Distinct effects of ultraviolet B light on antioxidant expression in undifferentiated and differentiated mouse keratinocytes

Microsomal glutathione transferase 1 in cancer and the regulation of ferroptosis

Microsomal glutathione transferase 1 (MGST1) is a member of the MAPEG family (membrane associated proteins in eicosanoid and glutathione metabolism), defined according to enzymatic activities, sequence motifs, and structural properties. MGST1 is a homotrimer which can bind three molecules of glutathione (GSH), with one modified to a thiolate anion displaying one-third-of-sites-reactivity. MGST1 has both glutathione transferase and peroxidase activities. Each is based on stabilizing the GSH thiolate in the same active site. MGST1 is abundant in the liver and displays a broad subcellular distribution with high levels in endoplasmic reticulum and mitochondrial membranes, consistent with a physiological role in protection from reactive electrophilic intermediates and oxidative stress. In this review paper, we particularly focus on recent advances made in understanding MGST1 activation, induction, broad subcellular distribution, and the role of MGST1 in apoptosis, ferroptosis, cancer progression, and therapeutic responses.

Photoprotective Effects of Dendrobium nobile Lindl. Polysaccharides against UVB-Induced Oxidative Stress and Apoptosis in HaCaT Cells

Acute ultraviolet (UV)-B radiation is the major external factor causing photodamage. In this study, we aimed to determine the effects of Dendrobium nobile Lindl. polysaccharides (DNPs) on photodamage in HaCaT keratinocytes after UVB irradiation and the underlying mechanisms. We found that DNPs significantly attenuated the decline in the viability and proliferation of HaCaT cells after UVB irradiation. Moreover, DNPs scavenged reactive oxygen species (ROS), improved the activities of endogenous antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase, and reduced the levels of malondialdehyde, while partially attenuating cell cycle arrest, suggesting their antioxidant and anti-apoptotic properties. The mitogen-activated protein kinase (MAPK) pathway was found to be important for the attenuation of UVB-induced photodamage in the HaCaT cells. Furthermore, DNPs exerted cytoprotective effects by downregulating UVB-induced ROS-mediated phosphorylation of MAPKs, including p38, c-Jun N-terminal kinase, and extracellular signal-regulated kinase, and by inhibiting p53 expression as well as the apoptotic cascade response. Therefore, DNPs ameliorated UVB-induced oxidative damage and apoptosis in HaCaT cells via the regulation of MAPKs. Our findings thus highlight the Dendrobium nobile Lindl polysaccharides as promising therapeutic candidates for UVB-induced photodamage.

Hyperoside and Quercitrin in Houttuynia cordata Extract Attenuate UVB-Induced Human Keratinocyte Cell Damage and Oxidative Stress via Modulation of MAPKs and Akt Signaling Pathway

Ultraviolet radiation is a major environmental harmful factor on human skin. In this paper, we investigate the potential mechanism of Houttuynia cordata extract on UVB-induced HaCaT keratinocyte cell death and inflammation. We found that Houttuynia cordata ethyl acetate extract fraction (HC-EA) protected against UVB-induced cell damage. The HPLC results indicate that quercitrin and hyperoside are the major polyphenolics in HC-EA and are responsible for providing protection against UVB-induced cell death. These responses were associated with the regulation of caspase-9 and caspase-3 activation, which rescued HaCaT cells from UVB-induced apoptosis. In addition, HC-EA, quercitrin, and hyperoside attenuated UVB-induced inflammatory mediators, including IL-6, IL-8, COX-2, and iNOS. Furthermore, the treatment of cells with HC-EA and its active compounds abolished intracellular ROS and increased levels of heme oxygenase-1 and superoxide dismutase. UVB-induced ROS production mediated Akt and mitogen activated protein kinases (MAPKs) pathways, including p38, ERK, and JNK. Our results show HC-EA, quercitrin, and hyperoside decreased UVB-induced p38 and JNK phosphorylation, while increasing ERK and Akt phosphorylation. MAPKs and Akt mediated cell survival and death were confirmed by specific inhibitors to Akt and MAPKs. Thus, HC-EA, which contains quercitrin and hyperoside, protected keratinocyte from UVB-induced oxidative damage and inflammation through the modulation of MAPKs and Akt signaling.

