In vitro and in vivo transfer of bcl-2 gene into keratinocytes suppresses UVB-induced apoptosis

Dimethyl Itaconate Reduces α-MSH-Induced Pigmentation via Modulation of AKT and p38 MAPK Signaling Pathways in B16F10 Mouse Melanoma Cells

Dimethyl itaconate (DMI) exhibits an anti-inflammatory effect. Activation of nuclear factor erythroid 2-related factor 2 (NRF2) is implicated in the inhibition of melanogenesis. Therefore, DMI and itaconic acid (ITA), classified as NRF2 activators, have potential uses in hyperpigmentation reduction. The activity of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB), an important transcription factor for MITF gene promoter, is regulated by glycogen synthase kinase 3β (GSK3β) and protein kinase A (PKA). Here, we investigated the inhibitory effect of ITA and DMI on alpha-melanocyte-stimulating hormone (α-MSH)-induced MITF expression and the modulatory role of protein kinase B (AKT) and GSK3β in melanogenesis in B16F10 mouse melanoma cells. These cells were incubated with α-MSH alone or in combination with ITA or DMI. Proteins were visualized and quantified using immunoblotting and densitometry. Compared to ITA, DMI treatment exhibited a better inhibitory effect on the α-MSH-induced expression of melanogenic proteins such as MITF. Our data indicate that DMI exerts its anti-melanogenic effect via modulation of the p38 mitogen-activated protein kinase (MAPK) and AKT signaling pathways. In conclusion, DMI may be an effective therapeutic agent for both inflammation and hyperpigmentation.

Inactivation of the Cytoprotective Major Vault Protein by Caspase-1 and -9 in Epithelial Cells during Apoptosis

Inflammasome activation induces caspase-1-dependent secretion of the proinflammatory cytokine IL-1β. In addition, caspase-1 activates the protein GSDMD in immune cells, causing pyroptosis, a lytic type of cell death. In contrast, UVB irradiation of human primary keratinocytes induces NLRP1 inflammasome activation, cytokine secretion, and caspase-1-dependent apoptosis, rather than pyroptosis. Here, we addressed the molecular mechanisms underlying the role of caspase-1 in UVB-induced cell death of human primary keratinocytes. We show that GSDMD is a poor substrate of caspase-1 in human primary keratinocytes and that its activation upon UVB irradiation supports secretion of IL-1β. We screened for novel substrates of caspase-1 by a mass spectrometry-based approach and identified the specific cleavage of the major vault protein (MVP) at D441 by caspase-1 and -9. MVP is the main component of vaults, highly conserved ribonucleoprotein particles, whose functions are poorly understood. Cleavage of MVP is a common event occurring in human primary keratinocytes and fibroblasts undergoing apoptosis induced by different stimuli. In contrast, MVP cleavage could not be detected in pyroptotic cells. Cleavage of MVP by caspase-1 and -9 inactivates this cytoprotective protein. These results demonstrate a proapoptotic activity of caspase-1 and a crosstalk with caspase-9 upon inactivation of the cytoprotective MVP in apoptotic epithelial cells.

Antioxidant and cytoprotective effects of Stachys riederi var. japonica ethanol extract on UVA‑irradiated human dermal fibroblasts

Stachys riederi is one of the largest genera in the flowering plant family Lamiaceae. The aqueous extract of Stachys riederi var. japonica is known for its anti‑allergic effect. In the present study, the antioxidant and cytoprotective effects of Stachys riederi var. japonica ethanol extract (SREE) on ultraviolet A (UVA)‑irradiated human dermal fibroblasts (HDFs) were evaluated. At 100 µg/ml, SREE significantly inhibited production of reactive oxygen species (ROS) in UVA‑irradiated HDFs. SREE at 100 µg/ml additionally markedly interfered with the loss of mitochondrial membrane potential (ΔΨm) in these cells. In addition, SREE at 100 µg/ml attenuated UVA‑induced DNA fragmentation and caspase‑3 activation in HDFs. SREE at 100 µg/ml additionally increased mRNA and protein expressions of Bcl‑2 and decreased those of Bax and cytochrome c in UVA‑irradiated HDFs. In summary, to the best of our knowledge, these results demonstrate for the first time that SREE exhibited antioxidant and cytoprotective effects on UVA‑irradiated HDFs, which may be mediated through suppression of ROS generation, inhibition of the loss of ΔΨm and inhibition of apoptosis.

