Inducibility of kappa immunoglobulin enhancer-binding protein Nf-kappa B by a posttranslational mechanism

NF-kappa B is a nuclear protein, found only in cells that transcribe immunoglobulin light chain genes, that interacts with a defined site in the kappa immunoglobulin enhancer. This protein can be induced in pre-B cells by stimulation with bacterial lipopolysaccharide (LPS). The induction involves a posttranslational activation, and the combined action of LPS and cycloheximide causes a superinduction. An active phorbol ester also induces this factor, and with kinetics more rapid than those for LPS stimulation. Phorbol-ester-mediated induction of NF-kappa B was observed in a T cell line (Jurkat) and a nonlymphoid cell line (HeLa), and is therefore not restricted to B-lymphoid cells. We interpret these results to indicate that factors that control transcription of specific genes in specific cells may be activated by posttranslational modification of precursor factors present more widely.

Stimulation by cyclic adenosine monophosphate of plasmid deoxyribonucleic acid replication and catabolite repression of the plasmid deoxyribonucleic acid-protein relaxation complex

Colicinogenic factors ColE1 and ColE2 are bacterial plasmids that exist in Escherichia coli as supercoiled deoxyribonucleic acid (DNA) and as strand-specific, relaxation complexes of supercoiled DNA and protein. Newly replicated ColE1 DNA becomes complexed with protein after the replication event. This association of DNA and protein can take place under conditions in which DNA or protein synthesis is arrested. The addition of cyclic adenosine monophosphate (c-AMP) to normal cells growing in glucose medium results in a six- to tenfold stimulation in the rate of synthesis of the protein component(s) of the complex and a three- to fivefold stimulation in the rate of ColE1 DNA replication. Employing mutants deficient in catabolite gene activator protein or adenylate cyclase, it was shown that synthesis of both the plasmid-determined protein colicin E1 and the protein component(s) of the ColE1 relaxation complex is mediated through the c-AMP-catabolite gene activator protein system. Addition of c-AMP to ColE2-containing cells results in the stimulation of synthesis of ColE2 DNA and relaxation protein(s) as well as in the production of a protein component of the ColE2 relaxation complex that renders it sensitive to induced relaxation by heat treatment. In the case of ColE2, synthesis of the relaxation protein(s) is not dependent upon catabolite gene activator protein.

Nonhistone chromosomal proteins and gene regulation

Evidence from several model systems suggests that nonhistone chromosomal proteins may regulate gene expression in eukaryotic cells. The data indicate that the synthesis of new species of nonhistone chromosomal proteins as well as modifications of preexisting nonhistone chromosomal proteins are involved in the control of transcription. However, from the vast number of proteins included in this class, it is apparent that, in addition to regulating the transcription of defined genome loci, the nonhistone chromosomal proteins include enzymes that have a general function, proteins that are involved in determining the structure of chromatin, as well as proteins that serve as recognition sites for binding of regulatory macromolecules. The presence of a nucleoplasmic pool of nonhistone chromosomal proteins which may exchange with the chromatin has also been reported (89). While it is clear that the nonhistone chromosomal proteins play a key role in the regulation of gene expression, the exact manner in which they interact with the genome to initiate, modify, or augment the transcription of specific RNA molecules remains to be resolved.

RecFOR proteins load RecA protein onto gapped DNA to accelerate DNA strand exchange: a universal step of recombinational repair

Genetic evidence suggests that the RecF, RecO, and RecR (RecFOR) proteins participate in a common step of DNA recombination and repair, yet the biochemical event requiring collaboration of all three proteins is unknown. Here, we show that the concerted action of the RecFOR complex directs the loading of RecA protein specifically onto gapped DNA that is coated with single-stranded DNA binding (SSB) protein, thereby accelerating DNA strand exchange. The RecFOR complex recognizes the junction between the ssDNA and dsDNA regions and requires a base-paired 5' terminus at the junction. Thus, the RecFOR complex is a structure-specific mediator that targets recombinational repair to ssDNA-dsDNA junctions. This reaction reconstitutes the initial steps of recombinational gapped DNA repair and uncovers an event also common to the repair of ssDNA-tailed intermediates of dsDNA-break repair. We propose that the behavior of the RecFOR proteins is mimicked by functional counterparts that exist in all organisms.

