Group II intron ribozymes that cleave DNA and RNA linkages with similar efficiency, and lack contacts with substrate 2'-hydroxyl groups

BACKGROUND

Group II introns are self-splicing RNAs that have mechanistic similarity to the spliceosome complex involved in messenger RNA splicing in eukaryotes. These autocatalytic molecules can be reconfigured into highly specific, multiple-turnover ribozymes that cleave oligonucleotides in trans. We set out to use a simplified system of this kind to study the mechanism of cleavage.

RESULTS

Unlike other catalytic RNA molecules, the group II ribozymes cleave DNA linkages almost as readily as RNA linkages. One ribozyme variant cleaves DNA linkages with an efficiency comparable to that of restriction endonuclease EcoRI. Single deoxynucleotide substitutions in the substrate showed that the ribozymes bind substrate without engaging 2'-hydroxyl groups.

CONCLUSIONS

The ribose 2'-hydroxyl group at the cleavage site has little role in transition-state stabilization by group II ribozymes. Substrate 2'-hydroxyl groups are not involved in substrate binding, suggesting that only base-pairing is required for substrate recognition.

Four outbreaks of human trichinellosis in Henan Province

Four outbreaks of human trichinellosis caused by eating pork together had occurred successively in two rural areas and two cities of Henan Province, where the disease is endemic. Of the 110 persons involved, 54 had the onset. All of them had the history of eating pork. In the outbreak of Dengzhou, in those persons who dined together, men were all uninfected and 13 women were infected. The difference found between sexes was suggested to be related with spirit drinking. In these 54 patients, the latent period ranged from 3 to 28 days. The relevant clinical symptoms and signs were fever, edema, myalgia, rash, headache, nausea, abdominal pain and diarrhea. Vomiting was uncommon. Most patients were hospitalized and all cases recovered in two weeks after proper treatment with albendazole.

Tumor growth inhibition mediated by lymphotoxin: evidence of B lymphocyte involvement in the antitumor response

The antitumor effect of lymphotoxin (LT) and the underlying cellular mechanism were analyzed. To achieve an increased local concentration of LT at the site of tumor growth, which mimics the physiological fashion of cytokine action, we transfected the murine plasmacytoma J558L cells with a human LT expression plasmid and selected several clones that produce varying levels of LT for analysis of their tumorigenicity. The LT produced by the transfected J558L cells effectively suppressed tumor growth in syngeneic BALB/c mice without any obvious side effects. This antitumor function is indirect and LT specific, because the tumor cells did not show altered growth kinetics after the gene transfer in vitro, and tumor growth inhibition in vivo could partially be reversed by an anti-LT mAb. In nude mice, LT producing tumors were initially suppressed, but most mice developed a tumor at the end of the study. However, the requirement of T cells for complete tumor rejection could be compensated for by higher amounts of LT secretion. Furthermore, the antitumor activity of LT seems to involve B lymphocytes in the absence of functional T lymphocytes since a significant difference existed between tumor growth of J558-LT cells in nude and in SCID mice. LT-producing tumors but not parental tumors were massively infiltrated by B220+ cells in nude mice. The secretion of LT by tumor cells also induced a heavy infiltration of Mac-1+ and Mac-3+ cells and a moderate infiltration of Gr-1+ cells, both in nude and in SCID mice. Together, LT-producing J558L cells are rejected by a complex immunological mechanism, which seems to involve T as well as B and other cells. This distinguishes LT from a number of other cytokines analyzed in analogous experiments.

Human lymphotoxin has at least equal antitumor activity in comparison to human tumor necrosis factor but is less toxic in mice

