Early Events in UV Carcinogenesis—DNA Damage, Target Cells and Mutant p53 Foci

Ultraviolet B-induced LGI3 secretion protects human keratinocytes

Leucine-rich glioma inactivated 3 (LGI3) is known to be expressed mainly in the brain. However, the expression and physiological roles of LGI3 in skin cells remain unknown. In this study, it was found for the first time that LGI3 is expressed mostly by normal human keratinocytes. Furthermore, ELISA analysis showed that HaCaT human keratinocytes increased LGI3 secretion after exposure to ultraviolet B (UVB) in a time- and dose-dependent manner. We next investigated the possible role of LGI3 in keratinocytes. LGI3 (50 ng/ml) increased survival of HaCaT cells by 20% after UVB irradiation (150 mJ/cm(2) ). It was also found that LGI3 stimulates the phosphorylation of Akt, which is involved in the cell survival-signalling cascade. Furthermore, LGI3 led to the phosphorylation of MDM2 and subsequent p53 degradation. Taken together, the data suggest that LGI3 may regulate p53 levels and that keratinocyte-derived LGI3 may act as a novel cytokine for skin homoeostasis.

SKHIN/Sprd, a new genetically defined inbred hairless mouse strain for UV-induced skin carcinogenesis studies

Strains of mice vary in their susceptibility to ultra-violet (UV) radiation-induced skin tumors. Some strains of hairless mice (homozygous for the spontaneous Hr(hr) mutation) are particularly susceptible to these tumors. The skin tumors that develop in hairless mice resemble, both at the morphologic and molecular levels, UV-induced squamous cell carcinomas (SCC) and their precursors in human. The most commonly employed hairless mice belong to the SKH1 stock. However, these mice are outbred and their genetic background is not characterized, which makes them a poor model for genetic studies. We have developed a new inbred strain from outbred SKH1 mice that we named SKHIN/Sprd (now at generation F31). In order to characterize the genetic background of this new strain, we genotyped a cohort of mice at F30 with 92 microsatellites and 140 single nucleotide polymorphisms (SNP) evenly distributed throughout the mouse genome. We also exposed SKHIN/Sprd mice to chronic UV irradiation and showed that they are as susceptible to UV-induced skin carcinogenesis as outbred SKH1 mice. In addition, we proved that, albeit with low efficiency, inbred SKHIN/Sprd mice are suitable for transgenic production by classical pronuclear microinjection. This new inbred strain will be useful for the development of transgenic and congenic strains on a hairless inbred background as well as the establishment of syngeneic tumor cell lines. These new tools can potentially help elucidate a number of features of the cutaneous response to UV irradiation in humans, including the effect of genetic background and modifier genes.

Functional interplay between p63 and p53 controls RUNX1 function in the transition from proliferation to differentiation in human keratinocytes

The interfollicular epidermis is continuously renewed, thanks to a regulated balance between proliferation and differentiation. The ΔNp63 transcription factor has a key role in the control of this process. It has been shown that ΔNp63 directly regulates Runt-related transcription factor 1 (RUNX1) transcription factor expression in mouse keratinocytes. The present study showed for the first time that RUNX1 is expressed in normal human interfollicular epidermis and that its expression is tightly regulated during the transition from proliferation to differentiation. It demonstrated that ΔNp63 directly binds two different RUNX1 regulatory DNA sequences and modulates RUNX1 expression differentially in proliferative or differentiated human keratinocytes. It also showed that the regulation of RUNX1 expression by ΔNp63 is dependent on p53 and that this coregulation relies on differential binding and activation of RUNX1 regulatory sequences by ΔNp63 and p53. We also found that RUNX1 inhibits keratinocyte proliferation and activates directly the expression of KRT1, a critical actor in early keratinocyte differentiation. Finally, we described that RUNX1 expression, similar to ΔNp63 and p53, was strongly expressed and downregulated in basal cell carcinomas and squamous cell carcinomas respectively. Taken together, these data shed light on the importance of tight control of the functional interplay between ΔNp63 and p53 in regulating RUNX1 transcription factor expression for proper regulation of interfollicular epidermal homeostasis.

Chemical consequences of cutaneous photoageing

Human skin, in common with other organs, ages as a consequence of the passage of time, but in areas exposed to solar ultraviolet radiation, the effects of this intrinsic ageing process are exacerbated. In particular, both the severity and speed of onset of age-related changes, such as wrinkle formation and loss of elasticity, are enhanced in photoaged (also termed extrinsically aged) as compared with aged, photoprotected, skin. The anatomy of skin is characterised by two major layers: an outer, avascular, yet highly cellular and dynamic epidermis and an underlying vascularised, comparatively static and cell-poor, dermis. The structural consequences of photoageing are mainly evident in the extracellular matrix-rich but cell-poor dermis where key extracellular matrix proteins are particularly susceptible to photodamage. Most investigations to date have concentrated on the cell as both a target for and mediator of, ultraviolet radiation-induced photoageing. As the main effectors of dermal remodelling produced by cells (extracellular proteases) generally have low substrate specificity, we recently suggested that the differential susceptibility of key extracellular matrix proteins to the processes of photoageing may be due to direct, as opposed to cell-mediated, photodamage.

