Oligomerization of Clostridium perfringens epsilon-toxin is dependent upon membrane fluidity in liposomes

Clostridium perfringens epsilon-toxin binds to receptors on MDCK cells and forms a heptamer in membranes. The mechanism behind the oligomerization of epsilon-toxin was studied using carboxyfluorescein (CF)-loaded liposomes composed of various phosphatidylcholines (PCs). The toxin caused CF to leak from liposomes in a dose-dependent manner. The toxin-induced leakage of CF, binding of the toxin to liposomes, and formation of a functional oligomer increased as the phase-transition temperature (Tm) of the PC used in the liposomes decreased. Surface plasmon resonance analysis using an HPA sensorchip (BIAcore) also revealed that the binding of the toxin to liposomes increased with a decrease in the Tm of the PC used in liposomes. The oligomer that was formed in 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]TID)-treated liposomes was labeled, indicating that it inserts into a hydrophobic region. Furthermore, the rate of epsilon-toxin-induced CF leakage was enhanced by treatment with phosphatidylethanolamine or diacylglycerol, which is known to favor a lamellar-to-inverted hexagonal (L-H) phase transition. We show that membrane fluidity in the liposome plays an important role in the binding of the toxin to liposomes, insertion into the hydrophobic region in the bilayer of liposomes, and the assembly process in the bilayer.     

Identification of hepatitis C virus (HCV) 2a-derived epitope peptides having the capacity to induce cytotoxic T lymphocytes in human leukocyte antigen-A24+ and HCV2a-infected patients

Since virus-specific cytotoxic T lymphocytes (CTLs) play a critical role in preventing the spread of hepatitis C virus (HCV), vaccine-based HCV-specific CTL induction could be a promising strategy to treat HCV-infected patients. In this study, we tried to identify HCV2a-derived epitopes, which can induce human leukocyte antigen (HLA)-A24-restricted and peptide-specific CTLs. Peripheral blood mononuclear cells of HCV2a-infected patients or healthy donors were stimulated in vitro with HCV2a-derived peptides, which were prepared based on the HLA-A24 binding motif. As a result, three peptides (HCV2a 576-584, HCV2a 627-635, and HCV2a 1085-1094) efficiently induced peptide-specific CTLs from HLA-A24(+) HCV2a-infected patients as well as healthy donors. The cytotoxicity was exhibited by peptide-specific CD8(+) T cells in an HLA-A24-restricted manner. In addition, the HCV2a 627-635 peptide was frequently recognized by immunoglobulin G of HCV2a-infected patients. These results indicate that the identified three HCV2a peptides might be applicable to peptide-based immunotherapy for HLA-A24(+) HCV2a-infected patients.     

Thirteen novel deoxynivalenol-degrading bacteria are classified within two genera with distinct degradation mechanisms

The mycotoxin deoxynivalenol (DON), a secondary metabolite produced by species of the plant pathogen Fusarium, causes serious problems in cereal crop production because of its toxicity towards humans and livestock. A biological approach for the degradation of DON using a DON-degrading bacterium (DDB) appears to be promising, although information about DDBs is limited. We isolated 13 aerobic DDBs from a variety of environmental samples, including field soils and wheat leaves. Of these 13 strains, nine belonged to the Gram-positive genus Nocardioides and other four to the Gram-negative genus Devosia. The degradation phenotypes of the two Gram types were clearly different; all washed cells of the 13 strains degraded 100 μg mL(-1) DON to below the detection limit (0.5 μg mL(-1)), but the conditions inducing the DON-degrading activities differed between the two Gram types. The HPLC profiles of the DON metabolites were also distinct between the two genera, although all strains produced 3-epi-deoxynivalenol. The Gram-positive strains showed DON assimilation in media containing DON as a carbon source, whereas the Gram-negatives did not. Our results suggest that aerobic DDBs are distributed within at least two phylogenetically restricted genera, suggesting independent evolution of the DON-degradation mechanisms.     

