Fra-1 replaces c-Fos-dependent functions in mice

Epiberberine inhibits bone metastatic breast cancer-induced osteolysis

ETHNOPHARMACOLOGICAL RELEVANCE

The anti-tumor related diseases of Coptidis Rhizoma (Huanglian) were correlated with its traditional use of removing damp-heat, clearing internal fire, and counteracting toxicity. In the recent years, Coptidis Rhizoma and its components have drawn extensive attention toward their anti-tumor related diseases. Besides, Coptidis Rhizoma is traditionally used as an anti-inflammatory herb. Epiberberine (EPI) is a significant alkaloid isolated from Coptidis Rhizoma, and exhibits multiple pharmacological activities including anti-inflammatory. However, the effect of epiberberine on breast cancer and the inflammatory factors of metastatic breast cancer-induced osteolysis has not been demonstrated clearly.

AIM OF THE STUDY

Bone metastatic breast cancer can lead to osteolysis via inflammatory factors-induced osteoclast differentiation and function. In this study, we try to analyze the effect of epiberberine on breast cancer and the inflammatory factors of metastatic breast cancer-induced osteolysis.

METHODS

To evaluate whether epiberberine could suppress bone metastatic breast cancer-induced osteolytic damage, healthy female Balb/c mice were intratibially injected with murine triple-negative breast cancer 4T1 cells. Then, we examined the inhibitory effect and underlying mechanism of epiberberine on breast cancer-induced osteoclastogenesis in vitro. Xenograft assay was used to study the effect of epiberberine on breast cancer cells in vivo. Moreover, we also studied the inhibitory effects and underlying mechanisms of epiberberine on RANKL-induced osteoclast differentiation and function in vitro.

RESULTS

The results show that epiberberine displayed potential therapeutic effects on breast cancer-induced osteolytic damage. Besides, our results show that epiberberine inhibited breast cancer cells-induced osteoclast differentiation and function by inhibiting secreted inflammatory cytokines such as IL-8. Importantly, we found that epiberberine directly inhibited RANKL-induced differentiation and function of osteoclast without cytotoxicity. Mechanistically, epiberberine inhibited RANKL-induced osteoclastogensis via Akt/c-Fos signaling pathway. Furthermore, epiberberine combined with docetaxel effectively protected against bone loss induced by metastatic breast cancer cells.

CONCLUSIONS

Our findings suggested that epiberberine may be a promising natural compound for treating bone metastatic breast cancer-induced osteolytic damage by inhibiting IL-8 and is worthy of further exploration in preclinical and clinical trials.

Genomic Profiling of the Craniofacial Ossifying Fibroma by Next-Generation Sequencing

BACKGROUND

Ossifying fibroma (OF) of the craniofacial skeleton is a fibro-osseous lesion characterized by various patterns of bone formation in a cellular fibroblastic stroma. The molecular landscape of OF remains mostly unknown. There are a few known pathogenic abnormalities in OF, including HRPT2 mutations in conventional OF and SATB2 translocations in juvenile psammomatoid OF. On the other hand, conflicting reports exist regarding MDM2 gene amplification and chromosomal copy number alterations (CNA) in OF.

METHODS

Surgically removed biopsies and curettage specimens from OF patients were obtained. Clinical, radiographic, and pathologic features of tumors were reviewed. Genomic DNA was extracted from formalin-fixed, paraffin-embedded blocks of tumor tissue. Capture-based DNA next-generation sequencing targeting the coding regions 529 cancer genes and select introns was performed.

RESULTS

We identified 17 OF cases from 8 male and 8 female patients with mean age of 22 years (range 1-58 years). Nine case occurred in the gnathic bones and 8 in the extragnathic craniofacial bones. These cases included 3 juvenile psammomatoid OF, 6 conventional OF and 8 juvenile trabecular OF. Large-scale CNAs were present in 6 of 17 cases. Seven cases (41%) had focal amplifications including FOSB (n = 2, 11%), FOS (n = 4, 23%), COL1A1 (n = 4, 23%) and TBX3 (n = 5, 29%). Three cases (17%) had pathogenic CDC73 mutations. No cases showed focal MDM2 amplification.

CONCLUSIONS

Here, we provided a comprehensive molecular characterization of OF that reveals a heterogeneous genetic profile with occasional large-scale CNAs (n = 6, 35%). FOS, FOSB, and TBX3 genes that regulate AP-1 transcriptional complex are frequently altered in OF (n = 7, 41%), chiefly in juvenile trabecular OF. These genes encode transcription factors that act as downstream effectors of the MAP kinase signaling pathway. MDM2 amplification is an exceedingly rare event in OF, if present at all, so identification of this event should continue to raise concern for low-grade gnathic osteosarcoma. In summary, our findings suggest that OF represents a heterogeneous group of tumors at the genetic level but dysregulation of the AP-1 pathway may play a role in pathogenesis of juvenile trabecular OF.

The Molecular Mechanisms Study of Engeletin Suppresses RANKL-Induced Osteoclastogenesis and Inhibits Ovariectomized Murine Model Bone Loss

Objective

Osteoclastogenesis, the process of osteoclast differentiation, plays a critical role in bone homeostasis. Overexpression of osteoclastogenesis can lead to pathological conditions, such as osteoporosis and osteolysis. This study aims to investigate the role of Engelitin in the process of RAW264.7 cell differentiation into osteoclasts induced by RANKL, as well as in a mouse model of bone loss following ovariectomy.

Methods

We used RANKL-stimulated RAW264.7 cells as an in vitro osteoclast differentiation model. The effects of Eng on morphological changes during osteoclast differentiation were evaluated using TRAP and F-actin staining. The effects of Eng on the molecular level of osteoclast differentiation were evaluated using Western blot and q-PCR. The level of reactive oxygen species was evaluated using the DCFH-DA staining method. We then used ovariectomized mice as a bone loss animal model. The effects of Eng on changes in bone loss in vivo were evaluated using micro-CT and histological analysis staining.

Results

In the in vitro experiments, Eng exhibited dose-dependent inhibition of osteoclast formation and F-actin formation. At the molecular level, Eng dose-dependently suppressed the expression of specific RNAs (NFATc1, c-Fos, TRAP, Cathepsin K, MMP-9) involved in osteoclast differentiation, and inhibited the phosphorylation of proteins such as IκBα, P65, ERK, JNK, and P38. Additionally, Eng dose-dependently suppressed ROS levels and promoted the expression of antioxidant enzymes such as Nrf2, HO-1, and NQO1. In the in vivo experiments, Eng improved bone loss in ovariectomized mice.

Conclusion

Our study found that Eng inhibited RANKL-induced osteoclast differentiation through multiple signaling pathways, including MAPKs, NF-κB, and ROS aggregation. Furthermore, Eng improved bone loss in ovariectomized mice.

Hsa_Circ_0005044 Promotes Osteo/Odontogenic Differentiation of Dental Pulp Stem Cell Via Modulating miR-296-3p/FOSL1

Circular RNAs (circRNAs) are a form of RNAs that lack coding potential. The role of such circRNAs in dental pulp stem cell (DPSC) osteo/odontogenic differentiation remains to be determined. In this study, circRNA expression profiles in DPSC osteo/odontogenic differentiation process were analyzed by RNA-seq. qRT-PCR was used to confirm the differential expression of circ_0005044, miR-296-3p, and FOSL1 in DPSC osteogenic differentiation process. Circ_0005044, miR-296-3p, and FOSL1 were knocked down or overexpressed. Osteoblastic activity and associated mineral activity were monitored via alkaline phosphatase (ALP) and alizarin red S (ARS) staining. Interactions between miR-296-3p, circ_0005044, and FOSL1 were assessed through luciferase reporter assays. Finally, an in vivo system was used to confirm the relevance of circ_0005044 to osteoblastic differentiation. As results, we detected significant circ_0005044 and FOSL1 upregulation in DPSC osteo/odontogenic differentiation process, as well as concomitant miR-296-3p downregulation. When knocking down circ_0005044 or overexpressed miR-296-3p, this significantly inhibited osteogenesis. Luciferase reporter assay confirmed that miR-296-3p was capable of binding to conserved sequences in the wild-type forms of both the circ_0005044 and FOSL1. Furthermore, knocking down circ_0005044 in vivo significantly attenuated bone formation. Therefore, the circ_0005044/miR-2964-3p/FOSL1 axis regulates DPSC osteo/odontogenic differentiation, which may provide potential molecular targets for dental-pulp complex regeneration.

