Bacterial lipopolysaccharide inhibits colonic carrier-mediated uptake of thiamin pyrophosphate: roles for TLR4 receptor and NF-κB/P38/JNK signaling pathway

This study investigated the effect of the bacterial endotoxin lipopolysaccharide (LPS) on colonic uptake of thiamin pyrophosphate (TPP), the biologically active form of vitamin B1 that is generated by gut microbiota. We used three complementary models in our study: in vitro (human-derived colonic epithelial NCM460), ex vivo (human differentiated colonoid monolayers), and in vivo (mouse colonic tissue). The results showed that exposure of NCM460 cells to LPS leads to a significant inhibition of carrier-mediated TPP uptake as well as in decreased expression of the colonic TPP transporter (cTPPT) protein, mRNA, and heterologous nuclear RNA (hnRNA) compared with untreated controls. Similarly, exposure of human differentiated colonoid monolayers and mice to LPS caused significant inhibition in colonic carrier-mediated TPP uptake and in cTPPT protein, mRNA, and hnRNA expression. The effect of LPS on colonic TPP uptake and cTTPT expression was also found to be associated with a significant reduction in activity of the SLC44A4 promoter as well as in decreased expression of the nuclear factor Elf-3 (E74-like ETS transcription factor 3), which is needed for promoter activity. Finally, we found that knocking down the Toll-like receptor 4 (TLR4) and blocking the nuclear factor kappa B (NF-κB), JNK, and p38 signaling pathways with the use of pharmacological inhibitors lead to significant abrogation in the degree of LPS-mediated inhibition in TPP uptake and cTPPT expression. These results demonstrated that exposure of colonic epithelia to LPS inhibits colonic TPP uptake via transcriptional mechanism(s) and that the effect is mediated via TLR4 receptor and NF-κB/p38/JNK signaling pathways.NEW & NOTEWORTHY This study examined the effect of the bacterial lipopolysaccharide (LPS) on the colonic uptake of thiamin pyrophosphate (TPP), the biologically active form of vitamin B1. Three complementary models were used: in vitro (human NCM460 cells), ex vivo (human colonoids), and in vivo (mice). The results showed LPS to significantly suppress TPP uptake and the expression of its transporter, and that these effects are mediated via the membrane TLR4 receptor, and involve the NF-κB/p38/JNK signaling pathways.

Competition between pre-mRNAs for the splicing machinery drives global regulation of splicing

During meiosis in yeast, global splicing efficiency increases and then decreases. Here we provide evidence that splicing improves due to reduced competition for the splicing machinery. The timing of this regulation corresponds to repression and reactivation of ribosomal protein genes (RPGs) during meiosis. In vegetative cells, RPG repression by rapamycin treatment also increases splicing efficiency. Downregulation of the RPG-dedicated transcription factor gene IFH1 genetically suppresses two spliceosome mutations, prp11-1 and prp4-1, and globally restores splicing efficiency in prp4-1 cells. We conclude that the splicing apparatus is limiting and that pre-messenger RNAs compete. Splicing efficiency of a pre-mRNA therefore depends not just on its own concentration and affinity for limiting splicing factor(s), but also on those of competing pre-mRNAs. Competition between RNAs for limiting processing factors appears to be a general condition in eukaryotes for a variety of posttranscriptional control mechanisms including microRNA (miRNA) repression, polyadenylation, and splicing.

HnRNPH1/H2, U1 snRNP, and U11 snRNP cooperate to regulate the stability of the U11-48K pre-mRNA

Alternative splicing (AS) is a major contributor to proteome diversity, but it also regulates gene expression by introducing premature termination codons (PTCs) that destabilize transcripts, typically via the nonsense-mediated decay (NMD) pathway. Such AS events often take place within long, conserved sequence elements, particularly in genes encoding various RNA binding proteins. AS-NMD is often activated by the protein encoded by the same gene, leading to a self-regulating feedback loop that maintains constant protein levels. However, cross-regulation between different RNA binding proteins is also common, giving rise to finely tuned regulatory networks. Recently, we described a feedback mechanism regulating two protein components of the U12-dependent spliceosome (U11-48K and U11/U12-65K) through a highly conserved sequence element. These elements contain a U11 snRNP-binding splicing enhancer (USSE), which, through the U11 snRNP, activates an upstream U2-type 3'ss, resulting in the degradation of the U11-48K mRNA by AS-NMD. Through phylogenetic analysis, we now identify a G-rich sequence element that is conserved in fishes as well as mammals. We show that this element binds hnRNPF/H proteins in vitro. Knockdown of hnRNPH1/H2 or mutations in the G-run both lead to enhanced activation of the 3'ss in vivo, suggesting that hnRNPH1/H2 proteins counteract the 3'ss activation. Furthermore, we provide evidence that U1 binding immediately downstream from the G-run similarly counteracts the U11-mediated activation of the alternative 3'ss. Thus, our results elucidate the mechanism in which snRNPs from both spliceosomes together with hnRNPH1/H2 proteins regulate the recognition and activation of the highly conserved alternative splice sites within the U11-48K pre-mRNA.

Interaction between FLASH and Lsm11 is essential for histone pre-mRNA processing in vivo in Drosophila

Metazoan replication-dependent histone mRNAs are the only nonpolyadenylated cellular mRNAs. Formation of the histone mRNA 3' end requires the U7 snRNP, which contains Lsm10 and Lsm11, and FLASH, a processing factor that binds Lsm11. Here, we identify sequences in Drosophila FLASH (dFLASH) that bind Drosophila Lsm11 (dLsm11), allow localization of dFLASH to the nucleus and histone locus body (HLB), and participate in histone pre-mRNA processing in vivo. Amino acids 105-154 of dFLASH bind to amino acids 1-78 of dLsm11. A two-amino acid mutation of dLsm11 that prevents dFLASH binding but does not affect localization of U7 snRNP to the HLB cannot rescue the lethality or histone pre-mRNA processing defects resulting from an Lsm11 null mutation. The last 45 amino acids of FLASH are required for efficient localization to the HLB in Drosophila cultured cells. Removing the first 64 amino acids of FLASH has no effect on processing in vivo. Removal of 13 additional amino acids of dFLASH results in a dominant negative protein that binds Lsm11 but inhibits processing of histone pre-mRNA in vivo. Inhibition requires the Lsm11 binding site, suggesting that the mutant dFLASH protein sequesters the U7 snRNP in an inactive complex and that residues between 64 and 77 of dFLASH interact with a factor required for processing. Together, these studies demonstrate that direct interaction between dFLASH and dLsm11 is essential for histone pre-mRNA processing in vivo and for proper development and viability in flies.

Heterogeneous nuclear ribonucleoproteins (hnRNPs) in cellular processes: Focus on hnRNP E1's multifunctional regulatory roles

Heterogeneous nuclear ribonucleoproteins (hnRNPs) comprise a family of RNA-binding proteins. The complexity and diversity associated with the hnRNPs render them multifunctional, involved not only in processing heterogeneous nuclear RNAs (hnRNAs) into mature mRNAs, but also acting as trans-factors in regulating gene expression. Heterogeneous nuclear ribonucleoprotein E1 (hnRNP E1), a subgroup of hnRNPs, is a KH-triple repeat containing RNA-binding protein. It is encoded by an intronless gene arising from hnRNP E2 through a retrotransposition event. hnRNP E1 is ubiquitously expressed and functions in regulating major steps of gene expression, including pre-mRNA processing, mRNA stability, and translation. Given its wide-ranging functions in the nucleus and cytoplasm and interaction with multiple proteins, we propose a post-transcriptional regulon model that explains hnRNP E1's widespread functional diversity.

