Transcription Factor Elk-1 Research Articles

Functional Link between miR-200a and ELK3 Regulates the Metastatic Nature of Breast Cancer.

Triple-negative breast cancer (TNBC) refers to breast cancer that does not have receptors for estrogen, progesterone, and HER2 protein. TNBC accounts for 10–20% of all cases of breast cancers and is characterized by its metastatic aggressiveness, poor prognosis, and limited treatment options. Here, we show that the metastatic nature of TNBC is critically regulated by a functional link between miR-200a and the transcription factor ELK3. We found that the expression levels of miR-200a and the ELK3 mRNA were negatively correlated in the luminal and TNBC subtypes of breast cancer cells. In vitro experiments revealed that miR-200a directly targets the 3’ untranslated region (UTR) of the ELK3 mRNA to destabilize the transcripts. Furthermore, ectopic expression of miR-200a impaired the migration and invasion of TNBC cells by reducing the expression level of the ELK3 mRNA. In in vivo studies, transfection of MDA-MB 231 cells (a claudin-low TNBC cell type) with exogenous miR-200a reduced their extravasation into the lung during 48 h after tail vein injection, and co-transfection of the cells with an expression plasmid harboring ELK3 that lacked an intact 3’UTR recovered their extravasation ability. Overall, our findings provide evidences that miR-200a and ELK3 is functionally linked to regulate invasive characteristics of breast cancers.

The super-cooling compound icilin stimulates c-Fos and Egr-1 expression and activity involving TRPM8 channel activation, Ca2+ ion influx and activation of the ternary complex factor Elk-1

The TRPM8 cation channel can be activated by the cooling compound icilin. Recently, we showed that stimulation of TRPM8 channels induces a signaling cascade leading to the activation of the transcription factor AP-1. Additionally, expression of the AP-1 constituent c-Fos has been shown to be induced following TRPM8 stimulation. c-Fos is frequently used as a marker for neuronal activity. Here, we have analyzed the mechanism connecting TRPM8 stimulation and c-Fos expression. Furthermore, we analyzed the expression of the neuronal activity-responsive transcription factor Egr-1 following TRPM8 activation. The results show that icilin-induced stimulation of TRPM8 channels increased c-Fos promoter activity and induced c-Fos expression. Moreover, icilin stimulation increased Egr-1 promoter activity and induced the expression of Egr-1. Pharmacological inhibition of TRPM8 blocked the icilin-induced expression of Egr-1 and c-Fos. An influx of Ca2+ ions into the cells via TRPM8 was necessary to stimulate Egr-1 and c-Fos expression following icilin treatment. Genetic experiments revealed that serum response elements within the Egr-1 and c-Fos promoters are crucial to couple TRPM8 stimulation with enhanced transcription of both the Egr-1 and c-Fos genes. These data were corroborated by experiments showing that TRPM8 stimulation increased the transcriptional activation potential of Elk-1, a SRE binding protein. c-Fos is important for neuronal excitability and survival. Egr-1 plays an important role in synaptic plasticity, consolidation and reconsolidation of long-term memory. Elk-1 may preserve neurons against toxic insults but may also induce depressive behaviour. The fact that TRPM8 stimulation activates the transcription factors c-Fos, Egr-1, and Elk-1 connects TRPM8 signaling with maintaining important brain functions.

Misregulation of ELK1, AP1, and E12 Transcription Factor Networks Is Associated with Melanoma Progression.

Melanoma is among the most malignant cutaneous cancers and when metastasized results in dramatically high mortality. Despite advances in high-throughput gene expression profiling in cancer transcriptomic studies, our understanding of mechanisms driving melanoma progression is still limited. We present here an in-depth bioinformatic analysis of the melanoma RNAseq, chromatin immunoprecipitation (ChIP)seq, and single-cell (sc)RNA seq data to understand cancer progression. Specifically, we have performed a consensus network analysis of RNA-seq data from clinically re-grouped melanoma samples to identify gene co-expression networks that are conserved in early (stage 1) and late (stage 4/invasive) stage melanoma. Overlaying the fold-change information on co-expression networks revealed several coordinately up or down-regulated subnetworks that may play a critical role in melanoma progression. Furthermore, by incorporating histone lysine-27 acetylation information and highly expressed genes identified from the single-cell RNA data from melanoma patient samples, we present a comprehensive list of pathways, putative protein-protein interactions (PPIs) and transcription factor (TF) networks that are driving cancer progression. From this analysis, we have identified Elk1, AP1 and E12 TF networks that coordinately change expression in late melanoma when compared to early melanoma, implicating these TFs in melanoma progression. Additionally, the sumoylation-associated interactome is upregulated in invasive melanoma. Together, this bioinformatic analysis potentially implicates a combination of TF networks and PPIs in melanoma progression, which if confirmed in the experimental systems, could be used as targets for drug intervention in melanoma.

