The CTCF insulator protein is posttranslationally modified by SUMO

Area of Science:

• Molecular Biology
• Epigenetics
• Gene Regulation

Background:

• CTCF is a conserved zinc finger protein crucial for gene regulation and nuclear organization.
• CTCF functions as a gene repressor, notably for the c-myc oncogene.

Purpose of the Study:

• To investigate the posttranslational modification of CTCF by SUMO (Small Ubiquitin-like Modifier).
• To elucidate the functional consequences of CTCF SUMOylation on gene repression and DNA binding.
• To explore the interaction between CTCF, SUMOylation, and Polycomb proteins in nuclear organization.

Main Methods:

• In vivo and in vitro SUMOylation assays for CTCF.
• Identification of SUMOylation sites on CTCF.
• DNA binding assays for modified CTCF.
• Colocalization studies with CTCF and Polycomb protein Pc2.
• Assessment of Pc2's role as a SUMO E3 ligase for CTCF.

Main Results:

• CTCF is SUMOylated both in vivo and in vitro at two major sites.
• SUMOylation does not impede CTCF's DNA binding affinity.
• SUMOylation of CTCF enhances its repressive activity on the c-myc P2 promoter.
• CTCF and Pc2 colocalize in nuclear Polycomb bodies.
• Pc2 may function as a SUMO E3 ligase for CTCF, promoting SUMOylation by SUMO 2 and 3.

Conclusions:

• CTCF undergoes SUMOylation, expanding the known posttranslational modifications of this protein.
• SUMOylation plays a role in regulating CTCF's function, particularly its gene-repressive capacity.
• The interaction with Pc2 suggests a mechanism for SUMOylation-mediated epigenetic regulation involving CTCF.