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F Tashiro

Publications and source records attributed to F Tashiro.

At least 73 records · Page 4Linked to original sources
PubMed1990

Modulation of c-myc gene expression by extracellular stimuli in rat hepatoma cells.

Modulation of c-myc gene expression by extracellular stimuli in H4IIE rat hepatoma cells was investigated by Northern blot analysis. Treatment of these cells with phorbol 12-O-tetradecanoate 13-acetate (TPA), insulin and concanavalin A (Con A) resulted in transient accumulation of c-myc transcripts within 2 hours. The induction of c-myc mRNA was dose dependent with similar responses for all three agents. The maximally induced c-myc mRNA levels varied from 5- to 15-fold of the control. Treatment with cycloheximide (10 micrograms/ml) and H7, a protein kinase C inhibitor (20 microM), inhibited this induction, suggesting that c-myc induction by these agents requires protein synthesis and protein kinase C activation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1989

Expression vector system based on the chicken beta-actin promoter directs efficient production of interleukin-5.

We examined the promoter activity of the 1.3-kb chicken beta-actin gene sequence located between the 5' flanking region and the proximal region of the second exon. This promoter region showed higher promoter activity than the simian virus 40 (SV40) early promoter or the Rous sarcoma virus (RSV) long terminal repeat (LTR) as assayed by transient lacZ gene expression in mouse L cells. Furthermore, replacement of the 3' splice sequence in this promoter by that derived from the rabbit beta-globin gene resulted in a approximately 2.5-fold enhancement in the synthesis of beta-galactosidase (beta Gal). Introduction of the SV40 origin of DNA replication (ori) into the vector carrying this hybrid promoter, which we designate the AG promoter, markedly enhanced the production of beta Gal in an SV40 T antigen-producing cell, BMT10. We have constructed a useful vector containing the strong AG promoter, several unique restriction sites, a SV40 polyadenylation signal and the SV40 ori for transient expression of cDNA in BMT10 or COS cells. We demonstrate the use of this vector for efficient production of interleukin-5 in BMT10 cells.

Actins↗
PubMed1989

Transgenic mouse model of familial amyloidotic polyneuropathy.

Familial amyloidotic polyneuropathy (FAP) is a dominantly inherited disorder, characterized by the extracellular deposition of amyloid fibrils composed of variant transthyretin (TTR), and by prominent peripheral nerve involvement. We demonstrate that the main cause of this disease is the presence of a point mutation in the TTR gene. However, neither the time of onset nor the clinical course is predictable. To elucidate the molecular pathogenesis of this disease, we constructed transgenic mice carrying and expressing the human mutant TTR gene. In these mice, amyloid is deposited in the alimentary tract as early as age six months, and becomes more remarkable with aging. These transgenic mice should be useful in elucidating factors which modulate the time of onset and the clinical course of FAP, and in establishing therapy for this intractable disorder.

Amyloidosis↗
PubMed1988

Modulation of hormonal induction of tyrosine aminotransferase and glucocorticoid receptors by aflatoxin B1 and sterigmatocystin in Reuber hepatoma cells.

Employing Reuber rat hepatoma cells, H4-II-E, the effects of aflatoxin B1 (AFB1) and sterigmatocystin (STC), which exhibit a similar cytotoxicity but a marked difference in hepatocarcinogenicity, on the hormonal induction of tyrosine aminotransferase (TAT), on glucocorticoid receptors, and on their nuclear acceptor sites were investigated. AFB1 strongly inhibited hydrocortisone-inducible TAT activity. The IC50 value was 0.2 micrograms/ml. AFB1 also showed weak inhibitory effects on insulin- and dibutyryl cyclic AMP-inducible TAT activities. In contrast, the IC50 of STC on hydrocortisone-inducible TAT activity was 3.5 micrograms/ml, about 10 times higher than that of AFB1. Dibutyryl cyclic AMP- and insulin-inductions were not depressed by STC. AFB1 inhibited the formation of cytosolic glucocorticoid receptor-hormone complexes (GRCs) but STC did not. Moreover, AFB1, activated in vitro by the microsomal cytochrome P-450 system, interfered more markedly in the formation of cytosolic GRCs than STC did. Sucrose density gradient analysis of GRCs and Scatchard analysis revealed that AFB1 and STC mainly impaired glucocorticoid receptors and GRC-acceptor sites, respectively. The present data suggest a marked difference between AFB1 and STC with regard to the inhibition of hormonal induction of liver specific enzymes.

