Parameters of protection against ultraviolet radiation-induced skin cell damage

Melatonin inhibits senescence-associated melanin pigmentation through the p53-TYR pathway in human primary melanocytes and the skin of C57BL/6 J mice after UVB irradiation

UVB exposure accelerates skin aging and pigmentation. Melatonin effectively regulates tyrosinase (TYR) activity and aging. The purpose of this study was to determine the association between premature senescence and pigmentation, and the mechanism of melanin synthesis effected by melatonin. Primary melanocytes were extracted and identified from the male foreskin. To inhibit TYR expression, primary melanocytes were transduced with the lentivirus pLKD-CMV-EGFP-2A-Puro-U6-TYR. The wild-type TYR^(+/+) and TYR^(-/-) or TYR^(+/-) knockout C57BL/6 J mice were used to determine the role of TYR on melanin synthesis in vivo. Results showed that UVB-induced melanin synthesis is dependent on TYR in primary melanocytes and mice. Furthermore, in primary melanocytes pretreated with Nutlin-3 or PFT-α to up or downregulate p53, results showed that premature senescence and melanin synthesis increased in primary melanocytes after UVB irradiation at 80 mJ/cm², and further increased after being treated with Nutlin-3, while significantly decreased with PFT-α. In addition, melatonin inhibited UVB-induced premature senescence associated with inactivation of p53 and phosphorylation of p53 on Ser15 (ser-15), a decrease of melanin synthesis accompanied by reduced TYR expression. Moreover, skin erythema and pigmentation induced by UVB were reduced in the dorsal and ear skin of mice topically pretreated with 2.5% melatonin. These indicate that melatonin inhibits UVB-induced senescence-associated pigmentation via the p53-TYR pathway in primary melanocytes and prevents pigmentation obviously in the dorsal and ear skin of C57BL/6 J mice after UVB irradiation. KEY MESSAGES: P53 links UVB irradiation-induced senescence and senescence-associated pigmentation and regulates TYR in primary melanocytes after UVB irradiation. Melatonin inhibits senescence-associated pigmentation through the p53-TYR pathway in primary melanocytes. Melatonin prevents skin erythema and melanin pigmentation induced by UVB irradiation in the dorsal and ear skin of C57BL/6J mice.

Protective Effect of Castanopsis sieboldii Extract against UVB-Induced Photodamage in Keratinocytes

Ultraviolet B (UVB) rays disrupt the skin by causing photodamage via processes such as reactive oxygen species (ROS) production, endoplasmic reticulum (ER) stress, DNA damage, and/or collagen degradation. Castanopsis sieboldii is an evergreen tree native to the southern Korean peninsula. Although it is known to have antioxidant and anti-inflammatory effects, its protective effect against photodamage in keratinocytes has not been investigated. Thus, in the present study, we investigated the effect of 70% ethanol extract of C. sieboldii leaf (CSL3) on UVB-mediated skin injuries and elucidated the underlying molecular mechanisms. CSL3 treatment restored the cell viability decreased by UVB irradiation. Moreover, CSL3 significantly inhibited UVB- or tert-butyl hydroperoxide-mediated ROS generation in HaCaT cells. ER stress was inhibited, whereas autophagy was upregulated by CSL3 treatment against UVB irradiation. Additionally, CSL3 increased collagen accumulation and cell migration, which were decreased by UVB exposure. Notably, epigallocatechin gallate, the major component of CSL3, improved the cell viability decreased by UVB irradiation through regulation of ER stress and autophagy. Conclusively, CSL3 may represent a promising therapeutic candidate for the treatment of UVB-induced skin damage.

The Impact of Oxidative Stress and AKT Pathway on Cancer Cell Functions and Its Application to Natural Products

Oxidative stress and AKT serine-threonine kinase (AKT) are responsible for regulating several cell functions of cancer cells. Several natural products modulate both oxidative stress and AKT for anticancer effects. However, the impact of natural product-modulating oxidative stress and AKT on cell functions lacks systemic understanding. Notably, the contribution of regulating cell functions by AKT downstream effectors is not yet well integrated. This review explores the role of oxidative stress and AKT pathway (AKT/AKT effectors) on ten cell functions, including apoptosis, autophagy, endoplasmic reticulum stress, mitochondrial morphogenesis, ferroptosis, necroptosis, DNA damage response, senescence, migration, and cell-cycle progression. The impact of oxidative stress and AKT are connected to these cell functions through cell function mediators. Moreover, the AKT effectors related to cell functions are integrated. Based on this rationale, natural products with the modulating abilities for oxidative stress and AKT pathway exhibit the potential to regulate these cell functions, but some were rarely reported, particularly for AKT effectors. This review sheds light on understanding the roles of oxidative stress and AKT pathway in regulating cell functions, providing future directions for natural products in cancer treatment.

