PubMed Health⌕ Search

Biomedical subjects

Akiko Tanaka

Publications and source records attributed to Akiko Tanaka.

At least 19 recordsLinked to original sources
PubMed2007

Preconditioning stress prevents cold restraint stress-induced gastric lesions in rats: roles of COX-1, COX-2, and PLA2.

We investigated the protective effect of mild stress on gastric lesions induced by cold-restraint stress, especially concerning prostaglandins (PGs)/cyclo-oxygenase (COX) isozymes. Rats were exposed to severe stress (cold-restraint stress at 10 degrees C for 6 hr) or mild stress (cold-restraint stress at 10 degrees C for 30 min and kept at room temperature for 60 min) followed by severe stress. Severe stress induced gastric lesions, with a concomitant decrease in body temperature (BT). The ulcerogenic response was inhibited by atropine but worsened by indomethacin and SC-560 but not rofecoxib, although none of these agents had any effect on the change in BT. Mild stress suppressed the gastric ulceration and the decrease in BT induced by severe stress, and these effects were reversed by both COX-1 and COX-2 inhibitors. The expression of COX-2 in the stomach was up-regulated from 4 hr after severe stress and this response was slightly expedited by mild stress. COX-2 was also expressed in the hypothalamus under normal and stressed conditions. Quinacrine (phospholipase A(2) inhibitor) attenuated the protective effect of mild stress on the ulceration and decrease in BT caused by severe stress. TA-0910 (TRH analogue) at a low dose also prevented the gastric ulceration and the decrease in BT induced by severe stress. These results suggest that mild stress protects against cold-restraint stress-induced gastric ulceration, and the effect is peripherally and centrally mediated by PGs derived from both COX-1 and COX-2 through the activation of phospholipase A(2). TRH may also be involved in the protective effect of mild stress, probably through regulation of the thermogenic system.

Animals↗
PubMed2007

Dexamethasone damages the rat stomach but not small intestine during inhibition of COX-1.

We previously reported that inhibition of both COX-1 and COX-2 is required for the gastrointestinal ulcerogenic properties of nonsteroidal anti-inflammatory drugs (NSAIDs). Inhibition of COX-1 up-regulates COX-2 expression, and the prostaglandins (PGs) produced by COX-2 help to maintain the mucosal integrity during inhibition of COX-1. In the present study we investigated whether dexamethasone damages rat gastrointestinal mucosa during inhibition of COX-1 and further developed the idea that COX-2 expression is a key event in the ulcerogenic actions of NSAIDs. Dexamethasone was given p.o. in the absence or presence of SC-560 (a selective COX-1 inhibitor), and the stomach or intestine was examined 8 or 24 hr later, respectively. Neither dexamethasone nor SC-560 alone damaged the gastrointestinal mucosa. In the presence of SC-560, however, dexamethasone damaged the stomach but not small intestine. SC-560 decreased PGE(2) levels in both tissues, with a gradual recovery accompanying the up-regulation of COX-2 expression, and both the recovery of PGE(2) levels and the expression of COX-2 were inhibited by dexamethasone. In the animals treated with SC-560, iNOS expression was up-regulated in the intestinal but not the gastric mucosa, and this response was also inhibited by dexamethasone. These results suggest a risk from steroid therapy in the stomach when COX-2 expression is up-regulated. Dexamethasone does not provoke damage in the intestine, despite inhibiting the up-regulation of COX-2 expression under conditions of PG deficiency; at least one of the reasons is that this agent prevents the expression of iNOS, a major factor in the pathogenesis of intestinal lesions.

Animals↗
PubMed2006

Crystal structure of the human BRD2 bromodomain: insights into dimerization and recognition of acetylated histone H4.

The BET (bromodomains and extra terminal domain) family proteins recognize acetylated chromatin through their bromodomain and act as transcriptional activators. One of the BET proteins, BRD2, associates with the transcription factor E2F, the mediator components CDK8 and TRAP220, and RNA polymerase II, as well as with acetylated chromatin during mitosis. BRD2 contains two bromodomains (BD1 and BD2), which are considered to be responsible for binding to acetylated chromatin. The BRD2 protein specifically recognizes the histone H4 tail acetylated at Lys12. Here, we report the crystal structure of the N-terminal bromodomain (BD1, residues 74-194) of human BRD2. Strikingly, the BRD2 BD1 protein forms an intact dimer in the crystal. This is the first observation of a homodimer among the known bromodomain structures, through the buried hydrophobic core region at the interface. Biochemical studies also demonstrated BRD2 BD1 dimer formation in solution. The two acetyllysine-binding pockets and a negatively charged secondary binding pocket, produced at the dimer interface in BRD2 BD1, may be the unique features that allow BRD2 BD1 to selectively bind to the acetylated H4 tail.

