Biomedical subjects

H Nishitani

Publications and source records attributed to H Nishitani.

At least 19 recordsLinked to original sources

PubMed2004

DNA replication licensing.

The DNA replication licensing system ensures that chromosomal DNA is replicated precisely once before cell division occurs. A DNA helicase must be loaded on origin DNA for replication to initiate. Considerable evidence suggests that the MCM complex acts as a replicative helicase in eukaryotes. When the MCM complex is loaded on the chromatin, the replication origin is formally defined as being licensed for replication. Licensing takes place several hours before origins are activated to undergo replication in S-phase. Genetic and biochemical studies show that the licensing process is well conserved in eukaryotes. Cyclin Dependent Kinases (CDKs), the master regulators of the cell cycle, coordinate the initiation of the two key cell cycle events, replication of DNA and its segregation at mitosis. Eukaryotes have developed complex regulatory mechanisms to ensure that origin licensing is coordinated with these events so that genome integrity is preserved during successive cell divisions.

Animals↗

PubMed2004

Imaging findings of urachal mucinous cystadenocarcinoma associated with pseudomyxoma peritonei.

Pseudomyxoma peritonei is an uncommon neoplastic condition in which gelatinous fluid-like materials are observed in the peritoneal cavity caused by the dissemination of mucinous adenocarcinoma. Although ruptured appendiceal mucocele is the most common cause, tumors arising from other organs may also cause pseudomyxoma peritonei. We report the imaging findings of an extremely rare case of urachal mucinous adenocarcinoma associated with pseudomyxoma peritonei on computed tomography and magnetic resonance imaging with histopathologic correlation.

Aged↗

PubMed2003

A novel nuclear protein, Twa1, and Muskelin comprise a complex with RanBPM.

A truncated human RanBPM has been isolated as a protein binding to Ran, Ras-like nuclear small GTPase. Full-sized human RanBPM cDNA which was recently isolated, was found to encode a protein of 90 kDa which comprises a large protein complex. Consistent with this finding, several proteins were found to be co-precipitated with RanBPM by immunoprecipitation analysis. Accordingly, in the present study, we screened the human cDNA library by the two-hybrid method using RanBPM cDNA as bait. One novel protein designated as Twa1 (Two hybrid associated protein No. 1 with RanBPM), and two known proteins, a human homologue (hMuskelin) of mouse Muskelin and HSMpp8 were isolated repeatedly. Twa1 was well conserved through evolution and was localized within the nucleus. Interestingly, in addition to Muskelin and RanBPM, Twa1 was found to possess the LisH-CTLH motif which is detected in proteins involved in microtubule dynamics, cell migration, nucleokinesis and chromosome segregation. These functions overlap with functions suggested for the RanGTPase cycle. Immunoprecipitation and gel-filtration analyses indicated that both Twa1 and hMuskelin did indeed comprise a protein complex with RanBPM. Taken together with the fact that RanBPM interacts with Ran, our present findings suggested that there is an as yet uncovered function of the RanGTPase cycle.

Adaptor Proteins, Signal Transducing↗

PubMed2002

A characteristic feature of acute haematomas in the brain on echo-planar diffusion-weighted imaging.

Diffusion-weighted MRI (DWI) is used in the diagnosis of acute ischaemic disease of the brain, but it is not clear whether or not it can be used to differentiate an acute haematoma from an infarct. Our purpose was to identify any characteristic feature of acute haematomas which can be recognised on DWI and to evaluate the usefulness of DWI in acute cerebral stroke. We examined nine patients with acute haemorrhage using CT and MRI including DWI. We measured the volume and apparent diffusion coefficient (ADC) of the haematomas. All showed heterogeneous signal on DWI, and the centre of the large (>20 ml) haematomas especially a mixed pattern with high and low signal. The characteristic feature of acute haematomas was a peripheral low-signal region, found in all subjects regardless of the size of the haematoma; acute infarcts did not show this. This low-signal rim on DWI may be useful for differentiating an acute haematoma from an infarct.

