Characterization of junD: a new member of the jun proto-oncogene family

Progress in the Study of Fra-2 in Respiratory Diseases

Fos-related antigen-2 (Fra-2) is a member of the activating protein-1 (AP-1) family of transcription factors. It is involved in controlling cell growth and differentiation by regulating the production of the extracellular matrix (ECM) and coordinating the balance of signals within and outside the cell. Fra-2 is not only closely related to bone development, metabolism, and immune system and eye development but also in the progression of respiratory conditions like lung tumors, asthma, pulmonary fibrosis, and chronic obstructive pulmonary disease (COPD). The increased expression and activation of Fra-2 in various lung diseases has been shown in several studies. However, the specific molecular mechanisms through which Fra-2 affects the development of respiratory diseases are not yet understood. The purpose of this research is to summarize and delineate advancements in the study of the involvement of transcription factor Fra-2 in disorders related to the respiratory system.

Mutant Ras and inflammation-driven skin tumorigenesis is suppressed via a JNK-iASPP-AP1 axis

Concurrent mutation of a RAS oncogene and the tumor suppressor p53 is common in tumorigenesis, and inflammation can promote RAS-driven tumorigenesis without the need to mutate p53. Here, we show, using a well-established mutant RAS and an inflammation-driven mouse skin tumor model, that loss of the p53 inhibitor iASPP facilitates tumorigenesis. Specifically, iASPP regulates expression of a subset of p63 and AP1 targets, including genes involved in skin differentiation and inflammation, suggesting that loss of iASPP in keratinocytes supports a tumor-promoting inflammatory microenvironment. Mechanistically, JNK-mediated phosphorylation regulates iASPP function and inhibits iASPP binding with AP1 components, such as JUND, via PXXP/SH3 domain-mediated interaction. Our results uncover a JNK-iASPP-AP1 regulatory axis that is crucial for tissue homeostasis. We show that iASPP is a tumor suppressor and an AP1 coregulator.

Identification of Unique Key miRNAs, TFs, and mRNAs in Virulent MTB Infection Macrophages by Network Analysis

Although Mycobacterium tuberculosis (MTB) has existed for thousands of years, its immune escape mechanism remains obscure. Increasing evidence signifies that microRNAs (miRNAs) play pivotal roles in the progression of tuberculosis (TB). RNA sequencing was used to sequence miRNAs in human acute monocytic leukemia cells (THP-1) infected by the virulent MTB-1458 strain and the avirulent vaccine strain Mycobacterium bovis Bacillus Calmette-Guérin (BCG). Sets of differentially expressed miRNAs (DE-miRNAs) between MTB-1458/BCG-infected groups and uninfected groups were identified, among which 18 were differentially expressed only in the MTB-1458-infected THP-1 group. Then, 13 transcription factors (TFs) and 81 target genes of these 18 DE-miRNAs were matched. Gene Ontology classification as well as Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that the candidate targets were predominantly involved in apoptotic-associated and interferon-γ-mediated signaling pathways. A TF-miRNA-mRNA interaction network was constructed to analyze the relationships among these 18 DE-miRNAs and their targets and TFs, as well as display the hub miRNAs, TFs, and target genes. Considering the degrees from network analysis and the reported functions, this study focused on the BHLHE40-miR-378d-BHLHE40 regulation axis and confirmed that BHLHE40 was a target of miR-378d. This cross-talk among DE-miRNAs, mRNAs, and TFs might be an important feature in TB, and the findings merited further study and provided new insights into immune defense and evasion underlying host-pathogen interactions.

JUND-dependent up-regulation of HMOX1 is associated with cisplatin resistance in muscle-invasive bladder cancer

The standard-of-care for metastatic muscle-invasive bladder cancer (MIBC) is platinum-based chemotherapy regimens. Acquired resistance that occurs frequently through unidentified mechanisms, however, remains the major obstacle for implementing therapeutic effectiveness. Here, using data mining and analysis on clinical samples, we show that expression of JUND, a core component of activator protein-1 family, was significantly induced in cisplatin (CDDP)-resistant MIBC. Accumulation of nuclear JUND was associated with low post-chemotherapy survival in MIBC patients. In both genetically engineered cell models and murine xenograft models, we provided evidence that bladder cancer (BC) cells with excessive JUND expression were less responsive to CDDP treatment. This CDDP resistance was further demonstrated to be mediated, at least in part, by transactivation of HMOX1 [the gene encoding heme oxygenase-1 (HO-1)], one of the most important antioxidant signalling pathways of cell adaptation to stress. One mutation within the HMOX1 promoter successfully abolished oxidative stress-enhanced and JUND-driven HMOX1 promoter activation, suggesting that this unique site synergized for maximal HO-1 induction in CDDP-challenged BC cells. Overall, our data highlight an indispensible role of JUND, both as a target as a modifier of the oxidative stress signalling, in conferring an adaptive response during the pathogenesis of CDDP resistance in MIBC.

Hyperglycemia Induces Myocardial Dysfunction via Epigenetic Regulation of JunD

RATIONALE

Hyperglycemia -induced reactive oxygen species are key mediators of cardiac dysfunction. JunD (Jund proto-oncogene subunit), a member of the AP-1 (activator protein-1) family of transcription factors, is emerging as a major gatekeeper against oxidative stress. However, its contribution to redox state and inflammation in the diabetic heart remains to be elucidated.

OBJECTIVE

The present study investigates the role of JunD in hyperglycemia-induced and reactive oxygen species-driven myocardial dysfunction.

METHODS AND RESULTS

JunD mRNA and protein expression were reduced in the myocardium of mice with streptozotocin-induced diabetes mellitus as compared to controls. JunD downregulation was associated with oxidative stress and left ventricular dysfunction assessed by electron spin resonance spectroscopy as well as conventional and 2-dimensional speckle-tracking echocardiography. Furthermore, myocardial expression of free radical scavenger superoxide dismutase 1 and aldehyde dehydrogenase 2 was reduced, whereas the NOX2 (NADPH [nicotinamide adenine dinucleotide phosphatase] oxidase subunit 2) and NOX4 (NADPH [nicotinamide adenine dinucleotide phosphatase] oxidase subunit 4) were upregulated. The redox changes were associated with increased NF-κB (nuclear factor kappa B) binding activity and expression of inflammatory mediators. Interestingly, mice with cardiac-specific overexpression of JunD via the α MHC (α- myosin heavy chain) promoter (α MHC JunD^tg) were protected against hyperglycemia-induced cardiac dysfunction. We also showed that JunD was epigenetically regulated by promoter hypermethylation, post-translational modification of histone marks, and translational repression by miRNA (microRNA)-673/menin. Reduced JunD mRNA and protein expression were confirmed in left ventricular specimens obtained from patients with type 2 diabetes mellitus as compared to nondiabetic subjects.

CONCLUSIONS

Here, we show that a complex epigenetic machinery involving DNA methylation, histone modifications, and microRNAs mediates hyperglycemia-induced JunD downregulation and myocardial dysfunction in experimental and human diabetes mellitus. Our results pave the way for tissue-specific therapeutic modulation of JunD to prevent diabetic cardiomyopathy.

Angiogenesis in odontogenic keratocyst and dentigerous cyst: Evaluation of JunB and VEGF expression

BACKGROUND

Nowadays, different clinical behaviors of odontogenic cysts, little information about their biological agents, importance of diagnosis, and early diagnosis of these lesions have encouraged the researchers to conduct new studies. JunB acts as a regulator of vascular endothelial growth factor (VEGF) protein production and affects vessel proliferation and tissue angiogenesis. Hence, this study was conducted to compare angiogenesis through VEGF and JunB expression in odontogenic keratocysts (OKCs) and dentigerous cysts (DCs).