Marine fungal DHICA as a UVB protectant: Assessment under in vitro and in vivo conditions

The present study explores UVB protective role of a melanin precursor namely DHICA (5,6- Dihydroxyindole-2-carboxylic acid) expressed by the marine imperfect fungus Aspergillus nidulans. In brief, A. nidulans grown in a modified growth medium for the period of 5 days at 25 °C under shaking conditions and the extracellular medium free from fungal biomass used for the extraction of DHICA. The extracted DHICA further exposed to partial purification and subjected to UVB protection studies using HaCaT cells and Balb/c mice independently. DHICA obtained in the present study found soluble in water. Experiments on HaCaT cell compatibility revealed nil cell death up to 500 μM concentration of DHICA. UVB protection studies under in vitro conditions emphasizes DHICA significantly protect HaCaT cells from UVB exposure by quenching the generated ROS, reducing cell apoptosis, maintain the cellular integrity and sequentially down regulating the LPO (Lipid peroxidation) and up-regulating the antioxidant enzyme (SOD (Superoxide Dismutase), Catalase, GPx (Glutathione peroxidase)) respectively. Further, experiments on cell cycle arrest analysis, gelatin zymography, and western blot analysis on COX-2 and TNF-alpha, IHC (Immunohistochemistry) on apoptotic markers (Bax, Bcl2) substantiate the protective role of DHICA. Furthermore, in vivo studies on BALB/c mice carried out and compared with the sunscreen cream with sun protective factor (SPF) of 20. Analysis of skin sections of experimental samples revealed that an appreciable reduction in the epidermal thickness of the skin samples of mice pre-exposed to DHICA followed by UVB exposure compared to UVB exposure alone. RT-PCR results on various inflammatory apoptotic markers also suggested that DHICA has UVB protective potential. The observations made in the present study explore the possible application of DHICA alone as a sun-protective agent for skin care.

UVB damage onset and progression 24 h post exposure in human-derived skin cells

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UVB radiation (280–320 nm) exposure and cellular damages assessment in vitro.

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Damage progression assessed immediately and 24 h post exposure using cultured human cells with more prominent damages expressed 24 h post exposure.

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Cytotoxicity assessment investigated mitochondria, lysosomes, cell membrane and, DNA damages.

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The research reported significant cellular and DNA damages in addition to upregulation and downregulation of various apoptotic proteins.

The focus of this research was on UVB radiation (280–320 nm) responsible for cellular changes in skin of acute and chronically exposed individuals. This study investigated the acute cellular damages triggered by UVB exposure of cultured human fibroblasts and keratinocyte cells immediately and 24 h post exposure in order to understand damage onset and progression. The study evaluated a number of cellular parameters including mitochondria, lysosomes, cell membrane, DNA damages as well as pro and anti-apoptotic protein expression levels. Cellular organelle damages were assessed by a battery of in vitro toxicological assays using MTS and Neutral red cytotoxicity assays. Cell membrane damages were also assessed by measuring lactate dehydrogenase (LDH) enzyme leakage from UVB exposed cells. Lastly DNA damages was assessed using the comet assay while protein expression was evaluated using Western Blot.

In this study we reported in all our assay systems (MTS, NR and LDH) that cellular damages were UVB dose dependent with damages amplified 24 h post exposure. Our results also indicated that incubation of exposed cells for a period of 24 h increased the sensitivity of the assay systems used. The increased sensitivity in detecting early cytotoxic damages was manifested though organelle damage measurement at very low doses which were not manifested immediately post exposure. The data also indicated that HaCaT cells were most sensitive in detecting UVB triggered damages immediately and 24 h post exposure using the MTS assay. We also established upregulation and downregulation of various apoptotic proteins at various time points post exposure. The presented data clearly indicated the need for a comprehensive assessment of UVB damages 4 and 24 h post exposure due to the different assay sensitivities in addition to various signaling mechanisms activated at different time points post exposure.

