Requirement for phosphatidylinositol 3-kinase in epidermal growth factor-induced AP-1 transactivation and transformation in JB6 P+ cells

Structure and chemopreventive activity of fucoidans from the brown alga Alaria angusta

Six fucoidan fractions were isolated from the brown alga Alaria angusta. Structures of enzymatic hydrolysis products of the fraction 1AaF2 (Fuc:Gal ~ 1:1; 33 % of sulfates) by fucanase from Wenyingzhuangia fucanilytica were studied by chemical and instrumental (NMR spectroscopy and mass-spectrometry) methods. It was shown that 1AaF2 consisted of two structurally different fucoidans: a sulfated 1,3;1,4-α-L-fucan and an enzyme-resistant sulfated and acetylated complex fucogalactan (Fuc:Gal ~ 1:2; 19 % of sulfates) 1AaF2_HMP containing extended 1,3-linked fucose and 1,3/1,4-linked galactose fragments (up to 5 residues). The fractions 1AaF2 and 1AaF2_HMP were a non-cytotoxic, possessed dose-dependent chemopreventive effect on EGF-induced neoplastic cell transformation of mouse normal epidermal JB6 Cl41 cells and inhibited the colony formation of human melanoma SK-MEL-28 cells.

XIAP RING domain mediates miR-4295 expression and subsequently inhibiting p63α protein translation and promoting transformation of bladder epithelial cells

The X-linked inhibitor of apoptosis protein (XIAP) contains three N-terminal BIR domains that mediate anti-apoptosis and one C-terminal RING finger domain whose function(s) are not fully defined. Here we show that the RING domain of XIAP strongly inhibits the expression of p63α, a known tumor suppressor. XIAP knockdown in urothelial cells or RING deletion in knockin mice markedly upregulates p63α expression. This RING-mediated p63α downregulation is critical for the malignant transformation of normal urothelial cells following EGF treatment. We further show that the RING domain promotes Sp1-mediated transcription of miR-4295 which targets the 3′UTR of p63α mRNA and consequently inhibits p63α translation. Our results reveal a previously unknown function of the RING of XIAP in promoting miR-4295 transcription, thereby reducing p63α translation and enhancing urothelial transformation. Our data offer novel insights into the multifunctional effects of the XIAP RING domain on urothelial tumorigenesis and the potential for targeting this frequently overexpressed protein as a therapeutic alternative.

SR 11302, an AP-1 Inhibitor, Reduces Metastatic Lesion Formation in Ex Vivo 4D Lung Cancer Model

Activator protein (AP) -1 is a transcription factor, plays important role in cell differentiation, proliferation and apoptosis. Analysis of tumor cells grown on ex vivo 4D lung cancer model shows increase in components of AP-1, c-Fos and c-Jun in circulating tumor cells (CTC) compared to primary tumor. Our aim was to determine whether the AP-1 inhibitor SR11302 reduces metastatic lesion formation in the 4D model. Human lung cancer cell lines A549, H1299, and H460 were grown in the 4D model and treated with SR11302 (1 μM). We compared the number of cells in the metastatic site upon SR11302 treatment and number of viable CTCs isolated from the 4D model with parental cells treated/untreated with SR11302 on a petri dish. There were significantly fewer tumor cells per high-power field on metastatic site in 4D model seeded with H460 (p = 0.009), A549 (p = 0.01), or H1299 (p = 0.02) cells treated with SR11302. Furthermore, the CTCs from SR11302 treated 4D models, seeded with H460 (p = 0.04), A549 (p = 0.008), or H1299 (p = 0.01) cells had significantly fewer viable tumor cells after 4 days in culture than the respective untreated control. However, the SR11302 had no impact on the viability of parental H460 (p = 0.87), A549 (p = 0.93), or H1299 (p = 0.25) cells grown on a petri dish (2D). SR11302 reduces metastatic lesion formation in the ex vivo 4D lung cancer model due to the presence of an independent yet common pathway among three cell lines. The ex vivo 4D model may provide a tool to better understand the complex process of metastasis.

Cdk3-promoted epithelial-mesenchymal transition through activating AP-1 is involved in colorectal cancer metastasis

Cyclin dependent kinase-3 (Cdk3) is a positive regulator of the G1 mammalian cell cycle phase. Cdk3 is involved in cancer progression, but very little is known about its mechanism in cancer development and progression. Herein, we found that Cdk3 increased colorectal cancer metastasis through promoting epithelial-mesenchymal transition (EMT) shift. Cdk3 was found to highly express in metastatic cancer and induce cell motility and invasion. Cdk3 was shown to phosphorylate c-Jun at Ser 63 and Ser 73 in vitro and ex vivo. Cdk3-phosphorylated c-Jun at Ser 63 and Ser 73 resulted in an increased AP-1 activity. Ectopic expression of Cdk3 promoted colorectal cancer from epithelial to mesenchymal transition conjugating AP-1 activation, while AP-1 inhibition dramatically decreased Cdk3-increased EMT shift. These results showed that the Cdk3/c-Jun signaling axis mediating epithelial-mesenchymal transition plays an important role in colorectal cancer metastasis.

Extracellular signal-regulated kinases 1/2 and Akt contribute to triclosan-stimulated proliferation of JB6 Cl 41-5a cells

Triclosan is a broad spectrum anti-bacterial agent widely used in many personal care products, household items, medical devices, and clinical settings. Human exposure to triclosan is mainly through oral and dermal routes. In previous studies, we found that sub-chronic dermal exposure of B6C3F1 mice to triclosan induced epidermal hyperplasia and focal necrosis; however, the mechanisms for these responses remain elusive. In this study, using mouse epidermis-derived JB6 Cl 41-5a cells, we found that triclosan stimulated cell growth in a concentration- and time-dependent manner. Enhanced cell proliferation was demonstrated by a substantial increase in the percentage of BrdU-positive cells, an elevation in the protein levels of cyclin D1 and cyclin A, and a reduction in the protein level of p27(Kip1). Western blotting analysis revealed that triclosan induced the activation of extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNK), p38, and Akt. Pre-treatment of the cells with PD184352, an inhibitor of the upstream kinase MEK1/2, or with wortmannin, an inhibitor of phosphoinositide 3-kinase, blocked triclosan-mediated phosphorylation of ERK1/2 and Akt, respectively, and substantially suppressed triclosan-stimulated cell proliferation, whereas the JNK inhibitor SP600125 or the p38 inhibitor SB203580 had little to no effect on triclosan-stimulated cell proliferation. The phosphorylation activation of ERK1/2 and Akt was further confirmed on the skin of mice dermally administered triclosan. These data suggest that the activation of ERK1/2 and Akt is involved in triclosan-stimulated proliferation of JB6 Cl 41-5a cells.

Cyclin d1 downregulation contributes to anticancer effect of isorhapontigenin on human bladder cancer cells

Isorhapontigenin (ISO) is a new derivative of stilbene compound that was isolated from the Chinese herb Gnetum Cleistostachyum and has been used for treatment of bladder cancers for centuries. In our current studies, we have explored the potential inhibitory effect and molecular mechanisms underlying isorhapontigenin anticancer effects on anchorage-independent growth of human bladder cancer cell lines. We found that isorhapontigenin showed a significant inhibitory effect on human bladder cancer cell growth and was accompanied with related cell cycle G(0)-G(1) arrest as well as downregulation of cyclin D1 expression at the transcriptional level in UMUC3 and RT112 cells. Further studies identified that isorhapontigenin downregulated cyclin D1 gene transcription via inhibition of specific protein 1 (SP1) transactivation. Moreover, ectopic expression of GFP-cyclin D1 rendered UMUC3 cells resistant to induction of cell-cycle G(0)-G(1) arrest and inhibition of cancer cell anchorage-independent growth by isorhapontigenin treatment. Together, our studies show that isorhapontigenin is an active compound that mediates Gnetum Cleistostachyum's induction of cell-cycle G(0)-G(1) arrest and inhibition of cancer cell anchorage-independent growth through downregulating SP1/cyclin D1 axis in bladder cancer cells. Our studies provide a novel insight into understanding the anticancer activity of the Chinese herb Gnetum Cleistostachyum and its isolate isorhapontigenin.

