UVB-induced Activator Protein-1 Research Articles

Effects of Time on Phenolics and in vitro Bioactivity in Autoclave Extraction of Graviola (Annona muricata) Leaf

We investigated the effects of different autoclave extraction times (1-6 h) on the antioxidant, antidiabetic, and anti-inflammatory activities of phenolic compounds isolated from graviola (Annona muricata) leaves. In terms of yield and content of total polyphenols, total flavonoids, rutin, and kaempferol-3-O-rutinoside, the optimal extraction time was 4 h. At this time point, water extracts from graviola leaves (WEG) exhibited the highest DPPH radical scavenging activity, ferric reducing antioxidant power, and α-glucosidase inhibitory activity. The α-glucosidase inhibitory activity of WEG was significantly stronger than that of acarbose. Furthermore, WEG significantly suppressed lipopolysaccharide-induced nitric oxide production in RAW 264.7 cells and inhibited UVB-induced activator protein-1 (AP-1)-dependent transcription in human keratinocytes. In conclusion, WEG can be used as functional food ingredients in the food industry.

Oral Supplementation with Cocoa Extract Reduces UVB-Induced Wrinkles in Hairless Mouse Skin

Cacao beans contain various bioactive phytochemicals that could modify the pathogeneses of certain diseases. Here, we report that oral administration of cacao powder (CP) attenuates UVB-induced skin wrinkling by the regulation of genes involved in dermal matrix production and maintenance. Transcriptome analysis revealed that 788 genes are down- or upregulated in the CP supplemented group, compared with the UVB-irradiated mouse skin controls. Among the differentially expressed genes, cathepsin G and serpin B6c play important roles in UVB-induced skin wrinkle formation. Gene regulatory network analysis also identified several candidate regulators responsible for the protective effects of CP supplementation against UVB-induced skin damage. CP also elicited antiwrinkle effects via inhibition of UVB-induced matrix metalloproteinases-1 expression in both the human skin equivalent model and human dermal fibroblasts. Inhibition of UVB-induced activator protein-1 via CP supplementation is likely to affect the expression of matrix metalloproteinases-1. CP supplementation also downregulates the expression of cathepsin G in human dermal fibroblasts. 5-(3',4'-Dihydroxyphenyl)-γ-valerolactone, a major invivo metabolite of CP, showed effects similar to CP supplementation. These results suggest that cacao extract may offer a protective effect against photoaging by inhibiting the breakdown of dermal matrix, which leads to an overall reduction in wrinkle formation.

Cyanidin-3-O-(2″-xylosyl)-glucoside, an anthocyanin from Siberian ginseng (Acanthopanax senticosus) fruits, inhibits UVB-induced COX-2 expression and AP-1 transactivation

Cyanidin-3-O-(2″-xylosyl)-glucoside (C-3-O-(2″-xylosyl)-G) was analyzed as an active constituent from the fruit of Siberian ginseng (Acanthopanax senticosus) using a HPLC diode array detection-electrospray ionization/mass spectrometry analysis system and the effect of C-3-O-(2″-xylosyl)-G on UVB-induced inflammatory signaling in JB6 P+ cells was investigated. C-3-O-(2″-xylosyl)-G inhibited UVB-induced cyclooxygenase (COX)-2 expression and promoter binding activity in JB6 P+ cells and JB6 P+ cells stably transfected with the COX-2 luciferase reporter plasmid. It inhibited both the UVB-induced activator protein-1 (AP-1) and nuclear factor (NF)-κB transactivation in JB6 P+ cells stably transfected with the AP-1 and NF-κB luciferase reporter plasmids. Additionally, C-3-O-(2″-xylosyl)-G significantly suppressed UVB-induced upregulated phosphorylation of c-Jun N terminal kinase, MEK/extracellular signaling kinase, and mitogen activated protein kinase kinase (MAPKK) 3/6 in JB6 P+ cells. These results indicate that C-3-O-(2″-xylosyl)-G may be a promising chemopreventive material that acts by suppressing COX-2 expression and AP-1 and NF-κB transactivation and JNK, MAPKK3/6, and MEK/ERK1/2 phosphorylation.

