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M Komatsu

Publications and source records attributed to M Komatsu.

At least 19 recordsLinked to original sources
PubMed2001

Size-related and size-unrelated functional heterogeneity among pancreatic islets.

Functional heterogeneity of pancreatic islets was systematically analyzed for the first time using freshly isolated single rat pancreatic islets. First, 60 islets were sequentially exposed to 3, 9.4, 15.6, and 24.1 mM glucose for 30 min each in incubation experiments: 36 (60%) responded in a concentration-dependent and 19 (32%) in an all-or-none manner, and 5 (8%) islets did not respond to high glucose. As a group, the larger the islet, the higher the beta cell glucose sensitivity. However, glucose-stimulated elevation of [Ca2+]i in the beta cell. insulin/glucagon ratio in the islet, and expression of glucose transporter 2, glucokinase, and pancreatic duodenal homeobox factor-1 in the beta cell were not significantly related to islet size. Second, 50 islets were stimulated with 16.7 mM glucose in perifusion. A biphasic insulin release was found in 39 (78%), and no or little first phase response in 11 (22%) islets, irrespective of the islet size. Nevertheless, when the response was plotted as a group, it was clearly biphasic. Islet size, insulin content and the amount of insulin release were positively correlated with each other. In conclusion, there are size-related and size-unrelated functional diversity among pancreatic islets. The reason for such heterogeneity remained to be determined.

Animals↗
PubMed2001

Interaction of Myc-associated zinc finger protein with DCC, the product of a tumor-suppressor gene, during the neural differentiation of P19 EC cells.

Expression of the DCC (deleted in colorectal cancer) protein is strongly induced during the neural differentiation of mouse P19 embryonal carcinoma (EC) cells that occurs when these cells are treated with retinoic acid (RA). Myc-associated zinc finger protein (MAZ) is a DNA-binding protein that is widely expressed and functions in human, mouse and hamster cells as an activator, an initiator or a terminator of transcription. However, the biological functions of MAZ remain elusive. We report here that MAZ associates with the cytoplasmic domain of the DCC protein in vivo and in vitro. Yeast two-hybrid assays confirmed this association. An immunofluorescence study demonstrated that DCC protein is expressed at elevated levels in neuron-like P19 EC cells, in particular in axons, in which the MAZ protein is also expressed. We found that MAZ was translocated from the nucleus to the cytoplasm during the RA-induced terminal differentiation of P19 EC cells with resultant loss of the ability of MAZ to bind to the ME1a1 site of the c-myc promoter. Taken together, our observations imply that the DCC protein might play a critical role as a signaling molecule in the regulation of the transcriptional activity of MAZ during the neural differentiation of P19 EC cells.

Active Transport, Cell Nucleus↗
PubMed2001

Evidence for the association of ultraviolet-C and H(2)O(2)-induced apoptosis with acid sphingomyelinase activation.

Ceramide appears to be a potent second messenger implicated in the regulation of diverse cellular processes such as cell growth and differentiation, gene transcription, ligand binding, and cell death. Environmental stress-induced apoptosis is believed to be associated with the sphingomyelin degradation pathway, which generates ceramide as a second messenger in initiating the apoptosis response. To date, two distinct sphingomyelinases, a lysosomal acid sphingomyelinase (ASM), which is deficient in patients affected with types A and B Niemann-Pick disease (NPD), and a neutral, magnesium-dependent sphingomyelinase (NSM), are candidate enzymes which respond to apoptotic stimulations and cause sphingomyelin hydrolysis and subsequent ceramide generation. Using Epstein-Barr virus (EBV)-transformed lymphoblast cells from type A NPD patient which have defined splicing site mutation in the ASM gene, we showed that ASM-deficient cells were defective in ultraviolet-C (UV-C) and hydrogen peroxide (H(2)O(2)) induced apoptosis. As another induction of apoptosis, we exposed this cell line to serum starvation which influences to p53 expression and leads to apoptosis. There were no differences by the degree of apoptosis between ASM-deficient lymphoblast cells and normal lymphoblast cells. These results are evidence that ASM plays one of the important roles in apoptosis induction by UV-C and H(2)O(2).

Alternative Splicing↗
PubMed2001

Reversal of drug resistance mediated by multidrug resistance protein (MRP) 1 by dual effects of agosterol A on MRP1 function.