Differential glucocorticoid effects on stress-induced gene expression in the paraventricular nucleus of the hypothalamus and ACTH secretion in the rat

Although previous studies have examined the extent to which adrenocorticotropic hormone (ACTH) secretion depends on endogenous glucocorticoid levels, few have examined the parallel glucocorticoid dependency of gene expression within the corticotropin releasing hormone (CRH) neuron containing subregion of the hypothalamic paraventricular nucleus (PVN). This study examined resting and stress-induced expression of three immediate early genes (c-fos, zif268, and NGFI-B mRNAs) and two phenotypic restricted immediate early genes that code for ACTH secretagogues (CRH and arginine vasopressin [AVP] hnRNAs) in the PVN of adrenalectomized (ADX) rats given either 0.9% saline to drink for 5 days or saline with corticosterone (CORT; 25 microg/ml). CORT-containing saline was replaced with saline 18 h before testing to ensure clearance of CORT at the time of testing. Dependent measures were examined 0, 15, 30, 60, or 120 min after 30 min restraint. Compared to sham surgery, ADX produced a large upregulation of basal ACTH secretion but only a trend for an increase in basal PVN CRH and parvocellular (mp) PVN AVP hnRNA expression, and a marked augmentation of restraint-induced ACTH secretion and the expression of all five genes examined. CORT containing saline partially normalized basal and restraint-induced ACTH secretion and restraint-induced AVP hnRNA, c-fos mRNA, and zif268 mRNA in the PVN in ADX rats. In contrast, expression patterns of restraint-induced PVN CRH hnRNA and NGFI-B mRNA were not different between ADX rats with or without CORT replacement. Given that there was no circulating CORT present at the time of restraint challenge in either group of ADX rats, the differential impact of CORT replacement on restraint-induced PVN gene expression must reflect differential dependency of the expression of these genes in the PVN on the prior presence of CORT.

Focus on the intermediate state: immature mRNA of cytochromes P450--methods and insights

The scattered and limited data on hnRNAs (pre-mRNAs) of cytochromes P450 (CYP) are compiled and discussed for the first time. The methods for determination and quantification of hnRNAs are compared. In most cases, CYP hnRNA levels were determined as a parameter of transcriptional activity. It is known, however, that some CYPs, in particular CYP2E1, are in addition specifically and extensively regulated by post-transcriptional processes. Obviously, these processes also influence the processing of CYP hnRNAs so that their levels cannot be considered a mere result of transcription. The underlying mechanisms of post-transcriptional CYP hnRNA and mRNA regulation are not well understood. It is our aim therefore to bring together available data on CYP hnRNA and to discuss them in the light of recent advances in knowledge concerning pre-mRNA processing and interactions between RNA and low molecular weight interfering RNAs. By doing this, we hope to drive research in a direction which appears promising in providing some long-awaited answers with respect to mechanisms of post-transcriptional CYP regulation.

Dexamethasone and stressor-magnitude regulation of stress-induced transcription of HPA axis secretagogues in the rat

Regulation of the production of hypothalamic-pituitary-adrenal (HPA) axis secretagogues, corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), may be differentially sensitive to the negative feedback effects of glucocorticoids. We chose to study this phenomenon by examining the ability of dexamethasone to influence CRH and AVP heteronuclear RNA (hnRNA) levels in an escapable/inescapable (ES/IS) foot-shock stress paradigm. On Day 1, adult male rats were subjected to either ES or IS foot-shock; on Day 2, saline or dexamethasone (100 microg/kg) was administered 2 h prior to the stressor. We found that ES/IS foot-shock stimulated similar robust increases in plasma adrenocorticotrophic hormone (ACTH) and corticosterone concentrations, and medial parvocellular division of the paraventricular nucleus (mpPVN) AVP and CRH hnRNA and c-fos mRNA levels in saline-treated ES/IS rats. Dexamethasone pretreatment suppressed ACTH and corticosterone levels similarly in IS and ES animals. Dexamethasone pretreatment also suppressed mpPVN CRH and AVP hnRNA levels at 30 min. However, by 120 min, the mpPVN AVP hnRNA levels in dexamethasone-treated rats were similar to those measured in the saline group. We also found that rats that received the most shocks on Day 1 had greater HPA axis activation on Day 2. We conclude that the magnitude of the foot-shock stressor, determined by learned and immediate cues, is important in determining the magnitude of the HPA response.

Differential kinetics of oxytocin and vasopressin heteronuclear RNA expression in the rat supraoptic nucleus in response to chronic salt loading in vivo

Previous studies have shown that the secretion of oxytocin and vasopressin from the posterior pituitary always accompanies systemic hyperosmotic stimuli in rats, and that oxytocin and vasopressin mRNAs consistently increase in response to prolonged hyperosmotic stimuli. Hence, it has been widely interpreted that oxytocin and vasopressin secretion and gene expression are closely coupled. In the present study, we used both vasopressin and oxytocin intron- specific probes to measure vasopressin and oxytocin heteronuclear RNA (hnRNA) levels, respectively, by in situ hybridisation in the rat supraoptic nucleus (SON) in conjunction with radioimmunoassays of vasopressin and oxytocin peptide levels in plasma and in the posterior pituitary in normally hydrated rats and after 1-5 days of salt loading. Increased oxytocin secretion in response to hyperosmotic stimuli exceeded vasopressin secretion at every time point studied. Vasopressin hnRNA in the SON increased to near maximal levels within minutes after the hyperosmotic stimulus, and was maintained throughout all 5 days of salt loading. By contrast, oxytocin hnRNA did not significantly change from control levels until approximately 2 days after hyperosmotic stimulation, and was not maximal until 3 days. In summary, increases in oxytocin gene transcription in response to osmotic stimuli are dramatically delayed compared to increases in vasopressin gene transcription under the same conditions. These data indicate that oxytocin gene transcription is not as closely correlated with pituitary peptide secretion as is vasopressin gene transcription, and suggests that there is a fundamental difference in excitation-secretion-transcription coupling mechanisms that regulate these two closely related genes in the rat magnocellular neurones in the SON.

Changes in vasoactive intestinal peptide and arginine vasopressin expression in the suprachiasmatic nucleus of the rat brain following footshock stress

The neuropeptides, arginine vasopressin (AVP) and vasoactive intestinal polypeptide (VIP) are synthesized by neurons of the suprachiasmatic nucleus (SCN) of the hypothalamus and are important regulators of SCN function. Previous studies have demonstrated that acute exposure to stressors can disrupt circadian activity rhythms, suggesting the possibility of stress-related alterations in the expression of these neuropeptides within SCN neurons. In this study, we examined the effect of intermittent footshock stress on AVP mRNA and heterogeneous nuclear RNA (hnRNA) and VIP mRNA expression in neurons of the SCN. Young adult male Sprague/Dawley rats were subjected to 15 s of scrambled intermittent footshock (0.50 mA pulses, 1 pulse/s, 300 ms duration) every 5 min for 30 min. Animals were sacrificed 75 or 135 min after the onset of stress and brains examined for AVP mRNA and hnRNA, and VIP mRNA using in situ hybridization. Footshock stress increased AVP hnRNA levels at the 75 min time point whereas AVP mRNA was elevated at both the 75 and 135 min time points. In contrast, footshock stress decreased the number of cells expressing VIP mRNA in the SCN without changing hybridization level per cell. These data indicate that the disruptive effect of stress on activity rhythms correlate with alterations in the expression of regulatory peptides within the SCN.

Quantitative analysis of thyroid-stimulating hormone messenger RNA and heterogeneous nuclear RNA in hypothyroid rats

Thyroid-stimulating hormone (TSH) stimulates the synthesis and release of thyroid hormones including triiodothyronine (T3) and thyroxine (T4). Semiquantitative analyses using northern blot and in situ hybridization suggested that TSH gene transcription is upregulated under conditions of hypothyroidism. However, no quantitative analysis of TSH gene expression using real-time polymerase chain reaction (PCR) has been reported. In this study, we quantitated the TSHbeta messenger ribonucleic acid (mRNA) level as well as the TSHbeta heterogeneous nuclear ribonucleic acid (hnRNA) level in the anterior pituitary of hypothyroid rats, by real-time PCR using the LightCycler system. The hnRNA is the primary deoxyribonucleic acid (DNA) transcript, which reflects the transcription rate more reliably than the mRNA because of its short half-life. In the anterior pituitary of rats with methimazol-induced chronic hypothyroidism, both mRNA and hnRNA expression of TSHbeta were upregulated fourfold relative to normal rats (n=4). Our method provides a rapid and accurate measure of gene transcription. In the present report, we described a technique for accurate measurement of TSHbeta hnRNA level.

The CRF1 receptor antagonist R121919 attenuates the neuroendocrine and behavioral effects of precipitated lorazepam withdrawal

RATIONALE

Corticotropin-releasing factor (CRF) is the primary physiologic regulator of the hypothalamic-pituitary-adrenal (HPA) axis and serves to globally coordinate the mammalian stress response. Hyperactivity of central nervous system CRF neurotransmission, acting primarily via the CRF(1) receptor, has been strongly implicated in the pathophysiology of depression and anxiety. Furthermore, there is evidence of enhanced CRF transcription, release, and neuronal activity after the administration of and withdrawal from several drugs of abuse, including cannabis, cocaine, ethanol, and morphine. Treatment with CRF antagonists has been demonstrated to reduce the severity of certain drug withdrawal symptoms, implicating a specific role for activation of CRF neurons in mediating the anxiogenic and stress-like reactions observed after abrupt drug discontinuation.

