jun: oncogene and transcription factor

Identification and functional analysis of myeloid differentiation factor 88 (MyD88) in early development of Haliotis diversicolor

Myeloid differentiation factor 88 (MyD88) is a universal adaptor protein and plays an important role in the signal transduction of Toll like receptors (TLR) family. In this study, the MyD88 gene from the Haliotis diversicolor (hdMyD88) was identified. The full-length cDNA of hdMyD88 has a 1927 base pairs (bp), with an open reading frame of 1314 bp encoding 437 amino acids including a death domain (DD) at the N-terminus and TIR domain at the C-terminus which are typical features of MyD88 family proteins. Three conserved boxes are also found in the hdMyD88, which are similar to MyD88 in vertebrates. The expression levels of hdMyD88 mRNA at different early embryonic developmental stages of abalone were measured by qPCR revealed that their constitutive expression at all developmental stages analyzed with the considerably highest values at 8 cell stage and the lowest level at the trochosphere stage. Additionally, the mRNA expression of hdMyD88 decreased significantly (P < 0.05) after MyD88-dsRNA soak in the stage of trochosphere and veliger than EGFP-dsRNA group and blank control group. Whole embryo in situ hybridization showed that the positive signals of hdMyD88 were in visceral mass of trochophore larvae and veliger larvae. These results indicate hdMyD88 may could respond to pathogenic infection and may play an important role in early innate immunity in the process of abalone larval development.

Crosstalk between phytochemicals and inflammatory signaling pathways

Novel bioactive constituents from natural sources are actively being investigated. The phytochemicals in these phenolic compounds are believed to have a variety of beneficial effects on human health. Several phenolic compounds have been found in plants. The antioxidant potential of phenols has been discussed in numerous studies along with their anti-inflammatory effects on pro-inflammatory cytokine, inducible cyclooxygenase-2, and nitric oxide synthase. Through current study, an attempt is made to outline and highlight a wide variety of inflammation-associated signaling pathways that have been modified by several natural compounds. These signaling pathways include nuclear factor-kappa B (NF-кB), activator protein (AP)-1, protein tyrosine kinases (PTKs), mitogen-activated protein kinases (MAPKs), nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factors, tyrosine phosphatidylinositol 3-kinase (PI3K)/AKT, and the ubiquitin-proteasome system. In light of the influence of natural substances on signaling pathways, their impact on the production of inflammatory mediator is highlighted in this review.

Fra-2 overexpression upregulates pro-metastatic cell-adhesion molecules, promotes pulmonary metastasis, and reduces survival in a spontaneous xenograft model of human breast cancer

Purpose

The transcription factor Fra-2 affects the invasive potential of breast cancer cells by dysregulating adhesion molecules in vitro. Previous results suggested that it upregulates the expression of E- and P-selectin ligands. Such selectin ligands are important members of the leukocyte adhesion cascade, which govern the adhesion and transmigration of cancer cells into the stroma of the host organ of metastasis. As so far, no in vivo data are available, this study was designed to elucidate the role of Fra-2 expression in a spontaneous breast cancer metastasis xenograft model.

Methods

The effect of Fra-2 overexpression in two stable Fra-2 overexpressing clones of the human breast cancer cell line MDA MB231 on survival and metastatic load was studied after subcutaneous injection into scid and E- and P-selectin-deficient scid mice.

Results

Fra-2 overexpression leads to a significantly shorter overall survival and a higher amount of spontaneous lung metastases not only in scid mice, but also in E- and P-deficient mice, indicating that it regulates not only selectin ligands, but also selectin-independent adhesion processes.

Conclusion

Thus, Fra-2 expression influences the metastatic potential of breast cancer cells by changing the expression of adhesion molecules, resulting in increased adherence to endothelial cells in a breast cancer xenograft model.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00432-021-03812-2.

Transcriptome-wide high-throughput mapping of protein-RNA occupancy profiles using POP-seq

Interaction between proteins and RNA is critical for post-transcriptional regulatory processes. Existing high throughput methods based on crosslinking of the protein–RNA complexes and poly-A pull down are reported to contribute to biases and are not readily amenable for identifying interaction sites on non poly-A RNAs. We present Protein Occupancy Profile-Sequencing (POP-seq), a phase separation based method in three versions, one of which does not require crosslinking, thus providing unbiased protein occupancy profiles on whole cell transcriptome without the requirement of poly-A pulldown. Our study demonstrates that ~ 68% of the total POP-seq peaks exhibited an overlap with publicly available protein–RNA interaction profiles of 97 RNA binding proteins (RBPs) in K562 cells. We show that POP-seq variants consistently capture protein–RNA interaction sites across a broad range of genes including on transcripts encoding for transcription factors (TFs), RNA-Binding Proteins (RBPs) and long non-coding RNAs (lncRNAs). POP-seq identified peaks exhibited a significant enrichment (p value < 2.2e−16) for GWAS SNPs, phenotypic, clinically relevant germline as well as somatic variants reported in cancer genomes, suggesting the prevalence of uncharacterized genomic variation in protein occupied sites on RNA. We demonstrate that the abundance of POP-seq peaks increases with an increase in expression of lncRNAs, suggesting that highly expressed lncRNA are likely to act as sponges for RBPs, contributing to the rewiring of protein–RNA interaction network in cancer cells. Overall, our data supports POP-seq as a robust and cost-effective method that could be applied to primary tissues for mapping global protein occupancies.

Identification of a Transcriptomic Prognostic Signature by Machine Learning Using a Combination of Small Cohorts of Prostate Cancer

Determining which treatment to provide to men with prostate cancer (PCa) is a major challenge for clinicians. Currently, the clinical risk-stratification for PCa is based on clinico-pathological variables such as Gleason grade, stage and prostate specific antigen (PSA) levels. But transcriptomic data have the potential to enable the development of more precise approaches to predict evolution of the disease. However, high quality RNA sequencing (RNA-seq) datasets along with clinical data with long follow-up allowing discovery of biochemical recurrence (BCR) biomarkers are small and rare. In this study, we propose a machine learning approach that is robust to batch effect and enables the discovery of highly predictive signatures despite using small datasets. Gene expression data were extracted from three RNA-Seq datasets cumulating a total of 171 PCa patients. Data were re-analyzed using a unique pipeline to ensure uniformity. Using a machine learning approach, a total of 14 classifiers were tested with various parameters to identify the best model and gene signature to predict BCR. Using a random forest model, we have identified a signature composed of only three genes (JUN, HES4, PPDPF) predicting BCR with better accuracy [74.2%, balanced error rate (BER) = 27%] than the clinico-pathological variables (69.2%, BER = 32%) currently in use to predict PCa evolution. This score is in the range of the studies that predicted BCR in single-cohort with a higher number of patients. We showed that it is possible to merge and analyze different small and heterogeneous datasets altogether to obtain a better signature than if they were analyzed individually, thus reducing the need for very large cohorts. This study demonstrates the feasibility to regroup different small datasets in one larger to identify a predictive genomic signature that would benefit PCa patients.

Molecular cloning

Transcription factor c-Jun is a member of AP-1 transcription complex that can be induced by various pathogens and plays a broad regulatory role in vertebrate immune response. In this study, the complete c-Jun cDNA of large yellow croaker Larimichthys crocea (Lcc-Jun) was cloned, whose open reading frame (ORF) is 984 bp long and encodes a protein of 327 amino acids (aa). The deduced Lcc-Jun protein contains three highly conserved domains, a transactivation domain (TAD, Met¹-His¹¹⁸), a DNA binding domain (DBD, Lys²¹⁸-Arg²⁴³), and a Leucine zipper domain (LZD, Leu²⁷¹-Leu²⁹⁹), as found in other specie c-Jun. Lcc-Jun was constitutively expressed in all examined tissues, with the higher levels in blood, heart, and head kidney. Its transcripts were not only induced in spleen and head kidney by poly (I: C) or LPS, but also up-regulated in primary head kidney leukocytes (PKL), macrophages (PKM), and granulocytes (PKG), suggesting that Lcc-Jun may be involved in immune responses induced by poly (I: C), a viral mimic, and LPS, a Gram-negative bacterial component. Overexpression of Lcc-Jun in PKL increased the expression of cytokines and transcription factors involved in T helper 1 (Th1: TNF-α, IFN-γ, and T-bet) and Th2 (IL-4/13 A/B, IL-6, and GATA3) cell development and differentiation, suggesting that Lcc-Jun may play a role in regulation of Th1/Th2 cell response. These results therefore led us to suggest that the c-Jun-mediated signaling pathways may have an important immune-modulatory function in teleost fish.