Adult↗

PubMed2001

The human licensing factor for DNA replication Cdt1 accumulates in G1 and is destabilized after initiation of S-phase.

S-phase onset is controlled, so that it occurs only once every cell cycle. DNA is licensed for replication after mitosis in G(1), and passage through S-phase removes the license to replicate. In fission yeast, Cdc6/18 and Cdt1, two factors required for licensing, are central to ensuring that replication occurs once per cell cycle. We show that the human Cdt1 homologue (hCdt1), a nuclear protein, is present only during G(1). After S-phase onset, hCdt1 levels decrease, and it is hardly detected in cells in early S-phase or G(2). hCdt1 can associate with the DNA replication inhibitor Geminin, however these two proteins are mostly expressed at different cell cycle stages. hCdt1 mRNA, in contrast to hCdt1 protein, is expressed in S-phase-arrested cells, and its levels do not change dramatically during a cell cycle, suggesting that proteolytic rather than transcriptional controls ensure the timely accumulation of hCdt1. Consistent with this view, proteasome inhibitors stabilize hCdt1 in S-phase. In contrast, hCdc6/18 levels are constant through most of the cell cycle and are only low for a brief period at the end of mitosis. These results suggest that the presence of active hCdt1 may be crucial for determining when licensing is legitimate in human cells.

Animals↗

PubMed2001

Full-sized RanBPM cDNA encodes a protein possessing a long stretch of proline and glutamine within the N-terminal region, comprising a large protein complex.

Previously isolated RanBPM, a Ran-binding protein in the microtubule-organizing center, which had been thought to play a role in Ran-stimulated microtubule assembly, turned out to be a truncated protein. To clarify the function of RanBPM, we cloned the full-sized RanBPM cDNA that encodes a 90 kDa protein, compared to the previously isolated cDNA that encoded a 55 kDa protein. The newly cloned 5' coding region contains a great number of cytidine and guanidine nucleotides, like the CpG island. Thus, full-sized RanBPM cDNA encodes a long stretch of proline and glutamine residues in the N-terminal region. It comprises a protein complex of more than 670 kDa. Ran was detected in this complex when RanBPM and Ran were both ectopically expressed. New antibodies to RanBPM were prepared against three different regions of RanBPM. All of them detected a 90 kDa protein that is predominantly localized both in the nucleus and in the cytoplasmic region surrounding the centrosome, but none of them stained the centrosome. In this context, our previous notion that RanBPM is a centrosomal protein should be discarded. RanBPM is well conserved in the animal kingdom. It may play an important role in uncovering Ran-dependent nuclear events.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Evaluation of female intrapelvic tumors by clinical proton MR spectroscopy.

We measured metabolites in large tumors of the female pelvis (23 cases total: 6 malignant cases, 17 benign cases) using single-voxel proton magnetic resonance (MR) spectroscopy and evaluated the clinical significance of this method in the differential diagnosis of female pelvic tumors. The characteristically obtained signal was lactate, which was detected not only in all the malignant tumors but also in some of the benign tumors. However, the lactate signals of the malignant tumors tended to form higher peaks than those of benign tumors, which was a finding consistent with the result of the earlier in vitro study reported in ovarian tumors. The signal of choline-containing compounds (Cho) was found only in solid tumors, and the signal intensity varied among different histological types of tumors, possibly reflecting metabolic activity of the cell membrane. We considered that proton MR spectroscopy (MRS) of intrapelvic tumors would be useful for the diagnosis of the nature of female intrapelvic tumors. J. Magn. Reson. Imaging 2001;13:912-917.

Adult↗

PubMed2001

Multivariate analysis of regional metabolic differences in normal ageing on localised quantitative proton MR spectroscopy.

