Role of p38 MAPK in UVB-induced inflammatory responses in the skin of SKH-1 hairless mice

The p38 mitogen-activated protein kinase (MAPK) signaling pathway is activated by numerous inflammatory mediators and environmental stresses. We assessed the effects of ultraviolet B (UVB) on the p38 MAPK pathway and determined whether cyclooxygenase (COX)-2 expression is downstream of this kinase in the skin of UVB-irradiated SKH-1 mice. SKH-1 mice were irradiated with a single dose of UVB (360 mJ per cm2), and activation of the epidermal p38 MAPK pathway was assessed. UVB-induced phosphorylation of p38 MAPK occurred in a time-dependent manner. Phosphorylation of MAPK-activated protein kinase-2 (MAPKAPK-2) also was detected and correlated with an increase in its kinase activity. Phosphorylation of heat shock protein 27 (HSP27), a substrate for MAPKAPK-2, also was detected post-irradiation. Oral administration of the p38 inhibitor, SB242235, prior to UVB irradiation, blocked activation of the p38 MAPK cascade, and abolished MAPKAPK-2 kinase activity and phosphorylation of HSP27. Moreover, SB242235 inhibited expression of the pro-inflammatory cytokines interleukin (IL)-6 and KC (murine IL-8) and COX-2. Our data demonstrate that UVB irradiation of murine skin activates epidermal p38 MAPK signaling and induces a local pro-inflammatory response. Blockade of the p38 MAPK pathway may offer an effective approach to reducing or preventing skin damage resulting from acute solar radiation.     

p38 Mitogen-Activated protein kinase mediates dual role of ultraviolet B radiation in induction of maturation and apoptosis of monocyte-derived dendritic cells

Although ultraviolet B (UVB) induces apoptosis and functional perturbations in dendritic cells (DC), for example, Langerhans cells (LC), it also stimulates some LC into maturation after irradiation in vivo. To analyze its reciprocal effects on DC, we elucidated the direct effect of UVB on DC in vitro using human monocyte-derived DC (MoDC). UVB from 50 to 200 J per m2 stimulated the maturation of MoDC with (1) augmented expression of CD86 and HLA-DR, (2) enhanced production of IL-1beta, IL-6, IL-8, and TNF-alpha at both the mRNA and protein levels, and (3) enhanced allostimulatory capacity on a per-cell basis, whereas the exceeded doses induced apoptotic cell death. Western-blot analysis of MoDC after UVB demonstrated a concentration-dependent phosphorylation of p38- and c-JUN N-terminal kinase (JNK)-mitogen-activated protein kinases (MAPK), but not that of extracellular signal-regulated kinases. p38 MAPK-inhibitor, SB203580, inhibited both UVB-induced maturation and apoptosis of MoDC. Interestingly, MoDC that had undergone apoptosis exhibited an augmented expression of HLA-DR without upregulation of CD86 antigen, suggesting their tolerogenic phenotype. Thus, our study revealed a dual effect of UVB, to stimulate maturation or to induce apoptosis in MoDC, depending on the dosage, via p38 MAPK pathway.     

Differential phosphorylation of mitogen-activated protein kinase families by epidermal growth factor and ultraviolet B irradiation in SV40-transformed human keratinocytes