Regenerative and reparative effects of human chorion-derived stem cell conditioned medium on photo-aged epidermal cells

Epidermal cells are an important regenerative source for skin wound healing. Aged epidermal cells have a low ability to renew themselves and repair skin injury. Ultraviolet (UV) radiation, particularly UVB, can cause photo-aging of the skin by suppressing the viability of human epidermal cells. A chorion-derived stem cell conditioned medium (CDSC-CNM) is thought to have regenerative properties. This study aimed to determine the regenerative effects of CDSC-CNM on UVB-induced photo-aged epidermal cells. Epidermal cells were passaged four times and irradiated with quantitative UVB, and non-irradiated cells served as a control group. Cells were then treated with different concentrations of CDSC-CNM. Compared to the non-irradiated group, the proliferation rates and migration rates of UVB-induced photo-aged epidermal cells significantly decreased (p < 0.05) with increasing intracellular radical oxygen species (ROS) generation and DNA damage. After treatment with CDSC-CNM, photo-aged epidermal cells significantly improved their viability, and their ROS generation and DNA damage decreased. The secretory factors in CDSC-CNM, including epidermal growth factor (EGF), transforming growth factor-β (TGF-β), interleukin (IL)-6, and IL-8 and the related signaling pathway protein levels, increased compared to the control medium (CM). The potential regenerative and reparative effects of CDSC-CNM indicate that it may be a candidate material for the treatment of prematurely aged skin. The functions of the secretory factors and the mechanisms of CDSC-CNM therapy deserve further attention.

Isolating subpopulations of human epidermal basal cells based on polyclonal serum against trypsin-resistant CSPG4 epitopes

Chondroitin sulfate proteoglycan 4 (CSPG4) is highly expressed by human epidermal keratinocytes located at the tip of the dermal papilla where keratinocytes show characteristics of stem cells. However, since available antibodies to CSPG4 are directed against trypsin-sensitive epitopes we have been unable to study these keratinocytes isolated directly from skin samples by flow cytometry. By choosing epitopes of CSPG4 relatively close to the cell membrane we were able to generate a polyclonal antibody that successfully detects CSPG4 on keratinocytes after trypsinization. Although CSPG4-positive basal cells express higher levels of Itgβ1 the colony-forming efficiency is slightly lower than CSPG4-negative basal cells. Sorting the directly isolated keratinocytes based on Itgβ1 did not reveal differences in colony-forming efficiency between keratinocytes expressing high or low levels of Itgβ1. However, after the first passage Itgβ1 could be used to predict colony-forming efficiency whether the culture was established from CSPG4-positive or CSPG4-negative basal cell keratinocytes. Although we were unable to detect differences in the colony-forming assay, global gene expression profiling showed that CSPG4-positive basal cell keratinocytes are distinct from CSPG4-negative basal cell keratinocytes. Our study demonstrates that it is possible to generate antibodies against trypsin-resistant epitopes of CSPG4. Our study also documents a marked change in behaviour upon cell culturing and challenges the way we assess for stemness within the human epidermal basal layer.

A systems-biological study on the identification of safe and effective molecular targets for the reduction of ultraviolet B-induced skin pigmentation

Melanogenesis is the process of melanin synthesis through keratinocytes-melanocytes interaction, which is triggered by the damaging effect of ultraviolet-B (UVB) rays. It is known that melanogenesis influences diverse cellular responses, including cell survival and apoptosis, via complex mechanisms of feedback and crosstalk. Therefore, an attempt to suppress melanin production by modulating the melanogenesis pathway may induce perturbations in the apoptotic balance of the cells in response to UVB irradiation, which results in various skin diseases such as melasma, vitiligo, and skin cancer. To identify such appropriate target strategies for the reduction of UVB-induced melanin synthesis, we reconstructed the melanogenesis signaling network and developed a Boolean network model. Mathematical simulations of the melanogenesis network model revealed that the inhibition of beta-catenin in the melanocytes effectively reduce melanin production while having minimal influence on the apoptotic balance of the cells. Exposing cells to a beta-catenin inhibitor decreased pigmentation but did not significantly change the B-cell Chronic lymphocytic leukemia/lymphoma 2 expression, a potent regulator of apoptotic balance. Thus, our systems analysis suggests that the inhibition of beta-catenin may be the most appropriate target strategy for the reduction of UVB-induced skin pigmentation.

