Biomedical subjects

Ken-ichi Ito

Publications and source records attributed to Ken-ichi Ito.

8 recordsLinked to original sources

PubMed2003

Mutation of proline residues in the NH(2)-terminal region of the multidrug resistance protein, MRP1 (ABCC1): effects on protein expression, membrane localization, and transport function.

The Multidrug Resistance Protein, MRP1 (ABCC1) confers drug resistance and transports organic anions such as leukotriene C(4) (LTC(4)) and 17beta-estradiol 17-(beta-D-glucuronide) (E(2)17betaG). Previous studies showed that portions of the first membrane spanning domain (MSD1) and the cytoplasmic loop (CL3) connecting it to MSD2 are important for MRP1 transport function. We have replaced 12 prolines in MSD1 and CL3 with alanine and determined the effects of these substitutions on MRP1 expression and transport activity. All singly substituted MRP1-Pro mutants could be expressed in HeLa cells, except MRP1-P104A. The expressed mutants also transported LTC(4) and E(2)17betaG, and their K(m) (LTC(4)) values were similar to wild-type MRP1. Expression of the double mutant MRP1-P42/51A was reduced by >80% although it localized to the plasma membrane and transported organic anions. MRP1 expression was also reduced when the first transmembrane helix (amino acids 37-54) was deleted. In contrast, the phenotypes of the multiply substituted CL3 mutants MRP1-P196/205/207/209A and MRP1-P235/255A were comparable to wild-type MRP1. However, Pro(255)-substituted MRP1 mutants showed reduced immunoreactivity with a monoclonal antibody (MAb) whose epitope is located in CL3. We conclude that certain prolines in MSD1 and CL3 play a role in the expression and structure of MRP1.

Alanine↗

PubMed2003

Mutation of the class I beta-tubulin gene does not predict response to paclitaxel for breast cancer.

Mutation of the class I beta-tubulin gene has been reported to be one of the mechanisms that cause resistance to paclitaxel. To assess the relationship between paclitaxel-resistance and class I beta-tubulin gene mutation in breast cancer, Japanese patients with breast cancer were screened for the class I beta-tubulin gene mutation. Total RNA was isolated from 82 breast cancer specimens and the corresponding normal tissues. Twenty-four of the 82 patients were treated with paclitaxel preoperatively and 12 of them did not respond to the treatment. Of the 82 breast cancer patients, 15 (18.3%) had silent polymorphism in exon 4, Leu217Leu (CTG/CTA). However, no mutations showing amino acid substitution of the beta-tubulin gene were detected in any of the patients, including 12 patients who did not respond to paclitaxel. Class I beta-tubulin gene mutation with amino acid substitution was not detected in 82 breast cancer specimens. Our results suggest that mutation of the class I beta-tubulin gene is unlikely to play an important role in the mechanism of resistance to paclitaxel in breast cancer.

Adult↗

PubMed2003

Cardiac myxoma: its origin and tumor characteristics.

Cardiac myxoma is most common among primary cardiac tumors, and its origin and tumor characteristics have been gradually elucidated by recent advances in molecular biology. Prichard's structure in the interatrial septum which was reported to be a candidate for the origin of cardiac myxoma, was revealed to be age-related changes. In hereditary cardiac myxoma "Carney complex", chromosomal abnormalities involving chromosomes 2p, 12 and 17q have been reported, however, no genetic abnormalities of these locus were found in the development of sporadic cases. Cardiac myxoma has multiple differentiating potentials, and recently various amounts of cardiomyocyte-specific transcription factor genes were identified. This indicates that cardiac myxoma might arise from mesenchymal cardiomyocyte progenitor cells. Various cytokines and growth factors such as vascular endothelial growth factor, basic fibroblast growth factor, monocyte chemotactic protein-1 and interleukin-6 were involved in tumor growth and angiogenesis. Although cardiac myxoma usually presents as a benign neoplasm, reports suggesting its malignancy, including recurrence of the tumor, locally invasive myxoma, extension from the heart, and distant metastasis are increasing. These genetic and molecular approaches to cardiac myxoma may prompt the development of therapeutic modalities for treatment of malignancies and cardiac cell regeneration.

Heart Neoplasms↗

PubMed2002

Trans-translation mediated by Bacillus subtilis tmRNA.

Trans-translation, in which a ribosome switches between translation of an mRNA and a tmRNA, produces a chimera polypeptide of an N-terminal truncated polypeptide and a C-terminal tag-peptide encoded by tmRNA. One of the tmRNA binding proteins, a ribosomal protein S1, has not been found in a group of Gram-positive bacteria. In this study, the trans-translation reaction with tmRNA from Bacillus subtilis belonging to this group was examined. When a truncated gene lacking a termination codon was expressed in B. subtilis, a 15-amino acid tag-peptide derived from tmRNA was identified in the C-termini of the trans-translation products. An identical tag-peptide was also found at the C-termini of the products from a truncated gene, when it was coexpressed with B. subtilis tmRNA in Escherichia coli. B. subtilis tmRNA was functional, although much less efficiently, in the in vitro poly(U)-dependent tag-peptide synthesis system of E. coli. A comparison of two bacterial tmRNAs suggests that the rule for determining the tag-initiation point on tmRNA may be the same in Gram-positive and Gram-negative bacteria.

Amino Acid Sequence↗

PubMed2002

Temperature dependence of synaptic responses in guinea pig hippocampal CA1 neurons in vitro.

