Molecular events associated with apoptosis and proliferation induced by ultraviolet-B radiation in the skin of hairless mice

Protective Effects of Orange Sweet Pepper Juices Prepared by High-Speed Blender and Low-Speed Masticating Juicer against UVB-induced Skin Damage in SKH-1 Hairless Mice

Sweet pepper fruits (Capsicum annuum L.) contain various nutrients and phytochemicals that enhance human health and prevent the pathogenesis of certain diseases. Here, we report that oral administration of orange sweet pepper juices prepared by a high-speed blender and low-speed masticating juicer reduces UVB-induced skin damage in SKH-1 hairless mice. Sweet pepper juices reduced UVB-induced skin photoaging by the regulation of genes involved in dermal matrix production and maintenance such as collagen type I α 1 and matrix metalloproteinase-2, 3, 9. Administration of sweet pepper juices also restored total collagen levels in UVB-exposed mice. In addition, sweet pepper juices downregulated the expression of pro-inflammatory proteins such as cyclooxygenase-2, interleukin (IL)-1β, IL-17, and IL-23, which was likely via inhibiting the NF-κB pathway. Moreover, primary antioxidant enzymes in the skin were enhanced by oral supplementation of sweet pepper juices, as evidenced by increased expression of catalase, glutathione peroxidase, and superoxide dismutase-2. Immunohistochemical staining showed that sweet pepper juices reduced UVB-induced DNA damage by preventing 8-OHdG formation. These results suggest that sweet pepper juices may offer a protective effect against photoaging by inhibiting the breakdown of dermal matrix, inflammatory response, and DNA damage as well as enhancing antioxidant defense, which leads to an overall reduction in skin damage.

Influence of Caralluma adscendens Var. attenuata cold cream on UV-B damaged skin epidermal cells: a novel approach

Ultraviolet radiation-induced sunburns are characterized by pigmented, wrinkled, and dried skin, with rashes and red spots. Chemical sunscreen lotion shows beneficial effects, but it shows the adverse side effect while in continuous usage. Natural substances of plant origin are deemed a possible cause of UV radiation through sunscreen resources. On this basis, we formulated the cold cream from the Caralluma adscendens Var. attenuata (CAVA) plant extract. The phytocompounds were studied by using GC-MS. The antioxidant potential of the plant extract was determined, and the CAVA showed cytotoxicity on A375 skin melanoma cells determined by MTT assay. The FT-IR spectra analysis confirmed the chemical nature of crude and crosslinking between cold creams. The cream was applied topically to rats pre-exposed to UV-B radiation (32,800 J/m2) four times/week (on alternate days). UV-B exposed without any treatment rats showed increased red spots or wrinkles (5 cm2). In contrast, the cold cream treatment application on irradiated skin has significantly reduced the size of rashes and red spots and the wound was contracted in a dose-dependent manner. Furthermore, histopathology of the experimental rat skin confirmed that CAVA cream treatment significantly reduced the epidermal thickening, damage in dermis and epidermis layers, and restructured the hair follicles. This study suggests that the cream formulated using CAVA can alleviate the damages caused by the UV-B-irradiation at a high level and safeguard the skin tissues.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02694-y.

Penta-1,2,3,4,6-O-Galloyl-β-D-Glucose Inhibits UVB-Induced Photoaging by Targeting PAK1 and JNK1

Penta-O-galloyl-β-D-glucose (PGG) is a gallotannin polyphenolic compound that occurs naturally in fermented Rhus verniciflua. The present study aimed to examine the effect of PGG on UVB-induced skin aging and its molecular mechanisms in HaCaT human keratinocytes and SKH-1 hairless mice models. PGG suppressed UVB-induced matrix metalloproteinase-1 (MMP-1) expression in HaCaT cells by inhibiting phosphorylation of RAF/MEK/ERK, MKK3/6/p38, and c-Jun. UVB-induced ERK and p38 signaling pathways that induce the MMP-1 expression were mediated by PAK1 in HaCaT cells. PGG suppressed PAK1 and JNK1 kinase activities, and directly bound both PAK1 in an ATP-competitive manner and JNK1 in an ATP-noncompetitive manner. Consistently, PGG decreased UVB-induced wrinkle formation, epidermal thickness, type 1 collagen and MMP-13 expression in mouse skin. Overall, these results indicate that PGG exhibits anti-photoaging effects in vitro and in vivo by the suppression of PAK1 and JNK1 kinase activities, and may be useful for the prevention of skin aging.

