发状念珠蓝细菌细胞对Cu2+、Cr2+和Pb2+胁迫的响应

[目的] 对发状念珠蓝细菌细胞进行重金属离子Cu2+(CuSO4)、Cr2+(CrCl2)和Pb2+(PbCl2)胁迫,探讨发状念珠蓝细菌细胞对重金属离子胁迫的响应.[方法] 25℃,80 μmol/(m·s)光照下,BG11培养液培养发状念珠蓝细菌,利用不同浓度(0、0.1、1.0、10、100 mg/L) Cu2+、Cr2+和pb2+胁迫发状念珠蓝细菌细胞,测定其质膜透性、超氧化物歧化酶活性、丙二醛含量、脯氨酸含量、可溶性蛋白含量以及海藻糖含量,分析发状念珠蓝细菌细胞对重金属离子胁迫的响应.[结果] 在Cu2、Cr2和pb2胁迫下,发状念珠蓝细菌细胞的外渗率和丙二醛(malondialdehyde)含量随着重金属离子浓度的升高而升高,相对渗透率和膜脂过氧化水平的变化趋势一致.超氧化物歧化酶(superoxide dismutase)活性随重金属离子浓度的升高先升后降,脯氨酸含量随着重金属离子处理浓度的升高,呈先降后升的趋势,可溶性糖含量随浓度的增大而减少.[结论] 低浓度的重金属离子可以诱导发状念珠蓝细菌细胞产生结构和生理的应激响应,高浓度会导致发状念珠蓝细菌细胞膜结构和功能的严重损害.     

Metschnikowia henanensis sp. nov., a new anamorphic yeast species isolated from rotten wood in China

Four yeast strains were isolated from rotting wood samples collected from two sites in the Baotianman Nature Reserve and the Laojieling Nature Reserve in China. DNA sequence comparison and other taxonomic characteristics identified the strains as a single novel species of the genus Metschnikowia. The name Metschnikowia henanensis sp. nov. is proposed to accommodate these highly divergent organisms with the type strain BY-97^T (= CICC 1982^T = CBS 12677^T). The novel species produced chlamydospores, but it did not exhibit ascospore formation in sporulation media for 4 weeks. Molecular phylogeny from the D1/D2 domains of the large subunit (LSU) rRNA gene sequences placed this new species in a basal position to the Metschnikowia viticola/Candida kofuensis/Metschnikowia noctiluminum subclade, and an undescribed Candida species namely strains IMB-EMP4 and IMB-EMP5 was a close sister to M. henanensis.     

Structural Insights into the Neutralization Mechanism of Monoclonal Antibody 6C2 against Ricin

Ricin belongs to the type II ribosome-inactivating proteins that depurinate the universally conserved α-sarcin loop of rRNA. The RNA N-glycosidase activity of ricin also largely depends on the ribosomal proteins that play an important role during the process of rRNA depurination. Therefore, the study of the interaction between ricin and the ribosomal elements will be better to understand the catalysis mechanism of ricin. The antibody 6C2 is a mouse monoclonal antibody exhibiting unusually potent neutralizing ability against ricin, but the neutralization mechanism remains unknown. Here, we report the 2.8 Å crystal structure of 6C2 Fab in complex with the A-chain of ricin (RTA), which reveals an extensive antigen-antibody interface that contains both hydrogen bonds and van der Waals contacts. The complementarity-determining region loops H1, H2, H3, and L3 form a pocket to accommodate the epitope on the RTA (residues Asp⁹⁶–Thr¹¹⁶). ELISA results show that Gln⁹⁸, Glu⁹⁹, Glu¹⁰², and Thr¹⁰⁵ (RTA) are the key residues that play an important role in recognizing 6C2. With the perturbation of the 6C2 Fab-RTA interface, 6C2 loses its neutralization ability, measured based on the inhibition of protein synthesis in a cell-free system. Finally, we propose that the neutralization mechanism of 6C2 against ricin is that the binding of 6C2 hinders the interaction between RTA and the ribosome and the surface plasmon resonance and pulldown results confirm our hypothesis. In short, our data explain the neutralization mechanism of mAb 6C2 against ricin and provide a structural basis for the development of improved antibody drugs with better specificity and higher affinity.     

