Ultraviolet B radiation regulates cysteine‐rich protein 1 in human keratinocytes

Background: Cysteine‐rich protein 1 (CRP1) is a growth‐inhibitory cytoskeletal protein that is induced by ultraviolet (UV) C radiation radiation in fibroblasts. Our aim was to investigate the effects of UV radiation on CRP1 in keratinocytes, the main cell type subjected to UV radiation in the human body. Methods: The effects of physiologically relevant doses of UVB radiation on CRP1 protein levels were studied in cultured primary keratinocytes and transformed cell lines (HaCaT, A‐431) by immunoblotting. UVB‐induced keratinocyte apoptosis was assessed by flow cytometry and monitoring caspase activity. Expression of CRP1 in human skin in vivo was studied by immunohistochemistry in samples of normal skin, actinic keratosis (AK) representing UV‐damaged skin and squamous cell carcinoma (SCC), a UV‐induced skin cancer. Results: CRP1 expression increased by UVB radiation in primary but not in immortalized keratinocytes. Upon high, apoptosis‐inducing doses of UV radiation, CRP1 was cleaved in a caspase‐dependent manner. In normal skin, CRP1 was expressed in smooth muscle cells, vasculature, sweat glands, sebaceous glands and hair root sheath, but very little CRP1 was present in keratinocytes. CRP1 expression was elevated in basal cells in AK but not in SCC. Conclusion: CRP1 expression is regulated by UVB in human keratinocytes, suggesting a role for CRP1 in the phototoxic responses of human skin.     

Particulate matter induces pro‐inflammatory cytokines via phosphorylation of p38 MAPK possibly leading to dermal inflammaging

Particulate matter (PM) is known to have harmful effects on human health. Epidemiological studies have suggested that PM exposure is related to skin diseases and extrinsic skin ageing. However, the mechanisms by which PM affects skin are unclear. The aim of this study was to investigate the mechanism of action of PMs on epidermal inflammation and skin ageing using a co‐culture of human keratinocytes (HaCaT) and fibroblasts (HDF). SRM 1648a (pmA) and 1649b (pmB), which mainly comprise heavy metals and polycyclic aromatic hydrocarbons, respectively, were used as reference PMs. Cytotoxic effects, activation of AhR, phosphorylation of p38 kinase and ROS generation were examined in PM‐treated HaCaT cells. The phosphorylation of p38 MAPK induced by PMs was shown to be critically important for the increases in IL‐1α and IL‐1β expression. Moreover, the mRNA and protein expression levels of MMP1 and COX2 were markedly increased in HDF cells co‐cultured with PM‐treated HaCaT cells. In conclusion, PMs induce the expression of pro‐inflammatory cytokines in keratinocytes via the p38 MAPK pathway, and these interleukins increase the expression of MMP1 and COX2 in HDF cells. These results suggest that PMs trigger skin ageing via p38 MAPK activation and interleukin secretion in epidermal keratinocytes.     

Effect of ultraviolet radiation on the expression of pp38MAPK and furin in human keratinocyte-derived cell lines

