The ETS domain transcription factor Elk-1 regulates the expression of its partner protein, SRF

The alkylglycerone phosphate synthase sustains the resistance of gastric cancer cells to ferroptosis induced by Apatinib

BACKGROUND

Apatinib is a targeted therapy used in the treatment of advanced gastric cancer. However, many gastric cancer patients develop resistance to Apatinib, and the mechanisms underlying this resistance remain unclear. Previous studies have shown that Apatinib can induce ferroptosis in gastric cancer cells. More recent research suggests that polyunsaturated ether phospholipids are closely associated with tumor cell sensitivity to ferroptosis, and may represent key molecules involved in the resistance of tumor cells to ferroptosis.

METHODS

We established Apatinib-resistant gastric cancer cell lines and assessed their tolerance to ferroptosis. We identified key enzymes responsible for the ferroptosis tolerance observed in drug-resistant cells using lipidomics and transcriptomics analysis. Molecular and biological experiments were conducted to elucidate the molecular mechanisms underlying Apatinib resistance mediated by ferroptosis tolerance in gastric cancer cells.

RESULTS

Apatinib resistance is closely linked to ferroptosis resistance, which is driven by a reduction in the levels of polyunsaturated ether phospholipids-phospholipids that are particularly susceptible to oxidation and induce ferroptosis. The downregulation of key enzymes involved in polyunsaturated ether phospholipid synthesis, such as AGPS, mediates tolerance to both ferroptosis and Apatinib in gastric cancer cells, both in vitro and in vivo. Mechanistically, the expression of AGPS in tumor cells is regulated by the transcription factor ELK1. Drug-resistant cells acquire Apatinib tolerance by downregulating both ELK1 and AGPS expression.

CONCLUSIONS

Apatinib-resistant gastric cancer cells exhibit reduced expression of the transcription factor ELK1, which regulates the expression of AGPS. This reduction contributes to the resistance and malignancy of gastric cancer cells.

Resolving the role of podoplanin in the motility of papillary thyroid carcinoma-derived cells using RNA sequencing

The intracellular level of podoplanin (PDPN), a transmembrane protein of still unclear function, is frequently altered in metastatic tumors. High expression of PDPN is frequently observed in papillary thyroid cancer (PTC) specimens. Similarly, PTC-derived cell lines (BCPAP and TPC1, harboring the BRAF V600E mutation and RET/PTC1 fusion, respectively), also present enhanced PDPN yield. We previously reported that depletion of PDPN impairs migration of TPC1 cells, but augments metastasis of BCPAP cells. Interestingly, this phenomenon stays in contrast to the migratory pattern observed for wild-type cells, where TPC1 exhibited higher motility than BCPAP cells. Here, we aimed to elucidate the potential role of PDPN in regulation of molecular mechanisms leading to the diverse metastatic features of the studied PTC-derived cells. We consider that this phenomenon may be caused by alternative regulation of signaling pathways due to the presence of the mutated BRAF allele or RET/PTC1 fusion. The high-throughput RNA sequencing (RNA-seq) technique was used to uncover the genes and signaling pathways affected in wild-type and PDPN-depleted TPC1 and BCPAP cells. We found that changes in the expression of various factors of signaling pathways, like RHOA and RAC1 GTPases and their regulators, are linked with both high PDPN levels and presence of the BRAF V600E mutation. We imply that the suppressed motility of wild-type BCPAP cells results from overactivation of RHOA through natively high PDPN expression. This process is accompanied by inhibition of the PI3K kinase and consequently RAC1, due to overactivation of RAS-mediated signaling and the PTEN regulator.

p38 MAPK pathway-dependent SUMOylation of Elk-1 and phosphorylation of PIAS2 correlate with the downregulation of Elk-1 activity in heat-stressed HeLa cells

Stress-activated and mitogen-activated protein kinases (MAPKs) regulate gene expression by post-translational modifications of transcription factors. Elk-1, a transcription factor that regulates the expression of immediate early genes, is amenable to regulation by all the three mammalian MAPKs. In the present report, using inhibitors specific for different MAPK pathways, we show that during exposure of HeLa cells to heat stress, Elk-1 is SUMOylated with SUMO1 by p38 MAPK pathway-dependent mechanisms. Elk-1-phosphorylation levels were significantly reduced under similar conditions. We also show that transcriptional activity of Elk-1 as assessed by luciferase reporter expression and qPCR estimation of the expression of genes regulated by Elk-1 was downregulated upon exposure to heat stress; this downregulation was reversed when heat exposure was performed in the presence of either SB203580 (p38 MAPK inhibitor) or ginkgolic acid (inhibitor of SUMOylation). Elk-1 induced transcription is also regulated by PIAS2 which acts as a coactivator upon the activation of extracellular signal-regulated kinases (ERKs) and as a corepressor upon its phosphorylation by p38 MAPK. Since heat stress activates the p38 MAPK pathway, we determined if PIAS2 was phosphorylated in heat-stressed HeLa cells. Our studies indicate that in HeLa cells exposed to heat stress, PIAS2 is phosphorylated by p38 MAPK pathway-dependent mechanisms. Collectively, the results presented demonstrate that in heat-stressed HeLa cells, p38 MAPK pathway-dependent SUMOylation of Elk-1 and phosphorylation of PIAS2 correlate with the downregulation of transactivation by Elk-1.