The Fra-1: Novel role in regulating extensive immune cell states and affecting inflammatory diseases

Fra-1(Fos-related antigen1), a member of transcription factor activator protein (AP-1), plays an important role in cell proliferation, apoptosis, differentiation, inflammation, oncogenesis and tumor metastasis. Accumulating evidence suggest that the malignancy and invasive ability of tumors can be significantly changed by directly targeting Fra-1. Besides, the effects of Fra-1 are gradually revealed in immune and inflammatory settings, such as arthritis, pneumonia, psoriasis and cardiovascular disease. These regulatory mechanisms that orchestrate immune and non-immune cells underlie Fra-1 as a potential therapeutic target for a variety of human diseases. In this review, we focus on the current knowledge of Fra-1 in immune system, highlighting its unique importance in regulating tissue homeostasis. In addition, we also discuss the possible critical intervention strategy in diseases, which also outline future research and development avenues.

Echinacoside Inhibits Osteoclast Function by Down-Regulating PI3K/Akt/C-Fos to Alleviate Osteolysis Caused by Periprosthetic Joint Infection

Infected osteolysis as a common secondary osteoporosis is associated with excessive osteoclastogenesis and bone resorption. The inhibition of osteoclastogenesis and bone resorption have been demonstrated an effective approach in the treatment of osteolytic diseases. Echinacoside (ECH) is a natural phenylethanoid glycoside with multiple biological functions, including anti-inflammatory, antioxidant, and osteoblast differentiation promotion. However, the effects of ECH on osteoclast differentiation and bone resorption function remain unknown. In vitro, we investigated the effects of ECH on osteoclast differentiation and bone resorption induced by RANKL and its potential mechanisms. In vivo, we established a periprosthetic joint infection (PJI) rat model and demonstrated the changes of infected osteolysis and osteoclasts activities in surgical sites. ECH (20 mg/kg) was injected intraperitoneally after debridement for 4 weeks. Radiological evaluation and bone histomorphometric analysis was performed to assess the efficacy of ECH. The results showed that ECH inhibited osteoclast differentiation, F-actin belts formation, bone resorption function and osteoclast-specific gene expression by preventing NFATc1 translocation, down-regulating its expression and affecting the PI3K/Akt/c-Fos pathway in vitro. ECH also alleviated in vivo PJI-induced osteolysis and maintained bone mass by inhibiting osteoclast activity. Our study indicated that ECH attenuated RANKL-induced osteoclastogenesis and PJI-induced bone loss and was shown as a potentially effective therapeutic agent for osteoclast-related bone diseases.

A systematic comparison of FOSL1, FOSL2 and BATF-mediated transcriptional regulation during early human Th17 differentiation

Th17 cells are essential for protection against extracellular pathogens, but their aberrant activity can cause autoimmunity. Molecular mechanisms that dictate Th17 cell-differentiation have been extensively studied using mouse models. However, species-specific differences underscore the need to validate these findings in human. Here, we characterized the human-specific roles of three AP-1 transcription factors, FOSL1, FOSL2 and BATF, during early stages of Th17 differentiation. Our results demonstrate that FOSL1 and FOSL2 co-repress Th17 fate-specification, whereas BATF promotes the Th17 lineage. Strikingly, FOSL1 was found to play different roles in human and mouse. Genome-wide binding analysis indicated that FOSL1, FOSL2 and BATF share occupancy over regulatory regions of genes involved in Th17 lineage commitment. These AP-1 factors also share their protein interacting partners, which suggests mechanisms for their functional interplay. Our study further reveals that the genomic binding sites of FOSL1, FOSL2 and BATF harbour hundreds of autoimmune disease-linked SNPs. We show that many of these SNPs alter the ability of these transcription factors to bind DNA. Our findings thus provide critical insights into AP-1-mediated regulation of human Th17-fate and associated pathologies.

ATF4, DLX3, FRA1, MSX2, C/EBP-ζ, and C/EBP-α Shape the Molecular Basis of Therapeutic Effects of Zoledronic Acid in Bone Disorders

OBJECTIVE

Zoledronic Acid (ZA) is one of the common treatment choices used in various boneassociated conditions. Also, many studies have investigated the effect of ZA on Osteoblastic-Differentiation (OSD) of Mesenchymal Stem Cells (MSCs), but its clear molecular mechanism(s) has remained to be understood. It seems that the methylation of the promoter region of key genes might be an important factor involved in the regulation of genes responsible for OSD. The present study aimed to evaluate the changes in the mRNA expression and promoter methylation of central Transcription Factors (TFs) during OSD of MSCs under treatment with ZA.

MATERIALS AND METHODS

MSCs were induced to be differentiated into the osteoblastic cell lineage using routine protocols. MSCs received ZA during OSD and then the methylation and mRNA expression levels of target genes were measured by Methylation Specific-quantitative Polymerase Chain Reaction (MS-qPCR) and real-time PCR, respectively. The osteoblastic differentiation was confirmed by Alizarin Red Staining and the related markers to this stage.

RESULTS

Gene expression and promoter methylation level for DLX3, FRA1, ATF4, MSX2, C/EBPζ, and C/EBPa were up or down-regulated in both ZA-treated and untreated cells during the osteodifferentiation process on days 0 to 21. ATF4, DLX3, and FRA1 genes were significantly up-regulated during the OSD processes, while the result for MSX2, C/EBPζ, and C/EBPa was reverse. On the other hand, ATF4 and DLX3 methylation levels gradually reduced in both ZA-treated and untreated cells during the osteodifferentiation process on days 0 to 21, while the pattern was increasing for MSX2 and C/EBPa. The methylation pattern of C/EBPζ was upward in untreated groups while it had a downward pattern in ZA-treated groups at the same scheduled time. The result for FRA1 was not significant in both groups at the same scheduled time (days 0-21).

CONCLUSION

The results indicated that promoter-hypomethylation of ATF4, DLX3, and FRA1 genes might be one of the mechanism(s) controlling their gene expression. Moreover, we found that promoter-hypermethylation led to the down-regulation of MSX2, C/EBP-ζ and C/EBP-α. The results implicate that ATF4, DLX3 and FRA1 may act as inducers of OSD while MSX2, C/EBP-ζ and C/EBP-α could act as the inhibitor ones. We also determined that promoter-methylation is an important process in the regulation of OSD. However, yet there was no significant difference in the promoter-methylation level of selected TFs in ZA-treated and control cells, a methylation- independent pathway might be involved in the regulation of target genes during OSD of MSCs.

The AP1 Transcription Factor Fosl2 Promotes Systemic Autoimmunity and Inflammation by Repressing Treg Development

Regulatory T cells (Tregs) represent a major population in the control of immune homeostasis and autoimmunity. Here we show that Fos-like 2 (Fosl2), a TCR-induced AP1 transcription factor, represses Treg development and controls autoimmunity. Mice overexpressing Fosl2 (Fosl2^tg) indeed show a systemic inflammatory phenotype, with immune infiltrates in multiple organs. This phenotype is absent in Fosl2^tg × Rag2^-/- mice lacking T and B cells, and Fosl2 induces T cell-intrinsic reduction of Treg development that is responsible for the inflammatory phenotype. Fosl2^tg T cells can transfer inflammation, which is suppressed by the co-delivery of Tregs, while Fosl2 deficiency in T cells reduces the severity of autoimmunity in the EAE model. We find that Fosl2 could affect expression of FoxP3 and other Treg development genes. Our data highlight the importance of AP1 transcription factors, in particular Fosl2, during T cell development to determine Treg differentiation and control autoimmunity.

Gamabufotalin Inhibits Osteoclastgenesis and Counteracts Estrogen-Deficient Bone Loss in Mice by Suppressing RANKL-Induced NF-κB and ERK/MAPK Pathways

Osteolytic bone disease is a condition of imbalanced bone homeostasis, characterized mainly by excessive bone-resorptive activity, which could predispose these populations, such as the old and postmenopausal women, to developing high risk of skeletal fragility and fracture. The nature of bone homeostasis is the coordination between the osteoblasts (OBs) and osteoclasts (OCs). Abnormal activation of osteoclasts (OCs) could compromise the bone homeostasis, constantly followed by a clutch of osteolytic diseases, including postmenopausal osteoporosis, osteoarthritis, and rheumatoid arthritis. Thus, it is imperatively urgent to explore effective medical interventions for patients. The traditional Chinese medicine (TCM) gamabufotalin (CS-6) is a newly identified natural product from Chansu and has been utilized for oncologic therapies owing to its good clinical efficacy with less adverse events. Previous study suggested that CS-6 could be a novel anti-osteoporotic agent. Nevertheless, whether CS-6 suppresses RANK-(receptor activator of nuclear factor-κ B ligand)/TRAF6 (TNF receptor-associated factor 6)-mediated downstream signaling activation in OCs, as well as the effects of CS-6 on OC differentiation in vivo, remains elusive. Therefore, in this present study, we aimed to explore the biological effects of CS-6 on osteoclastogenesis and RANKL-induced activation of related signaling pathways, and further to examine the potential therapeutic application in estrogen-deficient bone loss in the mice model. The results of in vitro experiment showed that CS-6 can inhibit RANKL-induced OC formation and the ability of bone resorption in a dose-dependent manner at both the early and late stages of osteoclastogenesis. The gene expression of OC-related key genes such as tartrate-resistant acid phosphatase (TRAP), CTSK, DC-STAMP, MMP9, and β3 integrin was evidently reduced. In addition, CS-6 could mitigate the systemic estrogen-dependent bone loss and pro-inframammary cytokines in mice in vivo. The molecular mechanism analysis suggested that CS-6 can suppress RANKL/TRAF6-induced early activation of NF-κB and ERK/MAPK signaling pathways, which consequently suppressed the transcription activity of c-Fos and NFATc1. Taken together, this present study provided ample evidence that CS-6 has the promise to become a therapeutic candidate in treating osteolytic conditions mediated by elevated OC formation and bone resorption.

