The double lives of shuttling mRNA binding proteins

K-Homology Type Splicing Regulatory Protein: Mechanism of Action in Cancer and Immune Disorders

K homology-type splicing regulatory protein (KSRP) is emerging as a key player in cancer biology, and immunology. As a single-strand nucleic acid binding protein it functions in both transcriptional and post-transcriptional regulation, while facilitating multiple stages of RNA metabolism to affect proliferation and control cell fate. However, it must interact with other proteins to determine the fate of its bound substrate. Here we provide an minireview of this important regulatory protein and describe its complex subcellular functions to affect RNA metabolism, stability, miRNA biogenesis and maturation, stress granule function, metastasis, and inflammatory processes.

RNase L activation in the cytoplasm induces aberrant processing of mRNAs in the nucleus

The antiviral endoribonuclease, RNase L, is activated by the mammalian innate immune response to destroy host and viral RNA to ultimately reduce viral gene expression. Herein, we show that RNase L and RNase L-mediated mRNA decay are primarily localized to the cytoplasm. Consequently, RNA-binding proteins (RBPs) translocate from the cytoplasm to the nucleus upon RNase L activation due to the presence of intact nuclear RNA. The re-localization of RBPs to the nucleus coincides with global alterations to RNA processing in the nucleus. While affecting many host mRNAs, these alterations are pronounced in mRNAs encoding type I and type III interferons and correlate with their retention in the nucleus and reduction in interferon protein production. Similar RNA processing defects also occur during infection with either dengue virus or SARS-CoV-2 when RNase L is activated. These findings reveal that the distribution of RBPs between the nucleus and cytosol is dictated by the availability of RNA in each compartment. Thus, viral infections that trigger RNase L-mediated cytoplasmic RNA in the cytoplasm also alter RNA processing in the nucleus, resulting in an ingenious multi-step immune block to protein biogenesis.

Comprehensive evolutionary analysis and nomenclature of plant G3BPs

Stress induces extensive reprogramming of mRNA metabolism, which includes the transcription and translation of stress-related genes and the formation of stress granules. RasGAP SH3 domain-binding proteins (G3BPs, also called Rasputins) form a highly conserved family of proteins found throughout eukaryotic evolution, which coordinate signal transduction and posttranscriptional gene regulation and play a key role in the formation of stress granules. G3BPs play a role in osmotic, oxidative, and biotic stress in mammals, and recent results revealed that they play similar functions in higher plants. Although simple eukaryotes such as yeast have only one G3BP gene, higher plants show a massive expansion of their G3BP genes into distinct subfamilies. However, because this family of genes has not been well-characterized in plants, functions that have evolved during this expansion remain unidentified. Therefore, we carried out a phylogenetic analysis of G3BPs in different eukaryotes, particularly focusing on the green lineage. On the basis of this evolutionary analysis of G3BPs in eukaryotes, we propose a uniform nomenclature for plant G3BPs that should help predict the evolutionary and functional diversification in this family.

Long Noncoding RNAs Regulate the Inflammatory Responses of Macrophages

Long noncoding RNAs (lncRNAs) are defined as transcripts with more than 200 nucleotides that have little or no coding potential. In recent years, due to the development of next-generation sequencing (NGS), a large number of studies have revealed that lncRNAs function as key regulators to maintain immune balance and participate in diverse physiological and pathological processes in the human body. Notably, overwhelming evidence suggests that lncRNAs can regulate innate immune responses, the differentiation and development of immune cells, inflammatory autoimmune diseases, and many other immunological processes with distinct regulatory mechanisms. In this review, we summarized the emerging roles of lncRNAs in macrophage development and polarization. In addition, the potential value of lncRNAs as diagnostic biomarkers and novel therapeutic targets for the treatment of aberrant immune responses and inflammatory diseases are discussed.

PSPC1 is a new contextual determinant of aberrant subcellular translocation of oncogenes in tumor progression

Dysregulation of nucleocytoplasmic shuttling is commonly observed in cancers and emerging as a cancer hallmark for the development of anticancer therapeutic strategies. Despite its severe adverse effects, selinexor, a selective first-in-class inhibitor of the common nuclear export receptor XPO1, was developed to target nucleocytoplasmic protein shuttling and received accelerated FDA approval in 2019 in combination with dexamethasone as a fifth-line therapeutic option for adults with relapsed refractory multiple myeloma (RRMM). To explore innovative targets in nucleocytoplasmic shuttling, we propose that the aberrant contextual determinants of nucleocytoplasmic shuttling, such as PSPC1 (Paraspeckle component 1), TGIF1 (TGF-β Induced Factor Homeobox 1), NPM1 (Nucleophosmin), Mortalin and EBP50, that modulate shuttling (or cargo) proteins with opposite tumorigenic functions in different subcellular locations could be theranostic targets for developing anticancer strategies. For instance, PSPC1 was recently shown to be the contextual determinant of the TGF-β prometastatic switch and PTK6/β-catenin reciprocal oncogenic nucleocytoplasmic shuttling during hepatocellular carcinoma (HCC) progression. The innovative nucleocytoplasmic shuttling inhibitor PSPC1 C-terminal 131 polypeptide (PSPC1-CT131), which was developed to target both the shuttling determinant PSPC1 and the shuttling protein PTK6, maintained their tumor-suppressive characteristics and exhibited synergistic effects on tumor suppression in HCC cells and mouse models. In summary, targeting the contextual determinants of nucleocytoplasmic shuttling with cargo proteins having opposite tumorigenic functions in different subcellular locations could be an innovative strategy for developing new therapeutic biomarkers and agents to improve cancer therapy.

Moonlighting Proteins: The Case of the Hexokinases

Moonlighting proteins are defined as proteins with two or more functions that are unrelated and independent to each other, so that inactivation of one of them should not affect the second one and vice versa. Intriguingly, all the glycolytic enzymes are described as moonlighting proteins in some organisms. Hexokinase (HXK) is a critical enzyme in the glycolytic pathway and displays a wide range of functions in different organisms such as fungi, parasites, mammals, and plants. This review discusses HXKs moonlighting functions in depth since they have a profound impact on the responses to nutritional, environmental, and disease challenges. HXKs’ activities can be as diverse as performing metabolic activities, as a gene repressor complexing with other proteins, as protein kinase, as immune receptor and regulating processes like autophagy, programmed cell death or immune system responses. However, most of those functions are particular for some organisms while the most common moonlighting HXK function in several kingdoms is being a glucose sensor. In this review, we also analyze how different regulation mechanisms cause HXK to change its subcellular localization, oligomeric or conformational state, the response to substrate and product concentration, and its interactions with membrane, proteins, or RNA, all of which might impact the HXK moonlighting functions.