SV-40 transformed human keratinocytes (SVHK cells) were stimulated with epidermal growth factor (EGF) and ultraviolet B (UVB) irradiation. Following the stimulation, cell growth, apoptosis, and the activities of mitogen-activated protein (MAP) kinase families were analyzed. EGF (100 ng/ml) increased SVHK cell number compared with control cells cultured in serum-free DMEM medium. The EGF-stimulated cells did not show DNA fragmentation. In contrast, UVB irradiation (40 mJ/cm(2)) markedly decreased viable cell number that was accompanied with DNA fragmentation. EGF stimulated extracellular signal-regulated kinase (ERK) and stress-activated protein kinase/c-Jun N-terminal kinase (JNK). Following the EGF stimulation, phosphorylated ERK and JNK were detected by phospho-p42/44 MAP kinase antibody and phospho-SAPK/JNK antibody, respectively. On the other hand, UVB irradiation stimulated the phosphorylation of p38 and JNK but not of ERK. The stimulation of ERK and JNK induced by EGF was observed earlier than the stimulation of p38 and JNK induced by UVB. PD98059, a specific MAP kinase kinase (MAPKK) 1 (also referred to as MEK1) inhibitor, inhibited EGF-dependent cell proliferation, that was associated with the inhibition of ERK and JNK phosphorylation. In contrast, UVB-induced overall cell death was not significantly affected by PD98059, that inhibited phosphorylation of JNK but not of p38. PD98059, however, significantly augmented UVB-induced cell death earlier time points (30 min--2 h). These results indicate that ERK and JNK are activated following EGF stimulation that might be associated with cell proliferation. On the other hand, UVB-induced apoptosis seems to be mostly associated with the activation of p38. JNK stimulation might provide an anti-apoptotic tonus during the UVB-induced, p38-associated SVHK cell death.     

Responses of the 27-kDa heat shock protein to UVB irradiation in human epidermal melanocytes

Abstract:  Solar ultraviolet radiation (UVR) is a major environmental hazard for the skin, and UVB (280–320 nm) has been proposed to be a main factor for melanoma development. In response to sunlight exposure, the skin has adapted a number of innate resistance mechanisms. Among them is the small heat shock protein of 27 kDa (HSP27) known to play a role in the protection of cells from variety of environmental insults including UV irradiation. In this study, we demonstrated that UVB irradiation of cultured normal epidermal melanocytes initiates changes in HSP27 phosphorylation and localization. In unstressed melanocytes, HSP27 was present as the non-phosphorylated isoform. UVB irradiation with a physiological dose (7–25 mJ/cm²) resulted in the formation of a mono-phosphorylated isoform and sometimes a bi-phosphorylated isoform. The UVB-induced HSP27 phosphorylation was inhibited when melanocytes were treated with the antioxidant N -acetyl cysteine or inhibitor of p38 MAP kinase prior to UVB exposure, suggesting that UVB induced HSP27 phosphorylation through reactive oxygen species/p38 MAP kinase pathway. In response to UBV irradiation, HSP27 in melanocytes translocated from the cytoplasm to the nucleus. The HSP27 responses may provide some protective role against UVB-induced cell damage in the skin.     

Erythroid differentiation regulator 1 (Erdr1) is a proapototic factor in human keratinocytes

Skin is constantly exposed to physical and chemical stressors. The exposure of keratinocytes to ultraviolet B (UVB) irradiation causes epidermal damage via induction of apoptosis. Erythroid differentiation regulator 1 (Erdr1) modulates growth and survival of cells under various stressful conditions, but the function of Erdr1 in human keratinocyte apoptosis has not been investigated so far. Here, we investigated the effect of Erdr1 on UVB-induced apoptosis in human keratinocytes and also examined the underlying regulatory mechanism. First, Erdr1 expression was detected in human primary keratinocytes and normal human skin tissues. Expression of Erdr1 was enhanced in human keratinocytes following UVB irradiation. Knock-down of Erdr1 led to resistance to UVB-induced apoptosis. Also, Erdr1 overexpression increased UVB-induced apoptosis and induced caspase-3 activation. Furthermore, the extracellular signal-regulated kinase (ERK) inhibitor PD98059 and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 significantly reduced Erdr1 expression following UVB irradiation. These results indicate that UVB induces Erdr1 via a MAPK-dependent mechanism. Taken together, these findings suggest that Erdr1 has a role as a proapoptotic factor in human keratinocytes and acts via ERK and p38 MAPK pathways. Therefore, Erdr1 may be a potential therapeutic target to reduce apoptosis in keratinocytes in conditions such as psoriasis and skin cancer.     