Histological observation of hairless mice skin after exposure to Simulated Solar Light: Comparison between the histological findings with different methodologies and 3R principle correlations

BACKGROUND

Albino hairless mouse (AHM) has been used as a biological model in photodermatology. However, the experimental landscape is diverse to follow and need particular attention.

PURPOSE

Irradiation parameters were investigated for the development of a protocol to assess alterations in the AHM skin using Simulated Solar Light (SSL). The present study was compared with published articles (last 15 years) according to irradiation protocols, morphological findings to minimize animal suffering and UV exposure.

MATERIALS AND METHODS

Three groups: Control (G1), experimental - sunburn (G2) and skin photodamage assay (G3). G2 were immobilized and exposed to SSL once for 15, 30 and 45min. G3 were exposed to SSL, without immobilization, for 15min once a day for one week. The dorsal skin was analyzed using hematoxylin and eosin technique.

RESULTS

G2 displayed different sunburn degrees. Based on the profile of the observed morphological alterations, a 15min irradiation was chosen as the exposure time to expose G3, without immobilization, for 5 consecutive days.

CONCLUSION

These conditions produced the same morphological changes in the AHM with a shorter solar exposure time, without immobilizing the animals but using environmental exposure fluences, conforming to 3R (reduction - refinement - replacement) recommendations.

Autophagy in UV Damage Response

UV radiation exposure from sunlight and artificial tanning beds is the major risk factor for the development of skin cancer and skin photoaging. UV-induced skin damage can trigger a cascade of DNA damage response signaling pathways, including cell cycle arrest, DNA repair and, if damage is irreparable, apoptosis. Compensatory proliferation replaces the apoptotic cells to maintain skin barrier integrity. Disruption of these processes can be exploited to promote carcinogenesis by allowing the survival and proliferation of damaged cells. UV radiation also induces autophagy, a catabolic process that clears unwanted or damaged proteins, lipids and organelles. The mechanisms by which autophagy is activated following UV exposure, and the functions of autophagy in UV response, are only now being clarified. Here, we summarize the current understanding of the mechanisms governing autophagy regulation by UV, the roles of autophagy in regulating cellular response to UV-induced photodamage and the implications of autophagy modulation in the treatment and prevention of photoaging and skin cancer.

Protective effects of Aloe sterols against UVB-induced photoaging in hairless mice

BACKGROUND

Aloe vera is a traditional medical plant whose gel has been widely used in skin care. Previously, we have identified Aloe sterols from Aloe vera as active ingredients. This study investigated the protective effects of Aloe sterols without polysaccharides, against ultraviolet B (UVB)-induced skin photoaging in mice using Aloe vera gel extract (AVGE) obtained by supercritical fluid extraction.

METHODS

Aloe vera gel extract was supplemented in the diet (12 or 120 ppm), and HR-1 hairless mice were exposed to UVB irradiation for 7 weeks. Skin measurements and histological and analytical studies were performed.

RESULTS

Repeated UVB irradiation induced rough wrinkling of skin with water content reduction and hyperkeratosis. AVGE administration resulted in the significant improvement of UVB-induced skin dryness, epidermal thickness, and wrinkle formation. The AVGE group also suppressed the degenerations of dermal collagen fibers and the appearance of cutaneous apoptosis cells induced by UVB. Furthermore, AVGE administration reduced the excess elevation of pro-inflammatory cytokines (IL-1β and TNF-α) and matrix metalloproteinases (MMP-2, MMP-9, MMP-12, and MMP-13) in UVB-exposed skin.

CONCLUSION

The dietary ingestion of Aloe sterols protected against chronic UVB damage in mouse skin, and our results suggest that Aloe sterols may prevent skin photoaging through the anti-inflammation and MMP regulation.