We previously isolated agosterol A (AG-A) from a marine Spongia sp. and found that it completely reversed colchicine resistance in P-glycoprotein (Pgp)-over-expressing KB-C2 cells and vincristine resistance in multidrug-resistance protein (MRP)1-over-expressing CV60 cells. However, a tri-deacetylated derivative of AG-A (IAG-A) showed almost no activity in reversing Pgp- or MRP1-mediated drug resistance. In this study, we examined the mechanisms by which AG-A reverses MRP1-mediated drug resistance by investigating the interaction between agosterols and MRP1 in MRP1-over-expressing human KB carcinoma (KB/MRP) cells. [3H]-Leukotriene C4 (LTC4), [3H]-2,4-dinitrophenyl-S-glutathione uptake into membrane vesicles prepared from KB/MRP cells and intracellular [3H]-vincristine accumulation and efflux in KB/MRP cells were measured with or without AG-A and/or inactive IAG-A. AG-A reduced MRP1-mediated [3H]-LTC4 transport in a dose-dependent manner, but IAG-A did not. Inhibition by AG-A was competitive, with a K(i) value of 31 microM. AG-A at 10 microM enhanced the accumulation of [3H]-vincristine in KB/MRP cells to the level of that in control cells in the absence of the agent. Likewise, ATP-dependent efflux of [3H]-vincristine from KB/MRP cells was enhanced compared with KB-3-1 cells and inhibited by AG-A. In addition, AG-A reduced intracellular levels of glutathione, a compound required for MRP1-mediated transport of some anti-cancer drugs. These findings suggest that AG-A reverses MRP1-mediated drug resistance by directly inhibiting the capacity of MRP1 to transport drugs. In addition, the capacity of AG-A to reduce cellular glutathione levels may contribute to the modulating activity of MRP1.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

A new locus for a dominant form of multinodular goiter on 3q26.1-q26.3.

A mass screening program for congenital hypothyroidism has markedly improved prognosis of children with congenital hypothyroidism and also revealed several cases with unknown pathogenesis. We here report two independent Japanese multigeneration families with multinodular goiter (MNG) with euthyroidism and with high TSH. The propositi, 3- and 8-year-old girls in two families, were found during a mass screening. An autosomal dominant pattern of inheritance was suggested in both families. The clinical examinations suggested impaired hormonogenesis but discarded known defects in iodine transport, organification, deficiency of hydrogen peroxide, and thyroid peroxidase. Linkage analysis of the two families including 10 members each using 343 microsatellite markers mapped a single locus independently at D3S1618 (theta = 0) on 3q26.1-q26.3 with a two-point LOD score 3.62 (1.81 for each family) and multipoint LOD score of 3.61 (1.80 for each family). Haplotype inspection delimited an 18-cM interval between D3S1565 and D3S3686.

Adult↗
PubMed2001

The LAX1 and FRIZZY PANICLE 2 genes determine the inflorescence architecture of rice by controlling rachis-branch and spikelet development.

We have analyzed two mutants that exhibit altered panicle architecture in rice (Oryza sativa L.). In lax1-2, which is a new and stronger allele of the previously reported lax mutant, initiation and/or maintenance of rachis-branches, lateral spikelets, and terminal spikelets was severely prevented. In situ hybridization analysis using OSH1, a rice knotted1 (kn1) ortholog, confirmed the absence of lateral meristems in lax1-2 panicles. These defects indicate that the LAX1 gene is required for the initiation/maintenance of axillary meristems in the rice panicle. In addition to its role in forming lateral meristems, the wild-type LAX1 gene acts as a floral meristem identity gene which specifies the terminal spikelet meristem. A comparison of the defects in lax1-1 and lax1-2 plants suggested that the sensitivities to reduced LAX1 activity were not uniform among different types of meristems. In the fzp2 mutant panicle, the basic branching pattern of the panicle was indistinguishable from that of the wild type; however, specification of both terminal and lateral spikelet meristems was blocked, and sequential rounds of branching occurred at the point where the spikelet meristems are initiated in the wild-type panicle. This resulted in the generation of a panicle composed of excessive ramification of rachis-branches. The lax1-1 fzp2 double mutants exhibited a novel, basically additive, phenotype, which suggests that LAX1 and FZP2 function in genetically independent pathways.

Alleles↗
PubMed2001

Muc4/sialomucin complex, an intramembrane modulator of ErbB2/HER2/Neu, potentiates primary tumor growth and suppresses apoptosis in a xenotransplanted tumor.