MATERIALS AND METHODS

A total of 25 paraffin blocks of OKCs and 25 DCs were included in this experimental descriptive cross-sectional study, and immunohistochemical expression of VEGF and JunB was evaluated. Percentage and score of expression were recorded for each sample, and independent t-test, Mann-Whitney U, and Spearman statistical tests were run to analyze the data. The statistical significance level was set at <0.05.

RESULTS

From 50 studied samples, 39.6% belonged to women and 60.4% belonged to men, with mean age of 34.2 ± 1.7 years. The mean percentages of JunB expression were 52.88 ± 17.35 and 74.6 ± 18.55 for DC and OKC samples, respectively. This expression was significantly higher in OKC than DC, and it had significantly higher scores as well (P = P = 0.0001 and 0.00033, respectively). The means of VEGF were 20.2% ±11.86 and 52.6% ±19.98 in DC and OKC samples, respectively. The mean VEGF expression was significantly higher in OKC than DC (P = 0.045), and it had significantly higher scores, too (P = 0.000). Furthermore, there was a significant correlation between VEGF and JunB expression in the studied samples (r_s = 0.3 and P = 0.005).

CONCLUSION

Based on the results of this study, it seems evaluation of angiogenesis through JunB expression can be helpful in the prediction of more aggressive behavior in pathologic lesions such as OKC.

Epigenetics and Immunometabolism in Diabetes and Aging

SIGNIFICANCE

A strong relationship between hyperglycemia, impaired insulin pathway, and cardiovascular disease in type 2 diabetes (T2D) is linked to oxidative stress and inflammation. Immunometabolic pathways link these pathogenic processes and pose important potential therapeutic targets. Recent Advances: The link between immunity and metabolism is bidirectional and includes the role of inflammation in the pathogenesis of metabolic disorders such as T2D, obesity, metabolic syndrome, and hypertension and the role of metabolic factors in regulation of immune cell functions. Low-grade inflammation, oxidative stress, balance between superoxide and nitric oxide, and the infiltration of macrophages, T cells, and B cells in insulin-sensitive tissues lead to metabolic impairment and accelerated aging.

CRITICAL ISSUES

Inflammatory infiltrate and altered immune cell phenotype precede development of metabolic disorders. Inflammatory changes are tightly linked to alterations in metabolic status and energy expenditure and are controlled by epigenetic mechanisms.

FUTURE DIRECTIONS

A better comprehension of these mechanistic insights is of utmost importance to identify novel molecular targets. In this study, we describe a complex scenario of epigenetic changes and immunometabolism linking to diabetes and aging-associated vascular disease. Antioxid. Redox Signal. 29, 257-274.

Hijacking of the AP-1 Signaling Pathway during Development of ATL

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of a fatal malignancy known as adult T-cell leukemia (ATL). One way to address the pathology of the disease lies on conducting research with a molecular approach. In addition to the analysis of ATL-relevant signaling pathways, understanding the regulation of important and relevant transcription factors allows researchers to reach this fundamental objective. HTLV-1 encodes for two oncoproteins, Tax and HTLV-1 basic leucine-zipper factor, which play significant roles in the cellular transformation and the activation of the host's immune responses. Activating protein-1 (AP-1) transcription factor has been linked to cancer and neoplastic transformation ever since the first representative members of the Jun and Fos gene family were cloned and shown to be cellular homologs of viral oncogenes. AP-1 is a dimeric transcription factor composed of proteins belonging to the Jun (c-Jun, JunB, and JunD), Fos (c-Fos, FosB, Fra1, and Fra2), and activating transcription factor protein families. Activation of AP-1 transcription factor family by different stimuli, such as inflammatory cytokines, stress inducers, or pathogens, results in innate and adaptive immunity. AP-1 is also involved in various cellular events including differentiation, proliferation, survival, and apoptosis. Deregulated expression of AP-1 transcription factors is implicated in various lymphomas such as classical Hodgkin lymphomas, anaplastic large cell lymphomas, diffuse large B-cell lymphomas, and adult T-cell leukemia. Here, we review the current thinking behind deregulation of the AP-1 pathway and its contribution to HTLV-induced cellular transformation.

Ageing, metabolism and cardiovascular disease

Age is one of the major risk factors associated with cardiovascular disease (CVD). About one-fifth of the world population will be aged 65 or older by 2030, with an exponential increase in CVD prevalence. It is well established that environmental factors (overnutrition, smoking, pollution, sedentary lifestyles) may lead to premature defects in mitochondrial functionality, insulin signalling, endothelial homeostasis and redox balance, fostering early senescent features. Over the last few years, molecular investigations have unveiled common signalling networks which may link the ageing process with deterioration of cardiovascular homeostasis and metabolic disturbances, namely insulin resistance. These different processes seem to be highly interconnected and their interplay may favour adverse vascular and cardiac phenotypes responsible for myocardial infarction, stroke and heart failure. In the present review, we carefully describe novel molecular cues underpinning ageing, metabolism and CVD. In particular, we describe a dynamic interplay between emerging pathways such as FOXOs, AMPK, SIRT1, p66(Shc) , JunD and NF-kB. This overview will provide the background for attractive molecular targets to prevent age-driven pathology in the vasculature and the heart.

Promoter-level expression clustering identifies time development of transcriptional regulatory cascades initiated by ErbB receptors in breast cancer cells

The analysis of CAGE (Cap Analysis of Gene Expression) time-course has been proposed by the FANTOM5 Consortium to extend the understanding of the sequence of events facilitating cell state transition at the level of promoter regulation. To identify the most prominent transcriptional regulations induced by growth factors in human breast cancer, we apply here the Complexity Invariant Dynamic Time Warping motif EnRichment (CIDER) analysis approach to the CAGE time-course datasets of MCF-7 cells stimulated by epidermal growth factor (EGF) or heregulin (HRG). We identify a multi-level cascade of regulations rooted by the Serum Response Factor (SRF) transcription factor, connecting the MAPK-mediated transduction of the HRG stimulus to the negative regulation of the MAPK pathway by the members of the DUSP family phosphatases. The finding confirms the known primary role of FOS and FOSL1, members of AP-1 family, in shaping gene expression in response to HRG induction. Moreover, we identify a new potential regulation of DUSP5 and RARA (known to antagonize the transcriptional regulation induced by the estrogen receptors) by the activity of the AP-1 complex, specific to HRG response. The results indicate that a divergence in AP-1 regulation determines cellular changes of breast cancer cells stimulated by ErbB receptors.

Transcriptional and epigenetic substrates of methamphetamine addiction and withdrawal: evidence from a long-access self-administration model in the rat

Methamphetamine use disorder is a chronic neuropsychiatric disorder characterized by recurrent binge episodes, intervals of abstinence, and relapses to drug use. Humans addicted to methamphetamine experience various degrees of cognitive deficits and other neurological abnormalities that complicate their activities of daily living and their participation in treatment programs. Importantly, models of methamphetamine addiction in rodents have shown that animals will readily learn to give themselves methamphetamine. Rats also accelerate their intake over time. Microarray studies have also shown that methamphetamine taking is associated with major transcriptional changes in the striatum measured within a short or longer time after cessation of drug taking. After a 2-h withdrawal time, there was increased expression of genes that participate in transcription regulation. These included cyclic AMP response element binding (CREB), ETS domain-containing protein (ELK1), and members of the FOS family of transcription factors. Other genes of interest include brain-derived neurotrophic factor (BDNF), tyrosine kinase receptor, type 2 (TrkB), and synaptophysin. Methamphetamine-induced transcription was found to be regulated via phosphorylated CREB-dependent events. After a 30-day withdrawal from methamphetamine self-administration, however, there was mostly decreased expression of transcription factors including junD. There was also downregulation of genes whose protein products are constituents of chromatin-remodeling complexes. Altogether, these genome-wide results show that methamphetamine abuse might be associated with altered regulation of a diversity of gene networks that impact cellular and synaptic functions. These transcriptional changes might serve as triggers for the neuropsychiatric presentations of humans who abuse this drug. Better understanding of the way that gene products interact to cause methamphetamine addiction will help to develop better pharmacological treatment of methamphetamine addicts.

