Galrão AL, Camargo RY, Friguglietti CU, Moraes L, Cerutti JM, Serrano-Nascimento C, Suzuki MF, Medeiros-Neto G, Rubio IGS. Hypermethylation of a New Distal Sodium/Iodide Symporter (NIS) enhancer (NDE) is associated with reduced NIS expression in thyroid tumors.
J Clin Endocrinol Metab 2014;
99:E944-52. [PMID:
24432988 DOI:
10.1210/jc.2013-1450]
[Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
CONTEXT
In thyroid tumors, reduced radioiodine uptake is associated with worse patient outcome concomitantly with low sodium/iodide symporter (NIS) mRNA expression. Previous studies showed that CpG-island methylation in the NIS proximal promoter does not correlate with mRNA expression.
OBJECTIVES
The aim of the study was to identify new CpG-islands within the NIS 5'region and investigate the involvement of their methylation in NIS expression.
DESIGN
DNA was obtained from 30 pairs of thyroid samples: tumor (T) and surrounding nontumor (NT) samples. All T samples had reduced NIS mRNA expression compared to NT samples.
MAIN OUTCOME MEASURES
Methylation degree was quantified by bisulfite sequencing, and NIS expression by real-time PCR and Western blot. Reporter gene assays were performed to determine CpG-island functionality. Tumor cell cultures were treated with 5-Aza demethylating agent to determine NIS expression, methylation status, and (125)I uptake.
RESULTS
We identified a new CpG-island2 with 14 CpG sites, located -2152/-1887 relative to ATG site. CpG-island2 was hypermethylated in T compared to NT samples, in both benign and malignant tumor groups. There was a significant inverse correlation between NIS mRNA expression and degree of CpG-island2 methylation in NT and T samples. This sequence increased the expression of a reporter gene; thus, it was considered a new enhancer. Cell culture treatments with 5-Aza reduced CpG-island2 methylation levels concomitantly with restoration of NIS mRNA and protein expression and (125)I uptake.
CONCLUSIONS
We identified a new distal enhancer, NIS distal enhancer, that regulates gene expression through DNA methylation. This enhancer is hypermethylated in T compared to NT samples and is associated with decreased NIS expression in tumors. This epigenetic deregulation may be an early event in tumorigenesis.
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