UV-induced Skin Cancer Research Articles

Cyclosporin A, but not everolimus, inhibits DNA repair mediated by calcineurin: implications for tumorigenesis under immunosuppression

Unlike other immunosuppressive drugs including everolimus, cyclosporin A causes a dramatic increase of UV-induced skin cancer, a feature that is reminiscent of xeroderma pigmentosum (XP), where defective nucleotide excision repair (NER) of UV-induced DNA damage results in cutaneous carcinogenesis. The molecular basis of the clinically important differential activities of cyclosporin A and everolimus is still unclear. We measured post-UV cell survival of cyclosporin A- and everolimus-treated human fibroblasts and lymphoblasts using a cell proliferation assay (MTT). The cellular NER capacity was assessed by host cell reactivation. Using an ELISA and specific antibodies, cyclobutane pyrimidine and pyrimidine-6,4-pyrimidone photoproduct removal from the cellular genome was measured. The effect of calcineurin on NER was investigated using a calcineurin A expression vector and specific RNAi. Cyclosporin A led to a dose dependent decrease in post-UV cell survival, inhibited NER and blocked photoproduct removal. In contrast, none of these effects where seen in everolimus-treated cells. Overexpression of calcineurin A resulted in increased NER and complemented the Cyclosporin A-induced reduction of NER. Downregulation of calcineurin using RNAi inhibited NER comparable to cyclosporin A-treatment. We conclude that cyclosporin A, but not everolimus, leads to an increased skin cancer risk via a calcineurin signalling-dependent impairment of NER.

The conserved factor DE-ETIOLATED 1 cooperates with CUL4-DDB1DDB2to maintain genome integrity upon UV stress

Plants and many other eukaryotes can make use of two major pathways to cope with mutagenic effects of light, photoreactivation and nucleotide excision repair (NER). While photoreactivation allows direct repair by photolyase enzymes using light energy, NER requires a stepwise mechanism with several protein complexes acting at the levels of lesion detection, DNA incision and resynthesis. Here we investigated the involvement in NER of DE-ETIOLATED 1 (DET1), an evolutionarily conserved factor that associates with components of the ubiquitylation machinery in plants and mammals and acts as a negative repressor of light-driven photomorphogenic development in Arabidopsis. Evidence is provided that plant DET1 acts with CULLIN4-based ubiquitin E3 ligase, and that appropriate dosage of DET1 protein is necessary for efficient removal of UV photoproducts through the NER pathway. Moreover, DET1 is required for CULLIN4-dependent targeted degradation of the UV-lesion recognition factor DDB2. Finally, DET1 protein is degraded concomitantly with DDB2 upon UV irradiation in a CUL4-dependent mechanism. Altogether, these data suggest that DET1 and DDB2 cooperate during the excision repair process.

P38 MAP kinase plays a functional role in UVB‐Induced mouse skin carcinogenesis

UVB irradiation of epidermal keratinocytes results in the activation of the p38 mitogen-activated protein kinase (MAPK) pathway and subsequently activator protein-1 (AP-1) transcription factor activation and cyclooxygenase-2 (COX-2) expression. AP-1 and COX-2 have been shown to play functional roles in UVB-induced mouse skin carcinogenesis. In this study, the experimental approach was to express a dominant negative p38α MAPK (p38DN) in the epidermis of SKH-1 hairless mice and assess UVB-induced AP-1 activation, COX-2 expression, and the skin carcinogenesis response in these mice compared to wild-type littermates. We observed a significant inhibition of UVB-induced AP-1 activation and COX-2 expression in p38DN transgenic mice, leading to a significant reduction of UVB-induced tumor number and growth compared to wild-type littermates in a chronic UVB skin carcinogenesis model. A potential mechanism for this reduction in tumor number and growth rate is an inhibition of chronic epidermal proliferation, observed as reduced Ki-67 staining in p38DN mice compared to wild-type. Although we detected no difference in chronic apoptotic rates between transgenic and nontransgenic mice, analysis of acutely irradiated mice demonstrated that expression of the p38DN transgene significantly inhibited UVB-induced apoptosis of keratinocytes. These results counter the concerns that inhibition of p38 MAPK in a chronic situation could compromise the ability of the skin to eliminate potentially tumorigenic cells. Our data indicate that p38 MAPK is a good target for pharmacological intervention for UV-induced skin cancer in patients with sun damaged skin, and suggest that inhibition of p38 signaling reduces skin carcinogenesis by inhibiting COX-2 expression and proliferation of UVB-irradiated cells.

