Inhibition of the cellular response to interferons by products of the adenovirus type 5 E1A oncogene.

Expression of the E1A oncogene of adenovirus type 5 inhibits the response of interferon (IFN)-inducible constructs to Type I (alpha,beta) and II (gamma) IFNs in transient transfection assays. In human cell lines stably expressing E1A mRNA and protein acquisition of an antiviral state and the induction of a number of genes in response to alpha- and gamma-IFNs is inhibited. A short IFN-stimulable response element (ISRE) present in the 5' flanking region of a number of genes mediates induction by alpha- and gamma-IFNs. In cells expressing E1A there is a substantial reduction in the levels of the ISRE-binding factors E and M, inducible by alpha-IFN, and of factor G, inducible by gamma-IFN. In E1A-expressing cells the E alpha subunit of factor E is activated normally in response to alpha-IFN; the defect is in the production or activation of the E gamma subunit. The inhibitory activity of E1A is lost upon deletion of the CR1 domain. The induction of HLA class II genes by gamma-IFN, which involves a different DNA response element(s), and of beta-IFN mRNA in response to double-stranded RNA are also inhibited by E1A. An essential component(s) of a number of signalling pathways must, therefore, be subject, directly or indirectly, to inhibition by E1A.     

Construction of a dihydrofolate reductase-deficient mutant of Escherichia coli by gene replacement.

The dihydrofolate reductase (fol) gene in Escherichia coli has been deleted and replaced by a selectable marker. Verification of the delta fol::kan strain has been accomplished using genetic and biochemical criteria, including Southern analysis of the chromosomal DNA. The delta fol::kan mutation is stable in E. coli K549 [thyA polA12 (Ts)] and can be successfully transduced to other E. coli strains providing they have mutations in their thymidylate synthetase (thyA) genes. A preliminary investigation of the relationship between fol and thyA gene expression suggests that a Fol- cell (i.e., a dihydrofolate reductase deficiency phenotype) is not viable unless thymidylate synthetase activity is concurrently eliminated. This observation indicates that either the nonproductive accumulation of dihydrofolate or the depletion of tetrahydrofolate cofactor pools is lethal in a Fol- ThyA+ strain. Strains containing the thyA delta fol::kan lesions require the presence of Fol end products for growth, and these lesions typically increase the doubling time of the strain by a factor of 2.5 in rich medium.     

The effect of polymerised fibrin on the catalytic activities of one-chain tissue-type plasminogen activator as revealed by an analogue resistant to plasmin cleavage

A one-chain recombinant tissue-type plasminogen activator (EC 2.4.31.-) (tPA) analogue was constructed in which Arg-275 of the activation site was changed to Gly by site-directed mutagenesis. This analogue, tPA-Gly275, was very resistant to plasmin (EC 2.4.21.5) cleavage. It has been used to gain information about the activity of the uncleaved one-chain tPA form, also when plasmin is generated as a result of a plasminogen activation reaction. The amidolytic activity of tPA-Gly275 with less than Glu-Gly-Arg-pNA was investigated and compared to that of one-chain and two-chain wild-type recombinant tPA. A small but significant intrinsic amidolytic activity was observed with the analogue as well as the wild-type one-chain tPA form. However, it was much lower than that of two-chain tPA. Polymerised fibrin enhanced the amidolytic activity of both one-chain tPA forms but not of two-chain tPA. Measurements of the plasminogen activation kinetics in the absence of fibrin revealed that tPA-Gly275 possessed a significant intrinsic activity. However, it was 30-fold lower than that of two-chain tPA. Addition of polymerised fibrin profoundly enhanced the plasminogen activation rate of both tPA-Gly275 and wild-type one- and two-chain tPA to approximately the same maximal level. The results were interpreted to mean that fibrin binding can induce an activated state of the intact tPA one-chain form.     

