中波紫外线诱导皮肤角质形成细胞凋亡机制的研究进展

紫外线照射表皮后引起DNA损伤的表皮细胞通过日晒伤细胞(凋亡的角质形成细胞)的形成来清除。p53、Fas、Trp53等基因的表达促进角质形成细胞凋亡,而survivin的表达则抑制角质形成细胞凋亡。紫外线照射后皮肤可产生环丁烷嘧啶二聚体和6-4光产物,这两种光产物可以作为UVB诱导凋亡的起始信号。凋亡在清除DNA损伤的皮肤起着重要作用。在皮肤中通过凋亡清除DNA损伤的细胞,防止日光诱导癌变,而不是依赖于DNA损伤的校正修复。silibinin对中波紫外线引起人HaCaT永生化角质形成细胞凋亡具有双向调控作用。对UVB引起角质形成细胞凋亡的调控药物,值得进一步研究。     

角质形成细胞的凋亡失调及相关皮肤病

角质形成细胞的凋亡在调节表皮发育和抑癌中起着关键作用，凋亡可平衡角质形成细胞的增殖来保持表皮厚度，促使角质层形成和清除恶化前细胞。除正常发展程序外，角质形成细胞的凋亡能被紫外线和其他刺激诱发，凋亡在保持皮肤细胞内环境稳定和一些皮肤病的发病机制中起着重要作用。     

中波紫外线诱导HaCaT细胞凋亡中TF-1细胞凋亡相关基因19的表达

目的：研究在中波紫外线(UVB）诱导正常永生化角质形成细胞(HaCaT）凋亡过程中，T细胞凋亡相关基因19(TFAR 19）的表达时相及位置，方法：使用流式细胞仪、膜联蛋白V(Annexin—V）、激光扫描共聚焦显微镜等方法进行研究。结果：在凋亡过程中，TFAR 19逐渐向核周聚积，最后向核膜内移位，在核膜及其周围以及核内表达。结论：在UVB诱导HaCaT细胞凋亡的早期和晚期过程中TFAR 19均有表达。     

砷化物抑制银屑病角质形成细胞增殖的研究

银屑病主要表现为角质形成细胞过度增殖及凋亡异常,其中角质形成细胞过度增殖是由于细胞凋亡功能障碍或失调所致,凋亡缺陷在银屑病的发病机制巾发挥着重要作用。研究表明,砷化物可以通过对Fas/Fas配体、端粒和端粒酶的影响以及联合阻断JNK等多种途径诱导角质形成细胞凋亡,从而抑制其过度增殖。因此,砷化物有望成为一种局部治疗银屑病的新型药物。     

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。     

γ—干扰素诱导角质形成细胞凋亡及其Fas抗原表达研究

目的：探讨γ－干扰素在银屑病发病中的作用。方法 通过流式细胞仪测定角持形成细胞中亚二倍体细胞含量、片段化DNA分析及AnnexinV法检测经γ－干扰素诱导的角质形成细胞凋亡;采用组织化学、流式细胞仪测定经γ－干扰素作用后的角质形成细胞Fas抗原表达。结果 γ－干扰素上调角质形成细胞Fas抗原表达（P＜0．01）,诱导角质形成细胞凋亡（P＜0．01）。结论 γ－干扰素可能通过上调角质形成细胞Fas抗原表达,进而诱导角质形成细胞凋亡而参与银屑病发病。     

Stevens-Johnson综合征/中毒性表皮坏死松解症角质形成细胞死亡机制的研究进展

角质形成细胞的凋亡涉及代谢及免疫机制,前者可能是亲电子的药物活性代谢产物经线粒体途径诱导凋亡.Stevens-Johnson综合征免疫机制则较复杂,CD8+细胞毒T细胞、自然杀伤细胞、单核细胞及调节T细胞等免疫细胞参与发病.肿瘤坏死因子α、可溶性FasL、颗粒溶素、肿瘤坏死因子相关凋亡诱导配体和肿瘤坏死因子样弱凋亡因子等细胞因子参与了凋亡作用的放大.在角质形成细胞的坏死中,警报素家族成员S100A、α防御素、高迁移率族蛋白B1均参与.     