Acetylation↗
PubMed2006

Structure of the UNC5H2 death domain.

UNC5Hs (UNC5H1-4) are netrin 1 receptors that are involved in axonal guidance and neuronal migration. They are dependence receptors that mediate apoptosis in the absence of netrin 1. UNC5H2-induced apoptosis depends on the interaction of the death domain at the C-terminus with the DAP-kinase death domain and caspase cleavage near the transmembrane region. Here, the crystal structure of the mouse UNC5H2 death domain has been determined at 2.1 A resolution. The domain adopts a six-helix bundle fold, which is similar to those of the other members of the death-domain superfamily. The UNC5H2 death domain is a dimer in the crystal and in solution. This homodimerized structure may represent the structure of the death domain when netrin 1 binds to the UNC5H2 receptor. Homodimerization of UNC5H2 may block the access of caspase to the cleavage site. In the death-domain dimer, residues in alpha3 and the 3(10)-helix preceding alpha3 and the residues in alpha4 make significant contacts, mainly by hydrophobic and van der Waals interactions.

Amino Acid Sequence↗
PubMed2006

Role of endogenous nitric oxide (NO) and NO synthases in healing of indomethacin-induced intestinal ulcers in rats.

We examined the roles of nitric oxide (NO) and NO synthase (NOS) isozymes in the healing of indomethacin-induced small intestinal ulcers in rats. Animals were given indomethacin (10 mg/kg, s.c.) and killed 1, 4 and 7 days after the administration. Indomethacin (2 mg/kg), N(G)-nitro-L-arginine methyl ester (L-NAME: a nonselective NOS inhibitor: 10 mg/kg) and aminoguanine (a relatively selective iNOS inhibitor: 20 mg/kg) were given s.c. once daily for 6 days, the first 3 days or the last 3 days during a 7-day experimental period. Both indomethacin and L-NAME significantly impaired healing of these lesions, irrespective of whether they were given for 6 days, first 3 days or last 3 days. The healing was also impaired by aminoguanine given for the first 3 days but not for the last 3 days. Expression of iNOS mRNA in the intestine was up-regulated after ulceration, persisting for 2 days thereafter, and the Ca(2+)-independent iNOS activity also markedly increased with a peak response during 1-2 days after ulceration. Vascular content in the ulcerated mucosa as measured by carmine incorporation was decreased when the healing was impaired by indomethacin and L-NAME given for either the first or last 3 days as well as aminoguanidine given for the first 3 days. These results suggest that endogenous NO plays a role in healing of intestinal lesions, in addition to prostaglandins, yet the NOS isozyme mainly responsible for NO production differs depending on the stage of healing: iNOS in the early stage and cNOS in the late stage.

Animals↗
PubMed2006

Crystal structure of the RUN domain of the RAP2-interacting protein x.

Rap2-interacting protein x (RPIPx) is a homolog of RPIP8, a specific effector of Rap2 GTPase. The N-terminal region of RPIP8, which contains the RUN domain, interacts with Rap2. Using cell-free synthesis and NMR, we determined that the region encompassing residues 83-255 of mouse RPIPx, which is 40-residues larger than the predicted RUN domain (residues 113-245), is the minimum fragment that forms a correctly folded protein. This fragment, the RPIPx RUN domain, interacted specifically with Rap2B in vitro in a nucleotide-dependent manner. The crystal structure of the RPIPx RUN domain was determined at 2.0 A of resolution by the multiwavelength anomalous dispersion (MAD) method. The RPIPx RUN domain comprises eight anti-parallel alpha-helices, which form an extensive hydrophobic core, followed by an extended segment. The residues in the core region are highly conserved, suggesting the conservation of the RUN domain-fold among the RUN domain-containing proteins. The residues forming a positively charged surface are conserved between RPIP8 and its homologs, suggesting that this surface is important for Rap2 binding. In the crystal the putative Rap2 binding site of the RPIPx RUN domain interacts with the extended segment in a segment-swapping manner.

Amino Acid Sequence↗
PubMed2006

The crystal structure of mouse Nup35 reveals atypical RNP motifs and novel homodimerization of the RRM domain.