Non-Redundant and Overlapping Oncogenic Readouts of Non-Canonical and Novel Colorectal Cancer KRAS and NRAS Mutants.

RAS oncogene family members are molecular switches of signaling pathways that control cell growth, proliferation, differentiation, and survival. In colorectal cancer, Kirsten-RAS (KRAS) and neuroblastoma-RAS (NRAS) are the commonly mutated isoforms. Activating mutations in RAS result in cellular transformation independent of upregulated epidermal growth factor receptor (EGFR)-initiated signaling. The present study characterized the functional consequences of non-canonical/novel KRAS and NRAS mutants identified in a targeted next-generation sequencing study of colorectal cancer specimens from Filipino patients. In vitro assays in NIH3T3 cells showed that similar to the canonical KRAS G12D mutant, overexpression of KRAS G12S, A59T, and Y137C, but not NRAS G12D and NRAS A11V, confer higher proliferation and migration rates. HCT116 cells transfected with the novel NRAS A11V and the canonical NRAS G12D, but not the KRAS mutants, display enhanced resistance to apoptosis. All four non-canonical/novel KRAS and NRAS mutants induce gross changes in F-actin cytoskeletal organization and cellular morphology of NIH3T3 cells. Only KRAS G12S and KRAS A59T appear to deregulate extracellular signal-regulated kinase (ERK) and its downstream target ETS transcription factor ELK1 (ELK1). Elucidation of differential effector engagement responsible for the variable phenotypic readouts of the mutants is warranted. If validated by mouse studies and clinical correlates, these can have wider implications in choosing treatment options.

Circular RNA hsa_circ_0000515 acts as a miR-326 sponge to promote cervical cancer progression through up-regulation of ELK1.

This study investigates the role of circular RNA (circRNA) hsa_circ_0000515 in cervical cancer and the underlying mechanism associated with microRNA-326 (miR-326). hsa_circ_0000515 and ETS transcription factor ELK1 (ELK1) were initially over-expressed and miR-326 was down-regulated in cervical cancer tissues and cells. Low hsa_circ_0000515 expression was found to be associated with favorable prognosis of patients with cervical cancer. A series of mimics, inhibitors, over-expression plasmids or siRNAs were introduced into cervical cancer cells to alter the expression of hsa_circ_0000515, miR-326 and ELK1. In vitro experiments exhibited that silencing of hsa_circ_0000515 or upregulation of miR-326 resulted in suppressed proliferation and invasion, along with induced apoptosis and autophagy of cervical cancer cells. Dual-luciferase reporter assay, RNA pull-down and RIP assays highlighted that hsa_circ_0000515 was able to act as a ceRNA of miR-326 to increase ELK1. Furthermore, enhancement of ELK1 expression resulted in enhanced proliferation and invasion but repressed apoptosis and autophagy of cervical cancer cells. In vivo experiments further confirmed the suppressed tumor growth by hsa_circ_0000515 silencing. Our findings demonstrated that hsa_circ_0000515 acts as a tumor promoter in cervical cancer. The study provides evidence for targeting hsa_circ_0000515 for therapeutic purposes in treating cervical cancer.

