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Biomedical subjects

K Mitani

Publications and source records attributed to K Mitani.

At least 37 records · Page 2Linked to original sources
PubMed2001

Stable integration of transgenes delivered by a retrotransposon-adenovirus hybrid vector.

Helper-dependent adenoviruses show great promise as gene delivery vectors. However, because they do not integrate into the host chromosome, transgene expression cannot be maintained indefinitely. To overcome these limitations, we have inserted an L1 retrotransposon/transgene element into a helper-dependent adenovirus to create a novel chimeric gene delivery vector. Efficient adenovirus-mediated delivery of the L1 element into cultured human cells results in subsequent retrotransposition and stable integration of the transgene. L1 retrotransposition frequency was found to correlate with increasing multiplicity of infection by the chimeric vector, and further retrotransposition from newly integrated elements was not observed on prolonged culture. Therefore, this vector, which utilizes components of low immunogenic potential, represents a novel two-stage gene delivery system capable of achieving high titers via the initial helper-dependent adenovirus stage and permanent transgene integration via the retrotransposition stage.

Adenoviridae↗
PubMed2001

The corepressor CtBP interacts with Evi-1 to repress transforming growth factor beta signaling.

Evi-1 is a zinc finger nuclear protein whose inappropriate expression leads to leukemic transformation of hematopoietic cells in mice and humans. This was previously shown to block the antiproliferative effect of transforming growth factor beta (TGF-beta). Evi-1 represses TGF-beta signaling by direct interaction with Smad3 through its first zinc finger motif. Here, it is demonstrated that Evi-1 represses Smad-induced transcription by recruiting C-terminal binding protein (CtBP) as a corepressor. Evi-1 associates with CtBP1 through one of the consensus binding motifs, and this association is required for efficient inhibition of TGF-beta signaling. A specific inhibitor for histone deacetylase (HDAc) alleviates Evi-1-mediated repression of TGF-beta signaling, suggesting that HDAc is involved in the transcriptional repression by Evi-1. This identifies a novel function of Evi-1 as a member of corepressor complexes and suggests that aberrant recruitment of corepressors is one of the mechanisms for Evi-1-induced leukemogenesis.

Alcohol Oxidoreductases↗
PubMed2001

Mutations of the Smad4 gene in acute myelogeneous leukemia and their functional implications in leukemogenesis.

The Smad family proteins are critical components of the transforming growth factor (TGF)-beta signaling pathway. TGF-beta is a multipotent cytokine that elicits many biological functions. In particular, TGF-beta exhibits effects on the cell cycle manifested by G1-phase arrest, differentiation, or apoptosis of several target cells, suggesting that disruption of TGF-beta signaling pathway could be involved in cancer formation. Here we show one missense mutation of the Smad4 gene in the MH1 domain (P102L) and one frame shift mutation resulting in termination in the MH2 domain (Delta(483 - 552)) in acute myelogeneous leukemia. Both of the mutated Smad4 proteins lack transcriptional activities. Concomitant expression of the P102L mutant with wild-type Smad4 inactivates wild-type Smad4 through inhibiting its DNA-binding ability. The Delta(483 - 552) mutant blocks nuclear translocation of wild-type Smad4 and thus disrupts TGF-beta signaling. This is the first report showing that mutations in the Smad4 gene are associated with the pathogenesis of acute myelogeneous leukemia and the obtained results should provide useful insights into the mechanism whereby disruption of TGF-beta signaling pathway could lead to acute myelogeneous leukemia. Oncogene (2001) 20, 88 - 96.

Animals↗
PubMed2001

Low frequency of BCL10 gene mutations in B-cell non-Hodgkin's lymphoma.

The BCL10 gene was identified at the breakpoint region of the t(1;14)(p22;q32) translocation in mucosa-associated lymphoid tissue lymphoma. Initially, mutations in the BCL10 gene were reported to occur at a high frequency in various types of lymphomas and solid tumors. However, subsequent studies showed that the mutations were rarely recognized. To evaluate the frequency and spectrum of its mutations in B-cell non-Hodgkin's lymphoma (B-NHL), we screened 56 cases with B-NHL by mutation analysis of exons 2 and 3 of the gene. In addition to 2 polymorphisms, a frame-shift mutation and a missense mutation were identified in 2 cases (3.6%): 1 with diffuse large B-cell lymphoma and the other with mantle cell lymphoma. Both cases showed mutations within exon 3, resulting in a C-terminal truncation in the former and a C-terminal amino acid substitution in the latter. Reverse transcriptase-polymerase chain reaction analysis of the former case revealed that both the mutated and the wild-type alleles were transcribed with or without a sequence modification. Our results, together with recent reports, indicate that BCL10 gene mutations take place in a small population of B-NHL and are not associated with specific histological subtypes.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Oncogenic mechanisms of Evi-1 protein.