Aflatoxin B1↗
PubMed1987

The cytochrome P-450-dependent hydroxylation of T-2 toxin in various animal species.

Gas-liquid chromatography was used to investigate the hepatic and intestinal metabolism of T-2 toxin, a cytotoxic and immunodepressive trichothecene produced by species of Fusarium. The hepatic S-9 and microsomal fractions of various species hydroxylated T-2 toxin to form 3'-hydroxy-T-2. HT-2 toxin, a deacetylated metabolite of T-2 toxin formed by reactions involving microsomal esterases, was also hydroxylated, to 3'-hydroxy HT-2 toxin. Experiments with inhibitors and inducers of the cytochrome P-450-dependent system revealed that these two hydroxylation reactions were catalysed by the cytochrome P-450-dependent monooxygenase system. Species comparisons using rats, mice, guinea-pigs, rabbits, pigs, cows and chickens showed that the rate of the hydroxylation reaction was highest in the hepatic microsomes of guinea-pigs, followed by mice. Chickens possessed a low activity both in the hydrolysis and hydroxylation reactions. No hydroxylated metabolites were produced by the intestinal microsomes of rabbits. These two hydroxylated metabolites were far less cytotoxic to Reuber hepatoma cells than the parent compound, T-2 toxin.

Animals↗
PubMed1986

Expression of the c-Ha-ras and c-myc genes in aflatoxin B1-induced hepatocellular carcinomas.

Expression and activation of several c-oncogenes in seven hepatocellular carcinomas from seven separate rats treated with aflatoxin B1 (AFB1) were examined by Northern and Southern blot analyses. Both c-Ha-ras and c-myc transcripts were elevated at high levels in all hepatomas. Moreover, in one of them, T2-1 hepatoma, the c-myc gene was amplified only in a tumor part of liver without significant rearrangement. N-ras specific transcripts were not elevated in these hepatomas. The present data suggest that the consistently increased expression or deregulation of the c-myc and c-Ha-ras genes may play an important role in the development of hepatomas induced by AFB1.

Aflatoxin B1↗
PubMed1985

Tetrahymena thermophila glutamine tRNA and its gene that corresponds to UAA termination codon.

Nucleotide sequence analysis of one of several tRNA genes cloned from Tetrahymena thermophila macronuclear DNA indicated that it corresponds to a tRNA species having TTA as anticodon. Subsequently, the tRNA species corresponding to that gene was isolated and its nucleotide sequence was determined by post-labeling techniques. The nucleotide sequence was found to be pG-G-U-U-C-C-A-U-A-m2G-U-A-psi-A-G-D-G-G-D- D-A-G-U-A-C-U-G-G-G-G-A-Cm-U-Um-U-A-i6A-A-psi-C-C-C-U-U-G-A-C- m5C-U-G-G-G-U-psi-C-G-m1A-A-U-C-C-C-A-G-U-G-G-G-A-C-C-U-C-C-AOH. This tRNA sequence exactly matched the DNA sequence of the corresponding tRNA gene. The first position of anticodon is 2'-O-methyluridine (Um), forming UmUA as the anticodon, which presumably recognizes the ochre termination codon UAA. This tRNA species is aminoacylated with glutamine by a Tetrahymena crude aminoacyl tRNA synthetase fraction, suggesting that ochre termination codon is used as a glutamine codon during cytoplasmic protein synthesis in Tetrahymena.

Animals↗
PubMed1983

Species differences in zearalenone-reductase activity.