Xeroderma pigmentosum

The recessively inherited nucleotide excision repair (NER) defect syndrome xeroderma pigmentosum (XP) serves as a model disease for UV-induced skin cancer. XP is characterized by sun-sensitivity, freckling, and poikilodermic skin changes in sun-exposed areas, and a more than 1000-fold increased risk of skin cancer including melanoma as well as basal and squamous cell carcinomas. Seven XP complementation groups (XP-A to XP-G) are known to date representing the defective genes in XP patients. An additional "variant" form (XPV) which is clinically indistinguishable from the complementation groups exhibits defective translesional synthesis. An enhanced understanding of skin cancer development in general can help to identify individuals at an increased risk who should take special precautions, for example to avoid occupational exposures. The position of skin cancer induced by UV-light as an occupational disease in the ordinance on industrial diseases (BKV) is currently a topic of research and discussion in Germany.

Physicians involved in the care of patients with high risk of skin cancer should be trained regarding sun protection measures: evidence from a cross sectional study

Knowledge, regarding sun protection, is essential to change behaviour and to reduce sun exposure of patients at risk for skin cancer. Patient education regarding appropriate or sun protection measures, is a priority to reduce skin cancer incidence. The aim of this study was to evaluate the knowledge about sun protection and the recommendations given in a population of non-dermatologists physicians involved in the care of patients at high risk of skin cancer. This study is a cross-sectional study. Physicians were e-mailed an anonymous questionnaire evaluating the knowledge about risk factors for skin cancer, sun protection and about the role of the physician in providing sun protection recommendations. Of the responders, 71.4% considered that the risk of skin cancer of their patients was increased when compared with the general population. All the responders knew that UV-radiations can contribute to induce skin cancers and 71.4% of them declared having adequate knowledge about sun protection measures. A proportion of 64.2% of them declared that they were able to give sun protection advices: using sunscreens (97.8%), wearing covering clothes (95.5%), performing regular medical skin examination (91.1%), to avoid direct sunlight exposure (77.8%), avoiding outdoor activities in the hottest midday hours (73.3%) and practising progressive exposure (44.4%). Non-dermatologist physicians reported a correct knowledge of UV-induced skin cancer risk factors. The majority of responders displayed adequate knowledge of sun protection measures and declared providing patients with sun protection recommendation on a regular basis. Several errors persisted.

Microarray analysis of microRNA expression in skin of Xpc+/− mice and wild-type mice

MicroRNAs (miRNAs) are noncoding RNA molecules of 21-24 nt that regulate the expression of target genes in a post-transcriptional manner. Evidence indicates that miRNAs play essential roles in embryogenesis, cell differentiation, and pathogenesis of human diseases including skin cancer. To investigate possible mechanisms of photocarcinogenesis, we describe a comparison between miRNA expression profile of Xpc heterozygous partially repair-deficient mice and WT repair-proficient mice. We analyzed the miRNA expression profiles in 2 pairs of Xpc(+/-) mice and WT mice, using a mammalian miRNA microarray containing whole mice mature and precursor miRNA sequences. MiRBase and GO analysis were employed for the prediction of miRNA targets. A total of 20 miRNAs were differentially expressed in which 13 miRNAs down-regulated and 7 miRNAs up-regulated in Xpc heterozygous mice compared with the WT counterpart. Differentially expressed miRNAs were predicted to have some relationships with several signaling pathway in skin cells, of which regulation of epidermal growth factor receptor signaling pathway and transforming growth factor beta receptor signaling pathway should be noted. The differential miRNA expression identified in this study may be of use in the diagnosis and/or treatment of UV-induced skin cancers.

