Human AAT gene transfer to pig liver improved by using a perfusion isolated organ endovascular procedure

OBJECTIVE

The efficiency of endovascular liver gene transfer in pigs is evaluated by comparing two models of retrograde catheterization: single lobe catheterization with portal inflow (open procedure) versus whole liver isolation with portal and inferior vena cava blockage (close procedure).

METHODS

Percutaneous endovascular catheterization was performed in pigs. Open procedure (n = 3): 8Fr balloon catheter placement in a suprahepatic branch through the jugular vein. Closed procedure (n = 3): simultaneous catheterization of the intrahepatic portal vein (transhepatic catheterization, 10Fr balloon catheter), the supra- and infrahepatic cava veins (8Fr balloon catheters through the jugular and femoral veins). In both models, 200 ml of hAAT DNA solution (20 μg/ml) were retrogradely injected at 20 ml/s. Tissue samples (8 per liver) were obtained 14 days later and the exogenous DNA, RNA and protein per cell were quantified. Blood samples were collected periodically for transaminase determination in all the animals.

RESULTS

The open procedure achieved lower (approx. 1000-fold) DNA delivery, resulting in a significantly lower (p < 0.001) gene transcription (> 100-fold). The closed model also achieved a higher translation index, although differences were smaller (p < 0.001).

CONCLUSIONS

Portal inflow blockage increased the delivery, transcription and translation indexes, significantly improving the final procedure efficacy when compared with an open procedure.

KEY POINTS

Endovascular hydrodynamic pig liver gene transfer: open procedure versus closed procedure. Open procedure resulted in much lower DNA delivery than closed model. Open procedure reached significantly lower gene transcription index. Translation index with closed model was higher than with the open.

Low RNA translation activit limits the efficacy of hydrodynamic gene transfer to pig liver in vivo

BACKGROUND

Hydrodynamic gene delivery has proved an efficient strategy for nonviral gene therapy in the murine liver but it has been less efficient in pigs. The reason for such inefficiency remains unclear. The present study used a surgical strategy to seal the whole pig liver in vivo.

METHODS

A solution of enhanced green fluorescent protein (eGFP) DNA was injected under two different venous injection conditions (anterograde and retrograde), employing flow rates of 10 and 20 ml/s in each case, with the aim of identifying the best gene transfer conditions. The gene delivery and information decoding steps were evaluated by measuring the eGFP DNA, mRNA and protein copy number 24 h after transfection. In addition, gold nanoparticles (diameters of 4 and 15 nm) were retrogradely injected (10 ml/s) to observe, by electron microscopy, the ability of the particle to access the hepatocyte.

RESULTS

The gene delivery level was higher with anterograde injection, whereas the efficacy of gene expression was better with retrograde injection, suggesting differences in the decoding processes. Thus, retrograde injection mediates gene transcription (mRNA copy/cell) equivalent to that of intermediate expression proteins but the mRNA translation was lower than that of rare proteins. Electron microscopy showed that nanoparticles within the hepatocyte were almost exclusively 4 nm in diameter.

CONCLUSIONS

The results suggest that the low activity of mRNA translation limits the final efficacy of the gene transfer procedure. On the other hand, the gold nanoparticles study suggests that elongated DNA conformation could offer advantages in that the access of 15-nm particles is very limited.

[Role of antithrombin iii in cardiac surgery]

Coagulation of blood is of multidisciplinary interest. Cardiac surgery produces major changes in the delicate balance between pro-and anti-coagulant serum factors. The role of antithrombin iii has been analysed after finding evidence that associated decreased levels of protein activity to postoperative morbidity and mortality. Supplementing exogenous antithrombin is considered with the aim of optimising outcomes. Its intrinsic anticoagulant and anti-inflammatory properties have stimulated a growing interest, and suggests new lines of research.

The three α1-adrenoceptor subtypes show different spatio-temporal mechanisms of internalization and ERK1/2 phosphorylation

We analyzed the kinetic and spatial patterns characterizing activation of the MAP kinases ERK 1 and 2 (ERK1/2) by the three α1-adrenoceptor (α1-AR) subtypes in HEK293 cells and the contribution of two different pathways to ERK1/2 phosphorylation: protein kinase C (PKC)-dependent ERK1/2 activation and internalization-dependent ERK1/2 activation. The different pathways of phenylephrine induced ERK phosphorylation were determined by western blot, using the PKC inhibitor Ro 31-8425, the receptor internalization inhibitor concanavalin A and the siRNA targeting β-arrestin 2. Receptor internalization properties were studied using CypHer5 technology and VSV-G epitope-tagged receptors. Activation of α1A- and α1B-ARs by phenylephrine elicited rapid ERK1/2 phosphorylation that was directed to the nucleus and inhibited by Ro 31-8425. Concomitant with phenylephrine induced receptor internalization α1A-AR, but not α1B-AR, produced a maintained and PKC-independent ERK phosphorylation, which was restricted to the cytosol and inhibited by β-arrestin 2 knockdown or concanavalin A treatment. α1D-AR displayed constitutive ERK phosphorylation, which was reduced by incubation with prazosin or the selective α1D antagonist BMY7378. Following activation by phenylephrine, α1D-AR elicited rapid, transient ERK1/2 phosphorylation that was restricted to the cytosol and not inhibited by Ro 31-8425. Internalization of the α1D-AR subtype was not observed via CypHer5 technology. The three α1-AR subtypes present different spatio-temporal patterns of receptor internalization, and only α1A-AR stimulation translates to a late, sustained ERK1/2 phosphorylation that is restricted to the cytosol and dependent on β-arrestin 2 mediated internalization.

