Vertical distribution of bacterial community structure in the sediments of two eutrophic lakes revealed by denaturing gradient gel electrophoresis (DGGE) and multivariate analysis techniques

Vertical distribution of bacterial community structure was investigated in the sediments of two eutrophic lakes of China, Lake Taihu and Lake Xuanwu. Profiles of bacterial communities were generated using a molecular fingerprinting technique, denaturing gradient gel electrophoresis (DGGE) followed by DNA sequence analysis, and the results were interpreted with multivariate statistical analysis. To assess changes in the genetic diversity of bacterial communities with changing depth, DGGE banding patterns were analysed by cluster analysis. Distinct clusters were recognized in different sampling stations of Lake Taihu. Canonical correspondence analysis (CCA) was carried out to infer the relationship between environmental variables and bacterial community structure. DGGE samples collected at the same sampling site clustered together in both lakes. Total phosphorus, organic matter and pH were considered to be the key factors driving the changes in bacterial community composition.     

Effect of UV-C treatment on modulating antioxidative system and proline metabolism of bamboo shoots subjected to chilling stress

Bamboo shoots are highly nutritious but difficult to preserve even under low temperature since they are sensitive to chilling. In the present research, bamboo shoots were exposed to UV-C light (4.1 kJ/m²) prior to 56 days storage at 1 °C to evaluate the potential of UV-C treatment on alleviating chilling injury (CI) of bamboo shoots under cold storage. CI incidence and physiological and biochemical characteristics associated with CI were determined during storage. The results showed that UV-C treatment apparently inhibited the development of CI and resulted lower EI and MDA content than that of the control. Further investigation demonstrated that UV-C treatment increased activities of CAT, APX, GR and DPPH scavenging activity of bamboo shoots, which greatly contribute to alleviating CI. The increases in both O₂ ^? production rate and H₂O₂ content of UV-C-treated bamboo shoots were significantly delayed, PAL activity was increased which contributed to enhancing accumulation of TP, and endogenous proline synthesis was promoted, which resulted from the increased activity of P5CS and decreased PDH activity. The results above suggest that the improved antioxidative defense system and enhanced proline accumulation is the underlying mechanism that UV-C treatment enhanced chilling tolerance in bamboo shoots.     

Targeting Hedgehog signaling pathway and autophagy overcomes drug resistance of BCR-ABL-positive chronic myeloid leukemia

The frontline tyrosine kinase inhibitor (TKI) imatinib has revolutionized the treatment of patients with chronic myeloid leukemia (CML). However, drug resistance is the major clinical challenge in the treatment of CML. The Hedgehog (Hh) signaling pathway and autophagy are both related to tumorigenesis, cancer therapy, and drug resistance. This study was conducted to explore whether the Hh pathway could regulate autophagy in CML cells and whether simultaneously regulating the Hh pathway and autophagy could induce cell death of drug-sensitive or -resistant BCR-ABL⁺ CML cells. Our results indicated that pharmacological or genetic inhibition of Hh pathway could markedly induce autophagy in BCR-ABL⁺ CML cells. Autophagic inhibitors or ATG5 and ATG7 silencing could significantly enhance CML cell death induced by Hh pathway suppression. Based on the above findings, our study demonstrated that simultaneously inhibiting the Hh pathway and autophagy could markedly reduce cell viability and induce apoptosis of imatinib-sensitive or -resistant BCR-ABL⁺ cells. Moreover, this combination had little cytotoxicity in human peripheral blood mononuclear cells (PBMCs). Furthermore, this combined strategy was related to PARP cleavage, CASP3 and CASP9 cleavage, and inhibition of the BCR-ABL oncoprotein. In conclusion, this study indicated that simultaneously inhibiting the Hh pathway and autophagy could potently kill imatinib-sensitive or -resistant BCR-ABL⁺ cells, providing a novel concept that simultaneously inhibiting the Hh pathway and autophagy might be a potent new strategy to overcome CML drug resistance.     

