Stabilization of Snail by HuR in the process of hydrogen peroxide induced cell migration

Snail functions as a key regulator in the induction of a phenotypic change called epithelial to mesenchymal transition (EMT). Aberrant expression of Snail prevails in the onset and development of tumor. Here, we have observed increased expression of Snail under the treatment of hydrogen peroxide (H(2)O(2)). Investigation into the underlying mechanisms revealed that stabilization of Snail mRNA contributes partially to this process. H(2)O(2)-induced the luciferase activity of the reporter construct contains the 3'UTR of Snail. Deletion of the AU-rich elements in the UTR eliminated the response of the reporter to H(2)O(2), suggesting the potential role of HuR in the process. Lowering of endogenous HuR levels through knockdown of HuR by siRNA greatly reduced the inducability and half-life of Snail mRNA, which consequently inhibited the downregulation of E-cadherin by H(2)O(2). Our findings indicate that HuR plays a major role in regulating H(2)O(2)-induced Snail expression by enhancing Snail mRNA stability, which in turn enhances cell migrating ability through repressing expression of E-cadherin.

Analysis of genetic elements regulating the methionine adenosyltransferase gene in Leishmania infantum

Methionine adenosyltransferase (MAT) is an important enzyme for metabolic processes, inasmuch as its product, S-adenosylmethionine (AdoMet), plays a key role in trans-methylation, trans-sulphuration and polyamine synthesis. Our prior studies have shown that the Leishmania infantum genome contains two identical copies of the gene encoding MAT (MAT2 gene), arranged in head-to-tail configuration and alternating with another gene, called LORIEN that contains a zinc-finger motif. Both genes are constitutively expressed throughout the promastigote stage of the parasite cell cycle, and their flanking regions were detected by RT-PCR. Luciferase (luc) reporter assays indicated the presence of regulatory elements within the MAT2 3'UTR and intergenic region, and fragments responsible for such regulation were identified by deletional analysis. By site-directed mutagenesis of the wild-type -42 AG recognized in the trans-splicing of the MAT2 gene, the AG slightly downstream (position -36) was observed to be able to generate the same levels of luc expression, thus suggesting that potentially this gene has alternative spliced leader acceptor sites. The stability of MAT2 and LORIEN transcripts was very similar in both logarithmic and stationary phases. However, cycloheximide (CHX) inhibition of protein synthesis increased MAT2 and LORIEN mRNA levels in the logarithmic phase only, an indication that these genes are regulated in promastigotes at the post-transcriptional level by protein factors that targets both transcripts for degradation. However, during the stationary phase, another CHX-independent factor also led to MAT2 and LORIEN mRNAs degradation, indicating the existence of different mechanisms operating on the post-transcriptional regulation of these two genes.

Integration of chloroplast nucleic acid metabolism into the phosphate deprivation response in Chlamydomonas reinhardtii

Cell survival depends on the cell's ability to acclimate to phosphorus (P) limitation. We studied the chloroplast ribonuclease polynucleotide phosphorylase (PNPase), which consumes and generates phosphate, by comparing wild-type Chlamydomonas reinhardtii cells with strains with reduced PNPase expression. In the wild type, chloroplast RNA (cpRNA) accumulates under P limitation, correlating with reduced PNPase expression. PNPase-deficient strains do not exhibit cpRNA variation under these conditions, suggesting that in the wild type PNPase limits cpRNA accumulation under P stress. PNPase levels appear to be mediated by the P response regulator PHOSPHORUS STARVATION RESPONSE1 (PSR1), because in psr1 mutant cells, cpRNA declines under P limitation and PNPase expression is not reduced. PNPase-deficient cells begin to lose viability after 24 h of P depletion, suggesting that PNPase is important for cellular acclimation. PNPase-deficient strains do not have enhanced sensitivity to other physiological or nutrient stresses, and their RNA and cell growth phenotypes are not observed under P stress with phosphite, a phosphate analog that blocks the stress signal. In contrast with RNA metabolism, chloroplast DNA (cpDNA) levels declined under P deprivation, suggesting that P mobilization occurs from DNA rather than RNA. This unusual phenomenon, which is phosphite- and PSR1-insensitive, may have evolved as a result of the polyploid nature of cpDNA and the requirement of P for cpRNA degradation by PNPase.