Overexpression of the membrane mucin MUC4/Sialomucin complex (SMC) has been observed during malignant progression of mammary tumors in both humans and rats, suggesting that deregulation of MUC4/SMC expression might facilitate development of these malignancies. As previously reported, overexpression of SMC results in suppression of both cell adhesion and immune killing of tumor cells. SMC also acts as a ligand for ErbB2/Neu, modulating phosphorylation of the receptor tyrosine kinase in the presence and absence of heregulin. The present studies investigated the effect of Muc4/SMC up-regulation on primary tumor growth using a tetracycline-inducible SMC expression system in a xenotransplanted tumor model. SMC up-regulation provoked rapid growth of transfected A375 melanoma in nude mice. Up-regulation of SMC, however, did not significantly increase proliferation of A375 cells in vitro. Instead, a strong suppression of apoptosis was observed in situ in SMC-overexpressing tumors. These data suggest that Muc4/SMC expression promotes tumor growth in vivo at least in part via suppression of tumor cell apoptosis. Importantly, reduction of apoptosis was also observed in vitro, indicating that anti-apoptotic effect of SMC is independent of tumor-host interactions. These findings strongly suggest that SMC up-regulation alters intracellular signaling to favor cell survival, providing for the first time evidence for the regulation of programmed cell death by a gene of the MUC family.

Apoptosis↗
PubMed2001

The C-terminal region of an Apg7p/Cvt2p is required for homodimerization and is essential for its E1 activity and E1-E2 complex formation.

Apg7p/Cvt2p, a protein-activating enzyme, is essential for both the Apg12p-Apg5p conjugation system and the Apg8p membrane targeting in autophagy and cytoplasm-to-vacuole targeting in the yeast Saccharomyces cerevisiae. Similar to the ubiquitin-conjugating system, both Apg12p and Apg8p are activated by Apg7p, an E1-like enzyme. Apg12p is then transferred to Apg10p, an E2-like enzyme, and conjugated with Apg5p, whereas Apg8p is transferred to Apg3p, another E2-like enzyme, followed by conjugation with phosphatidylethanolamine. Evidence is presented here that Apg7p forms a homodimer with two active-site cysteine residues via the C-terminal region. The dimerization of Apg7p is independent of the other Apg proteins and facilitated by overexpressed Apg12p. The C-terminal 123 amino acids of Apg7p (residues 508 to 630 out of 630 amino acids) are sufficient for its dimerization, where there is neither an ATP binding domain nor an active-site cysteine essential for its E1 activity. The deletion of its carboxyl 40 amino acids (residues 591-630 out of 630 amino acids) results in several defects of not only Apg7p dimerization but also interactions with two substrates, Apg12p and Apg8p and Apg12p-Apg5p conjugation, whereas the mutant Apg7p contains both an ATP binding domain and an active-site cysteine. Furthermore, the carboxyl 40 amino acids of Apg7p are also essential for the interaction of Apg7p with Apg3p to form the E1-E2 complex for Apg8p. These results suggest that Apg7p forms a homodimer via the C-terminal region and that the C-terminal region is essential for both the activity of the E1 enzyme for Apg12p and Apg8p as well as the formation of an E1-E2 complex for Apg8p.

Amino Acid Sequence↗
PubMed2001

Enhancement of fibrinolytics with a laser-induced liquid jet.

BACKGROUND AND OBJECTIVE: There are several problems inherent in the treatment of cerebral embolisms, such as the narrow therapeutic time window and the severe side effects of fibrinolytic drugs. There is thus need of a new method of removing a cerebral thrombus more rapidly using smaller amounts of fibrinolytics. STUDY DESIGN/MATERIALS AND METHODS: The liquid-jet generator was made by insertion of an optical fiber (diameter: 0.6 mm) into a balloon catheter (6 Fr). A pulsed holmium (Ho) YAG laser (pulse duration time = 350 micros) was used as a laser source. The maximum penetration depth of a liquid jet generated with this device into a gelatin artificial thrombus was measured at various stand-off distances (L; distance between the optical fiber end and the catheter exit). Based on the result, a stand-off distance of 13 mm was chosen to investigate the enhancement of urokinase (UK) efficacy by only a single operation of the liquid-jet device in artificial thrombi made of human blood. RESULTS: Maximum penetration depth increased in proportion to L and reached a maximum value (9 mm) when L was around 13 mm. Fibrinolysis rates (%) after incubation with a small amount of UK for 10 and 30 minutes were predominantly raised by a single use of the laser-induced liquid jet (5.4 +/- 2.4 vs. 22.6 +/- 6.1 and 7.3 +/- 3.8 vs. 38.3 +/- 5.6, respectively (mean +/- SD, P < 0.001)). CONCLUSIONS: A laser-induced liquid jet effectively promoted fibrinolysis in vitro with use of only a small amount of fibrinolytics.

