Suppression of JNK/ERK dependent autophagy enhances Jaspine B derivative-induced gastric cancer cell death via attenuation of p62/Keap1/Nrf2 pathways.

Gastric cancer is one of the most common cancers with few effective treatments, a new treatment agent is desperately needed. C-2, a Jaspine B derivative, has shown anti-cancer efficacy in gastric cancer cells. The anti-cancer mechanism, however, remains unknown. As a result, we investigate the anti-cancer effect and the underlying mechanism of C-2 in gastric cancer cells. The results showed that C-2 selectively reduced the proliferation of gastric cancer cells when compared to normal epithelial gastric cells. Western blotting and flow cytometry further demonstrated that Caspase9 is involved in causing cell death. Meanwhile, C-2 triggered autophagy in gastric cancer cells, inhibition of which with LY294002 can enhance the anti-proliferative activity of C-2. Next, we found that C-2 triggered autophagy through activating JNK/ERK, and that inhibitors of these proteins exacerbated C-2 induced cell death. Mechanically, enhanced phosphorylation of JNK/ERK elevated Beclin-1 by disturbing Beclin-1/Bcl-xL or Beclin-1/Bcl-2 complexes, resulting in autophagy and up-regulation of p62. Finally, p62 binds Keap1 competitively to release Nrf2, boosting Nrf2 translocation from the cytoplasm to the nucleus and triggering expression of Nrf2 target genes, so enhancing survival. C-2 inhibited the growth of gastric cancer cells, while JNK/ERK dependent autophagy antagonized C-2 induced cell growth inhibition through p62/Keap1/Nrf2 pathway.

PfSETvs methylation of histone H3K36 represses virulence genes in Plasmodium falciparum.

The variant antigen Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), which is expressed on the surface of P. falciparum-infected red blood cells, is a critical virulence factor for malaria. Each parasite has 60 antigenically distinct var genes that each code for a different PfEMP1 protein. During infection the clonal parasite population expresses only one gene at a time before switching to the expression of a new variant antigen as an immune-evasion mechanism to avoid the host antibody response. The mechanism by which 59 of the 60 var genes are silenced remains largely unknown. Here we show that knocking out the P. falciparum variant-silencing SET gene (here termed PfSETvs), which encodes an orthologue of Drosophila melanogaster ASH1 and controls histone H3 lysine 36 trimethylation (H3K36me3) on var genes, results in the transcription of virtually all var genes in the single parasite nuclei and their expression as proteins on the surface of individual infected red blood cells. PfSETvs-dependent H3K36me3 is present along the entire gene body, including the transcription start site, to silence var genes. With low occupancy of PfSETvs at both the transcription start site of var genes and the intronic promoter, expression of var genes coincides with transcription of their corresponding antisense long noncoding RNA. These results uncover a previously unknown role of PfSETvs-dependent H3K36me3 in silencing var genes in P. falciparum that might provide a general mechanism by which orthologues of PfSETvs repress gene expression in other eukaryotes. PfSETvs knockout parasites expressing all PfEMP1 proteins may also be applied to the development of a malaria vaccine.

The protein amide ¹H(N) chemical shift temperature coefficient reflects thermal expansion of the N-H···O=C hydrogen bond.

The protein amide (1)H(N) chemical shift temperature coefficient can be determined with high accuracy by recording spectra at different temperatures, but the physical mechanism responsible for this temperature dependence is not well understood. In this work, we find that this coefficient strongly correlates with the temperature coefficient of the through-hydrogen-bond coupling, (3h)J(NC'), based on NMR measurements of protein GB3. Parallel tempering molecular dynamics simulation suggests that the hydrogen bond distance variation at different temperatures/replicas is largely responsible for the (1)H(N) chemical shift temperature dependence, from which an empirical equation is proposed to predict the hydrogen bond thermal expansion coefficient, revealing responses of individual hydrogen bonds to temperature changes. Different expansion patterns have been observed for various networks formed by ß strands.