Additive effect of heat on the UVB-induced tyrosinase activation and melanogenesis via ERK/p38/MITF pathway in human epidermal melanocytes

Heat is known as an environmental factor that causes significant skin pigmentation, but its effects on melanogenesis have been poorly studied. It has been shown that mitogen-activated protein kinase (MAPK) is involved in ultraviolet B (UVB) and stress-induced melanogenesis in melanocytes. In this study, we investigated the effects of heat and UVB, on melanocyte melanogenesis, differentiation, and MAPK phosphorylation. The results showed that heat (1 h at 40 °C for 5 days) increased cell dendrites, enlarged cell bodies, and induced extracellular signal-regulated kinases (ERK)/p38/MITF activation but did not influence melanogenesis of human epidermal melanocytes from skin phototype III. UVB irradiation (20 mJ/cm² for 5 days) induced melanogenesis and c-jun N-terminal kinases (JNK)/p38/MITF/tyrosinase activation in melanocytes from skin phototype III. UVB combined with heat resulted in much more significant tyrosinase activation and melanogenesis as compared with UVB alone in melanocytes from skin phototype III. Furthermore, heat treatment and UVB irradiation induced JNK, ERK, and p38 activation but not melanogenic and morphological changes in melanocytes from skin phototype I. These findings suggested that heat promoted melanocyte differentiation, probably via heat-induced ERK/p38/MITF/activation. Furthermore, heat had an additive effect on the UVB-induced tyrosinase activation and melanogenesis. These results provide a new clue for dermatologists for the treatment of hypopigmented skin disease with heat combined with UVB irradiation.     

蛋白激酶B和丝裂原活化蛋白激酶在烟酸保护的HaCaT细胞抵抗中波紫外线损伤中的作用

目的 探讨烟酸保护由UVB诱导的角质形成细胞损伤的胞内信号传导分子机制。 方法 UVB照射和烟酸处理HaCaT细胞,TUNEL法检测细胞凋亡,Western印迹检测蛋白激酶B（Akt）/丝裂原活化蛋白激酶（MAPK）通路相关蛋白Akt、P38、JNK、ERK1/2的磷酸化水平变化。ELISA检测细胞分泌内皮素1（ET-1）及碱性成纤维细胞生长因子（bFGF）的水平。结果 Western印迹结果表明,UVB照射和烟酸处理HaCaT细胞后,p-Akt、p-P38、p-JNK、p-ERK1/2蛋白在60 min内都显著激活（P < 0.01）。烟酸预处理后的HaCaT细胞再经UVB照射,可以发现p-Akt、p-P38、p-ERK1/2信号分子在2 h内激活更显著（P < 0.01）。３个抑制剂加UVB照射组较3个单独抑制剂组ET-1、bFGF表达降低,差异均有统计学意义,其中LY294002组、SB203580组ET-1、bFGF水平最低;烟酸预保护的抑制剂处理组HaCaT细胞在UVB照射后,LY294002和U0126组没有出现ET-1、bFGF水平回升,SB203580组bFGF水平出现回升。结论　Akt信号分子在烟酸保护的HaCaT细胞抵抗UVB损伤中起一定的调控作用。     

UVB irradiation differential regulate miRNAs expression in skin photoaging

BackgroundUVB irradiation can cause acute damage such as sunburn, or photoaging and melanoma, all of which are major health threats.ObjectiveThis study was designed to investigate the mechanism of skin photoaging induced by UVB radiation in mice through the analysis of the differential expression of miRNAs.MethodsA UVB irradiation photoaging model was constructed. HE and Masson special stains were used to examine the modifications in the epidermis and dermis of mice. The miRNA expression profiles of the mouse skin model exposed to UVB radiation and the normal skin of mice were analyzed using miRNA-sequence analysis. GO and Pathway analysis were employed for the prediction of miRNA targets.ResultsA total of 23 miRNAs were evaluated for significantly different expressions in comparison to normal skin. Among them, 7 miRNAs were up-regulated and 16 were down-regulated in the skin with photoaging of mice exposed to UVB irradiation. The differential expression of miRNA is related to a variety of signal transduction pathways, among which mmu-miR-195a-5p and mitogen-activated protein kinase (MAPK) signal pathways are crucial. There was a significant differential expression of miRNA in the skin of normal mice in comparison with the skin with photoaging induced by UVB irradiation.Study limitationsDue to time and energy constraints, the specific protein level verification, MAPK pathway exploration, and miR-195a-5p downstream molecular mechanism need to be further studied in the future.ConclusionsUVB-induced skin photoaging can be diagnosed and treated using miRNA.     

