C-Terminal Binding Protein (CtBP) a critical regulator of ErbB2/3 signaling in PDAC
Pancreatic ductal adenocarcinoma (PDAC) remains among the most lethal of human cancers underscoring the need to identify new therapeutic vulnerabilities. Previously, we reported high expression of transcriptional co-regulators C-terminal binding proteins (CtBP) 1 and 2 in human PDAC, however their precise role in PDAC formation or progression remains unclear. Here, we have studied PDAC tumor dependency on CtBPs for growth and metastasis using an orthotopic syngeneic pancreatic tumor mouse model. CRISPR-based homozygous deletion of Ctbp2 dramatically decreased PDAC tumor growth, drastically reduced metastatic potential, and significantly prolonged survival. Interrogating differential gene expression of the orthotopic PDAC tumors from CtBP2 WT vs. CtBP2 KO cohorts, we identified significant downregulation of the EGFR-superfamily receptor ErbB3 in CtBP2 KO tumors, and further determined that CtBP regulates expression of both the ErbB2 and 3 EGFR superfamily genes in PDAC cells. We therefore hypothesized that CtBP regulation of physiologic ErbB2/3 signaling contributes, in part, to PDAC growth and metastasis. Indeed, we observed that CtBP2 KO cells exhibited severely attenuated activation of phospho-Akt after neuregulin stimulation of ErbB2/3, and we demonstrate that human PDAC cells also show CtBP dependence of ErbB2/3 expression. Our results suggest that a subset of PDAC tumors is dependent on physiologic ErbB2/3 signaling and could be targeted by pharmacologic inhibitors of ErbB2 and/or ErbB3. Providing proof of concept, the ErbB2-targeted multikinase inhibitor lapatinib, but not the ErbB1/EGFR targeted agent erlotinib, effectively killed ErbB3 expressing PDAC cells, while CtBP2 KO cells where ErbB3 expression was extinguished, were resistant to lapatinib. Taken together, our data suggests that ErBb2/3 targeted therapeutics can effectively target a critical PDAC dependency on physiologic ErbB2/3 signaling which is the result of CtBP's oncogenic transcriptional program that drives PDAC tumor progression. Overall design: We have studied the impact of Ctbp2 deletion in PDAC using an orthotopic syngeneic pancreatic tumor mouse model using a mouse PDAC cell line derived from a CKP (K-Ras G12D/ p53 null) PDAC tumor. Ctbp2 was then deleted homozygously in the CKP cell line using CRISPR/Cas9. RNA-seq was performed to determine gene expression differences between KO and WT Ctbp2 expressing cells.