The CTCF Insulator Protein Is Posttranslationally Modified by SUMO

Abstract

The CTCF protein is a highly conserved zinc finger protein that is implicated in many aspects of gene regulation and nuclear organization. Its functions include the ability to act as a repressor of genes, including the c-myc oncogene. In this paper, we show that the CTCF protein can be posttranslationally modified by the small ubiquitin-like protein SUMO. CTCF is SUMOylated both in vivo and in vitro, and we identify two major sites of SUMOylation in the protein. The posttranslational modification of CTCF by the SUMO proteins does not affect its ability to bind to DNA in vitro. SUMOylation of CTCF contributes to the repressive function of CTCF on the c-myc P2 promoter. We also found that CTCF and the repressive Polycomb protein, Pc2, are colocalized to nuclear Polycomb bodies. The Pc2 protein may act as a SUMO E3 ligase for CTCF, strongly enhancing its modification by SUMO 2 and 3. These studies expand the repertoire of posttranslational modifications of CTCF and suggest roles for such modifications in its regulation of epigenetic states.

Sumoylation at chromatin governs coordinated repression of a transcriptional program essential for cell growth and proliferation

“…S3E). Sumoylation of CTCF has been shown to repress its transcriptional activation function (MacPherson et al 2009;Kitchen and Schoenherr 2010), in agreement with the idea that many SUMO peaks in cluster III correspond to sumoylated CTCF bound to promoters of inactive developmentally regulated genes. Moreover, a global analysis shows colocalization of a significant subset (27%) of all SUMO1 peaks with experimentally determined sites for both CTCF and its interacting partner, the cohesin subunit STAG1 (Supplemental Fig.…”

tDNA insulators and the emerging role of TFIIIC in genome organization

“…Instead, insulator proteins appear to be involved in mediating long-range inter-and intra-chromosomal arrangements that can direct the nuclear co-localization of specific sequences. For example, insulator proteins localize to both repressive Polycomb (Pc) bodies 7 and active transcription factories, 8 and have been shown to underlie interactions between Pc target sites 9 and the maintenance of H3K27me3 within repressive Pc domains. 6 Mapping of interactions facilitated by insulator protein CTCF in mouse embryonic stem cells suggests insulators also contribute to genome organization by forming chromatin loops in which active or repressed genes are harnessed for coregulation, and by facilitating enhancer-promoter interactions.…”

“…In both D. melanogaster and mammals, insulator proteins interact with and localize to nuclear substructures, including the nuclear and nucleolar peripheries, 56 and coalesce into distinct nuclear foci termed insulator bodies, 7,57 together suggesting insulators interact and direct the localization of associated chromatin to defined nuclear compartments. Supporting evidence comes from recent demonstration that insulators underlie long-range Pc interactions and are important for the maintenance of H3K27me3 levels within Pc domains in Drosophila.…”

CTCF terminal segments are unstructured

“…Suggestively, CTCF function can be disrupted by mutation of residues in the terminal segments that are modified by phosphorylation 34,35 and sumoylation. 36 The N-terminal segment serves as a substrate for poly(ADP-ribosyl)ation in vitro. 37 Moreover, the classical zinc fingers of CTCF bind DNA, 1,38 but these domains in other transcription factors also bind proteins.…”