Biomedical subjects
K Ihara
Publications and source records attributed to K Ihara.
[A case of true enterolithiasis with acute appendicitis].
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DNA replication errors produced by the replicative apparatus of Escherichia coli.
It has been hard to detect forward mutations generated during DNA synthesis in vitro by replicative DNA polymerases, because of their extremely high fidelity and a high background level of pre-existing mutations in the single-stranded template DNA used. Using the oriC plasmid DNA replication in vitro system and the rpsL forward mutation assay, we examined the fidelity of DNA replication catalyzed by the replicative apparatus of Escherichia coli. Upon DNA synthesis by the fully reconstituted system, the frequency of rpsL-mutations in the product DNA was increased to 1.9x10(-4), 50-fold higher than the background level of the template DNA. Among the mutations generated in vitro, single-base frameshifts predominated and occurred with a pattern similar to those induced in mismatch-repair deficient E. coli cells, indicating that the major replication error was slippage at runs of the same nucleotide. Large deletions and other structural alterations of DNA appeared to be induced also during the action of the replicative apparatus.
Biochemical and crystallographic characterization of a Rho effector domain of the protein serine/threonine kinase N in a complex with RhoA.
The effector domain of human protein serine/threonine kinase N (PKN), an effector protein for the small GTP-binding protein Rho, was expressed and purified for protein characterization and crystallization in a complex form with human RhoA. In solution, RhoA binds to the PKN effector domain with 1:2 stoichiometry in a GTP-dependent manner. The obtained complex crystals diffract to 2.2 A resolution.
Rubinstein-Taybi syndrome: a girl with a history of neuroblastoma and premature thelarche.
A 7-year-old girl with Rubinstein-Taybi syndrome (RTS) who had a history of neuroblastoma and premature thelarche is reported. The neuroblastoma was detected at age 6 months on a nation-wide neuroblastoma screening program, surgically removed, and took a favorable clinical course with minimal therapy. She developed isolated breasts at age 6 years, had normal plasma levels of estradiol, follicular-stimulating hormone (FSH), and luteinizing hormone (LH), and showed a FSH-predominant pattern on the LH-releasing hormone stimulation test. In view of these findings, she was diagnosed to have premature thelarche. Premature thelarche may not be uncommon in girls with RTS.
Identification of mutations in the c-mpl gene in congenital amegakaryocytic thrombocytopenia.
Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare disorder expressed in infancy and characterized by isolated thrombocytopenia and megakaryocytopenia with no physical anomalies. Our previous hematological analysis indicated similarities between human CAMT and murine c-mpl (thrombopoietin receptor) deficiency. Because the c-mpl gene was considered as one of the candidate genes for this disorder, we analyzed the genomic sequence of the c-mpl gene of a 10-year-old Japanese girl with CAMT. We detected two heterozygous point mutations: a C-to-T transition at the cDNA nucleotide position 556 (Q186X) in exon 4 and a single nucleotide deletion of thymine at position 1,499 (1,499 delT) in exon 10. Both mutations were predicted to result in a prematurely terminated c-Mpl protein, which, if translated, lacks all intracellular domains essential for signal transduction. Each of the mutations was segregated from the patient's parents. Accordingly, the patient was a compound heterozygote for two mutations of the c-mpl gene, each derived from one of the parents. The present study suggests that at least a certain type of CAMT is caused by the c-mpl mutation, which disrupts the function of thrombopoietin receptor.
Cutting edge: dominant effect of Ile50Val variant of the human IL-4 receptor alpha-chain in IgE synthesis.
Two variants of the IL-4R alpha-chain (IL-4Ralpha) gene have been recently identified in association with different atopic disorders. To clarify the etiological relationship between the two variants, we analyzed responsiveness to IL-4 of transfectants with four kinds of IL-4Ralpha carrying either Val or Ile at 50 and either Gln or Arg at 551. The substitution of Ile for Val augmented STAT6 activation, proliferation, and transcription activity of the Iepsilon promoter by IL-4, whereas that of Arg for Gln did not change these IL-4 signals. Arg551 was not associated with atopic asthma in the Japanese population. CD23 expression and IgE synthesis by IL-4 were augmented in Ile50-bearing PBMC, compared with those bearing Val50. Taken together, substitution of Arg551 does not enhance the IL-4 signal for generation of germline epsilon transcript, whereas the substitution of Ile50 contributes to enhancement of IgE synthesis.
Evolution of the archaeal rhodopsins: evolution rate changes by gene duplication and functional differentiation.
