Development of recombinant OmpA and OmpB proteins as diagnostic antigens for rickettsial disease

In this study the diagnostic potential of Rickettsia conorii recombinant antigens was analyzed. For this, site-specific PCR primers were used to clone the OmpA and OmpB genes of R. conorii into pMAL-c2X plasmids. Six fragments of OmpA and four of OmpB were expressed as fusion proteins with maltose-binding protein in Escherichia coli. OmpA_1350-1784, OmpB_801-1269, and OmpB_1227-1634 regions from truncated proteins were selected as diagnostic candidate antigens by ELISA using control sera. ELISA results of three antigens were compared to the results obtained by using a commercial ELISA kit which contained whole OmpA and OmpB antigens from R. conorii . For this analysis, 40 serum samples taken from febrile patients and uninfected controls were tested. Of the 20 R. conorii test results which were positive with the commercial kit, 18 were shown to be positive by ELISA using OmpA_1350-1784 (a sensitivity of 90%). The specificity of the ELISA was 100%; all of the 20 samples shown to be negative using the commercial kit were also negative in our assay. The sensitivities of the ELISA using the OmpB_801-1269 and OmpB_1227-1634 were 90% and 95%, respectively. The specificities of the OmpB_801-1269 and the OmpB_1227-1634 were 100% and 95%, respectively. These results suggest that specific regions of OmpA and OmpB effectively detect antibodies against R. conorii , and the truncated recombinant antigens could be used for development of diagnostic tools for rickettsial disease.     

Mutual Regulation of ntcA and hetR during Heterocyst Differentiation Requires Two Similar PP2C-Type Protein Phosphatases,PrpJ1 and PrpJ2, in Anabaena sp. Strain PCC 7120