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

ADAM17 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.

Summary: We show the involvement of ERK1/2 and NF-κB pathways in the stimulation of mouse Adam17 expression and determine functional Elk-1- and NF-κB binding sites in its promoter.

Original article. Transcription factors regulate Forkhead box O1 gene promoter activity in pancreatic β-cells

Background: Transcription factors of the Forkhead box O (Fox O) family have important roles in cellular proliferation, apoptosis, differentiation, and stress resistance. In pancreatic β-cells, FoxO1 protein plays an important role in β-cells development. The molecular mechanism of transcriptional regulation of basal FoxO1 gene expression in pancreatic β-cells is not fully understood.

Objectives: Explore the potential transcription factors regulating FoxO1 promoter activity using pancreatic β-cell line (RINm5F cells)

Methods: Promoter screening method, luciferase reporter gene analysis, transient expression assay system, and deletion analysis of a -974/-18 bp 5’ upstream region of the mouse FoxO1 gene were used in this study.

Results: An inhibition domain (-974/-321) and an activation domain (-321/-18) was identified through deletion analysis of a -974/-18 bp 5’ upstream region of the mouse FoxO1 gene. Using the promoter screening method, several transcription factors were selected. Luciferase reporter studies showed that these factors could regulate FoxO1 promoter activity in RINm5F cells. Among these factors, cAMP response-element binding protein (CREB) could positively regulate FoxO1 promoter activity. Signal transducer and activator of transcription 1 (STAT1) played a negative role on FoxO1 promoter. In addition, ETS oncogene family member Elk-1 did not affect the FoxO1 promoter activity.

Conclusion: Two transcription factors (CREB and STAT1) could effectively regulate the mouse FoxO1 gene promoter activity.

Transcription factor Elk-1 participates in the interleukin-1β-dependent regulation of expression of immediate early response gene 3 (IER3)

Immediate early response gene 3 (IER3) encodes a protein involved in the regulation of apoptosis and differentiation. Recently the role of IER3 in the regulation of extracellular signal-regulated kinases (ERKs) was discovered. IER3 prolongs ERKs activation by inhibition of phosphatase PP2A. Here we show that interleukin-1β (IL-1β)-induced IER3 expression is mediated by the ERK1/2 target, transcription factor Elk-1. We identified sequences in the IER3 promoter responsible for its ERKs-dependent activation, namely ETS5/6. Elk-1 binds to these sequences and is phosphorylated following IL-1β stimulation. Mutation of ETS5/6 binding site abolishes activation of IER3 promoter by IL-1β as well as by the constitutively active form of Elk-1 (Elk-VP16). Thus IER3 acts not only as a regulator of ERKs activation, but also as a ERKs-Elk-1-dependent downstream effector.

MKL1/2 and ELK4 co-regulate distinct serum response factor (SRF) transcription programs in macrophages

BACKGROUND

Serum response factor (SRF) is a widely expressed transcription factor involved in multiple regulatory programs. It is believed that SRF can toggle between disparate programs of gene expression through association with different cofactors. However, the direct evidence as to how these factors function on a genome-wide level is still lacking.

RESULTS

In the present study, I explored the functions of SRF and its representative cofactors, megakaryoblastic leukemia 1/2 (MKL1/2) and ETS-domain protein 4 (ELK4), during fungal infection challenge in macrophages. The knockdown study, combined with gene expression array analysis, revealed that MKL1/2 regulated SRF-dependent genes were related to actin cytoskeleton organization, while ELK4 regulated SRF-dependent genes were related to external stimulus responses. Subsequent chromatin immunoprecipitation coupled with massively parallel sequencing (ChIP-seq) suggested that many of these regulations were mediated directly in cis.

CONCLUSIONS

I conclude that SRF utilizes MKL1/2 to fulfill steady state cellular functions, including cytoskeletal organization, and utilizes ELK4 to facilitate acute responses to external infection. Together, these findings indicate that SRF, along with its two cofactors, are important players in both cellular homeostasis and stress responses in macrophages.

Net expression inhibits the growth of pancreatic ductal adenocarcinoma cell PL45 in vitro and in vivo

Pancreatic ductal adenocarcinoma has a poor prognosis due to late diagnosis and a lack of effective therapeutic options. Thus, it is important to better understand its molecular mechanisms and to develop more effective treatments for the disease. The ternary complex factor Net, which exerts its strong inhibitory function on transcription of proto-oncogene gene c-fos by forming ternary complexes with a second transcription factor, has been suspected of being involved in pancreatic cancer and other tumors biology. In this study, we found that the majority of pancreatic ductal adenocarcinoma tissues and cell lines had weak or no expression of Net, whereas significantly high level of Net expression occurred in paired adjacent normal tissues we studied. Furthermore, using in vitro and in vivo model systems, we found that overexpression of Net inhibited cell growth and survival and induced cell apoptosis in human pancreatic ductal adenocarcinoma cell PL45; the mechanisms by which Net inhibited the cell cycle progression were mainly through P21-Cyclin D1/CDK4 Pathway. Our data thus suggested that Net might play an important role in pancreatic carcinogenesis, possibly by acting as a tumor suppressor gene.