Baicalin protects human fibroblasts against ultraviolet B-induced cyclobutane pyrimidine dimers formation

Exposure to ultraviolet B (UVB) irradiation is a major risk factor for the development of skin cancer. Therefore, it is important to identify agents that can offer protection against UVB-caused DNA damage. Photocarcinogenesis is caused largely by mutations at the sites of incorrectly repaired DNA photoproducts, of which the most common are the cyclobutane pyrimidine dimers (CPDs). In this study, a DNA damage model of UVB irradiation-induced fibroblasts was established. The immunocytochemical staining, immuno dot blotting and Western blotting were employed in the study. We demonstrated that pre-treatment of fibroblasts with Baicalin dose-dependently reduced the amount of UVB-generated CPDs. Compared with UVB irradiated cells, UVB-induced p53 accumulation was less pronounced in Baicalin-treated cells. Taken together, these results suggest that Baicalin prevent CPDs formation induced by UVB. Baicalin is therefore a promising protective substance against UVB radiation.     

Polydeoxyribonucleotide promotes cyclobutane pyrimidine dimer repair in UVB-exposed dermal fibroblasts

BACKGROUND: DNA is the main cellular chromophore for ultraviolet B (UVB). Its absorption leads to the generation of typical photoproducts. The most frequent types (about 80%) are cyclobutane pyrimidine dimers (CPDs). Several studies have suggested that treatment with deoxyribonucleosides can protect some cell types from DNA damage. The aim of this work was to evaluate the ability of the polydeoxyribonucleotide (PDRN) to protect human dermal fibroblasts from UVB-induced DNA damage. METHODS: Human dermal fibroblasts were irradiated with 600 mJ/cm(2) of UVB radiation. Cells were analyzed at increasing time points from irradiation to study the recovery from UVB-induced DNA photodamage. Damage repair was subsequently assessed by immunocytochemical analysis of CPDs levels and by measurement of p53 protein expression. RESULTS: The extracellular addition of 100 microg/ml PDRN immediately after irradiation caused a strong activation of p53 protein in the first 24 h. This signal was accompanied by an increase in CPDs repair rates at early time points of recovery. CONCLUSIONS: The addition of PDRN to the culture medium supports CPDs repair probably providing a faster supply of precursors for the deoxyribonucleotide triphosphates pool necessary to UVB-damaged cells. This condition could promote the action of the salvage pathway, thereby accelerating DNA repair, but other inducible responses linked to increased p53 expression could be involved.     

Role of protein kinase C delta in X-ray-induced apoptosis of keratinocyte

Abstract:  In this study, we investigated the process of X-ray-induced apoptosis of skin keratinocyte, and the functional role of protein kinase C delta (PKCδ) and downstream signalling cascade. High-dose X-ray irradiation (10 Gy) led to the apoptosis of HaCaT keratinocyte, accompanied by PKCδ cleavage. Treatment with PKCδ inhibitor and adenoviral transduction of dominant-negative PKCδ clearly inhibited the X-ray-induced apoptosis of keratinocyte. In addition, X-ray induced the phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) and inhibition by ERK1/2 inhibitor abrogated the X-ray-induced apoptosis. Interestingly, overexpression of dominant-negative PKCδ markedly blocked the X-ray-induced phosphorylation of ERK1/2, suggesting that ERK1/2 is the functional downstream effector of PKCδ. Next, we investigated the difference between UVB and X-ray response. UVB induced the apoptosis of keratinocyte in a PKCδ-dependent manner, similar to X-ray response. However, UVB irradiation induced the phosphorylation of c-jun N-terminal kinases (JNK) and inhibition of JNK significantly protected the UVB-induced apoptosis. These results demonstrate that PKCδ is a key regulator in X-ray-induced apoptosis of keratinocyte and suggest that there is subtle difference in downstream signalling cascade between UVB and X-ray response of keratinocyte.     

