Deregulated expression of human c-jun transforms primary rat embryo cells in cooperation with an activated c-Ha-ras gene and transforms rat-1a cells as a single gene

The m7G Reader NCBP2 Promotes Pancreatic Cancer Progression by Upregulating MAPK/ERK Signaling

PDAC is one of the most common malignant tumors worldwide. The difficulty of early diagnosis and lack of effective treatment are the main reasons for its poor prognosis. Therefore, it is urgent to identify novel diagnostic and therapeutic targets for PDAC patients. The m7G methylation is a common type of RNA modification that plays a pivotal role in regulating tumor development. However, the correlation between m7G regulatory genes and PDAC progression remains unclear. By integrating gene expression and related clinical information of PDAC patients from TCGA and GEO cohorts, m7G binding protein NCBP2 was found to be highly expressed in PDAC patients. More importantly, PDAC patients with high NCBP2 expression had a worse prognosis. Stable NCBP2-knockdown and overexpression PDAC cell lines were constructed to further perform in-vitro and in-vivo experiments. NCBP2-knockdown significantly inhibited PDAC cell proliferation, while overexpression of NCBP2 dramatically promoted PDAC cell growth. Mechanistically, NCBP2 enhanced the translation of c-JUN, which in turn activated MEK/ERK signaling to promote PDAC progression. In conclusion, our study reveals that m7G reader NCBP2 promotes PDAC progression by activating MEK/ERK pathway, which could serve as a novel therapeutic target for PDAC patients.

[Steps to Regulatory Science]

The research achievements in the field of regulatory science from the beginning of my research are described in an overview. First, I was interested in the complexity of development and pursued my studies on the mechanisms of DNA replication and repair, the mutagenicity of air pollutants, and the oncogene. After researching new phenomena based on the discovery of basic research in molecular/biochemistry, my research interests turned to the field of regulatory science which applies scientific evidence to social systems. I was able to successfully contribute to the field of drinking water quality in Japan through the establishment of drinking water quality standards and standard values, primarily for organic and agricultural chemicals, the development of analysis techniques, and the creation of an organization for ensuring safety. Research on the water quality in public water areas, which are also the sources of drinking water, was another subject in which I was involved. I took part in developing the concept and evaluation methodology for the environmental impact assessment of active pharmaceutical ingredients as well as conducting environmental monitoring on urban rivers in Japan. I have also been engaged in studies on the security and safety of human health with an ecosystem conservation background. It has been a great pleasure to collaborate on research projects with so many people toward a common aim.

Selective antagonism of cJun for cancer therapy

The activator protein-1 (AP-1) family of transcription factors modulate a diverse range of cellular signalling pathways into outputs which can be oncogenic or anti-oncogenic. The transcription of relevant genes is controlled by the cellular context, and in particular by the dimeric composition of AP-1. Here, we describe the evidence linking cJun in particular to a range of cancers. This includes correlative studies of protein levels in patient tumour samples and mechanistic understanding of the role of cJun in cancer cell models. This develops an understanding of cJun as a focal point of cancer-altered signalling which has the potential for therapeutic antagonism. Significant work has produced a range of small molecules and peptides which have been summarised here and categorised according to the binding surface they target within the cJun-DNA complex. We highlight the importance of selectively targeting a single AP-1 family member to antagonise known oncogenic function and avoid antagonism of anti-oncogenic function.

CREB acts as a common transcription factor for major epigenetic repressors; DNMT3B, EZH2, CUL4B and E2F6

CREB signaling is known for several decades, but how it regulates both positive and negative regulators of cell proliferation is not well understood. On the other hand functions of major epigenetic repressors such as DNMT3B, EZH2 and CUL4B for their repressive epigenetic modifications on chromatin have also been well studied. However, there is very limited information available on how these repressors are regulated at their transcriptional level. Here, using computational tools and molecular techniques including site directed mutagenesis, promoter reporter assay, chromatin immunoprecipitation (ChIP), we identified that CREB acts as a common transcription factor for DNMT3B, EZH2, CUL4B and E2F6. ChIP assay revealed that pCREB binds to promoters of these repressors at CREs and induce their transcription. As expected, the expression of these repressors and their associated repressive marks particularly H3K27me3 and H2AK119ub are increased and decreased upon CREB overexpression and knock-down conditions respectively in the cancer cells indicating that CREB regulates the functions of these repressors by activating their transcription. Since CREB and these epigenetic repressors are overexpressed in various cancer types, our findings showed the molecular relationship between them and indicate that CREB is an important therapeutic target for cancer therapy.

The Emerging Role of Estrogens in Thyroid Redox Homeostasis and Carcinogenesis

Reactive oxygen species (ROS) are the most critical class of free radicals or reactive metabolites produced by all living organisms. ROS regulate several cellular functions through redox-dependent mechanisms, including proliferation, differentiation, hormone synthesis, and stress defense response. However, ROS overproduction or lack of appropriate detoxification is harmful to cells and can be linked to the development of several diseases, such as cancer. Oxidative damage in cellular components, especially in DNA, can promote the malignant transformation that has already been described in thyroid tissue. In thyrocyte physiology, NADPH oxidase enzymes produce large amounts of ROS that are necessary for hormone biosynthesis and might contribute to the high spontaneous mutation rate found in this tissue. Thyroid cancer is the most common endocrine malignancy, and its incidence is significantly higher in women than in men. Several lines of evidence suggest the sex hormone estrogen as a risk factor for thyroid cancer development. Estrogen in turn, besides being a potent growth factor for both normal and tumor thyroid cells, regulates different mechanisms of ROS generation. Our group demonstrated that the thyroid gland of adult female rats exhibits higher hydrogen peroxide (H₂O₂) production and lower enzymatic antioxidant defense in comparison with male glands. In this review, we discuss the possible involvement of thyroid redox homeostasis and estrogen in the development of thyroid carcinogenesis.

Role of C-Jun N-terminal Kinase in Hepatocellular Carcinoma Development

Hepatocellular carcinoma (HCC) is among the most frequently occurring cancers and the leading causes of cancer mortality worldwide. Identification of the signaling pathways regulating liver carcinogenesis is critical for developing novel chemoprevention and targeted therapies. C-Jun N-terminal kinase (JNK) is a member of a larger group of serine/threonine (Ser/Thr) protein kinases known as the mitogen-activated protein kinase (MAPK) family. JNK is an important signaling component that converts external stimuli into a wide range of cellular responses, including cell proliferation, differentiation, survival, migration, invasion, and apoptosis, as well as the development of inflammation, fibrosis, cancer growth, and metabolic diseases. Because of the essential roles of JNK in these cellular functions, deregulated JNK is often found to contribute to the development of HCC. Recently, the functions and molecular mechanisms of JNK in HCC development have been addressed using mouse models and human HCC cell lines. Furthermore, recent studies demonstrate that the activation of JNK by oncogenes can promote the development of cancers by regulating the transforming growth factor (TGF)-β/Smad pathway, which makes the oncogenes/JNK/Smad signaling pathway an attractive target for cancer therapy. Additionally, JNK-targeted therapy has a broad potential for clinical applications. In summary, we are convinced that promising new avenues for the treatment of HCC by targeting JNK are on the horizon, which will undoubtedly lead to better, more effective, and faster therapies in the years to come.