Absence of increased oxygen consumption in brown adipose tissue of rats exhibiting "cafeteria" diet-induced thermogenesis

Young male Sprague-Dawley rats were induced to overeat (approximately 45%) by provision of a "cafeteria" (CAF) diet of palatable human foods. Normophagic rats fed a commercial chow or a semisynthetic diet served as controls. The CAF rats exhibited (a) the reduced food efficiency and the propranolol-inhibitable elevation in resting metabolic rate (resting VO2) that are indicative of a facultative diet-induced thermogenesis (DIT) by which excess energy gain is resisted, and (b) certain changes in brown adipose tissue (BAT) that are among those taken as evidence for BAT as the effector of DIT, e.g., increased protein content and increased mitochondrial binding of GDP. To assess directly and quantitatively the contribution by BAT to the elevation in VO2 (apparent DIT) of the CAF rats, BAT O2 consumption was determined (Fick principle) from measurements of tissue blood flow (microsphere method) and the arteriovenous difference in blood O2 across interscapular BAT (IBAT). To obtain the measurements, the animals were fitted under halothane anesthesia with vascular cannulas for intraventricular injection of microspheres and sampling of arterial blood and the venous effluent of IBAT. After recovery from anesthesia and rewarming to normal body temperature the animals were placed singly in a temperature-controlled metabolic chamber and the measurements, which also included determination of resting VO2, were made 1.5-2 h later about 11:30 h. As determined from measurements made at 28 degrees C (thermoneutrality) mean values of resting VO2 for the cannulated rats were unchanged from those of intact (unoperated) CAF or control rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

The noradrenaline content and innervation of brown adipose tissue in the young rabbit

This work examined the noradrenaline content of brown adipose tissue, the metabolic response to endogenous noradrenaline released during tyramine infusion, and the innervation of brown fat at the electron microscopic level in the young rabbit. The noradrenaline content (ng/g) of the interscapular and cervical fat deposits ranged from 256 +/- 51 to 343 +/- 59 and 399 +/- 18 to 694 +/- 92, respectively, in four groups of rabbits (1-2, 7-8, 12-13, and 25-27 days of age). There was considerable variation amongst animals in each age group, but no evidence of a major increase or decrease in noradrenaline content during the first 4 weeks of life. Intravenous infusion of tyramine (100 micrograms X kg-1 X min-1) increased plasma noradrenaline concentration, oxygen consumption, and blood flow to brown fat. Thus noradrenaline released from endogenous sites, as well as injected noradrenaline, will initiate the thermogenic response of brown fat. Ultrastructurally, unmyelinated axons that were not organized in a fascicle were observed adjacent to the adipocytes in the late gestation fetus. By 1 week of age of axons were surrounded by Schwann cell cytoplasm which formed a fascicle. However, no evidence of myelination was found up to 21 days of age. Collectively, the data indicate that the brown adipocyte is fully responsive at 1-2 days of age even though myelination of the nerves is incomplete, and that the incomplete development of the sympathetic nerves at birth is not a factor in the synthesis of noradrenaline in the very young rabbit. In addition, brown fat of the newborn rabbit is not as thermogenically active as the brown fat of the cold-acclimated rat.     

A radioenzymatic assay for quinolinic acid

A new and rapid method for the determination of the excitotoxic tryptophan metabolite quinolinic acid is based on its enzymatic conversion to nicotinic acid mononucleotide and, in a second step utilizing [3H]ATP, further to [3H] deamido-NAD. Specificity of the assay is assured by using a highly purified preparation of the specific quinolinic acid-catabolizing enzyme, quinolinic acid phosphoribosyltransferase, in the initial step. The limit of sensitivity was found to be 2.5 pmol of quinolinic acid, sufficient to conveniently determine quinolinic acid levels in small volumes of human urine and blood plasma.     

Cloning and expression of a cDNA encoding a catalytically active fragment of calf thymus DNA polymerase alpha

A calf thymus cDNA expression library was constructed in the EcoRI site of lambda gt11 and probed with an antibody raised against calf thymus DNA polymerase alpha. Three classes of antibody-reactive clones were isolated. The largest class carried a 1.9 kilobase calf cDNA insert and expressed a 165-175 kilodalton beta-galactosidase:calf fusion protein which displayed DNA polymerase activity. The characteristic responses of the polymerase activity to alpha-specific inhibitors and antibodies identified the 1.9 kilobase cDNA as a sequence specifically derived from the structural gene encoding the pol alpha catalytic core.     

