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

Intrafollicular Retinoic Acid Signaling Is Important for Luteinizing Hormone-Induced Oocyte Meiotic Resumption

It has been clear that retinoic acid (RA), the most active vitamin A (VA) derivative, plays a central role in governing oocyte meiosis initiation. However, it has not been functionally determined if RA participates in luteinizing hormone (LH)-induced resumption from long-lasting oocyte meiotic arrest, which is essential for haploid oocyte formation. In the present study, using well-established in vivo and in vitro models, we identified that intrafollicular RA signaling is important for normal oocyte meiotic resumption. A mechanistic study indicated that mural granulosa cells (MGCs) are the indispensable follicular compartment for RA-prompted meiotic resumption. Moreover, retinoic acid receptor (RAR) is essential for mediating RA signaling to regulate meiotic resumption. Furthermore, we found zinc finger protein 36 (ZFP36) is the transcriptional target of RAR. Both RA signaling and epidermal growth factor (EGF) signaling were activated in MGCs in response to LH surge, and two intrafollicular signalings cooperate to induce rapid Zfp36 upregulation and Nppc mRNA decrease, which is critical to LH-induced meiotic resumption. These findings extend our understanding of the role of RA in oocyte meiosis: RA not only governs meiotic initiation but also regulates LH-induced meiotic resumption. We also emphasize the importance of LH-induced metabolic changes in MGCs in this process.

Identification of Bcl2 as a Stably Expressed qPCR Reference Gene for Human Colon Cancer Cells Treated with Cottonseed-Derived Gossypol and Bioactive Extracts and Bacteria-Derived Lipopolysaccharides

Cottonseed contains many bioactive molecules including plant polyphenols. Cottonseed value might be increased by providing high-value bioactive polyphenols for improving nutrition and health. However, there was a lack of molecular evidence for cottonseed bioactivity in mammalian cells. One widely used method for evaluating the bioactivity of natural products is quantitative real-time-PCR (qPCR). The selection of stably expressed internal reference genes is a crucial task of qPCR assay for data analysis. The rationale for reference gene selection is that a lower standard deviation of the cycle of threshold (Cq) among the treatments indicates a more stable expression of the gene. The objective of this study was to select reference genes in human colon cancer cells (COLO 205) treated with cottonseed-derived gossypol and bioactive extracts along with bacterial endotoxin lipopolysaccharides (LPS). SYBR Green qPCR was used to analyze the mRNA levels of a wide range of biomarkers involved in glucose transport, lipid biosynthesis, inflammatory response, and cancer development. qPCR data (10,560 Cq values) were generated from 55 genes analyzed from 64 treatments with triplicate per treatment for each gene. The data showed that B-cell lymphoma 2 (Bcl2) mRNA was the most stable among the 55 mRNAs analyzed in the human colon cancer cells. Glyceraldehyde 3 phosphate dehydrogenase (Gapdh) and ribosome protein L32 (Rpl32) mRNAs were not good qPCR references for the colon cancer cells. These observations were consistent regardless of the treatment comparison between gossypol and LPS, glanded and glandless seed extracts, seed coat and kernel extracts, or treatment for 8 and 24 h. These results suggest that Bcl2 is a preferable reference gene for qPCR assays in human colon cancer cells treated with cottonseed-derived gossypol and bioactive extracts as well as LPS. The extensive qPCR results firmly support the conclusion that the Bcl2 gene is stably expressed at the mRNA level in the human colon cancer cells regardless of the treatment, suggesting that Bcl2 gene expression is not regulated at the mRNA level but at the post-transcriptional level. These results should facilitate studies designated to evaluate bioactivity on gene expression regulation by cottonseed molecules and other natural and synthetic molecules for nutrition and health uses.

