Arabidopsis cell-free extract, ACE, a new in vitro translation system derived from Arabidopsis callus cultures

The analysis of post-transcriptional regulatory mechanisms in plants has benefited greatly from the use of cell-free extract systems. Arabidopsis as a model system provides extensive genetic resources; however, to date a suitable cell-free translation system from Arabidopsis has not been available. In this study, we devised an Arabidopsis cell-free extract (ACE) to be used for in vitro translation studies. Protoplasts were prepared from callus cultures derived from Arabidopsis seedlings, and cell-free extracts were prepared after evacuolation of the protoplasts by Percoll gradient centrifugation. The new ACE system exhibits translation activity comparable with that of the wheat germ extract system. We demonstrated that ACE prepared from the 5'-3' exoribonuclease-deficient mutant of Arabidopsis, xrn4-5, exhibited increased stability of an uncapped mRNA as compared with that from wild-type Arabidopsis. We applied the ACE system to study post-transcriptional regulation of AtCGS1. AtCGS1 codes for cystathionine γ-synthase (CGS) that catalyzes the first committed step of methionine and S-adenosyl-l-methionine (AdoMet) biosynthesis in plants, and is feedback regulated by mRNA degradation coupled with translation elongation arrest. The ACE system was capable of reproducing translation elongation arrest and subsequent AtCGS1 mRNA degradation that are induced by AdoMet. The ACE system described here can be prepared in a month after seed sowing and will make it possible to study post-transcriptional regulation of plant genes while taking advantage of the genetics of Arabidopsis.

miR-346 controls release of TNF-α protein and stability of its mRNA in rheumatoid arthritis via tristetraprolin stabilization

TNF-α is a major cytokine implicated in rheumatoid arthritis. Its expression is regulated both at the transcriptional and posttranscriptional levels and recent data demonstrated that miRNAs are implicated in TNF-α response in macrophages. LPS-activated FLS isolated from RA patients express TNF-α mRNA but not the mature protein. This prompted us to look for miRNAs which could be implicated in this anti-inflammatory effect. Using a microarray, we found two miRNAs, miR-125b and miR-939 predicted to target the 3′-UTR of TNF-α mRNA, to be up-regulated in RA FLS in response to LPS, but their repression did not restore mature TNF-α expression in FLS. We showed previously that miR-346, which is upregulated in LPS-activated FLS, inhibited Btk expression that stabilized TNF-α mRNA. Blocking miR-346 reestablished TNF-α expression in activated FLS. Interestingly, transfection of miR-346 in LPS-activated THP-1 cells inhibited TNF-α secretion. We also demonstrated that TTP, a RNA binding protein which inhibited TNF-α synthesis, is overexpressed in activated FLS and that inhibition of miR-346 decreases its expression. Conversely, transfection of miR-346 in LPS-activated THP-1 cells increased TTP mRNA expression and inhibited TNF-α release. These results indicate that miR-346 controls TNF-α synthesis by regulating TTP expression.

Effective siRNA delivery and target mRNA degradation using an amphipathic peptide to facilitate pH-dependent endosomal escape

Effective delivery of siRNA (small interfering RNA) into the cells requires the translocation of siRNA into the cytosol. One potential delivery strategy uses cell-delivery peptides that facilitate this step. In the present paper, we describe the characterization of an amphipathic peptide that mediates the uptake of non-covalently bound siRNA into cells and its subsequent release into the cytosol. Biophysical characterization of peptide and peptide/siRNA mixtures at neutral and lysosomal (acidic) pH suggested the formation of α-helical structure only in endosomes and lysosomes. Surprisingly, even though the peptide enhanced the uptake of siRNA into cells, no direct interaction between siRNA and peptide was observed at neutral pH by isothermal titration calorimetry. Importantly, we show that peptide-mediated siRNA uptake occurred through endocytosis and, by applying novel endosomal-escape assays and cell-fractionation techniques, we demonstrated a pH-dependent alteration in endosome and lysosome integrity and subsequent release of siRNA and other cargo into the cytosol. These results indicate a peptide-mediated siRNA delivery through a pH-dependent and conformation-specific interaction with cellular membranes and not with the cargo.