Osteoclastogenesis is negatively regulated by D-serine produced by osteoblasts

We have shown the functional expression by chondrocytes of serine racemase (SR) which is responsible for the synthesis of D-serine (Ser) from L-Ser in cartilage. In this study, we evaluated the possible functional expression of SR by bone-forming osteoblasts and bone-resorbing osteoclasts. Expression of SR mRNA was seen in osteoblasts localized at the cancellous bone surface in neonatal rat tibial sections and in cultured rat calvarial osteoblasts endowed to release D-Ser into extracellular medium, but not in cultured osteoclasts differentiated from murine bone marrow progenitor cells. Sustained exposure to D-Ser failed to significantly affect alkaline phosphatase activity and Ca(2+) accumulation in cultured osteoblasts, but significantly inhibited differentiation and maturation in a concentration-dependent manner at a concentration range of 0.1-1 mM without affecting cellular survival in cultured osteoclasts. By contrast, L-Ser promoted osteoclastic differentiation in a manner sensitive to the inhibition by D-Ser. Matured osteoclasts expressed mRNA for the amino acid transporter B(0,+) (ATB(0,+) ) and the system alanine, serine, and cysteine amino acid transporter-2 (ASCT2), which are individually capable of similarly incorporating extracellular L- and D-Ser. Knockdown of these transporters by siRNA prevented both the promotion by L-Ser and the inhibition by D-Ser of osteoclastic differentiation in pre-osteoclastic RAW264.7 cells. These results suggest that D-Ser may play a pivotal role in osteoclastogenesis through a mechanism related to the incorporation mediated by both ATB(0,+) and ASCT2 of serine enantiomers in osteoclasts after the synthesis and subsequent release from adjacent osteoblasts.     

Inhibitory role of E2F-1 in the regulation of tumor suppressor p53 during DNA damage response

Appropriate regulation of DNA damage response is pivotal for maintaining genome stability. p53 as well as E2F-1 plays a critical role during DNA damage response, however, the physiological significance of their interaction has been elusive. In the present study, we found that E2F-1 has an inhibitory effect on p53 during adriamycin (ADR)-mediated DNA damage response. Upon ADR exposure, p53 and E2F-1 were markedly induced at protein and mRNA levels in p53-procifient U2OS and HCT116 cells, and formed a stable complex as examined by co-immunoprecipitation experiments. Of note, chromatin immunoprecipitation (ChIP) experiments revealed that ADR-mediated induction coincides with the efficient recruitment of p53 and E2F-1 onto the promoters of p53-target genes, such as p21(WAF1) and BAX. Subsequent RT-PCR and luciferase reporter assays demonstrated that E2F-1 strongly attenuates p53-dependent transactivation of p53-target genes. Importantly, siRNA-mediated knockdown of E2F-1 stimulated apoptosis in response to ADR, which was associated with an accelerated response of p21(WAF1) and BAX. Collectively, our present findings suggest that E2F-1 participates in p53-mediated DNA damage response and might have a checkpoint function to limit overactive p53.     

Infectious endogenous retroviruses in cats and emergence of recombinant viruses

Endogenous retroviruses (ERVs) comprise a significant percentage of the mammalian genome, and it is poorly understood whether they will remain as inactive genomes or emerge as infectious retroviruses. Although several types of ERVs are present in domestic cats, infectious ERVs have not been demonstrated. Here, we report a previously uncharacterized class of endogenous gammaretroviruses, termed ERV-DCs, that is present and hereditary in the domestic cat genome. We have characterized a subset of ERV-DC proviral clones, which are numbered according to their genomic insertions. One of these, ERV-DC10, located in the q12-q21 region on chromosome C1, is an infectious gammaretrovirus capable of infecting a broad range of cells, including human. Our studies indicate that ERV-DC10 entered the genome of domestic cats in the recent past and appeared to translocate to or reintegrate at a distinct locus as infectious ERV-DC18. Insertional polymorphism analysis revealed that 92 of 244 domestic cats had ERV-DC10 on a homozygous or heterozygous locus. ERV-DC-like sequences were found in primate and rodent genomes, suggesting that these ERVs, and recombinant viruses such as RD-114 and BaEV, originated from an ancestor of ERV-DC. We also found that a novel recombinant virus, feline leukemia virus subgroup D (FeLV-D), was generated by ERV-DC env transduction into feline leukemia virus in domestic cats. Our results indicate that ERV-DCs behave as donors and/or acceptors in the generation of infectious, recombinant viruses. The presence of such infectious endogenous retroviruses, which could be harmful or beneficial to the host, may affect veterinary medicine and public health.     