Nicotinamide Attenuates UV-Induced Stress Damage in Human Primary Keratinocytes from Cancerization Fields

UVB radiation directly damages DNA, increases ROS and nitric oxide (NO) release, and promotes inflammation leading to genomic instability and cell death. Nicotinamide (NAM) is the precursor of NAM adenine dinucleotide, essential for cell energy production and DNA damage repair. NAM protects HaCat cells from UV-induced impairment; however, little is known about its effects on human primary keratinocytes and those isolated from field cancerization (i.e., field cancerization human primary keratinocytes [FC-HPKs]). We examined the role of NAM against UV-induced oxidative stress damages in FC-HPKs, isolated from precancerous lesions and skin cancers, and in normal human epidermal keratinocytes. Cells were treated for 18, 24, and 48 hours with NAM (5, 25, and 50 μM, respectively) before UVB irradiation. FC-HPK showed four-fold higher basal ROS levels than normal human epidermal keratinocytes; NAM downregulated ROS production only in irradiated FC-HPKs, which showed a greater sensibility to UV rays. UV exposure increased OGG1, inducible nitric oxide synthase, and IL-1β expression, an effect counteracted by NAM pretreatment. Intracellular nitric oxide production and DNA damages were inhibited by NAM exposure before irradiation. Collectively, our findings indicate that pretreatment with 25 μM NAM 24 hours before UVB irradiation effectively prevents oxidative stress formation, DNA damage, and inflammation in both normal human epidermal keratinocytes and FC-HPKs.

Synthesis and Evaluation of Chalcone Derivatives as Novel Sunscreen Agent

Ultraviolet (UV) irradiation is a serious problem for skin health thus the interest in the research to develop sunscreen agent has been increasing. Chalcone is a promising compound to be developed as its chromophore absorbs in the UV region. Therefore, in the present work, we synthesized eight chalcone derivatives through Claisen-Schmidt condensation at room temperature. The evaluation of the optical properties of each chalcone derivatives in the UV region was conducted through spectroscopic and computational studies. The synthesized chalcones were obtained in good yields and they were active in the UV region. The results revealed that more methoxy substituents to chalcone leads toward red shift. All chalcone derivatives have high molar absorptivity value (21,000-56,000) demonstrating that they have the potential to be used as the sunscreen agent. The cytotoxicity assay showed that chalcone derivatives were demonstrating low toxicity toward normal human fibroblast cell, which is remarkable. Therefore, we concluded that the synthesized chalcones in this work were potential to be developed as novel sunscreen agents in real application.

Induction of Autophagy by Baicalin Through the AMPK-mTOR Pathway Protects Human Skin Fibroblasts from Ultraviolet B Radiation-Induced Apoptosis

Background

Baicalin, a natural product isolated from Scutellaria radix, has been reported to exert anti-oxidant and anti-apoptotic effects on skin, but the underlying mechanism remains poorly understood. This study aimed to investigate the possible mechanism of anti-UVB effect of baicalin in human skin fibroblasts.

Methods

Cell proliferation was estimated by CCK-8 Kit. Apoptotic incidence was detected by flow cytometry with Annexin V-PE/PI apoptosis detection kit. Autophagy was determined by the evaluation of fluorescent LC3 puncta and Western blotting. Cell signalling was analysed by Western blotting.

Results

Baicalin exerted cytoprotective effects in UVB-induced HSFs. Moreover, baicalin increased autophagy and suppressed UVB-induced apoptosis of HSFs. Pretreatment with 3-MA, an autophagy inhibitor, attenuated baicalin-induced HSFs autophagy and promoted apoptosis. Baicalin activated AMPK, which leads to suppression of basal mTOR activity in cultured HSFs. Administration of compound C, an AMPK inhibitor, abrogated AMPK phosphorylation and increased mTOR phosphorylation and apoptosis compared with baicalin alone.

Conclusion

Taken together, these results indicate the important role of mTOR inhibition in UVB protection by baicalin and provide a new target and strategy for better prevention of UV-induced skin disorders.

