FOXD3 acts as a repressor of the mitochondrial S-adenosylmethionine carrier (SLC25A26) gene expression in cancer cells.

The mitochondrial S-adenosylmethionine carrier (SAMC), encoded by the SLC25A26 gene, catalyzes the uptake of S-adenosylmethionine (SAM) from the cytosol into mitochondria in exchange for S-adenosylhomocysteine (SAH), produced inside the mitochondria. In the last years we have been functionally characterizing the promoter of SLC25A26 gene. In this study we show that a silencer activity is present in the region from -756 bp to -504 bp, which specifically binds a protein present in Caski cells nuclear extracts. By in silico analysis, EMSA, ChIP, overexpressing and silencing experiments this protein was identified as FOXD3 which acts as a repressor of SLC25A26 expression. Interestingly, the repressor activity of FOXD3 is completely abolished by treating Caski cells with folate via a mechanism that involves methylation of FOXD3 gene promoter. This finding could have important impact in cancer cells where SLC25A26 is downregulated. Finally, the DPE and INR putative sites were also identified.