The nuclear pore complex mediates the transport of macromolecules across the nuclear envelope (NE). The vertebrate nuclear pore protein Nup35, the ortholog of Saccharomyces cerevisiae Nup53p, is suggested to interact with the NE membrane and to be required for nuclear morphology. The highly conserved region between vertebrate Nup35 and yeast Nup53p is predicted to contain an RNA-recognition motif (RRM) domain. Due to its low level of sequence homology with other RRM domains, the RNP1 and RNP2 motifs have not been identified in its primary structure. In the present study, we solved the crystal structure of the RRM domain of mouse Nup35 at 2.7 A resolution. The Nup35 RRM domain monomer adopts the characteristic betaalphabetabetaalphabeta topology, as in other reported RRM domains. The structure allowed us to locate the atypical RNP1 and RNP2 motifs. Among the RNP motif residues, those on the beta-sheet surface are different from those of the canonical RRM domains, while those buried in the hydrophobic core are highly conserved. The RRM domain forms a homodimer in the crystal, in accordance with analytical ultracentrifugation experiments. The beta-sheet surface of the RRM domain, with its atypical RNP motifs, contributes to homodimerization mainly by hydrophobic interactions: the side-chain of Met236 in the beta4 strand of one Nup35 molecule is sandwiched by the aromatic side-chains of Phe178 in the beta1 strand and Trp209 in the beta3 strand of the other Nup35 molecule in the dimer. This structure reveals a new homodimerization mode of the RRM domain.

Amino Acid Motifs↗
PubMed2006

Oral but not parenteral aspirin upregulates COX-2 expression in rat stomachs. a relationship between COX-2 expression and PG deficiency.

AIM: We compared the ulcerogenic effects of aspirin (ASA) and indomethacin in the rat gastric mucosa depending on the route of administration, together with the expression of COX-2. METHODS: Animals fasted for 18 h were given ASA or indomethacin, either p.o. or s.c., and the stomach was examined 4 h later. RESULTS: Indomethacin decreased mucosal PGE(2 )level, increased gastric motility, and caused gastric lesions with the up-regulation of COX-2 expression, irrespective of the route of administration. ASA induced both damage and COX-2 expression in the stomach when given p.o. but not s.c., despite decreasing the PGE(2) level similarly via either route of administration. Gastric motility was temporarily increased and gastric potential difference (PD) was markedly decreased by ASA given p.o. PGE(2) and atropine, although preventing ASA-induced gastric lesions as well as hypermotility, affected neither the COX-2 expression nor PD reduction induced by p.o. ASA. By contrast, the COX-2 expression induced by indomethacin was prevented by both PGE(2) and atropine. CONCLUSION: ASA given p.o. caused damage in the stomach, together with the up-regulation of COX-2 expression, and this expression may be due to the topical irritative action, rather than being a result of PG deficiency. The expression of COX-2 after indomethacin is associated with gastric hypermotility due to PG deficiency.

Administration, Oral↗
PubMed2006

Phenothiazine and carbazole-related compounds inhibit mitotic kinesin Eg5 and trigger apoptosis in transformed culture cells.

The effects of phenothiazine and carbazole derivatives on the cell-cycle progression of human transformed culture cells were analyzed. After 2 days incubation, 5 microM 1-phenethylamino-3-phenothiazin-10-yl-propan-2-ol (1) induced strong mitotic arrest followed by cell death, and 20 microM 1-(3,6-dichloro-9H-carbazol-9-yl)-3-phenethylamino-2-propanol (5) and 1-(3,6-dibromo-9H-carbazol-9-yl)-3-phenethylamino-2-propanol (6) also induced cell death. The TUNEL-positive nuclei characteristic of apoptotic cell death were detected in cells treated with the compounds. We observed beta- and gamma-tubulins in the arrested cells after the addition of compound 1, and found that more than 90% of the mitotic cells exhibited the monoastral spindle instead of the normal bipolar spindle. The inhibitory effects of compounds 1, 5, and 6 on the microtubule-activated ATPase activity of mitotic kinesin Eg5, which is essential for bipolar spindle formation, were obtained. The most effective inhibitor, compound 1, had an IC(50) of 1.52 microM. We also examined their toxicities on various cell lines. Compound 1 had less toxicity with the non-transformed cell line WI-38, whereas it exhibited strong toxicity with the transformed cell lines WI38VA13, HL-60 and HeLa. On the other hand, a high dose of compound 6 caused cell death in both types of culture cells. These results suggest that compound 1, an Eg5 inhibitor, selectively kills transformed culture cells.

Animals↗
PubMed2006

Roles of endogenous prostaglandins and cyclooxygenase isozymes in healing of indomethacin-induced small intestinal lesions in rats.