T-LAK Cell-originated Protein Kinase (TOPK) Phosphorylation of Prx1 at Ser-32 Prevents UVB-induced Apoptosis in RPMI7951 Melanoma Cells through the Regulation of Prx1 Peroxidase Activity

Protein kinases are potential targets for the prevention and control of UV-induced skin cancer. T-cell-originated protein kinase (TOPK) is highly expressed in skin cancer cells, but its specific function is still unknown. We investigated the role of TOPK in UVB-induced apoptosis in RPMI7951 human melanoma cells. Liquid chromatography-tandem mass spectrometry analysis was used to identify proteins that bind with TOPK. Immunofluorescence, Western blot, and flow cytometry were used to assess the effect of UVB on TOPK, peroxiredoxin 1 (Prx1), and apoptosis in RPMI7951 cells. TOPK binds with Prx1 and its phosphorylation of Prx1 at Ser-32 is important for regulation of H(2)O(2)-mediated signal transduction. Analysis of the CD spectra of Prx1 and mutant Prx1 (S32A) proteins showed that the secondary structure of Prx1 was significantly altered by phosphorylation of Prx1 at Ser-32. UVB irradiation induced phosphorylation of TOPK in RPMI7951 human melanoma cells and phosphorylated TOPK co-localized with Prx1 in the nucleus. UVB induced the peroxidase activity of Prx1 in vitro and ex vivo. Following treatment with UVB, H(2)O(2) levels and apoptosis were increased in RPMI7951 cells stably expressing TOPK siRNA or stably mutant Prx1 (S32A). Phosphorylation of Prx1 (Ser-32) by TOPK prevents UVB-induced apoptosis in RPMI7951 melanoma cells through regulation of Prx1 peroxidase activity and blockade of intracellular H(2)O(2) accumulation.

The Role of Macrophage Migration Inhibitory Factor (MIF) in Ultraviolet Radiation-Induced Carcinogenesis

Ultraviolet (UV) radiation is the most common cause of physical injury to the skin due to environmental damage, and UV exposure substantially increases the risk of actinic damage to the skin. The inflammatory changes induced by acute UV exposure include erythema (sunburn) of the skin, while chronic exposure to solar UV radiation causes photo-aging, immunosuppression, and ultimately, carcinogenesis of the skin. After skin damage by UV radiation, the cells are known to secrete many cytokines, including interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-α. and macrophage migration inhibitory factor (MIF). MIF was originally identified as a lymphokine that concentrates macrophages at inflammatory loci, and is known to be a potent activator of macrophages in vivo. MIF is considered to play an important role in cell-mediated immunity. Since the molecular cloning of MIF cDNA, MIF has been re-evaluated as a proinflammatory cytokine and pituitary-derived hormone that potentiates endotoxemia. MIF is ubiquitously expressed in various tissues, including the skin. Recent studies have suggested a potentially broader role for MIF in growth regulation because of its ability to antagonize p53-mediated gene activation and apoptosis. This article reviews the latest findings on the roles of MIF with regard to UV-induced skin cancer.