Different expression of adrenoceptors and GRKs in the human myocardium depends on heart failure etiology and correlates to clinical variables

Downregulation of β(1)- adrenergic receptors (β(1)-ARs) and increased expression/function of G-protein-coupled receptor kinase 2 (GRK2) have been observed in human heart failure, but changes in expression of other ARs and GRKs have not been established. Another unresolved question is the incidence of these compensatory mechanisms depending on heart failure etiology and treatment. To analyze these questions, we quantified the mRNA/protein expressions of six ARs (α(1A), α(1B), α(1D), β(1), β(2), and β(3)) and three GRKs (GRK2, GRK3, and GRK5) in left (LV) and right ventricle (RV) from four donors, 10 patients with ischemic cardiomyopathy (IC), 14 patients with dilated cardiomyopathy (DC), and 10 patients with nonischemic, nondilated cardiopathies (NINDC). We correlated the changes in the expressions of ARs and GRKs with clinical variables such as left ventricular ejection fraction (LVEF) and left ventricular end-systolic and left ventricular end-diastolic diameter (LVESD and LVEDD, respectively). The main findings were 1) the expression of the α(1A)-AR in the LV positively correlates with LVEF; 2) the expression of GRK3 and GRK5 inversely correlates with LVESD and LVEDD, supporting previous observations about a protective role for both kinases in failing hearts; and 3) β(1)-AR expression is downregulated in the LV and RV of IC, in the LV of DC, and in the RV of NINDC. This difference, better than an increased expression of GRK2 (not observed in IC), determines the lower LVEF in IC and DC vs. NINDC.

MicroRNAs-10a and -10b contribute to retinoic acid-induced differentiation of neuroblastoma cells and target the alternative splicing regulatory factor SFRS1 (SF2/ASF)

MicroRNAs (miRNAs) are an emerging class of non-coding endogenous RNAs involved in multiple cellular processes, including cell differentiation. Treatment with retinoic acid (RA) results in neural differentiation of neuroblastoma cells. We wanted to elucidate whether miRNAs contribute to the gene expression changes induced by RA in neuroblastoma cells and whether miRNA regulation is involved in the transduction of the RA signal. We show here that RA treatment of SH-SY5Y neuroblastoma cells results in profound changes in the expression pattern of miRNAs. Up to 42 different miRNA species significantly changed their expression (26 up-regulated and 16 down-regulated). Among them, the closely related miR-10a and -10b showed the most prominent expression changes. Induction of miR-10a and -10b by RA also could be detected in LA-N-1 neuroblastoma cells. Loss of function experiments demonstrated that miR-10a and -10b are essential mediators of RA-induced neuroblastoma differentiation and of the associated changes in migration, invasion, and in vivo metastasis. In addition, we found that the SR-family splicing factor SFRS1 (SF2/ASF) is a target for miR-10a -and -10b in HeLa and SH-SY5Y neuroblastoma cells. We show here that changes in miR-10a and -10b expression levels may regulate SFRS1-dependent alternative splicing and translational functions. Taken together, our results give support to the idea that miRNA regulation plays a key role in RA-induced neuroblastoma cell differentiation. The discovery of SFRS1 as direct target of miR-10a and -10b supports the emerging functional interaction between two post-transcriptional mechanisms, microRNAs and splicing, in the neuronal differentiation context.

Alpha1-adrenoceptors in the rat cerebral cortex: new insights into the characterization of alpha1L- and alpha1D-adrenoceptors

Among the three alpha(1)-adrenoceptor subtypes (alpha(1A), alpha(1B) and alpha(1D)) a peculiar intracellular localization and poor coupling to membrane signals of cloned alpha(1D)-adrenoceptor have been reported. In addition, the alpha(1L)-adrenoceptor (low affinity for prazosin), a functional phenotype of alpha(1A), has been described. The purpose of this work was to analyze the expression, cellular localization and coupling to membrane signalling (inositol phosphate accumulation) of alpha(1)-adrenoceptor subtypes in a native tissue, the rat cerebral cortex. mRNA for the three subtypes was quantified by real-time RT-PCR (alpha(1D)>alpha(1B)>>alpha(1A)). alpha(1)-Adrenoceptors were also detected by immunoblotting, revealing alpha(1A)- and alpha(1B)-adrenoceptors to be predominantly expressed in the membrane fraction and the alpha(1D)-adrenoceptor to be localized in the cytosolic fraction. Competitive radioligand binding studies revealed the presence of alpha(1D)-adrenoceptor in tissue homogenates, whereas only alpha(1A)- and alpha(1B)-subtypes were detected in membranes. The proportion of alpha(1A)-adrenoceptor increased after treatment with noradrenaline, suggesting differences in agonist-mediated trafficking. Saturation experiments detected high- and low (alpha(1A/L))-prazosin binding sites, the latter of which disappeared on incubation with GppNHp. The alpha(1A/L)-adrenoceptor was heavily implicated in the inositol phosphate response, while the alpha(1D)-subtype did not play a relevant role. These results suggest that the predominant cytosolic localization of alpha(1D)-adrenoceptor lies behind its poor coupling to membrane signalling such as inositol phosphate pathway. The fact that the alpha(1L)-adrenoceptor detected in radioligand binding studies disappeared in the presence of GppNHp implies that it represents a conformational state of the alpha(1A)-adrenoceptor coupled to G-protein.

Proteomic analysis of phosphorylated nuclear proteins underscores novel roles for rapid actions of retinoic acid in the regulation of mRNA splicing and translation

Retinoic acid (RA) signaling is mediated by the retinoic acid receptor (RAR), belonging to the nuclear hormone receptor superfamily. In addition to its classical transcriptional actions, RAR also mediates rapid transcription-independent (nongenomic) actions, consisting in the activation of signal transduction pathways, as the phosphatidyl-inositol-3-kinase or the ERK MAPK-signaling pathways. RA-induced rapid transcription-independent actions play a role in different physiological contexts. As an effort toward understanding the functions of those rapid actions on signaling elicited by RA, we have identified nuclear proteins the phosphorylation state of which is rapidly modified by RA treatment in neuroblastoma cells, using a proteomic approach. Our results show that RA treatment led to changes in the phosphorylation patterns in two families of proteins: 1) those related to chromatin dynamics in relation to transcriptional activation, and 2) those related to mRNA processing and, in particular, mRNA splicing. We show that treatment of neuroblastoma cells with RA leads to alteration of the regulation of pre-mRNA splicing and mRNA translation. Thus, our results underscore novel functions for the rapid signaling elicited by RAR in the regulation of mRNA processing. We conclude that RA activation of signaling pathways can indeed regulate mRNA processing as part of a cellular response orchestrated by the nuclear receptor RAR.

