The E1B 19K protein associates with lamins in vivo and its proper localization is required for inhibition of apoptosis

Expression of the E1B 19K protein is required to inhibit apoptosis induced by E1A during adenovirus infection and transformation. E1B 19K is homologous to Bcl-2 in function and the two proteins also share limited amino acid sequence homology. Consequently, the E1B 19K and Bcl-2 proteins bind to and inhibit the cellular death-inducing proteins Bax, Bak and Nbk/Bik. Both E1B 19K and Bcl-2 localize to membranes of the nucleus and the endoplasmic reticulum. In addition to membrane association, and unlike Bcl-2, the E1B 19K protein is found associated with intermediate filament proteins in the cytoplasm and the nuclear lamina and copurifies with the lamins both during infection and transformation. While a membrane targeting domain at the C-terminus of Bcl-2 ensures its proper localization, the mechanism by which the E1B 19K protein localizes is unknown. Not surprisingly, lamin A fragments were cloned from a yeast two-hybrid screen for E1B 19K-interacting proteins. The interaction was demonstrated in yeast and mammalian cells in vivo and in vitro and was unique and specific to E1B 19K, with no interaction evident between Bcl-2 and lamin A. Mutants of lamin A/C which localized inappropriately in the cytoplasm or nucleus but retained E1B 19K binding, interfered with the nuclear envelope and cytoplasmic membrane targeting of the E1B 19K protein. Improper localization impaired the ability of the E1B 19K protein to inhibit apoptosis. Thus, proper localization of the E1B 19K protein is required for its function and the interaction of the E1B 19K protein with lamin A/C may represent a means for nuclear envelope localization.     

Covalent binding of agaritine to DNA in vivo

14C-Ring-labelled agaritine was administered orally to eight C57BL/6 mice at a chemical dose of 7.5 mg and radioactive dose of 1.2 x 10(9) dpm/kg body weight. After 24 hr, the animals were killed and DNA from stomach, liver and kidneys was purified by a phenol-free method involving proteinase K digestion of chromatin and coprecipitated proteins, followed by hydroxylapatite chromatography, dialysis and precipitation with ethanol. An increase in radioactivity was found in DNA of all three organs examined. Stomach DNA had the highest levels: 160 and 30 dpm/mg DNA in males and females, respectively. Liver and kidney DNA both showed levels of approximately 1 dpm/mg, with no measurable gender differences. Expressed in the units of the covalent binding index (CBI), agaritine has a potency of 42 in mouse stomach in males and 8 in females. The CBI of agaritine in liver and kidney was 0.2-0.3 in both sexes. The genotoxic activity of agaritine is thus very weak. The cumulative lifetime cancer risk of agaritine consumption in mushrooms is estimated to lie at approximately 10(-5).     

Epidermal growth factor receptor and its inhibition in radiotherapy: in vivo findings

Increasing evidence shows that dysregulated epidermal growth factor receptor (EGFR) signalling plays an important part in neoplasia. When over expressed or mutated, EGFR is frequently associated with more aggressive tumour growth, poor patient prognosis and resistance of tumours to cytotoxic agents, including radiation. The present studies with murine carcinomas showed that there is an inverse correlation between the level of EGFR and tumour radiocurability. Likewise, the present clinical study in patients with head and neck cancer shows that EGFR over expression correlates with poorer tumour response to radiotherapy. Adding EGFR to tumour cells in vitro protected cells against the cytotoxic action of radiation, whereas blocking EGFR with anti-EGFR antibodies enhanced cell radiosensitivity. A casual relationship between EGFR and increased cellular resistance to radiation was established by transferring the EGFR gene into low EGFR-expressing radiosensitive tumour cells, which then become radioresistant. Radiation activated EGFR and its downstream signalling pathways in radioresistant but not in radiosensitive tumours, and this effect was associated with increased resistance to radiation, and enhanced repopulation in irradiated tumours. Increasing evidence shows that blockage of EGFR or interference with any of the steps in its signal transduction cascade can counteract negative outcomes of EGFR signalling, which has recently been explored as a therapeutic strategy in cancer treatment. The present findings demonstrate that treatment of human tumour xenografts with C225, an anti-EGFR monoclonal antibody, dramatically enhanced tumour response to radiation. Overall, the findings show that over expression of EGFR may serve as a predictor of tumour treatment outcome by radiotherapy and as a therapeutic target to enhance the efficacy of radiotherapy.     