中波紫外线激活HaCaT细胞炎症信号通路的实验研究

目的 探讨中波紫外线(UVB)对角质形成细胞(KC)炎症信号通路的影响.方法 UVB(40 mJ/cm²)照射永生化人角质形成细胞株HaCaT细胞,分别于照射后0、10、30、60、120、240min收集细胞蛋白和核蛋白,蛋白质印迹法检测NF-κB信号传导通路中的重要分子-磷酸化IκB-α(P-IκB-α)、IκB-α和NF-κB p65蛋白的动态变化,以及MAPK家族的蛋白分子ERK1/2、p38、c-JNK等磷酸化激活的动态变化.结果 蛋白质印迹法检测结果显示,UVB照射后0.5h IκB-α开始发生磷酸化和降解,在第2、4小时时更加明显;细胞核蛋白p65的量在照射后0.5h开始升高,在随后的2h时达到高峰.UVB照射后10 min HaCaT细胞内的ERK1/2、p38、c-JNK蛋白的磷酸化就开始增加.结论 UVB照射KC可激活细胞内的NF-κB及MAPK信号传导通路.     

Involvement of EGF receptor activation in the induction of cyclooxygenase-2 in HaCaT keratinocytes after UVB

Because selective inhibition of cyclooxygenase-2 (COX-2) suppressed the induction of skin tumors in mice by UV and as UV has been shown to induce expression of COX-2 in skin and cells, COX-2 may be crucial for photocarcinogenesis of the skin. We studied the mechanism of UVB-induced expression of COX-2 focusing on the signal transduction pathway involved. Hydrogen peroxide (H2O2) treatment of HaCaT cells induced expression of COX-2 and pretreatment with the antioxidant N-acetylcysteine (NAC) partly inhibited the UVB-induced expression of COX-2 protein in HaCaT cells, suggesting that oxidative stress contributes to COX-2 induction. To examine the signaling pathways involved in the UVB-induced expression of COX-2 in HaCaT cells, we analysed the expression of COX-2 protein after treatment with various inhibitors of signaling molecules. Inhibition of EGFR by a specific inhibitor and by a neutralizing antibody suppressed the induction of COX-2 expression by UV. Although a neutralizing antibody to transforming growth factor-alpha (TGF-alpha) suppressed COX-2 expression induced by TGF-alpha, it did not suppress COX-2 expression by UV, indicating that a direct activation of EGFR is involved. Treatment of cells at low temperature (4 degrees C) inhibited UVB-induced JNK activation, but it did not inhibit COX-2 expression by UV. Inhibitors of MEK, p38 MAP kinase and PI3-kinase, suppressed the induction of COX-2 expression by UV. In contrast, an erbB-2 inhibitor augmented the UVB-induced increase of COX-2 protein. These data indicate that oxidative stress in association with activation of EGFR, ERK, p38 MAP kinase, and PI3-kinase plays crucial roles in the UVB induction of expression of COX-2.     

中波紫外线照射对表皮朗格汉斯细胞p53蛋白磷酸化表达的影响

目的：研究皮肤朗格汉斯（Langerhans）细胞（LC）在不同剂量中波紫外线（UVB）照射前、后p53蛋白磷酸化水平的差异。方法：联合采用密度梯度离心和免疫磁珠的方法分离纯化LC,将LC分为实验组和对照组,实验组分别接受30、60和90mJ／cm^2 UVB辐射,辐射后4h提取总蛋白,采用Western—blotting法检测各组细胞中p53蛋白及磷酸化p53蛋白的表达量,并比较两者之间的差异。结果：接受UVB辐射后,皮肤LC中p53蛋白表达基本无变化,而p53蛋白磷酸化水平显著升高,差异具有统计学意义,并呈剂量依赖性。结论：UVB辐射可刺激p53蛋白磷酸化,并呈剂量依赖性,进而诱导p53蛋白活化,发挥其下游功能。     

Subphysiological concentrations of extracellular calcium sensitize normal human keratinocytes to UVB-induced apoptosis