Background: Ultraviolet radiation (UVR) is known to induce the activation of stress‐inflammation signal transduction pathways, and to induce the activity of many proteases in skin cells. It is unknown whether the activation of proteases such as furin is related to changes in the phosphorylation status of p38MAPK. Methods: The effect of UVR on immortalized keratinocyte (HaCaT) and squamous cell carcinoma (Colo16) cells was investigated with respect to cell survival, phosphorylation of p38MAPK, and the proprotein convertase, furin. The cells were exposed to either a low or a high dose of UVA and/or UVB and the viability was monitored over 48 h, along with changes in the intracellular expression of p38MAPK and furin. Results: Low‐dose UVA (2 kJ/m²) and/or UVB (0.2 kJ/m²) radiation had no effect on cell viability, except in UVA‐irradiated Colo16 cells. High UVA (20 kJ/m²) caused a loss of cell viability in HaCaT cells, but not in Colo16 cells. The opposite effect was seen in cells exposed to a high UVB dose (2 kJ/m²). The viability of both cell cultures decreased when exposed to high‐dose UVA+B radiation. UV irradiation downregulated the expression of phosphorylated p38 (pp38) in HaCaT cells irrespective of the UV dose and type. In Colo16 cells, UV radiation induced pp38 expression in the cells following exposure, with the highest increase in cells exposed to high‐dose UVA. The expression of furin in UV‐irradiated HaCaT cells was similar to that seen for pp38 expression. In Colo16 cells, UV radiation induced furin expression, with the highest increase seen in cells 24 h after exposure to both high‐dose UVB and UVA+B radiation. Conclusion: The results show that there are differences between the effect of UV types and doses on cell function in the keratinocyte‐derived cell lines examined in this study. The level of furin expression in Colo16 cells correlated to changes in pp38 levels in the cells following exposure to UV radiation, but not in HaCaT cells. From an improved understanding of the signalling pathways and their downstream events and how these may differ as a result of tumorigenesis, it may enable the development of inhibitors, which may have therapeutic applications.     

A comparative study of UV-induced cell signalling pathways in human keratinocyte-derived cell lines

Ultraviolet (UV) radiation can activate the p38 mitogen-activated protein kinase (MAPK), Jun N-terminal kinase (JNK) and nuclear factor-κB (NFκB) pathways in skin cells. HaCaT cells are widely used as a primary keratinocyte substitute to study these pathways. However, like most squamous cell carcinomas (SCCs), it contains a dysfunctional p53. It is unclear if HaCaT cells activate these signalling pathways similarly to SCC cells (Colo16) or to primary human epidermal keratinocytes (HEK). In this study, the UV activation (UVA, UVB, UVA + B, UVB + A) of p38 MAPK, JNK and NFκB pathways, and TNFα secretion by HEK, HaCaT and Colo16 cells were investigated. The signalling pathway activation was UV-type and dose-dependent with UVB + A radiation inducing a high p38 and JNK activation. HaCaT cells exhibited 2- to 4-fold higher activity of the p38 (771 % at 60 min) and JNK (794 % at 30 min) pathways following UVB + A radiation than did HEK cells (p38: 367 % at 15 min and JNK: 184 % at 30 min). While both HaCaT and Colo16 cells did not activate the NFκB pathway, Colo16 cells had a lower p38 and higher JNK activity than HaCaT cells. Irradiated HaCaT cells produced less TNFα (UVB: 3.5 pg/ml), while HEK cells produced the most (UVB: 1,296 pg/ml). When co-exposed to IL1α, irradiated HaCaT had the greatest fold of TNFα release (UVB: 16.2-fold, UVA + B: 8.9-fold and UVB + A: 6.1-fold). The pattern of activation and TNFα secretion of HaCaT cells mirrored that of Colo16 cells. It is likely that the presence of molecular alterations in HaCaT cells may be responsible for its different responses to that seen for HEK cells. The results of this study suggest caution in using HaCaT cells as a substitute for normal keratinocytes in investigating UV-induced cells signalling pathways.     

A low UVB dose, with the potential to trigger a protective p53-dependent gene program, increases the resilience of keratinocytes against future UVB insults

One protein central in the response of human keratinocytes to ultraviolet B damage is p53. By transactivating genes involved in either cell cycle arrest or DNA repair, p53 has a leading role in the recovery from this damage. Considering this role, we wished to investigate whether the triggering of a p53-dependent gene program by repetitive ultraviolet B (UVB) exposure can induce an adaptive response in human skin cells. In particular, we examined two p53-target genes, p21/WAF1 and p53R2, with a crucial role in p53-induced cell cycle arrest and p53-induced DNA repair respectively. Exposure to a mild UVB dose was able to induce an adaptive response in human keratinocytes, leading to increased survival of cells that maintain their capacity to repair DNA damage upon exposure to apoptotic doses of UVB. Our study indicates that this adaptation response is only achieved if the interval between subsequent UVB insults allows sufficient time for the p53-induced protective gene program to be induced. Our results also demonstrate that small but quickly recurring UVB exposures are as harmful as one intense, continual exposure to UVB irradiation. Future research will be oriented toward investigating alternative ways to induce an adaptive response without pre-exposing the cells to UV.     

