Abstract
The SET1 family of proteins, and in particular MLL1, are essential regulators of transcription and key mediators of normal development and disease. Here, we summarize the detailed characterization of the methyltransferase activity of SET1 complexes and the role of the key subunits, WDR5, RbBP5, ASH2L, and DPY30. We present new data on full kinetic characterization of human MLL1, MLL3, SET1A, and SET1B trimeric, tetrameric, and pentameric complexes to elaborate on substrate specificities and compare our findings with what has been reported before. We also review exciting recent work identifying potent inhibitors of oncogenic MLL1 function through disruption of protein–protein interactions within the MLL1 complex.
Highlights
We present new data on full kinetic characterization of human MLL1, MLL3, SET1A, and SET1B trimeric, tetrameric, and pentameric complexes to elaborate on substrate specificities and compare our findings with what has been reported before
MLL1-fusions preferentially regulate a subset of the genes that are wildtype mixed lineage leukemia (MLL) targets and significantly increase the transcription of developmentally important genes involved in the disease phenotype.[27,28]
Taking advantage of available amino acid sequence of WDR5-interacting motif (WIN) motif of MLL1, we developed a peptide (WIN: GSARAEVHLRKS) displacement assay to screen in a 384-well format for compounds that bind to WD repeat domain 5 (WDR5) and inactivate MLL1 by disrupting MLL1– WDR5–RB binding protein 5 (RbBP5) complex.[90]
Summary
Kinetic characterization of human SET1 family of proteins One of the questions that has already been proposed and investigated is whether the components of the SET1 complexes affect the ability of the catalytic subunit to mono-, di- or trimethylate.[65,66] To further investigate this and fully characterize the kinetics of HMT activity of SET1 family members and compare their substrate specificities, we reconstituted human MLL1 (3745–3969), MLL3 (4706–4911), SET1A (1491– 1707), and SET1B (1815–2037) trimeric (MWR), tetrameric (MWRA) and pentameric (MWRAD) complexes (W; 1–334, R; 1–538, A; 1–628, D; 1–99) as described in the Supporting Information Materials and Methods.
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