The amino acid sequences of 25 archaeal retinal proteins from 13 different strains of extreme halophiles were analyzed to establish their molecular phylogenetic relationship. On the basis of amino acid sequence similarity, these proteins apparently formed a distinct family designated as the archaeal rhodopsin family (ARF), which was not related to other known proteins, including G protein-coupled receptors. The archaeal rhodopsin family was further divided into four clusters with different functions; H+ pump (bacteriorhodopsin), Cl- pump (halorhodopsin), and two kinds of sensor (sensory rhodopsin and phoborhodopsin). These four rhodopsin clusters seemed to have occurred by gene duplication(s) before the generic speciation of halophilic archaea, based on phylogenetic analysis. Therefore, the degrees of differences in amino acid sequences within each cluster simply reflected the divergent evolution of halophilic archaea. By comparing the branch lengths after speciation points of the reconstituted tree, we calculated the relative evolution rates of the four archaeal rhodopsins bacteriorhodopsin:halorhodopsin:sensory rhodopsin: phoborhodopsin to be 5:4:3:10. From these values, the degrees of functional and structural restriction of each protein can be inferred. The branching topology of four clusters grouped bacteriorhodopsin and halorhodopsin versus sensory rhodopsin and phoborhodopsin by likelihood mapping. Using bacteriorhodopsin (and halorhodopsin) as an outgroup, the gene duplication point of sensory rhodopsin/phoborhodopsin was determined. By calculating the branch lengths between the gene duplication point and each halophilic archaea speciation point, we could speculate upon the relative evolution rate of pre-sensory rhodopsin and pre-phoborhodopsin. The evolution rate of pre-sensory rhodopsin was fivefold faster than that of pre-phoborhodopsin, which suggests that the original function of the ancestral sensor was similar to that of phoborhodopsin, and that sensory rhodopsin evolved from pre-sensory rhodopsin by the accumulation of mutations. The changes in evolution rate by gene duplication and functional differentiation were demonstrated in the archaeal rhodopsin family using the gene duplication date and halobacterial speciation date as common time stamps.
Association of interleukin-4 receptor and interleukin-4 promoter gene polymorphisms with systemic lupus erythematosus.
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High-intensity basal ganglia lesions on T1-weighted images in two toddlers with elevated blood manganese with portosystemic shunts.
We report two toddlers with portosystemic shunts who had symmetrical high-signal globus pallidus lesions on T1- but not T2-weighted MRI, and measurement of whole blood manganese at 2 years of age. These cases suggest that portosystemic shunts can cause elevation of blood manganese and result in manganese accumulation in the globus pallidus, causing high signal on T1-weighted images even in asymptomatic toddlers.
Molecular epidemiology of C9 deficiency heterozygotes with an Arg95Stop mutation of the C9 gene in Japan.
Deficiency of the ninth component of human complement (C9) is the most common complement deficiency in Japan, with an incidence of approximately one homozygote in 1000, but is very rare in other countries. Genetic analyses of Japanese C9 deficiency have shown that a C-to-T transition leading to TGA stop codon for Arg95 in exon 4 of the C9 gene (Arg95Stop) is common in Japanese C9 deficiency. To determine the prevalence of heterozygous carriers of the Arg95Stop mutation in a Japanese population, we collected DNA samples from 300 individuals in two of the four main islands of Japan. Heterozygote detection was performed with an allele-specific polymerase chain reaction (PCR) system designed to detect exclusively only one of the normal and mutant alleles, followed by confirmation with PCR/single-strand conformation polymorphism (SSCP) analysis and direct sequencing. Twenty individuals were heterozygous for the Arg95Stop mutation. None was homozygous. The prevalence of carriers of the Arg95Stop mutation was 6.7% (20/300). An estimated frequency (0.12%) of complete C9 deficiency due to homozygous Arg95Stop mutation was consistent with frequencies determined by serological studies.
Novel polymorphism in the 5'-untranslated region of the interleukin-4 gene.
We found a novel polymorphism C/T change at position -34 counting from the first ATG codon, of the interleukin-4 (IL-4) gene, located between the TATA box and the first ATG on exon 1. The allelic frequency of this C/T polymorphism in 64 independent Japanese samples was 0.37:0.63. In addition, PCR-restriction fragment length polymorphism analysis revealed that the -34T/T polymorphism was always associated with -590T/T, a known polymorphism that increases IL-4 transcriptional activity.
The structural basis of Rho effector recognition revealed by the crystal structure of human RhoA complexed with the effector domain of PKN/PRK1.
The small G protein Rho has emerged as a key regulator of cellular events involving cytoskeletal reorganization. Here we report the 2.2 A crystal structure of RhoA bound to an effector domain of protein kinase PKN/PRK1. The structure reveals the antiparallel coiled-coil finger (ACC finger) fold of the effector domain that binds to the Rho specificity-determining regions containing switch I, beta strands B2 and B3, and the C-terminal alpha helix A5, predominantly by specific hydrogen bonds. The ACC finger fold is distinct from those for other small G proteins and provides evidence for the diverse ways of effector recognition. Sequence analysis based on the structure suggests that the ACC finger fold is widespread in Rho effector proteins.
Oversecretion of IL-18 in haemophagocytic lymphohistiocytosis: a novel marker of disease activity.