The role of prostaglandins (PGs)/cyclooxygenase (COX) in the healing of indomethacin-induced small intestinal ulcers was examined in rats. Animals were given indomethacin (10 mg/kg s.c.) and killed 1, 2, 3, 5, and 7 days later. Indomethacin (2 mg/kg), 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC560; COX-1 inhibitor; 3 mg/kg), and rofecoxib (COX-2 inhibitor; 3 mg/kg) were given p.o. once daily for 6 days, during the first 3 days or last 3 days of the experimental period. All COX inhibitors given for 6 days significantly impaired the healing of these ulcers. Healing was also impaired by rofecoxib given for the first 3 days or by SC560 given for the last 3 days. The expression of COX-2 mRNA in the intestine was up-regulated after ulceration, persisting for 3 days and dissipating thereafter. Mucosal PGE2 contents decreased within 3 h after ulceration, recovered 24 h later, and increased above normal 1 approximately 3 days later. The PGE2 content at 4 days after ulceration was decreased by rofecoxib but not SC560, whereas that at 7 days was suppressed by SC560 but not rofecoxib. Vascular content in the ulcerated mucosa decreased when the healing was impaired by COX inhibitors. The deleterious effect of indomethacin on healing was mimicked by a prostacyclin E receptor (EP) 4 antagonist and reversed by coadministration of PGE2 as well as an EP4 agonist. In conclusion, endogenous PGs play a role in the healing of intestinal ulcers through EP4 receptors, yet the COX isozyme involved differs depending on the stage of healing; COX-2 in the early stage and COX-1 in the late stage.

Animals↗
PubMed2006

Solution structure of the antifreeze-like domain of human sialic acid synthase.

The structure of the C-terminal antifreeze-like (AFL) domain of human sialic acid synthase was determined by NMR spectroscopy. The structure comprises one alpha- and two single-turn 3(10)-helices and two beta-strands, and is similar to those of the type III antifreeze proteins. Evolutionary trace analyses of the type III antifreeze protein family suggested that the class-specific residues in the human and bacterial AFL domains are important for their substrate binding, while the class-specific residues of the fish antifreeze proteins are gathered on the ice-binding surface.

Amino Acid Sequence↗
PubMed2006

An Arabidopsis SBP-domain fragment with a disrupted C-terminal zinc-binding site retains its tertiary structure.

SQUAMOSA promoter-binding proteins (SBPs) form a major family of plant-specific transcription factors, mainly related to flower development. SBPs share a highly conserved DNA-binding domain of approximately 80 amino acids (SBP domain), which contains two non-interleaved zinc-binding sites formed by eight conserved Cys or His residues. In the present study, an Arabidopsis SPL12 SBP-domain fragment that lacks a Cys residue involved in the C-terminal zinc-binding pocket was found to retain a folded structure, even though only a single Zn2+ ion binds to the fragment. Solution structure of this fragment determined by NMR is very similar to the previously determined structures of the full SBP domains of Arabidopsis SPL4 and SPL7. Considering the previous observations that chelating all the Zn2+ ions of SBPs resulted in the complete unfolding of the structure and that a mutation of the Cys residue equivalent to that described above impaired the DNA-binding activity, we propose that the Zn2+ ion at the N-terminal site is necessary to maintain the overall tertiary structure, while the Zn2+ ion at the C-terminal site is necessary for the DNA binding, mainly by guiding the basic C-terminal loop to correctly fit into the DNA groove.

Amino Acid Sequence↗
PubMed2006

Factors involved in upregulation of inducible nitric oxide synthase in rat small intestine following administration of nonsteroidal anti-inflammatory drugs.

We investigated the functional mechanisms underlying the expression of inducible nitric oxide (NO) synthase (iNOS) in the rat small intestine following the administration of nonsteroidal anti-inflammatory drugs (NSAIDs) and found a correlation with the intestinal ulcerogenic properties of NSAIDs. Conventional NSAIDs (indomethacin, diclofenac, naproxen, and flurbiprofen), a selective cyclooxygenase (COX)-1 inhibitor (SC-560) and a selective COX-2 inhibitor (rofecoxib) were administered p.o., and the intestinal mucosa was examined 24 hours later. Indomethacin decreased prostaglandin E2 (PGE2) production in the intestinal mucosa and caused intestinal hypermotility and bacterial invasion as well as the upregulation of iNOS expression and NO production, resulting in hemorrhagic lesions. Other NSAIDs similarly inhibited PGE2 production and caused hemorrhagic lesions with intestinal hypermotility as well as iNOS expression. Hypermotility in response to indomethacin was prevented by both PGE2 and atropine but not ampicillin, yet all these agents inhibited not only bacterial invasion but also expression of iNOS as well, resulting in prevention of intestinal lesions. SC-560, but not rofecoxib, caused a decrease in PGE2 production, intestinal hypermotility, bacterial invasion, and iNOS expression, yet this agent neither increased iNOS activity nor provoked intestinal damage because of the recovery of PGE2 production owing to COX-2 expression. Food deprivation totally attenuated both iNOS expression and lesion formation in response to indomethacin. In conclusion, the expression of iNOS in the small intestine following administration of NSAIDs results from COX-1 inhibition and is functionally associated with intestinal hypermotility and bacterial invasion. This process plays a major pathogenic role in the intestinal ulcerogenic response to NSAIDs.