The impact of alpha1-adrenoceptors up-regulation accompanied by the impairment of beta-adrenergic vasodilatation in hypertension

In human and animal hypertension models, increased activity of G-protein-coupled receptor kinase (GRK) 2 determines a generalized decrease of beta-adrenergic vasodilatation. We analyzed the possibility of differential changes in the expression and functionality of alpha(1A), alpha(1B), alpha(1D), beta(1), beta(2), and beta(3)-ARs also being involved in the process. We combined the quantification of mRNA levels with immunoblotting and functional studies in aortas of young and adult spontaneously hypertensive rats (SHRs) and their controls (Wistar Kyoto). We found the expression and function of beta(1)-adrenoceptors in young prehypertensive SHRs to be higher, whereas a generalized increase in the expression of the six adrenoceptors and GRK2 was observed in aortas of adult hypertensive SHRs. alpha(1D)- and beta(3)-adrenoceptors, the subtypes that are more resistant to GRK2-mediated internalization and mostly expressed in rat aorta, exhibited an increased functional role in hypertensive animals, showing two hemodynamic consequences: 1) an increased sensitivity to the vasoconstrictor stimulus accompanied by a decreased sensitivity to the vasodilator stimulus (alpha(1D)-ARs are the most sensitive to agonists, and beta(3)-ARs are the least sensitive to agonists); and 2) a slower recovery of the basal tone after adrenergic stimulus removal because of the kinetic characteristic of the alpha(1D) subtype. These functional changes might be involved in the greater sympathetic vasoconstrictor tone observed in hypertension.

Rapid, nongenomic actions of retinoic acid on phosphatidylinositol-3-kinase signaling pathway mediated by the retinoic acid receptor

Retinoic acid (RA) treatment of SH-SY5Y neuroblastoma cells results in activation of phosphatidylinositol-3-kinase (PI3K) signaling pathway, and this activation is required for RA-induced differentiation. Here we show that RA activates PI3K and ERK1/2 MAPK signaling pathways through a rapid, nongenomic mechanism that does not require new gene transcription or newly synthesized proteins. Activation of PI3K by RA appears to involve the classical nuclear receptor, retinoic acid receptor (RAR), on the basis of the pharmacological profile of the activation, loss, and gain of function experiments with mouse embryo fibroblast-RAR(alpha beta gamma)(L-/L-) null cells, and the physical association between liganded RAR and PI3K activity. The association of RAR with the two subunits of PI3K was differentially regulated by the ligand. Immunoprecipitation experiments performed in SH-SY5Y cells showed stable association between RARalpha and p85, the regulatory subunit of PI3K, independently of the presence of RA. In contrast, ligand administration increased the association of p110, the catalytic subunit of PI3K, to this complex. The intracellular localization of RAR proved to be relevant for PI3K activation. A chimerical RAR fusing c-Src myristylation domain to the N terminus of RARalpha (Myr-RARalpha) was targeted to plasma membrane. Transfection of Myr-RARalpha to mouse embryo fibroblast-RAR(alpha beta gamma)(L-/L-) null cells and COS-7 cells results in strong activation of the PI3K signaling pathway, although both in the absence as well in the presence of RA. Our results support a mechanism in which ligand binding to RAR would play a major role in the assembly and intracellular location of a signaling complex involving RAR and the subunits of PI3K.

cDNA cloning and 1.75 A crystal structure determination of PPL2, an endochitinase and N-acetylglucosamine-binding hemagglutinin from Parkia platycephala seeds

Parkia platycephala lectin 2 was purified from Parkia platycephala (Leguminosae, Mimosoideae) seeds by affinity chromatography and RP-HPLC. Equilibrium sedimentation and MS showed that Parkia platycephala lectin 2 is a nonglycosylated monomeric protein of molecular mass 29 407+/-15 Da, which contains six cysteine residues engaged in the formation of three intramolecular disulfide bonds. Parkia platycephala lectin 2 agglutinated rabbit erythrocytes, and this activity was specifically inhibited by N-acetylglucosamine. In addition, Parkia platycephala lectin 2 hydrolyzed beta(1-4) glycosidic bonds linking 2-acetoamido-2-deoxy-beta-D-glucopyranose units in chitin. The full-length amino acid sequence of Parkia platycephala lectin 2, determined by N-terminal sequencing and cDNA cloning, and its three-dimensional structure, established by X-ray crystallography at 1.75 A resolution, showed that Parkia platycephala lectin 2 is homologous to endochitinases of the glycosyl hydrolase family 18, which share the (betaalpha)8 barrel topology harboring the catalytic residues Asp125, Glu127, and Tyr182.

1alpha,25-Dihydroxyvitamin D3 regulates the expression of Id1 and Id2 genes and the angiogenic phenotype of human colon carcinoma cells

1alpha,25-Dihydroxyvitamin D3 (1alpha,25(OH)2D3) has antitumor activity in addition to its classical action on calcium metabolism and bone tissue biology. It is thought to regulate the expression of multiple target genes and thus modulate processes critical for tumor growth and metastases. Here we show that 1alpha,25(OH)2D3 differentially regulates the expression of Id1 and Id2 genes, members of a family of transcriptional regulators of cell proliferation and differentiation. 1alpha,25(OH)2D3 induced epithelial differentiation in SW480-ADH human colon carcinoma cell line by promoting expression of the proteins implicated in adherent junction formation, including E-cadherin, and by inhibiting beta-catenin transcriptional activity. 1alpha,25(OH)2D3 activated the human Id1 gene promoter and rapidly induced Id1 RNA and protein. Ectopic overexpression of Id1 was not sufficient to induce E-cadherin, which was critical for the morphological changes induced by 1alpha,25(OH)2D3 in SW480-ADH cells. Conversely, Id2 transcription rate, RNA and protein levels were decreased by 1alpha,25(OH)2D3. Id2 downregulation by 1alpha,25(OH)2D3 mediated the antiproliferative effect of 1alpha,25(OH)2D3 on SW480-ADH cells. In addition, we showed that 1alpha,25(OH)2D3 changed the levels of the inducer of angiogenesis, vascular endothelial growth factor and the potent antiangiogenic factor thrombospondin-1, leading to a balanced change in the angiogenic potential of SW480-ADH human colon carcinoma cells.

