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.
BACKGROUND
Therapy of thyroid carcinoma uses its radioiodine concentration ability for treatment. Dedifferentiated cells lose radioiodine uptake from human sodium-iodide symporter (hNIS) gene transcription failure consequent to genomic structure (chromatin compaction) and composition (CpG methylation).


OBJECTIVE
We explored restoring hNIS expression in human thyroid carcinoma cells using thyroid adenoma and carcinoma cell lines: KAK-1, NPA87, BHT-101, and KAT-4B, with quantitative RT-PCR, chromatin immunoprecipitation, deoxyribonuclease I sensitivity assays, and luciferase reporter construct transfections containing hNIS promoter regions.


RESULTS
Combined 5-azacytidine and sodium butyrate restores hNIS gene transcription in KAK-1 to levels approaching radioiodine-treatable tumors. Despite induction of H4 acetylation, there was no deoxyribonuclease I sensitivity enhancement in two regions of the hNIS gene promoter. Cycloheximide in cells transfected with luciferase reporter construct, 1.3 kb hNIS gene promoter, stimulated normalized luciferase expression, singly and synergistically with 5-azacytidine, in a dose-dependent, time course-dependent, cell type-specific, and promoter-specific fashion. Both anisomycin and emetine, but not puromycin, had similar effects. Cycloheximide 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.
Li
Wei
W
Thyroid Cancer Research Laboratory, Medical Service, Veterans Affairs Medical Center, Lexington, Kentucky 40511, USA.
Venkataraman
Gopalakrishnan M
GM
Ain
Kenneth B
KB
D000236:Adenoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D001374:Azacitidine / Q000494:pharmacology*; D002087:Butyrates / Q000494:pharmacology; D045744:Cell Line, Tumor; D003513:Cycloheximide / Q000494:pharmacology; D003850:Deoxyribonuclease I / Q000378:metabolism; D004357:Drug Synergism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D017930:Genes, Reporter; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*; D027981:Symporters / Q000235:genetics* / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014162:Transfection; D000099209:Sodium-Iodide Symporters
D001374:Azacitidine; D002087:Butyrates; D003513:Cycloheximide; D003850:Deoxyribonuclease I; D008156:Luciferases; D011500:Protein Synthesis Inhibitors; D027981:Symporters; D000099209:Sodium-Iodide Symporters