Inhibitory effects of flavonoids on the reduction of progesterone to 20alpha-hydroxyprogesterone in rat liver

The first aim of this study is to characterize the reduction of progesterone in rat liver. Progesterone was mainly reduced to 20alpha-hydroxyprogesterone in the cytosolic fraction of rat liver. The amount of 20alpha-hydroxyprogesterone formed from progesterone in the cytosolic fraction was significantly larger in the males than in the females and this enzyme reaction proceeded not only in the presence of NADPH, but also in the presence of NADH. Furthermore, we attempted to evaluate the inhibitory effects of 15 flavonoids on the NADPH-dependent reduction of progesterone to 20alpha-hydroxyprogesterone in liver cytosol of male rats. The order of the inhibitory potencies was luteolin>apigenin>quercetin>myricetin=fisetin=kaempferol. Other flavonoids exhibited lower inhibitory potencies. Energy-minimized molecular models demonstrated that a planar benzopyrone ring (A and C rings) with a coplanar phenyl ring (B ring) is a structural characteristic determining the inhibitory effects of flavonoids other than isoflavones.     

PYPAF3, a PYRIN-containing APAF-1-like protein, is a feedback regulator of caspase-1-dependent interleukin-1beta secretion

PYPAF3 is a member of the PYRIN-containing apoptotic protease-activating factor-1-like proteins (PYPAFs, also called NALPs). Among the members of this family, PYPAF1, PYPAF5, PYPAF7, and NALP1 have been shown to induce caspase-1-dependent interleukin-1beta secretion and NF-kappaB activation in the presence of the adaptor molecule ASC. On the other hand, we recently discovered that PYNOD, another member of this family, is a suppressor of these responses. Here, we show that PYPAF3 is the second member that inhibits caspase-1-dependent interleukin-1beta secretion. In contrast, PYPAF2/NALP2 does not inhibit this response but rather inhibits the NF-kappaB activation that is induced by the combined expression of PYPAF1 and ASC. Both PYPAF2 and PYPAF3 mRNAs are broadly expressed in a variety of tissues; however, neither is expressed in skeletal muscle, and only PYPAF2 mRNA is expressed in heart and brain. They are also expressed in many cell lines of both hematopoietic and non-hematopoietic lineages. Stimulation of monocytic THP-1 cells with lipopolysaccharide or interleukin-1beta induced PYPAF3 mRNA expression. Furthermore, the stable expression of PYPAF3 in THP-1 cells abrogated the ability of the cells to produce interleukin-1beta in response to lipopolysaccharide. These results suggest that PYPAF3 is a feedback regulator of interleukin-1beta secretion. Thus, PYPAF2 and PYPAF3, together with PYNOD, constitute an anti-inflammatory subgroup of PYPAFs.     

Degradation of the tumor suppressor Smad4 by WW and HECT domain ubiquitin ligases

Smad4 mediates signaling by the transforming growth factor-beta (TGF-beta) superfamily of cytokines. Smad signaling is negatively regulated by inhibitory (I) Smads and ubiquitin-mediated processes. Known mechanisms of proteasomal degradation of Smads depend on the direct interaction of specific E3 ligases with Smads. Alternatively, I-Smads elicit degradation of the TGF-beta receptor by recruiting the WW and HECT domain E3 ligases, Smurfs, WWP1, or NEDD4-2. We describe an equivalent mechanism of degradation of Smad4 by the above E3 ligases, via formation of ternary complexes between Smad4 and Smurfs, mediated by R-Smads (Smad2) or I-Smads (Smad6/7), acting as adaptors. Smurfs, which otherwise cannot directly bind to Smad4, mediated poly-ubiquitination of Smad4 in the presence of Smad6 or Smad7. Smad4 co-localized with Smad7 and Smurf1 primarily in the cytoplasm and in peripheral cell protrusions. Smad2 or Smad7 mutants defective in Smad4 interaction failed to induce Smurf1-mediated down-regulation of Smad4. A Smad4 mutant defective in Smad2 or Smad7 interaction could not be effectively down-regulated by Smurf1. We propose that Smad4 is targeted for degradation by multiple ubiquitin ligases that can simultaneously act on R-Smads and signaling receptors. Such mechanisms of down-regulation of TGF-beta signaling may be critical for proper physiological response to this pathway.     

Arginine-specific gingipains from Porphyromonas gingivalis stimulate production of hepatocyte growth factor (scatter factor) through protease-activated receptors in human gingival fibroblasts in culture

Cystein proteinases (gingipains) from Porphyromonas gingivalis cleave a broad range of in-host proteins and are considered to be key virulence factors in the onset and development of adult periodontitis and host defense evasion. In periodontitis, an inflammatory disease triggered by bacterial infection, the production of hepatocyte growth factor (HGF) is induced not only by various factors derived from the host, such as inflammatory cytokines, but also by bacterial components. In this study we examined the possible enhanced production of HGF produced by human gingival fibroblasts upon stimulation with gingipains. Arginine-specific gingipain (Rgp) caused a marked production of HGF into the supernatant, the induction of HGF expression on the cell surface, and the up-regulation of HGF mRNA expression in a dose-dependent and an enzymatic activity-dependent manner. Because it has been reported that Rgp activated protease-activated receptors (PARs), we examined whether the induction of HGF triggered by Rgps on human gingival fibroblasts occurred through PARs. An RNA interference assay targeted to PAR-1 and PAR-2 mRNA revealed that gingipains-induced secretion of HGF was significantly inhibited by RNA interference targeted to PAR-1 and PAR-2. In addition, the Rgps-mediated HGF induction was completely inhibited by the inhibition of phospholipase C and was clearly inhibited by RNA interference targeted to p65, which is an NF-kappaB component. These results suggest that Rgps activated human gingival fibroblasts to secrete HGF in the inflamed sites and the mechanism(s) involved may actively participate in both inflammatory and reparative processes in periodontal diseases.     

