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Biomedical subjects

X Sun

Publications and source records attributed to X Sun.

At least 397 records · Page 22Linked to original sources
PubMed1996

A protein of the SR family of splicing factors binds extensively to exonic Balbiani ring pre-mRNA and accompanies the RNA from the gene to the nuclear pore.

We report on the molecular cloning and intracellular localization of a heterogeneous nuclear ribonucleoprotein (hnRNP), Ct-hrp45, one of the major components of pre-mRNP particles in Chironomus tentans. It is shown that hrp45 belongs to the SR family of splicing factors and exhibits high sequence similarity to Drosophila SRp55/B52 and human SF2/ASF. The distribution of hrp45 within the C. tentans salivary gland cells is studied by immunocytology. The hrp45 protein is found to be abundant in the nucleus, whereas it is undetectable in the cytoplasm. The fate of hrp45 in specific pre-mRNP particles, the Balbiani ring (BR) granules, is revealed by immunoelectron microscopy. It is observed that hrp45 is associated with the growing BR pre-mRNP particles and is being added continuously concomitant with the growth of the transcript, indicating that hrp45 is bound extensively to exon 4, which comprises 80-90% of the primary transcript. Furthermore, hrp45 remains bound to the BR RNP particles in the nucleoplasm and is not released until the particles translocate through the nuclear pore. Thus, hrp45 behaves as an hnRNP protein linked to exon RNA (and perhaps also to the introns) rather than as a spliceosome component connected to the assembly and disassembly of spliceosomes. It seems that hrp45, and possibly also other SR family proteins, is playing an important role in the structural organization of pre-mRNP particles and is perhaps participating not only in splicing but also in other intranuclear events.

Amino Acid Sequence↗
PubMed1996

MEF, a novel transcription factor with an Elf-1 like DNA binding domain but distinct transcriptional activating properties.

To isolate novel ETS genes expressed in hematopoietic cells we used a nested, degenerate oligonucleotide PCR based technique to obtain a cDNA fragment that encodes an ETS domain from a human megakaryocytic cell line. This fragment was used to isolate a full length, 4.2 kb cDNA that encodes a 663 amino acid protein which we call MEF (myeloid elf-1-like factor). MEF contains a central ETS domain and is expressed in a variety of myeloid leukemia cell lines and in normal adult hematopoietic tissue such as spleen, thymus and peripheral blood, as well as non-hematopoietic tissue such as ovary, placenta and colon. Using an oligonucleotide binding selection assay, and bacterially expressed MEF, we demonstrated that MEF recognizes a consensus DNA binding sequence nearly identical to elf-1 (..WGGA..) and then showed that MEF specifically bound to known elf-1 binding sites in the human GM-CSF and IL-3 promoters. To characterize the functional effect of MEF on transcription, we performed co-transfection experiments in myeloid cells, and T cells, and demonstrated transactivation of both promoters by MEF, but not by elf-1. MEF is a new member of the elf-1/E74 family of ETS proteins, that has DNA binding properties similar to elf-1 but distinct transcriptional activating effects in several hematopoietic cell lineages.

Adult↗
PubMed1996

Corticofugal control of central auditory sensitivity in the big brown bat, Eptesicus fuscus.

Using bats as a model auditory system, we studied corticofugal control of auditory sensitivity of neurons in the inferior colliculus. We demonstrate for the first time that the corticocollicular pathway continuously regulates acoustic signal processing in the inferior colliculus by increasing the threshold, reducing the auditory spatial response area, and sharpening the frequency tuning curve of recorded inferior collicular neurons. Regulation of auditory sensitivity of recorded inferior collicular neurons was observed when the corticocollicular pathway was activated by electrical stimulation in the auditory cortex. The effect of this corticofugal regulation of auditory sensitivity in inferior collicular neurons can also be produced by ionophoretical application of GABA to the collicular recording site. This regulation of ascending acoustic information by commands originating from higher brain centers may provide the bat with a mechanism to actively control acoustic signal processing and thus optimize acoustic signal analysis.

Animals↗
PubMed1996

Immunosuppressant FK506 induces interleukin-6 production through the activation of transcription factor nuclear factor (NF)-kappa(B). Implications for FK506 nephropathy.