OBJECTIVES/METHODS

To extend these findings, we investigated whether pretreatment with the selective CRF(1) receptor antagonist R121919 decreases the behavioral and neuroendocrine activation observed after the precipitation of benzodiazepine (BZ) withdrawal in BZ-dependent rats.

RESULTS

Pretreatment with R121919 attenuated the subsequent HPA axis activation, behavioral measures of anxiety, and expression of the CRF gene in the paraventricular nucleus of the hypothalamus, as measured by CRF heteronuclear RNA, which occurs after flumazenil-precipitation of withdrawal from the BZ, lorazepam.

CONCLUSIONS

These results indicate that the activation of CRF neuronal systems may be a common neurobiological mechanism in withdrawal from drugs of abuse and moreover, that the CRF(1) receptor subtype plays a major role in mediating the effects of CRF on neuroendocrine and behavioral responses during BZ withdrawal. Therefore, CRF(1) receptor antagonists may be of therapeutic utility in the treatment of drug withdrawal syndromes.

Repression of cyclin D1 as a target for germ cell tumors

Metastatic germ cell tumors (GCT) are curable, however GCTs refractory to cisplatin-based chemotherapy have a poor prognosis. This study explores D-type cyclins as molecular targets in GCTs because all-trans-retinoic acid (RA)-mediated differentiation of the human embryonal carcinoma (EC) cell line NT2/D1 is associated with G1 cell cycle arrest and proteasomal degradation of cyclin D1. RA effects on D-type cyclins are compared in human EC cells that are RA sensitive or dually RA and cisplatin resistant (NT2/D1-R1) and in clinical GCTs that have both EC and mature teratoma components. Notably, GCT differentiation was associated with reduced cyclin D1 but increased cyclin D3 expression. RA was shown here to repress cyclin D1 through a transcriptional mechanism in addition to causing its degradation. The siRNA-mediated repression of individual cyclin D species resulted in growth inhibition in both RA sensitive and resistant EC cells. Only repression of cyclin D1 occurred in vitro and when clinical GCTs mature, implicating cyclin D1 as a molecular therapeutic target. To confirm this, the EGFR-tyrosine kinase inhibitor, Erlotinib, was used to repress cyclin D1. This inhibited proliferation in RA and cisplatin sensitive and resistant EC cells. Taken together, these findings implicate cyclin D1 targeting agents for the treatment of GCTs.

Long L1 insertions in human gene introns specifically reduce the content of corresponding primary transcripts

LINE-1 (L1) retrotransposons comprise about 17% of the human genome and include a recently transposed set of Ta-L1 elements that are polymorphic in humans. Although it is widely believed that L1s play an essential role in shaping and functioning of mammalian genomes, the understanding of the impact of L1 insertions on gene expression is far from being comprehensive. Here we compared hnRNA contents for allele pairs of genes heterozygous for Ta-L1 insertions in their introns in human cell lines of various origin. We demonstrated that some Ta-L1 insertions correlated with decreased content of the corresponding hnRNAs. This effect was characteristic of only nearly full-sized L1s and seemed to be tissue specific.

Activation of stress‐related hypothalamic neuropeptide gene expression during morphine withdrawal

Morphine withdrawal results in serious affective and somatic symptoms including activation of the hypothalamo-pituitary-adrenocortical (HPA) axis. To reveal secretory, activational and transcriptional changes in the hypothalamus of morphine-dependent rats during naloxone precipitated opioid withdrawal, we measured corticosterone secretion, c-Fos induction and heteronuclear (hn)RNA levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in naïve and morphine dependent animals injected with saline or 5 mg/kg naloxone. Naloxone precipitated morphine withdrawal resulted in a significant increase in corticosterone secretion and induction of neuronal activation in the hypothalamic paraventricular nucleus (PVH) 2 h after challenge. Using probes complementary to intronic sequences of genes encoding neuropeptides in parvocellular neurosecretory neurons of the PVH, we found robust increases in CRH and AVP hnRNAs in morphine dependent rats during naloxone precipitated withdrawal. Naïve rats and animals that were implanted with morphine pellets for 8 days did not display significant up-regulation of ongoing neuropeptide expression in the parvocellular compartment of the PVH. In addition to hypophyseotropic neurons, naloxone precipitated withdrawal resulted in a marked activation in autonomic-related projection neurons in PVH and in the magnocellular neurons in the PVH and supraoptic nuclei. These activations however were not associated with induction of CRH or AVP hnRNAs.

Regulation of osmotic stress transcription factor 1 (Ostf1) in tilapia(Oreochromis mossambicus) gill epithelium during salinity stress

Mechanisms of induction of osmotic stress transcription factor 1 (Ostf1)were analyzed in gill epithelium of tilapia exposed to salinity stress. Experiments with primary cultures of gill epithelial cells revealed that hyperosmotic Ostf1 induction was independent of systemic factors. In addition,the synthetic glucocorticoid receptor agonist dexamethasone did not affect Ostf1 levels, arguing against cortisol being the signal for Ostf1 induction during hyperosmotic stress. Exposure of primary gill cell cultures to a hyperosmotic agent that is cell permeable and non-hypertonic (glycerol) did not trigger Ostf1 induction. However, when gill cells were exposed to hypertonicity (either in the form of NaCl or other forms) Ostf1 was rapidly and significantly induced. Analysis of hnRNA and mRNA levels revealed that Ostf1 upregulation in gill cells of intact fish and primary cultures of gill epithelial cells was mediated by transient mRNA stabilization. In addition to the initial transient mRNA stabilization a subsequent transcriptional induction of Ostf1 was observed. In cultured gill cells increase in Ostf1 mRNA synthesis was stable and very potent, whereas in gill cells of intact fish this increase was transient. This observation suggests positive feedback by Ostf1 or one of its targets and negative feedback by systemic factors on Ostf1 transcription.

We conclude that Ostf1 induction in gill epithelial cells of tilapia exposed to salinity stress (1) is independent of cortisol or other systemic factors; (2) depends on hypertonicity as the signal; and (3) is based on transient mRNA stabilization. Moreover, our data on primary cell cultures show that systemic signals are necessary to prevent sustained transcriptional induction of Ostf1 during hyperosmotic stress, indicating feedback regulation and a high degree of complexity of osmosensing and signaling networks in euryhaline fishes.

Expression of clock and clock-driven genes in the rat suprachiasmatic nucleus during late fetal and early postnatal development

The SCN as a site of the circadian clock itself exhibits rhythmicity. A molecular clockwork responsible for the rhythmicity consists of clock genes and their negative and positive transcriptional-translational feedback loops. The authors' previous work showed that rhythms in clock gene expression in the rat SCN were not yet detectable at embryonic day (E) 19 but were already present at postnatal day (P) 3. The aim of the present study was to elucidate when during the interval E19-P3 the rhythms start to develop in clock gene expression and in clock-controlled, namely in arginine-vasopressin (AVP), gene expression. Daily profiles of Per1, Per2, Cry1, Bmal1, and Clock mRNA and of AVP heteronuclear (hn) RNA as an indicator of AVP gene transcription were assessed in the SCN of fetuses at E20 and of newborn rats at P1 and P2 by the in situ hybridization method. At E20, formation of a rhythm in Per1 expression was indicated, but no rhythms in expression of other clock genes or of the AVP gene were detected. At P1, rhythms in Per1, Bmal1, and AVP and a forming rhythm in Per2 but no rhythm in Cry1 expression were present in the SCN. The Per1 mRNA rhythm was, however, only slightly pronounced. The Bmal1 mRNA rhythm, although pronounced, exhibited still an atypical shape. Only the AVP hnRNA rhythm resembled that of adult rats. At P2, marked rhythms of Per1, Per2, and Bmal1 and a forming rhythm of Cry1, but not of Clock, expression were present. The data suggest that rhythms in clock gene expression for the most part develop postnatally and that other mechanisms besides the core clockwork might be involved in the generation of the rhythmic AVP gene expression in the rat SCN during early ontogenesis.