We performed multivariate analysis of regional differences and normal age-related changes in metabolites in the lentiform nucleus and frontal lobe, as measured by proton MRS. The cerebrospinal fluid (CSF) in the measurement area was estimated and the metabolite concentration adjusted. The concentration of N-acetylaspartate (NAA) in the lentiform nucleus decreased with ageing (F = 4.11, P < 0.01), but that in the frontal lobe did not change (F = 0.93, P = 0.45). This is in marked contrast with pathological dementia, such as Alzheimer's disease. In this multivariate analysis, the normal change in metabolism with ageing differed depending on the cerebral region, suggesting that metabolite concentrations, especially that of NAA may be useful metabolic indices for discriminate normal ageing from pathological dementia.

Adult↗

PubMed2001

Regional magnetic resonance spectroscopy of the brain in autistic individuals.

We studied the variations in the concentration of metabolites with brain region and age in autistic individuals and normal controls using multiple analysis of covariance. We examined 55 autistic individuals (2-21 years old, 47 male and eight female) and 51 normal children (3 months-15 years old, 26 boys and 25 girls). Single volumes of interest were placed in the frontal, parietal and temporal region on both sides, the brain stem and cingulate gyrus. The concentration of each metabolite was quantified by the water reference method. The concentration of N-acetylaspartate in the temporal regions (Brodmann's areas 41 and 42) in the autistic individuals were significantly lower than those in the controls (P < 0.05), but concentrations in other regions were not significantly different between the autistic individuals and controls. This suggests low density or dysfunction of neurones in Brodmann's areas 41 and 42 in autistic individual, which might be related to the disturbances of the sensory speech centre (Wernicke's area) in autism.

Adolescent↗

PubMed2001

Localization of human airway trypsin-like protease in the airway: an immunohistochemical study.

Human airway trypsin-like protease (HAT) has been isolated from mucoid sputum of patients with chronic airway diseases. In order to clarify the cellular source of this novel protease in the human airway, we examined the localization of immunoreactive HAT in bronchial tissues obtained at surgery and fixed in 4% paraformaldehyde using an extremely sensitive immunohistochemical technique called a catalyzed signal amplification method and a monoclonal antibody against recombinant HAT. HAT immunoreactivity was demonstrated in cytoplasm of ciliated cells of bronchial epithelium and/or at the basal part of cilia. No positive reaction was found in submucosal glands or mast cells. The heterogeneous distribution of HAT immunoreactivity within the bronchial epithelium indicates that its expression might be changeable and that it might be closely related to the physiological status of the airway epithelium. Non-specific but intense reaction caused by endogenous avidin-binding activity (EABA) was selectively detected in submucosal glands, but was effectively blocked by successive treatments with avidin and biotin. These results indicate that HAT may be synthesized in the ciliated cells and that it may play some physiological roles within the epithelial layer and on the airway surface. It is necessary to keep in mind that some cells show strong EABA, especially when a highly sensitive immunohistochemical technique is applied.

Antibodies, Monoclonal↗

PubMed2001

Status of PACS and technology assessment in Japan.

The situation of PACS installations in Japan from 1987 to 1999 has been investigated. By 1999, 751 PACS units have been installed. Of these, 613 are small-size PACS with less than four image display terminals, 96 are medium-size with 5-14 terminals and 42 are large-size with 15 up to 300 terminals. The 42 hospitals with large sized PACS have been retrospectively investigated from 1984 for PACS experiments and from 1989 for PACS operation. Most of these 42 hospitals have increased the number of PACS terminals by installing additional PACS units instead of reinforcing the existing single PACS. Some (23%) PACS installations have obviously not been successful because of low image transfer speed and inadequate image quality. The use of DICOMM interfaces has increased the number of modalities connected to PACS and influenced the spread of PACS installations in Japan. The status of HIS and RIS coupling to PACS and the use of PACS in primary diagnosis or in image referral are discussed. Assessment of PACS is now in a very early stage. Baseline studies of HIS/RIS/PACS effectiveness have been carried out to assess quantitatively the PACS merit. Radiologists' answers to the questionnaire on PACS usage do not fully support the finding that the number of PACS installations is growing in Japan.