Transcriptional regulation of the human mitochondrial peptide deformylase (PDF)

The last years of research have been particularly dynamic in establishing the importance of peptide deformylase (PDF), a protein of the N-terminal methionine excision (NME) pathway that removes formyl-methionine from mitochondrial-encoded proteins. The genomic sequence of the human PDF gene is shared with the COG8 gene, which encodes a component of the oligomeric golgi complex, a very unusual case in Eukaryotic genomes. Since PDF is crucial in maintaining mitochondrial function and given the atypical short distance between the end of COG8 coding sequence and the PDF initiation codon, we investigated whether the regulation of the human PDF is affected by the COG8 overlapping partner. Our data reveals that PDF has several transcription start sites, the most important of which only 18 bp from the initiation codon. Furthermore, luciferase-activation assays using differently-sized fragments defined a 97 bp minimal promoter region for human PDF, which is capable of very strong transcriptional activity. This fragment contains a potential Sp1 binding site highly conserved in mammalian species. We show that this binding site, whose mutation significantly reduces transcription activation, is a target for the Sp1 transcription factor, and possibly of other members of the Sp family. Importantly, the entire minimal promoter region is located after the end of COG8's coding region, strongly suggesting that the human PDF preserves an independent regulation from its overlapping partner.

EGF activates TTP expression by activation of ELK-1 and EGR-1 transcription factors

Background

Tristetraprolin (TTP) is a key mediator of processes such as inflammation resolution, the inhibition of autoimmunity and in cancer. It carries out this role by the binding and degradation of mRNA transcripts, thereby decreasing their half-life. Transcripts modulated by TTP encode proteins such as cytokines, pro-inflammatory agents and immediate-early response proteins. TTP can also modulate neoplastic phenotypes in many cancers. TTP is induced and functionally regulated by a spectrum of both pro- and anti-inflammatory cytokines, mitogens and drugs in a MAPK-dependent manner. So far the contribution of p38 MAPK to the regulation of TTP expression and function has been best described.

Results

Our results demonstrate the induction of the gene coding TTP (ZFP36) by EGF through the ERK1/2-dependent pathway and implicates the transcription factor ELK-1 in this process. We show that ELK-1 regulates ZFP36 expression by two mechanisms: by binding the ZFP36 promoter directly through ETS-binding site (+ 883 to +905 bp) and by inducing expression of EGR-1, which in turn increases ZFP36 expression through sequences located between -111 and -103 bp.

Conclusions

EGF activates TTP expression via ELK-1 and EGR-1 transcription factors.

Elk-1 a transcription factor with multiple facets in the brain

The ternary complex factor (TCF) Elk-1 is a transcription factor that regulates immediate early gene (IEG) expression via the serum response element (SRE) DNA consensus site. Elk-1 is associated with a dimer of serum response factor (SRF) at the SRE site, and its phosphorylation occurs at specific residues in response to mitogen-activated protein kinases (MAPKs), including c-Jun-N terminal kinase (JNK), p38/MAPK, and extracellular-signal regulated kinase (ERK). This phosphorylation event is critical for triggering SRE-dependent transcription. Although MAPKs are fundamental actors for the instatement and maintenance of memory, and much investigation of their downstream signaling partners have been conducted, no data yet clearly implicate Elk-1 in these processes. This is partly due to the complexity of Elk-1 sub-cellular localization, and hence functions, within neurons. Elk-1 is present in its resting state in the cytoplasm, where it colocalizes with mitochondrial proteins or microtubules. In this particular sub-cellular compartment, overexpression of Elk-1 is toxic for neuronal cells. When phosphorylated by the MAPK/ERK, Elk-1 translocates to the nucleus where it is implicated in regulating chromatin remodeling, SRE-dependent transcription, and neuronal differentiation. Another post-translational modification is the conjugation to SUMO (Small Ubiquitin-like MOdifier), which relocalizes Elk-1 in the cytoplasm. Thus, Elk-1 plays a dual role in neuronal functions: pro-apoptotic within the cytoplasm, and pro-differentiation within the nucleus. To address the role of Elk-1 in the brain, one must be aware of its multiple facets, and design molecular tools that will shut down Elk-1 expression, trafficking, or activation, in specific neuronal compartments. We summarize in this review the known molecular functions of Elk-1, its regulation in neuronal cells, and present evidence of its possible implication in model systems of synaptic plasticity, learning, but also in neurodegenerative diseases.

Activation and repression of cellular immediate early genes by serum response factor cofactors

The induction of expression of many cellular immediate early genes (IEG) involves the transcription factor serum response factor (SRF). Two families of SRF coactivators have also been implicated in IEG induction, the ternary complex factors (TCFs), ELK1, Sap1, and Net, and the myocardin-related factors, MKL1 and MKL2. We found that serum induction of some SRF target genes is preferentially regulated by MKL1/2, whereas others are redundantly activated by both TCFs and MKL1/2. Yet ELK1 can also repress transcription. Binding of ELK1 and MKL1 to SRF has been found to be mutually exclusive in vitro, suggesting that ELK1 could repress expression of IEGs by blocking MKL1 binding. We characterized the in vivo binding of MKL1 and ELK1 to target genes and found an inverse relationship of serum-induced MKL1 binding and serum-decreased ELK1 binding. However, experiments with short hairpin RNA-mediated MKL1/2 depletion and expression of a nuclear MKL1 (N100) variant in stably transfected cells failed to alter ELK1 binding, suggesting that ELK1 binding to target genes is regulated independently of MKL1/2. Nevertheless, we found that short interfering RNA-mediated depletion of TCFs increased target gene expression in cells containing the N100 MKL1 activator, most notably in cells under continuous growth conditions. These results indicate that the TCFs can function both as activators and repressors of target gene expression depending upon the cellular growth conditions.

