Functional antagonism by GM-CSF on TNF-alpha-induced CD83 expression in human neutrophils

TNFalpha-induced expression of CD83 in leukocytes is mediated by NF-kappab. The aim of our present study was to investigate the underlying mechanism of a unique functional antagonism between GM-CSF and TNFalpha-induced up-regulation of CD83 in human neutrophils. CD83 was down-regulated by co-stimulation of neutrophils with TNFalpha and GM-CSF compared to TNFalpha alone both at the level of mRNA and protein. In marked contrast, the expression of IL-1RA was up-regulated under the same conditions. The down-regulation of CD83 was not mediated by modulation of the NF-kappab signaling pathway. Neither was it mediated by a decrease in mRNA stability of CD83. NF-kappab was modulated under these conditions as both the expression of the target gene IL-1RA as well as the phosphorylation of IkBalpha were up-regulated. Our results show that co-stimulation with pro-inflammatory cytokines such as TNFalpha and GM-CSF can have differential effects on inflammatory pathways initiated in the same target cell. GM-CSF can both synergize with TNFalpha in the case of expression of IL1-RA and antagonize in the case of CD83. Therefore, expression of CD83 as read out for activation of neutrophils in patients with inflammatory diseases is complicated by the presence of cross-modulating cytokines such as GM-CSF.

Nuclear factor-kappaB is a critical mediator of Ste20-like proline-/alanine-rich kinase regulation in intestinal inflammation

Inflammatory bowel disease (IBD) is thought to result from commensal flora, aberrant cellular stress, and genetic factors. Here we show that the expression of colonic Ste20-like proline-/alanine-rich kinase (SPAK) that lacks a PAPA box and an F-alpha helix loop is increased in patients with IBD. The same effects were observed in a mouse model of dextran sodium sulfate-induced colitis and in Caco2-BBE cells treated with the pro-inflammatory cytokine tumor necrosis factor (TNF)-alpha. The 5'-flanking region of the SPAK gene contains two transcriptional start sites, three transcription factor Sp1-binding sites, and one transcription factor nuclear factor (NF)-kappaB-binding site, but no TATA elements. The NF-kappaB-binding site was essential for stimulated SPAK promoter activity by TNF-alpha, whereas the Sp1-binding sites were important for basal promoter activity. siRNA-induced knockdown of NF-kappaB, but not of Sp1, reduced TNF-alpha-induced SPAK expression. Nuclear run-on and mRNA decay assays demonstrated that TNF-alpha directly increased SPAK mRNA transcription without affecting SPAK mRNA stability. Furthermore, up-regulation of NF-kappaB expression and demethylation of the CpG islands induced by TNF-alpha also played roles in the up-regulation of SPAK expression. In conclusion, our data indicate that during inflammatory conditions, TNF-alpha is a key regulator of SPAK expression. The development of compounds that can either modulate or disrupt the activity of SPAK-mediated pathways is therefore important for the control and attenuation of downstream pathological responses, particularly in IBD.

Insulin and dexamethasone dynamically regulate adipocyte 11beta-hydroxysteroid dehydrogenase type 1

The adipocyte enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) amplifies local glucocorticoid action by generating active glucocorticoids from inactive metabolites and has emerged as a key player in the pathogenesis of central obesity and metabolic syndrome. However, the regulation of adipocyte 11beta-HSD1 is incompletely understood. Therefore, the present study was designed to investigate the effects of insulin and glucocorticoid as well as their underlying molecular mechanisms on 11beta-HSD1 activity and expression in 3T3-L1 adipocytes and determine whether the in vitro findings could be confirmed in vivo. Our main in vitro findings are 1) insulin stimulated whereas dexamethasone inhibited 11beta-HSD1 activity and expression in a time- and concentration-dependent manner; 2) the effect of dexamethasone was mimicked by both cortisol and corticosterone but blocked by the glucocorticoid receptor antagonist RU486; 3) the p38 MAPK inhibitor SB220025, but not the ERK inhibitor U0126 or the phosphatidylinositol 3-kinase inhibitor LY294002, prevented insulin stimulation of 11beta-HSD1 activity; and 4) although dexamethasone did not alter the half-life of 11beta-HSD1 mRNA, insulin doubled it. Taken together, these in vitro results demonstrate that insulin stimulates adipocyte 11beta-HSD1 through a posttranscriptional mechanism that involves activation of the p38 MAPK signaling pathway, whereas dexamethasone exerts an opposite effect by a glucocorticoid receptor-mediated transcriptional mechanism. In contrast, both insulin and dexamethasone augmented 11beta-HSD1 activity and expression in rat white adipose tissue in vivo, thus confirming the role of insulin but revealing a fundamental difference regarding the role of dexamethasone in regulating adipocyte 11beta-HSD1 between the two model systems.

