PKCθ-induced phosphorylations control the ability of Fra-1 to stimulate gene expression and cancer cell migration

FOSL1's Oncogene Roles in Glioma/Glioma Stem Cells and Tumorigenesis: A Comprehensive Review

This review specifically examines the important function of the oncoprotein FOSL1 in the dimeric AP-1 transcription factor, which consists of FOS-related components. FOSL1 is identified as a crucial controller of invasion and metastatic dissemination, making it a potential target for therapeutic treatment in cancer patients. The review offers a thorough examination of the regulatory systems that govern the influence exerted on FOSL1. These include a range of changes that occur throughout the process of transcription and after the translation of proteins. We have discovered that several non-coding RNAs, such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), play a significant role in regulating FOSL1 expression by directly interacting with its mRNA transcripts. Moreover, an investigation into the functional aspects of FOSL1 reveals its involvement in apoptosis, proliferation, and migration. This work involves a comprehensive analysis of the complex signaling pathways that support these diverse activities. Furthermore, particular importance is given to the function of FOSL1 in coordinating the activation of several cytokines, such as TGF-beta, and the commencement of IL-6 and VEGF production in tumor-associated macrophages (TAMs) that migrate into the tumor microenvironment. There is a specific emphasis on evaluating the predictive consequences linked to FOSL1. Insights are now emerging on the developing roles of FOSL1 in relation to the processes that drive resistance and reliance on specific treatment methods. Targeting FOSL1 has a strong inhibitory effect on the formation and spread of specific types of cancers. Despite extensive endeavors, no drugs targeting AP-1 or FOSL1 for cancer treatment have been approved for clinical use. Hence, it is imperative to implement innovative approaches and conduct additional verifications.

Multiple Fra-1-bound enhancers showing different molecular and functional features can cooperate to repress gene transcription

BACKGROUND

How transcription factors (TFs) down-regulate gene expression remains ill-understood, especially when they bind to multiple enhancers contacting the same gene promoter. In particular, it is not known whether they exert similar or significantly different molecular effects at these enhancers.

RESULTS

To address this issue, we used a particularly well-suited study model consisting of the down-regulation of the TGFB2 gene by the TF Fra-1 in Fra-1-overexpressing cancer cells, as Fra-1 binds to multiple enhancers interacting with the TGFB2 promoter. We show that Fra-1 does not repress TGFB2 transcription via reducing RNA Pol II recruitment at the gene promoter but by decreasing the formation of its transcription-initiating form. This is associated with complex long-range chromatin interactions implicating multiple molecularly and functionally heterogeneous Fra-1-bound transcriptional enhancers distal to the TGFB2 transcriptional start site. In particular, the latter display differential requirements upon the presence and the activity of the lysine acetyltransferase p300/CBP. Furthermore, the final transcriptional output of the TGFB2 gene seems to depend on a balance between the positive and negative effects of Fra-1 at these enhancers.

CONCLUSION

Our work unveils complex molecular mechanisms underlying the repressive actions of Fra-1 on TGFB2 gene expression. This has consequences for our general understanding of the functioning of the ubiquitous transcriptional complex AP-1, of which Fra-1 is the most documented component for prooncogenic activities. In addition, it raises the general question of the heterogeneity of the molecular functions of TFs binding to different enhancers regulating the same gene.

FRA-1 as a Regulator of EMT and Metastasis in Breast Cancer

Among FOS-related components of the dimeric AP-1 transcription factor, the oncoprotein FRA-1 (encoded by FOSL1) is a key regulator of invasion and metastasis. The well-established FRA-1 pro-invasive activity in breast cancer, in which FOSL1 is overexpressed in the TNBC (Triple Negative Breast Cancer)/basal subtypes, correlates with the FRA-1-dependent transcriptional regulation of EMT (Epithelial-to-Mesenchymal Transition). After summarizing the major findings on FRA-1 in breast cancer invasiveness, we discuss the FRA-1 mechanistic links with EMT and cancer cell stemness, mediated by transcriptional and posttranscriptional interactions between FOSL1/FRA-1 and EMT-regulating transcription factors, miRNAs, RNA binding proteins and cytokines, along with other target genes involved in EMT. In addition to the FRA-1/AP-1 effects on the architecture of target promoters, we discuss the diagnostic and prognostic significance of the EMT-related FRA-1 transcriptome, along with therapeutic implications. Finally, we consider several novel perspectives regarding the less explored roles of FRA-1 in the tumor microenvironment and in control of the recently characterized hybrid EMT correlated with cancer cell plasticity, stemness, and metastatic potential. We will also examine the application of emerging technologies, such as single-cell analyses, along with animal models of TNBC and tumor-derived CTCs and PDXs (Circulating Tumor Cells and Patient-Derived Xenografts) for studying the FRA-1-mediated mechanisms in in vivo systems of EMT and metastasis.

