed tumors significantly earlier than any other group.

Nkx3-1 and LEF-1 function as transcriptional inhibitors of estrogen receptor activity

Estrogen receptor (ER)-associated cofactors and cooperating transcription factors are one of the primary components determining transcriptional activity of estrogen target genes and may constitute potential therapeutic targets. Recent mapping of ER-binding sites on a genome-wide scale has provided insight into novel cooperating factors based on the enrichment of transcription factor motifs within the ER-binding sites. We have used the ER-binding sites in combination with sequence conservation to identify the statistical enrichment of Nkx and LEF motifs. We find that Nkx3-1 and LEF-1 bind to several ER cis-regulatory elements in vivo, but they both function as transcriptional repressors of estrogen signaling. We show that Nkx3-1 and LEF-1 can inhibit ER binding to chromatin, suggesting competition for common chromatin-binding regions. These data provide insight into the role of Nkx3-1 and LEF-1 as potential regulators of the hormone response in breast cancer.

Hedgehog signaling, keratin 6 induction, and sebaceous gland morphogenesis: implications for pachyonychia congenita and related conditions

Keratins 6a and b (K6a, K6b) belong to a subset of keratin genes with constitutive expression in epithelial appendages, and inducible expression in additional epithelia, when subjected to environmental challenges or disease. Mutations in K6a or K6b cause a broad spectrum of epithelial lesions that differentially affect nail, hair, and glands in humans. Some lesions reflect a loss of the structural support function shared by K6, other keratins, and intermediate filament proteins. The formation of sebaceous gland-derived epithelial cysts does not fit this paradigm, raising the question of the unique functions of different K6 isoforms in this setting. Here, we exploit a mouse model of constitutively expressed Gli2, a Hedgehog (Hh) signal effector, to show that K6a expression correlates with duct fate in sebaceous glands (SGs). Whether in the setting of Gli2 transgenic mice skin, which develops a prominent SG duct and additional pairs of highly branched SGs, or in wild-type mouse skin, K6a expression consistently coincides with Hh signaling in ductal tissue. Gli2 expression modestly transactivates a K6a promoter-driven reporter in heterologous systems. Our findings thus identify K6 as a marker of duct fate in SGs, partly in response to Hh signaling, with implications for the pathological expansion of SGs that arises in the context of certain keratin-based diseases and related disorders.