Inhibitory effect of ERK1/2 and AP-1 by hyperoside isolated from Acanthopanax sessiliflorus

Consumption of fruits and vegetables is correlated with a lower incidence of cancer. Here, we identified hyperoside as an active compound from Acanthopanax sessiliflorus, and investigated the effect of hyperoside on UVB-induced transactivation of activator protein 1 (AP-1) and on the mitogen-activated protein kinase signalling pathway in JB6 P+cells. Hyperoside inhibited UVB-induced AP-1 transactivation. It inhibited the UVB-induced phosphorylation of p90RSK. Kinase assays revealed that hyperoside significantly inhibited ERK1/2 activity. Furthermore, hyperoside bound to ERK1/2 to suppress its activity. In addition, phosphorylation of cAMP response element binding protein (CREB) and signal transducers and activators of transcription (STAT) 3 were suppressed by hyperoside. Overall, these results indicate that hyperoside may be a promising chemopreventive agent that acts by suppressing the transactivation of AP-1 and the phosphorylation of p90RSK, CREB, and STAT3 through the binding and inhibition of ERK1/2.

Abstract 1370: Characterizing the molecular activity of isothiocyanate analogues of sulforaphane: Will a longer carbon chain yield better protection against UVB-induced non-melanoma skin cancer

Abstract Sulforaphane (SFN, chemical name 1-isothiocyanato-4-(methylsulfinyl)-butane) is a natural product found in cruciferous vegetables such as broccoli. Although SFN is known to inhibit several models of cancer, including skin cancer, the molecular mechanisms of this inhibition remain unclear. This is partially due to the myriad of activities that SFN is known to exert in the cell. One of the transcription factors known to play a key role in UV-induced non-melanoma skin cancer (NMSC) is Activator Protein-1 (AP-1). We have recently found that SFN blocks AP-1 activity in HaCaT keratinocytes and mouse skin due to a specific interaction with a cysteine required for DNA binding by AP-1 family members (Cancer Res 2009; 69: (17)). We have since investigated whether structurally-related analogues of SFN could also act as efficient inhibitors of AP-1 activity in keratinocytes. We have compared the activity of three SFN analogues whose only structural difference from SFN is the length of the carbon chain between the isothiocyanato and sulfinyl groups. They are 1-Isothiocyanato-7-(methylsulfinyl)-heptane (Iso-7, found in watercress), 1-Isothiocyanato-8-(methylsulfinyl)-octane (Iso-8, also found in watercress) and 1-Isothiocyanato-9-(methylsulfinyl)-nonane (Iso-9, found in shepard's purse seed). AP-1 luciferase assays in HaCaT cells indicate that all three analogues significantly inhibit UVB-induced AP-1 activity. Iso-7 treatment resulted in an even greater inhibition of AP-1 luciferase than SFN, although Iso-8 and Iso-9 were both less effective than SFN. In addition, there has recently been considerable interest regarding the ability of SFN to act as a histone deacetylase (HDAC) inhibitor. However, there is no evidence in the literature with respect to SFN acting as an HDAC inhibitor in keratinocytes. A commercial HDAC inhibitor (HDAC inhibitor III, Calbiochem) was thus tested for its affect on AP-1 luciferase in keratinocytes alongside SFN. This commercial HDAC inhibitor failed to inhibit AP-1 activity after UVB at low doses (100nM), and instead strongly activated AP-1 activity at higher doses (500nM and above), opposite of the SFN response. Western blots also indicate that while the commercial HDAC inhibitor strongly induces acetylation of histone H4 in keratinocytes, SFN and its analogues do not. Together, these results indicate that HDAC inhibition may not play a strong role in the chemopreventive action of SFN in UV-exposed keratinocytes, and that SFN analogues, especially Iso-7, deserve further scrutiny as potentially powerful natural products for chemoprevention of NMSC via AP-1 inhibition. This work was supported in part by the following grants: 5K07CA132956, 3K07CA132956-02S1, P01 CA27502 and P30 CA23074. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1370. doi:10.1158/1538-7445.AM2011-1370