FK506 is a powerful immunosuppressive drug currently in use that inhibits the activation of several transcription factors (nuclear factor (NF)-AT and NF-kappaB) critical for T cell activation. We show here that, contrary to the situation in T cells, FK506 activates transcription factor NF-kappaB in nonlymphoid cells such as fibroblasts and renal mesangial cells. We further show that FK506 induces NF-kappaB-regulated IL-6 production in vitro and in vivo, in particular in kidney. IL-6 has been shown previously to produce renal abnormalities in vivo, such as mesangioproliferative glomerulonephritis. Similar renal abnormalities were also observed in FK506-treated animals. These results thus suggest a causal relationship between FK506-induced NF-kappaB activation/IL-6 production and some of FK506-induced renal abnormalities.

Animals↗
PubMed1996

Developmental age-dependent upregulation of choline acetyltransferase and vesicular acetylcholine transporter mRNA expression in neonatal rat septum by nerve growth factor.

We examined the effect of intraventricular injection of nerve growth factor (NGF) on the choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) mRNA expression in the septa of neonatal rats. Rat pups were injected with 2.5 S NGF or cytochrome-c (control) on postnatal days (PN) 4 and 18, and sacrificed 3 days after injections for analysis of ChAT and VAChT mRNA levels by dot-blot hybridization of total septal RNA. In the NGF-treated pups, the ChAT and VAChT mRNA levels were elevated 3- and 2-fold, respectively, at PN7, and 1.8- and 1.3-fold at PN21. These results indicate that (1) NGF upregulates the expression of both ChAT and VAChT genes, (2) NGF has a greater effect on the expression of ChAT mRNA than VAChT mRNA, and (3) the effect of exogenous NGF on the expression of both genes diminishes with developmental age.

Age Factors↗
PubMed1996

Quinone-induced apoptosis in human colon adenocarcinoma cells via DT-diaphorase mediated bioactivation.

DT-diaphorase (DTD) activity has been related to bioactivation and cytotoxicity of antitumor quinones. A pair of human colon adenocarcinoma cell lines, HT29 and BE, were used in this study to examine the role of DTD in antitumor quinone induced apoptosis. HT29 cells have elevated levels of DTD whereas BE cells lack functional DTD due to a point mutation which results in a complete lack of DTD activity. MeDZQ, a quinone that is efficiently bioactivated by DTD, induced apoptosis both in HT29 and BE cells, but with a much higher incidence in HT29, as assessed by morphological criteria and the formation of oligonucleosomal fragments of DNA. Two other quinone compounds which are also substrates for DTD, i.e. streptonigrin and mitomycin C, also preferentially induced apoptosis in HT29 cells, which could be inhibited by dicoumarol. Our data suggest that bioreductive activation of antitumor quinones by DTD results in induction of apoptosis in human colon carcinoma cells.

Adenocarcinoma↗
PubMed1996

The mitochondrial KATP channel as a receptor for potassium channel openers.

The biochemical properties of the mitochondrial KATP channel are very similar to those of plasma membrane KATP channels, including inhibition by low concentrations of ATP and glyburide (Paucek, P., Mironova, G., Mahdi, F., Beavis, A. D., Woldegiorgis, G., and Garlid, K. D. (1992) J. Biol. Chem. 267, 26062-26069). Plasma membrane KATP channels are highly sensitive to the family of drugs known as K+ channel openers, raising the question whether mitochondrial KATP channels are similarly sensitive to these agents. We addressed this question by measuring K+ flux in intact rat liver mitochondria and in liposomes containing KATP channels purified from rat liver and beef heart mitochondria. K+ channel openers completely reversed ATP inhibition of K+ flux in both systems. In liposomes, ATP-inhibited K+ flux was restored by diazoxide (K1/2 = 0.4 microM), cromakalim (K1/2 = 1 microM), and two developmental cromakalim analogues, EMD60480 and EMD57970 (K1/2 = 6 nM). Similar K1/2 values were observed in intact mitochondria. These potencies are well within the range observed with plasma membrane KATP channels. We also compared the potencies of these K+ channel openers on the plasma membrane KATP channel purified from beef heart myocytes. The KATP channel from cardiac mitochondria is 2000-fold more sensitive to diazoxide than the channel from cardiac sarcolemma, indicating that two distinct receptor subtypes coexist within the myocyte. We suggest that the mitochondrial KATP channel is an important intracellular receptor that should be taken into account in considering the pharmacology of K+ channel openers.

Adenosine Triphosphate↗
PubMed1996

The free radical of the anaerobic ribonucleotide reductase from Escherichia coli is at glycine 681.

