Thyroglobulin autoregulation of thyroid-specific gene expression and follicular function.
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Animals↗
Biomedical subjects
A Grassadonia
Publications and source records attributed to A Grassadonia.
Thyroglobulin repression of thyroid transcription factor 1 (TTF-1) gene expression is mediated by decreased DNA binding of nuclear factor I proteins which control constitutive TTF-1 expression.
Follicular thyroglobulin (TG) selectively suppresses the expression of thyroid-restricted transcription factors, thereby altering the expression of thyroid-specific proteins. In this study, we investigated the molecular mechanism by which TG suppresses the prototypic thyroid-restricted transcription factor, thyroid transcription factor 1 (TTF-1), in rat FRTL-5 thyrocytes. We show that the region between bp -264 and -153 on the TTF-1 promoter contains two nuclear factor I (NFI) elements whose function is involved in TG-mediated suppression. Thus, NFI binding to these elements is critical for constitutive expression of TTF-1; TG decreases NFI binding to the NFI elements in association with TG repression. NFI is a family of transcription factors that is ubiquitously expressed and contributes to constitutive and cell-specific gene expression. In contrast to the contribution of NFI proteins to constitutive gene expression in other systems, we demonstrate that follicular TG transcriptionally represses all NFI RNAs (NFI-A, -B, -C, and -X) in association with decreased NFI binding and that the RNA levels decrease as early as 4 h after TG treatment. Although TG treatment for 48 h results in a decrease in NFI protein-DNA complexes measured in DNA mobility shift assays, NFI proteins are still detectable by Western analysis. We show, however, that the binding of all NFI proteins is redox regulated. Thus, diamide treatment of nuclear extracts strongly reduces the binding of NFI proteins, and the addition of higher concentrations of dithiothreitol to nuclear extracts from TG-treated cells restores NFI-DNA binding to levels in extracts from untreated cells. We conclude that NFI binding to two NFI elements, at bp -264 to -153, positively regulates TTF-1 expression and controls constitutive TTF-1 levels. TG mediates the repression of TTF-1 gene expression by decreasing NFI RNA and protein levels, as well as by altering the binding activity of NFI, which is redox controlled.
Amino Acid Sequence↗
Thyroglobulin regulates follicular function and heterogeneity by suppressing thyroid-specific gene expression.
Thyroglobulin (TG) is the primary synthetic product of the thyroid and the macromolecular precursor of thyroid hormones. TG synthesis, iodination, storage in follicles, and lysosomal degradation can each modulate thyroid hormone formation and secretion into the circulation. Thyrotropin (TSH), via its receptor (the TSHR), increases thyroid hormone levels by upregulating expression of the sodium iodide symporter (NIS), thyroid peroxidase (TPO), and TG genes. TSH does this by modulating the expression and activity of the thyroid-specific transcription factors, thyroid transcription factor (TTF)-1, TTF-2, and Pax-8, which coordinately regulate NIS, TPO, TG, and the TSHR. Major histocompatibility complex (MHC) class I gene expression, which is also regulated by TTF-1 and Pax-8 in the thyroid, is simultaneously decreased; this maintains self tolerance in the face of TSH-increased gene products necessary for thyroid hormone formation. We now show that follicular TG, 27S > 19S > 12S, counter-regulates TSH-increased thyroid-specific gene transcription by suppressing the expression of the TTF-1, TTF-2, and Pax-8 genes. This decreases expression of the TG, TPO, NIS and TSHR genes, but increases class I expression. TG action involves an apical membrane TG-binding protein; however, it acts transcriptionally, targeting, for example, a sequence within 1.15 kb of the start of TTF-1 transcription. TG does not affect ubiquitous transcription factors regulating TG, TPO, NIS and/or TSHR gene expression. TG activity is not duplicated by thyroid hormones or iodide. We hypothesize that TG-initiated, transcriptional regulation of thyroid-restricted genes is a normal, feedback, compensatory mechanism which regulates follicular function, regulates thyroid hormone secretion, and contributes to follicular heterogeneity.
Animals↗
Prognostic value of a novel interferon-inducible 90K tumor antigen.
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Antigens, Neoplasm↗
Thymidylate synthase level and DNA-ploidy pattern as possible prognostic factors in human colorectal cancer: a preliminary study.
5-Fluorouracil is the drug chosen for the treatment of patients with advanced colorectal carcinoma; its major site of action is thymidylate synthase (TS), resulting in pronounced and prolonged inhibition of DNA synthesis. The aim of this study was to evaluate the possibility of considering TS level in human colorectal carcinomas of previously untreated patients (pts) as a prognostic factor. Our data demonstrate that there is no association with age, sex, tumor site and tumor size; however, there is a relationship between TS levels and staging: in fact, the TS values are higher (P < 0.05) in Dukes-A tumors than in the others. A significant association was also found between the TS levels and survival parameters: in fact, pts with longer disease-free and overall survivals had a significantly increased TS level compared to pts with a poorer outcome (P < 0.05). Moreover, pts with DNA-aneuploid tumors had lower TS level (median = 0.044 pmol/mg protein) than diploid pts who had higher TS level (median = 0.093 pmol/mg protein); however the difference is not significant. Our result are based on preliminary data; however, they seem to support the hypothesis that a high TS level is a favourable prognostic factor in human colorectal carcinoma.
Adenocarcinoma↗
A phase I study of 5-day continuous venous infusion of carboplatin at circadian rhythm-modulated rate compared with constant rate.
The circadian rhythm-modulated delivery of anticancer drugs has been shown to reduce toxicity and improve anticancer efficacy. The aim of this phase I trial was to compare the feasibility and tolerability of carboplatin (CBDCA) administered at circadian-modulated or flat infusion rate in 24 patients with advanced cancer. Each treatment cycle consisted of a 5-day continuous intravenous infusion of CBDCA, to be repeated at 28-day intervals. Three dose levels were determined, with a CBDCA dose 15%, 40% and 60% over that calculated using Calvert's formula. Two schedules were compared: schedule A (forty-four courses), with a at circadian rhythm-modulated rate (peak at 16.00 hr) and schedule B (fifty courses), at a constant rate. At the first and second dose level neither of the administered cycles were accompanied by hematologic toxicity higher than Grade 3. At the third dose level, two cycles out of 15 for schedule A and two out of 20 for schedule B were accompanied by Grade 4 thrombocytopenia. The repeat cycles were delayed from day 28 to 42 in some patients, with no differences between circadian-modulated and flat infusion. Three partial responses out of 9 evaluable patients were observed in schedule A and 2 out of 10 evaluable patients in schedule B. We showed no potential advantage of the chronomodulated 5-day CBDCA continuous infusion method over the flat rate method. Although antitumor effects were observed in this pilot study, this treatment cannot be assessed for efficacy relative to other schedules.
Adult↗