Hepatocyte growth factor promotes motor neuron survival and synergizes with ciliary neurotrophic factor

Hepatocyte growth factor (HGF) has been shown to function as a potent mitogen for a variety of cells, transducing its signal through the c-met tyrosine kinase receptor. Ciliary neurotrophic factor (CNTF) is a cytokine that has been shown to promote survival of motor neurons. We show here that c-met mRNA is present in the embryonic rat spinal cord. Peak expression of c-met (at E14) coincides with the period of naturally occurring cell death in motor neurons, suggesting a possible role of HGF in the regulation of this process. Utilizing a neuron-enriched culture system, we established that HGF, like CNTF, stimulates choline acetyltransferase (CAT) activity in motor neurons. When co-administered to motor neuron cultures, saturating concentrations of HGF and CNTF produced a synergistic increase in CAT levels. We show that this synergy reflects enhanced motor neuron survival. Exposure of motor neuron cultures to the cytostatic agent vincristine markedly decreased CAT levels; co-treatment with HGF and CNTF (but not either factor alone) restored CAT activity to control levels. Our findings indicate that HGF is a survival factor for motor neurons, that it acts synergistically with CNTF, and that HGF and CNTF can together be neuroprotective in the face of vincristine toxicity.     

A human alloantibody interferes with binding of factor IXa to the factor VIII light chain

Inhibitory antibodies directed against factor VIII develop in a substantial number of patients with hemophilia A as a consequence of factor VIII replacement therapy. These antibodies usually recognize discrete epitopes within the A2 and/or the C2 domains of factor VIII. Here, we have characterized the antibodies present in the plasma of a patient affected by severe hemophilia A. The antibodies reacted readily with the metabolically labeled factor VIII light chain and fragments thereof when analyzed by immunoprecipitation. The inhibitory activity could be neutralized by the complete light chain, whereas only slight neutralization occurred with a fragment comprising the isolated C2 domain. Binding of the majority of antibodies to in vitro synthesized factor VIII fragments was dependent on the presence of amino acid residues Gln1778-Met1823, a region known to contain a factor IXa binding site. Functional characterization showed that purified IgG from the patient's serum inhibited binding of factor IXa to immobilized factor VIII light chain in a dose-dependent manner. These data indicate that human alloantibodies may inhibit factor VIII activity by interfering with factor IXa-factor VIIIa complex assembly.     

Presenilin 1 associates with glycogen synthase kinase-3beta and its substrate tau

Families bearing mutations in the presenilin 1 (PS1) gene develop Alzheimer's disease. Previous studies have shown that the Alzheimer-associated mutations in PS1 increase production of amyloid beta protein (Abeta1-42). We now show that PS1 also regulates phosphorylation of the microtubule-associated protein tau. PS1 directly binds tau and a tau kinase, glycogen synthase kinase 3beta (GSK-3beta). Deletion studies show that both tau and GSK-3beta bind to the same region of PS1, residues 250-298, whereas the binding domain on tau is the microtubule-binding repeat region. The ability of PS1 to bring tau and GSK-3beta into close proximity suggests that PS1 may regulate the interaction of tau with GSK-3beta. Mutations in PS1 that cause Alzheimer's disease increase the ability of PS1 to bind GSK-3beta and, correspondingly, increase its tau-directed kinase activity. We propose that the increased association of GSK-3beta with mutant PS1 leads to increased phosphorylation of tau.     