P38 MAP kinase plays a functional role in UVB‐Induced mouse skin carcinogenesis

UVB irradiation of epidermal keratinocytes results in the activation of the p38 mitogen-activated protein kinase (MAPK) pathway and subsequently activator protein-1 (AP-1) transcription factor activation and cyclooxygenase-2 (COX-2) expression. AP-1 and COX-2 have been shown to play functional roles in UVB-induced mouse skin carcinogenesis. In this study, the experimental approach was to express a dominant negative p38α MAPK (p38DN) in the epidermis of SKH-1 hairless mice and assess UVB-induced AP-1 activation, COX-2 expression, and the skin carcinogenesis response in these mice compared to wild-type littermates. We observed a significant inhibition of UVB-induced AP-1 activation and COX-2 expression in p38DN transgenic mice, leading to a significant reduction of UVB-induced tumor number and growth compared to wild-type littermates in a chronic UVB skin carcinogenesis model. A potential mechanism for this reduction in tumor number and growth rate is an inhibition of chronic epidermal proliferation, observed as reduced Ki-67 staining in p38DN mice compared to wild-type. Although we detected no difference in chronic apoptotic rates between transgenic and nontransgenic mice, analysis of acutely irradiated mice demonstrated that expression of the p38DN transgene significantly inhibited UVB-induced apoptosis of keratinocytes. These results counter the concerns that inhibition of p38 MAPK in a chronic situation could compromise the ability of the skin to eliminate potentially tumorigenic cells. Our data indicate that p38 MAPK is a good target for pharmacological intervention for UV-induced skin cancer in patients with sun damaged skin, and suggest that inhibition of p38 signaling reduces skin carcinogenesis by inhibiting COX-2 expression and proliferation of UVB-irradiated cells.

Antioxidant Activity of Vaccinium stamineum: Exhibition of Anticancer Capability in Human Lung and Leukemia Cells

Fruit of deerberry [Vaccinium stamineum L.] were evaluated for their antioxidant capacity and anticancer properties in JB6 P (+) mouse epidermal cells, human lung and leukemia cells. Deerberries contain potent free radical scavenging activities. Pretreatment of JB6 P (+) mouse epidermal cells with deerberry fruit extracts produced an inhibition on the activation of activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB) induced by either 12- O-tetradecanoylphorbol 13-acetate (TPA) or ultraviolet-B (UVB). Deerberry fruit extracts also blocked TPA- or UVB-induced phosphorylation of ERKs and MEK 1/2, two upstream regulators of AP-1 and inhibited proliferation of human leukemia HL-60 cancer cells and human lung epithelial cancer A549 cells and induced apoptosis of HL-60 cells. These results suggest that the inhibition of TPA- or UVB-induced AP-1 and NF-kappaB activity, inhibition of HL-60 cells and cancer A549 cells proliferation and induction of apoptotic in human leukemia HL-60 cancer cells may be mediated through the ERKs and MEK 1/2 signal pathway.

Silibinin inhibits UVB- and epidermal growth factor–induced mitogenic and cell survival signaling involving activator protein-1 and nuclear factor-κB in mouse epidermal JB6 cells

UVB radiation is the major etiologic factor in the development of nonmelanoma skin cancer. In addition to tumor-initiating effect, UVB also causes tumor promotion via mitogenic and survival signaling. Studies have shown strong preventive effects of silibinin against both UVB-induced and chemically induced tumor promotion in mouse skin models; however, mechanisms are not understood completely. Here, we used tumor promoter-sensitive JB6 mouse epithelial cell model and studied the effect of silibinin on two different mitogens [UVB and epidermal growth factor (EGF)] that induce mitogenic and cell survival signaling pathways. UVB (50-800 mJ/cm(2)) dose-dependently induced phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun-NH(2)-kinase 1/2 (JNK1/2), and p38 kinase (p38K) as well as Akt, with an optimum response at 400 mJ/cm(2) UVB dose. UVB caused a biphasic phosphorylation of ERK1/2 in a time kinetics study. Silibinin treatment before or immediately after UVB exposure, or both, resulted in a strong decrease in UVB-caused phosphorylation of ERK1/2 and Akt in both dose- and time-dependent manner, without any substantial response on JNK1/2 and p38K. Silibinin also suppressed UVB-induced activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB) activation, which are activated by ERK1/2 and Akt. Silibinin treatment under similar conditions also strongly inhibited EGF-induced ERK1/2, JNK1/2, and p38K as well as Akt phosphorylation, and also suppressed EGF-induced AP-1 and NF-kappaB activation. Because AP-1 and NF-kappaB are important nuclear transcription factors for tumor promotion, these results suggest that silibinin possibly prevents skin tumor promotion by inhibiting UVB- and EGF-induced mitogenic and cell survival signaling involving both AP-1 and NF-kappaB.

