The mammalian Jun proteins: redundancy and specificity

Circadian oscillations of cytosine modification in humans contribute to epigenetic variability, aging, and complex disease

BACKGROUND

Maintenance of physiological circadian rhythm plays a crucial role in human health. Numerous studies have shown that disruption of circadian rhythm may increase risk for malignant, psychiatric, metabolic, and other diseases.

RESULTS

Extending our recent findings of oscillating cytosine modifications (osc-modCs) in mice, in this study, we show that osc-modCs are also prevalent in human neutrophils. Osc-modCs may play a role in gene regulation, can explain parts of intra- and inter-individual epigenetic variation, and are signatures of aging. Finally, we show that osc-modCs are linked to three complex diseases and provide a new interpretation of cross-sectional epigenome-wide association studies.

CONCLUSIONS

Our findings suggest that loss of balance between cytosine methylation and demethylation during the circadian cycle can be a potential mechanism for complex disease. Additional experiments, however, are required to investigate the possible involvement of confounding effects, such as hidden cellular heterogeneity. Circadian rhythmicity, one of the key adaptations of life forms on Earth, may contribute to frailty later in life.

Tobacco Exposure Enhances Human Papillomavirus 16 Oncogene Expression via EGFR/PI3K/Akt/c-Jun Signaling Pathway in Cervical Cancer Cells

High-risk human papillomavirus (HR-HPV) infection is not a sufficient condition for cervical cancer development because most infections are benign and naturally cleared. Epidemiological studies revealed that tobacco smoking is a cofactor with HR-HPV for cervical cancer initiation and progression, even though the mechanism by which tobacco smoke cooperates with HR-HPV in this malignancy is poorly understood. As HR-HPV E6/E7 oncoproteins overexpressed in cervical carcinomas colocalize with cigarette smoke components (CSC), in this study we addressed the signaling pathways involved in a potential interaction between both carcinogenic agents. Cervical cancer-derived cell lines, CaSki (HPV16; 500 copies per cell) and SiHa (HPV16; 2 copies per cell), were acutely exposed to CSC at various non-toxic concentrations and we found that E6 and E7 levels were significantly increased in a dose-dependent manner. Using a reporter construct containing the luciferase gene under the control of the full HPV16 long control region (LCR), we also found that p97 promoter activity is dependent on CSC. Non-synonymous mutations in the LCR-resident TPA (12-O-tetradecanoylphorbol 13-acetate)-response elements (TRE) had significantly decreased p97 promoter activation. Phosphoproteomic arrays and specific inhibitors revealed that CSC-mediated E6/E7 overexpression is at least in part reliant on EGFR phosphorylation. In addition, we showed that the PI3K/Akt pathway is crucial for CSC-induced E6/E7 overexpression. Finally, we demonstrated that HPV16 E6/E7 overexpression is mediated by JUN. overexpression, c-Jun phosphorylation and recruitment of this transcription factor to TRE sites in the HPV16 LCR. We conclude that acute exposure to tobacco smoke activates the transcription of HPV16 E6 and E7 oncogenes through p97 promoter activation, which involves the EGFR/PI3K/Akt/C-Jun signaling pathway activation in cervical cancer cells.

Comparison of gene expression profiles between human erythroid cells derived from fetal liver and adult peripheral blood

Background

A key event in human development is the establishment of erythropoietic progenitors in the bone marrow, which is accompanied by a fetal-to-adult switch in hemoglobin expression. Understanding of this event could lead to medical application, notably treatment of sickle cell disease and β-thalassemia. The changes in gene expression of erythropoietic progenitor cells as they migrate from the fetal liver and colonize the bone marrow are still rather poorly understood, as primary fetal liver (FL) tissues are difficult to obtain.

Methods

We obtained human FL tissue and adult peripheral blood (AB) samples from Thai subjects. Primary CD34⁺ cells were cultured in vitro in a fetal bovine serum-based culture medium. After 8 days of culture, erythroid cell populations were isolated by flow cytometry. Gene expression in the FL- and AB-derived cells was studied by Affymetrix microarray and reverse-transcription quantitative PCR. The microarray data were combined with that from a previous study of human FL and AB erythroid development, and meta-analysis was performed on the combined dataset.

Results

FL erythroid cells showed enhanced proliferation and elevated fetal hemoglobin relative to AB cells. A total of 1,391 fetal up-regulated and 329 adult up-regulated genes were identified from microarray data generated in this study. Five hundred ninety-nine fetal up-regulated and 284 adult up-regulated genes with reproducible patterns between this and a previous study were identified by meta-analysis of the combined dataset, which constitute a core set of genes differentially expressed between FL and AB erythroid cells. In addition to these core genes, 826 and 48 novel genes were identified only from data generated in this study to be FL up- and AB up-regulated, respectively. The in vivo relevance for some of these novel genes was demonstrated by pathway analysis, which showed novel genes functioning in pathways known to be important in proliferation and erythropoiesis, including the mitogen-activated protein kinase (MAPK) and the phosphatidyl inositol 3 kinase (PI3K)-Akt pathways.

Discussion

The genes with upregulated expression in FL cells, which include many novel genes identified from data generated in this study, suggest that cellular proliferation pathways are more active in the fetal stage. Erythroid progenitor cells may thus undergo a reprogramming during ontogenesis in which proliferation is modulated by changes in expression of key regulators, primarily MYC, and others including insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3), neuropilin and tolloid-like 2 (NETO2), branched chain amino acid transaminase 1 (BCAT1), tenascin XB (TNXB) and proto-oncogene, AP-1 transcription factor subunit (JUND). This reprogramming may thus be necessary for acquisition of the adult identity and switching of hemoglobin expression.

Plasmatic membrane toll-like receptor expressions in human astrocytomas

Toll-like receptors (TLRs) are the first to identify disturbances in the immune system, recognizing pathogens such as bacteria, fungi, and viruses. Since the inflammation process plays an important role in several diseases, TLRs have been considered potential therapeutic targets, including treatment for cancer. However, TLRs’ role in cancer remains ambiguous. This study aims to analyze the expression levels of plasmatic cell membrane TLRs (TLR1, TLR2, TLR4, TLR5, and TLR6) in human astrocytomas the most prevalent tumors of CNS different grades (II-IV). We demonstrated that TLR expressions were higher in astrocytoma samples compared to non-neoplastic brain tissue. The gene and protein expressions were observed in GBM cell lines U87MG and A172, proving their presence in the tumor cells. Associated expressions between the known heterodimers TLR1-TLR2 were found in all astrocytoma grades. In GBMs, the mesenchymal subtype showed higher levels of TLR expressions in relation to classical and proneural subtypes. A strong association of TLRs with the activation of cell cycle process and signaling through canonical, inflammasome and ripoptosome pathways was observed by in silico analysis, further highlighting TLRs as interesting targets for cancer treatment.

