Promoter demethylation and chromatin remodeling by green tea polyphenols leads to re‐expression of GSTP1 in human prostate cancer cells

Abstract

Epigenetic silencing of gluthathione-S-transferase pi (GSTP1) is recognized as being a molecular hallmark of human prostate cancer. We investigated the effects of green tea polyphenols (GTPs) on GSTP1 re-expression and further elucidated its mechanism of action and long-term safety, compared with nucleoside-analog inhibitor of DNA methyltransferase (DNMT), 5-aza-2 0 -deoxycitidine. Exposure of human prostate cancer LNCaP cells to 1-10 lg/ml of GTP for 1-7 days caused a concentration-and time-dependent re-expression of GSTP1, which correlated with DNMT1 inhibition. Methyl-specific-PCR and sequencing revealed extensive demethylation in the proximal GSTP1 promoter and regions distal to the transcription factor binding sites. GTP exposure in a time-dependent fashion diminished the mRNA and protein levels of MBD1, MBD4 and MeCP2; HDAC 1-3 and increased the levels of acetylated histone H3 (LysH9/18) and H4. Chromatin immunoprecipitation assays demonstrated that cells treated with GTP have reduced MBD2 association with accessible Sp1 binding sites leading to increased binding and transcriptional activation of the GSTP1 gene. Exposure of cells to GTP did not result in global hypomethylation, as demonstrated by methyl-specific PCR for LINE-1 promoter; rather GTP promotes maintenance of genomic integrity. Furthermore, exposure of cells to GTP did not cause activation of the prometaststic gene S100P, a reverse response noted after exposure of cells to 5-aza-2 0 deoxycitidine. Our results, for the first time, demonstrate that GTP has dual potential to alter DNA methylation and chromatin modeling, the 2 global epigenetic mechanisms of gene regulation and their lack of toxicity makes them excellent candidates for the chemoprevention of prostate cancer.Aberrant hypermethylation of CpG islands in the glutathione-S-transferase pi (GSTP1) gene promoter is increasingly being recognized as a precursor to the genesis of prostate cancer. 1,2 GSTP1 is a member of the glutathione S-transferase superfamily that catalyzes conjugation of the glutathione peptide with electrophilic compounds, including carcinogens, resulting in less toxic and more readily excretable metabolites. 3,4 A genetic variant of GSTP1 has been associated with cancer susceptibility 5 and mice lacking GSTP1 exhibit increased skin tumorigenesis, 6 findings that corroborate the notion that GSTP1 is a tumor suppressor. In contrast, overexpression of GSTP1 has been associated with the development of some types of cancer and has been noted to be associated with the acquisition of drug resistance in some neoplasms. 7,8 The 5 0 -untranslated region of GSTP1 contains GC-rich regions including CpG islands occupied by 2 putative Sp1 binding sites that play a central role in regulating basal levels of GSTP1 transcription. 9 Detailed bisulfite sequencing analysis of the CpG islands spanning the core promoter region of the GSTP1 gene has demonstrated that methylation is extensive at essentially all CpG sites in androgen-responsive human prostate cancer LNCaP and MDA PCa 2b cells. ...

Requirement and Epigenetics Reprogramming of Nrf2 in Suppression of Tumor Promoter TPA-Induced Mouse Skin Cell Transformation by Sulforaphane

“…3). Epigenetic regulation, including DNA methylation and histone modification, is an important process in cancer development, and the epigenetic regulatory activity of certain dietary phytochemicals with cancer chemopreventive potential has been demonstrated, including curcumin (21), EGCG (20), and genistein (44). We have previously shown that the expression of Nrf2 can be attenuated by DNA CpG methylation in both the prostate tumor tissue of TRAMP mice and tumorigenic TRAMP C1 cells (12).…”

Green tea polyphenols induce cell death in breast cancer MCF-7 cells through induction of cell cycle arrest and mitochondrial-mediated apoptosis

“…As a putative cancer chemotherapeutic agent derived from dietary constituents, GTPs have been suggested to play a significant role in the resistance of a variety of cancers including liver, breast, prostate, lung, and skin by numerous studies of cell cultures and animal models (Luo et al, 2006;Thangapazham et al, 2007;Lu et al, 2008;Pandey et al, 2010). GTPs are the major active component group of green tea, accounting for 30%-42% of the dry weight of the solids in brewed green tea, and are mainly composed of catechins (Khan and Mukhtar, 2007).…”

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

“…Molecular modeling and docking studies supported the binding of EGCG to DNMT3B in HeLa cells [108]. EGCG (5-20 μM) or Pholyphenon E® (1-10 μg/mL) treatments of different PCa cell lines, have determined a dose-and time-dependent reexpression of GSTP1 enzyme concomitantly with the down-regulation of DNMT1 [41,106]. The reexpression of GSTP1, induced by treatment with EGCG or Polyphenon E® may be, at least in part, responsible for the quenching of free radicals species and reduction of DNA damage associated with oxidative stress [41].…”

“…Cancer development involves a complex multistep process caused and associated to many genetic insults that include genetic mutation as well epigenetic alteration [105]. Many tumor suppressor and receptor genes have been reported to be hypermethylated and transcriptionally silenced during the development of various human cancers, including PCa [106]. The major epigenetic mechanisms that control gene expression are DNA methylation, histone modifications and expression of noncoding regulatory micro RNA (miRNAs).…”

“…Inhibition of histone deacetylases (HDACs) in cancer cells causes re-expression of genes epigenetically silenced during carcinogenesis [118]. Polyphenon E® administration has been reported to cause inhibition of HDACs activity and expression in PCa cell lines [106,119]. Molecular modeling and docking studies in HeLa cells suggested that EGCG inhibits HDAC1 activity by direct binding of the enzyme [108].…”