Ginger: is it ready for prime time?

On the basis of substantial preclinical data showing the preventive efficacy of ginger and its constituents in vitro and in animal models, as well as a phase I pilot trial indicating that ginger extract is well tolerated in humans, Citronberg and colleagues conducted a pilot trial of ginger extract (2 g/day for 28 days) on biomarkers of cell proliferation [human telomerase reverse transcriptase (hTERT), MIB-1], differentiation (p21waf1/cip1), and apoptosis (Bax, Bcl-2) in colonic mucosa from individuals at high-risk for colorectal cancer. Results from the trial suggest that ginger may reduce proliferation in normal-appearing colorectal epithelium and increase apoptosis relative to proliferation, especially in the differentiation zone of colon crypts. The authors suggest that these results support a larger study to confirm the pilot data. Before proceeding with a larger trial, however, it seems prudent to confirm ginger as a chemopreventive for colorectal cancer in animals, particularly when tested in postinitiation protocols and to identify reliable molecular biomarkers of effect that could be evaluated in clinical trials. Pharmacokinetic studies to examine the distribution and localization of ginger compounds and metabolites in the differentiation and proliferative zones of colonic crypts in animals and humans would also be informative. Finally, because the effects of ginger on normal colonic mucosa seem minimal, consideration should be given to the conduct of future trials in humans with premalignant colorectal disease.

The requirement of c-Jun N-terminal kinase 2 in regulation of hypoxia-inducing factor-1α mRNA stability

The mRNA of hif-1α is considered as being constitutively and ubiquitously expressed, regardless of the level of oxygen tension. However many recent reports have showed that hif-1α mRNA could be regulated by natural antisense transcripts, potential microRNAs, and low O(2). In this study, it was found that a deficiency of JNK2 expression reduced HIF-1α protein induction in response to nickel treatment resulting from the impaired expression of hif-1α mRNA. Both the promoter luciferase assay and mRNA degradation assay clearly showed that depletion of JNK2 affected stability of hif-1α mRNA, rather than regulated its transcription. In addition, nucleolin, a classic histone chaperone, was demonstrated to physically bind to hif-1α mRNA and maintain its stability. Further investigation indicated that JNK2 regulated nucleolin expression and might in turn stabilize hif-1α mRNA. Collectively, we provided one more piece of evidence for the oncogenic role of JNK2 and nucleolin in regulating the cancer microenvironments by controlling HIF-1α expression.

Induction of apoptosis by sulforaphane in highly metastatic B16F-10 melanoma cells

Sulforaphane (SFN) is a naturally occurring isothiocyanate found in cruciferous vegetables, such as broccoli, cabbage, cauliflower, etc. SFN has received a great deal of attention because of its ability to inhibit cell proliferation and induce apoptosis in several tumor cell lines. Previously, we have demonstrated that SFN inhibits the metastasis of B16F-10 melanoma cells in both in vivo and in vitro models. Melanomas are among the aggressive tumor types because of their notorious resistance to treatment and their high tendency to metastasize. In this study, we investigated the influence of SFN on the induction of apoptosis in B16F-10 melanoma cells, which was evidenced by morphological changes such as membrane blebbing, presence of apoptotic bodies, DNA condensation, and also by nuclear DNA fragmentation. SFN-induced apoptosis was associated with the activation of caspases 3 and 9, Bax, and p53 and the downregulation of Bcl-2, caspase-8, Bid, and NF-kB. Caspase-3 is a most likely candidate to mediate SFN-induced apoptosis. In addition to the caspase-dependent pathway, our results also showed the involvement of proinflammatory cytokines, namely tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, IL-6, IL-12p40, and granulocyte-macrophage colony-stimulating factor (GM-CSF), and the nuclear translocation of factors kappa B (NF-κB) p65, NF-κB p50, NF-κB c-Rel, c-FOS, ATF-2, and CREB-1 in SFN-induced apoptosis. These results raise the possibility that SFN may be a promising candidate for molecular-targeting chemotherapy against melanoma.

Isorhamnetin suppresses skin cancer through direct inhibition of MEK1 and PI3-K

3'-Methoxy-3,4',5,7-tetrahydroxyflavone (isorhamnetin) is a plant flavonoid that occurs in fruits and medicinal herbs. Isorhamnetin exerts anticancer effects, but the underlying molecular mechanism for the chemopreventive potential of isorhamnetin remains unknown. Here, we report anti-skin cancer effects of isorhamnetin, which inhibited epidermal growth factor (EGF)-induced neoplastic cell transformation. It also suppressed anchorage-dependent and -independent growth of A431 human epithelial carcinoma cells. Isorhamnetin attenuated EGF-induced COX-2 expression in JB6 and A431 cells. In an in vivo mouse xenograft using A431 cells, isorhamnetin reduced tumor growth and COX-2 expression. The EGF-induced phosphorylation of extracellular signal-regulated kinases, p90 and p70 ribosomal S6 kinases, and Akt was suppressed by isorhamnetin. In vitro and ex vivo kinase assay data showed that isorhamnetin inhibited the kinase activity of MAP (mitogen-activated protein)/ERK (extracellular signal regulated kinase) kinase (MEK) 1 and PI3-K (phosphoinositide 3-kinase) and the inhibition was due to direct binding with isorhamnetin. Notably, isorhamnetin bound directly to MEK1 in an ATP-noncompetitive manner and to PI3-K in an ATP-competitive manner. This report is the first mechanistic study identifying a clear molecular target for the anticancer activity of isorhamnetin. Overall, these results indicate that isorhamnetin has potent anticancer activity and it primarily targets MEK and PI3-K, which might contribute to the chemopreventive potential of certain foods.

Arsenite stabilizes HIF-1α protein through p85α-mediated up-regulation of inducible Hsp70 protein expression

Hypoxia-inducible factor-1α (HIF-1α) has been reported to regulate over 100 gene expressions in response to hypoxia and other stress conditions. In the present study, we found that arsenite could induce HIF-1α protein accumulation in both mouse epidermal Cl41 cells and mouse embryonic fibroblasts (MEFs). Knockout of p85α, a regulatory subunit of PI-3K, in MEFs (p85α(-/-)) dramatically decreased the arsenite-induced HIF-1α accumulation, indicating that p85α is crucial for arsenite effects on the stabilization of HIF-1α protein. Our further studies suggest that arsenite could induce inducible Hsp70 expression, and transfection of inducible Hsp70 into p85α(-/-) MEFs could restore HIF-1α protein accumulation. Moreover, the results using EMSA and Supershift assays indicate that p85α is crucial for arsenite-induced activation of the heat-shock transcription factor 1 (HSF-1), which is responsible for transcription of inducible Hsp70. Taken together, p85α-mediated HIF-1α stabilization upon arsenite exposure is specifically through HSF-1 activation and subsequent up-regulation of the inducible Hsp70 expression.