Downregulation of miR-541 induced by heat stress contributes to malignant transformation of human bronchial epithelial cells via HSP27

Environmental factors are one of the important factors affecting the occurrence of lung cancer. However, few studies have been done on the relationship between hot environment and lung cancer. In the present study, we demonstrated that heat stress leads to anchorage-independent proliferation, mitochondrial apoptosis, and autophagy of Beas-2B cells, which are normal lung bronchial epithelial cells. Heat shock protein 27 (HSP27) promoted heat stress-induced anchorage-independent proliferation and autophagy, but suppressed mitochondrial apoptosis, indicating that HSP27 might act as an oncogene in the malignant transformation of lung epithelial cells. We also showed that HSP27 promoted autophagy of these cells under heat stress via autophagy related 7 (ATG7) and ETS Transcription Factor ELK1 (ELK1), a transcription factor of ATG7, under heat stress. In addition, we showed that HSP27 translation could be repressed by microRNA miR-541, and the biological effects of miR-541 were the opposite to HSP27, suggesting that HSP27 is a downstream target of miR-541. In this study, we characterized a new mechanism whereby HSP27 promotes cell transformation during the onset of lung cancer. Our studies provide new insights into the molecular mechanisms underlying the lung carcinogenic effect of heat exposure. Specifically, heat stress promotes translation of HSP27 by inhibiting miR-541 accumulation, ultimately resulting in activation of autophagy, inhibition of mitochondrial apoptotic pathway and malignant transformation of Human Bronchial Epithelial Cells. This study identifies miR-541 as a potential prognostic biomarker or therapeutic target to improve theory of environmental carcinogenesis.

Early epigenomic and transcriptional changes reveal Elk-1 transcription factor as a therapeutic target in Huntington’s disease

Huntington's disease (HD) is a chronic neurodegenerative disorder characterized by a late clinical onset despite ubiquitous expression of the mutant Huntingtin gene (HTT) from birth. Transcriptional dysregulation is a pivotal feature of HD. Yet, the genes that are altered in the prodromal period and their regulators, which present opportunities for therapeutic intervention, remain to be elucidated. Using transcriptional and chromatin profiling, we found aberrant transcription and changes in histone H3K27acetylation in the striatum of R6/1 mice during the presymptomatic disease stages. Integrating these data, we identified the Elk-1 transcription factor as a candidate regulator of prodromal changes in HD. Exogenous expression of Elk-1 exerted beneficial effects in a primary striatal cell culture model of HD, and adeno-associated virus-mediated Elk-1 overexpression alleviated transcriptional dysregulation in R6/1 mice. Collectively, our work demonstrates that aberrant gene expression precedes overt disease onset in HD, identifies the Elk-1 transcription factor as a key regulator linked to early epigenetic and transcriptional changes in HD, and presents evidence for Elk-1 as a target for alleviating molecular pathology in HD.

Mechanical strain promotes skin fibrosis through LRG-1 induction mediated by ELK1 and ERK signalling

Biomechanical force and pathological angiogenesis are dominant features in fibro-proliferative disorders. Understanding the role and regulation of the mechanical microenvironment in which pathological angiogenesis occurs is an important challenge when investigating numerous angiogenesis-related diseases. In skin fibrosis, dermal fibroblasts and vascular endothelial cells are integral to hypertrophic scar formation. However, few studies have been conducted to closely investigate their relationship. Here we show, that leucine-rich-alpha-2-glycoprotein 1 (LRG-1) a regulator of pathological angiogenesis, links biomechanical force to angiogenesis in skin fibrosis. We discover that LRG-1 is overexpressed in hypertrophic scar tissues, and that depletion of Lrg-1 in mouse skin causes mild neovascularization and skin fibrosis formation in a hypertrophic scarring model. Inhibition of FAK or ERK attenuates LRG-1 expression through the ELK1 transcription factor, which binds to the LRG-1 promoter region after transcription initiation by mechanical force. Using LRG-1 to uncouple mechanical force from angiogenesis may prove clinically successful in treating fibro-proliferative disorders.

Decoding and targeting the molecular basis of MACC1-driven metastatic spread: Lessons from big data mining and clinical-experimental approaches.