Zinc‐induced Structural Effects Enhance Oxygen Consumption and Superoxide Generation in Synthetic Pheomelanins on UVA/Visible Light Irradiation†

The abnormal susceptibility of red-haired individuals to UV-induced inflammation and skin cancers is commonly attributed to the marked photoreactivity of pheomelanin pigments, which would be responsible for the sustained generation of reactive oxygen species in the skin following sun exposure. The structural factors determining pheomelanin photolability remain mostly unknown. Here, we describe the effects of zinc ions, typically found at high levels in red hair, in enhancing both oxygen consumption and superoxide production in model pheomelanin pigments following irradiation with UVA and visible light. Electron paramagnetic resonance (EPR) oximetry and EPR-spin trapping experiments with synthetic pheomelanins, prepared by oxidation of dopa and cysteine or isomeric cysteinyldopas under different conditions, indicate a higher photoreactivity of the pigments prepared in the presence of zinc ions compared with those obtained in the absence of the metal. Quantitative analysis of thiazole-containing structural markers of the synthetic pheomelanins provides evidence that the effect of zinc ions is due to modification of the formation pathway and structural features of the pigments. Overall, these results point to a hitherto unrecognized critical role of zinc ions in pheomelanogenesis, which may affect the intrinsic photoreactivity of the pigment.

Regulation of Human Skin Pigmentation in situ by Repetitive UV Exposure: Molecular Characterization of Responses to UVA and/or UVB

UV radiation is a major environmental factor that affects pigmentation in human skin and can eventually result in various types of UV-induced skin cancers. The effects of various wavelengths of UV on melanocytes and other types of skin cells in culture have been studied, but little is known about gene expression patterns in situ following in situ exposure of human skin to different types of UV (UVA and/or UVB). Paracrine factors expressed by keratinocytes and/or fibroblasts that affect skin pigmentation might be regulated differently by UV, as might their corresponding receptors expressed on melanocytes. To test the hypothesis that different mechanisms are involved in the pigmentary responses of the skin to different types of UV, we used immunohistochemical and whole human genome microarray analyses to characterize human skin in situ to examine how melanocyte-specific proteins and paracrine melanogenic factors are regulated by repetitive exposure to different types of UV compared with unexposed skin as a control. The results show that gene expression patterns induced by UVA or UVB are distinct-UVB eliciting dramatic increases in a large number of genes involved in pigmentation as well as in other cellular functions, whereas UVA had little or no effect on these. The expression patterns characterize the distinct responses of the skin to UVA or UVB, and identify several potential previously unidentified factors involved in UV-induced responses of human skin.

Agents that Reverse UV-Induced Immune Suppression and Photocarcinogenesis Affect DNA Repair

UV exposure induces skin cancer, in part, by inducing immune suppression. Repairing DNA damage, neutralizing the activity of cis-urocanic acid, and reversing oxidative stress abrogate UV-induced immune suppression and skin cancer induction, suggesting that DNA, UCA, and lipid photo-oxidation serve as UV photoreceptors. What is not clear is whether signaling through each of these different photoreceptors activates independent pathways to induce biological effects or whether there is a common checkpoint where these pathways converge. Here, we show that agents known to reverse photocarcinogenesis and photoimmune suppression, such as platelet-activating factor (PAF) and serotonin (5-HT) receptor antagonists, regulate DNA repair. Pyrimidine dimer repair was accelerated in UV-irradiated mice injected with PAF and 5-HT receptor antagonists. Nucleotide excision repair (NER), as measured by unscheduled DNA synthesis, was accelerated by PAF and 5-HT receptor antagonists. Injecting PAF and 5-HT receptor antagonists into UV-irradiated Xeroderma pigmentosum complementation group A-deficient mice, which lack the enzymes responsible for NER, did not accelerate photoproduct repair. Similarly, UV-induced formation of 8-oxo-deoxyguanosine was reduced by PAF and 5-HT receptor antagonists. We conclude that PAF and 5-HT receptor antagonists accelerate DNA repair caused by UV radiation, which prevents immune suppression and interferes with photocarcinogenesis.

