20S proteasome prevents aggregation of heat-denatured proteins without PA700 regulatory subcomplex like a molecular chaperone

The eukaryotic 20S proteasome is the multifunctional catalytic core of the 26S proteasome, which plays a central role in intracellular protein degradation. Association of the 20S core with a regulatory subcomplex, termed PA700 (also known as the 19S cap), forms the 26S proteasome, which degrades ubiquitinated and nonubiquitinated proteins through an ATP-dependent process. Although proteolytic assistance by this regulatory particle is a general feature of proteasome-dependent turnover, the 20S proteasome itself can degrade some proteins directly, bypassing ubiquitination and PA700, as an alternative mechanism in vitro. The mechanism underlying this pathway is based on the ability of the 20S proteasome to recognize partially unfolded proteins. Here we show that the 20S proteasome recognizes the heat-denatured forms of model proteins such as citrate synthase, malate dehydrogenase. and glyceraldehydes-3-phosphate dehydrogenase, and prevents their aggregation in vitro. This process was not followed by the refolding of these denatured substrates into their native states, whereas PA700 or the 26S proteasome generally promotes their reactivation. These results indicate that the 20S proteasome might play a role in maintaining denatured and misfolded substrates in a soluble state, thereby facilitating their refolding or degradation.     

Characterization of inhibitor binding sites of mitochondrial complex I using fluorescent inhibitor

Recent progress in complex I research suggests that a wide variety of complex I inhibitors share a common large binding domain with partially overlapping sites. To verify this concept, we carried out real-time displacement tests of a fluorescent ligand with various competitors using a novel quinazoline-type inhibitor (aminoquinazoline, AQ). In the presence of an excess amount of the competitors, the binding of AQ to the enzyme was completely suppressed, being in line with the concept mentioned above. However, AQ bound to the enzyme was not displaced by subsequent addition of an increasing amount of competitors in the concentration range expected from the relative magnitude of the K(d) values of AQ and competitors, rather, much higher concentrations of the competitors were needed to displace bound AQ. These results cannot be explained merely by the premise of a common or partially overlapping binding site(s) between AQ and competitors. On the other hand, double-inhibitor titration of steady state complex I activity suggested that additivity of inhibition is not necessarily observed for all pairs of complex I inhibitors. Our results are discussed in light of the cooperativity of the inhibitor binding sites.     

Expression of normal cellular prion protein (PrP(c)) on T lymphocytes and the effect of copper ion: Analysis by wild-type and prion protein gene-deficient mice

The purpose of this report was to determine the effect of prion protein (PrP) gene disruption on T lymphocyte function. Previous studies have suggested that normal cellular prion protein (PrP(c)) binds to copper and Cu(2+) is essential for interleukin-2 (IL-2) mRNA synthesis. In this study, IL-2 mRNA levels in a copper-deficient condition were investigated using T lymphocytes from prion protein gene-deficient (PrP(0/0)) and wild-type mice. Results showed that Cu(2+) deficiency had no effect on PrP(c) expression in Con A-activated splenocytes. However, a delay in IL-2 gene expression was observed in PrP(0/0) mouse T lymphocyte cultures using Con A and Cu(2+)-chelator. These results suggest that PrP(c) expression may play an important role in rapid Cu(2+) transfer in T lymphocytes. The rapid transfer of Cu(2+) in murine T lymphocytes could be one of the normal functions of PrP(c).     

Mouse round spermatids developed in vitro from preexisting spermatocytes can produce normal offspring by nuclear injection into in vivo-developed mature oocytes