Global transcriptomic profiling using small volumes of whole blood: a cost-effective method for translational genomic biomarker identification in small animals

Blood is an ideal tissue for the identification of novel genomic biomarkers for toxicity or efficacy. However, using blood for transcriptomic profiling presents significant technical challenges due to the transcriptomic changes induced by ex vivo handling and the interference of highly abundant globin mRNA. Most whole blood RNA stabilization and isolation methods also require significant volumes of blood, limiting their effective use in small animal species, such as rodents. To overcome these challenges, a QIAzol-based RNA stabilization and isolation method (QSI) was developed to isolate sufficient amounts of high quality total RNA from 25 to 500 μL of rat whole blood. The method was compared to the standard PAXgene Blood RNA System using blood collected from rats exposed to saline or lipopolysaccharide (LPS). The QSI method yielded an average of 54 ng total RNA per μL of rat whole blood with an average RNA Integrity Number (RIN) of 9, a performance comparable with the standard PAXgene method. Total RNA samples were further processed using the NuGEN Ovation Whole Blood Solution system and cDNA was hybridized to Affymetrix Rat Genome 230 2.0 Arrays. The microarray QC parameters using RNA isolated with the QSI method were within the acceptable range for microarray analysis. The transcriptomic profiles were highly correlated with those using RNA isolated with the PAXgene method and were consistent with expected LPS-induced inflammatory responses. The present study demonstrated that the QSI method coupled with NuGEN Ovation Whole Blood Solution system is cost-effective and particularly suitable for transcriptomic profiling of minimal volumes of whole blood, typical of those obtained with small animal species.

T3 rapidly modulates TSHβ mRNA stability and translational rate in the pituitary of hypothyroid rats

Whereas it is well known that T3 inhibits TSHβ gene transcription, its effects on TSHβ mRNA stability and translation have been poorly investigated. This study examined these possibilities, by evaluating the TSHβ transcripts poly(A) tail length, translational rate and binding to cytoskeleton, in pituitaries of thyroidectomized and sham-operated rats treated with T3 or saline, and killed 30 min thereafter. The hypothyroidism induced an increase of TSHβ transcript poly(A) tail, as well as of its content in ribosomes and attachment to cytoskeleton. The hypothyroid rats acutely treated with T3 exhibited a reduction of TSHβ mRNA poly(A) tail length and recruitment to ribosomes, indicating that this treatment decreased the stability and translation rate of TSHβ mRNA. Nevertheless, acute T3 administration to sham-operated rats provoked an increase of TSHβ transcripts binding to ribosomes. These data add new insight to an important role of T3 in rapidly regulating TSH gene expression at posttranscriptional level.

Mechanism of regulation of bcl-2 mRNA by nucleolin and A+U-rich element-binding factor 1 (AUF1)

The antiapoptotic Bcl-2 protein is overexpressed in a variety of cancers, particularly leukemias. In some cell types this is the result of enhanced stability of bcl-2 mRNA, which is controlled by elements in its 3'-untranslated region. Nucleolin is one of the proteins that binds to bcl-2 mRNA, thereby increasing its half-life. Here, we examined the site on the bcl-2 3'-untranslated region that is bound by nucleolin as well as the protein binding domains important for bcl-2 mRNA recognition. RNase footprinting and RNA fragment binding assays demonstrated that nucleolin binds to a 40-nucleotide region at the 5' end of the 136-nucleotide bcl-2 AU-rich element (ARE(bcl-2)). The first two RNA binding domains of nucleolin were sufficient for high affinity binding to ARE(bcl-2). In RNA decay assays, ARE(bcl-2) transcripts were protected from exosomal decay by the addition of nucleolin. AUF1 has been shown to recruit the exosome to mRNAs. When MV-4-11 cell extracts were immunodepleted of AUF1, the rate of decay of ARE(bcl-2) transcripts was reduced, indicating that nucleolin and AUF1 have opposing roles in bcl-2 mRNA turnover. When the function of nucleolin in MV-4-11 cells was impaired by treatment with the nucleolin-targeting aptamer AS1411, association of AUF1 with bcl-2 mRNA was increased. This suggests that the degradation of bcl-2 mRNA induced by AS1411 results from both interference with nucleolin protection of bcl-2 mRNA and recruitment of the exosome by AUF1. Based on our findings, we propose a model that illustrates the opposing roles of nucleolin and AUF1 in regulating bcl-2 mRNA stability.