Copper Alters the Conformation and Transcriptional Activity of the Tumor Suppressor Protein p53 in Human Hep G2 Cells

The tumor suppressor protein p53 plays a role in the molecular response to DNA damage by acting as a DNA-binding transcription factor that regulates specific target genes to arrest the cell cycle, induce repair mechanisms, and initiate apoptotic cell death. To test the effect of copper on the transcriptional activity of p53, Hep G2 cells were transiently transfected with a luciferase reporter gene downstream from multiple p53 response elements. Co-transfection with the p53 gene resulted in a 6-fold increase in luciferase activity, showing that p53 acts as a transcription factor in this system. However, in the presence of copper, luciferase activity was significantly reduced. Oligonucleotide arrays representing 145 known p53-associated genes were hybridized with biotinylated cDNAs from mRNA extracted from control and copper-treated Hep G2 cells. Among the genes that were differentially regulated were fos, RB1, glutathione peroxidase, TGF-β, and 15-lipoxygenase, a gene known to be activated by mutant p53. Although control Hep G2 cells synthesize wild-type p53, immunocytochemistry identified not only wild type, but also mutant p53 in the presence of copper and other agents that induce oxidative damage. Thus, this report not only identifies genes that may play a role in copper-mediated apoptosis, but also suggests that copper-induced oxidative processes result in the synthesis of mutant p53 with altered transcriptional properties.

The effects of Origanum hypericifolium essential oil application and ultraviolet B irradiation on mouse skin: An ultrastructural study

Exposure to UV radiation can cause histopathological and ultrastructural changes in the skin. Origanum hypericifolium, an endemic Turkish plant,essential oil is mainly composed of monoterpenes. The effects of undiluted O. hypericifolium oil on the ultrastructural characteristics of the UVB-irradiated dorsal skin of mice were investigated using transmission electron microscopy. The BALB/c mice were shaved of dorsal hair and randomly housed into 4 groups: 1: control; 2: UVB-irradiated; 3: oil applied; and 4: oil applied and UVB-irradiated. The oil was applied topically to the dorsal skins of the mice on alternate days for 1week prior to UVB exposure. The skins were irradiated for a total dose of 3.5J/cm(2). The sections were stained with hematoxylin and eosin, semithin sections were stained with toluidine blue and ultrathin sections were contrasted with uranyl acetate/lead citrate. There were histopathological changes such as parakeratosis and squamous hyperplasia in the epidermal cell layers (Groups 3 and 4). There were also ultrastructural changes including lacunae formations throughout the stratum corneum layer (Groups 2, 3, and 4), enlargement of intercellular spaces (Groups 2 and 3), reduced desmosomes, narrow and elongated interdigitations, shortened, relatively indistinct and electron dense intermediate keratin filament bundles (Group 3). There were various sizes of cytoplasmic and perinucleolar vacuoles (Groups 3 and 4) and apoptotic bodies phagocytized by keratinocytes (Group 4). I conclude that undiluted oil has side-effects and the potential to inflict injury to the skin. The oil does not ameliorate the negative effects of UVB on epidermal skin cells.

Orally administered hyaluronan affects skin dryness and epidermal thickening in photoaged hairless mice

The oral administration of hyaluronans (HAs) (molecular weight, 300k and less than 10k) to photoaged hairless mice increased the moisture content of the stratum corneum and decreased the epidermal thickness, respectively. Furthermore, orally administered HAs suppressed the low-molecular weight of HA content of the skin. This study indicates oral administered HAs may ameliorate the skin condition resulting from photoaging.

Oral administration of hyaluronan prevents skin dryness and epidermal thickening in ultraviolet irradiated hairless mice

Hyaluronan is a component of the extracellular matrix that plays a role in water retention in tissues. In this study, we orally administered hyaluronans of varying molecular weights (300k and less than 10k) repeatedly to hairless mice exposed to ultraviolet (UV) irradiation and examined their effects on the skin of these mice. UV irradiation induces a marked increase in the epidermal thickness of the dorsal skin and a marked decrease in the skin moisture content; however, orally administered hyaluronan, particularly that with a molecular weight of less than 10k, markedly reversed the increase and decrease in the epidermal thickness and skin moisture content, respectively. Furthermore, on analyzing the mice skin, orally administered hyaluronan with a molecular weight of less than 10k increased the levels of the HAS2 gene expression in the skin. Based on these findings, it is assumed that orally administered hyaluronans, with molecular weight of 300k and less than 10k, reversed UV irradiation-induced skin disturbance. In particular, it was considered that the increase in the skin moisture content by orally administered hyaluronan, with a molecular weight of less than 10k, was related to the effect on skin cells.

