Turnover and translation of in vitro synthesized messenger RNAs in transfected, normal cells

Matrix Metalloproteinase-9-Dependent Release of IL-1β by Human Eosinophils

Asthma is often associated with airway eosinophilia, and therapies targeting eosinophils are now available to treat severe eosinophilic asthma. Eosinophilic asthma is often due to a type-2 immune response and production of IL-5, which leads to eosinophilopiesis and recruitment of mature eosinophils in the airways. A concomitant type-2 and type-17 response has been reported in some individuals. IL-17 may be enhanced by IL-1β production and can lead to neutrophilic inflammation. In fact, both eosinophilic and neutrophilic (mixed granulocytic) inflammation are simultaneously present in a large population of patients with asthma. In monocyte/macrophage cell populations, release of mature IL-1β occurs via toll-like receptor ligand-induced activation of the inflammasome. Within the inflammasome, a cascade of events leads to the activation of caspase-1, which cleaves pro-IL-1β protein into a mature, releasable, and active form. We have demonstrated that eosinophils can release IL-1β in a Toll-like receptor ligand-independent fashion. The objective of this study was to determine the mechanisms underlying the production and maturation of IL-1β in cytokine-activated eosinophils. Using eosinophils from circulating blood and from bronchoalveolar lavage fluid after an airway allergen challenge, the present study demonstrates that cytokine-activated eosinophils express and release a bioactive form of IL-1β with an apparent size less than the typical 17 kDa mature form produced by macrophages. Using a zymography approach and pharmacological inhibitors, we identified matrix metalloproteinase-9 (MMP-9) as a protease that cleaves pro-IL-1β into a ~15 kDa form and allows the release of IL-1β from cytokine-activated eosinophils. Therefore, we conclude that activated eosinophils produce MMP-9, which causes the release of IL-1β in an inflammasome/caspase-1-independent manner. The production of IL-1β by eosinophils may be a link between the eosinophilic/type-2 immune response and the neutrophilic/type-17 immune response that is often associated with a more severe and treatment-refractory type of asthma.

Effect of Kisspeptin on the Developmental Competence and Early Transcript Expression in Porcine Oocytes Parthenogenetically Activated with Different Methods

Recent studies showed the modulatory effect of kisspeptin (KP) on calcium waves through the cell membrane and inside the cell. Spermatozoon can induce similar ooplasmic calcium oscillations at fertilization to trigger meiosis II. Here, we evaluated the effect of KP supplementation with 6-dimethylaminopurine (6-DMAP) for 4 h on embryonic development after oocyte activation with single electric pulse, 5 µM ionomycin, or 8% ethanol. Compared to control nonsupplemented groups, KP significantly improved embryo developmental competence electric- and ethanol-activated oocytes in terms of cleavage (75.3% and 58.6% versus 64% and 48%, respectively, p < 0.05) and blastocyst development (31.3% and 10% versus 19.3% and 4%, respectively, p < 0.05). MOS expression was increased in electrically activated oocytes in presence of KP while it significantly reduced CCNB1 expression. In ionomycin treated group, both MOS and CCNB1 showed significant increase with no difference between KP and control groups. In ethanol-treated group, KP significantly reduced CCNB1 but no effect was observed on MOS expression. The early alterations in MOS and CCNB1 mRNA transcripts caused by KP may explain the significant differences in the developmental competence between the experimental groups. Kisspeptin supplementation may be adopted in protocols for porcine oocyte activation through electric current and ethanol to improve embryonic developmental competence.

Respecifying human iPSC-derived blood cells into highly engraftable hematopoietic stem and progenitor cells with a single factor

Derivation of human hematopoietic stem cells (HSCs) from induced pluripotent stem cells (iPSCs) offers considerable promise for cell therapy, disease modeling, and drug screening. However, efficient derivation of functional iPSC-derived HSCs with in vivo engraftability and multilineage potential remains challenging. Here, we demonstrate a tractable approach for respecifying iPSC-derived blood cells into highly engraftable hematopoietic stem and progenitor cells (HSPCs) through transient expression of a single transcription factor, MLL-AF4 These induced HSPCs (iHSPCs) derived from iPSCs are able to fully reconstitute the human hematopoietic system in the recipient mice without myeloid bias. iHSPCs are long-term engraftable, but they are also prone to leukemic transformation during the long-term engraftment period. On the contrary, primary HSPCs with the same induction sustain the long-term engraftment without leukemic transformation. These findings demonstrate the feasibility of activating the HSC network in human iPSC-derived blood cells through expression of a single factor and suggest iHSPCs are more genomically instable than primary HSPCs, which merits further attention.

TNF-alpha and Notch signaling regulates the expression of HOXB4 and GATA3 during early T lymphopoiesis

During the early thymus colonization, Notch signaling activation on hematopoietic progenitor cells (HPCs) drives proliferation and T cell commitment. Although these processes are driven by transcription factors such as HOXB4 and GATA3, there is no evidence that Notch directly regulates their transcription. To evaluate the role of NOTCH and TNF signaling in this process, human CD34⁺ HPCs were cocultured with OP9-DL1 cells, in the presence or absence of TNF. The use of a Notch signaling inhibitor and a protein synthesis inhibitor allowed us to distinguish primary effects, mediated by direct signaling downstream Notch and TNF, from secondary effects, mediated by de novo synthesized proteins. A low and physiologically relevant concentration of TNF promoted T lymphopoiesis in OP9-DL1 cocultures. TNF positively modulated the expression of both transcripts in a Notch-dependent manner; however, GATA3 induction was mediated by a direct mechanism, while HOXB4 induction was indirect. Induction of both transcripts was repressed by a GSK3β inhibitor, indicating that activation of canonical Wnt signaling inhibits rather than induces their expression. Our study provides novel evidences of the mechanisms integrating Notch and TNF-alpha signaling in the transcriptional induction of GATA3 and HOXB4. This mechanism has direct implications in the control of self-renewal, proliferation, commitment, and T cell differentiation.