Thin-layer and high-pressure liquid chromatography (HPLC) were used to investigate in several animal species the hepatic metabolites of zearalenone (ZEN), a non-steroidal oestrogenic fungal toxin produced by species of Fusarium. ZEN was reduced to zearalenol (ZEL) by the S-9 fraction of rat-liver homogenates in the presence of NADH or NADPH. In this species ZEN reductase showed two peaks of activity at pH 4.5 and 7.4. Of the species tested, cows showed the highest activity of NADH-dependent ZEN reductase in the hepatic S-9 fraction, followed in decreasing order by mice, pigs, rats, rabbits and guinea-pigs. The S-9 fraction of hamster liver showed optimal activity at pH 5.5 and 8.0 with NADH and at pH 6.0 and 8.5 with NADPH; NADPH was more efficient than NADH only in this species. HPLC showed that alpha-ZEL was a major hepatic metabolite in the rat, mouse, pig, cow and rabbit in incubations at pH 4.5 with either NADH or NADPH and at pH 7.4 with NADH, although at pH 7.4 with NADPH, beta-ZEL was the predominant metabolite. In guinea-pigs, both alpha- and beta-ZELs were produced in roughly similar amounts irrespective of the pH and cofactor, while in hamsters beta-ZEL was the major metabolite. These findings indicate that there are two types of ZEN reductase differing in optimum pH and that the stereospecific reduction of ZEN depends on the source of S-9 and cofactors. Since the oestrogenic activity of alpha-ZEL is about ten times greater than that of ZEN, the possible presence of ZEN metabolites in edible tissues of livestock fed on ZEN-contaminated feeds is an important mycotoxicological problem.

Alcohol Oxidoreductases↗
PubMed1983

Zearalenone reductase from rat liver.

Zearalenone is known to be reduced by rat liver preparations to a more active estrogenic metabolite, alpha-zearalenol. To elucidate the enzymatic feature of zearalenone reductase, we worked out a simple assay procedure for this enzyme using [3H]-zearalenone and thin layer chromatography (TLC). The NAD(P)H-dependent zearalenone reductase localized in the microsomes was most active at pH 4-4.5, while the reductase localized in the cytosol was active at neutral pH. The former enzyme reduced zearalenone only to alpha-zearalenol and the latter reduced both alpha-zearalenol and beta-zearalenol. The microsomal enzyme was solubilized with Triton X-100 and purified by DEAE-Sephadex, hydroxyapatite and Sepharose 4B column chromatographies. The partially purified enzyme showed the following properties. a) The molecular weight of the enzyme was estimated to be about 230,000 by Sepharose 4B chromatography. b) The apparent Km value of the enzyme was 1.0 X 10(-5) M for zearalenone at an NADPH concentration of 1 mM. c) The enzyme activity was inhibited by a high concentration of KCl but not by 1 mM Co2+, Mn2+, Zn2+, EDTA, or 20 mM N-ethylmaleimide.

Alcohol Oxidoreductases↗
PubMed1983

Metabolism of T-2 toxin in Curtobacterium sp. strain 114-2.

The metabolic pathway of T-2 toxin in Curtobacterium sp. strain 114, one of the T-2 toxin-assimilating soil bacteria, was investigated by thin-layer and gas-liquid chromatographic analyses. T-2 toxin added to the basal medium as a single carbon and energy source was biotransformed into HT-2 toxin and an unknown metabolite. Infrared, mass spectrum, proton magnetic resonance, and other physico-chemical analyses identified this new metabolite as T-2 triol. T-2 toxin was first deacetylated by the bacterium into HT-2 toxin, and this metabolite was then biotransformed into T-2 triol without formation of neosolaniol and T-2 tetraol. No trichothecenes remained in the culture medium after prolonged culture. Some properties of T-2 toxin-hydrolyzing enzymes were observed with whole cells, the cell-free soluble fraction, and the culture filtrate. Besides T-2 toxin, trichothecenes such as diacetoxyscirpenol, neosolaniol, nivalenol, and fusarenon-X were also assimilated by this bacterium.

Bacteria↗
PubMed1982

Synthesis of a specific protein induced by zearalenone and its derivatives in rat uterus.

Zearalenone and its derivatives (alpha-zearalenol and alpha-zearalanol), estrogenic mycotoxins produced by Fusarium species, when added in vivo and in vitro to immature rat uteri, induced the incorporation of labeled amino acids into a specific uterine protein (induced protein). When immature rat uteri were incubated with alpha-zearalenol in vitro, the maximum induction of the induced protein synthesis was obtained with 1 x 10(-6) M and the induction was detected 15 min after the start of the incubation. Moreover, this induction was strongly inhibited by prior addition of inhibitors of RNA synthesis such as alpha-amanitin and actinomycin D. The molecular weight of the induced protein obtained by the in vivo and in vitro treatments with zearalenone and alpha-zearalenol was estimated to be about 52,000 by means of SDS-polyacrylamide gel electrophoresis. These findings clearly indicate that these estrogenic mycotoxins, despite their non-steroidal structures, exhibit an estrogenic activity toward target tissues in a similar manner to that of natural estrogens.