Dual c-Jun N-terminal kinase-cyclin D1 and extracellular signal-related kinase-c-Jun disjunction in human melanoma

BACKGROUND

Activity of both c-Jun and cyclin D1 is deemed critical for melanoma cell proliferation. This functionality is corroborated by frequently elevated expression and activity of these proteins in human melanomas. Correspondingly, alleviating c-Jun and cyclin D1 function is vital to the success of antimelanoma therapeutics.

OBJECTIVES

To understand the role of the c-Jun N-terminal kinase (JNK) signalling pathway in melanoma cell proliferation and survival.

METHODS

The effect of JNK inhibitors SP600125 and JNK-IN-8 on the proliferation and survival of genetically highly representative human melanoma cell lines was studied in assays of proliferation and apoptosis. Changes in c-Jun and cyclin D1 protein and mRNA levels in response to JNK and mitogen-activated protein kinase kinase (MEK) inhibition were investigated through immunoblotting and quantitative reverse-transcription polymerase chain reaction. The effects of JNK and MEK inhibitors on cell-cycle distribution were assessed by flow cytometry.

RESULTS

We demonstrate the requirement of JNK signalling in melanoma cell proliferation and survival. While JNK inhibition suppressed the expression and activity of c-Jun, it failed to suppress cyclin D1 levels. Consistently with its inability to downregulate cyclin D1, JNK inhibition failed to induce G1 arrest. In contrast, the blockade of MEK-extracellular signal-regulated kinase (ERK) signalling, although unable to suppress c-Jun activity and expression, paradoxically abated cyclin D1 levels and triggered G1 arrest. This previously unreported dual disconnect between JNK-cyclin D1 and ERK-c-Jun levels was confirmed by concomitant JNK and BRAF inhibition, which suppressed both c-Jun and cyclin D1 levels and exhibited a heightened antiproliferative response.

CONCLUSIONS

Dual disjunction between JNK-cyclin D1 and ERK-c-Jun signalling forms the basis for further investigation of combined JNK and MAPK signalling blockade as a more effective therapeutic approach in human melanoma.

Polyphenol Compound as a Transcription Factor Inhibitor

A target-based approach has been used to develop novel drugs in many therapeutic fields. In the final stage of intracellular signaling, transcription factor–DNA interactions are central to most biological processes and therefore represent a large and important class of targets for human therapeutics. Thus, we focused on the idea that the disruption of protein dimers and cognate DNA complexes could impair the transcriptional activation and cell transformation regulated by these proteins. Historically, natural products have been regarded as providing the primary leading compounds capable of modulating protein–protein or protein-DNA interactions. Although their mechanism of action is not fully defined, polyphenols including flavonoids were found to act mostly as site-directed small molecule inhibitors on signaling. There are many reports in the literature of screening initiatives suggesting improved drugs that can modulate the transcription factor interactions responsible for disease. In this review, we focus on polyphenol compound inhibitors against dimeric forms of transcription factor components of intracellular signaling pathways (for instance, c-jun/c-fos (Activator Protein-1; AP-1), c-myc/max, Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and β-catenin/T cell factor (Tcf)).

Elevated DDX21 regulates c-Jun activity and rRNA processing in human breast cancers

INTRODUCTION

The DDX21 RNA helicase has been shown to be a nucleolar and nuclear protein involved in ribosome RNA processing and AP-1 transcription. DDX21 is highly expressed in colon cancer, lymphomas, and some breast cancers, but little is known about how DDX21 might promote tumorigenesis.

METHODS

Immunohistochemistry was performed on a breast cancer tissue array of 187 patients. In order to study the subcellular localization of DDX21 in both tumor tissue and tumor cell lines, indirect immunofluorescence was applied. The effect of DDX21 knockdown was measured by cellular apoptosis, rRNA processing assays, soft agar growth and mouse xenograft imaging. AP-1 transcriptional activity was analyzed with a luciferase reporter and bioluminescence imaging, as well as qRT-PCR analysis of downstream target, cyclin D1, to determine the mechanism of action for DDX21 in breast tumorigenesis.

RESULTS

Herein, we show that DDX21 is highly expressed in breast cancer tissues and established cell lines. A significant number of mammary tumor tissues and established breast cancer cell lines exhibit nuclear but not nucleolar localization of DDX21. The protein expression level of DDX21 correlates with cell proliferation rate and is markedly induced by EGF signaling. Mechanistically, DDX21 is required for the phosphorylation of c-Jun on Ser73 and DDX21 deficiency markedly reduces the transcriptional activity of AP-1. Additionally, DDX21 promotes rRNA processing in multiple breast cancer cell lines. Tumor cells expressing high levels of endogenous DDX21 undergo apoptosis after acute DDX21 knockdown, resulting in significant reduction of tumorigenicity in vitro and in vivo.

CONCLUSIONS

Our findings indicate that DDX21 expression in breast cancer cells can promote AP-1 activity and rRNA processing, and thus, promote tumorigenesis by two independent mechanisms. DDX21 could serve as a marker for a subset of breast cancer patients with higher proliferation potential and may be used as a therapeutic target for a subset of breast cancer patients.

The 2 Faces of JNK Signaling in Cancer

c-Jun NH2-terminal kinase (JNK) was discovered almost 20 years ago as the protein kinase responsible for phosphorylating c-Jun at Ser-63 and Ser-73. These sites had previously been demonstrated to be essential for the stimulation of c-Jun activity and for cooperation with Ha-ras in oncogenic transformation. This led to the idea that JNK was a positive regulator of cellular transformation. However, the analysis of jnk gene deletion in various mouse models of cancer has produced conflicting findings, with some studies supporting the pro-oncogenic function of JNK and others providing evidence that JNK acts as a tumor suppressor. This review will discuss how these unexpected findings have increased our understanding of the role of JNK signaling in cancer and have provided a source of new working hypotheses.

