SUMMARY Stimulator of interferon genes (STING, also named MITA, MYPS or ERIS) is an intracellular DNA sensor that induces type I interferon through its interaction with TANK-binding kinase 1 (TBK1). Here we found that the nucleotide-binding, leucine-rich repeat containing protein, NLRC3, reduced STING-dependent innate immune activation in response to cytosolic DNA, cyclic di-GMP (c-di-GMP) and DNA viruses. NLRC3 associated with both STING and TBK1, and impeded STING-TBK1 interaction and downstream type I interferon production. Using purified recombinant proteins NLRC3 was found to interact directly with STING. Furthermore, NLRC3 prevented proper trafficking of STING to perinuclear and punctated region, known to be important for its activation. In animals, herpes simplex virus 1 (HSV-1)-infected Nlrc3−/− mice exhibited enhanced innate immunity, reduced morbidity and viral load. This demonstrates the intersection of two key pathways of innate immune regulation, NLR and STING, to fine tune host response to intracellular DNA, DNA virus and c-di-GMP

beta-Arrestins bind to activated seven transmembrane-spanning (7TMS) receptors (G protein-coupled receptors) after the receptors are phosphorylated by G protein-coupled receptor kinases (GRKs), thereby regulating their signaling and internalization. Here, we demonstrate an unexpected and analogous role of beta-arrestin 2 (betaarr2) for the single transmembrane-spanning type III transforming growth factor-beta (TGF-beta) receptor (TbetaRIII, also referred to as betaglycan). Binding of betaarr2 to TbetaRIII was also triggered by phosphorylation of the receptor on its cytoplasmic domain (likely at threonine 841). However, such phosphorylation was mediated by the type II TGF-beta receptor (TbetaRII), which is itself a kinase, rather than by a GRK. Association with betaarr2 led to internalization of both receptors and down-regulation of TGF-beta signaling. Thus, the regulatory actions of beta-arrestins are broader than previously appreciated, extending to the TGF-beta receptor family as well.

8-0xguanie nucleotide can pair with cytosine and adenine nucleotides at almost equal efficiencies.Once 8-oxodGTP is formed in the cellular nucleotide po-, this mutagenic nucleotide is incorporated into DNA and would cause transversion mutations. The MutT protein ofEscherichia coli possesses enzyme activity to hydrolyze 8-oxodGTP to the corresponding nucleoside monophosphate and thus may be responsible for preventing the occurrence of such mutations. Here we show that the human cell has an enzyme specifically hydrolyzing 8-oxodGTP in a fashion similar to that seen with MutT protein. The human 8-oxodGTPase has been found in cell-free extracts from Jurkat cells and purified >400-fold.Analyses by gel filtration and gel electrophoresis revealed that the molecular mass of the native form of human 8-oxodGTPase is 18 kDa. Mg2+ ion is required for the enzyme action and the optimum pH for the reaction is pH 8.0. The enzyme hydrolyzes 8-oxodGTP to 8-oxodGMP with a K.m value of 12.5 pM. dGTP and dATP are also degraded to dGMP and dAMP, respectively, with Km values 70 times greater than that for 8-oxodGTP. dTTP and dCTP are not hydrolyzed. These properties of the human 8-oxodGTPase are similar to those observed with the E. coli MutT protein, suggesting that the function of protecting the genetic information from the threat of endogenous oxygen radicals is widely distributed in organisms.Mutator mutants that show an increased frequency of spontaneous mutations have led to elucidation of the multiple pathways of spontaneous mutagenesis. Studies on Escherichia coli mutator genes and their products revealed that a major cause of spontaneous mutation is errors of DNA replication and that the cell possesses multistep mechanisms to correct such errors (1). In addition, certain types of spontaneous DNA damage would cause mutations (2) and the cell comes equipped with mechanisms to repair such damage.Among 15 known E. coli mutator genes, 12 are shown to be involved in correction of replicational errors and/or spontaneous DNA damage (1, 3-6). Recently we obtained evidence that the mutT mutator gene is involved in a hitherto unknown mechanism for reducing spontaneous mutation frequency (7).A mutT mutator mutant shows a frequency of A-T -COG transversion 100-10,000 times the level of the wild type (8).The MutT protein specifically prevented misincorporation of dGMP onto poly(dA)/oligo(dT)20 template DNA in vitro (9).This antimutagenic effect of MutT protein appeared to be catalytic and was achieved through its action on dGTP but not on DNA or DNA polymerase (H.M. and M.S., unpublished results). We and others noted that the MutT protein has a weak nucleoside triphosphatase activity with a substrate preference to dGTP (9, 10). Subsequently we found that the nucleotide that is misincorporated opposite the dA residue of the template is not dGMP but rather its oxidized form, 8-oxodGMP. When 8-oxodGTP was added to an in vitro DNA replication system, 8-oxodGMP was incorporated opposite dA and dC residues of the template, with almost e...

Background: Nucleotide binding and oligomerization domain-containing protein 2 (NOD2) is a protein involved in the recognition of bacterial pathogens through detection of muramyl dipeptide.Results: Purified recombinant NOD2 was found to bind ATP and muramyl dipeptide.Conclusion: NOD2 is an intracellular signaling receptor for muramyl dipeptide.Significance: These results help to define the molecular events involved in NOD2 signaling.