We investigated the significance of interleukin (IL)-18 levels in the pathophysiology of haemophagocytic lymphohistiocytosis (HLH). IL-18 levels were significantly elevated in all nine patients with active HLH compared with those of healthy controls. Serial determination of IL-18 levels in three cases, showed a gradual decrease compared with those of IL-12, interferon (IFN)-gamma or soluble Fas ligand (sFasL) in the course of clinical improvement, and seemed to be elevated until complete disappearance of disease activity. IL-18 and IFN-gamma (CC 0.711, P = 0.018), and IFN-gamma and sFasL (CC 0.849, P = 0.0049) levels were significantly correlated. On the other hand, correlation between IL-12 and IFN-gamma, IL-18 and sFasL, or IL-18 and IL-12 was not observed. IL-18, IFN-gamma and sFasL levels significantly correlated with disease activity such as fever and alanine transaminase (ALT) levels. IL-18 mRNA expression was enhanced in spleen, but not in peripheral blood mononuclear cells (MNC), bone marrow MNC, liver from patients of active HLH, or the tumour from a patient with lymphoma-associated haemophagocytic syndrome (LAHS). These results suggest that IL-18 may play important roles in the pathogenesis of HLH, particularly through induction of Th1 cells. IL-18 measurement may be useful for the diagnosis and for the detection of smouldering disease activity.
Molecular cloning of A1-ATPase gene from extremely halophilic archaeon Haloarcula japonica strain TR-1.
The genes encoding A1-ATPase A- and B-subunits were cloned from Haloarcula japonica strain TR-1. Nucleotide sequencing analysis of the A1-ATPase gene revealed that the A- and B-subunits consisted of 586 and 473 amino acids, respectively. The deduced amino acid sequences of the A- and B-subunits of Ha. japonica showed high identities with those of Halobacterium salinarum and Haloferax volcanii. The consensus ATP-binding motif was found in the A-subunit.
Halobacterial rhodopsins.
Following the discovery of the bacteriorhodopsin proton pump in Halobacterium halobium (salinarum), not only the halorhodopsin halide pump and two photosensor rhodopsins (sensory rhodopsin and phoborhodopsin) in the same species, but also homologs of these four rhodopsins in strains of other genera of Halobacteriaceae have been reported. Twenty-eight full (and partial) sequences of the genomic DNA of these rhodopsins have been analyzed. The deduced amino acid sequences have led to new strategies and tactics for understanding bacterial rhodopsins on a comparative basis, as summarized briefly in this article. The data discussed include (i) alignment of the sequences to qualify/characterize the conserved residues; (ii) assignment of residues that cause differences in function(s)/properties; and (iii) phylogeny of the halobacterial rhodopsins to suggest their evolutionary paths. The four kinds of rhodopsin in each strain are assumed, on the basis of their genera-specific distributions, to have arisen by at least two gene-duplication processes during evolution prior to generic speciation. The first duplication of the rhodopsin ancestor gene yielded two genes, each of which was duplicated again to give four genes in the ancestor halobacterium. The bacterium carrying four rhodopsin genes, after accumulating mutations, became ready for generic speciation and the delivery of four rhodopsins to each species. The original rhodopsin ancestor is speculated to be closest to the proton pump (bacteriorhodopsin).
Vascularized fibular graft after excision of giant cell tumor of the distal radius. A case report.
Although hemiarthroplasty of the wrist using vascularized proximal fibula has been described often, long term results with documentation of results are insufficient. A case of giant cell tumor of the distal radius with remarkable extraskeletal extension is reported. Vascularized fibula including its proximal head was used to replace the defect created after en bloc resection of the tumor. There was no deterioration in radiographic findings or function of the new joint at the time of the 10-year followup. Satisfactory range of motion of the wrist and the forearm was maintained. There was no instability in the joint, and grip strength measured 65% of the opposite side. Postoperative magnetic resonance imaging showed survival of the whole graft, including the subchondral portion. In addition to thorough revascularization of the graft, appropriate soft tissue reconstruction using dynamic tendon transfer contributed to the success. When these requirements are fulfilled, the graft can provide a functional and durable result. Although this is a single experience, the authors recommend wrist arthroplasty, rather than arthrodesis, in carefully selected patients.
Limb-sparing surgery with reinnervated free-muscle transfer following radical excision of soft-tissue sarcoma in the extremity.
Limb-sparing surgery is the preferred approach in the management of patients with high-grade soft-tissue sarcomas when local disease can be completely resected. However, conventional treatment focuses only on restoration of basic functions to the remnant limb. Lost functions are not restored to normal, leaving the patient with variable degrees of functional disabilities. This in turn may necessitate further massive reconstructive procedures. Transferred reinnervated free muscles were used to reconstruct functions lost after radical resection of malignant soft-tissue sarcoma of the extremities in 17 patients. The long-term functional outcome included survival of transplanted muscle, speed of neural recovery, and muscle strength and disabilities. All muscles survived. Postoperative follow-up ranged from 27 to 106 months. All muscles except those in a 75-year-old patient were successfully reinnervated. Powerful strength and almost normal limb functions were obtained. Functional scoring of the patients according to the rating system of the Musculoskeletal Tumor Society was 87 percent for the lower extremity and 93 percent for the upper extremity. All patients are presently disease-free. Use of the reinnervated free-muscle transfer in limb-sparing surgery after resection of soft-tissue sarcoma in the extremity may be indicated in the young adult when radical excision of the tumor will result in severe motor functional loss, provided adequate clearance can be obtained and that there is no presence of distant metastasis.