金黄色葡萄球菌性超抗原诱发银屑病发病机理探讨

目的探讨金黄色葡萄球菌性超抗原诱发银屑病的机制。方法3H-TdR掺入法测定细胞增殖反应,亚二倍体细胞含量测定,片段化DNA分析,膜联蛋白V(AnnexinV)法测定细胞凋亡,流式细胞仪检测细胞表面抗原表达。结果金黄色葡萄球菌肠毒素B活化的淋巴细胞培养上清液作用于角质形成细胞48h,可促进角质形成细胞增殖,诱导角质形成细胞表达HLA-DR和Fas抗原;再次加入上清液继续作用48h,则诱导角质形成细胞凋亡（P<0.01）。结论金黄色葡萄球菌肠毒素B作为超抗原活化T细胞,使之释放细胞因子,后者使角质形成细胞首先活化增殖,继而凋亡。     

中波紫外线诱导表皮细胞凋亡机制研究进展

中波紫外线作为日光紫外线的组成部分,可在表皮细胞引起多种生物学效应,也是诱导细胞凋亡的一种有效刺激因子,其发生机制与多种因素有关,包括p53、bcl-2等基因表达的改变,p38丝裂原激活蛋白激酶、c-jun N-末端蛋白激酶、蛋白激酶C、白介素-1β转换酶等蛋白激酶的激活以及多种因子和抗氧化物的产生等.这种过程在角质形成细胞、黑素细胞、郎格汉斯细胞均可发生,在防止皮肤肿瘤发生中起着一定作用,与诱导皮肤局部免疫抑制也有着密切关系.     

中波紫外诱导表皮细胞凋亡机制研究进展

中波紫外线作为日光紫外线的组成部分，可在表皮细胞引起多种生物学效应，也是诱导细胞凋亡的一种有效的刺激因子，其发生机制与多种因素有关，包括p53、bcl-2等基因表达的改变，p38丝裂原激活蛋白激酶、c-jun N-末端蛋白激酶、蛋白激酶C、白介素-1β转换酶等蛋白酶的激活吧及多种因子和抗氧化物的产生等。这种过程在角质形成细胞、黑素细胞、郎格汉斯细胞均可发生，在防止皮肤肿瘤发生中起着一定作用，与诱导皮肤局部免疫抑制也有密切关系。     

Pro- and anti-apoptotic effects of nitric oxide in irradiated keratinocytes: the role of superoxide

Ultraviolet radiation (UV) induces apoptosis in keratinocytes by both p53- and death receptor-dependent pathways. It also generates free radicals in keratinocytes, including the synthesis of nitric oxide (NO) by constitutive and inducible NO synthases (NOS). NO has both pro- and anti-apoptotic effects. We wished to determine which of these was predominant in keratinocytes. Human CCD1106 keratinocytes were irradiated with UVB in the presence and absence of several NOS antagonists. Apoptosis was measured by flow cytometry with annexin V binding. NOS antagonism consistently altered UVB-induced apoptosis measured 18 h after irradiation. In 9 of 13 experiments, NOS antagonism increased apoptosis. However, in 4 of 13 experiments, NOS antagonism reduced apoptosis. We postulated that the variable effects of NO might be due to a critical balance between UVB-induced NO and superoxide production. We predicted that NO would be anti-apoptotic in the presence of low O(-)(2), but pro-apoptotic when NO combined with O(-)(2) to form peroxynitrite. Though superoxide dismutase reduced apoptosis after UVB, addition of peroxynitrite did not affect apoptosis. We conclude that NO released by UV irradiation is anti-apoptotic; however, the levels of O(-)(2) may be a determinant of NO action.     