Resveratrol regulates p66Shc activation in HaCaT cells

Please cite this paper as: Resveratrol regulates p66Shc activation in HaCaT cells. Experimental Dermatology 2010; 19 : 895–903. Abstract: Skin is exposed to both endogenous and environmental oxidant agents, leading to the harmful generation of reactive oxygen species. Particular interest has been pointed on plant antioxidants, such as resveratrol, because of their wide‐ranging biological activity and clinical potential. Resveratrol exerts antioxidant, metabolism‐regulating and pro‐apoptotic/anti‐cancer effects on a variety of experimental models and has been suggested to protect skin from ultraviolet‐induced photodamaging and photoaging. In parallel, also the biological significance of p66Shc, a member of the Src Homologue and Collagene homologue family with redox activity, is getting further attention. Because of the striking intersection among the activities of resveratrol with those of p66Shc, we investigated whether resveratrol would activate p66Shc in human immortalised keratinocytes (HaCaT cells), a well known and largely used model for skin keratinocytes. HaCaT cells were treated with resveratrol (10–150 μm ) for different times. The effect of resveratrol on the proliferation of HaCaT cells and the activation of ERK1/2, AKT, and p66Shc was investigated by cell counting, fluorescence‐activated cell sorting, and western blot analysis of total or immunoprecipitated cell extracts. In HaCaT cells, resveratrol induces dose‐ and time‐dependent growth arrest, p66Shc‐Ser36 phosphorylation, ERK1/2 phosphorylation and AKT dephosphorylation. Finally, we showed that resveratrol‐induced p66Shc‐Ser36 phosphorylation is dependent on ERK1/2 activation. Interestingly, these resveratrol‐induced molecular effects were associated with reduced adhesion and reversible growth arrest rather than cell death pathways. This is the first evidence linking resveratrol with p66Shc and suggests that p66Shc may contribute to the effect of resveratrol on cell proliferation and function in the outermost layer of the skin.     

Astaxanthin,a xanthophyll carotenoid,inhibits ultraviolet‐induced apoptosis in keratinocytes

Intra‐cellular reactive nitrogen/oxygen species and apoptosis play important roles in ultraviolet (UV)‐induced inflammatory responses in the skin. Astaxanthin (AST), a xanthophyll carotenoid, exhibits diverse clinical benefits. The protective effects of AST against UV‐induced apoptosis were investigated in the present study. Astaxanthin (5 μm ) caused a significant decrease in the protein content and the mRNA levels of inducible nitric oxide (iNOS) and cyclooxygenase (COX)‐2, and decreased the release of prostaglandin E2 from HaCaT keratinocytes after UVB (20 mJ/cm²) or UVC (5 mJ/cm²) irradiation. No significant protective effects against UV‐induced reactive oxygen species (ROS) were observed in AST‐pretreated cells. Astaxanthin caused a significant inhibition of UV‐irradiation‐induced apoptosis, as evidence by a DNA fragmentation assay. Furthermore, we found that the treatment with AST caused a reduction in the UVB‐ or UVC‐induced protein and mRNA expression of macrophage migration inhibitory factor (MIF), IL‐1β and TNF‐α in HaCaT keratinocytes. These results suggest that AST effectively protects against UV‐induced inflammation by decreasing iNOS and COX‐2, and thereby inhibiting the apoptosis of keratinocytes.     