The anaerobic ribonucleoside triphosphate reductase of Escherichia coli is an iron-sulfur protein carrying an oxygen-sensitive organic radical, which is essential for catalysis. The radical was tentatively proposed to be on glycine 681, based on a comparison with the glycyl radical-containing enzyme pyruvate formate-lyase. By EPR spectroscopy of selectively 2H- and 13C-labeled anaerobic ribonucleotide reductase, the radical was now unambiguously assigned to carbon-2 of a glycine residue. The large 1H hyperfine splitting (1.4 millitesla) was assigned to the alpha-proton. Site-directed mutagenesis was used to change glycine 681 into an alanine residue. In separate experiments, the two adjacent residues, cysteine 680 and tyrosine 682, were changed into serine and phenylalanine, respectively. All mutated proteins were retained on dATP-Sepharose, indicating that the mutant proteins had intact allosteric sites. They also contained amounts of iron comparable with the wild type reductase and showed the same iron-sulfur-related spectrum, suggesting that the mutant proteins were properly folded. Of the three mutant proteins only the G681A protein completely lacked the detectable glycyl radical as well as enzyme activity. Our results identify glycine 681 as the stable free radical site in E. coli anaerobic ribonucleotide reductase.

Base Sequence↗
PubMed1996

Protein-protein interactions in eukaryotic transcription initiation: structure of the preinitiation complex.

We have used alanine scanning to analyze protein-protein interactions by human TATA-element binding protein (TBP) within the transcription preinitiation complex. The results indicate that TBP interacts with RNA polymerase II and general transcription factors IIA, IIB, and IIF within the functional transcription preinitiation complex and define the determinants of TBP for each of these interactions. The results permit construction of a model for the structure of the preinitiation complex.

Adenoviruses, Human↗
PubMed1996

A pre-mRNA-binding protein accompanies the RNA from the gene through the nuclear pores and into polysomes.

In the larval salivary glands of C. tentans, it is possible to visualize by electron microscopy how Balbiani ring (BR) pre-mRNA associates with proteins to form pre-mRNP particles, how these particles move to and through the nuclear pore, and how the BR RNA is engaged in the formation of giant polysomes in the cytoplasm. Here, we study C. tentans hrp36, an abundant protein in the BR particles, and establish that it is similar to the mammalian hnRNP A1. By immuno-electron microscopy it is demonstrated that hrp36 is added to BR RNA concomitant with transcription, remains in nucleoplasmic BR particles, and is translocated through the nuclear pore still associated with BR RNA. It appears in the giant BR RNA-containing polysomes, where it remains as an abundant protein in spite of ongoing translation.

Amino Acid Sequence↗
PubMed1996

Intensive care unit admissions with cirrhosis: risk-stratifying patient groups and predicting individual survival.

Prognosis for acutely ill patients with cirrhosis is influenced by the severity of hepatic abnormalities and by dysfunction of other organ systems. The purpose of this study was to examine the usefulness of the Acute Physiology, Age, and Chronic Health Evaluation (APACHE III) prognostic system for risk-stratifying groups of intensive care unit (ICU) patients with cirrhosis and in predicting individual survival. We used data for 17,440 ICU admissions at 40 American hospitals to select 117 of the 537 patients with a history of cirrhosis who were ventilated on ICU day 1, a group known to have a high mortality rate. We then calculated each patient's probability of hospital death on ICU days 1 through 7, using seven previously validated multivariate equations. Hospital mortality was 63% for the 117 study patients. The most important determinants of risk for hospital death on ICU day 1 were the acute physiology score of APACHE III, ICU admission diagnosis, and operative status. Daily changes in the acute physiology score caused a rise or fall in the probability of hospital mortality and was useful in assessing individual response to therapy. APACHE III accurately risk stratifies critically ill patients with cirrhosis because it accounts for many of the factors known to influence prognosis. This capability can be used to assess severity of illness and risk-stratify patients with cirrhosis during clinical trials. Daily prognostic estimates based on physiological changes over time reflect patient response and can help physicians to assess the incremental benefit of therapy.

Adult↗
PubMed1996

Application of the APACHE III prognostic system in Brazilian intensive care units: a prospective multicenter study.