Cyclin D1 induction by benzo[a]pyrene-7,8-diol-9,10-epoxide via the phosphatidylinositol 3-kinase/Akt/MAPK- and p70s6k-dependent pathway promotes cell transformation and tumorigenesis

Benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), the major metabolite of B[a]P, has been well recognized as one ubiquitous carcinogen, but the molecular mechanism involved in its carcinogenic effect remains obscure. In the present study, we found that bronchial epithelial cells (Beas-2B) and hepatocytes treated with B[a]PDE presented a significant increase of cyclin D1 expression. Moreover, Akt, p70(s6k), and MAPKs including JNK, Erks, and p38 were notably activated in B[a]PDE-treated Beas-2B cells, whereas NF-kappaB, NFAT, and Egr-1 were not. Our results demonstrated that JNK and Erks were required in B[a]PDE-induced cyclin D1 expression because the inhibition of JNK or Erks by a selective chemical inhibitor or dominant negative mutant robustly impaired the cyclin D1 induction by B[a]PDE. Furthermore, we found that overexpression of the dominant negative mutant of p85 (regulatory subunit of phosphatidylinositol 3-kinase) or Akt dramatically suppressed B[a]PDE-induced JNK and Erk activation as well as cyclin D1 expression, suggesting that cyclin D1 induction by B[a]PDE is via the phosphatidylinositol 3-kinase/Akt/MAPK-dependent pathway. In addition, we clarified that p70(s6k) is also involved in B[a]PDE-induced cyclin D1 expression because rampamycin pretreatment dramatically reduced cyclin D1 induction by B[a]PDE. More importantly, we demonstrated that up-regulated cyclin D1 by B[a]PDE plays a critical role in oncogenic transformation and tumorigenesis of Beas-2B cells. These results not only broaden our knowledge of the molecular mechanism of B[a]PDE carcinogenicity but also lead to the further study of chemoprevention of B[a]PDE-associated human cancers.

Standardized ginger (Zingiber officinale) extract reduces bacterial load and suppresses acute and chronic inflammation in Mongolian gerbils infected with cagAHelicobacter pylori

Previous investigations demonstrated that a standardized extract of ginger rhizome inhibited the growth of Helicobacter pylori in vitro with a minimum inhibitory concentration in the range 0.78 to 12.5 mug/mL. In the present work, the extract was tested in a rodent model of H. pylori-induced disease, the Mongolian gerbil, to examine the effects of the extract on both prevention and eradication of infection. The extract was administered to Mongolian gerbils at a daily dose of 100 mg/kg body weight in rations either 3 weeks prior to infection or 6 weeks post-infection. Treatment with the standardized ginger extract reduced H. pylori load as compared with controls and significantly (P<0.05) reduced both acute and chronic muscosal and submucosal inflammation, cryptitis, as well as epithelial cell degeneration and erosion induced by H. pylori. Importantly, the extract did not increase morbidity or mortality. Further investigations of the mechanism demonstrated that the ginger extract inhibited the activity of cyclooxygenase-2, with 50% inhibitory concentration (IC(50)) of 8.5 mug/mL in vitro, inhibited the nuclear factor-kappaB transcriptional response in kBZ Jurkat cells (human T lymphocytes) with an IC(50) of 24.6 mug/mL, and significantly inhibited the release of interleukin (IL)-1beta, IL-6, IL-8, and tumor necrosis factor-alpha from lipopolysaccharide-stimulated human peripheral blood mononuclear cells with IC(50) values of 3.89, 7.7, 8.5, and 8.37 mug/mL, respectively. These results suggest ginger extracts may be useful for development as agents to reduce H. pylori-induced inflammation and as for gastric cancer chemoprevention.

c-Jun/AP-1 pathway-mediated cyclin D1 expression participates in low dose arsenite-induced transformation in mouse epidermal JB6 Cl41 cells

Arsenic is a well-documented human carcinogen associated with skin carcinogenesis. Our previous work reveals that arsenite exposure is able to induce cell transformation in mouse epidermal cell JB6 Cl41 through the activation of ERK, rather than JNK pathway. Our current studies further evaluate downstream pathway in low dose arsenite-induced cell transformation in JB6 Cl41 cells. Our results showed that treatment of cells with low dose arsenite induced activation of c-Jun/AP-1 pathway, and ectopic expression of dominant negative mutant of c-Jun (TAM67) blocked arsenite-induced transformation. Furthermore, our data indicated that cyclin D1 was an important downstream molecule involved in c-Jun/AP-1-mediated cell transformation upon low dose arsenite exposure, because inhibition of cyclin D1 expression by its specific siRNA in the JB6 Cl41 cells resulted in impairment of anchorage-independent growth of cells induced by low dose arsenite. Collectively, our results demonstrate that c-Jun/AP-1-mediated cyclin D1 expression is at least one of the key events implicated in cell transformation upon low dose arsenite exposure.

Interleukin (IL) 1beta induction of IL-6 is mediated by a novel phosphatidylinositol 3-kinase-dependent AKT/IkappaB kinase alpha pathway targeting activator protein-1

Here we describe a novel role for the phosphatidylinositol 3-kinase/AKT pathway in mediating induction of interleukin-6 (IL-6) in response to IL-1. Pharmacological inhibition of phosphatidylinositol 3-kinase (PI3K) inhibited IL-6 mRNA and protein production. Overexpression of either dominant-negative AKT or IkappaB kinase alpha mutant, IKKalphaT23A, containing a mutation in a functional AKT phosphorylation site, shown previously to be important for NFkappaB activation, completely abrogated IL-6 promoter activation in response to IL-1. However, mutation of the consensus NFkappaB site on the IL-6 promoter did not abrogate promoter activation by IL-1 in contrast to the AP-1 site mutation. IL-1 induces phosphorylation of IKKalpha on the NFkappaB inducing kinase (NIK) phosphorylation sites Ser(176)/Ser(180) and on the Thr(23) site, and although phosphorylation of IKKalphaT23 is inhibited both by LY294002 and wortmannin, phosphorylation of Ser(176)/Ser(180) is not. Neither inhibition of PI 3-kinase/AKT nor IKKalphaT23A overexpression affected IkappaBalpha degradation in response to IL-1. Only partial inhibition by dominant-negative AKT and no inhibitory effect of IKKalphaT23A was observed on an IL-6 promoter-specific NFkappaB site in contrast to significant inhibitory effects on the AP-1 site. Taken together, we have discovered a novel PI 3-kinase/AKT-dependent pathway in response to IL-1, encompassing PI 3-kinase/AKT/IKKalphaT23 upstream of AP-1. This novel pathway is a parallel pathway to the PI 3-kinase/AKT upstream of NFkappaB and both are involved in IL-6 gene transcription in response to IL-1.

Benzo(a)pyrene-caused increased G1-S transition requires the activation of c-Jun through p53-dependent PI-3K/Akt/ERK pathway in human embryo lung fibroblasts

Benzo(a)pyrene (B(a)P) is a potent lung carcinogen mainly derived from tobacco smoking and environmental contamination, however, the molecular mechanisms by which it accelerates the cell cycle progression and induces the abnormal cell proliferation are still far away from understood. Our current analysis of human embryo lung fibroblasts (HELF) showed that B(a)P exposure was able to promote cell cycle G(1)-S phase transition. This effect was correlated with c-Jun activation because inhibition of c-Jun by its dominant negative mutant (TAM67) reversed B(a)P action on cell cycle with the down-regulation of expression of cyclin D1, pRb and E2F1. Further study found that overexpression of dominant negative mutants of, PI-3K or Akt, dramatically reduced B(a)P-induced the activation of c-Jun and extracellular signaling regulated kinase (ERK), but not c-Jun NH2 terminal kinase (JNK). Inhibition of p53 by either its inhibitor pifithrin-alpha or p53 siRNA markedly increased B(a)P-induced the activation of c-Jun, Akt and ERK in this context. Take together, our results indicate that c-Jun activation by p53-dependent PI-3K/Akt/ERK pathway is responsible for B(a)P-induced cell cycle alternations in human embryo lung fibroblasts.