TFregulomeR reveals transcription factors' context-specific features and functions

Transcription factors (TFs) are sequence-specific DNA binding proteins, fine-tuning spatiotemporal gene expression. Since genomic occupancy of a TF is highly dynamic, it is crucial to study TF binding sites (TFBSs) in a cell-specific context. To date, thousands of ChIP-seq datasets have portrayed the genomic binding landscapes of numerous TFs in different cell types. Although these datasets can be browsed via several platforms, tools that can operate on that data flow are still lacking. Here, we introduce TFregulomeR (https://github.com/benoukraflab/TFregulomeR), an R-library linked to an up-to-date compendium of cistrome and methylome datasets, implemented with functionalities that facilitate integrative analyses. In particular, TFregulomeR enables the characterization of TF binding partners and cell-specific TFBSs, along with the study of TF’s functions in the context of different partnerships and DNA methylation levels. We demonstrated that TFs’ target gene ontologies can differ notably depending on their partners and, by re-analyzing well characterized TFs, we brought to light that numerous leucine zipper TFBSs derived from ChIP-seq experiments documented in current databases were inadequately characterized, due to the fact that their position weight matrices were assembled using a mixture of homodimer and heterodimer binding sites. Altogether, analyses of context-specific transcription regulation with TFregulomeR foster our understanding of regulatory network-dependent TF functions.

Induction of E6AP by microRNA-302c dysregulation inhibits TGF-β-dependent fibrogenesis in hepatic stellate cells

Hepatic stellate cells (HSCs) are essential for liver fibrosis. E6 associated protein (E6AP) is one of the E3-ubiquitin-protein ligase and has been studied in proliferation and cellular stress. Currently, no information is available on the role of E6AP on transforming growth factor-β (TGF-β) signaling and hepatic fibrogenesis. This study examined whether E6AP is overexpressed in activated HSCs, and if so, its effect on hepatic fibrogenesis and the molecular mechanism. E6AP was expressed higher in HSCs than hepatocytes, and was up-regulated in activated HSCs, HSCs from the livers of carbon tetrachloride-injected mice, or TGF-β-treated LX-2 cells. The TGF-β-mediated E6AP up-regulation was not due to altered mRNA level nor protein stability. Thus, we performed microRNA (miRNA, miR) analysis and found that miR-302c was dysregulated in TGF-β-treated LX-2 cells or activated primary HSCs. We revealed that miR-302c was a modulator of E6AP. E6AP overexpression inhibited TGF-β-induced expression of plasminogen activator inhibitor-1 in LX-2 cells, albeit it was independent of Smad pathway. Additionally, E6AP inhibited TGF-β-mediated phosphorylation of mitogen-activated protein kinases. To conclude, E6AP overexpression due to decreased miR-302c in HSCs attenuated hepatic fibrogenesis through inhibition of the TGF-β-induced mitogen-activated protein kinase signaling pathway, implying that E6AP and other molecules may contribute to protection against liver fibrosis.

Glutathione peroxidase-1 inhibits transcription of regenerating islet-derived protein-2 in pancreatic islets

Our group previously demonstrated that overexpression of selenium-dependent glutathione peroxidase-1 (GPX1) in mice (OE) led to escalated glucose-stimulated insulin secretion and hyperinsulinemia. Because we found a strong correlation of this phenotype with a diminished expression of regenerating islet-derived protein 2 (REG2) in the OE pancreatic islets, the present study was to reveal underlying mechanisms for that down-regulation of REG2 by GPX1 as a major scavenger of reactive oxygen species. We first treated the OE and wild-type (WT) mice and their islets with ROS-generating diquat, streptozotocin, and H₂O₂ and ROS-scavenging ebselen and N-acetylcysteine (NAC). Their effects on pancreatic and islet REG2 protein and(or) secretion were opposite (P < 0.05). Thereafter, we identified 13 transcriptional factors with putative binding sites in the Reg2 proximate promoter, and found that only activator protein-1 (AP-1) and albumin D box-binding protein (DBP) mRNA and protein levels were affected (elevated) (P < 0.05) by the GPX1 overproduction in the OE pancreatic islets compared with the WT islets. Contrary to that of Reg2 expression, their mRNA abundances in the cultured islets were elevated (P < 0.05) by ebselen and NAC, but decreased (P < 0.05) by H₂O_2. Both AP-1 and DBP could bind to the Reg2 promoter at the location of -168 to 0 base pair (bp) in the OE islets. Deleting the AP-1 (-143/-137 and -60/-57 bp) and(or) DBP (-35/-29 bp) binding domains in the Reg2 promoter attenuated and(or) abolished the inhibition of Reg2 promoter activation by ebselen as the GPX1 mimic in βTC-3 cells. In conclusion, the down-regulation of Reg2 expression in the GPX1-overproducing pancreatic islets was mediated by a transcriptional inhibition of the gene through two ROS responsive transcription factors AP-1 and DBP. Our findings reveal GPX1 as a novel regulator of Reg2 expression, and linking these two previously-unrelated proteins will have broad biomedical implications.

Transforming growth factor-β1 regulates the nascent hematopoietic stem cell niche by promoting gluconeogenesis

The understanding of hematopoietic stem cell (HSC) emergence is important to generate HSCs from pluripotent precursors. However, integrated signaling network that regulates the niche of nascent HSCs remains unclear. Herein, we uncovered a novel role of TGF-β1 in the metabolic niche of HSC emergence using the tgf-β1b^-/- zebrafish. Our findings first showed that Tgf-β1 transcripts were enriched in the nascent HSCs. Loss of tgf-β1b caused a decrease of nascent HSCs within the aorta-gonad-mesonephros. Moreover, tgf-β1b⁺ cells were runx1⁺ HSCs and underwent an endothelial-to-hematopoietic-transition process. Although the autocrine of Tgf-β1 in HSCs rather than endothelial cells was highly demanded to regulate HSC generation, we found that tgf-β1b promoted HSC emergence through the endothelial c-Jun N-terminal kinase/c-Jun signaling. Chromatin immunoprecipitation (ChIP)-sequencing data showed that tgf-β1b/c-Jun targeted g6pc3 of FoxO signaling to promote gluconeogenesis and maintain a high glucose level in the niche. Furthermore, loss of tgf-β1b increased the endoplasmic-reticulum stress and oxidative stress by disturbing metabolic homeostasis. Adding a low dose of TGF-β1 protein could promote the differentiation of mouse embryonic stem cells towards HSCs in vitro. Altogether, our study provided insights into a new feature of TGF-β1 in the regulation of glucose metabolism and nascent HSC niche, which may contribute to therapies of hematological malignancies.

Phytoconstituents as apoptosis inducing agents: strategy to combat cancer

Advancement in the field of cancer molecular biology has aided researchers to develop various new chemopreventive agents which can target cancer cells exclusively. Cancer chemopreventive agents have proficiency to inhibit, reverse and delay process of carcinogenesis during its early and later course. Chemopreventive agents can act as antioxidative, antimutagenic/antigenotoxic, anti-inflammatory agents or via aiming various molecular targets in a cell to induce cell death. Apoptosis is a kind of cell death which shows various cellular morphological alterations such as cell shrinkage, blebbing of membrane, chromatin condensation, DNA fragmentation, formation of apoptotic bodies etc. Nowadays, apoptosis is being one of the new approaches for the identification and development of novel anticancer therapies. For centuries, plants are known to play part in daily routine from providing food to management of human health. In the last two decades, diverse phytochemicals and various botanical formulations have been characterized as agents that possess potential to execute cancer cells via inducing apoptosis. Data obtained from the research carried out globally pointed out that natural products are the potential candidates which have capability to combat cancer. In the present review, we surveyed literature on natural products which throws light on the mechanism through which these phytochemicals induce apoptosis in cancer cells.

