Mutagenicity of cooked hamburger is reduced by addition of onion to ground beef

Addition of onion effectively reduced mutagenicity of cooked hamburger when tested on Salmonella typhimurium TA98 strain with metabolic activation. The components of onion that participated in the reduction of mutagenicity were sugars. Addition of starch or glucose to ground beef the amount equivalent to that in onion reduced the mutagenicity of cooked hamburger. Addition of onion may cause imbalance of the sugar content of ground beef that effectively produces mutagenicity. Mutagenicity of the heated model mixture of glucose/glycine/creatinine in diethyleneglycol–water was reduced by an excessive amount of glucose. Hence, Japanese cooking-style with addition of onion can reduce mutagenicity of hamburger.     

Complete genome sequence of the dehalorespiring bacterium Desulfitobacterium hafniense Y51 and comparison with Dehalococcoides ethenogenes 195

Desulfitobacterium strains have the ability to dechlorinate halogenated compounds under anaerobic conditions by dehalorespiration. The complete genome of the tetrachloroethene (PCE)-dechlorinating strain Desulfitobacterium hafniense Y51 is a 5,727,534-bp circular chromosome harboring 5,060 predicted protein coding sequences. This genome contains only two reductive dehalogenase genes, a lower number than reported in most other dehalorespiring strains. More than 50 members of the dimethyl sulfoxide reductase superfamily and 30 paralogs of the flavoprotein subunit of the fumarate reductase are encoded as well. A remarkable feature of the genome is the large number of O-demethylase paralogs, which allow utilization of lignin-derived phenyl methyl ethers as electron donors. The large genome reveals a more versatile microorganism that can utilize a larger set of specialized electron donors and acceptors than previously thought. This is in sharp contrast to the PCE-dechlorinating strain Dehalococcoides ethenogenes 195, which has a relatively small genome with a narrow metabolic repertoire. A genomic comparison of these two very different strains allowed us to narrow down the potential candidates implicated in the dechlorination process. Our results provide further impetus to the use of desulfitobacteria as tools for bioremediation.     

Herbal constituent sequoyitol improves hyperglycemia and glucose intolerance by targeting hepatocytes, adipocytes, and β-cells

The prevalence of insulin resistance and type 2 diabetes increases rapidly; however, treatments are limited. Various herbal extracts have been reported to reduce blood glucose in animals with either genetic or dietary type 2 diabetes; however, plant extracts are extremely complex, and leading compounds remain largely unknown. Here we show that 5-O-methyl-myo-inositol (also called sequoyitol), a herbal constituent, exerts antidiabetic effects in mice. Sequoyitol was chronically administrated into ob/ob mice either orally or subcutaneously. Both oral and subcutaneous administrations of sequoyitol decreased blood glucose, improved glucose intolerance, and enhanced insulin signaling in ob/ob mice. Sequoyitol directly enhanced insulin signaling, including phosphorylation of insulin receptor substrate-1 and Akt, in both HepG2 cells (derived from human hepatocytes) and 3T3-L1 adipocytes. In agreement, sequoyitol increased the ability of insulin to suppress glucose production in primary hepatocytes and to stimulate glucose uptake into primary adipocytes. Furthermore, sequoyitol improved insulin signaling in INS-1 cells (a rat β-cell line) and protected INS-1 cells from streptozotocin- or H?O?-induced injury. In mice with streptozotocin-induced β-cell deficiency, sequoyitol treatments increased plasma insulin levels and decreased hyperglycemia and glucose intolerance. These results indicate that sequoyitol, a natural, water-soluble small molecule, ameliorates hyperglycemia and glucose intolerance by increasing both insulin sensitivity and insulin secretion. Sequoyitol appears to directly target hepatocytes, adipocytes, and β-cells. Therefore, sequoyitol may serve as a new oral diabetes medication.     