Thalidomide destabilizes cyclooxygenase-2 mRNA by inhibiting p38 mitogen-activated protein kinase and cytoplasmic shuttling of HuR

We investigated the effect of thalidomide on transcriptional and post-transcriptional cyclooxygenase-2 (COX-2) expression, including a pathway leading to COX-2 mRNA destabilization. We found that thalidomide inhibited the interleukin-1beta (IL-1beta)-mediated induction of COX-2 protein and mRNA in Caco-2 cells. Transient transfection with a COX-2 promoter construct demonstrated that thalidomide did not affect IL-1beta-induced transcriptional activation of COX-2, although it did decrease the stability of COX-2 mRNA and suppress IL-1beta-induced cytoplasmic shuttling of an mRNA stabilizing protein, HuR. Thalidomide also suppressed IL-1beta-induced p38 mitogen-activated protein kinase (MAPK) activation, while a p38 MAPK inhibitor destabilized COX-2 mRNA and the cytoplasmic shuttling of HuR induced by IL-1beta. These data suggest that one of the molecular mechanisms of thalidomide may be destabilization of COX-2 mRNA through inhibition of cytoplasmic shuttling of HuR and p38 MAPK.

The inhibition of TNF-α-induced E-selectin expression in endothelial cells via the JNK/NF-κB pathways by highly N-acetylated chitooligosaccharides

Chitooligosaccharides (COS) have been shown to regulate various cellular and biological functions. However, the effect of COS on inflammatory responses of the cells remains unclear. We investigated the regulatory effect of highly N-acetylated COS (NACOS) on tumor necrosis factor-alpha (TNF-alpha)-induced endothelial cell (EC) E-selectin expression, which is crucial for leukocyte recruitment. ECs were kept as controls or pre-treated with NACOS for different times, and then stimulated with TNF-alpha for 4h. The results show that pre-treating ECs with NACOS inhibited the TNF-alpha-induced E-selectin expression in a dose- and time-dependent manner. This NACOS-mediated inhibition in E-selectin expression was regulated at the transcriptional level, but not due to changes in mRNA stability. Stimulation of ECs with TNF-alpha-induced rapid increases in the phosphorylation of their mitogen-activated protein kinases (MAPKs) [extracellular signal-regulated kinase (ERK), c-Jun-NH2-terminal kinase (JNK), and p38 MAPK]; the inhibitor for JNK (i.e., SP600125), but not those for ERK (i.e., PD98059) and p38 MAPK (i.e., SB203580), attenuated this TNF-alpha-induced E-selectin expression. Pre-treating ECs with NACOS inhibited the TNF-alpha-induced JNK activation, suggesting that JNK was involved in the inhibitory effect of NACOS on TNF-alpha-induced E-selectin expression. Pre-treating ECs with NACOS inhibited the TNF-alpha-induced p65 and p50 mRNA expressions. Gel shifting and chromatin immunoprecipitation assays showed that NACOS blocked the TNF-alpha-induced increases in the binding activity and in vivo promoter binding of nuclear factor-kappaB (NF-kappaB) in ECs. Our findings provide a molecular mechanism by which NACOS inhibit TNF-alpha-induced E-selectin expression in ECs, and a basis for using NACOS in pharmaceutical therapy against inflammation.

Identification of two distinct hybrid state intermediates on the ribosome

High spatial and time resolution single-molecule fluorescence resonance energy transfer measurements have been used to probe the structural and kinetic parameters of transfer RNA (tRNA) movements within the aminoacyl (A) and peptidyl (P) sites of the ribosome. Our investigation of tRNA motions, quantified on wild-type, mutant, and L1-depleted ribosome complexes, reveals a dynamic exchange between three metastable tRNA configurations, one of which is a previously unidentified hybrid state in which only deacylated-tRNA adopts its hybrid (P/E) configuration. This new dynamic information suggests a framework in which the formation of intermediate states in the translocation process is achieved through global conformational rearrangements of the ribosome particle.