The ethyl acetate fraction of Sargassum muticum attenuates ultraviolet B radiation-induced apoptotic cell death via regulation of MAPK- and caspase-dependent signaling pathways in human HaCaT keratinocytes

CONTEXT

Our previous work demonstrated that an ethyl acetate extract derived from Sargassum muticum (Yendo) Fenshol (SME) protected human HaCaT keratinocytes against ultraviolet B (UVB)-induced oxidative stress by increasing antioxidant activity in the cells, thereby inhibiting apoptosis.

OBJECTIVE

The aim of the current study was to further elucidate the anti-apoptotic mechanism of SME against UVB-induced cell damage.

MATERIALS AND METHODS

The expression levels of several apoptotic-associated and mitogen-activated kinase (MAPK) signaling proteins were determined by western blot analysis of UVB-irradiated HaCaT cells with or without prior SME treatment. In addition, the loss of mitochondrial membrane potential (Δψm) was detected using flow cytometry or confocal microscopy and the mitochondria membrane-permeate dye, JC-1. Apoptosis was assessed by quantifying DNA fragmentation and apoptotic body formation. Furthermore, cell viability was evaluated using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.

RESULTS

SME absorbed electromagnetic radiation in the UVB range (280-320 nm) of the UV/visible light spectrum. SME also increased Bcl-2 and Mcl-1 expression in UVB-irradiated cells and decreased the Bax expression. Moreover, SME inhibited the UVB-induced disruption of mitochondrial membrane potential and prevented UVB-mediated increases in activated caspase-9 and caspase-3 (an apoptotic initiator and executor, respectively) levels. Notably, treatment with a pan-caspase inhibitor enhanced the anti-apoptotic effects of SME in UVB-irradiated cells. Finally, SME reduced the UVB-mediated phosphorylation of p38 MAPK and JNK, and prevented the UVB-mediated dephosphorylation of Erk1/2 and Akt.

DISCUSSION AND CONCLUSION

The present results indicate that SME safeguards HaCaT keratinocytes from UVB-mediated apoptosis by inhibiting a caspase-dependent signaling pathway.

Epidermal expression of neuropilin 1 protects murine keratinocytes from UVB-induced apoptosis

Background

Neuropilin 1 (NRP1) is expressed on several cell types including neurons and endothelial cells, where it functions as an important regulator in development and during angiogenesis. As a cell surface receptor, NRP1 is able to bind to members of the VEGF family of growth factors and to secreted class 3 semaphorins. Neuropilin 1 is also highly expressed in keratinocytes, but the function of NRP1 in epidermal physiology and pathology is still unclear.

Methods and Results

To elucidate the role of NRP1 in skin in vivo we generated an epidermis-specific neuropilin 1 knock out mouse model by using the Cre-LoxP-System. Mice were viable and fertile and did not display any obvious skin or hair defects. After challenge with UVB irradiation, we found that deletion of epidermal NRP1 leads to increased rates of apoptosis both in vitro and in vivo. NRP1-deficient primary keratinocytes cultured in vitro showed significantly higher rates of apoptosis 24 hours after UVB. Likewise, there is a significant increase of active caspase 3 positive cells in the epidermis of Keratin 14-Cre-NRP1 (−/−) mice 24 hours after UVB irradiation. By Western Blot analysis we could show that NRP1 influences the cytosolic levels of Bcl-2, a pro-survival member of the Bcl-2 family. After UVB irradiation the amounts of Bcl-2 decrease in both protein extracts from murine epidermis and in NRP1-deficient keratinocytes in vitro, whereas wild type cells retain their Bcl-2 levels. Likewise, levels of phospho-Erk and Rac1 were lower in NRP1-knock out keratinocytes, whereas levels of pro-apoptotic p53 were higher.