Role of glucocorticoids and cAMP-mediated repression in limiting corticotropin-releasing hormone transcription during stress

The role of glucocorticoids and the repressor isoform of cAMP response element (CRE) modulator (CREM), inducible cAMP early repressor (ICER), in limiting corticotropin-releasing hormone (CRH) transcription during restraint stress were examined in both intact and adrenalectomized rats receiving glucocorticoid replacement. CRH primary transcript, measured by intronic in situ hybridization, increased after 30 min of restraint and returned to basal levels by 90 min, despite the persistent stressor. The decline was independent of circulating glucocorticoids, because adrenalectomized rats displayed an identical pattern. ICER mRNA in the hypothalamic paraventricular nucleus (PVN) increased after 30 min and remained elevated for up to 4 h in a glucocorticoid-independent manner. Western blot and electrophoretic mobility shift assay analyses showed increases in endogenous ICER in the PVN of rats subjected to restraint stress for 3 h. Chromatin immunoprecipitation assays showed the recruitment of CREM by the CRH CRE in conjunction with decreases in RNA polymerase II (Pol II) binding in the PVN region of rats restrained for 3 h. These data show that stress-induced glucocorticoids do not mediate the limitation of CRH transcription. Furthermore, the ability of CREM to bind the CRH CRE and the time relationship between elevated CREM and reduced Pol II recruitment by the CRH promoter suggest that inhibitory isoforms of CREM induced during stress contribute to the decline in CRH gene transcription during persistent stimulation.

Low doses of dexamethasone can produce a hypocorticosteroid state in the brain

The synthetic glucocorticoid dexamethasone (dex) blocks stress-induced hypothalamic-pituitary-adrenal (HPA) activation primarily at the level of the anterior pituitary because multidrug resistance P-glycoprotein hampers its penetration in the brain. Here, we tested the hypothesis that central components of the HPA axis would escape dex suppression under conditions of potent peripheral glucocorticoid action. We subchronically treated rats with low or high doses of dex. The animals were subjected on the last day of treatment for 30 min to a restraint stressor after which central and peripheral markers of HPA axis activity were measured. Basal and stress-induced corticosterone secretion, body weight gain, adrenal and thymus weight, as well as proopiomelanocortin mRNA in the anterior pituitary were reduced in a dose-dependent manner by dex administered either 5 d sc or 3 wk orally. In the brain, the highest dose dex suppressed CRH mRNA and CRH heteronuclear RNA in the paraventricular nucleus (PVN). However, in the peripherally active low-dose range of dex CRH mRNA and heteronuclear RNA showed resistance to suppression, and CRH mRNA expression in the PVN was in fact enhanced under the long-term treatment condition. In the PVN, c-fos mRNA was suppressed by the highest dose of dex, but this effect showed a degree of resistance after long-term oral treatment. c-fos mRNA responses in the anterior pituitary followed those in PVN and reflect central drive of the HPA axis even if corticosterone responses are strongly reduced. The results support the concept that low doses of dex can create a hypocorticoid state in the brain.

Expression of immediate early genes and vasopressin heteronuclear RNA in the paraventricular and supraoptic nuclei of rats after acute osmotic stimulus

Monitoring the expression of immediate early genes (IEGs) is useful for following stress-induced cellular responses in the neuroendocrine system. We have examined the transcriptional activities of four IEGs (c-fos, junB, NGFI-A and NGFI-B) and of the arginine vasopressin (AVP) gene in the hypothalamic paraventicular (PVN) and supraoptic nuclei (SON) of rats after acute osmotic stimuli, using in situ hybridization histochemistry. After intraperitoneal (i.p.) administration of hypertonic saline (2% body weight, 900 mOsm/kg), the expression levels of all IEG mRNAs were increased significantly both in the PVN and SON at as early as 10 min, peaked at 30 min and remained elevated until 60 min. The expression of AVP heteronuclear (hn)RNA also peaked at 30 min, and remained elevated until 180 min. Thirty min after i.p. administration of hypertonic saline (600 mOsm/kg), the expression levels of all IEG mRNAs in the PVN and SON were significantly increased in comparison with those after i.p. administration of isotonic saline (290 mOsm/kg). Regression analysis revealed that expression levels of the IEG mRNAs and AVP hnRNA were positively correlated with the plasma concentration of sodium, and the rates of increase of the expression levels of all IEG mRNAs were similar. The expression levels of all IEG mRNAs examined are useful markers for following the changes of the AVP gene transcription in the PVN and SON after acute osmotic stimuli in rats.

Posttranscriptional regulation of myosin heavy chain expression in the heart by triiodothyronine

Triiodothyronine (T3) regulates cardiac contractility in part by regulating the expression of several important cardiac myocyte genes. In the rat, the T3-mediated induction of alpha-myosin heavy chain (MHC) transcription in hypothyroid hearts is rapid, exhibiting zero-order kinetics, whereas the repression of beta-MHC in these same hearts is much slower. To elucidate the mechanism for T3 transcriptional as well as posttranscriptional regulation of both MHC gene isoforms, we used an RT-PCR-based transcription assay and the RNA polymerase II inhibitor actinomycin D in an in vivo model to simultaneously measure specific alpha- and beta-MHC heterogeneous nuclear RNA (hnRNA), mRNA kinetics, and MHC antisense RNA. In vivo actinomycin D treatment blocked alpha-MHC transcription in euthyroid rats by >80% at 2 h and suggested a half-life of alpha-MHC hnRNA of approximately 1 h, whereas actinomycin D inhibited beta-MHC transcription in hypothyroid rats by >75% at 6 h, suggesting a significantly longer hnRNA half-life of approximately 4 h. The effect of actinomycin D on beta-MHC transcription was independent of T3. T3 treatment in hypothyroid animals caused beta-MHC mRNA to decline more rapidly than beta-MHC hnRNA, demonstrating, for the first time, a posttranscriptional mechanism(s). The measured change in beta-MHC mRNA half-life indicates a T3-mediated destabilization of beta-MHC mRNA. To understand the mechanism by which T3 destabilizes beta-MHC mRNA, we measured beta-MHC antisense RNA. beta-MHC antisense RNA is present in euthyroid myocytes, but levels are not significant in hypothyroid myocytes. This differential expression may explain some of the effects of T3 on MHC posttranscriptional regulation.

Long-term effects of a single exposure to immobilization stress on the hypothalamic-pituitary-adrenal axis: transcriptional evidence for a progressive desensitization process

In the present work we have characterized the long-term influence of a single exposure to the stress of immobilization (IMO) on the hypothalamic-pituitary-adrenal (HPA) axis of adult rats. Rats without prior stress (control) and rats exposed to IMO for 2 h on day 1 (IMO+4wk) or on day 21 (IMO+1wk) were killed on day 28, either without stress (basal), immediately after IMO for 1 h (IMO), or 1 h after termination of IMO (post-IMO). IMO caused a strong activation of c-fos mRNA and corticotropin-releasing factor (CRF) and vasopressin (AVP) heteronuclear RNA (hnRNA) in the paraventricular nucleus of the hypothalamus in control rats; this activation was essentially maintained in the post-IMO period. The overall AVP hnRNA response to day 28 stress was not affected by prior stress. Post-IMO c-fos mRNA and CRF hnRNA levels were lower in previously stressed rats, as compared with controls. Whereas the effect of prior IMO on both peripheral HPA hormones and c-fos mRNA was maximal in IMO+1wk rats, the effect of prior stress on CRF hnRNA was only observed in IMO+4wk rats. The present data indicate that prior single IMO triggers a process of desensitization of the HPA responsiveness to IMO over the course of the following weeks. Although the various components of the HPA axis were modified in the same direction, a clear temporal dissociation was found among them, revealing the fine tuning of stress-induced activation of the HPA axis.

