Biomedical subjects

A Acebrón

Publications and source records attributed to A Acebrón.

6 recordsLinked to original sources

PubMed1999

Thyroid-specific gene expression in the multi-step process of thyroid carcinogenesis.

Thyroid-specific transcription factors TTF-1 and Pax-8 play a decisive role in the determination and maintenance of cellular phenotype activating thyroglobulin (Tg), thyroperoxidase (TPO), thyrotropin receptor (TSH-R) and the sodium/iodide symporter (NIS) gene transcription. In the present work, we have studied the expression of TTF-1 and Pax-8 and their target genes in samples derived from thyroid neoplasms of follicular origin, as well as in medullary carcinoma (MTC), obtained from surgery or from fine needle aspiration (FNA) biopsies. The results show that TTF-1 and Pax-8 are expressed in well differentiated adenomas and that their expression decreases in less differentiated papillary and follicular carcinomas and is lost in undifferentiated anaplastic carcinomas. Parallel levels of Tg, TPO and TSH-R expression were found in the same neoplasm samples. Interestingly TSH-R and TTF-1 gene expression was found in MTC samples. Furthermore, the expression of the thyroid-specific genes and their transcription factors is lost in thyroid cells derived from follicular, papillary and anaplastic human carcinomas. In these cells, Tg, TPO and TSH-R promoter activities were absent. Cotransfection with expression vectors for TTF-1 and Pax-8 resulted in the stimulation of transcription to a different extent for each promoter. These results may be clinically relevant for the evaluation and prognosis of thyroid cancer since the loss of specific markers correlates with the degree of tumor differentiation.

Carcinoma, Medullary↗

PubMed1998

Ha-ras interference with thyroid cell differentiation is associated with a down-regulation of thyroid transcription factor-1 phosphorylation.

Mechanisms responsible for the lack of thyroid-specific differentiation markers in Ha-ras transformed FRTL-5 cells have been investigated. In vivo cell labeling and immunoprecipitation demonstrate that phosphorylation of the thyroid transcription factor-1 (TTF-1) is clearly reduced in thyroid cells transformed with the Ha-ras oncogene. Fingerprinting analysis of phosphotryptic peptides from FRTL-5 and Ha-ras-FRTL-5 cells also reveals a heterogeneous pattern of TTF-1 phosphorylation in the transformed cell line. This heterogeneity is localized in the amino terminal cluster of phosphoserines, as determined by transfection of HeLa cells with TTF-1 mutants in which serine residues have been replaced by alanines. Amplification and nucleotide sequence of the 5'-coding region of the TTF-1 gene in Ha-ras-FRTL-5 cells rule out the possibility that differences in phosphorylation were the consequence of any mutational event affecting residues within the N-terminal protein sequence. Hypophosphorylated TTF-1 is still able to bind its DNA consensus sequence within the thyroglobulin promoter, although a reporter construct whose expression is exclusively dependent on TTF-1 is not transactivated. Transfection of Ha-ras-FRTL-5 cells with an expression vector encoding the cAMP dependent protein kinase A (PKA) catalytic subunit partially reestablishes TTF-1 transcriptional activity. Taken together, these results indicate that the lack of specific thyroid gene expression in Ha-ras-FRTL-5 cells could be a direct consequence of the inability of TTF-1 to promote transcription.

Amino Acid Sequence↗

PubMed1995

Function of the homeo and paired domain proteins TTF-1 and Pax-8 in thyroid cell proliferation.

The thyroid transcription factors TTF-1 and Pax-8 are homeobox- and paired box-containing genes, respectively, that are responsible for thyroid-specific gene expression, thyroid development, and thyroid cell differentiation. However, it is not clear if such factors play a role in thyroid cell proliferation. The antisense oligonucleotide strategy was used in order to clarify this point. Treatment of quiescent FRTL-5 thyroid cells with TTF-1 or Pax-8 antisense oligonucleotides caused a significant reduction in thyroid-stimulating hormone and insulin-like growth factor-I-stimulated cell proliferation, measured by DNA synthesis and cell counting. The same results were obtained with forskolin indicating that the TTF-1 or Pax-8 role in mediating the thyroid-stimulating hormone growth effect occurred via the cAMP pathway. The effect was higher with TTF-1 as the blockage by this factor caused a 65% decrease in cell proliferation compared to the control. Pax-8 blocking lead only to a 30% decrease. The blocking of both thyroid transcription factors together did not result in an additive effect. These data provide direct evidence that both homeo and paired box gene expression is essential for FRTL-5 thyroid cell proliferation, with each one possibly playing a different regulatory role.

Animals↗

PubMed1995

Congenital human thyroglobulin defect due to low expression of the thyroid-specific transcription factor TTF-1.