Protein Kinase C (PKC) Isozymes as Diagnostic and Prognostic Biomarkers and Therapeutic Targets for Cancer

Protein kinase C (PKC) is a large family of calcium- and phospholipid-dependent serine/threonine kinases that consists of at least 11 isozymes. Based on their structural characteristics and mode of activation, the PKC family is classified into three subfamilies: conventional or classic (cPKCs; α, βI, βII, and γ), novel or non-classic (nPKCs; δ, ε, η, and θ), and atypical (aPKCs; ζ, ι, and λ) (PKCλ is the mouse homolog of PKCι) PKC isozymes. PKC isozymes play important roles in proliferation, differentiation, survival, migration, invasion, apoptosis, and anticancer drug resistance in cancer cells. Several studies have shown a positive relationship between PKC isozymes and poor disease-free survival, poor survival following anticancer drug treatment, and increased recurrence. Furthermore, a higher level of PKC activation has been reported in cancer tissues compared to that in normal tissues. These data suggest that PKC isozymes represent potential diagnostic and prognostic biomarkers and therapeutic targets for cancer. This review summarizes the current knowledge and discusses the potential of PKC isozymes as biomarkers in the diagnosis, prognosis, and treatment of cancers.

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.

PCAT19 Regulates the Proliferation and Apoptosis of Lung Cancer Cells by Inhibiting miR-25-3p via Targeting the MAP2K4 Signal Axis

Both PCAT19 and miR-25-3p have been reported in lung cancer studies, but whether there is a correlation between the two and whether they jointly regulate the progress of lung cancer have not been reported yet. Therefore, this study carried out a further in-depth research. The expression of PCAT19 was detected in lung cancer (LC) tissues and cells by quantitative real-time polymerase chain reaction (qRT-PCR). The effect of PCAT19 on tumor growth was detected in a tumor-bearing model of nude mice. PCAT19-transfected cells were treated with Honokiol and anisomycin. The effects of PCAT19 on proliferation, apoptosis, and cycle of LC cells were investigated by biomolecule experiments. The effects of PCAT19 on the expressions of mitogen-activated protein kinase- (MAPK-) related proteins were evaluated by western blotting. The expression of PCAT19 was decreased in LC tissues and related to patient survival, tumor size, and pathology. In addition, upregulation of PCAT19 hindered LC cell proliferation, miR-25-3p expression, and the activation of extracellular regulated protein kinases (ERK) 1/2, p38, and c-Jun N-terminal kinase (JNK), while facilitating LC cell apoptosis. Furthermore, upregulation of PCAT19 reversed the effects of Honokiol and anisomycin on promoting cell proliferation and inhibiting cell apoptosis. Collectively, our findings show that upregulated PCAT19 suppresses proliferation yet promotes the apoptosis of LC cells through modulating the miR-25-3p/MAP2K4 signaling axis.

PKCθ-mediated serine/threonine phosphorylations of FAK govern adhesion and protrusion dynamics within the lamellipodia of migrating breast cancer cells

The cytoskeleton and cell-matrix adhesions constitute a dynamic network that controls cellular behavior during development and cancer. The Focal Adhesion Kinase (FAK) is a central actor of these cell dynamics, promoting cell-matrix adhesion turnover and active membrane fluctuations. However, the initial steps leading to FAK activation and subsequent promotion of cell dynamics remain elusive. Here, we report that the serine/threonine kinase PKCθ participates in the initial steps of FAK activation. PKCθ, which is strongly expressed in aggressive human breast cancers, controls the dynamics of cell-matrix adhesions and active protrusions through direct FAK activation, thereby promoting cell invasion and lung metastases. Using various tools for in vitro and live cell studies, we precisely decipher the molecular mechanisms of FAK activation. PKCθ directly interacts with the FAK FERM domain to open FAK conformation through PKCθ's specific V3 domain, while phosphorylating FAK at newly identified serine/threonine residues within nascent adhesions, inducing cell dynamics and aggressive behavior. This study thus places PKCθ-directed FAK opening and phosphorylations as an original mechanism controlling dynamic, migratory, and invasive abilities of aggressive breast cancer cells, further strengthening the emerging oncogenic function of PKCθ.

