CP190 and CTCF mediated enhancer blocking is augmented by SUMOylation

Chromatin insulators shield promoters and chromatin domains from neighbouring enhancers or chromatin regions with opposing activities. Insulator binding proteins and their cofactors mediate the boundary function. In general, covalent modification of proteins by the Small Ubiqutin-like Modifier (SUMO) is an important mechanism to control the interaction of proteins within complexes. Here we addressed the impact of SUMO in respect to insulator function, chromatin binding of insulator factors and formation of insulator speckles. SUMOylation augments the enhancer blocking function of four different insulator sequences and increases the genome-wide binding of the insulator cofactor CP190. A model is discussed with enhanced chromatin binding of SUMOylated CP190 causing fusion of insulator speckles, which may allow for more efficient insulation. ChIP-seq of FLAG-tagged SUMO, CTCF and CP190 before and after induction of FLAG-SUMO