Peptide analysis,stability studies,and structural modeling explain contradictory peptide motifs and unique properties of the NOD mouse MHC class II molecule H2-A(g7)

The MHC class II molecule H2-A(g7) is the chief genetic determinant in insulin-dependent diabetes mellitus of the non-obese diabetic (NOD) mice. Poor peptide binding ability, as well as presentation of a unique subset of peptides by this molecule was suggested to promote autoimmunity in this strain. However, several laboratories have presented results in favor of an H2-A(g7) molecule that can avidly bind many different peptides. The crystal structures of H2-A(g7) in complex with two different peptides did not completely resolve this issue. To analyze the peptide binding capacity and the motif requirements of H2-A(g7), we eluted natural ligands from purified H2-A(g7) molecules isolated from the H2-A(g7)-transfected M12-C3 cells. A low peptide yield dominated by a few peptide ligands was found. Pool sequencing and alignment of individual ligands on the basis of molecular modeling revealed a peptide-binding motif with basic/aliphatic/small hydrophilic amino acids at relative position 1 (p1), aliphatic amino acids at p4, Ala at p6, and acidic amino acids and Ser/Gly at p9, as well as acidic residues at p10/11. Though weak, the binding of individual ligands, as well as the importance of an acidic C-terminal residue was confirmed by peptide binding studies to isolated H2-A(g7) molecules. Furthermore, the H2-A(g7) molecule incompletely dissociated into its constituent chains in SDS-electrophoresis under nonreducing conditions. This provides additional evidence of its weak affinity for peptides, which probably arises from the combination of beta56His/beta57Ser/beta78Ala and other unique H2-A(g7) residues in contact with the antigenic peptide. These results allow a better understanding of the role of this molecule in the development of autoimmunity and the identification of epitopes relevant to diabetes.     

Synthesis and properties of thermotropic liquid-crystalline polymers containing transition metals

New thermotropic, liquid-crystalline polyesters ( 5a, b, 6a, b ) with mesogenic bipyridinediyl units were synthesized. They form complexes with Fe(II) and Cu(II) salts. Homopolyesters 5a, b , containing no metal or less than a certain amount of metal, are smectic. A nematic mesophase was observed in the case of copolyester 6a, b . The structural properties of a polyester complex 5a with Cu, as crystal, liquid-crystal and isotropic liquid, were examined by ESR.     

Ocular tracking of moving targets: effects of perturbing the background

Primates are able to track a moving target with their eyes, even when the target is seen against a stationary textured background. In this situation, the tracking eye movement induces motion of the background images on the retina (reafference) that competes with the motion of the target's retinal image, potentially disrupting the tracking of the target. Previous work on humans reported that brief perturbations of the background in the opposite direction to pursuit were much less disruptive than perturbations in the same direction as pursuit. Furthermore, if the background moved together with the pursuit target--so as to effectively eliminate the reafference--then the effects of a subsequent background perturbation showed less dependence on direction. This suggested that the direction selectivity to background perturbations during pursuit against a stationary background was due, at least in part, to the prior motion of the background secondary to the pursuit. We now report similar findings in monkeys, and in addition, have investigated the effect of moving the background while the animal was fixating a stationary target. In this situation, the ocular tracking responses to subsequent brief perturbations of the moving background were weaker when the perturbations were in the same direction as the prior background motion than when in the opposite direction. This suggests that the selective insensitivity to the reafferent visual input associated with pursuit across a stationary background is, at least in part, independent of pursuit per se and attributable to a progressive reduction in the sensitivity to sustained background motion.     

XIdax, an inhibitor of the canonical Wnt pathway, is required for anterior neural structure formation in Xenopus.

Wnt signaling pathways are involved during various stages in the development of many species. In Xenopus, the accumulation of beta-catenin on the dorsal side of embryo is required for induction of the organizer, while the head structure formation requires inhibition of Wnt signaling. Here, we report a role for xIdax, a negative regulator of Wnt signaling. XIdax is expressed in neural tissues at the neurula stage, and in the restricted region of the tadpole brain. Ectopic expression of xIdax inhibits the target gene expression, suggesting that xIdax can inhibit canonical Wnt signaling. To examine the function of xIdax, a morpholino oligo for xIdax (xIdaxMO) was designed. An injection into an animal pole cell caused a loss of forebrain. The anterior neural marker expression is decreased in xIdaxMO-injected embryo, suggesting that xIdax is required for anterior neural development. Moreover, a negative regulator that acts downstream of xIdax rescued this defect. We propose that Idax functions are dependent on the canonical Wnt pathway and are crucial for the anterior neural development.     

C and V proteins of Sendai virus target signaling pathways leading to IRF-3 activation for the negative regulation of interferon-beta production

We here report a molecular basis for downregulation of interferon (IFN)-beta production by V and C proteins of Sendai virus (SeV). The infection of HeLa cells with SeV poorly induced IFN-beta even if the expression of C/C' was disrupted. In contrast, when the expression of C/C'/Y1/Y2 or V/W was disrupted, SeV infection strongly induced IFN-beta production and significantly activated the interferon regulatory factor (IRF)-3 pathway. The independent expression of C or V inhibited the double-stranded (ds) RNA- or Newcastle disease virus (NDV)-induced activation of IRF-3 and NF-kappa B, as well as the IFN-beta promoter. This inhibitory effect was also observed when Y1, Y2, or a C-terminal half fragment (aa 85-204) of C was independently expressed. Phosphorylation and homodimer formation of IRF-3 were suppressed not only in cells infected with SeV capable of expressing both C/C'/Y1/Y2 (or Y1/Y2) and V/W, but also in HeLa cells constitutively expressing Y1. These results suggest that C, Y1, Y2, and V block signaling pathways leading to IRF-3 activation to downregulate IFN-beta production.     