Characterization of xenobiotic metabolizing enzymes of a reconstructed human epidermal model from adult hair follicles

In this study, a comprehensive characterization of xenobiotic metabolizing enzymes (XMEs) based on gene expression and enzyme functionality was made in a reconstructed skin epidermal model derived from the outer root sheath (ORS) of hair follicles (ORS-RHE). The ORS-RHE model XME gene profile was consistent with native human skin. Cytochromes P450 (CYPs) consistently reported to be detected in native human skin were also present at the gene level in the ORS-RHE model. The highest Phase I XME gene expression levels were observed for alcohol/aldehyde dehydrogenases and (carboxyl) esterases. The model was responsive to the CYP inducers, 3-methylcholanthrene (3-MC) and β-naphthoflavone (βNF) after topical and systemic applications, evident at the gene and enzyme activity level. Phase II XME levels were generally higher than those of Phase I XMEs, the highest levels were GSTs and transferases, including NAT1. The presence of functional CYPs, UGTs and SULTs was confirmed by incubating the models with 7-ethoxycoumarin, testosterone, benzo(a)pyrene and 3-MC, all of which were rapidly metabolized within 24h after topical application. The extent of metabolism was dependent on saturable and non-saturable metabolism by the XMEs and on the residence time within the model. In conclusion, the ORS-RHE model expresses a number of Phase I and II XMEs, some of which may be induced by AhR ligands. Functional XME activities were also demonstrated using systemic or topical application routes, supporting their use in cutaneous metabolism studies. Such a reproducible model will be of interest when evaluating the cutaneous metabolism and potential toxicity of innovative dermo-cosmetic ingredients.

Nrf2 Regulates the Sensitivity of Mouse Keratinocytes to Nitrogen Mustard via Multidrug Resistance-Associated Protein 1 (Mrp1)

Sulfur mustard and nitrogen mustard (mechlorethamine, HN2) are potent vesicants developed as chemical warfare agents. These electrophilic, bifunctional alkylating agents cause skin injury, including inflammation, edema, and blistering. HN2 covalently modifies macromolecules such as DNA, RNA, and proteins or is scavenged by glutathione, forming adducts that can contribute to toxicity. Multidrug resistance-associated protein 1 (Mrp1/MRP1) is a transmembrane ATPase known to efflux glutathione-conjugated electrophiles. In the present studies, we examined the effects of modulating Mrp1-mediated transport activity on the sensitivity of primary and PAM212 mouse keratinocytes to HN2. Primary keratinocytes, and to a lesser extent, PAM212 cells, express Mrp1 mRNA and protein and possess Mrp1 functional activity, as measured by calcein efflux. Sulforaphane, an activator of Nrf2, increased Mrp1 mRNA, protein, and functional activity in primary keratinocytes and PAM212 cells and decreased their sensitivity to HN2-induced growth inhibition (IC(50) = 1.4 and 4.8 µM in primary keratinocytes and 1 and 13 µM in PAM212 cells, in the absence and presence of sulforaphane, respectively). The Mrp1 inhibitor, MK-571, reversed the effects of sulforaphane on HN2-induced growth inhibition in both primary keratinocytes and PAM212 cells. In primary keratinocytes from Nrf2(-/-) mice, sulforaphane had no impact on Mrp1 expression or activity, or on sensitivity to HN2, demonstrating that its effects depend on Nrf2. These data suggest that Mrp1-mediated efflux is important in regulating HN2-induced keratinocyte growth inhibition. Enhancing HN2 efflux from keratinocytes may represent a novel strategy for mitigating vesicant-induced cytotoxicity.

Oxidatively generated damage to cellular DNA by UVB and UVA radiation

This review article focuses on a critical survey of the main available information on the UVB and UVA oxidative reactions to cellular DNA as the result of direct interactions of UV photons, photosensitized pathways and biochemical responses including inflammation and bystander effects. UVA radiation appears to be much more efficient than UVB in inducing oxidatively generated damage to the bases and 2-deoxyribose moieties of DNA in isolated cells and skin. The UVA-induced generation of 8-oxo-7,8-dihydroguanine is mostly rationalized in terms of selective guanine oxidation by singlet oxygen generated through type II photosensitization mechanism. In addition, hydroxyl radical whose formation may be accounted for by metal-catalyzed Haber-Weiss reactions subsequent to the initial generation of superoxide anion radical contributes in a minor way to the DNA degradation. This leads to the formation of both oxidized purine and pyrimidine bases together with DNA single-strand breaks at the exclusion, however, of direct double-strand breaks. No evidence has been provided so far for the implication of delayed oxidative degradation pathways of cellular DNA. In that respect putative characteristic UVA-induced DNA damage could include single and more complex lesions arising from one-electron oxidation of the guanine base together with aldehyde adducts to amino-substituted nucleobases.