Differential inhibition of UVB‐induced AP‐1 and NF‐κB transactivation by components of the jun bZIP domain

Potential targets for chemoprevention of nonmelanoma skin cancer include UV-induced nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) activation in keratinocytes. Inhibition of both these ultraviolet light B (UVB)-induced transcription factors has been shown with the dominant-negative c-jun mutant, TAM67; however, its mechanism of action has not yet been determined. Here we demonstrated that transient transfection of a mouse keratinocyte cell line (308) with a dominant-negative phosphorylation mutant of c-Jun before exposure to 250 J/m(2) UVB inhibits transactivation mediated by both AP-1 and NF-kappaB transcription factors to levels below those of UVB exposed controls. Through the utilization of immunoprecipitation techniques, protein-protein interactions between NF-kappaB family members IkappaBalpha, IkappaBbeta, p50, and p65 (Rel-A) were identified with an Xpress tagged dominant-negative c-Jun (TAM67) protein. Expression of the leucine zipper domain of the TAM67 protein inhibited UVB-induced NF-kappaB transactivation but not AP-1 transactivation. Expression of the bZIP domain of the TAM67 protein was able to inhibit transactivation mediated by both transcription factors. These data demonstrate that TAM67 is able to inhibit two significant UVB-induced molecular targets AP-1 and NF-kappaB, and that the inhibition of these two transcription factor families is potentially due to protein-protein interactions between different regions of the dominant-negative c-Jun protein.

Inhibition of p38 Mitogen-Activated Protein Kinase and Phosphatidylinositol 3-Kinase Decreases UVB-Induced Activator Protein-1 and Cyclooxygenase-2 in a SKH-1 Hairless Mouse Model

Activation of activator protein-1 (AP-1) and increased expression of cyclooxygenase-2 (COX-2) have been clearly shown to play a functional role in UVB-induced skin tumor promotion. In this study, we examined UVB-induced signal transduction pathways in SKH-1 mouse epidermis leading to increases in COX-2 expression and AP-1 activity. We observed rapid increases in p38 mitogen-activated protein kinase (MAPK) signaling through activation of p38 MAPK and its downstream target, MAPK activated protein kinase-2. UVB also increased phosphatidylinositol 3-kinase (PI3K) signaling as observed through increases in AKT and GSK-3beta phosphorylation. Activation of the p38 MAPK and PI3K pathways results in the phosphorylation of cyclic AMP-responsive element binding protein, which was also observed in UVB-irradiated SKH-1 mice. Topical treatment with SB202190 (a specific inhibitor of p38 MAPK) or LY294002 (a specific inhibitor of PI3K) significantly decreased UVB-induced AP-1 activation by 84% and 68%, respectively, as well as COX-2 expression. Our data show that in mouse epidermis, UVB activation of the p38 MAPK and PI3K pathways leads to AP-1 activation and COX-2 expression.

Phase II enzyme inducer, sulforaphane, inhibits UVB-induced AP-1 activation in human keratinocytes by a novel mechanism.