Analysis of Variance↗
PubMed2001

Hospital outbreak of MEN-1-derived extended spectrum beta-lactamase-producing Klebsiella pneumoniae.

An outbreak of Klebsiella pneumoniae resistant to broad spectrum cephalosporins occurred in a hospital in the Kinki area in Japan. During 18 months, from February 1998 to July 1999, 23 strains were isolated from 21 patients (10 with pneumonia, 4 with urinary tract infection, 1 with sepsis, 1 with vaginosis, 1 with a wound infection, and 1 with both pneumonia and sepsis; 3 patients showed noninfective colonization with K. pneumoniae) in seven wards, including the intensive care unit. MEN-1-derived gene was detected by polymerase chain reaction from the majority of the strains. Ninety-nine strains of K. pneumoniae were isolated during this period. The isolation rate of K. pneumoniae resistant to broad spectrum cephalosporins was 21%. We distinguished three clones by pulsed-field gel electrophoresis and randomly amplified polymorphic DNA analysis, and one of them was isolated from 18 patients. The presence of an R-plasmid of more than 160 kb was confirmed by plasmid analysis, but it was not possible to obtain transconjugants from all strains. This outbreak of K. pneumoniae was immediately confirmed by genetic analysis, and it was promptly ended by the infection control procedures. This is the first hospital outbreak of MEN-1-producing K. pneumoniae in Japan.

Aged↗
PubMed2001

Muc4/sialomucin complex in the mammary gland and breast cancer.

MUC4 is a one of the membrane mucins of the mucin gene (MUC) family, characterized by mucin tandem repeat domains and a transmembrane domain which associates it with the cell plasma membrane. Although MUC4 is encoded by a single gene, it is produced by epithelial cells as a heterodimer through a proteolytic cleavage mechanism. This heterodimer is found in both membrane and soluble forms associated with epithelia. Functionally, MUC4 is proposed to provide a protective mechanism for vulnerable epithelia, such as those of the airway, eye, female reproductive tract and mammary gland. The protective mechanism(s) may be highjacked by some carcinomas, such as those of the breast, to increase tumor progression. Two mechanisms are proposed to contribute to the MUC4 functions. First, MUC4 acts as an anti-adhesive or anti-recognition barrier at epithelial or tumor cell surfaces. Second, MUC4 can bind the receptor tyrosine kinase ErbB2 and alter its cellular signaling. Expression of MUC4 in mammary gland is repressed by posttranscriptional mechanisms involving basement membrane and TGF-beta, which are relieved during pregnancy to permit secretion of MUC4 into milk. These mechanisms are also abrogated in some breast cancers, providing a scenario for promotion of tumor progression. These observations imply important functions for MUC4 in both normal mammary function and in breast cancer.

Animals↗
PubMed2001

Clinical significance of TT virus in chronic hepatitis C.

BACKGROUND AND AIMS: Much is still unknown about the clinical significance of TT virus (TTV), which has been reported as a candidate for non A-G hepatitis virus. The aim of this study was to clarify the clinical significance of TTV in patients coinfected with TTV and hepatitis C virus (HCV). METHODS: The 95 subjects studied had chronic hepatitis C (CHC), and underwent interferon (IFN) therapy. TT Virus DNA was detected by using polymerase chain reaction. The nucleotide sequences were determined by using a dideoxy chain termination method. A phylogenetic tree was drawn up by using the neighbor-joining method. RESULTS: TT Virus DNA was detected in 37.9% of patients with the use of an open reading frame 1 (ORF1) primer, and in 88.4% of patients by using a 5' untranslated region (5' UTR) primer. Using both sets of primers, no differences were found between TTV-DNA-positive and -negative subjects with CHC in the clinical findings. Serum TTV DNA was eradicated in 30.6% of patients with the ORF1 primer, and in 19.1% of patients with the 5' UTR primer at 6 months after the cessation of IFN therapy. The levels of TTV DNA before IFN therapy were significantly lower in the viral eradication group than in non-eradication group. The changes in alanine aminotransferase (ALT) concentrations were significantly correlated with changes in HCV-RNA in CHC patients with TTV. Moreover, there was no correlation between the changes in TTV DNA and the course of ALT. CONCLUSION: Hepatocellular injury in patients with chronic hepatitis who are coinfected with HCV and TTV appears to primarily be caused by HCV and is less attributable to TTV.