Regulation of keratinocyte expression of stress proteins and antioxidants by the electrophilic nitrofatty acids 9- and 10-nitrooleic acid

Nitric oxide and various by-products including nitrite contribute to tissue injury by forming novel intermediates via redox-mediated nitration reactions. Nitration of unsaturated fatty acids generates electrophilic nitrofatty acids such as 9-nitrooleic acid (9-NO) and 10-nitrooleic acid (10-NO), which are known to initiate intracellular signaling pathways. In these studies, we characterized nitrofatty acid-induced signaling and stress protein expression in mouse keratinocytes. Treatment of keratinocytes with 5-25μM 9-NO or 10-NO for 6h upregulated mRNA expression of heat shock proteins (hsp's) 27 and 70; primary antioxidants heme oxygenase-1 (HO-1) and catalase; secondary antioxidants glutathione S-transferase (GST) A1/2, GSTA3, and GSTA4; and Cox-2, a key enzyme in prostaglandin biosynthesis. The greatest responses were evident with HO-1, hsp27, and hsp70. In keratinocytes, 9-NO activated JNK and p38 MAP kinases. JNK inhibition suppressed 9-NO-induced HO-1, hsp27, and hsp70 mRNA and protein expression, whereas p38 MAP kinase inhibition suppressed HO-1. In contrast, inhibition of constitutive expression of Erk1/2 suppressed only hsp70, indicating that 9-NO modulates expression of stress proteins by distinct mechanisms. 9-NO and 10-NO also upregulated expression of caveolin-1, the major structural component of caveolae. Western blot analysis of caveolar membrane fractions isolated by sucrose density centrifugation revealed that HO-1, hsp27, and hsp70 were localized within caveolae after nitrofatty acid treatment of keratinocytes, suggesting a link between induction of stress response proteins and caveolin-1 expression. These data indicate that nitrofatty acids are effective signaling molecules in keratinocytes. Moreover, caveolae seem to be important in the localization of stress proteins in response to nitrofatty acids.

Modulation of keratinocyte expression of antioxidants by 4-hydroxynonenal, a lipid peroxidation end product

4-Hydroxynonenal (4-HNE) is a lipid peroxidation end product generated in response to oxidative stress in the skin. Keratinocytes contain an array of antioxidant enzymes which protect against oxidative stress. In these studies, we characterized 4-HNE-induced changes in antioxidant expression in mouse keratinocytes. Treatment of primary mouse keratinocytes and PAM 212 keratinocytes with 4-HNE increased mRNA expression for heme oxygenase-1 (HO-1), catalase, NADPH:quinone oxidoreductase (NQO1) and glutathione S-transferase (GST) A1-2, GSTA3 and GSTA4. In both cell types, HO-1 was the most sensitive, increasing 86-98 fold within 6h. Further characterization of the effects of 4-HNE on HO-1 demonstrated concentration- and time-dependent increases in mRNA and protein expression which were maximum after 6h with 30 μM. 4-HNE stimulated keratinocyte Erk1/2, JNK and p38 MAP kinases, as well as PI3 kinase. Inhibition of these enzymes suppressed 4-HNE-induced HO-1 mRNA and protein expression. 4-HNE also activated Nrf2 by inducing its translocation to the nucleus. 4-HNE was markedly less effective in inducing HO-1 mRNA and protein in keratinocytes from Nrf2-/- mice, when compared to wild type mice, indicating that Nrf2 also regulates 4-HNE-induced signaling. Western blot analysis of caveolar membrane fractions isolated by sucrose density centrifugation demonstrated that 4-HNE-induced HO-1 is localized in keratinocyte caveolae. Treatment of the cells with methyl-β-cyclodextrin, which disrupts caveolar structure, suppressed 4-HNE-induced HO-1. These findings indicate that 4-HNE modulates expression of antioxidant enzymes in keratinocytes, and that this can occur by different mechanisms. Changes in expression of keratinocyte antioxidants may be important in protecting the skin from oxidative stress.

