Modulation of retinoic acid receptor alpha activity by lysine methylation in the DNA binding domain

Metabolic labeling and detection with a methylated lysine-specific antibody confirm lysine methylation of RAR alpha in mammalian cells. We previously reported Lys ³⁴⁷ trimethylation of mouse retinoic acid receptor alpha (RAR alpha) in the ligand binding domain (LBD) that affected ligand sensitivity of the dissected LBD. Here we report two monomethylated residues, Lys ¹⁰⁹ and Lys ¹⁷¹ identified by LC-ESI-MS/MS in the DNA binding domain (DBD) and the hinge region, which affect retinoic acid (RA) sensitivity, coregulator interaction and heterodimerization with retinoid X receptor (RXR) in the context of the full-length protein. Constitutive negative mutation at Lys ¹⁰⁹, but not Lys ¹⁷¹, reduces RA-dependent activation. Methylation at Lys ¹⁰⁹ plays a more dominant role than trimethylation at Lys ³⁴⁷ in terms of RA activation of the full-length receptor. Lys ¹⁰⁹ is located in a homologous sequence (CEGCKGFFRRS) of the DBD in RARs and is conserved in the nuclear receptor superfamily even across the species boundary. This study uncovers a potential role for monomethylation at Lys ¹⁰⁹ in coordinating the synergy between DBD and LBD for ligand-dependent activation of RAR alpha.