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Epidemiologic studies have provided solid evidence for the neurotoxic effect of lead for decades of years. In view of the fact that children are more vulnerable to the neurotoxicity of lead, lead exposure has been an urgent public health concern. The modes of action of lead neurotoxic effects include disturbance of neurotransmitter storage and release, damage of mitochondria, as well as induction of apoptosis in neurons, cerebrovascular endothelial cells, astroglia and oligodendroglia. Our studies here, from a novel point of view, demonstrates that lead specifically caused induction of COX-2, a well known inflammatory mediator in neurons and glia cells. Furthermore, we revealed that COX-2 was induced by lead in a transcription-dependent manner, which relayed on transcription factor NFAT, rather than AP-1 and NFκB, in glial cells. Considering the important functions of COX-2 in mediation of inflammation reaction and oxidative stress, our studies here provide a mechanistic insight into the understanding of lead-associated inflammatory neurotoxicity effect via activation of pro-inflammatory NFAT3/COX-2 axis., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Background: Hexavalent chromium [Cr(VI)] is recognized as a human carcinogen via inhalation. However, the molecular mechanisms by which Cr(VI) causes cancers are not well understood., Objectives: We evaluated cyclooxygenase-2 (COX-2) expression and the signaling pathway leading to this induction due to Cr(VI) exposure in cultured cells., Methods: We used the luciferase reporter assay and Western blotting to determine COX-2 induction by Cr(VI). We used dominant negative mutant, genetic knockout, gene knockdown, and chromatin immunoprecipitation approaches to elucidate the signaling pathway leading to COX-2 induction., Results: We found that Cr(VI) exposure induced COX-2 expression in both normal human bronchial epithelial cells and mouse embryonic fibroblasts in a concentration- and time-dependent manner. Deletion of IKKβ [inhibitor of transcription factor NFκB (IκB) kinase β; an upstream kinase responsible for nuclear factor κB (NFκB) activation] or overexpression of TAM67 (a dominant-negative mutant of c-Jun) dramatically inhibited the COX-2 induction due to Cr(VI), suggesting that both NFκB and c-Jun/AP-1 pathways were required for Cr(VI)-induced COX-2 expression. Our results show that p65 and c-Jun are two major components involved in NFκB and AP-1 activation, respectively. Moreover, our studies suggest crosstalk between NFκB and c-Jun/AP-1 pathways in cellular response to Cr(VI) exposure for COX-2 induction., Conclusion: We demonstrate for the first time that Cr(VI) is able to induce COX-2 expression via an NFκB/c-Jun/AP-1-dependent pathway. Our results provide novel insight into the molecular mechanisms linking Cr(VI) exposure to lung inflammation and carcinogenesis.

The chronic lung inflammatory activity and carcinogenicity of nickel compounds have been well documented by previous studies from epidemiology both in vitro and in vivo. However, the molecular mechanism involved in nickel-induced chronic lung inflammation is much less understood. The current study demonstrates that exposure of human bronchial epithelial cells (Beas-2B) to nickel compounds results in the induction of the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) and transactivation of nuclear factor of activated T cells (NFAT), nuclear factor-kappaB (NF-kappaB), and activator protein-1 (AP-1). Further studies show that neither overexpression of IKKbeta-KM, a kinase inactive mutant of IKKbeta, nor the ectopic expression of a dominant negative mutant of NFAT could inhibit the TNF-alpha induction by nickel exposure. Overexpression of TAM67, a dominant-negative mutant of c-Jun, dramatically reduced the TNF-alpha induction, suggesting that AP-1 is a mediator of TNF-alpha induction in nickel responses. Our results show that ERKs are AP-1 upstream kinases responsible for TNF-alpha induction by nickel exposure; although JNKs, ERKs, and p38K were all activated in the Beas-2B cells exposed to nickel compounds. Our results demonstrate that inflammatory TNF-alpha could be induced by nickel exposure in Beas-2B cells specifically through an ERKs/AP-1-dependent pathway.

Arsenite has been well-proved to act as both an environmental carcinogen as well as a tumor therapeutic agent. AP-1 is one of the transcription factors that can be induced upon arsenite stimulation. However, the study on the mechanism and the function of the arsenite-induced AP-1 transactivation remains far complete. Here we demonstrated that high dose of arsenite induced apoptotic response in mouse fibroblasts correlating with AP-1 transactivation, which events were mediated by both IKKalpha and IKKbeta, two major protein kinases responsible for NF-kappaB activation. In addition, the regulatory effect of IKKs on the arsenite-induced AP-1 activation was delivered by sequential induction of GADD45alpha expression and the activation of MAPKK (MKK3/4/6) and MAPK (JNK and p38K)-dependent pathways. We further provided evidence that p50, but not p65 subunit of NF-kappaB, was involved in GADD45alpha induction and the subsequent MAPKK/MAPK/AP-1 activation under arsenite exposure, while functional NF-kappaB induced by arsenite stimulation consisted of p65 but not of p50 subunit. Therefore, we concluded that both IKKalpha and IKKbeta can mediate arsenite-induced AP-1 transactivation through NF-kappaB activity-independent manner.

