DNMT1 forms a complex with Rb, E2F1 and HDAC1 and represses transcription from E2F-responsive promoters

Abstract

Methylation of CpG islands is associated with transcriptional silencing and the formation of nuclease-resistant chromatin structures enriched in hypoacetylated histones. Methyl-CpG-binding proteins, such as MeCP2, provide a link between methylated DNA and hypoacetylated histones by recruiting histone deacetylase, but the mechanisms establishing the methylation patterns themselves are unknown. Whether DNA methylation is always causal for the assembly of repressive chromatin or whether features of transcriptionally silent chromatin might target methyltransferase remains unresolved. Mammalian DNA methyltransferases show little sequence specificity in vitro, yet methylation can be targeted in vivo within chromosomes to repetitive elements, centromeres and imprinted loci. This targeting is frequently disrupted in tumour cells, resulting in the improper silencing of tumour-suppressor genes associated with CpG islands. Here we show that the predominant mammalian DNA methyltransferase, DNMT1, co-purifies with the retinoblastoma (Rb) tumour suppressor gene product, E2F1, and HDAC1 and that DNMT1 cooperates with Rb to repress transcription from promoters containing E2F-binding sites. These results establish a link between DNA methylation, histone deacetylase and sequence-specific DNA binding activity, as well as a growth-regulatory pathway that is disrupted in nearly all cancer cells.

Site-specific DNA methylation by a complex of PU.1 and Dnmt3a/b

“…In vitro translated 35 S-labeled luciferase, CBP1890, MeCP2, Dnmt3a and Dnmt3b were incubated with the 50% slurry of 20 ml of immobilized GST protein and GST-PU.1 fusion protein, and bound proteins were subjected to Nu-PAGE followed by autoradiography. Epigenetic transcriptional repression of PU.1-mediated reporter activity by Dnmt3s Several studies have shown that Dnmt3a and Dnmt3b are associated with HDAC1 and HDAC2 in vivo and in vitro (Robertson et al, 2000;Bachman et al, 2001;Fuks et al, 2001). Histone deacetylase removes the acetyl groups from the amino-terminal of the histone tails, which triggers the assembly of a tightly packed chromatin inaccessible to the transcriptional machinery (Jenuwein and Allis, 2001).…”

Functional epigenetics identifies a protocadherin PCDH10 as a candidate tumor suppressor for nasopharyngeal, esophageal and multiple other carcinomas with frequent methylation

“…Epigenetic silencing can occur via promoter methylation and/or modification of histone tails in the chromatin. These two epigenetic events are closely linked and affect each other through the interaction of DNMT with the HDAC complex at methylated CpG sites (Robertson et al, 2000;Rountree et al, 2000). Pharmacologic (such as Aza treatment) or genetic demethylation (through double KO of DNMT1 and DNMT3B) results in the hypomethylation of genomic DNA, thus restoring the expression of methylation-silenced genes (Rhee et al, .…”

Retinoblastoma family genes

“…Additionally, HP1, a protein which binds methylated lysine 9 and is associated with transcriptionally silent regions of chromatin, can bind Rb (Nielsen et al, 2001). Furthermore, Rb interacts with the DNA methyltransferase enzyme DNMT1, which cooperates to repress reporter genes (Robertson et al, 2000); however, DNA methylation was not detected at the repressed promoters, suggesting that the effect of DNMT1 may not be through its enzymatic activity but instead might help recruit other co-repressors.…”