Correlation between mRNA levels and functional role of alpha1-adrenoceptor subtypes in arteries: evidence of alpha1L as a functional isoform of the alpha1A-adrenoceptor

The mRNA levels for the three alpha1-adrenoceptor subtypes, alpha1A, alpha1B, and alpha1D, were quantified by real-time RT-PCR in arteries from Wistar rats. The alpha1D-adrenoceptor was prominent in both aorta (79.0%) and mesenteric artery (68.7%), alpha1A predominated in tail (61.7%) and small mesenteric artery (73.3%), and both alpha1A- and alpha1D-subtypes were expressed at similar levels in iliac artery. The mRNA levels of the alpha1B-subtype were a minority in all vessels (1.7-11.1%). Concentration-response curves of contraction in response to phenylephrine or relaxation in response to alpha1-adrenoceptor antagonists on maximal sustained contraction induced by phenylephrine were constructed from control vessels and vessels pretreated with 100 micromol/l chloroethylclonidine (CEC) for 30 min. The significant decrease in the phenylephrine potency observed after CEC treatment together with the inhibitory potency displayed by 8-{2-[4-(2-methoxyphenyl)-1-piperazinyl]-8-azaspiro (4,5) decane-7-dionedihydrochloride} (BMY-7378, an alpha1D-adrenoceptor antagonist) confirm the relevant role of alpha1D-adrenoceptors in aorta and iliac and proximal mesenteric arteries. The potency of 5-methylurapidil (an alpha1A-adrenoceptor antagonist) and the changes in the potency of both BMY-7378 and 5-methylurapidil after CEC treatment provided evidence of a mixed population of alpha1A- and alpha1D-adrenoceptors in iliac and distal mesenteric arteries. The low potency of prazosin (pIC50 < 9) as well as the high 5-methylurapidil potency in tail and small mesenteric arteries suggest the main role of alpha1A/alpha1L-adrenoceptors with minor participation of the alpha1D-subtype. The mRNA levels and CEC treatment corroborated this pattern and confirmed that the alpha1L-adrenoceptor could be a functional isoform of the alpha1A-subtype.

Transcriptional profiling of early onset diet-induced atherosclerosis in apolipoprotein E-deficient mice

Excessive dietary fat and cholesterol exacerbate atherosclerosis. To obtain unbiased insight into the early pathological changes induced by fat feeding in the artery wall, we used high-density microarrays to generate transcriptional profiles of aortic tissue from two groups of atherosclerosis-prone apolipoprotein E-null mice: controls maintained on standard chow and experimental animals exposed short-term to a Western-type diet, a regimen which produced severe hypercholesterolemia without significant development of atheromas. By applying rigorous selection criteria, we identified 311 genes differentially regulated by these dietary conditions. The set of diet-regulated genes exhibited striking functional relationships and represented both novel and known regulatory networks implicated in injury of the artery wall, including cell adhesion genes, histocompatibility antigen and major histocompatibility complex genes, flavin-containing monooxygenases, interferon-regulated genes, small inducible cytokines, collagen and procollagen genes, and complement system components. Further examination of genes identified by this study will provide insights into the molecular mechanisms by which high-fat cholesterol-rich dietary regime initiates pathological alterations in healthy arteries.

Profile of P‐glycoprotein Distribution in the Rat and Its Possible Influence on the Salbutamol Intestinal Absorption Irocess

The intrinsic absorption of salbutamol in different intestinal segments of the rat was measured and related with the corresponding intestinal P-glycoprotein (P-gp) expression levels. The apparent absorption rate constants (k(a), h(-1)) observed in each fraction by means of the "in situ" rat gut absorption method after perfusion of a 0.29-mM isotonic solution of salbutamol were used as absorption indexes. In a separate series of studies, a semiquantitative analysis of the mRNA expression of P-gp by means of polymerase chain reaction and Western blot with an antibody raised against the P-gp were also performed. The "in situ" k(a) values determined in the different segments (h(-1)) showed that the absorption is not homogeneous along the intestinal tract, that is, 0.499 +/- 0.054 for colon, 0.474 +/- 0.052 for the proximal segment, 0.345 +/- 0.014 for the mean, and 0.330 +/- 0.023 for the distal fraction. Addition of verapamil to the perfusion fluid did provide a better absorption of salbutamol in the distal segment. The analysis of the mRNA expression and levels of P-gp showed that the enzyme content in each section of the intestine was inversely related to salbutamol absorption.

Glucocorticoid Receptor Counteracts Tumorigenic Activity of Akt in Skin through Interference with the Phosphatidylinositol 3-Kinase Signaling Pathway

The skin-targeted overexpression of the glucocorticoid receptor (GR) in transgenic mice dramatically impairs the inflammatory responses to tumor promoter agents and suppresses skin tumor development. The antiinflammatory, rapid effects of corticosteroids are partially exerted through interference of GR with the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway in several tissues, a highly relevant pathway in the mouse skin tumor progression process. In this work, we aimed to elucidate whether a cross-talk mechanism between GR and PI3K/Akt occurred in intact skin as well as the biological relevance of this interaction during skin tumorigenesis. We report that, in transgenic mice overexpressing the receptor, GR physically associated with p85 alpha/PI3K in skin, resulting in decreased Akt and I kappa B kinase activity. GR activation by dexamethasone in normal mouse skin also decreased Akt activity within minutes, whereas cotreatment with the GR antagonist RU486 abolished dexamethasone action. Indeed, GR exerted a nongenomic action because keratinocyte transfection with a transcriptionally defective receptor mutant still decreased PI3K and Akt activity. Moreover, GR coexpression greatly reduced the accelerated growth of malignant tumors and increased Akt activity induced by Akt-transfected keratinocytes, as shown by in vivo tumorigenic assays. Overall, our data strongly indicate that GR/PI3K-Akt cross-talk constitutes a major mechanism underlying the antitumor effect of glucocorticoids in skin.