Effects of a melanogenic bicyclic monoterpene diol on cell cycle, p53, TNF-alpha, and PGE2 are distinct from those of UVB

PURPOSE: Bicyclic monoterpene (BMT) diols are small-molecule compounds that mimic ultraviolet radiation (UVR) by inducing melanogenesis. The objective of this study was to compare the effects of 2,2-dimethyl-3-propanyldiol-norbornane (AGI-1140), a novel BMT diol, and ultraviolet B (UVB) on additional cellular responses. METHODS: S91 mouse melanoma cells were treated with a range of concentrations of AGI-1140, and examined for induction of melanogenesis and nitric oxide (NO). The effect of AGI-1140 on dendrite outgrowth from human melanocytes was examined by quantitative microscopy. The effect of AGI-1140 and UVB on phosphorylation of p53 serine 15 in human keratinocytes was examined by Western blotting, while the release of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E2 (PGE2) was determined by enzyme-linked immunosorbent assay. The effects of AGI-1140 and UVB on cell cycle arrest of human melanocytes, keratinocytes, fibroblasts, and endothelial cells were compared using fluorescence-activated cell sorting. RESULTS: Similar to UVB, AGI-1140 induced both melanogenesis and NO in melanoma cells. AGI-1140 also induced dendrite outgrowth from melanocytes, indicative of differentiation. However, whereas UVB induced G2 cell cycle arrest with phosphorylation of p53 at serine 15, AGI-1140 induced G1 cell cycle arrest without this phosphorylation. Additionally, unlike UVB, AGI-1140 did not increase the secretion of TNF-alpha or PGE2, mediators of UVB-induced immunosuppressive and inflammatory responses in the skin that may contribute to carcinogenesis. CONCLUSION: This study shows that melanogenesis can be induced by AGI-1140 without many of the deleterious effects associated with UVB.     

The cytoprotective effects of exogenous DNA fragments.

Ultraviolet irradiation of normal human keratinocytes induces a cytotoxic effect. The chromophore for this effect is believed to be genomic DNA. However, DNA damage is known to be repaired in UVB irradiated keratinocytes. The trigger for this DNA repair is potentially damaged DNA itself. To test the hypothesis that damaged DNA can induce the host cell's own DNA repair mechanism, we treated the keratinocytes with the damaged DNA and evaluated its cytoprotective effects. We have observed that fragmented calf thymus DNA irradiated and damaged with a UVC light can induce a protective effect in cultured human keratinocytes. Keratinocytes treated with UVC damaged DNA fragments are less susceptible to UVB irradiation-induced cell death as measured by neutral red uptake. Unirradiated exogenous DNA did not induce this protective effect. Similar protective effects can be seen with irradiated salmon sperm DNA. UVC damaged DNA fragments induced 60% increase in protection in human HaCaT keratinocyte in culture to the cell death induced by UVB. Similar protection was observed with UVC irradiated oligothymidylic acid (dT3-dT5) which increased the survival of human HaCaT keratinocytes after UVB irradiated by 50%. Isolated mononucleotides, irradiated or not, do not increase UVB survivability. Cellular DNA synthesis was greatly inhibited by UVB, becoming undetectable at 40 mJ/cm(2). Exogenous treatment with damaged fragments causes immediate and significant inhibition of total cellular DNA synthesis. This inhibition was dose dependent. Cells that undergo damage to their DNA are known to inhibit endogenous DNA synthesis via p53 suppressor gene activation. This is believed to allow them sufficient time to repair the host DNA. The cellular response to exogenous damaged DNA may be a similar mechanism.     

p53蛋白在UVB诱导凋亡的富集表皮干细胞的角质形成细胞中的表达

目的研究p53蛋白在中波紫外线(ultraviolet lightB,UVB)诱导凋亡的富集表皮干细胞的角质形成细胞群中的表达情况。方法分离富集人表皮干细胞的角质形成细胞群和正常角质形成细胞群,使用UVB诱导两种细胞群凋亡,蛋白印迹法比较不同剂量UVB诱导前后两组细胞的p53蛋白表达的差异。结果两种细胞在不同剂量的UVB照射后p53蛋白表达均比照射前显著增加,在20mJ/cm2与40mJ/cm2照射剂量时,富集人表皮干细胞的角质形成细胞群p53蛋白表达高于正常角质形成的细胞群,差异有统计学意义(P<0.05)。结论富集人表皮干细胞的角质形成细胞p53蛋白表达比其它角质形成细胞对中波紫外线的照射易感。     

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.     