The functional consequences of variation in transcription factor binding

One goal of human genetics is to understand how the information for precise and dynamic gene expression programs is encoded in the genome. The interactions of transcription factors (TFs) with DNA regulatory elements clearly play an important role in determining gene expression outputs, yet the regulatory logic underlying functional transcription factor binding is poorly understood. Many studies have focused on characterizing the genomic locations of TF binding, yet it is unclear to what extent TF binding at any specific locus has functional consequences with respect to gene expression output. To evaluate the context of functional TF binding we knocked down 59 TFs and chromatin modifiers in one HapMap lymphoblastoid cell line. We then identified genes whose expression was affected by the knockdowns. We intersected the gene expression data with transcription factor binding data (based on ChIP-seq and DNase-seq) within 10 kb of the transcription start sites of expressed genes. This combination of data allowed us to infer functional TF binding. Using this approach, we found that only a small subset of genes bound by a factor were differentially expressed following the knockdown of that factor, suggesting that most interactions between TF and chromatin do not result in measurable changes in gene expression levels of putative target genes. We found that functional TF binding is enriched in regulatory elements that harbor a large number of TF binding sites, at sites with predicted higher binding affinity, and at sites that are enriched in genomic regions annotated as “active enhancers.”

An important question in genomics is to understand how a class of proteins called “transcription factors” controls the expression level of other genes in the genome in a cell-type-specific manner – a process that is essential to human development. One major approach to this problem is to study where these transcription factors bind in the genome, but this does not tell us about the effect of that binding on gene expression levels and it is generally accepted that much of the binding does not strongly influence gene expression. To address this issue, we artificially reduced the concentration of 59 different transcription factors in the cell and then examined which genes were impacted by the reduced transcription factor level. Our results implicate some attributes that might influence what binding is functional, but they also suggest that a simple model of functional vs. non-functional binding may not suffice.

Cleavage of the JunB transcription factor by caspases generates a carboxyl-terminal fragment that inhibits activator protein-1 transcriptional activity

The activator protein-1 (AP-1) family transcription factor, JunB, is an important regulator of proliferation, apoptosis, differentiation, and the immune response. In this report, we show that JunB is cleaved in a caspase-dependent manner in apoptotic anaplastic lymphoma kinase-positive, anaplastic large cell lymphoma cell lines and that ectopically expressed JunB is cleaved in murine RAW 264.7 macrophage cells treated with the NALP1b inflammasome activator, anthrax lethal toxin. In both cases, we identify aspartic acid 137 as the caspase cleavage site and demonstrate that JunB can be directly cleaved in vitro by multiple caspases at this site. Cleavage of JunB at aspartic acid 137 separates the N-terminal transactivation domain from the C-terminal DNA binding and dimerization domains, and we show that the C-terminal cleavage fragment retains both DNA binding activity and the ability to interact with AP-1 family transcription factors. Furthermore, this fragment interferes with the binding of full-length JunB to AP-1 sites and inhibits AP-1-dependent transcription. In summary, we have identified and characterized a novel mechanism of JunB post-translational modification and demonstrate that the C-terminal JunB caspase cleavage product functions as a potent inhibitor of AP-1-dependent transcription.

Selective up-regulation of JunD transcript and protein expression in vasopressinergic supraoptic nucleus neurones in water-deprived rats

The magnocellular neurones (MCN) of the supraoptic nucleus (SON) undergo reversible changes during dehydration. We hypothesise that alterations in steady-state transcript levels might be partially responsible for this plasticity. In turn, regulation of transcript abundance might be mediated by transcription factors. We have previously used microarrays to identify changes in the expression of mRNAs encoding transcription factors in response to water deprivation. We observed down-regulation of 11 and up-regulation of 31 transcription factor transcripts, including members of the activator protein-1 gene family, namely c-fos, c-jun, fosl1 and junD. Because JunD expression and regulation within the SON has not been previously described, we have used in situ hybridisation and the quantitative reverse transcriptase-polymerase chain reaction to confirm the array results, demonstrating a significant increase in JunD mRNA levels following 24 and 72 h of water deprivation. Western blot and immunohistochemistry revealed a significant increase in JunD protein expression following dehydration. Double-staining fluorescence immunohistochemistry with a neurone-specific marker (NeuN) demonstrated that JunD staining is predominantly neuronal. Additionally, JunD immunoreactivity is observed primarily in vasopressin-containing neurones with markedly less staining seen in oxytocin-containing MCNs. Furthermore, JunD is highly co-expressed with c-Fos in MCNs of the SON following dehydration. These results suggest that JunD plays a role in the regulation of gene expression within MCNs of the SON in association with other Fos and Jun family members.

Variation in the composition of the AP1 complex in PC12 cells following induction by NGF and TPA

The rat pheochromocytoma cell line PC 12 differentiates in response to NGF. Exposure to NGF induces a class of genes termed immediate early that includes many transcription factors including c-jun and c-fos which can constitute the AP1 complex. Induction of such transcription factors by NGF could be a method by which the cell redirects its program of gene expression that results in differentiation. In this study, it is demonstrated that the complement of transcription factors that constitute the AP1 complex alters with the continued passage of PC12 cells. PC 12 cells from early passage contain no AP1 activity, whereas with passage the cells constitutively express an AP1 complex; however, no morphological differences are observed. The AP1 binding activity can be further induced in all PC12 cells studied by NGF or TPA. The analysis of c-jun, c-fos, and the fos-related antigens that can constitute the AP1 complex demonstrated compositional variation of this complex by passage in culture and by exposure to NGF or TPA. As these AP1 transcription complexes may mediate the action of NGF in PC12 cells it is important to correlate the changes in composition of the complex with differentiation.

Transcriptional regulation of the mouse CD11c promoter by AP-1 complex with JunD and Fra2 in dendritic cells

CD11c, a member of the β(2) integrin family of adhesion molecule, is expressed on the surface of myeloid lineages and activated lymphoid cells and forms a heterodimeric receptor with CD18. We analyzed the mouse CD11c promoter structure to elucidate the transcriptional regulation in dendritic cells (DCs). By reporter assay, the -84/-65 region was identified to be essential for activity of the mouse CD11c promoter in the mouse bone marrow-derived (BM) DCs and monocyte cell line RAW264.7. An electrophoretic mobility shift assay using a number of antibodies against transcription factors revealed that the target region was recognized by a complex including JunD and Fra2, which are transcription factors belonging to the AP-1 family. The direct interaction of JunD and Fra2 with the CD11c promoter was further confirmed by a chromatin immunoprecipitation assay using CD11c-positive cells purified from BMDCs. Finally, mouse JunD and/or Fra2 siRNA was introduced into BMDCs to evaluate the involvement of these factors against CD11c transcription and found that Fra2 siRNA reduced cell surface expression level of CD11c. These results indicate that AP-1 composed with JunD and Fra2 protein plays a primary role in enhancing the transcription level of the CD11c gene in DC.

