A Direct Assay for Measuring the Activity and Inhibition of Coactivator-Associated Arginine Methyltransferase 1

Abstract

Coactivator-associated arginine methyltransferase 1 (CARM1) is a member of the family of protein arginine methyltransferases. CARM1 catalyzes methyl group transfer from the cofactor S -adenosyl- l -methionine (AdoMet) to both histone and nonhistone protein substrates. CARM1 is involved in a range of cellular processes, mainly involving RNA transcription and gene regulation. As the aberrant expression of CARM1 has been linked to tumorigenesis, the enzyme is a potential therapeutic target, leading to the development of inhibitors and tool compounds engaging with CARM1. To evaluate the effects of these compounds on the activity of CARM1, sensitive and specific analytical methods are needed. While different methods are currently available to assess the activity of methyltransferases, these assays mainly focus on either the measurement of the cofactor product S -adenosyl- l -homocysteine (AdoHcy) or employ radioactive or expensive reagents, each with their own advantages and limitations. To complement the tools currently available for the analysis of CARM1 activity, we here describe the development of a convenient assay employing peptide substrates derived from poly(A)-binding protein 1 (PABP1). This operationally straightforward liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based approach allows for the direct detection of substrate methylation with minimal workup. The method was validated, and its value in characterizing CARM1 activity and inhibition was demonstrated through a comparative analysis involving a set of established small molecules and peptide-based CARM1 inhibitors.

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“…It should be noted that the IC 50 is in ten micromolar range for EZM2302 and TP-064, which is much higher than what has been reported previously . The major reason for this was because the activity was measured using a commercially available kit (MTase Glo), which has been known to have high background signals from the automethylation at arginine residue R551 in CARM1 protein . The inhibitory effects of iCARM1 and EZM2302 or TP-064 on histone methylation were compared in vitro.…”

“… 29 The major reason for this was because the activity was measured using a commercially available kit (MTase Glo), which has been known to have high background signals from the automethylation at arginine residue R551 in CARM1 protein. 43 The inhibitory effects of iCARM1 and EZM2302 or TP-064 on histone methylation were compared in vitro. iCARM1 seemed to be more specific than EZM2302 and TP-064.…”