Regulation of heme oxygenase-1 gene by peptidoglycan involves the interaction of Elk-1 and C/EBPalpha to increase expression

Heme oxygenase (HO)-1 is a cytoprotective enzyme with anti-inflammatory properties. HO-1 is induced during a systemic inflammatory response, and expression of HO-1 is beneficial during sepsis of a Gram-positive source. Systemic infection from Gram-positive organisms has emerged as an important cause of sepsis, with Staphylococcus aureus as a common etiology. An important mediator of Gram-positive infections is peptidoglycan (PGN), a cell wall component of these organisms. Here, we demonstrate that HO-1 played an important, protective role in vivo, as mice deficient in HO-1 were very sensitive to the lethal effects of PGN derived from S. aureus. PGN induced HO-1 protein and mRNA levels, and this regulation occurred at the level of gene transcription. The PGN-responsive region of the HO-1 promoter (from -117 to -66 bp) contains a functional EBS, and Ets proteins are known to be involved in the regulation of inflammatory responses. We showed previously that Ets factors (activators Ets-2 and Ets-1 and repressor Elk-3) regulate HO-1 expression by Gram-negative endotoxin. However, during exposure to a Gram-positive stimulus in the present study, Elk-1 was a potent activator of HO-1 in conjunction with PGN. The ability of Elk-1 to induce HO-1 promoter activity was independent of direct DNA binding, but rather occurred by interacting with the CCAAT/enhancer-binding protein-alpha (C/EBPalpha), which binds to DNA. Moreover, silencing of C/EBPalpha in macrophages prevented induction of HO-1 promoter activity by either Elk-1 or PGN. These data provide further insight into the regulation and function of HO-1 by a mediator of Gram-positive bacteria.

Human biliverdin reductase suppresses Goodpasture antigen-binding protein (GPBP) kinase activity: the reductase regulates tumor necrosis factor-alpha-NF-kappaB-dependent GPBP expression

The Ser/Thr/Tyr kinase activity of human biliverdin reductase (hBVR) and the expression of Goodpasture antigen-binding protein (GPBP), a nonconventional Ser/Thr kinase for the type IV collagen of basement membrane, are regulated by tumor necrosis factor (TNF-alpha). The pro-inflammatory cytokine stimulates kinase activity of hBVR and activates NF-kappaB, a transcriptional regulator of GPBP mRNA. Increased GPBP activity is associated with several autoimmune conditions, including Goodpasture syndrome. Here we show that in HEK293A cells hBVR binds to GPBP and down-regulates its TNF-alpha-stimulated kinase activity; this was not due to a decrease in GPBP expression. Findings with small interfering RNA to hBVR and to the p65 regulatory subunit of NF-kappaB show the hBVR role in the initial stimulation of GPBP expression by TNF-alpha-activated NF-kappaB; hBVR was not a factor in mediating GPBP mRNA stability. The interacting domain was mapped to the (281)CX(10)C motif in the C-terminal 24 residues of hBVR. A 7-residue peptide, KKRILHC(281), corresponding to the core of the consensus D(delta)-Box motif in the interacting domain, was as effective as the intact 296-residue hBVR polypeptide in inhibiting GPBP kinase activity. GPBP neither regulated hBVR expression nor TNF-alpha dependent NF-kappaB expression. Collectively, our data reveal that hBVR is a regulator of the TNF-alpha-GPBP-collagen type IV signaling cascade and uncover a novel biological interaction that may be of relevance in autoimmune pathogenesis.

Transcription factors Elk-1 and SRF are engaged in IL1-dependent regulation of ZC3H12A expression

Background

MCPIP is a novel CCCH zinc finger protein described as an RNase engaged in the regulation of immune responses. The regulation of expression of the gene coding for MCPIP - ZC3H12A is poorly explored.

Results

Here we report that the proinflammatory cytokine IL-1β rapidly induces the synthesis of MCPIP in primary monocyte-derived macrophages and HepG2 cells. This up-regulation takes place through the MAP kinase pathway and following activation of the transcription factor Elk-1. Using a ZC3H12A reporter construct we have shown that a ZC3H12A promoter region, stretching from -76 to +60, mediates activation by IL-1β. This region contains binding sites for Elk-1 and its partner SRF. Chromatin immunoprecipitation analysis confirms in vivo binding of both transcription factors to this region of the ZC3H12A promoter.

Conclusions

We conclude that the transcription factor Elk-1 plays an important role in the activation of ZC3H12A expression in response to IL-1β stimulation.

