|
|
The Iodine Group | |
|
Home | Orthoiodosupplementation | Body | Disease | Special | Overviews |
||
|
|
Venkataraman
Protein synthesis inhibitors, in synergy with 5-azacytidine, restore sodium/iodide symporter gene expression in human thyroid adenoma cell line, KAK-1, suggesting trans-active transcriptional repressor.Li W, Venkataraman GM, Ain KB. J Clin Endocrinol Metab. 2007 Mar;92(3):1080-7. Epub 2006 Dec 12.
"Context: Therapy of thyroid carcinoma utilizes its radioiodine concentration ability for treatment. Dedifferentiated cells lose radioiodine uptake from sodium-iodide symporter (hNIS) gene transcription failure consequent to genomic structure (chromatin compaction) and composition (CpG methylation).
Objective/Methods: We explored restoring hNIS expression in human thyroid carcinoma cells using thyroid adenoma and carcinoma cell lines: KAK-1, NPA'87, BHT-101, and KAT-4B, with quantitative RT-PCR, chromatin immunoprecipitation, DNase I sensitivity assays, and luciferase reporter construct transfections containing hNIS promoter regions.
Results: Combined 5-azacytidine (azaC) and sodium butyrate (NaB) restores hNIS gene transcription in KAK-1 to levels approaching radioiodine-treatable tumors. Despite induction of H4 acetylation, there was no DNase I sensitivity enhancement in two regions of the hNIS gene promoter. Cycloheximide (CHX) in cells transfected with luciferase reporter construct, 1.3 kb hNIS gene promoter, stimulated normalized luciferase expression, singly and synergistically with azaC, in dose-dependent, time course-dependent, cell type-specific, and promoter-specific fashion. Both anisomycin and emetine, but not puromycin, had similar effects. CHX also increased endogenous hNIS mRNA. Transfections with reporter constructs containing consecutive deletions of hNIS gene promoter sequences revealed responsible sequences at -427 to -131 bp. Deletion of 1.2 kb promoter region upstream of -131 bp enhanced basal luciferase reporter activity 3-fold above the activity of full length promoter construct, supporting inhibitory properties of this region.
Conclusions: This suggests that trans-active protein factor(s) represses endogenous hNIS transcription in KAK-1 cells under basal conditions, accounting for loss of iodine uptake. Inhibition of this repressive activity increases endogenous hNIS transcription and presents a novel target to restore hNIS expression in dedifferentiated thyroid carcinoma."
Expression of hypothalamic-pituitary-thyroid axis related genes in the human skin.Slominski A, Wortsman J, Kohn L, Ain KB, Venkataraman GM, Pisarchik A, Chung JH, Giuliani C, Thornton M, Slugocki G, Tobin DJ. J Invest Dermatol. 2002 Dec;119(6):1449-55.
"The skin is commonly affected in thyroid diseases, but the mechanism for this association is still unclear. As the skin expresses numerous neuroendocrine elements, we tested the additional cutaneous expression of mediators operating in the hypothalamic-pituitary-thyroid axis. We found significant expression of the thyroid-stimulating hormone receptor mRNA in cultured keratinocytes, epidermal melanocytes, and melanoma cells. The presence of thyroid-stimulating hormone receptor was confirmed by northern analyses and the thyroid-stimulating hormone receptor was found to be functionally active in cyclic adenosine monophosphate signal assays. Thyroid-stimulating hormone receptor expressing cells also expressed the sodium iodide symporter and thyroglobulin genes. We also found expression of deiodinases 2 and 3 (mainly deiodinase 2) in whole skin biopsy specimens, and in the majority of epidermal and dermal cells by reverse transcription-polymerase chain reaction followed by sequencing of the amplified gene segments. There was selective expression of the gene for thyroid-stimulating hormone beta; detection of the thyroid-releasing hormone gene was minimal and thyroid-releasing hormone receptor mRNA was not detected in most of the samples. Expression of functional thyroid-stimulating hormone receptor in the skin may have significant physiologic and pathologic consequences, particularly in autoimmune conditions associated with production of stimulating antibodies against the thyroid-stimulating hormone receptor. We conclude that the expanding list of neuroendocrine elements expressed in the skin supports a strong role for this system in cutaneous biology."
Restoration of iodide uptake in dedifferentiated thyroid carcinoma: relationship to human Na+/I-symporter gene methylation status.Venkataraman GM, Yatin M, Marcinek R, Ain KB. J Clin Endocrinol Metab. 1999 Jul;84(7):2449-57.
"Disseminated dedifferentiated thyroid epithelial carcinoma, which cannot sufficiently concentrate therapeutic radioiodide, is a terminal disease without any effective systemic treatment or chemotherapy. This is a likely consequence of loss of human sodium-iodide symporter (hNIS) function. We hypothesized that hNIS transcriptional failure in thyroid carcinoma could be consequent to methylation of DNA in critical regulatory regions and could be reversed with chemical demethylation treatment. Analysis of hNIS messenger ribonucleic acid (mRNA) expression in 23 tumor samples revealed that although loss of this expression corresponded to loss of clinical radioiodide uptake, some thyroid carcinomas with hNIS mRNA expression did not concentrate iodide, suggesting additional posttranscriptional mechanisms for loss of hNIS function. In addition, analysis of DNA methylation in CpG-rich regions of the hNIS promoter extending to the first intron failed to define specific methylation patterns associated with transcriptional failure in human thyroid tumor samples. In seven human thyroid carcinoma cell lines lacking hNIS mRNA, treatment with 5-azacytidine or sodium butyrate was able to restore hNIS mRNA expression in four cell lines and iodide transport in two cell lines. Investigation of methylation patterns in these cell lines revealed that successful restoration of hNIS transcription was associated with demethylation of hNIS DNA in the untranslated region within the first exon. This was also associated with restoration of expression of thyroid transcription factor-1. These results suggest a role for DNA methylation in loss of hNIS expression in thyroid carcinomas as well as a potential application for chemical demethylation therapy in restoring responsiveness to therapeutic radioiodide."
Cloning of the human sodium-iodide symporter promoter and characterization in a differentiated human thyroid cell line, KAT-50.Venkataraman GM, Yatin M, Ain KB. Thyroid. 1998 Jan;8(1):63-9. [abstract only]
"Elucidation of the regulation of human sodium-iodide symporter (hNIS) gene expression is critical to understanding its effects on iodide concentration abilities of thyroid and thyroid carcinomas. To explore this issue, a 1.2-kb portion of the 5'-flanking region of the hNIS gene was isolated and characterized. Transient transfections with chimeric luciferase-reporter constructs into a differentiated human thyroid cell line, KAT-50, as well as non-thyroidal cells, defined an active promoter with tissue-specificity. Reverse-transcriptase polymerase chain reaction analysis for hNIS mRNA expression in normal human tissues was positive in thyroid, salivary gland, omentum, and gallbladder. KAT-50 cells expressed hNIS mRNA and were capable of thyrotropin-responsive iodide uptake in vitro. Despite the failure to exhibit iodide concentration in clinical anaplastic carcinoma tumors, 4 of 5 cell lines from this cancer phenotype expressed hNIS mRNA. Definition of the active promoter provides further insights and tools to uncover new approaches to use of radioiodine for therapy of thyroid carcinomas."
|
|
Home | Orthoiodosupplementation | Body | Disease | Special Topics | OverviewsThe Iodine Group | Books | Disclaimers | Contact Us | Search
|
||