Synthesis and structure-activity relationships of berberine analogues as a novel class of low-density-lipoprotein receptor up-regulators

Berberine (BBR, 1) is a novel cholesterol-lowering agent that up-regulates low-density-lipoprotein receptor (LDLR) expression through a mechanism different from that of statins. Because of the unique mode of action and good safety record, BBR provoked our interest to do structure modification at different domains for its cholesterol-lowering activity. Nineteen BBR analogues with substituents on the benzene ring D were synthesized in the present study. The analysis of structure-activity relationship (SAR) indicated that the two methoxyl groups in an ortho-distribution on this benzene ring afforded a good activity. Among the 19 analogues, compound 8j bearing a methoxyl at both 10- and 11-position showed an increased LDLR up-regulatory activity in respect to BBR, and therefore has been selected as a promising cholesterol-lowering drug candidate for further evaluation.

Role of the RNA-binding protein tristetraprolin in glucocorticoid-mediated gene regulation

Glucocorticoids (GCs) are the mainstay of anti-inflammatory therapy. Modulation of posttranscriptional regulation (PTR) of gene expression by GCs is a relevant yet poorly characterized mechanism of their action. The RNA-binding protein tristetraprolin (TTP) plays a central role in PTR by binding to AU-rich elements in the 3'-untranslated region of proinflammatory transcripts and accelerating their decay. We found that GCs induce TTP expression in primary and immortalized human bronchial epithelial cells. To investigate the importance of PTR and the role of TTP in GC function, we compared the effect of GC treatment on genome-wide gene expression using mouse embryonic fibroblasts (MEFs) obtained from wild-type and TTP(-/-) mice. We confirmed that GCs induce TTP in MEFs and observed in TTP(-/-) MEFs a striking loss of up to 85% of GC-mediated gene expression. Gene regulation by TNF-alpha was similarly affected, as was the antagonistic effect of GC on TNF-alpha-induced response. Inflammatory genes, including cytokines and chemokines, were among the genes whose sensitivity to GCs was affected by lack of TTP. Silencing of TTP in WT MEFs by small interfering RNA confirmed loss of GC response in selected targets. Immunoprecipitation of ribonucleoprotein complexes revealed binding of TTP to several validated transcripts. Changes in the rate of transcript degradation studied by actinomycin D were documented for only a subset of transcripts bound to TTP. These results reveal a strong and previously unrecognized contribution of PTR to the anti-inflammatory action of GCs and point at TTP as a key factor mediating this process through a complex mechanism of action.

Therapeutic gene silencing delivered by a chemically modified small interfering RNA against mutant SOD1 slows amyotrophic lateral sclerosis progression

Inherited neurodegenerative diseases, such as Huntington disease and subset of Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis, are caused by the mutant genes that have gained undefined properties that harm cells in the nervous system, causing neurodegeneration and clinical phenotypes. Lowering the mutant gene expression is predicted to slow the disease progression and produce clinical benefit. Administration of small interfering RNA (siRNA) can silence specific genes. However, long term delivery of siRNA to silence the mutant genes, a requirement for treatment of these chronic central nervous system (CNS) diseases, remains a critical unsolved issue. Here we designed and tested a chemically stabilized siRNA against human Cu,Zn-superoxide dismutase (SOD1) in a mouse model for amyotrophic lateral sclerosis. We show that the modified siRNA has enhanced stability and retains siRNA activity. Administration of this siRNA at the disease onset by long term infusion into the CNS resulted in widespread distribution of this siRNA, knocked down the mutant SOD1 expression, slowed the disease progression, and extended the survival. These results bring RNA interference therapy one step closer to its clinical application for treatment of chronic, devastating, and fatal CNS disorders.

[Herpes simplex virus type 1 ICP27 induces apoptotic cell death by increasing intracellular reactive oxygen species]

HSV-1 ICP27, an immediate early protein of herpes simplex virus type 1, is involved in viral replication, transcriptional activation, RNA stability, apoptosis, and reactivation from viral latency. The reactivation from viral latency is closely related to apoptosis and oxidative stress. To understand the effect of ICP27 upon apoptosis, we tested for cell death of ICP27-expressing cells (3-3) in the presence of hydrogen peroxide. Under oxidative stress, 3-3 cells were sensitive to death, displaying typical apoptosis features such as oligonucleosomal DNA fragmentation, chromatin condensation, and G0/G1 accumulation. To dissect the sensitizing mechanism of ICP27 in apoptosis, we analyzed the level of intracellular reactive oxygen species (ROS) in 3-3 cells. We found that 3-3 cells exhibited increased ROS levels compared to Vero cells devoid of ICP27. We also observed that the increased levels of intracellular ROS in 3-3 cells were caused by disturbances in antioxidant enzymes. In 3-3 cells, the elevated ROS increased the AP-1 activity, subsequently the expression of Bax increased, and the expression of Bcl2 was reduced. In addition, 3-3 cells were sensitive to various apoptotic agents. Taken together, these results indicate that HSV-I ICP27 sensitizes the cells to apoptosis by elevating the intracellular levels of ROS.