Radiation-induced acid ceramidase confers prostate cancer resistance and tumor relapse

Escape of prostate cancer (PCa) cells from ionizing radiation-induced (IR-induced) killing leads to disease progression and cancer relapse. The influence of sphingolipids, such as ceramide and its metabolite sphingosine 1-phosphate, on signal transduction pathways under cell stress is important to survival adaptation responses. In this study, we demonstrate that ceramide-deacylating enzyme acid ceramidase (AC) was preferentially upregulated in irradiated PCa cells. Radiation-induced AC gene transactivation by activator protein 1 (AP-1) binding on the proximal promoter was sensitive to inhibition of de novo ceramide biosynthesis, as demonstrated by promoter reporter and ChIP-qPCR analyses. Our data indicate that a protective feedback mechanism mitigates the apoptotic effect of IR-induced ceramide generation. We found that deregulation of c-Jun induced marked radiosensitization in vivo and in vitro, which was rescued by ectopic AC overexpression. AC overexpression in PCa clonogens that survived a fractionated 80-Gy IR course was associated with increased radioresistance and proliferation, suggesting a role for AC in radiotherapy failure and relapse. Immunohistochemical analysis of human PCa tissues revealed higher levels of AC after radiotherapy failure than those in therapy-naive PCa, prostatic intraepithelial neoplasia, or benign tissues. Addition of an AC inhibitor to an animal model of xenograft irradiation produced radiosensitization and prevention of relapse. These data indicate that AC is a potentially tractable target for adjuvant radiotherapy.

p21-activated kinase 3 (PAK3) is an AP-1 regulated gene contributing to actin organisation and migration of transformed fibroblasts

Activating Protein 1 (AP-1) plays a vital role in cell proliferation, differentiation and apoptosis. While de-regulation of AP-1 has been linked to many cancers, little is known regarding its downstream transcriptional targets that associate with cellular transformation. Previous studies identified PAK3, a serine/threonine kinase, as a potential AP-1 target gene. PAK3 has been implicated in a variety of pathological disorders and over-expression of other PAK-family members has been linked to cancer. In this study, we investigate AP-1 regulation of PAK3 expression and the role of PAK3 in cJun/AP-1-associated cellular transformation. Our results showed elevated PAK3 expression at both the mRNA and protein level in cJun-over-expressing Rat1a fibroblasts, as well as in transformed human fibroblasts. Elevated PAK3 expression in cJun/AP-1 over-expressing cells associated with a significant increase in PAK3 promoter activation. This increased promoter activity was lost when a single putative Jun binding site, which can bind AP-1 directly both in vitro and in vivo, was mutated. Further, inhibition of PAK3 using siRNA showed a regression in the cell morphology, migratory potential and actin organisation associated with AP-1 transformed cells. Our study is a first to describe a role for AP-1 in regulating PAK3 expression and suggest that PAK3 is an AP-1 target required for actin organization and migration observed in transformed cells.

AP1 transcription factors in epidermal differentiation and skin cancer

AP1 (jun/fos) transcription factors (c-jun, junB, junD, c-fos, FosB, Fra-1, and Fra-2) are key regulators of epidermal keratinocyte survival and differentiation and important drivers of cancer development. Understanding the role of these factors in epidermis is complicated by the fact that each protein is expressed, at different levels, in multiple cells layers in differentiating epidermis, and because AP1 transcription factors regulate competing processes (i.e., proliferation, apoptosis, and differentiation). Various in vivo genetic approaches have been used to study these proteins including targeted and conditional knockdown, overexpression, and expression of dominant-negative inactivating AP1 transcription factors in epidermis. Taken together, these studies suggest that individual AP1 transcription factors have different functions in the epidermis and in cancer development and that altering AP1 transcription factor function in the basal versus suprabasal layers differentially influences the epidermal differentiation response and disease and cancer development.

Mixed lineage kinase 3 is required for matrix metalloproteinase expression and invasion in ovarian cancer cells

Mixed lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase (MAP3K) that activates MAPK signaling pathways and regulates cellular responses such as proliferation, migration and apoptosis. Here we report high levels of total and phospho-MLK3 in ovarian cancer cell lines in comparison to immortalized nontumorigenic ovarian epithelial cell lines. Using small interfering RNA (siRNA)-mediated gene silencing, we determined that MLK3 is required for the invasion of SKOV3 and HEY1B ovarian cancer cells. Furthermore, mlk3 silencing substantially reduced matrix metalloproteinase (MMP)-1, -2, -9 and -12 gene expression and MMP-2 and -9 activities in SKOV3 and HEY1B ovarian cancer cells. MMP-1, -2, -9 and-12 expression, and MLK3-induced activation of MMP-2 and MMP-9 requires both extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) activities. In addition, inhibition of activator protein-1 (AP-1) reduced MMP-1, MMP-9 and MMP-12 gene expression. Collectively, these findings establish MLK3 as an important regulator of MMP expression and invasion in ovarian cancer cells.

JunD/AP-1-mediated gene expression promotes lymphocyte growth dependent on interleukin-7 signal transduction

Interleukin-7 (IL-7) is an essential cytokine for lymphocyte growth that has the potential for promoting immune reconstitution. This feature makes IL-7 an ideal candidate for therapeutic development. As with other cytokines, signaling through the IL-7 receptor induces the JAK/STAT pathway. However, the broad scope of IL-7 regulatory targets likely necessitates the use of other signaling components whose identities remain poorly defined. To this end, we used an IL-7 dependent T-cell line to examine how expression of the glycolytic enzyme, Hexokinase II (HXKII) was regulated by IL-7 in a STAT5-independent manner. Our studies revealed that IL-7 promoted the activity of JNK (Jun N-terminal Kinase), and that JNK, in turn, drove the expression of JunD, a component of the Activating Protein 1 (AP-1) transcription factors. Gel shifts showed that the AP-1 complex induced by IL-7 contained JunD but not c-Fos or c-Jun. Inhibition of JNK/JunD blocked glucose uptake and HXKII gene expression, indicating that this pathway was responsible for promoting HXKII expression. Because others had shown that JunD was a negative regulator of cell growth, we performed a bioinformatics analysis to uncover possible JunD-regulated gene targets. Our search revealed that JunD could control the expression of proteins involved in signal transduction, cell survival and metabolism. One of these growth promoters was the oncogene, Pim-1. Pim-1 is an IL-7-induced protein that was inhibited when the activities of JNK or JunD were blocked, showing that in IL-7 dependent T-cells JunD can promote positive signals transduced through Pim-1. This was confirmed when the IL-7-induced proliferation of CD8 T-cells was impaired upon JunD inhibition. These results show that engagement of the IL-7 receptor drives a signal that is more complex than the JAK/STAT pathway, activating JNK and JunD to induce rapid growth stimulation through the expression of metabolic and signaling factors like HXKII and Pim-1.

Insulin resistance and hepatocarcinogenesis

Hepatocellular carcinoma (HCC) accounts for 85-90% of liver cancers and is one of the most frequent carcinomas in the world. HCCs classically develop against the background of chronic liver diseases. Common causes of such liver diseases are viral hepatitis, alcoholic hepatitis, or immune-related diseases; however, 15-50% of patients with HCCs have none of these classic antecedents, especially in developed countries. In this context, obesity and diabetes mellitus have been found to exhibit an increased risk of HCC. Both conditions are associated with insulin resistance. The tumorigenic effects of insulin resistance and complementary hyperinsulinemia could be mediated directly by insulin signaling, or indirectly related to changes in endogeneous hormone metabolism, particularly insulin-like growth factor I. Conversely, insulin resistance may be a consequence of obesity and hepatic inflammation, both of which can themselves promote tumorigenesis, mainly through cytokine production and/or generation of oxidative stress. Because the prevalence of obesity is now increasing throughout the world, insulin resistance is sure to be emphasized as a major factor in hepatocarcinogenesis in the foreseeable future.

