Dual action on promoter demethylation and chromatin by an isothiocyanate restored GSTP1 silenced in prostate cancer

Abstract

Prostate carcinoma is characterized by the silencing of pi-class glutathione S-transferase gene (GSTP1), which encodes a detoxifying enzyme. The silencing of GSTP1, due to aberrant methylation at the CpG island in the promoter/5'-UTR, occurs in the vast majority of prostate tumors and precancerous lesions. It is a pathologic marker and probably an underlying cause of oxidative damage and inflammation at tumor initiation. Inhibition of the aberrant promoter methylation could therefore be an effective mean to prevent carcinogenesis. Several isothiocyanates, including phenethyl isothiocyanate (PEITC), found naturally in cruciferous vegetables, induced growth arrest and apoptosis in prostate cancer cells in culture and xenografts. The effects of PEITC to reactivate GSTP1 were investigated. Exposure of prostate cancer LNCaP cells to PEITC inhibited the activity and level of histone deacetylases (HDACs), and induced selective histone acetylation and methylation for chromatin unfolding. Concurrently PEITC demethylated the promoter and restored the unmethylated GSTP1 in both androgen-dependent and -independent LNCaP cancer cells to the level found in normal prostatic cells, as quantified by methylation-specific PCR and pyrosequencing. The dual action of PEITC on both the DNA and chromatin was more effective than 5'-Aza-2'-deoxycytidine, sodium butyrate, or trichostatin A (TSA), and may de-repress the methyl-binding domain (MBD) on gene transcription. The PEITC-mediated cross-talk between the DNA and chromatin in demethylating and reactivating GSTP1 genes, which is critically inactivated in prostate carcinogenesis, underlines a primary mechanism of cancer chemoprevention. Consequently, new approaches could be developed, with isothiocyanates to prevent and inhibit malignancies.

Phenethyl Isothiocyanate, a Dual Activator of Transcription Factors NRF2 and HSF1

“…In these cells, PEITC exposure induced demethylation of the CpG island of the GSTP1 promoter, and ultimately reactivated GSTP1 expression 64. In this study, PEITC was shown to decrease the activity of HDAC1 and HDAC2, and decrease the expression of the HDAC1.…”

Hypermethylation of promoter regions of the APC1A and p16INK4a genes in relation to prognosis and tumor characteristics in cervical cancer patients

“…With Pyrosequencing, as many as 10 CpG sites can be studied in the same assay (14,15). CpG sites are thought to be involved in cancer development and have been extensively studied (13,(16)(17)(18)(19)(20)(21)(22), and it has been shown that exposure of carcinogens affects the DNA methylation patterns (23)(24)(25). Furthermore, the significance of the methylation pattern is also shown by the SNRPN gene which is a candidate for diagnostic tests in Prader-Willi syndrome and Angelman syndrome (26).…”

Deficient histone acetylation and excessive deacetylase activity as epigenomic marks of prostate cancer cells

“…Lysates from cell cultures or tissues were prepared in the presence of HDAC inhibitor sodium butyrate at 5 mM final concentration as previously described. Histones were isolated using an acid extraction procedure (18,19). The procedures for quantitative Western blotting were performed as previously described (18), with site-specific antibodies against acetylated lysines 4, 9, 14, 23, or 27 of histone H3 (Millipore).…”

“…HDAC activity of classes I, II, and Sirt1 was detected with a previously described procedure using a HDAC assay kit (Biomol International) (18). The assay uses a synthetic acetylated lysine side chain as a substrate to react with the deacetylase samples in a 96-well microplate.…”