Protein kinase C and chemical-induced abnormal palate development

The protein kinase C (PKC) family of proteins mediates the action of growth factors and other ligands by activating a network of transcription factors that bind to TRE sequences in the promoters of many genes that regulate cell proliferation, differentiation, extracellular matrix synthesis, apoptosis and others in a cell type-, isozymeand context-specific manner. The critical role of PKC in embryonic development is indicated by early death of embryos in which one or more of these isozymes are inactivated. Our studies together with others show that palatal PKC signalling is functional and may be essential for normal palate development. Although single gene knockouts have failed to exhibit the cleft palate (CP) phenotype, owing to compensation by other kinases, many chemicals including the mycotoxin, secalonic acid D, disrupt palatal PKC signalling leading to altered palatal mesenchymal gene expression. The potential relevance of such effects to chemical-induced CP is discussed.

Brown Pine Leaf Extract and Its Active Component Trans-Communic Acid Inhibit UVB-Induced MMP-1 Expression by Targeting PI3K

Japanese red pine (Pinus densiflora) is widely present in China, Japan, and Korea. Its green pine leaves have traditionally been used as a food as well as a coloring agent. After being shed, pine leaves change their color from green to brown within two years, and although the brown pine leaves are abundantly available, their value has not been closely assessed. In this study, we investigated the potential anti-photoaging properties of brown pine leaves for skin. Brown pine leaf extract (BPLE) inhibited UVB-induced matrix metalloproteinase-1 (MMP-1) expression to a greater extent than pine leaf extract (PLE) in human keratinocytes and a human skin equivalent model. HPLC analysis revealed that the quantity of trans-communic acid (TCA) and dehydroabietic acid (DAA) significantly increases when the pine leaf color changes from green to brown. BPLE and TCA elicited reductions in UVB-induced MMP-1 mRNA expression and activator protein-1 (AP-1) transactivation by reducing DNA binding activity of phospho-c-Jun, c-fos and Fra-1. BPLE and TCA also inhibited UVB-induced Akt phosphorylation, but not mitogen activated protein kinase (MAPK), known regulators of AP-1 transactivation. We additionally found that BPLE and TCA inhibited phosphoinositide 3-kinase (PI3K), the upstream kinase of Akt, in vitro. In summary, both BPLE and its active component TCA exhibit protective effects against UVB-induced skin aging. Taken together, these findings underline the potential for BPLE and TCA to be utilized as anti-wrinkling agents and cosmetic ingredients, as they suppress UVB-induced MMP-1 expression.

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.

Literature review of the role of hydroxyl radicals in chemically-induced mutagenicity and carcinogenicity for the risk assessment of a disinfection system utilizing photolysis of hydrogen peroxide

We have developed a new disinfection system for oral hygiene, proving that hydroxyl radicals generated by the photolysis of 1 M hydrogen peroxide could effectively kill oral pathogenic microorganisms. Prior to any clinical testing, the safety of the system especially in terms of the risk of carcinogenicity is examined by reviewing the literature. Previous studies have investigated indirectly the kinds of reactive oxygen species involved in some sort of chemically-induced mutagenicity in vitro by using reactive oxygen species scavengers, suggesting the possible involvement of hydroxyl radicals. Similarly, possible involvement of hydroxyl radicals in some sort of chemically-induced carcinogenicity has been proposed. Notably, it is suggested that the hydroxyl radical can play a role in heavy metal-induced carcinogenicity that requires chronic exposure to the carcinogen. In these cases, hydroxyl radicals produced by Fenton-like reactions may be involved in the carcinogenicity. Meanwhile, potential advantages have been reported on the use of the hydroxyl radical, being included in host immune defense by polymorphonuclear leukocytes, and medical applications such as for cancer treatment and antibiotics. From these, we conclude that there would seem to be little to no risk in using the hydroxyl radical as a disinfectant for short-term treatment of the oral cavity.

The role of retinoid deficiency and estrogens as cofactors in cervical cancer

Persistent infection with high-risk human papillomaviruses (HR-HPVs) is involved in cervical cancer (CC), a major cause of cancer mortality worldwide. Infection occurs primarily at the transformation zone (TZ), the most estrogen- and retinoid-sensitive region of the cervix. Development of CC affects a small percentage of HR-HPV-infected women and often takes decades after infection, suggesting that HR-HPV is a necessary but not sufficient cause of CC. Thus, other cofactors are necessary for progression from cervical HR-HPV infection to cancer such as long-term use of hormonal contraceptives, multiparity, smoking, as well as micronutrient depletion and in particular retinoid deficiency, which alters epithelial differentiation, cellular growth and apoptosis of malignant cells. Therefore, early detection of HR-HPV and management of precancerous lesions together with a profound understanding of additional risk factors could be a strategy to avoid this disease. In this review we focus on the synergic effect of estrogens, retinoid deficiency and HR-HPVs in the development of CC. These risk factors may act in concert to induce neoplastic transformation in squamous epithelium of the cervix, setting the stage for secondary genetic or epigenetic events leading to cervical cancer.

Herb medicine Gan-fu-kang attenuates liver injury in a rat fibrotic model

AIM OF THE STUDY

To verify therapeutic effects of Gan-fu-kang (GFK), a traditional Chinese medicine compound, in a rat model and to investigate the underlying mechanisms.

MATERIALS AND METHODS

Liver fibrosis was established by 12 weeks of carbon tetrachloride (CCl(4)) treatment (0.5mg/kg, twice per week) followed by 8 weeks of "recovery" in rats. Rats randomly received GFK (31.25, 312.5 and 3125 mg/kg/day, p.o.) or vehicle from weeks 9 to 20, and were sacrificed at the end of week 20 for histological, biochemical, and molecular biological examinations. In a separate set of experiments, rats received 12 weeks of CCl(4) treatment, concomitant with GFK (312.5mg/kg/day, p.o.) during the same period in some subjects, but were then sacrificed immediately. An additional group of rats receiving no CCl(4) treatment served as normal controls.

RESULTS AND CONCLUSIONS

(1) CCl(4) treatment resulted in severe liver damage and fibrosis. (2) In the main block of the 20-week study, GFK attenuated liver damage and fibrosis. (3) In the 12-week study, GFK produced prevention effect against hepatic injury. (4) GFK suppressed the expression of tissue inhibitor of metalloproteinase-1 (TIMP-1), type I collagen, platelet-derived growth factor-BB (PDGF-BB)/PDGF receptor-beta chains (PDGFRbeta) and mitogen-activated protein kinases (MAPKs)/active protein-1 (AP-1) signal pathways. Taken together, these results indicated that GFK could attenuate liver injuries in both settings. Our findings also suggest that the AP-1 pathway is the likely molecular substrate for the observed GFK effects.