The Roles of Skin Langerhans Cells in Immune Tolerance and Cancer Immunity

Langerhans cells (LC) are a unique population of tissue-resident macrophages with dendritic cell (DC) functionality that form a network of cells across the epidermis of the skin. Their location at the skin barrier suggests an important role for LC as immune sentinels at the skin surface. The classification of LC as DC over the past few decades has driven the scientific community to extensively study how LC function as DC-like cells that prime T cell immunity. However, LC are a unique type of tissue-resident macrophages, and recent evidence also supports an immunoregulatory role of LC at steady state and during specific inflammatory conditions, highlighting the impact of cutaneous environment in shaping LC functionality. In this mini review, we discuss the recent literature on the immune tolerance function of LC in homeostasis and disease conditions, including malignant transformation and progression; as well as LC functional plasticity for adaption to microenvironmental cues and the potential connection between LC population heterogeneity and functional diversity. Future investigation into the molecular mechanisms that LC use to integrate different microenvironment cues and adapt immunological responses for controlling LC functional plasticity is needed for future breakthroughs in tumor immunology, vaccine development, and treatments for inflammatory skin diseases.

DHPW1 attenuation of UVB-induced skin photodamage in human immortalized keratinocytes

Ultraviolet radiation (UVB) can result in photodamage to the skin and can seriously threaten health, particularly in the elderly. Oxidative stress and the inflammatory response have been shown to play a significant role in the process. In a previous study, we isolated, purified and identified a polysaccharide from the extract of Dendrobium huoshanense (DHPW1). In this study we evaluated the effect of DHPW1 on ameliorating the UVB photodamage of human immortalized keratinocytes (HaCaT). Cell proliferation and cell scratch assays were used to evaluate the viability of the HaCaT treated with DHPW1, and a fluorescent probe and Western blot analysis were used to examine the production of reactive oxygen species (ROS) and the expression of proinflammatory factors IL-1β, IL-6, and NF-κB(p65). The results show that, compared with the control group (UVB irradiation only), DHPW1 significantly improved the viability of UVB-irradiated HaCaT and enhanced the migration rate of the cell scratch after 24 h. The scratch-healing rate reached 90 % after 36 h. DHPW1 also significantly inhibited UVB-induced oxidative stress and expression of proinflammatory factors . Compared with the control group, the production of ROS decreased by 49.11 %, and the relative protein expression of IL-6 and NF-κB(p65) decreased by up to 13.30 % and 31.02 %, respectively. It is concluded that DHPW1 can significantly improve viability and wound closure rate of UVB-irradiated HaCaT. In addition, it can reduce the expression of IL-1 and IL-6 by inhibiting the transcription of NF-κB(p65), thereby reducing inflammation and oxidative stress in UVB-irradiated HaCaT.

IKKα mediates UVB-induced cell apoptosis by regulating p53 pathway activation

Exposure to ultraviolet B (UVB) has been demonstrated to induce DNA damage as well as angiogenesis-related photo-damages, which are implicated in a variety of medical problems, including sunburn, photo-aging and skin cancers. However, the molecular mechanism related to UVB-induced photo-injuries remained fully elucidated. Here we revealed that one of the catalytic subunits of the IKK complex, IKKα, played a critical role in mediating UVB-induced apoptotic responses in two kinds of UVB sensitive cells, human keratinocyte (HaCat) and mouse embryonic fibroblasts (MEFs). This function of IKKα was unrelated to NF-κB activity, but was delivered by inducing phosphorylation and acetylation of p53 and upregulating the expression of the pro-apoptotic p53 target gene, PERP. Although IKKα kinase activity was required for mediating post-translational modifications and transactivation of 53 and PERP induction, IKKα did not show direct binding ability toward p53. Instead, IKKα could interact with CHK1, the protein kinase leading to p53 phosphorylation, and trigger CHK1 activation and CHK1/p53 complex formation. At the same time, IKKα could also interact with p300 and CBP, the acetyltransferases responsible for p53 acetylation, and trigger p300/CBP activation and p300/p53 or CBP/p53 complex formation under UVB exposure. Taken together, we have identified a novel NF-κB-independent role of IKKα in mediating UVB-induced apoptosis by regulating p53 pathway activation. Targeting IKKα/p53/PERP pathway might be helpful to prevent skin photo-damages induced by sunlight.

Height and Risk of Vitiligo: A Nationwide Cohort Study

Adult height is linked to the risk of several diseases, but its association with vitiligo has not been established. This study aimed to investigate the relationship between adult height and vitiligo incidence. Korean nationwide claims data from 15,980,754 individuals (20 years of age or older) who received a health checkup during the period 2005–2008, were examined. Subjects were categorized into age- and gender-specific height quintiles. Participants were followed until vitiligo diagnosis or until the end of 2015. The Cox proportional-hazards model for cumulative risk was computed for height categories. During the follow-up period, 29,196 cases (136,020,214 person-years) of newly diagnosed vitiligo were reported. A positive association was found between height and risk of vitiligo in which the hazard ratio between the highest and lowest quintiles of height was 1.36 (95% confidence interval: 1.31–1.42). While more diverse cohort studies are needed, our findings suggest that taller stature increases the risk of vitiligo.

Phenformin: AMP(K)ed for Potential Repurposing

The results in the article by Zhou et al. (2020) demonstrate that the antidiabetic drug phenformin inhibits skin tumor growth and promotes keratinocyte differentiation, and an underlying mechanism is also defined. In this commentary, additional potential mechanisms through which phenformin may exert its antitumorigenic effect are described. Thus, the proposed repurposing of phenformin to treat skin cancer has merit.