MIF antagonist (CPSI-1306) protects against UVB-induced squamous cell carcinoma

Macrophage migration inhibitory factor (MIF) is a homotrimeric proinflammatory cytokine implicated in chronic inflammatory diseases and malignancies, including cutaneous squamous cell carcinomas (SCC). To determine whether MIF inhibition could reduce UVB light-induced inflammation and squamous carcinogenesis, a small-molecule MIF inhibitor (CPSI-1306) was utilized that disrupts homotrimerization. To examine the effect of CPSI-1306 on acute UVB-induced skin changes, Skh-1 hairless mice were systemically treated with CPSI-1306 for 5 days before UVB exposure. In addition to decreasing skin thickness and myeloperoxidase (MPO) activity, CPSI-1306 pretreatment increased keratinocyte apoptosis and p53 expression, decreased proliferation and phosphohistone variant H2AX (γ-H2AX), and enhanced repair of cyclobutane pyrimidine dimers. To examine the effect of CPSI-1306 on squamous carcinogenesis, mice were exposed to UVB for 10 weeks, followed by CPSI-1306 treatment for 8 weeks. CPSI-1306 dramatically decreased the density of UVB-associated p53 foci in non-tumor-bearing skin while simultaneously decreasing the epidermal Ki67 proliferation index. In addition to slowing the rate of tumor development, CPSI-1306 decreased the average tumor burden per mouse. Although CPSI-1306-treated mice developed only papillomas, nearly a third of papillomas in vehicle-treated mice progressed to microinvasive SCC. Thus, MIF inhibition is a promising strategy for prevention of the deleterious cutaneous effects of acute and chronic UVB exposure.

IMPLICATIONS

Macrophage migration inhibitory factor is a viable target for the prevention of UVB-induced cutaneous SSCs.

Grp1-associated scaffold protein regulates skin homeostasis after ultraviolet irradiation

Grp1-associated scaffold protein (Grasp), the product of a retinoic acid-induced gene in P19 embryonal carcinoma cells, is expressed primarily in brain, heart, and lung of the mouse. We report herein that Grasp transcripts are also found in mouse skin in which the Grasp gene is robustly induced following acute ultraviolet-B (UVB) exposure. Grasp(-/-) mice were found to exhibit delayed epidermal proliferation and a blunted apoptotic response after acute UVB exposure. Immunohistochemical analyses revealed that the nuclear residence time of the tumor suppressor protein p53 was reduced in Grasp(-/-) mice after UVB exposure. Taken together, our results suggest that a physiological role of Grasp may be to regulate skin homeostasis after UVB exposure, potentially by influencing p53-mediated apoptotic responses in skin.

Pyrithione-zinc Prevents UVB-induced Epidermal Hyperplasia by Inducing HIF-1alpha

Epidermal keratinocytes overgrow in response to ultraviolet-B (UVB), which may be associated with skin photoaging and cancer development. Recently, we found that HIF-1alpha controls the keratinocyte cell cycle and thereby contributes to epidermal homeostasis. A further study demonstrated that HIF-1alpha is down-regulated by UVB and that this process is involved in UVB-induced skin hyperplasia. Therefore, we hypothesized that the forced expression of HIF-1alpha in keratinocytes would prevent UVB-induced keratinocyte overgrowth. Among several agents known to induce HIF-1alpha, pyrithione-zinc (Py-Zn) overcame the UVB suppression of HIF-1alpha in cultured keratinocytes. Mechanistically, Py-Zn blocked the degradation of HIF-1alpha protein in keratinocytes, while it did not affect the synthesis of HIF-1alpha. Moreover, the p21 cell cycle inhibitor was down-regulated after UVB exposure, but was robustly induced by Py-Zn. In mice repeatedly irradiated with UVB, the epidermis became hyperplastic and HIF-1alpha disappeared from nuclei of epidermal keratinocytes. However, a cream containing Py-Zn effectively prevented the skin thickening and up-regulated HIF-1alpha to the normal level. These results suggest that Py-Zn is a potential agent to prevent UVB-induced photoaging and skin cancer development. This work also provides insight into a molecular target for treatment of UVB-induced skin diseases.