A recombinant vector derived from the host range-restricted and highly attenuated MVA strain of vaccinia virus stimulates protective immunity in mice to influenza virus

The immunogenicity of a recombinant virus derived from modified vaccinia virus Ankara (MVA), a host range-restricted, highly attenuated and safety-tested strain, was investigated. Plasmid transfer vectors that provide strong synthetic early/late promoters for the simultaneous expression of two genes as well as a transient or stable selectable marker and flanking sequences for homologous recombination with the MVA genome were constructed. A recombinant MVA containing influenza virus haemagglutinin and nucleoprotein genes was isolated in avian cells and shown to express both proteins efficiently upon infection of human or mouse cells in which abortive replication occurs. Mice, inoculated by various routes with recombinant MVA, produced antibody and cytotoxic T-lymphocyte responses to influenza virus proteins and were protected against a lethal influenza virus challenge as effectively as mice immunized with a recombinant derived from the replication-competent WR strain of vaccinia virus.

Docetaxel induces cell death through mitotic catastrophe in human breast cancer cells

Apoptosis has long been considered to be the prevailing mechanism of cell death in response to chemotherapy. Currently, a more heterogeneous model of tumor response to therapy is acknowledged wherein multiple modes of death combine to generate the overall tumor response. The resulting mechanisms of cell death are likely determined by the mechanism of action of the drug, the dosing regimen used, and the genetic background of the cells within the tumor. This study describes a nonapoptotic response to docetaxel therapy in human breast cancer cells of increasing cancer progression (MCF-10A, MCF-7, and MDA-mb-231). Docetaxel is a microtubule-stabilizing taxane that is being used in the clinic for the treatment of breast and prostate cancers and small cell carcinoma of the lung. The genetic backgrounds of these cells were characterized for the status of key pathways and gene products involved in drug response and cell death. Cellular responses to docetaxel were assessed by characterizing cell viability, cell cycle checkpoint arrest, and mechanisms of cell death. Mechanisms of cell death were determined by Annexin V binding and scoring of cytology-stained cells by morphology and transmission electron microscopy. The primary mechanism of death was determined to be mitotic catastrophe by scoring of micronucleated cells and cells undergoing aberrant mitosis. Other, nonapoptotic modes of death were also determined. No significant changes in levels of apoptosis were observed in response to docetaxel.

The synthesis of acidic chromosomal proteins during the cell cycle of HeLa S-3 cells. I. The accelerated accumulation of acidic residual nuclear protein before the initiation of DNA replication

The synthesis and accumulation of acidic proteins in the tightly bound residual nuclear fraction goes on throughout the cell cycle of continuously dividing populations of HeLa S-3 cells; however, during late G(1) there is an increased rate of synthesis and accumulation of these proteins which precedes the onset of DNA synthesis. Unlike that of the histones, whose synthesis is tightly coupled to DNA replication, the synthesis of acidic residual nuclear proteins is insensitive to inhibitors of DNA synthesis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of acidic residual nuclear proteins shows different profiles during the G(1), S, and G(2) phases of the cell cycle. These results suggest that, in contrast to histones whose synthesis appears to be highly regulated, the acidic residual proteins may have a regulatory function in the control of cell proliferation in continuously dividing mammalian cells.

Synthesis of the nuclear protein cyclin (PCNA) and its relationship with DNA replication

Synthesis of the nuclear protein cyclin (MW 36 000) and DNA in quiescent mouse fibroblasts is coordinately induced by serum and purified growth factors. Inhibition of DNA synthesis by hydroxyurea or aphidicolin in serum-stimulated quiescent cells does not affect the induction of cyclin. The levels of cyclin synthesis decrease rapidly at the end of the S phase. Immunofluorescence studies reveal that there are dramatic changes in the nuclear distribution of cyclin during S phase and that these depend on DNA synthesis or events during S phase. These observations strengthen the notion that cyclin is an important component of the events leading to DNA replication.

Influenza a virus M2 ion channel activity is essential for efficient replication in tissue culture