Troglitazone, a ligand of peroxisome proliferator-activated receptor-{gamma}, stabilizes NUCB2 (Nesfatin) mRNA by activating the ERK1/2 pathway: isolation and characterization of the human NUCB2 gene

We recently identified a novel satiety peptide, nesfatin-1, containing 82 amino acids derived from the precursor peptide, nucleobindin 2 (NUCB2), from a troglitazone (TZ)-induced cDNA library. We examined the molecular mechanism underlying TZ-induced NUCB2 mRNA expression. Although TZ induced the mRNA expression in HTB185 cells, a nuclear run-on assay revealed no significant change in the transcription of the gene. Surprisingly, HTB185 cells possessed no functional peroxisome proliferator-activated receptor-gamma. We therefore examined the effect of TZ on the mRNA's stability. The half-life of NUCB2 mRNA was approximately 6 h, and incubation with TZ increased this to 27 h. Furthermore, this increase was completely inhibited by an ERK inhibitor, PD98059, and phosphorylated ERK1/2 was significantly increased after 30 min incubation with TZ. In addition, we cloned the entire NUCB2 gene and identified four adenylate/uridylate-rich elements (AREs) in the 3' untranslated region (UTR), to which several proteins of HTB185 extracts treated with TZ bound. The reporter assay fused with 3'UTR showed that the second and third AREs were crucial. Furthermore, the human NUCB2 gene spanned 55 kb and contained 14 exons and 13 introns. The transcriptional start site formed clusters around 246 bp upstream from the translational start site. We confirmed that a construct containing 5889 bp of the promoter region was very active in neuron-derived cell lines but not stimulated by TZ. These findings demonstrated a novel action of derivatives of thiazolidinediones, oral insulin-sensitizing antidiabetic agents, to stabilize the mRNA of NUCB2 through AREs in the 3'UTR by activating the ERK1/2 pathway independently of peroxisome proliferator-activated receptor-gamma.

Interaction between thymidylate synthase and its cognate mRNA in zebrafish embryos

Thymidylate synthase (TS), which catalyzes the de novo synthesis of dUMP, is an important target for cancer therapy. In this report, the effects of 5-fluorouracil (5-FU) and ZD1694 on the regulation of TS gene expression were evaluated in zebrafish embryos. Our results revealed that the expression of TS was increased by about six-fold when embryos were treated with 1.0 µM 5-FU and there was a greater than 10-fold increase in the TS protein level after treatment with 0.4 µM ZD1694. Northern blot analysis confirmed that expression of TS mRNA was identical in treated or untreated embryos. Gel shift and immunoprecipitation assays revealed that zebrafish TS was specifically bound with its cognate mRNA in vitro and in vivo. We identified a 20 nt RNA sequence, TS:N20, localized to the 5′-UTR of TS mRNA, which corresponded to nt 13–32; TS:N20 bound to the TS protein with an affinity similar to that of the full-length TS mRNA. The MFold program predicted that TS:N20 formed a stable stem-loop structure similar to that of the cis-acting element found in human TS mRNA. Variant RNAs with either a deletion or mutation in the core motif of TS:N20 were unable to bind to the TS protein. In vitro translation experiments, using the rabbit lysate system, confirmed that zebrafish TS mRNA translation was significantly repressed when an excess amount of TS protein was included in the system. Additionally, a TS stability experiment confirmed that treatment of zebrafish embryos with 5-FU could increase the TS stability significantly, and the half life of TS protein was about 2.7 times longer than in untreated embryos. Our study revealed a structural requirement for the interaction of TS RNA with TS protein. These findings also demonstrated that the increase in TS protein induced by 5-FU occurs at the post-transcriptional level and that increased stability and translation efficiency both contributed to the increase in TS protein levels induced by TS inhibitors.