Botanicals in Dermatology

Botanical extracts and single compounds are increasingly used in cosmetics but also in over-the-counter drugs and food supplements. The focus of the present review is on controlled clinical trials with botanicals in the treatment of acne, inflammatory skin diseases, skin infections, UV-induced skin damage, skin cancer, alopecia, vitiligo, and wounds. Studies with botanical cosmetics and drugs are discussed, as well as studies with botanical food supplements. Experimental research on botanicals was considered to a limited extent when it seemed promising for clinical use in the near future. In acne therapy, Mahonia, tea tree oil, and Saccharomyces may have the potential to become standard treatments. Mahonia, Hypericum, Glycyrrhiza and some traditional Chinese medicines appear promising for atopic dermatitis. Some plant-derived substances like dithranol and methoxsalen (8-methoxypsoralen) [in combination with UVA] are already accepted as standard treatments in psoriasis; Mahonia and Capsicum (capsaicin) are the next candidates suggested by present evidence. Oral administration and topical application of antioxidant plant extracts (green and black tea, carotenoids, coffee, and many flavonoids from fruits and vegetables) can protect skin from UV-induced erythema, early aging, and irradiation-induced cancer. Hair loss and vitiligo are also traditional fields of application for botanicals. According to the number and quality of clinical trials with botanicals, the best evidence exists for the treatment of inflammatory skin diseases, i.e. atopic dermatitis and psoriasis. However, many more controlled clinical studies are needed to determine the efficacy and risks of plant-derived products in dermatology. Safety aspects, especially related to sensitization and photodermatitis, have to be taken into account. Therefore, clinicians should not only be informed of the beneficial effects but also the specific adverse effects of botanicals used for dermatologic disorders and cosmetic purposes.

UV-induced skin cancer at workplace and evidence-based prevention

The present review is aimed at providing an overview of skin cancer with particular focus on occupational concern and giving evidence-based recommendation for effective prevention at workplace. We performed a systematic search of literature using PubMed and the Cochrane Library. Outcome of preventive strategies depends either on efficacy of the strategy itself but also on acceptance and implementation of protective means among the persons at possible risk for hazardous health effects. Epidemiological studies have reported significantly more non-melanoma skin cancer in men than in women. Life-style choices and difference in immunosuppression play a major role in this gender disparity. Tumor biology of skin cancer is diverging: severe blistering sunburns corresponding to intermittent intense UV exposures are associated with an increased risk for both melanoma and basal cell carcinoma (BCC); whereas the risk of squamous cell carcinoma (SCC) and actinic keratoses (AK) is strongly associated with chronic UV exposure. Several clinical trials give evidence that long-term use of sunscreen prevents the appearance of non-melanotic skin cancer such as AK and SCC, but not of BCC. All technical and organizing measures aimed at reducing UV exposure at workplace belong to first-line prevention; however, there is much room for improvement. The efficacy of personal protection means (second-line strategy) strongly depends on the workers' compliance which is quite low at workplace. Evidence-based data confirming the benefit of sun protective strategies are scarce, general recommendations are mainly based on the avoidance of UV radiation being identified as potential risk factor for non-melanoma skin cancer in epidemiological studies. Occupational screenings should include regular interventions aimed at enhancing a clear understanding of risk factors for individuals and finally improving the acceptance and maintenance for UV-protective means at workplace.

Abstract 5657: Ursolic acid prevents activation of oncogenic factors in UV-treated HaCaT cells