AP1 factor inactivation in the suprabasal epidermis causes increased epidermal hyperproliferation and hyperkeratosis but reduced carcinogen-dependent tumor formation

Activator protein one (AP1) (jun/fos) factors comprise a family of transcriptional regulators (c-jun, junB, junD, c-fos, FosB, Fra-1 and Fra-2) that are key controllers of epidermal keratinocyte survival and differentiation, and are important drivers of cancer development. Understanding the role of these factors in epidermis is complicated by the fact that each member is expressed in defined cell layers during epidermal differentiation, and because AP1 factors regulate competing processes (that is, proliferation, apoptosis and differentiation). We have proposed that AP1 factors function differently in basal versus suprabasal epidermis. To test this, we inactivated suprabasal AP1 factor function in mouse epidermis by targeted expression of dominant-negative c-jun (TAM67), which inactivates function of all AP1 factors. This produces increased basal keratinocyte proliferation, delayed differentiation and extensive hyperkeratosis. These findings contrast with previous studies showing that basal layer AP1 factor inactivation does not perturb resting epidermis. It is interesting that in spite of extensive keratinocyte hyperproliferation, susceptibility to carcinogen-dependent tumor induction is markedly attenuated. These novel observations strongly suggest that AP1 factors have distinct roles in the basal versus suprabasal epidermis, confirm that AP1 factor function is required for normal terminal differentiation, and suggest that AP1 factors have a different role in normal epidermis versus cancer progression.

Chapter 9: Oxidative stress in malignant progression: The role of Clusterin, a sensitive cellular biosensor of free radicals

Clusterin/Apolipoprotein J (CLU) gene is expressed in most human tissues and encodes for two protein isoforms; a conventional heterodimeric secreted glycoprotein and a truncated nuclear form. CLU has been functionally implicated in several physiological processes as well as in many pathological conditions including ageing, diabetes, atherosclerosis, degenerative diseases, and tumorigenesis. A major link of all these, otherwise unrelated, diseases is that they are characterized by increased oxidative injury due to impaired balance between production and disposal of reactive oxygen or nitrogen species. Besides the aforementioned diseases, CLU gene is differentially regulated by a wide variety of stimuli which may also promote the production of reactive species including cytokines, interleukins, growth factors, heat shock, radiation, oxidants, and chemotherapeutic drugs. Although at low concentration reactive species may contribute to normal cell signaling and homeostasis, at increased amounts they promote genomic instability, chronic inflammation, lipid oxidation, and amorphous aggregation of target proteins predisposing thus cells for carcinogenesis or other age-related disorders. CLU seems to intervene to these processes due to its small heat-shock protein-like chaperone activity being demonstrated by its property to inhibit protein aggregation and precipitation, a main feature of oxidant injury. The combined presence of many potential regulatory elements in the CLU gene promoter, including a Heat-Shock Transcription Factor-1 and an Activator Protein-1 element, indicates that CLU gene is an extremely sensitive cellular biosensor of even minute alterations in the cellular oxidative load. This review focuses on CLU regulation by oxidative injury that is the common molecular link of most, if not all, pathological conditions where CLU has been functionally implicated.

Single- and multi-wall carbon nanotubes versus asbestos: are the carbon nanotubes a new health risk to humans?

Carbon nanotubes (CNT), since their discovery, have become one of the most promising nanomaterials in many industrial and biomedical applications. Due to their unique physicochemical properties, interest is growing in the manufacture of CNT-based products and their subsequent marketing. Since their discovery, the prospect of possible undesirable human health effects has been a focus of many scientific studies. Although CNT possess unique physical properties that include (1) nanoscale diameter, (2) a wide length distribution ranging from tens of nanometers to several micrometers, and (3) high aspect ratio, the fibrous-like shape and durability suggest that their toxic properties may be analogous to those observed with other fibrous particles, such as asbestos. The present study provides a summary of published findings on CNT bioactivity, such as the potential of CNT, especially of multi-wall carbon nanotubes (MWCNT), to activate signaling pathways modulating transcription factor activity, induce apoptosis, induce DNA damage, and initiate biological responses. Assessment of risks to human health and adoption of appropriate exposure controls is critical for the safe and successful introduction of CNT -based products for future applications.

Cooperation between GLI and JUN enhances transcription of JUN and selected GLI target genes

Sustained Hedgehog (HH) signaling is implicated in basal cell carcinoma of the skin and other types of cancer. Here we show that GLI1 and GLI2, the main transcriptional activators of the HH pathway, directly regulate expression of the activator protein 1 (AP-1) family member JUN, a transcription factor controlling keratinocyte proliferation and skin homeostasis. Activation of the JUN promoter by GLI is dependent on a GLI-binding site and the AP-1 sites known to be involved in self-activation of JUN. Transcription of JUN is greatly enhanced in the presence of GLI and requires activated JUN protein. GLI2act is a more potent activator than GLI1 in these experiments and physical interaction with phosphorylated JUN was only detected for GLI2act. The synergistic effect of GLI and JUN extends to the activation of further GLI target genes as shown by shRNA-mediated knockdown of JUN in human keratinocytes. Some of these cooperatively activated genes are involved in cell-cycle progression, which is consistent with a significant reduction of the proliferative potential of GLI in the absence of JUN. These results suggest a novel connection between HH/GLI pathway activity and JUN, which may contribute to the oncogenic activity of HH/GLI signaling in skin.

Simultaneous blockade of AP-1 and phosphatidylinositol 3-kinase pathway in non-small cell lung cancer cells

c-Jun is a major constituent of AP-1 transcription factor that transduces multiple mitogen growth signals, and it is frequently overexpressed in non-small cell lung cancers (NSCLCs). Earlier, we showed that blocking AP-1 by the overexpression of a c-Jun dominant-negative mutant, TAM67, inhibited NSCLC cell growth. The phosphatidylinositol 3-kinase (PI3K)/Akt signal transduction pathway is important in transformation, proliferation, survival and metastasis of NSCLC cells. In this study, we used NCI-H1299 Tet-on clone cells that express TAM67 under the control of inducible promoter to determine the effects of inhibition of AP-1 and PI3K on cell growth. The PI3K inhibitor, LY294002, produced a dose-dependent inhibition of growth in H1299 cells and that inhibition was enhanced by TAM67. TAM67 increased dephosphorylation of Akt induced by LY294002 and reduced the TPA response element DNA-binding of phosphorylated c-Jun. TAM67 increased G1 cell cycle blockade induced by LY294002, which was partially associated with cyclin A decrease and p27^Kip1 accumulation. Furthermore, TAM67 and LY294002 act, at least additively, to inhibit anchorage-independent growth of the H1299 cells. These results suggest that AP-1 and PI3K/Akt pathways play an essential role in the growth of some NSCLC cells.