Type 1 angiotensin receptor (AT1-R)-mediated decrease in type 2 angiotensin receptor mRNA level is dependent on Gq and extracellular signal-regulated kinase 1//2 in AT1-R-transfected PC12 cells

Angiotensin II (Ang II) functions through two major Ang II receptor subtypes, type 1 (AT1-R) and type 2 (AT2-R), both of which are classified to be G protein-coupled receptors. AT2-R is highly expressed at the fetal stage, and in heart remodelling and brain ischaemia; therefore, it is important to clarify the regulatory mechanisms of AT2-R expression. Although AT1-R is generally believed to modulate AT2-R expression in some tissues or cells, the exact mechanism remains to be clarified. In the present study, we examined the effect of AT1-R stimulation on expression of endogenous rat AT2-R (rAT2-R) in AT1-R-transfected PC12 cells. rAT2-R mRNA and protein expression were decreased by Ang II in PC12 cells transfected with rAT1A-R in a time-dependent manner, mediated through a decline in mRNA stability. The C-terminus of G protein-coupled receptor (GPCR) is important for GPCR-mediated signal transduction. Therefore, we used C-terminus-deleted human AT1-R (hAT1-327STOP), which is thought to be a nondesensitised mutant of hAT1-R. As a result, Ang II decreased rAT2-R mRNA expression to a greater extent in cells transfected with hAT1-327STOP than with wild-type hAT1-R. The decrease was completely reversed by AT1-R antagonist candesartan, G(q) inhibitor YM254980, and mitogen-activated protein kinase (MAPK) kinase 1/2 inhibitor U0126, but not by pertussis toxin, which uncouples the receptor with G(i), or p38 MAPK inhibitor SB203580. We suggest, possibly for the first time, that the hAT1-R/G(q)/extracellular signal-regulated kinase 1/2 pathway is involved in the down-regulation of AT2-R using PC12 cells transfected with AT1-R.

Does the nonsense-mediated mRNA decay mechanism prevent the synthesis of truncated BRCA1, CHK2, and p53 proteins?

The nonsense-mediated mRNA decay (NMD) mechanism is an evolutionarily conserved process ensuring the degradation of transcripts carrying premature termination codon(s). NMD is believed to prevent the synthesis of truncated proteins that could be detrimental to the cell. However, although numerous studies have assessed the efficiency of this mechanism at the mRNA level, data are lacking in regard to whether NMD fulfills its expected goal at the protein level. In this study, we have investigated whether endogenous alleles of breast cancer predisposing genes carrying nonsense codons were able to produce detectable amounts of truncated proteins in lymphoblastoid cell lines. A total of 20 truncating BRCA1 mutations were analyzed, along with the 1100delC CHEK2 and the 770delT TP53 mutations. All the studied alleles triggered NMD, the amount of mutant transcript ranging from 16 to 63% of that of the wild-type species. We found that BRCA1 and CHK2 truncated proteins could not be detected, even when NMD was inhibited. This suggests that BRCA1 and CHK2 truncated proteins are highly unstable. Conversely, the p53 protein encoded by the 770delT allele is as abundant as the wild-type protein, as removal of the C-terminal p53 domain leads to a stabilized mutant protein, whose abundance is markedly increased when NMD is inhibited. Therefore, our results show that it is not possible to infer the presence of truncated proteins in cells from carriers of a truncated mutation without experimental verification, as each case is expected to be different.

Variable-length poly-C tract polymorphisms of the beta2-adrenergic receptor 3'-UTR alter expression and agonist regulation

