Decreased 5-Hydroxymethylcytosine (5-hmC) is an Independent Poor Prognostic Factor in Gastric Cancer Patients

Abstract

DNA methylation at the 5 position of cytosine (5-mC) is a key epigenetic mark that is involved in various biological and pathological processes. 5-mC can be converted to 5-hydroxymethylcytosine (5-hmC) by the ten-eleven translocation (TET) family of DNA hydroxylases. Increasing evidence suggests that large-scale loss of 5-hmC is an epigenetic hallmark of several human cancers. However, the value of 5-hmC in diagnosis and prognosis of human cancers, including gastric cancer (GC), remains largely unknown. The aim of this study is to determine 5-hmC levels in GCs and explore its association with clinicopathological characteristics and clinical outcome of GC patients. Using immunohistochemistry (IHC) and dot-blot assays, we demonstrated that 5-hmC was dramatically decreased in GCs compared with matched normal tissues. We also found a strong link between decreased 5-hmC and the reduction of TET1 gene expression, but not TET2 or 3, suggesting that decreased TET1 expression might be one of the mechanisms underlying 5-hmC loss in GCs. Wilcoxon tests showed that 5-hmC content was significantly associated with most of clinicopathological characteristics, such as tumor size (P = 0.016), Bormman type (P < 0.0001), tumor invasion (P = 0.001), TNM stage (P < 0.0001), the number of lymph nodes metastasis (P = 0.002), and survival status (P < 0.0001). It is noteworthy that decreased 5-hmC was significantly associated with poor survival of GC patients. Collectively, our findings indicate that decreased 5-hmC may be crucial to the clinical pathology of GC and is a strong and independent poor prognostic factor in GCs.

Robust quantitative assessments of cytosine modifications and changes in the expressions of related enzymes in gastric cancer

“…Very recently, Yang et al [12] reported that 5-hmC levels were markedly and negatively correlated with tumor invasion; that is, with the TNM stage and the number of lymph node metastases in GCs. They measured the 5-hmC level using a DNA dot blot assay and the down-regulation of TET1 transcripts was notably associated with a reduction of 5-hmC levels in GCs.…”

“…Because dot blot analysis is based on the antigen-antibody reaction direct assessments of the absolute amount of 5-mC, 5-hmC, 5-fC, and 5-caC are not possible. Moreover, since the signal intensities of dot blot images become easily saturate, the standard curve used in the analyses is not linear [12]. In contrast to dot blot analysis, liquid chromatography coupled with tandem mass spectrometry (LC-MS/ MS) can calculate the absolute quantity of the modifications and its standard curve is completely linear.…”

Regulation and Functional Significance of 5-Hydroxymethylcytosine in Cancer

“…This loss of 5hmC in genomic context may lead to gene body hypermethylation as observed in kidney cancer and can hypermethylate promoters of tumor suppressor genes (TSG) that are frequently observed in cancers [24]. Reduced 5hmC is a predictive marker for poor prognosis and survival for multiple cancers like breast, astrocytoma, laryngeal squamous cell carcinoma, renal, oesophageal, gastric and hepatocellular carcinoma (HCC) [24][25][26][27][28][29][30]. Moreover, mutations in TET2 are frequently observed with decrease in 5hmC in hematological cancers, additionally mutations of 5hmC regulating enzymes like IDH1/2, SDH and FH were also observed [19,20,31,32].…”

Low level of 5-Hydroxymethylcytosine predicts poor prognosis in non-small cell lung cancer

“…In recent years, 5-hmC has become more extensively studied. Previous studies have reported its position and prognostic value in a variety of tumors (17). However, the relationship between 5-hmC level and the progression of lung cancer and prognosis of patients with lung cancer remains unknown.…”