Peroxiredoxin I and II in human eyes: cellular distribution and association with pterygium and DNA damage

Peroxiredoxin I and II are both 2-Cys members of the peroxiredoxin family of antioxidant enzymes and inactivate hydrogen peroxide. On western blotting, both enzymes appeared as 22-kD proteins and were present in the sclera, retina and iris. Immunohistochemistry showed strong cytoplasmic labeling in the basal cells of the corneal epithelial layer and the corneoscleral limbus. The melanocytes within the stroma of the iris and the anterior epithelial cells of the lens also showed strong cytoplasmic labeling. The fibrous structure of the stroma and the posterior surface of the ciliary body were also labeled. There was also strong labeling for both enzymes in the photoreceptors and the inner and outer plexiform layers of the retina. There was increased labeling of peroxiredoxin I and II in pterygium. In normal conjunctiva and cornea, only the basal cell layer showed labeling for peroxiredoxin I and II, whereas, in pterygia, there was strong cytoplasmic labeling in most cells involving the full thickness of the epithelium. Co-localization of the DNA oxidation product 8-hydroxy-2'-deoxyguanosine antibody with the nuclear dye 4',6'-diamidino-2-phenylindole dihydrochloride indicated that the majority of the oxidative damage was cytoplasmic; this suggested that the mitochondrial DNA was most affected by the UV radiation in this condition.

The generation of 4-hydroxynonenal, an electrophilic lipid peroxidation end product, in rabbit cornea organ cultures treated with UVB light and nitrogen mustard

The cornea is highly sensitive to oxidative stress, a process that can lead to lipid peroxidation. Ultraviolet light B (UVB) and nitrogen mustard (mechlorethamine) are corneal toxicants known to induce oxidative stress. Using a rabbit air-lifted corneal organ culture model, the oxidative stress responses to these toxicants in the corneal epithelium was characterized. Treatment of the cornea with UVB (0.5 J/cm(2)) or nitrogen mustard (100 nmol) resulted in the generation of 4-hydroxynonenal (4-HNE), a reactive lipid peroxidation end product. This was associated with increased expression of the antioxidant, heme oxygenase-1 (HO-1). In human corneal epithelial cells in culture, addition of 4-HNE or 9-nitrooleic acid, a reactive nitrolipid formed during nitrosative stress, caused a time-dependent induction of HO-1 mRNA and protein; maximal responses were evident after 10h with 30 μM 4-HNE or 6h with 10 μM 9-nitrooleic acid. 4-HNE and 9-nitrooleic acid were also found to activate Erk1/2, JNK and p38 MAP kinases, as well as phosphoinositide-3-kinase (PI3)/Akt. Inhibition of p38 blocked 4-HNE- and 9-nitrooleic acid-induced HO-1 expression. Inhibition of Erk1/2, and to a lesser extent, JNK and PI3K/Akt, suppressed only 4-HNE-induced HO-1, while inhibition of JNK and PI3K/Akt, but not Erk1/2, partly reduced 9-nitrooleic acid-induced HO-1. These data indicate that the actions of 4-HNE and 9-nitrooleic acid on corneal epithelial cells are distinct. The sensitivity of corneal epithelial cells to oxidative stress may be an important mechanism mediating tissue injury induced by UVB or nitrogen mustard.