Human eosinophil activin A synthesis and mRNA stabilization are induced by the combination of IL-3 plus TNF

Eosinophils contribute to immune regulation and wound healing/fibrosis in various diseases including asthma. Growing appreciation for the role of activin A in such processes led us to hypothesize that eosinophils are a source of this TGF-β superfamily member. TNFα (TNF) induces activin A by other cell types and is often present at the site of allergic inflammation along with the eosinophil activating common β (βc) chain-signaling cytokines (IL-5, IL-3, GM-CSF). Previously, we established that the combination of TNF plus a βc chain-signaling cytokine synergistically induces eosinophil synthesis of the remodeling enzyme MMP-9. Therefore, eosinophils were stimulated ex vivo by these cytokines and in vivo through an allergen-induced airway inflammatory response. In contrast to IL-5+TNF or GM-CSF+TNF, the combination of IL-3+TNF synergistically induced activin A synthesis and release by human blood eosinophils. IL-3+TNF enhanced activin A mRNA stability, which required sustained signaling of pathways downstream of p38 and ERK MAP kinases. In vivo, following segmental airway allergen challenge of subjects with mild allergic asthma, activin A mRNA was upregulated in airway eosinophils compared to circulating eosinophils, and ex vivo, circulating eosinophils tended to release activin A in response to IL-3+TNF. These data provide evidence that eosinophils release activin A and that this function is enhanced when eosinophils are present in an allergen-induced inflammatory environment. Moreover, these data provide the first evidence for post-transcriptional control of activin A mRNA. We propose that, an environment rich in IL-3+TNF will lead to eosinophil–derived activin A, which plays an important role in regulating inflammation and/or fibrosis.

Embryonic-maternal cross-talk via exosomes: potential implications

A myriad of locally produced factors into the microenvironment of the reproductive tract is regulated, not one-way but rather, through embryonic-maternal cross-talk. In this mini-review, we focused on the exosomes, which are cell-derived vesicles of 30-100 nm in diameter, as a communicating language facilitating this dialog. These nanovesicles are secreted from pre-implantation embryos, oviduct epithelium, and endometrium as well as from the placenta, and contain proteins, messenger RNA (mRNA), microRNA, and DNA cargoes, and have pleiotropic effects on both embryonic and maternal environments. A better understanding of the molecular mechanisms mediating this cross-talk will lead to the development of new regulating agents, with novel diagnostic, biological, and therapeutic potential for either supporting or hindering the normal reproductive functions.

Improvement of cloned embryos development by co-culturing with parthenotes: a possible role of exosomes/microvesicles for embryos paracrine communication

It is well known that embryos cultured in a group can create a microenvironment through secretion of autocrine and paracrine factors that can support and improve the embryos' development when compared to the embryos cultured individually. In this study, we used a co-culture system for paracrine communication between different kinds of embryos. The results showed that co-culture of porcine parthenogenetic (PA) embryos significantly improved the in vitro development of cloned (nuclear transfer, NT) embryos. To reveal the possible mechanism of communication between the two groups, we isolated exosomes/microvesicles (EXs/MVs) from the PA embryos conditioned medium (PA-CM) through differential centrifugation and identified them through transmission electron microscope and immunoflourescence against exosomal/membrane marker CD9. Furthermore, these EXs/MVs were found to contain mRNA of pluripotency genes (Oct4, Sox2, Klf4, c-Myc, and Nanog), and the PKH67-labeled EXs/MVs could be internalized by the NT embryos. The current study demonstrates that cloned embryos' developmental competence can be improved through co-culturing with PA embryos and revealed, for the first time, that in vitro-produced embryos can secrete EXs/MVs as a possible communication tool within their microenvironment. Moreover, it provides a new paradigm for embryo-to-embryo communication in vitro.

A versatile ribosomal protein promoter-based reporter system for selective assessment of RNA stability and post-transcriptional control

Assessment of post-transcriptional control relies on use of transcriptional inhibitors and is masked by copious and cryptic transcriptional induction. We screened several cellular promoters that are constitutively active yet noninducible to external stimuli. The ribosomal protein RPS30 promoter was chosen; its TATA signal and sp1 site location were optimized. The modified promoter (RPS30M) is selective to post-transcriptional effects of AU-rich elements (ARE) in the 3'UTR, while it is not transcriptionally responsive to a wide variety of agents including pro-inflammatory cytokines and RNA-binding proteins. Specific cis-acting elements can be appended to RPS30M by a cloning-free approach to allow coupled transcriptional/post-transcriptional assessment, as demonstrated with NF-kappaB and beta-catenin/wnt signaling experiments. Moreover, efficient tetracycline-regulated RPS30M was created for quantitative assessment of the half-lives of mRNAs containing AREs. The described approach provides enhanced versatility and suitability for selective post-transcriptional assessment with or without transcriptional induction.

Defective histone acetylation is responsible for the diminished expression of cyclooxygenase 2 in idiopathic pulmonary fibrosis

Diminished cyclooxygenase 2 (COX-2) expression in fibroblasts, with a resultant defect in the production of the antifibrotic mediator prostaglandin E(2), plays a key role in the pathogenesis of idiopathic pulmonary fibrosis (IPF). Here, we have characterized the molecular mechanism. We found that COX-2 mRNA levels in fibroblasts from patients with IPF (F-IPF) were significantly lower than those in fibroblasts from nonfibrotic lungs (F-NL) after transforming growth factor beta1 and interleukin-1beta treatment but that COX-2 mRNA degradation rates were similar, suggesting defective transcription. A reporter gene assay showed that there were no clear differences between F-IPF and F-NL in transcription factor involvement and activation in COX-2 gene transcription. However, a chromatin immunoprecipitation assay revealed that transcription factor binding to the COX-2 promoter in F-IPF was reduced compared to that in F-NL, an effect that was dynamically linked to reduced histone H3 and H4 acetylation due to decreased recruitment of histone acetyltransferases (HATs) and increased recruitment of transcriptional corepressor complexes to the COX-2 promoter. The treatment of F-IPF with histone deacetylase (HDAC) inhibitors together with cytokines increased histone H3 and H4 acetylation. Both HDAC inhibitors and the overexpression of HATs restored cytokine-induced COX-2 mRNA and protein expression in F-IPF. The results demonstrate that epigenetic abnormality in the form of histone hypoacetylation is responsible for diminished COX-2 expression in IPF.

Effect of uncoupling endothelial nitric oxide synthase on calcium homeostasis in aged porcine endothelial cells

AIMS

The requirement of endothelial NO synthase (NOS3) calcium to produce NO is well described, although the effect of NO on intracellular calcium levels [Ca(2+)](i) is still confusing. Therefore, NO and [Ca(2+)](i) cross-talk were studied in parallel in endothelial cells possessing a functional or a dysfunctional NO pathway.