Fra-1 regulates its target genes via binding to remote enhancers without exerting major control on chromatin architecture in triple negative breast cancers

The ubiquitous family of dimeric transcription factors AP-1 is made up of Fos and Jun family proteins. It has long been thought to operate principally at gene promoters and how it controls transcription is still ill-understood. The Fos family protein Fra-1 is overexpressed in triple negative breast cancers (TNBCs) where it contributes to tumor aggressiveness. To address its transcriptional actions in TNBCs, we combined transcriptomics, ChIP-seqs, machine learning and NG Capture-C. Additionally, we studied its Fos family kin Fra-2 also expressed in TNBCs, albeit much less. Consistently with their pleiotropic effects, Fra-1 and Fra-2 up- and downregulate individually, together or redundantly many genes associated with a wide range of biological processes. Target gene regulation is principally due to binding of Fra-1 and Fra-2 at regulatory elements located distantly from cognate promoters where Fra-1 modulates the recruitment of the transcriptional co-regulator p300/CBP and where differences in AP-1 variant motif recognition can underlie preferential Fra-1- or Fra-2 bindings. Our work also shows no major role for Fra-1 in chromatin architecture control at target gene loci, but suggests collaboration between Fra-1-bound and -unbound enhancers within chromatin hubs sometimes including promoters for other Fra-1-regulated genes. Our work impacts our view of AP-1.

DNA or Protein Methylation-Dependent Regulation of Activator Protein-1 Function

Epigenetic regulation and modification govern the transcriptional mechanisms that promote disease initiation and progression, but can also control the oncogenic processes, cell signaling networks, immunogenicity, and immune cells involved in anti-inflammatory and anti-tumor responses. The study of epigenetic mechanisms could have important implications for the development of potential anti-inflammatory treatments and anti-cancer immunotherapies. In this review, we have described the key role of epigenetic progression: DNA methylation, histone methylation or modification, and protein methylation, with an emphasis on the activator protein-1 (AP-1) signaling pathway. Transcription factor AP-1 regulates multiple genes and is involved in diverse cellular processes, including survival, differentiation, apoptosis, and development. Here, the AP-1 regulatory mechanism by DNA, histone, or protein methylation was also reviewed. Various methyltransferases activate or suppress AP-1 activities in diverse ways. We summarize the current studies on epigenetic alterations, which regulate AP-1 signaling during inflammation, cancer, and autoimmune diseases, and discuss the epigenetic mechanisms involved in the regulation of AP-1 signaling.

The Emerging Function of PKCtheta in Cancer

Protein Kinase C theta (PKCθ) is a serine/threonine kinase that belongs to the novel PKC subfamily. In normal tissue, its expression is restricted to skeletal muscle cells, platelets and T lymphocytes in which PKCθ controls several essential cellular processes such as survival, proliferation and differentiation. Particularly, PKCθ has been extensively studied for its role in the immune system where its translocation to the immunological synapse plays a critical role in T cell activation. Beyond its physiological role in immune responses, increasing evidence implicates PKCθ in the pathology of various diseases, especially autoimmune disorders and cancers. In this review, we discuss the implication of PKCθ in various types of cancers and the PKCθ-mediated signaling events controlling cancer initiation and progression. In these types of cancers, the high PKCθ expression leads to aberrant cell proliferation, migration and invasion resulting in malignant phenotype. The recent development and application of PKCθ inhibitors in the context of autoimmune diseases could benefit the emergence of treatment for cancers in which PKCθ has been implicated.