The impact of UVB exposure and differentiation state of primary keratinocytes on their interaction with quantum dots

In this study we utilised an in vitro model system to gain insight into the potential cellular interactions that quantum dot (QD) nanoparticles may experience while transiting the viable skin epidermis, and we consider the effects of UVB exposure. UVB skin exposure is known to induce a skin barrier defect that facilitates QD stratum corneum penetration. Primary human keratinocytes were cultured in low and high calcium to induce basal and differentiated phenotypes, respectively. Results suggest that differentiation state plays a role in keratinocyte response to UVB exposure and exposure to negatively charged CdSe/ZnS core/shell QD. QD cell uptake increased with QD dose but association with differentiated cells was significantly lower than the basal keratinocyte phenotype. Differentiated keratinocytes were also less sensitive to the cytotoxic effects of UVB exposure. We did not observe an effect of UVB preexposure on QD cytotoxicity level despite the fact that fluorescent microscopy and flow cytometry data suggest that UVB may slightly increase QD uptake in the basal cell phenotype. The implications of these findings for assessing potential risk of human skin exposure are discussed.

MC1R variant allele effects on UVR-induced phosphorylation of p38, p53, and DDB2 repair protein responses in melanocytic cells in culture

Variant alleles of the human melanocortin 1 receptor (MC1R) reduce the ability of melanocytes to produce the dark pigment eumelanin, with R alleles being most deficient. Cultured melanocytes of MC1R R/R variant genotype give reduced responses to [Nle(4), D-Phe(7)]α-melanocyte-stimulating hormone (NDP-MSH) ligand stimulation and lower levels of DNA repair than MC1R wild-type strains. p38 controls xeroderma pigmentosum (XP)-C recruitment to DNA damage sites through regulating ubiquitylation of the DNA damage-binding protein 2 (DDB2) protein, and p53 is implicated in the nuclear excision repair process through its regulation of XP-C and DDB2 protein expression. We report the effects of MC1R ligand treatment and UVR exposure on phosphorylation of p38 and p53, and DDB2 protein expression in MC1R variant strains. Wild-type MC1R melanocyte strains grown together with keratinocytes in coculture, when treated with NDP-MSH and exposed to UVR, gave synergistic activation of p38 and p53 phosphorylation, and were not replicated by R/R variant melanocytes, which have lower basal levels of phosphorylated forms of p38. Minor increases in p38 phosphorylation status in R/R variant melanocyte cocultures could be attributed to the keratinocytes alone. We also found that MC1R wild-type strains regulate DDB2 protein levels through p38, but MC1R R/R variant melanocytes do not. This work confirms the important functional role that the MC1R receptor plays in UVR stress-induced DNA repair.

Microsomal glutathione transferase 1: mechanism and functional roles

Microsomal glutathione transferase 1 (MGST1) belongs to a superfamily named MAPEG (membrane-associated proteins in eicosanoid and glutathione metabolism). This family is represented in all life forms, except archae. Of the six human members, three are specialized in the synthesis of leukotrienes and prostaglandin E, whereas the others (MGST1-3) have potential roles in drug metabolism. MGST1 has a well-established role in the conjugation of electrophiles and oxidative stress protection, whereas MGST2 and 3 have been less studied. Here, we review the recent advances regarding the structure, mechanism, and functional roles of MGST1. Emerging data show that the enzyme is overexpressed in certain tumors and support a role for the enzyme in protecting cells from cytostatic drugs.

UVB light regulates expression of antioxidants and inflammatory mediators in human corneal epithelial cells

The cornea is highly sensitive to ultraviolet B (UVB) light-induced oxidative stress, a process that results in the production of inflammatory mediators which have been implicated in tissue injury. In the present studies, we characterized the inflammatory response of human corneal epithelial cells to UVB (2.5-25mJ/cm(2)). UVB caused a dose-dependent increase in the generation of reactive oxygen species in the cells. This was associated with increases in mRNA expression of the antioxidants Cu,Zn superoxide dismutase (SOD), Mn-SOD, catalase and heme oxygenase-1 (HO-1), as well as the glutathione S-transferases (GST), GSTA1-2, GSTA3, GSTA4, GSTM1, and mGST2. UVB also upregulated expression of the proinflammatory cytokines, IFNγ, IL-1β, TGFβ and TNFα, and enzymes important in prostaglandin (PG) biosynthesis including cyclooxygenase-2 (COX-2) and the PG synthases mPGES-2, PGDS, PGFS and thromboxane synthase, and in leukotriene biosynthesis including 5-lipoxygenase (5-LOX), 15-LOX-2, and the epidermal and platelet forms of 12-LOX. UVB was found to activate JNK and p38 MAP kinases in corneal epithelial cells; ERK1/2 MAP kinase was found to be constitutively active, and its activity increased following UVB treatment. Inhibition of p38 blocked UVB-induced expression of TNFα, COX-2, PGDS and 15-LOX-2, while JNK inhibition suppressed TNFα and HO-1. These data indicate that UVB modulates corneal epithelial cell expression of antioxidants and proinflammatory mediators by distinct mechanisms. Alterations in expression of these mediators are likely to be important in regulating inflammation and protecting the cornea from UVB-induced oxidative stress.