A new miRNA regulator, miR-672, reduces cardiac hypertrophy by inhibiting JUN expression

Cardiac hypertrophy is one of the initial symptoms of many heart diseases. We found that miR-672-5p may participate in the regulation of heart disease development in mouse, but the association between miR-672-5p and cardiac hypertrophy remains unclear. In the present study, we found that the abundance of miR-672-5p decreased in hypertrophic cardiomyocytes induced by phenylephrine, angiotensin II (Ang II) and insulin-like growth factor 1. Putative target genes of miR-672-5p were identified using four pipelines, miRWalk, miRanda, RNA22 and Targetscan, and a total of 834 genes were predicted by all four pipelines. Among these target genes, 98 were associated with the development of heart disease. PPI networks showed that the Jun proto-oncogene product (JUN), a subunit of the AP-1 transcription factor, had the highest node degree, and it was defined as the hub gene of the PPI networks. Luciferase assays showed that miR-672-5p bound to the 3' UTR of the JUN gene and decreased luciferase activity, indicating that JUN is a target of miR-672-5p. Finally, we found that increasing the abundance of miR-672-5p in cardiomyocytes controlled the relative cell area in Ang II-stimulated hypertrophic cardiomyocytes. Correspondingly, the abundance of JUN, a target of miR-672-5p, was decreased in hypertrophic cardiomyocytes on both mRNA and protein levels, implying that miR-672-5p had suppressive effects on cardiac hypertrophy through regulating the expression of Jun in cardiomyocytes.

Ubiquitin-Specific Protease USP6 Regulates the Stability of the c-Jun Protein

The c-Jun gene encodes a transcription factor that has been implicated in many physiological and pathological processes. c-Jun is a highly unstable protein that is degraded through a ubiquitination/proteasome-dependent mechanism. However, the deubiquitinating enzyme (DUB) that regulates the stability of the c-Jun protein requires further investigation. Here, by screening a DUB expression library, we identified ubiquitin-specific protease 6 (USP6) and showed that it regulates the stability of the c-Jun protein in a manner depending on its enzyme activity. USP6 interacts with c-Jun and antagonizes its ubiquitination. USP6 overexpression upregulates the activity of the downstream signaling pathway mediated by c-Jun/AP-1 and promotes cell invasion. Moreover, many aberrant genes that are upregulated in USP6 translocated nodular fasciitis are great potential targets regulated by c-Jun. Based on our data, USP6 is an enzyme that deubiquitinates c-Jun and regulates its downstream cellular functions.

Dexamethasone inhibits inflammatory response via down regulation of AP-1 transcription factor in human lung epithelial cells

The production of inflammatory mediators by epithelial cells in inflammatory lung diseases may represent an important target for the anti-inflammatory effects of glucocorticoids. Activator protein-1 is a major activator of inflammatory genes and has been proposed as a target for inhibition by glucocorticoids. We have used human pulmonary type-II A549 cells to examine the effect of dexamethasone on the phorbol ester (PMA)/Lipopolysaccharide (LPS) induced pro-inflammatory cytokines and AP-1 factors. A549 cells were treated with and without PMA or LPS or dexamethasone and the cell viability and nitric oxide production was measured by MTT assay and Griess reagent respectively. Expression of pro-inflammatory cytokines and AP-1 factors mRNA were measured using semi quantitative RT-PCR. The PMA/LPS treated cells show significant 2-3 fold increase in the mRNA levels of pro-inflammatory cytokines (IL-1β, IL-2, IL-6, IL-8 and TNF-α), cyclo‑oxygenase-2 (COX-2) and specific AP-1 factors (c-Jun, c-Fos and Jun-D). Whereas, pretreatment of cells with dexamethasone significantly inhibited the LPS induced nitric oxide production and PMA/LPS induced mRNAs expression of above pro-inflammatory cytokines, COX-2 and AP-1 factors. Cells treated with dexamethasone alone at both the concentrations inhibit the mRNAs expression of IL-1β, IL-6 and TNF-α compared to control. Our study reveals that dexamethasone decreased the mRNAs expression of c-Jun and c-Fos available for AP-1 formation suggested that AP-1 is the probable key transcription factor involved in the anti-inflammatory activity of dexamethasone. This may be an important molecular mechanism of steroid action in asthma and other chronic inflammatory lung diseases which may be useful for treatment of lung inflammatory diseases.

Static and Dynamic DNA Loops form AP-1-Bound Activation Hubs during Macrophage Development

The three-dimensional arrangement of the human genome comprises a complex network of structural and regulatory chromatin loops important for coordinating changes in transcription during human development. To better understand the mechanisms underlying context-specific 3D chromatin structure and transcription during cellular differentiation, we generated comprehensive in situ Hi-C maps of DNA loops in human monocytes and differentiated macrophages. We demonstrate that dynamic looping events are regulatory rather than structural in nature and uncover widespread coordination of dynamic enhancer activity at preformed and acquired DNA loops. Enhancer-bound loop formation and enhancer activation of preformed loops together form multi-loop activation hubs at key macrophage genes. Activation hubs connect 3.4 enhancers per promoter and exhibit a strong enrichment for activator protein 1 (AP-1)-binding events, suggesting that multi-loop activation hubs involving cell-type-specific transcription factors represent an important class of regulatory chromatin structures for the spatiotemporal control of transcription.

The Role of p16INK4a Pathway in Human Epidermal Stem Cell Self-Renewal, Aging and Cancer

The epidermis is a self-renewing tissue. The balance between proliferation and differentiation processes is tightly regulated to ensure the maintenance of the stem cell (SC) population in the epidermis during life. Aging and cancer may be considered related endpoints of accumulating damages within epidermal self-renewing compartment. p16^INK4a is a potent inhibitor of the G1/S-phase transition of the cell cycle. p16^INK4a governs the processes of SC self-renewal in several tissues and its deregulation may result in aging or tumor development. Keratinocytes are equipped with several epigenetic enzymes and transcription factors that shape the gene expression signatures of different epidermal layers and allow dynamic and coordinated expression changes to finely balance keratinocyte self-renewal and differentiation. These factors converge their activity in the basal layer to repress p16^INK4a expression, protecting cells from senescence, and preserving epidermal homeostasis and regeneration. Several stress stimuli may activate p16^INK4a expression that orchestrates cell cycle exit and senescence response. In the present review, we discuss the role of p16^INK4a regulators in human epidermal SC self-renewal, aging and cancer.

A Review of the Scaffold Protein Menin and its Role in Hepatobiliary Pathology

Multiple endocrine neoplasia type 1 (MEN1) is a familial cancer syndrome with neuroendocrine tumorigenesis of the parathyroid glands, pituitary gland, and pancreatic islet cells. The MEN1 gene codes for the canonical tumor suppressor protein, menin. Its protein structure has recently been crystallized, and it has been investigated in a multitude of other tissues. In this review, we summarize recent advancements in understanding the structure of the menin protein and its function as a scaffold protein in histone modification and epigenetic gene regulation. Furthermore, we explore its role in hepatobiliary autoimmune diseases, cancers, and metabolic diseases. In particular, we discuss how menin expression and function are regulated by extracellular signaling factors and nuclear receptor activation in various hepatic cell types. How the many signaling pathways and tissue types affect menin's diverse functions is not fully understood. We show that small-molecule inhibitors affecting menin function can shed light on menin's broad role in pathophysiology and elucidate distinct menin-dependent processes. This review reveals menin's often dichotomous function through analysis of its role in multiple disease processes and could potentially lead to novel small-molecule therapies in the treatment of cholangiocarcinoma or biliary autoimmune diseases.

