5-Aza-2'-deoxycytidine-mediated reductions in G9A histone methyltransferase and histone H3 K9 di-methylation levels are linked to tumor suppressor gene reactivation.
The epigenetic silencing of tumor suppressor genes is a common event during carcinogenesis, and often involves aberrant DNA methylation and histone modification of gene regulatory regions, resulting in the formation of a transcriptionally repressive chromatin state. Two examples include the antimetastatic, tumor suppressor genes, desmocollin 3 (DSC3) and MASPIN, which are frequently silenced in this manner in human breast cancer. Treatment of the breast tumor cell lines MDA-MB-231 and UACC 1179 with 5-aza-2'-deoxycytidine (5-aza-CdR) induced transcriptional reactivation of both genes in a dose-dependent manner. Importantly, DSC3 and MASPIN reactivation was closely and consistently linked with significant decreases in promoter H3 K9 di-methylation. Moreover, 5-aza-CdR treatment also resulted in global decreases in H3 K9 di-methylation, an effect that was linked to its ability to mediate dose-dependent, post-transcriptional decreases in the key enzyme responsible for this epigenetic modification, G9A. Finally, small interfering RNA (siRNA)-mediated knockdown of G9A and DNMT1 led to increased MASPIN expression in MDA-MB-231 cells, to levels that were supra-additive, verifying the importance of these enzymes in maintaining multiple layers of epigenetic repression in breast tumor cells. These results highlight an additional, complimentary mechanism of action for 5-aza-CdR in the reactivation of epigenetically silenced genes, in a manner that is independent of its effects on DNA methylation, further supporting an important role for H3 K9 methylation in the aberrant repression of tumor suppressor genes in human cancer.
Wozniak
R J
RJ
Department of Pharmacology and Toxicology, Arizona Cancer Center, University of Arizona, Tucson, AZ 85724-5024, USA.
Klimecki
W T
WT
Lau
S S
SS
Feinstein
Y
Y
Futscher
B W
BW
D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D045744:Cell Line, Tumor; D000077209:Decitabine; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016147:Genes, Tumor Suppressor; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase / Q000037:antagonists & inhibitors*; D006657:Histones / Q000378:metabolism*; D006801:Humans; D008745:Methylation; D011496:Protein Methyltransferases; D020133:Reverse Transcriptase Polymerase Chain Reaction
D004791:Enzyme Inhibitors; D006657:Histones; D000077209:Decitabine; D000076983:Histone Methyltransferases; D011496:Protein Methyltransferases; D011495:Histone-Lysine N-Methyltransferase; D001374:Azacitidine