Iron chelators inhibit VCAM-1 expression in human dermal microvascular endothelial cells

Vascular cell adhesion molecule (VCAM)-1 expression may be coupled to redox-sensitive regulatory pathways, and iron may play a role in generation of reactive oxygen species that participate in these signaling pathways. To investigate the role of iron in TNF alpha-induced VCAM-1 gene expression, human dermal microvascular endothelial cells (HDMEC) were stimulated with TNF alpha in the presence of iron chelators and examined for expression of VCAM-1. The iron chelators dipyridyl (DP) and desferoxamine (DFO) inhibited VCAM-1 protein and mRNA induction in a concentration- and time-dependent manner. The induction of VCAM-1 was not inhibited by nonmetal binding reactive oxygen species (ROS) scavengers, implying a direct effect of iron in the expression of these adhesion molecules. The effect of iron was mediated at the level of gene transcription since pretreatment with DP abrogated the TNF alpha-mediated up-regulation of VCAM-1 heterogeneous nuclear RNA. Pretreatment of HDMEC with DP prior to TNFalpha treatment had no effect on p65 nuclear localization, DNA binding, or serine phosphorylation. DP pretreatment inhibited TNF alpha- and IFN gamma-mediated interferon regulatory factor 1 (IRF-1) protein expression, although restoration of IRF-1 expression failed to reconstitute VCAM-1 expression. DP treatment also blocked VCAM-1 induction in human umbilical vein endothelium and blocked induction of a host of NF-kB activated genes in HDMEC including ICAM-1, IL-8, and tissue factor. I kappa B alpha, an NF-kappa B inducible and constitutively accessible gene not requiring chromatin remodeling for transcription, was not affected by DP treatment. These data suggest that iron plays a critical role in TNF alpha mediated VCAM-1 induction in HDMEC, and the target for iron effects may be IRF-1, NF-kappa B, and potentially chromatin remodeling.

Transcriptional responses of the rat vasopressin gene to acute and repeated acute osmotic stress

To determine the impact of hypertonic saline administration upon rat arginine vasopressin (AVP) gene transcription in supraoptic nucleus neurons, a probe complementary to the first intron (AVP1) of AVP was used to measure changes in AVP heteronuclear RNA (hnRNA) levels. Animals that received hypertonic saline had increases in AVP1 after 15 and 30 min, with a return to baseline levels by 180 min. In a double injection paradigm, animals were given an injection of normal or hypertonic saline followed 180 min later by a second injection of normal or hypertonic saline and sacrificed 30 min later. When both injections were hypertonic saline (H-H), AVP1 levels were greater than levels seen after a single hypertonic saline injection, or after an injection of normal saline followed by a second injection of hypertonic saline (N-H). This study shows acute, repeated exposure to hypertonic saline causes a robust increase in vasopressin gene transcription. Since a second hyperosmotic stimulus is known to increase neuronal firing rate and activity, our results suggest that a correlation exists with intracellular mechanisms regulating vasopressin gene transcription.

Dual requirement for yeast hnRNP Nab2p in mRNA poly(A) tail length control and nuclear export

Recent studies of mRNA export factors have provided additional evidence for a mechanistic link between mRNA 3'-end formation and nuclear export. Here, we identify Nab2p as a nuclear poly(A)-binding protein required for both poly(A) tail length control and nuclear export of mRNA. Loss of NAB2 expression leads to hyperadenylation and nuclear accumulation of poly(A)(+) RNA but, in contrast to mRNA export mutants, these defects can be uncoupled in a nab2 mutant strain. Previous studies have implicated the cytoplasmic poly(A) tail-binding protein Pab1p in poly(A) tail length control during polyadenylation. Although cells are viable in the absence of NAB2 expression when PAB1 is overexpressed, Pab1p fails to resolve the nab2Delta hyperadenylation defect even when Pab1p is tagged with a nuclear localization sequence and targeted to the nucleus. These results indicate that Nab2p is essential for poly(A) tail length control in vivo, and we demonstrate that Nab2p activates polyadenylation, while inhibiting hyperadenylation, in the absence of Pab1p in vitro. We propose that Nab2p provides an important link between the termination of mRNA polyadenylation and nuclear export.

Specific interaction of Smn, the spinal muscular atrophy determining gene product, with hnRNP-R and gry-rbp/hnRNP-Q: a role for Smn in RNA processing in motor axons?

Spinal muscular atrophy (SMA), the most common hereditary motor neuron disease in children and young adults is caused by mutations in the telomeric survival motor neuron (SMN1) gene. The human genome, in contrast to mouse, contains a second SMN gene (SMN2) which codes for a gene product which is alternatively spliced at the C-terminus, but also gives rise to low levels of full-length SMN protein. The reason why reduced levels of the ubiquitously expressed SMN protein lead to specific motor neuron degeneration without affecting other cell types is still not understood. Using yeast two-hybrid techniques, we identified hnRNP-R and the highly related gry-rbp/hnRNP-Q as novel SMN interaction partners. These proteins have previously been identified in the context of RNA processing, in particular mRNA editing, transport and splicing. hnRNP-R and gry-rbp/hnRNP-Q interact with wild-type Smn but not with truncated or mutant Smn forms identified in SMA. Both proteins are widely expressed and developmentally regulated with expression peaking at E19 in mouse spinal cord. hnRNP-R binds RNA through its RNA recognition motif domains. Interestingly, hnRNP-R is predominantly located in axons of motor neurons and co-localizes with Smn in this cellular compartment. Thus, this finding could provide a key to understand a motor neuron-specific Smn function in SMA.

Colitis induces CRF expression in hypothalamic magnocellular neurons and blunts CRF gene response to stress in rats

We investigated hypothalamic neuronal corticotropin-releasing factor (CRF) gene expression changes in response to visceral inflammation induced by 2,4,6-trinitrobenzenesulfonic acid (TNB) and acute stress. Seven days after TNB, rats were subjected to water-avoidance stress (WAS) or restraint for 30 min and euthanized. Hypothalamic CRF primary transcripts (heteronuclear RNA, hnRNA) and CRF and arginine vasopressin (AVP) mRNAs were assessed by in situ hybridization. Antisense (35)S-labeled cRNA probes against CRF mRNA intronic and exonic sequences and an oligonucleotide probe against the AVP mRNA were used. TNB induced macroscopic lesions and a fivefold elevation in myeloperoxidase activity in the colon. Colitis increased CRF hnRNA and mRNA signals in the magnocellular part of the paraventricular nucleus of the hypothalamus (PVN) and supraoptic neurons, whereas AVP mRNA was not altered. Colitis did not modify CRF hnRNA signal in the parvocellular part of the PVN (pPVN), plasma corticosterone, and serum osmolarity levels. However, CRF hnRNA expression in the pPVN and the rise in corticosterone and defecation induced by WAS or restraint were blunted in colitic rats. These data show that colitis upregulates CRF gene synthesis in magnocellular hypothalamic neurons but dampens CRF gene transcription in the pPVN and plasma corticosterone responses to environmental acute stressors.

Direct stimulation of arginine vasopressin gene transcription by cAMP in parvocellular neurons of the paraventricular nucleus in organotypic cultures

The regulation of arginine vasopressin (AVP) gene transcription in the paraventricular nucleus (PVN) was studied in rat hypothalamic organotypic cultures using intronic in situ hybridization. While AVP heteronuclear (hn) RNA was not detected in the PVN under basal conditions, a marked induction of AVP hnRNA was observed after 2 and 3 h incubation of slices with forskolin. In contrast to the stimulatory effects of forskolin, phorbol 12-myristate 13-acetate (PMA) was completely ineffective in inducing AVP hnRNA in the PVN at any time examined (1-3 h). Forskolin-induced AVP hnRNA expression was unaffected by blockage of neurotransmission by the sodium channel inhibitor, tetrodotoxin, indicating that forskolin acts directly on AVP cells in the PVN. Dual staining in situ hybridization of forskolin-stimulated hypothalamic sections using both radio labeled AVP hnRNA and digoxigenin-labeled CRH mRNA probes revealed colocalization of both transcripts, indicating AVP hnRNA is expressed in the parvocellular neurons. The data demonstrate that cAMP directly activates AVP gene transcription in parvocellular neurons of the PVN.

Insulin alters heterogeneous nuclear ribonucleoprotein K protein binding to DNA and RNA

The interaction of the multimodular heterogeneous nuclear ribonucleoprotein (hnRNP) K protein with many of its protein and nucleic acid partners is regulated by extracellular signals. Acting as a docking platform, K protein could link signal-transduction pathways to DNA- and RNA-directed processes such as transcription, mRNA processing, transport, and translation. Treatment of hepatocyte culture with insulin increased K protein tyrosine phosphorylation. Insulin altered K protein interaction with RNA and DNA in vitro. Administration of insulin into mice had similar effects on K protein in liver. Coimmunoprecipitations of RNA with K protein revealed preferential in vivo K protein binding of a subset of transcripts, including the insulin-inducible c-fos mRNA. These results suggest a class of insulin pathways that signal nucleic acid-directed processes that involve K protein.