The RNA binding protein Tudor-SN is essential for stress tolerance and stabilizes levels of stress-responsive mRNAs encoding secreted proteins in Arabidopsis

Tudor-SN (TSN) copurifies with the RNA-induced silencing complex in animal cells where, among other functions, it is thought to act on mRNA stability via the degradation of specific dsRNA templates. In plants, TSN has been identified biochemically as a cytoskeleton-associated RNA binding activity. In eukaryotes, it has recently been identified as a conserved primary target of programmed cell death-associated proteolysis. We have investigated the physiological role of TSN by isolating null mutations for two homologous genes in Arabidopsis thaliana. The double mutant tsn1 tsn2 displays only mild growth phenotypes under nonstress conditions, but germination, growth, and survival are severely affected under high salinity stress. Either TSN1 or TSN2 alone can complement the double mutant, indicating their functional redundancy. TSN accumulates heterogeneously in the cytosol and relocates transiently to a diffuse pattern in response to salt stress. Unexpectedly, stress-regulated mRNAs encoding secreted proteins are significantly enriched among the transcripts that are underrepresented in tsn1 tsn2. Our data also reveal that TSN is important for RNA stability of its targets. These findings show that TSN is essential for stress tolerance in plants and implicate TSN in new, potentially conserved mechanisms acting on mRNAs entering the secretory pathway.

2,3,7,8-Tetrachlorodibenzo-para-dioxin increases aromatase (CYP19) mRNA stability in MCF-7 cells

Dioxins are industrial pollutants that can be bio-accumulative in our food chain. Humans can be exposed to this class of pollutant through contaminated food, air, drinking water, etc. Displaying both pro- and anti-estrogenic properties, these pollutants are also known as endocrine disruptors. The link between breast cancer and TCDD exposure has not been resolved, although TCDD is classified as 'known human carcinogen'. Estrogen is a documented risk factor for breast carcinogenesis. In the present study, effect of 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) on estrogen synthesis was investigated in the breast cancer cells MCF-7. Our results showed that TCDD increased the aromatase activity in a time- and dose-dependent manner. Real-time PCR and western blot analysis verified the induced expression by 2-3-fold; however, gene reporter assay revealed that the promoter activity of exons I.3 and II was not elevated. Further investigation indicated that TCDD slowed down the CYP19 mRNA degradation with concurrent activation of ERK. The ERK inhibitor U0126 could reverse the extended stability of the transcripts. In summary this study demonstrated that TCDD might induce a post-transcriptional regulatory mechanism of gene expression in breast cancer cells.

Escape from hsa-miR-519c enables drug-resistant cells to maintain high expression of ABCG2

Overexpression of ABCG2 has been reported in cell lines selected for drug resistance and it is widely believed to be important in the clinical pharmacology of anticancer drugs. We and others have previously identified and validated two microRNAs (miRNA; hsa-miR-519c and hsa-miR-520h) targeting ABCG2. In this study, the shortening of the ABCG2 3' untranslated region (3'UTR) was found to be a common phenomenon in several ABCG2-overexpressing resistant cell lines, which as a result removes the hsa-miR-519c binding site and its repressive effects on mRNA stability and translation blockade, thereby contributing to drug resistance. On the other hand, reduced expression of hsa-miR-520h, previously thought to have allowed ABCG2 overexpression, was found to be caused by the sequestering of the miRNA by the highly expressed ABCG2. In drug-sensitive cells, inhibitors against hsa-miR-519c and hsa-miR-520h could augment the cytotoxic effect of mitoxantrone, suggesting a substantial role for both miRNAs in controlling ABCG2 level and thereby anticancer drug response. However, in drug-resistant cells, altering the levels of the two miRNAs did not have any effect on sensitivity to mitoxantrone. Taken together, these studies suggest that in ABCG2-overexpressing drug-resistant cells, hsa-miR-519c is unable to affect ABCG2 expression because the mRNA lacks its binding site, whereas hsa-miR-520h is sequestered and unable to limit ABCG2 expression. Given the recent observation that a truncated 3'UTR is also observed in ABCG2-overexpressing human embryonic stem cells, our results in drug-resistant cell lines suggest that 3'UTR truncation is a relatively common mechanism of ABCG2 regulation.