ATF2 partly mediated the expressions of proliferative factors and inhibited pro-inflammatory factors' secretion in arsenite-treated human uroepithelial cells

Inorganic arsenic (iAs) could induce the expression of activating transcription factor-2 (ATF2) in the human urinary bladder epithelial cell line (SV-HUC-1 cells). ATF2, as a member of the bZIP transcription factor family, has been implicated in a transcriptional response leading to cell growth, migration and malignant tumor progression. However, little is known about the effects of ATF2 on proliferative factors in iAs treated human urothelial cells. In this study, ATF2 siRNA was employed to investigate the relationship between ATF2 activation and the expressions of proliferative factors, such as BCL2, cyclin D1, COX-2, MMP1 and PCNA, and pro-inflammatory factors (TNFα, TGFα and IL-8) in SV-HUC-1 cells. The results showed that low concentration arsenite increased the expressions of proliferative factors BCL2, cyclin D1, COX-2, MMP1 and PCNA in SV-HUC-1 cells, and ATF2 siRNA partly decreased the expressions of BCL2, cyclin D1, and COX-2. A neutralizing antibody of IL-8 was used for attenuating the levels of IL-8 and neutralizing antibody of IL-8 did not relieve the expressions of ATF2 and proliferative factors induced by arsenite in SV-HUC-1 cells. In addition, ATF2 knockdown did not decrease the expressions of pro-inflammatory cytokines induced by arsenite in SV-HUC-1 cells, but dramatically increased mRNA expressions of TNFα, TGFα and IL-8 under arsenite and non-arsenite conditions. In conclusion, our present study indicated that ATF2, but not IL-8, played a partial role in the expressions of proliferative factors induced by arsenite in human uroepithelial cells.

Wallerian demyelination: chronicle of a cellular cataclysm

Wallerian demyelination is characteristic of peripheral nerve degeneration after traumatic injury. After axonal degeneration, the myelinated Schwann cell undergoes a stereotypical cellular program that results in the disintegration of the myelin sheath, a process termed demyelination. In this review, we chronologically describe this program starting from the late and visible features of myelin destruction and going backward to the initial molecular steps that trigger the nuclear reprogramming few hours after injury. Wallerian demyelination is a wonderful model for myelin degeneration occurring in the diverse forms of demyelinating peripheral neuropathies that plague human beings.

WD-repeat protein WDR13 is a novel transcriptional regulator of c-Jun and modulates intestinal homeostasis in mice

Background

WDR13 is a member of the WD repeat protein family and is expressed in several tissues of human and mice. Previous studies in our laboratory showed that the lack of this gene in mice resulted in mild obesity, hyperinsulinemia, enhanced beta cell proliferation and protection from inflammation. However, the molecular mechanism of WDR13 action is not well understood.

Methods

In the present study, we used AOM/DSS to induce colitis-mediated colorectal tumor after establishing expression of Wdr13 gene in colon. Further, we have used human colon cancer cell lines, HT29 and COLO205, and mouse primary embryonic fibroblast to understand the molecular mechanism of WDR13 action.

Results

We observed that mice lacking Wdr13 gene have reduced number of tumors and are more susceptible to DSS-induced colon ulcers. We also show that WDR13 is a part of multi protein complex c-Jun/NCoR1/HDAC3 and it acts as a transcriptional activator of AP1 target genes in the presence of JNK signal. Consistent with in vitro data, we observed reduced expression of AP1 target genes in colon after AOM/DSS treatment in Wdr13 knockout mice as compared to that in wild type.

Conclusion

Mice lacking Wdr13 gene showed reduced expression of AP1 target genes and protection from colitis-induced colorectal tumors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3118-7) contains supplementary material, which is available to authorized users.

AP-1 Expression and its Clinical Relevance in Immune Disorders and Cancer

The inflammatory response is known to have a significant role in certain autoimmune diseases and malignancies. We review current knowledge regarding the functions of activator protein 1 (AP-1) as an important modulator in several immune disorders and carcinomas. AP-1 is overexpressed in rheumatoid arthritis and in long-term allogeneic hematopoietic stem cell transplantation survivors; however, decreased expression of AP-1 has been observed in psoriasis, systematic lupus erythematosus and in patients who do not survive after hematopoietic stem cell transplantation. AP-1 also is implicated in the control of various cancer cells. Higher levels of AP-1 components are present in breast and endometrial carcinomas, colorectal cancer and in acute myeloid leukemia, Hodgkin׳s lymphoma and anaplastic large cell lymphoma, with downregulation in ovarian and gastric carcinomas and in patients with chronic myelogenous leukemia. AP-1 may enable the development of helpful markers to identify early-stage disease or to predict severity.

cel-mir-237 and its homologue, hsa-miR-125b, modulate the cellular response to ionizing radiation

Elucidating the mechanisms involved in sensitizing radioresistant tumors to ionizing radiation (IR) treatments while minimizing injury to surrounding normal tissue is an important clinical goal. Due to their sequence-derived specificity and properties as gene regulators in IR-affected pathways, microRNAs (miRNAs) could serve as adjuvant therapeutic agents that alter cellular sensitivity to radiation treatment. To identify radiosensitizing miRNAs, we initially utilized the Caenorhabditis elegans vulval cell model, an in vivo system developed to study IR-dependent radiosensitivity as a measure of clonogenic cell death. We tested several candidate miRNA-deletion mutants post γ-irradiation and identified cel-mir-237 as a miRNA which when deleted caused animals to be more resistant to IR, whereas cel-mir-237 overexpressing strains were IR sensitive. In addition, wild-type animals downregulated cel-mir-237 levels post IR in a time-dependent manner. We identified jun-1 (JUN transcription factor homolog) as a novel target of cel-mir-237. Specifically, jun-1 transcript levels increased in wild-type animals post γ-irradiation, and loss of cel-mir-237 also resulted in higher jun-1 expression. As expected, loss of jun-1 resulted in IR sensitivity, similar to the phenotype of cel-mir-237 overexpressors. As miR-237 is the homolog of human miR-125, we validated our findings in MCF-7 and MDA-MB-231 breast cancer cell lines, which harbor lower hsa-miR-125b levels than normal human mammary epithelial cells (HMECs). Forced expression of hsa-miR-125b in these cells resulted in radiosensitivity, as seen by reduced clonogenic survival, enhanced apoptotic activity and enhanced senescence post IR. Finally, re-expression of c-JUN in MDA-MB-231 cells promoted radioresistance and abrogated miR-125-mediated radiosensitization. Our findings suggest that overexpression of cel-mir-237 and its homolog, hsa-miR-125b, functions as sensitizers to γ-irradiation in both a nematode in vivo model and breast cancer cells, and could potentially be utilized as an adjuvant therapeutic to enhance radiation sensitivity.