A Surface of the Kinase Domain Critical for the Allosteric Activation of G Protein-coupled Receptor Kinases

G protein-coupled receptor (GPCR) kinases (GRKs) phosphorylate activated GPCRs and initiate their desensitization. Many prior studies suggest that activated GPCRs dock to an allosteric site on the GRKs and thereby stimulate kinase activity. The extreme N-terminal region of GRKs is clearly involved in this process, but its role is not understood. Using our recent structure of bovine GRK1 as a guide, we generated mutants of solvent-exposed residues in the GRK1 kinase domain that are conserved among GRKs but not in the extended protein kinase A, G, and C family and evaluated their catalytic activity. Mutation of select residues in strands β1 and β3 of the kinase small lobe, αD of the kinase large lobe, and the protein kinase A, G, and C kinase C-tail greatly impaired receptor phosphorylation. The most dramatic effect was observed for mutation of an invariant arginine on the β1-strand (∼1000-fold decrease in k_cat/K_m). These residues form a continuous surface that is uniquely available in GRKs for protein-protein interactions. Surprisingly, these mutants, as well as a 19-amino acid N-terminal truncation of GRK1, also show decreased catalytic efficiency for peptide substrates, although to a lesser extent than for receptor phosphorylation. Our data suggest that the N-terminal region and the newly identified surface interact and stabilize the closed, active conformation of the kinase domain. Receptor binding is proposed to promote this interaction, thereby enhancing GRK activity.G protein-coupled receptor kinases (GRKs)² are members of the protein kinase A (PKA), G, and C (AGC) family that phosphorylate Ser/Thr residues in the cytoplasmic loops and C termini of activated G protein-coupled receptors (GPCRs) (1). Receptor phosphorylation facilitates the binding of arrestin, which uncouples heterotrimeric G proteins, promotes receptor internalization, and activates arrestin-dependent signaling pathways (2, 3). Although playing a beneficial role in receptor desensitization, GRKs are implicated in a range of human diseases, including retinal degeneration, hypertension, heart failure, rheumatoid arthritis, opiate addiction, and various cancers (2, 4). Seven GRKs have been identified in mammals. They can be divided into the following three subgroups based on their sequence homology: GRK1 (GRK1 and GRK7), GRK2 (GRK2 and GRK3), and GRK4 (GRK4, GRK5, and GRK6). The primary structures of the three GRK subgroups are similar, consisting of tandem regulator of G protein signaling homology (RH) and kinase domains. Less conserved sequences involved in phospholipid membrane attachment are found at their C termini (Fig. 1A).Open in a separate windowFIGURE 1.GRK surface residues potentially important for GPCR phosphorylation. A, domain architecture of bGRK1. B, sequence alignment of regions from GRKs that were targeted in this study with other AGC kinases. Colored boxes map these regions back to the domain structure shown in A. Regions of the core kinase domain that contain residues conserved in the GRK subfamily, but not in the extended AGC kinase family, are highlighted in brown. Conserved residues of the AGC kinase C-tail are highlighted in green. Positions investigated in this study are indicated with asterisks. Only one PDB accession code for each kinase of known structure is shown in parentheses. Residue numbers correspond to those of bGRK1. The PXXP, turn, and hydrophobic (HF) motifs (highlighted in gray) are characteristic features found in most AGC kinase C-tails (22). Yeast, Saccharomyces cerevisiae; M.tb, Mycobacterium tuberculosis. C, ribbon diagram of the bGRK1₅₃₅-H₆·ATP complex. The model is a hybrid that contains all the ordered elements from the two unique chains resolved in the crystal structure (PDB accession number 3C4W), such that the observed N terminus and a nearly complete AST region of the kinase C-tail are displayed in a single model. The RH domain is colored gray, and the β-strands and α-helices of the core kinase domain are dark and light brown, respectively. The hinge region joining the kinase small and large lobes (between β5 and αD) is colored yellow. The N-terminal region and the AGC kinase C-tail are shown in green and the AST loop in cyan. The ATP molecule bound in the active site is shown as a stick model, and the two associated Mg²⁺ ions are colored black. D, conservation scores of GRKs mapped onto the surface of bGRK1. The area boxed in C is shown. The conservation scores were calculated by comparing the sequence conservation of residues from the core kinase domain of GRKs with those of the entire AGC family (see text). Residues are colored using a gradient, from magenta (more conserved in GRKs than the AGC kinases) to white (as conserved in GRKs as in AGC kinases) and to yellow (more variable in GRKs than in AGC kinases). The RH domain, which was not included in this calculation, is colored gray. Highest conservation among GRKs cluster at two sites, “site 1” and “site 2.” Site 1 corresponds to a region of the small lobe left exposed by the shorter AST loop found in GRKs relative to other AGC