正弦波同步触发电路及其晶闸管充电装置中的应用

正弦波同步触发电路是为晶闸管提供触发脉冲。阐述了正弦波同步触发电路的组成及各部分的作用,具体分析了一些出现故障的原因,并在十几年运行的经验基础上,提出了一些解决实际问题的方法。     

The estimation of the number of binding sites for antibody on antigen molecules with reference to factor VIII and its antibody

The theoretical basis for determining the number of antibody sites on antigen molecules is examined. The theoretical considerations are applied to factor VIII molecules. Examples based on data available at the Oxford Haemophilia Centre are calculated to illustrate the approach. It is concluded that there are few sites on each factor VIII molecule for human antibody. The three antibodies for which reasonable data were available suggest 1-3 sites for human antibody. The data for rabbit antibody suggest 5-6 sites per factor VIII molecule.     

Annexin XIIIb associates with lipid microdomains to function in apical delivery

A member of the annexin XIII sub-family, annexin XIIIb, has been implicated in the apical exocytosis of epithelial kidney cells. Annexins are phospholipid-binding proteins that have been suggested to be involved in membrane trafficking events although their actual physiological function remains open. Unlike the other annexins, annexin XIIIs are myristoylated. Here, we show by immunoelectron microscopy that annexin XIIIb is localized to the trans-Golgi network (TGN), vesicular carriers and the apical cell surface. Polarized apical sorting involves clustering of apical proteins into dynamic sphingolipid-cholesterol rafts. We now provide evidence for the raft association of annexin XIIIb. Using in vitro assays and either myristoylated or unmyristoylated recombinant annexin XIIIb, we demonstrate that annexin XIIIb in its native myristoylated form stimulates specifically apical transport whereas the unmyristoylated form inhibits this route. Moreover, we show that formation of apical carriers from the TGN is inhibited by an anti-annexin XIIIb antibody whereas it is stimulated by myristoylated recombinant annexin XIIIb. These results suggest that annexin XIIIb directly participates in apical delivery.     

Growth factor receptor-bound protein 2 SH2/SH3 domain binding to CD28 and its role in co-signaling

The co-stimulatory antigen CD28 has been shown to bind to several intracellular proteins including phosphatidylinositol 3-kinase, growth factor receptor-bound protein 2 (Grb2), and ITK. Paradoxically, Grb2 and phosphatidylinositol 3-kinase binding has been mapped to a similar pYMNM motif within the CD28 cytoplasmic tail. Given the importance of CD28 co-signaling to T cell function, questions exist regarding the mechanism by which Grb2 binds to CD28, and whether the interaction plays a role in co-stimulation. To biochemically characterize Grb2/CD28 binding, we initially utilized glutathione S-transferase-Grb2 fusion proteins carrying inactivating mutations within the SH2 and SH3 domains of Grb2, and assessed their ability to bind to CD28. In vitro binding experiments indicated that the Grb2 SH2 domain is critical for the association, while the SH3 domain plays an additional role in facilitating optimal binding. Enhanced binding via the SH3 domains was not observed when the C-terminal PXXP motif within CD28 was disrupted, thereby indicating that both SH2 and SH3 domains contribute to CD28 binding. Mutations that alter Grb2 binding were found to block the CD28-dependent interleukin-2 production. Further, tyrosine phosphorylation of Vav and the costimulation-dependent activation of Jun N-terminal kinase was blocked in cells defective in CD28/Grb2 binding. These results provide evidence for an alternate CD28-mediated signaling process involving Grb2 binding to the co-receptor.     