Ultraviolet (UV) light-induced activation of activator protein-1 (AP-1), resulting at least in part from oxidative stress, promotes skin carcinogenesis. It has not yet been determined whether elevating cellular phase II enzymes and glutathione (GSH) levels inhibits the AP-1 activation. We have, therefore, examined the effects of two well-known inducers of phase II enzymes, sulforaphane (SF) and tert-butylhydroquinone (tBHQ), on UVB-induced AP-1 activation, with an AP-1-luciferase reporter plasmid that was stably transfected into human HaCaT keratinocytes (HCL14 cells). Exposure of HCL14 cells to SF or tBHQ led to the induction of quinone reductase-1 (QR-1), a marker of global cellular phase II enzymes, as well as elevation of cellular GSH levels. Incubation of the cells with 1-10 microM SF or 11-45 microM tBHQ for 24 h resulted in up to 1.4-fold and 1.7-fold increase of QR-1 activity, respectively, and up to 1.5-fold and 1.6-fold increases in cellular GSH levels, respectively. AP-1 activation was dramatically enhanced by irradiating HCL14 cells with 250 J/m(2) of UVB. While the above SF treatment dose-dependently reduced the UVB-induced AP-1 activation in HCL14 cells, the tBHQ treatment did not, suggesting that elevating cellular phase II enzymes and GSH levels may not lead to inhibition of UVB-induced AP-1 activation. Indeed, depleting cellular GSH by 80% did not affect UVB-induced AP-1 activation either. Subsequent electrophoretic mobility shift assays (EMSA) showed that SF added directly to the EMSAs inhibited AP-1 DNA binding activity, whereas tBHQ was ineffective. Taken together, our results indicated that elevating phase II enzymes and GSH levels in human keratinocytes does not lead to significant inhibition of UVB-induced AP-1 activation. The inhibitory effect of SF on UVB-induced AP-1 activation appears to be at least partly due to the direct inhibition of AP-1 DNA binding activity. This direct effect of SF on AP-1 DNA binding is a novel mechanism for the action of a drug inhibitor of AP-1 activation.

Chemopreventive activity of parthenolide against UVB-induced skin cancer and its mechanisms.

Parthenolide (PN) is a major sesquiterpene lactone of feverfew (Tanacetum parthanium) with known anti-inflammatory activity. However, the anticancer effects of PN have not been well studied. In the present investigation, we examined the cancer chemopreventive property of PN using a combination of in vivo and in vitro approaches. We first tested the anticancer effect of PN in UVB-induced skin cancer model. Mice fed with PN (1 mg/day) showed a delayed onset of papilloma incidence, a significant reduction in papilloma multiplicity (papilloma/mouse) and sizes when compared with the UVB-only group. To our surprise, neither PN nor the known cyclooxygenase (COX)-2 inhibitor celecoxib inhibit UVB-induced COX-2 expression and epidermal prostaglandin E2 (PGE2) production. We next investigated the molecular mechanism(s) involved in its anticancer effects using cultured JB6 murine epidermal cells. Non-cytotoxic concentrations of PN significantly inhibited UVB-induced activator protein-1 DNA binding and transcriptional activity. In addition, PN pre-treatment also inhibited c-Jun-N-terminal kinase (JNK) and p38 kinase activation. More importantly, we found that impaired AP-1, JNK and p38 signaling led to the sensitization of JB6 cells to UVB-induced apoptosis. Data from our study for the first time confirm the anticancer property of PN in an animal model, and provide evidence that the inhibitory effects on AP-1 and mitogen-activated protein kinases serve as one of the underlying mechanisms for the cancer chemopreventive property of PN.

New unusual iridoids from the leaves of noni ( Morinda citrifolia L.) show inhibitory effect on ultraviolet B-induced transcriptional activator protein-1 (AP-1) activity

A novel iridoid dimer in whose structure the two iridoid units are connected by a rare ether group, together with two new unusual iridoids showing significant inhibition of UVB-induced Activator Protein-1 (AP-1) activity in cell cultures, have been isolated from the leaves of noni ( Morinda citrifolia L.). Their structures were determined on the basis of detailed high-field 1D and 2D spectral analysis. Their inhibitory effect on UVB-induced transcriptional Activator Protein-1 (AP-1) activity are also discussed.

Nordihydroguaiaretic acid-mediated inhibition of ultraviolet B-induced activator protein-1 activation in human keratinocytes.

