Skin Tumor Development Research Articles

Effects of high-fat diets rich in either omega-3 or omega-6 fatty acids on UVB-induced skin carcinogenesis in SKH-1 mice

Our previous studies reported that caffeine or voluntary exercise decreased skin tumor multiplicity, in part, by decreasing fat levels in the dermis. These data suggest that tissue fat may play an important role in regulating ultraviolet light (UV) B-induced skin tumor development. In the present study, we explored the effects of high-fat diets rich in either omega-3 or omega-6 fatty acids on UVB-induced skin carcinogenesis. SKH-1 mice were irradiated with 30 mJ/cm(2) of UVB once a day, two times per week for 39 weeks. During UVB treatment, one group of mice was given a high-fat fish oil (HFFO) diet rich in omega-3 fatty acids and the other group of mice was given a high-fat mixed-lipids (HFMLs) diet rich in omega-6 fatty acids. The results showed that, compared with HFML diet, HFFO treatment (i) increased latency for the development of UVB-induced skin tumors; (ii) decreased the formation of papilloma, keratoacanthoma and carcinoma by 64, 52 and 46%, respectively and (iii) decreased the size of papilloma, keratoacanthoma and carcinoma by 98, 80 and 83%, respectively. Mechanistic studies with antibody array revealed that compared with HFML diet, administration of HFFO to the mice significantly decreased the UVB-induced increases in the levels of TIMP-1, LIX and sTNF R1 as well as other several proinflammatory cytokines and stimulated the UVB-induced apoptosis in the epidermis. Our results indicate that omega-3 fatty acids in HFFO diet have beneficial effects against UVB-induced skin carcinogenesis, and these effects may be associated with an inhibition on UVB-induced inflammatory response.

Abstract 4620: Development of honokiol for the prevention of UVB-induced skin tumor development

Abstract Skin cancer is the most prevalent of all cancers and its incidence is expected to increase substantially. UVB is major etiologic factor in the skin cancer development. Honokiol, a plant ligan isolated from bark and seed cones of Magnolia officinalis, has been shown to have chemopreventive effects on UVB-induced skin cancer development in our laboratory. The objectives of this investigation are to study chemopreventive effects of dose response of honokiol on UVB-induced skin tumor development in SKH-1mice and to prepare topical formulations of honokiol that deliver effective concentration of drug locally. Female SKH-1 mice were divided into 4 groups. Group 1 received acetone one hour before UVB treatment; Group 2, 3 and 4 received honokiol (0.2 ml of 30, 45 and 60 μg in acetone, topical) before each UVB treatment. Mice were treated with UVB dose of 30 mJ/cm2/day for 25 weeks. Tumor counts and group weights were taken weekly. Honokiol pretreated groups resulted in 36-78% reduction in tumor multiplicity compared to control. Honokiol pretreatment (60 μg) decreased tumor incidence by 40 %. Topical formulation of honokiol gel was prepared by using carbomer 940 as base and propylene glycol as penetration enhancer. Drug content and content uniformity were determined. Release studies and permeation studies were studied in detail. This study is supported by Translational Cancer Research Center funded as 2010 Research Initiative Center by the State of South Dakota Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4620. doi:10.1158/1538-7445.AM2011-4620

Abstract 810: Dietary grape seed proanthocyanidins inhibit UV-induced immunosuppression through stimulation of CD8+ effector T cells and inactivation of regulatory CD4+ T cells