Overlapping promoter targeting by Elk-1 and other divergent ETS-domain transcription factor family members

ETS-domain transcription factors play important roles in controlling gene expression in a variety of different contexts; however, these proteins bind to very similar sites and it is unclear how in vivo specificity is achieved. In silico analysis is unlikely to reveal specific targets for individual family members and direct experimental approaches are therefore required. Here, we take advantage of an inducible dominant-negative expression system to identify a group of novel target genes for the ETS-domain transcription factor Elk-1. Elk-1 is thought to mainly function through cooperation with a second transcription factor SRF, but the targets we identify are largely SRF-independent. Furthermore, we demonstrate that there is a high degree of overlapping, cell type-specific, target gene binding by Elk-1 and other ETS-domain transcription factors. Our results are therefore consistent with the notion that there is a high degree of functional redundancy in target gene regulation by ETS-domain transcription factors in addition to the specific target gene regulation that can be dictated through heterotypic interactions exemplified by the Elk-1-SRF complex.

Extracellular signal-regulated kinase mitogen-activated protein kinase signaling initiates a dynamic interplay between sumoylation and ubiquitination to regulate the activity of the transcriptional activator PEA3

Many transcription factors are controlled through SUMO modification, and in the majority of cases this modification results in enhancements in their repressive properties. In some instances, SUMO modification and its associated repressive activities can be reversed by the action of intracellular signaling pathways, leading to enhanced transcriptional capacities of transcription factors. Here we have investigated sumoylation of the ETS domain transcription factor PEA3 and its interplay with the extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase signaling pathway. PEA3 is modified by SUMO in vitro and in vivo on multiple sites in its N-terminal region. Activation of the ERK MAP kinase pathway promotes sumoylation of PEA3. Importantly, sumoylation of PEA3 is required for maximal activation of target gene promoters, including MMP-1 and COX-2. Molecularly, sumoylation is selectively required for synergistic activation of target gene expression with the coactivator CBP. Moreover, sumoylation of PEA3 is required for ubiquitination of PEA3 and promotes its degradation, suggesting that SUMO-mediated recycling of PEA3 plays a role in PEA3-mediated promoter activation. Thus, in contrast to the majority of other transcription factors studied, sumoylation of PEA3 plays a positive role in PEA3-mediated transcriptional activation and the ERK MAP kinase pathway cooperates with rather than antagonizes this process.

Modulation of pulmonary vascular smooth muscle cell phenotype in hypoxia: role of cGMP-dependent protein kinase and myocardin

We have previously reported that in ovine fetal pulmonary venous smooth muscle cells (FPVSMC), decreased expression of cGMP-dependent protein kinase (PKG) by hypoxia could explain hypoxia-induced SMC phenotype modulation. In this study, we investigated the role of myocardin, a possible downstream effector of PKG, in SMC phenotype modulation induced by 1 and 24 h of hypoxia. Hypoxia for 1 h induced the phosphorylation of E-26-like protein 1 (Elk-1), indicating a quick activation of Elk-1 after hypoxia. Either hypoxia (1 h) or treatment with DT-3, a PKG inhibitor, increased associations of Elk-1 with myosin heavy chain (MHC) gene and serum response factor (SRF), which was paralleled by a decrease in association of myocardin with MHC gene and SRF. Exposure to hypoxia of FPVSMC for 24 h significantly decreased the promoter activity of multiple SMC marker genes, downregulated protein and mRNA expression of myocardin, and upregulated mRNA expression of Elk-1, but had no significant effects on the phosphorylation of Elk-1. Inhibition of myocardin by siRNA transfection downregulated the expression of SMC marker proteins, while overexpression of myocardin prevented the hypoxia-induced decrease in expression of SMC marker proteins. Inhibition of PKG by siRNA transfection downregulated the expression of myocardin, but upregulated that of Elk-1. Overexpression of PKG prevented hypoxia-induced effects on protein expression of myocardin and Elk-1. These data suggest that PKG induces displacement of myocardin from SRF and upregulates myocardin expression, thus activating the SMC genes transcription. The inhibitory effects of hypoxia on PKG may explain hypoxia-induced SMC phenotype modulation by decreasing the effects of PKG on myocardin.

Alteration of Mitogen-Activated Protein Kinase Pathway After Soman Poisoning

The p38 mitogen-activated protein kinase (MAPK) and activated MAPK transcription factors c-jun, c-myc, and elk-1 were investigated in rat enterocytes after sublethal poisoning with soman to study the pathogenetic mechanism of nonspecific long-term effects of nerve agents. Wistar rats were poisoned by intramuscular administration of soman at a dose 60 microg x kg(-1) (70% LD(50)) and sacrificed by cervical dislocation 3 and 5 days after poisoning. Control groups were administered physiologic saline instead of soman. Protein expression in immunohistochemically stained samples from colon transversum of control and poisoned rats was measured using image analysis. In comparison with control groups, activated p38 MAPK from soman-poisoned rats was significantly depressed at both time intervals. c-myc and c-jun expression was significantly increased 3 days after soman poisoning. On the other hand, a decrease in c-myc and c-jun expression was observed 5 days after soman poisoning. No changes in elk-1 expression were found. Long-term depression of MAPK pathway members might allow cells to proliferate in poisoned rats. This mechanism can be linked with apoptosis and carcinogenesis.

