Type I interferon production enhances susceptibility to Listeria monocytogenes infection

Numerous bacterial products such as lipopolysaccharide potently induce type I interferons (IFNs); however, the contribution of this innate response to host defense against bacterial infection remains unclear. Although mice deficient in either IFN regulatory factor (IRF)3 or the type I IFN receptor (IFNAR)1 are highly susceptible to viral infection, we show that these mice exhibit a profound resistance to infection caused by the Gram-positive intracellular bacterium Listeria monocytogenes compared with wild-type controls. Furthermore, this enhanced bacterial clearance is accompanied by a block in L. monocytogenes-induced splenic apoptosis in IRF3- and IFNAR1-deficient mice. Thus, our results highlight the disparate roles of type I IFNs during bacterial versus viral infections and stress the importance of proper IFN modulation in host defense.

Toll-like receptors induce a phagocytic gene program through p38

Toll-like receptor (TLR) signaling and phagocytosis are hallmarks of macrophage-mediated innate immune responses to bacterial infection. However, the relationship between these two processes is not well established. Our data indicate that TLR ligands specifically promote bacterial phagocytosis, in both murine and human cells, through induction of a phagocytic gene program. Importantly, TLR-induced phagocytosis of bacteria was found to be reliant on myeloid differentiation factor 88–dependent signaling through interleukin-1 receptor–associated kinase-4 and p38 leading to the up-regulation of scavenger receptors. Interestingly, individual TLRs promote phagocytosis to varying degrees with TLR9 being the strongest and TLR3 being the weakest inducer of this process. We also demonstrate that TLR ligands not only amplify the percentage of phagocytes uptaking Escherichia coli, but also increase the number of bacteria phagocytosed by individual macrophages. Taken together, our data describe an evolutionarily conserved mechanism by which TLRs can specifically promote phagocytic clearance of bacteria during infection.

BRCA1 Associates with Processive RNA Polymerase II

The human BRCA1 tumor suppressor interacts with transcriptional machinery, including RNA polymerase II (RNA pol II). We demonstrated that interaction with RNA pol II is a conserved feature of BRCA1 proteins from several species. We found that full-length BRCA1 proteins universally fail to activate transcription in classic GAL4-UAS one-hybrid assays and that the activity associated with the human BRCA1 C terminus was poorly conserved in closely related homologs of the gene. Fractionation studies demonstrated that BRCA1 proteins from all species tested interacted specifically with hyperphosphorylated pol II (IIO), in preference to hypophosphorylated RNA pol II (IIA) expected at promoters. BRCA1-RNA pol II complexes showed evidence of a multiply phosphorylated heptad repeat domain in the catalytic subunit (p220) of RNA pol II, and the complex was highly functional in transcriptional run-off assays. Interestingly, endogenous BRCA1 associated with a large fraction of the processive RNA pol II activity present in undamaged cells, and the interaction was disrupted by DNA-damaging agents. Preferential interaction with processive RNA pol II in undamaged cells places BRCA1 in position to link late events in transcription with repair processes in eukaryotic cells.

Combinatorial regulation of the murine RAG-2 promoter by Sp1 and distinct lymphocyte-specific transcription factors

The recombination activation genes, RAG-1 and RAG-2, encode the critical components of the recombinase complex responsible for the generation of functional antigen receptor genes. In order to gain an insight into the transcription factors and cis-acting elements that regulate the lymphocyte-specific expression of RAG-2, the promoter-region of this gene was isolated and characterized. This analysis demonstrated that a relatively small promoter fragment could confer lymphocyte-restricted expression to a reporter construct. Our work and that of others subsequently revealed that RAG-2 promoter expression is positively regulated by BSAP (PAX-5) and c-Myb transcription factors in B- and T-lineage cells, respectively. Although BSAP and c-Myb were deemed necessary for lymphocyte-specific expression, our analysis also uncovered a G-rich region at the 5'-end of the core promoter that was essential for full activity in lymphocyte cell lines. Site-directed mutagenesis revealed that a GA-box within the G-rich region was required for full promoter activity and subsequent DNA binding assays demonstrated that this element was specifically recognized by Sp1. Apart from showing that Sp1 interacts within the RAG-2 promoter, we also demonstrate that the Sp1-binding site is necessary for the high-level activation of this promoter.

alpha-Fetoprotein-specific tumor immunity induced by plasmid prime-adenovirus boost genetic vaccination

alpha-Fetoprotein (AFP) is a potential target for immunotherapy in hepatocellular carcinoma; both the murine and human T-cell repertoires can recognize AFP-derived epitopes in the context of the MHC. Protective immunity can be generated with AFP-engineered dendritic cell-based vaccines. We now report a DNA-based immunization strategy using a prime-boost approach: coadministration of plasmid DNA encoding murine AFP and murine granulocyte-macrophage colony-stimulating factor followed by boosting with an AFP-expressing nonreplicating adenoviral vector. This immunization strategy can elicit a high frequency of Th1-type AFP-specific cells leading to tumor protective immunity in mice at levels comparable with AFP-engineered dendritic cells. This cell-free mode of immunization is better suited for large-scale vaccine efforts for patients with hepatocellular carcinoma.

