Fetal liver development requires a paracrine action of oncostatin M through the gp130 signal transducer

Fetal liver, the major site of hematopoiesis during embryonic development, acquires additional various metabolic functions near birth. Although liver development has been characterized biologically as consisting of several distinct steps, the molecular events accompanying this process are just beginning to be characterized. In this study, we have established a novel culture system of fetal murine hepatocytes and investigated factors required for development of hepatocytes. We found that oncostatin M (OSM), an interleukin-6 family cytokine, in combination with glucocorticoid, induced maturation of hepatocytes as evidenced by morphological changes that closely resemble more differentiated hepatocytes, expression of hepatic differentiation markers and intracellular glycogen accumulation. Consistent with these in vitro observations, livers from mice deficient for gp130, an OSM receptor subunit, display defects in maturation of hepatocytes. Interestingly, OSM is expressed in CD45(+) hematopoietic cells in the developing liver, whereas the OSM receptor is expressed predominantly in hepatocytes. These results suggest a paracrine mechanism of hepatogenesis; blood cells, transiently expanding in the fetal liver, produce OSM to promote development of hepatocytes in vivo.     

Antioxidative polyphenols from berries of Pimenta dioica

The ethyl acetate-soluble part of allspice, berries of Pimenta dicica, showed strong antioxidant activity and radical-scavenging activity against 1,1diphenyl-2-picrylhydrazl (DPPH) radical. From the ethyl acetate-soluble part, two new compounds, 5-galloyloxy-3-4-dihydroxypentanoic acid and 5-(5-carboxmethyl-2-oxocyclopenty)3Z-penteny 6-O-galloy-beta-D-glucoside were isolated together with 11 known polyphenols by repeated column chromatography. Their structures were elucidated on the basis of MS and various NMR spectroscopic data. All isolated compounds were evaluated for antioxidative effects on oxidation of methyl linoleate under aeration and heating, anf on peroxidation of liposome induced by 2-2'-azobis-(2-amidinopropane)dihydrocloride (AAPH) as water-soluble initiator along with their radical-scavenging activity against DPPH. Quercetin and its glycoside showed remarkable activity for scavenging DPPH radical and inhibiting peroxidation of liposome. Two new compounds also exhibited strong DPPH radical-scavenging activity and inhibitory effect on the peroxidation od liposome as myricetin.     

Design and synthesis of dysidiolide analogs from vitamin D3: novel class of Cdc25A inhibitors

Potent dysidiolide analogs were synthesized by structural hybridization of dysidiolide and vitamin D(3). These analogs exhibited strong inhibitory activity toward dual-specificity phosphatase Cdc25A (IC(50)=0.44-0.89 microM).     

Structure of the model peptides of Bombyx mori silk-elastin like protein studied with solid state NMR

The peptides (AG)(6)(VPGVG)(AG)(7) and (AG)(5)(VPGVG)(2)(AG)(5) are models for a new type of protein with both composition and properties such as Bombyx mori silk and elastin. In this paper, we report the solid-state NMR results for these samples and related peptides; the structures after dialysis of the 9 M LiBr aqueous solution and after treatment with formic acid were determined and compared. The detailed structural analyses were performed using deconvolution subroutines assuming Gaussian line shapes for the Ala Cbeta peaks of the (AG)(n) sequences in these peptides. The peptide (AG)(6)(VPGVG)(AG)(7) took the silk II structure after the dialysis, which is in contrast to the silk I form of (AG)(15) after the same treatment. However, a drastic structural change of the (AG)(n) sequences was observed for (AG)(5)(VPGVG)(2)(AG)(5); the fraction of distorted beta-turn was 81% after the dialysis, but the distorted beta-sheet became dominant (84%) after treatment with formic acid. The local structures of the Gly residue of the VG units in the elastin-like subunits, (VPGVG) and (VPGVG)(2), were the distorted structures with a distribution of the torsion angles, which was derived from the 2D spin diffusion NMR spectral pattern of (AG)(5)VPG[1-(13)C]V[1-(13)C]GVPGVG(AG)(5). Observation of this distribution of the Gly residue was independent of the treatment, dialysis or formic acid.     

Testing the relationship between foldability and the early folding events of dihydrofolate reductase from Escherichia coli

A "folding element" is a contiguous peptide segment crucial for a protein to be foldable and is a new concept that could assist in our understanding of the protein-folding problem. It is known that the presence of the complete set of folding elements of dihydrofolate reductase (DHFR) from Escherichia coli is essential for the protein to be foldable. Since almost all of the amino acid residues known to be involved in the early folding events of DHFR are located within the folding elements, a close relationship between the folding elements and early folding events is hypothesized. In order to test this hypothesis, we have investigated whether or not the early folding events are preserved in circular permutants and topological mutants of DHFR, in which the order of the folding elements is changed but the complete set of folding elements is present. The stopped-flow circular dichroism (CD) measurements show that the CD spectra at the early stages of folding are similar among the mutants and the wild-type DHFR, indicating that the presence of the complete set of folding elements is sufficient to preserve the early folding events. We have further examined whether or not sequence perturbation on the folding elements by a single amino acid substitution affects the early folding events of DHFR. The results show that the amino acid substitutions inside of the folding elements can affect the burst-phase CD spectra, whereas the substitutions outside do not. Taken together, these results indicate that the above hypothesis is true, suggesting a close relationship between the foldability of a protein and the early folding events. We propose that the folding elements interact with each other and coalesce to form a productive intermediate(s) early in the folding, and these early folding events are important for a protein to be foldable.     