Crystal structure of a prostate kallikrein isolated from stallion seminal plasma: a homologue of human PSA

Prostate-specific kallikrein, a member of the gene family of serine proteases, was initially discovered in semen and is the most useful serum marker for prostate cancer diagnosis and prognosis. We report the crystal structure at 1.42A resolution of horse prostate kallikrein (HPK). This is the first structure of a serine protease purified from seminal plasma. HPK shares extensive sequence homology with human prostate-specific antigen (PSA), including a predicted chymotrypsin-like specificity, as suggested by the presence of a serine residue at position S1 of the specificity pocket. In contrast to other kallikreins, HPK shows a structurally distinct specificity pocket. Its entrance is blocked by the kallikrein loop, suggesting a possible protective or substrate-selective role for this loop. The HPK structure seems to be in an inactivated state and further processing might be required to allow the binding of substrate molecules. Crystal soaking experiments revealed a binding site for Zn(2+) and Hg(2+), two known PSA inhibitors.

Activation of the phosphatidylinositol 3-kinase/Akt signaling pathway by retinoic acid is required for neural differentiation of SH-SY5Y human neuroblastoma cells

Retinoic acid (RA) induces neural differentiation of SH-SY5Y neuroblastoma cells. We show that the mRNA levels of the differentiation-inhibiting basic helix-loop-helix transcription factors ID1, ID2, and ID3 are down-regulated during RA-induced differentiation of SH-SY5Y cells. The levels of ID proteins decreased in parallel to the observed transcriptional repression. The expression of other basic helix-loop-helix genes changed during RA-induced differentiation: expression of neuroblast-specific ASCL1 (HASH-1) gene was promptly reduced after RA treatment, whereas expression of differentiation-promoting genes NEUROD6 (NEX-1, HATH-2) and NEUROD1 was increased. Treatments with 12-O-tetradecanoylphorbol-13-acetate, another inducer of neuroblastoma cell differentiation, also resulted in coordinated down-regulation of ID gene expression, underscoring the role of ID genes in differentiation. Down-regulation of ID gene expression by RA involves a complex mechanism because full transcriptional repression required newly synthesized proteins and signaling by phosphatidylinositol 3-kinase (PI3K). RA treatment activates the PI3K/Akt signaling pathway, resulting in increased PI3K activity in extracts from RA-treated cells and a rapid increase in phosphorylation of Akt in Ser-473. Inhibition of PI3K by LY294002 impaired RA-induced differentiation, as assessed by morphological and biochemical criteria. We propose that RA, by activating the PI3K/Akt signaling pathway, plays an important role in the regulation of neuronal cell survival.

Transcriptional repression of neurotrophin receptor trkB by thyroid hormone in the developing rat brain

Expression of the neurotrophin receptor trkB is regulated by thyroid hormone (T3) during development of the rat brain. trkB mRNA levels, coding for the full-length and the truncated isoforms, are increased in the cerebral cortex of neonatal experimental hypothyroid animals. Run-on transcription assays with nuclei from postnatal day 15, hypothyroid, and control cerebral cortices demonstrated that an increase in the transcription rate of the trkB gene accounts for the observed effect. Transient transfection experiments using a reporter plasmid containing a 7-kilobase pair DNA fragment upstream of the mouse trkB gene showed that unliganded thyroid hormone receptor (T3R) increases promoter activity, whereas addition of T3 reverses that activity below basal levels. Deletion analysis shows that the T3-dependent repression requires binding of the T3R to a specific region located downstream of the transcription start site. This region, at nucleotide position -465/-432, contains an array of thyroid hormone response half-sites that bind preferentially T3R as heterodimers with retinoid X receptor and whose deletion causes loss of the T3-dependent repression. These half-sites are able to confer negative regulation by T3 to a heterologous promoter, thus indicating the functionality of these sequences. These results demonstrate that, in the developing rat brain, T3 down-regulates the expression of the trkB gene through the active repression of a novel negative response element located downstream of its transcription initiation site.

Alcohol exposure alters the expression pattern of neural cell adhesion molecules during brain development

Neural cell adhesion molecules (NCAMs) play critical roles during development of the nervous system. The aim of this study is to investigate the possible effect of ethanol exposure on the pattern of expression and sialylation of NCAM isoforms during postnatal rat brain development because alterations in NCAM content and distribution have been associated with defects in cell migration, synapse formation, and memory consolidation, and deficits in these processes have been observed after in utero alcohol exposure. The expression of NCAM isoforms in the developing cerebral cortex of pups from control and alcohol-fed mothers was assessed by western blotting, ribonuclease protection assay, and immunocytochemistry. The highly sialylated form of NCAM [polysialic acid (PSA)-NCAM] is mainly expressed during the neonatal period and then is down-regulated in parallel with the appearance of NCAM 180 and NCAM 140. Ethanol exposure increases PSA-NCAM levels during the neonatal period, delays the loss of PSA-NCAM, decreases the amount of NCAM 180 and NCAM 140 isoforms, and reduces sialyltransferase activity during postnatal brain development. Neuraminidase treatment of ethanol-exposed neonatal brains leads to more intense band degradation products, suggesting a higher content of NCAM polypeptides carrying PSA in these samples. However, NCAM mRNA levels are not changed by ethanol. Immunocytochemical analysis demonstrates that ethanol triggers an increase in PSA-NCAM immunolabeling in the cytoplasm of astroglial cells, accompanied by a decrease in immunogold particles over the plasma membrane. These findings indicate that ethanol exposure during brain development alters the pattern of NCAM expression and suggest that modification of NCAM could affect neuronal-glial interactions that might contribute to the brain defects observed after in utero alcohol exposure.

Astrocytes in culture express the full-length Trk-B receptor and respond to brain derived neurotrophic factor by changing intracellular calcium levels: effect of ethanol exposure in rats

Although cultured astroglial cells were reported to express exclusively the truncated non-catalytic Trk B receptor for brain-derived neurotrophic factor (BDNF), we detect here, using a sensitive ribonuclease protection assay, mRNAs for both truncated (TrkB-T) and the full length catalytic (TrkB-fl) form of BDNF receptor in developing cortical astrocytes and neurons in culture. Cortical neurons and immature astroglia, such as radial glia and proliferating astrocytes, express both the protein and mRNAs for TrkB-fl and TrkB-T, whereas the differentiation of astrocytes leads to a decrease in the trkB-fl mRNA, being the truncated TrkB the predominant receptor in differentiating and confluent astrocytes. The levels of TrkB-fl expression in proliferating and differentiating astrocytes and neurons correlates with the cell response to BDNF, monitored by the rise in intracellular [Ca(2+)](i). Foetal exposure to ethanol alters astroglial development and delays the reduction in trkB-fl mRNA levels observed with differentiation of astrocytes. These results demonstrate that immature astrocytes are able to express the catalytic Trk B receptors and to respond to BDNF with the activation of conventional signal transduction pathways. The results suggest that this signalling pathway is more activated in ethanol-exposed cells.

