TET1 is a tumour suppressor that inhibits colon cancer growth by derepressing inhibitors of the WNT pathway

Ten eleven translocation (TET) enzymes catalyse the oxidative reactions of 5-methylcytosine (5mC) to promote the demethylation process. The reaction intermediate 5-hydroxymethylcytosine (5hmC) has been shown to be abundant in embryonic stem cells and tissues, but strongly depleted in human cancers. Genetic mutations of TET2 gene were associated with lleukemia, whereas TET1 downregulation has been shown to promote malignancy in breast cancer. Here, we report that TET1 is downregulated in colon tumours from the initial stage. TET1 silencing in primary epithelial colon cells increase their cellular proliferation while its re-­­expression in colon cancer cells inhibits their proliferation and the growth of tumour xenografts even at later stages. We found that TET1 binds and maintains hypomethylated the promoter of the DKK genes inhibitors of the WNT signalling to promote their expression. Downregulation of TET1 during colon cancer initiation leads to repression, by DNA methylation the promoters of the inhibitors of the WNT pathway resulting in a constitutive activation of the WNT pathway. Thus the DNA hydroxymethylation mediated by TET1 controlling the WNT signalling is a key player of tumour growth. These results provide new insights for understanding how tumours escape cellular controls Overall design: Transcriptome analysis of Caco-2 cell line expressing TET1 protein.

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Neri F, Dettori D, Incarnato D, Krepelova A, Rapelli S, Maldotti M, Parlato C, Paliogiannis P, Oliviero S