Mitochondrial Sirtuins in Skin and Skin Cancers

Mammalian sirtuins (SIRTs 1-7) are a family of NAD+-dependent deacetylases with distinct subcellular localization and biological functions that regulate various important cellular processes. Among these, SIRTs -3, -4 and -5 are located in the mitochondria and have been implicated in caloric restriction, oxidative stress, aging and various human diseases. Emerging evidence has found dysregulation of mitochondrial sirtuins in multiple dermatological conditions, including responses to ultraviolet radiation (UVR), suggesting their importance in maintaining skin health. In this review, we discuss the roles and implications of mitochondrial sirtuins in cutaneous cellular processes, and their emerging potential as a target for the management of skin diseases, including skin cancer. Among mitochondrial sirtuins, SIRT3 is the most studied and linked to multiple skin conditions and diseases (keratinocyte differentiation, wound healing, chronological aging, UVR and ozone response, systemic sclerosis, melanoma, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC)). SIRT4 has been connected to keratinocyte differentiation, chronological aging, UVR response, alopecia, BCC and SCC. Further, SIRT5 has been associated with keratinocyte differentiation, melanoma, BCC and SCC. Overall, while there is compelling evidence for the involvement of mitochondrial sirtuins in skin, additional detailed studies are needed to understand their exact roles in skin and skin cancers.

RIPK1 regulates the survival of human melanocytes upon endoplasmic reticulum stress

Vitiligo is a common congenital or acquired disfiguring skin disorder. At present, endoplasmic reticulum (ER) stress has been identified to serve a critical role in the pathogenesis of vitiligo. Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is a protein serine/threonine kinase. The specific molecular mechanism of RIPK1 in human melanocytes upon ER stress remains to be determined. In the present study, RIPK1 was significantly downregulated in tunicamycin (TM)-induced ER stressed-human melanocytes. Subsequently, to explore the role of RIPK1 in ER stress-induced human melanocytes, human melanocytes were transfected with control or RIPK1 plasmids for 24 h and then treated with 3 µM TM for 48 h. Reverse transcription-quantitative PCR and western blot analysis indicated that the expression levels of protein kinase R-like endoplasmic reticulum kinase, eukaryotic translation initiation factor 2 subunit 1 and CCAAT-enhancer-binding protein homologous protein were significantly increased in the TM-treated group compared with the controls. In addition, the effect of high RIPK1 expression on ER stress-induced human melanocyte survival was studied. The present results indicated that TM inhibited cell viability and promoted apoptosis in human primary epidermal melanocytes. Western blot analysis demonstrated that the expression of Bax and caspase-3 was upregulated and the expression of Bcl-2 was downregulated in TM-treated human melanocytes. The effects of TM on human melanocytes were reversed by RIPK1 overexpression. Therefore, RIPK1 overexpression may have an effect on the PI3K/AKT/mTOR signaling pathway in human melanocytes under ER stress. The results of the current study demonstrated that RIPK1 could protect human melanocytes from cell damage induced by ER stress by regulating the PI3K/AKT/mTOR and ER stress signaling pathways, thereby serving a protective role in the occurrence and development of vitiligo.

ΜicroRNA‑421 participates in vitiligo development through regulating human melanocyte survival by targeting receptor‑interacting serine/threonine kinase 1

Vitiligo is a common localized or generalized skin pigmentation disorder. Endoplasmic reticulum (ER) stress may be implicated in the development of vitiligo. microRNA-421 (miR-421) has been reported to be dysregulated in various human tumors. However, there is no report to date on the role of miR-421 in vitiligo development. The present study demonstrated that 3 µM tunicamycin (TM) increased the expression of the ER stress-related proteins protein kinase RNA-like endoplasmic reticulum kinase (PERK), α subunit of eukaryotic translation initiation factor 2 (eIF2α) and C/EBP homologous protein (CHOP) in human primary epidermal melanocytes. Moreover, TM suppressed melanocyte viability and induced apoptosis. Reverse transcription-quantitative PCR analysis demonstrated that TM promoted miR-421 expression in human melanocytes. Next, TargetScan and dual luciferase reporter gene assay indicated that receptor-interacting serine/threonine kinase 1 (RIPK1) was a direct target of miR-421. RIPK1 expression was significantly downregulated in TM-induced human melanocytes. Subsequently, the effect of miR-421 downregulation on the damage of human melanocytes induced by ER stress was investigated. Human melanocytes were transfected with inhibitor control, miR-421 inhibitor, miR-421 inhibitor + control-short hairpin (sh)RNA, or miR-421 inhibitor + RIPK1-shRNA for 24 h and then treated with TM (3 µM) for 48 h. TM was found to upregulate PERK, eIF2α and CHOP protein expression in human melanocytes, which was reduced by an miR-421 inhibitor. In addition, the miR-421 inhibitor increased viability and reduced apoptosis in TM-treated melanocytes. Furthermore, all these effects of the miR-421 inhibitor on TM-induced human melanocytes were reversed by RIPK1-shRNA. Further analyses revealed that the miR-421 inhibitor activated the phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin signaling pathway in TM-induced human melanocytes. These data collectively suggest that miR-421 may serve as a new treatment target in vitiligo development.