OBJECTIVE: To compare patients and their outcomes at ten Brazilian intensive care units (ICUs) with those reported from the United States. DESIGN: Prospective multicenter inception cohort study. SETTING: Ten Brazilian adult medical-surgical ICUs. PATIENTS: 1734 consecutive adult ICU admissions. MEASUREMENTS AND RESULTS: We used demographic, clinical and physiologic information and the APACHE III prognostic system to predict risk of hospital death for 1734 ICU admissions. We then divided the observed by the predicted hospital death rate to calculate standardized mortality ratios (SMRs) for patient groups and each ICU. Hospital mortality for Brazilian patients (34%) was double that found in the United States (17%, p < 0.01). Discrimination of survivors from non-survivors using APACHE III was good (area under a receiver operating characteristic curve = 0.82), but the predicted risk of death was significantly (p < 0.0001) lower than observed outcome (SMR = 1.67). Three of the ten Brazilian ICUs, however, had SMRs of 1.01 to 1.1 and no significant difference between observed and predicted outcomes; the remaining seven ICUs had significantly higher SMRs, ranging from 1.50 to 2.30. CONCLUSION: The APACHE III prognostic system was a good discriminator of hospital mortality for ICU admissions at 10 Brazilian ICUs. There was substantial and significant variation, however, in SMRs among the Brazilian ICUs, which suggests that further evaluations of international differences in intensive care using a common risk assessment system should be performed and factors associated with variations in risk-adjusted mortality scrutinized.

APACHE↗
PubMed1996

The importance of technology for achieving superior outcomes from intensive care. Brazil APACHE III Study Group.

OBJECTIVE: To test the hypothesis that technology availability, staffing, and diagnostic diversity in an intensive care unit (ICU) are associated with the ability to decrease hospital mortality. DESIGN: Prospective multicenter descriptive cohort study. SETTING: Ten Brazilian medical-surgical ICUs. PATIENTS: 1734 consecutive adult ICU admissions. MEASUREMENTS AND RESULTS: We recorded the amount of technology, number of diagnoses, and availability of nurses at each ICU. We also used demographic, clinical and physiologic information for an average of 173 admissions to each ICU to calculate standardized mortality ratios (SMRs) for each ICU. The mean SMR for the ten ICUs was 1.67 (range 1.01-2.30). A greater availability of ICU equipment and services was significantly (p < 0.001) associated with a lower SMR. CONCLUSION: The ability of Brazilian ICUs to reduce hospital mortality is associated with the amount of technology available in these units.

Adult↗
PubMed1996

Severity stratification and outcome prediction for multisystem organ failure and dysfunction.

Multiple organ system failure or dysfunction (MOSF/MODS) remains a major cause of morbidity and mortality in hospitalized adults. Among intensive care unit (ICU) patients the extent of physiologic derangement, the type of associated disease or injury, increasing age, and life-threatening comorbid conditions are the major determinants of risk for developing MOSF and for survival during the 1980s. Hospital mortality for patients with a single organ system failure (OSF) lasting more than 1 day approached 40%; and for those with two OSFs hospital mortality increased to 60%. These outcomes did not change over the decade. For patients with three or more OSFs persisting after 3 days of OSF, however, data suggest that between 1982 and 1990 the mortality has been reduced from 98% to 84% (p = 0.0003). Because of variations in the types and combinations of OSFs, associated disease, and extent of physiologic derangement, it is difficult to interpret variations in mortality among patients with one or more OSFs defined using categorical criteria. For this and other reasons, outcome prediction based on a comprehensive assessment of patient risk factors is a more sensitive, specific, useful approach to quantifying MODS than a simple count of the number and duration of OSFs. Because repeated assessment of risk factors during subsequent ICU days reflects complications and response to therapy, daily outcome predictions are even more precise than estimates at ICU admission. The ability to more accurately predict survival from MODS/MOSF can improve our ability to test new therapies, evaluate how outcome has changed over time, and assess the efficacy of supportive therapy for individuals.

Adult↗
PubMed1996

Differential axonal transport of soluble and insoluble tau in the rat sciatic nerve.

Axonal transport of microtubule-associated protein tau was studied in the motor fibers of the rat sciatic nerve 1-4 weeks after labeling of the spinal cord with [35S]methionine. As 60-70% of low molecular weight tau in this system was found to be insoluble in 1% Triton-containing buffer, labeled proteins in 6-mm consecutive nerve segments were first separated into Triton-soluble and insoluble fractions. Two-dimensional gel electrophoresis and immunoblotting with anti-tau antibody confirmed the presence of tau among labeled, transported proteins in both fractions. Isoform composition of labeled tau was similar to that of bulk axonal tau, the most acidic species with apparent molecular mass of 66 kDa being the major component. Transport profiles obtained by measuring radioactivities associated with this major isoform showed that soluble and insoluble tau were transported at different rates. Insoluble tau, which contained the majority of tau-associated radioactivity, was transported at 1.7 mm/day in slow component a (SCa), whereas soluble tau was transported faster, at 3 mm/day, corresponding to the rate of slow component b (SCb). Cotransport of insoluble tau with insoluble tubulin in SCa suggests its association with stable microtubules.

Animals↗