Although Evi-1 is thought to promote growth or block differentiation in some cell types, its biological functions have not been elucidated. To explore the mechanisms underlying Evi-1-induced oncogenesis, we investigated whether Evi-1 affects the signaling of transforming growth factor beta (TGF-beta), which inhibits proliferation of a wide range of cell types and is one of the most studied growth regulatory factors. We demonstrated that Evi-1 represses TGF-beta signaling and antagonizes its growth-inhibitory effects. Two separate regions of Evi-1 are responsible for this repression, one of which is the first zinc-finger domain. Through this domain, Evi-1 physically interacts with Smad3, an intracellular mediator of TGF-beta signaling, thereby suppressing the transcriptional activity of Smad3. These results define a novel function of Evi-1 as a repressor of signaling components of TGF-beta. We also demonstrated that Evi-1 represses Smad-induced transcriptional activation by recruiting CtBP as a corepressor. Evi-1 associates with CtBP1 through one of the CtBP-binding consensus motifs within the region from amino acid 544 to 607, and this association is required for the efficient inhibition of TGF-beta signaling. A specific histone deacetylase (HDAc) inhibitor, trichostatin A (TSA), alleviates Evi-1-mediated repression of TGF-beta signaling, suggesting that HDAc is involved in transcriptional repression by Evi-1. This identifies a novel function of Evi-1 as a member of corepressor complexes and suggests that aberrant recruitment of corepressors is one of the mechanisms involved in Evi-1-induced leukemogenesis. These results indicate that specific HDAc inhibitors may be useful in the treatment of Evi-1-induced neoplastic tumors, including myeloid leukemias.

Animals↗
PubMed2001

Argyrophilic grain disease mimicking temporal Pick's disease: a clinical, radiological, and pathological study of an autopsy case with a clinical course of 15 years.

This report concerns an autopsy case of argyrophilic grain disease (AGD) mimicking temporal Pick's disease. The patient was a Japanese woman without hereditary burden who was 89 years old at the time of death. She developed memory impairment and began wandering at the age of 74, followed by prominent character changes about 6 years after disease onset. A neurological examination 5 months before her death revealed poor rapport, unconcern, severe dementia, and double incontinence, without aphasia or muscle rigidity. Serial neuroradiological examination revealed progressive enlargement of the bilateral inferior horns of the lateral ventricle, reflecting progressive atrophy of the medial temporal lobes. Macroscopically, neuropathological examination showed circumscribed atrophy of the bilateral amygdalae, hippocampi, parahippocampal gyri, and lateral occipitotemporal gyri. Histologically, there was neuronal loss in the areas mentioned above, the caudate nucleus, putamen, thalamus, substantia nigra, and locus ceruleus, with ballooned neurons in the cerebral cortex and amygdala. Numerous argyrophilic grains with coiled bodies were present not only in the limbic system, but also in the affected cerebrum. Rare neurofibrillary changes were present in the limbic areas, consistent with Braak stage II, with no senile plaques. Based on these findings and a review of the literature, we note that AGD is clinicopathologically similar not only to mesolimbocortical dementia, but also to atypical senile dementia of Alzheimer type. This report may contribute to the elucidation of the clinicopathological hallmarks of AGD.

Aged↗
PubMed2001

Characterization of anti-myocardial autoantibodies in Japanese patients with dilated cardiomyopathy.

Few previous reports have comprehensively screened all the anti-myocardial autoantibodies (AMCA) in relation to other clinical profiles in patients with idiopathic dilated cardiomyopathy (IDC), so the present study used both immunohistochemistry (FITC) and immunoblotting (IB) for screening patients with IDC in order to characterize the clinical significance of AMCA. Sera were collected from 100 patients with IDC and age-matched 100 healthy control subjects (CTL). For FITC, an unfixed frozen section of human myocardium was used for the standard indirect immunofluorescence; for IB, total cardiac homogenates of the same myocardium were blotted to serum at 2 sets of dilution (1:200 and 1:10,000). The positive rates of AMCA detection for each method were as follows (IDC vs CTL); 39% vs 6% for FITC, 38% vs 4% for IB (1:200), and 10% vs 0% for IB (1:10,000). Fifty-nine patients with IDC and 8 CTL were positive for AMCA by either method, and 18 patients with IDC and 2 CTL were positive for AMCA by both methods. IB-positivity at 1:200 was an independent predictor by multiple logistic regression analysis of non-sustained ventricular tachycardias as well as left ventricular end-diastolic diameter and plasma norepinephrine concentration.