Differential Androgen Deprivation Therapies with Anti-androgens Casodex/Bicalutamide or MDV3100/Enzalutamide versus Anti-androgen Receptor ASC-J9? Lead to Promotion versus Suppression of Prostate Cancer Metastasis

Despite the fact that androgen deprivation therapy (ADT) can effectively reduce prostate cancer (PCa) size, its effect on PCa metastasis remains unclear. We examined the existing data on PCa patients treated with ADT plus anti-androgens to analyze ADT effects on primary tumor size, prostate-specific antigen (PSA) values, and metastatic incidence. We found that the current ADT with anti-androgens might lead to primary tumor reduction, with PSA decreased yet metastases increased in some PCa patients. Using in vitro and in vivo metastasis models with four human PCa cell lines, we evaluated the effects of the currently used anti-androgens, Casodex/bicalutamide and MDV3100/enzalutamide, and the newly developed anti-AR compounds, ASC-J9® and cryptotanshinone, on PCa cell growth and invasion. In vitro results showed that 10 μm Casodex or MDV3100 treatments suppressed PCa cell growth and reduced PSA level yet significantly enhanced PCa cell invasion. In vivo mice studies using an orthotopic xenograft mouse model also confirmed these results. In contrast, ASC-J9® led to suppressed PCa cell growth and cell invasion in in vitro and in vivo models. Mechanism dissection indicated these Casodex/MDV3100 treatments enhanced the TGF-β1/Smad3/MMP9 pathway, but ASC-J9® and cryptotanshinone showed promising anti-invasion effects via down-regulation of MMP9 expression. These findings suggest the potential risks of using anti-androgens and provide a potential new therapy using ASC-J9® to battle PCa metastasis at the castration-resistant stage.     

Neuron-derived IgG Protects Neurons from Complement-dependent Cytotoxicity

Passive immunity of the nervous system has traditionally been thought to be predominantly due to the blood-brain barrier. This concept must now be revisited based on the existence of neuron-derived IgG. The conventional concept is that IgG is produced solely by mature B lymphocytes, but it has now been found to be synthesized by murine and human neurons. However, the function of this endogenous IgG is poorly understood. In this study, we confirm IgG production by rat cortical neurons at the protein and mRNA levels, with 69.0 ± 5.8% of cortical neurons IgG-positive. Injury to primary-culture neurons was induced by complement leading to increases in IgG production. Blockage of neuron-derived IgG resulted in more neuronal death and early apoptosis in the presence of complement. In addition, FcγRI was found in microglia and astrocytes. Expression of FcγR I in microglia was increased by exposure to neuron-derived IgG. Release of NO from microglia triggered by complement was attenuated by neuron-derived IgG, and this attenuation could be reversed by IgG neutralization. These data demonstrate that neuron-derived IgG is protective of neurons against injury induced by complement and microglial activation. IgG appears to play an important role in maintaining the stability of the nervous system.     

Rootstocks improve cucumber photosynthesis through nitrogen metabolism regulation under salt stress