Beta(2)-adrenergic receptors (beta(2)-AR) expressed on airway epithelial and smooth muscle cells regulate mucociliary clearance and relaxation and are the targets for beta-agonists in the treatment of obstructive lung disease. However, the clinical responses display extensive interindividual variability, which is not adequately explained by genetic variability in the 5'-flanking or coding region of the intronless beta(2)-AR gene. The nonsynonymous coding polymorphism most often associated with a bronchodilator phenotype (Arg16) is found within three haplotypes that differ by the number of Cs (11, 12, or 13) within a 3'-untranslated region (UTR) poly-C tract. To examine potential effects of this variability on receptor expression, BEAS-2B cells were transfected with constructs containing the beta(2)-AR (Arg16) coding sequence followed by its 3'-UTR with the various polymorphic poly-C tracts. beta(2)Arg16-11C had 25% lower mRNA expression and 33% lower beta(2)-AR protein expression compared with the other two haplotypes. Consistent with this lower steady-state expression, beta(2)Arg16-11C mRNA displayed more rapid and extensive degradation after actinomycin D treatment compared with beta(2)Arg16-12C and -13C. However, beta(2)Arg16-12C underwent 50% less downregulation of receptor expression during beta-agonist exposure compared with the other two haplotypes. Thus these haplotypes direct a potential low-response phenotype due to decreased steady-state receptor expression combined with wild-type agonist-promoted downregulation (beta(2)Arg16-11C) and a high-response phenotype due to increased baseline expression combined with decreased agonist-promoted downregulation (beta(2)Arg16-12C). This heterogeneity may contribute to the variability of clinical responses to beta-agonist, and genotyping to identify these 3'-UTR polymorphisms may improve predictive power within the context of beta(2)-AR haplotypes in pharmacogenetic studies.

The transcriptional inhibitor thiolutin blocks mRNA degradation in yeast

Thiolutin is commonly used as a general inhibitor of transcription in yeast. It has been used to calculate mRNA decay rates by stopping the transcription and then determining the relative abundance of individual mRNAs at different times after inhibition. We report here that thiolutin is also an inhibitor of mRNA degradation, and thus its use can lead to miscalculations of mRNA half-lives. The inhibition of mRNA decay seems to affect the mRNA degradation pathway without impeding poly(A) shortening, given that the decay rate of total poly(A) amount is not reduced by thiolutin. Moreover, the thiolutin-dependent inhibition of mRNA degradation has variable effects on different functional groups of genes, suggesting that they use various degradation pathways for their mRNAs.

Reactive oxygen species mediate Na+-induced SOS1 mRNA stability in Arabidopsis

Salt Overly Sensitive 1 (SOS1), a plasma membrane Na+/H+ antiporter in Arabidopsis, is a salt tolerance determinant crucial for the maintenance of ion homeostasis in saline stress conditions. SOS1 mRNA is unstable at normal growth conditions, but its stability is substantially increased under salt stress and other ionic and dehydration stresses. In addition, H2O2 treatment increases the stability of SOS1 mRNA. SOS1 mRNA is inherently unstable and rapidly degraded with a half-life of approximately 10 min. Rapid decay of SOS1 mRNA requires new protein synthesis. Stress-induced SOS1 mRNA stability is mediated by reactive oxygen species (ROS). NADPH oxidase is also involved in the upregulation of SOS1 mRNA stability, presumably through the control of extracellular ROS production. The cis-element required for SOS1 mRNA instability resides in the 500-bp region within the 2.2 kb at the 3' end of the SOS1 mRNA. Furthermore, mutations in the SOS1 gene render sos1 mutants more tolerant to paraquat, a non-selective herbicide causing oxidative stress, indicating that SOS1 plays negative roles in tolerance of oxidative stress. A hypothetical model for the signaling pathway involving SOS1-mediated pH changes, NADPH oxidase activation, apoplastic ROS production and downstream signaling transduction is proposed, and the biological significance of ROS-mediated induction of SOS1 mRNA stability is discussed.

Somatostatin inhibits basal and growth hormone-stimulated hepatic insulin-like growth factor-I production

Growth of vertebrates is controlled by the growth hormone (GH)-insulin-like growth factor-I (IGF-I) system, and somatostatins (SSs) have been shown to inhibit growth by reducing the release of growth hormone (GH) from the pituitary. In this study, we used rainbow trout to assess the effects of SSs on the production of IGF-I. Somatostatin-14 (SS-14-I) implantation for 15 days significantly reduced steady-state levels of IGF-I mRNA in liver and lowered IGF-I concentration in plasma compared to control animals. The direct effects of SSs were examined on hepatocytes incubated in vitro. SS-14-I inhibited basal and GH-stimulated IGF-I mRNA expression. SS-14-I inhibition of GH-stimulated IGF-I expression was concentration- and time-dependent; the ED(50) was ca. 40 ng/ml and the maximum response was observed after 6h. All SS isofoms tested, including the N-terminally extended form of SS-14-I, SS-28-I, and the [Tyr(7), Gly(10)]-substituted forms of SS, SS-14-II, SS-25-II and SS-28-II, inhibited GH-stimulated IGF-I mRNA expression. The inhibitory effects of SS-14-I on steady-state levels of IGF-I mRNA resulted from reduced IGF-I mRNA transcription and not from altered mRNA stability. SS-14-I also reduced basal and GH-stimulated release of IGF-I into culture medium. These results indicate that SSs regulate growth in an extrapituitary manner by reducing hepatic IGF-I biosynthesis and secretion.

