WRN counteracts the NHEJ pathway upon camptothecin exposure

We investigated the function of the interaction between WRN (Werner syndrome gene product) and Ku70 and between WRN and DNA-PKcs, which are components of the DNA-PKcs/Ku70/Ku80 complex, by generating KU70(-/-)/WRN(-/-) and DNA-PKcs(-/-/-)/WRN(-/-) double-gene knockout chicken DT40 cells. When treated with camptothecin (CPT), an inhibitor of DNA topoisomerase I, WRN(-/-) cells showed higher sensitivity than wild-type cells, whereas KU70(-/-) and DNA-PKcs(-/-/-) cells showed hyper-resistance. Disruption of KU70 or DNA-PKcs suppressed the sensitivity of WRN(-/-) cells to CPT, rendering them as resistant to CPT treatment as KU70(-/-) and DNA-PKcs(-/-/-) cells. On the other hand, CPT sensitivity of BLM(-/-) cells, which are defective in a RecQ helicase similar to WRN, was enhanced by deletion of KU70. The implications for the function of WRN in the non-homologous end-joining pathway of DNA repair involving Ku70 and DNA-PKcs, which may be the cause of lethality in the presence of CPT, will be discussed.     

The interplay of processivity, substrate inhibition and a secondary substrate binding site of an insect exo-beta-1,3-glucanase

Abracris flavolineata midgut contains a processive exo-beta-glucanase (ALAM) with lytic activity against Saccharomyces cerevisiae, which was purified (yield, 18%; enrichment, 37 fold; specific activity, 1.89 U/mg). ALAM hydrolyses fungal cells or callose from the diet. ALAM (45 kDa; pI 5.5; pH optimum 6) major products with 0.6 mM laminarin as substrate are beta-glucose (61%) and laminaribiose (39%). Kinetic data obtained with laminaridextrins and methylumbelliferyl glucoside suggest that ALAM has an active site with at least six subsites. The best fitting of kinetic data to theoretical curves is obtained using a model where one laminarin molecule binds first to a high-affinity accessory site, causing active site exposure, followed by the transference of the substrate to the active site. The two-binding-site model is supported by results from chemical modifications of amino acid residues and by ALAM action in MUbetaGlu plus laminarin. Low laminarin concentrations increase the modification of His, Tyr and Asp or Glu residues and MUbetaGlu hydrolysis, whereas high concentrations abolish modification and inhibit MUbetaGlu hydrolysis. Our data indicate that processivity results from consecutive transferences of substrate between accessory and active site and that substrate inhibition arises when both sites are occupied by substrate molecules abolishing processivity.     

Lack of Correlation between the Kinase Activity of LRRK2 Harboring Kinase-Modifying Mutations and Its Phosphorylation at Ser910, 935, and Ser955

Leucine-rich repeat kinase 2 (LRRK2) is extensively phosphorylated in cells within a region amino-terminal to the leucine-rich repeat domain. Since phosphorylation in this region of LRRK2, including Ser910, Ser935, Ser955, and Ser973, is significantly downregulated upon treatment with inhibitors of LRRK2, it has been hypothesized that signaling pathways downstream of the kinase activity of LRRK2 are involved in regulating the phosphorylation of LRRK2, although the precise mechanism has remained unknown. Here we examined the effects of LRRK2 inhibitors on the phosphorylation state at Ser910, Ser935, and Ser955 in a series of kinase-inactive mutants of LRRK2. We found that the responses of LRRK2 to the inhibitors varied among mutants, in a manner not consistent with the above-mentioned hypothesis. Notably, one of the kinase-inactive mutants, T2035A LRRK2, underwent phosphorylation, as well as the inhibitor-induced dephosphorylation, at Ser910, Ser935, and Ser955, to a similar extent to those observed with wild-type LRRK2. These results suggest that the kinase activity of LRRK2 is not involved in the common mechanism of inhibitor-induced dephosphorylation of LRRK2.     