Abstract The immunosuppressive effects of solar ultraviolet (UV) radiation, particularly UVB (290-320 nm), are well recognized. Experimental evidence indicates that UV-induced immunosuppression is a risk factor for skin cancer development, including melanoma and non-melanoma, in mice and clinical evidence suggests that it is also a risk factor in humans. Conversely, animals with an enhanced immune response exhibit a lower risk of skin tumor development on chronic UV exposure. Dietary grape seed proanthocyanidins (GSPs) have been shown to inhibit UVB-induced immunosuppression in mice; however, the cellular and molecular mechanisms underlying this inhibitory effect of GSPs are not yet clearly understood. To characterize the cell population responsible for the GSPs-mediated inhibition of UVB-induced immunosuppression, we used an adoptive transfer approach. Splenocytes and draining lymph nodes were harvested from mice that had been administered dietary GSPs, exposed to UVB, and sensitized by topical application of 2,4-dinitorfluorobenzene (DNFB) onto the UVB-exposed skin. CD8+ and CD4+ T cells were positively selected and transferred into naïve mice that were subsequently challenged by application of DNFB on the ear skin. Naïve recipients that received CD8+ T cells from GSPs-treated, UVB-irradiated donors exhibited full contact hypersensitivity (CHS) response. CHS is considered to be a prototypic T-cell mediated immune response. Naïve mice that received CD4+ regulatory T cells from GSPs-treated, UVB-exposed mice were able to mount a CHS response after sensitization and subsequent challenge with DNFB. On culture, the CD8+ T cells from GSPs-treated, UVB-exposed mice secreted higher levels of Th1 cytokines (IL-2, IFNγ) than CD8+ T cells from UVB-irradiated mice not treated with GSPs. CD4+ T cells from GSPs-treated, UVB-exposed mice secreted significantly lower levels of Th2 cytokines (IL-4 and IL-10) than CD4+ T cells from UVB-exposed mice not treated with GSPs. These data suggest that dietary GSPs inhibit UVB-induced immunosuppression by stimulating CD8+ effector T cells and diminishing regulatory CD4+ T cells in mice. This property of GSPs can be used as an alternative strategy to augment the induction of CD8+ effector T cells and to diminish the development of CD4+ regulatory T cells and that may lead to the prevention of skin cancer risk in humans. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 810. doi:10.1158/1538-7445.AM2011-810

The Roles of ADAMs Family Proteinases in Skin Diseases

A disintegrin and metalloproteinases (ADAMs) are members of a new gene family of transmembrane and secreted proteins, which belong to the zinc proteinase superfamily. These molecules are involved in various biological events such as cell adhesion, cell fusion, cell migration, membrane protein shedding, and proteolysis. Growing evidence now attests to the potential involvement of ADAMs proteinases in diverse processes such as skin wound healing, inflammation, pigmentation, tumor development, cell proliferation, and metastasis. This paper focuses on the roles of ADAMs proteinases in a wide variety of skin diseases.

TRPV1-antagonist AMG9810 promotes mouse skin tumorigenesis through EGFR/Akt signaling

In addition to capsaicin, a transient receptor potential channel vanilloid subfamily 1 (TRPV1) agonist, two kinds of antagonists against this receptor are used as therapeutic drugs for pain relief. Indeed, a number of small molecule TRPV1 antagonists are currently undergoing Phase I/II clinical trials to determine their effect on relieving chronic inflammatory pain and migraine headache pain. However, we previously reported that the absence of TRPV1 in mice results in a striking increase in skin carcinogenesis, suggesting that chronic blockade of TRPV1 might increase the risk of tumor development. In this study, we found that a typical TRPV1 antagonist, AMG9810, promotes mouse skin tumor development. The topical application of AMG9810 resulted in a significant increase in the expression level of the epidermal growth factor receptor (EGFR) and its downstream Akt/mammalian target of rapamycin (mTOR)-signaling pathway. This increase was not only observed in AMG9810-treated tumor tissue but was also found in skin tissue treated with AMG9810. In telomerase-immortalized primary human keratinocytes, AMG9810 promoted proliferation that was mediated through the EGFR/Akt/mTOR-signaling pathway. In summary, our data suggest that the TRPV1 antagonist, AMG9810, promotes mouse skin tumorigenesis mediated through EGFR/Akt/mTOR signaling. Thus, the application of this compound for pain relief might increase the risk of skin cancer.