Human-specific induction of glutathione peroxidase-3 by proteasome inhibition in cardiovascular cells

Glutathione peroxidase-3 (GPx-3) is a key antioxidant enzyme in the plasma. GPx-3 was previously identified as the major antioxidative enzyme that was induced upon nontoxic proteasome inhibition in endothelial cells. Here, we investigated the determinants of the proteasome inhibitor-induced expression of GPx-3. Nontoxic proteasome inhibition massively upregulates GPx-3 RNA and protein in human umbilical cord vein cells within 24 h. Surprisingly, induction of GPx-3 was species-specific for human cells. The exponential upregulation of GPx-3 is mediated by transcriptional activation of the human GPx-3 promoter and, in addition, stabilization of GPx-3 mRNA: in reporter gene assays with full-length and deleted variants of the human GPx-3 promoter we identified a putative antioxidative response element (ARE) as essential and also sufficient for transcriptional activation of GPx-3 by proteasome inhibition. However, the ARE-specific antioxidative transcription factor Nrf2 is not involved in the activation of GPx-3. UV-crosslinking using the 3'UTR of GPx-3 revealed an altered protein binding pattern in the presence of proteasome inhibitors, thus indicating regulation of mRNA stability of human GPx-3. As GPx-3 is secreted into the plasma, our data point toward a borderline defense mechanism of endothelial cell-derived GPx-3 to protect the vasculature from oxidative stress.

The Th17 cytokine IL-22 induces IL-20 production in keratinocytes: a novel immunological cascade with potential relevance in psoriasis

Psoriasis is a common chronic skin disease. Recent studies demonstrated that IL-20 and IL-22, cytokines produced by keratinocytes and T cells, respectively, both inhibit keratinocyte terminal differentiation and induce psoriasis-like epidermis alterations. Here, we investigated the relationship between these mediators. Although IL-20 was not able to regulate IL-22 production, IL-22 induced IL-20 mRNA and protein in human keratinocytes. However, IL-22 had only a minimal effect, if any, on IL-19 and IL-26. Cutaneous IL-20 was also elevated in mice following IL-22 application. Accordingly, some of IL-22's effects on differentiation-regulating genes were partially mediated by an endogenous, secreted protein and attenuated by anti-IL-20 Ab. Like IL-22, IL-17A and TNF-alpha induced IL-20 in keratinocytes, whereas IFN-gamma and IL-20 itself did not. Furthermore, IL-17A and TNF-alpha individually strengthened the IL-22-induced IL-20 production. In lesional skin of psoriasis patients, highly elevated IL-20 levels strongly correlated with IL-22, and to a lesser extent, with IL-17A and TNF-alpha. As previously shown for IL-22, IL-20 blood levels correlated with the disease severity, although with a lower significance. This study demonstrates that a T-cell mediator induces a tissue cell mediator with similar effects to its own and therefore suggests the existence of a novel type of pathogenetic cascade.

Exendin-4 inhibits interleukin-1beta-induced iNOS expression at the protein level, but not at the transcriptional and posttranscriptional levels, in RINm5F beta-cells

Cytokines such as interleukin-1beta (IL-1beta) stimulate inducible nitric oxide synthase (iNOS) expression and nitric oxide overproduction leading to beta-cell damage. Meanwhile, glucagon-like peptide-1 (GLP-1) and its potent analog exendin-4 (EX-4) were well known for beta-cell proliferation. However, the protective mechanisms of GLP-1 in beta-cells exposed to cytokines were not fully elucidated. Therefore, the effects of EX-4 on the IL-1beta-induced iNOS gene expression were investigated employing RINm5F beta-cells. EX-4 inhibited IL-1beta-induced iNOS protein expression and nitrite production. However, northern blot and promoter analyses showed that EX-4 failed to inhibit IL-1beta-induced iNOS mRNA expression and iNOS promoter activity. By electrophoretic mobility shift assay (EMSA), EX-4 did not alter the binding activity of NF-kappaB to the iNOS promoter. Consistent with the EMSA result, EX-4 did not inhibit nuclear translocation of p65. We also tested the effect of EX-4 on iNOS mRNA stability. Actinomycin D chase experiments showed that EX-4 did not affect the decay rate of iNOS mRNA and the promoter assay using the construct containing 3'-untranslated region of iNOS showed that EX-4 did not alter the stability of iNOS mRNA. Meanwhile, forskolin significantly inhibited IL-1beta-induced iNOS protein, which was reversed by H-89, a protein kinase A (PKA) inhibitor. Moreover, EX-4 pretreatment restored IL-1beta-induced decrease in cAMP toward control level. Additionally, the cycloheximide chase study demonstrated that EX-4 significantly accelerated iNOS protein degradation. We therefore concluded that EX-4 inhibited IL-1beta-induced iNOS protein and nitrite production via cAMP/PKA system irrespective of both transcriptional and posttranscriptional mechanisms of iNOS gene, and this inhibitory effect of EX-4 appears to be regulated at posttranslational level.