The chemopreventive properties of edible berries have been demonstrated both in vitro and in vivo, however, the specific molecular mechanisms underlying their anti-cancer effects are largely unknown. Our previous studies have shown that a methanol extract fraction of freeze-dried black raspberries inhibits benzoapyrene (BaP)-induced transformation of Syrian hamster embryo cells. This fraction also blocks activation of activator protein-1 (AP-1) and nuclear factor kappaB (NF-kappaB) induced by benzoapyrene diol-epoxide (BaPDE) in mouse epidermal JB6 Cl 41 cells. To determine if different berry types exhibit specific mechanisms for their anti-cancer effects, we compared the effects of extract fractions from both black raspberries and strawberries on BaPDE-induced activation of various signaling pathways in Cl 41 cells. Black raspberry fractions inhibited the activation of AP-1, NF-kappaB, and nuclear factor of activated T cells (NFAT) by BaPDE as well as their upstream PI-3K/Akt-p70(S6K) and mitogen-activated protein kinase pathways. In contrast, strawberry fractions inhibited NFAT activation, but did not inhibit the activation of AP-1, NF-kappaB or the PI-3K/Akt-p70(S6K) and mitogen-activated protein kinase pathways. Consistent with the effects on NFAT activation, tumor necrosis factor-alpha (TNF-alpha) induction by BaPDE was blocked by extract fractions of both black raspberries and strawberries, whereas vascular endothelial growth factor (VEGF) expression, which depends on AP-1 activation, was suppressed by black raspberry fractions but not strawberry fractions. These results suggest that black raspberry and strawberry components may target different signaling pathways in exerting their anti-carcinogenic effects., ((c) 2007 Wiley-Liss, Inc.)

Cyclooxygenase-2 (COX-2) is reported to be one of the early-response gene products induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). However, the relevance of COX-2 in TPA-induced cell transformation and the underlying mechanisms remains to be explored. Initially, we verified COX-2 induction after TPA treatment in mouse embryonic fibroblasts (MEF) and mouse epidermal cells Cl 41. More importantly, introduction of COX-2 small interfering RNA in MEFs or Cl 41 cells suppressed the cell transformation caused by TPA treatment. This inhibition could be reversed by overexpression of human full-length COX-2, indicating that COX-2 is at least one of the critical molecules involved in TPA-induced cell transformation. We further showed that TPA-promoted cell cycle progression was partially suppressed by COX-2 small interfering RNA, indicating that COX-2 also participated in TPA-associated cell cycle progression. Investigation of the upstream signaling pathways revealed that c-Jun-NH(2)-kinase 1 (JNK1), but not JNK2, played important roles in COX-2 induction, because knockout of JNK1 gene rather than JNK2 gene markedly impaired COX-2 induction. Furthermore, inhibition of c-Jun/activator protein 1 pathway or JNKs/c-Jun pathway by overexpression of dominant negative mutants of c-Jun, or MKK4 and MKK7 together, resulted in impairment of COX-2 induction, suggesting that JNK1/c-Jun/activator protein 1 pathway is involved in TPA-associated COX-2 induction. In contrast, IKK/p65 nuclear factor-kappaB pathway was not implicated because knockout of IKKalpha, IKKbeta, or p65 gene did not affect COX-2 induction although nuclear factor-kappaB was activated by TPA. In addition, the TPA-promoted cell cycle progression was found impaired in JNK1-deficient, but not in JNK2-deficient, MEFs. Our results show that JNK1-associated COX-2 induction is implicated in TPA-associated cell transformation and cell cycle progression.

Deferoxamine (DFO) is a drug widely used for iron overload treatment to reduce body iron burden. In the present study, it was shown in mouse epidermal JB6 cells that all iron compounds transiently induced extracellular signal-regulated kinases (ERK) phosphorylation, whereas DFO further enhanced ERK phosphorylation over long periods. The ERK phosphorylation by DFO treatment appears to be due to the inhibition of MAPK phosphatases (MKP) by DFO. The combined effects of iron-initiated MAPK activation and DFO-mediated MKP inhibition resulted in a synergistic enhancement on AP-1 activities. The results indicate that the interplay between MAPK and MKP is important in regulating the extent of AP-1 activation. It is known that administration of DFO in iron overload patients often results in allergic responses at the injection sites. The results suggest that this synergistic AP-1 activation might play a role in DFO-induced skin immune responses of iron overload patients.