PI-3K/Akt pathway-dependent cyclin D1 expression is responsible for arsenite-induced human keratinocyte transformation

BACKGROUND

Long-term exposure of arsenite leads to human skin cancer. However, the exact mechanisms of arsenite-induced human skin carcinogenesis remain to be defined.

OBJECTIVES

In this study, we investigated the potential role of PI-3K/Akt/cyclin D1in the transformation of human keratinocytic cells upon arsenite exposure.

METHODS

We used the soft agar assay to evaluate the cell transformation activity of arsenite exposure and the nude mice xenograft model to determine the tumorigenesis of arsenite-induced transformed cells. We used the dominant negative mutant and gene knockdown approaches to elucidate the signaling pathway involved in this process.

RESULTS

Our results showed that repeated long-term exposure of HaCat cells to arsenite caused cell transformation, as indicated by anchorage-independent growth in soft agar. The tumorigenicity of these transformed cells was confirmed in nude mice. Treatment of cells with arsenite also induced significant activation of PI-3K and Akt, which was responsible for the anchorage-independent cell growth induced by arsenite exposure. Furthermore, our data also indicated that cyclin D1 is an important downstream molecule involved in PI-3K/Akt-mediated cell transformation upon arsenite exposure based on the facts that inhibition of cyclin D1 expression by dominant negative mutants of PI-3K, and Akt, or the knockdown of the cyclin D1 expression by its specific siRNA in the HaCat cells resulted in impairing of anchorage-independent growth of HaCat cells induced by arsenite.

CONCLUSION

Our results demonstrate that PI-3K/Akt-mediated cyclin D1 expression is at least one key event implicated in the arsenite human skin carcinogenic effect.

Enhanced self-renewal capability in hepatic stem/progenitor cells drives cancer initiation

BACKGROUND & AIMS

Transformed hematopoietic stem/progenitor cells with an enhanced or acquired self-renewal capability function as leukemic stem cells. In a variety of solid cancers, stem/progenitor cells could be also targets of carcinogenesis. However, it remains unclear whether disruption of stem cell function directly contributes to cancer initiation. We sought to elucidate the mechanisms of self-renewal in hepatic stem/progenitor cells and the relation between stem cell function and hepatocarcinogenesis.

METHODS

Functional analyses of polycomb-group protein Bmi1 and Wnt/beta-catenin, the molecules that are responsible for the self-renewal capability of many types of stem cells, were conducted in c-Kit(-)CD29(+)CD49f(+/low)CD45(-)Ter-119(-) hepatic stem/progenitor cells using retrovirus- or lentivirus-mediated gene transfer. The tumorigenicity of these cells transduced with the indicated retroviruses was also assessed by transplantation into nonobese diabetic/severe combined immunodeficient mice.

RESULTS

Forced expression of Bmi1 and constitutively active beta-catenin mutant similarly promoted the self-renewal of hepatic stem/progenitor cells. The transplantation of Bmi1- or beta-catenin-transduced cells clonally expanded from single hepatic stem/progenitor cells produced tumors, which exhibited the histologic features of combined hepatocellular and cholangiocarcinoma.

CONCLUSIONS

These observations imply that the dysregulated self-renewal of hepatic stem/progenitor cells serves as an early event in hepatocarcinogenesis, and they highlight the important roles of Bmi1 and the Wnt/beta-catenin pathway in regulating the self-renewal of normal or cancer stem cells in liver.

Cot, a novel kinase of histone H3, induces cellular transformation through up-regulation of c-fos transcriptional activity

Post-translational modification of histones is critical for gene expression, mitosis, cell growth, apoptosis, and cancer development. Thus, finding protein kinases that are responsible for the phosphorylation of histones at critical sites is considered an important step in understanding the process of histone modification. The serine/threonine kinase Cot is a member of the mitogen-activated protein kinase (MAPK) kinase kinase family. We show here that Cot can phosphorylate histone H3 at Ser-10 in vivo and in vitro, and that the phosphorylation of histone H3 at Ser-10 is required for Cot-induced cell transformation. We found that activated Cot is recruited to the c-fos promoter resulting in increased activator protein-1 (AP-1) transactivation. The formation of the Cot-c-fos promoter complex was also apparent when histone H3 was phosphorylated at Ser-10. Furthermore, the use of dominant negative mutants of histone H3 revealed that Cot was required for phosphorylation of histone H3 at Ser-10 to induce neoplastic cell transformation. These results revealed an important function of Cot as a newly discovered histone H3 kinase. Moreover, the transforming ability of Cot results from the coordinated activation of histone H3, which ultimately converges on the regulation of the transcriptional activity of the c-fos promoter, followed by AP-1 transactivation activity.

Suppression of osteoclastogenesis by N,N-dimethyl-D-erythro-sphingosine: a sphingosine kinase inhibition-independent action

N,N-Dimethyl-D-erythro-sphingosine (DMS) competitively inhibits sphingosine kinase (SPHK) and has been widely used to assess the role of SPHK during cellular events, including motility, proliferation, and differentiation. In the present study, the effect of DMS on the differentiation of bone marrow macrophages (BMMs) to osteoclasts was investigated. When the osteoclast precursor cells were treated with DMS, the receptor activator of nuclear factor kappaB ligand (RANKL)-induced osteoclastogenesis was completely blocked. We were surprised to find, however, that knock-down of SPHK by small interfering RNA (siRNA) in BMMs did not reduce osteoclastogenesis. Furthermore, both overexpression of SPHK and exogenous addition of sphingosine-1-phosphate, the product of SPHK activity, failed to overcome the antiosteoclastogenic effect of DMS. These results suggest that DMS inhibited osteoclastogenesis independently of SPHK. Subsequent characterization of the DMS-mediated suppression of osteoclastogenesis revealed that DMS did not affect RANKL-induced activation of JNK, p38, NF-kappaB, and Ca2+ oscillation. On the other hand, DMS strongly inhibited two separate signaling pathways, the RANKL-induced activation of ERK and Akt, which eventually converged on the transcription factors c-Fos and NFATc1. There was significant increase in the osteoclast formation in the presence of DMS when BMMs were overexpressed with c-Fos, suggesting that c-Fos was a critical downstream target of DMS for the inhibition of osteoclastogenesis. Taken together, our data demonstrate that DMS has an antiosteoclastogenic function independently of its SPHK inhibitory activity. Considering previously reported anticancer properties of DMS, our study may also propose that DMS is an ideal drug candidate for bone metastases, for which osteoclastic bone-resorption is crucial.

Identification and analysis of the promoter region of the human PLC-δ4 gene

The delta4 isoform of phospholipase C (PLC-delta4) is thought to be associated with various cellular functions and disease status. However, little is known about how its function is controlled in cells, particularly in terms of the regulation of its expression. To understand the regulation mechanisms of the PLC-delta4 gene transcription, the 5'-flanking region (-2046 approximately +5) (the nucleotide sequence data reported in this paper have been submitted to the EMBL/GenBank/DDBJ data bank under accession numbers DQ302751) of the human PLC-delta4 gene was isolated from human genomic DNA. It was a TATA-less promoter with very GC-rich sequences near the transcription start site. The activity of the PLC-delta4 promoter was shown in various human and mouse cell lines by luciferase reporter assay. Serial deletion analysis identified the core promoter region as being between -402 and -67, in which an E-box and an AP-1 binding site played important roles in the promoter activity. In addition, we also showed that 12-O-tetradecanoylphorbol-1,3-acetate (TPA), a PKC activator and tumor promoter, induced the activity of the PLC-delta4 promoter via the AP-1 binding site. In summary, this study identified a core promoter region of the hPLC-delta4 gene and the factor binding sites responsible for the promoter activity. These results will provide important new information to further understand the regulatory mechanism of the PLC-delta4 function.