Wounding enhances epidermal tumorigenesis by recruiting hair follicle keratinocytes

Chronic wounds and acute trauma constitute well-established risk factors for development of epithelial-derived skin tumors, although the underlying mechanisms are largely unknown. Basal cell carcinomas (BCCs) are the most common skin cancers displaying a number of features reminiscent of hair follicle (HF)-derived cells and are dependent on deregulated Hedgehog (Hh)/GLI signaling. Here we show, in a mouse model conditionally expressing GLI1 and in a model with homozygous inactivation of Ptch1, mimicking the situation in human BCCs, that the wound environment accelerates the initiation frequency and growth of BCC-like lesions. Lineage tracing reveals that both oncogene activation and wounding induce emigration of keratinocytes residing in the lower bulge and the nonpermanent part of the HFs toward the interfollicular epidermis (IFE). However, only oncogene activation in combination with a wound environment enables the participation of such cells in the initiation of BCC-like lesions at the HF openings and in the IFE. We conclude that, in addition to the direct enhancement of BCC growth, the tumor-promoting effect of the wound environment is due to recruitment of tumor-initiating cells originating from the neighboring HFs, establishing a link between epidermal wounds and skin cancer risk.

Mice Lacking MSK1 and MSK2 Show Reduced Skin Tumor Development in a Two-Stage Chemical Carcinogenesis Model

Mitogen- and stress-activated protein kinase (MSK)1/2 are two kinases involved in inflammation as well as in cell transformation. Purpose: To examine the role of MSK1/2 in skin tumor development. Results: MSK1/2 knockout mice developed significantly fewer skin tumors compared with wild-type mice. The myeloperoxidase activity in TPA-treated skin from MSK1/2 knockout mice was significantly elevated compared with wild-type mice. Furthermore, the mRNA and protein levels of IL-1β as well as the mRNA expression of TNF-α were significantly increased in MSK1/2 knockout mice. Conclusion: These data provide in vivo evidence that MSK1/2 signaling represents a novel tumor-promoting axis in skin carcinogenesis.

Upregulation of the EP1 receptor for prostaglandin E2 promotes skin tumor progression

Prostaglandin E(2) (PGE(2) ) has been shown to promote the development of murine skin tumors. EP1 is 1 of the 4 PGE(2) G-protein-coupled membrane receptors expressed by murine keratinocytes. EP1 mRNA levels were increased ∼2-fold after topical treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) or exposure to ultraviolet (UV) light, as well as increased ∼3- to 12-fold in tumors induced by 7,12-dimethyl-benz[a]anthracene (DMBA) initiation/TPA promotion or by UV exposure. To determine the effect of EP1 levels on tumor development, we generated BK5.EP1 transgenic mice that overexpress EP1 in the basal layer of the epidermis. Skins of these mice were histologically indistinguishable from wild type (WT) mice and had similar levels of proliferation after TPA treatment. Using a DMBA/TPA carcinogenesis protocol, BK5.EP1 mice had a reduced tumor multiplicity compared to WT mice, likely due to the observed down-regulation of protein kinase C (PKC). However, the BK5.EP1 mice had an ∼8-fold higher papilloma to carcinoma conversion rate. When DMBA/anthralin was used, BK5.EP1 mice produced more tumors than WT mice, as well as a ninefold increase in carcinomas, indicating that the tumor response is dependent on the type of tumor promoter agent used. Additionally, although almost undetectable in WT mice, cyclooxygenase-2 (COX-2) was expressed in the untreated epidermis of BK5.EP1 mice. While TPA highly induced COX-2 in WT mice, COX-2 expression in the BK5.EP1 mice did not change after TPA treatment; PGE(2) levels were likewise affected. These data indicate that EP1 is more important in tumor progression than in tumor promotion and that it indirectly regulates COX-2 expression.