Identification of Salvia haenkei as gerosuppressant agent by using an integrated senescence-screening assay

Cellular senescence is a stable cell cycle arrest that is the causative process of aging. The PI3K/AKT/mTOR pathway is implicated in the control of cellular senescence and inhibitors of this pathway have been successfully used for life span prolongation experiments in mammals. PTEN is the major regulator of the PI3K/AKT/mTOR pathway and loss of PTEN promotes a senescence response termed PICS. Here we report a novel-screening assay, for the identification of compounds that block different types of senescence response. By testing a library of more than 3000 natural and chemical compounds in PTEN deficient cells we have found that an extract from Salvia haenkei (SH), a native plant of Bolivia is a potent inhibitor of PICS. SH also decreases replicative and UV-mediated senescence in human primary fibroblasts and in a model of in vitro reconstructed human epidermis. Mechanistically, SH treatment affects senescence driven by UV by interfering with IL1-α signalling. Pre-clinical and clinical testing of this extract by performing toxicity and irritability evaluation in vitro also demonstrate the safety of SH extract for clinical use as anti-aging skin treatment.

Protein activation mapping of human sun-protected epidermis after an acute dose of erythemic solar simulated light

Ultraviolet radiation is an important etiologic factor in skin cancer and a better understanding of how solar stimulated light (SSL) affects signal transduction pathways in human skin which is needed in further understanding activated networks that could be targeted for skin cancer prevention. We utilized Reverse Phase Protein Microarray Analysis (RPPA), a powerful technology that allows for broad-scale and quantitative measurement of the activation/phosphorylation state of hundreds of key signaling proteins and protein pathways in sun-protected skin after an acute dose of two minimal erythema dose (MED) of SSL. RPPA analysis was used to map the altered cell signaling networks resulting from acute doses of solar simulated radiation (SSL). To that end, we exposed sun-protected skin in volunteers to acute doses of two MED of SSL and collected biopsies pre-SSL and post-SSL irradiation. Frozen biopsies were subjected to laser capture microdissection (LCM) and then assessed by RPPA. The activation/phosphorylation or total levels of 128 key signaling proteins and drug targets were selected for statistical analysis. Coordinate network-based analysis was performed on specific signaling pathways that included the PI3k/Akt/mTOR and Ras/Raf/MEK/ERK pathways. Overall, we found early and sustained activation of the PI3K-AKT-mTOR and MAPK pathways. Cell death and apoptosis-related proteins were activated at 5 and 24 h. Ultimately, expression profile patterns of phosphorylated proteins in the epidermal growth factor receptor(EGFR), AKT, mTOR, and other relevant pathways may be used to determine pharmacodynamic activity of new and selective topical chemoprevention agents administered in a test area exposed to SSL to determine drug-induced attenuation or reversal of skin carcinogenesis pathways.

Skin exposure to ultraviolet radiation leads to the activation of proteins involved in carcinogenic pathways. Janine Einspahr and Clara Curiel-Lewandrowski of the Arizona Cancer Center and colleagues in the US exposed normally ultraviolet protected skin of 12 individuals to two times the dose of solar-simulated light needed to induce redness. Skin biopsies were taken before and after exposure and 128 proteins known to be involved in key cancer signaling pathways were examined using ‘reverse phase protein microarray analysis’. They found early and sustained activation of multiple signaling pathways, in addition to activation of cell death and apoptosis-related proteins. The study may serve as a model for investigating the pathways involved in chronic or ultraviolet-induced carcinogenesis, which may ultimately lead to the development of targeted therapies to attenuate or reverse skin cancer pathways.

Novel approaches to vitiligo treatment via modulation of mTOR and NF-κB pathways in human skin melanocytes

Vitiligo is a skin depigmentation disorder with an increasing prevalence. Among recognized mechanisms is the oxidative stress that affects melanocytes which are responsible for skin pigmentation. Studies have shown that high concentration of hydrogen peroxide, or H₂O₂, induces apoptotic activities. Few studies have been done with lower doses of H₂O₂. Using human skin melanocytes, we investigated the effect of moderate concentration of H₂O₂ on melanocyte dendrites. Confocal data show that H₂O₂ at 250 µM induces loss of dendrites, as indicated by cytoskeletal proteins. α-melanocyte stimulating hormone or α-MSH pretreatment protects against H₂O₂-induced loss of dendrites, while α-MSH alone enhances dendrites. PI3K/AKT inhibitor LY294002 and mTORC1 inhibitor Rapamycin inhibit α-MSH-induced dendrites. In this study, we also investigated the effect of TNFα on cultured human skin melanocytes, since TNFα plays important roles in vitiligo. Confocal data demonstrate that TNFα induces NFκB activation. Western blot analysis shows that TNFα induces IκB phosphorylation and degradation. Interestingly, α-MSH does not have any effect of TNFα-induced IκB degradation and NF-κB activation. α-MSH, however, activates mTORC1 pathway. TNFα induces p38 but not AMPKα activation. Collectively, our data suggest that modulation of mTOR and NF-κB pathways may be a novel approach for better clinical management of vitiligo.