Conclusion

NRP1 expression in keratinocytes is dispensable for normal skin development. Upon UVB challenge, NRP1 contributes to the prevention of keratinocyte apoptosis. This pro-survival function of NRP1 is accompanied by the maintenance of high levels of the antiapoptotic regulator Bcl-2 and by lower levels of pro-apoptotic p53.

Skin mild hypoxia enhances killing of UVB-damaged keratinocytes through reactive oxygen species-mediated apoptosis requiring Noxa and Bim

The naturally occurring skin hypoxia has emerged as a crucial host factor of the epidermal microenvironment. We wanted to systematically investigate how reduced oxygen availability of the epidermis modulates the response of keratinocytes and melanocytes to noxious ultraviolet B radiation (UVB). We report that the exposure of normal human keratinocytes (NHKs) or melanocytes (NHEMs) to mild hypoxia drastically impacts cell death responses following UVB irradiation. The hypoxic microenvironment favors survival and reduces apoptosis of UVB-irradiated NHEMs and their malignant counterparts (melanoma cells). In contrast, NHKs, but not the transformed keratinocytes, under hypoxic conditions display increased levels of reactive oxygen species (ROS) and are significantly sensitized to UVB-mediated apoptosis as compared to NHKs treated under normoxic conditions. Prolonged exposure of UVB-treated NHKs to hypoxia triggers a sustained and reactive oxygen species-dependent activation of the stress kinases p38(MAPK) and JNKs, which in turn, engage the activation of Noxa and Bim proapoptotic proteins. Combined silencing of Noxa and Bim significantly inhibits UVB-mediated apoptosis under hypoxic conditions, demonstrating that hypoxia results in an amplification of the intrinsic apoptotic pathway. Physiologically occurring skin hypoxia, by facilitating the specific removal of UVB-damaged keratinocytes, may represent a decisive host factor impeding important steps of the photocarcinogenesis process.

Bcl-2 family members: essential players in skin cancer

Skin cancer has reached epidemic proportions and is considered to be a direct consequence of ultraviolet (UV) radiation exposure. Excessive exposure of epidermal cells to UV results in apoptosis of irreparably damaged cells to avoid malignant transformation. The Bcl-2 family of proteins is emerging as a crucial regulator of epidermal homeostasis and cell's fate in the stressed skin. Not surprisingly, deregulation of Bcl-2 family members is also chiefly involved in skin carcinogenesis and response to cancer therapy. Here we discuss the physiopathological role of epidermal Bcl-2 family members, their implications in skin carcinogenesis and as potential targets in cancer therapy.

Uncovering the role of hypoxia inducible factor-1α in skin carcinogenesis

The hypoxia inducible factor-1α (HIF-1α) is a pleiotropic transcription factor typically activated in response to low oxygen tension as well as other stress factors in normoxic conditions. Upon activation HIF-1α mediates the transcriptional activation of target genes involved in a variety of processes comprising stress adaptation, metabolism, growth and invasion, but also apoptotic cell death. The molecular mechanisms, signaling pathways and downstream targets evoked by the activation of HIF-1α in epidermal cells are becoming increasingly understood and underscore the participation of HIF-1α in crucial processes including malignant transformation and cancer progression. Recent studies have implicated HIF-1α as an integral part of the multifaceted signal transduction initiated by the exposure of keratinocytes to ultraviolet radiation B (UVB), which represents the most ubiquitous hazard for human skin and the principal risk factor for skin cancer. HIF-1α activation by UVB exposure contributes to either repair or the removal of UVB-damaged keratinocytes by inducing apoptosis, thus revealing a tumor suppressor role for HIF-1α in these cells. On the other hand, the constitutive expression of HIF-1α evoked by the mild hypoxic state of the skin has been implicated as a positive factor in the transformation of normal melanocytes into malignant melanoma, one of the most aggressive types of human cancers. Here we review the uncovered and complex role of HIF-1α in skin carcinogenesis.

