Catalase-peroxidase StKatG is a bacterial manganese oxidase from endophytic Salinicola tamaricis.

Manganese (Mn) oxides in iron/manganese plaques are widely distributed in the rhizosphere of wetland plants and contribute significantly to elemental cycling and pollutant removal. Mn oxides are primarily produced by bacterial processes using Mn oxidases. However, the molecular mechanism underlying the formation of rhizosphere Mn oxides is still largely unknown. This study identified a manganese-oxidizing enzyme, the catalase-peroxidase StKatG, from an endophytic bacterium Salinicola tamaricis from the wetland plant. The gene encoding StKatG was cloned and overexpressed in Escherichia coli. The recombinant StKatG displayed different structure and enzymatic properties from the previously reported Mn oxidases. The enzyme activity of StKatG yielded Mn oxides with the mixed-valent state: Mn(II), Mn(III), and Mn(IV). The optimum pH and temperature for StKatG are 7.5 and 50 °C, respectively. Structurally, StKatG is organized into two domains, whereas the reported Mn oxidases are mainly single-domain proteins. Based on the site-directed mutagenesis studies, the presence of aspartic acid (Asp) residues in the loop of StKatG are critical to Mn-oxidizing activity. These findings identified a novel bacterial Mn oxidase and provided insights into the molecular mechanism of Mn oxidation in the plant rhizosphere.

Roquin binds microRNA-146a and Argonaute2 to regulate microRNA homeostasis.

Roquin is an RNA-binding protein that prevents autoimmunity and inflammation via repression of bound target mRNAs such as inducible costimulator (Icos). When Roquin is absent or mutated (Roquin(san)), Icos is overexpressed in T cells. Here we show that Roquin enhances Dicer-mediated processing of pre-miR-146a. Roquin also directly binds Argonaute2, a central component of the RNA-induced silencing complex, and miR-146a, a microRNA that targets Icos mRNA. In the absence of functional Roquin, miR-146a accumulates in T cells. Its accumulation is not due to increased transcription or processing, rather due to enhanced stability of mature miR-146a. This is associated with decreased 3' end uridylation of the miRNA. Crystallographic studies reveal that Roquin contains a unique HEPN domain and identify the structural basis of the 'san' mutation and Roquin's ability to bind multiple RNAs. Roquin emerges as a protein that can bind Ago2, miRNAs and target mRNAs, to control homeostasis of both RNA species.

C. elegans RNA-dependent RNA polymerases rrf-1 and ego-1 silence Drosophila transgenes by differing mechanisms.

Drosophila possesses the core gene silencing machinery but, like all insects, lacks the canonical RNA-dependent RNA polymerases (RdRps) that in C. elegans either trigger or enhance two major small RNA-dependent gene silencing pathways. Introduction of two different nematode RdRps into Drosophila showed them to be functional, resulting in differing silencing activities. While RRF-1 enhanced transitive dsRNA-dependent silencing, EGO-1 triggered dsRNA-independent silencing, specifically of transgenes. The strain w; da-Gal4; UAST-ego-1, constitutively expressing ego-1, is capable of silencing transgene including dsRNA hairpin upon a single cross, which created a powerful tool for research in Drosophila. In C. elegans, EGO-1 is involved in transcriptional gene silencing (TGS) of chromosome regions that are unpaired during meiosis. There was no opportunity for meiotic interactions involving EGO-1 in Drosophila that would explain the observed transgene silencing. Transgene DNA is, however, unpaired during the pairing of chromosomes in embryonic mitosis that is an unusual characteristic of Diptera, suggesting that in Drosophila, EGO-1 triggers transcriptional silencing of unpaired DNA during embryonic mitosis.

Breakdown in repression of IFN-γ mRNA leads to accumulation of self-reactive effector CD8+ T cells.

Tight regulation of virus-induced cytotoxic effector CD8(+) T cells is essential to prevent immunopathology. Naturally occurring effector CD8(+) T cells, with a KLRG1(hi) CD62L(lo) phenotype typical of short-lived effector CD8(+) T cells (SLECs), can be found in increased numbers in autoimmune-prone mice, most notably in mice homozygous for the san allele of Roquin. These SLEC-like cells were able to trigger autoimmune diabetes in a susceptible background. When Roquin is mutated (Roquin(san)), effector CD8(+) T cells accumulate in a cell-autonomous manner, most prominently as SLEC-like effectors. Excessive IFN-γ promotes the accumulation of SLEC-like cells, increases their T-bet expression, and enhances their granzyme B production in vivo. We show that overexpression of IFN-γ was caused by failed posttranscriptional repression of Ifng mRNA. This study identifies a novel mechanism that prevents accumulation of self-reactive cytotoxic effectors, highlighting the importance of regulating Ifng mRNA stability to maintain CD8(+) T cell homeostasis and prevent CD8-mediated autoimmunity.

Expression of Caenorhabditis elegans RNA-directed RNA polymerase in transgenic Drosophila melanogaster does not affect morphological development.

Drosophila melanogaster, along with all insects and the vertebrates, lacks an RdRp gene. We created transgenic strains of Drosophila melanogaster in which the rrf-1 or ego-1 RdRp genes from C. elegans were placed under the control of the yeast GAL4 upstream activation sequence. Activation of the gene was performed by crossing these lines to flies carrying the GAL4 transgene under the control of various Drosophila enhancers. RT-PCR confirmed the successful expression of each RdRp gene. The resulting phenotypes indicated that introduction of the RdRp genes had no effect on D. melanogaster morphological development.

Protein kinase C is involved in arsenic trioxide-induced apoptosis and inhibition of proliferation in human bladder cancer cells.

OBJECTIVE: Arsenic trioxide (ATO) is a potent antitumor agent used to treat acute promyelocytic leukemia, and recently solid tumors including bladder cancers. However, a mechanism to explain its antitumor activity in bladder cancers is unclear. Here, we investigated the role of protein kinase C (PKC) in ATO-induced apoptosis and inhibition of proliferation in bladder cancer cells. METHODS: T24 human bladder carcinoma cells were incubated with different concentrations of ATO in the presence or absence of PMA (PKC activator) or H7 (PKC inhibitor). Cell proliferation was assessed by MTT assay, and apoptosis by TUNEL and electron microscopy. Flow cytometry was used to analyze cell cycle distribution, radioimmunoassay to measure PKC activity, and Western blot analysis to detect caspase-3. RESULTS: ATO inhibited proliferation and induced apoptosis of T24 cells in a dose-dependent manner, caused an increase of percentage of cells in the G(1) phase and a decrease in the S and G(2) phases, and upregulated the expression of activated caspase-3 and reduced PKC activity. These effects were abrogated by PMA, but enhanced by H7. CONCLUSIONS: PKC is involved in the anticancer activity of ATO for T24 bladder cancer cells, suggesting that targeting the PKC pathway may represent a potential approach to enhance the efficacy of ATO to treat bladder cancers.

Different preparations of intravenous immunoglobulin vary in their efficacy to neutralize streptococcal superantigens: implications for treatment of streptococcal toxic shock syndrome.

Eight different batches of intravenous immunoglobulin from 3 different manufacturers were tested for neutralizing activities against all currently known streptococcal superantigens. Statistically significant variation among different intravenous immunoglobulin preparations (P<.0001) and between individual streptococcal superantigens (P<.0001) was observed. These results might be helpful for optimizing the type and dose of intravenous immunoglobulin used in adjunctive therapy for severe invasive streptococcal disease.