Molecular events involved in the increased expression of matrix metalloproteinase-9 by T lymphocytes of mammary tumor-bearing mice

Matrix metalloproteinases (MMPs) are a family of extracellular proteinases whose contributions to cancer progression have been studied because of their matrix-degrading abilities and elevated expression in advanced stage tumors. Recent findings suggest a role for MMPs during the multiple stages of tumor progression including establishment and growth, migration, invasion, metastasis, and angiogenesis. MMP-9 regulation at the molecular level can be studied by measuring the effect(s) of a variety of physiological and pharmacological agents on cells. Multiple signaling molecules such as protein kinase C, pertussis toxin-sensitive guanine nucleotide-binding protein G, and protein tyrosine kinases are known to mediate the secretion of MMPs in cell lines. We previously reported an upregulation of MMP-9 in T cells of mammary tumor-bearing mice. In this study, pharmacologic inhibitors were used to dissect the signaling pathways involved in the upregulation of MMP-9 in the splenic T cells of normal and mammary tumor-bearing mice. Staurosporine, a protein kinase inhibitor, stimulated MMP-9 secretion by normal T lymphocytes, while the constitutively high levels of MMP-9 produced by tumor bearers' T cells were decreased by Genistein, a specific tyrosine kinase inhibitor, and Rottlerin, a PKC inhibitor. Using a NF-kappaB specific probe to the murine MMP-9 promoter, electromobility shift assays of nuclear proteins from normal and tumor bearers' splenic T cells revealed a pattern of higher intensity bands from the tumor bearers' nuclear extracts, indicating a greater amount of these transcription factors bound to the recognition motif. When mammary tumor bearers' T cells were cultured with the NF-kappaB inhibitors, N-p-Tosyl-L-lysine chloromethyl ketone hydrochloride and Bay 11-7082, there was a subsequent decreased production of MMP-9. These results suggest that the tumor burden may be activating various signaling pathways within splenic T lymphocytes to upregulate MMP-9 expression.

Ultraviolet radiation (UVR) activates p38 MAP kinase and induces post-transcriptional stabilization of the C/EBPδ mRNA in G0 growth arrested mammary epithelial cells

The G(0) growth arrest (quiescent) state is highly conserved in evolution to promote survival under adverse environmental conditions. To maintain viability, G(0) growth arrested cells limit gene expression to essential growth control and pro-survival genes. CCAAT enhancer binding protein delta (C/EBPdelta), a member of the C/EBP family of nuclear proteins, is highly expressed in G(0) growth arrested mammary epithelial cells (MECs). Although C/EBPdelta gene transcription is elevated during G(0) growth arrest, C/EBPdelta mRNA and protein are relatively short lived, suggesting tight control of the cellular C/EBPdelta content in unstressed, quiescent cells. Treatment of G(0) growth arrested MECs with ultraviolet radiation (UVR) dramatically increases the C/EBPdelta mRNA half-life (approximately 4-fold) and protein content (approximately 3-fold). The mRNA stabilizing effects of UVR treatment are mediated by the C/EBPdelta mRNA 3'untranslated region, which contains an AU rich element. UVR increased p38 MAP kinase (MAPK) activation and SB203580, a p38 MAPK inhibitor, blocked UVR-induced C/EBPdelta mRNA stabilization. UVR increased the nuclear to cytoplasmic translocation of HuR, an ARE-binding protein that functions in mRNA stabilization. Finally, HuR siRNA treatment blocked UVR-induced stabilization of the C/EBPdelta and C/EBPbeta mRNAs but had no effect on C/EBPzeta (CHOP) mRNA stability. In summary, G(0) growth arrested MECs respond to UVR treatment by activating p38 MAPK, increasing HuR translocation and HuR/C/EBPdelta mRNA binding and stabilizing the C/EBPdelta mRNA. These results identify post-transcriptional stabilization of the C/EBPdelta mRNA as a mechanism to increase C/EBPdelta levels in the stress response of quiescent cells to UVR.

