The structure-activity relationships of mansonone F, a potent anti-MRSA sesquiterpenoid quinone: SAR studies on the C6 and C9 analogs

For the systematic SAR study on mansonone F, a series of C6 and C9 analogs of mansonone F have been synthesized and their anti-MRSA activities were evaluated. Most of the analogs exhibited good or excellent anti-MRSA activities. In particular, the 6-n-butylmansonone F showed fourfold higher antibacterial activities compared to that of vancomycin.     

Inhibition of matrix metalloproteinase-9 prevents neutrophilic inflammation in ventilator-induced lung injury

Neutrophils are considered to play a central role in ventilator-induced lung injury (VILI). However, the pulmonary consequences of neutrophil accumulation have not been fully elucidated. Matrix metalloproteinase-9 (MMP-9) had been postulated to participate in neutrophil transmigration. The purpose of this study was to investigate the role of MMP-9 in the neutrophilic inflammation of VILI. Male Sprague-Dawley rats were divided into three groups: 1) low tidal volume (LVT), 7 ml/kg of tidal volume (VT); 2) high tidal volume (HVT), 30 ml/kg of VT; and 3) HVT with MMP inhibitor (HVT+MMPI). As a MMPI, CMT-3 was administered daily from 3 days before mechanical ventilation. Degree of VILI was assessed by wet-to-dry weight ratio and acute lung injury (ALI) scores. Neutrophilic inflammation was determined from the neutrophil count in the lung tissue and myeloperoxidase (MPO) activity in the bronchoalveolar lavage fluid (BALF). MMP-9 expression and activity were examined by immunohistochemical staining and gelatinase zymography, respectively. The wet-to-dry weight ratio, ALI score, neutrophil infiltration, and MPO activity were increased significantly in the HVT group. However, in the HVT+MMPI group, pretreatment with MMPI decreased significantly the degree of VILI, as well as neutrophil infiltration and MPO activity. These changes correlated significantly with MMP-9 immunoreactivity and MMP-9 activity. Most outcomes were significantly worse in the HVT+MMPI group compared with the LVT group. In conclusion, VILI mediated by neutrophilic inflammation is closely related to MMP-9 expression and activity. The inhibition of MMP-9 protects against the development of VILI through the downregulation of neutrophil-mediated inflammation.     

Chromosomal promoter replacement of the isoprenoid pathway for enhancing carotenoid production in E. coli

For metabolic engineering it is advantageous in terms of stability, genetic regulation, and metabolic burden to modulate expression of relevant genes on the chromosome rather than relying on over-expression of the genes on multi-copy vectors. Here we have increased the production of beta-carotene in Escherichia coli by replacing the native promoter of the chromosomal isoprenoid genes with the strong bacteriophage T5 promoter (P(T5)). We recombined PCR fragments with the lambda-Red recombinase to effect chromosomal promoter replacement, which allows direct integration of a promoter along with a selectable marker that can subsequently be excised by the Flp/FRT site-specific recombination system. The resulting promoter-engineered isoprenoid genes were combined by serial P1 transductions into a host strain harboring a reporter plasmid containing beta-carotene biosynthesis genes allowing a visual screen for yellow color indicative of beta-carotene accumulation. Construction of an E. coli P(T5)-dxs P(T5)-ispDispF P(T5)-idi P(T5)-ispB strain resulted in producing high titers (6mg/g dry cell weight) of beta-carotene. Surprisingly, over-expression of the ispB gene, which was expected to divert carbon flow from the isoprenoid pathway to quinone biosynthesis, resulted in increased beta-carotene production. We thus demonstrated that chromosomal promoter engineering of the endogenous isoprenoid pathway yielded high levels of beta-carotene in a non-carotenogenic E. coli. The high isoprenoid flux E. coli can be used as a starting strain to produce various carotenoids by introducing heterologous carotenoid genes.     

Identification of essential amino acid residues in valine dehydrogenase from Streptomyces albus

Cys-29 and Cys-251 of Streptomyces albus valine dehydrogenase (ValDH) were highly conserved in the corresponding region of NAD(P)(+)-dependent amino acid dehydroganase sequences. To ascertain the functional role of these cysteine residues in S. albus ValDH, site-directed mutagenesis was performed to change each of the two residues to serine. Kinetic analyses of the enzymes mutated at Cys-29 and Cys-251 revealed that these residues are involved in catalysis. We also constructed mutant ValDH by substituting valine for leucine at 305 by site-directed mutagenesis. This residue was chosen, because it has been proposed to be important for substrate discrimination by phenylalanine dehydrogenase (PheDH) and leucine dehydrogenase (LeuDH). Kinetic analysis of the V305L mutant enzyme revealed that it is involved in the substrate binding site. However it displayed less activity than the wild type enzyme toward all aliphatic and aromatic amino acids tested.     

