Expression level and DNA methylation status of glutathione-S-transferase genes in normal murine prostate and TRAMP tumors.
BACKGROUND
Glutathione-S-transferase (Gst) genes are downregulated in human prostate cancer, and GSTP1 silencing is mediated by promoter DNA hypermethylation in this malignancy. We examined Gst gene expression and Gst promoter DNA methylation in normal murine prostates and Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) tumors.


METHODS
Primary and metastatic tumors were obtained from TRAMP mice, and normal prostates were obtained from strain-matched WT mice (n = 15/group). Quantitative real-time RT-PCR was used to measure GstA4, GstK1, GstM1, GstO1, and GstP1 mRNA expression, and Western blotting and immunohistochemical staining was used to measure GstM1 and GstP1 protein expression. MassARRAY Quantitative Methylation Analysis was used to measure DNA methylation of the 5' CpG islands of GstA4, GstK1, GstM1, GstO1, and GstP1. TRAMP-C2 cells were treated with the epigenetic remodeling drugs decitabine and trichostatin A (TSA) alone and in combination, and Gst gene expression was measured.


RESULTS
Of the genes analyzed, GstM1 and GstP1 were expressed at highest levels in normal prostate. All five Gst genes showed greatly reduced expression in primary tumors compared to normal prostate, but not in tumor metastases. Gst promoter methylation was unchanged in TRAMP tumors compared to normal prostate. Combined decitabine + TSA treatment significantly enhanced the expression of 4/5 Gst genes in TRAMP-C2 cells.


CONCLUSIONS
Gst genes are extensively downregulated in primary but not metastatic TRAMP tumors. Promoter DNA hypermethylation does not appear to drive Gst gene repression in TRAMP primary tumors; however, pharmacological studies using TRAMP cells suggest the involvement of epigenetic mechanisms in Gst gene repression.
Mavis
Cory K
CK
Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
Morey Kinney
Shannon R
SR
Foster
Barbara A
BA
Karpf
Adam R
AR
D000230:Adenocarcinoma / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D045744:Cell Line, Tumor; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D000077209:Decitabine; D004338:Drug Combinations; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D020868:Gene Silencing; D051549:Glutathione S-Transferase pi / Q000235:genetics / Q000378:metabolism; D005982:Glutathione Transferase / Q000235:genetics*; D006877:Hydroxamic Acids / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009362:Neoplasm Metastasis / Q000235:genetics; D011467:Prostate / Q000201:enzymology*; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism
D000964:Antimetabolites, Antineoplastic; D004338:Drug Combinations; D006877:Hydroxamic Acids; D012333:RNA, Messenger; C012589:trichostatin A; D000077209:Decitabine; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; C496557:Gstp1 protein, mouse; D001374:Azacitidine