METHODS AND RESULTS

Dysfunctional porcine endothelial cells were obtained either in vitro by successive passages or in vivo from regenerated endothelium 1 month after coronary angioplasty. Activity of NOS3 was characterized by conversion of arginine to citrulline, BH(4) intracellular availability, cGMP, and superoxide anion production. Imaging of the Ca(2+) indicator FURA 2-AM was recorded and sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) pump activity was analysed by (45)Ca(2+) uptake into cells. In endothelial cells with a functional NO pathway, NOS3 inhibition increased [Ca(2+)](i) and, conversely, an NO donor decreased it. In aged cells with an uncoupled NOS3 as shown by the reduced BH(4) level, the increase in superoxide anion and the lower production of cGMP and the decrease in NO bioavailability were linearly correlated with the increase in basal [Ca(2+)](i). Moreover, when stimulated by bradykinin, the calcium response was reduced while its decay was slowed down. These effects on the calcium signalling were abolished in calcium-free buffer and were similarly induced by SERCA inhibitors. In aged cells, NO improved the reduced SERCA activity and tended to normalize the agonist calcium response.

CONCLUSION

In control endothelial cells, NO exerts a negative feedback on cytosolic Ca(2+) homeostasis. In aged cells, uncoupled NOS3 produced NO that was insufficient to control the [Ca(2+)](i). Consequently, under resting conditions, SERCA activity decreased and [Ca(2+)](i) increased. These alterations were reversible as exogenous NO, in a cGMP-independent way, refilled intracellular calcium stores, reduced calcium influx, and improved the agonist-evoked calcium response. Therefore, prevention of the decrease in NO in dysfunctional endothelium would normalize the calcium-dependent functions.

Secretion of biologically active recombinant human granulocyte-macrophage colony-stimulating factor by transduced gastric cancer cells

PURPOSE

Gastric cancer has the highest incidence rate among cancers in Asia. The advanced type of signet ring cell carcinoma has poor prognosis compared to other types of gastric cancer. The immuno-gene therapy with cytokine-based tumor vaccines has not yet been investigated for gastric cancer. The granulocyte macrophage colony-stimulating factor (GM-CSF)-based tumor vaccine has been demonstrated as the most potent stimulator for specific and long-lasting systemic tumor immunity.

MATERIALS AND METHODS

In the present study, KATO III cells, the human signet ring cell gastric carcinoma cell line, were genetically modified by the transduction with the human GM-CSF cDNA or the modified hGM-CSF in replication-deficient retroviruses. The genomic integrations and mRNA expressions of the transgenes were determined by Southern and Northern blot analyses.

RESULTS

Wild type (wt) or modified hGM-CSF was integrated into the genome of KATO III cells. The modified hGM-CSF mRNA was more stable than that of wt. The KATO III cells with the modified hGM-CSF produced higher level of hGM-CSF (12.4-19 ng/10(6)cells/48hrs) than that with wt hGM-CSF, when determined by enzyme-linked immunosorbent assay (ELISA). The secreted recombinant hGM-CSF could support the proliferation of the GM-CSF-dependent cell line, indicating that the hGM-CSF secreted by the transduced KATO III cells has biological activities. Irradiated, transduced KATO III cells continued to secret hGM-CSF without proliferation.

CONCLUSION

Our results suggest that GM-CSF secreting KATO III cells could be tested for the treatment of gastric cancer as an allogeneic tumor vaccine as a part of immunotherapeutic treatment.

Limitation in use of luciferase reporter genes for 3'-untranslated region analysis

Luciferase reporter genes are widely used for the functional characterization of regulatory elements in 3'-untranslated region (3'-UTR). Using a transient expression assay system with pancreatic cell lines, we demonstrated that luciferase reporter gene constructs show not only the elements with special sequences in 3'-UTR that can affect luciferase activity, but also elements containing random sequences that were ligated into the same site. The extent of the decrease in luciferase activity was dependent on the length of the DNA fragments. Our findings strongly suggested a need to re-examine the 3'-UTR characterizations of many eukaryotic genes which have been studied to date with luciferase reporter genes.

Circadian changes in granulocyte-macrophage colony-stimulating factor message in circulating eosinophils

BACKGROUND

Granulocyte-macrophage colony-stimulating factor (GM-CSF), which stimulates eosinophil recruitment, activation, and survival, is expressed by activated eosinophils. Although eosinophil recruitment and enhanced survival have been associated with nocturnal asthma (NA), the contribution of GM-CSF to NA is unknown.

OBJECTIVE

To determine whether circulating eosinophil GM-CSF expression correlates with the symptoms of NA.

METHODS

The GM-CSF messenger RNA (mRNA) expression at 4 PM and 4 AM was determined by reverse-transcriptase polymerase chain reaction with Southern blot analysis in subjects with and without NA and in controls.

RESULTS

A total of 142 asthma subjects were screened for nocturnal asthma with 1-week home peak expiratory flow rate (PEFR) monitoring. Eleven subjects had NA (>20% diurnal variation in PEFR on 4 of 7 days), and 6 met the criteria for non-NA (<10% diurnal variation in PEFR on 7 of 7 days); 8 controls were studied. In subjects with NA, GM-CSF mRNA expression in circulating eosinophils increased 3-fold at 4 AM compared with 4 PM. Diurnal changes in GM-CSF mRNA expression were not detected in the non-NA and control groups.

CONCLUSIONS

Day-night variation in eosinophil GM-CSF expression is associated with circadian variation in airway function in asthma, a key manifestation of asthma severity.