Fra-1 Inhibits Cell Growth and the Warburg Effect in Cervical Cancer Cells via STAT1 Regulation of the p53 Signaling Pathway

The oncogenesis of cervical cancer is a multi-factor and multi-step process, and major risk factors include oncogene activation with tumor suppressor gene inactivation, viral factors, and immune factors. For example, the human papillomavirus (HPV) has been linked to the occurrence of cervical cancer. At present, the pathogenesis of cervical cancer remains unclear. Fra-1 (Fos-related antigen 1, also known as FOSL1) is a member of the Fos family and an important nuclear transcription factor that regulates normal cell growth, differentiation, and apoptosis. In the present study, we found that Fra-1 inhibited the proliferation of cervical cancer cells while also promoting apoptosis and affecting cell cycle distribution. Moreover, Fra-1 up-regulated STAT1 expression and modulated p53 signal pathway activity in cervical cancer cells. Overexpression of Fra-1 inhibited cell senescence by altering sirtuin 1 (SIRT1) expression in HeLa cells, and Fra-1 overexpression restored mitochondrial disorder and suppressed metabolic reprogramming in HeLa cells. Silencing of STAT1 impaired the inhibitory effect of Fra-1 on cervical cancer cell growth, while knock-down of STAT1 reversed the effect on cell senescence and mitochondrial dysfunction caused by Fra-1 in HeLa cells. Silencing of STAT1 also recovered metabolic reprogramming in cervical cancer cells. In summary, our results show that Fra-1 inhibited cervical cancer cell growth and the Warburg effect via STAT1-mediated regulation of the p53 signaling pathway.

Identification, Structure-Activity Relationships of Marine-Derived Indolocarbazoles, and a Dual PKCθ/δ Inhibitor with Potent Antipancreatic Cancer Efficacy

Protein kinases C (PKCs) are a family of serine/threonine kinases involved in various cellular processes, including proliferation, differentiation, cell survival, and apoptosis. Here, we report the identification, structure-activity relationship (SAR), and 3D-QSAR studies of 69 natural indolocarbazoles, including 15 new compounds, from marine streptomyces strains. Interestingly, we found that the chair conformational isomer of 7-oxo-staurosporine (compound 15) inhibited PKCθ more potently than the corresponding boat isomer. An evaluation of kinase selectivity and antitumor efficacy revealed that 15 was a potent dual PKCθ/δ inhibitor and that it could efficiently inhibit tumor growth in pancreatic cancer (PC) by inducing cellular apoptosis and suppressing the NF-κB/p-P65 pathway. In addition, we demonstrated that overexpression of p-PKCδ and p-P65 was associated with poor survival rates in patients with PC, and p-PKCθ expression also showed significant positive correlations with p-PKCδ and p-P65 levels. Finally, the PC patient-derived xenograft model further confirmed the potential anti-PC efficacy of 15.

Identification of small molecule drugs and development of a novel autophagy-related prognostic signature for kidney renal clear cell carcinoma

Abnormal autophagic levels have been implicated in the pathogenesis of multiple cancers, however, its role in tumors is complex and has not yet been explored clearly. Hence, we aimed to explore the prognostic values of autophagy-related genes (ARGs) for kidney renal clear cell carcinoma (KIRC). Differentially expressed ARGs and transcription factors (TFs) were identified in KIRC patients obtaining from the The Cancer Genome Atlas (TCGA) database. Then, networks between TFs and ARGs, gene ontology functional annotations and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis were conducted. Next, we performed consensus clustering, COX regression analysis and Lasso regression analysis to identify the prognostic ARGs. Finally, an individual prognostic index (PI, riskScore) was established. Based on TCGA cohort and ArrayExpress cohort, Survival analysis, ROC curve, independent prognostic analysis, and clinical correlation analysis were also performed to evaluate this PI. Based on differentially expressed ARGs, KIRC patients were successfully divided into two clusters (P = 5.916e-04). AS for PI, it was constructed based on 11 ARGs and significantly classified KIRC patients into high-risk group and low-risk group in terms of OS (P = 4.885e-15 for TCGA cohort, P = 6.366e-03 for ArrayExpress cohort). AUC of its ROC curve reached 0.747 for TCGA cohort and 0.779 for ArrayExpress cohort. What's more, this PI was proven to be a valuable independent prognostic factor in both univariate and multivariate COX regression analysis (P < .001). Prognostic nomograms were also performed to visualize the relationship between individual predictors and survival rates in patients with KIRC. By means of connectivity map database, emetine, cephaeline and co-dergocrine mesilate related to ARGs were found to be negatively correlated with KIRC. This study provided an effective PI for KIRC and also displayed networks between TFs and ARGs. KIRC patients were successfully divided into two clusters based on differentially expressed ARGs. Besides, small molecule drugs related to ARGs were also identified for KIRC.