A p38(MAPK)/HIF-1 pathway initiated by UVB irradiation is required to induce Noxa and apoptosis of human keratinocytes

The signal transduction pathways leading to apoptosis of human keratinocytes responding to UVB irradiation are complex and not completely understood. Previously, we reported that in UVB-irradiated keratinocytes, p38(MAPK) instigates Bcl-2-associated X protein (Bax) activation and mitochondrial apoptosis. However, the molecular mechanism underlying the pro-apoptotic function of p38(MAPK) remained unclear. Here, we show that in UVB-treated human primary keratinocytes the activation of p38(MAPK) is necessary to upregulate Noxa, a BH3-only pro-apoptotic dominantly induced by UVB and required for apoptosis. Whereas p53-silencing was marginally cytoprotective and poorly affected Noxa expression, p38(MAPK) inhibition in p53-silenced keratinocytes or in p53(-/-) cells could still efficiently prevent Noxa induction and intrinsic apoptosis after UVB, indicating that p38(MAPK) signals mainly through p53-independent mechanisms. Furthermore, p38(MAPK) was required for the induction and activation of hypoxia-inducible factor 1 (HIF-1) in response to UVB, and HIF-1 knockdown reduced Noxa expression and apoptosis. In UVB-irradiated keratinocytes, Noxa targeted the anti-apoptotic myeloid cell leukemia sequence 1 (Mcl-1) for degradation, and small-interfering RNA (siRNA)-mediated knockdown of Noxa or p38(MAPK) inhibition restored levels of Mcl-1 and abolished apoptosis. Thus, the pro-apoptotic mechanisms orchestrated by p38(MAPK) in human keratinocytes in response to UVB involve an HIF-1/Noxa axis, which prompts the downregulation of anti-apoptotic Mcl-1, thereby favoring Bax-mediated mitochondrial apoptosis of UVB-damaged keratinocytes.

Cell death in the skin

The skin is the largest organ of the body and protects the organism against external physical, chemical and biological insults, such as wounding, ultraviolet radiation and micro-organisms. The epidermis is the upper part of the skin that is continuously renewed. The keratinocytes are the major cell type in the epidermis and undergo a specialized form of programmed cell death, called cornification, which is different from classical apoptosis. In keep with this view, several lines of evidence indicate that NF-kB is an important factor providing protection against keratinocyte apoptosis in homeostatic and inflammatory conditions. In contrast, the hair follicle is an epidermal appendage that shows cyclic apoptosis-driven involution, as part of the normal hair cycle. The different cell death programs need to be well orchestrated to maintain skin homeostasis. One of the major environmental insults to the skin is UVB radiation, causing the occurrence of apoptotic sunburn cells. Deregulation of cell death mechanisms in the skin can lead to diseases such as cancer, necrolysis and graft-versus-host disease. Here we review the apoptotic and the anti-apoptotic mechanisms in skin homeostasis and disease.

Effect of UV irradiation on colorectal cancer cells with acquired TRAIL resistance

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily. TRAIL shows strong cytotoxicity to many cancer cells but minimal cytotoxicity to most normal cells. Interestingly, our recent studies have demonstrated that pretreatment with TRAIL induces acquired resistance to TRAIL (Song et al. 2007 J Biol Chem 282: 319). Acquired TRAIL resistance develops within 1 day and gradually decays within 5 days after TRAIL treatment. In our current study, we examined whether human colorectal carcinoma CX-1 cells with acquired TRAIL resistance are resistant to UV irradiation as well. CX-1 cells were treated with 200 ng/ml TRAIL for 6 h and incubated various times (0.25-5 days) and then challenged to UV irradiation. Unexpectedly, we observed an increase in apoptosis in acquired TRAIL resistant cells after UVC as well as UVB exposure. This was due to an increase in caspase activation which was mediated through cytochrome c release. These results suggest that cells with acquired TRAIL resistance are sensitive to UV irradiation.

Cystatin A suppresses ultraviolet B-induced apoptosis of keratinocytes

BACKGROUND

Cystatin A is a cysteine proteinase inhibitor abundantly expressed in keratinocytes. Although cystatin A is one of the cornified cell envelope constituents and expressed in the upper epidermis, its precise function is still unknown. Ultraviolet B irradiation (UVB) induces apoptosis accompanied with the activation of cysteine proteinases, caspases.

OBJECTIVE

We investigated the effect of cystatin A on UVB-induced apoptosis of keratinocytes.

METHODS

We assessed the caspase activities and apoptotic cell numbers induced by UVB ittadiation in cystatin A gene transfected keratinocytes.