Fas ligand induces cell-autonomous IL-23 production in dendritic cells, a mechanism for Fas ligand-induced IL-17 production

Fas ligand (FasL) has the potential to induce inflammation accompanied by massive neutrophil infiltration. We previously reported that FasL rapidly induces the production of various inflammatory cytokines including IL-1beta and IL-17. In this study, we investigated the mechanism of the FasL-induced IL-17 production. We found that the culture supernatant of mouse resident peritoneal exudate cells (PEC) cocultured with FasL-expressing tumor (FFL) cells induced IL-17 production in freshly isolated resident PEC. Anti-IL-1beta Ab strongly inhibited the IL-17-inducing activity. However, rIL-1beta by itself induced only weak IL-17 production. Intriguingly, anti-IL-12 Ab but not an IL-15-neutralizing agent, IL15R-Fc, strongly inhibited the FasL-induced IL-17-inducing activity. IL-23, which shares the p40 subunit with IL-12, but not IL-12 itself, induced IL-17 production synergistically with IL-1beta in resident PEC. FasL induced the production of IL-23 in PEC in vivo and in vitro, and IL-17 production following the i.p. injection of FFL cells was severely impaired in p40-/- mice, indicating that IL-23 plays an important role in the FasL-induced IL-17 production. FFL also induced the production of IL-23 in bone marrow- or PEC-derived dendritic cells (DCs). Finally, FasL induced only weak p40 production in a mixture of p40-/- and Fas-/- DC, indicating that FasL induces IL-23 production in DC mainly in a cell-autonomous manner.     

Smad mediates BMP-2-induced upregulation of FGF-evoked PC12 cell differentiation

To gain insight into presenilin-1 (PS1) structural aspects, we explored the structure–function relationship of its N- and C-terminal (NTF and CTF, respectively) complexes. We demonstrated that both NTF and CTF act as independent but inter-changing binding units capable of binding each other (NTF/CTF) or their homologues (NTF/NTF; CTF/CTF). The Alzheimer’s disease-associated PS1 mutations Y115H and M146L do not affect their ability to hetero- and/or homodimerize, thus conserving their basic integrity and function(s). These results suggest that PS1 associates intra-molecularly to form higher order complexes, which may be needed for endoproteolytic cleavage and/or γ-secretase-associated activity.     

Subunit arrangement in V-ATPase from Thermus thermophilus

The V0V1-ATPase of Thermus thermophilus catalyzes ATP synthesis coupled with proton translocation. It consists of an ATPase-active V1 part (ABDF) and a proton channel V0 part (CLEGI), but the arrangement of each subunit is still largely unknown. Here we found that acid treatment of V0V1-ATPase induced its dissociation into two subcomplexes, one with subunit composition ABDFCL and the other with EGI. Exposure of the isolated V0 to acid or 8 m urea also produced two subcomplexes, EGI and CL. Thus, the C subunit (homologue of d subunit, yeast Vma6p) associates with the L subunit ring tightly, and I (homologue of 100-kDa subunit, yeast Vph1p), E, and G subunits constitute a stable complex. Based on these observations and our recent demonstration that D, F, and L subunits rotate relative to A3B3 (Imamura, H., Nakano, M., Noji, H., Muneyuki, E., Ohkuma, S., Yoshida, M., and Yokoyama, K. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 2312-2315; Yokoyama, K., Nakano, M., Imamura, H., Yoshida, M., and Tamakoshi, M. (2003) J. Biol. Chem. 278, 24255-24258), we propose that C, D, F, and L subunits constitute the central rotor shaft and A, B, E, G, and I subunits comprise the surrounding stator apparatus in the V0V1-ATPase.     

Potential role for 53BP1 in DNA end-joining repair through direct interaction with DNA

Upon DNA damage, p53-binding protein 1 (53BP1) relocalizes to sites of DNA double-strand breaks and forms discrete nuclear foci, suggesting its role in DNA damage responses. We show that 53BP1 changed its localization from the detergent soluble to insoluble fraction after treatment of cells with x-ray, but not with ultraviolet or hydroxyurea. Either DNase or phosphatase treatment of the insoluble fraction released 53BP1 into the soluble fraction, showing that 53BP1 binds to chromatin in a phosphorylation-dependent manner after X-irradiation of cells. 53BP1 was retained at discrete nuclear foci in X-irradiated cells even after detergent extraction of cells, showing that the chromatin binding of 53BP1 occurs at sites of DNA double-strand breaks. The minimal domain for focus formation was identified by immunofluorescence staining of cells ectopically expressed with 53BP1 deletion mutants. This domain consisted of conserved Tudor and Myb motifs. The Tudor plus Myb domain possessed chromatin binding activity in vivo and bound directly to both double-stranded and single-stranded DNA in vitro. This domain also stimulated end-joining by DNA ligase IV/Xrcc4, but not by T4 DNA ligase in vitro. We conclude that 53BP1 has the potential to participate directly in the repair of DNA double-strand breaks.