Expression and differential intracellular localization of two major forms of human 8-oxoguanine DNA glycosylase encoded by alternatively spliced OGG1 mRNAs

We identified seven alternatively spliced forms of human 8-oxoguanine DNA glycosylase (OGG1) mRNAs, classified into two types based on their last exons (type 1 with exon 7: 1a and 1b; type 2 with exon 8: 2a to 2e). Types 1a and 2a mRNAs are major in human tissues. Seven mRNAs are expected to encode different polypeptides (OGG1-1a to 2e) that share their N terminus with the common mitochondrial targeting signal, and each possesses a unique C terminus. A 36-kDa polypeptide, corresponding to OGG1-1a recognized only by antibodies against the region containing helix-hairpin-helix-PVD motif, was copurified from the nuclear extract with an activity introducing a nick into DNA containing 8-oxoguanine. A 40-kDa polypeptide corresponding to a processed form of OGG1-2a was detected in their mitochondria using antibodies against its C terminus. Electron microscopic immunocytochemistry and subfractionation of the mitochondria revealed that OGG1-2a locates on the inner membrane of mitochondria. Deletion mutant analyses revealed that the unique C terminus of OGG1-2a and its mitochondrial targeting signal are essential for mitochondrial localization and that nuclear localization of OGG1-1a depends on the NLS at its C terminus.     

Development of HIV/AIDS vaccine using chimeric gag-env virus-like particles

We attempted to develop a candidate HIV/AIDS vaccine, by using unprocessed HIV-2 gag pr45 precursor protein. We found that a 45 kDa unprocessed HIV-2 gag precursor protein (pr45), with a deletion of a portion of the viral protease, assembles as virus-like particles (VLP). We mapped the functional domain of HIV-2 gag VLP formation in order to find the minimum length of gag protein to form VLP. A series of deletion mutants was constructed by sequentially removing the C-terminal region of HIV-2 gag precursor protein and expressed truncated genes in Spodoptera frugiperda (SF) cells by infecting recombinant baculoviruses. We found that deletion of up to 143 amino acids at the C-terminus of HIV-2 gag, leaving 376 amino acids at the N-terminus of the protein, did not affect VLP formation. There is a proline-rich region at the amino acid positions 373 to 377 of HIV-2 gag, and replacement of these proline residues by site-directed mutagenesis completely abolished VLP assembly. Our data demonstrate that the C-terminal p12 region of HIV-2 gag precursor protein, and zinc finger domains, are dispensable for gag VLP assembly, but the presence of at least one of the three prolines at amino acid positions 373, 375 or 377 of HIV-2NIH-Z is required for VLP formation. Animals immunized with these gag particles produced high titer antibodies and Western blot analyses showed that anti-gag pr45 rabbit sera react with p17, p24 and p55 gag proteins of HIV-1. We then constructed chimeric gag genes, which carry the hypervariable V3 region of HIV-1 gp120, because the V3 loop is known to interact with chemokine receptor as a coreceptor, and known to induce the major neutralizing antibodies and stimulate the cytoxic T lymphocyte responses in humans and mice. We expressed chimeric fusion protein of HIV-2 gag with 3 tandem copies of consensus V3 domain that were derived from 245 different isolates of HIV-1. In addition, we also constructed and expressed chimeric fusion protein that contains HIV-2 gag with V3 domains of HIV-1IIIB, HIV-1MN, HIV-1SF2 and HIV-1RF. The chimeric gag-env particles had a spherical morphology, and the size was slightly larger than that of a gag particle. Immunoprecipitation and Western blot analyses show that these chimeric proteins were recognized by HIV-1 positive human sera and antisera raised against V3 peptides, as well as by rabbit anti-gp120 serum. We obtained virus neutralizing antibodies in rabbits by immunizing these gag-env VLPs. In addition, we found that gag-env chimeric VLPs induce a strong CTL activity against V3 peptide-treated target cells. Our results indicate that V3 peptides from all major clades of HIV-1 carried by HIV-2 gag can be used as a potential HIV/AIDS vaccine.     

Geldanamycin induces cell cycle arrest in K562 erythroleukemic cells

Geldanamycin (GA), a benzoquinone ansamycin, is one of the specific inhibitors of 90-kDa heat shock protein and induces growth inhibition and apoptosis in certain cancer cell lines. We have investigated the mechanism of GA-induced growth inhibition in K562 erythroleukemic cells. DNA flow-cytometric analysis indicated that GA-induced growth arrest was associated with G2/M phase arrest of the cell cycle. GA treatment down-regulated the expression of cyclin B1 and inhibited phosphorylation of Cdc2 protein, both key regulatory proteins at the G2/M boundary. GA also markedly inhibited the Cdc2 kinase activity, which may be in part a result of up-regulation of p27KIP1 by GA. The present results suggest a novel mechanism that p27KIP1 could be involved in the regulation of G2 to M phase transition.     

