The AT-hook of the Chromatin Architectural Transcription Factor High Mobility Group A1a Is Arginine-methylated by Protein Arginine Methyltransferase 6

Riccardo Sgarra,Jaeho Lee,Michela A Tessari,Sandro Altamura,Barbara Spolaore,Vincenzo Giancotti,Mark T Bedford,Guidalberto Manfioletti

doi:10.1074/jbc.m510231200

Abstract

The HMGA1a protein belongs to the high mobility group A (HMGA) family of architectural nuclear factors, a group of proteins that plays an important role in chromatin dynamics. HMGA proteins are multifunctional factors that associate both with DNA and nuclear proteins that have been involved in several nuclear processes, such as transcriptional regulation, viral integration, DNA repair, RNA processing, and chromatin remodeling. The activity of HMGA proteins is finely modulated by a variety of post-translational modifications. Arginine methylation was recently demonstrated to occur on HMGA1a protein, and it correlates with the apoptotic process and neoplastic progression. Methyltransferases responsible for these modifications are unknown. Here we show that the protein arginine methyltransferase PRMT6 specifically methylates HMGA1a protein both in vitro and in vivo. By mass spectrometry, the sites of methylation were unambiguously mapped to Arg(57) and Arg(59), two residues which are embedded in the second AT-hook, a region critical for both protein-DNA and protein-protein interactions and whose modification may cause profound alterations in the HMGA network. The in vivo association of HMGA and PRMT6 place this yet functionally uncharacterized methyltransferase in the well established functional context of the chromatin structure organization.

Highlights

high mobility group A (HMGA) proteins contain about 100 amino acid residues and have three DNA-binding domains called AT-hooks that mediate their ability to interact with the narrow minor groove of AT-rich DNA sequences (6)
We have identified HMGA1a as an in vivo cellular substrate of PRMT6 and mapped the methylated residues
PRMT6 is a novel arginine methyltransferase that was recently discovered by data base screening (31)

Summary

Introduction

HMGA proteins contain about 100 amino acid residues and have three DNA-binding domains called AT-hooks that mediate their ability to interact with the narrow minor groove of AT-rich DNA sequences (6). We have reported the identification of PRMT6 as a protein methyltransferase able to efficiently methylate in vitro and in vivo HMGA1a. We report that PRMT6 methylates HMGA1a at the level of Arg57 and Arg59 within the second AT-hook domain.

Results

Conclusion