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 can form heterocysts for N₂ fixation. Initiation of heterocyst differentiation depends on mutual regulation of ntcA and hetR. Control of hetR expression by NtcA is partially mediated by nrrA, but other factors must be involved in this regulation. Anabaena has two closely related PP2C-type protein phosphatases, PrpJ1 (formerly PrpJ) and PrpJ2; PrpJ1 is involved in heterocyst maturation. In this study, we show that PrpJ2, like PrpJ1, has Mn²⁺-dependent phosphatase activity. We further demonstrate that whereas prpJ2 is dispensable for cell growth under different nitrogen regimens tested, a double mutant with both prpJ1 and prpJ2 disrupted did not initiate heterocyst differentiation. Ectopic expression of hetR in the double mutant could rescue the failure to initiate heterocyst development, but the heterocysts formed, like those of a prpJ1 single mutant, were not mature. The expression of prpJ2 was enhanced during heterocyst development, and the upregulation of the gene was directly under the control of NtcA. Upregulation of both ntcA and hetR was affected in the double mutant. We propose that PrpJ1 and PrpJ2 together are required for mutual regulation of ntcA and hetR and are thus involved in regulation of the initiation of heterocyst differentiation.Many cyanobacteria can fix N₂ when combined nitrogen sources become limiting in the growth medium. The nitrogenase enzymatic complex responsible for nitrogen fixation is very sensitive to oxygen, and oxygen is produced by photosynthesis by cyanobacteria. The strategy used by some filamentous diazotrophic cyanobacteria to resolve this oxygen paradox is to perform photosynthesis and nitrogen fixation in two distinct cell types, differentiated cells called heterocysts that provide a microoxic environment for nitrogenase and vegetative cells which perform oxygenic photosynthesis (22, 36, 39). One such organism is Anabaena sp. strain PCC 7120. In this strain, heterocysts account for 5 to 10% of the cells and appear in a semiregular pattern along each filament. Therefore, the process of heterocyst differentiation provides a prokaryotic model to study developmental pattern formation. Three factors account for the microoxic environment in heterocysts: the heterocyst envelope composed of an inner layer of glycolipid surrounded by an outer layer of polysaccharides that limits oxygen penetration, the lack of oxygen-producing photosystem II, and an increased rate of respiration to consume oxygen (36).The initiation of heterocyst differentiation and the formation of the heterocyst pattern are governed by multiple signals and the concerted actions of several proteins as positive or negative regulators (for a recent review, see 39). The accumulation of 2-oxoglutarate following limitation of combined nitrogen is a trigger that initiates heterocyst development by stimulating the DNA-binding activity of NtcA, a protein involved in the regulation of carbon and nitrogen metabolism, as well as initiation of heterocyst differentiation (7, 12, 13, 18, 20, 32, 35). HetR, a protease with DNA-binding activity, plays a central role in the early steps of heterocyst differentiation (14, 40). Both ntcA and hetR are autoregulated, and the expression of hetR and the expression of ntcA are mutually dependent because upregulation of one of theses genes is dependent on the other gene (3, 4, 23). How HetR regulates the expression of ntcA remains unknown. No NtcA-binding site has been found in the upstream region of hetR, and the regulation of hetR by NtcA could be partially due to the action of the response regulator NrrA (8, 9, 24). However, NrrA cannot be the only link between ntcA and hetR, because when nrrA was inactivated, both heterocyst differentiation and hetR upregulation were only delayed (8). Indeed, ccbP, encoding a calcium-binding protein, is regulated by NtcA, and it has been proposed that the pool of calcium affects the activity of HetR (31).The genome of Anabaena sp. strain PCC 7120 contains a large number of genes encoding two-component signaling systems, protein Ser/Thr and/or Tyr kinases, and phosphatases, including eight genes encoding PP2C-type Ser/Thr phosphatases (16, 26, 34, 38). Some of these genes are involved in heterocyst development, mostly in heterocyst maturation and functioning (8, 11, 17, 19, 21, 25, 30, 37). We have shown previously that PrpJ is a PP2C-type protein phosphatase located on the plasma membrane (15). A prpJ1 mutant (strain S20) failed to grow under diazotrophic conditions and formed heterocysts lacking the major heterocyst-specific glycolipid (HGL), in contrast to other mutants whose mutations affect either the synthesis or the deposition of both the major and minor HGLs (1, 2, 10, 28) or only the minor HGL (30). Therefore, PrpJ represents a new regulatory branch for heterocyst maturation, possibly involving regulation of only a subset of genes involved in glycolipid synthesis. These observations indicate that multiple input pathways participate in the maturation of heterocysts. When proheterocysts were formed, filaments of the prpJ1 mutant, fragmented extensively at the junctions between proheterocysts and vegetative cells, resulting in free nonmature heterocysts and filaments that were 11 cells long on average (15).Open reading frame all2470 encodes one member of the PP2C family of protein phosphatases in Anabaena sp. strain PCC 7120 (35). The deduced amino acid sequence of All2470 is similar to that of PrpJ, and these two proteins have similar architectures, with an N-terminal domain having an unknown function, a central domain similar to the catalytic domains of PP2C-type protein phosphatases, and a C-terminal domain with a putative transmembrane motif (Fig. ​(Fig.1).1). The amino acid sequences of these two proteins share 40% identity overall, and their catalytic domains are 45% identical. Because these two protein phosphatases are very similar, here we use the designations PrpJ1 (formerly PrpJ) for All1731 and PrpJ2 for All2470. In the present study, we show that PrpJ1 and PrpJ2 are involved in the initiation of heterocyst differentiation by acting on the mutual regulation of ntcA and hetR.Open in a separate windowFIG. 1.(A) Different domains of PrpJ1 and PrpJ2. The length of each domain (in number of residues) is indicated in parentheses. TM, putative transmembrane domain. (B) Genomic environment of prpJ2 and strategy for inactivating prpJ2 by insertion of an antibiotic resistance cassette (Neo^r). The arrow for the Neo^r cassette indicates the orientation of the resistance cassette relative to that of prpJ2.     