The amantadine-sensitive ion channel activity of influenza A virus M2 protein was discovered through understanding the two steps in the virus life cycle that are inhibited by the antiviral drug amantadine: virus uncoating in endosomes and M2 protein-mediated equilibration of the intralumenal pH of the trans Golgi network. Recently it was reported that influenza virus can undergo multiple cycles of replication without M2 ion channel activity (T. Watanabe, S. Watanabe, H. Ito, H. Kida, and Y. Kawaoka, J. Virol. 75:5656-5662, 2001). An M2 protein containing a deletion in the transmembrane (TM) domain (M2-del(29-31)) has no detectable ion channel activity, yet a mutant virus was obtained containing this deletion. Watanabe and colleagues reported that the M2-del(29-31) virus replicated as efficiently as wild-type (wt) virus. We have investigated the effect of amantadine on the growth of four influenza viruses: A/WSN/33; N31S-M2WSN, a mutant in which an asparagine residue at position 31 in the M2 TM domain was replaced with a serine residue; MUd/WSN, which possesses seven RNA segments from WSN plus the RNA segment 7 derived from A/Udorn/72; and A/Udorn/72. N31S-M2WSN was amantadine sensitive, whereas A/WSN/33 was amantadine resistant, indicating that the M2 residue N31 is the sole determinant of resistance of A/WSN/33 to amantadine. The growth of influenza viruses inhibited by amantadine was compared to the growth of an M2-del(29-31) virus. We found that the M2-del(29-31) virus was debilitated in growth to an extent similar to that of influenza virus grown in the presence of amantadine. Furthermore, in a test of biological fitness, it was found that wt virus almost completely outgrew M2-del(29-31) virus in 4 days after cocultivation of a 100:1 ratio of M2-del(29-31) virus to wt virus, respectively. We conclude that the M2 ion channel protein, which is conserved in all known strains of influenza virus, evolved its function because it contributes to the efficient replication of the virus in a single cycle.

DNA packaging in mouse spermatids. Synthesis of protamine variants and four transition proteins

A comparison of the protein compositions of mouse late-step spermatids and cauda epididymal sperm has revealed that the relative distribution of the two amino acid sequence variants of mouse protamine differ markedly in spermatids and sperm. Sonication-resistant spermatids contain the two variants in a ratio of 1:1, while the ratio of these two proteins in cauda epididymal sperm is approx. 2:1. Labeling studies in vivo have shown that this difference is due, in part, to an asynchrony in the time of synthesis of the two protamine variants. Both proteins are synthesized in late-step spermatids, but synthesis of the tyrosine variant in sperm chromatin begins approximately one day before synthesis of the more predominant histidine variant. Analyses of the time of synthesis of protamine and the four transition proteins in late-step spermatids allowed us to estimate the spermatid stage in which these proteins are deposited on DNA and relate these events to the onset of sonication resistance in maturing spermatids. These results indicate that: (1) synthesis and deposition of protamine begins coincident with the onset of sonication resistance in early step 12 spermatids; (2) protamine deposition is complete by mid-step 15; and (3) synthesis of the transition proteins occurs coincident with protamine synthesis.

Changes in the nuclear distribution of cyclin (PCNA) but not its synthesis depend on DNA replication

Synthesis of cyclin in serum-stimulated quiescent 3T3 cells increases shortly before DNA synthesis after 10 h of stimulation, reaching a maximum after 16 h. Inhibition of DNA synthesis by hydroxyurea does not affect the increase of cyclin following stimulation, as determined by quantitative two-dimensional gel electrophoresis. The levels of cyclin decrease dramatically at the end of the S-phase. Cells kept in the presence of hydroxyurea (G1/S boundary) do not show this decrease in cyclin, indicating that its amounts are regulated by events occurring during the S-phase. Immunofluorescence studies of serum-stimulated quiescent cells in the presence of hydroxyurea, using proliferating cell nuclear antigen (PCNA) autoantibodies, confirm the results obtained by protein analysis. They also reveal that there are dramatic changes in the nuclear distribution of cyclin and that these depend on DNA synthesis or events occurring during the S-phase. Cyclin (PCNA) is no longer detectable at the end of the S-phase. However, pulse-chase experiments indicate that this protein is very stable, suggesting that it possibly interacts with other macromolecules rendering it inaccessible to the antibody. These results strengthen the notion that cyclin is an important component of the events leading to DNA replication and cell division.

Cytoplasmic inclusions of respiratory syncytial virus-infected cells: formation of inclusion bodies in transfected cells that coexpress the nucleoprotein, the phosphoprotein, and the 22K protein

Immunofluorescence staining and immunoelectron microscopy of respiratory syncytial (RS) virus-infected cells revealed the presence of cytoplasmic inclusions that were specifically labeled with monoclonal antibodies directed against the nucleoprotein (NP), the phosphoprotein (P), or the 22K protein. Transient expression of these three proteins with the vaccinia-T7 system, either individually or in different combinations, demonstrated that coexpression of NP and P was sufficient to induce the formation of cytoplasmic inclusions similar to those found in RS virus-infected cells. In addition, the 22K protein was also incorporated to the inclusions when coexpressed with both NP and P proteins. Immunobinding assays revealed the presence of NP-P and NP-22K complexes in extracts of RS virus-infected cells. These complexes were also detected in extracts of transfected cells that coexpressed the corresponding proteins. The implications of these results for the RS virus replicative cycle are discussed.