Human T-cell leukemia virus type 1 (HTLV-1) bZIP factor requires cellular transcription factor JunD to upregulate HTLV-1 antisense transcription from the 3' long terminal repeat

Infection with the human T-cell leukemia virus type 1 (HTLV-1) results in a variety of diseases including adult T-cell leukemia (ATL), a fatal malignancy characterized by the uncontrolled proliferation of virally infected CD4(+) T cells. The HTLV-1 basic leucine zipper factor (HBZ) is believed to contribute to development and maintenance of ATL. Unlike the other HTLV-1 genes, the hbz gene is encoded on the complementary strand of the provirus and therefore is not under direct control of the promoter within the 5' long terminal repeat (LTR) of the provirus. This promoter can undergo inactivating genetic or epigenetic changes during the course of ATL that eliminates expression of all viral genes except that of hbz. In contrast, repressive modifications are not known to occur on the hbz promoter located in the 3' LTR, and hbz expression has been consistently detected in all ATL patient samples. Although Sp1 regulates basal transcription from the HBZ promoter, other factors that activate transcription remain undefined. In this study, we used a proviral reporter construct deleted of the 5' LTR to show that HBZ upregulates its own expression through cooperation with JunD. Activation of antisense transcription was apparent in serum-deprived cells in which the level of JunD was elevated, and elimination of JunD expression by gene knockout or shRNA-mediated knockdown abrogated this effect. Activation through HBZ and JunD additionally required Sp1 binding at the hbz promoter. These data favor a model in which JunD is recruited to the promoter through Sp1, where it heterodimerizes with HBZ thereby enhancing its activity. Separately, hbz gene expression led to an increase in JunD abundance, and this effect correlated with emergence of features of transformed cells in immortalized fibroblasts. Overall, our results suggest that JunD represents a novel therapeutic target for the treatment of ATL.

Global expression analysis identified a preferentially nerve growth factor-induced transcriptional program regulated by sustained mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) and AP-1 protein activation during PC12 cell differentiation

Neuronal differentiation of PC12 cells in response to NGF is a prototypical model in which signal duration determines a biological response. Sustained ERK activity induced by NGF, as compared with transient activity induced by EGF, is critical to the differentiation of these cells. To characterize the transcriptional program activated preferentially by NGF, we compared global gene expression profiles between cells treated with NGF and EGF for 2-4 h, when sustained ERK signaling in response to NGF is most distinct from the transient signal elicited by EGF. This analysis identified 69 genes that were preferentially up-regulated in response to NGF. As expected, up-regulation of these genes was mediated by sustained ERK signaling. In addition, they were up-regulated in response to other neuritogenic treatments (pituitary adenylate cyclase-activating polypeptide and 12-O-tetradecanoylphorbol-13-acetate plus dbcAMP) and were enriched for genes related to neuronal differentiation/function. Computational analysis and chromatin immunoprecipitation identified binding of CREB and AP-1 family members (Fos, FosB, Fra1, JunB, JunD) upstream of >30 and 50%, respectively, of the preferentially NGF-induced genes. Expression of several AP-1 family members was induced by both EGF and NGF, but their induction was more robust and sustained in response to NGF. The binding of Fos family members to their target genes was similarly sustained in response to NGF and was reduced upon MEK inhibition, suggesting that AP-1 contributes significantly to the NGF transcriptional program. Interestingly, Fra1 as well as two other NGF-induced AP-1 targets (HB-EGF and miR-21) function in positive feedback loops that may contribute to sustained AP-1 activity.

Menin and JunD regulate gastrin gene expression through proximal DNA elements

Mutations in the MEN1 gene correlate with multiple endocrine neoplasia I (MEN1). Gastrinomas are the most malignant of the neuroendocrine tumors associated with MEN1. Because menin and JunD proteins interact, we examined whether JunD binds to and regulates the gastrin gene promoter. Both menin and JunD are ubiquitous nuclear proteins that we showed colocalize in the gastrin-expressing G cells of the mouse antrum. Transfection with a JunD expression vector alone induced endogenous gastrin mRNA in AGS human gastric cells, and the induction was blocked by menin overexpression. We mapped repression by menin to both a nonconsensus AP-1 site and proximal GC-rich elements within the human gastrin promoter. Chromatin immunoprecipitation assays, EMSAs, and DNA affinity precipitation assays documented that JunD and Sp1 proteins bind these two elements and are both targets for menin regulation. Consistent with menin forming a complex with histone deacetylases, we found that repression of gastrin gene expression by menin was reversed by trichostatin A. In conclusion, proximal DNA elements within the human gastrin gene promoter mediate interactions between JunD, which induces gastrin gene expression and menin, which suppresses JunD-mediated activation.

Mouse models of endocrine tumours

Since the onset of the genomic era, there has been tremendous progress in identifying the genetic causes of endocrine tumours. Although this knowledge is valuable in its own right, understanding the molecular basis of tumourigenesis allows the development of new therapies targeted at the causative defects. Understanding the connection between genotype and phenotype is a complex process, which can only be partially understood from the analysis of primary tumours or from the studies of cells in vitro. To bridge this gap, genetically modified mice have been developed to allow molecular dissection of the relevant defects in an intact organism. In this article, we discuss the status of genetic modelling for hereditary and sporadic endocrine tumourigenesis with a goal towards providing a view of how this technology will be of future benefit to clinicians developing specifically targeted therapies for endocrine tumours.

Induced ATF-2 represses CDK4 transcription through dimerization with JunD inhibiting intestinal epithelial cell growth after polyamine depletion

Intestinal epithelium is a rapidly self-renewing tissue in the body, and its homeostasis is tightly regulated by numerous factors including polyamines. Decreased levels of cellular polyamines increase activating transcription factor (ATF)-2, but the exact role and mechanism of induced ATF-2 in the regulation of intestinal epithelial cell (IEC) growth remain elusive. Cyclin-dependent kinase (CDK) 4 is necessary for the G1-to-S phase transition during the cell cycle, and its expression is predominantly controlled at the transcription level. Here, we reported that induced ATF-2 following polyamine depletion repressed CDK4 gene transcription in IECs by increasing formation of the ATF-2/JunD heterodimers. ATF-2 formed complexes with JunD as measured by immunoprecipitation using the ATF-2 and JunD antibodies and by glutathione S-transferase (GST) pull-down assays using GST-ATF-2 fusion proteins. Studies using various mutants of GST-ATF-2 revealed that formation of the ATF-2/JunD dimers depended on the COOH-terminal basic region-leucine zipper domain of ATF-2. Polyamine depletion increased ATF-2/JunD complex and inhibited CDK4 transcription as indicated by a decrease in the levels of CDK4-promoter activity and its mRNA. ATF-2 silencing not only prevented inhibition of CDK4 transcription in polyamine-deficient cells but also abolished repression of CDK4 expression induced by ectopic JunD overexpression. ATF-2 silencing also promoted IEC growth in polyamine-depleted cells. These results indicate that induced ATF-2/JunD association following polyamine depletion represses CDK4 transcription, thus contributing to the inhibition of IEC growth.

Ligand-specific sequential regulation of transcription factors for differentiation of MCF-7 cells

Background

Sharing a common ErbB/HER receptor signaling pathway, heregulin (HRG) induces differentiation of MCF-7 human breast cancer cells while epidermal growth factor (EGF) elicits proliferation. Although cell fates resulting from action of the aforementioned ligands completely different, the respective gene expression profiles in early transcription are qualitatively similar, suggesting that gene expression during late transcription, but not early transcription, may reflect ligand specificity. In this study, based on both the data from time-course quantitative real-time PCR on over 2,000 human transcription factors and microarray of all human genes, we identified a series of transcription factors which may control HRG-specific late transcription in MCF-7 cells.

Results

We predicted that four transcription factors including EGR4, FRA-1, FHL2, and DIPA should have responsibility of regulation in MCF-7 cell differentiation. Validation analysis suggested that one member of the activator protein 1 (AP-1) family, FOSL-1 (FRA-1 gene), appeared immediately following c-FOS expression, might be responsible for expression of transcription factor FHL2 through activation of the AP-1 complex. Furthermore, RNAi gene silencing of FOSL-1 and FHL2 resulted in increase of extracellular signal-regulated kinase (ERK) phosphorylation of which duration was sustained by HRG stimulation.