Critical role of poly(ADP‐ribose) polymerase‐1 in modulating the mode of cell death caused by continuous oxidative stress

Continuously generated hydrogen peroxide (H₂O₂) inhibits typical apoptosis and instead initiates a caspase‐independent, apoptosis‐inducing factor (AIF)‐mediated pyknotic cell death. This may be related to H₂O₂‐mediated DNA damage and subsequent ATP depletion, although the exact mechanisms by which the mode of cell death is decided after H₂O₂ exposure are still unclear. Accumulated evidence and our previous data led us to hypothesize that continuously generated H₂O₂, not an H₂O₂ bolus, induces severe DNA damage, signaling poly(ADP‐ribose) polymerase‐1 (PARP‐1) activation, ATP depletion, and eventually caspase‐independent cell death. Results from the present study support that H₂O₂ generated continuously by glucose oxidase causes excessive DNA damage and PARP‐1 activation. Blockage of PARP‐1 by a siRNA transfection or by pharmacological inhibitor resulted in the significant inhibition of ATP depletion, loss of mitochondrial membrane potential, nuclear translocation of AIF and endonuclease G, and eventually conversion to caspase‐dependent apoptosis. Overall, the current study demonstrates the different roles of PARP‐1 inhibition in modulation of cell death according to the method of H₂O₂ exposure, that is, continuous generation versus a direct addition. J. Cell. Biochem. 108: 989–997, 2009. © 2009 Wiley‐Liss, Inc.     

A novel low molecular weight phospholipase D from Streptomyces sp. CS684

With the aim of isolating economically viable enzymes from a microbial source, a novel phospholipase D (PLD) was purified from Streptomyces sp. CS684 (PLD(684)). PLD(684) had molecular weight of 29 kDa, which makes it the second smallest PLD reported so far. The enzyme activity was optimum at pH 6 and 45 degrees C, and enhanced by various detergents. It was stable from pH 7 to 9 and at or below 45 degrees C when assayed after 40 h and 2h, respectively. The K(m) and V(max) values for phosphatidylcholine were 1.16 mM and 1453.74 micromol min(-1)mg(-1), respectively. It catalyzed the transphosphatidylation of glycerol, but not that of l-serine, myo-inositol or ethanolamine. Low molecular weight PLD(684) with transphosphatidylation activity may be utilized in the industrial production of rare and commercially important phospholipids.     

Malachite green induces cardiovascular defects in developing zebrafish (Danio rerio) embryos by blocking VEGFR-2 signaling

Malachite green (MG) is a triphenyl methane dye used in various fields that demonstrates high toxicity to bacteria and mammalian cells. When bud stage zebrafish embryos were treated with MG at 125, 150, and 175 ppb for 14 h, the development of trunk including intersomitic vessels was inhibited in MG-treated flk-1-GFP transgenic embyos. MG clearly induced whole growth retardation. MG induced severe cell death in trunk intersomite region of zebrafish embryos and in human vascular endothelial cells in a dose-dependent manner. MG inhibited heart rates and cardiac looping. MG attenuated whole blood formation and inhibited vascular endothelial growth factor (VEGF)-induced receptor (R)-2 phosphorylation in vascular endothelial cells. In conclusion, MG significantly alters the cardiovascular development causing growth retardation in zebrafish through the blocking VEGFR-2 activation in early cardiovascular development. It suggests that MG may be an environmental toxic agent with the potential to induce embryonic cardiovascular defects in vertebrates.     

Silencing of Kv4.1 potassium channels inhibits cell proliferation of tumorigenic human mammary epithelial cells

Potassium channel activity has been shown to facilitate cell proliferation in cancer cells. In the present study, the role of Kv4.1 channels in immortal and tumorigenic human mammary epithelial cells was investigated. Kv4.1 protein expression was positively correlated with tumorigenicity. Moreover, transfection with siRNAs targeting Kv4.1 mRNA suppressed proliferation of tumorigenic mammary epithelial cells. Experiments using mRNA isolated from human breast cancer tissues revealed that the level of Kv4.1 mRNA expression varied depending on the stage of the tumor. Kv4.1 protein expression increased during stages T2 and T3 compared to normal tissue. These results demonstrated that Kv4.1 plays a role in proliferation of tumorigenic human mammary epithelial cells. In addition, elevated Kv4.1 expression may be useful as a diagnostic marker for staging mammary tumors and selective blockers of Kv4.1 may serve to suppress tumor cell proliferation.     