TTF-1 and Pax-8 are thyroid-specific transcription factors, from homeo and paired box genes, respectively, that are responsible for thyroid development and for thyroglobulin and thyroperoxidase gene expression. However, TTF-1 and Pax-8 preferentially bind to the thyroglobulin and thyroperoxidase promoters, respectively. Here, we have studied a patient with defective thyroglobulin synthesis. Thyroglobulin mRNA was found at very low levels while the mRNA for thyroperoxidase was found to be more abundant compared with control tissue. The low levels of thyroglobulin mRNA are caused by a transcriptional defect due to the virtual absence of TTF-1 expression as determined by Northern blot analysis, reverse transcriptase-PCR, and electrophoretic mobility shift assays. The level of Pax-8 mRNA was the same in the goiter and in the control thyroid. These results are the first reported evidence of a congenital goiter with a thyroglobulin synthesis defect due to the low expression of the thyroid-specific transcription factor TTF-1. Moreover, these data suggest that TTF-1 and Pax-8 would be differentially regulating thyroglobulin and thyroperoxidase gene transcription.

Base Sequence↗

PubMed1992

Expression of thyroglobulin gene in maternal and fetal thyroid in rats.

The relationship between the changes in thyroglobulin (Tg) mRNA and Tg proteins during thyroid development in the fetus and in maternal thyroid glands during gestation and lactation is studied. While the appearance of Tg mRNA (fetal day 15) showed good temporal correlation with that of 12S Tg, no 19S Tg could be detected until 3 days later. The 12S Tg was the predominant protein on days 18 and 19 of gestation in the fetus, while 19S Tg was the predominant protein on fetal days 21-22 and during the postnatal period in the offspring; by the 20th postnatal day, the 19S Tg content per gland was 4 times the amount of 12S (155 vs. 37 micrograms/gland; P less than 0.001). The 19S iodine content in the fetus was the same as that in 12S up to the 21st day of gestation, except for lower values on day 18. From fetal day 22 and through the postnatal period, the iodine content in 19S was 1.6-5.9 times greater than that in 12S. Therefore, the ratio of atoms of iodine per mol Tg during the experimental period changed from 0.75 to 19.5 for 19S and from 0.72 to 7.2 for 12S. The levels of all of the iodoamino acids were low on fetal days 17-19, after which they increased at different rates for each protein. The greatest increase in monoiodotyrosine and T3 corresponded to 12S, while diiodotyrosine and especially T4 showed a greater increase in 19S than in 12S Tg; 20 days after birth, the T4 content in 19S was about 3 times greater than that in 12S Tg. The soluble thyroid proteins from pregnant, lactating, and nonpregnant female controls contained a main protein, 19S, and a smaller amount of 27S. Both 19S Tg and 19S iodine contents were already lower than those in nonpregnant rats at 14 days of pregnancy, and the levels continued to decrease during the experimental period. In contrast, the 27S Tg and 27S iodine levels remained constant and similar to nonpregnant values. Surprisingly, a decrease in the level of Tg mRNA was observed during pregnancy and lactation. We have no explanation for the dramatic decrease in Tg mRNA during the last days of pregnancy. Further studies should help to elucidate the mechanism responsible for the changes in Tg gene expression in the thyroids of pregnant and lactating rats.

Animals↗

PubMed1992

Insulin and insulin-like growth factor I regulate a thyroid-specific nuclear protein that binds to the thyroglobulin promoter.

The mechanism responsible for the stimulation of thyroglobulin (Tg) gene expression by insulin and insulin-like growth factor I (IGF-I) in rat thyroid FRTL-5 cells has been investigated. Both insulin and IGF-I stimulate transcription from the Tg promoter in a transient transfection assay demonstrating that the promoter used contains the DNA signals necessary for insulin and IGF-I regulation. Promoter mutations that interfere with the binding of thyroid transcription factor 1 (TTF-1), TTF-2, and the ubiquitous transcription factor abolish the insulin/IGF-I response, indicating that the three factors may be involved in the observed transcriptional control. Protein-DNA binding studies did not reveal any effect of insulin/IGF-I on the ubiquitous transcription factor and the TTF-1 binding capacity. Instead, TTF-2 is absent in nuclear extracts from cells depleted of serum and insulin. Addition of insulin or IGF-I restores the TTF-2 concentration to normal levels and requires ongoing protein synthesis. The insulin effect was maximal at 24 h and at a concentration of 1 microgram/ml. The same effect was observed with a 10-fold lower concentration of IGF-I. These results suggest that insulin (probably through the IGF-I receptor) and IGF-I modulate the levels of TTF-2, which results in an increased expression of the Tg gene.

Animals↗