Downregulation of TUG1 promotes melanogenesis and UVB‐induced melanogenesis

Studies have revealed that taurine upregulated gene 1 (TUG1), an important member of the long non‐coding RNA family, is involved in the regulation of cell growth, tumorigenesis and invasion, insulin secretion and so on. However, its role in melanogenesis has not been explored. This study attempts to explore the effects of TUG1 on melanogenesis and its regulatory mechanisms. We evaluated the expression changes in melanogenesis‐related genes and detected phosphorylation levels of ERK, JNK and P38 in TUG1 downregulated melanocytes. After exposure of melanocytes to UVB irradiation, the expression of TUG1 and melanogenesis‐related genes was detected. We found that the expression of tyrosinase (TYR), tyrosine‐related protein 1 (TYRP1) and tyrosine‐related protein 2 (TYRP2) was upregulated and that the phosphorylation level of ERK was downregulated by downregulating TUG1. Inhibition of TUG1 could further upregulate the expression of UVB‐induced melanogenesis‐related genes. In conclusion, TUG1 negatively regulates melanocyte melanogenesis via the ERK pathway and plays a negative role in UVB‐induced melanogenesis.     

P38 and JNK signal pathways are involved in the regulation of phlorizin against UVB‐induced skin damage

Phlorizin is well known to inhibit sodium/glucose cotransporters in the kidney and intestine for the treatment of diabetes, obesity and stress hyperglycaemia. However, the effects of phlorizin against ultraviolet B (UVB) irradiation and its molecular mechanism are still unknown. We examined the effects of phlorizin on skin keratinocyte apoptosis, reactive oxygen species (ROS) production, pro‐inflammatory responses after UVB irradiation and the changes of some signal molecules by in vitro and in vivo assay. We observed that phlorizin pretreatments inhibited HaCaT cell apoptosis and overproduction of ROS induced by UVB. Phlorizin also decreased the expression of UVB‐induced pro‐inflammatory cytokines, such as interleukin‐1 beta (IL‐1β), interleukin‐6 (IL‐6) and interleukin‐8 (IL‐8) at the mRNA level. Topical application of phlorizin on UVB‐exposed skin of nude mice prevented the formation of scaly skin and erythema, inhibited the increase of epidermal thickness and reduced acute inflammation infiltration in skin. Additionally, PCR, Western blot and immunohistochemical data showed that phlorizin reversed the overexpression of cyclooxygenase‐2 (Cox‐2) induced by UVB irradiation both in vitro and in vivo. The activation of p38 and JNK mitogen‐activated protein kinases (MAPK) after UVB irradiation was also inhibited by phlorizin. These findings suggest that phlorizin is effective in protecting skin against UVB‐induced skin damage by decreasing ROS overproduction, Cox‐2 expression and the subsequent excessive inflammation reactions. It seemed that p38 and JNK MAPK signal pathways are involved in the regulation of the protective function of phlorizin.     

Heat shock-induced matrix metalloproteinase (MMP)-1 and MMP-3 are mediated through ERK and JNK activation and via an autocrine interleukin-6 loop

Although many studies have been performed to elucidate the molecular consequences of ultraviolet irradiation, little is known about the effect of infrared radiation on skin aging. In addition to photons, heat is likely to be generated as a consequence of infrared irradiation, and heat shock is widely considered to be an environmental stress. Here we investigated the effect of heat shock on the expressions of matrix metalloproteinase (MMP)-1, MMP-2, and MMP-3 in cultured human skin fibroblasts. Heat shock induced the expression of MMP-1 and MMP-3, but not MMP-2, at the mRNA and protein levels in a temperature-dependent manner, and caused the rapid activation of three distinct mitogen-activated protein kinases (MAPK), extracelluar signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK. The heat shock-induced MMP-1 and MMP-3 expression was suppressed by the inhibition of ERK and JNK but not by p38 MAPK inhibition. Furthermore, heat shock increased the synthesis and release of interleukin-6 (IL-6) into culture media. The specific inhibition of IL-6 using a monoclonal antibody against IL-6 greatly reduced the expression of MMP-1 and MMP-3 induced by heat shock. Taken together, our results suggest that ERK and JNK play an important role in the induction of MMP-1 and MMP-3 by heat shock and that the heat shock-induced expression of MMP-1 and MMP-3 is mediated via an IL-6-dependent autocrine mechanism.     