A qualitative study of the impact of living with neurofibromatosis type 2

Neurofibromatosis type 2 (Nf2) is an inherited autosomal dominant syndrome characterised by the development of nervous system tumours, ocular abnormalities and skin tumours. Symptoms of Nf2 can vary depending on the size and location of the tumour and include hearing loss, balance deficits and facial palsy. This study explored the physical, emotional and social impact of Nf2. Six patients were recruited through a neurofibromatosis clinic and underwent a semi-structured interview. Interviews were recorded and analysed using Framework analysis. Participants spoke of the negative impact of Nf2 on daily activities, including work. Social isolation resulted from the avoidance of social situations and was often a consequence of difficulties with communication due to loss of hearing. Patients expressed a range of negative emotional reactions in response to their diagnosis and the impact of the disease. Furthermore, the findings highlighted the important role of partners and family who were relied on for physical as well as emotional and psychological support. Patients also expressed frustration at the limited awareness of Nf2 among health professionals and a desire for improved access to information on Nf2 within their local community.

Network analysis of skin tumor progression identifies a rewired genetic architecture affecting inflammation and tumor susceptibility

BackgroundGermline polymorphisms can influence gene expression networks in normal mammalian tissues and can affect disease susceptibility. We and others have shown that analysis of this genetic architecture can identify single genes and whole pathways that influence complex traits, including inflammation and cancer susceptibility. Whether germline variants affect gene expression in tumors that have undergone somatic alterations, and the extent to which these variants influence tumor progression, is unknown.ResultsUsing an integrated linkage and genomic analysis of a mouse model of skin cancer that produces both benign tumors and malignant carcinomas, we document major changes in germline control of gene expression during skin tumor development resulting from cell selection, somatic genetic events, and changes in the tumor microenvironment. The number of significant expression quantitative trait loci (eQTL) is progressively reduced in benign and malignant skin tumors when compared to normal skin. However, novel tumor-specific eQTL are detected for several genes associated with tumor susceptibility, including IL18 (Il18), Granzyme E (Gzme), Sprouty homolog 2 (Spry2), and Mitogen-activated protein kinase kinase 4 (Map2k4).ConclusionsWe conclude that the genetic architecture is substantially altered in tumors, and that eQTL analysis of tumors can identify host factors that influence the tumor microenvironment, mitogen-activated protein (MAP) kinase signaling, and cancer susceptibility.

RETRACTED: Aberrant DNA hypermethylation patterns lead to transcriptional silencing of tumor suppressor genes in UVB-exposed skin and UVB-induced skin tumors of mice

Overexposure of the human skin to solar ultraviolet (UV) radiation is the major etiologic factor for development of skin cancers. Here, we report the results of epigenetic modifications in UV-exposed skin and skin tumors in a systematic manner. The skin and tumor samples were collected after chronic exposure of the skin of SKH-1 hairless mice to UVB radiation using a well-established photocarcinogenesis protocol. We found a distinct DNA hypermethylation pattern in the UVB-exposed epidermal skin and UVB-induced skin tumors that was associated with the elevated expression and activity of the DNA methyltransferases (Dnmt) 1, Dnmt3a and Dnmt3b. To explore the role of hypermethylation in skin photocarcinogenesis, we focused on the p16(INK4a) and RASSF1A tumor suppressor genes, which are transcriptionally silenced on methylation. We established that the silencing of these genes in UVB-exposed epidermis and UVB-induced skin tumors is associated with a network of epigenetic modifications, including hypoacetylation of histone H3 and H4 and increased histone deacetylation, as well as recruitment of methyl-binding proteins, including MeCP2 and MBD1, to the methylated CpGs. Higher levels of DNA methylation and DNMT activity in human squamous cell carcinoma specimens than in normal human skin suggest that the data are relevant clinically. Our data indicate for the first time that UVB-induced DNA hypermethylation, enhanced Dnmt activity and histone modifications occur in UVB-exposed skin and UVB-induced skin tumors and suggest that these events are involved in the silencing of tumor suppressor genes and in skin tumor development.