Assembly of AUF1 with eIF4G-poly(A) binding protein complex suggests a translation function in AU-rich mRNA decay

An AU-rich element (ARE) located in the 3'-untranslated region of many short-lived mRNAs functions as an instability determinant for these transcripts. AUF1/hnRNP D, an ARE-binding protein family consisting of four isoforms, promotes rapid decay of ARE-mRNAs. The mechanism by which AUF1 promotes rapid decay of ARE-mRNA is unclear. AUF1 has been shown to form an RNase-resistant complex in cells with the cap-initiation complex and heat shock proteins Hsp70 and Hsc70, as well as other unidentified factors. To understand the function of the AUF1 complex, we have biochemically investigated the association of AUF1 with the components of the translation initiation complex. We used purified recombinant proteins and a synthetic ARE RNA oligonucleotide to determine the hierarchy of protein interactions in vitro and the effect of AUF1 binding to the ARE on the formation of protein complexes. We demonstrate that all four AUF1 protein isoforms bind directly and strongly to initiation factor eIF4G at a C-terminal site regardless of AUF1 interaction with the ARE. AUF1 is shown to directly interact with poly(A) binding protein (PABP), both independently of eIF4G and in a complex with eIF4G. AUF1-PABP interaction is opposed by AUF1 binding to the ARE or Hsp70 heat shock protein. In vivo, AUF1 interaction with PABP does not alter PABP stability. Based on these and other data, we propose a model for the molecular interactions of AUF1 that involves translation-dependent displacement of AUF1-PABP complexes from ARE-mRNAs with possible unmasking of the poly(A) tail.

Optimized transfection of mRNA transcribed from a d(A/T)100 tail-containing vector

Studies employing mRNA transfection are currently limited by a lack of transcription vectors for generating a long poly(A) tail-containing mRNA and published methods for efficient mRNA transfection. We have constructed a transcription vector containing firefly luciferase gene (pBS-FLuc-A100) to generate luciferase mRNA with A100 tail followed by no heterologous sequence. The pBS-FLuc-A100 was propagated in XL1-Blue, in which the plasmid was more stable than in other bacterial strains. Optimal mRNA transfection conditions were determined using TransMessenger Transfection Reagent (Qiagen) and yeast tRNA as a carrier. Firefly luciferase expression, which peaked at about 12 h post-transfection, was detected with as little as 5 ng mRNA and was linear with mRNA amount up to 100 ng. When cells were transfected with luciferase mRNA containing different lengths of poly(A) tail, luciferase expression increased proportionally with poly(A) tail length up to 60A residues and then declined. Cell lines from monkey, mouse, and rat were transfected efficiently by this method. Like cellular ferritin heavy chain mRNA, which contains an iron response element in its 5'UTR, translation of transfected luciferase mRNA containing the 5'UTR of ferritin mRNA was iron-dependent. Our results demonstrate that the poly(A) vector and the transcription method described will be useful to study the regulation of gene expression at the mRNA level by UTRs.

The MHC class II transactivator (CIITA) mRNA stability is critical for the HLA class II gene expression in myelomonocytic cells

The human promyelocytic U937 cells express detectable levels of MHC class II (MHC-II) molecules. Treatment with 12-o--tetradecanoyl phorbol 13-acetate (TPA), inducing macrophage-like differentiation, produces a dramatic decrease of MHC-II expression as result of down-modulation of the activation of immune response gene 1 (AIR-1)-encoded MHC-II transactivator (CIITA). This event is specific, as MHC class I remains unaffected. Similar results are observed with U937 cells expressing an exogenous full-length CIITA. Molecular studies demonstrate that TPA treatment affects the stability of CIITA mRNA rather than CIITA transcription. Importantly, cis-acting elements within the distal 650 bp of the 1035-bp 3' untranslated region (3'UTR, nucleotides 3509-4543) are associated to transcript instability. Transcription inhibitors actinomycin D and 5,6-dichlororibofuranosyl benzimidazole, and the translation inhibitor cycloheximide significantly rescue the accumulation of CIITA mRNA in TPA-treated cells. A similar effect is also observed after treatment with staurosporine and the PKC-specific inhibitor GF109203X. The instability of CIITA mRNA produced by TPA in U937 cells is not seen in B cells. These results demonstrate the presence of an additional level of control of MHC-II expression in the macrophage cell lineage depending upon the control of CIITA mRNA stability, most likely mediated by differentiation-induced, 3'UTR-interacting factors which require kinase activity for their destabilizing function.

Verge: a novel vascular early response gene

Vascular endothelium forms a continuous, semipermeable barrier that regulates the transvascular movement of hormones, macromolecules, and other solutes. Here, we describe a novel immediate early gene that is expressed selectively in vascular endothelial cells, verge (vascular early response gene). Verge protein includes an N-terminal region of approximately 70 amino acids with modest homology (approximately 30% identity) to Apolipoprotein L but is otherwise unique. Verge mRNA and protein are induced selectively in the endothelium of adult vasculature by electrical or chemical seizures. Verge expression appears to be responsive to local tissue conditions, because it is induced in the hemisphere ipsilateral to transient focal cerebral ischemia. In contrast to the transient expression in adult, Verge mRNA and protein are constitutively expressed at high levels in the endothelium of developing tissues (particularly heart) in association with angiogenesis. Verge mRNA is induced in cultured endothelial cells by defined growth factors and hypoxia. Verge protein is dramatically increased by cysteine proteinase inhibitors, suggesting rapid turnover, and is localized to focal regions near the periphery of the cells. Endothelial cell lines that stably express Verge form monolayers that show enhanced permeability in response to activation of protein kinase C by phorbol esters. This response is accompanied by reorganization of the actin cytoskeleton and the formation of paracellular gaps. These studies suggest that Verge functions as a dynamic regulator of endothelial cell signaling and vascular function.

Molecular strategies for improving cytokine transgene expression in normal and malignant tissues

The augmentation and optimization of specific targeted transgene expression systems are important strategies for clinical research into gene therapy and DNA vaccination, due to safety considerations. In this study, we introduced 3' untranslated regions and transcriptional control modifications and direct tandem or combinational vector design strategies into a number of specific cytokine cDNA expression plasmids. The experiments were performed in parallel using both in vivo and in vitro transgene expression systems. In vivo studies were carried out using gene gun delivery of test vectors into mouse skin tissues. A combination of specific cell lines and fresh cell explants were used for in vitro and ex vivo transgene expression assay systems. The results from these comparative experiments demonstrated that a number of molecular biology manipulations can be readily adapted to define and significantly enhance the level or/and duration of transgene expression for a group of clinically relevant cytokine genes, with very similar effects for both in vivo and in vitro test systems. This cytokine transgene expression system may offer a favorable means for improving the efficiency of cytokine gene therapy and DNA vaccines in future clinical studies.