Phosphatidylinositol-3 kinase/Akt/p70S6K/AP-1 signaling pathway mediated benzo(a)pyrene-induced cell cycle alternation via cell cycle regulatory proteins in human embryo lung fibroblasts

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[a]pyrene diol-epoxide (B[a]PDE) upregulates COX-2 expression through MAPKs/AP-1 and IKKbeta/NF-kappaB in mouse epidermal Cl41 cells

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.

PTEN down regulates AP-1 and targets c-fos in human glioma cells via PI3-kinase/Akt pathway

The continual activation of signaling cascades results in dramatic consequences that include loss of cellular growth control and neoplastic transformation. We show here that phosphoinositide 3-kinase and its mediator Akt was constitutively activated in glioma and that this might be due to the aberrant expression of their natural antagonist PTEN. The PTEN (phosphatase and tensin homologue deleted on chromosome ten) tumor suppressor gene modulates cell growth and survival through mechanisms that are incompletely understood. In this study, we investigated the possibility that PTEN mediates its effects through modulation of transcription factor AP-1, which is in part due to decrease in c-fos expression which was dependent on PI3kinase activity. Consistent with a reduction in the c-fos levels, an AP-1 dependent reporter gene was poorly induced in the PTEN expressing cell lines. In contrast to its effect on c-fos, PTEN did not affect the expression of c-Jun and other fos family members. We also show that the effect of PTEN on c-fos expression was due to its ability to antagonize PI3-kinase and could be mimicked by the expression of dominant negative Akt mutant. Taken together, these data indicate that the aberrant expression of PTEN contributes to the activation of the PI3kinase/Akt pathway and its transcription factor mediators in glioma. We conclude that the ectopic expression of PTEN down regulates the proliferation of glioma cells through the suppression of AP-1 and that this target might be essential for its central role in the growth and survival of glioma cancer cells.

Pro/antioxidant status and AP-1 transcription factor in murine skin following topical exposure to cumene hydroperoxide

Organic peroxides, widely used in the chemical and pharmaceutical industries, can act as skin tumor promoters and cause epidermal hyperplasia. They are also known to trigger free radical generation. The present study evaluated the effect of cumene hydroperoxide (Cum-OOH) on the induction of activator protein-1 (AP-1), which is linked to the expression of genes regulating cell proliferation, growth and transformation. Previously, we reported that topical exposure to Cum-OOH caused formation of free radicals and oxidative stress in the skin of vitamin E-deficient mice. The present study used JB6 P+ mouse epidermal cells and AP-1-luciferase reporter transgenic mice to identify whether exposure to Cum-OOH caused activation of AP-1, oxidative stress, depletion of antioxidants and tumor formation during two-stage carcinogenesis. In vitro studies found that exposure to Cum-OOH reduced the level of glutathione (GSH) in mouse epidermal cells (JB6 P+) and caused the induction of AP-1. Mice primed with dimethyl-benz[a]anthracene (DMBA) were topically exposed to Cum-OOH (82.6 micromol) or the positive control, 12-O-tetradecanoylphorbol-13-acetate (TPA, 17 nmol), twice weekly for 29 weeks. Activation of AP-1 in skin was detected as early as 2 weeks following Cum-OOH or TPA exposure. No AP-1 expression was found 19 weeks after initiation. Papilloma formation was observed in both the DMBA-TPA- and DMBA-Cum-OOH-exposed animals, whereas skin carcinomas were found only in the DMBA-Cum-OOH-treated mice. A greater accumulation of peroxidative products (thiobarbituric acid-reactive substances), inflammation and decreased levels of GSH and total antioxidant reserves were also observed in the skin of DMBA-Cum-OOH-exposed mice. These results suggest that Cum-OOH-induced carcinogenesis is accompanied by increased AP-1 activation and changes in antioxidant status.

PI-3K/Akt signal pathway plays a crucial role in arsenite-induced cell proliferation of human keratinocytes through induction of cyclin D1

Exposure of arsenite can induce hyperproliferation of skin cells, which is believed to play important roles in arsenite-induced carcinogenesis by affecting both promotion and progression stages. However, the signal pathways and target genes activated by arsenite exposure responsible for the proliferation remain to be defined. In the present study, we found that: (1) exposure of human keratinocytic HaCat cells to arsenite caused an increase in cell proliferation, which was significantly inhibited by pretreatment of wortmannin, a specific chemical inhibitor of PI-3K/Akt signal pathway; (2) arsenite exposure was also able to activate PI-3K/Akt signal pathway, which thereby induced the elevation of cyclin D1 expression level in both HaCat cells and human primary keratinocytes based on that inhibition of PI-3K/Akt pathway by either pretreatment of wortmannin or the transfection of their dominant mutants, significantly inhibited cyclin D1 expression upon arsenite exposure; (3) PI-3K/Akt pathway is implicated in arsenite-induced proliferation of HaCat cells through the induction of cyclin D1 because either knockdown of cyclin D1 by its siRNA or inhibition of PI-3K/Akt signal pathway by their dominant mutants markedly impaired the proliferation of HaCat cells induced by arsenite exposure. Taken together, we provide the direct evidence that PI-3K/Akt pathway plays a role in the regulation of cell proliferation through the induction of cyclin D1 in human keratinocytes upon arsenite treatment. Given the importance of aberrant cell proliferation in cell transformation, we propose that the activation of PI-3K/Akt pathway and cyclin D1 induction may be the important mediators of human skin carcinogenic effect of arsenite.

Heparin (GAG-hed) inhibits LCR activity of human papillomavirus type 18 by decreasing AP1 binding

BACKGROUND

High risk HPVs are causative agents of anogenital cancers. Viral E6 and E7 genes are continuously expressed and are largely responsible for the oncogenic activity of these viruses. Transcription of the E6 and E7 genes is controlled by the viral Long Control Region (LCR), plus several cellular transcription factors including AP1 and the viral protein E2. Within the LCR, the binding and activity of the transcription factor AP1 represents a key regulatory event in maintaining E6/E7 gene expression and uncontrolled cell proliferation. Glycosaminoglycans (GAGs), such as heparin, can inhibit tumour growth; they have also shown antiviral effects and inhibition of AP1 transcriptional activity. The purpose of this study was to test the heparinoid GAG-hed, as a possible antiviral and antitumoral agent in an HPV18 positive HeLa cell line.

METHODS

Using in vivo and in vitro approaches we tested GAG-hed effects on HeLa tumour cell growth, cell proliferation and on the expression of HPV18 E6/E7 oncogenes. GAG-hed effects on AP1 binding to HPV18-LCR-DNA were tested by EMSA.

RESULTS

We were able to record the antitumoral effect of GAG-hed in vivo by using as a model tumours induced by injection of HeLa cells into athymic female mice. The antiviral effect of GAG-hed resulted in the inhibition of LCR activity and, consequently, the inhibition of E6 and E7 transcription. A specific diminishing of cell proliferation rates was observed in HeLa but not in HPV-free colorectal adenocarcinoma cells. Treated HeLa cells did not undergo apoptosis but the percentage of cells in G2/M phase of the cell cycle was increased. We also detected that GAG-hed prevents the binding of the transcription factor AP1 to the LCR.

CONCLUSION

Direct interaction of GAG-hed with the components of the AP1 complex and subsequent interference with its ability to correctly bind specific sites within the viral LCR may contribute to the inhibition of E6/E7 transcription and cell proliferation. Our data suggest that GAG-hed could have antitumoral and antiviral activity mainly by inhibiting AP1 binding to the HPV18-LCR.