S1 proteins C2 and D2 are novel hnRNPs similar to the transcriptional repressor, CArG box motif-binding factor A

S1 proteins A-D are liberated from thoroughly washed nuclei by mild digestion with DNase I or RNase A, and extracted selectively at pH 4.9 from the reaction supernatants. Here, we characterized the S1 proteins, focusing on protein D2, the most abundant S1 protein in the rat liver, and on protein C2 as well. Using a specific antibody, McAb 351, they were shown to occur in the extranucleolar nucleoplasm, and to be extracted partly in the nuclear soluble fraction. We demonstrate that the S1 proteins in this fraction exist constituting heterogeneous nuclear ribonucleoproteins (hnRNPs), through direct binding to hnRNAs, as revealed by centrifugation on density gradients, immunoprecipitation, and UV cross-linking. In hnRNPs, protein D2 occurred at nuclease-hypersensitive sites and C2 in the structures that gave rise to 40 S RNP particles. By microsequencing, protein D2 was identified with a known protein, CArG box motif-binding factor A (CBF-A), which has been characterized as a transcriptional repressor, and C2 as its isoform protein. In fact, CBF-A expressed from its cDNA was indistinguishable from protein D2 in molecular size and immunoreactivity to McAb 351. Thus, the present results demonstrate that S1 proteins C2 and D2 are novel hnRNP proteins, and suggest that the proteins C2 and D2 act in both transcriptional and post-transcriptional processes in gene expression.

Packing and delivery of a genetic message

Balbiani rings (BRs) 1 and 2 are two exceptionally large chromosomal puffs on chromosome IV in the salivary glands of the dipteran Chironomus tentans. The BR genes are 35-40 kb, contain four short introns, and encode salivary polypeptides of one million molecular weight. They have proven uniquely suited for visualization of the assembly and transport of a specific messenger ribonucleoprotein (RNP) particle. A BR transcript is packed with proteins into a thin RNP fibril, which is folded into a compact ring-like structure. The completed BR particle is released from the gene and moves randomly in the nucleoplasm before it becomes associated with the nuclear pore complex. The passage through the nuclear pore is a highly ordered process with a series of consecutive steps: initial binding, docking, unfolding, movement through the pore with the 5' end of the transcript in the lead, and exit into the cytoplasm. On the cytoplasmic side, the RNA becomes immediately engaged in protein synthesis. Recently, several major proteins in the BR particle have been identified and characterized. They are added to the BR RNA molecule concomitantly with transcription. During the ensuing RNA transport, the various proteins behave differently, some remaining in the nucleus, others entering the cytoplasm coupled to the RNA. The flow pattern of a given protein seems to be closely related to the specific function of the protein. The RNA-binding proteins are likely to play various active roles during gene expression rather than being solely packaging proteins. Finally, it is emphasized that the co-transcriptional loading of the transcript with proteins is probably a key process in gene expression that to a large extent determines the fate of an mRNA both in the nucleus and the cytoplasm.

Nociceptive stimulation increases NO synthase mRNA and vasopressin heteronuclearRNA in the rat paraventricular nucleus

Nociceptive stimulation causes neuroendocrine responses such as arginine vasopressin (AVP) release and activation of the hypothalamo-pituitary-adrenal (HPA) axis. We examined the effects of nociceptive stimulation on the expression levels of neuronal nitric oxide synthase (nNOS) mRNA, heteronuclear (hn)RNA for AVP and AVP mRNA in the rat paraventricular nucleus (PVN) and supraoptic nucleus (SON), using in situ hybridization histochemistry. For nociceptive stimulation, formalin (5%) or saline was injected subcutaneously (s.c.) into the bilateral hind paws of rats. The expression of the nNOS gene in the PVN was significantly increased 2 and 6 h after s.c. injection of formalin in comparison with that in untreated and saline injected rats. The expression of the nNOS gene in the SON did not change in the untreated, saline- and formalin-injected rats. The AVP hnRNA in the PVN and SON was also significantly increased 15, 30 min and 2 h after s.c. injection of formalin, though AVP mRNA did not change at any time points that we studied. Plasma concentration of AVP was significantly increased 15 min after s.c. injection of formalin. These results suggest that NO in the PVN may be involved in nociceptive stimulation-induced neuroendocrine responses.

Mechanisms involved in the homologous down-regulation of transcription of the follicle-stimulating hormone receptor gene in Sertoli cells

The action of follicle-stimulating hormone (FSH) in spermatogenesis is regulated at a fundamental level by controlling the number of competent receptors present at the surface of Sertoli cells. By controlling the number of receptors, the cell is able to modulate the timing and magnitude of subsequent signal transduction in response to FSH. One mechanism of control is the down-regulation of the steady state levels of the FSH receptor gene after exposure to FSH or agents that stimulate or prolong the cAMP signal transduction cascade (homologous down-regulation) in Sertoli cells. The goals of this study were to examine possible mechanisms involved in the down-regulation of mRNA levels of this gene. Analysis of transcription and processing by a PCR-based assay showed that treatment of Sertoli cells with FSH caused at least a 50% reduction of hnRNA for the FSH receptor gene. Reporter genes controlled by 5' flanking sequences of the FSH receptor gene that were transiently transfected into Sertoli cells were not down-regulated. In electrophoretic mobility shift assays (EMSA), cAMP-inducible nuclear protein complex containing c-Fos formed on the activator protein-1/cAMP responsive element-like site located at -216 to -210 in the promoter of the rat FSH receptor gene. We concluded from this study that there was no evidence for the putative role of ICER in the down-regulation of the FSH receptor promoter. In addition, the FSH-induced down-regulation of the transcription of the FSH receptor gene in Sertoli cells was prevented by the treatment of Sertoli cells with trichostatin A prior to the addition of FSH. This experiment coupled with other observations suggested that the down-regulation may be mediated by changes in chromatin structure.

Characterization of hnRNP A2 and B1 using monoclonal antibodies: intracellular distribution and metabolism through cell cycle

Heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 are nuclear RNA binding proteins involved in pre-RNA processing. The alternative splicing of the second mini exon of A2/B1 gene produces A2 and less abundant B1. It has been reported that patients with autoimmune diseases frequently have blood autoantibody valence for A2/B1, and recently that the overexpression, especially of B1, is useful for detecting cancers in early stage. Three anti-A2/B1 monoclonal antibodies were developed using recombinant A2 protein and synthesized peptides around the second splicing site. Three antibodies could separately recognize A2 and B1, and their specificity made them useful in the study of the biochemical and functional properties of A2 and B1. These antibodies have demonstrated differences between A2 and B1 in the intracellular distribution and in the metabolism through cell cycle. They are valuable reagents to clarify the clinical significance of A2/B1 in autoimmune diseases and cancers.

Lipoxygenase mRNA silencing in erythroid differentiation: The 3'UTR regulatory complex controls 60S ribosomal subunit joining

15-lipoxygenase (LOX) expression is translationally silenced in early erythroid precursor cells by a specific mRNA-protein complex formed between the differentiation control element in the 3' untranslated region (UTR) and hnRNPs K and E1. The 3'UTR regulatory complex prevents translation initiation by an unknown mechanism. We demonstrate that the 40S ribosomal subunit can be recruited and scan to the translation initiation codon even when the silencing complex is bound to the 3'UTR. However, the joining of the 60S ribosomal subunit at the AUG codon to form a translation competent 80S ribosome is inhibited, unless initiation is mediated by the IGR-IRES of the cricket paralysis virus. These findings identify the critical step at which LOX mRNA translation is controlled and reveal that 60S subunit joining can be specifically regulated.