长非编码RNA在胃癌发病机制中相关作用的研究进展

胃癌是死亡率位居全球第二的消化道恶性肿瘤,在我国的发病率呈逐年上升的趋势。研究发现,长非编码RNA(lncRNA)在胃癌患者癌细胞中存在异常表达,且与癌细胞的增殖、转移等生物学活动密切相关。lncRNA对于评估癌前病变的发生、判断化疗的疗效及胃癌的预后都有重要意义,但目前lncRNA在胃癌发生、发展过程中的作用机制尚不完全清楚。我们就lncRNA在胃癌发病机制中的最新研究进展做简要综述。     

Ginsenoside Rb1 inhibits matrix metalloproteinase 13 through down-regulating Notch signaling pathway in osteoarthritis

Mounting evidence suggests that an excess of matrix metalloproteinase-13 (MMP-13) plays an important role in the breakdown of extracellular matrix in osteoarthritis (OA). Here, the effects of ginsenoside Rb1 (GRb1) on the expression of MMP-13 in IL-1β-induced SW 1353 chondrosarcoma cells and an experimental rat model of OA induced by anterior cruciate ligament transection (ACLT) were investigated. SW1353 chondrosarcoma cells were pretreated with or without GRb1 and Notch signaling pathway inhibitor, DAPT, then were stimulated with IL-1β. In rats, experimental OA was induced by ACLT. These rats then received intra-articular injections of vehicle, an inhibitor of γ-secretase, DAPT, and/or GRb1. Expression of MMP-13, collagen type II (CII), Notch1, and jagged 1 (JAG1) were verified by western blotting and immunohistochemistry. In addition, levels of MMP-13 mRNA were detected using quantitative real-time PCR. In histological analyses, treatment with DAPT reduced the number of cartilage lesions present and the expressions of MMP-13, CII, Notch1, and JAG1. In addition, treatment with GRb1 was associated with lower levels of Notch1 and JAG1 in both IL-1β-induced SW1353 chondrosarcoma cells and in the rat OA model. Furthermore, the suppressive effect of GRb1 on MMP-13 was greater than that exhibited by the signaling pathway inhibitor. In conclusion, GRb1 inhibits MMP-13 through down-regulating Notch signaling pathway in OA.     

Secreted PCSK9 downregulates low density lipoprotein receptor through receptor-mediated endocytosis

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a protease that regulates low density lipoprotein receptor (LDLR) protein levels. The mechanisms of this action, however, remain to be defined. We show here that recombinant human PCSK9 expressed in HEK293 cells was readily secreted into the medium, with the prosegment associated with the C-terminal domain. Secreted PCSK9 mediated cell surface LDLR degradation in a concentration- and time-dependent manner when added to HEK293 cells. Accordingly, cellular LDL uptake was significantly reduced as well. When infused directly into C57B6 mice, purified human PCSK9 substantially reduced hepatic LDLR protein levels and resulted in increased plasma LDL cholesterol. When added to culture medium, fluorescently labeled PCSK9 was endocytosed and displayed endosomal-lysosomal intracellular localization in HepG2 cells, as was demonstrated by colocalization with DiI-LDL. PCSK9 endocytosis was mediated by LDLR as LDLR deficiency (hepatocytes from LDLR null mice), or RNA interference-mediated knockdown of LDLR markedly reduced PCSK9 endocytosis. In addition, RNA interference knockdown of the autosomal recessive hypercholesterolemia (ARH) gene product also significantly reduced PCSK9 endocytosis. Biochemical analysis revealed that the LDLR extracellular domain interacted directly with secreted PCSK9; thus, overexpression of the LDLR extracellular domain was able to attenuate the reduction of cell surface LDLR levels by secreted PCSK9. Together, these results reveal that secreted PCSK9 retains biological activity, is able to bind directly to the LDLR extracellular domain, and undergoes LDLR-ARH-mediated endocytosis, leading to accelerated intracellular degradation of the LDLR.     

Alternate coupling of receptors to Gs and Gi in pancreatic and submandibular gland cells.