Role of Ceramide in Apoptosis and Development of Insulin Resistance

This review presents data on the functional biochemistry of ceramide, one of the key sphingolipids with properties of a secondary messenger. Molecular mechanisms of the involvement of ceramide in apoptosis in pancreatic β-cells and its role in the formation of insulin resistance in pathogenesis of type 2 diabetes are reviewed. One of the main predispositions for the development of insulin resistance and diabetes is obesity, which is associated with ectopic fat deposition and significant increase in intracellular concentrations of cytotoxic ceramides. A possible approach to the restoration of tissue sensitivity to insulin in type 2 diabetes based on selective reduction of the content of cytotoxic ceramides is discussed.

Development of a Quantitative BRET Affinity Assay for Nucleic Acid-Protein Interactions

Protein-nucleic acid interactions play a crucial role in the regulation of diverse biological processes. Elucidating the roles that protein-nucleic acid complexes play in the regulation of transcription, translation, DNA replication, repair and recombination, and RNA processing continues to be a crucial aspect of understanding of cell biology and the mechanisms of disease. In addition, proteins have been demonstrated to interact with antisense oligonucleotide therapeutics in a sequence and chemistry dependent manner, influencing ASO potency and distribution in cells and in vivo. While many assays have been developed to measure protein-nucleic acid interactions, many suffer from lack of throughput and sensitivity, or challenges with protein purification and scalability. In this report we present a new BRET assay for the analysis of DNA-protein interactions which makes use of an extremely bright luciferase as a tag for the binding protein, along with a long-wavelength fluorophore conjugated to the nucleic acid. The resulting assay is high throughput, sensitive, does not require protein purification, and even allows for quantitative characterization of these interactions within the biologically relevant context of whole cells.

C-Jun recruits the NSL complex to regulate its target gene expression by modulating H4K16 acetylation and promoting the release of the repressive NuRD complex

The proto-oncogene c-Jun plays essential roles in various cellular processes, including cell proliferation, cell differentiation, and cellular apoptosis. Enormous efforts have been made to understand the mechanisms regulating c-Jun activation. The males absent on the first (MOF)-containing non-specific lethal (NSL) complex has been shown to positively regulate gene expression. However, the biological function of the NSL complex is largely unknown. Here we present evidence showing that c-Jun recruits the NSL complex to c-Jun target genes upon activation. The NSL complex catalyzes H4K16 acetylation at c-Jun target genes, thereby promoting c-Jun target gene transcription. More interestingly, we also found that the NSL complex promotes the release of the repressive NuRD complex from c-Jun target genes, thus activating c-Jun. Our findings not only reveal a new mechanism regulating c-Jun activation, but also identify the NSL complex as a c-Jun co-activator in c-Jun-regulated gene expression, expanding our knowledge of the function of the NSL complex in gene expression regulation.

The oncogenic transcription factor c-Jun regulates glutaminase expression and sensitizes cells to glutaminase-targeted therapy

Many transformed cells exhibit altered glucose metabolism and increased utilization of glutamine for anabolic and bioenergetic processes. These metabolic adaptations, which accompany tumorigenesis, are driven by oncogenic signals. Here we report that the transcription factor c-Jun, product of the proto-oncogene JUN, is a key regulator of mitochondrial glutaminase (GLS) levels. Activation of c-Jun downstream of oncogenic Rho GTPase signalling leads to elevated GLS gene expression and glutaminase activity. In human breast cancer cells, GLS protein levels and sensitivity to GLS inhibition correlate strongly with c-Jun levels. We show that c-Jun directly binds to the GLS promoter region, and is sufficient to increase gene expression. Furthermore, ectopic overexpression of c-Jun renders breast cancer cells dependent on GLS activity. These findings reveal a role for c-Jun as a driver of cancer cell metabolic reprogramming, and suggest that cancers overexpressing JUN may be especially sensitive to GLS-targeted therapies.

Cancer cells have previously been shown to be addicted to glutamine and glutaminase enzyme activity. Here, the authors show that overexpression of the JUN proto-oncogene in breast cancer cells regulates glutaminase expression and is sufficient to confer sensitivity to glutaminase-targeted therapy.

Functional Analysis of a Novel Genome-Wide Association Study Signal in SMAD3 That Confers Protection From Coronary Artery Disease

OBJECTIVE

A recent genome-wide association study meta-analysis identified an intronic single nucleotide polymorphism in SMAD3, rs56062135C>T, the minor allele (T) which associates with protection from coronary artery disease. Relevant to atherosclerosis, SMAD3 is a key contributor to transforming growth factor-β pathway signaling. Here, we seek to identify ≥1 causal coronary artery disease-associated single nucleotide polymorphisms at the SMAD3 locus and characterize mechanisms whereby the risk allele(s) contribute to coronary artery disease risk.

APPROACH AND RESULTS

By genetic and epigenetic fine mapping, we identified a candidate causal single nucleotide polymorphism rs17293632C>T (D', 0.97; r(2), 0.94 with rs56062135) in intron 1 of SMAD3 with predicted functional effects. We show that the sequence encompassing rs17293632 acts as a strong enhancer in human arterial smooth muscle cells. The common allele (C) preserves an activator protein (AP)-1 site and enhancer function, whereas the protective (T) allele disrupts the AP-1 site and significantly reduces enhancer activity (P<0.001). Pharmacological inhibition of AP-1 activity upstream demonstrates that this allele-specific enhancer effect is AP-1 dependent (P<0.001). Chromatin immunoprecipitation experiments reveal binding of several AP-1 component proteins with preferential binding to the (C) allele. We show that rs17293632 is an expression quantitative trait locus for SMAD3 in blood and atherosclerotic plaque with reduced expression of SMAD3 in carriers of the protective allele. Finally, siRNA knockdown of SMAD3 in human arterial smooth muscle cells increases cell viability, consistent with an antiproliferative role.

CONCLUSIONS

The coronary artery disease-associated rs17293632C>T single nucleotide polymorphism represents a novel functional cis-acting element at the SMAD3 locus. The protective (T) allele of rs17293632 disrupts a consensus AP-1 binding site in a SMAD3 intron 1 enhancer, reduces enhancer activity and SMAD3 expression, altering human arterial smooth muscle cell proliferation.

TLR4 signaling mediates AP-1 activation in an MPTP-induced mouse model of Parkinson's disease

OBJECTIVE

To evaluate the effects of Toll-like receptor 4 (TLR4) signaling on the activation of the transcription factor activator protein-1 (AP-1) in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of Parkinson's disease (PD).

METHODS

The following groups were evaluated: normal saline (NS)-treated WT mice, NS-treated TLR4-knockout (KO) mice, MPTP-treated WT mice, and MPTP-treated TLR4-KO mice. After establishing the mouse model, behavioral changes were evaluated. AP-1 expression was detected by RT-PCR, Western blotting, immunohistochemistry and immunofluorescence staining.

RESULTS

Compared to MPTP-treated WT mice, significantly reduced dyskinesia was observed in MPTP-treated TLR4-KO mice. AP-1 mRNA and protein levels were significantly up-regulated in the substantia nigras (SNs) of MPTP-treated WT mice relative to NS-treated mice (P<0.01); these levels were significantly reduced in MPTP-treated TLR4-KO mice relative to MPTP-treated WT mice (P<0.01). Immunohistochemical staining demonstrated that AP-1 was distributed throughout the SN in MPTP-treated mice, and immunofluorescence further showed that AP-1 was expressed in TH-positive neuronal cells and GFAP-positive astrocytes. In addition, immunofluorescence revealed that AP-1 expression was lower in TH-positive neurons and GFAP-positive astrocytes in the SNs of MPTP-treated TLR4-KO mice relative to MPTP-treated WT mice.