The extent of the Aznalcóllar pyritic sludge spill and its effects on soils

This paper presents some initial results from the Instituto Tecnológico Geominero de España's (ITGE) study of the Aznalcóllar mine spill. The spatial distribution of the pyritic sludge released was surveyed by using remote sensing data, aerial photography, and more than 700 field measurements on the sludge thickness. Initial estimation of the extent of the sludge was provided by radar data. Maps at 1:10,000 scale, drawn on the basis of field data and interpretation of aerial photos, show the distribution of the sludge, divided into 168 subsections on the basis of average thickness. GIS analysis provided estimates of the area and volume of the sludge. Three approaches were followed in order to survey the effects of the spill on the Guadiamar river alluvial soils: (1) Mineralogical and chemical characterization of the sludge and its evolution until its removal. Alteration products of the pyritic sludge were also analyzed. (2) Determination of geochemical background of soils in the Guadiamar river basin, in order to establish the content of heavy metals and other elements in the soil before the spill. (3) Assessment of the sludge effect on soils caused by the acid water and the deposited sludge, by comparison of the heavy metal content of soil under the sludge layer with that of background soil. Finally, an airborne multispectral survey was carried out over the Aznalcóllar-Doñana area to evaluate its efficiency for monitoring soil condition during and after sludge removal.

The mouse neurotrophin receptor trkB gene is transcribed from two different promoters

We have analysed a 7-kb region upstream of the mouse trkB coding sequence. The region showed promoter activity in transient transfection experiments and conferred tissue-specific expression to a reporter gene. Deletion analysis of this region demonstrated the presence of two alternative promoters named P1 and P2 that have been mapped by RNase protection. P1 has been located to 1.8 kb and P2 to 0.5 kb upstream of the trkB translation start site. From the P1 promoter, alternative splicing generates various transcripts. Interestingly, P2 is located in an intron of the transcripts produced from the P1 promoter. This peculiar arrangement results in different mRNA species that encode the same protein(s) but differ in their 5'-untranslated regions. In addition, transcription of the trkB locus results in two different trkB isoforms (kinase and truncated receptors) originated by alternative splicing of the mRNA, that possess differential spatial and temporal expression patterns. Using RT-PCR, we demonstrated that there was no linkage between promoter usage and alternative splicing, since transcripts initiated from each promoter encoded both kinase and truncated receptor proteins.

Stimulation of the myelin basic protein gene expression by 9-cis-retinoic acid and thyroid hormone: activation in the context of its native promoter

Thyroid hormone plays an important role in brain development, in part by regulating myelination. Previous studies have shown that the myelin basic protein (MBP) promoter is activated by thyroid hormone (T3) via a T3-response element (T3RE) at position -186. Surprisingly, although MBP levels are initially decreased in hypothyroid neonates, they approach later control levels, in most brain regions, despite persistent hypothyroidism. We have studied the T3-independent transcriptional regulation of this gene, using transient transfection assays. We found that, in the absence of T3, the RXR ligand, 9-cis-retinoic acid (9cRA) was able to stimulate transcription of the MBP promoter in a dose-dependent manner. This activation was unaffected by the mutation or deletion of the T3RE and required DNA sequences located between positions -162/+60. Accordingly, this MBP promoter fragment bound RXR in vitro. The 9cRA-dependent activation of the MBP promoter required the presence of both, the DNA binding and the ligand-dependent transactivation domain (AF-2) in RXR. Furthermore, as T3, 9cRA was able to stimulate MBP expression in the CG-4 cell line after differentiation to oligodendrocytes and increased the number of cells expressing the MBP protein in primary rat optic nerve glial cell cultures.

Leukemic transformation by the v-ErbA oncoprotein entails constitutive binding to and repression of an erythroid enhancer in vivo

v-ErbA, a mutated thyroid hormone receptor alpha (TRalpha), is thought to contribute to avian erythroblastosis virus (AEV)-induced leukemic transformation by constitutively repressing transcription of target genes. However, the binding of v-ErbA or any unliganded nuclear receptor to a chromatin-embedded response element as well as the role of the N-CoR-SMRT-HDAC co-repressor complex in mediating repression remain hypothetical. Here we identify a v-ErbA-response element, VRE, in an intronic DNase I hypersensitive site (HS2) of the chicken erythroid carbonic anhydrase II (CAII) gene. In vivo footprinting shows that v-ErbA is constitutively bound to this HS2-VRE in transformed, undifferentiated erythroblasts along with other transcription factors like GATA-1. Transfection assays show that the repressed HS2 region can be turned into a potent enhancer in v-ErbA-expressing cells by mutation of the VRE. Differentiation of transformed cells alleviates v-ErbA binding concomitant with activation of CAII transcription. Co-expression of a gag-TRalpha fusion protein in AEV-transformed cells and addition of ligand derepresses CAII transcription. Treatment of transformed cells with the histone deacetylase inhibitor, trichostatin A, derepresses the endogenous, chromatin-embedded CAII gene, while a transfected HS2-enhancer construct remains repressed. Taken together, our data suggest that v-ErbA prevents CAII activation by 'neutralizing' in cis the activity of erythroid transcription factors.