Unexpected Reduction of Skin Tumorigenesis on Expression of Cyclin-Dependent Kinase 6 in Mouse Epidermis

Cyclin-dependent kinases (CDKs) 4 and 6 are important regulators of the G(1) phase of the cell cycle, share 71% amino acid identity, and are expressed ubiquitously. As a result, it was assumed that each of these kinases plays a redundant role regulating normal and neoplastic proliferation. In previous reports, we have described the effects of CDK4 expression in transgenic mice, including the development of epidermal hyperplasia and increased malignant progression to squamous cell carcinoma. To study the role of CDK6 in epithelial growth and tumorigenesis, we generated transgenic mice carrying the CDK6 gene under the keratin 5 promoter (K5CDK6). Similar to K5CDK4 mice, epidermal proliferation increased substantially in K5CDK6 mice; however, no hyperplasia was observed. CDK6 overexpression also triggered keratinocyte apoptosis in interfollicular and follicular epidermis as a compensatory mechanism to override aberrant proliferation. Unexpectedly, CDK6 overexpression results in decreased skin tumor development compared with wild-type siblings. The inhibition in skin tumorigenesis was similar to that previously reported in K5-cyclin D3 mice. Furthermore, biochemical analysis of the K5CDK6 epidermis showed preferential complex formation between CDK6 and cyclin D3, suggesting that this particular complex plays an important role in tumor restraint. These studies provide in vivo evidence that CDK4 and CDK6 play a similar role as a mediator of keratinocyte proliferation but differ in apoptosis activation and skin tumor development.

FSP1 + Fibroblasts Promote Skin Carcinogenesis by Maintaining MCP-1-Mediated Macrophage Infiltration and Chronic Inflammation

Cancer development is often associated with increased fibroblast proliferation and extensive fibrosis; however, the role of fibroblasts during carcinogenesis remains largely unknown. Using the 7,12-dimethylbenz-(a)anthracene and 12-O-tetradecanoylphorbol-13-acetate-induced two-stage skin carcinogenesis model, we demonstrated here that there was a massive accumulation and proliferation of fibroblasts in the skin shortly after application of carcinogen. Selective abatement of these cells during the promotion stage drastically decreased incidence and progression of papillomas. This correlated well with reduced macrophage infiltration and impaired cytokine storm in the affected skin. 12-O-tetradecanoylphorbol-13-acetate stimulated skin fibroblasts, secreting high levels of monocyte chemotactic protein-1, and neutralization of this chemokine eliminated almost completely the fibroblast-induced chemotaxis of macrophages. These results strongly suggest that fibroblasts promote skin tumor development by producing monocyte chemotactic protein-1 and maintaining chronic inflammation.

The role of KLF4 in UVB-induced murine skin tumor development and its correlation with cyclin D1, p53, and p21Waf1/Cip1 in epithelial tumors of the human skin

The zinc-finger-type transcriptional factor KLF4 is expressed in a variety of tissues including skin. KLF4 can function as either a tumor suppressor or an oncogene, depending on the type of tissue in which it is expressed, by modulating the expression of various factors. To understand the role of KLF4 in human skin cancer and also to evaluate the expression of cyclin D1, p53, and p21(Waf1/Cip1) in relation to the expression of KLF4, we evaluated the pattern of KLF4 expression during UVB-induced skin tumor development in SKH-1 hairless mice and in human skin cancer. We also determined whether there are correlations between the expression of KLF4, cyclin D1, p53, and p21 and non-melanoma skin tumors. KLF4 expression was found in the basal layer of non-irradiated control murine skin. Chronic UVB irradiation caused a progressive decrease in KLF4 expression, which was substantially decreased in UVB-induced murine skin tumors. In human precancerous lesions, KLF4 expression was maintained in 64.3% of Bowen's disease samples and 90.0% of AK samples. In contrast, KLF4 expression was significantly reduced in human cancer lesions (p = 0.004). A positive correlation was found between the expression of KLF4 and p21(Waf1/Cip1) in AK, whereas there was a negative correlation between the expression of cyclin D1 and p21(Waf1/Cip1) in Bowen's disease. Thus, our results suggest that KLF4 may function as a tumor suppressor in the skin and that the deregulated expression of KLF4 in the context of p21(Waf1/Cip1) and cyclin D1 expression may be involved in skin tumorigenesis.

