Thymine DNA Glycosylase (TDG) is involved in the pathogenesis of intestinal tumors with reduced APC expression
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Jinfei Xu1,*, Salvatore Cortellino1,*, Rossella Tricarico1, Wen-Chi Chang2, Gabrielle Scher1, Karthik Devarajan3, Michael Slifker3, Robert Moore1, Maria Rosaria Bassi1, Elena Caretti1, Margie Clapper2, Harry Cooper4 and Alfonso Bellacosa1
1Cancer Epigenetics Program, Fox Chase Cancer Center, Philadelphia, PA 19111, USA
2Cancer Prevention and Control Program, Fox Chase Cancer Center, Philadelphia, PA 19111, USA
3Department of Biostatistics, Fox Chase Cancer Center, Philadelphia, PA 19111, USA
4Department of Pathology, Fox Chase Cancer Center, Philadelphia, PA 19111, USA
*These authors have contributed equally to this work
Alfonso Bellacosa, email: Alfonso.Bellacosa@fccc.edu
Keywords: TDG, APC, colorectal cancer, intestinal cancer
Received: July 17, 2017 Accepted: August 21, 2017 Published: September 23, 2017
Thymine DNA Glycosylase (TDG) is a base excision repair enzyme that acts as a thymine and uracil DNA N-glycosylase on G:T and G:U mismatches, thus protecting CpG sites in the genome from mutagenesis by deamination. In addition, TDG has an epigenomic function by removing the novel cytosine derivatives 5-formylcytosine and 5-carboxylcytosine (5caC) generated by Ten-Eleven Translocation (TET) enzymes during active DNA demethylation. We and others previously reported that TDG is essential for mammalian development. However, its involvement in tumor formation is unknown. To study the role of TDG in tumorigenesis, we analyzed the effects of its inactivation in a well-characterized model of tumor predisposition, the ApcMin mouse strain. Mice bearing a conditional Tdgflox allele were crossed with Fabpl::Cre transgenic mice, in the context of the ApcMin mutation, in order to inactivate Tdg in the small intestinal and colonic epithelium. We observed an approximately 2-fold increase in the number of small intestinal adenomas in the test Tdg-mutant ApcMin mice in comparison to control genotypes (p=0.0001). This increase occurred in female mice, and is similar to the known increase in intestinal adenoma formation due to oophorectomy. In the human colorectal cancer (CRC) TCGA database, the subset of patients with TDG and APC expression in the lowest quartile exhibits an excess of female cases. We conclude that TDG inactivation plays a role in intestinal tumorigenesis initiated by mutation/underexpression of APC. Our results also indicate that TDG may be involved in sex-specific protection from CRC.
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