SINEUP long non-coding RNA acts via PTBP1 and HNRNPK to promote translational initiation assemblies

SINEUPs are long non-coding RNAs (lncRNAs) that contain a SINE element, and which up-regulate the translation of target mRNA. They have been studied in a wide range of applications, as both biological and therapeutic tools, although the underpinning molecular mechanism is unclear. Here, we focused on the sub-cellular distribution of target mRNAs and SINEUP RNAs, performing co-transfection of expression vectors for these transcripts into human embryonic kidney cells (HEK293T/17), to investigate the network of translational regulation. The results showed that co-localization of target mRNAs and SINEUP RNAs in the cytoplasm was a key phenomenon. We identified PTBP1 and HNRNPK as essential RNA binding proteins. These proteins contributed to SINEUP RNA sub-cellular distribution and to assembly of translational initiation complexes, leading to enhanced target mRNA translation. These findings will promote a better understanding of the mechanisms employed by regulatory RNAs implicated in efficient protein translation.

Single mRNP Analysis Reveals that Small Cytoplasmic mRNP Granules Represent mRNA Singletons

Small cytoplasmic mRNP granules are implicated in mRNA transport, translational control, and decay. Using super-resolution microscopy and fluorescence correlation spectroscopy, we analyzed the molecular composition and dynamics of single cytoplasmic YBX1_IMP1 mRNP granules in live cells. Granules appeared elongated and branched, with patches of IMP1 and YBX1 distributed along mRNA, reflecting the attachment of the two RNA-binding proteins in cis. Particles form at the nuclear pore and do not associate with translating ribosomes, so the mRNP is a repository for mRNAs awaiting translation. In agreement with the average number of mRNA-binding sites derived from crosslinked immunoprecipitation (CLIP) analyses, individual mRNPs contain 5-15 molecules of YBX1 and IMP1 and a single poly(A) tail identified by PABPC1. Taken together, we conclude that small cytoplasmic mRNP granules are mRNA singletons, thus depicting the cellular transcriptome. Consequently, expression of functionally related mRNAs in RNA regulons is unlikely to result from coordinated assembly.

Doxorubicin inhibits PD-L1 expression by enhancing TTP-mediated decay of PD-L1 mRNA in cancer cells

Recent research revealed that doxorubicin (DOX) decreased expression of programmed death-ligand 1 (PD-L1) in cancer cells. However, the detailed mechanisms underlying this effect are not well established. Here, we demonstrate that doxorubicin down-regulates PD-L1 expression through induction of AU-rich element (ARE) binding protein tristetraprolin (TTP) in cancer cells. PD-L1 mRNA contain three AREs within its 3'UTR. Doxorubicin induced expression of TTP, increased TTP binding to the 3rd ARE of the PD-L1 3'UTR, and increased decay of PD-L1 mRNA. Inhibition of TTP abrogates the inhibitory effect of doxorubicin on PD-L1 expression. Our data suggest that TTP plays a key role in doxorubicin-mediated down-regulation of PD-L1 by enhancing degradation of PD-L1 mRNA in cancer cells.

The RNA-binding protein SART3 promotes miR-34a biogenesis and G1 cell cycle arrest in lung cancer cells

MicroRNAs (miRNAs or miRs) are small, noncoding RNAs that are implicated in the regulation of most biological processes. Global miRNA biogenesis is altered in many cancers, and RNA-binding proteins play a role in miRNA biogenesis, presenting a promising avenue for targeting miRNA dysregulation in diseases. miR-34a exhibits tumor-suppressive activities by targeting cell cycle regulators CDK4/6 and anti-apoptotic factor BCL-2, among other regulatory pathways such as Wnt, TGF-β, and Notch signaling. Many cancers exhibit down-regulation or loss of miR-34a, and synthetic miR-34a supplementation has been shown to inhibit tumor growth in vivo However, the post-transcriptional mechanisms that cause miR-34a loss in cancer are not entirely understood. Here, using a proteomics-mediated approach in non-small-cell lung cancer (NSCLC) cells, we identified squamous cell carcinoma antigen recognized by T-cells 3 (SART3) as a putative pre-miR-34a-binding protein. SART3 is a spliceosome recycling factor and nuclear RNA-binding protein with no previously reported role in miRNA regulation. We found that SART3 binds pre-miR-34a with higher specificity than pre-let-7d (used as a negative control) and elucidated a new functional role for SART3 in NSCLC cells. SART3 overexpression increased miR-34a levels, down-regulated the miR-34a target genes CDK4/6, and caused a cell cycle arrest in the G1 phase. In vitro binding experiments revealed that the RNA-recognition motifs within the SART3 sequence are responsible for selective pre-miR-34a binding. Our results provide evidence for a significant role of SART3 in miR-34a biogenesis and cell cycle progression in NSCLC cells.

Feedback to the central dogma: cytoplasmic mRNA decay and transcription are interdependent processes

Transcription and RNA decay are key determinants of gene expression; these processes are typically considered as the uncoupled beginning and end of the messenger RNA (mRNA) lifecycle. Here we describe the growing number of studies demonstrating interplay between these spatially disparate processes in eukaryotes. Specifically, cells can maintain mRNA levels by buffering against changes in mRNA stability or transcription, and can also respond to virally induced accelerated decay by reducing RNA polymerase II gene expression. In addition to these global responses, there is also evidence that mRNAs containing a premature stop codon can cause transcriptional upregulation of homologous genes in a targeted fashion. In each of these systems, RNA binding proteins (RBPs), particularly those involved in mRNA degradation, are critical for cytoplasmic to nuclear communication. Although their specific mechanistic contributions are yet to be fully elucidated, differential trafficking of RBPs between subcellular compartments are likely to play a central role in regulating this gene expression feedback pathway.

Tristetraprolin-mediated hexokinase 2 expression regulation contributes to glycolysis in cancer cells

Hexokinase 2 (HK2) catalyzes the first step of glycolysis and is up-regulated in cancer cells. The mechanism has not been fully elucidated. Tristetraprolin (TTP) is an AU-rich element (ARE)-binding protein that inhibits the expression of ARE-containing genes by enhancing mRNA degradation. TTP expression is down-regulated in cancer cells. We demonstrated that TTP is critical for down-regulation of HK2 expression in cancer cells. HK2 mRNA contains an ARE within its 3'-UTR. TTP binds to HK2 3'-UTR and enhances degradation of HK2 mRNA. TTP overexpression decreased HK2 expression and suppressed the glycolytic capacity of cancer cells, measured as glucose uptake and production of glucose-6-phosphate, pyruvate, and lactate. TTP overexpression reduced both the extracellular acidification rate (ECAR) and the oxygen consumption rate (OCR) of cancer cells. Ectopic expression of HK2 in cancer cells attenuated the reduction in glycolytic capacity, ECAR, and OCR from TTP. Taken together, these findings suggest that TTP acts as a negative regulator of HK2 expression and glucose metabolism in cancer cells.