In this review, we discuss the experimental evidence for ultraviolet radiation (and related reactive oxygen species)-mediated differential degradation of normally long lived dermal proteins including the fibrillar collagens, elastic fibre components, glycoproteins and proteoglycans. Whilst these components exhibit highly diverse primary and hence macro- and supra-molecular structures, we present evidence that amino acid composition alone may be a useful predictor of age-related protein degradation in both photoexposed and, as a consequence of differential oxidation sensitivity, photoprotected, tissues.

Infrequent p53 gene mutation but UV gradient-like p53 protein positivity in keloids

Keloids are characterized by extreme fibroblastic overgrowth of unknown pathogenesis after skin injury. Previous studies, mostly in non-Caucasian populations, suggest that p53 mutations may be involved. To substantiate this, we performed DNA sequence analysis of exons 4-8 of the p53 gene and immunohistochemical staining of p53 protein in archived keloidal tissue samples from 23 Caucasian patients. In contrast to previous reports, we found mutated p53 in keloidal tissue in a minority of cases (2/23; 12%). The G allele frequency and C allele frequency at the p53 polymorphic codon 72 were 0.72 (33/46) and 0.28 (13/46), respectively, in our study, a finding that was similar to the 0.77 (184/240) vs. 0.23 (56/240) (P = 0.4580; chi-squared test) observed in the Hap Map data of a European population but statistically significantly different from the 0.43 (547/1258) vs. 0.57 (711/1258) (P = 0.0002; chi-squared test) observed in the 1000 Genome project [Database of Single Nucleotide Polymorphisms (dbSNP). Bethesda (MD): National Center for Biotechnology Information, National Library of Medicine. dbSNP accession:rs1042522, (dbSNP Build ID: 132). Available from: (http://www.ncbi.nlm.nih.gov/SNP/] a difference most likely due to the different genetic background of the populations enrolled. However, one-third of the keloidal samples showed lesional nuclear p53 staining with a UV penetration gradient-like positivity (P ≤ 0.0084). Staining with an anti-cyclobutane pyrimidine dimer antibody revealed the total absence of short-term photoproducts in the epidermis as well as keloidal tissue. Furthermore, all fibroblasts expressing p53 stained negative for Ki-67, indicating that these cells were in a quiescent stage and p53 upregulation did not contribute to keloidal proliferation. We conclude that p53 plays no major role in the pathogenesis of keloids in the Caucasian population.

Poly(ADP-ribose) polymerase-1 inhibition by arsenite promotes the survival of cells with unrepaired DNA lesions induced by UV exposure

Human arsenic exposure is associated with increased risk of skin cancer, and arsenite greatly enhances ultraviolet (UV)-induced skin tumors in a mouse model of carcinogenesis. Inhibition of DNA repair is one proposed mechanism for the observed cocarcinogenicity. We have previously demonstrated that low concentrations of arsenite inhibit poly(ADP-ribose) polymerase (PARP)-1, thus interfering with DNA repair process triggered by UV radiation. Because overactivation of PARP-1 often leads to apoptotic cell death, and unrepaired DNA lesions promote genomic instability and carcinogenesis, we hypothesized that inhibition of PARP-1 by arsenic may promote the survival of potentially "initiated carcinogenic cells," i.e., cells with unrepaired DNA lesions. In the present study, we tested this hypothesis on UV-challenged HaCat cells. Cells were pretreated with 2μM arsenite for 24 h before UV exposure. Outcome parameters included apoptotic death rate, PARP-1 activation, apoptotic molecules, and retention of DNA lesions. UV exposure induced PARP-1 activation and associated poly(ADP-ribose) production, apoptosis-inducing factor release, cytochrome C release, and caspases activation, which led to apoptotic death in HaCat cells. Pretreatment with 2μM arsenite significantly inhibited UV-induced cell death as well as the associated molecular events. Notably, knockdown of PARP-1 with small interfering RNA completely abolished the antagonism of arsenite. Furthermore, arsenite pretreatment led to long-term retention of UV-induced cyclobutane pyrimidine dimers. Together, these results suggest that low concentration of arsenite reduces UV-induced apoptosis via inhibiting PARP-1, thus promoting the survival of cells with unrepaired DNA lesions, which may be an important mechanism underlying arsenic cocarcinogenic action.