Benzo(a)pyrene (B(a)P), a potent environmental procarcinogen, has been shown to cause cell cycle alternation. However, the mechanisms involved in this effect are not well understood yet. Our current results demonstrated that B(a)P exposure led to cell proliferation and a 33.5% increase in S phase cells as well as a 26.8% decrease in G1 phase cells in human embryo lung fibroblasts (HELFs). Those cell cycle alternations were accompanied with transactivation of activator protein-1 (AP-1) and phosphorylation of Akt and p70(S6K). These changes were blocked by overexpression of dominant negative mutants of phosphatidylinositol-3 kinase (Deltap85) or Akt (DN-Akt), respectively. Moreover, pretreatment of cells with rapamycin, a specific p70(S6K) inhibitor, inhibited B(a)P-induced AP-1 activation, cell cycle alteration and phosphorylation of p70(S6K), but had no effect on Akt phosphorylation. Our results, therefore, suggest that phosphatidylinositol-3 kinase (PI-3K)/Akt/p70(S6K)/AP-1 pathway participates in B(a)P-induced cell cycle alternations. Furthermore, we explored the effect of this pathway on cell cycle regulatory proteins. B(a)P markedly increases in the expression of cyclin D1 and E2F1 and phosphorylation of retinoblastoma protein (Rb). In addition, we found that inactivation of PI-3K, Akt or p70(S6K) could eliminate those effects on cell cycle regulatory proteins. Collectively, PI-3K/Akt/p70(S6K)/AP-1 pathway mediated B(a)P-induced alternation of cell cycle through regulation of cell cycle regulatory proteins such as cyclin D1, E2F1, and Rb in HELFs.

Benzo[alpha]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), the major metabolite of benzo[a]pyrene (B[a]P), shows an ultimate complete carcinogen in various animals and is a causative agent for human cancers. However, its effects on the activation of signal pathways and the expression of genes involved in its carcinogenic effect remain largely unknown. In this study, the effects of B[a]PDE on induction of cyclooxygenase (COX)-2 and the signal pathways leading to the induction were investigated. Treatment of mouse epidermal Cl41 cells with B[a]PDE caused an increase in the expression of COX-2 at both transcription and protein levels, while its parental compound B[a]P did not show significant inductive effect. The COX-2 induction by B[a]PDE was dependent on the activation of mitogen-activated protein kinases (MAPK)s/activation protein (AP)-1 pathway, because inhibition of AP-1 by either overexpression of TAM67 (dominant negative mutant of c-jun), or pretreatment of cells with PD98059 (MEK1/2-ERKs pathway inhibitor) or SB202190 (p38K inhibitor), markedly inhibited B[a]PDE-induced COX-2 expression. In addition, impairment of NF-kappaB pathway by either NEMO-BDBP (an NF-kappaB specific inhibitor) or IkappaB kinase (IKK)beta-KM (dominant negative mutant of IKKbeta) also caused marked reduction of COX-2 induction by B[a]PDE. In contrast, inhibition of nuclear factor of activated T cells (NFAT) with FK506, did not show any effect on B[a]PDE-induced COX-2 expression. Collectively, these data indicate that exposure of Cl41 cells to B[a]PDE can induce COX-2 expression by increasing its transcription, which requires the activation of MAPKs/AP-1 and IKKbeta/NF-kappaB pathways, but not NFAT pathway. In view of the importance of COX-2 in carcinogenesis, we anticipate that the induction of COX-2 by B[a]PDE may coordinate its mutagenic effects to facilitate the development of skin cancer., (Copyright 2006 Wiley-Liss, Inc.)