Adult↗
PubMed2001

Ala/Thr60 variant of the Leydig insulin-like hormone is not associated with cryptorchidism in the Japanese population.

BACKGROUND: Leydig insulin-like hormone (Insl3), a member of the insulin-like superfamily, is specifically expressed in Leydig cells of fetal and postnatal murine testis. Recently, the absence of the Insl3 gene has been reported to result in bilateral cryptorchidism in male mice and it has been suggested that mutations of the INSL3 gene may cause cryptorchidism in humans. METHODS: We sequenced the INSL3 gene from five Japanese patients with sporadic bilateral cryptorchidism. Patients' genome DNA was prepared from blood leukocytes. Two exons of the INSL3 gene were amplified by polymerase chain reaction and were sequenced directly. A restriction fragment length polymorphism assay was performed on 70 control samples for analysis of polymorphism. RESULTS: Three of five cases had a heterozygous single-base change, a G to A transition at position 178 of the INSL3 gene, which predicts an alanine (GCC) to threonine (ACC) change at codon 60 (designated A60T). However, the A60T mutation was also found in the normal Japanese population at an allele frequency of 26%, which suggests that this mutation is a common polymorphism and is not associated with the occurrence of cryptorchidism. CONCLUSIONS: No mutation has been found in the INSL3 gene from Japanese patients with idiopathic cryptorchidism. We did find the A60T polymorphism, which was not associated with the occurrence of cryptorchidism.

Adolescent↗
PubMed2001

Effects of nipradilol, a nitric oxide-releasing beta-adrenoceptor blocking agent, on phosphoenolpyruvate carboxykinase gene transcription in a rat hepatoma cell line.

Effects of nipradilol, a beta-adrenoceptor blocker with a nitroxy moiety, on phosphoenolpyruvate carboxykinase (PEPCK) gene transcription were examined using a rat hepatoma cell line, H4IIE cells. Dexamethasone was employed as an enhancer of PEPCK gene transcription. Nipradilol, but not timolol (a beta-blocker without a nitroxy moiety), attenuated PEPCK gene transcription both in the control and the dexamethasone-treated cells. The effects of nipradilol were eradicated by methylene blue (an inhibitor of cellular guanylate cyclase). Nipradilol is a unique beta-blocker that suppresses PEPCK gene transcription in hepatocytes likely through liberation of nitric oxide and resultant activation of guanylate cyclase.

Adrenergic beta-Antagonists↗
PubMed2001

Glutamate is not a major conveyer of ATP-sensitive K+ channel-independent glucose action in pancreatic islet beta cell.

Insulinotropic action of glucose can be categorized as 1) triggering of release, 2) augmentation of exocytosis elicited by Ca2+, and 3) time-dependent potentiation (TDP) of the exocytotic machinery. Glucose-induced closure of ATP-sensitive K+ (K+ATP) channel is required for the first but not for the latter two. We examined the legitimacy of a novel hypothesis that glutamate is a conveyer of the K+ATP channel-independent glucose action, using intact rat pancreatic islets. To this end, we compared glucose and cell permeable glutamate donors such as dimethylglutamate and glutamine for their potency of augmentation and TDP in the presence of diazoxide (250 micromol/l), a K+ATP channel opener. One millimolar leucine was employed as an activator of glutamate dehydrogenase (GDH) as needed. A high concentration (16.7 mmol/l) of glucose applied simultaneously with a depolarizing concentration (50 mmol/l) of K+ augmented (5.80 fold) insulin release elicited by the latter. Pretreatment of the islets with 16.7 mmol/l glucose caused TDP so that insulin release subsequently elicited by 50 mmol/l K+ alone was enhanced (4.70 fold). The augmentation and TDP caused by dimethylglutamate and glutamine (10 mmol/l each), respectively, were very weak (12% of the glucose effect utmost), and dramatically enhanced upon activation of GDH by leucine. Insulinotropic effect of the glutamate donors, but not that of 50 mmol/l K+, was eliminated by 2 mmol/l NaN3, a mitochondrial poison. Glutamate per se serves as a weakly metabolizable mitochondrial fuel, but not a direct conveyer of the K+ATP channel-independent glucose action in the islet beta cell.

Adenosine Triphosphate↗