AP-1 activity induced by co-stimulation is required for chromatin opening during T cell activation

Activation of T cells is dependent on the organized and timely opening and closing of chromatin. Herein, we identify AP-1 as the transcription factor that directs most of this remodeling. Chromatin accessibility profiling showed quick opening of closed chromatin in naive T cells within 5 h of activation. These newly opened regions were strongly enriched for the AP-1 motif, and indeed, ChIP-seq demonstrated AP-1 binding at >70% of them. Broad inhibition of AP-1 activity prevented chromatin opening at AP-1 sites and reduced the expression of nearby genes. Similarly, induction of anergy in the absence of co-stimulation during activation was associated with reduced induction of AP-1 and a failure of proper chromatin remodeling. The translational relevance of these findings was highlighted by the substantial overlap of AP-1-dependent elements with risk loci for multiple immune diseases, including multiple sclerosis, inflammatory bowel disease, and allergic disease. Our findings define AP-1 as the key link between T cell activation and chromatin remodeling.

DNA methylation loci in placenta associated with birthweight and expression of genes relevant for early development and adult diseases

Background

Birthweight marks an important milestone of health across the lifespan, including cardiometabolic disease risk in later life. The placenta, a transient organ at the maternal-fetal interface, regulates fetal growth. Identifying genetic loci where DNA methylation in placenta is associated with birthweight can unravel genomic pathways that are dysregulated in aberrant fetal growth and cardiometabolic diseases in later life.

Results

We performed placental epigenome-wide association study (EWAS) of birthweight in an ethnic diverse cohort of pregnant women (n = 301). Methylation at 15 cytosine-(phosphate)-guanine sites (CpGs) was associated with birthweight (false discovery rate (FDR) < 0.05). Methylation at four (26.7%) CpG sites was associated with placental transcript levels of 15 genes (FDR < 0.05), including genes known to be associated with adult lipid traits, inflammation and oxidative stress. Increased methylation at cg06155341 was associated with higher birthweight and lower FOSL1 expression, and lower FOSL1 expression was correlated with higher birthweight. Given the role of the FOSL1 transcription factor in regulating developmental processes at the maternal-fetal interface, epigenetic mechanisms at this locus may regulate fetal development. We demonstrated trans-tissue portability of methylation at four genes (MLLT1, PDE9A, ASAP2, and SLC20A2) implicated in birthweight by a previous study in cord blood. We also found that methylation changes known to be related to maternal underweight, preeclampsia and adult type 2 diabetes were associated with lower birthweight in placenta.

Conclusion

We identified novel placental DNA methylation changes associated with birthweight. Placental epigenetic mechanisms may underlie dysregulated fetal development and early origins of adult cardiometabolic diseases.

Clinical trial registration

ClinicalTrials.gov, NCT00912132

AP-1 Signaling by Fra-1 Directly Regulates HMGA1 Oncogene Transcription in Triple-Negative Breast Cancers

The architectural chromatin protein HMGA1 and the transcription factor Fra-1 are both overexpressed in aggressive triple-negative breast cancers (TNBC), where they both favor epithelial-to-mesenchymal transition, invasion, and metastasis. We therefore explored the possibility that Fra-1 might be involved in enhanced transcription of the HMGA1 gene in TNBCs by exploiting cancer transcriptome datasets and resorting to functional studies combining RNA interference, mRNA and transcriptional run-on assays, chromatin immunoprecipitation, and chromosome conformation capture approaches in TNBC model cell lines. Our bioinformatic analysis indicated that Fra-1 and HMGA1 expressions positively correlate in primary samples of patients with TNBC. Our functional studies showed that Fra-1 regulates HMGA1 mRNA expression at the transcriptional level via binding to enhancer elements located in the last two introns of the gene. Although Fra-1 binding is required for p300/CBP recruitment at the enhancer domain, this recruitment did not appear essential for Fra-1-stimulated HMGA1 gene expression. Strikingly, Fra-1 binding is required for efficient recruitment of RNA Polymerase II at the HMGA1 promoter. This is permitted owing to chromatin interactions bringing about the intragenic Fra-1-binding enhancers and the gene promoter region. Fra-1 is, however, not instrumental for chromatin loop formation at the HMGA1 locus but rather exerts its transcriptional activity by exploiting chromatin interactions preexisting to its binding. IMPLICATIONS: We demonstrate that Fra-1 bound to an intragenic enhancer region is required for RNA Pol II recruitement at the HMGA1 promoter. Thereby, we provide novel insights into the mechanisms whereby Fra-1 exerts its prooncogenic transcriptional actions in the TNBC pathologic context.

The AP-1 transcriptional complex: Local switch or remote command?

The ubiquitous family of AP-1 dimeric transcription complexes is involved in virtually all cellular and physiological functions. It is paramount for cells to reprogram gene expression in response to cues of many sorts and is involved in many tumorigenic processes. How AP-1 controls gene transcription has largely remained elusive till recently. The advent of the "omics" technologies permitting genome-wide studies of transcription factors has however changed and improved our view of AP-1 mechanistical actions. If these studies confirm that AP-1 can sometimes act as a local transcriptional switch operating in the vicinity of transcription start sites (TSS), they strikingly indicate that AP-1 principally operates as a remote command binding to distal enhancers, placing chromatin architecture dynamics at the heart of its transcriptional actions. They also unveil novel constraints operating on AP-1, as well as novel mechanisms used to regulate gene expression via transcription-pioneering-, chromatin-remodeling- and chromatin accessibility maintenance effects.

Rubiadin-1-methyl ether from Morinda officinalis How. Inhibits osteoclastogenesis through blocking RANKL-induced NF-κB pathway

Rubiadin-1-methyl ether (RBM) is a natural anthraquinone compound isolated from the root of Morinda officinalis How. In our previous study, RBM was found to have inhibitory effects on the TRAP activity of osteoclasts, which means that RBM may be a candidate for therapy of bone diseases characterized by enhanced bone resorption. However, the further effect of RBM on osteoclasts and the underlying mechanism remain unclear. In the present study, we investigated the effects of RBM isolated from Morinda officinalis How. on osteoclasts derived from bone marrow macrophages (BMMs) and the underlying mechanism in vitro. RBM at the dose that did not affect the viability of cells significantly inhibited RANKL-induced osteoclastogenesis and actin ring formation of osteoclast, while RBM performed a stronger effect at the early stage. In addition, RBM downregulated the expression of osteoclast-related proteins, including nuclear factor of activated T cells cytoplasmic 1 (NFATc1), cellular oncogene Fos (c-Fos), matrix metallopeptidase 9 (MMP-9) and cathepsin K (CtsK) as shown by Western blot. Furthermore, RBM inhibited the phosphorylation of NF-κB p65 and the degradation of IκBα as well as decreased the nuclear translocation of p65. Collectively, the results suggest that RBM inhibit osteoclastic bone resorption through blocking NF-κB pathway and may be a promising agent for the prevention and treatment of bone diseases characterized by excessive bone resorption.

Ferulic acid, a dietary polyphenol suppresses osteoclast differentiation and bone erosion via the inhibition of RANKL dependent NF-κB signalling pathway

AIMS

Bone erosion induced by enhanced osteoclast formation is a debilitating pathological phenomenon in rheumatoid arthritis (RA). Recent finding has revealed that ferulic acid is associated with reduced osteoclast differentiation and bone erosion. However, the underlying mechanism through which ferulic acid inhibited osteoclast differentiation and bone erosion still remains to be elucidated. This study assessed the therapeutic effects of ferulic acid on osteoclast differentiation and bone erosion by targeting RANKL dependent NF-κB pathway.