Spatial distribution of viruses associated with planktonic and attached microbial communities in hydrothermal environments

Viruses play important roles in marine surface ecosystems, but little is known about viral ecology and virus-mediated processes in deep-sea hydrothermal microbial communities. In this study, we examined virus-like particle (VLP) abundances in planktonic and attached microbial communities, which occur in physical and chemical gradients in both deep and shallow submarine hydrothermal environments (mixing waters between hydrothermal fluids and ambient seawater and dense microbial communities attached to chimney surface areas or macrofaunal bodies and colonies). We found that viruses were widely distributed in a variety of hydrothermal microbial habitats, with the exception of the interior parts of hydrothermal chimney structures. The VLP abundance and VLP-to-prokaryote ratio (VPR) in the planktonic habitats increased as the ratio of hydrothermal fluid to mixing water increased. On the other hand, the VLP abundance in attached microbial communities was significantly and positively correlated with the whole prokaryotic abundance; however, the VPRs were always much lower than those for the surrounding hydrothermal waters. This is the first report to show VLP abundance in the attached microbial communities of submarine hydrothermal environments, which presented VPR values significantly lower than those in planktonic microbial communities reported before. These results suggested that viral lifestyles (e.g., lysogenic prevalence) and virus interactions with prokaryotes are significantly different among the planktonic and attached microbial communities that are developing in the submarine hydrothermal environments.     

CRUMPLED LEAF (CRL) homologs of Physcomitrella patens are involved in the complete separation of dividing plastids

Plastid division is controlled by numerous nuclear genes. Arabidopsis thaliana CRUMPLED LEAF (AtCRL) is a plastid division-related gene, and the crl mutant exhibits a dwarf phenotype with abnormal cell division and a significant reduction in plastid numbers. However, the function of AtCRL is not fully understood. Here, we identified and characterized two AtCRL homologs, PpCRL1 and PpCRL2, in the moss Physcomitrella patens. PpCRL1 and PpCRL2 shared 77% amino acid identity with each other and 47% identity with AtCRL. Single PpCRL1 or -2 gene knockout (KO) mutants could not be distinguished from the wild-type mosses, but PpCRL1 and -2 double KO mutants displayed growth retardation of protonemata and gametophores and harbored approximately 10 large chloroplasts per cell. This indicates that PpCRL1 and PpCRL2 have redundant functions in chloroplast division and plant growth. Unlike the A. thaliana crl mutants, however, the PpCRL double KO mutants did not display abnormal orientation of the cell division plane. Complementation experiments showed that AtCRL partially rescued the defects in chloroplast size and number of the PpCRL double KO mutant. This suggests that PpCRL has a similar, but not identical, function to AtCRL. Time-lapse microscopic observation of the double PpCRL KO mutants revealed that some dumbbell-shaped chloroplasts failed to complete division at the late stage of plastid division; enlarged chloroplasts were thus generated. This strongly suggests that PpCRLs are involved in the complete separation of dividing chloroplasts.     

Evaluation of portable point-of-care CD4 counter with high sensitivity for detecting patients eligible for antiretroviral therapy

Background

Accurate, inexpensive point-of-care CD4+ T cell testing technologies are needed that can deliver CD4+ T cell results at lower level health centers or community outreach voluntary counseling and testing. We sought to evaluate a point-of-care CD4+ T cell counter, the Pima CD4 Test System, a portable, battery-operated bench-top instrument that is designed to use finger stick blood samples suitable for field use in conjunction with rapid HIV testing.

Methods

Duplicate measurements were performed on both capillary and venous samples using Pima CD4 analyzers, compared to the BD FACSCalibur (reference method). The mean bias was estimated by paired Student''s t-test. Bland Altman plots were used to assess agreement.

Results

206 participants were enrolled with a median CD4 count of 396 (range; 18–1500). The finger stick PIMA had a mean bias of −66.3 cells/µL (95%CI −83.4−49.2, P<0.001) compared to the FACSCalibur; the bias was smaller at lower CD4 counts (0–250 cells/µL) with a mean bias of −10.8 (95%CI −27.3−+5.6, P = 0.198), and much greater at higher CD4 cell counts (>500 cells/µL) with a mean bias of −120.6 (95%CI −162.8, −78.4, P<0.001). The sensitivity (95%CI) of the Pima CD4 analyzer was 96.3% (79.1–99.8%) for a <250 cells/ul cut-off with a negative predictive value of 99.2% (95.1–99.9%).

Conclusions

The Pima CD4 finger stick test is an easy-to-use, portable, relatively fast device to test CD4+ T cell counts in the field. Issues of negatively-biased CD4 cell counts especially at higher absolute numbers will limit its utility for longitudinal immunologic response to ART. The high sensitivity and negative predictive value of the test makes it an attractive option for field use to identify patients eligible for ART, thus potentially reducing delays in linkage to care and ART initiation.