Conclusion

Our analysis indicated that a time-dependent transcriptional regulatory network including c-FOS, FRA-1, and FHL2 is vital in controlling the ERK signaling pathway through a negative feedback loop for MCF-7 cell differentiation.

Adapted Boolean network models for extracellular matrix formation

BACKGROUND

Due to the rapid data accumulation on pathogenesis and progression of chronic inflammation, there is an increasing demand for approaches to analyse the underlying regulatory networks. For example, rheumatoid arthritis (RA) is a chronic inflammatory disease, characterised by joint destruction and perpetuated by activated synovial fibroblasts (SFB). These abnormally express and/or secrete pro-inflammatory cytokines, collagens causing joint fibrosis, or tissue-degrading enzymes resulting in destruction of the extra-cellular matrix (ECM).We applied three methods to analyse ECM regulation: data discretisation to filter out noise and to reduce complexity, Boolean network construction to implement logic relationships, and formal concept analysis (FCA) for the formation of minimal, but complete rule sets from the data.

RESULTS

First, we extracted literature information to develop an interaction network containing 18 genes representing ECM formation and destruction. Subsequently, we constructed an asynchronous Boolean network with biologically plausible time intervals for mRNA and protein production, secretion, and inactivation. Experimental gene expression data was obtained from SFB stimulated by TGFbeta1 or by TNFalpha and discretised thereafter. The Boolean functions of the initial network were improved iteratively by the comparison of the simulation runs to the experimental data and by exploitation of expert knowledge. This resulted in adapted networks for both cytokine stimulation conditions. The simulations were further analysed by the attribute exploration algorithm of FCA, integrating the observed time series in a fine-tuned and automated manner. The resulting temporal rules yielded new contributions to controversially discussed aspects of fibroblast biology (e.g., considerable expression of TNF and MMP9 by fibroblasts stimulation) and corroborated previously known facts (e.g., co-expression of collagens and MMPs after TNFalpha stimulation), but also revealed some discrepancies to literature knowledge (e.g., MMP1 expression in the absence of FOS).

CONCLUSION

The newly developed method successfully and iteratively integrated expert knowledge at different steps, resulting in a promising solution for the in-depth understanding of regulatory pathways in disease dynamics. The knowledge base containing all the temporal rules may be queried to predict the functional consequences of observed or hypothetical gene expression disturbances. Furthermore, new hypotheses about gene relations were derived which await further experimental validation.

c-Jun, Fra-2, and ATF-2 immunoreactivity in the jejunal tissues of the healthy rat

The aim of this study was to compare the localization of some activator protein-1 (AP-1) proteins in healthy rat jejunum. For this purpose, the AP-1 members c-Jun, Fra-2, and ATF-2 immunoreactivity (c-Jun-IR, Fra-2-IR, ATF-2-IR) in villus epithelial cells (ECs), intravillous lamina propria cells (LPCs), crypt cells (CCs), and smooth muscle cells (SMCs) were analyzed by immunohistochemical methods. Among all the cell groups, the lowest positivity ratio was found in c-Jun-IR and the highest positivity ratio was found in ATF-2-IR. For each group of ECs, LPCs, CCs, and SMCs, c-Jun-IR, Fra-2-IR, and ATF-2-IR were compared and statistically significant differences found. There were no significant differences among the cell groups with respect to c-Jun-IR and Fra-2-IR, but there was a statistically significant difference in ATF-2-IR. These findings suggest that each member of AP-1 is expressed differently and that ATF-2 is more active than c-Jun and Fra-2 in physiological conditions in healthy rat jejunum.

JunD represses transcription and translation of the tight junction protein zona occludens-1 modulating intestinal epithelial barrier function

The AP-1 transcription factor JunD is highly expressed in intestinal epithelial cells, but its exact role in maintaining the integrity of intestinal epithelial barrier remains unknown. The tight junction (TJ) protein zonula occludens (ZO)-1 links the intracellular domain of TJ-transmembrane proteins occludin, claudins, and junctional adhesion molecules to many cytoplasmic proteins and the actin cytoskeleton and is crucial for assembly of the TJ complex. Here, we show that JunD negatively regulates expression of ZO-1 and is implicated in the regulation of intestinal epithelial barrier function. Increased JunD levels by ectopic overexpression of the junD gene or by depleting cellular polyamines repressed ZO-1 expression and increased epithelial paracellular permeability. JunD regulated ZO-1 expression at the levels of transcription and translation. Transcriptional repression of ZO-1 by JunD was mediated through cAMP response element-binding protein-binding site within its proximal region of the ZO-1-promoter, whereas induced JunD inhibited ZO-1 mRNA translation by enhancing the interaction of the ZO-1 3'-untranslated region with RNA-binding protein T cell-restricted intracellular antigen 1-related protein. These results indicate that JunD is a biological suppressor of ZO-1 expression in intestinal epithelial cells and plays a critical role in maintaining epithelial barrier function.

JunD mediates androgen-induced oxidative stress in androgen dependent LNCaP human prostate cancer cells

BACKGROUND

Numerous and compelling evidence shows that high level of reactive oxygen species (ROS) plays a key role in prostate cancer occurrence, recurrence and progression. The molecular mechanism of ROS overproduction in the prostate gland, however, remains mostly unknown. Unique AP-1 transcription factor JunD has been shown to inhibit cell proliferation, promote differentiation and mediate stress responses in a variety of eukaryotic cells. We previously reported that androgen-androgen receptor induced ROS production in androgen-dependent LNCaP human prostate cancer cells is associated with increased JunD level/AP-1 transcriptional activity.

METHODS

LNCaP cells constitutively overexpressing a functionally inactive form of JunD (JunDDeltaTA) or stably transfected with JunD siRNA (siJunD) to suppress JunD protein expression were established. Overexpression of JunD in LNCaP cells using transient transfection method was applied to assess the induction of ROS production in LNCaP cells. DCF assay was used to measure the ROS concentrations in the transfected as well as non-transfected control cells. RT-PCR and Western blot analyses were used to confirm silencing or overexpression of JunD in the transfected cells.

RESULTS

In the absence of androgen, LNCaP cells transiently transfected with a JunD overexpressing vector have relatively enhanced cellular ROS levels as compared to LNCaP cells transfected with a vector control. LNCaP cells that fail to express functional JunD (JunDDeltaTA or siJunD) do not exhibit any increase in ROS production in response to androgen.

CONCLUSION

Based on these data, we conclude that JunD is an essential mediator of the androgen-induced increase in ROS levels in LNCaP cells.

Multiple facets of junD gene expression are atypical among AP-1 family members

JunD is a versatile AP-1 transcription factor that can activate or repress a diverse collection of target genes. Precise control of junD expression and JunD protein-protein interactions modulate tumor angiogenesis, cellular differentiation, proliferation and apoptosis. Molecular and clinical knowledge of two decades has revealed that precise JunD activity is elaborated by interrelated layers of constitutive transcriptional control, complex post-transcriptional regulation and a collection of post-translational modifications and protein-protein interactions. The stakes are high, as inappropriate JunD activity contributes to neoplastic, metabolic and viral diseases. This article deconvolutes multiple layers of control that safeguard junD gene expression and functional activity. The activity of JunD in transcriptional activation and repression is integrated into a regulatory network by which JunD exerts a pivotal role in cellular growth control. Our discussion of the JunD regulatory network integrates important open issues and posits new therapeutic targets for the neoplastic, metabolic and viral diseases associated with JunD/AP-1 expression.