We examined the growth, photosynthetic parameters, initial and total ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, the relative expression of rbcL, rbcS, and rca gene, and nitrogen metabolism of cucumber (Cucumis sativus L. cv. Jinchun No.2, CS) plants grafted onto figleaf gourd (Cucurbita ficifolia Bouché, CF) and pumpkin (Cucurbita moschata Duch. cv. Chaojiquanwang, CM) rootstocks. Growth inhibition under salt stress (90 mM NaCl) was characterized by the irreversible inhibition of CO₂ assimilation in the cucumber plants grafted onto cucumber rootstocks (CS/CS). In contrast, this effect was significantly alleviated by grafting the cucumber plants onto the CF and CM roots (CS/CF, CS/CM). Under NaCl stress, the CS/CF and CS/CM plants exhibited higher photosynthetic activity, higher initial and total Rubisco activity, and higher Rubisco-related gene expression than the CS/CS plants. Salinity resulted in a lesser increase in nitrate content and decrease in free amino acid content in the CS/CF and the CS/CM plants compared with the CS/CS plants. Accordingly, the activity of nitrate reductase, glutamine synthetase, and glutamate synthase decreased significantly, especially in the CS/CS plants. These results suggest that grafting cucumber plants onto salt-tolerant rootstocks enhances Rubisco activity and the expression of Rubisco-related genes by effectively accelerating nitrate transformation into amino acids under NaCl stress, thereby improving the photosynthetic performance of cucumber leaves.     

Focus: 50 Years of DNA Repair: The Yale Symposium Reports: Investigations of Homologous Recombination Pathways and Their Regulation

The DNA double-strand break (DSB), arising from exposure to ionizing radiation or various chemotherapeutic agents or from replication fork collapse, is among the most dangerous of chromosomal lesions. DSBs are highly cytotoxic and can lead to translocations, deletions, duplications, or mutations if mishandled. DSBs are eliminated by either homologous recombination (HR), which uses a homologous template to guide accurate repair, or by nonhomologous end joining (NHEJ), which simply rejoins the two broken ends after damaged nucleotides have been removed. HR generates error-free repair products and is also required for generating chromosome arm crossovers between homologous chromosomes in meiotic cells. The HR reaction includes several distinct steps: resection of DNA ends, homologous DNA pairing, DNA synthesis, and processing of HR intermediates. Each occurs in a highly regulated fashion utilizing multiple protein factors. These steps are being elucidated using a combination of genetic tools, cell-based assays, and in vitro reconstitution with highly purified HR proteins. In this review, we summarize contributions from our laboratory at Yale University in understanding HR mechanisms in eukaryotic cells.     

Participation of protein kinase C in the activation of Nrf2 signaling by ischemic preconditioning in the isolated rabbit heart

Activation of protein kinase C (PKC) is a critical intracellular signaling triggered by ischemic preconditioning (IPC), but the precise mechanisms underlying the actions of PKC in IPC-mediated cardioprotection remain unclear. Here, we investigated the role of PKC activation on the antioxidant activity by IPC in rabbit hearts. Isolated rabbit hearts were subjected to 60?min of global ischemia by cold cardioplegic arrest (4?°C) and 60?min of reperfusion (37?°C). IPC was induced by three cycles of 2-min ischemia following 3?min of reperfusion (37?°C) before cardioplegic arrest. IPC resulted in a better recovery of mechanical function, increased tissue reduced glutathione-to-oxidized glutathione ratio (GSH/GSSG), superoxide dismutase and catalase content, and decreased tissue malondialdehyde (MDA) content compared to control hearts subjected to 60?min of cardioplegic ischemia and 60?min of reperfusion. IPC also significantly induced activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and the inductions of antioxidant genes heme oxygenase-1 (HO-1) and manganese superoxide dismutase (MnSOD). Injection of phorbol 12-myristate 13 acetate, an activator of PKC, before cardioplegic ischemia induced translocation of PKC-?? and -?? isoforms to membrane fraction, nuclear accumulation of Nrf2, and conferred cardioprotection similar to IPC. Polymyxin B, an inhibitor of PKC, blocked the membrane translocation of PKC-?? and -?? during IPC, inhibited Nrf2 nuclear accumulation, and significantly diminished the IPC-induced cardioprotection when administrated before IPC. These results indicate that the activation of PKC induces the translocation of Nrf2 and the enhancement of endogenous antioxidant defenses in the IPC hearts and suggest that PKC may target Nrf2 to confer cardioprotection.