Size-dependent effects of tungsten carbide-cobalt particles on oxygen radical production and activation of cell signaling pathways in murine epidermal cells

Hard metal or cemented carbide consists of a mixture of tungsten carbide (WC) (85%) and metallic cobalt (Co) (5-15%). WC-Co is considered to be potentially carcinogenic to humans. However, no comparison of the adverse effects of nano-sized WC-Co particles is available to date. In the present study, we compared the ability of nano- and fine-sized WC-Co particles to form free radicals and propensity to activate the transcription factors, AP-1 and NF-kappaB, along with stimulation of mitogen-activated protein kinase (MAPK) signaling pathways in a mouse epidermal cell line (JB6 P(+)). Our results demonstrated that nano-WC-Co generated a higher level of hydroxyl radicals, induced greater oxidative stress, as evidenced by a decrease of GSH levels, and caused faster JB6 P(+) cell growth/proliferation than observed after exposure of cells to fine WC-Co. In addition, nano-WC-Co activated AP-1 and NF-kappaB more efficiently in JB6(+/+) cells as compared to fine WC-Co. Experiments using AP-1-luciferase reporter transgenic mice confirmed the activation of AP-1 by nano-WC-Co. Nano- and fine-sized WC-Co particles also stimulated MAPKs, including ERKs, p38, and JNKs with significantly higher potency of nano-WC-Co. Finally, co-incubation of the JB6(+/+) cells with N-acetyl-cysteine decreased AP-1 activation and phosphorylation of ERKs, p38 kinase, and JNKs, thus suggesting that oxidative stress is involved in WC-Co-induced toxicity and AP-1 activation.

NDRG2 suppresses cell proliferation through down-regulation of AP-1 activity in human colon carcinoma cells

Recently, the anti-tumor activity of N-myc downstream-regulated gene 2 (NDRG2) was elucidated, but the molecular mechanism of how NDRG2 works as a tumor suppressor is not well known. To determine the function of NDRG2 as a tumor suppressor, we established stable cell lines expressing NDRG2 protein or its mutant forms, and studied their effects on tumor cell growth. Interestingly, constitutive expression of wild-type NDRG2 induced the growth retardation of SW620 colon carcinoma cells. Introduction of NDRG2 into SW620 cells induced the decrease of c-Jun phosphorylation at Ser63, followed by the attenuation of activator protein-1 (AP-1) function as a transcriptional activator. Subsequently, the down-regulation of cyclin D1, which is known as a major target for AP-1 transcription activator, resulted in cell cycle arrest at G1/S phase. Additionally, treatment of NDRG2-siRNA on NDRG2-expressing cells has induced the recovery of c-Jun phosphorylation and cyclin D1 expression. Cell proliferation of those cells was also increased compared with untreated cells. NDRG2 mutants of which the phosphorylation sites at C-terminal region were removed by deletion or site-directed mutagenesis have shown no effect on cyclin D1 expression and could not induce cell growth retardation. In conclusion, NDRG2 modulates intracellular signals to control cell cycle through the regulation of cyclin D1 expression via phosphorylation pathway.

Roscovitine inhibits ERK1/2 activation induced by angiotensin II in vascular smooth muscle cells

Roscovitine is a potent CDK inhibitor often used as a biological tool in cell-cycle studies, but its working mechanism and real targets in vascular smooth muscle cells (VSMCs) remain unclear. In this study, we observed that ERK1/2 phosphorylation induced by Ang II was abrogated by pretreating VSMCs with roscovitine for 15h. Pretreating VSMCs with roscovitine also inhibited Ang II-induced c-Jun expression and phosphorylation. We further demonstrated that roscovitine could suppress the DNA binding activity of c-Jun and activation of angiotensinogen promoter by Ang II. These results suggest that roscovitine represses Ang II-induced angiotensinogen expression by inhibiting activation of ERK1/2 and c-Jun.

Molecular cloning and characterization of human Aph2 gene, involved in AP-1 regulation by interaction with JAB1

A human Aph2 gene (hAph2) was identified and cloned from a human placenta cDNA library. Bioinformatics analysis revealed hAPH2 protein shares 96% identity with mouse APH2 and contains a zf-DHHC domain (148-210aa), which is always involved in protein-protein or protein-DNA interaction. Differential expression patterns of hAph2 mRNA were observed in normal human tissues. Yeast two-hybrid screening found another hAPH2-interacting protein JAB1. The zf-DHHC domain of hAPH2 and the C-terminal of JAB1 were confirmed to be critical for the interaction. Fused with GFP and expressed in COS-7, NIH/3T3 and SMMC-7721 cell lines, hAPH2 showed predominant distribution in the cytoplasm and co-localized with JAB1 around the nucleus. Furthermore, overexpression of hAPH2 could increase apoptosis of COS-7 cells and negatively regulate JAB1-induced activation of AP-1 in a concentration dependent manner. The expression level of c-jun was also down-regulated by overexpression of hAPH2 in COS-7 cells. These data showed some basic characterization and function of hAph2 (hAPH2), dependent or independent with JAB1.

Human Nogo-C overexpression induces HEK293 cell apoptosis via a mechanism that involves JNK-c-Jun pathway

The neurite outgrowth inhibitor protein Nogo-A has been identified as an inhibitor of axonal regeneration, and Nogo-B as a regulator of vasculature remodeling, but the additional roles of Nogo isoforms, especially Nogo-C, have obtained little attention. Nogo-C is weakly expressed in liver and kidney compared to the high expression in skeletal muscle. Here we detected the weak expression of Nogo-C in human embryonic kidney cell line HEK293, and found that Nogo-C expressed in HEK293 could induce cell apoptosis. Further experiments demonstrated the activation of JNK/SAPK and c-Jun, but not p38 in Nogo-C expressed cells. And JNK-specific inhibitor SP600125 could reduce cell apoptosis induced by Nogo-C. Furthermore, the activation of caspase-3 and PARP, the expression and phosphorylation of p53 were also detected. The data first revealed Nogo-C expressed in HEK293 confers apoptosis by inducing caspase-3 and p53 activation through the JNK-c-Jun-dependent pathway.

Modulation of activator protein-1 (AP-1) and MAPK pathway by flavonoids in human prostate cancer PC3 cells

In last couple of decades the use of natural compounds like flavonoids as chemopreventive agents has gained much attention. Our current study focuses on identifying chemopreventive flavonoids and their mechanism of action on human prostate cancer cells. Human prostate cancer cells (PC3), stably transfected with activator protein 1 (AP-1) luciferase reporter gene were treated with four main classes of flavonoids namely flavonols, flavones, flavonones, and isoflavones. The maximum AP-1 luciferase induction of about 3 fold over control was observed with 20 microM concentrations of quercetin, chrysin and genistein and 50 microM concentration of kaempferol. At higher concentrations, most of the flavonoids demonstrated inhibition of AP-1 activity. The MTS assay for cell viability at 24 h showed that even at a very high concentration (500 microM), cell death was minimal for most of the flavonoids. To determine the role of MAPK pathway in the induction of AP-1 by flavonoids, Western blot of phospho MAPK proteins was performed. Four out of the eight flavonoids namely kaempferol, apigenin, genistein and naringenin were used for the Western Blot analysis. Induction of phospho-JNK and phospho-ERK activity was observed after two hour incubation of PC3-AP1 cells with flavonoids. However no induction of phospho-p38 activity was observed. Furthermore, pretreating the cells with specific inhibitors of JNK reduced the AP-1 luciferase activity that was induced by genistein while pretreatment with MEK inhibitor reduced the AP-1 luciferase activity induced by kaempferol. The pharmacological inhibitors did not affect the AP-1 luciferase activity induced by apigenin and naringenin. These results suggest the possible involvement of JNK pathway in genistein induced AP-1 activity while the ERK pathway seems to play an important role in kaempferol induced AP-1 activity.

