C-terminal of E1A binding protein 1 enhances the migration of gastric epithelial cells and has a clinicopathologic significance in human gastric carcinoma

NADH/NAD+ binding and linked tetrameric assembly of the oncogenic transcription factors CtBP1 and CtBP2

The activation of oncogenic C-terminal binding Protein (CtBP) transcriptional activity is coupled with NAD(H) binding and homo-oligomeric assembly, although the level of CtBP assembly and nucleotide binding affinity continues to be debated. Here, we apply biophysical techniques to address these fundamental issues for CtBP1 and CtBP2. Our ultracentrifugation results unambiguously demonstrate that CtBP assembles into tetramers in the presence of saturating NAD⁺ or NADH with tetramer to dimer dissociation constants about 100 nm. Isothermal titration calorimetry measurements of NAD(H) binding to CtBP show dissociation constants between 30 and 500 nm, depending on the nucleotide and paralog. Given cellular levels of NAD⁺ , CtBP is likely to be fully saturated with NAD under physiological concentrations suggesting that CtBP is unable to act as a sensor for NADH levels.

CTBP1 strengthens the cisplatin resistance of gastric cancer cells by upregulating RAD51 expression

Drug resistance is a key factor affecting the treatment of gastric cancer. The resistance of gastric cancer cells to anticancer drugs, such as cisplatin (DDP), remains a major challenge to patient recovery. The present study aimed to investigate the roles of C-terminal-binding protein 1 (CTBP1) in the DDP resistance of gastric cancer cells and to determine its regulatory effect on DNA repair protein RAD51 homolog 1 (RAD51). The DDP-resistant human gastric cancer AGS and HGC cell lines, AGS/DDP and HGC-27/DDP, respectively, were established and CTBP1 expression was detected by western blotting. In addition, Cell Counting Kit-8, colony formation and flow cytometry assays were performed to detect the proliferation and apoptosis of these two cell lines following CTBP1 knockdown. The expression levels of apoptosis-related proteins were detected by western blotting. In addition, RAD51 was overexpressed in CTBP1 knockdown cells, and proliferation and apoptosis were subsequently determined using the aforementioned methods. The results demonstrated that CTBP1 expression was notably increased in DDP-resistant gastric cancer cells. Furthermore, CTBP1 knockdown suppressed the proliferation and induced the apoptosis of AGS/DDP and HGC-27/DDP cells. Notably, CTBP1 promoted RAD51 expression in DDP-resistant gastric cancer cells. Overexpression of RAD51 in CTBP1 knockdown AGS/DDP and HGC-27/DDP cells rescued the proliferation and alleviated the apoptosis of these cells. Taken together, the results of the present study suggested that CTBP1 may enhance the DDP resistance of gastric cancer cells by activating RAD51 expression, thus providing a potential novel therapy (CTBP1 knockdown) for the clinical treatment of patients with gastric cancer.

NAD(H) phosphates mediate tetramer assembly of human C-terminal binding protein (CtBP)

C-terminal binding proteins (CtBPs) are cotranscriptional factors that play key roles in cell fate. We have previously shown that NAD(H) promotes the assembly of similar tetramers from either human CtBP1 and CtBP2 and that CtBP2 tetramer destabilizing mutants are defective for oncogenic activity. To assist structure-based design efforts for compounds that disrupt CtBP tetramerization, it is essential to understand how NAD(H) triggers tetramer assembly. Here, we investigate the moieties within NAD(H) that are responsible for triggering tetramer formation. Using multiangle light scattering (MALS), we show that ADP is able to promote tetramer formation of both CtBP1 and CtBP2, whereas AMP promotes tetramer assembly of CtBP1, but not CtBP2. Other NAD(H) moieties that lack the adenosine phosphate, including adenosine and those incorporating nicotinamide, all fail to promote tetramer assembly. Our crystal structures of CtBP1 with AMP reveal participation of the adenosine phosphate in the tetrameric interface, pinpointing its central role in NAD(H)-linked assembly. CtBP1 and CtBP2 have overlapping but unique roles, suggesting that a detailed understanding of their unique structural properties might have utility in the design of paralog-specific inhibitors. We investigated the different responses to AMP through a series of site-directed mutants at 13 positions. These mutations reveal a central role for a hinge segment, which we term the 120s hinge that connects the substrate with coenzyme-binding domains and influences nucleotide binding and tetramer assembly. Our results provide insight into suitable pockets to explore in structure-based drug design to interfere with cotranscriptional activity of CtBP in cancer.