Tualang honey protects keratinocytes from ultraviolet radiation-induced inflammation and DNA damage

Malaysian tualang honey possesses strong antioxidant and anti-inflammatory properties. Here, we evaluated the effect of tualang honey on early biomarkers of photocarcinogenesis employing PAM212 mouse keratinocyte cell line. Keratinocytes were treated with tualang honey (1.0%, v/v) before a single UVB (150 mJ cm(-2) ) irradiation. We found that the treatment of tualang honey inhibited UVB-induced DNA damage, and enhanced repair of UVB-mediated formation of cyclobutane pyrimidine dimers and 8-oxo-7,8-dihydro-2'-deoxyguanosine. Treatment of tualang honey inhibited UVB-induced nuclear translocation of NF-κB and degradation of IκBα in murine keratinocyte cell line. The treatment of tualang honey also inhibited UVB-induced inflammatory cytokines and inducible nitric oxide synthase protein expression. Furthermore, the treatment of tualang honey inhibited UVB-induced COX-2 expression and PGE2 production. Taken together, we provide evidence that the treatment of tualang honey to keratinocytes affords substantial protection from the adverse effects of UVB radiation via modulation in early biomarkers of photocarcinogenesis and provide suggestion for its photochemopreventive potential.

Pomegranate fruit extract inhibits UVB-induced inflammation and proliferation by modulating NF-κB and MAPK signaling pathways in mouse skin

There is considerable interest in the identification of natural agents capable of affording protection to skin from the adverse effects of solar ultraviolet B (UVB) radiation. Pomegranate (Punica granatum L.) fruit possesses as strong antioxidant, anti-inflammatory and antiproliferative properties. Recently, we have shown that oral feeding of pomegranate fruit extract (PFE) to mice afforded substantial protection from the adverse effects of single UVB radiation via modulation in early biomarkers of photocarcinogenesis. This study was designed to investigate the photochemopreventive effects of PFE (0.2%, wt/vol) after multiple UVB irradiations (180 mJ cm(-2), on alternative day, for a total of seven treatments) to the skin of SKH-1 hairless mice. Oral feeding of PFE to SKH-1 mice inhibited UVB-induced epidermal hyperplasia, infiltration of leukocytes, protein oxidation and lipid peroxidation. Immunoblot analysis demonstrated that oral feeding of PFE to mice inhibited UVB-induced (1) nuclear translocation and phosphorylation of nuclear factor kappa B/p65, (2) phosphorylation and degradation of IκBα, (3) activation of IKKα/ΙΚΚβ and (4) phosphorylation of mitogen-activated protein kinase proteins and c-Jun. PFE consumption also inhibited UVB-induced protein expression of (1) COX-2 and iNOS, (2) PCNA and cyclin D1 and (3) matrix metalloproteinases-2,-3 and -9 in mouse skin. Taken together, these data show that PFE consumption afforded protection to mouse skin against the adverse effects of UVB radiation by modulating UVB-induced signaling pathways.

Chronic UVR causes increased immunostaining of CD44 and accumulation of hyaluronan in mouse epidermis

Chronic intense UV radiation is the main cause of epidermal tumors. Because hyaluronan (HA), a large extracellular polysaccharide, is known to promote malignant growth, hyaluronan expression was studied in a model in which long-term UV radiation (UVR) induces epidermal tumors. Mouse back skin was exposed three times a week for 10.5 months to UVR corresponding to one minimal erythema dose, processed for histology, and stained for hyaluronan and the hyaluronan receptor CD44. This exposure protocol caused epidermal hyperplasia in most of the animals; tumors, mainly squamous cell carcinomas (SCCs), were found in ~20% of the animals. Specimens exposed to UVR showed increased hyaluronan and CD44 staining throughout the epidermal tissue. In hyperplastic areas, hyaluronan and CD44 stainings correlated positively with the degree of hyperplasia. Well-differentiated SCCs showed increased hyaluronan and CD44 staining intensities, whereas poorly differentiated tumors and dysplastic epidermis showed areas where HA and CD44 were locally reduced. The findings indicate that HA and CD44 increase in epidermal keratinocytes in the premalignant hyperplasia induced by UV irradiation and stay elevated in dysplasia and SCC, suggesting that the accumulation of hyaluronan and CD44 is an early marker for malignant transformation and may be a prerequisite for tumor formation.

UV-B induced alteration in purinergic receptors and signaling on HaCaT keratinocytes

Although there are a number of recognized risk factors resulting in cutaneous malignancies, very little is known about the exact mechanism. In keratinocytes different purinergic receptors have been implicated to play essential roles in deciding the fate of the cells through regulating proliferation and differentiation. While P2Y receptors seem to control the former, P2X receptors, among which the P2X(7) receptor is associated with the induction of apoptosis, are likely to be responsible for the latter. Forty mJ/cm(2) UV-B irradiation decreased the number of viable cells as assessed using MTT assay. This irradiation decreased the amount of both P2X(1) and P2Y(2) receptors and essentially destroyed the P2X(7) receptors in surviving cells. Morphology of ATP-induced Ca(2+) transients were altered in irradiated cells compared to control. The amplitude and the rate of rise of the transients were decreased and the return to resting [Ca(2+)](i) prolonged. This observation is consistent with the finding that in control cells mostly ionotropic, while in irradiated cells mostly metabotropic receptors were underlying the response to ATP. These alterations in the expression pattern of purinergic receptors and in the Ca(2+) transients could explain the observed decreased tendency for ATP-induced apoptosis and possibly contribute to the malignant transformation of keratinocytes.