JNK-dependent phosphorylation and nuclear translocation of EGR-1 promotes cardiomyocyte apoptosis

Myocardial apoptosis induced by myocardial ischemia and hyperlipemia are the main causes of high mortality of cardiovascular diseases. It is not clear whether there is a common mechanism responsible for these two kinds of cardiomyocyte apoptosis. Previous studies demonstrated that early growth response protein 1 (EGR-1) has a pro-apoptotic effect on cardiomyocytes under various stress conditions. Here, we found that EGR-1 is also involved in cardiomyocyte apoptosis induced by both ischemia and high-fat, but how EGR-1 enters the nucleus and whether nuclear EGR-1 (nEGR-1) has a universal effect on cardiomyocyte apoptosis are still unknown. By analyzing the phosphorylation sites and nucleation information of EGR-1, we constructed different mutant plasmids to confirm that the nucleus location of EGR-1 requires Ser501 phosphorylation and regulated by JNK. Furthermore, the pro-apoptotic effect of nEGR-1 was further explored through genetic methods. The results showed that EGR-1 positively regulates the mRNA levels of apoptosis-related proteins (ATF2, CTCF, HAND2, ELK1), which may be the downstream targets of EGR-1 to promote the cardiomyocyte apoptosis. Our research announced the universal pro-apoptotic function of nEGR-1 and explored the mechanism of its nucleus location in cardiomyocytes, providing a new target for the "homotherapy for heteropathy" to cardiovascular diseases.

Cottonseed extracts regulate gene expression in human colon cancer cells

Cotton plant provides economically important fiber and cottonseed, but cottonseed contributes 20% of the crop value. Cottonseed value could be increased by providing high value bioactive compounds and polyphenolic extracts aimed at improving nutrition and preventing diseases because plant polyphenol extracts have been used as medicinal remedy for various diseases. The objective of this study was to investigate the effects of cottonseed extracts on cell viability and gene expression in human colon cancer cells. COLO 225 cells were treated with ethanol extracts from glanded and glandless cottonseed followed by MTT and qPCR assays. Cottonseed extracts showed minor effects on cell viability. qPCR assay analyzed 55 mRNAs involved in several pathways including DGAT, GLUT, TTP, IL, gossypol-regulated and TTP-mediated pathways. Using BCL2 mRNA as the internal reference, qPCR analysis showed minor effects of ethanol extracts from glanded seed coat and kernel and glandless seed coat on mRNA levels in the cells. However, glandless seed kernel extract significantly reduced mRNA levels of many genes involved in glucose transport, lipid biosynthesis and inflammation. The inhibitory effects of glandless kernel extract on gene expression may provide a useful opportunity for improving nutrition and healthcare associated with colon cancer. This in turn may provide the potential of increasing cottonseed value by using ethanol extract as a nutrition/health intervention agent.

The mRNA-destabilizing protein Tristetraprolin targets "meiosis arrester" Nppc mRNA in mammalian preovulatory follicles

C-natriuretic peptide (CNP) and its receptor guanylyl cyclase, natriuretic peptide receptor 2 (NPR2), are key regulators of cyclic guanosine monophosphate (cGMP) homeostasis. The CNP-NPR2-cGMP signaling cascade plays an important role in the progression of oocyte meiosis, which is essential for fertility in female mammals. In preovulatory ovarian follicles, the luteinizing hormone (LH)-induced decrease in CNP and its encoding messenger RNA (mRNA) natriuretic peptide precursor C (Nppc) are a prerequisite for oocyte meiotic resumption. However, it has never been determined how LH decreases CNP/Nppc In the present study, we identified that tristetraprolin (TTP), also known as zinc finger protein 36 (ZFP36), a ubiquitously expressed mRNA-destabilizing protein, is the critical mechanism that underlies the LH-induced decrease in Nppc mRNA. Zfp36 mRNA was transiently up-regulated in mural granulosa cells (MGCs) in response to the LH surge. Loss- and gain-of-function analyses indicated that TTP is required for Nppc mRNA degradation in preovulatory MGCs by targeting the rare noncanonical AU-rich element harbored in the Nppc 3' UTR. Moreover, MGC-specific knockout of Zfp36, as well as lentivirus-mediated knockdown in vivo, impaired the LH/hCG-induced Nppc mRNA decline and oocyte meiotic resumption. Furthermore, we found that LH/hCG activates Zfp36/TTP expression through the EGFR-ERK1/2-dependent pathway. Our findings reveal a functional role of TTP-induced mRNA degradation, a global posttranscriptional regulation mechanism, in orchestrating the progression of oocyte meiosis. We also provided a mechanism for understanding CNP-dependent cGMP homeostasis in diverse cellular processes.