Human biliverdin reductase is an ERK activator; hBVR is an ERK nuclear transporter and is required for MAPK signaling

Activation of the MEK/ERK/Elk-signaling cascade is a mechanism for relaying mitogenic and stress stimuli for gene activation. MEK1 is the proximate kinase for activation of ERK1/2, and nuclear targeting of ERK1/2 is obligatory for Elk1 transcriptional activity. Human biliverdin reductase (hBVR) is a recently described Ser/Thr/Tyr kinase in the MAPK insulin/insulin-like growth factor 1 (IGF1)-signaling cascade. Using 293A cells and in vitro experiments, we detail the formation of a ternary complex of MEK/ERK/hBVR, activation of MEK1 and ERK1/2 kinase activities by hBVR, and phosphorylation of hBVR by ERK1/2. hBVR is nearly as effective as IGF1 in activating ERK; intact hBVR ATP-binding domain is necessary for Elk1 activation, whereas protein-protein interaction is the basis for hBVR activation of MEK1 and ERK. The two MAPK docking consensus sequences present in hBVR, F(162)GFP and K(275)KRILHCLGL (C- and D-box, respectively), are ERK interactive sites; interaction at each site is critical for ERK/Elk1 activation. Transfection with mutant hBVR-P(165) or peptides corresponding to the C- or D-box blocked activation of ERK by IGF1. Transfection with D-box mutant hBVR prevented the activation of ERK by wild-type protein and dramatically decreased Elk1 transcriptional activity. hBVR is a nuclear transporter of ERK; experiments with hBVR nuclear export signal (NES) and nuclear localization signal (NLS) mutants demonstrated its critical role in the nuclear localization of IGF-stimulated ERK for Elk1 activation. These findings, together with observations that si-hBVR blocked activation of ERK and Elk1 by IGF1 and prevented formation of ternary complex between MEK/ERK/hBVR, define the critical role of hBVR in ERK signaling and nuclear functions of the kinase.

A TAT-DEF-Elk-1 peptide regulates the cytonuclear trafficking of Elk-1 and controls cytoskeleton dynamics

The transcription factor Elk-1 plays a key role in cell differentiation, proliferation and apoptosis. This role is thought to arise from its phosphorylation by activated extracellular signal-regulated kinases (ERKs), a critical posttranslational event for the transcriptional activity of the ternary complex composed of Elk-1 and a dimer of serum response factor (SRF) at the serum response element (SRE) regulatory site of transcription. In addition to its nuclear localization, Elk-1 is found in the dendrites and soma of neuronal cells and recent evidence implicate a cytoplasmic proapoptotic function of Elk-1, via its association with the mitochondrial permeability transition pore complex. Thus, the nuclear versus cytoplasmic localization of Elk-1 seems to be crucial for its biological function. In this study we show that the excitatory neurotransmitter, glutamate, induces an ERK-dependent Elk-1 activation and nuclear relocalization. We demonstrate that Elk-1 phosphorylation on Ser383/389 has a dual function and triggers both Elk-1 nuclear translocation and SRE-dependent gene expression. Mutating these sites into inactive residues or using a synthetic penetrating peptide (TAT-DEF-Elk-1), which specifically interferes with the DEF docking domain of Elk-1, prevents Elk-1 nuclear translocation without interfering with ERK nor MSK1 (mitogen- and stress-activated protein kinase 1), a CREB kinase downstream from ERK- activation. This results in a differential regulation of glutamate-induced IEG regulation when compared with classical inhibitors of the ERK pathway. Using the TAT-DEF-Elk-1 peptide or the dominant-negative version of Elk-1, we show that Elk-1 phosphorylation controls dendritic elongation, SRF and Actin expression levels as well as cytoskeleton dynamics.

Helicobacter pylori dampens gut epithelial self-renewal by inhibiting apoptosis, a bacterial strategy to enhance colonization of the stomach

Colonization of the gastric pits in the stomach by Helicobacter pylori (Hp) is a major risk factor for gastritis, gastric ulcers, and cancer. Normally, rapid self-renewal of gut epithelia, which occurs by a balance of progenitor proliferation and pit cell apoptosis, serves as a host defense mechanism to limit bacterial colonization. To investigate how Hp overcomes this host defense, we use the Mongolian gerbil model of Hp infection. Apoptotic loss of pit cells induced by a proapoptotic agent is suppressed by Hp. The ability of Hp to suppress apoptosis contributed to pit hyperplasia and persistent bacterial colonization of the stomach. Infection with WT Hp but not with a mutant in the virulence effector cagA increased levels of the prosurvival factor phospho-ERK and antiapoptotic protein MCL1 in the gastric pits. Thus, CagA activates host cell survival and antiapoptotic pathways to overcome self-renewal of the gastric epithelium and help sustain Hp infection.

Antisense oligonucleotide Elk-1 suppresses the tumorigenicity of human hepatocellular carcinoma cells

In previous studies, we showed that reducing Ets-like protein-1 (Elk-1) expression inhibited protein kinase C alpha (PKC alpha) expression and decreased cell migration and invasion in human hepatocellular carcinoma (HCC). In this study, we have investigated the role of Elk-1 in tumorigenesis. SK-Hep-1 HCC cells were transfected with the ElK-1 antisense oligonucleotide (ODN). In the pretreated cells we detected a reduction of mRNA level using RT-PCR. The inhibitory rate of cell growth was measured by MTT assay. Pretreated-SK-Hep-1 HCC cells were implanted subcutaneously into nude mice to observe the tumor growth and calculate tumor inhibitory rate. The results showed that 5 microM of the antisense ODN Elk-1 suppressed both Elk-1 and PKC alpha production by SK-Hep-1 HCC cells after cationic liposome-mediated transfection, to 8% and 1% of control values, respectively, and the growth of SK-Hep-1 HCC cells was inhibited at 2-5 microM doses of the antisense ODN Elk-1. The control reagent, sense ODN Elk-1, showed no effects. In BALB/nude mice, SK-Hep-1 HCC cells transfected with the 5 microM antisense ODN Elk-1 formed tumors much smaller than those of sense ODN Elk-1 pretreated cells. The maximum inhibitory rate of tumor growth was 80.8+/-12.6% and the tumor formation time was prolonged from 13 to 25 days. These findings suggested the usefulness of antisense ODN Elk-1 as a new reagent for liver cancer therapy.