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.

Chemopreventive effect of farnesol on DMBA/TPA-induced skin tumorigenesis: involvement of inflammation, Ras-ERK pathway and apoptosis

AIMS

Naturally-derived farnesol has been reported for its chemopreventive and chemotherapeutic efficacy in various cancers. However, the mechanism of action of farnesol is still to be elucidated. The present study demonstrates the chemopreventive potential of farnesol on 9,10-dimethylbenz(a)anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted skin tumorigenesis in Swiss albino mice.

MAIN METHODS

Farnesol at three different doses 25, 50 and 100 mg/kg body weight was topically applied to the mouse skin, 30 min prior to TPA (2 microg/200 microl acetone) to evaluate edema, hyperplasia, expression of cyclooxygenase-2 (COX-2), oxidative stress response and hyperproliferation, and expression of Ras, Raf, p-ERK1/2, Bax and Bcl-2 in DMBA/TPA-induced tumors.

KEY FINDINGS

Farnesol at both the low doses significantly reduced the TPA-induced skin edema, hyperplasia, expression of COX-2 and oxidative stress response. Interestingly, higher dose of farnesol did not show any significant response. Pretreatment of farnesol significantly decreased TPA-induced ornithine decarboxylase (ODC) activity and [(3)H]thymidine incorporation in dose-dependent manner. During promotion phase, farnesol with higher dose significantly regressed tumor incidence and tumor burden with an extension of latency period of 4-8 weeks. More importantly, low doses of farnesol significantly inhibited Ras/Raf/ERK1/2 signaling pathway in mouse skin tumors whereas higher dose of farnesol induced the pathway. Moreover, farnesol at all doses altered Bax/Bcl-2 ratio which leads to induction of apoptosis as confirmed by DNA fragmentation.

SIGNIFICANCE

These findings revealed that oxidative stress, inflammation, Ras/Raf/ERK1/2 pathway and apoptosis collectively played a crucial role in the chemopreventive activity of farnesol to inhibit the murine skin tumorigenesis.

Ultraviolet B regulation of transcription factor families: roles of nuclear factor-kappa B (NF-kappaB) and activator protein-1 (AP-1) in UVB-induced skin carcinogenesis

Prolonged and repeated exposure of the skin to ultraviolet light (UV) leads not only to aging of the skin but also increases the incidence of non-melanoma skin cancer (NMSC). Damage of cells induced by ultraviolet B (UVB) light both at the DNA level and molecular level initiates the activation of transcription factor pathways, which in turn regulate the expression of a number of genes termed the "UV response genes". Two such transcription factor families that are activated in this way are those of the nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) families. These two transcription factor families have been identified to be involved in the processes of cell proliferation, cell differentiation and cell survival and therefore play important roles in tumorigenesis. The study of these two transcription factor pathways and the cross-talk between them in response to UVB exposure may help with the development of new chemopreventive strategies for the prevention of UVB-induced skin carcinogenesis.