Clinicopathological significance of expression of p-c-Jun, TCF4 and beta-Catenin in colorectal tumors

Background

A recent study has shown that phosphorylated c-Jun (p-c-Jun) interacts with TCF4 to form a complex that cooperatively enhances their transcriptional activity in the presence of β-Catenin, and that their interaction is critical for mouse intestinal tumorigenesis. To determine the significance of these three proteins in human colorectal tumors, we analyzed their nuclear expression by immunohistochemistry.

Methods

we analyzed their nuclear expression by immunohistochemistry using paraffin-embedded specimens of 68 resected colorectal tumors, which consisted of 19 adenomas, 14 high-grade intraepithelial neoplasia (HGINs) and 35 adenocarcinomas. We also analyzed the expression of MMP7, which has functional AP-1 and TCF binding sites in its promoter.

Results

Expression of p-c-Jun, TCF4 and β-Catenin were significantly higher in adenomas than in the adjacent normal epithelia. Expression of p-c-Jun and β-Catenin in HGINs and adenocarcinomas were also significantly higher than in the adjacent normal epithelia. p-c-Jun expression, but not TCF4 and β-Catenin, was higher in adenomas and HGINs than in adenocarcinomas, in which p-c-Jun expression was negatively correlated with pT stage progression. Furthermore, significant correlations of expression were observed between p-c-Jun and TCF4 (r = 0.25, p = 0.04), TCF4 and β-Catenin (r = 0.30, p = 0.01), p-c-Jun and MMP7 (r = 0.26, p = 0.03), and TCF4 and MMP7 (r = 0.39, p = 0.0008), respectively.

Conclusion

These results suggest that nuclear expression of p-c-Jun, TCF4 and β-Catenin have important roles in human colorectal tumor development and that p-c-Jun may play a pivotal role in the earlier stages of tumor development.

Epidermal growth factor receptor 1 (EGFR1) and its variant EGFRvIII regulate TATA-binding protein expression through distinct pathways

The epidermal growth factor receptor (EGFR) family regulates essential biological processes. Various epithelial tumors are linked to EGFR overexpression or expression of variant forms, such as the EGFR1 variant, EGFRvIII. Perturbations in expression of the transcription initiation factor, TATA-binding protein (TBP), alter cellular growth properties. Here we demonstrate that EGFR1 and EGFRvIII, but not HER2, induce TBP expression at a transcriptional level through distinct mechanisms. EGFR1 enhances the phosphorylation and function of Elk-1, recruiting it to the TBP promoter. In contrast, EGFRvIII robustly induces c-jun expression, stimulating recruitment of c-fos/c-jun to an overlapping AP-1 site. Enhancing c-jun expression alone induces TBP promoter activity through the AP-1 site. To determine the underlying mechanism for differences in Elk-1 function and c-jun expression by these receptors, we inhibited the internalization of EGFR1. Persistent EGFR1 cell surface occupancy mimics EGFRvIII-mediated effects on Elk-1 and c-jun and switches the requirement of Elk-1 to AP-1 for TBP promoter induction. Together, these studies define a new molecular mechanism for the regulation of TBP expression. In addition, we identify distinct molecular targets of EGFR1 and EGFRvIII and demonstrate the importance of receptor internalization in distinguishing their specific functions.

Growth inhibition of non-small cell lung cancer cells by AP-1 blockade using a cJun dominant-negative mutant

cJun, a major constituent of AP-1 transcription factor transducing multiple mitogen growth signals, is frequently overexpressed in non-small cell lung cancers (NSCLCs). The purpose of this study is to determine the effects of AP-1 blockade on the growth of NSCLC cells using a cJun dominant-negative mutant, TAM67. Transiently transfected TAM67 inhibited AP-1 transcriptional activity in NSCLC cell lines, NCI-H1299 (H1299), A549 and NCI-H520 (H520). The colony-forming efficiency of H1299 and A549 was reduced by TAM67, while that of H520 was not. To elucidate the effects of TAM67 on the growth of H1299, we established H1299 clone cells that expressed TAM67 under the control of a doxycycline-inducible promoter. In the H1299 clone cells, the induced TAM67 inhibited anchorage-dependent growth by promoting G1 cell-cycle block, but not by apoptosis. The induced TAM67 decreased the expression of a cell-cycle regulatory protein, cyclin A. TAM67 also inhibited anchorage-independent growth of these cells. Furthermore, TAM67 reduced growth of established xenograft tumours from these cells in nude mice. These results suggest that AP-1 plays an essential role in the growth of at least some of NSCLC cells.

Oncogenicity of DNA in vivo: tumor induction with expression plasmids for activated H-ras and c-myc

All vaccines and other biological products contain contaminating residual DNA derived from the production cell substrate. Whether this residual cell-substrate DNA can induce tumors in vaccine recipients and thus represent a risk factor has been debated for over 50 years without resolution. As a first step in resolving this issue, we have generated expression plasmids for the activated human H-ras oncogene and for the murine c-myc proto-oncogene. Their oncogenic activity was confirmed in vitro using the focus-formation transformation assay. Two strains of adult and newborn immune-competent mice were inoculated with different amounts of either plasmid alone or with a combination of the H-ras and c-myc plasmids. Tumors developed only in mice inoculated with both plasmids and only at the highest amount of DNA (12.5 microg of each plasmid). The NIH Swiss mouse was more sensitive than the C57BL/6 mouse, and newborn animals were more sensitive than adults. Cell lines were established from the tumors. PCR and Southern hybridization analyses demonstrated that both inoculated oncogenes were present in all of the tumor-derived cell lines and that the cells in the tumors were clonal. Western analysis demonstrated that both oncoproteins were expressed in these cell lines. These results demonstrate that cellular oncogenes can induce tumors following subcutaneous inoculation. Such information provides a possible way of evaluating and estimating the theoretical oncogenic risk posed by residual cell-substrate DNA in vaccines.

fos-jun conspiracy: implications for the cell

Two nuclear oncoproteins, fos and jun (AP-1), cooperate in forming a very stable heterodimeric complex that binds to the AP-1 site on DNA with high affinity. The 'leucine zipper' domain of both fos and jun is necessary for the formation of this heterodimer. Mutations of single residues within the leucine zipper domain have no effect on protein complex formation. However, results from mutagenesis of the first leucine of the heptad repeat in either fos or jun basic regions and alteration of the spacing between the basic and leucine zipper domains indicate that the basic region of fos plays a crucial role in determining the DNA binding affinity of the transcriptional complex. Mutations of the basic amino acids in fos protein prevent binding to the tumour promoter response element (TRE) in the presence of wild-type jun protein. Thus fos protein appears to be dominant in jun-fos binding to DNA, even though fos alone cannot bind to TRE. Mutants in the basic region of fos and jun can be exploited as dominant-negative mutants to ablate the normal fos cellular function.