Teth137, a Conserved Factor of Unknown Function from Thermoanaerobacter ethanolicus JW200, Represses the Transcription of the adhE Gene In Vitro.

Teth137, a 13.7 kD protein of unknown function from Thermoanaerobacter ethanolicus JW200, is encoded by 360 nucleotides and has been obtained by DNA-coupled column previously. However, no function study of Teth137 has been published. Homologous modeling of Teth137 shows the protein is comprised of a helix-turn-helix motif which is a typical DNA-binding domain. Therefore, it is speculated Teth137 is a DNA-binding protein and involved in transcription of the adhE gene (encodes alcohol dehydrogenase E). To investigate the function of Teth137, recombinant Teth137 is overexpressed in Escherichia coli JM109 and purified by DEAE column. Purified Teth137 exhibits the affinity with the adhE promoter region in gel electrophoresis mobility shift assay (GEMSA). Teth137 at the concentration of 48 µM retards the migration of 5 nM of probe in the presence of the competitor DNA. Mutant analysis indicates that S69, T70, P71 and T72 are critical to protein-DNA interface; Gly substitutions at these residues results in the loss of the binding ability with the adhE promoter region. Moreover, T. ethanolicus JW200 RNA polymerase, σ subunit and template plasmid are prepared for in vitro transcription assay to detect the regulation function of Teth137. The results of the in vitro transcription show that the transcription of 5 nM of the template plasmid is inhibited by 48 µM of Teth137.

PfSET2 Is Involved in Genome Organization of Var Gene Family in Plasmodium falciparum.

The three-dimensional (3D) genome structure of human malaria parasite Plasmodium falciparum is highly organized and plays important roles in regulating coordinated expression patterns of specific genes such as virulence genes which are involved in antigenic variation and immune escape. However, the molecular mechanisms that control 3D genome of the parasite remain elusive. Here, by analyzing genome organization of P. falciparum, we identify high-interacting regions (HIRs) with strong chromatin interactions at telomeres and virulence genes loci. Specifically, HIRs are highly enriched with repressive histone marks (H3K36me3 and H3K9me3) and form the transcriptional repressive center. Deletion of PfSET2, which controls H3K36me3 level, results in marked reduction of both intrachromosomal and interchromosomal interactions for HIRs. Importantly, such chromatin reorganization coordinates with dynamic changes in epigenetic feature in HIRs and transcriptional activation of var genes. Additionally, different cluster of var genes based on the pattern of chromatin interactions show distinct transcriptional activation potential after deletion of PfSET2. Our results uncover a fundamental mechanism that the epigenetic factor PfSET2 controls the 3D organization of heterochromatin to regulate the transcription activities of var genes family in P. falciparum. IMPORTANCE PfSET2 has been reported to play key role in silencing var genes in Plasmodium falciparum, while the underlying molecular mechanisms remain unclear. Here, we provide evidence that PfSET2 is essential to maintain 3D genome organization of heterochromatin region to keep var genes in transcription repressive state. These findings can contribute better understanding of the regulation of high-order chromatin structure in P. falciparum.

The mechanism for regulating ethanol fermentation by redox levels in Thermoanaerobacter ethanolicus.

Anaerobes can obtain the entire cell's ATP by glycolysis and remove resulting reducing power by fermentation. There is a delicate balance in redox status to obtain a maximal growth of these cells, and the conditions to change redox fluxes can induce kinds of changes in metabolism. The fundamental knowledge on sensing redox status and coupling redox signals with fermentation pathways is essential for the metabolic engineering to control redox fluxes at the molecular level. A redox sensing protein (RSP) was isolated by DNA affinity chromatography, and corresponding gene was mined from genomic sequences of Thermoanaerobacter spp. The RSP shares up to 41% identity with the regulatory proteins which sense NADH and control the expression of NADH dehydrogenase in aerobic microorganisms. The operator sites for RSP were located in all the operons for ethanol fermentation rather than in that of NADH dehydrogenase. The typical operator was identified as a palindromic sequence, -ATTGTTANNNNNNTAACAAT-. NADH caused a transition of RSP from an α-helix rich to ß-sheet rich conformation. In an in vitro transcription system of T. ethanolicus, RSP repressed the transcription of an alcohol dehydrogenase, whereas the repression was reversed by adding NADH. Base substitutes in the repeats of the palindrome reduced the affinity between RSP and the operator, and thus delicate regulation could be achieved. This study reveals for the first time a repressor/operator system that couples a redox signal with a fermentation pathway, and the results presented here provide valuable insights for the design of metabolic engineering.