Metastasis remains the key issue impacting cancer patient survival and failure or success of cancer therapies. Metastatic spread is a complex process including dissemination of single cells or collective cell migration, penetration of the blood or lymphatic vessels and seeding at a distant organ site. Hundreds of genes involved in metastasis have been identified in studies across numerous cancer types. Here, we analyzed how the metastasis-associated gene MACC1 cooperates with other genes in metastatic spread and how these coactions could be exploited by combination therapies: We performed (i) a MACC1 correlation analysis across 33 cancer types in the mRNA expression data of TCGA and (ii) a comprehensive literature search on reported MACC1 combinations and regulation mechanisms. The key genes MET, HGF and MMP7 reported together with MACC1 showed significant positive correlations with MACC1 in more than half of the cancer types included in the big data analysis. However, ten other genes also reported together with MACC1 in the literature showed significant positive correlations with MACC1 in only a minority of 5 to 15 cancer types. To uncover transcriptional regulation mechanisms that are activated simultaneously with MACC1, we isolated pan-cancer consensus lists of 1306 positively and 590 negatively MACC1-correlating genes from the TCGA data and analyzed each of these lists for sharing transcription factor binding motifs in the promotor region. In these lists, binding sites for the transcription factors TELF1, ETS2, ETV4, TEAD1, FOXO4, NFE2L1, ELK1, SP1 and NFE2L2 were significantly enriched, but none of them except SP1 was reported in combination with MACC1 in the literature. Thus, while some of the results of the big data analysis were in line with the reported experimental results, hypotheses on new genes involved in MACC1-driven metastasis formation could be generated and warrant experimental validation. Furthermore, the results of the big data analysis can help to prioritize cancer types for experimental studies and testing of combination therapies.

LRG1 Promotes Keratinocyte Migration and Wound Repair through Regulation of HIF-1α Stability

Re-epithelialization is a complex process during skin wound healing, and cell migration is an integral part of this phenomenon. Here we identified a role for LRG1 as a key regulator of epidermal keratinocyte migration where LRG1 acts via enhancement of HIF-1α stability. We showed that LRG1 is upregulated at murine skin wound edges and that addition of recombinant human LRG1 accelerates keratinocyte migration and skin wound healing. Furthermore, we identified transcription factor ELK3 as a downstream effector of LRG1. We confirmed that elevated ELK3 levels manipulated by LRG1 can promote cell migration through upregulation of HIF-1α stability. Because hyperglycemia complicatedly affects HIF-1α stability and activation, our findings provide insights into the molecular controls of wound-associated cell migration and identify potential therapeutic targets for the treatment of chronic diabetic wounds. In conclusion, we demonstrated that LRG1 promotes wound repair through keratinocyte migration and is important for normalization of an abnormal process of diabetic wound healing where HIF-1α stability is insufficient.

ELK1 has a dual activating and repressive role in human embryonic stem cells.

Background: The ERK MAPK pathway plays a pivotal role in regulating numerous cellular processes during normal development and in the adult but is often deregulated in disease scenarios. One of its key nuclear targets is the transcription factor ELK1, which has been shown to play an important role in controlling gene expression in human embryonic stem cells (hESCs). ELK1 is known to act as a transcriptional activator in response to ERK pathway activation but repressive roles have also been uncovered, including a putative interaction with the PRC2 complex. Methods: Here we probe the activity of ELK1 in hESCs by using a combination of gene expression analysis in hESCs and during differentiation following ELK1 depletion and also analysis of chromatin occupancy of transcriptional regulators and histone mark deposition that accompany changes in gene expression. Results: We find that ELK1 can exert its canonical activating activity downstream from the ERK pathway but also possesses additional repressive activities. Despite its co-binding to PRC2 occupied regions, we could not detect any ELK1-mediated repression at these regions. Instead, we find that ELK1 has a repressive role at a subset of co-occupied SRF binding regions. Conclusions: ELK1 should therefore be viewed as a dichotomous transcriptional regulator that can act through SRF to generate both activating and repressing properties at different genomic loci.