Phosphorylation regulates activity of 7-dehydrocholesterol reductase (DHCR7), a terminal enzyme of cholesterol synthesis

Cholesterol is essential for survival, but too much or too little can cause disease. Thus, cholesterol levels must be kept within close margins. 7-dehydrocholesterol reductase (DHCR7) is a terminal enzyme of cholesterol synthesis, and is essential for embryonic development. Largely, DHCR7 research is associated with the developmental disease Smith-Lemli-Opitz syndrome, which is caused by mutations in the DHCR7 gene. However, little is known about what regulates DHCR7 activity. Here we provide evidence that phosphorylation plays a role in controlling DHCR7 activity, which may provide a means to divert flux from cholesterol synthesis to vitamin D production. DHCR7 activity was significantly decreased when we used pharmacological inhibitors against two important kinases, AMP-activated protein kinase and protein kinase A. Moreover, mutating a known phosphorylated residue, S14, also decreased DHCR7 activity. Thus, we demonstrate that phosphorylation modulates DHCR7 activity in cells, and contributes to the overall synthesis of cholesterol, and probably vitamin D.

Hypoxia-Inducible Factor-1: A Critical Player in the Survival Strategy of Stressed Cells

HIF-1 activation has been well known as an adaptive strategy to hypoxia. Recently it became clear that hypoxia was often accompanied by insufficient supply of glucose or amino acids as a common result of poor circulation that frequently occurs in solid tumors and ischemic lesions, creating a mixed nutrient insufficiency. In response to nutrient insufficiency, stressed cells elicit survival strategies including activation of AMPK and HIF-1 to cope with the stress. Particularly, in solid tumors, HIF-1 promotes cell survival and migration, stimulates angiogenesis, and induces resistance to radiation and chemotherapy. Interestingly, radiation and some chemotherapeutics are reported to trigger the activation of AMPK. Here we discuss the recent advances that may potentially link the stress responsive mechanisms including AMPK activation, ATF4 activation and the enhancement of Hsp70/Hsp90 function to HIF-1 activation. Potential implication and application of the stress-facilitated HIF-1 activation in solid tumors and ischemic disorders will be discussed. A better understanding of HIF-1 activation in cells exposed to stresses is expected to facilitate the design of therapeutic approaches that specifically modulate cell survival strategy.

Activation of the PI3K/Akt/mTOR and MAPK Signaling Pathways in Response to Acute Solar-Simulated Light Exposure of Human Skin

The incidence of skin cancer is higher than all other cancers and continues to increase, with an average annual cost over $8 billion in the United States. As a result, identifying molecular pathway alterations that occur with UV exposure to strategize more effective preventive and therapeutic approaches is essential. To that end, we evaluated phosphorylation of proteins within the PI3K/Akt and MAPK pathways by immunohistochemistry in sun-protected skin after acute doses of physiologically relevant solar-simulated ultraviolet light (SSL) in 24 volunteers. Biopsies were performed at baseline, 5 minutes, 1, 5, and 24 hours after SSL irradiation. Within the PI3K/Akt pathway, we found activation of Akt (serine 473) to be significantly increased at 5 hours while mTOR (serine 2448) was strongly activated early and was sustained over 24 hours after SSL. Downstream, we observed a marked and sustained increase in phospho-S6 (serine 235/S236), whereas phospho-4E-BP1 (threonines 37/46) was increased only at 24 hours. Within the MAPK pathway, SSL-induced expression of phospho-p38 (threonine 180/tyrosine 182) peaked at 1 to 5 hours. ERK 1/2 was observed to be immediate and sustained after SSL irradiation. Phosphorylation of histone H3 (serine 10), a core structural protein of the nucleosome, peaked at 5 hours after SSL irradiation. The expression of both p53 and COX-2 was increased at 5 hours and was maximal at 24 hours after SSL irradiation. Apoptosis was significantly increased at 24 hours as expected and indicative of a sunburn-type response to SSL. Understanding the timing of key protein expression changes in response to SSL will aid in development of mechanistic-based approaches for the prevention and control of skin cancers.

Protein phosphatase-1 is involved in the maintenance of normal homeostasis and in UVA irradiation-induced pathological alterations in HaCaT cells and in mouse skin

The number of ultraviolet (UV) radiation-induced skin diseases such as melanomas is on the rise. The altered behavior of keratinocytes is often coupled with signaling events in which Ser/Thr specific protein kinases and phosphatases regulate various cellular functions. In the present study the role of protein phosphatase-1 (PP1) was investigated in the response of human keratinocyte (HaCaT) cells and mouse skin to UV radiation. PP1 catalytic subunit (PP1c) isoforms, PP1cα/γ and PP1cδ, are all localized to the cytoskeleton and cytosol of keratinocytes, but PP1cδ was found to be dominant over PP1α/γ in the nucleus. PP1c-silencing in HaCaT cells decreased the phosphatase activity and suppressed the viability of the cells. Exposure to a 10 J/cm(2) UVA dose induced HaCaT cell death and resulted in a 30% decrease of phosphatase activity. PP1c-silencing and UVA irradiation altered the gene expression profile of HaCaT cells and suggested that the expression of 19 genes was regulated by the combined treatments with many of these genes being involved in malignant transformation. Microarray analysis detected altered expression levels of genes coding for melanoma-associated proteins such as keratin 1/10, calcium binding protein S100A8 and histone 1b. Treatment of Balb/c mice with the PP1-specific inhibitor tautomycin (TM) exhibited increased levels of keratin 1/10 and S100A8, and a decreased level of histone 1b proteins following UVA irradiation. Moreover, TM treatment increased pigmentation of the skin which was even more apparent when TM was followed by UVA irradiation. Our data identify PP1 as a regulator of the normal homeostasis of keratinocytes and the UV-response.