Adult↗
PubMed2001

[Disease-related gene and tumor progression].

Chronic myelogenous leukemia is a stem cell tumor characterized by the t(9; 22)(q34; 11) translocation generating the BCR/ABL chimeric gene. The BCR/ABL fusion gene shows several functions, including inhibition of adhesion to stroma cells and extracellular matrix, activation of mitogenic signalings, inhibition of apoptosis, and degradation of inhibitory proteins, and thereby causes transformation of hematopoietic progenitors. Among its functions, the signal transduction pathways activated by the fusion gene are Ras and MAP kinase pathways, Jak-Stat pathways, PI3 kinase pathways, and Myc pathways. Molecular mechanisms in blastic crisis remains largely unknown. However, loss of functions of tumor suppressor genes such as p53, RB, and p16, activation of oncogene Ras, overexpression of Evi-1 might be involved in disease progression.

Animals↗
PubMed2000

Nonredundant roles of the elongation factor MEN in postimplantation development.

The MEN/ELL gene was cloned as a fusion partner of the MLL gene in the t(11;19)(q23;p13.1) translocation, which is found in adult myeloid leukemia. MEN belongs to a family of RNA polymerase II elongation factors and dysregulated production of MEN through the MLL promoter could cause malignant transformation of myeloid cells. To pursue the physiological role and determine the requirement of the MEN gene product in mouse development, we generated knockout mice (MEN-/-) by gene targeting in embryonic stem cells. After intercrossing heterozygous mice to generate homozygous mutants, we identified no homozygotes (MEN-/-) even at E9.5, as well as after birth, by Southern analysis. Moreover, histological examinations revealed degenerative changes in nearly one-fourth of E6.5 embryos, which were gradually resorbed by E8.5. Our findings demonstrated that MEN-/- mice are embryonic lethal, and die before E6.5 and after implantation. MEN should play a nonredundant role in postimplantation development of mice.

Adult↗
PubMed2000

Mutations of the AML1 gene in myelodysplastic syndrome and their functional implications in leukemogenesis.

The AML1 gene encodes a DNA-binding protein that contains the runt domain and is the most frequent target of translocations associated with human leukemias. Here, point mutations of the AML1 gene, V105ter (single-letter amino acid code) and R139G, (single-letter amino acid codes) were identified in 2 cases of myelodysplastic syndrome (MDS) by means of the reverse transcriptase-polymerase chain reaction single-strand conformation polymorphism method. Both mutations are present in the region encoding the runt domain of AML1 and cause loss of the DNA-binding ability of the resultant products. Of these mutants, V105ter has also lost the ability to heterodimerize with polyomavirus enhancer binding protein 2/core binding factor beta (PEBP2beta/CBFbeta). On the other hand, the R139G mutant acts as a dominant negative inhibitor by competing with wild-type AML1 for interaction with PEBP2beta/CBFbeta. This study is the first report that describes mutations of AML1 in patients with MDS and the mechanism whereby the mutant acts as a dominant negative inhibitor of wild-type AML1.

Amino Acid Substitution↗
PubMed2000

Acetylation of GATA-3 affects T-cell survival and homing to secondary lymphoid organs.

Acetylation of a transcription factor has recently been shown to play a significant role in gene regulation. Here we show that GATA-3 is acetylated in T cells and that a mutation introduced into amino acids 305-307 (KRR-GATA3) creates local hypoacetylation in GATA-3. Remarkably, KRR-GATA3 possesses the most potent suppressive effect when compared with other mutants that are disrupted in putative acetylation targets. Expressing this mutant in peripheral T cells results in defective T-cell homing to systemic lymphnodes, and prolonged T-cell survival after activation. These findings have significant implications in that the acetylation state of GATA-3 affects its physiological function in the immune system and, more importantly, provides evidence for the novel role of GATA-3 in T-cell survival and homing to secondary lymphoid organs.

