The fission yeast pfh1(+) gene encodes an essential 5' to 3' DNA helicase required for the completion of S-phase

The Cdc24 protein plays an essential role in chromosomal DNA replication in the fission yeast Schizosaccharomyces pombe, most likely via its direct interaction with Dna2, a conserved endonuclease–helicase protein required for Okazaki fragment processing. To gain insights into Cdc24 function, we isolated cold-sensitive chromosomal suppressors of the temperature-sensitive cdc24-M38 allele. One of the complementation groups of such suppressors defined a novel gene, pfh1⁺, encoding an 805 amino acid nuclear protein highly homologous to the Saccharomyces cerevisiae Pif1p and Rrm3p DNA helicase family proteins. The purified Pfh1 protein displayed single-stranded DNA-dependent ATPase activity as well as 5′ to 3′ DNA helicase activity in vitro. Reverse genetic analysis in S.pombe showed that helicase activity was essential for the function of the Pfh1 protein in vivo. Schizosaccharomyces pombe cells carrying the cold-sensitive pfh1-R20 allele underwent cell cycle arrest in late S/G2-phase of the cell cycle when shifted to the restrictive temperature. This arrest was dependent upon the presence of a functional late S/G2 DNA damage checkpoint, suggesting that Pfh1 is required for the comple tion of DNA replication. Furthermore, at their permissive temperature pfh1-R20 cells were highly sensitive to the DNA-alkylating agent methyl methanesulphonate, implying a further role for Pfh1 in the repair of DNA damage.     

Synthesis and biological evaluation of novel thioapio dideoxynucleosides

On the basis of the bioisosteric rationale to apio dideoxynucleosides, novel thioapio dideoxynucleosides have been synthesized, starting from 1,3-dihydroxyacetone via thioapio sugar acetate as a key intermediate. The intermediate was condensed with silylated pyrimidine bases such as N(4)-benzoylcytosine, uracil or thymine in the presence of TMSOTf to give the beta-anomers and alpha-anomers, respectively. The intermediate was also condensed with silylated 6-chloropurine to give the 6-chloropurine derivatives and which were converted to adenine derivatives and, N(6)-methyladenine derivatives and, and hypoxanthine derivatives and, respectively. The guanine analogues and were also synthesized from the condensation of sugar acetate with 2-acetamido-6-chloropurine. All synthesized final compounds were tested against HIV-1. Most of the synthesized compounds exhibited toxicity-dependent anti-HIV-1 activity, among which 6-chloropurine derivative was found to be the most cytotoxic and showed good cytotoxicity against colon cancer cell lines. Although we could not find good anti-HIV agents in this study, findings of some anticancer activity in this series will allow this class of nucleosides to be the new template for the development of new anticancer agents (Fig. 1).     

Phosphatidylcholine-specific phospholipase C and RhoA are involved in the thyrotropin-induced activation of phospholipase D in FRTL-5 thyroid cells

Liquid nitrogen (LN2) infusions are currently used in a slow controlled-rate freezing during cryopreservation. The effects of two different LN2 infusion frequencies (conventional, slow 50 infusions/min and high 120 infusions/min) were studied with frozen-thawed two-cell mouse embryos and their subsequent development to blastocysts. The embryos that were subjected to the high frequency LN2 infusion (HFLI) showed a significantly higher survival rate over the low frequency LN2 infusion (LFLI) (50.7 vs. 34.6%, P < 0.05). The blastocyst formation was also higher in HFLI (76.7%) than LFLI (44.0%, P < 0.05) with respective to the number of cells in a blastocyst of 71.6 8.0 (n = 20) and 62.5 +/- 4.7 (n = 20) (P < 0.05). The relative amount of H2O2 in an embryo that was assessed by a fluorescence intensity of 2',7'-dichlorofluorecein (DCF) showed a difference between the procedures with 16.6 +/- 1.6 (n = 21) and 23.4 +/- 1.8 (n = 24) for HFLI and LFLI, respectively (P < 0.05). Mitochondrial staining by Rhodamine 123 showed that the number and distribution of viable mitochondria were similar in both procedures, but fewer mitochondria were observed with a marked aggregation in the arrested embryos, indicating a mitochondrial disintegration. The mitochondrial membrane potential was visualized by a membrane potential-sensitive fluorescent probe, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1). There was a decrease in the number of mitochondria that had a high membrane potential, and they showed a peripheral redistribution along the cell membrane in LFLI. A fluorescent staining of the actin filaments revealed a discontinuity that was noticeably at the peripheral "actin band" in LFLI. The DNA fragmentation was assessed by the dUTP nick end-labeling (TUNEL). The results showed a higher DNA fragmentation of blastocyst nuclei in LFLI compared to HFLI (65.6 vs. 36.0%, P < 0.05). Based on these observations, it was concluded that HFLI was better than LFLI in the case of freezing the mouse 2-cell embryos for preserving cytoskeletons and mitochondrial integrities. This could subsequently lead to a higher survival and developmental rate of the cryopreserved mouse embryos.     