Plasmodium falciparum var Gene Is Activated by Its Antisense Long Noncoding RNA.

Plasmodium falciparum erythrocyte membrane protein 1, encoded by var gene, is an immunodominant antigen mediating immune evasion in humans. At a given time, only a single var gene is commonly expressed in one parasite. However, the regulation mechanism of var transcription remains largely unknown. In this study, we identified the antisense long non-coding RNA (aslncRNA) derived from var intron as an activation factor for the corresponding var gene. The exogenous artificial var aslncRNA transcribed by T7 RNA polymerase from episome can specifically activate the homologous var gene, and the exogenous aslncRNA activates transcription of both var mRNA and endogenous aslncRNA in a manner independent of the conserved intron sequence within the var gene family. Interestingly, the newly activated var gene and the previously dominant var gene then could be co-expressed in the same parasite nuclei, which suggests that the aslncRNA-mediated var gene activation could escape from the control of mutually exclusively expression of the var gene family. Together, our work shows that var aslncRNA is the activator responsible for var gene transcriptional regulation.

Dynamics of the GB3 loop regions from MD simulation: how much of it is real?

A total of 1.1 µs of molecular dynamics (MD) simulations were performed to study the structure and dynamics of protein GB3. The simulation motional amplitude of the loop regions is generally overestimated in comparison with the experimental backbone N-H order parameters S(2). Two-state behavior is observed for several residues in these regions, with the minor state population in the range of 3-13%. Further inspection suggests that the (φ, ψ) dihedral angles of the minor states deviate from the GB3 experimental values, implying the existence of nonnative states. After fitting the MD trajectories of these residues to the NMR RDCs, the minor state populations are significantly reduced by at least 80%, suggesting that MD simulations are strongly biased toward the minor states, thus overestimating the dynamics of the loop regions. The optimized trajectories produce intra, sequential H(N)-H(α) RDCs and intra (3)J(HNHα) that are not included in the trajectories fitting for these residues that are closer to the experimental data. Unlike GB3, 0.55 µs MD simulations of protein ubiquitin do not show distinctive minor states, and the derived NMR order parameters are better converged. Our findings indicate that the artifacts of the simulations depend on the specific system studied and that one should be cautious interpreting the enhanced dihedral dynamics from long MD simulations.

[Expression, purification and characterization of a thermostable pectate lyase from Thermotoga maritima].

The structure gene pelA from Thermotoga maritima MSB8 encoding pectate lyase was amplified and ligated into pHsh, resulting pHsh-pelA. Through structural optimization on pHsh-pelA, the ultimate plasmid, pHsh-pelC, which possessed the most appropriate structure and free energy of mRNA, was obtained. Pectate lyase C (PelC) was obtained after expressing pHsh-pelC in Escherichia coli JM109. The optimum activity of PelC was determined at pH 8.5 at 90 degrees C, with a half-life for almost 2 h at 95 degrees C. PelC was stable at the pH range of 8.2-9.8, and was dependent on Ca2+ for activity and stability. The enzyme kept stable for a long time and possessed a high level of activity at 60 degrees C. The kinetic assay using polygalacturonic acid (PGA) as substrate gave K(m) and V(max) of 0.11 mmol/L and 327 U per mg of protein. SDS-PAGE analysis showed that the molecular mass of the expressed recombinant PelC was about 43 kD, which was exactly the size predicted. The expression vector system of the heat shock plasmid pHsh owned such advantages as high expression level and cheap induction. Moreover, the superior stability of the recombinant enzyme laid the base for large-scale fermentation application.