Published online Oct 28, 2022. doi: 10.3748/wjg.v28.i40.5845
Peer-review started: February 6, 2022
First decision: April 10, 2022
Revised: May 6, 2022
Accepted: June 13, 2022
Article in press: June 13, 2022
Published online: October 28, 2022
Inflammatory bowel disease (IBD) constitutes a substantial risk factor for col
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.
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.
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.
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 and associated carcinogenesis.
Core Tip: Chronic inflammation of the colon is a risk factor for colorectal cancer. Intestinal inflammation has been associated with reduced gap junction-mediated intercellular communication and downregulation connexins [mainly connexin 43 (Cx43)]. The involvement of the demethylating enzyme ten-eleven translocation-2 (TET-2) (methylcytosine dioxygenase) in the inflammatory process has motivated the investigation of Cx43 and TET-2 expression in colitis and colorectal carcinoma. In vitro and in vivo data report on the upregulation of Cx43 in inflammatory states and a downregulation of TET-2. In human samples of colon adenocarcinoma, both TET-2 and Cx43 were downregulated, potentially implicating them in the malignant transformation of inflamed intestinal tissues.