UV-induced immunosuppression and the efficacy of vaccination

Exposure to ultraviolet radiation (UVR) suppresses immunity by complex pathways, initiated by chromophores located in the skin and ending with the generation of specific subsets of T and B regulatory cells. The primary and memory (recall) immune response to a wide variety of antigens, including microorganisms, can be reduced by UVR, leading to the possibility that the efficacy of vaccination could be similarly reduced. A limited number of animal models of vaccination demonstrate that this may indeed be the case. The situation in human subjects has not been rigorously assessed but there are indications from a variety of sources that UVR adversely affects the immune responses to several vaccines. These studies are reviewed and the implications for vaccine administration discussed. As vaccination represents a major public health measure world-wide for the control of an increasing number of common infections, it is important to maximise its efficacy; therefore further evaluation of UVR in the context of vaccination is required and warranted.

Expression of human endogenous retrovirus K is stimulated by ultraviolet radiation in melanoma

Human endogenous retroviruses (HERVs) represent a cellular reservoir of potentially pathogenic retroviral genes. A growing body of evidence indicates that the activation of endogenous retroviral sequences might be involved in the transformation of melanocytes. In this study, we investigated the effects of ultraviolet radiation (UVR) on the expression of human endogenous retrovirus type K (HERV-K) in melanoma cells and non-melanoma cells in vitro. Solely in melanoma cell lines, irradiation with UVB (200 mJ/cm(2)) resulted in a significant transcriptional activation of the retroviral pol gene as well as in an enhanced expression of the retroviral envelope protein (env). In addition, UVB treatment induced the production of retroviral particles in the supernatants of melanoma cell lines. These data indicate that HERV-K expression can be activated by UVB irradiation and suggest an involvement of HERV-K in UVR-related melanoma pathogenesis.

BRM and BRG1 subunits of the SWI/SNF chromatin remodelling complex are downregulated upon progression of benign skin lesions into invasive tumours

Background  Nonmelanoma skin cancer is caused by exposure to ultraviolet radiation within sunlight. Actinic keratoses (AKs) are benign precursor lesions that can develop into invasive squamous cell carcinoma (SCC). Little is known about the molecular events that lead to human skin cancer progression from benign to invasive. Objectives  To determine novel genes that may be involved in skin cancer progression based on data from an initial microarray screen of human skin cancers. Methods  The SWI/SNF chromatin remodelling ATPase subunit BRM was identified as being downregulated in SCC but not AK compared with normal skin in our microarray screen. Therefore reverse transcription-polymerase chain reaction, gene methylation and protein expression was used to study BRM and its alternative ATPase subunit BRG1 in a range of human skin cancers. Results  We found reduced levels of mRNA coding for BRM but not BRG1 in SCC. BRM mRNA levels in AK were similar to those in normal skin. Deregulation of BRM did not result from hypermethylation of CpG regions in the promoter of these genes. Both BRM and BRG1 protein was reduced by about 10-fold in 100% of SCC and basal cell carcinoma, but not in AK specimens examined. Conclusions  BRM protein may be decreased due to low levels of mRNA, while BRG1 protein loss appears to be post-translational. BRM and BRG1 may be novel tumour suppressor genes for human skin cancer. They appear to be involved after development of benign lesions, and are downregulated during progression towards invasion.

Caffeine promotes ultraviolet B-induced apoptosis in human keratinocytes without complete DNA repair

In response to ultraviolet B damage, keratinocytes undergo apoptosis to eliminate damaged cells, thereby preventing tumorigenic transformation. Caffeine, the most widely consumed psychoactive substance, produces complex pharmacological actions; it has been shown to be chemopreventive in non-melamona skin cancer in mice through increasing apoptosis. Here we have investigated the molecular and cellular mechanisms in the pro-apoptotic effect of caffeine on UVB-irradiated human HaCaT keratinocytes. Pretreatment with caffeine increased UVB-induced apoptosis in HaCaT cells. Caffeine blocked UVB-induced Chk1 phosphorylation. In addition, similar to the effect of the PI3K inhibitor LY294002, caffeine also inhibited phosphorylation of AKT and up-regulation of COX-2, two critical oncogenic pathways in skin tumorigenesis. However, phosphorylation of EGFR or ERK was unaffected. Inhibiting ATR pathways by siRNA targeting ATR had little effect on UVB-induced apoptosis or AKT activation, indicating that the inhibitory effect of caffeine on apoptosis and the AKT pathway does not require the ATR pathway. Inhibiting AKT by caffeine blocked UVB-induced COX-2 up-regulation. Expression of constitutively active AKT that was not inhibited by caffeine was found to protect cells from caffeine-promoted apoptosis post-UVB irradiation, indicating that AKT is an essential inhibitory target for caffeine to promote apoptosis. Caffeine specifically sensitized cells with unrepaired DNA damage to UVB-induced apoptosis. These findings indicate that in HaCaT keratinocytes, inhibiting the AKT/COX-2 pathways through an ATR-independent pathway is a critical molecular mechanism by which caffeine promotes UVB-induced apoptosis of unrepaired keratinocytes for elimination.