Gossypol decreased cell viability and down-regulated the expression of a number of genes in human colon cancer cells

Plant polyphenol gossypol has anticancer activities. This may increase cottonseed value by using gossypol as a health intervention agent. It is necessary to understand its molecular mechanisms before human consumption. The aim was to uncover the effects of gossypol on cell viability and gene expression in cancer cells. In this study, human colon cancer cells (COLO 225) were treated with gossypol. MTT assay showed significant inhibitory effect under high concentration and longtime treatment. We analyzed the expression of 55 genes at the mRNA level in the cells; many of them are regulated by gossypol or ZFP36/TTP in cancer cells. BCL2 mRNA was the most stable among the 55 mRNAs analyzed in human colon cancer cells. GAPDH and RPL32 mRNAs were not good qPCR references for the colon cancer cells. Gossypol decreased the mRNA levels of DGAT, GLUT, TTP, IL families and a number of previously reported genes. In particular, gossypol suppressed the expression of genes coding for CLAUDIN1, ELK1, FAS, GAPDH, IL2, IL8 and ZFAND5 mRNAs, but enhanced the expression of the gene coding for GLUT3 mRNA. The results showed that gossypol inhibited cell survival with decreased expression of a number of genes in the colon cancer cells.

Tumor suppressing effects of tristetraprolin and its small double-stranded RNAs in bladder cancer

Bladder cancer (BCa) is a common malignant tumor of urinary system with few treatments, so more useful therapeutic targets are still needed. Antitumor effects of tristetraprolin (TTP) have been explored in many type tumors, but its roles in bladder cancer are still unknown until now. In this study, public expression profiles and tissue microarray analysis showed that TTP mRNA and protein levels decreased in BCa relative to the normal bladder tissue. To explore biological functions of TTP in BCa, 488 TTP target genes, which could be both suppressed and bound by TTP, were identified by comprehensively analyzing publicly available high-throughput data obtained from Gene Expression Omnibus (GEO). Gene enrichment analysis showed that these genes were enriched in pathways such as cell cycle, epithelial to mesenchymal transition (EMT), and Wnt signaling. Clustering analysis and gene set variation analysis indicated that patients with high expression of TTP target genes had poorer prognosis and stronger tumor proliferation ability relative to the BCa patients with low expression of TTP target genes. In vitro experiments validated that TTP could suppress proliferation, migration, and invasiveness of BCa cells. And TTP could suppress mRNA expression of cyclin-dependent kinase 1 (CDK1) in BCa cells by target its 3' UTR. Then, we identified a new small double-stranded RNA (dsRNA) named dsTTP-973 which could increase TTP expression in BCa cells, in vivo and in vitro experiments revealed that dsTTP-973 could suppress aggressiveness of BCa. In conclusion, TTP played a role of tumor suppressor gene in BCa like other tumors, and its dsRNA named dsTTP-973 could induce TTP expression in BCa and suppress aggressiveness of BCa. With the help of materials science, dsTTP-973 may become a potential treatment for BCa in the future.

Tristetraprolin Promotes Hepatic Inflammation and Tumor Initiation but Restrains Cancer Progression to Malignancy

BACKGROUND & AIMS

Tristetraprolin (TTP) is a key post-transcriptional regulator of inflammatory and oncogenic transcripts. Accordingly, TTP was reported to act as a tumor suppressor in specific cancers. Herein, we investigated how TTP contributes to the development of liver inflammation and fibrosis, which are key drivers of hepatocarcinogenesis, as well as to the onset and progression of hepatocellular carcinoma (HCC).