Post-transcriptional regulation of human inducible nitric-oxide synthase expression by the Jun N-terminal kinase

Human inducible nitric-oxide synthase (iNOS) expression is regulated both at transcriptional and post-transcriptional levels. In the present study, the effect of Jun N-terminal kinase (JNK) on human iNOS expression was investigated. In A549/8 human alveolar epithelial cells, both the inhibition of JNK by a pharmacological inhibitor anthra[1,9-cd]pyrazol-6(2H)-one1,9-pyrazoloanthrone (SP600125) and small interfering RNA (siRNA)-mediated down-regulation of JNK led to a reduction of iNOS mRNA and protein expression. iNOS promoter activity was not affected by these treatments. Hence, JNK seems to regulate iNOS expression through post-transcriptional mechanisms by stabilizing iNOS mRNA. Our laboratory has shown recently that a cytokine-induced RNA binding protein tristetraprolin (TTP) is a major positive regulator of human iNOS expression by stabilizing iNOS mRNA. Therefore, the effect of JNK inhibition by SP600125 or down-regulation by siRNA on TTP expression was investigated. Both SP600125 and siRNA targeted at JNK resulted in a reduction of TTP protein expression without affecting the amount of TTP mRNA. These data suggest a post-transcriptional control of TTP expression by JNK. Moreover, the modulation of JNK signaling by SP600125 or siRNA did not change p38 phosphorylation. In summary, the results suggest that JNK regulates human iNOS expression by stabilizing iNOS mRNA possibly by a TTP-dependent mechanism.

Charge density of divalent metal cations determines RNA stability

RNA molecules are exquisitely sensitive to the properties of counterions. The folding equilibrium of the Tetrahymena ribozyme is measured by nondenaturing gel electrophoresis in the presence of divalent group IIA metal cations. The stability of the folded ribozyme increases with the charge density (zeta) of the cation. Similar scaling is found when the free energy of the RNA folded in small and large metal cations is measured by urea denaturation. Brownian dynamics simulations of a polyelectrolyte show that the experimental observations can be explained by nonspecific ion-RNA interactions in the absence of site-specific metal chelation. The experimental and simulation results establish that RNA stability is largely determined by a combination of counterion charge and the packing efficiency of condensed cations that depends on the excluded volume of the cations.

Metabolic regulation of IMD2 transcription and an unusual DNA element that generates short transcripts

Transcriptional regulation of IMD2 in yeast (Saccharomyces cerevisiae) is governed by the concentration of intracellular guanine nucleotide pools. The mechanism by which pool size is measured and transduced to the transcriptional apparatus is unknown. Here we show that DNA sequences surrounding the IMD2 initiation site constitute a repressive element (RE) involved in guanine regulation that contains a novel transcription-blocking activity. When this regulatory region is placed downstream of a heterologous promoter, short poly(A)(+) transcripts are generated. The element is orientation dependent, and sequences within the normally transcribed and nontranscribed regions of the element are required for its activity. The promoter-proximal short RNAs are unstable and serve as substrates for the nuclear exosome. These findings support a model in which intergenic short transcripts emanating from upstream of the IMD2 promoter are terminated by a polyadenylation/terminator-like signal embedded within the IMD2 transcription start site.

Estrogen does not regulate CD154 mRNA stability in systemic lupus erythematosus T cells

Previous studies in our laboratory showed a dose-dependent and hormone-specific increase in CD154 expression in T cells from females with systemic lupus erythematosus (SLE). This present study investigates if the estrogen-dependent increase in CD154 expression is due to stabilization of the messenger RNA. T cells from female SLE patients and controls were cultured for 18 h in serum-free medium without and with estradiol 17-beta (10(-7) M). T cells were either unstimulated (resting) or were activated by further culture on anti-CD3 coated plates. Actinomycin D (25 microg/mL) was added to parallel cultures to inhibit new messenger RNA synthesis. CD154 messenger RNA stability was assessed by reverse-transcription polymerase chain amplification. Resting SLE (n = 10, P = 0.88) and normal (n = 7, P = 0.65) T cells showed no significant differences in message stability in response to estradiol. CD154 messenger RNA was also not significantly stabilized in activated SLE (n = 10, P = 0.15) or activated normal (n = 6, P = 0.077) T cells in response to estradiol. These findings indicate that the estrogen-dependent increase in CD154 in SLE T cells is not due to stability of the mRNA. These data are consistent with the postulate that estradiol stimulates CD154 transcription in SLE T cells.