Evidence that Gsta4 modifies susceptibility to skin tumor development in mice and humans

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

Gsta4/GSTA4 is a novel susceptibility gene for NMSC that affects risk in both mice and humans.

Different oxidative stress response in keratinocytes and fibroblasts of reconstructed skin exposed to non extreme daily-ultraviolet radiation

Experiments characterizing the biological effects of sun exposure have usually involved solar simulators. However, they addressed the worst case scenario i.e. zenithal sun, rarely found in common outdoor activities. A non-extreme ultraviolet radiation (UV) spectrum referred as "daily UV radiation" (DUVR) with a higher UVA (320-400 nm) to UVB (280-320 nm) irradiance ratio has therefore been defined. In this study, the biological impact of an acute exposure to low physiological doses of DUVR (corresponding to 10 and 20% of the dose received per day in Paris mid-April) on a 3 dimensional reconstructed skin model, was analysed. In such conditions, epidermal and dermal morphological alterations could only be detected after the highest dose of DUVR. We then focused on oxidative stress response induced by DUVR, by analyzing the modulation of mRNA level of 24 markers in parallel in fibroblasts and keratinocytes. DUVR significantly modulated mRNA levels of these markers in both cell types. A cell type differential response was noticed: it was faster in fibroblasts, with a majority of inductions and high levels of modulation in contrast to keratinocyte response. Our results thus revealed a higher sensitivity in response to oxidative stress of dermal fibroblasts although located deeper in the skin, giving new insights into the skin biological events occurring in everyday UV exposure.

Induction of cytochrome P450 1 genes and stress response genes in developing zebrafish exposed to ultraviolet radiation

Ultraviolet (UV) radiation damages cell molecules, and has been suggested to up-regulate mammalian cytochrome P4501 (CYP1) genes through an aryl hydrocarbon receptor (AHR) mediated mechanism. In this study, embryos and larvae of zebrafish (Danio rerio) were exposed to UV to determine the effects on expression of CYP1 and stress response genes in vivo in these fish. Zebrafish embryos were exposed for varying times to UV on two consecutive days, with exposure beginning at 24 and 48h post-fertilization (hpf). Embryos exposed for 2, 4 or 6h twice over 2 days to UVB (0.62 W/m(2); 8.9-26.7 kJ/m(2)) plus UVA (2.05 W/m(2); 29.5-144.6 kJ/m(2)) had moderately (2.4+/-0.8-fold) but significantly up-regulated levels of CYP1A. UVA alone had no effect on CYP1A expression. Proliferating cellular nuclear antigen (PCNA) and Cu-Zn superoxide dismutase (SOD1) transcript levels were induced (2.1+/-0.2 and 2.3+/-0.5-fold, respectively) in embryos exposed to two 6-h pulses of 0.62 W/m(2) UVB (26.8 kJ/m(2)). CYP1A was induced also in embryos exposed to higher intensity UVB (0.93 W/m(2)) for two 3-h or two 4-h pulses (20.1 or 26.8 kJ/m(2)). CYP1B1, SOD1 and PCNA expression was induced by the two 3-h pulses of the higher intensity UVB, but not after two 4-h pulses of the higher intensity UVB, possibly due to impaired condition of surviving embryos, reflected in a mortality of 34% at that UVB dose. A single 8-h long exposure of zebrafish larvae (8dpf) to UVB at 0.93 W/m(2) (26.8 kJ/m(2)) significantly induced CYP1A and CYP1B1 expression, but other CYP1 genes (CYP1C1, CYP1C2 and CYP1D1) showed no significant increase. The results show that UVB can induce expression of CYP1 genes as well stress response genes in developing zebrafish, and that UVB intensity and duration influence the responses.