Cell apoptosis: requirement of H2AX in DNA ladder formation, but not for the activation of caspase-3

Immunofluorescence studies have revealed that H2AX is phosphorylated at the sites of DNA double-strand breaks induced by ionizing radiation and is required for recruitment of repair factors into nuclear foci after DNA damage. Therefore, the function of H2AX is believed to be associated primarily with repair of DNA damage. Here, we report a function of H2AX in cellular apoptosis. Our data showed that H2AX is phosphorylated by UVA-activated JNK. We also provided evidence showing that UVA induces caspase-3 and caspase-activated DNase (CAD) activity in both H2AX wild-type and H2AX knockout mouse embryonic fibroblasts (MEFs). However, DNA fragmentation occurred only in H2AX wild-type MEFs. Furthermore, H2AX phosphorylation was critical for DNA degradation triggered by CAD in vitro. Taken together, these data indicated that H2AX phosphorylation is required for DNA ladder formation, but not for the activation of caspase-3; and the JNK/H2AX pathway cooperates with the caspase-3/CAD pathway resulting in cellular apoptosis.

A review of the effects and mechanisms of polyphenolics in cancer

This paper is a comprehensive review of the effects of bioactive polyphenolic compounds commonly found in many fruits and vegetables on cancer. These include the pheniolic acids, anthocyanins, catechins, stilbenes and several other flavonoids. We have attempted to compile information from most of the major studies in this area into one source. The review encompasses the occurrence and bioavailability of the polyphenolics, the in vitro and in vivo evidence for their effects on cancer, both positive and negative, and the various mechanisms by which the chemicals may exert their effects. Although most of the work done to date indicates a chemopreventative activity of these compounds, there are some studies that show cancer-inducing or no effects. There are several common mechanisms by which these chemicals exert their effects that could be conducive to additive, synergistic, or antagonistic interactions. These include effects on cellular differentiation, proliferation, and apoptosis, effects on proteins and enzymes that are involved in these processes at a molecular level, and other various effects through altered immune function and chemical metabolism.

Hypoxia-induced mitogenic factor enhances angiogenesis by promoting proliferation and migration of endothelial cells

Our previous studies have indicated that hypoxia-induced mitogenic factor (HIMF) has angiogenic properties in an in vivo matrigel plug model and HIMF upregulates expression of vascular endothelial growth factor (VEGF) in mouse lungs and cultured lung epithelial cells. However, whether HIMF exerts angiogenic effects through modulating endothelial cell function remains unknown. In this study, mouse aortic rings cultured with recombinant HIMF protein resulted in enhanced vascular sprouting and increased endothelial cell spreading as confirmed by Dil-Ac-LDL uptake, von Willebrand factor and CD31 staining. In cultured mouse endothelial cell line SVEC 4-10, HIMF dose-dependently enhanced cell proliferation, in vitro migration and tubulogenesis, which was not attenuated by SU1498, a VEGFR2/Flk-1 receptor tyrosine kinase inhibitor. Moreover, HIMF stimulation resulted in phosphorylation of Akt, p38 and ERK1/2 kinases in SVEC 4-10 cells. Treatment of mouse aortic rings and SVEC 4-10 cells with LY294002, but not SB203580, PD098059 or U0126, abolished HIMF-induced vascular sprouting and angiogenic responses. In addition, transfection of a dominant-negative mutant of phosphatidylinositol 3-kinase (PI-3K), Deltap85, blocked HIMF-induced phosphorylation of Akt, endothelial activation and tubulogenesis. These results indicate that HIMF enhances angiogenesis by promoting proliferation and migration of endothelial cells via activation of the PI-3K/Akt pathways.

Recruitment of insulin receptor substrate-1 and activation of NF-kappaB essential for midkine growth signaling through anaplastic lymphoma kinase

Anaplastic lymphoma kinase (ALK) is a transmembrane receptor tyrosine kinase in the insulin receptor superfamily. We recently demonstrated that the growth factors pleiotrophin (PTN) and midkine (MK) are ligands for ALK and that upon ALK activation, insulin receptor substrate-1 (IRS-1) and other substrates are phosphorylated. Here, the role of IRS-1 in ligand-mediated ALK signaling is investigated in interleukin-3 (IL-3)-dependent 32D murine myeloid cells. These cells do not express ALK and IRS family members, and do not respond to exogenously added PTN or MK. We show that expression of ALK plus IRS-1 renders these cells independent of IL-3 owing to the activation of ALK by endogenous MK. Mutational analysis reveals that this transformed phenotype of 32D cells requires kinase-active ALK as well as the interaction of ALK with IRS-1. Furthermore, 32D/IRS-1/ALK cells display an enhanced activation of mitogen-activated protein kinase and PI3-kinase pathways, and a selective transcriptional activation of nuclear factor (NF)-kappaB. Small interfering RNA-mediated knockdown of the endogenous MK or p65/NF-kappaB revealed that both these are rate limiting for the transformed phenotype induced by ALK plus IRS-1. We conclude that the recruitment of IRS-1 to activated ALK and the activation of NF-kappaB are essential for the autocrine growth and survival signaling of MK.

Participation of the PI-3K/Akt-NF-kappa B signaling pathways in hypoxia-induced mitogenic factor-stimulated Flk-1 expression in endothelial cells

Background

Hypoxia-induced mitogenic factor (HIMF), a lung-specific growth factor, promotes vascular tubule formation in a matrigel plug model. We initially found that HIMF enhances vascular endothelial growth factor (VEGF) expression in lung epithelial cells. In present work, we tested whether HIMF modulates expression of fetal liver kinase-1 (Flk-1) in endothelial cells, and dissected the possible signaling pathways that link HIMF to Flk-1 upregulation.

Methods

Recombinant HIMF protein was intratracheally instilled into adult mouse lungs, Flk-1 expression was examined by immunohistochemistry and Western blot. The promoter-luciferase reporter assay and real-time RT-PCR were performed to examine the effects of HIMF on Flk-1 expression in mouse endothelial cell line SVEC 4–10. The activation of NF-kappa B (NF-κB) and phosphorylation of Akt, IKK, and IκBα were examined by luciferase assay and Western blot, respectively.

Results

Intratracheal instillation of HIMF protein resulted in a significant increase of Flk-1 production in lung tissues. Stimulation of SVEC 4–10 cells by HIMF resulted in increased phosphorylation of IKK and IκBα, leading to activation of NF-κB. Blocking NF-κB signaling pathway by dominant-negative mutants of IKK and IκBα suppressed HIMF-induced Flk-1 upregulation. Mutation or deletion of NF-κB binding site within Flk-1 promoter also abolished HIMF-induced Flk-1 expression in SVEC 4–10 cells. Furthermore, HIMF strongly induced phosphorylation of Akt. A dominant-negative mutant of PI-3K, Δp85, as well as PI-3K inhibitor LY294002, blocked HIMF-induced NF-κB activation and attenuated Flk-1 production.

Conclusion

These results suggest that HIMF upregulates Flk-1 expression in endothelial cells in a PI-3K/Akt-NF-κB signaling pathway-dependent manner, and may play critical roles in pulmonary angiogenesis.

