Synthesis and applications of stereospecifically (3)H-labeled arachidonic acids as mechanistic probes for lipoxygenase and cyclooxygenase catalysis

Stereospecifically (3)H-labeled substrates are useful tools in studying the mechanism of hydrogen abstractions involved in the oxygenation of polyunsaturated fatty acids. Here, we describe modified methods for the synthesis of arachidonic acids labeled with a single chiral tritium on the methylene groups at carbons 10 or 13. The appropriate starting material is a ketooctadecanoic acid which is prepared from an unsaturated C18 fatty acid precursor or by total synthesis. The (3)H label is introduced by NaB(3)H(4) reduction and the resulting tritiated hydroxy fatty acid then is tosylated, separated into the enantiomers by chiral phase HPLC, and subsequently transformed into stearic acids. A variety of stereospecifically labeled unsaturated fatty acids are obtained using literature methods of microbial transformation with the fungus Saprolegnia parasitica. Two applications are described: (i) In incubations of [10S-(3)H]- and [10R-(3)H]arachidonic acids in human psoriatic scales we show that a 12R-lipoxygenase accounts not only for synthesis of the major product 12R-HETE, but it contributes also, through subsequent isomerization, to the minor amounts of 12S-HETE. (ii) The [10R-(3)H]- and [10S-(3)H]arachidonic acids were also used to demonstrate that prostaglandin ring formation by cyclooxygenases does not involve carbocation formation at C-10 of arachidonic acid as was hypothesized recently.     

Identification and characterization of a Na(+)-independent neutral amino acid transporter that associates with the 4F2 heavy chain and exhibits substrate selectivity for small neutral D- and L-amino acids

A cDNA was isolated from the mouse brain that encodes a novel Na(+)-independent neutral amino acid transporter. The encoded protein, designated as Asc-1 (asc-type amino acid transporter 1), was found to be structurally related to recently identified mammalian amino acid transporters for the transport systems L, y(+)L, x(C)(-), and b(0,+), which are linked, via a disulfide bond, to the type II membrane glycoproteins, 4F2 heavy chain (4F2hc), or rBAT (related to b(0,+) amino acid transporter). Asc-1 required 4F2hc for its functional expression. In Western blot analysis in the nonreducing condition, a 118-kDa band, which seems to correspond to the heterodimeric complex of Asc-1 and 4F2hc, was detected in the mouse brain. The band shifted to 33 kDa in the reducing condition, confirming that Asc-1 and 4F2hc are linked via a disulfide bond. Asc-1-mediated transport was not dependent on the presence of Na(+) or Cl(-). Although Asc-1 showed a high sequence homology (66% identity at the amino acid level) to the Na(+)-independent broad scope neutral amino acid transporter LAT2 (Segawa, H., Fukasawa, Y., Miyamoto, K., Takeda, E., Endou, H., and Kanai, Y. (1999) J. Biol. Chem. 274, 19745-19751), Asc-1 also exhibited distinctive substrate selectivity and transport properties. Asc-1 preferred small neutral amino acids such as Gly, L-Ala, L-Ser, L-Thr, and L-Cys, and alpha-aminoisobutyric acid as substrates. Asc-1 also transported D-isomers of the small neutral amino acids, in particular D-Ser, a putative endogenous modulator of N-methyl-D-aspartate-type glutamate receptors, with high affinity. Asc-1 operated preferentially, although not exclusively, in an exchange mode. Asc-1 mRNA was detected in the brain, lung, small intestine, and placenta. The functional properties of Asc-1 seem to be consistent with those of a transporter subserving the Na(+)-independent small neutral amino acid transport system asc.     