Abstract The aim of this study was to determine the anti-cancer potential of the phytonutrient ursolic acid (UA) in a UV-treated HaCaT human keratinocyte cell line. Earlier studies have shown UA strongly inhibits DMBA/TPA-mediated carcinogenesis in SENCAR mice, but effects of UA on UV-induced skin cancer are unknown. Our hypothesis was that treating cells with UA, found in plant sources including rosemary and apple, may inhibit UV-induced cell death, ROS production, and transcription and activation of oncogenes and oncoproteins. These in vitro studies would suggest UA may inhibit UV-mediated skin carcinogenesis. HaCaT cells were seeded at 2,000 cells/well for MTT and DHR assays, and at 1.6 × 104 cells/cm2 for RT-PCR and Western blotting. 24 hours after seeding, cells were treated with concentrations of UA up to 25 μM. Cells were UV-treated with various doses using a transilluminator emitting 36% of its energy in the UVA range and 64% in the UVB range with a peak of 312 nm. For cell death assays, cells were incubated for 4 hours in media with MTT, UV treated, then dissolved in DMSO after various timepoints prior to measuring the absorbance at 570 nm. For quantification of intracellular H2O2, cells were incubated in media containing 5 µM DHR 123 for 1 hour prior to UV-treatment, followed by reading fluorescence at 530 nm with an excitation of 485 nm. RT-PCR was performed for bcl-2 and c-jun using SYBR green probe. Western blotting for phospho-p38 MAPK was done with whole cell lysates, isolated using RIPA buffer. Phospho-p65 and phospho-c-jun were quantified by blotting nuclear and cytosolic fractions, which were isolated using a hypotonic/hypertonic nuclear extraction procedure. We find that treating cells for 24 hours before UV and 12 hours post-UV with non-toxic doses of UA does not protect cells from UV-death. Also, pretreating this cell line with these doses of UA does not inhibit a UV-induced rise in intracellular H2O2 within an hour post-UV. However, RT-PCR results show UA treatment exacerbates a UV-induced rise in bcl-2 RNA levels and inhibits a UV-mediated increase in c-jun RNA 1 hour post-UV. Also, Western blotting reveals that 25 μM UA inhibits a 500 mJ/cm2-induced increase in phospho-p38 MAPK by 85%, and that treatment with 10 μM UA reduces 100 mJ/cm2-initiated nuclear accumulation of oncogenic phospho-c-jun by 47.6%, 1 hour after UV. Finally, treatment with 10 and 25 μM UA dose-dependently contributes to a decrease in nuclear phospho-p65 seen 1 hour post-UV treatment. These in vitro results show UA may prevent UV-mediated skin cancer by modulating the activities of the oncogenic transcription factors AP-1 and NFκB. Supported by NIH grants CA 102747 and P30 CA 54174-16S1. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5657.

Abstract 503: Curcumin protects UV-induced skin damage in SKH-1 hairless mouse

Abstract Exposure to ultraviolet (UV) light is the major etiologic factor leading to the development of cutaneous squamous and basal cell carcinoma and is also a risk factor for melanomas. UV elicits inflammation, epidermal hyperplasia and changes in the expression of numerous genes associated with proliferation and differentiation. Curcumin has been shown to exert an anti-inflammatory activity, interfere with multiple cell signaling pathways, and possess potential preventive effect against various cancers. The purpose of this study was to determine whether curcumin can protect UV-induced skin damage in hairless SKH-1 mice. Oral or topical application of curcumin prior to, or immediately after, UV irradiation resulted in a very strong protective effect against UV-induced thymine dimer expression in epidermis, accounting for 69-74% inhibition (p < 0.00). Curcumin treatment also resulted in upregulation of p53 and p21/Cip1 protein levels by 33-41% (p < 0.005) and 46-50% (p < 0.005), respectively. Oral or topical application of curcumin prior to, or immediately after UV irradiation strongly decreased the expression of proliferative cell nuclear antigen by 47- 56% (p < 0.005). In addition, curcumin treatment significantly suppressed UV-induced apoptosis as measured by TUNEL assays (p < 0.005). Furthermore, curcumin treatment also significantly inhibited NF-κB, cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), and nitric oxide (NO) levels. Our results suggest that curcumin possesses strong protective effect against UV-caused damage in epidermis. Taken together, these results provide a focus for the rational development of curcumin as a novel chemopreventive agent against UV-induced human skin cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 503.