Cell type-specific expression of nuclear lamina proteins during development of Xenopus laevis

The cell type-specific expression of the major nuclear lamina polypeptides ("lamins") during development of Xenopus was studied using two monoclonal antibodies (L(0)46F7: specific for LIII, the single lamin of oocytes; PKB8: specific for LI and LII of some somatic cells). In the oocyte, LIII localizes in the nuclear polymer, but upon nuclear envelope breakdown it is solubilized to a form sedimenting at 9 S. In early embryos, LIII contributes to nuclear lamina formation until its depletion. Correspondingly, LI and LII begin to be expressed at a specific point in embryogenesis and appear to be integrated with LIII into a common lamina structure. Later in development, LIII reappears as a prominent nuclear lamina protein but only in certain cells (neurons, muscle cells, and diplotene oocytes). We conclude that amphibian lamins represent a family of proteins expressed in relation to certain programs of cell differentiation.

Expression in plants and immunogenicity of plant virus-based experimental rabies vaccine

A new approach to the production and delivery of vaccine antigens is the use of engineered amino virus-based vectors. A chimeric peptide containing antigenic determinants from rabies virus glycoprotein (G protein) (amino acids 253-275) and nucleoprotein (N protein) (amino acids 404-418) was PCR-amplified and cloned as a translational fusion product with the alfalfa mosaic virus (AlMV) coat protein (CP). This recombinant CP was expressed in two plant virus-based expression systems. The first one utilized transgenic Nicotiana tabacum cv. Samsun NN plants providing replicative functions in trans for full-length infectious RNA3 of AlMV (NF1-g24). The second one utilized Nicotiana benthamiana and spinach (Spinacia oleracea) plants using autonomously replicating tobacco mosaic virus (TMV) lacking native CP (Av/A4-g24). Recombinant virus containing the chimeric rabies virus epitope was isolated from infected transgenic N. tabacum cv. Samsun NN plants and used for parenteral immunization of mice. Mice immunized with recombinant virus were protected against challenge infection. Based on the previously demonstrated efficacy of this plant virus-based experimental rabies vaccine when orally administered to mice in virus-infected unprocessed raw spinach leaves, we assessed its efficacy in human volunteers. Three of five volunteers who had previously been immunized against rabies virus with a conventional vaccine specifically responded against the peptide antigen after ingesting spinach leaves infected with the recombinant virus. When rabies virus non-immune individuals were fed the same material, 5/9 demonstrated significant antibody responses to either rabies virus or AlMV. Following a single dose of conventional rabies virus vaccine, three of these individuals showed detectable levels of rabies virus-neutralizing antibodies, whereas none of five controls revealed these antibodies. These findings provide clear indication of the potential of the plant virus-based expression systems as supplementary oral booster for rabies vaccinations.

Identification of the sequence responsible for the nuclear accumulation of the influenza virus nucleoprotein in Xenopus oocytes

Influenza virus nucleoprotein (NP), synthesized in Xenopus oocytes after injection of cloned NP cDNA, enters and accumulates in the nucleus. We have used in vitro mutagenesis of this cDNA to study the cellular distribution of mutated NP polypeptides. Mutants lacking amino acids 327-345 of wild-type NP enter the nucleus but do not accumulate there to the same extent as the wild-type protein, suggesting that this region has a role in nuclear accumulation. This possibility is further strengthened by similar studies involving the production of fusion proteins in which various amino-terminal sequences of the NP gene are fused to the complete chimpanzee alpha 1-globin sequence: when globin cDNA was injected into and expressed in oocytes the protein remains exclusively in the cytosol; however, when the globin cDNA is fused to a portion of NP cDNA that includes the region encoding amino acids 327-345, the resulting fusion protein enters and accumulates in the nucleus. Fusion proteins lacking this region of the NP enter but do not accumulate in the nucleus.