Abstract Normal human keratinocytes are stimulated to proliferate in serum-free medium containing subphysiological concentrations of calcium (0.09 mM, low calcium). In this study, we examined the effect of increased levels of extracellular calcium (2.0 mM, normal calcium) on UVB-induced apoptosis. Apoptosis was assessed by changes in cellular morphology, annexind V-FITC flow cytometry, and the formation of internucleosomal DNA ladders. High doses of UVB induced keratinocytes grown in low calcium medium to undergo apoptosis. In contrast, keratinocytes grown for 72 h in normal calcium medium were completely resistant to UVB-induced apoptosis. No apoptosis was observed even at UVB doses as high as 1200 J/m². However, despite the lack of UVB-induced cell death, keratinocytes grown in normal calcium medium lost the ability to proliferate following high levels of UVB irradiation. High doses of UVB also increased the expression of the differentiation-specific proteins involucrin and cytokeratin 10 in a dose-dependent manner. In addition, growth in normal calcium medium lowered the UVB-induced stimulation of the p53 protein and altered the normal subcellular localization pattern of p53. UVB irradiation of human keratinocytes grown in normal calcium medium may be inducing further cell differentiation in the absence of overt cell death. Received: 16 April 1998 / Received after revision: 31 August 1998 / Accepted: 23 September 1998     

p38 Mitogen-activated protein kinase inhibitor protects the epidermis against the acute damaging effects of ultraviolet irradiation by blocking apoptosis and inflammatory responses

The primary function of the epidermis is to provide a protective barrier against numerous environmental insults, including ultraviolet radiation (UVR). UVR, particularly in the UVB spectrum, is a potent carcinogen known to damage DNA directly or through the generation of free radicals. Although in the long term, protective measures such as apoptosis and inflammation may prove beneficial in safeguarding the epidermis against the propagation of potentially tumorigenic cells, after high-dose UV irradiation these biologic events may be acutely detrimental to the architectural and functional integrity of the tissue owing to rampant cell death and inflammatory responses, which can culminate in epidermal erosion and consequently loss of barrier functions. The mitogen-activated protein kinase (MAPK) signaling pathway is known to be activated by UVR and herein we identify p38 MAPK as a key modulator of these physiologic events. Mice treated with the p38 MAPK inhibitor SB202190 are protected against several detrimental effects of acute UV irradiation, namely, sunburn cell/apoptosis, inflammation, and a hyperproliferation response. Based on our results, selectively blocking p38 activation with the SB202190 inhibitor could prove beneficial in treating victims from severe sunburn or exposure to other chemical agents known to trigger the p38 pathway.     

UVB-induced interleukin-18 production is downregulated by tannic acids in human HaCaT keratinocytes

Tannic acids (TAs) are believed to be the key active components in plants, and are believed to be responsible for their anti-inflammatory, anti-viral effects and chemoprevention of cancer. However, the molecular mechanisms for the action of TA are unclear. This study examined the effects of TA on cutaneous inflammation with a human keratinocyte cell line (HaCaT). Interleukin-18 (IL-18) has multiple effects upon various cells involved in inflammatory response. In this study, the IL-18 mRNA expression and protein levels were reduced by a TA pretreatment. UV radiation can trigger the induction of the p38 mitogen-activated protein kinase (MAPK)-dependent signalling cascade. Immunoprecipitation and Western blot analysis was performed to determine if TA regulate the MAPK signalling pathway. TA significantly inhibited the activation of p38 MAPK and extracellular signal-regulated protein kinases. Moreover, TA-inhibited UVB enhanced the expression of the inflammatory mediators, IL-1, IL-6, tumor necrotic factor-alpha, cyclooxygenase-2 and prostaglandin E(2) in UVB-irradiated HaCaT cells. The topical application of TA on mouse skin treated with UVB irradiation has shown that TA inhibited the formation of erythema. These findings suggest that TA has significant anti-inflammatory effects on the UVB-induced response on the skin and may be a candidate natural compound for the regulation of cutaneous inflammation.