kinases. The AST region of protein kinase B (PDB accession number 1O6K) is superimposed for comparison (blue ribbon).All eukaryotic protein kinases, including GRKs, contain a core catalytic domain of ∼250 amino acids that can be divided into two subdomains, called the small (or N) and large (or C) lobes. The small lobe consists of a five-stranded β-sheet (β1–5) and a conserved helix, αC, whereas the large lobe is mostly α-helical. The active site is located at their interface, with the nucleotide-binding pocket formed primarily by the small lobe and the phosphoacceptor-binding site primarily by the large lobe. In their active conformation, kinases position the hydroxyl group of the phosphoacceptor substrate in the proper orientation with respect to the γ-phosphate of ATP via a network of interactions formed by conserved structural elements from both lobes. Control of this network often underlies the molecular basis for allosteric regulation of protein kinase activity (5–9).In GRKs, this allosteric regulation appears to be mediated by interactions with activated GPCRs. Steady-state kinetics indicate that the K_m values of receptor substrates are in the micromolar range, whereas those of peptide substrates, even those derived from receptors, are in the millimolar range (10–13). Moreover, the catalytic efficiency for peptide phosphorylation by GRKs is much lower than that for receptor phosphorylation, and it can be enhanced in the presence of activated receptors (11, 12, 14). Thus, in addition to the peptide phosphoacceptor-binding site of the large lobe, an additional allosteric receptor-docking site appears to be required to promote catalytic activity in GRKs.The molecular basis for how GRKs interact with activated GPCRs is poorly understood. In vitro, GRKs show little specificity among GPCRs, requiring only that the receptor be in an activated conformation. For example, although GRK1 is the predominant kinase expressed in rod outer segments, GRK1, GRK2, and GRK5 all phosphorylate bovine rhodopsin in a light-dependent manner with comparable catalytic efficiencies (15–17). Therefore, it seems likely that GRKs have a common molecular mechanism for the recognition of activated GPCRs. The region of GRKs most strongly linked to efficient receptor phosphorylation is the highly conserved N-terminal region, which is unique to the GRK subfamily and predicted to form an α-helix (Fig. 1B). Deletion of this region in GRK1, -2, or -5 abolishes receptor phosphorylation (18–20). Additionally, the binding of antibodies (18) or of recoverin (21) to the GRK1 N-terminal region inhibits receptor phosphorylation. In GRK5, it has also been suggested that the N terminus plays a role in phospholipid interactions (20). Another region that is likely involved in the allosteric regulation of GRKs is the AGC kinase C-terminal tail (C-tail), which is an extension of the kinase core domain and often plays a regulatory role in AGC kinases (22–24) (Fig. 1, B and C). The central segment of the C-tail, termed the active site tether (AST), contributes residues to the active site and is only well ordered in kinase domain structures that are in conformations resembling the active state.To date, crystal structures representing each GRK subgroup have been reported, i.e. bovine GRK1 (bGRK1), bovine GRK2 (bGRK2), and human GRK6 (hGRK6) (25–29). Although most of these structures were co-crystallized in the presence of ATP or nucleotide analogs, none adopted the closed, active conformation exhibited by nucleotide-bound PKA (30), and the AST region of their AGC kinase C-tails were either partially or totally disordered. Similarly, the N-terminal region important for receptor phosphorylation was only observed in one crystal structure, namely that of one chain of the bGRK1·ATP complex. Thus, the regions believed to be most important for receptor interaction were largely disordered in these structures, leaving the molecular basis for how GPCRs interact with GRKs unclear. Because the kinase domains in these structures appear to be otherwise competent for catalysis, it is expected that activated GPCRs bind in a manner that promotes full kinase domain closure. Interactions with negatively charged lipids in the cell membrane are also expected to play a role in this transition (20, 31, 32).In this study, we used recently determined structures of bGRK1 as a template to identify surface residues of the kinase domain that are conserved in GRKs but not in the extended AGC family. Biochemical characterization of site-directed mutants of these residues in bGRK1 identified a continuous surface on the small lobe and the AGC kinase C-tail that is critical for GRK activation by GPCRs. The residue whose mutation showed the largest effect on receptor phosphorylation is nearly as important as the N-terminal region, and the analogous residue is also critical in the other two GRK subgroups, represented by bGRK2 and hGRK6. Comparison with other AGC kinases reveals that this surface is uniquely available for protein-protein interactions in the GRK subfamily. A model for activation that involves cooperative interactions between the N-terminal region and the kinase domain is presented.     