Humans↗

PubMed2001

Thrombin promotes fibroblast proliferation during the early stages of experimental radiation pneumonitis.

Huang, L., Ogushi, F., Tani, K., Ogawa, H., Kawano, T., Endo, T., Izumi, K., Ueno, J., Nishitani, H. and Sone, S. Thrombin Promotes Fibroblast Proliferation during the Early Stages of Experimental Radiation Pneumonitis. Radiat. Res. 156, 45-52 (2001). To clarify the role of thrombin in the pathogenesis of radiation-induced pneumonitis, we measured the thrombin activity and fibroblast growth-inducing activity in bronchoalveolar lavage fluid obtained from the irradiated lungs of rats at 1, 2, 4, 8 and 18 weeks after irradiation. Thrombin activity was not detected in the bronchoalveolar lavage fluid from unirradiated rats, but the bronchoalveolar lavage fluid from irradiated rats showed significantly increased thrombin activity which reached a maximum at 4 weeks after treatment. Higher fibroblast growth-inducing activity was detected in the bronchoalveolar lavage fluid from irradiated rats at 4 and 18 weeks than in fluid from unirradiated rats. Bronchoalveolar lavage fluid from irradiated rats that were pretreated with the thrombin inhibitors antithrombin III and argatroban showed significantly inhibited fibroblast growth-inducing activity and thrombin activity at 4 weeks. However, these thrombin inhibitors did not inhibit fibroblast growth-inducing activity in bronchoalveolar lavage fluid from irradiated rats at 18 weeks. Purified rat thrombin similarly induced proliferation of fibroblasts derived from irradiated and unirradiated rats. These findings suggest that thrombin may play an important role as a fibroblast growth-inducing factor during the early stages of radiation pneumonitis.

Animals↗

PubMed2000

The Cdt1 protein is required to license DNA for replication in fission yeast.

To maintain genome stability in eukaryotic cells, DNA is licensed for replication only after the cell has completed mitosis, ensuring that DNA synthesis (S phase) occurs once every cell cycle. This licensing control is thought to require the protein Cdc6 (Cdc18 in fission yeast) as a mediator for association of minichromosome maintenance (MCM) proteins with chromatin. The control is overridden in fission yeast by overexpressing Cdc18 (ref. 11) which leads to continued DNA synthesis in the absence of mitosis. Other factors acting in this control have been postulated and we have used a re-replication assay to identify Cdt1 (ref. 14) as one such factor. Cdt1 cooperates with Cdc18 to promote DNA replication, interacts with Cdc18, is located in the nucleus, and its concentration peaks as cells finish mitosis and proceed to S phase. Both Cdc18 and Cdt1 are required to load the MCM protein Cdc21 onto chromatin at the end of mitosis and this is necessary to initiate DNA replication. Genes related to Cdt1 have been found in Metazoa and plants (A. Whitaker, I. Roysman and T. Orr-Weaver, personal communication), suggesting that the cooperation of Cdc6/Cdc18 with Cdt1 to load MCM proteins onto chromatin may be a generally conserved feature of DNA licensing in eukaryotes.

Cell Cycle↗

PubMed2000

Differences in water diffusion and lactate production in two different types of postinfectious encephalopathy.

We compared two different types of postinfectious encephalopathy using magnetic resonance imaging (MRI), including diffusion-weighted images and MR spectroscopy. Acute disseminated encephalomyelitis (ADEM) and acute necrotizing encephalopathy (ANE) showed different distribution of abnormal intensity areas and different diffusion of water measured by diffusion-weighted imaging (DWI). Proton MR spectroscopy (MRS) showed lactate production in both cases, which returned to a normal range; the rate of increased lactate production was much lower in the ANE case. Water diffusion showed a difference in pathophysiological background between the two encephalopathies, but the lactate elevation observed by proton MRS did not correlate with clinical severity.