Oleic acid-induced ADRP expression requires both AP-1 and PPAR response elements, and is reduced by Pycnogenol through mRNA degradation in NMuLi liver cells

Fatty acids stimulate lipid accumulation in parallel with increased expression of adipose differentiation-related protein (ADRP) in liver cells. Although it is generally considered that the fatty acid effect on ADRP expression is mediated by peroxisome proliferator-activated receptors (PPARs), we identified here an additional molecular mechanism using the NMuLi mouse liver nonparenchymal cell line, which expresses PPARgamma and delta but not alpha. Oleic acid (OA) and specific ligands for PPARgamma and -delta stimulated ADRP expression as well as the -2,090-bp ADRP promoter activity which encompasses the PPAR response element (PPRE) adjacent to an Ets/activator protein (AP)-1 site. When the AP-1 site was mutated, OA failed to stimulate the activity despite the presence of the PPRE, whereas ligands for PPARgamma and -delta did stimulate it and so did a PPARalpha ligand under the coexpression of PPARalpha. DNA binding of AP-1 was stimulated by OA but not by PPAR ligands. Because we previously demonstrated that Pycnogenol (PYC), a French maritime pine bark extract, suppressed ADRP expression in macrophages partly by suppression of AP-1 activity, we tested the effect of PYC on NMuLi cells. PYC reduced the OA-induced ADRP expression along with suppression of lipid droplet formation. However, PYC neither suppressed the OA-stimulated ADRP promoter activity nor DNA binding of AP-1 but, instead, reduced the ADRP mRNA half-life. All these results indicate that the effect of OA on ADRP expression requires AP-1 as well as PPRE, and PYC suppresses the ADRP expression in part by facilitating mRNA degradation. PYC, a widely used dietary supplement, could be beneficial for the prevention of excessive lipid accumulation such as hepatic steatosis.

Retinoids synergize with insulin to induce hepatic Gck expression

Hepatic GK (glucokinase) plays a key role in maintaining glucose homoeostasis. Many stimuli regulate GK activity by controlling its gene transcription. We hypothesized that endogenous lipophilic molecules modulate hepatic Gck expression. Lipophilic molecules were extracted from rat livers, saponified and re-constituted as an LE (lipophilic extract). LE synergized with insulin to induce primary hepatocyte, but not beta-cell, Gck expression in an SREBP-1c (sterol-regulatory-element-binding protein-1c)-independent manner. The dramatic induction of Gck mRNA resulted in a significant increase in GK activity. Subsequently, the active molecules were identified as retinol and retinal by MS after the purification of the active LE fractions. Retinoids synergized with insulin to induce Gck expression by the activation of both RAR [RA (retinoic acid) receptor] and RXR (retinoid X receptor). Inhibition of RAR activation completely abolished the effect of retinal. The hepatic GK specific activity and Gck mRNA levels of Zucker lean rats fed with a VAD [VA (vitamin A)-deficient] diet were significantly lower than those of rats fed with VAS (VA-sufficient) diet. Additionally, the hepatic Gck mRNA expression of Sprague-Dawley rats fed with a VAD diet was lower than that of rats fed with VA-marginal, -adequate or -supplemented diets. The reduced expression of Gck mRNA was increased after an intraperitoneal dose of RA in VAD rats. Furthermore, an intravenous injection of RA rapidly raised hepatic Gck expression in rats fed with a VAS control diet. Understanding the underlying mechanism that mediates the synergy may be helpful for developing a treatment strategy for patients with diabetes.