Antioxidant and anti-inflammatory activities of melanocortin peptides

The molecular pathways regulating ultraviolet (UV) radiation-induced apoptosis of melanocytes, a cell population crucially involved in the protection of epidermal keratinocytes against the harmful effects of UV light, are poorly characterized. We show that the α-melanocyte-stimulating hormone (α-MSH) blocks UVB-induced apoptosis of normal human melanocytes in vitro . The effect of α-MSH is not restricted to melanocytes but is also operative in cells that do not produce melanin, for example in human epidermal keratinocytes and in dermal fibroblasts. α-MSH not only delays but also protects melanocytes from UVB-induced cell death. The anti-apoptotic activity of α-MSH is not mediated by a filtering effect or induction of melanin synthesis. α-MSH also does not induce changes in the cell cycle distribution or expression of Bcl₂, Bcl_x, CD95 (Fas/APO-1) and FasL. In contrast, α-MSH markedly reduces the formation of cyclobutane pyrimidine dimers induced by UVB radiation. Human dermal fibroblasts carrying a defective XPA gene are not protected from UVB-induced apoptosis by α-MSH. These results highlight a novel biological activity of α-MSH as well as novel regulatory pathways within the UV response of skin cells targeted by this neuropeptide.     

Molecular mechanisms of UV-induced apoptosis

Sunburn cells, single standing cells with typical morphologic features occurring in UV-exposed skin, have been recognized as keratinocytes undergoing apoptosis following UV irradiation. Induction of apoptosis following UV exposure appears to be a protective mechanism, getting rid off severely damaged cells that bear the risk of malignant transformation. UV-mediated apoptosis is a highly complex process in which different molecular pathways are involved. These include DNA damage, activation of the tumor suppressor gene p53, triggering of cell death receptors either directly by UV or by autocrine release of death ligands, mitochondrial damage and cytochrome C release. Detailed knowledge about the interplay between these pathways will increase our understanding of photocarcinogenesis. This review briefly discusses recent findings concerning the molecular mechanisms underlying UV-induced apoptosis.     

Voriconazole enhances UV-induced DNA damage by inhibiting catalase and promoting oxidative stress

Cutaneous squamous cell carcinoma (cSCC) is the second most common form of skin cancer and is associated with cumulative UV exposure. Studies have shown that prolonged voriconazole use promotes cSCC formation; however, the biological mechanisms responsible for the increased incidence remain unclear. Here, we show that voriconazole directly increases oxidative stress in human keratinocytes and promotes UV-induced DNA damage as determined by comet assay, 8-oxoguanine immunofluorescence and mass spectrometry. Voriconazole treatment of human keratinocytes potentiates UV-induced apoptosis and activation of the p38 MAP kinase and 53BP1 UV stress response pathways. The p38 MAP kinase activation promoted by voriconazole exposure can be mitigated by pretreating keratinocytes with N-acetylcysteine. Voriconazole increases oxidative stress in keratinocytes by directly inhibiting catalase leading to lower intracellular NADPH levels and the triazole moieties in voriconazole are critical for inhibiting catalase. Furthermore, voriconazole is shown to promote UV-induced dysplasia in an in vivo model. Together, these data demonstrate that voriconazole potentiates oxidative stress in UV-irradiated keratinocytes through catalase inhibition. Use of antioxidants may mitigate the pro-oncogenic effects of voriconazole.     

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.     

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.     

Life and death signaling pathways contributing to skin cancer

Apoptosis is generally regarded as a critical regulatory event in the development of malignancies in several different organ systems (Thompson, 1995). Initially, oncologists focused on alterations in rates of proliferation and cell cycle kinetics, but more recently an emphasis on apoptosis has dominated the fight against cancer (Evan and Vousden, 2001). As approximately 1,000,000 individuals in the U.S.A. develop skin cancer each year, it is important to elucidate the molecular mechanisms that govern cell survival and cell death in the epidermis (Miller and Weinstock, 1994). Moreover, given that most skin cancers occur on sun-exposed skin, the pro-apoptotic and antiapoptotic response of keratinocytes (KC) to UV light is of particular relevance to the development of skin cancer (Brash et al, 1996). Whereas both squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) arise from epidermal KC, it is becoming increasingly apparent that the natural history of their development, their underlying molecular pathogenesis, and potential involvement of antiapoptotic pathways are significantly different. Nonetheless, as pointed out later in the text, significant progress is being made in our understanding of the pathophysiology of these relatively common epithelial-cell-derived neoplasms. In this review we will explore four topics: first, a review of the life and death signaling pathways operative in normal human skin that prevents premature apoptosis of KC with an emphasis on nuclear factor kappaB (NFkappaB) survival signals; second, the molecular pathways that are engaged and regulate apoptosis after normal KC are exposed to ultraviolet (UV) light; third, the apoptotic resistant mechanisms that premalignant and malignant KC utilize to avoid cell death; fourth, therapeutic strategies that can render malignant cells more susceptible to apoptosis with an emphasis on a death pathway mediated by the death ligand TRAIL.     