RESULTS

UVB-induced pro-caspase 3 cleavage and caspase 3 activation were suppressed in cystatin A expression vector-transfected SV40-transformed human keratinocytes (SVHK). Furthermore, the transfected SVHK cells were resistant to UVB-induced apoptosis. In contrast neither caspase 8 nor caspase 9 activities were affected by UVB irradiation in cystatin A-transfected SVHK cells. The effects were also observed in cystatin A expression adenovirus vector-transfected cultured normal human keratinocytes (NHK). Conversely knockdown of cystatin A by si-RNA induced marked apoptosis of NHK cells following UVB irradiation accompanied with increased caspase 3 activity. In order to confirm the antiapoptotic effect of cystatin A in vivo UVB irradiation was performed on cystatin A transgenic mice (cystatin A-tg). The epidermis from cystatin A-tg was resistant to UVB-induced apoptosis compared to control mice epidermis.

CONCLUSION

These results indicate that cystatin A suppresses UVB-induced apoptosis of keratinocytes by the inhibition of caspase 3 activation.

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.

Pathways involved in sunburn cell formation: deregulation in skin cancer

The incidence of squamous cell carcinoma of the skin is rising worldwide for decades. Chronic exposure to sunlight is the most important environmental risk factor for this type of skin cancer. This is predominantly due to the DNA damaging effect of ultraviolet-B (UVB) in sunlight. UVB induces also sunburn cells, i.e. apoptotic keratinocytes, which is a crucial protective mechanism against the carcinogenic effects of UVB irradiation. This process is regulated by a wide range of molecular determinants involved in the balance between pro- and anti-apoptotic pathways. Growing evidence suggests that the deregulation of this balance by chronic UVB irradiation, contributes to the development of skin cancer. This review gives a brief summary of major known pathways involved in the regulation of keratinocyte survival and cell death upon UVB damage and discusses the contribution of the deregulation of these cascades to photocarcinogenesis.

Ultraviolet radiation-induced apoptosis in keratinocytes: on the role of cytosolic factors

Epidemiological and experimental evidences have established solar ultraviolet (UV) radiation as the leading cause of skin cancers. Specifically, the frequency of non-melanoma skin cancer, one of the malignancies with the most rapidly increasing incidence, is directly related to the total exposure to solar UV light. As part of a general effort to elucidate the components of cellular signal transduction pathways, the mechanisms of cellular responses to UV radiation have received considerable attention over the last few years. These efforts were driven mainly by the conviction that understanding how normal cells respond to extracellular stimuli such as exposure to UV radiation will undoubtedly help in deciphering what goes wrong in a variety of clinical disorders including skin cancers and will assist in the development of novel therapeutic strategies. Studies over the last decade have established that UV radiation induces a bewildering array of signal transduction pathways, some of which could lead to apoptotic cell death. UV-induced cell death by apoptosis is considered to be a natural protective mechanism that removes damaged keratinocytes and circumvents the risk of malignant transformation. In this review, we summarize some of the most important findings regarding the response and role of mitogen-activated protein kinases in UVA and UVB radiation-induced signaling to apoptosis in keratinocytes. We will also briefly discuss what is known about the role of the BCL-2 family of proteins, the emerging role of lysosomal proteases and other important cytosolic signaling proteins in UV-induced apoptosis.

Induction of immune tolerance across major histocompatibility complex barrier by transfusion of ultraviolet B-irradiated immature dendritic cells

BACKGROUND

Transfusion of ultraviolet B (UVB)-irradiated peripheral blood mononuclear cells (PBMNCs) induces immunologic tolerance across the major histocompatibility complex (MHC) barrier in a murine model. It is necessary, however, to reduce contaminating platelets (PLTs) to a minimum. Ex vivo preparation of dendritic cells (DCs) offers an opportunity to rid the contaminating PLTs. The use of immature and mature DCs (iDCs and mDCs) with and without UVB irradiation for tolerance induction was therefore investigated.