The nuclear oncoprotein Fra-1: a transcription factor knocking on therapeutic applications' door

Among the FOS-related members of the AP-1 dimeric complex, the transcription factor Fra-1, encoded by FOSL1, is crucially involved in human tumor progression and metastasis, thus representing a promising therapeutic target. Here we review the state of the art and discuss the emerging topics and perspectives on FOSL1 and its gene product. First, we summarize the present knowledge on the FOSL1 transcriptional and epigenetic controls, driving Fra-1 accumulation in a variety of human solid tumors. We also present a model on the regulatory interactions between Fra-1, p53, and miRNAs. Then, we outline the multiple roles of Fra-1 posttranslational modifications and transactivation mechanisms of select Fra-1 target genes. In addition to summarizing the Fra-1-dependent gene networks controlling proliferation, survival, and epithelial-mesenchymal transitions (EMT) in multiple cancer cell types, we highlight the roles played by Fra-1 in nonneoplastic cell populations recruited to the tumor microenvironment, and in mouse models of tumorigenesis. Next, we review the prognostic power of the Fra-1-associated gene signatures, and envisage potential strategies aimed at Fra-1 therapeutic inhibition. Finally, we discuss several recent reports showing the emerging roles of Fra-1 in the mechanisms of both resistance and addiction to targeted therapies.

Differentially expressed autophagy-related genes are potential prognostic and diagnostic biomarkers in clear-cell renal cell carcinoma

We examined the role of differentially expressed autophagy-related genes (DEARGs) in clear cell Renal Cell Carcinoma (ccRCC) using high-throughput RNA-seq data from The Cancer Genome Atlas (TCGA). Cox regression analyses showed that 5 DEARGs (PRKCQ, BID, BAG1, BIRC5, and ATG16L2) correlated with overall survival (OS) and 4 DEARGs (EIF4EBP1, BAG1, ATG9B, and BIRC5) correlated with disease-free survival (DFS) in ccRCC patients. Multivariate Cox regression analysis using the OS and DFS prognostic risk models showed that expression of the nine DEARGs accurately and independently predicted the risk of disease recurrence or progression in ccRCC patients (area under curve or AUC values > 0.70; all p < 0.05). Moreover, the DEARGs accurately distinguished healthy individuals from ccRCC patients based on receiver operated characteristic (ROC) analyses (area under curve or AUC values > 0.60), suggesting their potential as diagnostic biomarkers for ccRCC. The expression of DEARGs also correlated with the drug sensitivity of ccRCC cell lines. The ccRCC cell lines were significantly sensitive to Sepantronium bromide, a drug that targets BIRC5. This makes BIRC5 a potential therapeutic target for ccRCC. Our study thus demonstrates that DEARGs are potential diagnostic and prognostic biomarkers and therapeutic targets in ccRCC.

Expression and function of FRA1 protein in tumors

AP-1 is a dimeric complex that is composed of JUN, FOS, ATF and MAF protein families. FOS-related antigen 1 (FRA1) which encoded by FOSL1 gene, belongs to the FOS protein family, and mainly forms an AP-1 complex with the protein of the JUN family to exert an effect. Regulation of FRA1 occurs at levels of transcription and post-translational modification, and phosphorylation is the major post-translational modification. FRA1 is mainly regulated by the mitogen-activated protein kinases signaling pathway and is degraded by ubiquitin-independent proteasomes. FRA1 can affect biological functions, such as tumor proliferation, differentiation, invasion and apoptosis. Studies have demonstrated that FRA1 is abnormally expressed in many tumors and plays a relevant role, but the specific condition varies from the target organs. FRA1 is overexpressed in breast cancer, lung cancer, colorectal cancer, prostate cancer, nasopharyngeal cancer, thyroid cancer and other tumors. However, the expression of FRA1 is decreased in cervical cancer, and the expression of FRA1 in ovarian cancer and oral squamous cell carcinoma is still controversial. In this review, we present a detailed description of the regulatory factors and functions of FRA1, also, the expression of FRA1 in various tumors and its function in relative tumor.

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.