The Rules and Functions of Nucleocytoplasmic Shuttling Proteins

Biological macromolecules are the basis of life activities. There is a separation of spatial dimension between DNA replication and RNA biogenesis, and protein synthesis, which is an interesting phenomenon. The former occurs in the cell nucleus, while the latter in the cytoplasm. The separation requires protein to transport across the nuclear envelope to realize a variety of biological functions. Nucleocytoplasmic transport of protein including import to the nucleus and export to the cytoplasm is a complicated process that requires involvement and interaction of many proteins. In recent years, many studies have found that proteins constantly shuttle between the cytoplasm and the nucleus. These shuttling proteins play a crucial role as transport carriers and signal transduction regulators within cells. In this review, we describe the mechanism of nucleocytoplasmic transport of shuttling proteins and summarize some important diseases related shuttling proteins.

Identification of RNA-binding proteins in exosomes capable of interacting with different types of RNA: RBP-facilitated transport of RNAs into exosomes

The RNA that is packaged into exosomes is termed as exosomal-shuttle RNA (esRNA); however, the players, which take this subset of RNA (esRNA) into exosomes, remain largely unknown. We hypothesized that RNA binding proteins (RBPs) could serve as key players in this mechanism, by making complexes with RNAs and transporting them into exosomes during the biosynthesis of exosomes. Here, we demonstrate the presence of 30 RBPs in exosomes that were shown to form RNA-RBP complexes with both cellular RNA and exosomal-RNA species. To assess the involvement of these RBPs in RNA-transfer into exosomes, the gene transcripts encoding six of the proteins identified in exosomes (HSP90AB1, XPO5, hnRNPH1, hnRNPM, hnRNPA2B1, and MVP) were silenced by siRNA and subsequent effect on esRNA was assessed. A significant reduction of total esRNA was observed by post-transcriptional silencing of MVP, compared to other RBPs. Furthermore, to confirm the binding of MVP with esRNA, a biotinylated-MVP was transiently expressed in HEK293F cells. Higher levels of esRNA were recovered from MVP that was eluted from exosomes of transfected cells, as compared to those of non-transfected cells. Our data indicate that these RBPs could end up in exosomes together with RNA molecules in the form of RNA-ribonucleoprotein complexes, which could be important for the transport of RNAs into exosomes and the maintenance of RNAs inside exosomes. This type of maintenance may favor the shuttling of RNAs from exosomes to recipient cells in the form of stable complexes.

Tristetraprolin inhibits mitochondrial function through suppression of α-Synuclein expression in cancer cells

Mitochondrial dynamics play critical roles in maintaining mitochondrial functions. Here, we report a novel mechanism for regulation of mitochondrial dynamics mediated by tristetraprolin (TTP), an AU-rich element (ARE)-binding protein. Overexpression of TTP resulted in elongated mitochondria, down-regulation of mitochondrial oxidative phosphorylation, reduced membrane potential, cytochrome c release, and increased apoptotic cell death in cancer cells. TTP overexpression inhibited the expression of α-Synuclein (α-Syn). TTP bound to the ARE within the mRNA 3′-untranslated regions (3′-UTRs) of α-Syn and enhanced the decay of α-Syn mRNA. Overexpression of α-Syn without the 3′-UTR restored TTP-induced defects in mitochondrial morphology, mitochondrial oxidative phosphorylation, membrane potential, and apoptotic cell death. Taken together, our data demonstrate that TTP acts as a regulator of mitochondrial dynamics through enhancing degradation of α-Syn mRNA in cancer cells. This finding will increase understanding of the molecular basis of mitochondrial dynamics.

Growing old, yet staying young: The role of telomeres in bats' exceptional longevity

Understanding aging is a grand challenge in biology. Exceptionally long-lived animals have mechanisms that underpin extreme longevity. Telomeres are protective nucleotide repeats on chromosome tips that shorten with cell division, potentially limiting life span. Bats are the longest-lived mammals for their size, but it is unknown whether their telomeres shorten. Using >60 years of cumulative mark-recapture field data, we show that telomeres shorten with age in Rhinolophus ferrumequinum and Miniopterus schreibersii, but not in the bat genus with greatest longevity, Myotis. As in humans, telomerase is not expressed in Myotis myotis blood or fibroblasts. Selection tests on telomere maintenance genes show that ATM and SETX, which repair and prevent DNA damage, potentially mediate telomere dynamics in Myotis bats. Twenty-one telomere maintenance genes are differentially expressed in Myotis, of which 14 are enriched for DNA repair, and 5 for alternative telomere-lengthening mechanisms. We demonstrate how telomeres, telomerase, and DNA repair genes have contributed to the evolution of exceptional longevity in Myotis bats, advancing our understanding of healthy aging.

Tumor-promoting function and prognostic significance of the RNA-binding protein T-cell intracellular antigen-1 in esophageal squamous cell carcinoma

T-cell intracellular antigen-1 (TIA1) is an RNA-binding protein involved in many regulatory aspects of mRNA metabolism. Here, we report previously unknown tumor-promoting activity of TIA1, which seems to be associated with its isoform-specific molecular distribution and regulation of a set of cancer-related transcripts, in esophageal squamous cell carcinoma (ESCC). Immunohistochemical overexpression of TIA1 ectopically localized in the cytoplasm of tumor cells was an independent prognosticator for worse overall survival in a cohort of 143 ESCC patients. Knockdown of TIA1 inhibited proliferation of ESCC cells. By exogenously introducing each of two major isoforms, TIA1a and TIA1b, only TIA1a, which was localized to both the nucleus and cytoplasm, promoted anchorage-dependent and anchorage-independent ESCC cell proliferation. Ribonucleoprotein immunoprecipitation, followed by microarray analysis or massive-parallel sequencing, identified a set of TIA1-binding mRNAs, including SKP2 and CCNA2. TIA1 increased SKP2 and CCNA2 protein levels through the suppression of mRNA decay and translational induction, respectively. Our findings uncover a novel oncogenic function of TIA1 in esophageal tumorigenesis, and implicate its use as a marker for prognostic evaluation and as a therapeutic target in ESCC.

The NF-κB-Responsive Long Noncoding RNA FIRRE Regulates Posttranscriptional Regulation of Inflammatory Gene Expression through Interacting with hnRNPU

Long noncoding RNAs, a newly identified class of noncoding RNAs, are important regulators of gene expression in innate immunity. We report in this study that the transcription of FIRRE, a conserved long noncoding RNA between humans and mice, is controlled by NF-κB signaling in macrophages and intestinal epithelial cells. Functionally, FIRRE appears to positively regulate the expression of several inflammatory genes in macrophages or intestinal epithelial cells in response to LPS stimulation via posttranscriptional mechanisms. Specifically, FIRRE physically interacts with heterogeneous nuclear ribonucleoproteins U, regulating the stability of mRNAs of selected inflammatory genes through targeting the AU-rich elements of their mRNAs in cells following LPS stimulation. Therefore, our data indicate a new regulatory role for NF-κB-responsive FIRRE in the posttranscriptional regulation of inflammatory genes in the innate immune system.

