CTBP1 x CTBP2

Corepressors CtBP1 and CtBP2 (CtBP1/2) are evolutionarily conserved transcriptional regulators that repress gene expression by recruiting chromatin modifiers, yet the structural basis of this process remains elusive. Here, we identify a direct interaction between CtBP1/2 and the histone H3 lysine 9 (H3K9) methyltransferase G9a. Crystallographic and biochemical analyses reveal that a CtBP1/2 tetramer simultaneously engages two G9a molecules through a motif within the pre-SET domain of G9a, which is absent in its paralog GLP. This interaction enhances G9a catalytic activity in a manner strictly dependent on the oligomeric state of CtBP1/2. Disruption of CtBP2 tetramerization diminishes its association with G9a and abolishes enzymatic activation, underscoring the functional importance of CtBP1/2 oligomerization. In colorectal cancer (CRC) cells, CtBP2 and G9a co-occupy the PTEN promoter, where disruption of their interface reduces H3K9me2 deposition, derepresses PTEN expression, attenuates PI3K-AKT signaling, and impairs CRC cell proliferation. Together, these findings establish a structural framework for CtBP-mediated regulation of G9a activity and highlight the CtBP1/2-G9a complex as a potential therapeutic target in colorectal cancer.

Chromatin regulation of transcriptional enhancers plays a central role in cell fate specification and differentiation. However, how the coordinated activity of transcription factors and chromatin-modifying enzymes regulates enhancers in neural stem cells and dictates subsequent stages of neuronal differentiation and migration is not well understood. The histone methyltransferase PRDM16 is expressed in neural stem cells of the developing mouse and human cerebral cortex, and is essential for determining the position of upper-layer cortical neurons. Here, we report that PRDM16 interacts with C-terminal binding protein 1 (CtBP1) and CtBP2 to control the transcriptional programs of cortical neurogenesis and regulate upper-layer neuron migration. PRDM16 and CtBP1/2 co-regulate enhancers by interacting with histone deacetylase 1 (HDAC1), HDAC2 and lysine-specific demethylase 1 (LSD1). In addition, our results suggest that the CCCTC-binding factor CTCF plays a key role in recruiting CtBP1/2 to cortical enhancers. These findings underscore that reduced interactions between PRDM16 and ubiquitous chromatin regulators may contribute to neurodevelopmental deficits in individuals with PRDM16 haploinsufficiency.

Although acute inflammatory responses are critical for survival, chronic inflammation is a leading cause of disease and mortality worldwide. Nevertheless, our mechanistic understanding of pathogenesis is still limited and precise treatment options are lacking. Here, we investigate the role of the transcriptional co-repressors C-terminal binding protein (CTBP) 1 and 2 in murine and human macrophage activation using loss-of-function models to show that CTBP2 but not CTBP1 controls inflammatory gene expression. We find that CTBP2 occupiescis-regulatory elements of inflammatory genes together with the transcription factors NF-κB and AP-1 and forms a co-repressor complex. Rescue ofCtbp1/2double knockout cells with WT, oligomeric CTBP2 attenuates inflammatory responses, whereas a monomeric mutant does not. Differential profiling of CTBP2’s WT and monomeric interactome confirms oligomer-specific interactions with multiple repressors. Conversely, monomers retain the ability to interact with AP-1 and RNA polymerase II, boosting gene expression. Our findings point to an important function for CTBP2 in fine-tuning inflammatory gene expression, potentially unveiling novel therapeutic targets for the treatment of inflammatory diseases.