Inhibition of HMGI-C protein synthesis suppresses retrovirally induced neoplastic transformation of rat thyroid cells

Elevated expression of the three high-mobility group I (HMGI) proteins (HMGI, HMGY, and HMGI-C) has previously been correlated with the presence of a highly malignant phenotype in epithelial and fibroblastic rat thyroid cells and in experimental thyroid, lung, mammary, and skin carcinomas. Northern (RNA) blot and run-on analyses demonstrated that the induction of HMGI genes in transformed thyroid cells occurs at the transcriptional level. An antisense methodology to block HMGI-C protein synthesis was then used to analyze the role of this protein in the process of thyroid cell transformation. Transfection of an antisense construct for the HMGI-C cDNA into normal thyroid cells, followed by infection with transforming myeloproliferative sarcoma virus or Kirsten murine sarcoma virus, generated cell lines that expressed significant levels of the retroviral transforming oncogenes v-mos or v-ras-Ki and removed the dependency on thyroid-stimulating hormones. However, in contrast with untransfected cells or cells transfected with the sense construct, those containing the antisense construct did not demonstrate the appearance of any malignant phenotypic markers (growth in soft agar and tumorigenicity in athymic mice). A great reduction of the HMGI-C protein levels and the absence of the HMGI(Y) proteins was observed in the HMGI-C antisense-transfected, virally infected cells. Therefore, the HMGI-C protein seems to play a key role in the transformation of these thyroid cells.

Triiodothyronine binding to isolated liver cell nuclei

Nuclei of euthyroid rat liver have been prepared from homogenates by sedimentation through 2.3M sucrose with or without a 0.25% Triton wash. Triiodothyronine is accumulated by these nuclei during incubation in vitro in solutions containing 0.32M sucrose, 1mM MgCl2 and 0.02M Tris-Cl buffer at pH 7.4 or 7.85. Specific T3 binding sites occupied at 10-1,000 pM T3 are saturated by excess unlabeled T3 (0.15 muM). Specific T3 binding at 20 C is maximal at 203 hr nad is proportional to amount of nuclei. Calcium ion enhances nuclear integrity by reduces T3 accumulation. EDTA and phosphate ion cause nuclear damage but increase T3 accumulation. Binding is unaffected by inhibition of energy dependent reactions or of RNA synthesis. It is markedly increased under certain conditions by addition of dithiothreitol (DDT). Binding does not require mediation of a cytosol protein. T3 binding is not prevented by RNAse or DNAse, but is obliterated by pronase. Te binds to a nuclear iodothyronine binding protein (NTBP) to form an NTBP-T3 complex similar to that form-d after in vivo administration of the hormone. The complex can be extracted from the nuclei by 0.4M KC-. T3 present in the NTBP-T3 complex resists accumulation by anion exchange resin at 0-2C, but is bound by resin after 20 min at 37C or after addition of 0.1 mM p-hydroxymercuribenzoate. At pH 7.85 and with 5 mM DTT, the apparent Ka for isolated nuclei is 0.2 times 10-10M-1 and the capacity is 508 pg T3/g wet tissue or 53 times 10-15 moles T3/100 mug DNA. The data may not represent total capacity, but rather the amount of T3 dissociated during the period of incubation so that NTBP-T3 can be exchanged with labeled T3. Among analogues tested, triiodothyroacetic acid appears to bind with four times the affinity of L-TX, D-T3 binds with equal affinity, and L-T4 with one-fourth the affinity of T3.

Recombinant RNA replicons derived from attenuated Venezuelan equine encephalitis virus protect guinea pigs and mice from Ebola hemorrhagic fever virus

RNA replicons derived from an attenuated strain of Venezuelan equine encephalitis virus (VEE), an alphavirus, were configured as candidate vaccines for Ebola hemorrhagic fever. The Ebola nucleoprotein (NP) or glycoprotein (GP) genes were introduced into the VEE RNA downstream from the VEE 26S promoter in place of the VEE structural protein genes. The resulting recombinant replicons, expressing the NP or GP genes, were packaged into VEE replicon particles (NP-VRP and GP-VRP, respectively) using a bipartite helper system that provided the VEE structural proteins in trans and prevented the regeneration of replication-competent VEE during packaging. The immunogenicity of NP-VRP and GP-VRP and their ability to protect against lethal Ebola infection were evaluated in BALB/c mice and in two strains of guinea pigs. The GP-VRP alone, or in combination with NP-VRP, protected both strains of guinea pigs and BALB/c mice, while immunization with NP-VRP alone protected BALB/c mice, but neither strain of guinea pig. Passive transfer of sera from VRP-immunized animals did not confer protection against lethal challenge. However, the complete protection achieved with active immunization with VRP, as well as the unique characteristics of the VEE replicon vector, warrant further testing of the safety and efficacy of NP-VRP and GP-VRP in primates as candidate vaccines against Ebola hemorrhagic fever.