Role of GHF-1 in the regulation of the rat growth hormone gene promoter by thyroid hormone and retinoic acid receptors

In non-pituitary HeLa cells the unliganded thyroid hormone or retinoic acid receptors cause a strong activation of the rat growth hormone promoter that is repressed by their ligands. In contrast, after expression of the pituitary-specific transcription factor GHF-1, thyroid hormone and retinoic acid produce a stimulation similar to that found in pituitary cells. Therefore, GHF-1 changes a ligand-dependent inhibition into a ligand-dependent activation. The essential role of GHF-1 on the rat growth hormone promoter was also demonstrated with AF-2-defective T3 receptor mutants that show a normal activation of this promoter in the presence of GHF-1. Furthermore, a truncated T3 receptor, which lacks the N-terminus and the DNA binding domain, was able to stimulate this promoter in the presence of GHF-1 and exogenous RXR receptors, suggesting the importance of protein to protein interactions in this regulation. This study shows that the final transcriptional effect depends not only on the type of regulatory promoter response elements but also on the presence of other transcriptional activators, in the case of the growth hormone promoter, the tissue-specific transcription factor GHF-1, which plays a coactivator-like role in this promoter.

Retinoid-dependent in vitro transcription mediated by the RXR/RAR heterodimer

The effects of retinoids on gene regulation are mediated by retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Here, we provide the first biochemical evidence that, in vitro, ligand governs the transcriptional activity of RXR alpha/RAR alpha by inducing conformational changes in the ligand-binding domains. Using limited proteolytic digestion we show that binding of the cognate ligand causes a conformational change in the carboxy-terminal part of the receptor. We also show that recombinant RXR alpha/RAR alpha is partially active in the absence of exogenously added ligand. Trans-activation depends critically on the ligand-dependent transcriptional activation function AF-2 of RAR alpha. Full activation by recombinant RXR alpha/RAR alpha, however, requires the addition of either all-trans RA, 9-cis RA, or other RAR-specific agonists, whereas an RAR alpha-specific antagonist abolishes trans-activation. Intriguingly, the ligand-dependent AF-2 of RXR does not contribute to the level of transcription from the RAR beta 2 promoter in vitro even when the cognate ligand (9-cis RA) is bound. Thus, the major role of RXR in trans-activation of the RAR beta 2 promoter is to serve as an auxiliary factor required for the binding of RAR which, in turn, is directly responsible for transcriptional activity.

Characterization of the ligand-dependent transactivation domain of thyroid hormone receptor

Transcriptional activation by nuclear receptors is achieved through autonomous activation functions (AFs), a constitutive N-terminal AF-1 and a C-terminal, ligand-dependent AF-2 that comprises a motif conserved between nuclear receptors. We have performed an extensive mutational analysis of the putative AF-2 domain of chicken thyroid hormone receptor alpha (cT3R alpha). We show that the AF-2 region mediates transactivation as well as transcriptional interference (squelching), not only between the thyroid hormone and vitamin (type II) receptors, but also between type II and steroid hormone (type I) receptors. Transcriptional activation and interference require equivalent doses of the cognate ligand, and mutations in the conserved motif that reduce ligand-induced transactivation also impair transcriptional interference. When fused to the Gal4 DNA binding domain, a 35 amino acid long fragment containing the conserved motif is able to transactivate and squelch, albeit in a ligand-independent manner. Our results define the AF-2 of cT3R alpha as an autonomous transactivation domain that, in its natural context, is governed by ligand. We propose that AF-2 is probably part of a surface for interaction with either a general transcription factor or a putative bridging factor, that might be utilized by type I and II receptors.

Improved method for PCR-mediated site-directed mutagenesis

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Unliganded T3R, but not its oncogenic variant, v-erbA, suppresses RAR-dependent transactivation by titrating out RXR

V-erbA is thought to be an antagonist of thyroid hormone receptor (T3R) function. Here we show that unliganded T3R, but not v-erbA, suppresses retinoic acid (RA)-dependent induction of the RAR-beta 2 promoter by competing for the common dimerization partner, the retinoid X receptor (RXR). Firstly, T3R suppression can be alleviated by co-transfection of RXR. Secondly, T3R, but not v-erbA, competes with RAR for RXR and causes the dissociation of a preformed RAR/RXR-RARE ternary complex in vitro. A single point mutation located in the dimerization interface of v-erbA (Pro349 to Ser) abolishes the transdominant phenotype when introduced at the respective position in T3R. The hypertransforming v-erbA variant r12, in which this mutation is reversed (Ser349 to Pro) suppresses RA-induced differentiation in chicken erythroid progenitors, while v-erbA does not. Our data thus suggest that unliganded T3R and v-erbA act as dominant suppressors through mechanistically distinct pathways.

Cooperativity in transactivation between retinoic acid receptor and TFIID requires an activity analogous to E1A

In embryonal carcinoma (EC) cells retinoic acid (RA) strongly induces transcription from the RA receptor beta 2 (RAR beta 2) promoter through an RA response element (RARE) located in close proximity to the TATA box. Here we demonstrate that recombinant human TATA box-binding protein, hTFIID, and RAR functionally cooperate in transactivation of the RAR beta 2 promoter in EC cells in a strictly RA-dependent manner. We demonstrate that the core domain of hTFIID is sufficient to mediate RAR-dependent transcription and that Drosophila, but not yeast, TFIID can substitute for hTFIID. In COS cells ectopic expression of the E1A protein is a prerequisite for hTFIID and RAR to cooperate in transactivation. We propose a model for transcriptional regulation of the RAR beta 2 promoter in EC cells in which RAR, following activation by RA, functionally interacts with hTFIID via an E1A-like activity present in EC cells.

Transcriptional control by steroid hormones

Gene regulation by steroid hormones leads to induction or repression of particular sets of genes. These effects are mediated by intracellular hormone receptors that, in the unliganded state, are maintained in an inactive form by unknown mechanisms possibly involving association with other cellular proteins. Induction of the mouse mammary tumor virus (MMTV) requires binding of the hormone receptor to a complex hormone-responsive element (HRE) located between 75 and 190 bp upstream from the start of transcription. The interaction of several receptor molecules with the four receptor binding sites in the HRE is highly cooperative on circular DNA molecules and each individual site is needed for optimal induction. In chromatin the HRE is precisely organized in phased nucleosomes. Following hormone treatment and receptor binding, changes in chromatin structure are detected that correlate with binding of transcription factors, including nuclear factor I, to the MMTV promoter. However, though nuclear factor I acts as a basal transcription factor on the MMTV promoter it does not cooperate with the hormone receptors in terms of binding to free DNA, and mutation of the nuclear factor I binding site does not eliminate hormonal stimulation. This residual induction is mediated by octamer motifs, upstream of the TATA box, that bind the ubiquitous transcription factor OTF-1. Mutation of these octamer motifs does not influence basal transcription in vitro, but completely abolishes the stimulatory effect of progesterone receptor.