Inhibition of nonsense-mediated mRNA decay (NMD) by a new chemical molecule reveals the dynamic of NMD factors in P-bodies

In mammals, nonsense-mediated mRNA decay (NMD) is a quality-control mechanism that degrades mRNA harboring a premature termination codon to prevent the synthesis of truncated proteins. To gain insight into the NMD mechanism, we identified NMD inhibitor 1 (NMDI 1) as a small molecule inhibitor of the NMD pathway. We characterized the mode of action of this compound and demonstrated that it acts upstream of hUPF1. NMDI 1 induced the loss of interactions between hSMG5 and hUPF1 and the stabilization of hyperphosphorylated isoforms of hUPF1. Incubation of cells with NMDI 1 allowed us to demonstrate that NMD factors and mRNAs subject to NMD transit through processing bodies (P-bodies), as is the case in yeast. The results suggest a model in which mRNA and NMD factors are sequentially recruited to P-bodies.

Stabilization of IGFBP-1 mRNA by ethanol in hepatoma cells involves the JNK pathway

BACKGROUND/AIMS

Insulin-like growth factor-binding protein-1 (IGFBP-1) modulates cell growth and metabolism in a variety of physiopathological conditions. The aim of this study was to determine the molecular mechanisms involved in IGFBP-1 upregulation by ethanol.

METHODS

We studied IGFBP-1 regulation by ethanol at the protein, mRNA and gene promoter levels in the human hepatocarcinoma cell line, HepG2, which does not express significantly ethanol-metabolizing enzymes.

RESULTS

Ethanol (35-150mM) induced the IGFBP-1 mRNA and protein up to 5-fold in a dose-dependent manner. A similar effect was observed using primary cultures of human hepatocytes. Various inhibitors of ethanol metabolism and the antioxidant N-acetylcysteine did not prevent ethanol effects. While ethanol did not modify the IGFBP-1 gene promoter activity, it elicited a 2- to 3-fold increase in IGFBP-1 mRNA half-life and this stabilization required the 5' and the 3' untranslated mRNA region. Ethanol triggered a rapid activation of c-Jun N-terminal Kinase (JNK) in HepG2 cells and IGFBP-1 induction was significantly decreased by a specific inhibitor of JNK.

CONCLUSIONS

This study reveals a novel pathway of gene regulation by alcohol which involves the activation of JNK and the consequent mRNA stabilization.

Angiotensin II-induced mitogen-activated protein kinase phosphatase-1 expression in bovine adrenal glomerulosa cells: implications in mineralocorticoid biosynthesis

Angiotensin II (AngII) stimulates aldosterone biosynthesis in the zona glomerulosa of the adrenal cortex. AngII also triggers the MAPK pathways (ERK1/2 and p38). Because ERK1/2 phosphorylation is a transient process, phosphatases could play a crucial role in the acute steroidogenic response. Here we show that the dual specificity (threonine/tyrosine) MAPK phosphatase-1 (MKP-1) is present in bovine adrenal glomerulosa cells in primary culture and that AngII markedly increases its expression in a time- and concentration-dependent manner (IC(50) = 1 nm), a maximum of 548 +/- 10% of controls being reached with 10 nm AngII after 3 h (n = 3, P < 0.01). This effect is completely abolished by losartan, a blocker of the AT(1) receptor subtype. Moreover, this AngII-induced MKP-1 expression is reduced to 250 +/- 35% of controls (n = 3, P < 0.01) in the presence of U0126, an inhibitor of ERK1/2 phosphorylation, suggesting an involvement of the ERK1/2 MAPK pathway in MKP-1 induction. Indeed, shortly after AngII-induced phosphorylation of ERK1/2 (220% of controls at 30 min), MKP-1 protein expression starts to increase. This increase is associated with a reduction in ERK1/2 phosphorylation, which returns to control values after 3 h of AngII challenge. Enhanced MKP-1 expression is essentially due to a stabilization of MKP-1 mRNA. AngII treatment leads to a 53-fold increase in phosphorylated MKP-1 levels and a doubling of MKP-1 phosphatase activity. Overexpression of MKP-1 results in decreased phosphorylation of ERK1/2 and aldosterone production in response to AngII stimulation. These results strongly suggest that MKP-1 is the specific phosphatase induced by AngII and involved in the negative feedback mechanism ensuring adequate ERK1/2-mediated aldosterone production in response to the hormone.

[The effect of Furolan on the physiological and biochemical characteristics of ripening winter wheat grain]

The effects of the preparation Furolan, (2-furyl-2)-1,3-dioxolane, on the degree of mRNA polyadenylation and the pattern of protein synthesis in the ripening grain of several soft winter wheat (Triticum aestivum L.) cultivars were studied. It was demonstrated that Furolan stabilized mRNA in a cultivar-specific manner, thereby accelerating to various degrees the biochemical processes taking place in the ripening grain. Of the wheat cultivars studied, Krasnodarskaya 99 was the most responsive cultivar with respect to a set of changes in nucleic-protein metabolism; the cultivar Deya was next followed by the cultivar Bat'ko. The cultivar Kroshka did not respond to the treatment with Furolan. The cultivar specificity of this preparation allows its practical application to be optimized.