Involvement of Mst1 in tumor necrosis factor-alpha-induced apoptosis of endothelial cells

Mammalian sterile 20-kinase 1 (Mst1), a member of the sterile-20 family protein kinase, plays an important role in the induction of apoptosis. However, little is know about the physiological activator of Mst1 and the role of Mst1 in endothelial cells (ECs). We examined whether Mst1 is involved in the tumor necrosis factor (TNF)-α-induced apoptosis of ECs. Western blot analysis revealed that TNF-α induced activation of caspase 3 and Mst1 in a time- and dose-dependent manner. TNF-α-induced Mst1 activation is almost completely prevented by pretreatment with Z-DEVD-FMK, a caspase 3 inhibitor. Nuclear staining with Hoechst 33258 and fluorescence-activated cell sorting of propidium iodide-stained cells showed that TNF-α induced apoptosis of EC. Diphenyleneiodonium, an inhibitor of NADPH oxidase, and N-acetylcysteine, a potent antioxidant, also inhibited TNF-α-induced activation of Mst1 and caspase 3, as well as apoptosis. Knockdown of Mst1 expression by short interfering RNA attenuated TNF-α-induced apoptosis but not cleavage of caspase 3. These results suggest that Mst1 plays an important role in the induction of TNF-α-induced apoptosis of EC. However, positive feedback mechanism between Mst1 and caspase 3, which was shown in the previous studies, was not observed. Inhibition of Mst1 function may be beneficial for maintaining the endothelial integrity and inhibition of atherogenesis.     

Distribution of L-azetidine-2-carboxylate N-acetyltransferase in yeast

The budding yeast Saccharomyces cerevisiae Sigma1278b contains the MPR1 gene encoding N-acetyltransferase, which detoxifies the L-proline analog L-azetidine-2-carboxylate (AZC). Of 131 yeasts tested, AZC acetyltransferase activity was detected in 17 strains of 41 strains that showed AZC resistance. Degenerate-PCR analysis revealed that two strains, i.e., Candida saitoana AKU4533 and Wickerhamia fluorescens AKU4722, contained a DNA fragment highly homologous to MPR1. This indicates that AZC acetyltransferases are widely distributed in yeasts.     

Endometriosis-associated hydrocele of the canal of Nuck with immunohistochemical confirmation: a case report

Background

The canal of Nuck is an embryological vestige of the processus vaginalis, and presents a potential site for endometriosis seeding. Hydroceles in this region are a rare cause of inguinal swelling in females. In addition, endometriosis localized to the canal of Nuck is exceedingly rare.

Case presentation

A 44-year-old Japanese woman presented with a painful mass overlying her right pubis. She underwent surgery to completely excise the mass. During surgery, division of the external oblique aponeurosis revealed a cyst that occupied the inguinal canal and it adhered to the transverse fascia, inguinal ligament, and pubic bone. The cyst was dissected from the round ligament, and the defect in the internal inguinal ring was repaired and reinforced with mesh. On macroscopic examination, the cyst had a heterogeneous fibrous aspect with dark brown inclusions. Microscopic examination revealed that the cyst was tortuous, lined by mesothelial-like cells, and accompanied by partial subcapsular hemorrhage. Endometrium-like tissue was observed in the cystic wall. Immunohistochemical staining for podoplanin confirmed the mesothelial origin of the cyst-lining cells. The epithelial cells and stromal cells were positive for estrogen receptors.

Conclusions

In this case of an endometriosis-associated hydrocele of the canal of Nuck, the mesothelial origin of the cyst-lining cells and endometriosis were confirmed by positive immunohistochemical staining for podoplanin and estrogen receptors, respectively. We determined that hydrocele resection and reinforcement of the anterior inguinal canal wall (if necessary) are appropriate treatments for this condition.