Mice with DNA repair gene Ercc1 deficiency in a neural crest lineage are a model for late-onset Hirschsprung disease

The Ercc1 gene is essential for nucleotide excision repair and is also important in recombination repair and the repair of interstrand crosslinks. We have previously used a floxed Ercc1 allele with a keratinocyte-specific Cre recombinase transgene to inactivate Ercc1 in the epidermal layer of the skin and so generate a mouse model for UV-induced non-melanoma skin cancer. Now, in an attempt to generate a model for UV-induced melanoma, we have used the floxed Ercc1 allele in combination with a Cre transgene under the control of the tyrosinase gene promoter to produce mice with Ercc1-deficient melanocytes that are hypersensitive to UV irradiation. These animals developed normally, but died when 4–6 months old with severe colonic obstruction. Melanocytes are derived from the neural crest and the tyrosinase promoter is also expressed in additional neural crest-derived lineages, including the progenitors of the parasympathetic nervous system that innervates the gastrointestinal tract and controls gut peristalsis. A functional enteric nervous system developed in floxed Ercc1 mice with the tyrosinase Cre transgene, but was found to have degenerated in the colons of affected mice. We suggest that accumulating unrepaired endogenous DNA damage in the Ercc1-deficient colonic parasympathetic ganglia leads to the degeneration of this network and results in a colonic obstructive disorder that resembles late-onset Hirschsprung disease in man.

Luteolin Inhibits Protein Kinase Cϵ and c-Src Activities and UVB-Induced Skin Cancer

Luteolin, a flavonoid present in various vegetables including onion and broccoli, has been reported to possess anticarcinogenic effects. However, its chemopreventive effect on UV-induced skin cancer and its mechanism are not fully understood. Herein, we examined the chemopreventive effect and associated mechanisms of luteolin in the JB6 P+ cell line and the SKH-1 hairless mouse model. Luteolin suppressed UVB-induced cyclooxygenase-2 expression and activator protein-1 and nuclear factor-kappaB activity in JB6 P+ cells. Immunoblot and kinase assay data showed that luteolin attenuated protein kinase C(epsilon) (PKC(epsilon)) and Src kinase activities and subsequently inhibited UVB-induced phosphorylation of mitogen-activated protein kinases and the Akt signaling pathway. In addition, pull-down assays revealed that luteolin binds directly to PKC(epsilon) and Src in an ATP-competitive manner. Importantly, luteolin suppressed tumor incidence, multiplicity, and overall size in SKH-1 hairless mice. Analysis of the skin by immunohistochemistry and immunoblotting showed that luteolin-treated groups had a substantial reduction in the levels of cyclooxygenase-2, tumor necrosis factor-alpha, and proliferating cell nuclear antigen compared with groups treated with only UVB. Further analysis using skin lysates showed that luteolin inhibited PKC(epsilon) and Src kinase activity. Together, these data suggest that luteolin exerts potent chemopreventive activity against UVB-induced skin cancer mainly by targeting PKC(epsilon)and Src.

The nuclear vitamin D receptor controls the expression of genes encoding factors which feed the “Fountain of Youth” to mediate healthful aging

The nuclear vitamin D receptor (VDR) binds 1,25-dihydroxyvitamin D 3 (1,25D), its high affinity renal endocrine ligand, to signal intestinal calcium and phosphate absorption plus bone remodeling, generating a mineralized skeleton free of rickets/osteomalacia with a reduced risk of osteoporotic fractures. 1,25D/VDR signaling regulates the expression of TRPV6, BGP, SPP1, LRP5, RANKL and OPG, while achieving feedback control of mineral ions to prevent age-related ectopic calcification by governing CYP24A1, PTH, FGF23, PHEX, and klotho transcription. Vitamin D also elicits numerous intracrine actions when circulating 25-hydroxyvitamin D 3, the metabolite reflecting vitamin D status, is converted to 1,25D locally by extrarenal CYP27B1, and binds VDR to promote immunoregulation, antimicrobial defense, xenobiotic detoxification, anti-inflammatory/anticancer actions and cardiovascular benefits. VDR also affects Wnt signaling through direct interaction with β-catenin, ligand-dependently blunting β-catenin mediated transcription in colon cancer cells to attenuate growth, while potentiating β-catenin signaling via VDR ligand-independent mechanisms in osteoblasts and keratinocytes to function osteogenically and as a pro-hair cycling receptor, respectively. Finally, VDR also drives the mammalian hair cycle in conjunction with the hairless corepressor by repressing SOSTDC1, S100A8/S100A9, and PTHrP. Hair provides a shield against UV-induced skin damage and cancer in terrestrial mammals, illuminating another function of VDR that facilitates healthful aging.