The Prostaglandin E2 Receptor, EP2, Stimulates Keratinocyte Proliferation in Mouse Skin by G Protein-dependent and β-Arrestin1-dependent Signaling Pathways

The prostaglandin E(2) (PGE(2)) G protein-coupled receptor (GPCR), EP2, plays important roles in mouse skin tumor development (Chun, K. S., Lao, H. C., Trempus, C. S., Okada, M., and Langenbach, R. (2009) Carcinogenesis 30, 1620-1627). Because keratinocyte proliferation is essential for skin tumor development, EP2-mediated signaling pathways that contribute to keratinocyte proliferation were investigated. A single topical application of the EP2 agonist, butaprost, dose-dependently increased keratinocyte replication via activation of epidermal growth factor receptor (EGFR) and PKA signaling. Because GPCR-mediated activation of EGFR can involve the formation of a GPCR-β-arrestin-Src signaling complex, the possibility of a β-arrestin1-Src complex contributing to EP2-mediated signaling in keratinocytes was investigated. Butaprost induced β-arrestin1-Src complex formation and increased both Src and EGFR activation. A role for β-arrestin1 in EP2-mediated Src and EGFR activation was demonstrated by the observation that β-arrestin1 deficiency significantly reduced Src and EGFR activation. In agreement with a β-arrestin1-Src complex contributing to EGFR activation, Src and EGFR inhibition (PP2 and AG1478, respectively) indicated that Src was upstream of EGFR. Butaprost also induced the activation of Akt, ERK1/2, and STAT3, and both β-arrestin1 deficiency and EGFR inhibition (AG1478 or gefitinib) decreased their activation. In addition to β-arrestin1-dependent EGFR activation, butaprost increased PKA activation, as measured by phospho-GSK3β (p-GSK3β) and p-cAMP-response element-binding protein formation. PKA inhibition (H89 or R(P)-adenosine-3',5'-cyclic monophosphorothioate (R(P)-cAMPS)) decreased butaprost-induced cAMP-response element-binding protein and ERK activation but did not affect EGFR activation, whereas β-arrestin1 deficiency decreased EGFR activation but did not affect butaprost-induced PKA activation, thus indicating that they were independent EP2-mediated pathways. Therefore, the results indicate that EP2 contributed to mouse keratinocyte proliferation by G protein-independent, β-arrestin1-dependent activation of EGFR and G protein-dependent activation of PKA.

Proanthocyanidins Inhibit Photocarcinogenesis through Enhancement of DNA Repair and Xeroderma Pigmentosum Group A–Dependent Mechanism

Dietary grape seed proanthocyanidins (GSP) inhibit photocarcinogenesis in mice; however, the molecular mechanisms underlying this effect have not been fully elucidated. As ultraviolet B (UVB)-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPDs) has been implicated in skin cancer risk, we studied whether dietary GSPs enhance repair of UVB-induced DNA damage and, if so, what is the potential mechanism? Supplementation of GSPs (0.5%, w/w) with AIN76A control diet significantly reduced the levels of CPD(+) cells in UVB-exposed mouse skin; however, GSPs did not significantly reduce UVB-induced CPD(+) cells in the skin of interleukin-12p40 (IL-12) knockout (KO) mice, suggesting that IL-12 is required for the repair of CPDs by GSPs. Using IL-12 KO mice and their wild-type counterparts and standard photocarcinogenesis protocol, we found that supplementation of control diet with GSPs (0.5%, w/w) significantly reduced UVB-induced skin tumor development in wild-type mice, which was associated with the elevated mRNA levels of nucleotide excision repair genes, such as XPA, XPC, DDB2, and RPA1; however, this effect of GSPs was less pronounced in IL-12 KO mice. Cytostaining analysis revealed that GSPs repaired UV-induced CPD(+) cells in xeroderma pigmentosum complementation group A (XPA)-proficient fibroblasts from a healthy individual but did not repair in XPA-deficient fibroblasts from XPA patients. Furthermore, GSPs enhance nuclear translocation of XPA and enhanced its interactions with other DNA repair protein ERCC1. Together, our findings reveal that prevention of photocarcinogenesis by GSPs is mediated through enhanced DNA repair in epidermal cells by IL-12- and XPA-dependent mechanisms.

