SETDB1 Triple Tudor Domain Ligand, ( R , R )-59, Promotes Methylation of Akt1 in Cells

Increased expression and hyperactivation of the methyltransferase SET domain bifurcated 1 (SETDB1) are commonly observed in cancer and central nervous system disorders. However, there are currently no reported SETDB1-specific methyltransferase inhibitors in the literature, suggesting that this is a challenging target. Here, we disclose that the previously reported small-molecule ligand for SETDB1’s triple tudor domain, ( R, R )-59, is unexpectedly able to increase SETDB1 methyltransferase activity both in vitro and in cells. Specifically, ( R, R )-59 promotes in vitro SETDB1-mediated methylation of lysine 64 of the protein kinase Akt1. Treatment with ( R, R )-59 also increased Akt1 threonine 308 phosphorylation and activation, a known consequence of Akt1 methylation, resulting in stimulated cell proliferation in a dose-dependent manner. ( R, R )-59 is the first SETDB1 small-molecule positive activator for the methyltransferase activity of this protein. Mechanism of action studies show that full-length SETDB1 is required for significant in vitro methylation of an Akt1-K64 peptide and that this activity is stimulated by ( R, R )-59 primarily through an increase in catalytic activity rather than a change in S -adenosyl methionine binding.