CONCLUSIONS

The TLR4 pathway may play an important role in regulating AP-1 activation.

Impaired dynamin 2 function leads to increased AP-1 transcriptional activity through the JNK/c-Jun pathway

Activation of AP-1 transcription factors, composed of the Jun and Fos proteins, regulates cellular fates, such as proliferation, differentiation or apoptosis. Among other stimuli, the AP-1 pathway can be initiated by extracellular ligands, such as growth factors or cytokines, which undergo internalization in complex with their receptors. Endocytosis has been implicated in the regulation of several signaling pathways; however its possible impact on AP-1 signaling remains unknown. Here we show that inhibition of dynamin 2 (Dyn2), a major regulator of endocytic internalization, strongly stimulates the AP-1 pathway. Specifically, expression of a dominant-negative Dyn2 K44A mutant increases the total levels of c-Jun, its phosphorylation on Ser63/73 and transcription of AP-1 target genes. Interestingly, DNM2 mutations implicated in human neurological disorders exhibit similar effects on AP-1 signaling. Mechanistically, Dyn2 K44A induces AP-1 by increasing phosphorylation of several receptor tyrosine kinases. Their activation is required to initiate a Src- and JNK-dependent signaling cascade converging on c-Jun and stimulating expression of AP-1 target genes. Cumulatively, our data uncover a link between the Dyn2 function and JNK signaling which leads to AP-1 induction.

Vitamin A depletion induced by cigarette smoke is associated with an increase in lung cancer-related markers in rats

BACKGROUND

We have previously demonstrated that cigarette smoke is associated with a significant reduction of retinoic acid in rat lungs and the formation of tracheal precancerous lesions. However, the underlying mechanism of cancer risk induced by vitamin A deficiency is unclear. The purpose of this study was to determine whether the cigarette smoke-induced depletion of vitamin A is related to changes in lung cancer risk-related molecular markers.

RESULTS

We investigated the roles of the retinoic acid receptors (RARs) as well as other biomarkers for potential cancer risk in the lungs of rats exposed to cigarette smoke. Twenty-four male weanling rats were fed a purified diet and divided equally into four groups. Three experimental groups were exposed to increasing doses of cigarette smoke from 20, 40 or 60 commercial cigarettes/day for 5 days/week. After 6 weeks, the retinoic acid concentrations in the lung tissue as measured via high performance liquid chromatography (HPLC) significantly decreased (P < 0.01) in cigarette smoke exposed groups. Western Blot analysis revealed that cigarette smoke exposure increased lung protein expression of RAR α in a threshold manner and decreased RAR β and RAR γ expression in a dose-dependent fashion. Protein expressions of cyclin E and proliferating cell nuclear antigen (PCNA) were increased significantly in a dose-dependent manner in cigarette smoke exposed-groups. Additionally, there was a significant increase in protein expression of cJun and cyclin D1 demonstrating a threshold effect similar to that exhibited by RARα, suggesting a potential independent signaling pathway for RARα in lung carcinogenesis.

CONCLUSIONS

Findings from this study suggest that cigarette smoke-induced lung retinoic acid depletion may involve two independent pathways, RARα- and RARβ-mediated, responsible for the increased cancer risk associated with cigarette smoke-induced vitamin A deficiency.

Voxel-based analysis of the immediate early gene, c-jun, in the honey bee brain after a sucrose stimulus

Immediate early genes (IEGs) have served as useful markers of brain neuronal activity in mammals, and more recently in insects. The mammalian canonical IEG, c-jun, is part of regulatory pathways conserved in insects and has been shown to be responsive to alarm pheromone in honey bees. We tested whether c-jun was responsive in honey bees to another behaviourally relevant stimulus, sucrose, in order to further identify the brain regions involved in sucrose processing. To identify responsive regions, we developed a new method of voxel-based analysis of c-jun mRNA expression. We found that c-jun is expressed in somata throughout the brain. It was rapidly induced in response to sucrose stimuli, and it responded in somata near the antennal and mechanosensory motor centre, mushroom body calices and lateral protocerebrum, which are known to be involved in sucrose processing. c-jun also responded to sucrose in somata near the lateral suboesophageal ganglion, dorsal optic lobe, ventral optic lobe and dorsal posterior protocerebrum, which had not been previously identified by other methods. These results demonstrate the utility of voxel-based analysis of mRNA expression in the insect brain.

DCC functions as an accelerator of thalamocortical axonal growth downstream of spontaneous thalamic activity

Controlling the axon growth rate is fundamental when establishing brain connections. Using the thalamocortical system as a model, we previously showed that spontaneous calcium activity influences the growth rate of thalamocortical axons by regulating the transcription of Robo1 through an NF-κB-binding site in its promoter. Robo1 acts as a brake on the growth of thalamocortical axons in vivo. Here, we have identified the Netrin-1 receptor DCC as an accelerator for thalamic axon growth. Dcc transcription is regulated by spontaneous calcium activity in thalamocortical neurons and activating DCC signaling restores normal axon growth in electrically silenced neurons. Moreover, we identified an AP-1-binding site in the Dcc promoter that is crucial for the activity-dependent regulation of this gene. In summary, we have identified the Dcc gene as a novel downstream target of spontaneous calcium activity involved in axon growth. Together with our previous data, we demonstrate a mechanism to control axon growth that relies on the activity-dependent regulation of two functionally opposed receptors, Robo1 and DCC. These two proteins establish a tight and efficient means to regulate activity-guided axon growth in order to correctly establish neuronal connections during development.

The E3 ubiquitin ligase Trim7 mediates c-Jun/AP-1 activation by Ras signalling

The c-Jun/AP-1 transcription factor controls key cellular behaviours, including proliferation and apoptosis, in response to JNK and Ras/MAPK signalling. While the JNK pathway has been well characterized, the mechanism of activation by Ras was elusive. Here we identify the uncharacterized ubiquitin ligase Trim7 as a critical component of AP-1 activation via Ras. We found that MSK1 directly phosphorylates Trim7 in response to direct activation by the Ras-Raf-MEK-ERK pathway, and this modification stimulates Trim7 E3 ubiquitin ligase activity. Trim7 mediates Lys63-linked ubiquitination of the AP-1 co-activator RACO-1, leading to RACO-1 protein stabilization. Consequently, Trim7 depletion reduces RACO-1 levels and AP-1-dependent gene expression. Moreover, transgenic overexpression of Trim7 increases lung tumour burden in a Ras-driven cancer model, and knockdown of Trim7 in established xenografts reduces tumour growth. Thus, phosphorylation-ubiquitination crosstalk between MSK1, Trim7 and RACO-1 completes the long sought-after mechanism linking growth factor signalling and AP-1 activation.