Hyaluronic acid or TNF-alpha plus fibronectin triggers granulocyte macrophage-colony-stimulating factor mRNA stabilization in eosinophils yet engages differential intracellular pathways and mRNA binding proteins

Eosinophils (Eos) accumulate in airways and lung parenchyma of active asthmatics. GM-CSF is a potent inhibitor of Eos apoptosis both in vitro and in vivo and is produced by activated fibroblasts, mast cells, T lymphocytes as well as Eos. Cytokine release by Eos is preceded by GM-CSF mRNA stabilization induced by TNF-alpha plus fibronectin. Hyaluronic acid (HA) is a major extracellular matrix proteoglycan, which also accumulates in the lung during asthma exacerbations. In this study we have analyzed the effects of HA on Eos survival and GM-CSF expression. We demonstrate that like TNF-alpha plus fibronectin, HA stabilizes GM-CSF mRNA, increases GM-CSF secretion, and prolongs in vitro Eos survival. GM-CSF mRNA stabilization accounts for most of the observed GM-CSF mRNA accumulation and protein production. Unlike TNF-alpha plus fibronectin, GM-CSF mRNA stabilization induction by HA requires continuous extracellular signal-regulated kinase phosphorylation. Finally, to identify potential protein regulators responsible for GM-CSF mRNA stabilization, immunoprecipitation-RT-PCR studies revealed increased GM-CSF mRNA associated with YB-1, HuR, and heterogeneous nuclear ribonucleoprotein (hnRNP) C after TNF-alpha plus fibronectin but only hnRNP C after HA. Thus, our data suggest that both TNF-alpha plus fibronectin and HA, which are relevant physiological effectors in asthma, contributes to long-term Eos survival in vivo by enhancing GM-CSF production through two different posttranscriptional regulatory pathways involving extracellular signal-regulated kinase phosphorylation and RNA binding proteins YB-1, HuR, and hnRNP C.

Selective degradation of AU-rich mRNAs promoted by the p37 AUF1 protein isoform

An AU-rich element (ARE) consisting of repeated canonical AUUUA motifs confers rapid degradation to many cytokine mRNAs when present in the 3' untranslated region. Destabilization of mRNAs with AREs (ARE-mRNAs) is consistent with the interaction of ARE-binding proteins such as tristetraprolin and the four AUF1 isoforms. However, the association of the AUF1-mRNA interaction with decreased ARE-mRNA stability is correlative and has not been directly tested. We therefore determined whether overexpression of AUF1 isoforms promotes ARE-mRNA destabilization and whether AUF1 isoforms are limiting components for ARE-mRNA decay. We show that the p37 AUF1 isoform and, to a lesser extent, the p40 isoform possess ARE-mRNA-destabilizing activity when overexpressed. Surprisingly, overexpressed p37 AUF1 also destabilized reporter mRNAs containing a noncanonical but AU-rich 3' untranslated region. Since overexpressed p37 AUF1 could interact in vivo with the AU-rich reporter mRNA, AUF1 may be involved in rapid turnover of mRNAs that lack canonical AREs. Moreover, overexpression of p37 AUF1 restored the ability of cells to rapidly degrade ARE-mRNAs when that ability was saturated and inhibited by overexpression of ARE-mRNAs. Finally, activation of ARE-mRNA decay often involves a translation-dependent step, which was eliminated by overexpression of p37 AUF1. These data indicate that the p37 AUF1 isoform and, to some extent, the p40 isoform are limiting factors that facilitate rapid decay of AU-rich mRNAs.

RNase L mediates transient control of the interferon response through modulation of the double-stranded RNA-dependent protein kinase PKR

The transient control of diverse biological responses that occurs in response to varied forms of stress is often a highly regulated process. During the interferon (IFN) response, translational repression due to phosphorylation of eukaryotic initiation factor 2alpha, eIF2alpha, by the double-stranded RNA-dependent protein kinase, PKR, constitutes a means of inhibiting viral replication. Here we show that the transient nature of the IFN response against acute viral infections is regulated, at least in part, by RNase L. During the IFN antiviral response in RNase L-null cells, PKR mRNA stability was enhanced, PKR induction was increased, and the phosphorylated form of eIF2alpha appeared with extended kinetics compared with similarly treated wild type cells. An enhanced IFN response in RNase L-null cells was also demonstrated by monitoring inhibition of viral protein synthesis. Furthermore, ectopic expression of RNase L from a plasmid vector prevented the IFN induction of PKR. These results suggest a role for RNase L in the transient control of the IFN response and possibly of other cytokine and stress responses.

Delineation of a novel pathway that regulates CD154 (CD40 ligand) expression

The expression of CD154 (CD40 ligand) by activated T lymphocytes plays a central role in humoral and cellular immunity. The fundamental importance of this protein in mounting an immune response has made it an attractive target for immunomodulation. Several studies have demonstrated that CD154 expression is regulated at the level of mRNA turnover in a manner distinct from other cytokine genes. We have purified, sequenced, and characterized the two major proteins that bind the CD154 3' untranslated region (3'UTR) as members of the polypyrimidine tract binding protein (PTB) family. One of these proteins is a previously unreported alternatively spliced PTB isoform, which we call PTB-T. These proteins interact with a polypyrimidine-rich region within the CD154 3'UTR that lacks any known cis-acting instability elements. The polypyrimidine-rich region of the CD154 3'UTR was both necessary and sufficient to mediate changes in reporter gene expression and mRNA accumulation, indicating the presence of a novel cis-acting instability element. The presence of a cis-acting instability element in the polypyrimidine-rich region was confirmed using a tetracycline-responsive reporter gene approach. The function of this cis-acting element appears to be dependent on the relative cytoplasmic levels of PTB and PTB-T. Cotransfection of vectors encoding PTB-T consistently decreased the CD154 3'UTR-dependent luciferase expression. In contrast, transfection of plasmids encoding PTB tended to increase CD154 3'UTR-dependent luciferase expression. Thus, the CD154 3'UTR contains a novel cis-acting element whose function is determined by the binding of PTB and PTB-T. These data identify a specific pathway that regulates CD154 expression that can potentially be selectively targeted for the treatment of autoimmune disease and allograft rejection.