Pterostilbene 4'-β-Glucoside Protects against DSS-Induced Colitis via Induction of Tristetraprolin

Pterostilbene, a dimethyl ester analog of resveratrol, has anti-inflammatory and antioxidative effects and alters cell proliferation. Tristetraprolin (TTP) promotes the degradation of proinflammatory mediators via binding to adenosine and uridine- (AU-) rich elements (ARE) located in the 3′-untranslated regions of mRNAs. Here, we utilized pterostilbene 4′-β-glucoside (4-PG), a compound derived from pterostilbene, to investigate whether it has anti-inflammatory effects on dextran sulfate sodium- (DSS-) induced colitis via TTP enhancement. TTP expression was increased in 4-PG dose- and time-dependent manners in RAW264.7 cells. The production of proinflammatory cytokine, such as TNF-α, was reduced by 4-PG in vitro. To investigate the role of TTP in the anti-inflammatory effects of 4-PG, we used DSS–induced colitis in TTP WT and KO mice as models. The expression levels of TTP and proinflammatory cytokines were determined in serum and colon tissue. 4-PG increased the expression of TTP while suppressing proinflammatory cytokines both in vitro and in vivo. These findings suggest that treatment with 4-PG mediates the anti-inflammatory effects of 4-PG on DSS-induced colitis via enhancing TTP expression.

Tristetraprolin suppresses the EMT through the down-regulation of Twist1 and Snail1 in cancer cells

Inhibition of epithelial-mesenchymal transition (EMT)-inducing transcription factors Twist and Snail prevents tumor metastasis but enhances metastatic growth. Here, we report an unexpected role of a tumor suppressor tristetraprolin (TTP) in inhibiting Twist and Snail without enhancing cellular proliferation. TTP bound to the AU-rich element (ARE) within the mRNA 3′UTRs of Twist1 and Snail1, enhanced the decay of their mRNAs and inhibited the EMT of cancer cells. The ectopic expression of Twist1 or Snail1 without their 3′UTRs blocked the inhibitory effects of TTP on the EMT. We also observed that TTP overexpression suppressed the growth of cancer cells. Our data propose a new model whereby TTP down-regulates Twist1 and Snail1 and inhibits both the EMT and the proliferation of cancer cells.

The long noncoding RNA ASNR regulates degradation of Bcl-2 mRNA through its interaction with AUF1

The identification and characterization of long non-coding RNAs (lncRNAs) in diverse biological processes has recently developed rapidly. The large amounts of non-coding RNAs scale consistent with developmental complexity in eukaryotes, indicating that most of these transcripts may have functions in the regulation of biological processes and disorder in the organisms. In particular, Understanding of the overall biological significance of lncRNAs in cancers still remains limited. Here, we found a nuclear-retained lncRNA, termed Lnc_ASNR (apoptosis suppressing-noncoding RNA), which serves as a repressor of apoptosis. Lnc_ASNR was discovered in a set of microarray data derived from four kinds of tumor and adjacent normal tissue samples, and displayed significant up-regulation in the tumor tissues. Using an RNA-pull down assay, we found that Lnc_ASNR interacted with the protein ARE/poly (U)-binding/degradation factor 1(AUF1), which is reported to promote rapid degradation of the Bcl-2 mRNA, an inhibitor of apoptosis. Lnc_ASNR binds to AUFI in nucleus, decreasing the cytoplasmic proportion of AUF1 which targets the B-cell lymphoma-2 (Bcl-2) mRNA. Taken together, the overall effect of Lnc_ASNR expression is thus a decrease in cell apoptosis indicating that Lnc_ASNR may play a vital role in tumorigenesis and carcinogenesis.

Tristetraprolin inhibits gastric cancer progression through suppression of IL-33

Tristetraprolin (TTP) is an adenine/uridine (AU)-rich element (ARE)-binding protein that can induce degradation of mRNAs. In this study, we report that TTP suppresses the expression of interleukin-33 (IL-33), a tumor-promoting inflammatory cytokine, and thereby inhibits the progression of gastric cancer (GC). Overexpression of TTP decreased the level of IL-33, whereas knockdown of TTP increased IL-33 levels. We also discovered that TTP inhibited the proliferation, migration, and invasion of GC cell lines through regulation of IL-33. Furthermore, TTP RNA and protein levels were remarkably reduced in GC and inversely correlated with IL-33 level, and they were also closely associated with depth of invasion, lymph node metastasis, advanced TNM stage, as well as survival rate. Taken together, these findings identified TTP as a downregulator of IL-33, and further suggest that TTP can serve as a novel biomarker for the diagnosis of GC and as a potential therapeutic target for GC treatment.

Tristetraprolin mediates the anti-proliferative effects of metformin in breast cancer cells

Metformin, which is a drug commonly prescribed to treat type 2 diabetes, has anti-proliferative effects in cancer cells; however, the molecular mechanisms underlying this effect remain largely unknown. The aim is to investigate the role of tristetraprolin (TTP), an AU-rich element-binding protein, in anti-proliferative effects of metformin in cancer cells. p53 wild-type and p53 mutant breast cancer cells were treated with metformin, and expression of TTP and c-Myc was analyzed by semi-quantitative RT-PCR, Western blots, and promoter activity assay. Breast cancer cells were transfected with siRNA against TTP to inhibit TTP expression or c-Myc and, after metformin treatment, analyzed for cell proliferation by MTS assay. Metformin induces the expression of tristetraprolin (TTP) in breast cancer cells in a p53-independent manner. Importantly, inhibition of TTP abrogated the anti-proliferation effect of metformin. We observed that metformin decreased c-Myc levels, and ectopic expression of c-Myc blocked the effect of metformin on TTP expression and cell proliferation. Our data indicate that metformin induces TTP expression by reducing the expression of c-Myc, suggesting a new model whereby TTP acts as a mediator of metformin’s anti-proliferative activity in cancer cells.

A Pleiotropic RNA-Binding Protein Controls Distinct Cell Cycle Checkpoints to Drive Resistance of p53-Defective Tumors to Chemotherapy

In normal cells, p53 is activated by DNA damage checkpoint kinases to simultaneously control the G1/S and G2/M cell cycle checkpoints through transcriptional induction of p21(cip1) and Gadd45α. In p53-mutant tumors, cell cycle checkpoints are rewired, leading to dependency on the p38/MK2 pathway to survive DNA-damaging chemotherapy. Here we show that the RNA binding protein hnRNPA0 is the "successor" to p53 for checkpoint control. Like p53, hnRNPA0 is activated by a checkpoint kinase (MK2) and simultaneously controls both cell cycle checkpoints through distinct target mRNAs, but unlike p53, this is through the post-transcriptional stabilization of p27(Kip1) and Gadd45α mRNAs. This pathway drives cisplatin resistance in lung cancer, demonstrating the importance of post-transcriptional RNA control to chemotherapy response.