A genome wide association study on Newfoundland colorectal cancer patients' survival outcomes

Background

In this study we performed genome-wide association studies to identify candidate SNPs that may predict the risk of disease outcome in colorectal cancer.

Methods

Patient cohort consisted of 505 unrelated patients with Caucasian ancestry. Germline DNA samples were genotyped using the Illumina® human Omni-1quad SNP chip. Associations of SNPs with overall and disease free survivals were examined primarily for 431 patients with microsatellite instability-low (MSI-L) or stable (MSS) colorectal tumors using Cox proportional hazards method adjusting for clinical covariates. Bootstrap method was applied for internal validation of results. As exploratory analyses, association analyses for the colon (n = 334) and rectal (n = 171) cancer patients were also performed.

Results

As a result, there was no SNP that reached the genomewide significance levels (p < 5x10⁻⁸) in any of the analyses. A small number of genetic markers (n = 10) showed nominal associations (p <10⁻⁶) for MSS/MSI-L, colon, or rectal cancer patient groups. These markers were located in two non-coding RNA genes or intergenic regions and none were amino acid substituting polymorphisms. Bootstrap analysis for the MSS/MSI-L cohort data suggested the robustness of the observed nominal associations.

Conclusions

Likely due to small number of patients, our study did not identify an acceptable level of association of SNPs with outcome in MSS/MSI-L, colon, or rectal cancer patients. A number of SNPs with sub-optimal p-values were, however, identified; these loci may be promising and examined in other larger-sized patient cohorts.

Electronic supplementary material

The online version of this article (doi:10.1186/s40364-015-0031-6) contains supplementary material, which is available to authorized users.

Deletion of Jun proteins in adult oligodendrocytes does not perturb cell survival, or myelin maintenance in vivo

Oligodendrocytes, the myelin-forming glial cells of the central nervous system (CNS), are fundamental players in rapid impulse conduction and normal axonal functions. JunB and c-Jun are DNA-binding components of the AP-1 transcription factor, which is known to regulate different processes such as proliferation, differentiation, stress responses and death in several cell types, including cultured oligodendrocyte/lineage cells. By selectively inactivating Jun B and c-Jun in myelinating oligodendrocytes in vivo, we generated mutant mice that developed normally, and within more than 12 months showed normal ageing and survival rates. In the adult CNS, absence of JunB and c-Jun from mature oligodendrocytes caused low-grade glial activation without overt signs of demyelination or secondary leukocyte infiltration into the brain. Even after exposure to toxic or autoimmune oligodendrocyte insults, signs of altered oligodendrocyte viability were mild and detectable only upon cuprizone treatment. We conclude that JunB and c-Jun expression in post-mitotic oligodendrocytes is mostly dispensable for the maintainance of white matter tracts throughout adult life, even under demyelinating conditions.

Molecular pathways of arterial aging

The incidence of stroke and myocardial infarction increases in aged patients and it is associated with an adverse outcome. Considering the aging population and the increasing incidence of cardiovascular disease, the prediction for population well-being and health economics is daunting. Accordingly, there is an unmet need to focus on fundamental processes underlying vascular aging. A better understanding of the pathways leading to arterial aging may contribute to design mechanism-based therapeutic approaches to prevent or attenuate features of vascular senescence. In the present review, we discuss advances in the pathophysiology of age-related vascular dysfunction including nitric oxide signalling, dysregulation of oxidant/inflammatory genes, epigenetic modifications and mechanisms of vascular calcification as well as insights into vascular repair. Such an overview highlights attractive molecular targets for the prevention of age-driven vascular disease.

Extracellular signal-regulated kinase signaling regulates the opposing roles of JUN family transcription factors at ETS/AP-1 sites and in cell migration

JUN transcription factors bind DNA as part of the AP-1 complex, regulate many cellular processes, and play a key role in oncogenesis. The three JUN proteins (c-JUN, JUNB, and JUND) can have both redundant and unique functions depending on the biological phenotype and cell type assayed. Mechanisms that allow this dynamic switching between overlapping and distinct functions are unclear. Here we demonstrate that JUND has a role in prostate cell migration that is the opposite of c-JUN's and JUNB's. RNA sequencing reveals that opposing regulation by c-JUN and JUND defines a subset of AP-1 target genes with cell migration roles. cis-regulatory elements for only this subset of targets were enriched for ETS factor binding, indicating a specificity mechanism. Interestingly, the function of c-JUN and JUND in prostate cell migration switched when we compared cells with an inactive versus an active RAS/extracellular signal-regulated kinase (ERK) signaling pathway. We show that this switch is due to phosphorylation and activation of JUND by ERK. Thus, the ETS/AP-1 sequence defines a unique gene expression program regulated by the relative levels of JUN proteins and RAS/ERK signaling. This work provides a rationale for how transcription factors can have distinct roles depending on the signaling status and the biological function in question.

Double lethal effects of fusion gene of wild-type p53 and JunB on hepatocellular carcinoma cells

This study explored the double lethal effects of pEGFP-C1-wtp53/junB fusion gene on hepatocellular carcinoma (HCC) cells. wtp53/junB fusion gene was constructed and transformed into HepG2 cell line. Expression of KAI1 was detected by quantitative real-time PCR and Western blotting, cells apoptosis rate was detected by flow cytometry, proliferation of cells was detected byMTT chromometry, cell transmigration was detected by using transwell systems. The results showed that after transformation with pEGFP-C1-wtp53/JunB, the expression level of KAI1 protein was up-regulated, being 8.13 times the blank control group in HepG2 cells and significantly higher than 2.87 times which transformed with pEGFP-C1-JunB, 3.11 times which transformed with pEGFP-C1-wtp53 (P<0.001). Apoptosis rate of HepG2 cells transformed with pEGFP-C1-wtp53/JunB was significantly higher than that of other groups (P<0.001), and invasive ability of HepG2 cells transformed with pEGFP-C1-wtp53/JunB was significantly lower than other groups(P<0.001). It was concluded that the fusion gene of wtp53 and JunB could not only inhibit the growth of hepatoma cells and promote tumor cell apoptosis, but also suppress the invasive ability of tumor cells by up-regulating the expression of KAI1.

The role of oxidative stress and inflammation in cardiovascular aging

Age is an independent risk factor of cardiovascular disease, even in the absence of other traditional factors. Emerging evidence in experimental animal and human models has emphasized a central role for two main mechanisms of age-related cardiovascular disease: oxidative stress and inflammation. Excess reactive oxygen species (ROS) and superoxide generated by oxidative stress and low-grade inflammation accompanying aging recapitulate age-related cardiovascular dysfunction, that is, left ventricular hypertrophy, fibrosis, and diastolic dysfunction in the heart as well as endothelial dysfunction, reduced vascular elasticity, and increased vascular stiffness. We describe the signaling involved in these two main mechanisms that include the factors NF-κB, JunD, p66^Shc, and Nrf2. Potential therapeutic strategies to improve the cardiovascular function with aging are discussed, with a focus on calorie restriction, SIRT1, and resveratrol.