Functional interactions between the Forkhead transcription factor FOXK1 and the MADS-box protein SRF

The combinatorial control of gene expression by the association of members of different families of transcription factors is a common theme in eukaryotic transcriptional control. The MADS-box transcription factors SRF and Mcm1 represent paradigms for such regulation through their interaction with numerous partner proteins. For example, in Saccharomyces cerevisiae, Mcm1 interacts with the forkhead transcription factor Fkh2. Here, we identify a novel interaction between SRF and the Forkhead transcription factor FOXK1 in human cells. The importance of this interaction is shown for the regulation of the SRF target genes SM alpha-actin and PPGB. The binding of FOXK1 to the SM alpha-actin and PPGB promoters requires the presence of SRF on the promoter. FOXK1 acts as a transcriptional repressor and it represses SM alpha-actin and PPGB expression. Thus FOXK1 represents an additional member of the growing repertoire of transcription factors that can interact with SRF and modulate the transcriptional output from SRF-regulated promoters.

ERK- and JNK-signalling regulate gene networks that stimulate metamorphosis and apoptosis in tail tissues of ascidian tadpoles

In ascidian tadpoles, metamorphosis is triggered by a polarized wave of apoptosis, via mechanisms that are largely unknown. We demonstrate that the MAP kinases ERK and JNK are both required for the wave of apoptosis and metamorphosis. By employing a gene-profiling-based approach, we identified the network of genes controlled by either ERK or JNK activity that stimulate the onset of apoptosis. This approach identified a gene network involved in hormonal signalling, in innate immunity, in cell-cell communication and in the extracellular matrix. Through gene silencing, we show that Ci-sushi, a cell-cell communication protein controlled by JNK activity, is required for the wave of apoptosis that precedes tail regression. These observations lead us to propose a model of metamorphosis whereby JNK activity in the CNS induces apoptosis in several adjacent tissues that compose the tail by inducing the expression of genes such as Ci-sushi.

Attenuation of ventricular hypertrophy and fibrosis in rats by pitavastatin: potential role of the RhoA-extracellular signal-regulated kinase-serum response factor signalling pathway

1. Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (statins) manifest pleiotropic effects that may contribute to their therapeutic efficacy. However, the mechanism of the beneficial action of statins on cardiac hypertrophy and fibrosis remains unclear. We have now investigated this action of pitavastatin in Dahl salt-sensitive (DS) rats. 2. The DS rats progressively develop marked hypertension when fed a diet containing 8% NaCl from 7 weeks of age. These animals exhibited pronounced cardiac hypertrophy and fibrosis, as well as upregulation of fetal-type cardiac gene expression at 12 weeks of age, compared with DS rats fed a diet containing 0.3% NaCl. The abundance of mRNAs for collagen types I and III, angiotensin-converting enzyme, transforming growth factor-beta1 and connective tissue growth factor was also increased in the heart of rats on the high-salt diet. 3. Treatment of rats on the high-salt diet with a non-antihypertensive dose of pitavastatin (0.3 or 1 mg/kg per day) from 7 to 12 weeks of age attenuated the development of cardiac hypertrophy and fibrosis, as well as inhibiting the upregulation of cardiac gene expression. Pitavastatin also blocked the translocation of RhoA to the membrane fraction of the left ventricle and RhoA activation, as well as the phosphorylation of the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)-1 and ERK-2 and an increase in the DNA binding activity of serum response factor (SRF) in the heart induced by the high-salt diet. 4. These findings suggest that the effects of pitavastatin on load-induced cardiac hypertrophy and fibrosis are independent of its cholesterol-lowering action and may be mediated, at least in part, through inhibition of RhoA-ERK-SRF signalling.

Overexpression of Ets-like protein 1 in human esophageal squamous cell carcinoma

AIM: To study the expression pattern of Ets-like protein 1 (Elk-1) in human esophageal squamous cell carcinoma (ESCC) and to analyze its relationship with clinicopathologic parameters.

METHODS: The expression of Elk-1 in fresh esophageal cancer tissues and their corresponding normal mucosae was detected immunohistochemically (IHC) by means of tissue microarray (TMA). Its correlation with clinical characteristics was evaluated and analyzed by univariate analysis. All statistical analyses were performed by SPSS version 13.0.

RESULTS: Expression level of transcription factor Elk-1 increased in 78.5% (84/107) ESCC tissues compared with their matched normal esophageal epithelium. However, the expression of Elk-1 did not show any obvious correlation with degree of differentiation of esophageal carcinoma (in well-differentiated, moderately-differentiated and poorly-differentiated tumors, the increased expression was 7/8, 60/74, and 19/25, respectively, P > 0.05). Moreover, no obvious correlation was found with lymph node metastasis and depth of invasion.