Role of the cytoplasmic isoform of RBFOX1/A2BP1 in establishing the architecture of the developing cerebral cortex

Background

RBFOX1 (also known as FOX1 or A2BP1) regulates alternative splicing of a variety of transcripts crucial for neuronal functions. Physiological significance of RBFOX1 during brain development is seemingly essential since abnormalities in the gene cause autism spectrum disorder (ASD) and other neurodevelopmental and neuropsychiatric disorders such as intellectual disability, epilepsy, attention deficit hyperactivity disorder, and schizophrenia. RBFOX1 was also shown to serve as a “hub” in ASD gene transcriptome network. However, the pathophysiological significance of RBFOX1 gene abnormalities remains to be clarified.

Methods

To elucidate the pathophysiological relevance of Rbfox1, we performed a battery of in vivo and in vitro analyses of the brain-specific cytoplasmic isoform, Rbfox1-iso2, during mouse corticogenesis. In vivo analyses were based on in utero electroporation, and the role of Rbfox1-iso2 in cortical neuron migration, neurogenesis, and morphology was investigated by morphological methods including confocal laser microscope-assisted time-lapse imaging. In vitro analyses were carried out to examine the morphology of primary cultured mouse hippocampal neurons.

Results

Silencing of Rbfox1-iso2 in utero caused defects in the radial migration and terminal translocation of cortical neurons during corticogenesis. Time-lapse imaging revealed that radial migration was apparently impaired by dysregulated nucleokinesis. Rbfox1-iso2 also regulated neuronal network formation in vivo since axon extension to the opposite hemisphere and dendritic arborization were hampered by the knockdown. In in vitro analyses, spine density and mature spine number were reduced in Rbfox1-iso2-deficient hippocampal neurons.

Conclusions

Impaired Rbfox1-iso2 function was found to cause abnormal corticogenesis during brain development. The abnormal process may underlie the basic pathophysiology of ASD and other neurodevelopmental disorders and may contribute to the emergence of the clinical symptoms of the patients with RBFOX1 gene abnormalities.

Electronic supplementary material

The online version of this article (doi:10.1186/s13229-015-0049-5) contains supplementary material, which is available to authorized users.

Tristetraprolin mediates anti-inflammatory effects of carbon monoxide on lipopolysaccharide-induced acute lung injury

Low-dose inhaled carbon monoxide is reported to suppress inflammatory responses and exhibit a therapeutic effect in models of lipopolysaccharide (LPS)-induced acute lung injury (ALI). However, the precise mechanism by which carbon monoxide confers protection against ALI is not clear. Tristetraprolin (TTP; official name ZFP36) exerts anti-inflammatory effects by enhancing decay of proinflammatory cytokine mRNAs. With the use of TTP knockout mice, we demonstrate here that the protection by carbon monoxide against LPS-induced ALI is mediated by TTP. Inhalation of carbon monoxide substantially increased the pulmonary expression of TTP. carbon monoxide markedly enhanced the decay of mRNA-encoding inflammatory cytokines, blocked the expression of inflammatory cytokines, and decreased tissue damage in LPS-treated lung tissue. Moreover, knockout of TTP abrogated the anti-inflammatory and tissue-protective effects of carbon monoxide in LPS-induced ALI. These results suggest that carbon monoxide-induced TTP mediates the protective effect of carbon monoxide against LPS-induced ALI by enhancing the decay of mRNA encoding proinflammatory cytokines.

TTP mediates cisplatin-induced apoptosis of head and neck cancer cells by down-regulating the expression of Bcl-2

The chemotherapeutic agent cisplatin is widely used for treatment of head and neck squamous cell carcinoma (HNSCC). B-cell lymphoma 2 (Bcl-2) is an anti-apoptotic protein that is overexpressed in cancer cells and confers resistance to cisplatin. Thus, inhibition of Bcl-2 expression may enhance the cisplatin sensitivity of cancer cells. In this study, we report that the AU-rich element (ARE) binding protein tristetraprolin (TTP) inhibits the expression of Bcl-2 and enhances cisplatin sensitivity of HNSCC cells. Cisplatin-sensitive HNSCC cells express high levels of TTP and low levels of Bcl-2, while cisplatin-resistant HNSCC cells have low levels of TTP and high levels of Bcl-2. Inhibition of TTP expression using siRNA increases levels of Bcl-2 and decreases cisplatin sensitivity in HNSCC cells. On the contrary, overexpression of TTP decreases Bcl-2 expression and increases sensitivity to cisplatin. Together, the results of the present study suggest that TTP expression enhances cisplatin sensitivity in HNSCC cells by reducing levels of Bcl-2.

The role of HuR in the post-transcriptional regulation of interleukin-3 in T cells

Human Interleukin-3 (IL-3) is a lymphokine member of a class of transiently expressed mRNAs harboring Adenosine/Uridine-Rich Elements (ARE) in their 3' untranslated regions (3'-UTRs). The regulatory effects of AREs are often mediated by specific ARE-binding proteins (ARE-BPs). In this report, we show that the human IL-3 3'-UTR plays a post-transcriptional regulation role in two human transformed cell lines. More specifically, we demonstrate that the hIL-3 3'-UTR represses the translation of a luciferase reporter both in HeLa and Jurkat T-cells. These results also revealed that the hIL-3 3'-UTR-mediated translational repression is exerted by an 83 nt region comprised mainly by AREs and some non-ARE sequences. Moreover, electrophoretic mobility shift assays (EMSAs) and UV-crosslinking analysis show that this hIL-3 ARE-rich region recruits five specific protein complexes, including the ARE-BPs HuR and TIA-1. HuR binding to this ARE-rich region appears to be spatially modulated during T-cell activation. Together, these results suggest that HuR recognizes the ARE-rich region and plays a role in the IL-3 3'-UTR-mediated post-transcriptional control in T-cells.

Tristetraprolin mediates anti-inflammatory effect of carbon monoxide against DSS-induced colitis

Endogenous carbon monoxide (CO) exerts anti-inflammatory effects. Tristetraprolin (TTP) is known to destabilize pro-inflammatory transcripts. Here we found that exogenous CO enhanced the decay of TNF-α mRNA and suppressed TNF-α expression in LPS-activated macrophages from wild-type (WT) mice. However, TTP deficiency abrogated the effects of exogenous CO. While CO treatment prior to DSS administration in WT mice significantly reduced inflammatory cytokine levels and colitis, it failed to reduce the pro-inflammatory cytokine levels and colitis in TTP knockout (KO) mice. Our results demonstrate that TTP is a key factor mediating the anti-inflammatory action of CO in DSS-induced colitis.

Purification of RNA-binding proteins

The majority of regulatory RNA sequences exert their function through interaction with proteins. Therefore, the identification of RNA-binding proteins is the key step in understanding the role of many RNA motifs. Here, we describe a straightforward method to identify RNA-binding proteins. In this approach, RNAs are immobilized on beads and incubated with protein lysates. After removing unbound fraction of proteins, the bound proteins are eluted by successive increasing of salt concentration. The lower the salt concentration, the lower is the binding affinity of a protein to the RNA. According to this principle, each elution fraction can contain a number of proteins which bind with similar affinity to the RNA. After gel electrophoretic separation and staining, each single protein band can be identified, isolated, and analyzed by mass spectrometry.