Phosphatidylinositol 3-kinase/Akt positively regulates Fas (CD95)-mediated apoptosis in epidermal Cl41 cells

Fas (CD95)-mediated apoptosis is an essential mechanism for the maintenance of homeostasis, and disruption of this death pathway contributes to many human diseases. The cell survival protein kinase Akt/protein kinase B (PKB) is a known regulator of apoptosis, but its role in Fas-mediated cell death and its regulatory mechanisms are unclear. In this study, we show that stimulation of the Fas receptor by its ligand (FasL) induces rapid phosphorylation of Akt/PKB and a parallel increase in cell apoptosis in epidermal Cl41 cells. Inhibition of PI3K/Akt by dominant-negative overexpression of PI3K (Deltap85) and Akt (Akt-T308A/S473A) protects the cells from apoptosis, indicating an unexpected proapoptotic role of PI3K/Akt in the Fas signaling process. Treatment of the cells with pharmacological inhibitors of PI3K, wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-1 (LY294002), similarly inhibits FasL-induced apoptosis and Akt/PKB phosphorylation, indicating that PI3K is an upstream mediator of Akt/PKB and is involved in Fas-mediated cell death. Electron spin resonance studies show that FasL treatment induces rapid generation of reactive oxygen species, and inhibition of ROS by antioxidants effectively inhibits Akt/PKB signaling, suggesting that FasL activation of Akt/PKB is redox sensitive. In cells transfected with dominant-negative PI3K/Akt, Fas expression is down-regulated, but FLIP expression is unaffected. Reporter gene and mRNA expression assays show that FasL activates fas transcriptional activity and this effect is inhibited by PI3K/Akt suppression. Together, our results indicate that the PI3K/Akt, in addition to its normal prosurvival role, also plays an apoptotic role in Fas-mediated cell death through a mechanism that involves transcriptional activation of Fas receptor.

NFAT3 is Required for EGF-Induced COX-2 Transcription, but Neither iNOS Transcription Nor Cell Transformation in Cl 41 Cells

Epidermal growth factor (EGF) has been reported to act as a tumor promoter in several tissues, such as skin, in association with the induction of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). However, molecular mechanisms involved in these regulations are not well defined. This study addressed a potential role of nuclear factor of activated T cells 3 (NFAT3) in EGF-induced COX-2 and iNOS transcription and cell transformation in mouse epidermal Cl 41 cells. We found that EGF markedly induced anchorage-independent growth (cell transformation) of Cl 41 cells, as well as COX-2 (> 6-fold) and iNOS (> 5-fold) promoter-dependent transcription. The EGF-induced COX-2 transcription was blocked by knockdown of NFAT3 with NFAT3 siRNA, whereas the transcription of iNOS and cell transformation induced by EGF were not affected. Although our recent studies supported that NFAT3 plays an essential role in chemical carcinogen benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE)-induced cell transformation, the data presented here demonstrated that NFAT3 is required for EGF-induced COX-2 transcription, but neither iNOS transcription nor cell transformation, indicating that the role of NFAT3 in regulating cell transformation is carcinogen-specific.

Hypoxia-induced mitogenic factor promotes vascular adhesion molecule-1 expression via the PI-3K/Akt-NF-kappaB signaling pathway

Hypoxia-induced mitogenic factor (HIMF), also known as FIZZ1 (found in inflammatory zone 1), is an important player in lung inflammation. However, the effects of HIMF on cell adhesion molecules involved in lung inflammation remain largely unknown. In the present work, we tested whether HIMF modulates vascular adhesion molecule (VCAM)-1 expression, and dissected the possible signaling pathways that link HIMF to VCAM-1 upregulation. Recombinant HIMF protein, instilled intratracheally into adult mouse lungs, results in a significant increase of VCAM-1 production in vascular endothelial, alveolar type II, and airway epithelial cells. In cultured mouse endothelial SVEC 4-10 and lung epithelial MLE-12 cells, we demonstrated that HIMF induces VCAM-1 expression via the phosphatidylinositol-3 kinase (PI-3K)/Akt-nuclear factor (NF)-kappaB signaling pathway. Knockdown of HIMF expression by small interference RNA attenuated LPS-induced VCAM-1 expression in vitro. We showed that HIMF induced phosphorylation of the IkappaB kinase signalsome and, subsequently, IkappaBalpha, leading to activation of NF-kappaB. Meanwhile, VCAM-1 production was correspondingly upregulated. Blocking NF-kappaB signaling pathway by expression of dominant-negative mutants of IkappaB kinase and IkappaBalpha suppressed HIMF-induced VCAM-1 upregulation. HIMF also strongly induced phosphorylation of Akt. A dominant-negative mutant of PI-3K, Deltap85, as well as PI-3K inhibitor, LY294002, also blocked HIMF-induced NF-kappaB activation and attenuated VCAM-1 production. Furthermore, LY294002 pretreatment abolished HIMF-enhanced mononuclear cells adhesion to endothelial and epithelial cells. Our findings connect HIMF to signaling pathways that regulate inflammation, and thus reveal the critical roles that HIMF plays in lung inflammation.

Effects of MAP kinase inhibitors on epidermal growth factor-induced neoplastic transformation of human keratinocytes

We previously reported data regarding the mechanism of neoplastic transformation in JB6 Cl41 mouse skin epidermal cells. However, experimental in vitro models for studying neoplastic transformation of human cells could provide further insight into the mechanisms of human cancer development. In this study, we have established a neoplastic transformation model with HaCaT cells, a human keratinocyte cell line, and showed the usefulness of this cell line for studying the mechanisms of neoplastic transformation. Epidermal growth factor (EGF) treatment induced a dose-dependent anchorage-independent cell transformation in HaCaT cells. Furthermore, PD98059, a mitogen-activated protein (MAP) kinase/ERK kinase (MEK) inhibitor, or SP600125, c-Jun N-terminal kinase (JNK) inhibitor, decreased cell growth, EGF-induced DNA synthesis and transformation. Unlike observations in the JB6 mouse epidermal cell model, SB203580, a stress-activated protein kinase-2/p38 alpha and beta (p38) inhibitor, increased EGF-induced transformation in HaCaT cells. These results suggest that extracellular-signal regulated kinase (ERK), JNK, or p38 are implicated in EGF-induced neoplastic transformation of human cells.

Identification of cyanidin glycosides as constituents of freeze-dried black raspberries which inhibit anti-benzo[a]pyrene-7,8-diol-9,10-epoxide induced NFkappaB and AP-1 activity

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.

VEGF is upregulated by hypoxia-induced mitogenic factor via the PI-3K/Akt-NF-kappaB signaling pathway

Background

Hypoxia-induced mitogenic factor (HIMF) is developmentally regulated and plays an important role in lung pathogenesis. We initially found that HIMF promotes vascular tubule formation in a matrigel plug model. In this study, we investigated the mechanisms which HIMF enhances expression of vascular endothelial growth factor (VEGF) in lung tissues and epithelial cells.

Methods

Recombinant HIMF protein was intratracheally instilled into adult mouse lungs, VEGF expression was examined by immunohistochemical staining and Western blot. The promoter-luciferase reporter assay, RT-PCR, and Western blot were performed to examine the effects of HIMF on VEGF expression in mouse lung epithelial cell line MLE-12. The activation of NF-kappa B (NF-κB) and phosphorylation of Akt, IKK and IκBα were examined by luciferase assay and Western blot, respectively.

Results

Intratracheal instillation of HIMF protein resulted in significant increase of VEGF, mainly localized to airway epithelial and alveolar type II cells. Deletion of NF-κB binding sites within VEGF promoter abolished HIMF-induced VEGF expression in MLE-12 cells, suggesting that activation of NF-κB is essential for VEGF upregulation induced by HIMF. Stimulation of lung epithelial cells by HIMF resulted in phosphorylation of IKK and IκBα, leading to activation of NF-κB. In addition, HIMF strongly induced Akt phosphorylation, and suppression of Akt activation by specific inhibitors and dominant negative mutants for PI-3K, and IKK or IκBα blocked HIMF-induced NF-κB activation and attenuated HIMF-induced VEGF production.