Heat-shock induction and cytoplasmic localization of transcripts from telomeric-associated sequences in Chironomus thummi

Transcription of telomeric-associated sequences has been detected in the salivary gland cells of the larvae Chironomus thummi. In this species, a heat shock induces puffing at some telomeres, especially at one of the telomeres of chromosome III. We found that this process was concomitant with an increase in the overall telomeric transcript levels. Transcription was also observed in all the telomeres under control conditions, by in situ hybridization, even when these telomeres appeared to be in a nonpuffed state. The telomeric transcripts were found in both, the nuclei and, at higher levels, in the cytoplasmic extracts of salivary gland cells. The heat-shock activation, however, appeared to be restricted to the nuclear level. Telomeric transcription and the peculiar behavior of C. thummi telomeres after a heat shock are discussed.

Structural features of a regulatory nucleosome

DNA sequences from the long terminal repeat of the mouse mammary tumor virus (MMTV-LTR) position nucleosomes both in vivo and in vitro. Here, were present chromatin reconstitution experiments showing that MMTV-LTR sequences from -236 to +204 accommodate two histone octamers in positions compatible with the in vivo data. This positioning is not influenced by the length of the DNA fragment and occurs in linear as well as in closed circular DNA molecules. MMTV-LTR DNA sequences show an intrinsic bendability that closely resembles its wrapping around the histone octamer. We propose that bendability is responsible for the observed rotational nucleosome positioning. Translational nucleosome positioning seems also to be determined by the DNA sequence. These data, along with the results from reconstitution experiments with insertion mutants, support a modular model of nucleosome phasing on MMTV-LTR, where the actual positioning of the histone octamer results from the additive effect of multiple features of the DNA sequence.

Identification of the spI products of Balbiani ring genes in Chironomus thummi

The spI fraction of high molecular weight secretory proteins was analysed in Chironomus thummi. These proteins are encoded by giant Balbiani ring (BR) genes which develop specifically in salivary gland cells. Each component of the spI fraction was studied electrophoretically from early and middle 4th instar larvae and prepupae, as well from galactose-treated larvae where changes in the relative puffing pattern of BR1 and BR2 are known to occur. The spI fraction consists of at least two bands with electrophoretic mobilities slower than those of the spI components of Camptochironomus. The slow migrating component remains throughout the 4th larval instar, while the amount of the faster component changes, being abundant in early 4th instar and prepupae, but not present (or very weak) in middle 4th instar. The correlated shifts in BR puffing pattern during these developmental stages suggest that the slow and fast components are encoded by BR2 and BR1. The spI fraction is modified by galactose treatment, the fast component being induced in parallel with a decrease in the slow component. These changes are correlated with changes in the steady-state levels of RNA: an increase in BR1 RNA and a decrease in BR2 RNA, and of proteins. These proteins could correspond to the spIb and spIa fractions allocated to BR2 and BR1, respectively, in Camptochironomus. After galactose treatment a new faster band sometimes appears, that could correspond to the spIc fraction of Camptochironomus. A possible spId equivalent was also identified. In conclusion the main features of the spI family in C. thummi are similar to those of spI in Camptochironomus.

Correlation between the activity of a 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole-insensitive puff and the synthesis of major heat-shock polypeptide, hsp70, in Chironomus thummi

The induction of puff III-A3b, a major heat-shock puff in Chironomus thummi salivary cells, was insensitive to the transcription inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), whereas no transcriptional activity could be detected at the other heat-shock puffs in the presence of this drug. In these conditions, a polypeptide with the same Mr and isoform pattern as those of the major heat-shock polypeptide, hsp70, was synthesized. These results suggest that hsp70 is encoded by locus III-A3b. In addition to DRB insensitivity, incorporation of [3H]UTP on puff III-A3b took place in an in vitro transcription assay under low-salt conditions (100 mM NaCl); no labelling could be detected at the other heat-shock puffs under these conditions. Although DRB has been reported as a specific inhibitor of RNA polymerase II-directed transcription, and although the low-salt conditions were not propitious for the activity of this enzyme, RNA polymerase II was detected on puff III-A3b and on the other heat-shock puffs by immunofluorescence with anti-RNA polymerase II antibodies.

Induction of the heat-shock response by carbon dioxide in Chironomus thummi

The effects of a set of stress treatments on gene expression of Chironomus thummi salivary gland cells have been analyzed. Among the treatments assayed, only during recovery from carbon dioxide have we observed a response similar to that previously described after heat-shock treatment: induction of the heat-shock puffs and synthesis of the heat-shock polypeptides. In these conditions, puffing and transcription of telomeric regions were observed, which led to the appearance of the temperature-inducible telomeric Balbiani ring T-BR-III. Other treatments failed to induce the heat-shock response, despite promoting real stress conditions to C. thummi larvae or salivary gland cells.

Telomeric DNA sequences differentially activated by heat shock in two Chironomus subspecies

The patterns of puffing, transcription and protein synthesis under heat shock were analysed in polytene nuclei of Chironomus thummi piger, in comparison with those obtained in the closely related subspecies C. th. thummi. Most chromosomal heat shock puffs, as well as heat shock induced polypeptides, in C. th. piger paralleled those previously reported for C. th. thummi. Nevertheless, we found a striking difference in behaviour in the induction of telomeric Balbiani rings by heat shock in the two subspecies. Although homologous sequences were present at all the telomeres in both subspecies, they were not always transcriptionally activated by heat shock. The most frequently puffed telomeres were that of chromosome III R in C. th. thummi and that of chromosome IV R in piger. Transcription of the same sequences from both telomeric Balbiani rings (T-BR-III and T-BR-IV) occurred under heat shock. The enigmatic behaviour of telomeres and the functional significance of T-BRs are discussed in relation to possible equivalents in other Diptera.