Cloning of JunA and JunB and comparison of mRNA expression levels in two Xiphophorus melanoma models

The cloning and mRNA expression analysis of Xiphophorus maculatus JunA and JunB proto-oncogenes (designated X-JunA and X-JunB, respectively) is described. In mammals, JunA and JunB proteins make up the activator protein-1 (AP-1) transcription factor with related Fos proteins. The deduced amino acid sequences of X-JunA and X-JunB exhibit moderate degrees of similarity when compared to their human homologues, while the regions considered functionally critical, namely, the transactivation domains, DNA-binding domain, and the leucine zipper, are highly conserved. X-JunA and X-JunB mRNA expression levels in six X. maculatus Jp 163 A tissues were assayed by real-time RT-PCR. In addition, X-JunA and X-JunB mRNA levels are compared in skin and tumor tissues derived from two distinct Xiphophorus backcross hybrid tumor models, one of which develops melanoma spontaneously, whereas the other requires induction via UVB exposure for melanoma development. X-JunB mRNA expression was higher than X-JunA expression in tissues from X. maculatus parental animals. X-JunB was also more highly expressed than X-JunA in both spontaneous and induced melanoma tissue and nonmelanotic skin tissue. However, X-JunA mRNA levels were significantly higher in the spontaneous melanomas compared to melanomas induced by UVB exposure. The authors speculate that these findings may indicate that JunA regulation is affected by regulatory differences between the two melanoma model systems.

Multiple endocrine neoplasia type 1 (MEN1): analysis of 1336 mutations reported in the first decade following identification of the gene

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by the occurrence of tumors of the parathyroids, pancreas, and anterior pituitary. The MEN1 gene, which was identified in 1997, consists of 10 exons that encode a 610-amino acid protein referred to as menin. Menin is predominantly a nuclear protein that has roles in transcriptional regulation, genome stability, cell division, and proliferation. Germline mutations usually result in MEN1 or occasionally in an allelic variant referred to as familial isolated hyperparathyroidism (FIHP). MEN1 tumors frequently have loss of heterozygosity (LOH) of the MEN1 locus, which is consistent with a tumor suppressor role of MEN1. Furthermore, somatic abnormalities of MEN1 have been reported in MEN1 and non-MEN1 endocrine tumors. The clinical aspects and molecular genetics of MEN1 are reviewed together with the reported 1,336 mutations. The majority (>70%) of these mutations are predicted to lead to truncated forms of menin. The mutations are scattered throughout the>9-kb genomic sequence of the MEN1 gene. Four, which consist of c.249_252delGTCT (deletion at codons 83-84), c.1546_1547insC (insertion at codon 516), c.1378C>T (Arg460Ter), and c.628_631delACAG (deletion at codons 210-211) have been reported to occur frequently in 4.5%, 2.7%, 2.6%, and 2.5% of families, respectively. However, a comparison of the clinical features in patients and their families with the same mutations reveals an absence of phenotype-genotype correlations. The majority of MEN1 mutations are likely to disrupt the interactions of menin with other proteins and thereby alter critical events in cell cycle regulation and proliferation.

Induction of deltaFosB in the periaqueductal gray by stress promotes active coping responses

We analyzed the influence of the transcription factor DeltaFosB on learned helplessness, an animal model of affective disorder wherein a subset of mice exposed to inescapable stress (IS) develop a deficit in escape behavior. Repeated IS induces DeltaFosB in the ventrolateral periaqueductal gray (vlPAG), and levels of the protein are highly predictive of an individual's subsequent behavorial deficit-with the strongest DeltaFosB induction observed in the most resilient animals. Induction of DeltaFosB by IS predominates in substance P-positive neurons in the vlPAG, and the substance P gene, a direct target for DeltaFosB, is downregulated upon DeltaFosB induction. Local overexpression of DeltaFosB in the vlPAG using viral-mediated gene transfer dramatically reduces depression-like behaviors and inhibits stress-induced release of substance P. These results indicate that IS-induced accumulation of DeltaFosB in the vlPAG desensitizes substance P neurons enriched in this area and opposes behavioral despair by promoting active defense responses.

Hint1 inhibits growth and activator protein-1 activity in human colon cancer cells

There is accumulating evidence that histidine triad (HIT) nucleotide-binding protein 1 (HINT1), a member of the evolutionary highly conserved HIT protein super family, is a novel tumor suppressor. However, the mechanism of action of HINT1 with respect to tumor suppression is not known. In the present study, we found that a series of human colon cancer cell lines displayed various levels of expression of HINT1, with a very low level in SW480 cells. This cell line also displayed partial methylation of the promoter region of the Hint1 gene, and treatment of these cells with 5-azadeoxycitidine increased expression of Hint1 mRNA and protein. Therefore, the decreased expression of HINT1 in SW480 cells seems to be due to epigenetic silencing. Increased expression of HINT1 in these cells, using a retrovirus vector (pLNCX2) that encodes either wild-type (WT) Hint1 or a point mutant (His(112)/Asn(112)) of Hint1, inhibited the proliferation of SW480 cells. Because of the important role of the activator protein-1 (AP-1) transcription factor in cancer cells, we examined possible effects of HINT1 on AP-1 transcription factor activity in SW480 cells transfected with an AP-1-luciferase reporter. We found that cotransfection with a pHA-Hint1 plasmid DNA significantly inhibited this activity. Studies with inhibitors indicated that AP-1 activity in SW480 cells requires the activity of c-Jun NH(2)-terminal kinase (JNK) 2 and not JNK1. Cotransfection with the Hint1 plasmid DNA also inhibited AP-1-luciferase reporter activity in WT mouse embryo fibroblast (MEF) studies, and studies with JNK1 deleted or JNK2 deleted MEFs confirmed the essential role for JNK2, but not JNK1, in mediating AP-1 activity. Recent studies indicate that the protein plenty of SH3 (POSH) provides a scaffold that enhances JNK activity. We found that cotransfection of a plasmid DNA encoding POSH stimulated the phosphorylation of c-Jun and also AP-1 reporter activity, and cotransfection with Hint1 inhibited both of these activities. Furthermore, coimmunoprecipitation studies provided evidence that HINT1 forms an in vivo complex with POSH and JNK. These results suggest that HINT1 inhibits AP-1 activity by binding to a POSH-JNK2 complex, thus inhibiting the phosphorylation of c-Jun. This effect could contribute to the tumor suppressor activity of HINT1.

Induced JunD in intestinal epithelial cells represses CDK4 transcription through its proximal promoter region following polyamine depletion

Maintenance of intestinal epithelial integrity requires cellular polyamines that regulate expression of various genes involved in cell proliferation, growth arrest and apoptosis. In prior studies, depletion of cellular polyamines has been shown to stabilize JunD, a member of the AP-1 (activator protein-1) family of transcription factors, leading to inhibition of intestinal epithelial cell proliferation, but the exact downstream targets of induced JunD remain elusive. CDK4 (cyclin-dependent kinase 4) is essential for the G1- to S-phase transition during the cell cycle and its expression is primarily controlled at the transcriptional level. In the present study, we show that induced JunD in IECs (intestinal epithelial cells) is a transcriptional repressor of the CDK4 gene following polyamine depletion. Increased JunD in polyamine-deficient cells was associated with a significant inhibition of CDK4 transcription, as indicated by repression of CDK4-promoter activity and decreased levels of CDK4 mRNA and protein, all of which were prevented by using specific antisense JunD oligomers. Ectopic expression of the wild-type junD also repressed CDK4-promoter activity and decreased levels of CDK4 mRNA and protein without any effect on CDK2 expression. Gel shift and chromatin immunoprecipitation assays revealed that JunD bound to the proximal region of the CDK4-promoter in vitro as well as in vivo, while experiments using different CDK4-promoter mutants showed that transcriptional repression of CDK4 by JunD was mediated through an AP-1 binding site within this proximal sequence of the CDK4-promoter. These results indicate that induced JunD in IECs represses CDK4 transcription through its proximal promoter region following polyamine depletion.