宽谱中波紫外线对人表皮黑素细胞非经典Wnt通路的作用研究

目的 探讨宽谱中波紫外线（BB-UVB）照射对黑素细胞增殖率、酪氨酸酶活性、黑素含量的影响。 方法 分别用0、10、20、30、40、50、100、200、300 mJ/cm2 BB-UVB照射原代培养的黑素细胞,采用CCK8法测定黑素细胞增殖率、多巴比色法测定酪氨酸酶活性、NaOH溶解法测定黑素含量。分别用0、30、50、100 mJ/cm2 BB-UVB照射黑素细胞,实时荧光定量PCR检测非经典Wnt通路相关基因mRNA的表达。100 mJ/cm2 BB-UVB照射黑素细胞,用Western 印迹检测作用前后非经典Wnt通路相关基因蛋白的表达。多组间比较采用单因素方差分析,两组间比较采用独立样本t检验。 结果 与对照组相比,10 ~ 300 mJ/cm2 BB-UVB照射后,细胞增殖率均逐渐降低,BB-UVB剂量 > 100 mJ/cm2时细胞存活率 < 50%,同时,10 ~ 100 mJ/cm2 BB-UVB照射后酪氨酸酶活性逐渐增加,100 mJ/cm2 BB-UVB组黑素含量明显增加,差异有统计学意义（均P < 0.05）。30、50、100 mJ/cm2 BB-UVB照射后,WIF-1 mRNA的表达均较对照组逐渐减少,JNK、MITF、RAC1、TYR的表达均较对照组逐渐升高,而30、50 mJ/cm2 BB-UVB组WNT5A mRNA表达量均较对照组降低,100 mJ/cm2 BB-UVB组WNT5A mRNA表达量则明显升高（P < 0.05）。100 mJ/cm2 BB-UVB照射后,WIF-1蛋白的表达量较对照组降低,WNT5A、JNK、MITF、RAC1、TYR蛋白表达较对照组升高（P < 0.05）。 结论 紫外线照射降低黑素细胞增殖率,提高黑素细胞酪氨酸酶活性和黑素含量。WIF-1基因可能抑制黑素生成。WIF-1基因表达降低可能通过非经典通路Wnt蛋白的综合作用激活JNK/MITF/TYR通路,最终促进黑素合成。     

Arsenite and arsenate activate extracellular signal-regulated kinases 1/2 by an epidermal growth factor receptor-mediated pathway in normal human keratinocytes

BACKGROUND: Inorganic arsenic is an environmental contaminant and is associated with the increased risk of human skin cancer. Arsenic has been reported to activate or inhibit a variety of cellular signalling pathways which has effects on cell growth, differentiation and apoptosis. However, the molecular mechanisms of these arsenic-induced biological effects are not completely understood. OBJECTIVES: To understand the molecular basis for the mode of action of arsenicals, we examined the effect of arsenite and arsenate on the activation of mitogen-activated protein kinases (MAPK) and the upstream signalling cascade in normal human epidermal keratinocytes (NHEK). METHODS: NHEK were exposed to arsenite or arsenate. Western blot analysis was performed to determine the activation of extracellular signal-regulated kinases (ERK) 1/2, c-jun N-terminal kinases (JNK), p38, and MAPK or ERK kinases (MEK) 1/2. Epidermal growth factor receptor (EGFR) tyrosine phosphorylation and recruitment of its adaptor proteins, Shc and Grb2, to EGFR were detected by immunoprecipitation and Western blot analysis. RESULTS: Both arsenicals activated ERK1/2, which are most highly activated in response to mitogenic stimulation, in addition to JNK and p38, which show greater activation in response to cellular stresses. The kinetics of ERK1/2 activation differed from those of JNK and p38 activation. Both arsenicals transiently activated ERK1/2 prior to JNK and p38 activation. MEK1/2, upstream kinases of ERK1/2, were also activated by arsenicals with similar time kinetics to that of ERK1/2 activation. To investigate a signalling pathway leading to activation of MEK1/2-ERK1/2, we examined the tyrosine phosphorylation of EGFR and Shc adapter protein. Both arsenicals stimulated tyrosine phosphorylation of EGFR and Shc. After arsenical treatment, Shc immunoprecipitates contained coprecipitated EGFR and Grb2, suggesting that both arsenicals induce the assembly of EGFR-Shc-Grb2 complexes. Both the EGFR inhibitor tyrphostin AG1478 and anti-EGFR blocking antibody markedly attenuated ERK1/2 activation induced by arsenicals, but did not affect JNK and p38 activation. CONCLUSIONS: Our data indicate that both arsenite and arsenate activate the EGFR-Shc-Grb2-MEK1/2-ERK1/2 signalling cascade in NHEK.     