Insulin-like growth factor-I induces cyclooxygenase-2 expression via PI3K, MAPK and PKC signaling pathways in human ovarian cancer cells

Elevated levels of insulin-like growth factor-I (IGF-I) are associated with ovarian carcinogenesis and progression. However, the molecular mechanisms by which IGF-I contributes to ovarian cancer development remain to be elucidated. Cyclooxygenase-2 (COX-2) is a crucial player in the pathogenesis of human malignancies. Herein we showed that IGF-I efficiently induced COX-2 expression and PGE(2) biosynthesis at physiologically relevant concentrations in human ovarian cancer cells. IGF-I treatment significantly increased COX-2 transcriptional activation. IGF-I also stabilized COX-2 mRNA through the COX-2 3'-untranslated region (3'-UTR), which appeared independent of the conserved AU-rich elements. We next investigated the signaling pathways involved in IGF-I-induced COX-2 expression. We found that PI3K inhibitor wortmannin or LY294002 blocked COX-2 expression induced by IGF-I. Wortmannin treatment or a dominant negative PI3K mutant significantly inhibited IGF-I-induced COX-2 mRNA stabilization, but only slightly decreased COX-2 transcriptional activation. We showed that ERK1/2 and p38 MAPKs were required for IGF-I-induced COX-2 expression and that activation of both pathways by IGF-I increased COX-2 transcriptional activation and its mRNA stability. IGF-I stimulated PKC activation in the cells and pretreatment with PKC inhibitor bisindolylmaleimide prevented IGF-I-induced COX-2 transcriptional activation and mRNA stabilization, and inhibited COX-2 mRNA and protein expression. Taken together, our data demonstrate that IGF-I induces COX-2 expression in human ovarian cancer cells, which is mediated by three parallel signaling cascades--PI3K, MAPK, and PKC pathways that differentially regulate COX-2 expression at transcriptional and post-transcriptional levels.

Cytokines direct the regulation of Bim mRNA stability by heat-shock cognate protein 70

Previous gene-targeting studies indicated that Bim, a BH3-only death activator, regulates total blood cell number. Cytokines contribute to this process by negatively regulating steady-state levels of Bim mRNA. Here we present a molecular mechanism for cytokine-mediated posttranscriptional regulation of Bim mRNA by heat-shock cognate protein 70 (Hsc70), which binds to AU-rich elements (AREs) in the 3'-untranslated region of specific mRNAs and enhances their stability. The RNA binding potential of Hsc70 is regulated by cochaperones including Bag-4 (also SODD), CHIP, Hip, and Hsp40. Cytokines regulate the expression or function of these cochaperones by activating Ras pathways. Thus, exposure of cells to cytokines ultimately leads to destabilization of Bim mRNA and promotion of cell survival. This unanticipated role of a chaperone/cochaperone complex in mRNA stability appears to be critical for hematopoiesis and leukemogenesis.

Signaling in Lipopolysaccharide-Induced Stabilization of Formyl Peptide Receptor 1 mRNA in Mouse Peritoneal Macrophages

To identify the TLR4-initiated signaling events that couple to formyl peptide receptor (FPR)1 mRNA stabilization, macrophages were treated with LPS along with a selection of compounds targeting several known signaling pathways. Although inhibitors of protein tyrosine kinases, MAPKs, and stress-activated kinases had little or no effect on the response to LPS, LY294002 (LY2) and parthenolide (an IkappaB kinase inhibitor) were both potent inhibitors. LY2 but not parthenolide blocked the LPS-induced stabilization of FPR1 mRNA. Although both LY2 and wortmannin effectively blocked PI3K activity, wortmannin had little effect on FPR1 expression and did not modulate the decay of FPR1 mRNA. Moreover, although LY2 was demonstrated to be a potent inhibitor of PI3K activity, a structural analog of LY2, LY303511 (LY3), which did not inhibit PI3K, was equally effective at preventing LPS-stimulated FPR1 expression. The mammalian target of rapamycin activity (measured as phospho-p70S6 kinase) was activated by LPS but not significantly blocked by LY2. In addition, although rapamycin blocked mTOR activity, it did not inhibit FPR1 mRNA expression. Finally, the mechanisms involved in stabilization of FPR1 by LPS could be distinguished from those involved in stabilization of AU-rich mRNAs because the prolonged half-life of FPR1 mRNA was insensitive to the inhibition of p38 MAPK. These findings demonstrate that LY2/LY3 targets a novel TLR4-linked signaling pathway that selectively couples to the stabilization of FPR1 mRNA.