Cooperative cell transformation by Myc/Mil(Raf) involves induction of AP-1 and activation of genes implicated in cell motility and metastasis

Avian fibroblasts transformed simultaneously by the v-myc and v-mil(raf) oncogenes of acute leukemia and carcinoma virus MH2 contain elevated levels of c-Fos and c-Jun, major components of the transcription factor complex AP-1. To define specific transcriptional targets in these cells, subtractive hybridization techniques were employed leading to the identification of strongly upregulated genes including OPN (osteopontin), 126MRP, and rac2. OPN is a cytokine and cell attachment protein which has been implicated in human tumor progression and metastasis, the calcium binding 126MRP protein is related to the human S100 protein family involved in invasive cell growth, and the Rac2 protein belongs to the Rho family of small GTPases regulating actin reorganization and cell migration. Promoter analysis indicated that OPN activation is mediated by a non-consensus AP-1 binding site located close to the transcription start site. Electrophoretic mobility shift assays, chromatin immunoprecipitation and transcriptional reporter gene analyses showed that c-Fos and c-Jun bind specifically to this site and that c-Fos efficiently transactivates the OPN promoter. High-level expression of OPN, 126MRP, or Rac2 proteins from a retroviral vector led to partial cell transformation, documented by morphological changes and anchorage-independent growth. The specific activation in v-myc/v-mil(raf)-transformed cells of target genes with intrinsic oncogenic potential may provide an explanation for the longstanding observation that concomitant expression of these oncogenes leads to strongly enhanced oncogenicity in vivo and in vitro compared to cell transformation by v-myc or v-mil(raf) alone.

Polymorphisms of 5' flanking region of chicken prolactin gene

The polymorphisms of 5' flanking region of chicken prolactin (cPRL) gene were examined in several populations of Chinese native Yuehuang, Taihe Silkie and imported White Leghorn Layer chickens. The 5' flanking regions (2638 bp) from Yuehuang, Taihe Silkie and White Leghorn chickens were subjected to sequencing analysis. Four single nucleotide polymorphisms (SNPs) were identified at position -2425(C/T), -2215(T/C), -2063(G/A) and -1967(A/G). A 24-bp indel (insertion or deletion) and a polyA length polymorphism were also identified. For the 24-bp indel locus, three genotypes (AA, AB and BB) were found in Yuehuang chickens, while only two genotypes were detected in Taihe Silkie (AB and BB) and Leghorn chickens (AA and BB). The genotype frequencies of AA, AB and BB were significantly different among the three breeds. For the polyA locus, although three genotypes (CC, CD and DD) were found, only one genotype (CC) was detected in White Leghorn chickens, while two or three genotypes were observed in Chinese native chickens. We used real-time quantitative PCR and radioimmunology assay to investigate the potential association of the 24-bp indel locus with cPRL mRNA expression, plasma cPRL and brooding behaviors, and observed that chickens with genotype AB, which are of the highest incidence of broodiness, had the highest cPRL mRNA levels, providing the possibility that this polymorphic site might be related to the broodiness in chickens via modulating the transcriptional level of cPRL gene. The dissociation among cPRL gene transcription, mRNA storage and hormone release was also observed.

MAPK/AP-1 signal pathway in tobacco smoke-induced cell proliferation and squamous metaplasia in the lungs of rats

Overwhelming evidence has demonstrated tobacco smoke (TS) is causally associated with various types of cancers, especially lung cancer. Sustained epithelial cell hyperplasia and squamous metaplasia are considered as preneoplastic lesions during the formation of lung cancer. The cellular and molecular mechanisms leading to lung cancer due to TS are not clear. Mitogen-activated protein kinases (MAPK)/activator protein-1 (AP-1) can be activated by various stimuli and play a critical role in the control of cell proliferation and differentiation. To date, information on the response of the MAPK/AP-1 pathway during hyperplasia and squamous metaplasia induced by TS is lacking. We therefore investigated the effects of TS on the development of epithelial hyperplasia and squamous metaplasia, regulation of MAPK/AP-1 activation, and expression of AP-1-regulated cell cycle proteins and differentiation markers in the lungs of rats. Exposure of rats to TS (30 mg/m(3) or 80 mg/m(3), 6 h/day, 3 days/week for 14 weeks) dramatically induced cell proliferation and squamous metaplasia in a dose-dependent manner, effects that paralleled the activation of AP-1-DNA binding activity. Phosphorylated ERK1/2, JNK, p38 and ERK5 were significantly increased by exposure to TS, indicating the activation of these MAPK pathways. Expression of Jun and Fos proteins were differentially regulated by TS. TS upregulated the expression of AP-1-dependent cell cycle proteins including cyclin D1 and proliferating cell nuclear antigen (PCNA). Among the AP-1-dependent cell differentiation markers, keratin 5 and 14 were upregulated, while loricrin, filaggrin and involucrin were downregulated following TS exposure. These findings suggest the important role of MAPK/AP-1 pathway in TS-induced pathogenesis, thus providing new insights into the molecular mechanisms of TS-associated lung diseases including lung cancers.

cFos is critical for MCF-7 breast cancer cell growth

The activating protein-1 (AP-1) transcription factor is a converging point of multiple signal transduction pathways in many cells. We have previously demonstrated that overexpressing Tam67, a dominant-negative (DN) form of cJun, blocks AP-1 activity and inhibits breast cancer cell growth. We hypothesized that Tam67 forms dimers with other AP-1 proteins to suppress the growth of breast cancer cells. In the present study, we used immunoprecipitation-Western blotting to demonstrate that Tam67 binds all Jun and Fos proteins in breast cancer cells. In addition, we used two variants of the Tam67 mutant to investigate whether Jun or Fos protein was required for breast cancer cell growth. We created a Tam/Fos mutant in which the cJun dimerization domain was replaced by the cFos dimerization domain, and a Tam/Squelcher mutant in which the cJun dimerization domain was deleted. We then isolated MCF-7 cell lines that stably expressed these cJun-DN mutants under the control of an inducible promoter. Using AP-1-dependent reporter assays, we observed that Tam67 and Tam/Fos mutants inhibited AP-1 transcriptional activity, while the Tam/Squelcher mutant did not. We then determined whether Tam/Fos or Tam/Squelcher inhibited breast cell growth as well as Tam67. We found that while Tam67 repressed cell growth, neither Tam/Fos nor Tam/Squelcher mutant affected cell growth. These results indicate that Tam67 likely inactivates Fos family member proteins to suppress breast cancer cell growth. Finally, we performed antisense experiments to knock down the expression of individual family members (cJun or cFos). Our results demonstrated that antisense cFos inhibited breast cancer cell proliferation and colony formation, while antisense cJun did not. These results suggest that Tam67 suppresses breast cancer cell growth by interacting with Fos family members, specifically with cFos, to produce an inactive AP-1 complex.

Polymorphic AP-1 Binding Site in Bovine CSN1S1 Shows Quantitative Differences in Protein Binding Associated with Milk Protein Expression

Polymorphisms in 5'-flanking regions of milk protein encoding genes can influence the binding activity of the affected response elements and thus have an impact on the expression of the gene products. However, precise quantitative data concerning the binding properties of such variable response elements have so far not been described. In this study we present the results of a quantitative fluorescent electromobility shift assay comparing the allelic variants of a polymorphic activator protein-1 binding site in the promoter region of the bovine alphas1-casein encoding gene (CSN1S1), which is affected by an A-->G exchange at -175 bp (CSN1S1(-175bp)). A supershift assay using a commercial c-jun antibody was carried out to verify the specificity of protein binding. The gel shift analysis revealed specific and significantly reduced protein binding of oligonucleotides containing the G variant of the CSN1S1(-175bp) binding site. Further investigations comprised genotyping of the variable CSN1S1(-175bp) activator protein-1 element by an NmuCl restriction fragment length polymorphism in 62 cows of the breed Simmental and 80 cows of the breed German Holstein. Single milk proteins from at least 4 milk samples per cow were quantified by alkaline urea polyacrylamide gel electrophoresis. Homozygotes for CSN1S1(-175bp)*G were not observed, and the allele frequencies were 0.19 in Simmental and 0.05 in German Holstein. Carriers of CSN1S1(-175bp)*G showed higher content (%) as well as quantity (g/d) of alphas1-casein than CSN1S1(-175bp)*A homozygotes, independent of breed. We assume that the positive association of the CSN1S1(-175bp)*G variant with CSN1S1 expression is likely to be caused by a reduced affinity of the affected response element to a c-jun-containing CSN1S1 dimer with repressor properties.