Red light interferes in UVA-induced photoaging of human skin fibroblast cells

The possible regulation mechanism of red light was determined to discover how to retard UVA-induced skin photoaging. Human skin fibroblasts were cultured and irradiated with different doses of UVA, thus creating a photoaging model. Fibroblasts were also exposed to a subtoxic dose of UVA combined with a red light-emitting diode (LED) for five continuous days. Three groups were examined: control, UVA and UVA plus red light. Cumulative exposure doses of UVA were 25 J cm(-2), and the total doses of red light were 0.18 J cm(-2). Various indicators were measured before and after irradiation, including cell morphology, viability, β-galactosidase staining, apoptosis, cycle phase, the length of telomeres and the protein levels of photoaging-related genes. Red light irradiation retarded the cumulative low-dose UVA irradiation-induced skin photoaging, decreased the expression of senescence-associated β-galactosidase, upregulated SIRT1 expression, decreased matrix metalloproteinase MMP-1 and the acetylation of p53 expression, reduced the horizon of cell apoptosis and enhanced cell viability. Furthermore, the telomeres in UVA-treated cells were shortened compared to those of cells in the red light groups. These results suggest that red light plays a key role in the antiphotoaging of human skin fibroblasts by acting on different signaling transduction pathways.

Tyrosine/cysteine cluster sensitizing human γD-crystallin to ultraviolet radiation-induced photoaggregation in vitro

Ultraviolet radiation (UVR) exposure is a major risk factor for age-related cataract, a protein-aggregation disease of the human lens often involving the major proteins of the lens, the crystallins. γD-Crystallin (HγD-Crys) is abundant in the nucleus of the human lens, and its folding and aggregation have been extensively studied. Previous work showed that HγD-Crys photoaggregates in vitro upon exposure to UVA/UVB light and that its conserved tryptophans are not required for aggregation. Surprisingly, the tryptophan residues play a photoprotective role because of a distinctive energy-transfer mechanism. HγD-Crys also contains 14 tyrosine residues, 12 of which are organized as six pairs. We investigated the role of the tyrosines of HγD-Crys by replacing pairs with alanines and monitoring photoaggregation using light scattering and SDS-PAGE. Mutating both tyrosines in the Y16/Y28 pair to alanine slowed the formation of light-scattering aggregates. Further mutant studies implicated Y16 as important for photoaggregation. Mass spectrometry revealed that C18, in contact with Y16, is heavily oxidized during UVR exposure. Analysis of multiple mutant proteins by mass spectrometry suggested that Y16 and C18 likely participate in the same photochemical process. The data suggest an initial photoaggregation pathway for HγD-Crys in which excited-state Y16 interacts with C18, initiating radical polymerization.

DNA-dependent protein kinase catalytic subunit (DNA-PKcs)-SIN1 association mediates ultraviolet B (UVB)-induced Akt Ser-473 phosphorylation and skin cell survival

BACKGROUND

The exposure of skin keratinocytes to Ultraviolet (UV) irradiation leads to Akt phosphorylation at Ser-473, which is important for the carcinogenic effects of excessive sun exposure. The present study investigated the underlying mechanism of Akt Ser-473 phosphorylation by UVB radiation.

RESULTS

We found that DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and mammalian target of rapamycin (mTOR) complex 2 (mTORC2) were both required for UVB-induced Akt Ser-473 phosphorylation in keratinocytes. Inhibition of DNA-PKcs activity via its inhibitor NU7026, a dominant-negative kinase-dead mutation, RNA interference (RNAi) or gene depletion led to the attenuation of UVB-induced Akt Ser-473 phosphorylation. Meanwhile, siRNA silencing or gene depletion of SIN1, a key component of mTORC2, abolished Akt Ser-473 phosphorylation by UVB. Significantly, we discovered that DNA-PKcs was associated with SIN1 in cytosol upon UVB radiation, and this complexation appeared required for Akt Ser-473 phosphorylation. Meanwhile, this DNA-PKcs-SIN1 complexation by UVB was dependent on epidermal growth factor receptor (EGFR) activation, and was disrupted by an EGFR inhibitor (AG1478) or by EGFR depletion. UVB-induced complexation between DNA-PKcs and mTORC2 components was also abolished by NU7026 and DNA-PKcs mutation. Finally, we found that both DNA-PKcs and SIN1 were associated with apoptosis resistance of UVB radiation, and inhibition of them by NU7026 or genetic depletion significantly enhanced UVB-induced cell death and apoptosis.

CONCLUSION

Taken together, these results strongly suggest that DNA-PKcs-mTORC2 association is required for UVB-induced Akt Ser-473 phosphorylation and cell survival, and might be important for tumor cell transformation.