Enhancement of UVB radiation-mediated apoptosis by sanguinarine in HaCaT human immortalized keratinocytes

In this article, we studied the chemopreventive effects of sanguinarine on UVB-mediated responses in human HaCaT immortalized keratinocytes. For our studies, HaCaT cells were treated with a low dose (50 nmol/L) of sanguinarine for 24 hours followed by irradiation with UVB (15 or 30 mJ/cm2). Our data showed that UVB exposure, at both doses, resulted in decreased cell viability and increased apoptosis. Interestingly, pretreatment of the cells with sanguinarine caused a significant enhancement in the antiproliferative response of UVB. These responses on UVB and/or sanguinarine treatments were associated with (a) decrease in Bcl-2 and Bcl-X(L) and (b) increase in Bax, Bid, and Bak protein levels. Bax knockdown and Bcl-2 overexpression resulted in a rescue of HaCaT cells from sanguinarine-mediated apoptosis. DNA cell cycle analysis revealed that UVB treatment resulted in an accumulation of cells in the G2-M phase of the cell cycle, whereas pretreatment of sanguinarine resulted in a significant shift of cells in the S phase at a low UVB dose and a further accumulation of cells in the G2-M phase at a higher UVB dose. These effects on cell cycle were accompanied with modulations in the protein levels of cyclin (B1, E, and A) and cdc2 and cyclin-dependent kinase 1. Furthermore, sanguinarine treatment was found to result in significant modulations in p53, p66Shc, MsrA, and superoxide dismutase levels. Based on our data, we suggest the sanguinarine may protect skin cells from UVB-mediated damages via apoptotic elimination of damaged cells that escape programmed cell death and therefore possess a potential of clonal expansion.

Keratinocyte apoptosis in epidermal development and disease

Keratinocyte (KC) apoptosis plays a critical role in regulating epidermal development and restraining carcinogenesis. Apoptosis balances proliferation to maintain epidermal thickness, contributes to stratum corneum formation and may eliminate pre-malignant cells. Apart from the normal developmental program, KC apoptosis can be triggered by UV light and other stimuli. Dysfunctional apoptosis occurs in some skin diseases, such as psoriasis and skin cancer. Here we review the current state of knowledge of KC apoptosis, with particular focus on apoptotic signaling pathways and molecular mechanisms of apoptosis control, and discuss new insights into the complex role of apoptosis in skin carcinogenesis that are emerging from mouse models.

Epidermal transit of replication-arrested, undifferentiated keratinocytes in UV-exposed XPC mice: an alternative to in situ apoptosis

The interplay among nucleotide excision repair, cell-cycle regulation, and apoptosis in the UV-exposed epidermis is extremely important to avoid mutations and malignant transformation. In Xpc(-/-) mice deficient in global genome nucleotide excision repair (GGR), a cell-cycle arrest of epidermal cells in late S-phase [with near-double normal diploid (4N) DNA content] was observed 48-72 h after UV exposure. This arrest resolved without apoptosis (96-168 h). We surmised that these arrested keratinocytes with persistent DNA damage were removed by epidermal turnover. In vivo BrdUrd pulse-chase labeling (>17 h after UV exposure) showed that DNA replication after UV exposure was resumed in Xpc(-/-) mice, but it did not reveal any evidence of retained BrdUrd-labeled S-phase cells in the basal layer of the epidermis at 72 h. Interestingly, by this time a maximum number of cytokeratin 10-negative and cytokeratin 5-positive cells had appeared in the suprabasal epidermal cell layers of UV-exposed Xpc(-/-) mice. Accumulation of these "basal cell"-like keratinocytes in the suprabasal layers was clearly aberrant and was not observed in WT and heterozygous mice. Flow cytometric analyses of single-cell suspensions from UV-exposed Xpc(-/-) epidermis further showed that the "near-4N" arrested cells retained cytokeratin 5 and lacked cytokeratin 10. Hence, we conclude that the arrested near-4N cells became detached from the basal layer without entering a proper differentiation program and were indeed subsequently lost through the epidermal turnover. This expulsion apparently constitutes an alternative route, different from in situ apoptosis, to eliminate DNA-damaged arrested cells from the epidermis.

Expression of apoptotic and cell proliferation regulatory proteins in actinic cheilitis

BACKGROUND

Actinic cheilitis (AC) is a pre-malignant lesion caused by ultraviolet (UV) radiation. The apoptotic proteins p53, bax, bcl-2, and the proliferation marker Ki-67, are known to play an important role in UV-exposed skin and carcinomas, therefore, these markers were assessed in AC and compared with normal lip and oral mucosa.

