S-adenosylhomocysteine hydrolase participates in DNA methylation inheritance

DNA (cytosine-5) methyltransferase 1 (DNMT1) is essential for mammalian development and maintenance of DNA methylation following DNA replication in cells. The DNA methylation process generates S-adenosyl-L-homocysteine, a strong inhibitor of DNMT1. Here we report that S-adenosylhomocysteine hydrolase (SAHH/AHCY), the only mammalian enzyme capable of hydrolyzing S-adenosyl-L-homocysteine binds to DNMT1 during DNA replication. SAHH activates DNMT1 in vitro and its overexpression in mammalian cells leads to hypermethylation of the genome, whereas its inhibition by adenosine periodate resulted in hypomethylation of the genome. Hypermethylation was consistent in both gene bodies and repetitive DNA elements leading to both down- and up-regulation of genes. Similarly, hypomethylation led to both up- and down-regulation of genes suggesting methylated regions influence gene expression either positively or negatively. Cells overexpressing SAHH specifically up-regulated metabolic pathway genes and down-regulated PPAR and MAPK signaling pathways genes. Therefore, we suggest that alteration of SAHH level in the cell leads to aberrant DNA methylation, altered metabolite levels and gene expression.