Wei Li

Publications (2)4.36 Total impact

• Article: Human sodium-iodide symporter (hNIS) gene expression is inhibited by a trans-active transcriptional repressor, NIS-repressor, containing PARP-1 in thyroid cancer cells.

  Wei Li, Kenneth B Ain
  [show abstract] [hide abstract]
  ABSTRACT: Radioiodine remains the only tumoricidal therapy for disseminated thyroid carcinomas; however, dedifferentiated tumors lose the expression of human sodium-iodide symporter (hNIS) gene, and cannot respond to this treatment. Previous studies suggested that a trans-active protein factor (NIS-repressor) represses endogenous hNIS transcription, likely contributing to the loss of radioiodine uptake, and defined the NIS-repressor binding site (NRBS) in the proximal hNIS promoter. Using electrophoretic mobility shift assay (EMSA), we found evidence of NIS-repressor in the nuclear extract from KAK-1 cells, and confirmed this result using nuclear extracts prepared from multiple verified thyroid cell lines. Luciferase reporter assays of hNIS promoter constructs and EMSA were used to define two core sequences, NRBS-P and NRBS-D, in the hNIS promoter as the binding sites for NIS-repressor. Electrophoretic analysis of KAK-1 nuclear extract proteins cross-linked with NRBS-P suggests that NIS-repressor is a protein complex. Analysis of KAK-1 nuclear extract proteins bound to NRBS-P, via liquid chromatography coupled with tandem mass spectroscopy, demonstrated poly(ADP-ribose) polymerase-1 (PARP-1) as a NIS-repressor component. Pharmacological inhibition of PARP-1 enzymatic activity using PJ34 stimulated both the luciferase reporter activity driven by hNIS promoter and the endogenous hNIS mRNA level. Supershift studies suggest that thyroid transcription factor 2 (TTF-2) is also associated with the NIS-repressor complex. NIS-repressor, including its PARP-1 component, presents a potential therapeutic target to restore radioiodine uptake in dedifferentiated thyroid carcinomas.
  Endocrine Related Cancer 03/2010; 17(2):383-98. · 4.36 Impact Factor
• Article: 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

  Wei Li, Gopalakrishnan M. Venkataraman, Kenneth B. Ain
  [show abstract] [hide abstract]
  ABSTRACT: Context: Therapy of thyroid carcinoma uses its radioiodine concen- tration ability for treatment. Dedifferentiated cells lose radioiodine uptake from human sodium-iodide symporter (hNIS) gene transcrip- tion failure consequent to genomic structure (chromatin compaction) and composition (CpG methylation). Objective and Methods: We explored restoring hNIS expression in humanthyroidcarcinomacellsusingthyroidadenomaandcarcinoma cell lines: KAK-1, NPA87, BHT-101, and KAT-4B, with quantitative RT-PCR, chromatin immunoprecipitation, deoxyribonuclease I sen- sitivity assays, and luciferase reporter construct transfections con- taining hNIS promoter regions. Results: Combined 5-azacytidine and sodium butyrate restores hNIS gene transcription in KAK-1 to levels approaching radioio- dine-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, stimu- lated 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. Cyclohexi- mide 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) re- presses 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 pre- sents a novel target to restore hNIS expression in dedifferentiated thyroid carcinoma. (J Clin Endocrinol Metab 92: 1080-1087, 2007)