Recent studies from our laboratory have shown that the transactivation of nuclear factor kappa B (NF kappa B) and activator protein-1 (AP-1) plays an important mechanistic role in ultraviolet (UV)-induced skin carcinogenesis in mice. We also demonstrated that a methanol extract (ME) fraction from black raspberries (Rubus occidentalis) (RO; RO-ME) inhibits benzo[a]pyrene-7,8-diol-9,10-epoxide [B(a)PDE]-induced activation of NF kappa B and AP-1 in cultured mouse epidermal cells. In the present study, we determined if RO-ME might also inhibit the induction of NF kappa B and AP-1 in mouse epidermal cells exposed to mid UV radiation (UVB) and short UV radiation (UVC) and whether methanol fractions from strawberries and blueberries would also be effective. Our results showed that RO-ME inhibited UVB-induced activation of NF kappa B in mouse epidermal cells in a time- and dose-dependent manner; however, the methanol fractions from strawberries and blueberries were ineffective. Interestingly, none of the fractions from all 3 berry types inhibited UVB- or UVC-induced activation of AP-1, suggesting that inhibition of UV-induced signaling pathways is specific for black raspberries and NF kappa B. Cyanidin-3-rutinoside, an anthocyanin found in abundance in black raspberries and not in strawberries or high-bush blueberries, was found to contribute to the inhibition of UVB-induced activation of NF kappa B. These results suggest that berries differ in their ability to influence signaling pathways leading to activation of NF kappa B and AP-1 when using UV light as the inducer.

Dietary freeze-dried black raspberries inhibit tumor induction by N-nitrosomethylbenzylamine in the rat esophagus, but the constituents responsible for this chemopreventive activity have not been identified. We fractionated freeze-dried black raspberries and used mouse epidermal JB6 Cl 41 cells stably transfected with either a nuclear factor kappa B (NFkappaB)- or an activator protein 1 (AP-1)-luciferase reporter, and treated with racemic anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), to assess the inhibitory effects of the fractions. The ethanol and water extracts of the freeze-dried black raspberries had inhibitory activity and these extracts were fractionated by HPLC to give several bioactive fractions. Further HPLC analysis yielded multiple subfractions, some of which inhibited BPDE-induced NFkappaB activity. Major constituents of the most active subfractions were identified by their spectral properties and in comparison with standards as cyanidin-3-O-glucoside, cyanidin 3-O-(2(G)-xylosylrutinoside) and cyanidin 3-O-rutinoside. Analysis of freeze-dried black raspberries indicated that these three components comprised approximately 3.4% of the material by dry weight. Consistent with these results, standard cyanidin-3-O-glucoside and cyanidin chloride were also good inhibitors of BPDE-induced NFkappaB activity. The results of this study demonstrate that cyanidin glycosides of freeze-dried black raspberries are bioactive compounds which could account for at least some of the chemopreventive activity observed in animal models.

Crystalline silica has long been well established as a fibrogenic agent, and recent evidence has implicated it as a potential human carcinogen. However, the mechanisms of silica-induced disease development and progression are not well understood. Our previous studies demonstrated that crystalline silica is able to activate activator protein-1 (AP-1) through mitogen-activated protein kinase (MAPK) pathways. The present study investigates the possible involvement of protein kinase C (PKC) in silica-induced activation of the MAPK/AP-1 signal transduction pathway. Treatment of mouse epidermal cells (JB6 cell line) with freshly fractured silica stimulated translocation of PKCalpha and PKCepsilon from the cytosol to the membrane and activated AP-1 transcription activity. Pretreatment of cells with PKC inhibitors, including RO-32-0432, calphostin C, and bisindolylmaleimide I, inhibited silica-induced AP-1 activation and phosphorylation of ERKs and p38 kinase. These inhibitory effects by PKC inhibitors were dose dependent. Furthermore, overexpression of dominant negative mutant (DNM) of PKCalpha or PKCepsilon markedly blocked AP-1 activation as well as phosphorylation of ERKs and p38 kinase induced by freshly fractured silica. These results demonstrate that PKCalpha and PKCepsilon are essential in silica-induced AP-1 activation through the MAP kinase (ERKs and p38 kinases) pathway.

Silica has been known to be a factor inducing acute injury and chronic pulmonary fibrosis. Silica has also been listed as a human carcinogen in 1996 by International Agency for Research on Cancer (IARC). However, the molecular mechanisms involved its pathologic effects are not well understood. In these studies, we found that exposure of human embryonic lung fibroblasts (HELF) to crystalline silica could cause increases in activation of extracellular signal-regulated kinases (ERKs), p38K, and c-Jun NH2-terminal amino kinases (JNKs), and HELF transformation. Interestingly, silica-induced transformation of HELF (S-HELF) led to increases in activated levels of ERKs and p46 of JNKs, and decrease in p38K activation, and no effect on activation of p54 of JNKs, as compared with those in parental HELF. Further studies showed that there are differential effects of ERKs, JNKs and p38K, as well as their downstream transcription factor AP-1, in regulation of expression of cyclin D1 and CDK4 and cell cycle alternations induced by silica. Cyclin D1 and CDK4 were increased in S-HELF as compared with those in HELF. Inhibition of ERKs activation by AG126, JNK by SP600125, and AP-1 by curcumin could reduced the induction of cyclin D1 and CDK4. There is no significant difference for cell cycle distribution between groups. These results demonstrate that ERKs and JNKs, but not p38K is responsible for induction of cyclin D1 and CDK4 in S-HELF, suggesting that overexpression of cyclin D1 and CDK4 caused by silica is mediated by ERK, JNK/AP-1signaling pathway.