Lysophosphatidic acid induces interleukin-6 and CXCL15 secretion from MLO-Y4 cells through activation of the LPA1 receptor and PKCθ signaling pathway

Lysophosphatidic acid (LPA) is a multifunctional phospholipid. Osteocytes are the most abundant cells in bone and can orchestrate bone formation and resorption, in part by producing cytokines that regulate osteoblast and osteoclast differentiation and activity. Interleukin (IL)-6 and IL-8 are two important cytokines that have potent effects on bone fracture healing. Previous studies suggest that platelet-derived LPA may influence fracture healing by inducing osteocyte dendrite outgrowth. However, the biological mechanism through which LPA induces cytokine production in osteocytes is poorly understood. In this study, we report that LPA markedly enhanced IL-6 and CXCL15 (mouse homologue of human IL-8) production in MLO-Y4 cells and that this enhancement was suppressed by the LPA_1/3-selective antagonist Ki16425, the G_i/o protein inhibitor PTX or the protein kinase C (PKC) inhibitor sotrastaurin. We also observed that of all the PKC isoform targets of sotrastaurin, only PKCθ was activated by LPA in MLO-Y4 cells and that this activation was blocked by sotrastaurin, Ki16425 or PTX. Taken together, the results of the present study demonstrate that LPA may be a potent inducer of IL-6 and CXCL15 production in MLO-Y4 cells and that this induction is associated with the activation of LPA₁, G_i/o protein and the PKCθ pathway. These findings may help us better understand the mechanism of fracture healing and contribute to the treatment of bone damage.

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.

ETS-domain containing protein (Elk1) suppression protects cortical neurons against oxygen-glucose deprivation injury

ETS-domain containing protein (Elk1), which is a transcription factor, is reported to be closely related to the apoptosis of primary neurons and could be activated by hypoxia in human microvascular endothelial cells. In this study, we aimed to investigate the role of Elk1 in cortical neurons under oxygen-glucose deprivation (OGD) conditions. The OGD model of cortical neurons was established the anoxia/hypoglycemia-induced injury and the in vivo model was established by middle cerebral artery occlusion (MCAO). Elk1 mRNA and protein expression was significantly up-regulated in neurons exposed to OGD for 24 h, and mRNA expression was also markedly increased in cerebral cortex of rats with MCAO after 10 days. The knockdown of Elk1 in neurons without OGD obviously constrained Fra-1 and promoted Nrf2 expression. Also, Elk1 inhibition suppressed neuronal apoptosis, caspase-3 activity, LDH leakage, and MDA and SOD contents, while it increased cell viability in the neurons with OGD. The overexpression of Fra-1 showed a reverse effect on caspase-3 activity, cell viability and SOD contents in neurons under OGD conditions compared with Elk1 knockdown. Thus, Elk1 inhibition has a protective effect on neurons against OGD-induced injury.

Integrin-uPAR signaling leads to FRA-1 phosphorylation and enhanced breast cancer invasion

Background

The Fos-related antigen 1 (FRA-1) transcription factor promotes tumor cell growth, invasion and metastasis. Phosphorylation of FRA-1 increases protein stability and function. We identify a novel signaling axis that leads to increased phosphorylation of FRA-1, increased extracellular matrix (ECM)-induced breast cancer cell invasion and is prognostic of poor outcome in patients with breast cancer.

Methods

While characterizing five breast cancer cell lines derived from primary human breast tumors, we identified BRC-31 as a novel basal-like cell model that expresses elevated FRA-1 levels. We interrogated the functional contribution of FRA-1 and an upstream signaling axis in breast cancer cell invasion. We extended this analysis to determine the prognostic significance of this signaling axis in samples derived from patients with breast cancer.

Results

BRC-31 cells display elevated focal adhesion kinase (FAK), SRC and extracellular signal-regulated (ERK2) phosphorylation relative to luminal breast cancer models. Inhibition of this signaling axis, with pharmacological inhibitors, reduces the phosphorylation and stabilization of FRA-1. Elevated integrin α_Vβ₃ and uPAR expression in these cells suggested that integrin receptors might activate this FAK-SRC-ERK2 signaling. Transient knockdown of urokinase/plasminogen activator urokinase receptor (uPAR) in basal-like breast cancer cells grown on vitronectin reduces FRA-1 phosphorylation and stabilization; and uPAR and FRA-1 are required for vitronectin-induced cell invasion. In clinical samples, a molecular component signature consisting of vitronectin-uPAR-uPA-FRA-1 predicts poor overall survival in patients with breast cancer and correlates with an FRA-1 transcriptional signature.

Conclusions

We have identified a novel signaling axis that leads to phosphorylation and enhanced activity of FRA-1, a transcription factor that is emerging as an important modulator of breast cancer progression and metastasis.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-0936-8) contains supplementary material, which is available to authorized users.