Impact of obesity on mammary gland inflammation and local estrogen production

Obesity rates have risen dramatically over the past century, having nearly doubled since 1980. Changes in diet and lifestyle have contributed to this occurrence in younger women, and changing hormone levels during the menopausal transition has no doubt exacerbated the issue in older women. The relationship between adiposity and breast cancer is clear in postmenopausal women, and is intimately linked to the increased expression of aromatase and the production of estrogens within the breast adipose. This, in turn, is highly dependent on the localized chronic inflammation observed in obese adipose. This review will therefore explore the relationship between obesity, inflammation and estrogens, with a particular focus on the molecular regulation of aromatase in the postmenopausal breast in the context of obesity and breast cancer.

Pituitary tumor-transforming gene 1 regulates the patterning of retinal mosaics

Neurons are commonly organized as regular arrays within a structure, and their patterning is achieved by minimizing the proximity between like-type cells, but molecular mechanisms regulating this process have, until recently, been unexplored. We performed a forward genetic screen using recombinant inbred (RI) strains derived from two parental A/J and C57BL/6J mouse strains to identify genomic loci controlling spacing of cholinergic amacrine cells, which is a subclass of retinal interneuron. We found conspicuous variation in mosaic regularity across these strains and mapped a sizeable proportion of that variation to a locus on chromosome 11 that was subsequently validated with a chromosome substitution strain. Using a bioinformatics approach to narrow the list of potential candidate genes, we identified pituitary tumor-transforming gene 1 (Pttg1) as the most promising. Expression of Pttg1 was significantly different between the two parental strains and correlated with mosaic regularity across the RI strains. We identified a seven-nucleotide deletion in the Pttg1 promoter in the C57BL/6J mouse strain and confirmed a direct role for this motif in modulating Pttg1 expression. Analysis of Pttg1 KO mice revealed a reduction in the mosaic regularity of cholinergic amacrine cells, as well as horizontal cells, but not in two other retinal cell types. Together, these results implicate Pttg1 in the regulation of homotypic spacing between specific types of retinal neurons. The genetic variant identified creates a binding motif for the transcriptional activator protein 1 complex, which may be instrumental in driving differential expression of downstream processes that participate in neuronal spacing.

ModuleRole: a tool for modulization, role determination and visualization in protein-protein interaction networks

Rapidly increasing amounts of (physical and genetic) protein-protein interaction (PPI) data are produced by various high-throughput techniques, and interpretation of these data remains a major challenge. In order to gain insight into the organization and structure of the resultant large complex networks formed by interacting molecules, using simulated annealing, a method based on the node connectivity, we developed ModuleRole, a user-friendly web server tool which finds modules in PPI network and defines the roles for every node, and produces files for visualization in Cytoscape and Pajek. For given proteins, it analyzes the PPI network from BioGRID database, finds and visualizes the modules these proteins form, and then defines the role every node plays in this network, based on two topological parameters Participation Coefficient and Z-score. This is the first program which provides interactive and very friendly interface for biologists to find and visualize modules and roles of proteins in PPI network. It can be tested online at the website http://www.bioinfo.org/modulerole/index.php, which is free and open to all users and there is no login requirement, with demo data provided by "User Guide" in the menu Help. Non-server application of this program is considered for high-throughput data with more than 200 nodes or user's own interaction datasets. Users are able to bookmark the web link to the result page and access at a later time. As an interactive and highly customizable application, ModuleRole requires no expert knowledge in graph theory on the user side and can be used in both Linux and Windows system, thus a very useful tool for biologist to analyze and visualize PPI networks from databases such as BioGRID.

AVAILABILITY

ModuleRole is implemented in Java and C, and is freely available at http://www.bioinfo.org/modulerole/index.php. Supplementary information (user guide, demo data) is also available at this website. API for ModuleRole used for this program can be obtained upon request.

Integrated mechanisms of CaMKII-dependent ventricular remodeling

CaMKII has been shown to be activated during different cardiac pathological processes, and CaMKII-dependent mechanisms contribute to pathological cardiac remodeling, cardiac arrhythmias, and contractile dysfunction during heart failure. Activation of CaMKII during cardiac stress results in a broad number of biological effects such as, on the one hand, acute effects due to phosphorylation of distinct cellular proteins as ion channels and calcium handling proteins and, on the other hand, integrative mechanisms by changing gene expression. This review focuses on transcriptional and epigenetic effects of CaMKII activation during chronic cardiac remodeling. Multiple mechanisms have been described how CaMKII mediates changes in cardiac gene expression. CaMKII has been shown to directly phosphorylate components of the cardiac gene regulation machinery. CaMKII phosphorylates several transcription factors such as CREB that induces the activation of specific gene programs. CaMKII activates transcriptional regulators also indirectly by phosphorylating histone deacetylases, especially HDAC4, which in turn inhibits transcription factors that drive cardiac hypertrophy, fibrosis, and dysfunction. Recent studies demonstrate that CaMKII also phosphorylate directly histones, which may contribute to changes in gene expression. These findings of CaMKII-dependent gene regulation during cardiac remodeling processes suggest novel strategies for CaMKII-dependent “transcriptional or epigenetic therapies” to control cardiac gene expression and function. Manipulation of CaMKII-dependent signaling pathways in the settings of pathological cardiac growth, remodeling, and heart failure represents an auspicious therapeutic approach.

Translational control of JunB, an AP-1 transcription factor, in activated human endothelial cells

Stimulated endothelial cells (EC) assume an activated phenotype with pro-inflammatory and prothrombotic features, requiring new gene and protein expression. New protein synthesis in activated EC is largely regulated by transcriptional events controlled by a variety of transcription factors. However, post-transcriptional control of gene expression also influences phenotype and allows the cell to alter protein expression in a faster and more direct way than is typically possible with transcriptional mechanisms. We sought to demonstrate that post-transcriptional control of gene expression occurs during EC activation. Using thrombin-activated EC and a high-throughput, microarray-based approach, we identified a number of gene products that may be regulated through post-transcriptional mechanisms, including the AP-1 transcription factor JunB. Using polysome profiling, cytoplasts and other standard cell biologic techniques, JunB is shown to be regulated at a post-transcriptional level during EC activation. In activated EC, the AP-1 transcription factor JunB, is regulated on a post-transcriptional level. Signal-dependent control of translation may regulate transcription factor expression and therefore, subsequent transcriptional events in stimulated EC.

BAG3 is upregulated by c-Jun and stabilizes JunD

BAG3 plays a regulatory role in a number of cellular processes, including cell proliferation, apoptosis, adhesion and migration, epithelial-mesenchymal transition (EMT), autophagy activation, and virus infection. The AP-1 transcription factors are implicated in a variety of important biological processes including cell differentiation, proliferation, apoptosis and oncogenesis. Recently, it has been reported that AP-1 protein c-Jun inhibits autophagy and enhances apoptotic cell death mediated by starvation. However, the molecular mechanisms remain unclear. For the first time, the current study demonstrated that serum starvation downregulated BAG3 at the transcriptional level via c-Jun. In addition, the current study reported that BAG3 stabilized JunD mRNA, which was, at least in part, responsible for the promotion of serum starvation mediated-growth inhibition by BAG3.