Natural agents: cellular and molecular mechanisms of photoprotection

The skin is the largest organ of the body that produces a flexible and self-repairing barrier and protects the body from most common potentially harmful physical, environmental, and biological insults. Solar ultraviolet (UV) radiation is one of the major environmental insults to the skin and causes multi-tiered cellular and molecular events eventually leading to skin cancer. The past decade has seen a surge in the incidence of skin cancer due to changes in life style patterns that have led to a significant increase in the amount of UV radiation that people receive. Reducing excessive exposure to UV radiation is desirable; nevertheless this approach is not easy to implement. Therefore, there is an urgent need to develop novel strategies to reduce the adverse biological effects of UV radiation on the skin. A wide variety of natural agents have been reported to possess substantial skin photoprotective effects. Numerous preclinical and clinical studies have elucidated that natural agents act by several cellular and molecular mechanisms to delay or prevent skin cancer. In this review article, we have summarized and discussed some of the selected natural agents for skin photoprotection.

The human health effects of ozone depletion and interactions with climate change

Depletion of the stratospheric ozone layer has led to increased solar UV-B radiation (280-315 nm) at the surface of the Earth. This change is likely to have had an impact on human exposure to UV-B radiation with consequential detrimental and beneficial effects on health, although behavioural changes in society over the past 60 years or so with regard to sun exposure are of considerable importance. The present report concentrates on information published since our previous report in 2007. The adverse effects of UV radiation are primarily on the eye and the skin. While solar UV radiation is a recognised risk factor for some types of cataract and for pterygium, the evidence is less strong, although increasing, for ocular melanoma, and is equivocal at present for age-related macular degeneration. For the skin, the most common harmful outcome is skin cancer, including melanoma and the non-melanoma skin cancers, basal cell carcinoma and squamous cell carcinoma. The incidence of all three of these tumours has risen significantly over the past five decades, particularly in people with fair skin, and is projected to continue to increase, thus posing a significant world-wide health burden. Overexposure to the sun is the major identified environmental risk factor in skin cancer, in association with various genetic risk factors and immune effects. Suppression of some aspects of immunity follows exposure to UV radiation and the consequences of this modulation for the immune control of infectious diseases, for vaccination and for tumours, are additional concerns. In a common sun allergy (polymorphic light eruption), there is an imbalance in the immune response to UV radiation, resulting in a sun-evoked rash. The major health benefit of exposure to solar UV-B radiation is the production of vitamin D. Vitamin D plays a crucial role in bone metabolism and is also implicated in protection against a wide range of diseases. Although there is some evidence supporting protective effects for a range of internal cancers, this is not yet conclusive, but strongest for colorectal cancer, at present. A role for vitamin D in protection against several autoimmune diseases has been studied, with the most convincing results to date for multiple sclerosis. Vitamin D is starting to be assessed for its protective properties against several infectious and coronary diseases. Current methods for protecting the eye and the skin from the adverse effects of solar UV radiation are evaluated, including seeking shade, wearing protective clothing and sunglasses, and using sunscreens. Newer possibilities are considered such as creams that repair UV-induced DNA damage, and substances applied topically to the skin or eaten in the diet that protect against some of the detrimental effects of sun exposure. It is difficult to provide easily understandable public health messages regarding "safe" sun exposure, so that the positive effects of vitamin D production are balanced against the negative effects of excessive exposure. The international response to ozone depletion has included the development and deployment of replacement technologies and chemicals. To date, limited evidence suggests that substitutes for the ozone-depleting substances do not have significant effects on human health. In addition to stratospheric ozone depletion, climate change is predicted to affect human health, and potential interactions between these two parameters are considered. These include altering the risk of developing skin tumours, infectious diseases and various skin diseases, in addition to altering the efficiency by which pathogenic microorganisms are inactivated in the environment.