Polyamines and mRNA stability in regulation of intestinal mucosal growth

The mammalian intestinal epithelium is a rapidly self-renewing tissue in the body, and its homeostasis is preserved through strict regulation of epithelial cell proliferation, growth arrest, and apoptosis. Polyamines are necessary for normal intestinal mucosal growth and decreasing cellular polyamines inhibits cell proliferation and disrupts epithelial integrity. An increasing body of evidence indicates that polyamines regulate intestinal epithelial cell renewal by virtue of their ability to modulate expression of various genes and that growth inhibition following polyamine depletion results primarily from the activation of growth-inhibiting genes rather than a simple decrease in expression of growth-promoting genes. In this review article, we will focus on changes in expression of growth-inhibiting genes following polyamine depletion and further analyze in some detail the mechanisms through which mRNA stability is regulated by RNA-binding proteins.

JunB and JunD Regulate Human Heme Oxygenase-1 Gene Expression in Renal Epithelial Cells

Heme oxygenase-1 is a highly inducible gene, the product of which catalyzes breakdown of the prooxidant heme. The purpose of this study was to investigate the regulation of the human heme oxygenase-1 gene in renal epithelial cells. DNase I hyper-sensitivity studies identified three distal sites (HS-2, -3, and -4) corresponding to approximately -4.0, -7.2, and -9.2 kb, respectively, of the heme oxygenase-1 promoter in addition to one proximal region, HS-1, which we have shown previously to be an E box. In vivo dimethyl sulfate footprinting of the HS-2 region revealed six individual protected guanines. Two mutations within HS-2 combined with a third mutation of the proximal E box abolished hemin- and cadmium-driven heme oxygenase-1 promoter activation, suggesting that these three sites synergized for maximal heme oxygenase-1 induction. Jun proteins bound to the antioxidant response element in the HS-2 region in vitro and associated with the heme oxygenase-1 promoter in vivo. JunB and JunD contribute opposing effects; JunB activated whereas JunD repressed heme oxygenase-1 expression in human renal epithelial cells, results that were corroborated in junB(-)(/)(-) and junD(-)(/)(-) cells. We propose that heme oxygenase-1 induction is controlled by a dynamic interplay of regulatory proteins, and we provide new insights into the molecular control of the human heme oxygenase-1 gene.

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

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

Expression pattern of JunD after acute or chronic l-DOPA treatment: Comparison with ΔFosB

In this study, we have used 6-hydroxydopamine-lesioned rats to examine changes in striatal junD and fosB/deltafosB expression induced by acute and chronic treatment with L-DOPA (5 and 15 days). Changes at the protein levels were studied using Western immunoblotting while mRNA changes were compared using in situ hybridization histochemistry. We observed a significant increase in the level of deltaFosB proteins after chronic treatment with L-DOPA, an effect that was not observed for JunD proteins. In addition, the upregulation of deltaFosB was already present after an acute treatment but increased upon chronic treatment. By contrast, junD and deltafosB mRNA were both upregulated significantly above control levels after an acute injection of L-DOPA. In conclusion, this study suggests a differential expression pattern of junD and deltafosB in a rat model of L-DOPA-induced dyskinesia. The upregulation of deltaFosB protein, but not JunD, is likely to reflect an increased stability of the deltaFosB proteins without ongoing enhanced transcription of the encoding genes.

Deregulation of AP-1 proteins in collagen gel-induced epithelial cell apoptosis mediated by low substratum rigidity

In this study, we established that collagen gel, but not collagen gel coating, induced apoptosis exclusively in epithelial cell lines, which indicated that low substratum rigidity might trigger cell apoptosis. To confirm this, we used collagen gels with different rigidities due to cross-linking or physical disruption of collagen fibrils caused by sonication. We found that collagen gel-induced apoptosis was inversely correlated with substratum rigidity. Low substratum rigidity collagen gel-induced apoptosis was neither prevented by Bcl-2 overexpression nor preceded by mitochondrial release of cytochrome c. This suggested that the mitochondrial pathway was not involved in low substratum rigidity-induced apoptosis. Low substratum rigidity activated c-Jun N-terminal kinase (JNK) within 4 h, but it also rapidly down-regulated c-Jun within 1 h and triggered persistent aberrant expression of c-Fos for at least 24 h. Either reduced c-Jun expression or c-Fos overexpression induced apoptosis in several epithelial cells. Inhibiting low substratum rigidity-induced JNK activation prevented aberrant c-Fos expression but only partially blocked low substratum rigidity-induced apoptosis. Taking these results together, we conclude that low substratum rigidity collagen gel induced apoptosis in epithelial cells and that deregulated AP-1 proteins mediated that apoptosis, at least in part.

Both the basal transcriptional activity of the GADD45A gene and its enhancement after ionizing irradiation are mediated by AP-1 element

The growth arrest and DNA damage-inducible gene 45A (GADD45A) is involved in the DNA repair, maintenance of genomic stability, cell cycle control and apoptosis, and thus plays an important role in cellular response to DNA damage. The GADD45A gene is responsive to a variety of DNA-damaging agents, including ionizing radiation (IR), methyl methanesulfonate (MMS), and ultraviolet (UV) radiation. It is generally thought that induction of the GADD45A gene after IR exposure is principally p53-dependent, requiring binding of the p53 protein to the p53-recognition sequence in the third intron. However, the involvement of factors other than p53 in transcriptional regulation of the GADD45A gene after IR exposure has not been elucidated. In the present study, we show that the 5'-flanking region containing two OCT sites and a CCAAT box, as well as p53 and AP-1 sites in the third intron, are required for the basal transcriptional activity of the reporter gene. In addition, AP-1 recognition element was shown to be involved in the transcriptional enhancement of the GADD45A gene after X-ray irradiation. Electrophoretic mobility shift analysis (EMSA) and Chromatin immunoprecipitation (ChIP) assay revealed that JunD binds to the third intron of the GADD45A gene. These observations suggest that AP-1 complexes containing JunD, in addition to p53, play an important role not only in transcriptional enhancement by IR but also in basal expression of the GADD45A gene via binding to the AP-1 site in the third intron.

Identification of human hepatic stimulator substance gene promoter and demonstration of dual regulation of AP1/AP4 cis-acting element in different cell lines

Human hepatic stimulator substance (hHSS) is a newly identified growth-promoting factor in the liver. HSS is capable of stimulating hepatic regeneration in partial hepatectomized rats, thus, promoting growth of hepatic tumor cells. To understand and elucidate the transcriptional regulation of hHSS gene, the 4890bp of 5'-flanking region of the gene have been isolated and sequenced. The transcriptional start site, located at 248nt upstream from the ATG starting codon, was identified by 5'-rapid amplification cDNA end (5'-RACE). The classical promoter sequences, such as TATA box or GAATT were not identified in the promoter region, instead a GC-rich segment was formed (>70%) by expanding to a longer than 400bp, and immediately upstream from the ATG start codon. The transient transfection assays, using promoter deletion constructs, showed that hHSS promoter was efficiently capable in driving the reporter expression not only in HepG2 cells, but also in Cos7 cells. A region spanning nucleotides in the range of -447 to -358bp revealed a negative regulation on promoter activity in HepG2 cells, but with positive regulation in Cos7 and Hela cells. The promoter activity was obviously influenced by AP1/AP4 (-375/-369nt) mutation in these three cell lines. EMSAs showed that the site was recognized by AP1 in HepG2 cell, and only by an AP4 protein in Cos7 cells. The c-Jun bound to the promoter was further verified by supershift in HepG2 cells and human liver tissue. Chromatin immuno-precipitation (ChIP) demonstrated that there was a direct association of c-Jun with hHSS promoter in HepG2 cells. The c-Jun strongly suppressed hHSS promoter activity in transient expression analyses in HepG2 cells. Mutations in the AP1 binding sites rescued suppression caused by c-Jun, suggesting this was a direct regulation of the hHSS promoter. In contrast, there was no significant effect in c-Jun over-expressed Cos7 and Hela cells. The tissue-specific function of c-Jun in hHSS promoter activity may in part help explain the differences in biology function of hHSS between liver and non-liver cells.