Cooperative assembly of an hnRNP complex induced by a tissue-specific homolog of polypyrimidine tract binding protein

Splicing of the c-src N1 exon in neuronal cells depends in part on an intronic cluster of RNA regulatory elements called the downstream control sequence (DCS). Using site-specific cross-linking, RNA gel shift, and DCS RNA affinity chromatography assays, we characterized the binding of several proteins to specific sites along the DCS RNA. Heterogeneous nuclear ribonucleoprotein (hnRNP) H, polypyrimidine tract binding protein (PTB), and KH-type splicing-regulatory protein (KSRP) each bind to distinct elements within this sequence. We also identified a new 60-kDa tissue-specific protein that binds to the CUCUCU splicing repressor element of the DCS RNA. This protein was purified, partially sequenced, and cloned. The new protein (neurally enriched homolog of PTB [nPTB]) is highly homologous to PTB. Unlike PTB, nPTB is enriched in the brain and in some neural cell lines. Although similar in sequence, nPTB and PTB show significant differences in their properties. nPTB binds more stably to the DCS RNA than PTB does but is a weaker repressor of splicing in vitro. nPTB also greatly enhances the binding of two other proteins, hnRNP H and KSRP, to the DCS RNA. These experiments identify specific cooperative interactions between the proteins that assemble onto an intricate splicing-regulatory sequence and show how this hnRNP assembly is altered in different cell types by incorporating different but highly related proteins.

Omega speckles - a novel class of nuclear speckles containing hnRNPs associated with noncoding hsr-omega RNA in Drosophila

Fluorescence RNA:RNA in situ hybridization studies in various larval and adult cell types of Drosophila melanogaster showed that the noncoding hsr-omega nuclear (hsromega-n) transcripts were present in the form of many small speckles. These speckles, which we name ‘omega speckles’, were distributed in the interchromatin space in close proximity to the chromatin. The only chromosomal site where hsromega-n transcripts localized was the 93D locus or the hsromega gene itself. The number of nucleoplasmic speckles varied in different cell types. Heat shock, which inhibits general chromosomal transcription, caused the individual speckles to coalesce into larger but fewer clusters. In extreme cases, only a single large cluster of hsromega-n transcripts localizing to the hsromega locus was seen in each nucleus. In situ immunocytochemical staining using antibodies against heterogenous nuclear RNA binding proteins (hnRNPs) like HRB87F, Hrp40, Hrb57A and S5 revealed that, in all cell types, all the hnRNPs gave a diffuse staining of chromatin areas and in addition, were present as large numbers of speckles. Colocalization studies revealed an absolute colocalization of the hnRNPs and the omegaspeckles. Heat shock caused all the hnRNPs to cluster together exactly, following the hsromega-n transcripts. Immunoprecipitation studies using the hnRNP antibodies further demonstrated a physical association of hnRNPs and hsromega transcripts. The omegaspeckles are distinct from interchromatin granules since nuclear speckles containing serine/arginine-rich SR-proteins like SC35 and SRp55 did not colocalize with the ω speckles. The speckled distribution of hnRNPs was completely disrupted in hsromega nullosomics. We conclude that the hsromega-n transcripts play essential structural and functional roles in organizing and establishing the hnRNP-containing omega speckles and thus regulate the trafficking and availability of hnRNPs and other related RNA binding proteins in the cell nucleus.

Stress regulation of adrenocorticosteroid receptor gene transcription and mRNA expression in rat hippocampus: time-course analysis

Neuronal glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) proteins mediate the transcriptional effects of circulating glucocorticoids. These receptors bind the same DNA response element, yet mediate quite different cellular functions. The present study tests the hypothesis that acute and chronic stress, which cause increases in glucocorticoids sufficient to bind the GR, will regulate expression of the GR and MR genes in the hippocampal formation. Analysis of MR gene transcription using an intronic MR probe revealed a transient 50% decrease in MR hnRNA in CA1, CA3 and dentate gyrus at 60-120 min post-stress, consistent with glucocorticoid down-regulation of the MR gene. However, no changes were seen in full-length MR mRNA at any post-stress time point. In contrast, GR hnRNA was not affected by acute stress, but GR mRNA was decreased 120 min post stress in all hippocampal subregions. Chronic stress exposure down-regulated GR mRNA in CA3 only; effects were first evident 7 days post stress and persisted for the entire stress time-course (28 days). There was no evidence for down-regulation of GR hnRNA or MR hnRNA/mRNA at any point in the chronic stress regimen. The transient decrease in MR hnRNA in the absence of mRNA changes suggests increased MR mRNA stability. In contrast, acute stress decreases the availability of GR mRNA without demonstrably affecting transcription, suggesting reduced GR mRNA stability. The results suggest that acute stress alters GR mRNA expression by largely post-transcriptional mechanisms. However, elevations in basal corticosterone secretion seen following chronic stress are not sufficient to markedly down-regulate GR/MR expression in a long-term fashion.

Regulation of EPC-1/PEDF in normal human fibroblasts is posttranscriptional

The EPC-1 (early population doubling level cDNA-1) gene, also known as pigment epithelium-derived factor, encodes a protein belonging to the serine protease inhibitor (serpin) superfamily that has been reported to inhibit angiogenesis and proliferation of several cell types. We have previously reported that the EPC-1 mRNA and the secreted EPC-1 protein are expressed at levels more than 100-fold higher in early passage, G(0), WI-38 cells compared to either proliferating or senescent WI-38 fibroblasts. To examine the molecular mechanisms that regulate changes in EPC-1 gene expression in WI-38 cells, we isolated and characterized the human EPC-1 gene and determined the mRNA cap site. Transcriptional assays showed no change in the transcription rates of EPC-1 between young proliferating, quiescent, and senescent WI-38 cells. These results suggest posttranscriptional regulation of the EPC-1 gene. Reverse transcriptase polymerase chain reaction measurements (of hnRNA) indicate regulation at the hnRNA level. The regulation of the EPC-1 gene at the level of hnRNA can explain the observed slow increase in the steady-state EPC-1 mRNA levels when cells become quiescent. The reduction of EPC-1 mRNA levels that occurs when cells exit G(0) and are induced to proliferate can be accounted for by a reduction of the EPC-1 mRNA stability in stimulated cells as compared to quiescent cells.

In vitro properties of the conserved mammalian protein hnRNP D suggest a role in telomere maintenance

Mammalian chromosomes terminate with a 3' tail which consists of reiterations of the G-rich repeat, d(TTAGGG). The telomeric tail is the primer for replication by telomerase, and it may also invade telomeric duplex DNA to form terminal lariat structures, or T loops. Here we show that the ubiquitous and highly conserved mammalian protein hnRNP D interacts specifically with the G-rich strand of the telomeric repeat. A single gene encodes multiple isoforms of hnRNP D. All isoforms bind comparably to the G-rich strand, and certain isoforms can also bind tightly and specifically to the C-rich telomeric strand. G-rich telomeric sequences readily form structures stabilized by G-G pairing, which can interfere with telomere replication by telomerase. We show that hnRNP D binding to the G-rich strand destabilizes intrastrand G-G pairing and that hnRNP D interacts specifically with telomerase in human cell extracts. This biochemical analysis suggest that hnRNP D could function in vivo to destabilize structures formed by telomeric G-rich tails and facilitate their extension by telomerase.

Interactive stimulation by luteinizing hormone and insulin of the steroidogenic acute regulatory (StAR) protein and 17alpha-hydroxylase/17,20-lyase (CYP17) genes in porcine theca cells

LH and insulin are postulated to jointly stimulate theca-cell androgen biosynthesis in patients with hyperthecosis or polycystic ovarian syndrome. To explore the mechanisms of putative LH and insulin steroidogenic synergy in primary culture of normal theca cells, we have implemented an in vitro serum-free monolayer culture system of Percoll-purified, porcine theca cells harvested from immature ovaries. Initial dose and time course analyses revealed that a maximally effective concentration of LH (100 ng/ml) or insulin (100 ng/ml) individually will drive androstenedione production (at 6 to 48 h) by 1.5- to 2.6- and 1.1- to 1.7-fold, respectively, while combined agonists act synergistically over the interval 12 to 48 h yielding a 3- to 4-fold joint effect. Coadministration of LH and insulin can augment theca-cell concentrations of CYP17 and StAR messenger RNA (mRNA) resulting in 3.4- to 3.9- and 3.8- to 4.1-fold increases at 24 to 48 h, respectively (P < 0.01). Combined LH and insulin stimulation also amplified the nuclear content of intron-specific heterogeneous nuclear (hn)RNAs encoding CYP17 and StAR. Insulin significantly enhanced LH-driven but not basal cAMP accumulation (14-18 vs. 3-5.5 pmol/microg DNA/12-48 h) (P < 0.01). A stable exogenous analog of cAMP, 8 Br-cAMP, mimicked LH's effect on steroidogenesis and StAR and CYP17 gene expression and with insulin stimulated StAR mRNA and hnRNA accumulation synergistically. However, unlike LH, 8 Br-cAMP did not synergize with insulin on theca-cell androstenedione biosynthesis or CYP17 mRNA and hnRNA expression. In summary, the present in vitro data identify molecular interactions of LH and insulin on StAR and CYP17 gene expression, thus establishing potent signaling interfaces between these distinct hormonal agonists in regulating theca-cell steroidogenesis.