Oral feeding of pomegranate fruit extract inhibits early biomarkers of UVB radiation-induced carcinogenesis in SKH-1 hairless mouse epidermis

Pomegranate from the plant Punica granatum L. possesses strong antioxidant and anti-inflammatory properties. Recently, we have demonstrated that treatment of normal human epidermal keratinocytes with pomegranate fruit extract (PFE) inhibited UVB-mediated activation of nuclear factor kappa B (NF-κB) and mitogen activated protein kinases pathways. Here, we evaluated the effect of PFE on early biomarkers of photocarcinogenesis employing SKH-1 hairless mice. PFE was provided in drinking water (0.2%, wt/vol) to SKH-1 hairless mice for 14 days before a single UVB (180 mJ cm(-2)) irradiation. We found that oral feeding of PFE inhibited UVB-induced: (1) skin edema; (2) hyperplasia; (3) infiltration of leukocytes; (4) lipid peroxidation; (5) hydrogen peroxide generation; (6) ornithine decarboxylase (ODC) activity; and (7) ODC, cyclooxygenase-2 and proliferating cell nuclear antigen protein expression. Oral feeding of PFE enhanced repair of UVB-mediated formation of cyclobutane pyrimidine dimers (CPDs) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG). Importantly, PFE treatment further enhanced UVB-mediated increase in tumor suppressor p53 and cyclin kinase inhibitor p21. Furthermore, oral feeding of PFE inhibited UVB-mediated: (1) nuclear translocation of NF-κB; (2) activation of IKKα; and (3) phosphorylation and degradation of IκBα. Taken together, we provide evidence that oral feeding of PFE to mice affords substantial protection from the adverse effects of UVB radiation via modulation in early biomarkers of photocarcinogenesis and provide suggestion for its photochemopreventive potential.

UVB-Induced p21 degradation promotes apoptosis of human keratinocytes

Skin cancer is the most common cancer in the United States. Ultraviolet B (UVB) radiation in sunlight is the major environmental factor causing skin cancer. p21, a p53-inducible protein, plays an important role in cell cycle, DNA repair, and apoptosis. Here we have investigated the effect of UVB radiation on p21 and its molecular mechanisms and function in human HaCaT keratinocytes, which we used as a premalignant cellular model because normal skin harbors numerous clones of p53-mutated keratinocytes. We found that in human HaCaT keratinocytes UVB induces rapid p21 down-regulation via a proteasomal degradation mechanism. In p53-defective HaCaT cells, the p21 protein levels remain decreased at a later time post-UVB, but in normal human and mouse epidermal keratinocytes with wild-type p53 the p21 levels are initially reduced but later increase post-UVB. These findings indicate that loss of p53 function leads to sustained p21 down-regulation in response to UVB damage. Degradation of p21 following UVB radiation does not require ATR, ATM, or both, because either the ATR/ATM inhibitor caffeine or siRNA knockdown of ATR, ATM, or both failed to reverse p21 degradation. However, inhibiting MDM2 or GSK3β partially reduced UVB-induced p21 degradation, while inhibiting both enzymes completely prevented it. Restoring the p21 protein levels in UVB-irradiated keratinocytes reduced apoptosis. Although at the molecular level increasing p21 expression has no effect on the protein levels of the Bcl-2 family members, it enhances the activation of AKT, a critical survival pathway to protect cells from apoptosis. Our results suggest a distinct mechanism of p21 degradation in keratinocytes by UVB, and this p21 degradation may significantly enhance UVB-induced apoptosis of premalignant keratinocytes with a p53 defect to eliminate damaged cells and therefore prevent skin cancer development.

Basal cell carcinoma: what's new under the sun

Basal cell carcinoma (BCC) is the most common skin cancer in white populations with an increasing incidence worldwide, thereby imposing an important public health problem. Its etiology is still unclear, but existing data indicate that the risk for BCC development is of multifactorial origin and results from the interplay of both constitutional and environmental factors. Yet, UV radiation (UVR) is believed to be the predominant causative risk factor in the pathogenesis of BCC. For years, BCC and squamous cell carcinoma (SCC) have been grouped together as "nonmelanoma skin cancer." However, it seems that there are considerable biologic differences between BCC and SCC, and thus each type of epithelial cancer should be addressed separately. The present review provides an overview of the intriguing etiologic link of BCC with UVR and attempts a comprehensive review of recent epidemiologic and molecular evidence that supports this association.

Season of birth and diagnosis for childhood cancer in Northern England, 1968-2005