Previous studies have shown that freeze-dried black raspberry extract fractions inhibit benzo(a)pyrene [B(a)P]-induced transformation of Syrian hamster embryo cells and benzo(a)pyrene diol-epoxide [B(a)PDE]-induced activator protein-1 (AP-1) activity in mouse epidermal Cl 41 cells. The phosphotidylinositol 3-kinase (PI-3K)/Akt pathway is critical for B(a)PDE-induced AP-1 activation in mouse epidermal Cl 41 cells. In the present study, we determined the potential involvement of PI-3K and its downstream kinases on the inhibition of AP-1 activation by black raspberry fractions, RO-FOO3, RO-FOO4, RO-ME, and RO-DM. In addition, we investigated the effects of these fractions on the expression of the AP-1 target genes, vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase (iNOS). Pretreatment of Cl 41 cells with fractions RO-F003 and RO-ME reduced activation of AP-1 and the expression of VEGF, but not iNOS. In contrast, fractions RO-F004 and RO-DM had no effect on AP-1 activation or the expression of either VEGF or iNOS. Consistent with inhibition of AP-1 activation, the RO-ME fraction markedly inhibited activation of PI-3K, Akt, and p70 S6 kinase (p70(S6k)). In addition, overexpression of the dominant negative PI-3K mutant delta p85 reduced the induction of VEGF by B(a)PDE. It is likely that the inhibitory effects of fractions RO-FOO3 and RO-ME on B(a)PDE-induced AP-1 activation and VEGF expression are mediated by inhibition of the PI-3K/Akt pathway. In view of the important roles of AP-1 and VEGF in tumor development, one mechanism for the chemopreventive activity of black raspberries may be inhibition of the PI-3K/Akt/AP-1/VEGF pathway.

Transcription factor p53 and phosphatase PTEN are two tumor suppressors that play essential roles in suppression of carcinogenesis. However, the mechanisms by which p53 mediates anticancer activity and the relationship between p53 and PTEN are not well understood. In the present study, we found that pretreatment of mouse epidermal Cl41 cells with pifithrin-alpha, an inhibitor for p53-dependent transcriptional activation, resulted in a marked increase in UV-induced activation of activator protein 1 (AP-1) and nuclear factor kappaB (NF-kappaB). Consistent with activation of AP-1 and NF-kappaB, pifithrin-alpha was also able to enhance the UV-induced phosphorylation of c-Jun-NH2-kinases (JNK) and p38 kinase, whereas it did not show any effect on phosphorylation of extracellular signal-regulated kinases. Furthermore, the UV-induced signal activation, including phosphorylation of JNK, p38 kinase, Akt, and p70S6K, was significantly enhanced in p53-deficient cells (p53-/-), which can be reversed by p53 reconstitution. In addition, knockdown of p53 expression by its small interfering RNA also caused the elevation of AP-1 activation and Akt phosphorylation induced by UV radiation. These results show that p53 has a suppressive activity on the cell signaling pathways leading to activation of AP-1 and NF-kappaB in cell response to UV radiation. More importantly, deficiency of p53 expression resulted in a decrease in PTEN protein expression, suggesting that p53 plays a critical role in the regulation of PTEN expression. In addition, overexpression of wild-type PTEN resulted in inhibition of UV-induced AP-1 activity. Because PTEN is a well-known phosphatase involved in the regulation of phosphatidylinositol 3-kinase (PI-3K)/Akt signaling pathway, taken together with the evidence that PI-3K/Akt plays an important role in the activation of AP-1 and NF-kappaB during tumor development, we anticipate that inhibition of AP-1 and NF-kappaB by tumor suppressor p53 seems to be mediated via PTEN, which may be a novel mechanism involved in anticancer activity of p53 protein.