Rapid induction of corticotropin-releasing hormone gene transcription in the paraventricular nucleus of the developing rat

Neonates from postnatal days (pnd) 4-14 display a minimal pituitary-adrenal response to mild stress, the so-called stress hyporesponsive period (SHRP). However, during the SHRP, maternal deprivation (deprived) alters the pituitary-adrenal system, enabling neonates to become endocrine responsive to specific stimuli. Although neonates do display stress-induced ACTH, there is limited evidence for enhanced CRH gene expression early in development. The present experiment examined whether a mild stimulus (isotonic saline injection) administered to deprived and nondeprived neonates would enhance CRH biosynthesis in the paraventricular nucleus. Using in situ hybridization we measured the time course of CRH heteronuclear RNA (hnRNA) and messenger RNA at 15, 30, and 240 min poststimulus. Pnd 6, 12, and 18 were included to examine the CRH gene response during and outside of the SHRP. Despite the minimal endocrine response of nondeprived pups during the SHRP, CRH hnRNA and messenger RNA were elevated at 15 min (all ages). Both transcripts were enhanced at 15-30 min in deprived (pnd 12 and 18) pups; however, the magnitude of the response was less than that in nondeprived pups. These data indicate that during ontogeny there is a rapid stimulus-induced CRH biosynthesis. Thus, during development, the central components of the hypothalamic-pituitary-adrenal axis may be stress hyperresponsive rather than hyporesponsive.

Nonsense mutations in the COL1A1 gene preferentially reduce nuclear levels of mRNA but not hnRNA in osteogenesis imperfecta type I cell strains

Osteogenesis imperfecta (OI) is a heterogeneous disorder of type I collagen resulting in varying degrees of severity. The mildest form of OI (Type I) is associated with bone fragility, normal or near normal stature and blue sclerae. All forms of OI are the result of mutations in COL1A1 or COL1A2, the genes that encode the proalpha1(I) and proalpha2(I) chains of type I collagen, respectively. Mutations identified in patients with OI type I lead to premature termination codons and allele-specific reductions of nuclear mRNA (termed nonsense-mediated mRNA decay or NMD), resulting in a COL1A1 null allele. In mammals, this process primarily effects RNA that co-purifies with the nuclear fraction of the cell. Using a semi-quantitative RT-PCR assay, we compare the relative amounts of normal and mutant transcripts in unprocessed hnRNA and mature mRNA isolated from the nuclear fraction of cells from 11 OI type I individuals with previously identified mutations distributed throughout the COL1A1 gene. While we detect about equal amounts of normal and mutant hnRNA from each cell strain, there is preferential reduction in the relative amount of mutant mRNA when compared to normal; only the cell strain with a mutation in the last exon escapes the major effects of NMD. Our data indicate that NMD targets mRNA rather than hnRNA for degradation, and that this occurs either during or after splicing but prior to cytoplasmic translation.

Local morphine withdrawal increases c-fos gene, Fos protein, and oxytocin gene expression in hypothalamic magnocellular neurosecretory cells

We measured stimulation of c-fos and oxytocin gene expression during excitation of oxytocin cells induced by systemic or local morphine withdrawal. Female rats were made morphine-dependent by intracerebroventricular morphine infusion over 5 d. Morphine withdrawal, induced by systemic injection of the opioid antagonist naloxone (5 mg/kg) in conscious or anesthetized rats, increased the density of c-fos messenger RNA and of oxytocin heterogeneous nuclear RNA in supraoptic nucleus cells compared with those of nonwithdrawn rats; c-fos messenger RNA was also increased in the magnocellular and parvocellular paraventricular nuclei of withdrawn rats. Morphine withdrawal increased the number of Fos-immunoreactive cells in the supraoptic and magnocellular paraventricular nuclei of conscious or pentobarbitone-anesthetized rats. Morphine withdrawal also increased Fos-immunoreactive cell numbers in the parvocellular paraventricular nucleus of conscious but not anesthetized rats. Central administration of the alpha(1)-adrenoreceptor antagonist benoxathian (5 microg/min) did not prevent morphine withdrawal-induced increases in the numbers of Fos-immunoreactive neurons in the supraoptic or magnocellular paraventricular nucleus. Unilateral microdialysis administration of naloxone (10(-5) M) into the supraoptic nucleus of anesthetized morphine-dependent rats increased Fos-immunoreactive cell numbers compared with the contralateral nucleus. Finally, we investigated whether dependence could be induced by chronic unilateral infusion of morphine into a supraoptic nucleus; systemic naloxone (5 mg/kg) increased Fos-immunoreactive cell numbers in the morphine-infused nucleus compared with the contralateral nucleus. Thus, morphine withdrawal excitation increases c-fos and oxytocin gene expression in supraoptic nucleus neurons. This occurs independently from excitation of their ascending noradrenergic inputs, and both dependence and withdrawal can be induced within the supraoptic nucleus.

A nuclear 3'-5' exonuclease involved in mRNA degradation interacts with Poly(A) polymerase and the hnRNA protein Npl3p

Inactivation of poly(A) polymerase (encoded by PAP1) in Saccharomyces cerevisiae cells carrying the temperature-sensitive, lethal pap1-1 mutation results in reduced levels of poly(A)(+) mRNAs. Genetic selection for suppressors of pap1-1 yielded two recessive, cold-sensitive alleles of the gene RRP6. These suppressors, rrp6-1 and rrp6-2, as well as a deletion of RRP6, allow growth of pap1-1 strains at high temperature and partially restore the levels of poly(A)(+) mRNA in a manner distinct from the cytoplasmic mRNA turnover pathway and without slowing a rate-limiting step in mRNA decay. Subcellular localization of an Rrp6p-green fluorescent protein fusion shows that the enzyme residues in the nucleus. Phylogenetic analysis and the nature of the rrp6-1 mutation suggest the existence of a highly conserved 3'-5' exonuclease core domain within Rrp6p. As predicted, recombinant Rrp6p catalyzes the hydrolysis of a synthetic radiolabeled RNA in a manner consistent with a 3'-5' exonucleolytic mechanism. Genetic and biochemical experiments indicate that Rrp6p interacts with poly(A) polymerase and with Npl3p, a poly(A)(+) mRNA binding protein implicated in pre-mRNA processing and mRNA nuclear export. These findings suggest that Rrp6p may interact with the mRNA polyadenylation system and thereby play a role in a nuclear pathway for the degradation of aberrantly processed precursor mRNAs.

The RRM protein NonA from Drosophila forms a complex with the RRM proteins Hrb87F and S5 and the Zn finger protein PEP on hnRNA

The RRM protein NonA, an ubiquitous nuclear protein present in puffs on polytene chromosomes, has been immunopurified as a RNA-protein complex from Drosophila Kc cells. Three other proteins present in the complex have been identified: X4/PEP (protein on ecdysone puffs), a 100-kDa zinc finger RNA-binding protein; the 70-kDa S5 protein, an as yet uncharacterized RNA-binding protein; and P11/Hrb87F, a 38-kDa RRM protein homologous to hnRNP protein A1 from mammals. Monoclonal antibodies against any of the protein components coprecipitate all four proteins although at different ratios. NonA does not coprecipitate with the hrp40 hnRNP proteins and immunolocalizes in a pattern distinct of major hnRNP proteins. Like NonA, X4/PEP, S5, and P11/Hrb87F are present on active sites on polytene chromosomes. The precipitated NonA complex is enriched for certain protein encoding RNAs, notably, histone H3 and H4 RNA.

The specific endoribonuclease activity of small nuclear and cytoplasmic alpha-RNPs

For the first time small nuclear ribonucleoprotein particles (alpha-RNP) tightly bound to chromatin as well as cytoplasmic alpha-RNP are shown to possess strong and regulated endonuclease activity specific for mRNAs and hnRNAs. The enzymatic nature of this activity is confirmed, and the optimal conditions detected. This RNase activity is controlled by the action of a differentiating stimulus, dimethylsulfoxide, in human K562 cells. Small alpha-RNP involvement in the coordinated control of stability of pre-messenger RNA and messenger RNA molecules is suggested.