Many Gs-coupled receptors can activate both cAMP and Ca2+ signaling pathways. Three mechanisms for dual activation have been proposed. One is receptor coupling to both Gs and G15 (a Gq class heterotrimeric G protein) to initiate independent signaling cascades that elevate intracellular levels of cAMP and Ca+2, respectively. The other two mechanisms involve cAMP-dependent protein kinase-mediated activation of phospholipase Cbeta either directly or by switching receptor coupling from Gs to Gi. These mechanisms were primarily inferred from studies with transfected cell lines. In native cells we found that two Gs-coupled receptors (the vasoactive intestinal peptide and beta-adrenergic receptors) in pancreatic acinar and submandibular gland duct cells, respectively, evoke a Ca2+ signal by a mechanism involving both Gs and Gi. This inference was based on the inhibitory action of antibodies specific for Galphas, Galphai, and phosphatidylinositol 4,5-bisphosphate, pertussis toxin, RGS4, a fragment of beta-adrenergic receptor kinase and inhibitors of cAMP-dependent protein kinase. By contrast, Ca2+ signaling evoked by Gs-coupled receptor agonists was not blocked by Gq class-specific antibodies and was unaffected in Galpha15 -/- knockout mice. We conclude that sequential activation of Gs and Gi, mediated by cAMP-dependent protein kinase, may represent a general mechanism in native cells for dual stimulation of signaling pathways by Gs-coupled receptors.     

CDK phosphorylates the polarisome scaffold Spa2 to maintain its localization at the site of cell growth

Polarisome is a protein complex that plays an important role in polarized growth in fungi by assembling actin cables towards the site of cell growth. For proper morphogenesis, the polarisome must localize to the right place at the right time. However, the mechanisms that control polarisome localization remain poorly understood. In this study, using the polymorphic fungus Candida albicans as a model, we have discovered that the cyclin‐dependent kinase (CDK) Cdc28 phosphorylates the polarisome scaffold protein Spa2 to govern polarisome localization during both yeast and hyphal growth. In a yeast cell cycle, Cdc28‐Clb2 phosphorylates Spa2 and controls the timing of polarisome translocation from the bud tip to the bud neck. And during hyphal development, Cdc28‐Clb2 and the hyphal‐specific Cdc28‐Hgc1 cooperate to enhance Spa2 phosphorylation to maintain the polarisome at the hyphal tip. Blocking the CDK phosphorylation causes premature tip‐to‐neck translocation of Spa2 during yeast growth and inappropriate septal localization of Spa2 in hyphae and abnormal hyphal morphology under certain inducing conditions. Together, our results generate new insights into the mechanisms by which fungi regulate polarisome localization in the control of polarized growth.     

Time-Course Association Mapping of the Grain-Filling Rate in Rice (Oryza sativa L.)

Detecting quantity trait locus (QTLs) and elite alleles that are associated with grain-filling rate (GFR) in rice is essential for promoting the utilization of hybrid japonica rice and improving rice yield. Ninety-five varieties including 58 landraces and 37 elite varieties from the core germplasm collection were genotyped with 263 simple sequence repeat (SSR) markers. The GFR of the 95 varieties was evaluated at five stages, 7, 14, 21, 28 and 35 days after flowering (DAF) both in 2011 and 2012. We found abundant phenotypic and genetic diversity in the studied population. A population structure analysis identified seven subpopulations. A linkage disequilibrium (LD) analysis indicated that the levels of LD ranged from 60.3 cM to 84.8 cM and artificial selection had enhanced the LD. A time-course association analysis detected 31 marker-GFR associations involving 24 SSR markers located on chromosomes 1, 2, 3, 4, 5, 6, 8, 9, 11 and 12 of rice at five stages. The elite alleles for high GFR at each stage were detected. Fifteen excellent parental combinations were predicted, and the best parental combination ‘Nannongjing62401×Laolaihong’ could theoretically increase 4.086 mg grain^-1 d^-1 at the five stages. Our results demonstrate that the time-course association mapping for GFR in rice could detect elite alleles at different filling stages and that these elite alleles could be used to improve the GFR via pyramiding breeding.