Tristetraprolin down-regulates IL-23 expression in colon cancer cells

Interleukin 23 (IL-23) is an inflammatory cytokine that plays an important role in tumor promotion. Expression of IL-23 is increased in cancer cells and correlates with tumor progression. However, the mechanisms regulating IL-23 expression in cancer cells are still unclear. Here we report that tristetraprolin (TTP), an AU-rich element (ARE)-binding protein, inhibits IL-23 production in CT26 mouse colon cancer cells. Overexpression of TTP decreased the stability of IL-23 mRNA and the expression level of IL-23 in CT26 cells. Conversely, inhibition of TTP by siRNA increased IL-23 production. TTP destabilized a luciferase mRNA reporter containing the IL-23 mRNA 3'UTR, which contains five AREs. Analyses of deletion and point mutants of the IL-23 mRNA 3'UTR demonstrated that the ARE cluster between the third and fifth AREs was responsible for TTP-mediated destabilization of IL-23 mRNA. A RNA electrophoretic mobility shift assay confirmed that TTP binds to this ARE cluster. Taken together, these results demonstrate that TTP acts as a negative regulator of IL-23 gene expression in mouse colon cancer cells and suggest its potential application as a novel therapeutic target to control IL-23-mediated tumor promotion.

hnRNP A2/B1 interacts with influenza A viral protein NS1 and inhibits virus replication potentially through suppressing NS1 RNA/protein levels and NS1 mRNA nuclear export

The NS1 protein of influenza viruses is a major virulence factor and exerts its function through interacting with viral/cellular RNAs and proteins. In this study, we identified heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) as an interacting partner of NS1 proteins by a proteomic method. Knockdown of hnRNP A2/B1 by small interfering RNA (siRNA) resulted in higher levels of NS vRNA, NS1 mRNA, and NS1 protein in the virus-infected cells. In addition, we demonstrated that hnRNP A2/B1 proteins are associated with NS1 and NS2 mRNAs and that knockdown of hnRNP A2/B1 promotes transport of NS1 mRNA from the nucleus to the cytoplasm in the infected cells. Lastly, we showed that knockdown of hnRNP A2/B1 leads to enhanced virus replication. Our results suggest that hnRNP A2/B1 plays an inhibitory role in the replication of influenza A virus in host cells potentially through suppressing NS1 RNA/protein levels and NS1 mRNA nucleocytoplasmic translocation.

Rhox in mammalian reproduction and development

Homeobox genes play essential roles in embryonic development and reproduction. Recently, a large cluster of homeobox genes, reproductive homeobox genes on the X chromosome (Rhox) genes, was discovered as three gene clusters, α, β, and γ in mice. It was found that Rhox genes were selectively expressed in reproduction-associated tissues, such as those of the testes, epididymis, ovaries, and placenta. Hence, it was proposed that Rhox genes are important for regulating various reproductive features, especially gametogenesis in male as well as in female mammals. It was first determined that 12 Rhox genes are clustered into α (Rhox1-4), β (Rhox5-9), and γ (Rhox10-12) subclusters, and recently Rhox13 has also been found. At present, 33 Rhox genes have been identified in the mouse genome, 11 in the rat, and three in the human. Rhox genes are also responsible for embryonic development, with considerable amounts of Rhox expression in trophoblasts, placenta tissue, embryonic stem cells, and primordial germ cells. In this article we summarized the current understanding of Rhox family genes involved in reproduction and embryonic development and elucidated a previously unreported cell-specific expression in ovarian cells.

Depletion of hnRNP A2/B1 overrides the nuclear retention of the HIV-1 genomic RNA

hnRNP A2 is a cellular protein that is important for nucleocytoplasmic and cytosolic trafficking of the HIV-1 genomic RNA. Both hnRNP A2's interaction with HIV-1 RNA and its expression levels influence the activities of Rev in mediating nucleocytoplasmic export of the HIV-1 genomic RNA. While the lack of Rev expression during HIV-1 gene expression results in nuclear retention of HIV-1 genomic RNA, we show here by fluorescence in situ hybridization and fractionation studies that the genomic RNA translocates to the cytoplasm when hnRNP A2/B1 are depleted from cells. Polyribosome analyses revealed that the genomic RNA was shunted into a cytoplasmic, dense polyribosomal fraction. This fraction contained several RNA-binding proteins involved in viral gene expression and RNA trafficking but did not contain the translation initiation factor, eIF4G1. Amino acid incorporation into nascent polypeptides in this fraction was also greatly reduced, demonstrating that this fraction contains mRNAs that are poorly translated. These results demonstrate that hnRNP A2/B1 expression plays roles in the nuclear retention of the HIV-1 genomic RNA in the absence of Rev and in the release of the genomic RNA from translationally inactive, cytoplasmic RNP complexes.

Tumor suppressor p53 plays a key role in induction of both tristetraprolin and let-7 in human cancer cells

Tristetraprolin (TTP) and let-7 microRNA exhibit suppressive effects on cell growth through down-regulation of oncogenes. Both TTP and let-7 are often repressed in human cancers, thereby promoting oncogenesis by derepressing their target genes. However, the precise mechanism of this repression is unknown. We here demonstrate that p53 stimulated by the DNA-damaging agent doxorubicin (DOX) induced the expression of TTP in cancer cells. TTP in turn increased let-7 levels through down-regulation of Lin28a. Correspondingly, cancer cells with mutations or inhibition of p53 failed to induce the expression of both TTP and let-7 on treatment with DOX. Down-regulation of TTP by small interfering RNAs attenuated the inhibitory effect of DOX on let-7 expression and cell growth. Therefore, TTP provides an important link between p53 activation induced by DNA damage and let-7 biogenesis. These novel findings provide a mechanism for the widespread decrease in TTP and let-7 and chemoresistance observed in human cancers.

Proteomic analysis of interleukin enhancer binding factor 3 (Ilf3) and nuclear factor 90 (NF90) interactome

Interleukin enhancer binding factor 3 (Ilf3) and Nuclear Factor 90 (NF90) are two ubiquitous proteins generated by alternative splicing from the ILF3 gene that provides each protein with a long and identical N-terminal domain of 701 amino acids and a specific C-terminal domain of 210 and 15 amino acids, respectively. They exhibit a high polymorphism due to their posttranscriptional and posttranslational modifications. Ilf3 and NF90 functions remain unclear although they have been described as RNA binding proteins but have been implicated in a large scale of cellular phenomena depending on the nature of their interacting partners, the composition of their protein complexes and their subcellular localization. In order to better understand the functions of Ilf3 and NF90, we have investigated their protein partners by an affinity chromatography approach. In this report, we have identified six partners of Ilf3 and NF90 that interact with their double-stranded RNA binding motifs: hnRNP A/B, hnRNP A2/B1, hnRNP A3, hnRNP D, hnRNP Q and PSF. These hnRNP are known to be implicated in mRNA stabilization, transport and/or translation regulation whereas PSF is a splicing factor. Furthermore, Ilf3, NF90 and most of their identified partners have been shown to be present in large complexes. Altogether, these data suggest an implication of Ilf3 and NF90 in mRNA metabolism. This work allows to establish a link between Ilf3 and NF90 functions, as RNA binding proteins, and their interacting partners implicated in these functions.