MAIN METHODS

RAW 264.7 monocyte/macrophage cells were left untreated/treated with 25, 50 and 100 μM ferulic acid prior to stimulation with/without RANKL and M-CSF. Osteoclast differentiation and formation was assessed by SEM and TRAP analysis whereas its functional activity of bone erosion was determined by pit formation assay. Crucial transcription factors (NF-κBp-65, NFATc1 and c-Fos) and osteoclast specific genes (TRAP, MMP-9 and Cathepsin K) were evaluated by quantitative RT-PCR. Further, the protein level expression of NF-κBp-65, NFAtc1, c-Fos and MMP-9 was assessed using western blot analysis.

KEY FINDINGS

Our results demonstrated that ferulic acid significantly attenuated RANKL induced osteoclast differentiation as evidenced from SEM and TRAP staining analysis. A remarkable decrease in the bone resorption activity of osteoclasts was also noticed upon ferulic acid treatment. In addition, the down-regulation of RANKL induced NF-κB activation and its associated downstream factors like NFATc1, c-Fos, TRAP, Cathepsin K and MMP-9 was also observed upon ferulic acid treatment.

SIGNIFICANCE

Thus, our findings evidence the anti-stimulatory and anti-resorptive role of ferulic acid via the inhibition of RANKL dependent NF-κB signalling pathway.

Up-regulation of FOS-like antigen 1 contributes to neuronal apoptosis in the cortex of rat following traumatic brain injury

Neuronal apoptosis is an important process of secondary brain injury which is induced by neurochemical signaling cascades after traumatic brain injury (TBI). Present study was designed to investigate whether FOS-like antigen 1 (Fra-1) is involved in the neuronal apoptosis. Western blot analysis and immunohistochemistry in a rat TBI model revealed a significant increase in the expression of Fra-1 in the ipsilateral brain cortex, which was in parallel with increase in the expression of active caspase-3. With immunofluorescence double-labeling, Fra-1 was colocalized with active caspase-3 and with NeuN, a neuronal marker. In an in vitro cell injury model, H₂O₂ exposure induced cell apoptosis and reduced cell viability and at the same time, a similar increased expression of active caspase-3, p53 and Fra-1 was found in PC12 cells. Down-regulation of Fra-1 through transfection with Fra-1 siRNA remarkably elevated cell viability, reduced the expression of active caspase-3 and p53, and decreased apoptosis of PC12 cells after H₂O₂ exposure. Taken together, present findings suggest that Fra-1 may be involved in the induction of neuronal apoptosis through up-regulating p53 signaling pathway and that this action may contribute to the secondary neuropathological process after TBI.

Up-Regulation of RANK Expression via ERK1/2 by Insulin Contributes to the Enhancement of Osteoclast Differentiation

Despite the importance of the receptor activator of nuclear factor (NF)-kappaB ligand (RANKL)-RANK signaling mechanisms on osteoclast differentiation, little has been studied on how RANK expression is regulated or what regulates its expression during osteoclastogenesis. We show here that insulin signaling increases RANK expression, thus enhancing osteoclast differentiation by RANKL. Insulin stimulation induced RANK gene expression in time- and dose-dependent manners and insulin receptor shRNA completely abolished RANK expression induced by insulin in bone marrow-derived monocyte/macrophage cells (BMMs). Moreover, the addition of insulin in the presence of RANKL promoted RANK expression. The ability of insulin to regulate RANK expression depends on extracellular signal-regulated kinase 1/2 (ERK1/2) since only PD98059, an ERK1/2 inhibitor, specifically inhibited its expression by insulin. However, the RANK expression by RANKL was blocked by all three mitogen-activated protein (MAP) kinases inhibitors. The activation of RANK increased differentiation of BMMs into tartrate-resistant acid phosphatase-positive (TRAP+) osteoclasts as well as the expression of dendritic cell-specific transmembrane protein (DC-STAMP) and d2 isoform of vacuolar (H+) ATPase (v-ATPase) Vo domain (Atp6v0d2), genes critical for osteoclastic cell-cell fusion. Collectively, these results suggest that insulin induces RANK expression via ERK1/2, which contributes to the enhancement of osteoclast differentiation.

Barley Seedling Extracts Inhibit RANKL-Induced Differentiation, Fusion, and Maturation of Osteoclasts in the Early-to-Late Stages of Osteoclastogenesis

The number of patients with osteoporosis is increasing worldwide, and a decrease in bone mass is a main risk factor for fracture. The prevention of bone loss is critical for improving the quality of life for patients. However, the long-term use of antiosteoporotic agents is limited due to their side effects. Barley has been traditionally ingested for thousands of years as a safe, natural food with pharmaceutical properties, and its seedling can enhance the biological activity of the medicinal components found in food. This study aimed to clarify the antiresorptive activity of barley seedling and its mode of action. Barley seedling extracts (BSE) dose-dependently inhibited RANKL-induced osteoclast differentiation with alteration of IκB degradation, c-Fos, and NFATc1 molecules in the early-to-middle stages of osteoclastogenesis. In the late phase of osteoclastogenesis, BSE also prevented DC-STAMP and cathepsin K, which are required for cell fusion and bone degradation, such as osteoclast function. In conclusion, barley seedling from natural foods may provide long-term safety and be useful for the prevention or treatment of osteoclast-mediated bone metabolic diseases, including osteoporosis.

Non-Canonical (RANKL-Independent) Pathways of Osteoclast Differentiation and Their Role in Musculoskeletal Diseases

Osteoclasts are multinucleated cells derived from mononuclear phagocyte precursors (monocytes, macrophages); in the canonical pathway of osteoclastogenesis, these cells fuse and differentiate to form specialised bone-resorbing osteoclasts in the presence of receptor activator for nuclear factor kappa B ligand (RANKL). Non-canonical pathways of osteoclastogenesis have been described in which several cytokines and growth factors are able to substitute for RANKL. These humoral factors can generally be divided into those which, like RANKL, are tumour necrosis family (TNF) superfamily members and those which are not; the former include TNFα lymphotoxin exhibiting inducible expression and competing with herpes simplex virus glycoprotein D for herpesvirus entry mediator, a receptor expressed by T lymphocytes (LIGHT), a proliferation inducing ligand (APRIL) and B cell activating factor (BAFF); the latter include transforming growth factor beta (TGF-β), interleukin-6 (IL-6), IL-8, IL-11, nerve growth factor (NGF), insulin-like growth factor-I (IGF-I) and IGF-II. This review summarises the evidence for these RANKL substitutes in inducing osteoclast differentiation from tissue-derived and circulating mononuclear phagocytes. It also assesses the role these factors are likely to play in promoting the pathological bone resorption seen in many inflammatory and neoplastic lesions of bone and joint including rheumatoid arthritis, aseptic implant loosening and primary and secondary tumours of bone.

Regulation of Hspb7 by MEF2 and AP-1: implications for Hspb7 in muscle atrophy

Mycocyte enhancer factor 2 (MEF2) and activator protein 1 (AP-1) transcription complexes have been individually implicated in myogenesis, but their genetic interaction has not previously been addressed. Using MEF2A, c-Jun and Fra-1 chromatin immunoprecipitation sequencing (ChIP-seq) data and predicted AP-1 consensus motifs, we identified putative common MEF2 and AP-1 target genes, several of which are implicated in regulating the actin cytoskeleton. Because muscle atrophy results in remodelling or degradation of the actin cytoskeleton, we characterized the expression of putative MEF2 and AP-1 target genes (Dstn, Flnc, Hspb7, Lmod3 and Plekhh2) under atrophic conditions using dexamethasone (Dex) treatment in skeletal myoblasts. Heat shock protein b7 (Hspb7) was induced by Dex treatment and further analyses revealed that loss of MEF2A using siRNA prevented Dex-regulated induction of Hspb7. Conversely, ectopic Fra-2 or c-Jun expression reduced Dex-mediated upregulation of Hspb7 whereas AP-1 depletion enhanced Hspb7 expression. In vivo, expression of Hspb7 and other autophagy-related genes was upregulated in response to atrophic conditions in mice. Manipulation of Hspb7 levels in mice also impacted gross muscle mass. Collectively, these data indicate that MEF2 and AP-1 confer antagonistic regulation of Hspb7 gene expression in skeletal muscle, with implications for autophagy and muscle atrophy.