Because of the severe toxicity of systemically applied tumor necrosis factor (TNF) in cancer patients, considerable efforts have been made to construct mutant TNF molecules, which retain antitumor activity, but display less toxicity. We compared tumor suppression in relation to the toxic effects of human TNF and human lymphotoxin (LT) in mice. The genes for these two cytokines were expressed in Chinese hamster ovary (CHO) cells. Intraperitoneal injection of parental and gene modified CHO cell lines producing similar amounts of biologically active TNF or LT, respectively, into nude mice showed that CHO-TNF cells killed the mice more rapidly than parental cells, but that CHO-LT tumor bearing mice lived significantly longer than mice injected with parental cells. Injection of the cells subcutaneously into severe combined immunodeficiency (SCID) mice allowed direct comparison of tumor suppression and toxic effects of the two cytokines. Both TNF and LT produced by the tumor effectively suppressed tumor growth by an indirect mechanism, LT being at least as effective as TNF. However, mice bearing CHO-TNF cells either died rapidly or developed cachexia, as shown by weight loss. In contrast, mice injected with CHO-LT cells never rapidly died and became cachectic much later than CHO-TNF cell injected animals, though serum levels of LT were higher than those of TNF. Analysis of soluble forms of TNF receptors (TNF-R1 and TNF-R2) in sera of tumor bearing mice showed that soluble TNF-R1 was downregulated in both CHO-TNF and CHO-LT, in comparison with CHO-neo cell injected mice and to normal SCID mice. The soluble form of TNF-R2 was induced by CHO cell lines. In CHO-TNF cell injected SCID mice, serum levels were significantly increased, whereas in mice injected with CHO-LT cells, serum levels of soluble TNF-R2 were decreased. Together, our results show a higher therapeutic index of LT compared with TNF.

Anesthetics reduce the magnitude of the membrane dipole potential. Measurements in lipid vesicles using voltage-sensitive spin probes

Lipid membranes possess a large internal dipole potential that greatly exceeds the magnitude of typical transmembrane or surface potentials. The volatile general anesthetics, halothane, isoflurane and enflurane were tested by the use of positively and negatively charged hydrophobic ion spin labels in lipid bilayer vesicles for their ability to modulate the membrane dipole potential. These anesthetics decreased the binding of negatively charged hydrophobic ion spin probes based on trinitrophenol, but increased the binding of positively charged hydrophobic ion probes based on triphenylalkylphosphoniums. They also enhanced the transit rates for both hydrophobic anions and cations; however, translocation rates were enhanced to a greater extent for the cation probes compared to the anion probes. The changes in binding constant for cations versus anions could be accurately accounted for using a simple model for the free energy profile for hydrophobic ions across membranes, and indicate that these anesthetics decrease the membrane dipole potential. From a fit of the experimental data to this model, anesthetics could promote a decrease in the dipole potential in two ways. First, anesthetics appear to modify the effective dipole moment in the membrane interface and may accomplish this by orienting their molecular dipole antiparallel to the intrinsic dipoles at the interface. Second, they modify the membrane dielectric constant, leading to a decrease in the field across the interface. At equivalent membrane concentrations, isoflurane, enflurane, and halothane produced similar changes in the dipole potential and decreased the dipole potential as much as 65 mV at a membrane mole fraction of 0.20.(ABSTRACT TRUNCATED AT 250 WORDS)

Advances in biopharmaceutical analysis in the People's Republic of China: 1991-1993

The methodological studies on biopharmaceutical analysis of drugs and their metabolites by liquid and gas chromatography with various detectors have been reviewed. Research articles were selected from well known journals published in the People's Republic of China between January 1991 and March 1993. The applications of these methods in bioavailability, pharmacokinetics, therapeutic drug monitoring and metabolic studies have also been discussed.

[Treatment of maxillofacial vascular malformation by arterial embolism and application of sclerosing agent]

30 cases of large cavernous and racemose hemangioma of the maxillofacial were treated selectively with arterial embolism of the tumor and inject Xiaozhiling into the tumor, from November 1990 to November 1993. This method has exact effect either to racemose or to cavernous hemangioma, without facial defect and functional damage. All the patients were followed up 6 months to 3 years. 27 cases were cured, 1 failed, 1 gave up treatment, 1 died of complication. Its mechanism, indications, prevention of complications and recurrence were discussed.

Fast purification of Phaseolus vulgaris isolectins

Phytohemagglutinin from red kidney bean has been purified by affinity chromatography on a human alpha 1-acid glycoprotein Sepharose 4B column. Further purification of the hemagglutinin's five isolectins was achieved on a Mono S column with an 86% protein recovery. Each sequentially eluted isolectin from the ion exchange column displayed either hemagglutinating or mitogenic activity. The main activity of each fraction was the result of the combination of varying proportions of the L and E subunits.