Role of transcription factor activator protein 1 (AP1) in epidermal growth factor-mediated protection against apoptosis induced by a DNA-damaging agent

We investigated the survival signals of epidermal growth factor (EGF) in human gastric adenocarcinoma cell line TMK-1. Treatment of TMK-1 cells with adriamycin (ADR) caused apoptosis and apoptosis-related reactions such as the release of cytochrome c from mitochondria and the activation of caspase 9. However, EGF treatment greatly reduced the ADR-induced apoptosis as well as these reactions. We previously reported that hepatocyte growth factor transmitted protective signals against ADR-induced apoptosis by causing activation of the phosphatidylinositol-3'-OH kinase (PtdIns3-K)/Akt signaling pathway in human epithelial cell line MKN74 [Takeuchi K & Ito F (2004) J Biol Chem279, 892-900]. However, PtdIns3-K/Akt signaling did not mediate the antiapoptotic action of EGF in TMK-1 cells. EGF increased the expression of the Bcl-X(L) protein, an antiapoptotic member of the Bcl-2 family, but not that of other anti (Bcl-2) or proapoptotic (Bad and Bax) protein members. Expression of the c-Fos and c-Jun, components of activator protein 1 (AP1), which are known to regulate bcl-X(L) gene transcription, were increased in response to EGF. Pretreatment of the cells with PD98059, an inhibitor of MAP kinase kinase, inhibited the EGF-induced c-Fos and c-Jun expression, AP1 DNA binding, Bcl-X(L) expression, and the resistance against ADR-induced apoptosis, suggesting that EGF transmitted the antiapoptotic signal in such a way that it activated AP1 via a MAP kinase signaling pathway. TMK-1 cells stably transfected with TAM67, c-Jun dominant-negative mutant, did not display EGF-induced Bcl-X(L) expression or resistance against ADR-induced apoptosis. These results indicate that AP1-mediated upregulation of Bcl-X(L) expression is critical for protection of TMK-1 cells against ADR-induced apoptosis.

Growth hormone-secreting tumors: genetic aspects and data from animal models

Hereditary cases of growth hormone (GH)-secreting tumors have been classified into three clinical entities: the multiple endocrine neoplasia type 1 (MEN1) syndrome, the Carney complex (CNC) and the isolated familial somatotropinomas (IFS). The genomic defects associated with MEN1 are all linked to various mutations of the MEN1 gene, which is located at chromosome 11q13 and codes for menin, a nuclear protein expressed in multiple tissues. Inactivation of the MEN1 gene appears to be only rarely associated with sporadic pituitary tumor development. A CNC-associated gene, the type 1 alpha regulatory subunit (R1alpha) of cAMP-dependent protein kinase A (PRKAR1A), is located at 17q23-24. A second CNC candidate gene is located at chromosome 2p15-16, with characteristics of inheritance consistent with an oncogene; however, this gene has not been identified yet. PRKAR1A mutations are infrequently associated with sporadic GH-secreting adenomas. A candidate IFS gene is located at 11q13, in proximity to the MEN1 gene, at a locus narrowed down to a 2.21-Mb area, with approximately 50 genes, that does not appear to include the MEN1 gene. Apart from the linkage of IFS to 11q13, a possible linkage to 2p16 has also been raised, although data are still inconclusive. This manuscript reviews genetic aspects of hereditary GH-secreting tumors, data from animal models resulting from the inactivation of the MEN1 and PRKAR1A tumor suppressor genes and available in vitro data regarding possible functions of menin, the product of the MEN1 gene.

Reg IV activates the epidermal growth factor receptor/Akt/AP-1 signaling pathway in colon adenocarcinomas

BACKGROUND & AIMS

Reg IV, a secreted protein and member of the Reg multigene family, is up-regulated in malignancies of the human gastrointestinal tract, including colorectal carcinoma (CRC). However, in vitro signal transduction pathway(s) utilized by Reg IV are not yet known.

METHODS

To determine the signaling pathway(s) responsive to Reg IV, we examined the effects of purified recombinant human Reg IV (rhR4) on HCT116 and HT29 colon adenocarcinoma cells.

RESULTS

Addition of rhR4 to cultures led to a dose-dependent increase in cell number similar to that observed after treatment with epidermal growth factor (EGF). In addition, rhR4 treatment resulted in rapid phosphorylation of EGF receptor at Tyr992 and Tyr1068 and Akt at Thr308 and Ser473. Using luciferase reporter gene assays, we demonstrated that Reg IV signaling through EGF receptor and Akt results in increased activator protein-1 (AP-1) transcription factor activity. Real-time reverse-transcription polymerase chain reaction and Western blot analyses revealed quantitative increases in c-Jun, JunB, JunD, and FosB expression associated with increased AP-1 activity. Electrophoretic mobility shift assay further revealed significant increases in AP-1 binding activity in rhR4-treated cells, with increased supershift in the presence of antibodies to JunB, JunD, and FosB. Furthermore, rhR4 treatments led to the increased expression of Bcl-2, Bcl-XL, survivin, and matrilysin, genes associated with a poor prognosis in advanced CRC.

CONCLUSIONS

Reg IV is a potent activator of the EGF receptor/Akt/AP-1 signaling pathway in CRC. Disruption of Reg signaling may have utility as a therapeutic intervention for human gastrointestinal adenocarcinomas.

Identification of genes specific to “oval cells” in the rat 2-acetylaminofluorene/partial hepatectomy model

Under certain conditions liver regeneration can be accomplished by hepatic progenitor cells ("oval cells"). So far, only few factors have been identified to be uniquely regulated by the "oval cell" compartment. Using macroarray analysis in a rat model of oval cell proliferation (treatment with 2-acetylaminofluorene and partial hepatectomy, AAF + PH), we identified 12 differentially expressed genes compared to appropriate control models (AAF treatment and sham operation or AAF treatment alone). Further analysis in models of normal liver regeneration (ordinary PH) and acute phase response (turpentine oil-treated rats) revealed that three out of 12 genes (thymidine kinase 1, Jun-D and ADP-ribosylation factor 4) were not affected by the hepatic acute phase reaction but similarly overexpressed in both "oval cell"-dependant and normal liver regeneration. We characterized Jun-D and ADP-ribosylation factors as novel factors upregulated in oval cells and in non-parenchymal liver cells of normally regenerating livers. However, two out of 12 differentially expressed genes were specifically expressed in oval cells: ras-related protein Rab-3b and Ear-2. On protein level, Rab-3b was increased in total liver homogenates and demonstrated only in clusters of oval cells. We postulate that Ear-2 and Rab-3b may represent novel regulatory factors specifically activated in "oval cells".

Interleukin-12: an update on its immunological activities, signaling and regulation of gene expression

Interleukin-12 (IL-12) is a heterodimeric cytokine composed of the p35 and p40 subunits. It is produced by antigen-presenting cells and plays a critical role in host defense against intracellular microbial infection and control of malignancy via its ability to stimulate both innate and adaptive immune effector cells. The potency of IL-12 renders itself to stringent regulation of the timing, locality and magnitude of its production during an immune response. Subversion of the delicate control and balance frequently leads to immunologic disorders. In this article, we provide an update, since our last review of the subject four years ago, on recent advances in: (1) uncovering of novel activities of IL-12 and related molecules in various immunological settings and models; and (2) dissection of the physiological pathways involved in the modulation of IL-12 production by pathogens and immune regulators. The increased understanding of IL-12 immunobiology and expression will likely benefit the development of therapeutic modalities to correct immune dysfunctions.