Suppression of a pokeweed mitogen-stimulated plaque-forming cell response by a human B lymphocyte-derived aggregated IgG-stimulated suppressor factor: suppressive B cell factor (SBF)

The mechanisms whereby formed immune complexes (IC) or immunoglobulin aggregates can suppress further antibody production were explored by culturing normal human peripheral blood mononuclear leukocytes (PBL) with heat-aggregated IgG (HAIgG) and collecting the culture supernatants at 24 hr. These supernatants were found to suppress a pokeweed mitogen (PWM)-induced rheumatoid factor plaque-forming cell (RF-PFC) response in normal individuals. PWM-induced anti-trinitrophenylated sheep red blood cell (TNP-SRBC) PFC were also inhibited by suppressor supernatants from HAIgG-stimulated PBL, suggesting that the polyclonal PFC response was inhibited by a suppressor factor. The suppressor factor inhibited PWM stimulated RF-PFC throughout the culture period, but suppression was maximal at the peak of the RF-PFC response. Suppressor factor was only effective at the initiation of cultures, suggesting that it inhibited early events in the PWM-stimulated RF-PFC response. Molecular weight determination of the suppressor factor by differential membrane fractionation suggested a m.w. range of 30,000 to 50,000, and chromatography on Sephadex G-100 showed a peak activity at an approximate m.w. of 32,000. Studies suggested the factor was not an interferon. Depletion of T lymphocytes by E rosetting and macrophages/monocytes by G-10 adherence did not affect the generation of suppressor factor. Depletion of T lymphocytes (OKT4, OKT8) and NK cells (Leu-11b) by antibody-dependent, complement-mediated cytotoxicity also did not affect the generation of suppressor factor. Depletion of B lymphocytes with OKB7 resulted in the generation of significantly less suppressor factor. Suppression produced by unstimulated purified B lymphocytes was approximately one-half that seen when B lymphocytes were stimulated with HAIgG. Differential membrane fractionation studies suggested that only HAIgG-stimulated B cell cultures contained peak activity in the 30,000 to 50,000 m.w. fraction. Supernatants from unstimulated purified T cells also generated suppression, which was approximately one-half of that seen with HAIgG-stimulated B cells, but no increase in suppressor activity was seen in T cell cultures after incubation with HAIgG. These studies demonstrate that HAIgG is capable of stimulating B lymphocytes to produce a lymphokine, suppressive B cell factor (SBF), which is capable of suppressing a polyclonal PFC response. SBF may be important in feedback control of human immunoglobulin production.     

Histamine releases PGI2 from human pulmonary artery

Histamine caused a triphasic response of human pulmonary artery strips in vitro, consisting of a small initial contraction followed by pronounced relaxation preceding a second contractile response. These characteristics were not seen with other contractile stimuli including 5-hdyroxytryptamine, leukotriene D₄, and KC1. The relaxant component of this response was ablated by removal of endothelium from the vascular strips or by pretreatment of the tissues with 1μM indomethacin. Measurement of the PGI₂ degradation product 6-keto-PGF_1α in supernatants from histamine-challenged tissues confirmed the synthesis of PGI₂. Supernatants from unstimulated or leukotriene-challenged tissues contained no detectable amounts of 6-keto-PGF_1α. The histamine H₁ antagonist diphenhydramine inhibited both the contractile and relaxant responses to histamine whereas the H₂ antagonist cimetidine affected neither component. The released PGI₂ significantly altered the dose-respons curve to histamine without inhibiting the maximal contractile responses. We conclude that histamine induces PGI₂ formation from pulmonary arterial endothelium via an H₁ receptor.     

Functional aspects of ano-rectal vascularity

The blood supply of the ano-rectum has been studied in cadaveric specimens by angiographic methods. The vascular anastomosis between the middle rectal and superior rectal vessels was found to be demonstrable on one side only. There appears to be a midline paucity of vessels in both the posterior and anterior rectal walls, and this may be important in the aetiology of anastomotic dehiscence in low anterior resection.