A novel role for the glucocorticoid receptor in the regulation of monocyte chemoattractant protein-1 mRNA stability

Monocyte chemoattractant protein-1 (MCP-1) plays an important role in attracting monocytes to sites of inflammation and is the dominant mediator of macrophage accumulation in atherosclerotic plaques. We have previously shown that glucocorticoids inhibit the secretion of MCP-1 in arterial smooth muscle cells (SMC) by markedly decreasing MCP-1 mRNA stability. We now report that the destabilization of MCP-1 mRNA is mediated by the glucocorticoid receptor (GR). The GR antagonist, RU486, blocked the effect of the glucocorticoid dexamethasone (Dex) on MCP-1 mRNA stability in SMC culture. Using a previously reported in vitro mRNA gel shift and stability assay, antibodies to the GR blocked the ability of cytoplasmic extracts from Dex-treated SMC to decay MCP-1 mRNA. Recombinant human GR (rhGR) bound in a concentration-dependent manner to in vitro transcribed MCP-1 mRNA, whereas other members of the steroid hormone receptor family did not. Binding of GR to MCP-1 mRNA was specific as it was not found to bind other mRNAs. Immunoprecipitation of GR in extracts from Dex-treated SMC followed by real-time reverse transcription-PCR demonstrated that endogenous GR was bound specifically to MCP-1 mRNA. The addition of exogenous rhGR blocked the ability of extracts from Dex-treated SMC to degrade MCP-1 mRNA, suggesting that exogenous rhGR can compete with an endogenous GR-containing degradative complex. These data suggest a novel role for the GR in binding to and facilitating mRNA degradation. These results provide novel insights into GR function and may provide a new approach to attenuate the inflammatory response mediated by MCP-1.

p53-Dependent p21 mRNA elongation is impaired when DNA replication is stalled

We have previously reported that when DNA replication is blocked in some human cell lines, p53 is impaired in its ability to induce a subset of its key target genes, including p21(WAF1/CIP1). Here, we investigated the reason for this impairment by comparing the effects of two agents, hydroxyurea (HU), which arrests cells in early S phase and impairs induction of p21, and daunorubicin, which causes a G(2) block and leads to robust activation of p21 by p53. HU treatment was shown to inhibit p21 mRNA transcription rather than alter its mRNA stability. Nevertheless, chromatin immunoprecipitation assays revealed that HU impacts neither p53 binding nor acetylation of histones H3 and H4 within the p21 promoter. Furthermore, recruitment of the TFIID/TATA-binding protein complex and the large subunit of RNA polymerase II (RNA Pol II) are equivalent after HU and daunorubicin treatments. Relative to daunorubicin treatment, however, transcription elongation of the p21 gene is significantly impaired in cells treated with HU, as evidenced by reduced occupancy of RNA Pol II at regions downstream of the start site. Likewise, in the p21 downstream region after administration of HU, there is less of a specifically phosphorylated form of RNA Pol II (Pol II-C-terminal domain serine 2P) which occurs only when the polymerase is elongating RNA. We propose that while the DNA replication checkpoint is unlikely to regulate the assembly of a p21 promoter initiation complex, it signals to one or more factors involved in the process of transcriptional elongation.

Differential regulation of the tyrosine hydroxylase and enkephalin neuropeptide transmitter genes in rat PC12 cells by short chain fatty acids: Concentration-dependent effects on transcription and RNA stability

At physiologic concentrations, butyrate regulates the expression of individual genes involving at least three mechanisms: (i) through induction of cis- and trans-acting butyrate-dependent transcription factors for selected genes, (ii) by inhibition of histone deacetylation and attendant chromatin remodeling and (iii) by affecting turnover of mRNAs. Our previous work illustrated gradual accumulation of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis and the neuropeptide transmitter proenkephalin (ppEnk) in butyrate-differentiated PC12 cells (Nankova, B.B., Chua, J., Mishra, R., Kobasiuk, C.D., La Gamma, E.F. 2003. Nicotinic induction of preproenkephalin and tyrosine hydroxylase gene expression in butyrate-differentiated rat PC12 cells: a model for adaptation to gut-derived environmental signals. Pediatr. Res. 53, 113-118.). However, at higher physiological concentrations (6 mM), TH mRNA levels are significantly reduced while ppEnk mRNA transcripts remained elevated. These differential effects suggest suppression of endogenous TH gene transcription, targeted degradation of TH mRNA or both. By using nuclear run-on assays, we found that transcription increased for both endogenous TH and ppEnk genes, even at time points and concentrations when reduced steady-state levels of TH mRNA were observed. The reduction in TH mRNA was blocked by cycloheximide consistent with a protein-dependent mechanism. We also observed a dose-dependent accumulation of luciferase reporter molecules driven by TH promoter in transient transfection experiments, data that provide additional support for separate regulatory pathways. Significantly, butyrate-dependent decreases in TH mRNA were also reflected in a reduction in TH protein. Our results suggest a novel mode of regulation for TH by butyrate operating via both transcriptional and post-transcriptional mechanisms. We speculate that, depending on plasma concentrations of butyrate, this naturally occurring signaling molecule can function as an in vivo molecular switch to alter levels of TH mRNA, its protein and thus the biosynthesis of endogenous catecholamines.