不同剂量中波紫外线照射对角质形成细胞增殖活力和自噬体表达影响的研究

【摘要】 目的 观察HaCaT细胞和原代角质形成细胞接受不同剂量中波紫外线（UVB）照射后细胞增殖活力和自噬体表达水平的变化,并初步评估增殖活力损伤程度和自噬体表达水平之间的相关性。 方法 两种细胞各分为5组,对照组、5、10、20、40 mJ/cm2 UVB照射组,照射结束后12 h进行MTT实验或单丹（磺）酰戊二胺（MDC）染色,全波长酶标仪下读取各孔A值,倒置荧光显微镜下随机选取视野,计数每视野下自噬体表达阴性细胞和阳性细胞数目。 结果 经不同剂量UVB照射后,HaCaT细胞的增殖活力（A值）较原代角质形成细胞下降更明显,其中HaCaT细胞10、20、40 mJ/cm2照射组（A值分别为1.367 ± 0.035、1.173 ± 0.034、0.873 ± 0.025）两两之间以及与对照组（1.519 ± 0.022）之间差异均有统计学意义（P < 0.01）;原代角质形成细胞仅10、20、40 mJ/cm2 UVB照射组（A值分别为0.782 ± 0.012、0.773 ± 0.021、0.725 ± 0.031）与对照组（0.887 ± 0.035）之间差异有统计学意义（P < 0.05）。5、10、20 mJ/cm2 UVB照射后两种细胞MDC染色,自噬体表达阳性的细胞比率均出现增加,但照射量至40 mJ/cm2时则出现下降,以原代角质形成细胞下降更明显,其中HaCaT细胞10 mJ/cm2和20 mJ/cm2 UVB照射组自噬体表达阳性率（分别为22.69% ± 2.15%、28.10% ± 2.92%）较对照组（10.18% ± 1.50%）有显著上升,而40 mJ/cm2组自噬体表达上升幅度出现下降（趋势卡方检验χ2 = 27.48,P < 0.01）;原代角质形成细胞对照组、5、10、20 mJ/cm2组间自噬体阳性率变化不大,但40 mJ/cm2组表达出现明显抑制（趋势卡方检验χ2 = 6.86,P < 0.01）。 结论 UVB对HaCaT细胞和原代角质形成细胞增殖活力的损伤均有剂量依赖性,原代角质形成细胞更耐受UVB损伤;5、10、20 mJ/cm2 UVB照射能促进HaCaT细胞自噬体表达增加,且有剂量依赖性,而对原代角质形成细胞自噬体表达水平未产生显著影响;40 mJ/cm2 UVB照射后HaCaT细胞自噬体表达有下降趋势,而显著抑制原代角质形成细胞自噬体水平的表达。 【关键词】 角质形成细胞; 自噬体; 紫外线     

E-cadherin and its downstream catenins are proteolytically cleaved in human HaCaT keratinocytes exposed to UVB

It has been reported that ultraviolet B (UVB) irradiation causes the loss of E-cadherin of melanocytes, leading them to escape from neighboring keratinocytes during melanoma development. However, little has been paid on its effect on E-cadherin of keratinocytes. In the present study we therefore focus on whether UVB affects expression of E-cadherin-catenin complex in human HaCaT keratinocytes. We found that E-cadherin, beta-, and gamma-catenin but not alpha-catenin were proteolytically cleaved in UVB-irradiated HaCaT keratinocytes. The effect was only observed in keratinocyte undergoing apoptosis. Cleavage of beta- and gamma-catenin was fully abolished by caspase-3 and caspase-8 inhibitors, whereas cleavage of E-cadherin was inhibited by neither caspase nor metalloproteinase inhibitors. Functional analysis showed that the cleavage resulted in the disruption of the physical association between E-cadherin and catenins, indicating that E-cadherin signaling was compromised in UVB-irradiated HaCaT keratinocytes. Because E-cadherin in keratinocytes plays important roles in mediating cell-cell adhesion in epidermis of skin, the loss of E-cadherin and signaling components in keratinocytes may lead to the disruption of skin integrity after UVB exposure.