Context: Previous genome-wide association studies have shown that single-nucleotide polymorphism (SNP) rs2439302 in chromosome 8p12 is significantly associated with papillary thyroid carcinoma (PTC) risk and dysregulated NRG1 expression. The underlying mechanisms remain to be discovered.
Objective: To evaluate the expression of NRG1 isoforms, candidate functional variants, and potential genes downstream of NRG1 in thyroid tissue.
Methods: Quantitative reverse transcription polymerase chain reaction was applied for gene expression analysis. SNaPshot assay, haplotype, and computer analyses were performed to evaluate candidate functional variants. Other functional assays [chromatin immunoprecipitation (ChIP) assay, luciferase assay, small interfering RNA knockdown, and RNA sequencing] were performed.
Results: Three NRG1 isoforms (NM_004495, NM_013958, and NM_001160008) tested were highly expressed in thyroid tissue. The expression levels of the three isoforms were significantly correlated with the genotypes of rs2439302. A DNA block of ~32 kb containing the risk G allele of rs2439302 was revealed, harboring multiple candidate functional variants. ChIP assay for active chromatin markers indicated at least nine regions in the DNA block showing strong H3Kme1 and H3K27Ac signals in thyroid tissue. Luciferase reporter assays revealed differential allelic activities associated with seven SNPs. Knocking down NRG1 in primary thyroid cells revealed downstream or interacting genes related to NRG1.
Conclusions: Our data suggest a role for transcriptional regulation of NRG1 in the predisposition to PTC.