Expression of the methylcytosine dioxygenase ten-eleven translocation-2 and connexin 43 in inflammatory bowel disease and colorectal cancer

Abstract

BACKGROUND Inflammatory bowel disease (IBD) constitutes a substantial risk factor for colorectal cancer. Connexin 43 (Cx43) is a protein that forms gap junction (GJ) complexes involved in intercellular communication, and its expression is altered under pathological conditions, such as IBD and cancer. Recent studies have implicated epigenetic processes modulating DNA methylation in the pathogenesis of diverse inflammatory and malignant diseases. The ten-eleven translocation-2 (TET-2) enzyme catalyzes the demethylation, hence, regulating the activity of various cancer-promoting and tumor-suppressor genes. AIM To investigate Cx43 and TET-2 expression levels and presence of 5-hydroxymethylcytosine (5-hmC) marks under inflammatory conditions both in vitro and in vivo . METHODS TET-2 expression was evaluated in parental HT-29 cells and in HT-29 cells expressing low or high levels of Cx43, a putative tumor-suppressor gene whose expression varies in IBD and colorectal cancer, and which has been implicated in the inflammatory process and in tumor onset. The dextran sulfate sodium-induced colitis model was reproduced in BALB/c mice to evaluate the expression of TET-2 and Cx43 under inflammatory conditions in vivo . In addition, archived colon tissue sections from normal, IBD (ulcerative colitis), and sporadic colon adenocarcinoma patients were obtained and evaluated for the expression of TET-2 and Cx43. Expression levels were reported at the transcriptional level by quantitative real-time polymerase chain reaction, and at the translational level by Western blotting and immunofluorescence. RESULTS Under inflammatory conditions, Cx43 and TET-2 expression levels increased compared to non-inflammatory conditions. TET-2 upregulation was more pronounced in Cx43-deficient cells. Moreover, colon tissue sections from normal, ulcerative colitis, and sporadic colon adenocarcinoma patients corroborated that Cx43 expression increased in IBD and decreased in adenocarcinoma, compared to tissues from non-IBD subjects. However, TET-2 expression and 5-hmC mark levels decreased in samples from patients with ulcerative colitis or cancer. Cx43 and TET-2 expression levels were also investigated in an experimental colitis mouse model. Interestingly, mice exposed to carbenoxolone (CBX), a GJ inhibitor, had upregulated TET-2 levels. Collectively, these results show that TET-2 levels and activity increased under inflammatory conditions, in cells downregulating gap junctional protein Cx43, and in colon tissues from mice exposed to CBX. CONCLUSION These results suggest that TET-2 expression levels, as well as Cx43 expression levels, are modulated in models of intestinal inflammation. We hypothesize that TET-2 may demethylate genes involved in inflammation and tumorigenesis, such as Cx43, potentially contributing to intestinal inflammation a...

Correlation of DNA methylation of DNMT3A and TET2 with oral squamous cell carcinoma

“…TET proteins regulate the equilibrium between DNA methylation and demethylation by regulating the dynamic transformation among cytosine, 5-mC, and 5-hmC [ 41 ]. However, missense and truncated TET mutations have been reported in nearly all types of solid tumors [ 42 ], and their reduced protein expression and 5-hmC levels are markers of many cancer types, including colorectal cancer [ 43 ], glioblastoma [ 24 ], cervical cancer [ 44 ], and pancreatic cancer [ 45 ]. The aforementioned studies are consistent with our findings, showing that modulating the DNMT3A and TET2 expression levels could effectively change the biological behavior of OSCC.…”

Epigenetic regulation and therapeutic strategies in ulcerative colitis

“…Moreover, DNA methylation is counteracted by the demethylation process catalyzed by TET enzymes, which mediate a series of oxidation reactions and convert methylated 5methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5formylcytosine (5fC) and sequentially 5-carboxylcytosine (5caC) (Wu and Zhang, 2017). A recent study has analyzed colon tissue samples from patients with UC and CRC as well as healthy counterparts, and corroborated that the expression of TET2 and 5hmC levels decrease in those samples from patients with UC or CRC (El-Harakeh et al, 2022) (Figure 1).…”

Effects of DNA methylation and its application in inflammatory bowel disease (Review)

“…TET3 plays a crucial role in maintaining tissue homeostasis by controlling the transcriptome and DNA methylome of the gut epithelium, particularly in response to luminal stresses ( 43 ). Recent research has suggested epigenetic mechanisms modulating DNAm in the pathophysiology of various inflammatory and cancerous diseases, and the TET-2 enzyme has been shown to catalyze the demethylation, thereby controlling the activity of numerous genes that promote and repress tumors ( 44 ). Additionally, comparing normal colon tissues to those with IBD and colon cancer, the expression of TET2 and its epigenetic mark 5hmC is significantly downregulated in the latter two conditions ( 45 ).…”

“…In human tissues, aberrant methylation induction is caused by DNMT activation owing to nitric oxide generation and TET inhibition due to nuclear factor κB activation ( 46 ). The expression of a protein called connexin 43 (Cx43), which is involved in gap junction complexes and intercellular communication, is altered in pathological diseases, such as cancer and IBD ( 44 ). The levels of Cx43 and the demethylating enzyme TET-2 are increased in inflammatory situations.…”

“…The levels of Cx43 and the demethylating enzyme TET-2 are increased in inflammatory situations. However, in sporadic colon adenocarcinomas, Cx43 expression is downregulated when TET-2 levels are low, which suggests that TET-2 functions to inhibit Cx43 and its potential to reduce tumors ( 44 ). In a different study, in vitro analyses revealed that TET2 overexpression and DNMT3A knockdown prevented oral squamous cell cancer from proliferating and migrating ( 47 ).…”