Body Water↗

PubMed2000

Premature chromatin condensation caused by loss of RCC1.

Hamster rcc1 mutant, tsBN2, prematurely enter mitosis during S phase. RCC1 is a guanine nucleotide exchanging factor for a small G protein Ran and localised on the chromatin, whereas RanGTPase activating protein is in the cytoplasm. Consistently, Ran shuttles between the nucleus and the cytoplasm, carrying out nucleus-cytosol exchange of macromolecules, which regulates the cell cycle. The finding that loss of RCC1 which disturbs nuclear protein export due to loss of RanGTP, abrogates the check point control suggests that RCC1 senses the status of the chromatin, such as replication, and couples it to the cell cycle progression through Ran.

Animals↗

PubMed2000

Overexpression of wild-type Akt1 promoted insulin-stimulated p70S6 kinase (p70S6K) activity and affected GSK3 beta regulation, but did not promote insulin-stimulated GLUT4 translocation or glucose transport in L6 myotubes.

We have developed a simple, direct and sensitive method to detect GLUT4 on the cell surface. Using this system, we found that PI3-kinase plays a key role in the signaling pathway of insulin-stimulated GLUT4 translocation. One of the down stream effectors of PI3-kinase is serine-threonine kinase Akt (protein kinase B, RAK-PK), but the involvement of Akt in insulin-stimulated GLUT4 translocation is controversial. To investigate whether Akt1 regulates insulin-stimulated GLUT4 translocation and glucose uptake in L6 myotubes, we established L6 myotubes stably expressing c-myc epitope-tagged GLUT4 (GLUT4myc) and mouse wild type (WT) Akt1. We found that overexpression of WT Akt1 promoted insulin-stimulated p70S6 kinase (p70S6K) activity and increased the basal activity of GSK3 beta, but did not promote insulin-stimulated GLUT4 translocation or glucose uptake. These data supported the result that Akt is not a main signaling molecule to transmit the signal of insulin-stimulated GLUT4 translocation or glucose uptake from insulin-activated PI3-kinase.

Amino Acid Sequence↗

PubMed2000

[Clinical evaluation of the diagnosis of neuronal reversibility with acute cerebral infarction using ADC by diffusion weighted echo planar imaging].

The possibility of diagnosing neuronal reversibility with acute cerebral infarction was studied using ADC measured by diffusion weighted imaging (DWI). The subjects were eleven patients who underwent DWI within 24 hours of onset. The area of abnormal signal on DWI during the acute stage was visually compared with that on T2-WI in the subacute phase. ADC was calculated in the two different abnormal areas on DWI, which were differentiated by the presence or absence of abnormality on T2-WI in the subacute phase. The abnormal signals of three cases showed an obviously narrowed area on DWI in the acute phase compared with the abnormality on T2-WI in the sub-acute phase. ADCs of the ischemic areas in DWI abnormalities that showed no abnormality on subacute T2-WI were slightly higher than those of the infarct areas with remaining abnormal signals on T2-WI. However, no statistically significant difference was found between these two regions, because there were large variations within each pixel. We considered that the diagnosis of neuronal reversibility in acute cerebral infarction was difficult using ADC values only and that other parameters such as perfusion or blood volume will be necessary to improve diagnostic quality prior to determining therapy.

Acute Disease↗

PubMed1999

Self-organization of microtubule asters induced in Xenopus egg extracts by GTP-bound Ran.

The nucleotide exchange activity of RCC1, the only known nucleotide exchange factor for Ran, a Ras-like small guanosine triphosphatase, was required for microtubule aster formation with or without demembranated sperm in Xenopus egg extracts arrested in meiosis II. Consistently, in the RCC1-depleted egg extracts, Ran guanosine triphosphate (RanGTP), but not Ran guanosine diphosphate (RanGDP), induced self-organization of microtubule asters, and the process required the activity of dynein. Thus, Ran was shown to regulate formation of the microtubule network.

Animals↗