Evidence That Gsta4 Modifies Susceptibility to Skin Tumor Development in Mice and Humans

The incidence of nonmelanoma skin cancer (NMSC) is equivalent to that of all other cancers combined. Previously, we mapped the 12-O-tetradecanoylphorbol-13-acetate (TPA) skin tumor promotion susceptibility locus, Psl1, to distal chromosome 9 in crosses of sensitive DBA/2 mice with relatively resistant C57BL/6 mice. Here, we used the mouse two-stage skin carcinogenesis model to identify the gene(s) responsible for the effects of Psl1. Interval-specific congenic mouse strains (n ≥ 59 mice per strain) were used to more precisely map the Psl1 locus. Having identified glutathione S-transferase α4 (Gsta4) as a candidate tumor promotion susceptibility gene that mapped within the delimited region, we analyzed Gsta4-deficient mice (n = 62) for susceptibility to skin tumor promotion by TPA. We used quantitative polymerase chain reaction, western blotting, and immunohistochemistry to verify induction of Gsta4 in mouse epidermis following TPA treatment and biochemical assays to associate Gsta4 activity with tumor promotion susceptibility. In addition, single-nucleotide polymorphisms (SNPs) in GSTA4 were analyzed in a case-control study of 414 NMSC patients and 450 control subjects to examine their association with human NMSC. Statistical analyses of tumor studies in mice were one-sided, whereas all other statistical analyses were two-sided. Analyses of congenic mice indicated that at least two loci, Psl1.1 and Psl1.2, map to distal chromosome 9 and confer susceptibility to skin tumor promotion by TPA. Gsta4 maps to Psl1.2 and was highly induced (mRNA and protein) in the epidermis of resistant C57BL/6 mice compared with that of sensitive DBA/2 mice following treatment with TPA. Gsta4 activity levels were also higher in the epidermis of C57BL/6 mice following treatment with TPA. Gsta4-deficient mice (C57BL/6.Gsta4(-/-) mice) were more sensitive to TPA skin tumor promotion (0.8 tumors per mouse vs 0.4 tumors per mouse in wild-type controls; difference = 0.4 tumors per mouse; 95% confidence interval = 0.1 to 0.7, P = .007). Furthermore, inheritance of polymorphisms in GSTA4 was associated with risk of human NMSC. Three SNPs were found to be independent predictors of NMSC risk. Two of these were associated with increased risk of NMSC (odds ratios [ORs] = 1.60 to 3.42), while the third was associated with decreased risk of NMSC (OR = 0.63). In addition, a fourth SNP was associated with decreased risk of basal cell carcinoma only (OR = 0.44). Gsta4/GSTA4 is a novel susceptibility gene for NMSC that affects risk in both mice and humans.

Identification of Epidermal Pdx1 Expression Discloses Different Roles of Notch1 and Notch2 in Murine KrasG12D-Induced Skin Carcinogenesis In Vivo