Induction of AP-1 activity by androgen activation of the androgen receptor in LNCaP human prostate carcinoma cells

BACKGROUND

The androgen receptor and activator protein-1 (AP-1) transcription factors affect growth regulation in normal and cancerous prostate cells. Effects of androgen-activated androgen receptor on AP-1 activity were determined in the LNCaP human prostate carcinoma cell model.

METHODS

Cells were exposed to 1 nM androgen +/- antiandrogen bicalutamide. Cellular growth and cell cycle effects were determined by DNA, viability, and bromodeoxyuridine (BrdU) fluorescence activated cell sorter (FACS) assays. AP-1 effects were determined by an AP-1-luciferase enzyme reporter vector for transcriptional activity, electrophoretic mobility shift assay (EMSA)/antibody supershift for DNA-binding, quantitative RT-PCR for mRNA, and immunoblot for protein.

RESULTS

Androgen induced G(1) growth arrest. This growth arrest was abrogated by treatment with bicalutamide, demonstrating that growth arrest by androgen was due to androgen receptor activation. Concurrently, AP-1 DNA-binding and transcriptional activity was induced over 96 hr androgen exposure, which was also inhibited by bicalutamide. Interestingly, although no change in AP-1 transcriptional activity was observed 24 hr after androgen exposure, there was an increase in Fra-2 expression and AP-1 DNA-binding. Paradoxically, while Fra-2 mRNA and protein levels continued to increase, binding of Fra-2 to the AP-1 site decreased over 96 hr, with a concomitant increase in JunD AP-1-binding and a marked increase in expression of the 35 kDa form of JunD. Enhanced expression of this short form of JunD is a novel effect of androgen exposure that occurred during the 24-96 hr time period, as growth effects emerged.

CONCLUSION

Activation of androgen receptor by androgen induces changes in AP-1 activity and AP-1 factor DNA-binding that may contribute significantly to androgen-induced changes in prostate cancer cell growth.

Detection of protein–DNA interactions in crude cellular extracts by fluorescence correlation spectroscopy

Fluorescence correlation spectroscopy (FCS) is a methodology to examine directly the translational diffusion of individual fluorescence-labeled molecules in solutions. Recent studies using FCS have quantified various bimolecular reactions without any need for amplification. To evaluate further the applicability of FCS, we studied the specific binding between proteins and DNA in crude biological samples. Using an automated FCS system that was recently developed in our laboratories and is capable of distinguishing two or more molecular species in a multicomponent analysis, we detected the binding of two representative transcription factors, activator protein-1 (AP-1) and nuclear factor kappa B (NF-kappaB), in nuclear extracts of HeLa cells quantitatively with each sequence-specific DNA. The binding rates of these specific interactions were markedly augmented when cells were treated with tumor necrosis factor alpha which is known to activate both AP-1 and NF-kappaB. We also observed the pyrrolidine-dithiocarbamate-induced reciprocal regulation of these transcription factors. These results indicated that FCS is a useful tool for the analysis of complex interactions of transcription factors with DNA even in crude cellular extracts, suggesting that it is a powerful methodology for the study of a wide variety of molecular events under various experimental conditions.

Ectopic expression of nonliganded retinoic acid receptor beta abrogates AP-1 activity by selective degradation of c-Jun in cervical carcinoma cells

Expression of the nuclear retinoic acid receptor beta2 (RARbeta2) gene is often disturbed in cervical carcinoma cells. One important mechanism by which RARbeta2 can exert growth inhibitory function is based on its ability to repress the AP-1 transcription factor in a ligand-dependent manner. Because less is known about the biological effects of RARbeta in the absence of ligand, the corresponding cDNA was stably introduced into HPV18-positive HeLa cervical carcinoma cells. In the present study we describe a novel mechanism by which AP-1 becomes inactivated. Constitutive expression of nonliganded RARbeta abrogated both AP-1 binding affinity and activity by a selective degradation of the c-Jun protein as major dimerization partner, without substitution by other members of the Jun family. Blockage of the proteasomal pathway completely rescued c-Jun and reconstituted the AP-1 function. Moreover, HeLa RARbeta2 clones treated either with tumor necrosis factor-alpha or transfected with a constitutive active upstream mitogen-activated protein kinase (MEKK1Delta) also resulted in c-Jun phosphorylation and restoration of AP-1 affinity and functionality similar to that found in nontransfected parental HeLa cells. These data revealed an important cross-talk between trans-repression of AP-1 and nonliganded RARbeta in human papillomavirus-positive cells. Because AP-1 activity was not irreversibly disturbed, but could be switched on through activation of the Jun N-terminal kinase pathway, a model for the transient activation of AP-1 even in the presence of RARbeta as repressor is suggested.

Expression and localization of the transcription factor JunD in the duct system of mouse submandibular gland

We studied the expression and localization of JunD, a component of the transcription factor activator protein-1 (AP-1), in the mouse submandibular gland with immunoblotting and immunohistochemistry. In adult mice, all seven Jun and Fos family members constituting the AP-1 complex were expressed more abundantly in the female gland than in the male gland, and JunD was the most abundant of the members. Immunoreactivity for JunD was localized exclusively in the duct system of the gland, in which it was localized to the nuclei of intercalated duct (ID) cells and a subpopulation of striated duct (SD) cells located adjacent to ID. In contrast, granular convoluted tubule (GCT) cells, which are much more abundant in the male gland, were devoid of JunD. During postnatal development of the male gland, JunD was lost from the duct cells as they differentiated to GCT cells at 3-5 weeks postpartum. When GCT differentiation was induced in adult female gland by testosterone administration, many JunD-negative SD cells were temporarily induced to express JunD after 6-24 hr, but those cells lost JunD as they completely converted to GCT cells by 48 hr. These results suggested that JunD is involved in the differentiation of the duct system of mouse submandibular gland, in which there is crosstalk between the androgen/androgen receptor system and the AP-1 complex.

The enhanced expression of c-Jun immunoreactivity in the adrenalectomized gerbil hippocampus

Recent in vitro and in vivo studies have shown that glucocorticoids have a profound influence on the survival of hippocampal neurones, and that the depletion of glucocorticoids as a result of adrenalectomy (ADX) reduces nerve growth factor levels in the hippocampus. It is also believed that ADX is associated with the seizure susceptibility of the Mongolian gerbil. In the present study, the choronological changes of c-jun immunoreactivity were investigated after ADX in the hippocampal formations in the seizure-prone gerbil model. In the sham hippocampus, c-jun immunoreactivity was not observed in the neurones of the hippocampus proper and dentate gyrus. C-jun immunoreactive neurones appeared 3 h after ADX in the neurones of the CA1 area and dentate gyrus, and these immunoreactivities peaked 24 h after ADX and then gradually decreased. These results suggest that, in the adrenalectomized gerbil, c-jun may be expressed in the neurones of the hippocampus in compensation for glucocorticoid deficit. The result of enhanced c-jun expression of the hippocampal formation provides anatomical support for the hypothesis that c-jun may play a role in the reduction of seizure activity.