Zygotic control of maternal cyclin A1 translation and mRNA stability

Cyclin mRNAs are unstable in the adult cell cycle yet are stable during the first 12 cell divisions in Xenopus laevis. We recently reported that cyclin A1 and B2 maternal mRNAs are deadenylated upon completion of the 12th division (Audic et al. [2001] Mol. Cell Biol. 21:1662-1671). Deadenylation is mediated by the 3' untranslated region (UTR) of the mRNA and precedes the terminal disappearance of the cyclin proteins, with both processes requiring zygotic transcription. The purpose of the current study was (1) to ask whether deadenylation leads to translational repression and/or destabilization of endogenous cyclin A1 and B2 mRNAs, and (2) to further characterize the regulatory sequences required. We show that zygote-driven deadenylation leads to translational repression and mRNA destabilization. A 99-nucleotide region of the 3'UTR of the cyclin A1 mRNA mediates both deadenylation and destabilization. Surprisingly, two AU-rich consensus elements within this region are dispensable for this activity. These results suggest that zygote-dependent deadenylation, translational repression, and mRNA destabilization by means of novel 3'UTR elements contribute to the disappearance of maternal cyclins. They also suggest that translational control of cyclins may play a role in the transition to the adult cell cycle. These data concur with previous studies in Drosophila showing that zygote-mediated degradation of maternal cdc25 mRNA may be a general mechanism whereby transition to the adult cell cycle proceeds.

Beta -Globin mRNA decay in erythroid cells: UG site-preferred endonucleolytic cleavage that is augmented by a premature termination codon

Previous work showed that human beta-globin mRNAs harboring a premature termination codon are degraded in the erythroid tissues of mice to products that lack sequences from the mRNA 5' end but contain a 5' cap-like structure. Whether these decay products are the consequence of endonucleolytic or 5'-to-3' exonucleolytic activity is unclear. We report that this beta-globin mRNA decay pathway is recapitulated in cultured mouse erythroleukemia (MEL) cells and targets nonsense-free mRNA to a lesser extent than nonsense-containing mRNA. S1 nuclease mapping and primer extension demonstrated that 70-80% of decay product 5' ends contain a UG dinucleotide. Detection of upstream counterparts of these decay products indicates that they are generated by endonucleolytic activity. Both crude and partially purified polysome extracts prepared from MEL cells contain an endonucleolytic activity that generates decay products comparable to those observed in vivo. These data suggest that an endonuclease with preference for UG dinucleotides is involved in the degradation of nonsense-containing and, to a lesser extent, nonsense-free human beta-globin mRNAs in mouse erythroid cells.

Y box-binding factor promotes eosinophil survival by stabilizing granulocyte-macrophage colony-stimulating factor mRNA

Short-lived peripheral blood eosinophils are recruited to the lungs of asthmatics after allergen challenge, where they become long-lived effector cells central to disease pathophysiology. GM-CSF is an important cytokine which promotes eosinophil differentiation, function, and survival after transit into the lung. In human eosinophils, GM-CSF production is controlled by regulated mRNA stability mediated by the 3' untranslated region, AU-rich elements (ARE). We identified human Y box-binding factor 1 (YB-1) as a GM-CSF mRNA ARE-specific binding protein that is capable of enhancing GM-CSF-dependent survival of eosinophils. Using a transfection system that mimics GM-CSF metabolism in eosinophils, we have shown that transduced YB-1 stabilized GM-CSF mRNA in an ARE-dependent mechanism, causing increased GM-CSF production and enhanced in vitro survival. RNA EMSAs indicate that YB-1 interacts with the GM-CSF mRNA through its 3' untranslated region ARE. In addition, endogenous GM-CSF mRNA coimmunoprecipitates with endogenous YB-1 protein in activated eosinophils but not resting cells. Thus, we propose a model whereby activation of eosinophils leads to YB-1 binding to and stabilization of GM-CSF mRNA, ultimately resulting in GM-CSF release and prolonged eosinophil survival.

In-vivo particle mediated delivery of mRNA to mammalian tissues: ballistic and biologic effects

Biolistic transmission of mRNA provides transient gene therapy to in vivo organs. This study documents particle mediated mRNA transmission to a solid organ and wound healing model using the mRNA of Green Fluorescent Protein to determine optimal delivery parameters. Renal function, bullet penetration, cellular injury, and Green Fluorescent Protein synthesis were quantified. Chimeric human epidermal growth factor-FLAG epitope cDNA or mRNA was transmitted to wounds in normal or steroid treated animals. Wound bursting strength, human epidermal growth factor-FLAG, and collagen synthesis were determined. Injury and bullet penetration correlated with the delivery velocity and bullet size. Optimal delivery parameters were established which provided widespread Green Fluorescent Protein synthesis. Human epidermal growth factor-FLAG treatment significantly increased collagen content and wound breaking strength in normal and steroid treated animals. FLAG protein synthesis was evident in mRNA treated fascia following treatment. We found the gene gun provides a novel method for efficient, in vivo delivery of mRNA-based therapeutic strategies to mammalian organs with minimal histologic damage allowing transient expression of protein in in vivo target tissues. Co-delivery of Green Fluorescent Protein mRNA may provide a useful positive control to determine effective transmission. Biolistic transmission of human epidermal growth factor-FLAG mRNA provides increased tissue epidermal growth factor levels and accelerates wound healing in normal and steroid exposed animals.

Granulocyte macrophage-colony-stimulating factor mRNA is stabilized in airway eosinophils and peripheral blood eosinophils activated by TNF-alpha plus fibronectin

Airway eosinophils show prolonged in vitro survival compared with peripheral blood eosinophils (PBEos). Recent studies have shown that autocrine production and release of GM-CSF is responsible for enhanced survival, but the mechanisms controlling cytokine production remain obscure. We compared GM-CSF mRNA decay in eosinophils from bronchoalveolar lavage (BALEos) after allergen challenge or from PBEos. BALEos showed prolonged survival in vitro (60% at 4 days) and expressed GM-CSF mRNA. The enhanced survival of BALEos was 75% inhibited at 6 days by neutralizing anti-GM-CSF Ab. Based on transfection studies, GM-CSF mRNA was 2.5 times more stable in BALEos than in control PBEos. Treatment of PBEos with fibronectin and TNF-alpha increased their in vitro survival, GM-CSF mRNA expression, and GM-CSF mRNA stability to a comparable level as seen in BALEos. These data suggest that TNF-alpha plus fibronectin may increase eosinophil survival in vivo by controlling GM-CSF production at a posttranscriptional level.

