Modulation of thyroid-specific gene expression in normal and nodular human thyroid tissues from adults: an in vivo effect of thyrotropin.

CONTEXT: Evidence from in vitro studies or animal models has shown that TSH affects thyrocytes by thyroid-specific expression modulation. OBJECTIVE: The objective of our study was to analyze the role of TSH in human thyroid gene expression in vivo. DESIGN/SETTING: Thirty-nine normal thyroid tissues were collected at the same center. STUDY SUBJECTS: Patients were divided into two groups based on serum TSH levels: 17 with normal TSH levels (1-4 mU/liter; group 1) and 22 with TSH levels below 0.5 mU/liter (group 2). INTERVENTION: Group 2 underwent thyroidectomy after suppressive L-T4 therapy. MAIN OUTCOME MEASURES: mRNA levels of thyroid genes such as sodium/iodide symporter (NIS), apical iodide transporter, pendrin, thyroglobulin, thyroperoxidase, TSH receptor, paired box transcription factor 8, and thyroid transcription factor-1 were evaluated by quantitative PCR. RESULTS: The reduction of TSH stimulation causes decreases in NIS and apical iodide transporter gene expression in normal tissues and more limited reductions in thyroglobulin, thyroperoxidase, and paired box transcription factor 8, but it has no significant effect on TSH receptor, pendrin, or thyroid transcription factor-1. Comparison of NIS levels in normal and nodular tissues from the same patient confirmed that it is differentially expressed in nodules only in the presence of normal TSH (P < 0.01). In patients with suppressed TSH, nodular NIS levels were similar to those in normal tissues. CONCLUSIONS: Our data represent the first demonstration in human thyroid tissues that TSH contributes to the regulation of thyrocyte differentiation by modulating thyroid gene levels. It exerts a particularly important effect on the transcription of NIS, which becomes very low after prolonged TSH suppression.

Recovery of NIS expression in thyroid cancer cells by overexpression of Pax8 gene.

BACKGROUND: Recovery of iodide uptake in thyroid cancer cells by means of obtaining the functional expression of the sodium/iodide symporter (NIS) represents an innovative strategy for the treatment of poorly differentiated thyroid cancer. However, the NIS gene expression alone is not always sufficient to restore radioiodine concentration ability in these tumour cells. METHODS: In this study, the anaplastic thyroid carcinoma ARO cells were stably transfected with a Pax8 gene expression vector. A quantitative RT-PCR was performed to assess the thyroid specific gene expression in selected clones. The presence of NIS protein was detected by Western blot and localized by immunofluorescence. A iodide uptake assay was also performed to verify the functional effect of NIS induction and differentiation switch. RESULTS: The clones overexpressing Pax8 showed the re-activation of several thyroid specific genes including NIS, Pendrin, Thyroglobulin, TPO and TTF1. In ARO-Pax8 clones NIS protein was also localized both in cell cytoplasm and membrane. Thus, the ability to uptake the radioiodine was partially restored, associated to a high rate of efflux. In addition, ARO cells expressing Pax8 presented a lower rate of cell growth. CONCLUSION: These finding demonstrate that induction of Pax8 expression may determine a re-differentiation of thyroid cancer cells, including a partial recovery of iodide uptake, fundamental requisite for a radioiodine-based therapeutic approach for thyroid tumours.

Expression, regulation, and function of paired-box gene 8 in the human placenta and placental cancer cell lines.