Nonsmall-cell lung cancer: chemoprevention studies

Lung cancer is the leading cause of cancer-related death in the world. Tobacco is an addictive agent producing carcinogenic effects that have been extremely difficult to prevent or detect in a curable stage. Important randomized controlled studies have been published in "healthy" smokers (primary prevention); patients with early lesions, such as mucosal dysplasia/metaplasia (secondary prevention); and those who have already had definitive treatment for their first tobacco-related malignancy (tertiary prevention). To date, the results have been generally disappointing. It is critical to remember that lung cancer is usually diagnosed decades after the patient has begun or even stopped smoking. We must intervene with more effective agents or combinations of agents and do it earlier in the process of carcinogenesis. Approximately 10% of patients with lung cancer either never smoked or only were "passive" smokers due to their environment, workplace. These "never-smokers" may actually benefit from retinoids, while current smokers have not benefited from alpha-tocopherol, retinal, N-acetylcysteine, or isotretinoin. Smokers are actually harmed by the concurrent use of beta-carotene. We now have unprecedented knowledge regarding the control of cellular growth and senescence. New diagnostic tools also allow detection of smaller lesions. We must use all our knowledge of the cancer biology, new risk models, more refined intermediate markers, and modern detection tools to focus more clearly on the pathology of lung cancer and design research to ask more probing and relevant questions so we can begin to put an end to the worldwide scourge of this terrible killer.

v-Jun stimulates both cdk2 kinase activity and G1/S progression via transcriptional repression of p21 CIP1

Previous studies have shown that the viral Jun (v-Jun) oncoprotein induces marked alterations in cell cycle control, which are associated with, and may be caused by, increased cdk2 kinase activity. Since p21 CIP1 is an important regulator of cdk2, we investigated whether aberrant expression of this cyclin-dependent kinase inhibitor might contribute to cell cycle deregulation by v-Jun. We find that the basal levels of p21 CIP1 mRNA and protein expression are greatly reduced in chick embryo fibroblasts (CEF) transformed by v-Jun, and that v-Jun blocks the increases in p21 CIP1 expression that normally accompany growth inhibition induced by serum deprivation or confluency in untransformed CEF. Importantly, ectopic expression of p21 CIP1 in v-Jun-transformed CEF inhibits both cdk2 kinase activity and cell cycle progression, indicating that these alterations in p21 CIP1 expression are likely to be functionally significant for growth deregulation. We also investigated the mechanism through which v-Jun disturbs p21 CIP1 expression and the possible involvement of a known p21 CIP1 regulator, p53, as an intermediate in this process. This analysis revealed that repression is mediated primarily at the level of p21 CIP1 gene transcription, however the mechanism is complex; both p53-dependent and -independent mechanisms contribute as judged by analysis of p21 CIP1 promoter mutants and other assays of p53 transcriptional activity.

The LIM-only protein FHL2 is a serum-inducible transcriptional coactivator of AP-1

Proteins with LIM domains have been implicated in transcriptional regulation. The four and half LIM domain (FHL) group of LIM-only proteins is composed of five members, some of which have been shown to have intrinsic activation function. Here we show that FHL2 is the only member of the family whose expression is inducible upon serum stimulation in cultured cells. Induction of FHL2 is coordinated in time with the increased levels of two early-response products, the oncoproteins Fos and Jun. FHL2 associates with both Jun and Fos, in vitro and in vivo. The FHL2-Jun interaction requires the Ser-63-Ser-73 JNK phosphoacceptor sites in c-Jun, but not their phosphorylation. FHL2 powerfully stimulates Fos- and Jun-dependent transcription, thereby acting as an inducible coactivator of AP-1 function. Moreover, we show that intracellular localization of FHL2 is controlled by signaling events and a Crm1-dependent active nuclear export mechanism. Thus, FHL2, as an inducible coactivator of AP-1, coordinately participates with Fos and Jun in the early transcriptional response to serum factors.

Interleukin-6 N-terminal peptides modulate the expression of junB protooncogene and the production of fibrinogen in HepG2 cells

Interleukin-6 (IL-6) is a helical cytokine exerting pleiotropic activities including the regulation of hematopoiesis, B cell activation and acute-phase reaction. The structure-function relationship of the molecule is the subject of intensive investigation using point and deletion mutants. Our objective was to analyse the role of the N-terminal 18-46 region in IL-6-mediated expression of junB protooncogene and fibrinogen production, reflecting the acute phase response, with synthetic overlapping peptides. mRNA expression of junB was monitored by competitive RT-PCR, while sandwich ELISA was used for the detection of fibrinogen in the supernatant of HepG2 human hepatoma cells. We found that even short synthetic octapeptides can be stimulatory (in the absence of IL-6) or inhibitory (in the presence of IL-6) in both assays. To establish the molecular mechanism by which synthetic peptides exert their biological effects electromobility shift assay was carried out using HepG2 nuclear extracts. Peptides inducing junB expression initiate gel shifts of STAT3/DNA complexes, which may indicate the involvement of this signal transduction pathway. Circular dicroism spectroscopy data suggest that 8-11-mer peptides representing different parts of the 18-46 region have a marked tendency to adopt ordered conformations in a water/trifluoroethanol (1:1 v/v) mixture. Competition studies with rhIL-6 and selected fluorophore-labelled peptides indicate the presence of more than one binding site on soluble IL-6 receptor. Considering the possible multiple etiologic role of IL-6 in the pathogenesis of various diseases, these peptides could be useful for dissection of IL-6 related biological effects.

The -148 to -124 region of c-jun interacts with a positive regulatory factor in rat liver and enhances transcription

The c-jun gene encodes the protein Jun, a component of the essential transcription factor, AP1. Jun/AP-1 occupies a central position in signal transduction pathways as it is responsible for the induction of a number of genes in response to growth promoters. However, the exact mechanisms leading to an enhanced expression of the c-jun gene itself during proliferation, differentiation, cell growth and development are not fully understood. Cell culture studies have given some insight in the mechanisms involved in the up-regulation of c-jun expression by UV irradiation and phorbol esters. However, it is well known that transformed cells do not accurately reflect the biology of a normal cell. We now report the identification of a positive regulatory factor from normal rat liver that activates transcription from the c-jun promoter by binding to the -148 to -124 region of c-jun. Preincubation of fractionated rat liver nuclear extract with an oligonucleotide encompassing this region of the gene significantly reduced transcription from cloned c-jun promoter. In vitro transfection studies using green fluorescent protein as a reporter gene under the control of the c-jun promoter with (-148 to +53) and without (-123 to +53) this region further confirmed its role in transcription. A DNA-binding protein factor, interacting with this region of c-jun was identified from rat liver by using electrophoretic mobility shift assays. This factor binds to its recognition sequence only in the phosphorylated form and exhibits high affinity and specificity. UV cross-linking studies, South-Western analysis and affinity purification collectively indicated the factor to be approximately 40 kDa and to bind to its recognition sequence as a dimer.

Increased expression and activation of c-Jun contributes to human amylin-induced apoptosis in pancreatic islet beta-cells

The role of c-Jun in apoptosis evoked by human amylin was investigated using human and rat insulinoma beta-cell lines. Two transient increases in the levels of c-jun mRNA were detected at 30 minutes and eight hours after treatment with human amylin. The level of c-Jun protein was also up-regulated in a time-dependent manner, reaching maximal levels after eight hours of exposure. However, no c-Jun induction was detected in cells treated with vehicle only or with rat amylin, indicating that the amyloidogenic feature of the human peptide may be important for c-Jun induction. We found that c-Jun was activated by phosphorylation specifically at Ser63 at four hours, but not at Ser73, after treatment with human amylin, preceding increased c-Jun protein. Furthermore, expression of an antisense c-jun (AS-c-jun), which suppressed protein levels of both c-Jun and phosphorylated-c-Jun, caused a marked reduction in apoptotic cell death, whereas the corresponding sense c-jun (S-c-jun) had no effect on changes of either c-Jun production or apoptosis. This indicated that increased expression and activation of c-Jun is required for human amylin-induced apoptosis. Immunocytochemical studies showed a significant increase in nuclear staining for c-Jun, phosphorylated-c-Jun (Ser63) and phosphorylated-JNK, suggesting that c-Jun may be activated through activation of JNK. In addition, electrophoretic mobility-shift assays showed that the increase in expression and phosphorylation of c-Jun was associated with increased AP-1 DNA binding activity. Supershift assays demonstrated that c-Jun, c-Fos and ATF-2 are part of the AP-1 complex, indicating that activated c-Jun is dimerized with c-Fos or ATF-2 for control of its target gene expression. Finally, we showed that human amylin triggers AP-1-mediated transcriptional activation. Our results suggest strongly that human amylin induces apoptosis through stimulation of expression and activation of c-Jun, and that co-expression and dimerization of c-Jun and c-fos or ATF-2 may be important for activation of the downstream apoptotic process.

