Expression Of TET2 In Gastric Carcinoma Tissues Is Associated With Tumor Metastasis And Prognosis

BackgroundDNA methylation at the 5-position of cytosine is one of the key epigenetic marks that play a crucial role in development, genome imprinting and regulation of gene expression. Recent studies have shown that teneleven translocation(TET) proteins can oxidize 5-methylcytosine(5m C) to 5-hydroxymethylcytosine(5hmC), which is further converted into 5-formylcytosine(5fC), and 5-carboxylcytosine(5caC), thereby mediating active DNA demethylation. TET gene family consists of three members: TET1, TET2 and TET3. A large number of epigenetics studies have shown that TET family proteins and 5hmC are involved in normal development as well as in many diseases. More recently, in the roles of 5hm C and TET protein family in tumor development is under intensive investigation. However, the contribution of TET family members to gastric carcinogenesis is still undefined.Gastric cancer(GC) is one of the most common tumors around the world. It is a type of malignancy that originates from neoplastic transformation of gastric mucosa epithelium. The development of GC is a multi-factor, multi-step progressive process, and is associated with environmental, dietary, Helicobacter Pylori infection and genetic factors. By affecting gene transcription, abnormal methylation can lead to gene mutations and incre ase the instability of chromosome structure, thereby promoting GC. These findings suggest that epigenetic modifiers, such as TET proteins, may play a role in development of GC. In the present study, we examined the expression of TET in GC tissues and correlate its expression level with multiple clinico-pathological parameters and patient prognosis. Our findings may lay a preliminary foundation for understanding the molecular mechanisms by which DNA demethylation contribute to gastric carcinogenesis, with possible implication for identifying novel molecular targets to reduce postoperative recurrence and tumor metastasis.ObjectivesWe examined the expression of TET in GC and the corresponding tumor adjacent tissues using micro-tissue array. We analyzed the association of TET expression with the differentiation, infiltration, lymph node metastasis and some other clinico-pathological parameters, and the prognosis of GC patients. Moreover, we tested the expression of E-cadherin in GC tissues. We analyzed the correlation between the expression of TET2 and E-cadherin and investigated the role of TET2 in GC metastasis.MethodsExperimental materials: human gastric cancer tissues and tumor adjacent tissues.Experimental procedure: Tissue micro-assay and HE staining was performed according to standard protocol to confirm the diagnosis of GC. Immunohistochemical(IHC) staining was performed to examne the expression of TET and E-cadherin in these samples. The IHC staining results were evaluated by two independent patholo gists according to the IRS(semi-quantitative Remmele scoring system), who scored the SI(IHC staining intensity) with the PP(percentage of positive cells). SI was scored between 0 and 3 as following: 0: no positive cells were observed, 1: all positive nuclei display a weak staining, 2: the most stained nuclei show a moderately positive, 3: the most stained nuclei display an intensive staining. PP was scored according to the following criteria: 0: no positive cells were observed, 1: only less than 10% nuclei display intense staining, 2: 11%–50% nuclei were observed, 3: 51%–80%, 4: more than 80%. Finally the IHC score was calculated by SI × PP. To analyze the relationship between the expression TET and E-cadherin, and their expression with clinico-pathological characteristics, patients were classified into three groups according to the IHC scores: low expression(0≤ IHC scores≤4) and high expression(4< IHC scores≤ 12).Patient follow-up: We obtained follow-up information of the GC patients, as well as the clinical treatment and prognosis. Bu analyzing the association between TET2 and E-cadherin, we futher explored the association of TET2 expression with epithelialmesenchymal transition(EMT) of GC cells.Results1. A total of 29 para-carcinoma tissues and 100 cases of histopathologically conformed GC were used in our study. By examing the expression of TET members, we found that the expression of all the TET is lower in GC than that of para-carcinoma tissue.2. TET1 expression was correlated with GC differentiation and TNM stages(P<0.05). In addition, the expression of TET2 was associated with tumor diameter, differentiation, lymph node metastasis and TNM stages(P<0.05). A correlation between T ET3 expression and lymph node metastasis was identified in GC patients(P<0.05).3. Among the three TET members, Only TET2 expression was significantly associated with the prognosis of postoperative patients. As compared to patients with T ET2-high tumors, lower expression of TET2 in GC tissues were significantly associated with shorter overall survival of the patients,(p<0.05).4. The expression of E-cadherin was reduced in GC as compared with para-carcinoma tissues. E-cadherin was negatively correlated with GC differentiation, TNM stages and lymph node metastasis(P<0.05). Importantly, both the expression of TET2 and E-cadherin was significantly associated with the Disease-Free Survival of patients.5. We found a positive correlation between the expression of TET2 and E-cadherin in GC tissues(p < 0.001).Conclusions1. The expression of TET members was relatively lower in GC tissue than that of para-carcinoma tissues, suggesting that TET may be involved in GC development.2. Reduced expression of TET2 in tumor tissues was associated with inferior outcomes of gastric cancers.3. The expression of TET2 was positively correlated with E-cadherin, implying that TET2 may be associated with GC metastasis.