Complement Membrane Attack and Tumorigenesis: A SYSTEMS BIOLOGY APPROACH

Tumor development driven by inflammation is now an established phenomenon, but the role that complement plays remains uncertain. Recent evidence has suggested that various components of the complement (C) cascade may influence tumor development in disparate ways; however, little attention has been paid to that of the membrane attack complex (MAC). This is despite abundant evidence documenting the effects of this complex on cell behavior, including cell activation, protection from/induction of apoptosis, release of inflammatory cytokines, growth factors, and ECM components and regulators, and the triggering of the NLRP3 inflammasome. Here we present a novel approach to this issue by using global gene expression studies in conjunction with a systems biology analysis. Using network analysis of MAC-responsive expression changes, we demonstrate a cluster of co-regulated genes known to have impact in the extracellular space and on the supporting stroma and with well characterized tumor-promoting roles. Network analysis highlighted the central role for EGF receptor activation in mediating the observed responses to MAC exposure. Overall, the study sheds light on the mechanisms by which sublytic MAC causes tumor cell responses and exposes a gene expression signature that implicates MAC as a driver of tumor progression. These findings have implications for understanding of the roles of complement and the MAC in tumor development and progression, which in turn will inform future therapeutic strategies in cancer.

Bag-1 promotes cell survival through c-Myc-mediated ODC upregulation that is not preferred under apoptotic stimuli in MCF-7 cells

Bag-1, Bcl-2 associated athanogene-1, is a multifunctional protein that can regulate a wide variety of cellular processes: proliferation, cell survival, transcription, apoptosis and motility. Bag-1 interacts with various targets in the modulation of these pathways; yet molecular details of Bag-1's involvement in each cellular event are still unclear. We first showed that forced Bag-1 expression promotes cell survival and prevents drug-induced apoptosis in MCF-7 breast cancer cells. Increased mRNA expressions of c-myc protooncogene and ornithine decarboxylase (ODC), biosynthetic enzyme of polyamines, were detected in Bag-1L+ cells, and western blots against the protein product of c-Myc and ODC confirmed these findings. Once ODC, a c-Myc target, gets activated, polyamine biosynthesis increases. We observed enhanced polyamine content in the Bag-1L+ cells. On the contrary, when polyamine catabolic mechanisms were investigated, Bag-1 silencing suppressed biosynthesis of polyamines because of the downregulation of ODC and upregulation of PAO. Exposure of cells to apoptotic inducers enhances the cell death mechanism by producing toxic products such as H2 O2 and aldehydes. Bag-1L+ cells prevented drug-induced PAO activation leading to a decrease in H2 O2 production following cisplatin or paclitaxel treatment. In this line, our results suggested that Bag-1 indirectly affects cell survival through c-Myc activated signalling that causes elevation of ODC levels, leading to an increase of the polyamine content.

Fusion events lead to truncation of FOS in epithelioid hemangioma of bone

Epithelioid hemangioma of bone is a locally aggressive vascular neoplasm. It can be challenging to diagnose because of the wide histological spectrum, which can make it difficult to differentiate from other vascular neoplasms such as epithelioid hemangioendothelioma or epithelioid angiosarcoma. COBRA-FISH karyotyping identified a balanced t(3;14) translocation. Transcriptome sequencing of the index case and two other epithelioid hemangiomas revealed a recurrent translocation breakpoint involving the FOS gene, which was fused to different partners in all three cases. The break was observed in exon 4 of the FOS gene and the fusion event led to the introduction of a stop codon. In all instances, the truncation of the FOS gene would result in the loss of the transactivation domain (TAD). Using FISH probes we found a break in the FOS gene in two additional cases, in none of these cases a recurrent fusion partner could be identified. In total, FOS was split in 5/7 evaluable samples. We did not observe point mutations leading to early stop codons in any of the 10 cases where RNA was available. Detection of FOS rearrangement may be a useful diagnostic tool to assist in the often difficult differential diagnosis of vascular tumors of bone. Our data suggest that the translocation causes truncation of the FOS protein, with loss of the TAD, which is thereby a novel mechanism involved in tumorigenesis.

BET inhibitors induce apoptosis through a MYC independent mechanism and synergise with CDK inhibitors to kill osteosarcoma cells

Osteosarcoma (OS) survival rates have plateaued in part due to a lack of new therapeutic options. Here we demonstrate that bromodomain inhibitors (BETi), JQ1, I-BET151, I-BET762, exert potent anti-tumour activity against primary and established OS cell lines, mediated by inhibition of BRD4. Strikingly, unlike previous observations in long-term established human OS cell lines, the antiproliferative activity of JQ1 in primary OS cells was driven by the induction of apoptosis, not cell cycle arrest. In further contrast, JQ1 activity in OS was mediated independently of MYC downregulation. We identified that JQ1 suppresses the transcription factor FOSL1 by displacement of BRD4 from its locus. Loss of FOSL1 phenocopied the antiproliferative effects of JQ1, identifying FOSL1 suppression as a potential novel therapeutic approach for OS. As a monotherapy JQ1 demonstrated significant anti-tumour activity in vivo in an OS graft model. Further, combinatorial treatment approaches showed that JQ1 increased the sensitivity of OS cells to doxorubicin and induced potent synergistic activity when rationally combined with CDK inhibitors. The greater level of activity achieved with the combination of BETi with CDK inhibitors demonstrates the efficacy of this combination therapy. Taken together, our studies show that BET inhibitors are a promising new therapeutic for OS.

Aberrantly expressed Fra-1 by IL-6/STAT3 transactivation promotes colorectal cancer aggressiveness through epithelial-mesenchymal transition

The pro-inflammatory cytokine interleukin-6 (IL-6) in tumor microenvironment has been suggested to promote development and progression of colorectal cancer (CRC). However, the underlying molecular mechanisms remain elusive. In this study, we demonstrate that fos-related antigen-1 (Fra-1) plays a critical role in IL-6 induced CRC aggressiveness and epithelial-mesenchymal transition (EMT). In CRC cell lines, the expression of Fra-1 gene was found significantly upregulated during IL-6-driven EMT process. The Fra-1 induction occurred at transcriptional level in a manner dependent on signal transducer and activator of transcription 3 (STAT3), during which both phosphorylated and acetylated post-translational modifications were required for STAT3 activation to directly bind to the Fra-1 promoter. Importantly, RNA interference-based attenuation of either STAT3 or Fra-1 prevented IL-6-induced EMT, cell migration and invasion, whereas ectopic expression of Fra-1 markedly reversed the STAT3-knockdown effect and enhanced CRC cell aggressiveness by regulating the expression of EMT-promoting factors (ZEB1, Snail, Slug, MMP-2 and MMP-9). Furthermore, Fra-1 levels were positively correlated with the local invasion depth as well as lymph node and liver metastasis in a total of 229 CRC patients. Intense immunohistochemical staining of Fra-1 was observed at the tumor marginal area adjacent to inflammatory cells and in parallel with IL-6 secretion and STAT3 activation in CRC tissues. Together, this study proposes the existence of an aberrant IL-6/STAT3/Fra-1 signaling axis leading to CRC aggressiveness through EMT induction, which suggests novel therapeutic opportunities for the malignant disease.

ATF-2 immunoreactivity in post-mitotic and terminally differentiated human odontoblasts

Activating transcription factor 2 (ATF-2/CRE-BP1; cAMP-responsive element binding protein 1) is a member of nuclear transcription factor activator protein-1 (AP-1) family. AP-1 regulates cellular processes including growth, proliferation, differentiation and apoptosis. However, biological relationship of cellular process to each member of the AP-1 family is not clear yet. The objective of the present study was to compare the ATF-2 immunoreactivity in the post-mitotic and terminally differentiated odontoblasts and in the pulpal fibroblasts which can be divided by mitosis when required. Fibroblasts at various stages of differentiation co-exist in the human dental pulp. ATF-2 was investigated immunohistochemically in 20 permanent human teeth. According to the findings obtained, the mean percentage of ATF-2 positive cells was 68.5 ± 19.2% in the odontoblasts and 22.8 ± 13.7% in the pulpal fibroblasts. The comparison of ATF-2 positivity revealed a statistically significant difference between odontoblasts and pulpal fibroblasts. These findings have suggested that ATF-2 is more associated with cell survival rather than cell proliferation, and revealed much of effectiveness in maintaining terminal differentiation than the various differentiation stages of the cells.

The AP-1 transcription factor Fra1 inhibits follicular B cell differentiation into plasma cells

Grötsch et al. find that the AP-1 transcription factor Fra-1 limits the generation of antibody-producing plasma cells. Absence of Fra1 in B cells results in abnormally high numbers of plasma cells and increased antibody responses after vaccination.

