continuous-fluorescence-based-endonuclease-coupled-dna-methylation

Continuous Fluorescence-Based Endonuclease-Coupled DNA Methylation Assay to Screen for DNA Methyltransferase Inhibitors

DNA methylation, a form of epigenetic gene regulation, is important for normal cellular function. In cells, proteins called DNA methyltransferases (DNMTs) ...

Bucknell University

In humans, the most common epigenetic DNA modification is methylation of the 5-carbon of cytosines, predominantly in CpG dinucleotides. DNA methylation is an important epigenetic mark associated with gene repression. Disruption of the normal DNA methylation pattern is known to play a role in the initiation and progression of many cancers. DNA methyltransferase 1 (DNMT1), the most abundant DNA methyltransferase in humans, is primarily responsible for maintenance of the DNA methylation pattern and is considered an important cancer drug target. Recently, laccaic acid A (LCA), a highly substituted anthraquinone natural product, was identified as a direct, DNA-competitive inhibitor of DNMT1. Here, we have successfully screened a small library of simplified anthraquinone compounds for DNMT1 inhibition. Using an endonuclease-coupled DNA methylation assay, we identified two anthraquinone compounds, each containing an aromatic substituent, that act as direct DNMT1 inhibitors. These simplified anthraquinone compounds retain the DNA-competitive mechanism of action of LCA and exhibit some selectivity for DNMT1 over DNMT3a. The newly identified compounds are at least 40-fold less potent than LCA, but have significantly less complex structures. Collectively, this data indicates that substituted anthraquinone compounds could serve as a novel scaffold for developing DNMT1-specific inhibitors.

Substituted anthraquinones represent a potential scaffold for DNA methyltransferase 1-specific inhibitors.

In eukaryotes, the most common epigenetic DNA modification is methylation of carbon 5 of cytosines, predominantly in CpG dinucleotides. Methylation patterns are established and maintained by a family of proteins known as DNA methyltransferases (DNMTs). DNA methylation is an important epigenetic mark associated with gene repression, and disruption of the normal DNA methylation pattern is known to play a role in several disease states. Methylation patterns are primarily maintained by DNMT1, which possesses specificity for methylation of hemimethylated DNA. DNMT1 is a multidomain protein with a C-terminal catalytic methyltransferase domain and a large N-terminal regulatory region. The replication focus targeting sequence (RFTS) domain, found in the regulatory region, is an endogenous inhibitor of DNMT1 activity. Recently, several mutations in the RFTS domain were shown to be causal for two adult onset neurodegenerative diseases; however, little is known about the impact of these mutations on the structure and function of DNMT1. Two of these mutations, G589A and V590F, are associated with development of autosomal dominant cerebellar ataxia, deafness, and narcolepsy (ADCA-DN). We have successfully expressed and purified G589A and V590F DNMT1 for  studies. The mutations significantly decrease the thermal stability of DNMT1, yet the mutant proteins exhibit 2.5-3.5-fold increases in DNA binding affinity. In addition, the mutations weaken RFTS-mediated inhibition of DNA methylation activity. Taken together, these data suggest these disease-associated mutations decrease protein stability and, at least partially, relieve normal RFTS-mediated autoinhibition of DNMT1.

Article	Year
Substituted anthraquinones represent a potential scaffold for DNA methyltransferase 1-specific inhibitors. PloS one\| PubMed ID: 31306451	2019
Disease-Associated Mutations G589A and V590F Relieve Replication Focus Targeting Sequence-Mediated Autoinhibition of DNA Methyltransferase 1. Biochemistry\| PubMed ID: 31804802	2019

Rebecca Switzer

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