BackgroundThe Ras and Notch signaling pathways are frequently activated during development to control many diverse cellular processes and are often dysregulated during tumorigenesis. To study the role of Notch and oncogenic Kras signaling in a progenitor cell population, Pdx1-Cre mice were utilized to generate conditional oncogenic KrasG12D mice with ablation of Notch1 and/or Notch2.Methodology/Principal FindingsSurprisingly, mice with activated KrasG12D and Notch1 but not Notch2 ablation developed skin papillomas progressing to squamous cell carcinoma providing evidence for Pdx1 expression in the skin. Immunostaining and lineage tracing experiments indicate that PDX1 is present predominantly in the suprabasal layers of the epidermis and rarely in the basal layer. Further analysis of keratinocytes in vitro revealed differentiation-dependent expression of PDX1 in terminally differentiated keratinocytes. PDX1 expression was also increased during wound healing. Further analysis revealed that loss of Notch1 but not Notch2 is critical for skin tumor development. Reasons for this include distinct Notch expression with Notch1 in all layers and Notch2 in the suprabasal layer as well as distinctive p21 and β-catenin signaling inhibition capabilities.Conclusions/SignificanceOur results provide strong evidence for epidermal expression of Pdx1 as of yet not identified function. In addition, this finding may be relevant for research using Pdx1-Cre transgenic strains. Additionally, our study confirms distinctive expression and functions of Notch1 and Notch2 in the skin supporting the importance of careful dissection of the contribution of individual Notch receptors.

Serological markers for papillomavirus infection and skin tumour development in the rodent model Mastomys coucha

This study used the rodent Mastomys coucha latently infected with Mastomys natalensis papillomavirus (MnPV) and Mastomys coucha PV2 (McPV2), which induce skin papillomas and anogenital condylomas, respectively, to investigate PV antibody responses as serological markers during pathogenesis. In a case-control study (137 animals), virus and tumour prevalence correlated with the seroresponse against the early E2 and late L1 viral proteins. A prospective study (53 animals) revealed for the first time the course of these antibody responses during all stages of a natural PV infection. Numerous tumour entities were observed on the eyelid and in the oral cavity. DNA analyses indicated that McPV2 was not restricted to condylomas but was also present in these mucosa-associated papillomas. The serological survey using a recently established glutathione S-transferase-capture ELISA detected a strong correlation between MnPV L1-specific antibodies and the presence of papillomas on the skin, eye and ear (P<0.001). Notably, extensive antibody responses to MnPV E2 were also detected in these cases. A prospective study revealed that E2 reactivity occurred by the age of 1 month. MnPV L1 antibodies were found at 2.5 months, indicating the initiation of productive viral infection. Thirty-one out of 34 L1-seropositive animals at the age of 4.5 months developed MnPV-associated tumours (positive predictive value=77 %), and none of the seronegative animals developed skin papillomas (negative predictive value=100 %). MnPV E2 and L1 serology thus provides a powerful tool for monitoring early infection and skin tumour progression in M. coucha.

Keratinocyte-Specific Stat3 Heterozygosity Impairs Development of Skin Tumors in Human Papillomavirus 8 Transgenic Mice

Human papillomaviruses (HPV) of the genus β are thought to play a role in human skin cancers, but this has been difficult to establish using epidemiologic approaches. To gain insight into the transforming activities of β-HPV, transgenic mouse models have been generated that develop skin tumors. Recent evidence suggests a central role of signal transducer and activator of transcription 3 (Stat3) as a transcriptional node for cancer cell-autonomous initiation of a tumor-promoting gene signature associated with cell proliferation, cell survival, and angiogenesis. Moreover, high levels of phospho-Stat3 have been detected in tumors arising in HPV8-CER transgenic mice. In this study, we investigate the in vivo role of Stat3 in HPV8-induced skin carcinogenesis by combining our established experimental model of HPV8-induced skin cancer with epidermis-restricted Stat3 ablation. Stat3 heterozygous epidermis was less prone to tumorigenesis than wild-type epidermis. Three of the 23 (13%) Stat3(+/-):HPV8 animals developed tumors within 12 weeks of life, whereas 54.3% of Stat3(+/+):HPV8 mice already exhibited tumors in the same observation period (median age for tumor appearance, 10 weeks). The few tumors that arose in the Stat3(+/-):HPV8 mice were benign and never progressed to a more malignant phenotype. Collectively, these results offer direct evidence of a critical role for Stat3 in HPV8-driven epithelial carcinogenesis. Our findings imply that targeting Stat3 activity in keratinocytes may be a viable strategy to prevent and treat HPV-induced skin cancer.