Animals↗
PubMed1981

alpha-Zearalenol, a major hepatic metabolite in rats of zearalenone, an estrogenic mycotoxin of Fusarium species.

The chemical and biological properties of the hepatic metabolite of zearalenone, an estrogenic and non-steroidal fungal toxin produced by Fusarium species, were investigated by employing TLC, GC/MS, high pressure liquid chromatography and fluorospectral analyses, as well as uterine weight bioassay in immature mice. All the chemical and physical data supported the view that the major metabolite, obtained by incubating zearalenone with S-9 and microsomes of rat liver in the presence of NADPH, is C-6'-alpha-hydroxylated zearalenone (alpha-zearalenol). The estrogenic activity of this metabolite was several times higher than that of the parent zearalenone, and the results of biological and toxicological evaluations of alpha-zearalenol are discussed.

Animals↗
PubMed1978

Ribonuclease H from rat liver. I. Partial purification and characterization of nuclear ribonuclease H1.

A ribonuclease H, an enzyme that specifically degrades the RNA moiety of RNA-DNA hybrid, has been partially purified from rat liver nuclei and characterized. Neither native or denatured DNA, nor single or double-stranded synthetic polyribonucleotides were degraded by the enzyme. The enzyme possesses a molecular weight of about 36,000 and requires alkaline pH, magnesium ions, and ammonium sulphate for maximum activity. The enzyme acts on the hybrid as an endonuclease, resulting in oligonucleotides with 3'-hydroxyl termini. The properties of this enzyme were distinct from those of the rat liver cytosol enzyme reported by Roewekamp and Sekeris in many respects, such as molecular weight, optimal pH and requirements for divalent cations. Preliminary experiments suggest that the nuclear enzyme is localized in the nucleoplasm and nucleoli. These results indicate that multiple forms of ribonuclease H exist in different regions of rat liver cells.

Animals↗
PubMed1978

Ribonuclease H from rat liver. II. Partial purification and characterization of cytosol ribonuclease H1.

We have detected in rat liver cytosol three enzymes (termed C-1, C-2, and C-3) which cleaved the RNA moiety of RNA-DNA hybrid. These enzymes were separated from each other by DEAE-Sephadex and Sephadex G-200 chromatography. C-1 and C-2 specifically act on the RNA moiety of RNA-DNA hybrid, while C-3 degrades single-stranded RNA as well as the RNA of the hybrid. The molecular weights of C-1, C-2, and C-3 are about 110,000, 35,000 and 110,000 daltons, respectively, and their activities are absolutely dependent on divalent cations such as Mg2+ and Mn2+. Cleavage by C-1 and C-2 is endonucleolytic, producing mostly oligonucleotides and a small amount of mononucleotides which possess 3'-hydroxyl termini. It seems likely that C-2 is originally present in the nucleus and is released into cytosol because of its loose binding to the nuclear components. As for biochemical properties, C-1 is very similar to the cytosol ribonuclease H initially reported by Roewekamp and Sekeris, and C-2 is very similar to the nuclear ribonuclease H reported by us in the preceding paper.

Animals↗
PubMed1976

Multiple forms of nuclear ribonuclease H from Tetrahymena pyriformis.

Three types of ribonuclease H were detected in the isolated macronuclei of Tetrahymena pyriformis GL, partially purified and characterized. They were eluted at around 0.15 M, 0.3 M and 0.4 M of ammonium chloride in phosphocellulose chromatography, and termed H-1, H-2 and H-3, respectively. The partially purified enzymes have following properties. a) These enzymes specifically hydrolyze the RNA moiety of RNA . DNA hybrid. Neither DNA moiety of RNA . DNA hybrid nor the RNA molecule dissociated by heat from RNA . DNA hybrid is hydrolyzed by these enzymes. b) The enzymes are most active at pH 8.5-9.0. c) They require divalent cations such as Mg2+ or Mn2+ for their activities. The optimal concentrations of these cations are different among these enzymes. d) The mode of cleavage by these enzymes is endonucleoytic, producing mostly oligonucleotides and a small amount of mononucleotides which possess 3'-hydroxyl and 5'-phosphate termini.

Ammonium Sulfate↗