P1‐206: PIAS1 SER‐503 PHOSPHORYLATION‐MEDIATED ELK‐1 SUMOYLATION PROMOTES NEURONAL SURVIVAL IN APP/PS1 MICE

PIAS1 is phosphorylated by IKKα at Ser-90 in a PIAS1 E3 ligase activity-dependent manner. Whether PIAS1 is also phosphorylated at other residues, and what potential functional significance such additional phosphorylation events might have, are not known. The transcription factor Elk-1 remains SUMOylated under basal conditions, but the role of Elk-1 SUMOylation in the brain is unknown. Here, we examined the functional significance of PIAS1-mediated Elk-1 SUMOylation in the context of Alzheimer's disease (AD) using the APP/PS1 mouse model of AD and amyloid beta microinjection in vivo. Novel phosphorylation site(s) on PIAS1 were identified by LC-MS/MS, and MAPK/ERK-mediated phosphorylation of Elk-1 was demonstrated using in vitro kinase assays. Elk-1 SUMOylation by PIAS1 in the brain was determined using in vitro SUMOylation assays. Apoptosis in the hippocampus was assessed by measuring GADD45α expression by Western blotting, and apoptosis of neurons in the hippocampus of APP/PS1 mice was assessed by TUNEL assay. Using LC-MS/MS, we identified a novel MAPK/ERK-mediated phosphorylation site on PIAS1 at Ser-503 and showed that this phosphorylation determines PIAS1 E3 ligase activity. In the rat brain, Elk-1 is SUMOylated by PIAS1, which decreases Elk-1 phosphorylation and downregulates GADD45α expression. Moreover, lentiviral-mediated transduction of Elk-1-SUMO1 in the hippocampus reduces the number of apoptotic neurons in APP/PS1 mice. MAPK/ERK-mediated phosphorylation of PIAS1 at Ser-503 determines PIAS1 E3 ligase activity. Moreover, PIAS1 mediates SUMOylation of Elk-1, and this modification functions as an endogenous defense mechanism against Aβ toxicity in vivo. Targeting Elk-1 SUMOylation could be considered a novel therapeutic strategy against AD.

203. ELK-1, Trauma and Negative Life Event Exposure

Trauma and life stress are considered as major environmental factors in psychiatric disorders. Recently, we have identified the transcription factor ELK-1, an effector of the glucocorticoid/ERK pathway, as a major key in pathophysiology of Major Depression and antidepressant response, and an interesting biomarker of antidepressant response. Mechanisms associated with ELK-1 variation are still unclear.

Protein inhibitor of activated STAT1 Ser503 phosphorylation‐mediated Elk‐1 SUMOylation promotes neuronal survival in APP/PS1 mice

Protein inhibitor of activated STAT1 (PIAS1) is phosphorylated by IKKα at Ser90 in a PIAS1 E3 ligase activity-dependent manner. Whether PIAS1 is also phosphorylated at other residues and the functional significance of these additional phosphorylation events are not known. The transcription factor Elk-1 remains SUMOylated under basal conditions, but the role of Elk-1 SUMOylation in brain is unknown. Here, we examined the functional significance of PIAS1-mediated Elk-1 SUMOylation in Alzheimer's disease (AD) using the APP/PS1 mouse model of AD and amyloid β (Aβ) microinjections in vivo. Novel phosphorylation site(s) on PIAS1 were identified by LC-MS/MS, and MAPK/ERK-mediated phosphorylation of Elk-1 demonstrated using in vitro kinase assays. Elk-1 SUMOylation by PIAS1 in brain was determined using in vitro SUMOylation assays. Apoptosis in hippocampus was assessed by measuring GADD45α expression by western blotting, and apoptosis of hippocampal neurons in APP/PS1 mice was assessed by TUNEL assay. Using LC-MS/MS, we identified a novel MAPK/ERK-mediated phosphorylation site on PIAS1 at Ser503 and showed this phosphorylation determines PIAS1 E3 ligase activity. In rat brain, Elk-1 was SUMOylated by PIAS1, which decreased Elk-1 phosphorylation and down-regulated GADD45α expression. Moreover, lentiviral-mediated transduction of Elk-1-SUMO1 reduced the number of hippocampal apoptotic neurons in APP/PS1 mice. MAPK/ERK-mediated phosphorylation of PIAS1 at Ser503 determines PIAS1 E3 ligase activity. Moreover, PIAS1 mediates SUMOylation of Elk-1, which functions as an endogenous defence mechanism against Aβ toxicity in vivo. Targeting Elk-1 SUMOylation could be considered a novel therapeutic strategy against AD.