METHODS

TTP expression was investigated in mouse/human models of hepatic metabolic diseases and cancer. The role of TTP in nonalcoholic steatohepatitis and HCC development was further examined through in vivo/vitro approaches using liver-specific TTP knockout mice and a panel of hepatic cancer cells.

RESULTS

Our data demonstrate that TTP loss in vivo strongly restrains development of hepatic steatosis and inflammation/fibrosis in mice fed a methionine/choline-deficient diet, as well as HCC development induced by the carcinogen diethylnitrosamine. In contrast, low TTP expression fostered migration and invasion capacities of in vitro transformed hepatic cancer cells likely by unleashing expression of key oncogenes previously associated with these cancerous features. Consistent with these data, TTP was significantly down-regulated in high-grade human HCC, a feature further correlating with poor clinical prognosis. Finally, we uncover hepatocyte nuclear factor 4 alpha and early growth response 1, two key transcription factors lost with hepatocyte dedifferentiation, as key regulators of TTP expression.

CONCLUSIONS

Although TTP importantly contributes to hepatic inflammation and cancer initiation, its loss with hepatocyte dedifferentiation fosters cancer cells migration and invasion. Loss of TTP may represent a clinically relevant biomarker of high-grade HCC associated with poor prognosis.

Human Cytomegalovirus miR-US5-2 Downregulation of GAB1 Regulates Cellular Proliferation and UL138 Expression through Modulation of Epidermal Growth Factor Receptor Signaling Pathways

Human cytomegalovirus (HCMV) causes significant disease in immunocompromised individuals, including transplant patients. HCMV establishes latency in hematopoietic stem cells in the bone marrow. The mechanisms governing latency and reactivation of viral replication are complex and not fully understood. HCMV-encoded miRNAs are small regulatory RNAs that reduce protein expression. In this study, we found that the HCMV miRNA miR-US5-2 targets the epidermal growth factor receptor (EGFR) adaptor protein GAB1 which directly affects downstream cellular signaling pathways activated by EGF. Consequently, miR-US5-2 blocks the EGF-mediated proliferation of human fibroblasts. Early growth response gene 1 (EGR1) is a transcription factor activated by EGFR signaling that regulates expression of HCMV UL138. We show that miR-US5-2 regulates UL138 expression through GAB1-mediated downregulation of the signaling pathways that lead to EGR1 expression. These data suggest that miR-US5-2, through downregulation of GAB1, could play a critical role during reactivation from latency by reducing proliferation and UL138 expression.

Regulation of epidermal growth factor (EGF) receptor (EGFR) signaling is critical for the replication of human cytomegalovirus (HCMV) as well as latency and reactivation in CD34⁺ hematopoietic progenitor cells. HCMV microRNAs (miRNAs) provide a means to modulate the signaling activated by EGF through targeting components of the EGFR signaling pathways. Here, we demonstrate that HCMV miR-US5-2 directly downregulates the critical EGFR adaptor protein GAB1 that mediates activation and sustained signaling through the phosphatidylinositol 3-kinase (PI3K) and MEK/extracellular signal-regulated kinase (ERK) pathways and cellular proliferation in response to EGF. Expression of HCMV UL138 is regulated by the transcription factor early growth response gene 1 (EGR1) downstream of EGFR-induced MEK/ERK signaling. We show that by targeting GAB1 and attenuating MEK/ERK signaling, miR-US5-2 indirectly regulates EGR1 and UL138 expression, which implicates the miRNA in critical regulation of HCMV latency.