Development of a gene cloning system for Streptomyces hygroscopicus subsp. yingchengensis, a producer of three useful antifungal compounds, by elimination of three barriers to DNA transfer

Streptomyces hygroscopicus 10-22 could not be transformed with any of the commonly used Streptomyces plasmid vectors and was resistant to plaque formation by the Streptomyces phages phi C31 and R4. Repeated selection resulted in the isolation of derivatives of S. hygroscopicus 10-22 that could be transformed with pIJ101- and pJV1-derived cloning vectors and of restriction-deficient derivatives that could accept DNA propagated in Streptomyces lividans 66. These new strains, which include three that still produce the original antibiotics, can be used as hosts for gene cloning. Insertion of nonreplicating vectors by homologous recombination and transposition of Tn4560 were demonstrated in S. hygroscopicus 10-22.

Tumor-cell-targeted cytokine gene transfer in experimental models for cancer therapy

The genetic manipulation of tumor cells to express immunostimulatory molecules provides a current approach for the analysis of immune reactions against tumor cells in vivo. Experiments with multiple cytokines have demonstrated that an array of different host effector cells can be recruited by different cytokines in vivo, but more studies are necessary to distinguish cytokine-specific effects from as yet uncharacterized influences of different tumor models. A technically feasible clinical application of this approach is to be seen in the generation of vaccines by introducing such immunostimulatory genes into cancer cells and boosting systemic immune reactions against the unmodified cells. The experimental basis of these vaccination studies is critically discussed.

[Pleural malignant mesothelioma complicated with disseminated intravascular coagulation]

Three cases of MPM complicated with DIC were reported in a total of 6862 autopsies (0.04%) from 1950 to 1989 year in our university hospital. All the three cases showed hemorrhagic patches, shock, decreased platelets and fibrinogen, and prolonged prothrombin and thrombin time. Hyaline thrombosis was observed in the pulmonary interstitial microvessels. We have also discussed the diagnosis and pathogenesis of DIC.

Expression of tumor necrosis factor by different tumor cell lines results either in tumor suppression or augmented metastasis

Tumor necrosis factor (TNF) produced by tumor cells after gene transfer can effectively suppress the growth of locally growing tumors. We wanted to test the effects of "local" TNF on the growth of a highly metastatic cell line. Therefore, a recombinant retrovirus allowing expression of the TNF gene by the beta-actin promotor has been constructed and used to infect the two tumor cell lines EB and ESB, which grow as solid tumor or metastasize, respectively. Expression of TNF by EB cells resulted in their rapid and dose-dependent rejection. In sharp contrast, mice injected with ESB cells producing similar amounts of TNF showed no signs of tumor suppression, but rather had reduced survival rates that correlated with enhanced hepatic metastases. The accelerated formation of liver metastases by ESB TNF cells could be reversed by an anti-TNF mAb. These results demonstrate the opposite effects TNF may have on tumor growth: suppression of a locally growing tumor and promotion of metastasis formation.

Mechanisms of rejection induced by tumor cell-targeted gene transfer of interleukin 2, interleukin 4, interleukin 7, tumor necrosis factor, or interferon gamma

Interleukin (IL)-2, IL-4, IL-7, tumor necrosis factor (TNF), or interferon-gamma (IFN-gamma) has been shown to be able to induce tumor rejection if produced locally by the tumor cells after gene transfer. To analyze whether the cellular rejection mechanisms are different or redundant we have expressed the cytokines in the same tumor cell line (J558L). Cell depletion experiments revealed that all cytokines required CD8+ T cells for complete long-term tumor eradication, although effective but transient host-dependent tumor suppression was also observed in the complete absence of CD8+ T cells. The transient tumor suppression induced by IL-2, IL-4, TNF, or IFN-gamma was also operative in nude and severe combined immunodeficient mice, whereas only tumor suppression induced by IL-7 was dependent on the presence of CD4+ T cells and was not evident in nude mice. The T-cell-independent effector arm of IL-2 and IFN-gamma but not IL-4 and TNF was mediated in part by natural killer cells. The transience of tumor suppression in the absence of T cells reflected loss of cytokine production in the case of TNF, IL-2, and IL-4 but not IFN-gamma. Immunohistologic analysis revealed all cytokine-producing tumors to be heavily infiltrated by macrophages. IL-4 and IL-7 tumors additionally contained eosinophils. The infiltration by T cells did not necessarily reflect their contribution to tumor rejection. Thus, the different cytokines activate heterogeneous transient tumor-suppressive mechanisms but always require CD8+ T cells for complete tumor rejection.