Post-transcriptional control of cyclooxygenase-2 gene expression. The role of the 3'-untranslated region

The cyclooxygenase (COX)-2 enzyme is responsible for increased prostaglandin formation in inflammatory states and is the major target of nonsteroidal anti-inflammatory drugs. Normally COX-2 expression is tightly regulated, however, constitutive overexpression plays a key role in colon carcinogenesis. To understand the mechanisms controlling COX-2 expression, we examined the ability of the 3'-untranslated region of the COX-2 mRNA to regulate post-transcriptional events. When fused to a reporter gene, the 3'-untranslated region mediated rapid mRNA decay (t(1/2) = 30 min), which was comparable to endogenous COX-2 mRNA turnover in serum-induced fibroblasts treated with actinomycin D or dexamethasone. Deletion analysis demonstrated that a conserved 116-nucleotide AU-rich sequence element (ARE) mediated mRNA degradation. In transiently transfected cells, this region inhibited protein synthesis approximately 3-fold. However, this inhibition did not occur through changes in mRNA stability since mRNA half-life and steady-state mRNA levels were unchanged. RNA mobility shift assays demonstrated a complex of cytoplasmic proteins that bound specifically to the ARE, and UV cross-linking studies identified proteins ranging from 90 to 35 kDa. Fractionation of the cytosol showed differential association of ARE-binding proteins to polysomes and S130 fractions. We propose that these factors influence expression at a post-transcriptional step and, if dysregulated, may increase COX-2 protein as detected in colon cancer.

Growth factor-mediated stabilization of amyloid precursor protein mRNA is mediated by a conserved 29-nucleotide sequence in the 3'-untranslated region

Using a cell-free translation system, we previously demonstrated that the turnover and translation of amyloid precursor protein (APP) mRNA was regulated by a 29-nucleotide instability element, located 200 nucleotides downstream from the stop codon. Here we have examined the regulatory role of this element in primary human capillary endothelial cells under different nutritional conditions. Optimal proliferation required a growth medium (endothelial cell growth medium) supplemented with epidermal, basic fibroblast, insulin-like, and vascular endothelial growth factors. In vitro transcribed mRNAs with the 5'-untranslated region (UTR) and coding region of beta-globin and the entire 3'-UTR of APP 751 were transfected into cells cultured in endothelial cell growth medium. Wild-type globin-APP mRNA containing an intact APP 3'-UTR and mutant globin-APP mRNA containing a mutated 29-nucleotide element decayed with identical half-lives (t 1/2 = 60 min). Removal of all supplemental growth factors from the culture medium significantly accelerated the decay of transfected wild-type mRNA (t 1/2 = 10 min), but caused only a moderate decrease in the half-life of transfected mutant mRNA (t 1/2 = 40 min). We therefore conclude that the 29-nucleotide 3'-UTR element is an mRNA destabilizer whose function can be inhibited by inclusion of the aforementioned mixture of growth factors in the culture medium.

Primary Peripheral Blood Eosinophils Rapidly Degrade Transfected Granulocyte-Macrophage Colony-Stimulating Factor mRNA

Despite increasing interest, very little information exists regarding gene regulatory mechanisms employed by eosinophils. This largely stems from the difficulty in transfecting these primary cells. In this study, we demonstrate that peripheral blood eosinophils (PBEos) can be successfully transfected with both GM-CSF cDNA and mRNA and reporter constructs by particle-mediated gene transfer. The transfection efficiency was 1.2% based on green fluorescent protein-positive cells. Promoter studies revealed CMV-driven expression vectors were initially active but rapidly quenched, while viral long terminal repeats had greater activity, indicating that certain viral constructs may be relatively poor to direct the production of transgenic proteins in PBEos. Exogenous GM-CSF mRNA was readily delivered and detected by Northern blot, permitting determination of its t1/2 in the absence of transcriptional poisons. These data show PBEos rapidly degraded GM-CSF mRNA with a t1/2 of 8 min. Mutant GM-CSF mRNAs, lacking the AUUUA motifs, were more stable, but were still rapidly degraded, suggesting the existence of accessory, destabilizing elements. We were able to measure minute amounts of intracellular GM-CSF after the transfection of mutant GM-CSF mRNA, but extracellular cytokine was below the sensitivity of our ELISA. However, the presence of secreted GM-CSF was established by in vitro, survival bioassay. In conclusion, the existence of this new technology should allow detailed studies of eosinophil-specific transcriptional and posttranscriptional regulation.

The 5'-untranslated region of GM-CSF mRNA suppresses translational repression mediated by the 3' adenosine-uridine-rich element and the poly(A) tail

Granulocyte-macrophage colony stimulating factor (GM-CSF) mRNA levels are controlled post-transcriptionally by the 3'-untranslated region (UTR) adenosine-uridine-rich element (ARE). In untransformed, resting cells, the ARE targets GM-CSF mRNA for rapid degradation, thereby significantly suppressing protein expression. We used a rabbit reticulocyte lysate (RRL) cell-free system to examine translational regulation of GM-CSF expression. We uncoupled decay rates from rates of translation by programming the RRL with an excess of mRNAs. Capped, full-length, polyadenyl-ated human GM-CSF mRNA (full-length 5'-UTR AUUUA+A90) and an ARE-modified version (full-length 5'-UTR AUGUA+A90) produced identical amounts of protein. When the 5'-UTR was replaced with an irrelevant synthetic leader sequence (syn 5'-UTR), translation of syn 5'-UTR AUUUA+A90 mRNA was suppressed by >20-fold. Mutation of the ARE or removal of the poly(A) tail relieved this inhibition. Thus, in the absence of a native 5'-UTR, the ARE and poly(A) tail act in concert to block GM-CSF mRNA translation. Substitutions of different regions of the native 5'-UTR revealed that the entire sequence was essential in maintaining the highest rates of translation. However, shorter 10-12 nt contiguous 5'-UTR regions supported 50-60% of maximum translation. The 5'-UTR is highly conserved, suggesting similar regulation in multiple species and in these studies was the dominant element regulating GM-CSF mRNA translation, overriding the inhibitory effects of the ARE and the poly(A) tail.