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.     

NF-kappaB inhibition reveals differential mechanisms of TNF versus TRAIL-induced apoptosis upstream or at the level of caspase-8 activation independent of cIAP2

Death ligands not only activate a death program but also regulate inflammatory signalling pathways, for example, through NF-kappaB induction. Although tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and TNF both activate NF-kappaB in human keratinocytes, only TRAIL potently induces apoptosis. However, when induction of NF-kappaB was inhibited with a kinase dead IKK2 mutant (IKK2-KD), TNF- but not TRAIL-induced apoptosis was dramatically enhanced. Acquired susceptibility to TNF-induced apoptosis was due to increased caspase-8 activation. To investigate the mechanism of resistance of HaCaT keratinocytes to TNF-induced apoptosis, we analyzed a panel of NF-kappaB-regulated effector molecules. Interestingly, the inhibitor of apoptosis protein (IAP) family member cIAP2, but not cIAP1, X-linked inhibitor of apoptosis, TNF receptor-associated factor (TRAF)-1, or TRAF2, was downregulated in sensitive but not in resistant HaCaT keratinocytes. Surprisingly, however, stable inducible expression of cIAP2 was not sufficient to render IKK2-KD-sensitized keratinocytes resistant to TNF, and reduction of cIAP2 alone did not increase the sensitivity of HaCaT keratinocytes to TNF. In conclusion, we demonstrate that inhibition of NF-kappaB dramatically sensitizes human keratinocytes to TNF- but not to TRAIL-induced apoptosis and that this sensitization for TNF was largely independent of cIAP2. Our data thus clearly exclude the candidates proposed to date to confer TNF apoptosis resistance and suggest the function of an unanticipated effector of NF-kappaB critical for the survival of HaCaT keratinocytes upstream or at the level of caspase-8 activation.     

beta-Carotene interferes with ultraviolet light A-induced gene expression by multiple pathways

Ultraviolet light A (UVA) exposure is thought to cause skin aging mainly by singlet oxygen ((1)O(2))-dependent pathways. Using microarrays, we assessed whether pre-treatment with the (1)O(2) quencher beta-carotene (betaC; 1.5 microM) prevents UVA-induced gene regulation in HaCaT human keratinocytes. Downregulation of growth factor signaling, moderate induction of proinflammatory genes, upregulation of immediate early genes including apoptotic regulators and suppression of cell cycle genes were hallmarks of the UVA effect. Of the 568 UVA-regulated genes, betaC reduced the UVA effect for 143, enhanced it for 180, and did not interact with UVA for 245 genes. The different interaction modes imply that betaC/UVA interaction involved multiple mechanisms. In unirradiated keratinocytes, gene regulations suggest that betaC reduced stress signals and extracellular matrix (ECM) degradation, and promoted keratinocyte differentiation. In irradiated cells, expression profiles indicate that betaC inhibited UVA-induced ECM degradation, and enhanced UVA induction of tanning-associated protease-activated receptor 2. Combination of betaC-promoted keratinocyte differentiation with the cellular "UV response" caused synergistic induction of cell cycle arrest and apoptosis. In conclusion, betaC at physiological concentrations interacted with UVA effects in keratinocytes by mechanisms that included, but were not restricted to (1)O(2) quenching. The retinoid effect of betaC was minor, indicating that the betaC effects reported here were predominantly mediated through vitamin A-independent pathways.