Anticancer effect of retinoic acid via AP-1 activity repression is mediated by retinoic acid receptor alpha and beta in gastric cancer cells

To uncover the mechanisms relating to the anticancer effect of retinoic acids in gastric cancer cells, the mediation of activator protein-1 (AP-1) activity repression by retinoic acid receptors (RARs) was investigated. All-trans retinoic acid (ATRA) inhibited AP-1 activity in BGC-823 cells (RARalpha(+), RARbeta(+)), but not in MKN-45 cells (RARalpha(lo), RARbeta(-)). Transient transfection of RARbeta expression vector into MKN-45 cells significantly resulted in direct repression of AP-1 activity in a receptor concentration-dependent manner, and this could be strengthened by ATRA. Stable transfection of RARbeta into MKN-45 cells directly inhibited cell growth and colony formation, and ATRA also enhanced these effects. Transient transfection of RARalpha into MKN-45 cells however, displayed receptor concentration-dependent AP-1 activity inhibition only in the presence of ATRA. Stable transfection of RARalpha into MKN-45 cells resulted in ATRA-dependent inhibition of cell growth and colony formation. For AP-1 binding activity induced by TPA, the repressive effect of ATRA was only observed in BGC-823 and RARalpha and RARbeta stably transfected MKN-45 cells, but not in intact MKN-45 cells. This indicates the necessity for sufficient cellular RARalpha and/or RARbeta in order for AP-1 activity repression to occur. Deletion of DNA binding domain (DBD) of RARbeta, but not ligand binding domain (LBD), eliminated the anti-AP-1 function of RARbeta. It is therefore concluded that both RARalpha and RARbeta are mediators in the anticancer function of ATRA via AP-1 activity inhibition, and that RARbeta, not RARalpha, can inhibit AP-1 activity to a certain extent directly by itself. Thus DBD, not LBD, is critical for anti-AP-1 activity.

JDP2, a repressor of AP-1, recruits a histone deacetylase 3 complex to inhibit the retinoic acid-induced differentiation of F9 cells

Up-regulation of the c-jun gene is a critical event in the retinoic acid (RA)-mediated differentiation of embryonal carcinoma F9 cells. Activating transcription factor 2 (ATF-2) and p300 cooperate in the activation of transcription of the c-jun gene during the differentiation of F9 cells. We show here that the overexpression of Jun dimerization protein 2 (JDP2), a repressor of AP-1, inhibits the transactivation of the c-jun gene by ATF-2 and p300 by recruitment of the histone deacetylase 3 (HDAC3) complex, thereby repressing the RA-induced transcription of the c-jun gene and inhibiting the RA-mediated differentiation of F9 cells. Moreover, chromatin immunoprecipitation assays showed that the JDP2/HDAC3 complex, which binds to the differentiation response element within the c-jun promoter in undifferentiated F9 cells, was replaced by the p300 complex in response to RA, with an accompanying change in the histone acetylation status of the chromatin, the initiation of transcription of the c-jun gene, and the subsequent differentiation of F9 cells. These results suggest that JDP2 may be a key factor that controls the commitment of F9 cells to differentiation and shed new light on the mechanism by which an AP-1 repressor functions.

TOJ3, a target of the v-Jun transcription factor, encodes a protein with transforming activity related to human microspherule protein 1 (MCRS1)

Using the established quail cell line Q/d3 conditionally transformed by the v-jun oncogene, cDNA clones (TOJ2, TOJ3, TOJ5, TOJ6) were isolated by representational difference analysis (RDA) that correspond to genes which were induced immediately upon conditional activation of v-jun. One of these genes, TOJ3, is immediately and specifically activated after doxycycline-mediated v-jun induction, with kinetics similar to the induction of well characterized direct AP-1 target genes. TOJ3 is neither activated upon conditional activation of v-myc, nor in cells or cell lines non-conditionally transformed by oncogenes other than v-jun. Sequence analysis revealed that the TOJ3-specific cDNA encodes a 530-amino acid protein with significant sequence similarities to the murine or human microspherule protein 1 (MCRS1, MSP58), a nucleolar protein that directly interacts with the ICP22 regulatory protein from herpes simplex virus 1 or with p120, a proliferation-related protein expressed at high levels in most human malignant tumor cells. Similar to its mammalian counterparts, the TOJ3 protein contains a bipartite nuclear localization motif and a forkhead associated domain (FHA). Using polyclonal antibodies directed against a recombinant amino-terminal TOJ3 protein segment, the activation of TOJ3 in jun-transformed fibroblasts was also demonstrated at the protein level by specific detection of a polypeptide with an apparent M(r) of 65 000. Retroviral expression of the TOJ3 gene in quail or chicken embryo fibroblasts induces anchorage-independent growth, indicating that the immediate activation of TOJ3 in fibroblasts transformed by the v-jun oncogene contributes to cell transformation.

A specific lysine in c-Jun is required for transcriptional repression by E1A and is acetylated by p300

The adenovirus E1A protein regulates transcription of cellular genes via its interaction with the transcriptional coactivators p300/CBP. The collagenase promoter activated by the c-Jun protein is repressed by E1A. Here we show that E1A repression is specific for c-Jun, as E1A does not repress the collagenase promoter activated by the homologous transcription factor EB1. Using chimeras of c-Jun and EB1, we demonstrate that a 12 amino acid region in the basic region of the c-Jun DNA-binding domain is essential for repression by E1A. Since repression requires the binding of p300 to E1A, we studied the involvement of p300 acetyltransferase activity in the repression mechanism. We demonstrate that c-Jun is acetylated in vivo, and mutational analysis identified Lys271 in the c-Jun basic region to be essential for repression of the collagenase promoter by E1A. In addition, Lys271 is acetylated both in vitro and in vivo. These results suggest that the specific repression of the collagenase promoter by E1A involves acetylation of c-Jun.

Nicotine affects the signaling of the death pathway, reducing the response of head and neck cancer cell lines to DNA damaging agents

BACKGROUND

Growing evidence suggests that tobacco can affect the responsiveness of cancer cells to treatment, particularly those of head and neck cancer. This article describes the effects of nicotine on the signaling of the death pathway, resulting in a decreased cytotoxicity of various anticancer agents such as cisplatin and gamma-radiation.

METHODS

Colony-forming assays (CFA), using the head and neck cancer cell lines UMSCC10b and UMSCC5 and DNA fragmentation assays, were used to determine the effect of nicotine on cytotoxicity of various anticancer agents, whereas PCR and a JNK activity test were used to study the effect of nicotine on message expression levels and activity of the JNK signaling pathway.

RESULTS

Nicotine consistently reduced the cytotoxic effect of DNA-damaging agents, such as cisplatin, UV, and gamma radiation, in UMSCC10b cells, increasing their IC(50) values by twofold, 1.7-fold, and 1.8-fold, respectively. These results were confirmed in a second squamous cell carcinoma cell line (UMSCC5), demonstrating an increase in IC(50) values for cDDP by twofold and 1.9-fold in the UMSCC10b andUMSCC5, respectively. In addition, nicotine reduced the DNA fragmentation 48 h after cDDP exposure in UMSCC10b and UMSCC5 cell lines by 30% and 33%, respectively. The latter, however, was not the result of an effect of nicotine on either the uptake of cDDP or repair of the cDDP-DNA-adducts. To further substantiate the adverse effect of nicotine, the JNK and gadd153 signaling pathways were studied. JNK activity was decreased by 1.8-fold, as well as the expression of its downstream target c-jun (1.9-fold), when tumor cells were exposed to cisplatin in the presence of nicotine. In addition, the gadd153 message was affected and reduced by 1.8-fold.

CONCLUSIONS

Nicotine adversely affects the cytotoxicity of DNA-damaging agents. Nicotine does not interfere with the repair of the damage but directly affects the signaling of the death pathway, reducing the signaling of the JNK1 pathway. The latter results in a decrease in efficacy of the anticancer treatment in tumors exposed to nicotine.