The aim of this study was to investigate seasonal variation in the incidence of cancer in children aged 0-14 years. Details of 2959 primary malignant cases (1659 males, 1300 females), diagnosed during the period 1968-2005, were extracted from a specialist registry (the Northern Region Young Persons' Malignant Disease Registry). Seasonal variation was analysed with respect to month of birth and diagnosis. The chi-squared heterogeneity test was used to test for non-uniform variation. Poisson regression analysis was used to fit sinusoidal (harmonic) models to the data, using month of birth and month of diagnosis, respectively, as covariates in separate models. There was significant sinusoidal variation based on month of birth for acute lymphoblastic leukaemia (ALL) aged 1-6 years (P = 0.04; peak in March). For 0- to 14-year-old boys, there was statistically significant sinusoidal variation in month of birth for acute non-lymphocytic leukaemia (P = 0.04; peak in September) and astrocytoma (P = 0.03; peak in October). Based on month of diagnosis, there was statistically significant sinusoidal variation in girls for all lymphomas (P = 0.048; peak in March) and Hodgkin lymphoma (HL) (P = 0.005; peak in January), and in boys for osteosarcoma (P = 0.049; peak in October). This study confirms previous findings of seasonal variation around the month of birth for childhood ALL (at the peak ages) and provides further evidence of seasonal variation around month of birth for astrocytoma and around month of diagnosis for HL. The results are consistent with a role for environmental factors in the aetiology of these diagnostic groups. Further studies are needed to examine putative candidate agents.

Reduction of IKKalpha expression promotes chronic ultraviolet B exposure-induced skin inflammation and carcinogenesis

Ultraviolet B light (UVB) is a common cause of human skin cancer. UVB irradiation induces mutations in the tumor suppressor p53 gene as well as chronic inflammation, which are both essential for UVB carcinogenesis. Inhibitor of nuclear factor kappaB kinase-alpha (IKKalpha) plays an important role in maintaining skin homeostasis, and expression of IKKalpha was found to be down-regulated in human and murine skin squamous cell carcinomas. However, the role of IKKalpha in UVB skin carcinogenesis has not been investigated. Thus, here we performed UVB carcinogenesis experiments on Ikkalpha(+/+) and Ikkalpha(+/-) mice. Ikkalpha(+/-) mice were found to develop a twofold greater number of skin tumors than Ikkalpha(+/+) mice after chronic UVB irradiation. In addition, tumor latency was significantly shorter and tumors were bigger in Ikkalpha(+/-) than in Ikkalpha(+/+) mice. At an early stage of carcinogenesis, an increase in UVB-induced p53 mutations as well as macrophage recruitment and mitogenic activity, and a decrease in UVB-induced apoptosis, were detected in Ikkalpha(+/-) compared with those in Ikkalpha(+/+) skin. Also, reduction of IKKalpha levels in keratinocytes up-regulated the expression of monocyte chemoattractant protein-1 (MCP-1/CCL2), TNFalpha, IL-1, and IL-6, and elevated macrophage migration, which might promote macrophage recruitment and inflammation. Therefore, these findings suggest that reduction of IKKalpha expression orchestrates UVB carcinogen, accelerating tumorigenesis.

Arsenite induced poly(ADP-ribosyl)ation of tumor suppressor P53 in human skin keratinocytes as a possible mechanism for carcinogenesis associated with arsenic exposure

Arsenite is an environmental pollutant. Exposure to inorganic arsenic in drinking water is associated with elevated cancer risk, especially in skin. Arsenite alone does not cause skin cancer in animals, but arsenite can enhance the carcinogenicity of solar UV. Arsenite is not a significant mutagen at non-toxic concentrations, but it enhances the mutagenicity of other carcinogens. The tumor suppressor protein P53 and nuclear enzyme PARP-1 are both key players in DNA damage response. This laboratory demonstrated earlier that in cells treated with arsenite, the P53-dependent increase in p21(WAF1/CIP1) expression, normally a block to cell cycle progression after DNA damage, is deficient. Here we show that although long-term exposure of human keratinocytes (HaCaT) to a nontoxic concentration (0.1 microM) of arsenite decreases the level of global protein poly(ADP-ribosyl)ation, it increases poly(ADP-ribosyl)ation of P53 protein and PARP-1 protein abundance. We also demonstrate that exposure to 0.1 microM arsenite depresses the constitutive expression of p21 mRNA and P21 protein in HaCaT cells. Poly(ADP-ribosyl)ation of P53 is reported to block its activation, DNA binding and its functioning as a transcription factor. Our results suggest that arsenite's interference with activation of P53 via poly(ADP-ribosyl)ation may play a role in the comutagenic and cocarcinogenic effects of arsenite.

PKCepsilon overexpression, irrespective of genetic background, sensitizes skin to UVR-induced development of squamous-cell carcinomas

Chronic exposure to UVR is the major etiologic factor in the development of human skin cancers including squamous-cell carcinoma (SCC). We have previously shown that protein Kinase C epsilon (PKCepsilon) transgenic mice on FVB/N background, which overexpress PKCepsilon protein approximately eightfold over endogenous levels in epidermis, exhibit about threefold more sensitivity than wild-type littermates to UVR-induced development of SCC. To determine whether it is PKCepsilon and not the mouse genetic background that determines susceptibility to UVR carcinogenesis, we cross-bred PKCepsilon FVB/N transgenic mice with SKH-1 hairless mice to generate PKCepsilon-overexpressing SKH-1 hairless mice. To evaluate the susceptibility of PKCepsilon SKH-1 hairless transgenic mice to UVR carcinogenesis, the mice were exposed to UVR (1-2 KJ m(-2)) three times weekly from a bank of six kodacel-filtered FS40 sunlamps. As compared with the wild-type hairless mice, PKCepsilon overexpression in SKH-1 hairless mice decreased the latency (12 weeks), whereas it increased the incidence (twofold) and multiplicity (fourfold) of SCC. The SKH hairless transgenic mice were observed to be as sensitive as FVB/N transgenic mice to UVR-induced development of SCC and expression of proliferative markers (proliferating cell nuclear antigen, signal transducers and activators of transcription 3, and extracellular signal-regulated kinase 1/2). The results indicate that PKCepsilon level dictates susceptibility, irrespective of genetic background, to UVR carcinogenesis.