Liver-specific inactivation of the abetalipoproteinemia gene completely abrogates very low density lipoprotein/low density lipoprotein production in a viable conditional knockout mouse

Conventional knockout of the microsomal triglyceride transfer protein large subunit (lMTP) gene is embryonic lethal in the homozygous state in mice. We have produced a conditional lMTP knockout mouse by inserting loxP sequences flanking exons 5 and 6 by gene targeting. Homozygous floxed mice were born live with normal plasma lipids. Intravenous injection of an adenovirus harboring Cre recombinase (AdCre1) produced deletion of exons 5 and 6 and disappearance of lMTP mRNA and immunoreactive protein in a liver-specific manner. There was also disappearance of plasma apolipoprotein (apo) B-100 and marked reduction in apoB-48 levels. Wild-type mice showed no response, and heterozygous mice, an intermediate response, to AdCre1. Wild-type mice doubled their plasma cholesterol level following a high cholesterol diet. This hypercholesterolemia was abolished in AdCre1-treated lMTP-/- mice, the result of a complete absence of very low/intermediate/low density lipoproteins and a slight reduction in high density lipoprotein. Heterozygous mice showed an intermediate lipoprotein phenotype. The rate of accumulation of plasma triglyceride following Triton WR1339 treatment in lMTP-/- mice was <10% that in wild-type animals, indicating a failure of triglyceride-rich lipoprotein production. Pulse-chase experiments using hepatocytes isolated from wild-type and lMTP-/- mice revealed a failure of apoB secretion in lMTP-/- animals. Therefore, the liver-specific inactivation of the lMTP gene completely abrogates apoB-100 and very low/intermediate/low density lipoprotein production. These conditional knockout mice are a useful in vivo model for studying the role of MTP in apoB biosynthesis and the biogenesis of apoB-containing lipoproteins.     

Interaction of SeqA and Dam methylase on the hemimethylated origin of Escherichia coli chromosomal DNA replication

Preferential binding of SeqA protein to hemimethylated oriC, the origin of Escherichia coli chromosomal replication, delays methylation by Dam methylase. Because the SeqA-oriC interaction appears to be essential in timing of chromosomal replication initiation, the biochemical functions of SeqA protein and Dam methylase at the 13-mer L, M, and R region containing 4 GATC sequences at the left end of oriC were examined. We found that SeqA protein preferentially bound hemimethylated 13-mers but not fully nor unmethylated 13-mers. Regardless of strand methylation, the binding of SeqA protein to the hemimethylated GATC sequence of 13-mer L was followed by additional binding to other hemimethylated GATC sequences of 13-mer M and R. On the other hand, Dam methylase did not discriminate binding of 13-mers in different methylation patterns and was not specific to GATC sequences. The binding specificity and higher affinity of SeqA protein over Dam methylase to the hemimethylated 13-mers along with the reported cellular abundance of this protein explains the dominant action of SeqA protein over Dam methylase to the newly replicated oriC for the sequestration of chromosomal replication. Furthermore, SeqA protein bound to hemimethylated 13-mers was not dissociated by Dam methylase, and most SeqA protein spontaneously dissociated 10 min after binding. Also, SeqA protein delayed the in vitro methylation of hemimethylated 13-mers by Dam methylase. These in vitro results suggest that the intrinsic binding instability of SeqA protein results in release of sequestrated hemimethylated oriC.     

Efficient integration of short interspersed element-flanked foreign DNA via homologous recombination

We investigated whether mouse short interspersed elements (SINEs) could influence the recombination frequency of foreign DNA. Vectors harboring a reporter gene in combinations of SINEs B1 and/or B2 or a portion of long interspersed element-1 were prepared and tested in vitro by a colony assay using HC11 murine mammary epithelial cells and in vivo by microinjection into fertilized mouse eggs. In transfected HC11 cells, the number of colonies surviving G418 selection increased by 3.5-fold compared with control when the reporter was flanked by fused B1-B2 sequences. Similar results were obtained from microinjection study; in fetuses 11.5 days post coitum, transgene positives in control and SINE-flanked vectors were 16 and 53%, respectively. Individual B1- and B2-harboring vectors showed equivalent activities with each other, as determined by the colony assay (2.8-fold versus 3.2-fold compared with control). We determined the contribution of homologous recombination to the SINE-mediated increase in integration frequency through a polymerase chain reaction-based strategy; in more than half of embryos transgenes underwent homologous recombinations involving B1 sequences. These results demonstrate that the SINE sequences can increase the integration rate of foreign DNA and that such an increase is most likely due to the enhancement of homologous recombination.     