CD40 cross-linking bypasses the absolute requirement for CD4 T cells during immunization with melanoma antigen gene-modified dendritic cells

Genetic immunization of mice with dendritic cells (DCs) engineered to express a melanoma antigen generates antigen-specific, MHC-restricted, CD4-dependent protective immune responses. We wanted to determine the role of CD4 cells and CD40 ligation of MART-1 gene-modified DC in an animal model of immunotherapy for murine melanoma. CD4 knock-out (CD4KO) or antibody-depleted mice were immunized with DC adenovirally transduced with the MART-1 gene (AdVMART1/DC) with or without CD40 cross-linking. Tumor protection was absent in CD4-depleted mice, but protection was reestablished when the CD40 receptor was engaged using three different constructs. Transduction of DCs with vectors expressing the Th1 cytokines interleukin (IL)-2, IL-7, or IL-12 could not reproduce the CD40-mediated maturation signal in this model. CD8 T-cell depletion in CD4KO mice immunized with CD40-ligated DCs abrogated the protective response. Pooled analysis of CD40 cross-linking of AdVMART1/DC administered to wild-type C57BL/6 mice revealed an overall enhancement of antitumor immunity. However, this effect was inconsistent between replicate studies. In conclusion, maturation of AdVMART1-transduced DCs through the CD40 ligation pathway can promote a protective CD8 T-cell-mediated immunity that is independent of CD4 T-cell help.

Regulation of the RAG-1 promoter by the NF-Y transcription factor

We have cloned the RAG-1 promoter region and have determined that almost all detectable promoter activity resides within a 208-bp fragment. Sequence analysis of this promoter region has identified potential recognition motifs for a number of lymphocyte-restricted and ubiquitous transcription factors. Subsequent assays have revealed that the NF-Y transcription factor interacts with a CCAAT site within the RAG-1 promoter and appears to play an important role in the positive transcriptional regulation of this gene.

Regulation of the RAG-1 promoter by the NF-Y transcription factor

We have cloned the RAG-1 promoter region and have determined that almost all detectable promoter activity resides within a 208-bp fragment. Sequence analysis of this promoter region has identified potential recognition motifs for a number of lymphocyte-restricted and ubiquitous transcription factors. Subsequent assays have revealed that the NF-Y transcription factor interacts with a CCAAT site within the RAG-1 promoter and appears to play an important role in the positive transcriptional regulation of this gene.

Characterization of an endonuclease activity which preferentially cleaves the G-rich immunoglobulin switch repeat sequences

B lymphocytes can alter selectively their immunoglobulin (Ig) isotype expressed by deletional rearrangement of the first active immunoglobulin heavy-chain (IgH) constant region (C mu) gene with one of six other constant region genes. Recombination breakpoints occur within highly repetitive "switch" (S) regions located upstream of each IgH constant region gene except C delta. Analysis of rearranged switch DNA junctions has not detected a consensus sequence, although the predominance of two pentamer motifs (TGGGG and TGAGC) at or near these breakpoints and throughout all murine S region sequences has led to their advocacy as the S recombination signals. In this paper, we describe the characterization and partial purification of a lymphoid-specific endo-nuclease activity which cleaves preferentially murine S region DNA. Enzyme activity selectively produced single- and double-stranded breaks at TGAGC and TGGG motifs within murine S mu and S alpha DNA. Rare cryptic cleavage sites were detected also within non-switch sequences, although cleavage intensities at these sites were reduced greatly, relative to consensus S region cleavages. Analogous activity was found in murine tissue extracts, although among the tissues assayed only spleen and thymus contained detectable activity. Subsequent biochemical characterization of this activity demonstrated that the responsible enzyme (Endo-SR) represented a previously unreported tissue-specific mammalian endonuclease. Endo-SR-specific activity could be enhanced by addition of Mg2+ or Ca2+ and inhibited by addition of Zn2+. Maximal specific activity was detected at pH 5.5 and sharply declined within +/- 0.5 pH units. In view of this enzyme's sequence- and tissue-specificity, we propose that Endo-SR is a strong candidate for an endonuclease activity associated with the switch recombination process.

The murine nucleolin protein is an inducible DNA and ATP binding protein which is readily detected in nuclear extracts of lipopolysaccharide-treated splenocytes

A 100-kDa DNA binding protein was found to be dramatically up-regulated upon the mitogenic stimulation of murine splenocytes with bacterial lipopolysaccharide (LPS). The induced DNA binding protein was also found to exhibit moderate binding specificity for the immunoglobulin isotype switch DNA repeats. Furthermore, the induction of the 100-kDa protein by LPS was found to be mediated by both an increase in the protein's stability and an increase in the synthesis of the protein. In vitro phosphorylation experiments revealed that the 100-kDa DNA binding protein was one of the most heavily phosphorylated proteins in both lymphoid and nonlymphoid nuclear extracts. Although this in vitro phosphorylation initially appeared to be mediated by a potent nuclear kinase activity, it was later determined that a significant part of the detected labeling was due to the direct binding of ATP by the 100-kDa protein. Antibodies raised to the 100-kDa DNA binding protein were used to isolate cDNA clones from a lymphocyte cDNA lambda gt11 expression library. Nucleotide sequence analysis revealed that the cloned cDNAs were identical to the mouse nucleolin gene. The beta-galactosidase fusion proteins (encoded by exons 3-14 of nucleolin) and a more severely truncated 45-kDa protein (encoded by exons 5-14 of nucleolin) were both found to bind strongly to DNA and ATP. Furthermore, the strength of DNA binding was found to be highly dependent on the overall dG content of the DNA probes. Our experiments also revealed that apart from binding ATP and G-rich DNA, nucleolin directly bound GTP, dATP, and dGTP, but not dCTP, dTTP, or dUTP. Computer analysis revealed that the putative ATP binding domains appear to fall within two of the phylogenetically conserved RNA binding domains of nucleolin.