The RNA-binding protein xCIRP2 is involved in apoptotic tail regression during metamorphosis in Xenopus laevis tadpoles

Frog metamorphosis induced by thyroid hormone (TH) involves not only cell proliferation and differentiation in reconstituted organs such as limbs, but also apoptotic cell death in degenerated organs such as tails. However, the molecular mechanisms directing the TH-dependent cell fate determination remain unclear. We have previously identified from newts an RNA-binding protein (nRBP) acting as the regulator governing survival and death in germ cells during spermatogenesis. To investigate the molecular events leading the tail resorption during metamorphosis, we analyzed the expression, the functional role in apoptosis, and the regulation of xCIRP2, a frog homolog of nRBP, in tails of Xenopus laevis tadpoles. At the prometamorphic stage, xCIRP2 protein is expressed in fibroblast, epidermal, nerve, and muscular cells and localized in their cytoplasm. When spontaneous metamorphosis progressed, the level of xCIRP2 mRNA remained unchanged but the amount of the protein decreased. In organ cultures of tails at the prometamorphic stage, xCIRP2 protein decreased before their lengths shortened during TH-dependent metamorphosis. The inhibition of calpain or proteasome attenuated the TH-induced decrease of xCIRP2 protein in tails, impairing their regression. These results suggest that xCIRP2 protein is downregulated through calpain- and proteasome-mediated proteolysis in response to TH at the onset of metamorphosis, inducing apoptosis in tails and thereby degenerating them.

Expression of proviral integration site for Moloney murine leukemia virus 1 (Pim-1) is post-transcriptionally regulated by tristetraprolin in cancer cells

The proviral integration site for Moloney murine leukemia virus 1 (Pim-1) is an oncogenic serine/threonine kinase that is up-regulated in several human cancers, facilitates cell cycle progression, and suppresses apoptosis. Previously, it has been reported that the Pim-1 3'-UTR plays important roles in the regulation of Pim-1 mRNA stability. However, the mechanisms explaining how Pim-1 mRNA stability is determined by its 3'-UTR are not well known. Here, we demonstrate that tristetraprolin (TTP) plays a critical role in the regulation of Pim-1 mRNA stability. Our results show that the level of Pim-1 expression is inversely correlated with TTP expression in human cancer cells. Pim-1 mRNA contains two AU-rich elements (ARE1 and ARE2) in the 3'-UTR. TTP bound to ARE2 and enhanced the decay of Pim-1 mRNA. Overexpression of TTP decreased Pim-1 expression and p21 and p27 phosphorylation and inhibited cell growth. Overexpression of Pim-1 cDNA without the 3'-UTR attenuated the inhibitory effects of TTP on p21 phosphorylation and cell growth. In addition, inhibition of p21 by siRNA attenuated the inhibitory effect of TTP on cell growth. Our results suggest that TTP post-transcriptionally down-regulates Pim-1 expression and that the overexpression of TTP may contribute to tumor suppression in part by down-regulating Pim-1 expression.

Involvement of the RNA-binding protein ARE/poly(U)-binding factor 1 (AUF1) in the cytotoxic effects of proinflammatory cytokines on pancreatic beta cells

AIMS/HYPOTHESIS

Chronic exposure of pancreatic beta cells to proinflammatory cytokines leads to impaired insulin secretion and apoptosis. ARE/poly(U)-binding factor 1 (AUF1) belongs to a protein family that controls mRNA stability and translation by associating with adenosine- and uridine-rich regions of target messengers. We investigated the involvement of AUF1 in cytokine-induced beta cell dysfunction.

METHODS

Production and subcellular distribution of AUF1 isoforms were analysed by western blotting. To test for their role in the control of beta cell functions, each isoform was overproduced individually in insulin-secreting cells. The contribution to cytokine-mediated beta cell dysfunction was evaluated by preventing the production of AUF1 isoforms by RNA interference. The effect of AUF1 on the production of potential targets was assessed by western blotting.

RESULTS

MIN6 cells and human pancreatic islets were found to produce four AUF1 isoforms (p42>p45>p37>p40). AUF1 isoforms were mainly localised in the nucleus but were partially translocated to the cytoplasm upon exposure of beta cells to cytokines and activation of the ERK pathway. Overproduction of AUF1 did not affect glucose-induced insulin secretion but promoted apoptosis. This effect was associated with a decrease in the production of the anti-apoptotic proteins, B cell leukaemia/lymphoma 2 (BCL2) and myeloid cell leukaemia sequence 1 (MCL1). Silencing of AUF1 isoforms restored the levels of the anti-apoptotic proteins, attenuated the activation of the nuclear factor-κB (NFκB) pathway, and protected the beta cells from cytokine-induced apoptosis.

CONCLUSIONS/INTERPRETATION

Our findings point to a contribution of AUF1 to the deleterious effects of cytokines on beta cell functions and suggest a role for this RNA-binding protein in the early phases of type 1 diabetes.

Ectopic over-expression of tristetraprolin in human cancer cells promotes biogenesis of let-7 by down-regulation of Lin28

Tristetraprolin (TTP) is a AU-rich element (ARE) binding protein and exhibits suppressive effects on cell growth through down-regulation of ARE-containing oncogenes. The let-7 microRNA has emerged as a significant factor in tumor suppression. Both TTP and let-7 are often repressed in human cancers, thereby promoting oncogenesis by derepressing their target genes. In this work, an unexpected link between TTP and let-7 has been found in human cancer cells. TTP promotes an increase in expression of mature let-7, which leads to the inhibition of let-7 target gene CDC34 expression and suppresses cell growth. This event is associated with TTP-mediated inhibition of Lin28, which has emerged as a negative modulator of let-7. Lin28 mRNA contains ARE within its 3′-UTR and TTP enhances the decay of Lin28 mRNA through binding to its 3′-UTR. This suggests that the TTP-mediated down-regulation of Lin28 plays a key role in let-7 miRNA biogenesis in cancer cells.

Tristetraprolin down-regulates IL-17 through mRNA destabilization

An excess of interleukin 17 (IL-17) may contribute to chronic inflammatory disorders, but mechanisms that regulate IL-17 in immune cells are unclear. Here we report that tristetraprolin (TTP) inhibits IL-17 production in human T cell lines. Overexpression of TTP decreased the expression of IL-17. Conversely, TTP inhibition by siRNA increased IL-17 production. IL-17 mRNA contains eight AREs within its 3'UTR. TTP bound directly to the IL-17 mRNA 3'UTR at a location between the fourth and seventh AREs and enhanced decay of IL-17 transcripts. These results suggest that TTP could control IL-17-mediated inflammation.

