Epigenetic dysregulation is a hallmark of cancer, and aberrant methylation of cytosine residues plays a crucial role in abnormal gene expression in cancer cells. Recent studies demonstrate that 5-hydroxymethylcytosine (5-hmC) generated through 5-methylcytosine (5-mC) oxidation is significantly depleted in various cancers. However, whether 5-hmC levels change during the stepwise progression of thyroid carcinoma and the mechanisms underlying this effect remain unknown. The aims of this study were (i) to assess 5-hmC levels in normal and cancerous thyroid tissues, and (ii) identify clinicopathologic and genetic factors associated with the dysregulated hydroxymethylation of cytosine. Enzyme-linked immunosorbent assay (ELISA) showed that 5-hmC was significantly reduced in TERT promoter-mutated papillary thyroid carcinomas (PTCs) and anaplastic thyroid carcinomas (ATCs), while there was no significant difference in 5-hmC levels between TERT promoter-wild-type PTCs and normal thyroid tissues. Results of semi-quantitative analysis of 5-hmC through immunohistochemistry correlated well with those of ELISA and confirmed the loss of 5-hmC in tumor cells. Immunohistochemistry confirmed lower 5-hmC positivity in TERT promoter-mutated PTCs (n = 10) and ATCs (n = 4) than in normal thyroid tissues (n = 8) and TERT promoter-wild-type PTCs (n = 63). Tumor size (> 1 cm) and advanced stage were associated with decreased global 5-hmC in PTCs, while age, gross extrathyroidal invasion, node metastasis, and BRAF mutation were not. Collectively, these findings demonstrated that loss of 5-hmC is an epigenetic hallmark of thyroid carcinomas with TERT promoter mutation, indicating that TERT promoter-mutated thyroid carcinoma has a distinct molecular profile.

表观遗传失调是癌症的标志，胞嘧啶残基的异常甲基化在癌细胞的异常基因表达中起着至关重要的作用。最近的研究表明，通过 5-甲基胞嘧啶 (5-mC) 氧化产生的 5-羟甲基胞嘧啶 (5-hmC) 在各种癌症中显着消耗。然而，在甲状腺癌的逐步进展过程中 5-hmC 水平是否发生变化以及这种影响的潜在机制仍然未知。本研究的目的是 (i) 评估正常和癌性甲状腺组织中的 5-hmC 水平，以及 (ii) 确定与胞嘧啶羟甲基化失调相关的临床病理和遗传因素。酶联免疫吸附试验 (ELISA) 显示TERT中 5-hmC 显着降低启动子突变的甲状腺乳头状癌 (PTC) 和未分化甲状腺癌 (ATC)，而TERT启动子野生型 PTC 和正常甲状腺组织之间的 5-hmC 水平没有显着差异。通过免疫组织化学对 5-hmC 进行半定量分析的结果与 ELISA 的结果具有很好的相关性，并证实了肿瘤细胞中 5-hmC 的丢失。免疫组织化学证实TERT启动子突变的 PTC ( n  = 10) 和 ATC ( n  = 4) 中的5-hmC 阳性率低于正常甲状腺组织 ( n  = 8) 和TERT启动子-野生型 PTC ( n = 63）。肿瘤大小 (> 1 cm) 和晚期与 PTCs 的整体 5-hmC 降低相关，而年龄、甲状腺外浸润、淋巴结转移和BRAF突变与此无关。总的来说，这些发现表明 5-hmC 的缺失是具有TERT启动子突变的甲状腺癌的表观遗传标志，表明TERT启动子突变的甲状腺癌具有独特的分子特征。