Cisplatin increases TNF-alpha mRNA stability in kidney proximal tubule cells

Cisplatin induces acute renal injury in part by increasing the production of TNF-alpha. However, the mechanism by which cisplatin increases renal TNF-alpha expression is not known. The transcription, translation, and stability of TNF-alpha mRNA are sites of regulation of TNF-alpha production. This study investigated the effects of cisplatin on TNF-alpha mRNA stability and the role of MAP kinases in this process in cultured renal proximal tubule cells. Cisplatin increased the expression of TNF-alpha mRNA by proximal tubule cells in a time- and dose-dependent manner, as well as activated p42/44 ERK kinase, p38 MAP kinase, and JNK in a dose-dependent manner. The inhibition of these pathways reduced TNF-alpha expression significantly. Cisplatin also increased the stability of TNF-alpha mRNA, but this effect was not mediated by MAP kinases and did not require the synthesis of a new protein. The treatment of cells with cisplatin induced the formation of complexes of cytosolic proteins and the AU-rich region of the TNF-alpha 3'UTR. These results are consistent with the view that cisplatin increases TNF-alpha mRNA stability in a MAP kinase-independent manner. The stabilization of TNF-alpha mRNA by cisplatin may involve the binding of certain proteins to AU-rich regions in the 3'UTR.

Regulation of luteinizing hormone receptor mRNA expression by a specific RNA binding protein in the ovary

The expression of LH receptor mRNA shows significant changes during different physiological states of the ovary. Previous studies from our laboratory have identified a post-transcriptional mechanism by which LH receptor mRNA is regulated following preovulatory LH surge or in response to hCG administration. A specific binding protein, identified as mevalonate kinase, binds to the open reading frame of LH receptor mRNA. The protein binding site is localized to nucleotides 203-220 of the LH receptor mRNA and exhibits a high degree of specificity. The expression levels of the protein show an inverse relationship to the LH receptor mRNA levels. The hCG-induced down-regulation of LH receptor mRNA can be mimicked by increasing the intracellular levels of cyclic AMP by a phosphodiesterase inhibitor. An in vitro mRNA decay assay showed that addition of the binding protein to the decay system caused accelerated LH receptor mRNA decay. Our results therefore show that LH receptor mRNA expression in the ovary is regulated post-transcriptionally by altering the rate of mRNA degradation by a specific mRNA binding protein.

GADD153 mediates celecoxib-induced apoptosis in cervical cancer cells

Celecoxib, a selective cyclooxygenase 2 inhibitor, is known to have anti-inflammatory activity and to induce apoptosis in various types of cancer cells. Here, we examined the molecular mechanism of celecoxib-induced apoptosis in cervical cancer cell lines (HeLa, CaSki and C33A). Screening of a microarray cDNA-chip containing 225 different genes revealed that growth arrest and DNA damage inducible gene (GADD153), a transcription factor involved in apoptosis, showed the strongest differential expression following celecoxib treatment in all three cervical cancer cell lines. Notably, siRNA-induced silencing of GADD153 suppressed celecoxib-induced apoptosis in all the three cell lines, and exogenous expression of GADD153 triggered apoptosis in cervical cancer cells in the absence of other apoptotic stimuli. A luciferase reporter gene assay and mRNA stability tests revealed that expression of GADD153 was regulated at both the transcriptional and post-transcriptional levels following celecoxib treatment. The region between -649 and -249, containing an intact C/EBP-ATF binding site, was required for the basal activity and celecoxib-induced stimulation of GADD153 promoter activity. Also, mRNA stability test showed that celecoxib prolonged the half-life of GADD153 mRNA. In terms of signaling pathway, addition of the NF-kappaB inhibitor, N-tosyl-L phenylalanyl-chloromethyl ketone (TPCK), had no effect on GADD153 expression levels. Celecoxib treatment induced Bak expression, whereas cell treated with siGADD153 or TPCK showed lower levels of celecoxib-induced Bak up-regulation. These novel findings collectively suggest that GADD153 may play a key role in celecoxib-induced apoptosis in cervical cancer cells by regulating the expression of proapoptotic proteins such as Bak.