The cornerstone of humoral immunity is the differentiation of B cells into antibody-secreting plasma cells. This process is tightly controlled by a regulatory gene network centered on the transcriptional repressor B lymphocyte–induced maturation protein 1 (Blimp1). Proliferation of activated B cells is required to foster Blimp1 expression but needs to be terminated to avoid overshooting immune reactions. Activator protein 1 (AP-1) transcription factors become quickly up-regulated upon B cell activation. We demonstrate that Fra1, a Fos member of AP-1, enhances activation-induced cell death upon induction in activated B cells. Moreover, mice with B cell–specific deletion of Fra1 show enhanced plasma cell differentiation and exacerbated antibody responses. In contrast, transgenic overexpression of Fra1 blocks plasma cell differentiation and immunoglobulin production, which cannot be rescued by Bcl2. On the molecular level, Fra1 represses Blimp1 expression and interferes with binding of the activating AP-1 member c-Fos to the Blimp1 promoter. Conversely, overexpression of c-Fos in Fra1 transgenic B cells releases Blimp1 repression. As Fra1 lacks transcriptional transactivation domains, we propose that Fra1 inhibits Blimp1 expression and negatively controls plasma cell differentiation through binding to the Blimp1 promoter. In summary, we demonstrate that Fra1 negatively controls plasma cell differentiation by repressing Blimp1 expression.

Genome-wide identification and characterization of functional neuronal activity-dependent enhancers

Experience-dependent gene transcription is required for nervous system development and function. However, the DNA regulatory elements that control this program of gene expression are not well defined. Here we characterize the enhancers that function across the genome to mediate activity-dependent transcription in mouse cortical neurons. We find that the subset of enhancers enriched for monomethylation of histone H3 Lys4 (H3K4me1) and binding of the transcriptional coactivator CREBBP (also called CBP) that shows increased acetylation of histone H3 Lys27 (H3K27ac) after membrane depolarization of cortical neurons functions to regulate activity-dependent transcription. A subset of these enhancers appears to require binding of FOS, which was previously thought to bind primarily to promoters. These findings suggest that FOS functions at enhancers to control activity-dependent gene programs that are critical for nervous system function and provide a resource of functional cis-regulatory elements that may give insight into the genetic variants that contribute to brain development and disease.

Regulation of steatohepatitis and PPARγ signaling by distinct AP-1 dimers

Nonalcoholic fatty liver disease (NAFLD) affects up to 30% of the adult population in Western societies, yet the underlying molecular pathways remain poorly understood. Here, we identify the dimeric Activator Protein 1 as a regulator of NAFLD. Fos-related antigen 1 (Fra-1) and Fos-related antigen 2 (Fra-2) prevent dietary NAFLD by inhibiting prosteatotic PPARγ signaling. Moreover, established NAFLD and the associated liver damage can be efficiently reversed by hepatocyte-specific Fra-1 expression. In contrast, c-Fos promotes PPARγ expression, while c-Jun exerts opposing, dimer-dependent functions. Interestingly, JunD was found to be essential for PPARγ signaling and NAFLD development. This unique antagonistic regulation of PPARγ by distinct AP-1 dimers occurs at the transcriptional level and establishes AP-1 as a link between obesity, hepatic lipid metabolism, and NAFLD.

Activator Protein 1 transcription factor Fos-related antigen 1 (Fra-1) is dispensable for murine liver fibrosis, but modulates xenobiotic metabolism

The Activator Protein 1 (AP-1) transcription factor subunit Fos-related antigen 1 (Fra-1) has been implicated in liver fibrosis. Here we used loss-of-function as well as switchable, cell type-specific, gain-of-function alleles for Fra-1 to investigate the relevance of Fra-1 expression in cholestatic liver injury and fibrosis. Our results indicate that Fra-1 is dispensable in three well-established, complementary models of liver fibrosis. However, broad Fra-1 expression in adult mice results in liver fibrosis, which is reversible, when ectopic Fra-1 is switched off. Interestingly, hepatocyte-specific Fra-1 expression is not sufficient to trigger the disease, although Fra-1 expression leads to dysregulation of fibrosis-associated genes. Both opn and cxcl9 are controlled by Fra-1 in gain-of-function and loss-of-function experiments. Importantly, Fra-1 attenuates liver damage in the 3,5-diethoxycarbonyl-1,4-dihydrocollidine-feeding cholestatic liver injury model. Strikingly, manipulating Fra-1 expression affects genes involved in hepatic transport and detoxification, in particular glutathione S-transferases. Molecular analyses indicate that Fra-1 binds to the promoters of cxcl9 and gstp1 in vivo. Furthermore, loss of Fra-1 sensitizes, while hepatic Fra-1 expression protects from acetaminophen-induced liver damage, a paradigm for glutathione-mediated acute liver failure.

CONCLUSION

These data define a novel function of Fra-1/AP-1 in modulating the expression of detoxification genes and the adaptive response of the liver to bile acids/xenobiotic overload.

The FOS transcription factor family differentially controls trophoblast migration and invasion

Extravillous trophoblast invasion is a fundamental component of human placentation. Invading trophoblast cells promote blood flow to the conceptus by actively remodeling the uterine vasculature. The extent of trophoblast invasion is tightly regulated; aberrant invasion is linked with several obstetrical complications. However, the transcriptional networks responsible for controlling the extent of trophoblast invasion are not well defined. Previous studies have identified high levels of FOS (FOS, FOSB, FOS-like (FOSL) 1, and FOSL2) proteins in extravillous trophoblast cells. These proteins form part of the activating protein-1 (AP-1) transcription factor complex and are implicated in regulating gene networks controlling cellular invasion in diverse biological systems. Therefore, we hypothesized that FOS family proteins play a role in regulating trophoblast invasion. We assessed expression of FOS family proteins in trophoblast cell lines and human placentae at different gestational ages. FOS, FOSB, and FOSL1 proteins were robustly increased in trophoblast cells subject to wound-based migration assays as well as Matrigel-based invasion assays. FOS knockdown resulted in cessation of proliferation and an induction of migration and invasion concomitant with robust expression of matrix metalloproteinase (MMP) 1, MMP3, and MMP10. Conversely, FOSL1 knockdown abrogated trophoblast migration and invasion and inhibited the production of MMP1, MMP3, and MMP10. In human placenta, FOS was expressed in proximal anchoring villi in conjunction with phospho-ERK. FOSL1 was temporally expressed only in the distal-most extravillous trophoblast cells, which represent a migratory cell population. Therefore, FOS and FOSL1 exert opposing effects on trophoblast invasion.

Fra-1 regulation of Matrix Metallopeptidase-1 (MMP-1) in metastatic variants of MDA-MB-231 breast cancer cells

Matrix Metallopeptidase 1 (MMP-1) expression has repeatedly been correlated to tumorigenesis and metastasis.  Yet, MMP-1 regulation in a metastatic context remains largely unknown.  Here we confirm differential MMP-1 expression in mammary carcinoma cells with varied metastatic potentials. We show that MMP-1 expression is regulated by an AP-1 element in its promoter in highly metastatic MDA-MB-231 mammary carcinoma cell derivatives.  Fra-1, an AP-1 family transcription factor, differentially binds this element in highly metastatic cells compared to low metastatic cells and is required for MMP-1 expression.  Overexpression of Fra-1 also caused increased MMP-1 expression. Fra-1 mRNA levels are unchanged in the cell variants, however its protein levels are higher in the metastatic cells. While there was no change in Fra-1 protein degradation rates, protein synthesis of Fra-1 was increased in the metastatic cell variant. These results demonstrate that Fra-1 and MMP-1 levels are differentially regulated in metastatic cell variants at the level of Fra-1 protein translation. Consistent with the importance of Fra-1 for tumor growth, we found that Fra-1 overexpression was sufficient to increase cell motility and anchorage independent growth.  These results suggest that increased Fra-1 translation is critical for regulation of MMP-1 and tumor cell metastasis.

The AP-1 transcription factor c-Jun prevents stress-imposed maladaptive remodeling of the heart

Systemic hypertension increases cardiac workload and subsequently induces signaling networks in heart that underlie myocyte growth (hypertrophic response) through expansion of sarcomeres with the aim to increase contractility. However, conditions of increased workload can induce both adaptive and maladaptive growth of heart muscle. Previous studies implicate two members of the AP-1 transcription factor family, junD and fra-1, in regulation of heart growth during hypertrophic response. In this study, we investigate the function of the AP-1 transcription factors, c-jun and c-fos, in heart growth. Using pressure overload-induced cardiac hypertrophy in mice and targeted deletion of Jun or Fos in cardiomyocytes, we show that c-jun is required for adaptive cardiac hypertrophy, while c-fos is dispensable in this context. c-jun promotes expression of sarcomere proteins and suppresses expression of extracellular matrix proteins. Capacity of cardiac muscle to contract depends on organization of principal thick and thin filaments, myosin and actin, within the sarcomere. In line with decreased expression of sarcomere-associated proteins, Jun-deficient cardiomyocytes present disarrangement of filaments in sarcomeres and actin cytoskeleton disorganization. Moreover, Jun-deficient hearts subjected to pressure overload display pronounced fibrosis and increased myocyte apoptosis finally resulting in dilated cardiomyopathy. In conclusion, c-jun but not c-fos is required to induce a transcriptional program aimed at adapting heart growth upon increased workload.