Melatonin down-regulates HIF-1 alpha expression through inhibition of protein translation in prostate cancer cells

Melatonin, the main secretory product of the pineal gland, has been shown to exert an oncostatic activity in cancer cells. Recently, several studies have shown that melatonin has antiangiogenic properties. However, the mechanism by which melatonin exerts antiangiogenenic effects is not understood. Hypoxia inducible factor (HIF)-1 is a transcription factor which mediates adaptive response to changes in tissue oxygenation. HIF-1 is a heterodimer formed by the association of a constitutively expressed HIF-1 beta subunit and a HIF-1 alpha subunit, the expression of which is highly regulated. In this study, pharmacologic concentrations of melatonin was found to inhibit expression of HIF-1 alpha protein under both normoxic and hypoxic conditions in DU145, PC-3, and LNCaP prostate cancer cells without affecting HIF-1 alpha mRNA levels. Consistent with the reduction in HIF-1 alpha protein levels, melatonin inhibited HIF-1 transcriptional activity and the release of vascular endothelial growth factor. We found that the suppression of HIF-1 alpha expression by melatonin correlated with dephosphorylation of p70S6K and its direct target RPS6, a pathway known to regulate HIF-1 alpha expression at the translational level. Metabolic labeling assays indicated that melatonin inhibits de novo synthesis of HIF-1 alpha protein. Taken together, these results suggest that the pharmacologic concentration of melatonin inhibits HIF-1 alpha expression through the suppression of protein translation in prostate cancer cells.

Role of ERK/mTOR signaling in TGFbeta-modulated focal adhesion kinase mRNA stability and protein synthesis in cultured rat IEC-6 intestinal epithelial cells

Increasing evidence is available showing the importance of the FAK (focal adhesion kinase) protein level in the migration and homeostasis of intestinal cells. TGFbeta (transforming growth factor beta) modulates FAK protein expression in a complex fashion not only by inducing the activation of p38 and Smad signaling resulting in increased fak promoter activity and increased FAK protein levels, but also by activating ERK (extracellular signal regulated kinases), p38, and the Smad pathway. We show that the blockade of ERK signaling by a specific MEK (MAPK kinase) inhibitor attenuates TGFbeta-induced FAK mRNA stability and reduces FAK protein levels in rat IEC-6 intestinal epithelial cells. The mTOR (mammalian target of rapamycin)-specific inhibitor rapamycin and small interfering RNAs for mTOR and p70(S6) kinase also block TGFbeta-induced FAK protein synthesis. Furthermore, we have found that a TGFbeta-induced increase in wound closures in monolayers of these cells is abolished in the presence ERK or mTOR inhibition. Thus, TGFbeta also modulates FAK protein levels in cultured rat IEC-6 intestinal epithelial cells via ERK activation, acting at the transcriptional level to complement Smad signaling and at on the translational level via the mTOR pathway downstream of ERK, which in turn promotes intestinal epithelial cell migration.

Small-molecule inhibitors of HIF-2a translation link its 5'UTR iron-responsive element to oxygen sensing

Cells transiently adapt to hypoxia by globally decreasing protein translation. However, specific proteins needed to respond to hypoxia evade this translational repression. The mechanisms of this phenomenon remain unclear. We screened for and identified small molecules that selectively decrease HIF-2a translation in an mTOR-independent manner, by enhancing the binding of Iron-Regulatory Protein 1 (IRP1) to a recently reported iron-responsive element (IRE) within the 5'-untranslated region (UTR) of the HIF-2a message. Knocking down the expression of IRP1 by shRNA abolished the effect of the compounds. Hypoxia derepresses HIF-2a translation by disrupting the IRP1-HIF-2a IRE interaction. Thus, this chemical genetic analysis describes a molecular mechanism by which translation of the HIF-2a message is maintained during conditions of cellular hypoxia through inhibition of IRP-1-dependent repression. It also provides the chemical tools for studying this phenomenon.

Clara cell 10-kDa protein expression in chronic rhinosinusitis and its cytokine-driven regulation in sinonasal mucosa

BACKGROUND

Clara cell 10-kDa protein (CC10) is a multifunction protein with anti-inflammatory and immunomodulatory effects; hence we compared the CC10 expression between chronic rhinosinusitis (CRS) patients with and without nasal polyps (NPs), analyzed its association with disease severity and response to surgery, and explored its regulation via cytokines.

METHODS

The plasma and tissue CC10 levels were compared between controls and CRS patients with and without NPs by means of quantitative RT-PCR, ELISA, and immunohistochemistry. Computed tomography (CT) scan and endoscopy findings and symptoms were scored. Nasal explant culture was used to explore the effect of TNF-alpha, IL-1beta, IL-4, INF-gamma, and IL-10 on CC10 gene regulation.