Protective effect of pomegranate-derived products on UVB-mediated damage in human reconstituted skin

Solar ultraviolet (UV) radiation, particularly its UVB (290-320 nm) component, is the primary cause of many adverse biological effects including photoageing and skin cancer. UVB radiation causes DNA damage, protein oxidation and induces matrix metalloproteinases (MMPs). Photochemoprevention via the use of botanical antioxidants in affording protection to human skin against UVB damage is receiving increasing attention. Pomegranate, from the tree Punica granatum, contains anthocyanins and hydrolysable tannins and possesses strong antioxidant and anti-tumor-promoting properties. In this study, we determined the effect of pomegranate-derived products--POMx juice, POMx extract and pomegranate oil (POMo)--against UVB-mediated damage using reconstituted human skin (EpiDerm(TM) FT-200). EpiDerm was treated with POMx juice (1-2 microl/0.1 ml/well), POMx extract (5-10 microg/0.1 ml/well) and POMo (1-2 microl/0.1 ml/well) for 1 h prior to UVB (60 mJ/cm(2)) irradiation and was harvested 12 h post-UVB to assess protein oxidation, markers of DNA damage and photoageing by Western blot analysis and immunohistochemistry. Pretreatment of Epiderm with pomegranate-derived products resulted in inhibition of UVB-induced (i) cyclobutane pyrimidine dimers (CPD), (ii) 8-dihydro-2'-deoxyguanosine (8-OHdG), (iii) protein oxidation and (iv) proliferating cell nuclear antigen (PCNA) protein expression. We also found that pretreatment of Epiderm with pomegranate-derived products resulted in inhibition of UVB-induced (i) collagenase (MMP-1), (ii) gelatinase (MMP-2, MMP-9), (iii) stromelysin (MMP-3), (iv) marilysin (MMP-7), (v) elastase (MMP-12) and (vi) tropoelastin. Gelatin zymography revealed that pomegranate-derived products inhibited UVB-induced MMP-2 and MMP-9 activities. Pomegranate-derived products also caused a decrease in UVB-induced protein expression of c-Fos and phosphorylation of c-Jun. Collectively, these results suggest that all three pomegranate-derived products may be useful against UVB-induced damage to human skin.

Ultraviolet A within sunlight induces mutations in the epidermal basal layer of engineered human skin

The ultraviolet B (UVB) waveband within sunlight is an important carcinogen; however, UVA is also likely to be involved. By ascribing mutations to being either UVB or UVA induced, we have previously shown that human skin cancers contain similar numbers of UVB- and UVA-induced mutations, and, importantly, the UVA mutations were at the base of the epidermis of the tumors. To determine whether these mutations occurred in response to UV, we exposed engineered human skin (EHS) to UVA, UVB, or a mixture that resembled sunlight, and then detected mutations by both denaturing high-performance liquid chromatography and DNA sequencing. EHS resembles human skin, modeling differential waveband penetration to the basal, dividing keratinocytes. We administered only four low doses of UV exposure. Both UVA and UVB induced p53 mutations in irradiated EHS, suggesting that sunlight doses that are achievable during normal daily activities are mutagenic. UVA- but not UVB-induced mutations predominated in the basal epidermis that contains dividing keratinocytes and are thought to give rise to skin tumors. These studies indicate that both UVA and UVB at physiological doses are mutagenic to keratinocytes in EHS.

Papillomaviruses in the causation of human cancers - a brief historical account

Approximately 35 years ago a role of human papillomaviruses (HPV) in cervical cancer has been postulated. Today it is well established that this very heterogeneous virus family harbours important human carcinogens, causing not only the vast majority of cervical, but also a substantial proportion of other anogenital and head and neck cancers. In addition, specific types have been linked to certain cutaneous cancers. In females, HPV infections on a global scale account for more than 50% of infection-linked cancers, in males for barely 5%. Vaccines against the high risk HPV types 16 and 18 represent the first preventive vaccines directly developed to protect against a major human cancer (cervical carcinoma). This review will cover some of the historical aspects of papillomavirus research; it tries briefly to analyze the present state of linking HPV to human cancers and will discuss some emerging developments.