Acetylation↗
PubMed2000

The evi-1 oncoprotein inhibits c-Jun N-terminal kinase and prevents stress-induced cell death.

Evi-1 encodes a nuclear protein involved in leukemic transformation of hematopoietic cells. Evi-1 possesses two sets of zinc finger motifs separated into two domains, and its characteristics as a transcriptional regulator have been described. Here we show that Evi-1 acts as an inhibitor of c-Jun N-terminal kinase (JNK), a class of mitogen-activated protein kinases implicated in stress responses of cells. Evi-1 physically interacts with JNK, although it does not affect its phosphorylation. This interaction is required for inhibition of JNK. Evi-1 protects cells from stress-induced cell death with dependence on the ability to inhibit JNK. These results reveal a novel function of Evi-1, which provides evidence for inhibition of JNK by a nuclear oncogene product. Evi-1 blocks cell death by selectively inhibiting JNK, thereby contributing to oncogenic transformation of cells.

Adaptation, Biological↗
PubMed2000

Association of insulin receptor substrate proteins with Bcl-2 and their effects on its phosphorylation and antiapoptotic function.

Insulin receptor substrate (IRS) proteins are docking proteins that couple growth factor receptors to various effector molecules, including phosphoinositide-3 kinase, Grb-2, Syp, and Nck. Here we show that IRS-1 associates with the loop domain of Bcl-2 and synergistically up-regulates antiapoptotic function of Bcl-2. IRS-2 but not IRS-3 binds to Bcl-2, and IRS-1 associates with Bcl-XL but not with Bax or Bik. Overexpression of IRS-1 suppresses phosphorylation of Bcl-2 induced by stimulation with insulin, and the hypophosphorylation may lead to its enhanced antiapoptotic activity. The binding site for Bcl-2 is located on the carboxyl half-domain of IRS-1. IRS-3, which lacks the corresponding region, dominant-negatively abrogates the survival effects of IRS-1 and Bcl-2. For the antiapoptotic activity of IRS-1, binding to Bcl-2 is more critical than activating phosphoinositide-3 kinase. Our results indicate that IRS proteins transmit signals from the insulin receptor to Bcl-2, thus regulating cell survival probably through regulating phosphorylation of Bcl-2.

Animals↗
PubMed2000

Real-time automated PCR for early diagnosis and monitoring of cytomegalovirus infection after bone marrow transplantation.

The purpose of this study was to assess the usefulness of real-time automated PCR as a quantitative, highly reproducible, and sensitive method to detect cytomegalovirus (CMV) DNA in blood specimens. Intra- and interassay precision rates were 0.89% (small number of copies [L]), 1.43% (middle number of copies [M]), and 1.12% (high number of copies [H]), and 4.46% (L), 1.51% (M), and 2.28% (H), respectively. The linearity of this assay was obtained between 10 and 10(7) copies/well, with a minimum detection limit of 20 copies/well. Specimens from 55 of 70 healthy subjects were found to be positive for CMV antibody, but CMV DNA was not detected in any of them. In the qualitative assessment of each specimen, the results of the CMV antigenemia assay and those of the real-time PCR assay agreed in 80% (plasma specimens), 79% (all nucleated cells), and 86% (blood) of the cases examined. For eight patients diagnosed as having CMV infection or disease, no sample was positive in the antigenemia assay earlier than in the real-time PCR assay. Furthermore, the results of this assay could be obtained within 8 h. We concluded that the real-time PCR assay is useful for rapid diagnosis of CMV infection and monitoring of clinical courses.

Adolescent↗
PubMed2000

[Essential thrombocythemia in transformation from myelodysplastic syndrome to acute myeloid leukemia with inv(3) after treatment for gastric cancer].

In March 1990, a 61-year-old man was given a diagnosis of essential thrombocythemia with a normal karyotype and subsequently treated with hydroxyurea. In November 1995, he underwent surgery for gastric cancer with thereafter received tegafur/uracil for 2 years. Refractory anemia with excess of blasts in transformation and chromosomal abnormalities including -5, -7, 20q-developed in August 1998. Combined chemotherapy with daunorubicin, cytarabine, mercaptopurine, and prednisolone, had only limited effectiveness. Acute myeloid leukemia was finally diagnosed in October 1998, and chromosomal analysis disclosed inv(3) in addition to -5 and -7. The appearance of inv(3) might be related to leukemic transformation of hematopoietic stem cell disease with an increase in the number of megakaryocytes and platelets.

Aged↗