Mechanisms for the Inhibition of DNA Methyltransferases by Tea Catechins and Bioflavonoids

Abstract

In the present investigation, we studied the modulating effects of several tea catechins and bioflavonoids on DNA methylation catalyzed by prokaryotic SssI DNA methyltransferase (DNMT) and human DNMT1. We found that each of the tea polyphenols [catechin, epicatechin, and (Ϫ)-epigallocatechin-3-O-gallate (EGCG)] and bioflavonoids (quercetin, fisetin, and myricetin) inhibited SssI DNMT-and DNMT1-mediated DNA methylation in a concentration-dependent manner. The IC 50 values for catechin, epicatechin, and various flavonoids ranged from 1.0 to 8.4 M, but EGCG was a more potent inhibitor, with IC 50 values ranging from 0.21 to 0.47 M. When epicatechin was used as a model inhibitor, kinetic analyses showed that this catecholcontaining dietary polyphenol inhibited enzymatic DNA methylation in vitro largely by increasing the formation of S-adenosyl-L-homocysteine (a potent noncompetitive inhibitor of DNMTs) during the catechol-O-methyltransferase-mediated Omethylation of this dietary catechol. In comparison, the strong inhibitory effect of EGCG on DNMT-mediated DNA methylation was independent of its own methylation and was largely due to its direct inhibition of the DNMTs. This inhibition is strongly enhanced by Mg 2ϩ . Computational modeling studies showed that the gallic acid moiety of EGCG plays a crucial role in its high-affinity, direct inhibitory interaction with the catalytic site of the human DNMT1, and its binding with the enzyme is stabilized by Mg 2ϩ . The modeling data on the precise molecular mode of EGCG's inhibitory interaction with human DNMT1 agrees perfectly with our experimental finding.DNA methylation at the C5-position of cytosine within the CpG dinucleotides represents an important mechanism for epigenetic control of gene expression and the maintenance of genome integrity. Although DNA hypermethylation is associated with inactivation of genes, global genomic hypomethylation is often associated with the induction of chromosomal instability (Chen et al., 1998). A number of recent studies have suggested that bioactive food components, including both essential and nonessential nutrients, can modify DNA methylation patterns in complex ways. For instance, consumption of a methyl-deficient diet led to hypomethylation of specific CpG sites within several oncogenes (such as c-myc, c-fos, and c-H-ras), resulting in elevated levels of mRNA for these genes (Wainfan and Poirier, 1992). A recent study showed that tea catechins are effective inhibitors of human DNA methyltransferase (DNMT)-mediated DNA methylation in vitro and in cultured cancer cells (Fang et al., 2003). DNA methylation is catalyzed by specific DNMTs. Multiple DNMTs are known to be present in humans, animals, and microorganisms, and they have varying degrees of specificity toward unmethylated and hemimethylated DNA substrates (Bestor and Ingram, 1983). S-Adenosyl-L-methionine (SAM) is the methyl donor in the DNMT-mediated DNA methylation, as in many other enzymatic methylation reactions [such as the catechol-O-methyltransferase (COMT)-med...

Epigenetic reprogramming and imprinting in origins of disease

“…Questions related to the susceptibility of developmental plasticity to phytoestrogens and long-term epigenetic memories remain unanswered. Beside bioflavonids, the tea polyphenol (−)-epigallocatechin-3-O-gallate (EGCG), is another natural compounds found to have modulating effects on DNA methylation [62]. EGCG was found to inhibit DNA methyltransferases and reactivate specific methylation-silenced genes in human colon and prostate cancer cell lines [63].…”

Modulation of gene methylation by genistein or lycopene in breast cancer cells

“…For example, the tea catechin epigallocatechin gallate (EGCG) has been shown to directly inhibit DNA methyltransferase DNMT1 and reverses the hypermethylation status of p16 in human esophageal carcinoma KYSE 510 cells [Fang et al, 2007]. In MCF-7 and MDA-MB-231 breast cancer cells, re-expression of the RARb gene by tea catechin was observed to be accompanied by reduced methylation of the promoter of that gene [Lee et al, 2005]. Sulforaphane, an isothiocyanate in broccoli, is an epigenetic modifier that inhibits histone deacetylase (HDAC) resulting in increased p21 expression with coordinate changes in histone H3 and H4 acetylation in HCT116 human HNPCC colon cancer cells and in prostate epithelial cell lines, BPH-1, LnCaP, and PC-3 [Myzak et al, 2004[Myzak et al, , 2006.…”

Green Tea Catechins for Prostate Cancer Prevention: Present Achievements and Future Challenges

“…Indeed, galloylated GTCs are methylated by COMT that catalyzes the transfer of a methyl group from the donor molecule SAM that in turn forms SAH. By this mechanism the SAM/SAH is reduced and inhibits DNMTs activity that depends on the intracellular availability of SAM as methyl donor [112]. Navarro-Perak et al [113] suggested that EGCG inhibits DHFR and/or folic acid uptake acting as an antifolate compound.…”