Molecular cloning and characterization of multispecific organic anion transporter 4 expressed in the placenta

A cDNA encoding a novel multispecific organic anion transporter, OAT4, was isolated from a human kidney cDNA library. The OAT4 cDNA consisted of 2210 base pairs that encoded a 550-amino acid residue protein with 12 putative membrane-spanning domains. The amino acid sequence of OAT4 showed 38 to 44% identity to those of other members of the OAT family. Northern blot analysis revealed that OAT4 mRNA is abundantly expressed in the placenta as well as in the kidney. When expressed in Xenopus oocytes, OAT4 mediated the high affinity transport of estrone sulfate (K(m) = 1.01 microM) and dehydroepiandrosterone sulfate (K(m) = 0.63 microM) in a sodium-independent manner. OAT4 also mediated the transport of ochratoxin A. OAT4-mediated transport of estrone sulfate was inhibited by several sulfate conjugates, such as p-nitrophenyl sulfate, alpha-naphthyl sulfate, beta-estradiol sulfate, and 4-methylumbelliferyl sulfate. By contrast, glucuronide conjugates showed little or no inhibitory effect on the OAT4-mediated transport of estrone sulfate. OAT4 interacted with chemically heterogeneous anionic compounds, such as nonsteroidal anti-inflammatory drugs, diuretics, sulfobromophthalein, penicillin G, and bile salts, whereas tetraethylammonium, an organic cation, did not. OAT4 is the first member of the multispecific organic anion transporter family, which is expressed abundantly in the placenta. OAT4 might be responsible for the elimination and detoxification of harmful anionic substances from the fetus.     

Upregulation of vascular endothelial growth factor receptors Flt-1 and Flk-1 following acute spinal cord contusion in rats.

To investigate the possible role of vascular endothelial growth factor (VEGF) in the injured spinal cord, we analyzed the distribution and time course of the two tyrosine kinase receptors for VEGF, Flt-1 and Flk-1, in the rat spinal cord following contusion injury using a weight-drop impactor. The semi-quantitative RT-PCR analysis of Flt-1 and Flk-1 in the spinal cord showed slight upregulation of these receptors following spinal cord injury. Although mRNAs for Flt-1 and Flk-1 were constitutively expressed in neurons, vascular endothelial cells, and some astrocytes in laminectomy control rats, their upregulation was induced in association with microglia/macrophages and reactive astrocytes in the vicinity of the lesion within 1 day in rats with a contusion injury and persisted for at least 14 days. The spatiotemporal expression of Flt-1 in the contused spinal cord mirrored that of Flk-1 expression. In the early phase of spinal cord injury, upregulation of Flt-1 and Flk-1 mRNA occurred in microglia/macrophages that infiltrated the lesion. In addition, the expression of both receptors increased progressively in reactive astrocytes within the vicinity of the lesion, predominately in the white matter, and almost all reactive astrocytes coexpressed Flt-1 or Flk-1 and nestin. These results suggest that VEGF may be involved in the inflammatory response and the astroglial reaction to contusion injuries of the spinal cord via specific VEGF receptors.     

Molecular authentication of ginseng cultivars by comparison of internal transcribed spacer and 5.8S rDNA sequences

Molecular authentication among three Panax species and within cultivars and accessions of P. ginseng was investigated using the DNA sequence in the ribosomal ITS1–5.8S–ITS2 region. Four single-nucleotide polymorphisms were identified between P. ginseng and other Panax species. In the electrophoresis profile, obtained after digestion with the enzyme TaqI, three fingerprinting patterns were obtained from cultivars and accessions of Panax species. Consequently, this authentication procedure based upon the restriction fragment length polymorphism in the ribosomal ITS1–5.8S–ITS2 region can now be utilized to differentiate these Panax species as well as major Korean cultivars such as Gopoong and Kumpoong from other cultivars and accessions in Panax species at the DNA level. O. T. Kim and K. H. Bang contributed equally to this paper.     

Functional characterization of <Emphasis Type="Italic">Vibrio cholerae</Emphasis> O1 WbeW enzyme responsible for initial reaction in O antigen biosynthesis

Vibrio cholerae O1 employs the ATP-binding cassette (ABC) transporter-dependent pathway for O antigen biosynthesis. Different from highly studied Klebsiella pneumoniae and Escherichia coli, it was reported that initial reaction of O antigen biosynthesis in V. cholerae O1 may be involved in WbeW protein, which is predicted to be a galactosyltransferase. In this work, we report expression and characterization of WbeW enzyme. WbeW was expressed as membrane-associated form in E. coli and it was obtained with high purity. The enzyme had a function of transferring Gal-1-P from UDP-Gal to Und-P, implying that initial glycan of O antigen in V. cholerae O1 can be composed of a Gal residue.     