Modulation of neoplastic gene regulatory pathways by the RNA-binding factor AUF1

The mRNA-binding protein AUF1 regulates the expression of many key players in cancer including proto-oncogenes, regulators of apoptosis and the cell cycle, and pro-inflammatory cytokines, principally by directing the decay kinetics of their encoded mRNAs. Most studies support an mRNA-destabilizing role for AUF1, although other findings suggest additional functions for this factor. In this review, we explore how changes in AUF1 isoform distribution, subcellular localization, and post-translational protein modifications can influence the metabolism of targeted mRNAs. However, several lines of evidence also support a role for AUF1 in the initiation and/or development of cancer. Many AUF1-targeted transcripts encode products that control pro- and anti-oncogenic processes. Also, overexpression of AUF1 enhances tumorigenesis in murine models, and AUF1 levels are enhanced in some tumors. Finally, signaling cascades that modulate AUF1 function are deregulated in some cancerous tissues. Together, these features suggest that AUF1 may play a prominent role in regulating the expression of many genes that can contribute to tumorigenic phenotypes, and that this post-transcriptional regulatory control point may be subverted by diverse mechanisms in neoplasia.

Tristetraprolin mediates anti-inflammatory effects of nicotine in lipopolysaccharide-stimulated macrophages

Nicotine inhibits the release of TNF-α from macrophage through activation of STAT3. Tristetraprolin (TTP) is known to destabilize pro-inflammatory transcripts containing AU-rich elements (ARE) in 3'-untranslated region (3'-UTR). Here we show that in LPS-stimulated human macrophages the anti-inflammatory action of nicotine is mediated by TTP. Nicotine induced activation of STAT3 enhanced STAT3 binding to the TTP promoter, increased TTP promoter activity, and increased TTP expression resulting in the suppression of LPS-stimulated TNF-α production. Overexpression of a dominant negative mutant of STAT3 (R382W) or down-regulation of STAT3 by siRNA abolished nicotine-induced TTP expression and suppression of LPS-stimulated TNF-α production. Nicotine enhanced the decay of TNF-α mRNA and decreased luciferase expression of a TNF-α 3'-UTR reporter plasmid in U937 cells. However, siRNA to TTP abrogated these effects of nicotine. In this experiment, we are reporting for the first time the involvement of TTP in the cholinergic anti-inflammatory cascade consisting of nicotine-STAT3-TTP-dampening inflammation.

p38 MAPK controls prothrombin expression by regulated RNA 3' end processing

Thrombin is a key protease involved in blood coagulation, complement activation, inflammation, angiogenesis, and tumor invasion. Although induced in many (patho-)physiological conditions, the underlying mechanisms controlling prothrombin expression remained enigmatic. We have now discovered that prothrombin expression is regulated by a posttranscriptional regulatory mechanism responding to stress and inflammation. This mechanism is triggered by external stimuli that activate p38 MAPK. In turn, p38 MAPK upmodulates canonical 3' end processing components and phosphorylates the RNA-binding proteins FBP2 and FBP3, which inhibit 3' end processing of mRNAs, such as prothrombin mRNA, that bear a defined upstream sequence element (USE) in their 3'UTRs. Upon phosphorylation, FBP2 and FBP3 dissociate from the USE, making it accessible to proteins that stimulate 3' end processing. We provide in vivo evidence suggesting the importance of this mechanism in inflammatory hypercoagulation and tumor invasion. Regulated 3' end processing thus emerges as a key mechanism of gene regulation with broad biological and medical implications.

Characterization of proteome alterations in Phanerochaete chrysosporium in response to lead exposure

BACKGROUND

Total soluble proteome alterations of white rot fungus Phanerochaete chrysosporium in response to different doses (25, 50 and 100 μM) of Pb (II) were characterized by 2DE in combination with MALDI-TOF-MS.

RESULTS

Dose-dependent molecular response to Pb (II) involved a total of 14 up-regulated and 21 down-regulated proteins. The induction of an isoform of glyceraldehyde 3-phosphate dehydrogenase, alcohol dehydrogenase class V, mRNA splicing factor, ATP-dependent RNA helicase, thioredoxin reductase and actin required a Pb (II) dose of at least 50 μM. Analysis of the proteome dynamics of mid-exponential phase cells of P. chrysosporium subjected to 50 μM lead at exposure time intervals of 1, 2, 4 and 8 h, identified a total of 23 proteins in increased and 67 proteins in decreased amount. Overall, the newly induced/strongly up-regulated proteins involved in (i) amelioration of lipid peroxidation products, (ii) defense against oxidative damage and redox metabolism, (iii) transcription, recombination and DNA repair (iv) a yet unknown function represented by a putative protein.

CONCLUSION

The present study implicated the particular role of the elements of DNA repair, post-tanscriptional regulation and heterotrimeric G protein signaling in response to Pb (II) stress as shown for the first time for a basidiomycete.

The human glucocorticoid receptor as an RNA-binding protein: global analysis of glucocorticoid receptor-associated transcripts and identification of a target RNA motif

Posttranscriptional regulation is emerging as a key factor in glucocorticoid (GC)-mediated gene regulation. We investigated the role of the human GC receptor (GR) as an RNA-binding protein and its effect on mRNA turnover in human airway epithelial cells. Cell treatment with the potent GC budesonide accelerated the decay of CCL2 mRNA (t(1/2) = 8 ± 1 min versus 62 ± 17 min in DMSO-treated cells) and CCL7 mRNA (t(1/2) = 15 ± 4 min versus 114 ± 37 min), but not that of CCL5 mRNA (t(1/2)=231 ± 8 min versus 266 ± 5 min) in the BEAS-2B cell line. This effect was inhibited by preincubation with an anti-GR Ab, indicating that GR itself plays a role in the turnover of these transcripts. Coimmunoprecipitation and biotin pulldown experiments showed that GR associates with CCL2 and CCL7 mRNAs, but not CCL5 mRNA. These methods confirmed CCL2 mRNA targeting by GR in human primary airway epithelial cells. Association of the GR was localized to the 5' untranslated region of CCL2 mRNA and further mapped to nt 44-60. The collection of transcripts associated with GR, identified by immunoprecipitation of GR-mRNA complexes followed by microarray analysis, revealed 479 transcripts that associated with GR. Computational analysis of the primary sequence and secondary structures of these transcripts yielded a GC-rich motif, which was shown to bind to GR in vitro. This motif was used to predict binding of GR to an additional 7889 transcripts. These results indicate that cytoplasmic GR interacts with a subset of mRNA through specific sequences and can regulate turnover rates, suggesting a novel posttranscriptional role for GR as an RNA-binding protein.