STUDY DESIGN AND METHODS

iDCs and mDCs were prepared by culture of Balb/c (H-2d) mouse marrow cells in the presence of granulocyte-macrophage-colony-stimulating factor and interleukin-4. Different dose schedules of iDCs were tested for tolerance induction in CBA (H-2k) mice. Tolerance induction by UVB-irradiated iDCs and mDCs was compared. Tolerance induction in two additional strains of mice (C3H and C57BL/6) was also studied. The induction of tolerance was tested by challenging transfusions of treated mice with PBMNCs from the donor strain. The induction of negative regulatory CD4+ T cells in tolerized mice was examined.

RESULTS

Four weekly transfusions of 5 x 10(4) UVB-irradiated iDCs from Balb/c mice efficiently induced immune tolerance in CBA and C3H mice. iDCs and mDCs without UVB irradiation could not induce immune tolerance. Tolerance induced by transfusions of UVB-irradiated iDCs was associated with the development of CD4+-regulatory T cells as demonstrated by an adoptive transfer study.

CONCLUSION

Transfusion of UVB-iDCs induces immune tolerance across the MHC barrier in certain combinations of mouse strains. The results support the idea that iDCs irradiated with UVB may be applied to induce immune tolerance across the MHC barrier.

The role of B-RAF in melanoma

Melanoma is a form of skin cancer that has a poor prognosis and which is on the rise in Western populations. If detected early, it is easily treated by surgical excision. However, once melanoma metastasises it is notoriously resistant to existing therapies and for many patients the outlook is dismal. Thus a full description of melanoma etiology and a full understanding of the genetic lesions that underlie this disease is required to allow us to develop new and effective therapeutic strategies for its treatment. RAF proteins are a family of serine/threonine-specific protein kinases that form part of a signalling module that regulates cell proliferation, differentiation and survival. In mammals there are three isoforms, A-RAF, B-RAF and C-RAF, and recently it was shown that the B-RAF isoform is mutated in a high proportion of melanomas. In light of these exciting findings, we review what we have learned about B-RAF and its role in cutaneous melanoma.

Ginsenoside F1 protects human HaCaT keratinocytes from ultraviolet-B-induced apoptosis by maintaining constant levels of Bcl-2

Ginsenosides, the major active ingredients of ginseng, show a variety of biomedical efficacies such as antiaging and antioxidation. Here, we investigate the protective activity of the ginsenoside F1, an enzymatically modified derivative of ginsenoside Rg1, against ultraviolet-B-induced damage in human HaCaT keratinocytes. Ginsenoside F1 significantly reduced ultraviolet-B-induced cell death and protected HaCaT cells from apoptosis caused by ultraviolet B irradiation. Furthermore, ginsenoside F1 prevented ultraviolet-B-induced cleavage of poly(ADP-ribose) polymerase in HaCaT cells. In search of the molecular mechanism responsible for the antiapoptotic effect of ginsenoside F1, we find that protection from ultraviolet-B-induced apoptosis is tightly correlated with ginsenoside-F1-mediated inhibition of ultraviolet-B-induced downregulation of Bcl-2 and Brn-3a expression.

Ultraviolet B radiation-induced apoptosis in human keratinocytes: cytosolic activation of procaspase-8 and the role of Bcl-2

In this study, we show that ultraviolet B radiation (UVB)-induced apoptosis of human keratinocytes involves mainly cytosolic signals with mitochondria playing a central role. Overexpression of Bcl-2 inhibited UVB-induced apoptosis by blocking the early generation of reactive oxygen species, mitochondrial cardiolipin degradation and cytochrome c release, without affecting Fas ligand (FasL)-induced cell death. It also prevented the subsequent activation of procaspase-3 and -8 as well as Bid cleavage in UVB-treated cells. Comparative analysis of UVB and FasL death pathways revealed a differential role and mechanism of caspase activation, with the UVB-induced activation of procaspase-8 only being a bystander cytosolic event rather than a major initiator mechanism, as is the case for the FasL-induced cell death. Our results suggest that Bcl-2 overexpression, by preventing reactive oxygen species production, helps indirectly to maintain the integrity of lysosomal membranes, and therefore inhibits the release of cathepsins, which contribute to the cytosolic activation of procaspase-8 in UVB-irradiated keratinocytes.