Resveratrol, a Polyphenolic Phytostilbene, Inhibits Endothelial Monocyte Chemotactic Protein-1 Synthesis and Secretion

BACKGROUND/AIMS

Resveratrol is a naturally occurring polyphenol phytoestrogen and one of several constituents of red wine thought to be cardioprotective. We investigated the effect of resveratrol on the expression of the atherogenic chemokine, monocyte chemotactic protein-1 (MCP-1).

METHODS

Human umbilical vein endothelial cells were stimulated with interleukin-1beta (IL-1beta) in the absence or presence of resveratrol. MCP-1 levels were determined by ELISA and MCP-1 mRNA was measured.

RESULTS

Resveratrol (1-100 microM) dose-dependently inhibited IL-1beta-stimulated MCP-1 secretion, with approximately 45% inhibition at 50 microM resveratrol. This was a Gi-protein- and NO-dependent effect. Resveratrol also significantly inhibited MCP-1 gene expression in a Gi-protein-dependent but NO-independent manner. While resveratrol had no effect on MCP-1 mRNA degradation, it inhibited MCP-1 promoter activity and reduced nuclear factor kappaB and activator protein-1 binding activity induced by IL-1beta. Moreover, while hemoxygenase-1 (HO-1) expression was induced by resveratrol in human umbilical vein endothelial cells, neither treatment with the HO-1 inhibitor tin-protoporphyrin IX nor siRNA-directed knockdown of HO-1 had any effect on the inhibition of MCP-1 mRNA or protein secretion by resveratrol.

CONCLUSION

These data demonstrate an inhibitory effect of resveratrol on MCP-1 synthesis and secretion, mediated via distinct signaling pathways. The inhibition of MCP-1 may represent a novel cardioprotective mechanism of resveratrol.

Structure and function of eukaryotic Ribonuclease P RNA

Ribonuclease P (RNase P) is the ribonucleoprotein endonuclease that processes the 5' ends of precursor tRNAs. Bacterial and eukaryal RNase P RNAs had the same primordial ancestor; however, they were molded differently by evolution. RNase P RNAs of eukaryotes, in contrast to bacterial RNAs, are not catalytically active in vitro without proteins. By comparing the bacterial and eukaryal RNAs, we can begin to understand the transitions made between the RNA and protein-dominated worlds. We report, based on crosslinking studies, that eukaryal RNAs, although catalytically inactive alone, fold into functional forms and specifically bind tRNA even in the absence of proteins. Based on the crosslinking results and crystal structures of bacterial RNAs, we develop a tertiary structure model of the eukaryal RNase P RNA. The eukaryal RNA contains a core structure similar to the bacterial RNA but lacks specific features that in bacterial RNAs contribute to catalysis and global stability of tertiary structure.

Arabidopsis DCP2, DCP1, and VARICOSE form a decapping complex required for postembryonic development

mRNA turnover in eukaryotes involves the removal of m7GDP from the 5' end. This decapping reaction is mediated by a protein complex well characterized in yeast and human but not in plants. The function of the decapping complex in the development of multicellular organisms is also poorly understood. Here, we show that Arabidopsis thaliana DCP2 can generate from capped mRNAs, m7GDP, and 5'-phosphorylated mRNAs in vitro and that this decapping activity requires an active Nudix domain. DCP2 interacts in vitro and in vivo with DCP1 and VARICOSE (VCS), an Arabidopsis homolog of human Hedls/Ge-1. Moreover, the interacting proteins stimulate DCP2 activity, suggesting that the three proteins operate as a decapping complex. Consistent with their role in mRNA decay, DCP1, DCP2, and VCS colocalize in cytoplasmic foci, which are putative Arabidopsis processing bodies. Compared with the wild type, null mutants of DCP1, DCP2, and VCS accumulate capped mRNAs with a reduced degradation rate. These mutants also share a similar lethal phenotype at the seedling cotyledon stage, with disorganized veins, swollen root hairs, and altered epidermal cell morphology. We conclude that mRNA turnover mediated by the decapping complex is required for postembryonic development in Arabidopsis.

