CpG island status as an epigenetic alteration for NIS promoter in thyroid neoplasms; a cross- sectional study with a systematic review

Abstract

Background Gene silence via methylation of the CpG island is the most common epigenetic modification in cancer. Aberrant DNA methylation interferes with active transcription and is also significantly associated with poor tumor differentiation and prognosis. Given the highly significant role of NIS in thyroid cancer differentiation, this cross-sectional study aimed to investigate the DNA methylation pattern in seven CpG islands (CpG1-7 including + 846, +918, + 929, +947, + 953, +955, and + 963, respectively) of the NIS promoter in patients diagnosed with PTC, FTC, and MNG compared with the matched non-tumoral tissues. Methods Thyroid specimens from 64 patients met the eligibility criteria, consisting of 28 PTCs, 9 FTCs, and 27 benign MNG cases. The expression of NIS mRNA was tested by qRT-PCR. The bisulfite sequencing PCR technique was performed was performed to evaluate the promoter methylation pattern of the NIS gene. Sequencing results were received in chromatograph, FASTA, SEQ, and pdf formats and were analyzed using Chromas. The methylation percentage at each position and for each sample was calculated by mC/ (mC + C) formula for all examined CpGs; following that, the methylation percentage was also calculated at each CpG site. Results NIS mRNA levels decreased in tissue samples of patients with PTC (P = 0.04) and FTC (P = 0.03) compared to their matched non-tumoral tissues. The methylation of NIS promoter was not common in PTC samples, but it was frequent in FTC (P < 0.05). Significant differences were observed in the methylation levels in the 4th (+ 947), 6th (+ 955), and 7th (+ 963) CpGs sites in the forward strand of NIS promoter between FTC tumoral and MNG tissues (76.34 ± 3.12 vs 40.43 ± 8.42, P = 0.004, 69.63 ± 3.03 vs 23.29 ± 6.84, P = 0.001 and 50.33 ± 5.65 vs 24 ± 6.89, P = 0.030, respectively). There was no significant correlation between the expression and methylation status of NIS in PTC and FTC tumoral tissues. Conclusion Perturbation in NIS promoter’s methylation individually may have a potential utility in differentiating MNG and FTC tissues. The absence of a distinct methylation pattern implies the importance of other epigenetic processes, which may alter the production of NIS mRNA. In addition, according to the reversibility of DNA methylation, it is anticipated that the design of particular targeted demethylation medicines will lead to a novel cancer therapeutic strategy.