Critical role of c-Jun overexpression in liver metastasis of human breast cancer xenograft model

Background

c-Jun/AP-1 has been linked to invasive properties of aggressive breast cancer. Recently, it has been reported that overexpression of c-Jun in breast cancer cell line MCF-7 resulted in increased AP-1 activity, motility and invasiveness of the cells in vitro and tumor formation in nude mice. However, the role of c-Jun in metastasis of human breast cancer in vivo is currently unknown.

Methods

To further investigate the direct involvement of c-Jun in tumorigenesis and metastasis, in the present study, the effects of c-Jun overexpression were studied in both in vitro and in nude mice.

Results

Ectopic overexpression of c-Jun promoted the growth of MCF-7 cells and resulted in a significant increase in the percentage of cells in S phase and increased motility and invasiveness. Introduction of c-Jun gene alone into weakly invasive MCF-7 cells resulted in the transfected cells capable of metastasizing to the nude mouse liver following tail vein injection.

Conclusion

The present study confirms that overexpression of c-Jun contributes to a more invasive phenotype in MCF-7 cells. It indicates an interesting relationship between c-Jun expression and increased property of adhesion, migration and in vivo liver metastasis of MCF-7/c-Jun cells. The results provide further evidence that c-Jun is involved in the metastasis of breast cancer. The finding also opens an opportunity for development of anti-c-Jun strategies in breast cancer therapy.

MAP kinase signalling pathways in cancer

Cancer can be perceived as a disease of communication between and within cells. The aberrations are pleiotropic, but mitogen-activated protein kinase (MAPK) pathways feature prominently. Here, we discuss recent findings and hypotheses on the role of MAPK pathways in cancer. Cancerous mutations in MAPK pathways are frequently mostly affecting Ras and B-Raf in the extracellular signal-regulated kinase pathway. Stress-activated pathways, such as Jun N-terminal kinase and p38, largely seem to counteract malignant transformation. The balance and integration between these signals may widely vary in different tumours, but are important for the outcome and the sensitivity to drug therapy.

Role of mitogen-activated protein kinase kinase 4 in cancer

Mitogen-activated protein (MAP) kinase kinase 4 (MKK4) is a component of stress activated MAP kinase signaling modules. It directly phosphorylates and activates the c-Jun N-terminal kinase (JNK) and p38 families of MAP kinases in response to environmental stress, pro-inflammatory cytokines and developmental cues. MKK4 is ubiquitously expressed and the targeted deletion of the Mkk4 gene in mice results in early embryonic lethality. Further studies in mice have indicated a role for MKK4 in liver formation, the immune system and cardiac hypertrophy. In humans, it is reported that loss of function mutations in the MKK4 gene are found in approximately 5% of tumors from a variety of tissues, suggesting it may have a tumor suppression function. Furthermore, MKK4 has been identified as a suppressor of metastasis of prostate and ovarian cancers. However, the role of MKK4 in cancer development appears complex as other studies support a pro-oncogenic role for MKK4 and JNK. Here we review the biochemical and functional properties of MKK4 and discuss the likely mechanisms by which it may regulate the steps leading to the formation of cancers.

Fra-1 a target for cancer prevention or intervention

The transcription factor activator protein-1 (AP-1) has been implicated as a driver of carcinogenesis since its original characterization. Oncogenic transcription factors like AP-1 are becoming new targets for cancer intervention. Inhibitors of AP-1 have been shown to block tumor promotion, transformation, progression and invasion. The Fos related antigen-1 (Fra-1) is activated in multiple cancers and gene ablation can suppress the invasive phenotypes of many tumor cell lines. This review focuses on the regulation of fosl1 expression, stabilization and activation of the Fra-1 polypeptide and on Fra-1-mediated tumorigenesis.

c-Jun activation is associated with proliferation and angiogenesis in invasive breast cancer

c-Jun is a component of the transcription factor activator protein 1 (AP-1), which binds and activates transcription at TRE/AP-1 elements. Extra- or intracellular signals, including growth factors, transforming oncoproteins, and UV irradiation, stimulate phosphorylation of c-Jun at serine 63/73 and activate c-Jun-dependent transcription. Therefore, activated c-Jun potentially plays an important role in carcinogenesis and cancer progression. To evaluate expression patterns of activated c-Jun in breast cancer in relation to angiogenesis and proliferation, we performed immunohistochemistry on 103 cases of invasive breast cancer with an antibody recognizing phosphorylated c-Jun at serine 73. Activated c-Jun showed a predominantly nuclear expression at the invasive front in 38% of invasive breast cancer cases. Furthermore, expression of activated c-Jun was seen in mitotic cells of the invasive front in 50% of cases. Occasionally, fibroblasts, endothelial cells, and benign breast cells showed nuclear expression. Activated nuclear c-Jun expression showed positive correlations with expression of hyperphosphorylated pRb, vascular endothelial growth factor, and with microvessel density. Mitotic c-Jun expression was associated with pRb and microvessel density. Stromal c-Jun expression showed positive relations with microvessel density. In survival analysis, no significant relation was found with activated c-Jun expression and survival, although a trend with poor survival was found for mitotic cells overexpressing activated c-Jun (P = .09). Our results show that activated c-Jun is predominantly expressed at the invasive front in breast cancer and is associated with proliferation and angiogenesis. Earlier studies have established a functional, in vitro link between activated c-Jun and tumor angiogenesis. Our present results in breast cancer patients confirm this relation in vivo for the first time. Therefore, c-Jun/AP-1 targeting may provide new ways to block tumor angiogenesis.

Cell context reveals a dual role for Maf in oncogenesis

Maf b-Zip transcription factors are involved in both terminal differentiation and oncogenesis. To investigate this apparent contradiction, we used two different primary cell types and performed an extensive analysis of transformation parameters induced by Maf proteins. We show that MafA and c-Maf are potent oncogenes in chicken embryo fibroblasts, while MafB appears weaker. We also provide the first evidence that MafA can confer growth factor independence and promote cell division at low density. Moreover, using MafA as a model, we identified several parameters that are critical for Maf transforming activities. Indeed, MafA ability to induce anchorage-independent cell growth was sensitive to culture conditions. In addition, the transforming activity of MafA was dependent on its phosphorylation state, since mutation on Ser65 impaired its ability to induce growth at low density and anchorage-independent growth. We next examined transforming activity of large Maf proteins in embryonic neuroretina cells, where they are known to induce differentiation. Unlike v-Jun, MafA, MafB and c-Maf did not show oncogenic activity in these cells. Moreover, they counteracted transformation induced by constitutive activation of the Ras/Raf/MEK pathway. Taken together, our results show that Maf proteins could display antagonistic functions in oncogenesis depending on the cellular context, and support a dual role for Maf as both oncogenes and tumor suppressor-like proteins.

Prognostic role of c-Jun activation in patients with areca quid chewing-related oral squamous cell carcinomas in Taiwan

BACKGROUND

Overexpression or activation of c-Jun has been implicated in the pathogenesis of several types of cancer. Treatment of oral cells with areca nut extract in culture can increase c-Jun proto-oncogene mRNA levels. The purpose of this study was to investigate the possible role of c-Jun activation in the pathogenesis and prognosis of areca quid chewing-related oral cancer in Taiwan.