Role of MAP kinases in regulating expression of antioxidants and inflammatory mediators in mouse keratinocytes following exposure to the half mustard, 2-chloroethyl ethyl sulfide

Dermal exposure to sulfur mustard causes inflammation and tissue injury. This is associated with changes in expression of antioxidants and eicosanoids which contribute to oxidative stress and toxicity. In the present studies we analyzed mechanisms regulating expression of these mediators using an in vitro skin construct model in which mouse keratinocytes were grown at an air-liquid interface and exposed directly to 2-chloroethyl ethyl sulfide (CEES), a model sulfur mustard vesicant. CEES (100-1000 microM) was found to cause marked increases in keratinocyte protein carbonyls, a marker of oxidative stress. This was correlated with increases in expression of Cu,Zn superoxide dismutase, catalase, thioredoxin reductase and the glutathione S-transferases, GSTA1-2, GSTP1 and mGST2. CEES also upregulated several enzymes important in the synthesis of prostaglandins and leukotrienes including cyclooxygenase-2 (COX-2), microsomal prostaglandin E synthase-2 (mPGES-2), prostaglandin D synthase (PGDS), 5-lipoxygenase (5-LOX), leukotriene A(4) (LTA(4)) hydrolase and leukotriene C(4) (LTC(4)) synthase. CEES readily activated keratinocyte JNK and p38 MAP kinases, signaling pathways which are known to regulate expression of antioxidants, as well as prostaglandin and leukotriene synthases. Inhibition of p38 MAP kinase suppressed CEES-induced expression of GSTA1-2, COX-2, mPGES-2, PGDS, 5-LOX, LTA(4) hydrolase and LTC(4) synthase, while JNK inhibition blocked PGDS and GSTP1. These data indicate that CEES modulates expression of antioxidants and enzymes producing inflammatory mediators by distinct mechanisms. Increases in antioxidants may be an adaptive process to limit tissue damage. Inhibiting the capacity of keratinocytes to generate eicosanoids may be important in limiting inflammation and protecting the skin from vesicant-induced oxidative stress and injury.

UVB light upregulates prostaglandin synthases and prostaglandin receptors in mouse keratinocytes

Prostaglandins belong to a class of cyclic lipid-derived mediators synthesized from arachidonic acid via COX-1, COX-2 and various prostaglandin synthases. Members of this family include prostaglandins such as PGE(2), PGF(2alpha), PGD(2) and PGI(2) (prostacyclin) as well as thromboxane. In the present studies we analyzed the effects of UVB on prostaglandin production and prostaglandin synthase expression in primary cultures of undifferentiated and calcium-differentiated mouse keratinocytes. Both cell types were found to constitutively synthesize PGE(2), PGD(2) and the PGD(2) metabolite PGJ(2). Twenty-four hours after treatment with UVB (25 mJ/cm(2)), production of PGE(2) and PGJ(2) increased, while PGD(2) production decreased. This was associated with increased expression of COX-2 mRNA and protein. UVB (2.5-25 mJ/cm(2)) also caused marked increases in mRNA expression for the prostanoid synthases PGDS, mPGES-1, mPGES-2, PGFS and PGIS, as well as expression of receptors for PGE(2) (EP1 and EP2), PGD(2) (DP and CRTH2) and prostacyclin (IP). UVB was more effective in inducing COX-2 and DP in differentiated cells and EP1 and IP in undifferentiated cells. UVB readily activated keratinocyte PI-3-kinase (PI3K)/Akt, JNK and p38 MAP signaling pathways which are known to regulate COX-2 expression. While inhibition of PI3K suppressed UVB-induced mPGES-1 and CRTH2 expression, JNK inhibition suppressed mPGES-1, PGIS, EP2 and CRTH2, and p38 kinase inhibition only suppressed EP1 and EP2. These data indicate that UVB modulates expression of prostaglandin synthases and receptors by distinct mechanisms. Moreover, both the capacity of keratinocytes to generate prostaglandins and their ability to respond to these lipid mediators are stimulated by exposure to UVB.