CONCLUSION: Increased expression of transcription factor Elk-1 may play an important role in esophageal carcinogenesis.

The LIM domain protein LPP is a coactivator for the ETS domain transcription factor PEA3

PEA3 is a member of a subfamily of ETS domain transcription factors which is regulated by a number of signaling cascades, including the mitogen-activated protein (MAP) kinase pathways. PEA3 activates gene expression and is thought to play an important role in promoting tumor metastasis and also in neuronal development. Here, we have identified the LIM domain protein LPP as a novel coregulatory binding partner for PEA3. LPP has intrinsic transactivation capacity, forms a complex with PEA3, and is found associated with PEA3-regulated promoters. By manipulating LPP levels, we show that it acts to upregulate the transactivation capacity of PEA3. LPP can also functionally interact in a similar manner with the related family member ER81. Thus, we have uncovered a novel nuclear function for the LIM domain protein LPP as a transcriptional coactivator. As LPP continually shuttles between the cell periphery and the nucleus, it represents a potential novel link between cell surface events and changes in gene expression.

PIASxalpha differentially regulates the amplitudes of transcriptional responses following activation of the ERK and p38 MAPK pathways

Activation of the MAP kinase pathways leads to changes in gene expression profiles through direct targeting of transcription factors and their coregulators. Here we identify PIASxalpha as a key regulator that determines the differential response of the transcription factor Elk-1 to the ERK and the stress-activated p38 MAP kinase pathways. While PIASxalpha functions as a coactivator to facilitate SUMO and HDAC-2 removal from Elk-1 in response to ERK pathway activation, PIASxalpha acts in the opposite manner to inhibit HDAC-2 and SUMO loss following stress-activated MAP kinase pathway signaling. Thus, PIASxalpha either enhances or dampens down the activation of Elk-1 target genes, depending on the pathway activated. p38 MAP kinase-mediated PIASxalpha phosphorylation allows it to switch between these two alternative modes of operation. Thus, PIASxalpha acts as a key signal integrator that permits different responses from the same transcription factor, depending on the signaling pathway that is activated.

Smooth muscle-specific genes are differentially sensitive to inhibition by Elk-1

Understanding the mechanism of smooth muscle cell (SMC) differentiation will provide the foundation for elucidating SMC-related diseases, such as atherosclerosis, restenosis, and asthma. In the current study, overexpression of Elk-1 in SMCs down-regulated expression of several endogenous smooth muscle-restricted proteins, including telokin, SM22alpha, and smooth muscle alpha-actin. In contrast, down-regulation of endogenous Elk-1 in smooth muscle cells increased the expression of only telokin and SM22alpha, suggesting that smooth muscle-specific promoters are differentially sensitive to the inhibitory effects of Elk-1. Consistent with this, overexpression of the DNA binding domain of Elk-1, which acts as a dominant-negative protein by displacing endogenous Elk-1, enhanced the expression of telokin and SM22alpha without affecting expression of smooth muscle alpha-actin. Elk-1 suppressed the activity of smooth muscle-restricted promoters, including the telokin promoter that does not contain a consensus Elk-1 binding site, through its ability to block myocardin-induced activation of the promoters. Gel mobility shift and chromatin immunoprecipitation assays revealed that Elk-1 binds to a nonconsensus binding site in the telokin promoter and Elk-1 binding is dependent on serum response factor (SRF) binding to a nearby CArG box. Although overexpression of the SRF-binding B-box domain of Elk-1 is sufficient to repress the myocardin activation of the telokin promoter, this repression is not as complete as that seen with an Elk-1 fragment that includes the DNA binding domain. In addition, reporter gene assays demonstrate that an intact Elk-1 binding site in the telokin promoter is required for Elk-1 to maximally inhibit promoter activity. Together, these data suggest that the differential sensitivity of smooth muscle-specific genes to inhibition by Elk-1 may play a role in the complex changes in smooth muscle-specific protein expression that are observed under pathological conditions.

PIASx acts as an Elk-1 coactivator by facilitating derepression

The ETS-domain transcription factor Elk-1 is a MAP kinase-inducible transcriptional activator protein. However, in the basal state, its activity is repressed by SUMO-dependent histone deacetylase (HDAC) recruitment. Relief of this repression accompanies the activation process. Here, we demonstrate that PIASx(alpha) acts to facilitate this derepression process. Members of the PIAS family of proteins can act as E3 enzymes that enhance the sumoylation status of a variety of substrates. However, PIASx-mediated coactivation of Elk-1 occurs in an E3 activity-independent manner. PIASx(alpha) binds to Elk-1 in vivo and enhances its transcriptional activity. The coactivating properties of PIASx(alpha) require Elk-1 to be modified with SUMO and the integrity of the SUMO binding motif in PIASx(alpha). PIASx(alpha) activates Elk-1 through alterations in the HAT/HDAC activities associated with Elk-1. In particular, PIASx(alpha) facilitates the loss of the repressive HDAC-2 from sumoylated Elk-1, a key event in the activation of Elk-1 in response to signalling through the ERK MAP kinase pathway. Our data therefore reveal a novel coactivator function for PIASx(alpha) through reversing SUMO-mediated repression of transcription factor activity.