Nordihydroguaiaretic acid (NDGA) is a polyphenolic compound from the Larrea tridentata bush that has been identified as a chemopreventive drug in animal studies. Topically applied NDGA has been shown to prevent phorbol ester promotion of tumors in mouse skin, suggesting that NDGA may be a candidate drug for the chemoprevention of skin cancer. Ultraviolet (UV) B irradiation from sunlight exposure is the major cause of human skin cancer. UVB irradiation causes epigenetic alterations in target keratinocytes, such as the upregulation of signal transduction pathways that induce the expression of transcription factors. Specifically, UVB induces activator protein-1 (AP-1), a transcription factor complex that alters normal cellular gene expression. A component of the UVB-induced AP-1 complex, c-fos, also was identified as a mediator of the signaling pathway that leads to AP-1 activation. Thus, NDGA was investigated as a potential inhibitory agent for UVB-induced signaling pathways in the human keratinocyte cell line HaCaT. NDGA significantly inhibited UVB-induced c-fos and AP-1 transactivation. In addition, NDGA was found to inhibit activity of phosphatidylinositol 3-kinase (PI 3-kinase), a UVB-inducible enzyme that contributes to the induced expression of c-fos and AP-1. Therefore, NDGA prevents UVB-induced c-fos expression and AP-1 transactivation by inhibiting the PI 3-kinase signaling pathway. Effective skin chemoprevention strategies may incorporate NDGA to inhibit components of the UVB-induced cell signaling pathways that increase AP-1 activity.

Inositol hexaphosphate inhibits ultraviolet B-induced signal transduction.

Inositol hexaphosphate (InsP6) has an effective anticancer action in many experimental models in vivo and in vitro. Ultraviolet B (UVB) radiation is believed to be responsible for many of the carcinogenic effects related to sun exposure, and alteration in UVB-induced signal transduction is associated with UVB-induced carcinogenesis. Here we report the effects of InsP6 on UVB-induced signal transduction. InsP6 strongly blocked UVB-induced activator protein-1 (AP-1) and NF-kappaB transcriptional activities in a dose-dependent manner. InsP6 also suppressed UVB-induced AP-1 and nuclear factor kappaB (NF-kappaB) DNA binding activities and inhibited UVB-induced phosphorylation of extracellular signal-regulated protein kinases (Erks) and c-Jun NH2-terminal kinases (JNKs). Phosphorylation of p38 kinases was not affected. InsP6 also blocked UVB-induced phosphorylation of IkappaB-alpha, which is known to result in the inhibition of NF-kappaB transcriptional activity. InsP6 does not block UVB-induced phosphotidylinositol-3' (PI-3) kinase activity, suggesting that the inhibition of UVB-induced AP-1 and NF-kappaB activities by InsP6 is not mediated through PI-3 kinase. Because AP-1 and NF-kappaB are important nuclear transcription factors that are related to tumor promotion, our work suggests that InsP6 prevents UVB-induced carcinogenesis by inhibiting AP-1 and NF-kappaB transcription activities.

Proteinase inhibitors I and II from potatoes block UVB-induced AP-1 activity by regulating the AP-1 protein compositional patterns in JB6 cells.

Proteinase inhibitor I (Inh I) and proteinase inhibitor II (Inh II) from potato tubers are effective proteinase inhibitors of chymotrypsin and trypsin. Inh I and Inh II were shown to suppress irradiation-induced transformation in mouse embryo fibroblasts suggesting that they possess anticarcinogenic characteristics. We have previously demonstrated that Inh I and Inh II could effectively block UV irradiation-induced activation of transcription activator protein 1 (AP-1) in mouse JB6 epidermal cells, which mechanistically may explain their anticarcinogenic actions. In the present study, we investigated the effects of Inh I and Inh II on the expression and composition pattern of the AP-1 complex following stimulation by UV B (UVB) irradiation in the JB6 model. We found that Inh I and Inh II specifically inhibited UVB-induced AP-1, but not NFkappaB, activity in JB6 cells. Both Inh I and Inh II up-regulated AP-1 constituent proteins, JunD and Fra-2, and suppressed c-Jun and c-Fos expression and composition in bound AP-1 in response to UVB stimulation. This regulation of the AP-1 protein compositional pattern in response to Inh I or Inh II may be critical for the inhibition of UVB-induced AP-1 activity by these agents found in potatoes.

Citrifolinin A, a new unusual iridoid with inhibition of Activator Protein-1 (AP-1) from the leaves of noni ( Morinda citrifolia L.)