ELK1 has a dual activating and repressive role in human embryonic stem cells

Background: The ERK MAPK pathway plays a pivotal role in regulating numerous cellular processes during normal development and in the adult but is often deregulated in disease scenarios. One of its key nuclear targets is the transcription factor ELK1, which has been shown to play an important role in controlling gene expression in human embryonic stem cells (hESCs). ELK1 is known to act as a transcriptional activator in response to ERK pathway activation but repressive roles have also been uncovered, including a putative interaction with the PRC2 complex. Methods: Here we probe the activity of ELK1 in hESCs by using a combination of gene expression analysis in hESCs and during differentiation following ELK1 depletion and also analysis of chromatin occupancy of transcriptional regulators and histone mark deposition that accompany changes in gene expression. Results: We find that ELK1 can exert its canonical activating activity downstream from the ERK pathway but also possesses additional repressive activities. Despite its co-binding to PRC2 occupied regions, we could not detect any ELK1-mediated repression at these regions. Instead, we find that ELK1 has a repressive role at a subset of co-occupied SRF binding regions. Conclusions: ELK1 should therefore be viewed as a dichotomous transcriptional regulator that can act through SRF to generate both activating and repressing properties at different genomic loci.

ELK1 has a dual activating and repressive role in human embryonic stem cells

Background: The ERK MAPK pathway plays a pivotal role in regulating numerous cellular processes during normal development and in the adult but is often deregulated in disease scenarios. One of its key nuclear targets is the transcription factor ELK1, which has been shown to play an important role in controlling gene expression in human embryonic stem cells (hESCs). ELK1 is known to act as a transcriptional activator in response to ERK pathway activation but repressive roles have also been uncovered, including a putative interaction with the PRC2 complex. Methods: Here we probe the activity of ELK1 in hESCs by using a combination of gene expression analysis in hESCs and during differentiation following ELK1 depletion and also analysis of chromatin occupancy of transcriptional regulators and histone mark deposition that accompany changes in gene expression. Results: We find that ELK1 can exert its canonical activating activity downstream from the ERK pathway but also possesses additional repressive activities. Despite its co-binding to PRC2 occupied regions, we could not detect any ELK1-mediated repression at these regions. Instead, we find that ELK1 has a repressive role at a subset of co-occupied SRF binding regions. This latter repressive role appears not to be exerted through competition with MRTF family co-activators. Conclusions: ELK1 should therefore be viewed as a dichotomous transcriptional regulator that can act through SRF to generate both activating and repressing properties at different genomic loci.

The role of NF-κB and Elk-1 in the regulation of mouse ADAM17 expression.

ABSTRACTADAM17 is a cell membrane metalloproteinase responsible for the release of ectodomains of numerous proteins from the cell surface. Although ADAM17 is often overexpressed in tumours and at sites of inflammation, little is known about the regulation of its expression. Here we investigate the role of NF-κB and Elk-1 transcription factors and upstream signalling pathways, NF-κB and ERK1/2 in ADAM17 expression in mouse brain endothelial cells stimulated with pro-inflammatory factors (TNF, IL-1β, LPS) or a phorbol ester (PMA), a well-known stimulator of ADAM17 activity. Notably, NF-κB inhibitor, IKK VII, interfered with the IL-1β- and LPS-mediated stimulation of ADAM17 expression. Furthermore, Adam17 promoter contains an NF-κB binding site occupied by p65 subunit of NF-κB. The transient increase in Adam17 mRNA in response to PMA was strongly reduced by an inhibitor of ERK1/2 phosphorylation, U0126. Luciferase reporter assay with vectors encoding the ERK1/2 substrate, Elk-1, fused with constitutively activating or repressing domains, indicated Elk-1 involvement in Adam17 expression. The site-directed mutagenesis of potential Elk-1 binding sites pointed to four functional Elk-1 binding sites in Adam17 promoter. All in all, our results indicate that NF-κB and Elk-1 transcription factors via NF-κB and ERK1/2 signalling pathways contribute to the regulation of mouse Adam17 expression.