Expression of steroidogenic acute regulatory protein mRNA in rat placenta during mid-late pregnancy

The production of a steroid hormone in the placenta is essential for maintaining the pregnancy and developing the fetus during gestation. In various steroidogenic tissues (including gonads and adrenal cortex), the steroidogenic-acute-regulatory protein (StAR) acutely transfers cholesterol from the outer to the inner mitochondrial membrane for rapid steroidogenesis. Although steroid hormones were synthesized in the rat placenta, the developmental expression of StAR has been poorly understood in the rat placenta during mid-late pregnancy. Therefore, the aim of the present study was to establish the expression and localization of StAR mRNA in the rat placenta during mid-late pregnancy using Northern blots and in situ hybridization. The Northern blot analysis showed that the StAR mRNA expression significantly changed as the gestation day (GD) progressed. The placental expression of StAR mRNA increased between GD 11 and 13, and then slightly decreased until term. In situ hybridization showed a strong StAR expression in giant trophoblast cells on GD 11 and 13, and a moderate expression in trophoblast and stroma cells within the villi of the labyrinth zone throughout the pregnancy. In this study, we reveal for the first time the existence of StAR mRNA in steroidogenic cells of the placenta during mid-late pregnancy. In conclusion, our results suggest that StAR may regulate steroidogenesis in the rat placenta to maintain the pregnancy and developing the fetus.     

Recombinant insect cell expression and purification of human beta-secretase (BACE-1) for X-ray crystallography

Human beta-secretase (BACE-1) is a type I integral membrane aspartic protease that catalyzes the internal cleavage of the amyloid precursor protein (APP), generating the N-terminus of the Abeta peptide. The generation and subsequent extracellular deposition of Abeta(1-42) peptide into amyloid plaques in the brain constitute one of the hallmarks of Alzheimer's disease (AD), a common debilitating neurodegenerative disorder. Inhibition of BACE-1 is considered an excellent therapeutic strategy against AD. To generate pure enzyme for protein crystallography and subsequent structure-based drug design, we have expressed a soluble, unglycosylated, 6xHis-tagged form of proBACE-1 in insect cells using baculovirus infection. To avoid production of a mixture of the pro-enzyme form and the mature form of BACE-1, the proprotein convertase furin was coexpressed with proBACE-1, leading to almost complete proteolytic activation of the recombinant enzyme. The mature enzyme was secreted in the conditioned medium of BACE-1/furin coinfected HighFive insect cells. Secreted BACE-1 protein was purified to homogeneity from the medium using subsequent Ni-chelate affinity chromatography, anion-exchange chromatography, hydrophobic interaction chromatography, and gel filtration. To avoid autoproteolysis, all purification steps were performed at pH values outside the activity range of BACE-1. The purified, biologically active enzyme was homogeneous on SDS/PAGE and had the expected sequence and molecular mass determined by N-terminal amino acid sequencing and mass spectrometry, respectively. Moreover, the preparation showed a single peak of the expected size with only 17% polydispersity using dynamic light scattering analysis. The yield of BACE-1 from fermentation cultures was approximately 0.1mg pure enzyme per liter of cell culture medium. The purified protein was successfully used to generate BACE-1/inhibitor co-crystals and to determine the crystal structure of the complex by X-ray analysis. The availability of substantial quantities of active, homogeneous enzyme will be of great help in future structure-based drug design efforts in the search for efficient protease inhibitor drugs to treat AD.     

Two neolignans from Perilla frutescens and their inhibition of nitric oxide synthase and tumor necrosis factor-alpha expression in murine macrophage cell line RAW 264.7

Two neolignans were isolated from leaves of Perilla frutescens (Labiatae) as inhibitors of nitric oxide syntheses (IC50 5.9 microM and 53.5 microM, respectively) and tumor necrosis factor-alpha in lipopolysaccharide-activated RAW 264.7 cells. Their structures were identified as 1beta,2alpha,3beta,4alpha-1,2-dimethyl-3,4-bis-(2,4,5-trimethoxyphenyl)-cyclobutane (magnosalin), and 1alpha,2beta,3beta,4alpha-1,2-dimethyl-3,4-bis-(2,4,5-trimethoxyphenyl)-cyclobutane (andamanicin), and their activities were confirmed as resulted from the suppressed expression of inducible nitric oxide synthase enzyme and from the secretion of tumor necrosis factor-alpha from activated macrophages.