Genome-wide analysis of mRNA decay rates and their determinants in Arabidopsis thaliana

To gain a global view of mRNA decay in Arabidopsis thaliana, suspension cell cultures were treated with a transcriptional inhibitor, and microarrays were used to measure transcript abundance over time. The deduced mRNA half-lives varied widely, from minutes to >24 h. Three features of the transcript displayed a correlation with decay rates: (1) genes possessing at least one intron produce mRNA transcripts significantly more stable than those of intronless genes, and this was not related to overall length, sequence composition, or number of introns; (2) various sequence elements in the 3' untranslated region are enriched among short- and long-lived transcripts, and their multiple occurrence suggests combinatorial control of transcript decay; and (3) transcripts that are microRNA targets generally have short half-lives. The decay rate of transcripts correlated with subcellular localization and function of the encoded proteins. Analysis of transcript decay rates for genes encoding orthologous proteins between Arabidopsis, yeast, and humans indicated that yeast and humans had a higher percentage of transcripts with shorter half-lives and that the relative stability of transcripts from genes encoding proteins involved in cell cycle, transcription, translation, and energy metabolism is conserved. Comparison of decay rates with changes in transcript abundance under a variety of abiotic stresses reveal that a set of transcription factors are downregulated with similar kinetics to decay rates, suggesting that inhibition of their transcription is an important early response to abiotic stress.

Trichostatin A and 5 Aza-2' deoxycytidine decrease estrogen receptor mRNA stability in ER positive MCF7 cells through modulation of HuR

Trichostatin A (TSA) and 5-Aza 2'deoxycytidine (AZA), two well characterized pharmacologic inhibitors of histone deacetylation and DNA methylation, affect estrogen receptor alpha (ER) levels differently in ER-positive versus ER-negative breast cancer cell lines. Whereas pharmacologic inhibition of these epigenetic mechanisms results in re-expression and increased estrogen receptor alpha (ER) levels in ER-negative cells, treatment in ER-positive MCF7 cells results in decreased ER mRNA and protein levels. This decrease is dependent upon protein interaction with the ER 3'UTR. Actinomycin D studies showed a 37.5% reduction in ER mRNA stability from 4 to 1.5 h in AZA/TSA treated MCF7 cell lines; an effect not seen in 231ER + cells transfected with the ER coding region but lacking incorporation of the 3'UTR. AZA/TSA do not appear to directly interact with the 3'UTR but rather decrease stability through altered subcellular localization of the RNA binding protein, HuR. siRNA inhibition of HuR expression reduces both the steady-state and stability of ER mRNA, suggesting that HuR plays a critical role in the control of ER mRNA stability. Our data suggest that epigenetic modulators can alter stability through modulation of HuR subcellular distribution. Taken together, these data provide a novel anti-estrogenic mechanism for AZA and TSA in ER positive human breast cancer cells.

Glycogen synthase kinase-3beta: homologous regulation of cell surface insulin receptor level via controlling insulin receptor mRNA stability in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, 48 h-treatment with 20 mmol/L LiCl, 1 mmol/L valproic acid, 30 micromol/L SB216763, 30 micromol/L SB415286, or 100 nmol/L insulin, a condition that inhibits constitutive active glycogen synthase kinase-3 (GSK-3), decreased cell surface (125)I-insulin binding capacity by approximately 39%, without altering the K(d) value; LiCl, SB216763 or insulin decreased insulin receptor (IR) and IR precursor levels, attenuating insulin-induced Tyr-autophosphorylation of IR. LiCl increased inhibitory Ser9-phosphorylation of GSK-3beta at 6 h, decreasing (125)I-insulin binding at 24 h. SB216763-induced (125)I-insulin binding reduction (IC(50) = 3 micromol/L) was preceded by beta-catenin level increase by SB216763 (EC(50) = 11 micromol/L), a hallmark of GSK-3 inhibition. Insulin-induced rapid (> 1 min) Ser9-phosphorylation of GSK-3beta (Nemoto et al. 2006) was followed by approximately 48% decrease of IR level. LiCl did not stimulate endocytosis, nor proteolysis of IR. LiCl destabilized IR mRNA (t(1/2) = 9.3 vs. 6.5 h), decreasing IR mRNA level by approximately 47%, without altering IR gene transcription. Decreases of (125)I-insulin binding and IR level, as well as increased Ser9-phosphorylation of GSK-3beta were restored to the control levels by washing the test compound-treated cells. Thus, GSK-3beta regulates IR level via controlling IR mRNA stability.