Pax proteins are transcriptional regulators that control a variety of developmental decisions in vertebrates. During development, the paired-box gene 8 (PAX8) is expressed in the thyroid, kidney, and several areas of the central nervous system. It is also expressed in the adult thyroid gland, in which it mediates TSH-induced modulation of the expression of important genes, such as those encoding thyroglobulin, thyroperoxidase, and the sodium/iodide symporter (NIS). Thus far, placental expression of PAX8 has been described only in mice. In the present study, we show that PAX8 is also expressed in the human placenta at term. In an in vitro model of placental cancer, the JAR choriocarcinoma cell line, human chorionic gonadotropin (hCG) increased levels of PAX8 mRNA and protein, and gel retardation assays indicated that the up-regulation of PAX8 protein expression is associated with an increase in its DNA-binding activity. The effects of hCG were mimicked by forskolin, indicating that they are cAMP dependent. Levels of mRNA for the Wilms' tumor 1 (WT1) and NIS genes were increased in JAR cells by hCG treatment, whereas overexpression of PAX8 increased only levels of WT1 mRNA. In cells transfected with PAX8-specific small interfering RNA, the stimulatory effects of hCG on WT1 mRNA levels were abolished, but hormonal enhancement of NIS mRNA levels was unchanged. These findings indicate that, in JAR cells, hCG activates a cAMP-dependent pathway that can up-regulate WT1 expression through PAX8.

Effects of histone acetylation on sodium iodide symporter promoter and expression of thyroid-specific transcription factors.

Inhibitors of histone deacetylases (HDACs) activate the sodium iodide symporter (NIS) expression in thyroid tumor cells. In this study, mechanisms accounting for these effects were investigated. Various human thyroid tumor cell lines (ARO, BCPAP, FRO, TPC-1) were treated with the HDAC inhibitors Na butyrate (NaB) and tricostatin A (TSA), and the effects on the expression of NIS and several thyroid-specific transcription factors together with the activity of NIS promoter were evaluated. TSA and NaB increased NIS mRNA levels in all cell lines. Among thyroid-specific transcription factors, only expression of PAX8 in ARO cells was increased. Down-regulation of thyroid-specific transcription factor-1 expression was observed in BCPAP and TPC-1 cell lines. Thyroid-specific transcription factor-2 mRNA was reduced in FRO, BCPAP, and TPC-1 cells. Histone acetylation had no significant effects on HEX expression. Altogether, these data indicate that the increase of NIS expression is not mediated by modification of expression of thyroid-specific transcription factors. Accordingly, in transfection experiments performed in the HeLa cell line (which does not express thyroid-specific transcription factors), treatment with TSA and NaB increased NIS promoter activity. Stimulation of NIS promoter activity was also obtained by overexpressing histone acetylating proteins pCAF and p300 in HeLa cells. Conversely, overexpression of the HDAC 1 enzyme inhibited basal activity of the NIS promoter. Effects of TSA and NaB on NIS expression were also evaluated in nonthyroid cell lines MCF-7, Hep-G2, and SAOS-2. In all cell lines TSA and NaB greatly increased NIS mRNA levels. We concluded that control of NIS expression by inhibition of HDAC appears not to be mediated by cell-specific mechanisms, suggesting it as a potential strategy to induce radioiodine sensitivity in different human tumors.

Regulation of iodide uptake and sodium/iodide symporter expression in the mcf-7 human breast cancer cell line.

Sodium/iodide symporter (NIS) expression has recently been described in human breast cancer, with emphasis on its potential exploitation for the treatment of these tumors with radioiodine. In this study, we analyzed the regulation of NIS expression and function in the MCF-7 human breast cancer cell line. Cell exposure to insulin, IGF-I, IGF-II, or prolactin induced significant increases in 125I uptake and the expression of both NIS mRNA and NIS protein. The latter increases were evident after 6 and 12 h of hormonal stimulation, respectively. In immunocytochemistry studies, NIS was detected mainly in the plasma membrane of MCF-7 cells. A low but significant increase in iodide uptake was produced by treatment with activators of the adenylyl cyclase (cAMP) or protein kinase C pathways. Our study demonstrates that: 1) MCF-7 breast cancer cells are capable of active iodide transport that can be stimulated by insulin, IGF-I, IGF-II, or prolactin; 2) both NIS transcript and protein are expressed in these cells, and this expression is also hormonally stimulated; and 3) MCF-7 iodide transport and NIS expression may be influenced by the activation of cAMP or protein kinase C-dependent signaling. These findings increase our understanding of the molecular mechanisms that regulate NIS expression in breast cancer cells, information that is fundamental for future research aimed at the development of targeted radioiodide treatment for this type of cancer.