Mass spectrometric quantification of neutral and sialylated N-glycans from a recombinant therapeutic glycoprotein produced in the two Chinese hamster ovary cell lines

Quality control and assurance of glycan profiles of a recombinant glycoprotein from lot to lot is a critical issue in the pharmaceutical industry. To develop an easy and simple quantitative and qualitative glycan profile method based on matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS), the modification with Girard’s reagent T (GT) was exploited. Because GT-derivatized quantification of oligosaccharides using MALDI-TOF MS is possible only with neutral glycans, sialylated glycans are not subjected to quantitative analysis with MALDI-TOF MS. To solve this problem, mild methyl esterification and subsequent GT derivatization were employed, enabling us to perform rapid qualitative and quantitative analysis of sialylated and neutral N-linked oligosaccharides using MALDI-TOF MS. This modified method was used in the comparative quantification of N-glycans from the recombinant therapeutic glycoprotein expressed in two different Chinese hamster ovary (CHO) cell lines. The percentages of sialylated N-glycans to total were 22.5 and 5.2% in CHO-I and CHO-II cells, respectively, resulting in a significant difference in the biological activity of the recombinant glycoprotein.     

Silibinin inhibits expression of HIF-1α through suppression of protein translation in prostate cancer cells

Silibinin is a polyphenolic flavonoid isolated from the milk thistle (Silybum marianum) and is reported to exhibit anticancer properties. Recently, it has been reported that silibinin inhibits hypoxia-inducible factor-1α (HIF-1α) expression in cancer cells. However, the precise mechanism by which silibinin decreases HIF-1 expression is not fully understood. In this study, silibinin inhibited basal and hypoxia induced expression levels of HIF-1α protein in LNCaP and PC-3 prostate cancer cells, while the rate of HIF-1α protein degradation and mRNA levels were not affected. We found that the decrease in HIF-1 protein by silibinin correlated with suppression of de novo synthesis of HIF-1α protein. Silibinin inhibited global protein synthesis coincided with reduction of eIF4F complex formation and induction of phosphorylation of the translation initiation factor 2α (eIF-2α) which can cause inhibition of general protein synthesis. These results suggest that silibinin’s activity to inhibit HIF-1α protein expression is associated with the suppression of global protein translation.     

Conserved Element of the Dicistrovirus IGR IRES that Mimics an E-site tRNA/Ribosome Interaction Mediates Multiple Functions

The internal ribosome entry site within the intergenic region (IGR IRES) of the Dicistroviridae family mimics a tRNA to directly assemble 80 S ribosomes and initiate translation at a non-AUG codon from the ribosomal A-site. A comparison of IGR IRESs within this viral family reveals structural similarity but little sequence similarity. However, a few specific conserved elements exist, which likely have important roles in IRES function. In this study, we have generated a battery of mutations to characterize the role of a conserved loop (L1.1) region of the IGR IRES. Mutating specific nucleotides within the L1.1 region inhibited IGR IRES-mediated translation in rabbit reticulocyte lysates. By assaying different steps in IRES function, we found that the mutant L1.1 IRESs had reduced affinity for 80 S ribosomes but not 40 S subunits, indicating that the L1.1 region mediated either binding to preformed 80 S or 60 S joining. Furthermore, mutations in L1.1 altered the position of the ribosome on the mutant IRES, indicating that the tRNA-like anticodon/codon mimic within the ribosomal P-site is disrupted. Structural studies have revealed that the L1.1 region interacts with the L1 stalk of the 60 S subunit, which is similar to the interactions between the T-loop of the E-site tRNA and ribosomal protein rpL1. Our results demonstrate that the conserved L1.1 region directs multiple steps in IGR IRES-mediated translation including ribosome binding and positioning, which are functions that the E-site tRNA may normally mediate during translation.