A new unusual iridoid, named citrifolinin A , showing significant inhibition of UVB-induced Activator Protein-1 (AP-1) activity in cell cultures, has been isolated from the leaves of Morinda citrifolia. Its structure was elucidated based on a detailed high-field 1D and 2D spectral analysis.

Inhibition of Ultraviolet B–Induced AP‐1 Activation by Theaflavins From Black Tea

Theaflavins are believed to be key active components in black tea for chemoprevention of cancer. However, the molecular mechanisms underlying the inhibitory effects of theaflavins are not clear. With the JB6 mouse epidermal cell line, we investigated the effects of theaflavins on ultraviolet (UV) B radiation–induced activator protein-1 (AP-1)–dependent transcriptional activation and compared them with (−)-epigallocatechin-3-gallate (EGCG), a major green tea polyphenol that has cancer chemopreventative activity. Theaflavins and EGCG inhibited UVB-induced AP-1 activation in a concentration-dependent manner. The inhibitory effects of theaflavins were stronger than those of EGCG. We found that theaflavins significantly inhibited activation of extracellular signal-regulated protein kinases and c-jun NH2-terminal kinases. Because the transcription factor AP-1 is important in the process of tumor promotion, the inhibitory effect of these polyphenols on AP-1 activation may further explain the anti–tumor promotion action of these tea constituents. Mol. Carcinog. 28:148–155, 2000. © 2000 Wiley-Liss, Inc.

Role of p38 mitogen-activated protein kinases in ultraviolet-B irradiation-induced activator protein 1 activation in human keratinocytes.

The effects of p38 mitogen-activated protein kinases on ultraviolet (UV) B irradiation-induced activator protein 1 (AP-1) activation were studied in a human keratinocyte cell line, HaCaT. The HaCaT cells were stably transfected with a plasmid containing a promoter fragment of human collagenase 1 driving a luciferase reporter gene. There is an AP-1-binding site within this fragment, without any other known transcription factor-binding sites. As we reported previously, UVB significantly induces activation of AP-1 and p38 in HaCaT cells. SB202190, a p38-specific inhibitor, inhibits UVB-induced p38 activation and c-fos gene expression. In the present study, we further examined the role of p38 in UVB-induced AP-1 activation. We observed that SB202190 strongly inhibited UVB-induced AP-1 transactivation at different time points and UVB doses in transfected HaCaT cells. Furthermore, SB202190 markedly inhibited UVB-induced AP-1 DNA binding as determined by mobility shift analyses. These results suggested, for the first time, that activation of p38 is required for UVB-induced AP-1 activation in human keratinocytes. In addition, a potential mechanism of UVB-induced AP-1 activation through p38 is to enhance AP-1 complex binding to its target DNA. Because c-fos gene expression plays a critical role in UVB-induced AP-1 activation and p38 is required for UVB-induced c-fos gene expression in HaCaT cells, as reported previously, a potential UVB signaling cascade for AP-1 activation in human keratinocytes has been determined. This cascade involves UVB, p38 activation, c-fos gene expression, and AP-1 activation.

Inhibition of Ultraviolet B-Induced AP-1 Activation by Theaflavins From Black Tea

Theaflavins are believed to be key active components in black tea for chemoprevention of cancer. However, the molecular mechanisms underlying the inhibitory effects of theaflavins are not clear. With the JB6 mouse epidermal cell line, we investigated the effects of theaflavins on ultraviolet (UV) B radiation-induced activator protein-1 (AP-1)-dependent transcriptional activation and compared them with (-)-epigallocatechin-3-gallate (EGCG), a major green tea polyphenol that has cancer chemopreventative activity. Theaflavins and EGCG inhibited UVB-induced AP-1 activation in a concentration-dependent manner. The inhibitory effects of theaflavins were stronger than those of EGCG. We found that theaflavins significantly inhibited activation of extracellular signal-regulated protein kinases and c-jun NH(2)-terminal kinases. Because the transcription factor AP-1 is important in the process of tumor promotion, the inhibitory effect of these polyphenols on AP-1 activation may further explain the anti-tumor promotion action of these tea constituents. Mol. Carcinog. 28:148-155, 2000.