RESULTS

Compared with controls, the CC10 expression in sinonasal mucosa was significantly inhibited in both CRS patients with and without NPs. There was a significant further decrease of CC10 expression in patients with NPs and asthma. No difference in CC10 plasma levels was found between controls and patients. CC10 levels inversely correlated with preoperative CT scores, and postoperative endoscopy and symptom scores. TNF-alpha, IL-1beta and IL-4 inhibited, whereas INF-gamma and IL-10 promoted CC10 production in nasal mucosa. A significantly faster decay of CC10 transcripts was seen after IL-1beta treatment. IL-1beta and IL-10 induced thyroid transcription factor-1 expression. INF-gamma increased, whereas IL-4 inhibited hepatocyte nuclear factor-3alpha expression.

CONCLUSION

CC10 may take part in the pathogenesis of CRS and correlates with disease severity and response to surgery. Different cytokines can regulate CC10 expression in nasal mucosa differentially through modulating mRNA stability and certain transcriptional factors expression.

Glycine-extended gastrin stimulates proliferation via JAK2- and Akt-dependent NF-kappaB activation in Barrett's oesophageal adenocarcinoma cells

Glycine-extended gastrin (G-Gly) is a mitogen for several gastrointestinal tissues although the mechanisms responsible are ill-defined and it is unknown if G-Gly can influence signalling in Barrett's oesophagus. G-Gly stimulated proliferation in OE19 and OE33 cells in a dose-dependant manner. This was unaffected by a CCK2 receptor antagonist but abolished by COX-2 inhibitors. G-Gly induced proliferation, COX-2 mRNA abundance, and PGE2 secretion, were all abolished by inhibition of JAK2, PI3-kinase, Akt or NF-kappaB. G-Gly stimulated phosphorylation of JAK2 and increased PI3-kinase activity in JAK2 immunoprecipitates. G-Gly increased Akt phosphorylation and kinase activity and NF-kappaB reporter activity in a JAK2-, PI3-kinase- and Akt-sensitive manner. G-Gly increased COX-2 promoter transcription in an Akt and NF-kappaB-dependent manner and also reduced COX-2 mRNA degradation in an Akt-insensitive manner. We conclude that G-Gly induced signalling involves a JAK2/PI3-kinase/Akt/NF-kappaB sequence leading to COX-2 transcription. G-Gly also seems to stabilise COX-2 mRNA via a separate pathway.

RNA as a new target for toxic and protective agents

In contrast to damage of genomic DNA and despite its potential to affect cell physiology, RNA damage is a poorly examined field in biomedical research. Potential triggers of RNA damage as well as its pathophysiological implications remain largely unknown. While less lethal than mutations in genome, such non-acutely lethal insults to cells have been recently associated with underlying mechanisms of several human chronic diseases. We investigated whether RNA damage could be related to the exposure of particular xenobiotics by testing the RNA-damaging activity of a series of chemicals with different mechanisms of action. Cultured human T-lymphoblastoid cells were treated with ethyl methanesulfonate (EMS), H(2)O(2), doxorubicin, spermine, or S-nitroso-N-acetylpenicillamine (SNAP). Furthermore, we studied the potential protective activity of a pomegranate extract against RNA damage induced by different chemicals. Special attention has been paid to the protective mechanisms of the extract. The protective effect of pomegranate can be mediated by alterations of the rates of toxic agent absorption and uptake, by trapping of electrophiles as well as free radicals, and protection of nucleophilic sites in RNA. We used two different treatment protocols (pre- and co-treatment) for understanding the mechanism of the inhibitory activity of pomegranate. We demonstrated that total RNA is susceptible to chemical attack. A degradation of total RNA could be accomplished with doxorubicin, H(2)O(2), spermine and SNAP. However, EMS, a well-known DNA-damaging agent, was devoid of RNA-damaging properties, while spermine and SNAP, although lacking of DNA-damaging properties, were able to damage RNA. Pomegranate reduced the RNA-damaging effect of doxorubicin, H(2)O(2), and spermine. Its inhibitory activity could be related with its ability to forms complexes with doxorubicin and H(2)O(2), or interacts with the intracellular formation of reactive species mediating their toxicity. For spermine, an alteration of the rates of spermine absorption and uptake can also be involved.