Expression of human fibroblast growth factor 2 mRNA is post-transcriptionally controlled by a unique destabilizing element present in the 3'-untranslated region between alternative polyadenylation sites

Fibroblast growth factor 2 (FGF-2) belongs to a family of 18 genes coding for either mitogenic differentiating factors or oncogenic proteins, the expression of which must be tightly controlled. We looked for regulatory elements in the 5823-nucleotide-long 3'-untranslated region of the FGF-2 mRNA that contains eight potential alternative polyadenylation sites. Quantitative reverse transcription-polymerase chain reaction revealed that poly(A) site utilization was cell type-dependent, with the eighth poly(A) site being used (95%) in primary human skin fibroblasts, whereas proximal sites were used in the transformed cell lines studied here. We used a cell transfection approach with synthetic reporter mRNAs to localize a destabilizing element between the first and second poly(A) sites. Although AU-rich, the FGF-2-destabilizing element had unique features: it involved a 122-nucleotide direct repeat, with both elements of the repeat being required for the destabilizing activity. These data show that short stable FGF-2 mRNAs are present in transformed cells, whereas skin fibroblasts contain mostly long unstable mRNAs, suggesting that FGF-2 mRNA stability cannot be regulated in transformed cells. The results also provide evidence of a multilevel post-transcriptional control of FGF-2 expression; such a stringent control prevents FGF-2 overexpression and permits its expression to be enhanced only in relevant physiological situations.

Lipopolysaccharide Modulates Cyclooxygenase-2 Transcriptionally and Posttranscriptionally in Human Macrophages Independently from Endogenous IL-1β and TNF-α

The pathogenesis of septicemia can be triggered by LPS, a potent stimulus for PG synthesis. The enzyme cyclooxygenase (COX) is a rate-limiting step in PG production. COX exists as two isoforms: COX-1, which is constitutively expressed in most cell types, and COX-2, which is inducible by LPS and cytokines in a variety of cells. In this study we determined the role of the proinflammatory cytokines IL-1β and TNF-α released by LPS-stimulated U937 human macrophages in the regulation of COX-2. Macrophages exposed to LPS showed a rapid and sustained expression of COX-2 mRNA and protein for up to 48 h, whereas PGE2 production was notably enhanced only after 12 h. LPS increased COX-2 gene transcription and activation of the transcription factor NF-κB in a transient manner. LPS-treated macrophages produced high levels of TNF-α and moderate amounts of IL-1β protein. However, neutralizing Abs against these cytokines had no effect on COX-2 mRNA and protein expression, nor did they affect the stability of COX-2 mRNA. Interestingly, in the presence of LPS or exogenous IL-1β, COX-2 transcripts were stabilized, and actinomycin D inhibited their degradation. Only when LPS or IL-1β was removed did COX-2 mRNA decay with a t1/2 of ≥5 h. In contrast, dexamethasone promoted a faster decay of the LPS-induced COX-2 transcripts (t1/2 = 2.5 h). These results clearly demonstrate that LPS can regulate COX-2 at both transcriptional and posttranscriptional levels independently from endogenous IL-1β and TNF-α in human macrophages.

Brain-derived peptides increase blood-brain barrier GLUT1 glucose transporter gene expression via mRNA stabilization

The present investigation studied the effect of the brain-derived peptide preparation Cerebrolysin (CI, EBEWE, Austria) on the turnover rate and gene expression of the blood-brain barrier (BBB) GLUT1 glucose transporter mRNA. Studies were performed in brain endothelial cultured cells transfected with the human (h) GLUT1 transcript. In control cells, the full length 2.8 Kb hGLUT1 mRNA was rapidly degraded following transfection, and the abundance of this transcript at 4 and 6 h was comparable to background mRNA levels seen in cells transfected without hGLUT1 mRNA. On the contrary, the decay of the hGLUT1 mRNA was stabilized in CI-treated cells resulting in a marked reduction in the fractional turnover rate (72.4 and 4.0%/h, control and CI, respectively). In parallel experiments, CI induced a significant increase in the levels of immunoreactive GLUT1 protein measured by enzyme-linked immunosorbent assay (ELISA). In conclusion, data presented here demonstrate that factors in CI increase BBB-GLUT1 transcript stability, and that this is associated with an induction of BBB-GLUT1 gene expression in brain endothelial cultured cells.

Endonucleolytic cleavage of RNA at 5' endogenous stem structures by human flap endonuclease 1

Structure-specific nucleases called 5' flap endonucleases cleave unannealed 5' arms of template-primer DNA model substrates at the start of the duplex and are involved in Okazaki fragment processing during DNA synthesis. To determine the possible use of the enzymes in RNA structure analysis, the cleavage of synthetic and native RNAs was examined using flap endonuclease 1 (Fen1) of HeLa cells. RNAs are cleaved at about 20% of the rate of DNA model substrates, and most of the cleavage sites are within 200 nucleotides of the 5' end. Hydrolysis of MFA2 mRNA of yeast shows that the cleavages are at the start of five possible stem structures of a folded secondary structure predicted on the basis of both chemical and enzymatic structure probing. 16S ribosomal RNA of Escherichia coli is cleaved at several 5' stem structures of its phylogenetically predicted folded structure. This type of RNA cleavage specificity may be very useful in secondary structure analysis in the future and also may be used by cells for specific 5' end-geared RNA cleavages.

hnRNP C increases amyloid precursor protein (APP) production by stabilizing APP mRNA

We have previously shown that heterogeneous nuclear ribonucleoprotein C (hnRNP C) and nucleolin bound specifically to a 29 nt sequence in the 3'-untranslated region of amyloid precursor protein (APP) mRNA. Upon activation of peripheral blood mononuclear cells, hnRNP C and nucleolin acquired APP mRNA binding activity, concurrent with APP mRNA stabilization. These data suggested that the regulated interaction of hnRNP C and nucleolin with APP mRNA controlled its stability. Here we have directly examined the role of the cis element and trans factors in the turnover and translation of APP mRNA in vitro . In a rabbit reticulocyte lysate (RRL) translation system, a mutant APP mRNA lacking the 29 nt element was 3-4-fold more stable and synthesized 2-4-fold more APP as wild-type APP mRNA. Therefore, the 29 nt element functioned as an APP mRNA destabilizer. RNA gel mobility shift assays with the RRL suggested the presence of endogenous nucleolin, but failed to show hnRNP C binding activity. However, wild-type APP mRNA was stabilized and coded for 6-fold more APP when translated in an RRL system supplemented with exogenous active hnRNP C. Control mRNAs lacking the 29 nt element were unaffected by hnRNP C supplementation. Therefore, occupancy of the 29 nt element by hnRNP C stabilized APP mRNA and enhanced its translation.