A potential mechanism underlying ethanol-induced alterations in gene expression is the disruption of transcription factor activity. Growth factor receptors, particularly receptor tyrosine kinases, play an important role in modulating many biological effects of ethanol. We demonstrated here that the expression of epidermal growth factor receptor (EGFR) mediated the effect of ethanol on the activity of transcription factor activator protein-1 (AP-1). Ethanol had little effect on AP-1 activity in the fibroblast cells devoid of EGFR (B82); however, it significantly suppressed AP-1 activity in B82 cells that were stably transfected with either a wild-type EGFR (B82L) or a kinase-deficient receptor (B82M721) in a concentration-dependent manner. EGF activated AP-1 only in B82L cells; the activation was mediated primarily by Akt and ERK. Ethanol inhibited EGF-induced EGFR autophosphorylation, phosphorylation of ERK as well as Akt and its substrate GSK-3beta, and subsequently blocked EGF-stimulated AP-1 activation in B82L cells. On the other hand, ethanol had little effect on EGF-stimulated JNK activation. Phorbol ester 12-O-teradecanoyl-phorbol-13-acetate (TPA) activated AP-1 in B82L and B82M721 cells, but not B82 cells. TPA-induced activation of ERK and PKCdelta was dependent on the expression of EGFR although the intrinsic kinase activity of EGFR was not required. In contrast, TPA-induced phosphorylation of p38 MAPK, JNKs and other PKC isoforms was independent of EGFR. Ethanol selectively inhibited TPA-induced phosphorylation of ERK and PKCdelta, and modestly suppressed TPA-stimulated AP-1 activation in B82L and B82M721 cells. Thus, EGFR plays a critical role in the interaction between ethanol and AP-1.

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives, such as benzo[a]pyrene (B[a]P), (+/-)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), and 5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE), are complete carcinogens. However, the tumor promotion effects of PAHs remain unclear. We therefore investigated the possible activation of activator protein-1 (AP-1) and nuclear factor-kappaB (NFkappaB) in mouse epidermal Cl41 cells after different PAHs treatments, including B[a]P, B[a]PDE, chrysene-1,2-diol-3,4-epoxid (CDE), and 5-MCDE. The results showed that B[a]PDE and 5-MCDE were able to activate AP-1 and NF-kappaB, whereas B[a]P showed only marginal effect on AP-1 activation, and B[a]P and CDE had no effect on NF-kappaB activation. Treatment with either B[a]PDE or 5-MCDE also resulted in mitogen-activated protein kinases (MAPKs) activation as well as inhibitory subunit kappa-B (IkappaBalpha) phosphorylation and degradation, whereas B[a]P and CDE had no effect. Pretreatment with PD98059, a specific inhibitor for extracellular signal-regulated protein kinases (ERKs) upstream kinase MEK1/2, or SB202190, a p38 kinase inhibitor, resulted in a dramatic inhibition of B[a]PDE-induced AP-1 transactivation. In addition, B[a]PDE-induced AP-1 activation was also inhibited by overexpressing a dominant negative mutant of JNK1 in the cells. All these suggest ERKs, c-jun N-terminal kinases (JNKs), and p38 kinase signal transduction pathways are required for AP-1 induction by B[a]PDE. Taken together, B[a]PDE and 5-MCDE are the active compounds of PAHs to initiate signaling pathways. Considering the important roles of AP-1 and NF-kappaB in tumor promotion, we speculated the activation of AP-1 and NF-kappaB by B[a]PDE and 5-MCDE may involve in their or their parent compounds' tumor promotion effects. This study may help in better understanding the tumor promotion effects of PAHs., (Copyright 2004 Wiley-Liss, Inc.)

Mouse skin tumorigenicity studies indicate that benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE) contributes to carcinogenesis as both a tumor initiator and promoter. However, the mechanisms that mediate B[a]PDE tumor promotion effects remain unclear. Our results demonstrated that in mouse epidermal Cl41 cells, B[a]PDE treatment resulted in marked activation of AP-1 and its upstream MAPKs, including ERKs, JNKs and p38K. B[a]PDE exposure also led to activation of phosphotidylinositol 3-kinase (PI-3K), Akt and p70 S6 kinase (p70S6k). B[a]PDE-induced AP-1 transactivation was inhibited by pretreatment of cells with PI-3K inhibitors, wortmannin or Ly294002. In contrast, inhibition of p70S6k with rapamycin did not show any inhibitory effects. An overexpression of dominant-negative mutant of PI-3K, Deltap85, impaired B[a]PDE-induced activation of PI-3K, Akt and AP-1 transactivation. Furthermore, an overexpression of dominant-negative Akt mutant, Akt-T308A/S473A, blocked B[a]PDE-induced activation of Akt, AP-1 and JNKs, while it did not affect the activation of p70S6k, ERKs and p38 kinase. These results demonstrated that B[a]PDE was able to induce AP-1 transactivation and this AP-1 induction was specific through PI-3K/Akt/JNKs-dependent and p70S6k-independent pathways. This study also indicated that Akt-T308A/S473A blocks B[a]PDE-induced AP-1 activation specific through impairing JNK pathway. These findings will help us to understand the signal transduction pathways involved in the carcinogenic effects of B[a]PDE.