METHODS

We immunohistochemically examined c-Jun protein activation in human oral squamous cell carcinomas (SCC) using an anti-phosphospecific c-Jun (pc-Jun) antibody on paraffin-embedded sections.

RESULTS

Positive pc-Jun staining was observed in 42 of 70 (60%) cases of oral SCC. No significant correlation was found between pc-Jun expression and patients' age, gender, oral habit, cancer location, clinical stage, tumor size and lymph node status. Kaplan-Meier curves showed that oral SCC patients with positive pc-Jun staining or positive lymph node metastasis had significantly shorter overall survival (p < 0.018 and 0.001, respectively, by log-rank test).

CONCLUSION

These results indicate that c-Jun activation may play an important role in the carcinogenesis of oral SCC. Positive pc-Jun staining may serve as an adjuvant marker of worse prognosis in patients with oral SCC in Taiwan.

Stimulation of cell growth by erythropoietin in RAW264.7 cells: Association with AP-1 activation

Erythropoietin (EPO), a hematopoietic factor, is required for normal erythrocyte developments, but it has been demonstrated to have many other functions, and its receptor is localized in other tissues. In the present study, we investigated whether EPO can promote other cell proliferation and possible molecular mechanisms. EPO restored the inhibition of the RAW264.7 and PC12 cell growth by fetal bovine serum (FBS) withdrawal in a dose dependent manner, but not that of other cell types tested. The restoring effect of EPO was completed when the RAW264.7 cells were cultured in the medium containing as low as 3% of FBS, and 10 U/mL EPO could replace FBS. The restoring effect of EPO in the RAW264.7 cells was associated with the increased of c-Fos and c-Jun expression as well as AP-1 activation. These data demonstrate that EPO can stimulate RAW264. 7 cell as well as PC12 cell growth even when the cells were cultured without FBS or in the presence of small amounts of FBS in the medium, and this stimulating effect is associated with the activation of AP-1 transcription factor.

Oncogenes as novel targets for cancer therapy (part III): transcription factors

This is the third paper in a four-part serial review on potential therapeutic targeting of oncogenes. The previous parts described the involvement of oncogenes in different aspects of cancer growth and development, and considered the new technologies responsible for the advancement of oncogene identification, target validation, and drug design. Because of such advances, new specific and more efficient therapeutic agents can be developed for cancer. This part of the review continues the exploration of various oncogenes that we have grouped within seven categories: growth factors, tyrosine kinases, intermediate signaling molecules, transcription factors, cell cycle regulators, DNA damage repair genes, and genes involved in apoptosis. Part one discussed growth factors and tyrosine kinases and part two discussed intermediate signaling molecules. This portion of the review covers transcription factors and the various strategies being used to inhibit their expression or decrease their activities.

Altered regulation of c-jun and its involvement in anchorage-independent growth of human lung cancers

The c-jun oncogene is frequently overexpressed in non-small-cell lung cancers (NSCLC), but its functional involvement in lung cancer development has not been clearly elucidated. In this study, we found that among the immediate-early serum responsible genes, exemplified by c-jun, c-fos and c-myc, induction of c-jun in a human bronchial epithelial cell line, BEAS-2B, was dependent on anchorage, in contrast to clear induction of c-fos and c-myc under both anchorage-dependent and -independent conditions. In fact, forced expression of c-jun in BEAS-2B cells significantly increased cell viability and colony formation in soft agar. Furthermore, we also found that such anchorage-dependent regulation of c-jun was lost in a significant fraction of human lung cancer cell lines. Interestingly, suppressed anchorage-independent but not anchorage-dependent growth was noted by constitutive expression of a dominant-negative c-jun mutant in a lung cancer cell line showing dysregulated and sustained c-jun expression in the absence of anchorage. These findings suggest that dysregulated c-jun expression may be involved in the acquisition of anchorage independence in the process of human lung carcinogenesis.

p75-Ras-GRF1 is a c-Jun/AP-1 target protein: its up regulation results in increased Ras activity and is necessary for c-Jun-induced nonadherent growth of Rat1a cells

The c-Jun/AP-1 transcription complex is associated with diverse cellular processes such as differentiation, proliferation, transformation, and apoptosis. These different biological endpoints are likely achieved by the regulation of specific target gene expression. We describe the identification of Ras guanine nucleotide exchange factor 1, Ras-GRF1, by microarray analysis as a c-Jun/AP-1 regulated gene essential for anchorage-independent growth of immortalized rat fibroblasts. Increased Ras-GRF1 expression, in response to inducible c-Jun expression in Rat1a fibroblasts, was confirmed by both real-time PCR and Northern blot analysis. We show that c-Jun/AP-1 can bind and activate the Ras-GRF1 promoter in vivo. A 75-kDa c-Jun/AP-1-inducible protein, p75-Ras-GRF1, was detected, and the inhibition of its expression with antisense oligomers significantly blocked c-Jun-regulated anchorage-independent cell growth. p75-Ras-GRF1 expression occurred with a concomitant increase in activated Ras (GTP bound), and the activation of Ras was significantly inhibited by antisense Ras-GRF1 oligomers. Moreover, p75-Ras-GRF1 could be coprecipitated with a Ras dominant-negative glutathione S-transferase (GST) construct, GST-Ras15A, demonstrating an interaction between p75-Ras-GRF1 and Ras. A downstream target of Ras activation, Elk-1, had increased transcriptional activity in c-Jun-expressing cells, and this activation was inhibited by dominant-negative Ras. In addition, c-Jun overexpression resulted in an increase in phospho-AKT while phosphorylation of ERK1/2 remained largely unaffected. The inhibition of phosphatidylinositol 3-kinase (PI3K)-AKT signal transduction by Ly294002 and wortmannin significantly blocked c-Jun-regulated morphological transformation, while inhibition of basal MEK-ERK activity with PD98059 and U0126 had little effect. We conclude that c-Jun/AP-1 regulates endogenous p75-Ras-GRF1 expression and that c-Jun/AP-1-regulated anchorage-independent cell growth requires activation of Ras-PI3K-AKT signal transduction.

Redox regulation of cell-cycle re-entry: cyclin D1 as a primary target for the mitogenic effects of reactive oxygen and nitrogen species

Reactive oxygen and nitrogen species inhibit or promote cell proliferation by modulating the cell signaling pathways that dictate decisions between cell survival, proliferation, and death. In the growth factor-dependent pathways that regulate mitogenesis, numerous positive and negative effectors of signaling are influenced by physiological fluctuations of oxidants, including receptor tyrosine kinases, small GTPases, mitogen-activated protein kinases, protein phosphatases, and transcription factors. The same mitogenic pathways that are sensitive to oxidant levels also directly regulate the expression of cyclin D1, a labile factor required for progression through the G1 phase on the cell cycle. Because the transition from G0 to G1 is the only phase of the cell cycle that is not regulated by cyclin-dependent kinases, but rather by redox-dependent signaling pathways, expression of cyclin D1 represents a primary regulatory node for the dose-dependent effects of oxidants on the induction of cell growth. We suggest that expression of cyclin D1 represents a useful marker for assessing the integration of proliferative and growth inhibitory effects of oxidants on the redox-dependent signaling events that control reentry into the cell cycle.