Acidosis inhibits mineralization in human osteoblasts

Osteoblasts and osteoclasts maintain bone volume. Acidosis affects the function of these cells including mineral metabolism. We examined the effect of acidosis on the expression of transcription factors and mineralization in human osteoblasts in vitro. Human osteoblasts (SaM-1 cells) derived from the ulnar periosteum were cultured with α-MEM containing 50 μg/ml ascorbic acid and 5 mM β-glycerophosphate (calcifying medium). Acidosis was induced by incubating the SaM-1 cells in 10 % CO₂ (pH approximately 7.0). Mineralization, which was augmented by the calcifying medium, was completely inhibited by acidosis. Acidosis depressed c-Jun mRNA and increased osteoprotegerin (OPG) production in a time-dependent manner. Depressing c-Jun mRNA expression using siRNA increased OPG production and inhibited mineralization. In addition, depressing OPG mRNA expression with siRNA enhanced mineralization in a dose-dependent manner. Acidosis or the OPG protein strongly inhibited mineralization in osteoblasts from neonatal mice. The present study was the first to demonstrate that acidosis inhibited mineralization, depressed c-Jun mRNA expression, and induced OPG production in human osteoblasts. These results suggest that OPG is involved in mineralization via c-Jun in human osteoblasts.

Signal-dependent fra-2 regulation in skeletal muscle reserve and satellite cells

Activator protein-1 (AP-1) is a ubiquitous transcription factor that paradoxically also has some tissue-specific functions. In skeletal muscle cells, we document that the AP-1 subunit, Fra-2, is expressed in the resident stem cells (Pax7-positive satellite cells) and also in the analogous undifferentiated ‘reserve' cell population in myogenic cultures, but not in differentiated myofiber nuclei. Silencing of Fra-2 expression enhances the expression of differentiation markers such as muscle creatine kinase and myosin heavy chain, indicating a possible role of Fra-2 in undifferentiated myogenic progenitor cells. We observed that Fra-2 is a target of cytokine-mediated extracellular signal-regulated kinase-1/2 signaling in cultured muscle cells, and extensive mass spectrometry and mutational analysis identified S320 and T322 as regulators of Fra-2 protein stability. Interestingly, Fra-2 S320 phosphorylation occurs transiently in activated satellite cells and is extinguished in myogenin-positive differentiating cells. Thus, cytokine-mediated Fra-2 expression and stabilization is linked to regulation of myogenic progenitor cells having implications for the molecular regulation of adult muscle stem cells and skeletal muscle regeneration.

AP1 transcription factors in epidermal differentiation and skin cancer

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

The restructuring of muscarinic receptor subtype gene transcripts in c-fos knock-out mice

Although c-Fos plays a key role in intracellular signalling, the disruption of the c-fos gene has only minor consequences on the central nervous system (CNS) function. As muscarinic receptors (MR) play important roles in many CNS functions (attention, arousal, and cognition), the c-fos knock-out might be compensated through MR changes. The aim of this study was to evaluate changes in the M1-M5 MR mRNA in selected CNS areas: frontal, parietal, temporal and occipital cortex, striatum, hippocampus, hypothalamus and cerebellum (FC, PC, TC, OC, stria, hip, hypo, and crbl, respectively). Knocking out the c-fos gene changed the expression of MR in FC (reduced M1R, M4R and M5R expression), TC (increased M4R expression), OC (decreased M2R and M3R expression) and hippocampus (reduced M3R expression). Moreover, gender differences were observed in WT mice: increased expression of all M1-M5R in the FC in males and M1-M4R in the striatum in females. A detailed analysis of MR transcripts showed pre-existing correlations in the amount of MR-mRNA between specific regions. WT mice showed three major types of cortico-cortical correlations: fronto-occipital, temporo-parietal and parieto-occipital. The cortico-subcortical correlations involved associations between the FC, PC, TC and striatum. In KO mice, a substantial rearrangement of the correlation pattern was observed: only a temporo-parietal correlation and correlations between the FC and striatum remained, and a new correlation between the hypothalamus and cerebellum appeared. Thus, in addition to the previously described dopamine receptor restructuring, the restructuring of MR mRNA correlations reveals an additional mechanism for adaptation to the c-fos gene knockout.

Old players with a newly defined function: Fra-1 and c-Fos support growth of human malignant breast tumors by activating membrane biogenesis at the cytoplasm

A shared characteristic of tumor cells is their exacerbated growth. Consequently, tumor cells demand high rates of phospholipid synthesis required for membrane biogenesis to support their growth. c-Fos, in addition to its AP-1 transcription factor activity, is the only protein known up to date that is capable of activating lipid synthesis in normal and brain tumor tissue. For this latter activity, c-Fos associates to the endoplasmic reticulum (ER) through its N-terminal domain and activates phospholipid synthesis, an event that requires it Basic Domain (BD) (aa 139–159). Fra-1, another member of the FOS family of proteins, is over-expressed in human breast cancer cells and its BD is highly homologous to that of c-Fos with two conservative substitutions in its basic amino acids. Consequently, herein we examined if Fra-1 and/or c-Fos participate in growth of breast cancer cells by activating phospholipid synthesis as found previously for c-Fos in brain tumors. We found both Fra-1 and c-Fos over-expressed in >95% of human ductal breast carcinoma biopsies examined contrasting with the very low or undetectable levels in normal tissue. Furthermore, both proteins associate to the ER and activate phospholipid synthesis in cultured MCF7 and MDA-MB231 breast cancer cells and in human breast cancer samples. Stripping tumor membranes of Fra-1 and c-Fos prior to assaying their lipid synthesis capacity in vitro results in non-activated lipid synthesis levels that are restored to their initial activated state by addition of Fra-1 and/or c-Fos to the assays. In MDA-MB231 cells primed to proliferate, blocking Fra-1 and c-Fos with neutralizing antibodies blocks lipid-synthesis activation and cells do not proliferate. Taken together, these results disclose the cytoplasmic activity of Fra-1 and c-Fos as potential targets for controlling growth of breast carcinomas by decreasing the rate of membrane biogenesis required for growth.

Interferon-β-induced miR-155 inhibits osteoclast differentiation by targeting SOCS1 and MITF

IFN-β is induced via a c-fos dependent mechanism that is present downstream of the receptor activator of NF-κB ligand (RANKL)-RANK signal transduction cascade during osteoclast differentiation. Increased production of IFN-β in turn inhibits osteoclastogenesis. However, the mechanism by which IFN-β exerts its suppressive function remains unclear. In the present study, we found that miR-155, an IFN-β-induced miRNA, mediated the suppressive effect of IFN-β on osteoclast differentiation by targeting SOCS1 and MITF, two essential regulators of osteoclastogenesis. These findings have not only demonstrated that miR-155 inhibits osteoclast differentiation, but also provided a new therapeutic target for treatment of osteoclast-mediated diseases.

Suppression of AP1 transcription factor function in keratinocyte suppresses differentiation

Our previous study shows that inhibiting activator protein one (AP1) transcription factor function in murine epidermis, using dominant-negative c-jun (TAM67), increases cell proliferation and delays differentiation. To understand the mechanism of action, we compare TAM67 impact in mouse epidermis and in cultured normal human keratinocytes. We show that TAM67 localizes in the nucleus where it forms TAM67 homodimers that competitively interact with AP1 transcription factor DNA binding sites to reduce endogenous jun and fos factor binding. Involucrin is a marker of keratinocyte differentiation that is expressed in the suprabasal epidermis and this expression requires AP1 factor interaction at the AP1-5 site in the promoter. TAM67 interacts competitively at this site to reduce involucrin expression. TAM67 also reduces endogenous c-jun, junB and junD mRNA and protein level. Studies with c-jun promoter suggest that this is due to reduced transcription of the c-jun gene. We propose that TAM67 suppresses keratinocyte differentiation by interfering with endogenous AP1 factor binding to regulator elements in differentiation-associated target genes, and by reducing endogenous c-jun factor expression.