A neutralizable epitope is induced on HGF upon its interaction with its receptor cMet

A new conformational neutralizable epitope is created on heptocyte growth factor (HGF), when it interacts with its receptor, cMet. By immunizing rabbits with HGF-cMet complex, we successfully generated a monoclonal antibody (SFN68) that inhibits HGF-cMet interaction, and blocks the biological function mediated by HGF. To define the epitope, we screened out an epitope-mimicking peptide, KSLSRHDHIHHH, from a phage display of combinatorial peptide library. In molecular mimicry this peptide bound to cMet and inhibited HGF-cMet interaction. No humoral response was induced to this epitope-mimicking peptide when immunization was done with HGF alone.     

Tributyltin and triphenyltin inhibit osteoclast differentiation through a retinoic acid receptor-dependent signaling pathway

Organotin compounds, such as tributyltin (TBT) and triphenyltin (TPT), have been widely used in agriculture and industry. Although these compounds are known to have many toxic effects, including endocrine-disrupting effects, their effects on bone resorption are unknown. In this study, we investigated the effects of organotin compounds, such as monobutyltin (MBT), dibutyltin (DBT), TBT, and TPT, on osteoclast differentiation using mouse monocytic RAW264.7 cells. MBT and DBT had no effects, whereas TBT and TPT dose-dependently inhibited osteoclast differentiation at concentrations of 3-30 nM. Treatment with a retinoic acid receptor (RAR)-specific antagonist, Ro41-5253, restored the inhibition of osteoclastogenesis by TBT and TPT. TBT and TPT reduced receptor activator of nuclear factor-kappaB ligand (RANKL) induced nuclear factor of activated T cells (NFAT) c1 expression, and the reduction in NFATc1 expression was recovered by Ro41-5253. Our results suggest that TBT and TPT suppress osteoclastogenesis by inhibiting RANKL-induced NFATc1 expression via an RAR-dependent signaling pathway.     

Bioconversion of 12-, 14-, and 16-membered ring aglycones to glycosylated macrolides in an engineered strain of <Emphasis Type="Italic">Streptomyces venezuelae</Emphasis>

To develop a system for combinatorial biosynthesis of glycosylated macrolides, Streptomyces venezuelae was genetically manipulated to be deficient in the production of its macrolide antibiotics by deletion of the entire biosynthetic gene cluster encoding the pikromycin polyketide synthases and desosamine biosynthetic enzymes. Two engineered deoxysugar biosynthetic pathways for the biosynthesis of thymidine diphosphate (TDP)-d-quinovose or TDP-d-olivose in conjunction with the glycosyltransferase–auxiliary protein pair DesVII/DesVIII derived from S. venezuelae were expressed in the mutant strain. Feeding the representative 12-, 14-, and 16-membered ring macrolactones including 10-deoxymethynolide, narbonolide, and tylactone, respectively, to each mutant strain capable of producing TDP-d-quinovose or TDP-d-olivose resulted in the successful production of the corresponding quinovose- and olivose-glycosylated macrolides. In mutant strains where the DesVII/DesVIII glycosyltransferase–auxiliary protein pair was replaced by TylMII/TylMIII derived from Streptomyces fradiae, quinovosyl and olivosyl tylactone were produced; however, neither glycosylated 10-deoxymethynolide nor narbonolide were generated, suggesting that the glycosyltransferase TylMII has more stringent substrate specificity toward its aglycones than DesVII. These results demonstrate successful generation of structurally diverse hybrid macrolides using a S. venezuelae in vivo system and provide further insight into the substrate flexibility of glycosyltransferases. Won Seok Jung and Ah Reum Han contributed equally to this work.