Involvement of HIF-1alpha in UVB-induced epidermal hyperplasia.

Keratinocyte overgrowth after UVB exposure is believed to contribute to skin photoageing and cancer development. However, little is known about the transcription factors that epigenetically regulate keratinocyte response to UVB. Recently, HIF-1alpha was found to play a role in epidermal homeostasis by controlling the keratinocyte cell cycle, and thus, we hypothesized that HIF-1alpha is involved in UVB-induced keratinocyte growth. In cultured keratinocytes, HIF-1alpha was found to be down-regulated shortly after UVB exposure and to be involved in UVB-induced proliferation. In mice repeatedly treated with UVB, the epidermis became hyperplasic and keratinocytes lacked HIF-1alpha in nuclei. Based on these results, we suggest that the deregulation of HIF-1alpha is associated with UVB-induced hyperplasia of the epidermis. This work provides insight of the molecular mechanism underlying UV-induced photoageing and skin cancer development.

Prevention of non-melanoma skin cancer in organ transplant patients by regular use of a sunscreen: a 24 months, prospective, case-control study

Skin cancers represent a major challenge within the ever growing group of long time surviving organ transplant recipients (OTR) world wide. Especially UV-induced non-melanoma skin cancers (NMSC) like invasive squamous cell carcinomas (SCC) and actinic keratoses (AK), and basal cell carcinoma (BCC), outnumber every other form of cancer in organ transplant recipients. Despite encouraging reports of protective effects of broad-spectrum sunscreens in immunocompetent patients, evidence for the prevention of NMSC in immunocompromised patients is still missing. To assess preventive effects of regular sun-screen use on AK, SCC and BCC in chronically immunocompromised organ transplant recipients. Hundred and twenty matched (age, sex, skin type, graft, transplant duration, previous post-transplant skin malignancies) organ transplant recipients (40 heart, 40 kidney, 40 liver grafted) were recruited for this prospective, single-center study. Both groups received equally written and oral information on sun protection measures. Sixty patients were provided with a free broad spectrum study-sunscreen (SPF>50, high-UVA absorption) for daily application of 2 mg cm(-2) to the head, neck, forearms, and hands. All 120 patients completed the 24 months study. Within this 24 month study interval 42 of the 120 patients developed 82 new AK (-102 sunscreen group vs. +82 control; P<0.01), 8 new invasive SCC (0 vs. 8; P<0.01) and 11 BCC (2 vs. 9; ns). In spite of equal numbers of AK at baseline, a marked difference in favor of the intent-to-treat sunscreen group was recorded after 24 months (89 vs. 273; P<0.01, mean difference 3.07 [1.76-4.36]) and the lesion count was significantly lower as compared to the initial visit (89 vs. 191; P<0.01, mean difference 1.7 [0.68-2.72]). With an average of 5.6 applications per week throughout the 24 months the study sunscreen was generally well tolerated. Serum 25-hydroxy vitamin D levels as marker for vitamin D status were decreased in all patients without adequate substitution and 25(OH)D was found to be lower in the sunscreen-group as compared to the control group (mean value 53 ng mL(-1) vs. 60 ng mL(-1)). Regular use of sunscreens, as part of a consequent UV-protection strategy, may prevent the development of further AK and invasive SCC and, to a lesser degree, BCC in immune-compromised organ transplant recipients.