The effect of peroxisome proliferator-activated receptor-gamma ligand on urological cancer cells

Peroxisome proliferator activator-receptor (PPAR)-gamma ligand induces growth arrest of cancer cells through apoptosis. In this study, we examined the effects of PPAR-gamma inhibitors on cell proliferation in renal cell carcinoma (RCC), bladder tumor (BT), and prostatic carcinoma (PC) cell lines. We investigated the inhibitory effect of PPAR-gamma ligands, troglitazone and 15-deoxy-Delta12,14-prostaglandin J2 (15dPGJ2) on RCC, BT and PC-derived cell lines using MTT assay and Hoechst staining. PPAR-gamma ligands (troglitazone and 15dPGJ2) induced the reduction of cell viability with the half-maximal concentration of growth inhibition of RCC, BT, and PC cell lines. Furthermore, counting cells at days 1, 2 and 3, clearly showed marked inhibition of cell proliferation using troglitazone and 15dPGJ2. All PPAR-gamma inhibitors stopped the growth of all RCC, BT and PC cells. Cells treated with PPAR-gamma inhibitors showed chromatin condensation, cellular shrinkage, small membrane-bound bodies (apoptotic bodies), and cytoplasmic condensation. These cellular changes were typically redundant characteristics of apoptosis. PPAR-gamma ligands may mediate potent antiproliferative effects against RCC, BT and PC cells through differentiation. Thus, PPAR-gamma may become a new target in treatment of urological tumors.     

Ultrastructure and chromogranin A immunogold labelling of ECL cell carcinoids

Poorly differentiated neuroendocrine cells can be difficult to recognise. Sensitive methods are needed to label cells that have lost their ultrastructural features and have reduced concentrations of neuroendocrine markers. In gastric neoplasms, enterochromaffin-like cells might dedifferentiate and lose their characteristic granules and secretory vesicles, making detection of such cells increasingly difficult. However, chromogranin A (CgA) immunogold labelling could provide sensitive and specific detection of gastric neuroendocrine cells. We present ultrastructural findings, CgA immunogold labelling as well as conventional immunohistochemical findings of two human enterochromaffin-like cell carcinoids. Electron-dense granules of poorly differentiated cells were less intensely labelled than granules in well-differentiated cells. Granules with atypical shape as well as punctuate granules previously found in neuroendocrine neoplasms were also CgA labelled. The CgA labelling efficacy after antigen retrieval in an alkaline solution was higher after heating in an autoclave at 135 degrees C compared to a microwave at 100 degrees C for both granules and secretory vesicles without significant deterioration of the ultrastructure. In conclusion, the use of CgA immunogold labelling could ensure a specific classification of cells with neuroendocrine granules and be a supplement to immunohistochemical examination of poorly differentiated tumours.     

Studies on formaldehyde resins, 19. General base catalysis in hydroxymethylation of melamine with formaldehyde

Hydroxymethylation of melamine with formaldehyde to form N-(hydroxymethyl)melamine (2,4-diamino-6-hydroxymethylamino-1,3,5-triazine) was investigated kinetically by the use of hydrogen phosphate/phosphate buffers in aqueous media at pH 11 ? 12. This reaction was found to follow a general base catalysis which results from the kinetic investigation, showing that the reaction takes place by a concerted mechanism involving base, melamine, and formaldehyde. This mechanism differs from that of the base catalyzed hydroxymethylation of phenol or benzamide with formaldehyde, because the acidic phenol and benzamide easily form their conjugate bases by addition of the basic catalyst in a preceding equilibrium step.     

Phase stability after aging and its influence on pin-on-disk wear properties of Ce-TZP/Al2O3 nanocomposite and conventional Y-TZP

Recently zirconia/alumina composites have been examined by many researchers as the new generation of bearing materials in total joint replacements. In this study, the phase stability of a Ce-TZP/Al(2)O(3) nanocomposite and conventional Y-TZP after aging, and its influence on wear resistance, were investigated. Very slight phase transformation was observed in both types of ceramics 18 months after the implantation of Ce-TZP/Al(2)O(3) or Y-TZP samples into rabbit tibiae. However, Y-TZP showed marked phase transformation (approximately 80%) after aging in an autoclave (121 degrees C) for 190 h or in physiological saline at 62 degrees C for 18 months, whereas the new composite remained almost resistant to degradation. According to the results of self-pairing pin-on-disk wear tests using ceramic specimens with or without autoclave aging, the wear factor was almost the same between Ce-TZP/Al(2)O(3) samples with and without aging (6.74 +/- 0.36 x 10(-8) and 6.04 +/- 0.95 x 10(-8) mm(3)/Nm, respectively). In contrast, although non-aged Y-TZP had the lowest wear factor (4.88 +/- 0.51 x 10(-8) mm(3)/Nm) of all specimens tested, aged Y-TZP showed 10-fold greater wear than nonaged Y-TZP. The present study suggests that Ce-TZP/Al(2)O(3) nanocomposite has much greater phase stability than Y-TZP, and that its wear properties are not influenced by aging.