5-Methylchrysene has been found to be a complete carcinogen in laboratory animals. However, the tumor promotion effects of (+/-)-anti-5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE) remain unclear. In the present work, we found that 5-MCDE induced marked activator protein-1 (AP-1) activation in Cl41 cells. 5-MCDE also induced a marked activation of phosphatidylinositol 3-kinase (PI-3K). Inhibition of PI-3K impaired 5-MCDE-induced AP-1 transactivation, suggesting that PI-3K is an upstream kinase involved in AP-1 activation by 5-MCDE. Furthermore, we found that Akt is a PI-3K downstream mediator for 5-MCDE-induced AP-1 transactivation, whereas another PI-3K downstream kinase, p70(S6K), was not involved in AP-1 activation by 5-MCDE. Moreover, inhibition of Akt activation blocked 5-MCDE-induced activation of extracellular signal-regulated protein kinases (ERKs) and c-Jun NH(2)-terminal kinases (JNKs), whereas it did not affect p38K activation. Consistently, overexpression of a dominant-negative mutant of ERK2 or JNK1 blocked the AP-1 activation by 5-MCDE. These results demonstrate that 5-MCDE is able to induce AP-1 activation, and the AP-1 induction is specifically through a PI-3K/Akt-dependent and p70(S6K)-independent pathway.

Consumption of fruits and vegetables has been associated with a low incidence of cancers and other chronic diseases. Previous studies suggested that fresh apples inhibit tumor cell proliferation. Here we report that oral administration of apple peel extracts decreased the number of nonmalignant and malignant skin tumors per mouse induced by 12-O-tetradecanolyphorbol-13-acetate (TPA) in 7,12-dimethylbenz(a)anthracene-initiated mouse skin. ESR analysis indicated that apple extract strongly scavenged hydroxyl (OH) and superoxide (O(2)(-)) radicals. Mechanistic studies showed that pretreatment with apple peel extract inhibited AP-1 transactivation induced by ultraviolet B irradiation or TPA in JB6 cells and AP-1-luciferase reporter transgenic mice. This inhibitory effect appears to be mediated by the inhibition of ERKs and JNK activity. The results provide the first evidence that an extract from fresh apple peel extract may inhibit tumor promoter-induced carcinogenesis and associated cell signaling, and suggest that the chemopreventive effects of fresh apple may be through its antioxidant properties by blocking reactive oxygen species-mediated AP-1-MAPK activation.

The transcription factor activator protein-1 (AP-1) has been implicated in a large variety of biological processes including cell differentiation, proliferation, apoptosis and oncogenic transformation. It is thought that the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced AP-1 activity is because of the activation of the PKC/MAPK/AP-1 pathway, although the detailed molecular mechanism has not been fully characterized. The tyrosine kinases of epidermal growth factor receptor (EGFR) lie at the head of a complex of signal transduction cascade that modulates cell proliferation, survival, adhesion, migration and differentiation. Currently, little is known about whether EGFR or its tyrosine kinase is necessary for TPA-induced AP-1 activation. In the present study, we investigated this issue using a well-characterized mouse fibroblast B82 cell line, which is devoid of the EGFR, and its stable transfectants with either wild-type EGFR (B82L) or tyrosine kinase-deficient EGFR (mutation at Lys-721) (B82M721). We demonstrated that the TPA or epidermal growth factor (EGF) induced AP-1 activation in the B82L cells that express wild-type EGFR, but not in the B82 cell, whereas autophosphorylation at tyrosine(1173) of EGFR in B82L cells was only induced by EGF, but not TPA. The expression of tyrosine kinase-deficient EGFR (mutation at Lys-721) (B82M721) resulted in deficiency of AP-1 induction in cellular response to EGF, while TPA treatment led to fully AP-1 activation. Furthermore, the mutation at Lys-721 of EGFR resulted in impairing of EGFR autophosphorylation at tyrosine(1173) induced by EGF. Based on these results, we conclude that TPA-induced AP-1 activation requires the basal level-EGFR protein, but not EGFR tyrosine kinase and EGFR autophosphorylation at tyrosine(1173), whereas both EGFR tyrosine kinase and EGFR autophosphorylation at Y(1173) play a critical role in EGF-induced AP-1 activation.