[A clinicopathological and immunohistochemical study of 49 cases of necrotizing lymphadenitis]

A clinicopathological and immunohistiochemical study of 49 cases of necrotizing lymphadenitis was made. Twenty-four patients were male and twenty-five female with the M:F ratio of 0.96:1. The patients ranged in age from 9 to 62 years with a mean of 26. Forty-nine patients had superficial lymphadenopathy, and twenty-two were accompanied by fever. The results also showed that there was multifoci necrosis present in the involved lymph nodes, particularly in the cortex or/and paracortex, with variable numbers of small lymphocytes, immunoblasts, histocytes and phagocytes, the latter with phagocytized nuclear debris derived from necrotizing T lymphocytes. However, granulocytes and plasmacytes were generally absent, and B lymphocytes rare. The pathogenesis of this disease remains unknown and the pathogen has not been found by Gram, Giemsa, PAS, Ziehl-Neelsen and Warthin-Starry stain. The diagnosis, differential diagnosis and etiology of this disease are discussed. We support the suggestion that this entity be called "Kikuchi-Fujimoto's disease" rather than "Histiocytic necrotizing lymphadenitis".

Vaccinations with tumor cells genetically engineered to produce different cytokines: effectivity not superior to a classical adjuvant

The potential of tumor cells (J558L) engineered to produce one of 5 different cytokines (interleukin 2, interleukin 4, interleukin 7, tumor necrosis factor, or gamma-interferon) to give rise to systemic immunity protective against a contralateral challenge with the parental cells was analyzed. The rejection of all cytokine-producing cells appeared to induce some systemic response capable of mediating the rejection of low numbers of subsequently contralaterally injected cells, but the effect was much less obvious with higher cell numbers. The injection of any possible combination of two of the cytokine producers did not reveal any synergistic effects. The cytokine gene-transfected tumor cells were not superior to the parental cells admixed with the adjuvant Corynebacterium parvum with respect to their potential as immunogens to induce immunity.

Differential disruption of simple drawing movements in patients with unilateral brain lesion

In examining the ability of patients with unilateral brain lesion to copy simple drawings of a house and a human face, 18 apoplectic patients confirmed by CT scanning were studied. We found that their drawing of a house was inferior to that of a face in 19 tests (90.5%) of 17 patients (94.4%). Marked differences existed in nearly 90% of these tests. No difference was found between the right-hemisphere and left-hemisphere group, except that more patients of the right-hemisphere group showed contralateral neglect, but in the house drawings only.

Anti-presynaptic membrane receptor antibodies in myasthenia gravis

Myasthenia gravis (MG) is considered as an autoimmune disease of neuromuscular junction resulting from antibodies directed to acetylcholine receptors (AChR). We describe the use of beta-bungarotoxin (beta-BuTx) and alpha-bungarotoxin (alpha-BuTx) to capture their corresponding proteins from preparation of crude human muscle receptor. beta-BuTx binds to presynaptic membrane receptor (PsmR) of the whole receptor fraction, while alpha-BuTx binds to AchR. The captured proteins were used as antigen in ELISA to detect antibodies to PsmR and to AchR in sera from 82 Chinese patients with MG and in controls. In MG, antibodies to PsmR only were detected in 13%, to AchR only in 11% and both to PsmR and AchR in 54%. Only 3 of 50 patients with other neurological diseases and none of 50 healthy subjects had these antibodies. Specificity tests for antibodies showed that the detection systems which we used are specific and confident. No correlation was found between antibody levels and clinical status. The significance of the PsmR antibodies in the pathogenesis of MG is unknown. We suggest that myasthenia gravis is not only due to damage of the postsynaptic membrane, but of presynaptic structures as well.