Conclusion

These results suggest that HIMF enhances VEGF production in mouse lung epithelial cells in a PI-3K/Akt-NF-κB signaling pathway-dependent manner, and may play critical roles in pulmonary angiogenesis.

Effects of polycyclic aromatic hydrocarbons (PAHs) on vascular endothelial growth factor induction through phosphatidylinositol 3-kinase/AP-1-dependent, HIF-1alpha-independent pathway

Previous studies have demonstrated that exposure to polycyclic aromatic hydrocarbons (PAHs) and its derivatives is associated with an increased risk of skin cancers, and the carcinogenic effect of PAHs is thought to involve both tumor initiation and promotion. Whereas PAH tumor initiation is well characterized, the mechanisms involved in the tumor promotion of PAHs remain elusive. In the present study, we investigated the effects of PAHs on vascular endothelial growth factor (VEGF) expression by comparison of its induction between the active metabolite and its parent compound (B[a]PDE versus B[a]P) or between active compound and its relatively inactive analog (5-MCDE versus CDE). We found that exposure of cells to (+/-)-anti-benzo-[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE) or (+/-)-anti-5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE) led to marked induction of VEGF in Cl41 cells, whereas benzo[a]pyrene (B[a]P) or chrysene-1,2-diol-3,4-epoxide (CDE) did not exhibit significant inductive effects. Exposure of cells to B[a]PDE and 5-MCDE did not induce HIF-1alpha activation, whereas AP-1 was significantly activated. Moreover, overexpression of TAM67 (a dominant-negative mutant c-Jun) dramatically blocked that VEGF induction. Electrophoretic mobility shift assay showed that AP-1 was only able to specifically recognize and bind to its AP-1 potential binding site within -1136 and -1115 of the VEGF promoter region. Site-directed mutation of this AP-1 binding site eliminated the VEGF transcriptional activity induced by B[a]PDE, suggesting that the AP-1 binding site between -1136 and -1115 in the VEGF promoter region is critical for VEGF induction by B[a]PDE. In addition, overexpression of Deltap85 (a dominant-negative mutant PI-3K) impaired B[a]PDE- and 5-MCDE-induced VEGF induction. Considering our previous findings that PI-3K is an upstream mediator for c-Jun/AP-1 activation, we conclude that the VEGF induction by B[a]PDE and 5-MCDE is through PI-3K/AP-1-dependent and HIF-1alpha-independent pathways. These findings may help us to understand the mechanisms involved in PAH carcinogenic effects.

Essential roles of PI-3K/Akt/IKKbeta/NFkappaB pathway in cyclin D1 induction by arsenite in JB6 Cl41 cells

Skin is a major target of carcinogenic trivalent arsenic (arsenite, As3+). It has been thought that cell proliferation is one of the central events involved in the carcinogenic effect of arsenite. Cyclin D1, a nuclear protein playing a pivotal role in cell proliferation and cell cycle transition from G1 to S phases, has been reported to be induced in human fibroblast by arsenite via uncertain molecular mechanisms. In the present study, the potential roles of PI-3K/Akt/IKKbeta/NFkappaB signal pathway in cyclin D1 induction by arsenite were addressed in mouse epidermal Cl41 cells. We found that exposure of Cl41 cells to arsenite was able to induce cell proliferation, activate PI-3K-->Akt/p70(S6k) signal pathway and increase cyclin D1 expression at both transcription and protein levels. Pre-treatment of Cl41 cells with PI-3K inhibitor, wortmannin, significantly inhibited the phosphorylation of Akt and p70(S6k) and thereby dramatically impaired the cyclin D1 induction by arsenite, implicating the importance of the PI-3K signal pathway in the cyclin D1 induction by arsenite. Furthermore, inhibition of PI-3K/Akt by overexpression of Deltap85 or DN-Akt blocked arsenite-induced IKK phosphorylation, IkappaBalpha degradation and cyclin D1 expression, indicating that IKK/NFkappaB is the downstream transducer of arsenite-triggered PI-3K/Akt cascade. Moreover, inhibition of IKKbeta/NFkappaB signal pathway by overexpression of its dominant negative mutant, IKKbeta-KM, also significantly blocked arsenite-induced cyclin D1 expression. Overall, arsenite exposure triggered PI-3K/Akt/IKKbeta/NFkappaB signal cascade which in turn plays essential roles in inducing cyclin D1 expression.

Modulation of signal transduction by tea catechins and related phytochemicals

Epidemiologic studies in human populations and experimental studies in rodents provide evidence that green tea and its constituents can inhibit both the development and growth of tumors at a variety of tissue sites. In addition, EGCG, a major biologically active component of green tea, inhibits growth and induces apoptosis in a variety of cancer cell lines. The purpose of this paper is to review evidence that these effects are mediated, at least in part, through inhibition of the activity of specific receptor tyrosine kinases (RTKs) and related downstream pathways of signal transduction. We also review evidence indicating that the antitumor effects of the related polyphenolic phytochemicals resveratrol, genistein, curcumin, and capsaicin are exerted via similar mechanisms. Some of these agents (EGCG, genistein, and curcumin) appear to directly target specific RTKs, and all of these compounds cause inhibition of the activity of the transcription factors AP-1 and NF-kappaB, thus inhibiting cell proliferation and enhancing apoptosis. Critical areas of future investigation include: (1) identification of the direct molecular target(s) of EGCG and related polyphenolic compounds in cells; (2) the in vivo metabolism and bioavailability of these compounds; (3) the ancillary effects of these compounds on tumor-stromal interactions; (4) the development of synergistic combinations with other antitumor agents to enhance efficacy in cancer prevention and therapy, and also minimize potential toxicities.

Essential role of PI-3K, ERKs and calcium signal pathways in nickel-induced VEGF expression

Exposure to a highly nickel-polluted environment has the potential to cause a variety of adverse health effects, such as the respiratory tract cancers. Since numerous studies have demonstrated that nickel generally has weak mutagenic activity, research focus had turned to cell signalling activation leading to gene modulation and epigenetic changes as a plausible mechanism of carcinogenesis. Previous studies have revealed that nickel compounds can induce the expression of vascular endothelial growth factor (VEGF), which is a key mediator of angiogenesis both in physiological and pathologic conditions. In the present study, we investigated the potential roles of PI-3K, ERKs, p38 kinase and calcium signalling in VEGF induction by nickel in Cl 41 cells. Exposure of Cl 41 cells to nickel compounds led to VEGF induction in both time- and dose-dependent manners. Pre-treatment of Cl 41 cells with PI-3K inhibitor, wortmannin or Ly294002, resulted in a striking inhibition of VEGF induction by nickel compounds, implicating the role of PI-3K in the induction. However, mTOR, one of downstream molecules of PI-3K, may not contribute to the induction because pre-treatment of Cl 41 cells with its inhibitor, rapamycin, did not show obvious decrease in nickel-induced VEGF expression. Furthermore, pre-treatment of Cl 41 cells with MEK1/2-ERKs pathway inhibitor, PD98059, significantly inhibited VEGF induction by both NiCl2 and Ni3S2, whereas p38 kinase inhibitor, SB202190, did not impair the induction. Pre-treatment of Cl 41 cells with intracellular calcium chelator, but not calcium channel blocker, inhibited VEGF induction by nickel. Collectively these data demonstrate that PI-3K, ERKs and cytosolic calcium, but not p38 kinase, play essential roles in VEGF induction by nickel compounds.

Involvement of protein kinase C in crystalline silica-induced activation of the MAP kinase and AP-1 pathway

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.

Loss of Tumor Suppressor p53 Decreases PTEN Expression and Enhances Signaling Pathways Leading to Activation of Activator Protein 1 and Nuclear Factor κB Induced by UV Radiation

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.