Identification of Novel Regulatory Cholesterol Metabolite, 5-Cholesten, 3β,25-Diol,Disulfate

Oxysterol sulfation plays an important role in regulation of lipid metabolism and inflammatory responses. In the present study, we report the discovery of a novel regulatory sulfated oxysterol in nuclei of primary rat hepatocytes after overexpression of the gene encoding mitochondrial cholesterol delivery protein (StarD1). Forty-eight hours after infection of the hepatocytes with recombinant StarD1 adenovirus, a water-soluble oxysterol product was isolated and purified by chemical extraction and reverse-phase HPLC. Tandem mass spectrometry analysis identified the oxysterol as 5-cholesten-3β, 25-diol, disulfate (25HCDS), and confirmed the structure by comparing with a chemically synthesized compound. Administration of 25HCDS to human THP-1-derived macrophages or HepG2 cells significantly inhibited cholesterol synthesis and markedly decreased lipid levels in vivo in NAFLD mouse models. RT-PCR showed that 25HCDS significantly decreased SREBP-1/2 activities by suppressing expression of their responding genes, including ACC, FAS, and HMG-CoA reductase. Analysis of lipid profiles in the liver tissues showed that administration of 25HCDS significantly decreased cholesterol, free fatty acids, and triglycerides by 30, 25, and 20%, respectively. The results suggest that 25HCDS inhibits lipid biosynthesis via blocking SREBP signaling. We conclude that 25HCDS is a potent regulator of lipid metabolism and propose its biosynthetic pathway.     

Enhancement of permeability in endothelial cells for the development of an antithrombogenic bioartificial hemofilter

For the development of an antithrombogenic bioartificial hemofilter, in which the inner surface of hollow fibers is lined by endothelial cells, it is essential to increase the permeability of the cells in order to achieve a sufficient ultrafiltrate. We tried to increase it by using an actin microfilament polymerization inhibitor, cytochalasin B (CyB). Fifty microg/mL CyB was added for 2 h to the culture medium of confluent rat glomerular endothelial cells (RGEC) and human umbilical vein endothelial cells (HUVEC). Under the 130 mmHg hydrostatic pressure, the CyB-treated group produced significantly more ultrafiltration than the non-treated control group and this increase was maintained for at least 7 days. Horseradish peroxidase (HRP) permeability acutely and reversibly increased in the CyB-treated group compared with the non-treated control group. Scanning electron microscopy revealed a larger average diameter and increased number of fenestrae on the CyB-treated endothelial cells, compared with the non-treated cells. This phenomenon also lasted for at least 7 days. The platelet adherence test showed that CyB did not deteriorate the antithrombogenic property of endothelial cells. These results indicate that CyB is potentially applicable for the enhancement of endothelial cell permeability in an antithrombogenic bioartificial hemofilter.     

<Emphasis Type="Italic">Pichia stipitis</Emphasis> xylose reductase helps detoxifying lignocellulosic hydrolysate by reducing 5-hydroxymethyl-furfural (HMF)

Background  

Pichia stipitis xylose reductase (Ps-XR) has been used to design Saccharomyces cerevisiae strains that are able to ferment xylose. One example is the industrial S. cerevisiae xylose-consuming strain TMB3400, which was constructed by expression of P. stipitis xylose reductase and xylitol dehydrogenase and overexpression of endogenous xylulose kinase in the industrial S. cerevisiae strain USM21.     

Reduced natural selection associated with low recombination in Drosophila melanogaster

Synonymous codons are not used equally in many organisms, and the extent of codon bias varies among loci. Earlier studies have suggested that more highly expressed loci in Drosophila melanogaster are more biased, consistent with findings from several prokaryotes and unicellular eukaryotes that codon bias is partly due to natural selection for translational efficiency. We link this model of varying selection intensity to the population-genetics prediction that the effectiveness of natural selection is decreased under reduced recombination. In analyses of 385 D. melanogaster loci, we find that codon bias is reduced in regions of low recombination (i.e., near centromeres and telomeres and on the fourth chromosome). The effect does not appear to be a linear function of recombination rate; rather, it seems limited to regions with the very lowest levels of recombination. The large majority of the genome apparently experiences recombination at a sufficiently high rate for effective natural selection against suboptimal codons. These findings support models of the Hill-Robertson effect and genetic hitchhiking and are largely consistent with multiple reports of low levels of DNA sequence variation in regions of low recombination.