METHODS

AC (n = 13), normal lip (n = 7) and oral mucosa (n = 6) biopsies were stained immunohistochemically for p53, bax, bcl-2 and Ki-67, to determine their expression and distribution.

RESULTS

p53 was over-expressed in AC as compared with normal lip and oral mucosa (P < 0.003). Although bcl-2 expression was higher in AC than in oral mucosa (P < 0.002), it was significantly reduced as compared with normal lip (P < 0.04). Bax expression remained unchanged, and Ki-67 was significantly increased in AC and normal lip as compared with oral mucosa (P < 0.05).

CONCLUSION

The results suggest that DNA-damaged cells by UV radiation in AC are eliminated by apoptosis.

Silibinin Up-regulates DNA-Protein Kinase-dependent p53 Activation to Enhance UVB-induced Apoptosis in Mouse Epithelial JB6 Cells

In the present study, we employed a well established JB6 mouse epithelial cell model to define the molecular mechanism of efficacy of a naturally occurring flavonoid silibinin against ultraviolet B (UVB)-induced skin tumorigenesis. UVB exposure of cells caused a moderate phosphorylation of ERK1/2 and Akt and a stronger phosphorylation of p53 at Ser(15), which was enhanced markedly by silibinin pretreatment. Kinase activity of ERK1/2 for Elk-1 and Akt for glycogen synthase kinase-3beta was also potently enhanced by silibinin pretreatment. Furthermore, silibinin increased the UVB-induced level of cleaved caspase 3 as well as apoptotic cells. Based on these observations, next we investigated the role of upstream kinases, ATM/ATR and DNA-PK, which act as sensors for UVB-induced DNA damage and transduce signals leading to DNA repair or apoptosis. Whereas UVB strongly activated ATM as observed by Ser(1981) phosphorylation, it was not affected by silibinin pretreatment. However, pretreatment of cells with the DNA-protein kinase (PK) inhibitor LY294002 strongly reversed silibinin-enhanced Akt-Ser(473) and p53-Ser(15) as well as ERK1/2 phosphorylation together with a dose-dependent decrease in cleaved caspase 3 and apoptosis (p < 0.05). In addition, silibinin pretreatment strongly enhanced H2A.X-Ser(139) phosphorylation and DNA-PK-associated kinase activity as well as the physical interaction of p53 with DNA-PK; pretreatment of cells with LY294002 but not caffeine abolished the silibinin-caused increase in both DNA-PK activation and p53-Ser(15) phosphorylations. Together, these findings suggest that silibinin preferentially activates the DNA-PK-p53 pathway for apoptosis in response to UVB-induced DNA damage, and that this could be a predominant mechanism of silibinin efficacy against UVB-induced skin cancer.

Analysis of genes responding to ultraviolet B irradiation of HaCaT keratinocytes using a cDNA microarray

BACKGROUND

Ultraviolet (UV) B irradiation causes many important biological changes in skin, which lead to pathophysiological alterations of the homeostatic environment.

OBJECTIVES

To gain more insight into the molecular events provoked by UVB irradiation, we performed cDNA microarray analysis.

METHODS

Immortalized HaCaT keratinocytes were irradiated with a high cytotoxic dose of UVB (50 mJ cm(-2)), and total RNA was isolated. Fluorescently labelled probes were prepared by reverse transcription and were hybridized with cDNA microarray slides made using 840 cDNA clones.

RESULTS

Time-course cDNA microarray analysis revealed the global gene expression profile after UVB exposure. Of 840 genes tested, 192 genes showed changes in their expression levels at one or more of four time points. The genes were clustered into four groups according to their expression patterns in a self-organizing maps analysis. Classification of these genes into nine functional categories revealed that UVB irradiation affected several biological processes. The genes that were first upregulated and then returned to normal levels included several genes related to the inhibition of cell growth and the proteasome pathway. Conversely, the expressions of many genes involved in the cytoskeleton, signal transduction, metabolism and transcription were first downregulated or unchanged and then upregulated later, reflecting the recovery of UVB-damaged cellular activities.

CONCLUSIONS

These results demonstrate the complexity of the transcriptional profile of the UVB response, and provide a basis for the global characterization of UV-regulated gene expression.