The N-terminal region of the luteovirus readthrough domain determines virus binding to Buchnera GroEL and is essential for virus persistence in the aphid

Luteoviruses and the luteovirus-like pea enation mosaic virus (PEMV; genus Enamovirus) are transmitted by aphids in a circulative, nonreplicative manner. Acquired virus particles persist for several weeks in the aphid hemolymph, in which a GroEL homolog, produced by the primary endosymbiont of the aphid, is abundantly present. Six subgroup II luteoviruses and PEMV displayed a specific but differential affinity for Escherichia coli GroEL and GroEL homologs isolated from the endosymbiotic bacteria of both vector and nonvector aphid species. These observations suggest that the basic virus-binding capacity resides in a conserved region of the GroEL molecule, although other GroEL domains may influence the efficiency of binding. Purified luteovirus and enamovirus particles contain a major 22-kDa coat protein (CP) and lesser amounts of an approximately 54-kDa readthrough protein, expressed by translational readthrough of the CP into the adjacent open reading frame. Beet western yellows luteovirus (BWYV) mutants devoid of the readthrough domain (RTD) did not bind to Buchnera GroEL, demonstrating that the RTD (and not the highly conserved CP) contains the determinants for GroEL binding. In vivo studies showed that virions of these BWYV mutants were significantly less persistent in the aphid hemolymph than were virions containing the readthrough protein. These data suggest that the Buchnera GroEL-RTD interaction protects the virus from rapid degradation in the aphid. Sequence comparison analysis of the RTDs of different luteoviruses and PEMV identified conserved residues potentially important in the interaction with Buchnera GroEL.     

GroEL and GroES control of substrate flux in the in vivo folding pathway of phage P22 coat protein

Our present understanding of the action of the chaperonins GroEL/S on protein folding is based primarily on in vitro studies, whereas the folding of proteins in the cellular milieu has not been as thoroughly investigated. We have developed a means of examining in vivo protein folding and assembly that utilizes the coat protein of bacteriophage P22, a naturally occurring substrate of GroEL/S. Here we show that amino acid substitutions in coat protein that cause a temperature-sensitive-folding (tsf) phenotype slowed assembly rates upon increasing the temperature of cell growth. Raising cellular concentrations of GroEL/S increased the rate of assembly of the tsf mutant coat proteins to nearly that of wild-type (WT) coat protein by protecting a thermolabile folding intermediate from aggregation, thereby increasing the concentration of assembly-competent coat protein. The rate of release of the tsf coat proteins from the GroEL/S-coat protein ternary complex was approximately 2-fold slower at non-permissive temperatures when compared with the release of WT coat protein. However, the rate of release of WT or tsf coat proteins at each temperature remained constant regardless of GroEL/S levels. Thus, raising the cellular concentration of GroEL/S increased the amount of assembly-competent tsf coat proteins not by altering the rates of folding but by increasing the probability of GroEL/S-coat protein complex formation.     

In vivo hormonal regulation of insulin-like growth factor binding protein-5 mRNA in the immature rat ovary

OBJECTIVE: Despite the potential importance of insulin-like growth factor binding protein-5 (IGFBP-5) to follicular development, the hormonal regulation of this antigonadotropic IGFBP has not been investigated. Therefore, it was the objective of this study to eludicate the role of gonadotropins and estrogen in the in vivo regulation of IGFBP-5 mRNA expression. METHODS: Two models of follicular development in immature rats were used. Specifically, rats were hypophysectomized and treated with FSH and/or diethylstilbestrol (DES). Alternatively, terminal follicular development was induced in intact immature rats by pregnant mare serum gonadotropin (PMSG) and hCG. The IGFBP-5 mRNA in whole ovarian RNA was assayed by Northern blot hybridization. Localization of expression in PMSG and hCG-stimulated ovaries was further assessed by in situ hybridization. RESULTS: Expression of IGFBP-5 mRNA was increased in ovaries from hypophysectomized rats. Treatment with FSH and/or DES did not alter the abundance of this mRNA. Treatment with PMSG induced a transient increase in IGFBP-5 expression that was localized in a subset of alpha-inhibin-negative follicles. At later times after PMSG, IGFBP-5 expression persisted in the surface epithelium but was not detected in large preovulatory follicles. In vitro studies affirmed the antigonadotropic action of IGFBP-5. CONCLUSION: In vivo expression of IGFBP-5 in the rat ovary is moderated by hormonal treatment both in terms of total expression and follicular localization.