Arginine biosynthesis in Campylobacter jejuni TGH9011: determination of the argCOBD cluster

Arginine biosynthetic genes from Campylobacter jejuni TGH9011 were cloned by functional complementation of the respective Escherichia coli arginine biosynthetic mutants. Complementation of argA, argB, argC, argD, argE, argF, and argH auxotrophs was accomplished using a pBR322-based C. jejuni TGH9011 plasmid library. By cross-complementation analyses, the first four steps of arginine biosynthesis were shown to be closely linked on the genome. Two additional clones complementing the first (ArgA) and fifth (ArgE) steps in arginine biosynthesis were obtained. Neither recombinant showed linkage to the arg cluster, to each other, nor to other arginine biosynthetic functions by cross-complementation. Genes argF and argH were not linked to other arginine biosynthetic genes by cross-complementation analysis. Restriction enzyme patterns of recombinant plasmids fell into five groups. Group I contained the arg(ABCD) complementing locus. Group II and Group III were the two genetic loci corresponding to the argA and argE complementing genes. Group II contains the hipO gene encoding N-benzoylglycine-amino-acid amidohydrolase, also known as hippurate hydrolase. Group III contains the hipO homolog of C. jejuni. Group IV represents the argF gene. Group V is the argH gene. Functional complementation of mutations in the first four steps of the arginine biosynthetic pathway was obtained on recombinant plasmid pARGC2. The predicted order of gene complementation was argCargA(argBargD). The sequence of the insert in plasmid pARGC2 revealed direct homologs for argC, argB, and argD. However, sequence analysis of the gene complementing ArgA function in two separate E. coli argA mutants determined that the C. jejuni gene was not a canonical argA gene. The gene complementing the argA defect, which we call argO, showed limited homology to the streptothricin acetyltransferase gene (sat) of Escherichia coli. The flanking open reading frames in pARGC2 showed no homologies to arginine biosynthetic genes. The structure of the argCOBD gene arrangement is discussed with reference to the presence and location of other arginine biosynthetic genes on the genome of C. jejuni and other bacterial organisms.     

IL-4 and IL-10 are both required for the induction of oral tolerance

Protection from the development of experimental autoimmune uveitis (EAU) can be induced by feeding mice interphotoreceptor retinoid binding protein before uveitogenic challenge with the same protein. Two different regimens are equally effective in inducing protective tolerance, although they seem to do so through different mechanisms: one involving regulatory cytokines (IL-4, IL-10, and TGF-beta), and the other with minimal involvement of cytokines. Here we studied the importance of IL-4 and IL-10 for the development of oral tolerance using mice genetically engineered to lack either one or both of these cytokines. In these animals we were able to protect against EAU only through the regimen inducing cytokine-independent tolerance. When these animals were fed a regimen that in the wild-type animal is thought to predominantly induce regulatory cells and is associated with cytokine secretion, they were not protected from EAU. Interestingly, both regimens were associated with reduced IL-2 production and proliferation in response to interphotoreceptor retinoid binding protein. These findings indicate that both IL-4 and IL-10 are required for induction of protective oral tolerance dependent on regulatory cytokines, and that one cytokine cannot substitute for the other in this process. These data also underscore the fact that oral tolerance, manifested as suppression of proliferation and IL-2 production, is not synonymous with protection from disease.     

Pregnancy ameliorates induction and expression of experimental autoimmune uveitis

Female patients suffering from autoimmune uveitis are reported to experience a temporary remission during pregnancy. Experimental autoimmune uveitis (EAU) is a model for human uveitis. Here we examine the effect of pregnancy on the development of EAU and its associated immunological responses. Susceptible C57BL/6 mice were immunized with interphotoreceptor retinoid-binding protein (IRBP). EAU scores and Ag-specific responses were evaluated 21 days later. Mice immunized during pregnancy developed significantly less EAU than nonpregnant controls. Their lymph node cells and splenocytes produced a distinct pattern of cytokines in response to IRBP: reduced IFN-gamma and IL-12 p40, but unchanged levels of TNF-alpha, IL-4, IL-5, and IL-10. Anti-IRBP Ab isotypes revealed an up-regulation of IgG1, indicating a possible Th2 bias at the humoral level. Ag-specific proliferation and delayed hypersensitivity, as well as mitogen-induced IFN-gamma production, remained undiminished, arguing against an overall immune deficit. Interestingly, pregnant mice that received an infusion of IRBP-primed lymphoid cells from nonpregnant donors also developed reduced EAU, suggesting that pregnancy suppresses not only the generation, but also the function of mature uveitogenic effector T cells. Pregnant mice at the time of immunization exhibited elevated levels of TGF-beta, but not of IL-10, in the serum. We suggest that protection from EAU during pregnancy is due primarily to a selective reduction of Ag-specific Th1 responses with only marginal enhancement of Th2 function, and that these effects may in part be secondary to elevated systemic levels of TGF-beta.