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Akio Matsushita

Publications and source records attributed to Akio Matsushita.

8 recordsLinked to original sources
PubMed2004

Thyroid-hormone-dependent negative regulation of thyrotropin beta gene by thyroid hormone receptors: study with a new experimental system using CV1 cells.

The molecular mechanism involved in the liganded thyroid hormone receptor suppression of the TSHbeta (thyroid-stimulating hormone beta, or thyrotropin beta) gene transcription is undetermined. One of the main reasons is the limitation of useful cell lines for the experiments. We have developed an assay system using non-pituitary CV1 cells and studied the negative regulation of the TSHbeta gene. In CV1 cells, the TSHbeta-CAT (chloramphenicol acetyltransferase) reporter was stimulated by Pit1 and GATA2 and suppressed by T3 (3,3',5-tri-iodothyronine)-bound thyroid hormone receptor. The suppression was dependent on the amounts of T3 and the receptor. Unliganded receptor did not stimulate TSHbeta activity, suggesting that the receptor itself is not an activator. Analyses using various receptor mutants revealed that the intact DNA-binding domain is crucial to the TSHbeta gene suppression. Co-activators and co-repressors are not necessarily essential, but are required for the full suppression of the TSHbeta gene. Among the three receptor isoforms, beta2 exhibited the strongest inhibition and its protein level was the most predominant in a thyrotroph cell line, TalphaT1, in Western blotting. The dominant-negative effects of various receptor mutants measured on the TSHbeta-CAT reporter were not simple mirror images of those in the positive regulation under physiological T3 concentration.

Animals↗
PubMed2003

Beta-catenin/Tcf-1-mediated transactivation of cyclin D1 promoter is negatively regulated by thyroid hormone.

Cyclin D1 is an oncogenic cyclin frequently over-expressed in cancer. To examine the effect of thyroid hormone (T3) and its receptor (TR) on the transcription of cyclin D1 gene, we co-transfected the chloramphenicol acetyl-transferase (CAT) reporter plasmid containing cyclin D1 promoter together with the expression plasmids for TRbeta1 and wild-type or mutant beta-catenin (SA) into 293T cells. In the presence of T3, beta-catenin-dependent transactivation of cyclin D1 promoter was suppressed by co-transfection of TRbeta1. The suppression by T3/TRbeta1 was in a dose-dependent manner. The CAT reporter gene in which Tcf/Lef-1 sites were fused to heterologous promoter was also suppressed by T3/TRbeta1. Furthermore, inhibition of endogenous wild-type beta-catenin by T3/TRbeta1 was observed in SW480 colon carcinoma cells with mutation of the adenomatous polyposis coli gene. These results indicate that the T3-bound TR inhibits the transcription of cyclin D1 through the Tcf/Lef-1 site, which is positively regulated by the Wnt-signaling pathway.

Cells, Cultured↗
PubMed2003

Embryonic lethal effect of expressing a dominant negative mutant human thyroid hormone receptor alpha1 in mice.

Resistance to thyroid hormone (RTH) is caused mainly by mutations of the thyroid hormone receptor (TR) beta gene. Although, in vitro, TRalpha1 and TRbeta1 mutants exhibit similar dominant negative effects against wild-type TR, no TRalpha mutants have ever been identified in RTH patients. It has been postulated that mutations in TRalpha gene may be lethal, compensated completely by intact TRbeta or associated with phenotypic manifestations different from RTH. To investigate the consequences of mutant TRalpha1 expression in vivo, we tried to generate two different lines of transgenic mice which express a strong or a weak dominant negative mutant TR alpha1, respectively. First, we expressed betaF451X identified in a patient with severe RTH and alphaF397X, which has an identical C-terminal truncation and a similarly strong dominant negative potency to betaF451X, under the control of human polypeptide chain elongation factor 1alpha promoter. Six betaF451X-transgenic mice were born from 223 transferred embryos, giving a transgenic frequency of 2.7%. By contrast, expression of alphaF397X resulted in quite a low transgenic frequency with 0.39% of the transferred embryos bearing the transgene. Only three transgenic mice were born with no apparently overt abnormalities, of which one male produced F1 offspring. The transgenic progeny expressed alphaF397X in the testis but we did not succeed in generating transgenic mice expressing alphaF397X in multiple organs. To avoid toxic effects mediated by a strong dominant negative activity of mutant TRalpha1, we exchanged alphaF397X for alphaK389E, which has an identical missense mutation and a relatively weak transdominant potency as betaK443E identified in a patient with mild RTH. When expressed by cytomegalovirus immediate early enhancer-chicken beta-actin promoter, we did not succeed in creating alphaK389E-transgenic mice despite three independent transgene-injections. These findings define crucial in vivo functions of mutant TRalpha1s during mouse fetal development and suggest the possibility that the expression of a dominant negative mutant TRalpha1 in extensive tissues from the early embryonal stages might be lethal.

Animals↗
PubMed2002

Synergistic effects of topoisomerase I inhibitor, 7-ethyl-10-hydroxycamptothecin, and irradiation in a cisplatin-resistant human small cell lung cancer cell line.

7-ethyl-10-[4-(1-piperidyl)-1-piperidyl] carbonyloxy-camptothecin, a topoisomerase I (topo I) inhibitor, is one of the most active agent against lung cancer, and its radiosensitizing effect has been reported recently. We evaluated a combination in vitro effect of irradiation and 7-ethyl-10-hydroxy-CPT (SN-38), an active metabolite of 7-ethyl-10-[4- (1-piperidyl)-1-piperidyl] carbonyloxy-camptothecin, on a human small cell lung cancer cell line (SBC-3) and its cisplatin-resistant subline (SBC-3/CDDP). Growth-inhibitory effects of irradiation with or without SN-38 were determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. A modified isobologram method was used to evaluate the treatment interaction. The combination of irradiation and SN-38 showed a synergistic inhibitory effect on the growth of SBC-3/CDDP despite its cross-resistance to irradiation and SN-38. In contrast, the same combination showed only an additive effect on the growth of parental SBC-3 cells. There was no significant difference in topo I protein expression between these two cell lines. In SBC-3 cells, topo I catalytic activity was suppressed by 4 Gy of irradiation, without a decrease of nuclear topo I protein, whereas the exposure of SBC-3 cells to 1 microM SN-38 subsequent to irradiation showed no remarkable additional effects on both topo I activity and protein content. On the other hand, in SBC-3/CDDP cells, topo I activity was unchanged by irradiation, but the subsequent exposure to SN-38 gave rise to a decrease in topo I activity, which was accompanied by a significant decrease in the topo I protein content (P = 0.02). These observations may indicate that SN-38 induces sequestration of topo I onto DNA in radiation-treated SBC-3/CDDP cells and suggest that the synergistic effect of irradiation and SN-38 in SBC-3/CDDP cells was considered attributable to DNA repair-related enhanced recruitment of topo I onto the damaged DNA.

Antineoplastic Agents↗
PubMed2002

[Familial congenital hypothyroidism due to loss of function mutation of the thyrotropin receptor (resistance to thyrotropin)].

The TSH receptor belongs to a subfamily of G protein-coupled receptors that mediates the effect of TSH in thyroid development and hormone synthesis. Similarly to many other G protein--coupled receptors, both gain and loss of function mutations have been found in the TSH receptor. Loss of function mutations in the TSH receptor gene were first described in three siblings with resistance to TSH in 1995. To date, 13 pedigrees with TSH receptor mutations of loss of function type have been reported. The phenotype of the patients varies from euthyroid hyperthyrotropinemia to severe congenital hypothyroidism with thyroid hypoplasia.

Humans↗