Capsaicin induces apoptosis in human osteosarcoma cells through AMPK-dependent and AMPK-independent signaling pathways

Recent studies have focused on the anti-tumor activity of capsaicin. However, the potential effects of capsaicin in osteosarcoma cells and the underlying mechanisms are not fully understood. In the current study, we observed that capsaicin-induced growth inhibition and apoptosis in cultured osteosarcoma cells (U2OS and MG63), which were associated with a significant AMP-activated protein kinase (AMPK) activation. AMPK inhibition by compound C or RNA interference suppressed capsaicin-induced cytotoxicity, while AMPK activators (AICAR and A769662) promoted osteosarcoma cell death. For the mechanism study, we found that AMPK activation was required for capsaicin-induced mTORC1 (mTOR complex 1) inhibition, B cell lymphoma 2 (Bcl-2) downregulation and Bax upregulation in MG63 cells. Capsaicin administration induced p53 activation, mitochondrial translocation and Bcl-2 killer association, such effects were dependent on AMPK activation. Interestingly, we observed a significant pro-apoptotic c-Jun NH2-terminal kinases activation by capsaicin in MG63 cells, which appeared to be AMPK independent. In conclusion, capsaicin possessed strong efficacy against human osteosarcoma cells. Molecular studies revealed that capsaicin activated AMPK-dependent and AMPK-independent signalings to mediate cell apoptosis. The results of this study should have significant translational relevance in managing this deadly malignancy.

The role of AKT/mTOR pathway in stress response to UV-irradiation: implication in skin carcinogenesis by regulation of apoptosis, autophagy and senescence

Induction of DNA damage by UVB and UVA radiation may generate mutations and genomic instability leading to carcinogenesis. Therefore, skin cells being repeatedly exposed to ultraviolet (UV) light have acquired multilayered protective mechanisms to avoid malignant transformation. Besides extensive DNA repair mechanisms, the damaged skin cells can be eliminated by induction of apoptosis, which is mediated through the action of tumor suppressor p53. In order to prevent the excessive loss of skin cells and to maintain the skin barrier function, apoptotic pathways are counteracted by anti-apoptotic signaling including the AKT/mTOR pathway. However, AKT/mTOR not only prevents cell death, but is also active in cell cycle transition and hyper-proliferation, thereby also counteracting p53. In turn, AKT/mTOR is tuned down by the negative regulators being controlled by the p53. This inhibition of AKT/mTOR, in combination with transactivation of damage-regulated autophagy modulators, guides the p53-mediated elimination of damaged cellular components by autophagic clearance. Alternatively, p53 irreversibly blocks cell cycle progression to prevent AKT/mTOR-driven proliferation, thereby inducing premature senescence. Conclusively, AKT/mTOR via an extensive cross talk with p53 influences the UV response in the skin with no black and white scenario deciding over death or survival.

Tryptophan cluster protects human γD-crystallin from ultraviolet radiation-induced photoaggregation in vitro

Exposure to ultraviolet radiation (UVR) is a significant risk factor for age-related cataract, a disease of the human lens and the most prevalent cause of blindness in the world. Cataract pathology involves protein misfolding and aggregation of the primary proteins of the lens, the crystallins. Human γD-crystallin (HγD-Crys) is a major γ-crystallin in the nucleus of the human lens. We report here analysis of UVR-induced damage to HγD-Crys in vitro. Irradiation of solutions of recombinant HγD-Crys with UVA/UVB light produced a rise in solution turbidity due to polymerization of the monomeric crystallins into higher molecular weight aggregates. A significant fraction of this polymerized protein was covalently linked. Photoaggregation of HγD-Crys required oxygen and its rate was protein concentration and UVR dose dependent. To investigate the potential roles of individual tryptophan residues in photoaggregation, triple W:F mutants of HγD-Crys were irradiated. Surprisingly, despite reducing UVR absorbing capacity, multiple W:F HγD-Crys mutant proteins photoaggregated more quickly and extensively than wild type. The results reported here are consistent with previous studies that postulated that an energy transfer mechanism between the highly conserved pairs of tryptophan residues in HγD-Crys could be protective against UVR-induced photodamage.

The mTOR inhibitor rapamycin opposes carcinogenic changes to epidermal Akt1/PKBα isoform signaling

Epidermal squamous cell carcinoma (SCC) is the most aggressive non-melanoma skin cancer and is dramatically increased in patients undergoing immunosuppression following solid organ transplantation, contributing substantially to morbidity and mortality. Recent clinical studies show that use of the mammalian target of rapamycin (mTOR) inhibitor rapamycin as a post-transplantation immunosuppressive significantly reduces SCC occurrence compared with other immunosuppressives, though the mechanism is not fully understood. We show that rapamycin selectively upregulates epidermal Akt1, while failing to upregulate epidermal Akt2. Rapamycin increases epidermal Akt1 phosphorylation via inhibition of the mTOR complex 1-dependent regulation of insulin receptor substrate-1. Epidermal Akt1 is commonly downregulated in SCC while Akt2 is upregulated. We now demonstrate similar Akt1 downregulation and Akt2 upregulation by ultraviolet (UV) radiation, the most important skin carcinogen. Hence, rapamycin's upregulation of Akt1 signaling could potentially oppose the effects of UV radiation and/or tumor-associated changes on Akt1 signaling. We show in skin culture that rapamycin does enhance restoration of Akt1 phosphorylation in skin recovering from UV radiation, suggesting a mechanism for rapamycin's antitumor activity in epidermis in spite of its efficient immunosuppressive properties.

Perifosine sensitizes UVB-induced apoptosis in skin cells: new implication of skin cancer prevention?