Effect of radix Salviae miltiorrhizae extract injection on survival of allogeneic heart transplantation

The effect of Radix Salviae Miltiorrhizae (RSM), a commonly used herbal blood circulation invigorator for the treatment of blood stasis in traditional Chinese medicine, on the duration of allograft survival following heterotopic heart transplantation in experimental animals was observed. The results in three heart transplantation models--auricular free graft in mice, abdominal graft in rats and cervical graft in rabbits--suggested that RSM injection in an appropriate dosage prolonged the survival time of cardiac allograft. The herb showed no significant toxicity. It was also found that RSM injection had a synergic effect with corticosteroids against graft rejection.

Heterogeneity of mRNA and protein products arising from the protein 4.1 gene in erythroid and nonerythroid tissues

Immunologically cross-reactive isoforms of the cytoskeletal element protein 4.1 have been identified in many tissues in which they exhibit heterogeneity of molecular weight, abundance, and intracellular localization. To examine the basis for isoform production in erythroid and nonerythroid tissues, we have compared the structure and expression of cDNAs isolated from human erythroid and nonerythroid sources. We have encountered cDNAs representing many distinct mRNA sequences. These exhibit complete nucleotide sequence homology along most of their lengths. Differences were confined to five sequence blocks designated Motifs I-V, which were present or absent in each mRNA moiety. Motif I was expressed only in erythroid cells; it encodes 21 amino acids in a well-characterized spectrin/actin binding domain. Motif II, located near the COOH terminus of the 80-kD "erythroid" protein 4.1 molecule is present in the vast majority of transcripts from both erythroid and nonerythroid cells. Motifs IV and V alter the 5' untranslated region: simultaneous insertion of Motif IV and deletion of Motif V in the untranslated region inserts a new initiator methionine and establishes a contiguous open reading frame encoding a novel 135-kD protein 4.1 molecule. By immunochemical analysis we have identified the longer isoform in cells. Our results are most consistent with tissue-specific alternative mRNA splicing of transcripts of the protein 4.1 gene to yield numerous isoforms. These isoforms exhibit tissue specificity and alter strategic portions of the molecule. Moreover, we describe a novel high molecular weight form of protein 4.1 that arises by splicing events which allow translation at an upstream site.

[Effect of oxymatrine on prolonging the survival time of cardiac tissue allograft in mice and its immunologic mechanisms]

Oxymatrine is an extract from Sophora flavescens Ait. A daily dose of 75 mg/kg or 225 mg/kg of oxymatrine was given to the recipient intramuscularly for 14 days. The survival time of cardiac tissue allograft was prolonged significantly to 12.2 days (at the dose of 75 mg/kg, P less than 0.05) and 15.7 days (at the dose of 225 mg/kg, P less than 0.001) by oxymatrine, while that in the control group was 10.8 days. The effects of oxymatrine on immune-function in BABL/c mice with or without heart allograft were further studied. Experiments showed that in vitro spontaneous proliferation of spleen cells increased markedly on the 10th day after transplantation, while the proliferation response to Con A of spleen cells decreased. The spontaneous proliferation and proliferation responses to Con A or to LPS of spleen cells could be inhibited significantly in normal mice by oxymatrine. The proliferation response to LPS of spleen cells and RPFC was inhibited obviously in transplanted mice by oxymatrine. However, oxymatrine did not affect the proliferation response to Con A of spleen cells, which had been decreased after transplantation. The results suggested that this drug exhibited selective immuno-suppression on function of B cells without obvious effect on T cell function in transplanted mice. This characteristics of the drug seemed beneficial for avoiding side-effect produced by the conventional immuno-suppressive agents.

Structure and evolution of mouse interleukin 6 gene

Restriction fragment length polymorphism in the interleukin 6 gene of murine rodents extending phylogenetically from Mus musculus domesticus to the rat has been analyzed. Most species exhibit distinct restriction site patterns. In contrast, limited polymorphism was found in the tumor necrosis factor alpha gene indicating different selective pressure acting on both genes. The gene encoding interleukin 6 was isolated from a genomic library and the exon/intron organization was determined by restriction analysis and limited DNA sequence analysis. It consists of five exons which distribute over about seven kilobases, thus resembling in structure and organization the human counterpart. Furthermore, no restriction fragment length polymorphisms in the interleukin 6 gene of autoimmune strains NZB, NZW, MRL-lpr/lpr and BxSB could be detected for either EcoRI, BamHI or HindIII.