Two-locus genome-wide linkage scan for prostate cancer susceptibility genes with an interaction effect

Prostate cancer represents a significant worldwide public health burden. Epidemiological and genetic epidemiological studies have consistently provided data supporting the existence of inherited prostate cancer susceptibility genes. Segregation analyses of prostate cancer suggest that a multigene model may best explain familial clustering of this disease. Therefore, modeling gene–gene interactions in linkage analysis may improve the power to detect chromosomal regions harboring these disease susceptibility genes. In this study, we systematically screened for prostate cancer linkage by modeling two-locus gene–gene interactions for all possible pairs of loci across the genome in 426 prostate cancer families from Johns Hopkins Hospital, University of Michigan, University of Umeå, and University of Tampere. We found suggestive evidence for an epistatic interaction for six sets of loci (target chromosome-wide/reference marker-specific P≤0.0001). Evidence for these interactions was found in two independent subsets from within the 426 families. While the validity of these results requires confirmation from independent studies and the identification of the specific genes underlying this linkage evidence, our approach of systematically assessing gene–gene interactions across the entire genome represents a promising alternative approach for gene identification for prostate cancer.     

Sphingosine-1-phosphate activates BKCa channels independently of G protein-coupled receptor in human endothelial cells

The effect of sphingosine-1-phosphate (S1P) on large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels was examined in primary cultured human umbilical vein endothelial cells by measuring intracellular Ca²⁺ concentration ([Ca²⁺]_i), whole cell membrane currents, and single-channel activity. In nystatin-perforated current-clamped cells, S1P hyperpolarized the membrane and simultaneously increased [Ca²⁺]_i. [Ca²⁺]_i and membrane potentials were strongly correlated. In whole cell clamped cells, BK_Ca currents were activated by increasing [Ca²⁺]_i via cell dialysis with pipette solution, and the activated BK_Ca currents were further enhanced by S1P. When [Ca²⁺]_i was buffered at 1 µM, the S1P concentration required to evoke half-maximal activation was 403 ± 13 nM. In inside-out patches, when S1P was included in the bath solution, S1P enhanced BK_Ca channel activity in a reversible manner and shifted the relationship between Ca²⁺ concentration in the bath solution and the mean open probability to the left. In whole cell clamped cells or inside-out patches loaded with guanosine 5'-O-(2-thiodiphosphate) (GDPS; 1 mM) using a patch pipette, GDPS application or pretreatment of cells with pertussis toxin (100 ng/ml) for 15 h did not affect S1P-induced BK_Ca current and channel activation. These results suggest that S1P enhances BK_Ca channel activity by increasing Ca²⁺ sensitivity. This channel activation hyperpolarizes the membrane and thereby increases Ca²⁺ influx through Ca²⁺ entry channels. Inasmuch as S1P activates BK_Ca channels via a mechanism independent of G protein-coupled receptors, S1P may be a component of the intracellular second messenger that is involved in Ca²⁺ mobilization in human endothelial cells. sphingolipid metabolites; intracellular second messenger; Ca²⁺ mobilization     

Phospholipase Cgamma1 negatively regulates growth hormone signalling by forming a ternary complex with Jak2 and protein tyrosine phosphatase-1B

Growth hormone binds to its membrane receptor (GHR), whereby it regulates many cellular functions, including proliferation, differentiation and chemotaxis. However, although the activation of growth hormone-mediated signalling is well understood, the precise mechanism responsible for its regulation has not been elucidated. Here, we demonstrate that phospholipase Cgamma1 (PLCgamma1) modulates the action of growth hormone-mediated signalling by interacting with tyrosine kinase Jak2 (janus kinase 2) in a growth hormone-dependent manner. In the absence of PLCgamma1 (PLCgamma1(-/-)), growth hormone-induced JAK2 and STAT5 phosphorylation significantly increased in mouse embryonic fibroblasts (MEFs). Furthermore, the re-expression of PLCgamma1 reduced growth hormone-induced Jak2 activation. Growth hormone-induced Jak2 phosphorylation was enhanced by siRNA-specific knockdown of PLCgamma1. Interestingly, PLCgamma1 physically linked Jak2 and protein tyrosine phosphatase-1B (PTP-1B) by binding to both using different domains, and this process was implicated in the modulation of cytokine signalling through Jak2. In addition, in PLCgamma1(-/-) MEFs, growth hormone-dependent c-Fos activation was upregulated and growth hormone-induced proliferation was potentiated. These results suggest that PLCgamma1 has a key function in the regulation of growth hormone-mediated signalling by negatively regulating Jak2 activation.