It has been shown that mature oocytes injected with nuclei from round spermatids collected from mouse testis can generate normal offspring and that round spermatids can develop in vitro. An undetermined issue is whether spermatids developed in vitro are capable of generating fertile offspring by nuclear injection into oocytes. Herein, we report the production of normal and fertile offspring by nuclear injection using haploid spermatid donors derived from mouse primary spermatocyte precursors cocultured with Sertoli cells. Cocultured spermatogonia and spermatocytes were characterized by their nuclear immunoreactive patterns determined by an antibody to phosphorylated histone H2AX (gamma-H2AX), a marker for DNA double-strand breaks. Cocultured round spermatid progenies display more than one motile flagellum, whose axonemes were recognized by antitubulin immunostaining. Flagellar wavelike movement and flagellar-driven propulsion of round spermatids developed in vitro were documented by videomicroscopy (http://www.sci.ccny.cuny.edu/ approximately kier). We also show that breeding of male and female mouse offspring generated by spermatid nuclear injection produced fertile offspring. In addition to their capacity to produce fertile offspring, cocultured, flagellated round spermatids can facilitate the analysis of the mechanisms of centriolar polarity, duplication, assembly, and flagellar growth, including the intraflagellar transport of cargo proteins.     

Synthesis of lipid A type carboxymethyl derivatives with ether chains instead of ester chains and their LPS-antagonistic activities

Synthesis of lipid A type carboxymethyl derivatives having ether chains at both the C-3 and C-3' positions and their LPS-antagonistic activities toward human U937 cells are described.     

Fibroblast growth factor (FGF)-4 can induce proliferation of cardiac cushion mesenchymal cells during early valve leaflet formation

While much has been learned about how endothelial cells transform to mesenchyme during cardiac cushion formation, there remain fundamental questions about the developmental fate of cushions. In the present work, we focus on the growth and development of cushion mesenchyme. We hypothesize that proliferative expansion and distal elongation of cushion mesenchyme mediated by growth factors are the basis of early valve leaflet formation. As a first step to test this hypothesis, we have localized fibroblast growth factor (FGF)-4 protein in cushion mesenchymal cells at the onset of prevalve leaflet formation in chick embryos (Hamburger and Hamilton stage 20-25). Ligand distribution was correlated with FGF receptor (FGFR) expression. In situ hybridization data indicated that FGFR3 mRNA was confined to the endocardial rim of the atrioventricular (AV) cushion pads, whereas FGFR2 was expressed exclusively in cushion mesenchymal cells. FGFR1 expression was detected in both endocardium and cushion mesenchyme as well as in myocardium. To determine whether the FGF pathways play regulatory roles in cushion mesenchymal cell proliferation and elongation into prevalvular structure, FGF-4 protein was added to the cushion mesenchymal cells explanted from stage 24-25 chick embryos. A significant increase in proliferative ability was strongly suggested in FGF-4-treated mesenchymal cells as judged by the incorporation of 5'-bromodeoxyuridine (BrdU). To determine whether cushion cells responded similarly in vivo, a replication-defective retrovirus encoding FGF-4 with the reporter, bacterial beta-galactosidase was microinjected into stage 18 chick cardiac cushion mesenchyme along the inner curvature where AV and outflow cushions converge. As compared with vector controls, overexpression of FGF-4 clearly induced expansion of cushion mesenchyme toward the lumen. To further test the proliferative effect of FGF-4 in cardiac cushion expansion in vivo (ovo), FGF-4 protein was microinjected into stage 18 chick inner curvature. An assay for BrdU incorporation indicated a significant increase in proliferative ability in FGF-4 microinjected cardiac cushion mesenchyme as compared with BSA-microinjected controls. Together, these results suggest a role of FGF-4 for cardiac valve leaflet formation through proliferative expansion of cushion mesenchyme.     

Cloning and characterization of a novel RING-B-box-coiled-coil protein with apoptotic function

We have identified a novel RING-B-box-coiled-coil (RBCC) protein (MAIR for macrophage-derived apoptosis-inducing RBCC protein) that consists of an N-terminal RING finger, followed by a B-box zinc finger, a coiled-coil domain, and a B30.2 domain. MAIR mRNA was expressed widely in mouse tissues and was induced by macrophage colony-stimulating factor in murine peritoneal and bone marrow macrophages. MAIR protein initially showed a granular distribution predominantly in the cytoplasm. The addition of zinc to transfectants containing MAIR cDNA as part of a heavy metal-inducible vector caused apoptosis of the cells characterized by cell fragmentation; a reduction in mitochondrial membrane potential; activation of caspase-7, -8, and -9, but not caspase-3; and DNA degradation. We also found that the RING finger and coiled-coil domains were required for MAIR activity by analysis with deletion mutants.