IMPORTANCE Human cytomegalovirus (HCMV) causes significant disease in immunocompromised individuals, including transplant patients. HCMV establishes latency in hematopoietic stem cells in the bone marrow. The mechanisms governing latency and reactivation of viral replication are complex and not fully understood. HCMV-encoded miRNAs are small regulatory RNAs that reduce protein expression. In this study, we found that the HCMV miRNA miR-US5-2 targets the epidermal growth factor receptor (EGFR) adaptor protein GAB1 which directly affects downstream cellular signaling pathways activated by EGF. Consequently, miR-US5-2 blocks the EGF-mediated proliferation of human fibroblasts. Early growth response gene 1 (EGR1) is a transcription factor activated by EGFR signaling that regulates expression of HCMV UL138. We show that miR-US5-2 regulates UL138 expression through GAB1-mediated downregulation of the signaling pathways that lead to EGR1 expression. These data suggest that miR-US5-2, through downregulation of GAB1, could play a critical role during reactivation from latency by reducing proliferation and UL138 expression.

Prostate cancer promotes a vicious cycle of bone metastasis progression through inducing osteocytes to secrete GDF15 that stimulates prostate cancer growth and invasion

Bone is the most frequent site of prostate cancer (PCa) metastasis; however, little is known about the role of the most common cell in bone, the osteocyte (OCy), in cancer biology. In this study we explored the crosstalk between PCa cells and OCys to determine if it contributes to PCa progression. PCa cells induced OCys to promote PCa proliferation, migration and invasion. A chemokine screen revealed that PCa cell induced OCys to produce growth-derived factor 15 (GDF15). Knockdown of GDF15 in OCys demonstrated that PCa cells conferred the ability on OCys to promote PCa proliferation, migration and invasion through GDF15. Consistent with this finding was the observation that the GDF15 receptor, GFRAL, was expressed on multiple PCa cell lines. Transcription factor array screening of PCa cells exposed to OCys with or without knockdown of GDF15 revealed that GDF15 in OCys promoted early growth response 1 (EGR1) expression in the PCa cells. Knockdown of EGR1 expression in PCa cells revealed it was required for the OCy-derived GDF15-mediated induction of in vitro PCa cell proliferation, migration and invasion. Subcutaneous co-injection of PCa cells and OCys into mice revealed that OCys promoted tumor growth in vivo, which was diminished by knockdown of GDF15 in the OCys. Knockdown of GDF15 in the tibiae diminished growth of PCa cancer cells injected into the tibiae, which was accompanied by decreased tumor cell proliferation and EGR1 expression. These results shed light on a novel mechanism through which PCa cells educate OCys to promote progression of PCa bone metastasis. They also suggest that targeting of GDF15-based and EGR1-based signaling pathways should be further explored for their potential to diminish progression of PCa bone metastasis.

RNA-seq transcriptome analysis of formalin fixed, paraffin-embedded canine meningioma

Meningiomas are the most commonly reported primary intracranial tumor in dogs and humans and between the two species there are similarities in histology and biologic behavior. Due to these similarities, dogs have been proposed as models for meningioma pathobiology. However, little is known about specific pathways and individual genes that are involved in the development and progression of canine meningioma. In addition, studies are lacking that utilize RNAseq to characterize gene expression in clinical cases of canine meningioma. The primary objective of this study was to develop a technique for which high quality RNA can be extracted from formalin-fixed, paraffin embedded tissue and then used for transcriptome analysis to determine patterns of gene expression. RNA was extracted from thirteen canine meningiomas-eleven from formalin fixed and two flash-frozen. These represented six grade I and seven grade II meningiomas based on the World Health Organization classification system for human meningioma. RNA was also extracted from fresh frozen leptomeninges from three control dogs for comparison. RNAseq libraries made from formalin fixed tissue were of sufficient quality to successfully identify 125 significantly differentially expressed genes, the majority of which were related to oncogenic processes. Twelve genes (AQP1, BMPER, FBLN2, FRZB, MEDAG, MYC, PAMR1, PDGFRL, PDPN, PECAM1, PERP, ZC2HC1C) were validated using qPCR. Among the differentially expressed genes were oncogenes, tumor suppressors, transcription factors, VEGF-related genes, and members of the WNT pathway. Our work demonstrates that RNA of sufficient quality can be extracted from FFPE canine meningioma samples to provide biologically relevant transcriptome analyses using a next-generation sequencing technique, such as RNA-seq.