Freeze-dried black raspberries have been shown to inhibit the development of chemically induced esophageal and colon cancer in rodents. In addition, organic extracts of black raspberries inhibit benzo(a)pyrene (BaP)-induced cell transformation in vitro. The molecular mechanisms through which black raspberries inhibit carcinogenesis remain unclear. We investigated the effects of black raspberry extracts on transactivation of activated protein 1 (AP-1) and nuclear factor kappaB (NFkappaB) induced by BaP diol-epoxide (BPDE), the ultimate carcinogen of BaP, in mouse epidermal JB6 Cl 41 (Cl 41) cells. Black raspberries were extracted with methanol, and the methanol extract was partitioned and chromatographed into several fractions designated RU-F003, RU-F004, RU-DM, and RU-ME. Pretreatment of Cl 41 cells with RU-F003, RU-DM, or RU-ME resulted in an inhibition of BPDE-induced AP-1 and NFkappaB activities. The RU-ME fraction was the most potent inhibitor among the fractions tested. In contrast, fraction RU-F004 did not inhibit BPDE-induced AP-1 or NFkappaB activities in Cl 41 cells. The inhibitory effects of RU-ME on BPDE-induced activation of AP-1 and NFkappaB appear to be mediated via inhibition of mitogen activated protein kinase activation and inhibitory subunit kappaB phosphorylation, respectively. Pretreatment of cells with berry fractions did not result in an inhibition of BPDE binding to DNA; thus, this was not a mechanism of reduced AP-1 and NFkappaB activities. None of the fractions was found to affect p53-dependent transcription activity. In view of the important roles of AP-1 and NFkappaB in tumor promotion/progression, these results suggest that the ability of black raspberries to inhibit tumor development may be mediated by impairing signal transduction pathways leading to activation of AP-1 and NFkappaB. The RU-ME fraction appears to be the major fraction responsible for the inhibitory activity of black raspberries.

Activator protein-1 (AP-1) and nuclear factor of activated T cells (NFAT) are two important transcription factors responsible for the regulation of cytokines, which are involved in cell proliferation and inflammation. Coal workers' pneumoconiosis (CWP) is an occupational lung disease that may be related to chronic inflammation caused by coal dust exposure. In the present study, we demonstrate that coal from the Pennsylvania (PA) coalmine region, which has a high prevalence of CWP, can activate both AP-1 and NFAT in JB6 mouse epidermal cells. In contrast, coal from the Utah (UT) coalmine region, which has a low prevalence of CWP, has no such effects. The PA coal stimulates mitogen-activated protein kinase (MAPK) family members of extracellular signal-regulated kinases (ERKs) and p38 MAPK but not c-Jun-NH(2)-terminal kinases, as determined by the phosphorylation assay. The increase in AP-1 by the PA coal was completely eliminated by the pretreatment of cells with PD98059, a specific MAPK kinase inhibitor, and SB202190, a p38 kinase inhibitor, further confirming that the PA coal-induced AP-1 activation is mediated through ERKs and p38 MAPK pathways. Deferoxamine (DFO), an iron chelator, synergistically enhanced the PA coal-induced AP-1 activity, but inhibited NFAT activity. For comparison, cells were treated with ferrous sulfate and/or DFO. We have found that iron transactivated both AP-1 and NFAT, and DFO further enhanced iron-induced AP-1 activation but inhibited NFAT. These results indicate that activation of AP-1 and NFAT by the PA coal is through bioavailable iron present in the coal. These data are in agreement with our previous findings that the prevalence of CWP correlates well with levels of bioavailable iron in coals from various mining regions.

The predominant exposure route for nickel compounds is by inhalation, and several studies have indicated the correlation between nickel exposure and respiratory cancers. The tumor-promoting effects of nickel compounds are thought to be associated with their transactivation of transcription factors. We have investigated the possible activation of activator protein-1 (AP-1) and nuclear factor KB (NF-kappaB) in mouse C141 epidermal cells and fibroblasts 3T3 and B82, and human bronchoepithelial BEAS-2B cells in response to nickel compound exposure. Our results show that NF-kappaB activity is induced by nickel exposure in 3T3 and BEAS-2B cells. Conversely, similar nickel treatment of these cells did not induce AP-1 activity, suggesting that nickel tumorigenesis occurs through NF-kappaB and not AP-1. We also investigated the role of NF-kappaB in the induction of Cap43 by nickel compounds using dominant negative mutant Ikappabeta kinase b-KM BEAS-2B transfectants.