Cyclic AMP induces phosphorylation of claudin-5 immunoprecipitates and expression of claudin-5 gene in blood-brain-barrier endothelial cells via protein kinase A-dependent and -independent pathways

Cyclic AMP (cAMP) promotes functions of tight junctions in endothelial cells, although its target remains unknown. We showed here that cAMP increased gene expression of claudin-5 and decreased that of claudin-1 in porcine blood-brain-barrier endothelial cells via protein kinase A (PKA)-independent and -dependent pathways, respectively. cAMP also enhanced immunoreactivity of claudin-5 along cell borders and in the cytoplasm, reorganized actin filaments, and altered signals of claudin-5, occludin, ZO-1, and ZO-2 along cell boundaries from zipperlike to linear patterns. In contrast, claudin-1 was detected only in the cytoplasm in a dotlike pattern, and its immunolabeling was reduced by cAMP. Interestingly, 31- and 62-kDa claudin-5 immunoprecipitates in the NP-40-soluble and -insoluble fractions, respectively, were highly phosphorylated on threonine residue(s) upon cAMP treatment. All these changes induced by cAMP, except for claudin-5 expression and its signals in the cytoplasm, were reversed by an inhibitor of PKA, H-89. We also demonstrated that cAMP elevated the barrier function of tight junctions in porcine blood-brain-barrier endothelial cells in PKA-dependent and -independent manners. These findings indicate that both PKA-induced phosphorylation of claudin-5 immunoprecipitates and cAMP-dependent but PKA-independent induction of claudin-5 expression could be involved in promotion of tight-junction function in endothelial cells.     

A neural network to predict melting temperature (Tm) of RNA duplex

A straightforward method to predict RNA duplex stability by neural network is described. The best network consists of three layers in which the input layer units are 12 (frequencies of 10 nearest-neighbors and 2 terminals), the hidden layer units are 3 and the output layer unit is 1 (measured Tm). This method to predict Tm has the advantage that the determinations of thermodynamic parameters is not needed.     

The N-terminal region of Sgs1, which interacts with Top3, is required for complementation of MMS sensitivity and suppression of hyper-recombination in sgs1 disruptants

The SGS1 gene of Saccharomyces (cerevisiae is a homologue of the genes affected in Bloom's syndrome, Werner's syndrome, and Rothmund-Thomson's syndrome. Disruption of the SGS1 gene is associated with high sensitivity to methyl methanesulfonate (MMS) and hydroxyurea (HU), and with hyper-recombination phenotypes, including interchromosomal recombination between heteroalleles. SGS1 encodes a protein which has a helicase domain similar to that of Escherichia coli RecQ. A comparison of amino acid sequences among helicases of the RecQ family reveals that Sgs1,WRN, and BLM share a conserved region adjacent to the C-terminal part of the helicase domain (C-terminal conserved region). In addition, Sgs1 contains two highly charged acidic regions in its N-terminal region and the HRDC (helicase and RNaseD C-terminal) domain at its C-terminal end. These regions were also found in BLM and WRN, and in Rqh1 from Schizosaccharomyces pombe. In this study, we demonstrate that the C-terminal conserved region, as well as the helicase motifs, of Sgs1 are essential for complementation of MMS sensitivity and suppression of hyper-recombination in sgs1 mutants. In contrast, the highly charged acidic regions, the HRDC domain, and the C-terminal 252 amino acids were dispensable for the complementation of these phenotypes. Surprisingly, the N-terminal 45 amino acids of Sgs1 were absolutely required for the suppression of the above phenotypes. Introduction of missense mutations into the region encoding amino acids 4-13 abolished the ability of Sgsl to complement MMS sensitivity and suppress hyper-recombination in sgs1 mutants, and also prevented its interaction with Top3, indicating that interaction with Top3 via the N-terminal region of Sgs1 is involved in the complementation of MMS sensitivity and the suppression of hyper-recombination.     

Fast compaction of alpha-lactalbumin during folding studied by stopped-flow X-ray scattering

To monitor the fast compaction process during protein folding, we have used a stopped-flow small-angle X-ray scattering technique combined with a two-dimensional charge-coupled device-based X-ray detector that makes it possible to improve the signal-to-noise ratio of data dramatically, and measured the kinetic refolding reaction of alpha-lactalbumin. The results clearly show that the radius of gyration and the overall shape of the kinetic folding intermediate of alpha-lactalbumin are the same as those of the molten globule state observed at equilibrium. Thus, the identity between the kinetic folding intermediate and the equilibrium molten globule state is firmly established. The present results also suggest that the folding intermediate is more hydrated than the native state and that the hydrated water molecules are dehydrated when specific side-chain packing is formed during the change from the molten globule to the native state.