Sulindac activates NF-κB signaling in colon cancer cells

BACKGROUND

The non-steroidal anti-inflammatory drug (NSAID) sulindac has shown efficacy in preventing colorectal cancer. This potent anti-tumorigenic effect is mediated through multiple cellular pathways but is also accompanied by gastrointestinal side effects, such as colon inflammation. We have recently shown that sulindac can cause up-regulation of pro-inflammatory factors in the mouse colon mucosa. The aim of this study was to determine the signaling pathways that mediate the transcriptional activation of pro-inflammatory cytokines in colon cancer epithelial cells treated with sulindac sulfide.

RESULTS

We found that sulindac sulfide increased NF-κB signaling in HCT-15, HCT116, SW480 and SW620 cells, although the level of induction varied between cell lines. The drug caused a decrease in IκBα levels and an increase of p65(RelA) binding to the NF-κB DNA response element. It induced expression of IL-8, ICAM1 and A20, which was inhibited by the NF-κB inhibitor PDTC. Sulindac sulfide also induced activation of the AP-1 transcription factor, which co-operated with NF-κB in up-regulating IL-8. Up-regulation of NF-κB genes was most prominent in conditions where only a subset of cells was undergoing apoptosis. In TNFα stimulated conditions the drug treatment inhibited phosphorylation on IκBα (Ser 32) which is consistent with previous studies and indicates that sulindac sulfide can inhibit TNFα-induced NF-κB activation. Sulindac-induced upregulation of NF-κB target genes occurred early in the proximal colon of mice given a diet containing sulindac for one week.

CONCLUSIONS

This study shows for the first time that sulindac sulfide can induce pro-inflammatory NF-κB and AP-1 signaling as well as apoptosis in the same experimental conditions. Therefore, these results provide insights into the effect of sulindac on pro-inflammatory signaling pathways, as well as contribute to a better understanding of the mechanism of sulindac-induced gastrointestinal side effects.

Arginine methylation of the c-Jun coactivator RACO-1 is required for c-Jun/AP-1 activation

c-Jun, the major component of the AP-1 transcription factor complex, has important functions in cellular proliferation and oncogenic transformation. The RING domain-containing protein RACO-1 functions as a c-Jun coactivator that molecularly links growth factor signalling to AP-1 transactivation. Here we demonstrate that RACO-1 is present as a nuclear dimer and that c-Jun specifically interacts with dimeric RACO-1. Moreover, RACO-1 is identified as a substrate of the arginine methyltransferase PRMT1, which methylates RACO-1 on two arginine residues. Arginine methylation of RACO-1 promotes a conformational change that stabilises RACO-1 by facilitating K63-linked ubiquitin chain formation, and enables RACO-1 dimerisation and c-Jun interaction. Abrogation of PRMT1 function impairs AP-1 activity and results in decreased expression of a large percentage of c-Jun target genes. These results demonstrate that arginine methylation of RACO-1 is required for efficient transcriptional activation by c-Jun/AP-1 and thus identify PRMT1 as an important regulator of c-Jun/AP-1 function.

IL-4 inhibition of IL-1 induced Matrix metalloproteinase-3 (MMP-3) expression in human fibroblasts involves decreased AP-1 activation via negative crosstalk involving of Jun N-terminal kinase (JNK)

Matrix metalloproteinase-3 (MMP-3) over-expression is associated with tissue destruction in the context of chronic inflammation. Previous studies showed that IL-4 inhibits induction of MMP-3 by IL-1β, and suggested that AP-1 might be involved. Here we show that IL-1 induced binding of transcription factor AP-1 to the MMP-3 promoter consists primarily of c-Jun, JunB, and c-Fos and that binding of c-Jun and c-Fos is inhibited by the combination of cytokines while binding of Jun B is not. Mutation of the AP-1 site in the MMP-3 promoter decreased the ability of IL-4 to inhibit its transcription in transfected MG-63 cells. Western blotting showed that both cytokines activate Jun N-terminal kinase (JNK), but with somewhat different kinetics, and that activation of JNK by both cytokines individually is inhibited by the combination. These results indicate that IL-4 inhibition of MMP-3 expression is associated with reduction of IL-1 induced binding of active forms of the AP-1 dimer, while less active JunB-containing dimers remain, and suggest that these changes are associated with decreased activation of JNK.

Jun is required in Isl1-expressing progenitor cells for cardiovascular development

Jun is a highly conserved member of the multimeric activator protein 1 transcription factor complex and plays an important role in human cancer where it is known to be critical for proliferation, cell cycle regulation, differentiation, and cell death. All of these biological functions are also crucial for embryonic development. Although all Jun null mouse embryos die at mid-gestation with persistent truncus arteriosus, a severe cardiac outflow tract defect also seen in human congenital heart disease, the developmental mechanisms are poorly understood. Here we show that murine Jun is expressed in a restricted pattern in several cell populations important for cardiovascular development, including the second heart field, pharyngeal endoderm, outflow tract and atrioventricular endocardial cushions and post-migratory neural crest derivatives. Several genes, including Isl1, molecularly mark the second heart field. Isl1 lineages include myocardium, smooth muscle, neural crest, endocardium, and endothelium. We demonstrate that conditional knockout mouse embryos lacking Jun in Isl1-expressing progenitors display ventricular septal defects, double outlet right ventricle, semilunar valve hyperplasia and aortic arch artery patterning defects. In contrast, we show that conditional deletion of Jun in Tie2-expressing endothelial and endocardial precursors does not result in aortic arch artery patterning defects or embryonic death, but does result in ventricular septal defects and a low incidence of semilunar valve defects, atrioventricular valve defects and double outlet right ventricle. Our results demonstrate that Jun is required in Isl1-expressing progenitors and, to a lesser extent, in endothelial cells and endothelial-derived endocardium for cardiovascular development but is dispensable in both cell types for embryonic survival. These data provide a cellular framework for understanding the role of Jun in the pathogenesis of congenital heart disease.

An integrated approach to characterize transcription factor and microRNA regulatory networks involved in Schwann cell response to peripheral nerve injury

Background

The regenerative response of Schwann cells after peripheral nerve injury is a critical process directly related to the pathophysiology of a number of neurodegenerative diseases. This SC injury response is dependent on an intricate gene regulatory program coordinated by a number of transcription factors and microRNAs, but the interactions among them remain largely unknown. Uncovering the transcriptional and post-transcriptional regulatory networks governing the Schwann cell injury response is a key step towards a better understanding of Schwann cell biology and may help develop novel therapies for related diseases. Performing such comprehensive network analysis requires systematic bioinformatics methods to integrate multiple genomic datasets.

Results

In this study we present a computational pipeline to infer transcription factor and microRNA regulatory networks. Our approach combined mRNA and microRNA expression profiling data, ChIP-Seq data of transcription factors, and computational transcription factor and microRNA target prediction. Using mRNA and microRNA expression data collected in a Schwann cell injury model, we constructed a regulatory network and studied regulatory pathways involved in Schwann cell response to injury. Furthermore, we analyzed network motifs and obtained insights on cooperative regulation of transcription factors and microRNAs in Schwann cell injury recovery.

Conclusions

This work demonstrates a systematic method for gene regulatory network inference that may be used to gain new information on gene regulation by transcription factors and microRNAs.