Estrogen-induced expression of Fos-related antigen 1 (FRA-1) regulates uterine stromal differentiation and remodeling

Concerted actions of estrogen and progesterone via their cognate receptors orchestrate changes in the uterine tissue, regulating implantation during early pregnancy. The uterine stromal cells undergo steroid-dependent differentiation into morphologically and functionally distinct decidual cells, which support embryonic growth and survival. The hormone-regulated pathways underlying this unique cellular transformation are not fully understood. Previous studies in the mouse revealed that, following embryo attachment, de novo synthesis of estrogen by the decidual cells is critical for stromal differentiation. In this study we report that Fos-related antigen 1 (FRA-1), a member of the Fos family of transcription factors, is a downstream target of regulation by intrauterine estrogen. FRA-1 expression was localized in the differentiating uterine stromal cells surrounding the implanted embryo. Attenuation of estrogen receptor α (Esr1) expression by siRNA mediated silencing in primary uterine stromal cells suppressed FRA-1 expression. Furthermore, chromatin immunoprecipitation demonstrated direct recruitment of ESR1 to an estrogen response element in the Fra-1 promoter. Down-regulation of Fra-1 expression during in vitro decidualization blocked stromal differentiation and resulted in a marked decrease in stromal cell migration. Interestingly, FRA-1 controls the expression of matrix metalloproteinases MMP9 and MMP13, which are critical modulators of stromal extracellular matrix remodeling. Collectively, these results suggest that FRA-1, induced in response to estrogen signaling via ESR1, is a key regulator of stromal differentiation and remodeling during early pregnancy.

TNFα inhibits the development of osteoclasts through osteoblast-derived GM-CSF

Inflammatory cytokines such as tumor necrosis factor-alpha (TNFα) are potent stimulators of osteoclast formation and bone resorption and are frequently associated with pathologic bone metabolism. The cytokine exerts specific effects on its target cells and constitutes a part of the cellular microenvironment. Previously, TNFα was demonstrated to inhibit the development of osteoclasts in vitro via an osteoblast-mediated pathway. In the present study, the molecular mechanisms of the inhibition of osteoclastogenesis were investigated in co-cultures of osteoblasts and bone marrow cells (BMC) and in cultures of macrophage-colony stimulating factor (M-CSF) dependent, non-adherent osteoclast progenitor cells (OPC) grown with M-CSF and receptor activator of NF-κB ligand (RANKL). Granulocyte-macrophage colony stimulating factor (GM-CSF), a known inhibitor of osteoclastogenesis was found to be induced in osteoblasts treated with TNFα and the secreted protein accumulated in the supernatant. Dexamethasone (Dex), an anti-inflammatory steroid, caused a decrease in GM-CSF expression, leading to partial recovery of osteoclast formation. Flow cytometry analysis revealed that in cultures of OPC, supplemented with 10% conditioned medium (CM) from osteoblasts treated with TNFα/1,25(OH)(2)D(3), expression of RANK and CD11c was suppressed. The decrease in RANK expression may be explained by the finding, that GM-CSF and the CM from wt osteoblasts were found to suppress the expression of c-Fos, Fra-1, and Nfatc-1. The failure of OPC to develop into CD11c(+) dendritic cells suggests that cell development is not deviated to an alternative differentiation pathway, but rather, that the monocytes are maintained in an undifferentiated, F4/80(+), state. The data further implies possible interactions among inflammatory cytokines. GM-CSF induced by TNFα acts on early hematopoietic precursors, inhibiting osteoclastogenesis while acting as the growth factor for M-CSF independent inflammatory macrophages. These in turn may condition a microenvironment enhancing osteoclast differentiation and bone resorption upon migration of the OPC from circulation to the bone/bone marrow compartment.

Binding site specificity and factor redundancy in activator protein-1-driven human papillomavirus chromatin-dependent transcription

Activator protein-1 (AP-1) regulates diverse gene responses triggered by environmental cues and virus-induced cellular stress. Although many signaling events leading to AP-1 activation have been described, the fundamental features underlying binding site selection and factor recruitment of dimeric AP-1 complexes to their target genes remain mostly uncharacterized. Using recombinant full-length human AP-1 dimers formed between c-Jun and Fos family members (c-Fos, FosB, Fra-1, Fra-2) for DNA binding and transcriptional analysis, we found that each of these AP-1 complex exhibits differential activity for distinct non-consensus AP-1 sites present in human papillomavirus (HPV), and each AP-1 complex is capable of activating transcription from in vitro-reconstituted HPV chromatin in a p300- and acetyl-CoA-dependent manner. Transcription from HPV chromatin requires AP-1-dependent and contact-driven recruitment of p300. Acetylation of dimeric AP-1 complexes by p300 enhances AP-1 binding to DNA. Using a human C-33A cervical cancer-derived cell line harboring the episomal HPV type 11 genome, we illustrate binding site selectivity recognized by c-Jun, JunB, JunD, and various Fos family members in a combinatorial and unique pattern, highlighting the diversity and importance of non-canonical binding site recognition by various AP-1 family proteins.

Yukmijihwang-tang inhibits receptor activator for nuclear Factor-κB ligand-induced osteoclast differentiation

Yukmijihwang-tang (YMT) is a traditional herbal medicine known to enhance memory in brain injury models. The aims of this study were to evaluate the inhibitory effect of YMT on osteoclast differentiation and to determine its molecular mechanism of action. YMT dose-dependently inhibited receptor activator for nuclear factor-κB (NF-κB) ligand (RANKL)-induced tartrate-resistant acid phosphatase (TRAP) activity and the formation of multinucleated osteoclasts in RAW264.7 cells. In addition, quantitative reverse transcription-polymerase chain reaction showed that YMT significantly decreased RANKL-induced expression of osteoclast differentiation-specific genes (TRAP, matrix metalloproteinase-9, cathepsin K, and the d2 isoform of vacuolar ATPase V(0) domain). Furthermore, YMT inhibited RANKL-induced phosphorylation of mitogen-activated protein kinases (extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38), phosphorylation of I-κBα, phosphorylation of NF-κB p65, and the expression of transcription factors Fra-2 and nuclear factor of activated T-cells, cytoplasmic 1. Furthermore, YMT inhibited the bone-resorptive activity of differentiated osteoclasts, suggesting that YMT inhibits osteoclast differentiation by suppressing RANKL-induced signaling molecules and transcription factors that affect the regulation of genes for osteoclast differentiation. As such, YMT may have therapeutic potential in bone diseases.

A genome-wide screen reveals a role for microRNA-1 in modulating cardiac cell polarity

Many molecular pathways involved in heart disease have their roots in evolutionarily ancient developmental programs that depend critically on gene dosage and timing. MicroRNAs (miRNAs) modulate gene dosage posttranscriptionally, and among these, the muscle-specific miR-1 is particularly important for developing and maintaining somatic/skeletal and cardiac muscle. To identify pathways regulated by miR-1, we performed a forward genetic screen in Drosophila using wing-vein patterning as a biological assay. We identified several unexpected genes that genetically interacted with dmiR-1, one of which was kayak, encodes a developmentally regulated transcription factor. Additional studies directed at this genetic relationship revealed a previously unappreciated function of dmiR-1 in regulating the polarity of cardiac progenitor cells. The mammalian ortholog of kayak, c-Fos, was dysregulated in hearts of gain- or loss-of-function miR-1 mutant mice in a stress-dependent manner. These findings illustrate the power of Drosophila-based screens to find points of intersection between miRNAs and conserved pathways in mammals.

Liver X receptor-retinoid X receptor (LXR-RXR) heterodimer cistrome reveals coordination of LXR and AP1 signaling in keratinocytes

Liver X receptors (LXRs) play a critical role in regulating lipid synthesis and transport in numerous tissues. In the skin, activation of LXR induces keratinocyte differentiation and improves epidermal permeability barrier homeostasis. To elucidate the mechanism of LXR action in skin, we mapped its cistrome by identifying LXRβ-RXRα binding sites using ChIP-on-chip in normal human epidermal keratinocytes (NHEKs). The cistrome was integrated with transcription data to obtain a global view of LXR action in keratinocyte biology. Here, we identify 2035 LXRβ-RXRα binding sites containing 4794 LXR response elements in NHEKs and show the presence of consensus heterodimer active regions in genes involved in keratinocyte lipid transport/synthesis and terminal differentiation. Bioinformatics analysis of the cistrome revealed an enrichment of AP1 cis-regulatory motifs in the vicinity of the LXRβ-RXRα binding sites. Importantly, we have demonstrated a direct interaction between LXR and Jun/Fos, indicating that the cooperation between LXR and AP1 may orchestrate keratinocyte differentiation. Finally, we corroborated these results by genome-wide mapping of the c-Fos and c-Jun cistromes in NHEKs, demonstrating that 77% of all the LXRβ-RXRα binding regions show the presence of AP1 motifs at adjacent locations. Our findings provide new insight into the mechanism of LXR action in keratinocyte differentiation, lipid production and barrier formation, further strengthening the validation of LXR as a potential therapeutic target for skin disorders including skin aging, psoriasis, and atopic dermatitis.