We demonstrate here that a relative low dose of perifosine significantly enhanced UVB-induced apoptosis in skin cells (keratinocytes and fibroblasts), associated with a significant increase of reactive oxygen species (ROS) and ceramide production as well as multiple perturbations of diverse cell signaling pathways, shifting to a significant pro-apoptosis outcomes. Perifosine inhibited UVB-induced pro-survival Akt/mammalian target of rapamycin (mTOR) and ERK activation, while facilitating pro-apoptotic AMP-activated protein kinas (AMPK), c-Jun-NH(2)-kinase (JNK), and p53 activation; these signaling changes together promoted a striking increase in skin cell apoptosis and a significantly reduced amount of DNA damages. Our results suggest that perifosine may represent a novel skin cancer prevention strategy.

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.

Activation of AMP-activated protein kinase contributes to doxorubicin-induced cell death and apoptosis in cultured myocardial H9c2 cells

Despite its potent antitumor effect, clinical use of Doxorubicin is limited because of serious side effects including myocardial toxicity. Understanding the cellular mechanism involved in this process in a better manner is beneficial for optimizing Doxorubicin treatment. In the current study, the authors focus on the AMP-activated protein kinase (AMPK) in the said process. In this study, the authors discovered for the first time that Doxorubicin induces AMPK activation in cultured rat embryonic ventricular myocardial H9c2 cells. Reactive oxygen species (ROS)-dependent LKB1 activation serves as the upstream signal for AMPK activation by Doxorubicin. Evidence in support of the activation of AMPK contributing to Doxorubicin-induced H9c2 cell death/apoptosis--probably by modulating multiple downstream signal targets, including regulating JNK, p53, and inhibiting mTORC1--is provided in this article.

A glycosidic spinasterol from Koreana stewartia promotes procollagen production and inhibits matrix metalloproteinase-1 expression in UVB-irradiated human dermal fibroblasts

Methanol extract of Koreana stewartia leaves (SKE) stimulated collagen production in ultraviolet-B (UVB)-irradiated human fibroblast cells. An active compound was isolated from SKE by successive partitioning and chromatography, and the chemical structure was determined to be 3-O-β-D-glucopyranosylspinasterol (spinasterol-Glc) by spectroscopic characterization. Spinasterol-Glc increased collagen production in the supernatant of UVB-irradiated dermal fibroblast cell cultures in a dose-dependent manner. The effects of spinasteol-Glc on expression of procollagen and matrix metalloproteinase-1 (MMP-1) were further evaluated. We found that the compound stimulated collagen production in UVB-treated fibroblasts than in vehicle-treated control cells by about 3-fold. In addition, we also demonstrate that the compound increased the mRNA and protein levels of procollagen in UVB-treated fibroblast cells, while it inhibited expression of MMP-1. These results indicate that spinasterol-Glc protects fibroblast cells from the adverse effects of UV radiation via stimulation of procollagen synthesis as well as inhibition of MMP-1 expression. Spinasterol-Glc may be useful in the future development of therapeutic and cosmetic applications.

Co-administration of perifosine with paclitaxel synergistically induces apoptosis in ovarian cancer cells: more than just AKT inhibition

Here we report an oral alkylphospholipid perifosine dramatically sensitizes chemo-resistant ovarian cancer cells to paclitaxel induced cell death and apoptosis in vitro. We found that co-administration perifosine with paclitaxel in human ovarian cancer cells led to the inhibition of AKT/mTOR complex 1 (mTORC1), a marked increase in ceramide and reactive oxygen species (ROS) production, and a striking increase in the activation of pro-apoptosis pathways, including caspase 3, c-Jun N-terminal kinases (JNK) and AMP-activated protein kinase (AMPK). These signaling events together caused a marked increase of cancer cell apoptosis. Combining paclitaxel with perifosine may represent a novel anti-ovarian cancer strategy.

Solar radiation induced skin damage: review of protective and preventive options

PURPOSE

Solar energy has a number of short- and long-term detrimental effects on skin that can result in several skin disorders. The aim of this review is to summarise current knowledge on endogenous systems within the skin for protection from solar radiation and present research findings to date, on the exogenous options for such skin photoprotection.

RESULTS

Endogenous systems for protection from solar radiation include melanin synthesis, epidermal thickening and an antioxidant network. Existing lesions are eliminated via repair mechanisms. Cells with irreparable damage undergo apoptosis. Excessive and chronic sun exposure however can overwhelm these mechanisms leading to photoaging and the development of cutaneous malignancies. Therefore exogenous means are a necessity. Exogenous protection includes sun avoidance, use of photoprotective clothing and sufficient application of broad-spectrum sunscreens as presently the best way to protect the skin. However other strategies that may enhance currently used means of protection are being investigated. These are often based on the endogenous protective response to solar light such as compounds that stimulate pigmentation, antioxidant enzymes, DNA repair enzymes, non-enzymatic antioxidants.

CONCLUSION

More research is needed to confirm the effectiveness of new alternatives to photoprotection such as use of DNA repair and antioxidant enzymes and plant polyphenols and to find an efficient way for their delivery to the skin. New approaches to the prevention of skin damage are important especially for specific groups of people such as (young) children, photosensitive people and patients on immunosuppressive therapy. Changes in public awareness on the subject too must be made.