Identifying candidate colon cancer tumor suppressor genes using inhibition of nonsense-mediated mRNA decay in colon cancer cells

Inhibition of the nonsense-mediated decay (NMD) mechanism in cells results in stabilization of transcripts carrying premature translation termination codons. A strategy referred to as gene identification by NMD inhibition (GINI) has been proposed to identify genes carrying nonsense mutations. Genes containing frameshift mutations in colon cancer cell line have been identified using a modified version of GINI. To increase the efficiency of identifying mutant genes using GINI, we have now further improved the strategy. In this approach, inhibition of NMD with emetine is complemented with inhibiting NMD by blocking the phosphorylation of the hUpf1 protein with caffeine. In addition, to enhance the GINI strategy, comparing mRNA level alterations produced by inhibiting transcription alone or inhibiting transcription together with NMD following caffeine pretreatment were used for the efficient identification of false positives produced as a result of stress response to NMD inhibition. To demonstrate the improved efficiency of this approach, we analysed colon cancer cell lines showing microsatellite instability. Bi-allelic inactivating mutations were found in the FXR1, SEC31L1, NCOR1, BAT3, PHF14, ZNF294, C19ORF5 genes as well as genes coding for proteins with yet unknown functions.

Endotoxic shock in AUF1 knockout mice mediated by failure to degrade proinflammatory cytokine mRNAs

Excessive production of proinflammatory cytokines, particularly tumor necrosis factor-alpha (TNFalpha) and interleukin-1beta (IL-1beta), plays a critical role in septic shock induced by bacterial endotoxin (endotoxemia). Precise control of cytokine expression depends on rapid degradation of cytokine mRNAs, mediated by an AU-rich element (ARE) in the 3' noncoding region and by interacting ARE-binding proteins, which control the systemic inflammatory response. To understand the function of the ARE-binding protein AUF1, we developed an AUF1 knockout mouse. We show that AUF1 normally functions to protect against the lethal progression of endotoxemia. Upon endotoxin challenge, AUF1 knockout mice display symptoms of severe endotoxic shock, including vascular hemorrhage, intravascular coagulation, and high mortality, resulting from overproduction of TNFalpha and IL-1beta. Overexpression of these two cytokines is specific, and shown to result from an inability to rapidly degrade these mRNAs in macrophages following induction. Neutralizing antibodies to TNFalpha and IL-1beta protect AUF1 knockout mice against lethal endotoxic shock. These and other data describe a novel post-transcriptional mechanism whereby AUF1 acts as a crucial attenuator of the inflammatory response, promoting the rapid decay of selective proinflammatory cytokine mRNAs following endotoxin activation. Defects in the AUF1 post-transcriptionally controlled pathway may be involved in human inflammatory disease.

Regulation of mRNA stability through a pentobarbital-responsive element

Pentobarbital, a general anesthetic and non-genotoxic carcinogen, can induce gene expression by activating transcription. In the Drosophila glutathione S-transferase D21 (gstD21) gene, pentobarbital's regulatory influence extends to the level of mRNA turnover. Transcribed from an intronless gene, gstD21 mRNA is intrinsically very labile. But exposure to pentobarbital renders it stabilized beyond what can be attributed to transcriptional activation. We aim here to identify cis-acting element(s) of gstD21 mRNA as contributors to the molecule's pentobarbital-mediated stabilization. In the context of hsp70 5'UTR and the 3'UTR of act5C, gstD21 mRNA, minus its native UTRs, is stable. Maintaining the same context of heterologous UTRs, we can reconstitute using the full-length gstD21 sequence the inherent instability of gstD21 mRNA and its stabilization by pentobarbital. Transgenic flies that express these chimeric gstD21 mRNA exhibit decay intermediates lacking 3'UTR, which are not stabilized by PB treatment. The 3'UTR sequence, when inserted downstream from a reporter transcript, stabilizes it 1.6-fold under PB treatment. The analysis of the decay intermediates suggests a polysome-associated decay pattern. We propose a regulatory model that features a 59-nucleotide pentobarbital-responsive element (PBRE) in the 3'UTR of gstD21 mRNA.