AP-1 dimers regulate transcription of the p14/p19ARF tumor suppressor gene

Evidence is accumulating about the role of individual AP-1 components in cell proliferation and transformation. Notably, Ras-mediated transformation is characterized by the upregulation of particular AP-1 members, such as c-Jun and Fra-1. The p14/p19ARF tumor suppressor gene is a key link between oncogenic Ras signaling and the p53 pathway. We explored the involvement of AP-1 dimers in the transcriptional regulation of the p14/p19ARF gene. We demonstrate that both the human and mouse ARF promoters are transcriptional targets of selective AP-1 dimers. The ARF promoter is regulated specifically by AP-1 heterodimers containing Fra-1. Overexpression of c-Jun approximately Fra-1 dimers in primary murine fibroblast cells led to the upregulation of the endogenous ARF protein and growth arrest. Conversely, inhibition of c-Jun or Fra-1 protein levels resulted in decreased ARF expression. In addition, we show that AP-1 dimers cooperate with oncogenic Ras in the transcriptional activation of the p14/p19ARF promoter. Thus, AP-1 heterodimers may contribute to the regulation of ARF expression upon oncogenic signaling.

Inhibition of AP-1 transcription activator induces myc-dependent apoptosis in HL60 cells

Transcriptional activation of AP-1 is intricately involved in cell proliferation and transformation. The natural product, nordihydroguaiaretic acid (NDGA) shows an inhibitory effect on the binding of jun/AP-1 protein to the AP-1 site in 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated HL60 cells. The NDGA inhibits the auto-regulated de novo synthesis of c-jun mRNA in TPA-stimulated HL60 cells. Our data also determine that this compound induces proliferation inhibition and apoptosis in human leukemia HL60 cells. To obtain information on the functional role of the AP-1 inhibition by NDGA in apoptosis signaling, the effects of pharmacological inhibition of AP-1 binding on c-myc, p53, and bax protein level were determined. Our results indicate that treatment of cells with NDGA enhances c-myc, p53, and bax protein levels. To rule out the possibility that NDGA will induce apoptosis because of the effects on proteins other than AP-1, we investigated the effect of another AP-1 inhibitor, SP600125, which is specific to Jun-N-terminal kinase. SP600125 decreased not only the phosphorylation level of jun protein but also AP-1/DNA binding activity. Also, apoptosis was observed to be induced by SP600125, concomitant with the increase in c-myc, p53, and bax protein level. In addition, apoptosis induced by both AP-1 inhibitors was accompanied by the activation of a downstream apoptotic cascade such as caspase 9, caspase 3, and poly[ADP-ribose]polymerase (PARP). When the cells were treated with NDGA or SP600125 in the presence of antisense c-myc oligonucleotides, apoptosis was not observed and an increase of c-myc, p53, and bax proteins was not manifested. All these results show that the inhibition of the transcription factor AP-1 action is related with either the drug-induced apoptosis or the drug toxicity of the HL60 cells. The apoptosis induced by AP-1 inhibition may be dependent on c-myc protein levels suggesting that the c-myc protein induces apoptosis at a low level of AP-1 binding activity. Altogether, our findings suggest that the presence of the AP-1 signal acts as a survival factor that determines the outcome of myc-induced proliferation or apoptosis.

Cyclin A is a c-Jun target gene and is necessary for c-Jun-induced anchorage-independent growth in RAT1a cells

Overexpression of c-Jun enables Rat1a cells to grow in an anchorage-independent manner. We used an inducible c-Jun system under the regulation of doxycycline in Rat1a cells to identify potential c-Jun target genes necessary for c-Jun-induced anchorage-independent growth. Induction of c-Jun results in sustained expression of cyclin A in the nonadherent state with only minimal expression in the absence of c-Jun. The promoter activity of cyclin A2 was 4-fold higher in Rat1a cells in which c-Jun expression was induced compared with the control cells. Chromatin immunoprecipitation demonstrated that c-Jun bound directly to the cyclin A2 promoter. Mutation analysis of the cyclin A2 promoter mapped the c-Jun regulatory site to an ATF site at position -80. c-Jun was able to bind to this site both in vitro and in vivo, and mutation of this site completely abolished promoter activity. Cyclin A1 was also elevated in c-Jun-overexpressing Rat1a cells; however, c-Jun did not regulate this gene directly, since it did not bind directly to the cyclin A1 promoter. Suppression of cyclin A expression via the introduction of a cyclin A antisense sequences significantly reduced the ability of c-Jun-overexpressing Rat1a cells to grow in an anchorage-independent fashion. Taken together, these results suggest that cyclin A is a target of c-Jun and is necessary but not sufficient for c-Jun-induced anchorage-independent growth. In addition, we demonstrated that the cytoplasmic oncogenes Ras and Src transcriptionally activated the cyclin A2 promoter via the ATF site at position -80. Using a dominant negative c-Jun mutant, TAM67, we showed that this transcriptional activation of cyclin A2 requires c-Jun. Thus, our results suggest that c-Jun is a mediator of the aberrant cyclin A2 expression associated with Ras/Src-induced transformation.

Reversible Regulation of the Transformed Phenotype of Ornithine Decarboxylase- and Ras-Overexpressing Cells by Dominant-Negative Mutants of c-Jun

c-Jun is an oncogenic transcription factor involved in the regulation of cell proliferation, apoptosis and transformation. We have previously reported that cell transformations induced by ornithine decarboxylase (ODC) and c-Ha-ras oncogene, commonly activated in various cancer cells, are associated with constitutively increased phosphorylation of c-Jun on Ser residues 63 and 73. In the present study, we examined the significance of c-Jun phosphorylation and activation on the phenotype of the ODC- and ras-transformants, by using specific inhibitors and dominant-negative (DN) mutants to c-Jun NH(2)-terminal kinase (JNK) and its upstream kinase, SEK1/MKK4 (mitogen-activated protein kinase kinase 4), and to c-Jun. The transformed morphology of both the ODC- and ras-expressing cells was reversed partially by JNK inhibitors and DN JNK1, more effectively by DN SEK1/MKK4 and phosphorylation-deficient c-Jun mutants (c-Jun(S63,73A), c-Jun(S63,73A,T91,93A)) and most potently by a transactivation domain deletion mutant of c-Jun (TAM67). Moreover, tetracycline-inducible TAM67 expression in ODC- and ras-transformed cells showed that the transformed phenotype of the cells is reversibly regulatable. TAM67 also inhibited the tumorigenicity of the cells in nude mice. These inducible cell lines, together with their parental cell lines, provide good models to identify the genes and proteins relevant to cellular transformation.