1. Temperature-dependent properties of synaptic transmission were studied by recording orthodromic responses of the population spike and excitatory postsynaptic potential in CA1 pyramidal neurons of guinea pig hippocampal slices. 2. Increasing the temperature of the perfusing medium from 30 to 43 degrees C resulted in a decrease in the amplitude of the population spike (A-PS) and a reduced slope of the excitatory postsynaptic potential (S-EPSP). Bath application of the gamma-aminobutyric acid receptor antagonist, picrotoxin, or a change in the calcium concentration of the perfusate did not affect the A-PS during heating. 3. Increasing the strength of the synaptic input to that eliciting a PS with an amplitude 50, 75, or 100% of maximal at 30 degrees C resulted in a significant increase in the A-PS during the middle phase of hyperthermia (35-39 degrees C). 4. The long-term potentiation (LTP) induced at either 30 or 37 degrees C showed the same percentage increase in both the amplitude of the population spike and the S-EPSP after delivery of a tetanus (100 Hz. 100 pulses) to CA1 synapses. 5. The results of the present study, therefore, indicate that the decrease in CA1 field potential was linearly related to the temperature of the slice preparation, while LTP was induced in these responses during heating from 30 to 37 degrees C.

Action Potentials↗

PubMed2002

Stromal sarcoma of the breast with leiomyosarcomatous pattern.

We report an unusual case of stromal sarcoma of the breast with leiomyosarcomatous pattern, which recurred locally and was finally treated by radical mastectomy. The tumor was composed of pleomorphic and hyperchromatic spindle-shaped cells arranged in an interdigitating fascicle. The nuclei were of moderate to severe atypia. An average of 10 mitoses per 10 high-power fields was seen. Immunohistochemically, the stromal cells were positive for vimentin and alpha-smooth muscle actin, but negative for S-100 protein, cytokeratin and desmin. The average Ki-67 (MIB1) labeling index in the stromal cells was 34%. Electron microscopic evaluation revealed further evidence of smooth muscle differentiation; stromal cells had frequently indented nuclei, well-developed rough endoplasmic reticulum, thin basal lamina and dense patch-like structures within the cytoplasm. Analysis of previous literature on 17 cases reveals mitotic activity of the tumor seemingly of little prognostic value. This case indicated difficulty in diagnosing leiomyosarcoma. The risk of local recurrence remains even if the surgical margin is free of tumor cells.

Breast Neoplasms↗

PubMed2002

Effects of the mono- and tetrasialogangliosides GM1 and GQ1b on ATP-induced long-term potentiation in hippocampal CA1 neurons.

The effects of the mono- and tetrasialogangliosides, GM1 and GQ1b, on ATP-induced long-term potentiation (LTP) were studied in CA1 neurons of guinea pig hippocampal slices. Application of 5 or 10 microM ATP for 10 min resulted in a transient depression followed by a slow augmentation of synaptic transmission, leading to LTP. LTP induced by treatment with 5 microM ATP was facilitated in hippocampal slices prepared from animals treated for 6 days with a ceramide analog, L-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propranol, which stimulates ganglioside biosynthesis. In addition, LTP induced by 5 microM ATP was significantly enhanced when naive slices were incubated with GQ1b but not with GM1. These results suggest that a cooperative effect between extracellular ATP and GQ1b enhances ATP-induced LTP in hippocampal CA1 neurons. In addition, the LTP induced by 10 microM ATP was blocked by coapplication of the NMDA antagonist AP5 (5 microM or 50 microM), and this effect was partially inhibited by GQ1b pretreatment of the slices, suggesting that in hippocampal CA1 neurons, the enhancing effect of GQ1b on ATP-induced LTP is mediated by modulation of NMDA receptors/Ca(2+) channels.

Adenosine Triphosphate↗

PubMed2002

A naturally occurring mutation in MRP1 results in a selective decrease in organic anion transport and in increased doxorubicin resistance.

The human 190 kDa multidrug resistance protein, MRP1, is a polytopic membrane glycoprotein that confers resistance to a wide range of chemotherapeutic agents. It also transports structurally diverse conjugated organic anions, as well as certain unconjugated and conjugated compounds, in a reduced glutathione-stimulated manner. In this study, we characterized a low-frequency (<1%) naturally occurring mutation in MRP1 expected to cause the substitution of a conserved arginine with serine at position 433 in a predicted cytoplasmic loop of the protein. Transport experiments with membrane vesicles prepared from transfected human embryonic kidney cells and HeLa cells revealed a two-fold reduction in the ATP-dependent transport of the MRP1 substrates, leukotriene C4 (LTC4) and oestrone sulphate. Kinetic analysis showed that this reduction was due to a decrease in Vmax for both substrates but Km was unchanged. In contrast, 17beta-oestradiol-17beta-(D-glucuronide) transport by the Arg433Ser mutant MRP1 was similar to that by wild-type MRP1. Fluorescence confocal microscopy showed that the mutant MRP1 was routed correctly to the plasma membrane. In contrast to the reduced LTC4 and oestrone sulphate transport, stably transfected HeLa cells expressing Arg433Ser mutant MRP1 were 2.1-fold more resistant to doxorubicin than cells expressing wild-type MRP1, while resistance to VP-16 and vincristine was unchanged. These results provide the first example of a naturally occurring mutation predicted to result in an amino acid substitution in a cytoplasmic region of MRP1 that shows an altered phenotype with respect to both conjugated organic anion transport and drug resistance.

ATP-Binding Cassette Transporters↗