Nine differentially expressed genes from a post mortem study and their association with suicidal status in a sample of suicide completers, attempters and controls

Several lines of evidence indicate that suicidal behaviour is partly heritable, with multiple genes implicated in its aetiology. We focused on nine genes (S100A13, EFEMP1, PCDHB5, PDGFRB, CDCA7L, SCN2B, PTPRR, MLC1 and ZFP36) which we previously detected as differentially expressed in the cortex of suicide victims compared to controls. We investigated 84 variants within these genes in 495 suicidal subjects (299 completers and 196 attempters) and 1513 controls (109 post-mortem and 1404 healthy). We evaluated associations with: 1) suicidal phenotype; 2) possible endophenotypes for suicidal behaviour. Overall positive results did not survive the correction threshold. However, we found a nominally different distribution of EFEMP1 genotypes, alleles and haplotypes between suicidal subjects and controls, results that were partially replicated when we separately considered the subgroup of suicide completers and post-mortem controls. A weaker association emerged also for PTPRR. Both EFEMP1 and PTPRR genes were also related to possible endophenotypes for suicidal behaviour such as anger, depression-anxiety and fatigue. Because of the large number of analyses performed and the low significance values further replication are mandatory. Nevertheless, neurotrophic gene variants, in particular EFEMP1 and PTPRR, may have a role in the pathogenesis of suicidal behaviour.

IF-combined smRNA FISH reveals interaction of MCPIP1 protein with IER3 mRNA

MCPIP1 and IER3 are recently described proteins essential for maintenance of immune homeostasis. IER3 is involved in the regulation of apoptosis and differentiation and has been shown lately to protect activated T cells and macrophages from apoptosis. MCPIP1 is an RNase critical for controlling inflammation-related mRNAs. MCPIP1 interacts with and degrades a set of stem-loop-containing mRNAs (including IL-6). Our results demonstrate the involvement of MCPIP1 in the regulation of IER3 mRNA levels. A dual luciferase assay revealed that over-expression of MCPIP1 resulted in a decrease of luciferase activity in the samples co-transfected with constructs containing luciferase CDS attached to IER3 3′UTR. We identified a stem-loop structure similar to that described to be important for destabilization of the IL-6 mRNA by MCPIP1. Examination of IER3 3′UTR sequence, structure and evolutionary conservation revealed that the identified stem-loop is buried within a bigger element. Deletion of this fragment abolished the regulation of IER3 3′UTR-containing transcript by MCPIP1. Finally, using immunofluorescence-combined single-molecule RNA FISH we have shown that the MCPIP1 protein co-localizes with IER3 mRNA. By this method we also proved that the presence of the wild-type NYN/PIN-like domain of MCPIP1 correlated with the decreased level of IER3 mRNA. RNA immunoprecipitation further confirmed the interaction of MCPIP1 with IER3 transcripts in vivo.

Summary: We identify IER3 mRNA as a newly discovered MCPIP1 target using recently described IF-based procedures, and also identify a conserved element involved in MCPIP1-dependent IER3 transcript destabilization.

Histone Deacetylase Inhibitors Activate Tristetraprolin Expression through Induction of Early Growth Response Protein 1 (EGR1) in Colorectal Cancer Cells

The RNA-binding protein tristetraprolin (TTP) promotes rapid decay of mRNAs bearing 3' UTR AU-rich elements (ARE). In many cancer types, loss of TTP expression is observed allowing for stabilization of ARE-mRNAs and their pathologic overexpression. Here we demonstrate that histone deacetylase (HDAC) inhibitors (Trichostatin A, SAHA and sodium butyrate) promote TTP expression in colorectal cancer cells (HCA-7, HCT-116, Moser and SW480 cells) and cervix carcinoma cells (HeLa). We found that HDAC inhibitors-induced TTP expression, promote the decay of COX-2 mRNA, and inhibit cancer cell proliferation. HDAC inhibitors were found to promote TTP transcription through activation of the transcription factor Early Growth Response protein 1 (EGR1). Altogether, our findings indicate that loss of TTP in tumors occurs through silencing of EGR1 and suggests a therapeutic approach to rescue TTP expression in colorectal cancer.