The mitogen-activated protein kinases p38 and ERK1/2 are increased in lesional psoriatic skin

BACKGROUND: Alterations in specific signal transduction pathways may explain the hyperproliferation and abnormal differentiation of the keratinocytes as well as the increased expression of inflammatory cytokines seen in psoriasis. Major signalling pathways used by eukaryotic cells to transduce extracellular signals into cellular responses impinge on the mitogen-activated protein kinases (MAPKs). OBJECTIVES: To investigate the expression of the MAPK p38, extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) in psoriatic skin. METHODS: Keratome biopsies were taken from patients with plaque-type psoriasis. Western blot analysis was used to determine p38, ERK and JNK activity and protein levels, whereas kinase assays were used to examine the kinase activity of p38. RESULTS: We demonstrated increased levels of the phosphorylated forms of p38 and ERK1/2 in lesional psoriatic skin compared with nonlesional psoriatic skin. No abnormality was found in the activation and expression of JNK1/2. Ex vivo kinase assays confirmed the increased activation of p38, and furthermore demonstrated increased kinase activity of the p38 isoforms p38alpha, p38beta and p38delta in lesional compared with nonlesional psoriatic skin. p38gamma was not detected in the psoriatic skin. Clearance of the psoriatic lesions, induced by climatotherapy at the Dead Sea for 4 weeks, led to a normalization in the activity of both p38 and ERK1/2. CONCLUSIONS: Taken together, our results demonstrate that the activity of the MAPKs p38alpha, p38beta and p38delta and ERK1/2 are increased in lesional psoriatic skin compared with nonlesional psoriatic skin, and that clearance of psoriasis normalizes the p38 and ERK1/2 activity. Thus, p38 and ERK1/2 might be potential targets in the treatment of psoriasis.     

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.     

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.     

A synthetic superoxide dismutase/catalase mimetic (EUK-134) inhibits membrane-damage-induced activation of mitogen-activated protein kinase pathways and reduces p53 accumulation in ultraviolet B-exposed primary human keratinocytes

Salen-manganese complexes exhibit powerful superoxide dismutase and catalase activity, with pharmacologic efficacy in several oxidative-stress-associated disease models. Ultraviolet (UV) B not only induces direct DNA damage, but also generates oxidative stress. EUK-134, a salen-manganese complex, might therefore confer a direct protection against UVB-induced oxidative stress and consequently alleviate UVB-damage-induced signal transduction. We investigated the effect of EUK-134 on the UVB-induced accumulation and stabilization of the p53 protein. p53 plays a central role in the UVB response, both as sensor of UVB damage and as a mediator of a protective response. Cells treated with EUK-134 before UVB irradiation showed a significantly lower accumulation of the p53 protein in a concentration-dependent fashion. Furthermore, EUK-134 severely reduced N-terminal phosphorylation of p53. The extracellular signal-regulated kinase ERK and the stress-activated kinases JNK and p38 have been implicated in the UVB-induced N-terminal phosphorylation and accumulation of p53. Pre-treatment with EUK-134 inhibited the UVB-induced activation of these mitogen-activated protein kinase (MAPK) pathways. We hypothesize that EUK-134, by direct protection of the membrane from UVB-induced oxidative damage, reduces oxidative stress induced MAPK signaling and consequently lowers the level of p53 induction. The protection conferred by EUK-134 resulted in a significant increase in cell survival following UVB irradiation.     

Expressional changes in the intracellular melanogenesis pathways and their possible role in the pathogenesis of vitiligo

BACKGROUND: Main pathway in human melanocytes through which signal from the melanocortin system reaches the melanogenesis enzymes is cAMP/PKA pathway and it is modulated by Wnt and MAPK pathways. In our previous study we established significant increase of melanocortin receptor expression in unaffected skin of vitiligo patients compared to healthy subjects. OBJECTIVE: The aim of this study was to assess the gene expression profile of the intracellular signalling pathways linking melanocortin system with enzymes involved in melanogenesis. METHODS: Using QRT-PCR method, mRNA expression levels of eight genes related to signal transduction from the melanocortin system to melanogenesis enzymes was measured in lesional and non-lesional skin of vitiligo patients and in the skin of healthy control subjects. Following genes were analyzed in the study: MITF, CREB1, p38, USF1, PIK3CB (PI3K), RPS6KB1, LEF1 and BCL2. RESULTS: The mRNA levels of MITF, LEF1, p38, PIK3CB and RPS6KB1 were decreased in lesional skin of vitiligo patients compared to skin of healthy control subjects. We also found increased expression of USF1 and BCL2 in non-lesional skin of vitiligo patients compared to skin of healthy control subjects. mRNA levels of MITF and BCL2 were decreased in lesional skin of vitiligo patients compared to non-lesional skin of vitiligo patients. CONCLUSIONS: Present study indicates increased expression of the genes of the intracellular melanogenesis pathway in the non-lesional skin of vitiligo patients. This finding suggests activation of melanogenesis pathway in the non-lesional skin of vitiligo.