Animals↗
PubMed2006

Solution structure of the SWIRM domain of human histone demethylase LSD1.

SWIRM is an evolutionarily conserved domain involved in several chromatin-modifying complexes. Recently, the LSD1 protein, which bears a SWIRM domain, was found to be a demethylase for Lys4-methylated histone H3. Here, we report a solution structure of the SWIRM domain of human LSD1. It forms a compact fold composed of 6 alpha helices, in which a 20 amino acid long helix (alpha4) is surrounded by 5 other short helices. The SWIRM domain structure could be divided into the N-terminal part (alpha1-alpha3) and the C-terminal part (alpha4-alpha6), which are connected to each other by a salt bridge. While the N-terminal part forms a SWIRM-specific structure, the C-terminal part adopts a helix-turn-helix (HTH)-related fold. We discuss a model in which the SWIRM domain acts as an anchor site for a histone tail.

Amino Acid Motifs↗
PubMed2006

Solution structures of the SURP domains and the subunit-assembly mechanism within the splicing factor SF3a complex in 17S U2 snRNP.

The SF3a complex, consisting of SF3a60, SF3a66, and SF3a120, in 17S U2 snRNP is crucial to spliceosomal assembly. SF3a120 contains two tandem SURP domains (SURP1 and SURP2), and SURP2 is responsible for binding to SF3a60. We found that the SURP2 fragment forms a stable complex with an SF3a60 fragment (residues 71-107) and solved its structure by NMR spectroscopy. SURP2 exhibits a fold of the alpha1-alpha2-3(10)-alpha3 topology, and the SF3a60 fragment forms an amphipathic alpha helix intimately contacting alpha1 of SURP2. We also solved the SURP1 structure, which has the same fold as SURP2. The protein-binding interface of SURP2 is quite similar to the corresponding surface of SURP1, except for two amino acid residues. One of them, Leu169, is characteristic of SF3a120 SURP2 among SURP domains. Mutagenesis showed that this single Leu residue is the critical determinant for complex formation, which reveals the protein recognition mechanism in the subunit assembly.

Amino Acid Sequence↗
PubMed2006

Solution structure of the kinase-associated domain 1 of mouse microtubule-associated protein/microtubule affinity-regulating kinase 3.

Microtubule-associated protein/microtubule affinity-regulating kinases (MARKs)/PAR-1 are common regulators of cell polarity that are conserved from nematode to human. All of these kinases have a highly conserved C-terminal domain, which is termed the kinase-associated domain 1 (KA1), although its function is unknown. In this study, we determined the solution structure of the KA1 domain of mouse MARK3 by NMR spectroscopy. We found that approximately 50 additional residues preceding the previously defined KA1 domain are required for its proper folding. The newly defined KA1 domain adopts a compact alpha+beta structure with a betaalphabetabetabetabetaalpha topology. We also found a characteristic hydrophobic, concave surface surrounded by positively charged residues. This concave surface includes the highly conserved Glu-Leu-Lys-Leu motif at the C terminus, indicating that it is important for the function of the KA1 domain.

Amino Acid Sequence↗
PubMed2005

Purification, crystallization and preliminary X-ray diffraction analysis of the histone chaperone cia1 from fission yeast.

In fission yeast, cia1+ is an essential gene that encodes a histone chaperone, a homologue of human CIA (CCG1-interacting factor A) and budding yeast Asf1p (anti-silencing function-1), which both facilitate nucleosome assembly by interacting with the core histones H3/H4. The conserved domain (residues 1-161) of the cia1+-encoded protein was expressed in Escherichia coli, purified to near-homogeneity and crystallized by the sitting-drop vapour-diffusion method. The protein was crystallized in the monoclinic space group C2, with unit-cell parameters a = 79.16, b = 40.53, c = 69.79 A, beta = 115.93 degrees and one molecule per asymmetric unit. The crystal diffracted to beyond 2.10 A resolution using synchrotron radiation.

Cell Cycle Proteins↗