Stimulation of TRPM3 channels increases the transcriptional activation potential of Elk-1 involving cytosolic Ca2+, extracellular signal-regulated protein kinase, and calcineurin

Stimulation of transient receptor potential M3 (TRPM3) channels with the steroid pregnenolone sulfate increases the transcriptional activation potential of Elk-1, a transcription factor that regulates serum response element-mediated transcription. Here, we show that an influx of Ca2+ ions into the cells is essential for the activation of Elk-1 following stimulation of TRPM3. Using genetically encoded Ca2+ buffers, we show that a rise in cytoplasmic Ca2+ is required for the upregulation of the transcriptional activation potential of Elk-1, while buffering of Ca2+ in the nucleus had no inhibitory effect on the transcriptional activity of Elk-1. Pharmacological and genetic experiments showed that extracellular signal-regulated protein kinase (ERK1/2) functions as signal transducer connecting TRPM3 channels with the Elk-1 transcription factor. Accordingly, dephosphorylation of ERK1/2 in the nucleus by MAP kinase phosphatase attenuated TRPM3-mediated Elk-1 activation. Moreover, we show that the Ca2+/calmodulin-dependent protein phosphatase calcineurin is part of a shut-off-device for the signaling cascade connecting TRPM3 channels with the activation of Elk-1. The fact that TRPM3 channel stimulation activates Elk-1 connects TRPM3 with the biological functions of Elk-1, including the regulation of proliferation, differentiation, survival, transcription, and cell migration.

ELK1-induced upregulation of long non-coding RNA MIR100HG predicts poor prognosis and promotes the progression of osteosarcoma by epigenetically silencing LATS1 and LATS2

Osteosarcoma (OS) is the commonest malignant bone tumor in the world. High incidence of OS has gradually become a social problem. Recent years, numerous studies have revealed that long non-coding RNAs (lncRNAs) are crucial regulators in the tumor progression. As a member of lncRNA family, MIR100HG has been reported to be an oncogene in breast cancer and acute megakaryoblastic leukemia. Nevertheless, the specific role of MIR100HG in osteosarcoma is still unclear. In this study, we investigated the biological function and molecular mechanism of MIR100HG in the progression of osteosarcoma. At first, we measured the high expression of MIR100HG in OS tissues and cell lines by qRT-PCR. Kaplan-Meier method revealed that high expression of MIR100HG is a factor for the poor prognosis of OS patients (P = 0.004). To explore the effect of MIR100HG on the biological processes of OS, loss-of-function assays were conducted in OS cells. Functionally, MIR100HG knockdown suppressed cell proliferation, cell cycle progression while promoted cell apoptosis. Mechanistically, MIR100HG was upregulated by the transcription factor ELK1. The upregulation of MIR100HG led to the inactivation of Hippo pathway. Furthermore, we found that MIR100HG inactivated Hippo pathway in OS cells by epigenetically silencing LATS1 and LATS2. Rescue assays demonstrated that LATS1/2 involved in MIR100HG-mediated OS progression. In summary, our study indicated that ELK1-induced upregulation of MIR100HG promoted OS progression by epigenetically silencing LATS1 and LATS2 and inactivating Hippo pathway.

Teriflunomide Is an Indirect Human Constitutive Androstane Receptor (CAR) Activator Interacting With Epidermal Growth Factor (EGF) Signaling.

The constitutive androstane receptor (CAR) is a nuclear receptor involved mainly in xenobiotic and endobiotic metabolism regulation. CAR is activated directly by its ligands via the ligand binding domain (LBD) or indirectly by inhibition of the epidermal growth factor (EGF) signaling. We found that leflunomide (LEF) and its main metabolite teriflunomide (TER), both used for autoimmune diseases treatment, induce the prototype CAR target gene CYP2B6 in primary human hepatocytes. As TER was discovered to be an EGF receptor antagonist, we sought to determine if TER is an indirect activator of CAR. In primary human hepatocytes and in differentiated HepaRG cells, we found that LEF and TER up-regulate CAR target genes CYP2B6 and CYP3A4 mRNAs and enzymatic activities. TER stimulated CAR+A mutant translocation into the nucleus but neither LEF nor TER activated the CAR LBD, CAR3 variant or pregnane X receptor (PXR) in gene reporter assays. Interestingly, TER significantly up-regulated CAR mRNA expression, a result which could be a consequence of both EGF receptor and ELK-1 transcription factor inhibition by TER or by TER-mediated activation of glucocorticoid receptor (GR), an upstream hormonal regulator of CAR. We can conclude that TER is a novel indirect CAR activator which through EGF inhibition and GR activation controls both detoxification and some intermediary metabolism genes.