Tristetraprolin and its role in regulation of airway inflammation

Chronic inflammatory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are clinically and socioeconomically important diseases globally. Currently the mainstay of anti-inflammatory therapy in respiratory diseases is corticosteroids. Although corticosteroids have proven clinical efficacy in asthma, many asthmatic inflammatory conditions (e.g., infection, exacerbation, and severe asthma) are not responsive to corticosteroids. Moreover, despite an understanding that COPD progression is driven by inflammation, we currently do not have effective anti-inflammatory strategies to combat this disease. Hence, alternative anti-inflammatory strategies are required. p38 mitogen-activated protein kinase (MAPK) has emerged as an important signaling molecule driving airway inflammation, and pharmacological inhibitors against p38 MAPK may provide potential therapies for chronic respiratory disease. In this review, we discuss some of the recent in vitro and in vivo studies targeting p38 MAPK, but suggest that p38 MAPK inhibitors may prove less effective than originally considered because they may block anti-inflammatory molecules along with proinflammatory responses. We propose that an alternative strategy may be to target an anti-inflammatory molecule farther downstream of p38 MAPK, i.e., tristetraprolin (TTP). TTP is an mRNA-destabilizing, RNA-binding protein that enhances the decay of mRNAs, including those encoding proteins implicated in chronic respiratory diseases. We suggest that understanding the molecular mechanism of TTP expression and its temporal regulation will guide future development of novel anti-inflammatory pharmacotherapeutic approaches to combat respiratory disease.

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.

Autophagy proteins regulate ERK phosphorylation

Autophagy is a conserved pathway that maintains cellular quality control. Extracellular signal-regulated kinase (ERK) controls various aspects of cell physiology including proliferation. Multiple signalling cascades, including ERK, have been shown to regulate autophagy, however whether autophagy proteins (ATG) regulate cell signalling is unknown. Here we show that growth factor exposure increases the interaction of ERK cascade components with ATG proteins in the cytosol and nucleus. ERK and its upstream kinase MEK localize to the extra-luminal face of autophagosomes. ERK2 interacts with ATG proteins via its substrate-binding domains. Deleting Atg7 or Atg5 or blocking LC3 lipidation or ATG5–ATG12 conjugation decreases ERK phosphorylation. Conversely, increasing LC3-II availability by silencing the cysteine protease ATG4B or acute trehalose exposure increases ERK phosphorylation. Decreased ERK phosphorylation in Atg5^−/− cells does not occur from overactive phosphatases. Our findings thus reveal an unconventional function of ATG proteins as cellular scaffolds in the regulation of ERK phosphorylation.

The spatial organisation of mitogen-activated protein kinase (MAPK) signalling by scaffold proteins is an important determinant of signalling specificity. Martinez-Lopez et al. show that pre-autophagosomal structures can also act as scaffolds, recruiting the MAPK ERK1/2 and regulating its phosphorylation.

Signal-dependent Elk-1 target genes involved in transcript processing and cell migration

Elk-1 was regarded as a transcription factor engaged mainly in the regulation of cell growth, differentiation, and survival. Recent findings show the engagement of Elk-1 in the control of expression of genes encoding proteins involved in transcript turnover, such as MCPIP1/ZC3H12A and tristetraprolin (TTP/ZFP36). Thus, Elk-1 plays an important role in the control of gene expression not only through the stimulation of expression of transcription factors, but also through regulation of transcript half-live. Moreover, Elk-1 is engaged in the regulation of expression of genes encoding proteins that control proteolytic activity, such as inhibitor of plasminogen activator-1 (PAI-1) and metalloproteinases-2 and -9 (MMP-2 and MMP-9). This review summarizes the biological roles of proteins with expression regulated by Elk-1, involved in transcripts turnover or in cell migration. The broad range of function of these proteins illustrates the complex role of Elk-1 in the regulation of cancer and inflammation.