Stabilization of SMAR1 mRNA by PGA2 involves a stem loop structure in the 5' UTR

Prostaglandins are anticancer agents known to inhibit tumor cell proliferation both in vitro and in vivo by affecting the mRNA stability. Here we report that a MAR-binding protein SMAR1 is a target of Prostaglandin A2 (PGA2) induced growth arrest. We identify a regulatory mechanism leading to stabilization of SMAR1 transcript. Our results show that a minor stem and loop structure present in the 5' UTR of SMAR1 (1-UTR) is critical for nucleoprotein complex formation that leads to SMAR1 stabilization in response to PGA2. This results in an increased SMAR1 transcript and altered protein levels, that in turn causes downregulation of Cyclin D1 gene, essential for G1/S phase transition. We also provide evidence for the presence of a variant 5' UTR SMAR1 (17-UTR) in breast cancer-derived cell lines. This form lacks the minor stem and loop structure required for mRNA stabilization in response to PGA2. As a consequence of this, there is a low level of endogenous tumor suppressor protein SMAR1 in breast cancer-derived cell lines. Our studies provide a mechanistic insight into the regulation of tumor suppressor protein SMAR1 by a cancer therapeutic PGA2, that leads to repression of Cyclin D1 gene.

Stabilized immune modulatory RNA compounds as agonists of Toll-like receptors 7 and 8

Viral and synthetic single-stranded RNAs are the ligands for Toll-like receptor (TLR)7 and TLR8. However, single-stranded RNA is rapidly degraded by ubiquitous RNases, and the studies reported to date have used RNA with lipid carriers. To overcome nuclease susceptibility of RNA, we have synthesized several RNAs incorporating a range of chemical modifications. The present study describes one pool of RNA compounds, referred to as stabilized immune modulatory RNA (SIMRA) compounds, in which two RNA segments are attached through their 3' ends. SIMRA compounds showed greater stability in human serum compared with linear RNA and activated human TLR8, but not TLR7, in HEK293 cells without using lipid carriers. Interestingly, another set of SIMRA compounds containing 7-deazaguanosine substituted for natural guanosine activated human TLR7 and TLR8. Additionally, TLR7- and TLR8-activating compounds, but not the compounds that activated only TLR8, stimulated mouse immune cells in vitro and in vivo and produced dose-dependent T helper 1-type cytokines. Both types of compounds activated human peripheral blood mononuclear cells, but only TLR7- and TLR8-activating compounds activated plasmacytoid dendritic cells and produced high levels of IFN-alpha. In monkeys, s.c. administration of both types of SIMRA compounds induced transient changes in peripheral blood monocytes and neutrophils, and activated T lymphocytes, monocytes, and NK cells. Both types of compounds induced IFN-gamma-inducible protein 10, but only the 7-deazaguanosine-containing compound that activated both TLR7 and TLR8 induced IFN-alpha in monkeys. This is a comprehensive study of RNA-based compounds containing structures and synthetic stimulatory motifs in mouse, monkey, and human systems without using lipid carriers.

Steroid-mediated regulation of the epithelial sodium channel subunits in mammary epithelial cells

The epithelial sodium channel (ENaC) is a key mediator of sodium transport in epithelia; however, little is known about ENaC expression in mammary epithelia. Using real-time PCR, we demonstrated the expression of the ENaC subunit mRNAs in mouse and human mammary cell lines and in vivo mouse mammary tissue. We determined the effects of glucocorticoids, progesterone, and prolactin on ENaC expression in four mammary cell lines. Dexamethasone induced all detectable ENaC subunits in noncancerous cell lines, HC11 and MCF10A. Interestingly, in cancerous cell lines (T-47D and MCF-7), both beta- and gamma- but not alphaENaC mRNAs were induced by dexamethasone. Progesterone induced ENaC mRNA only in T-47D cells, and prolactin had no effects. gammaENaC was rapidly induced by steroids, whereas induction of alpha- and betaENaC was slower; moreover, the induction of the beta-subunit required de novo protein synthesis. Dexamethasone treatment did not affect ENaC mRNA stability. Western blot analysis revealed immunoreactive bands corresponding to different forms of alpha-, beta-, and gammaENaC; dexamethasone significantly increased the intensity of alphaENaC (85 kDa) and betaENaC (90 kDa). We also showed an in vivo reduction in alphaENaC levels in the mammary tissue of lactating mice as compared with controls, whereas beta- and gammaENaC mRNA levels were significantly increased. Furthermore, dexamethasone in vivo significantly increased alpha-, beta-, and gammaENaC mRNA expression. Our data indicate that both mouse and human mammary cells express all ENaC subunits, and they are regulated by steroid hormones in a temporal and cell-specific manner both in culture and in vivo.