CtBP2 Promotes Human Cancer Cell Migration by Transcriptional Activation of Tiam1

Abstract

The mammalian COOH-terminal binding proteins (CtBPs) CtBP1 and CtBP2 are metabolically regulated transcriptional co-repressors that are degraded upon acute exposure to the alternative reading frame (ARF) tumor suppressor. We reported previously that CtBP stimulates cell migration in certain contexts via repression of PTEN transcription and activation of the phosphatidylinositol 3-kinase (PI3K) pathway. We have now identified an additional and direct mechanism for CtBP stimulation of cell migration via regulation of T-cell lymphoma invasion and metastasis 1 (Tiam1) protein. Tiam1 is a guanine nucleotide exchange factor (GEF) for Rac GTPase that plays a critical role in regulating cell adhesion, invasion, and migration and has been directly implicated in the promotion of cancer progression and metastasis. We noted a strict positive correlation between CtBP2 and Tiam1 expression levels and that CtBP promotion of cell migration required CtBP-dependent transcriptional activation of Tiam1. RNA interference (RNAi)-mediated knockdown of CtBP2 in human colon or lung carcinoma cells led to decreased Tiam1 protein and mRNA expression, while overexpression of CtBP2 increased Tiam1 expression levels. RNAi and overexpression studies also demonstrated that Tiam1 is a key downstream mediator of CtBP2-mediated cell migration. An analysis of the Tiam1 promoter revealed binding sites for the CtBP-interacting Kruppel-like factor 8 (KLF8), and a Tiam1 promoter luciferase reporter was induced in the presence of both KLF8 and CtBP2, consistent with KLF8-dependent CtBP transactivation of Tiam1. Chromatin immunoprecipitation analyses demonstrated CtBP2 occupancy of the Tiam1 promoter that was dependent on the presence of KLF8. Our results indicate that Tiam1 is a transcriptional activation target of CtBP2 and that this interaction promotes the pro-oncogenic function of CtBP2 leading to cancer cell migration. Transcriptional activation thus plays a role in CtBP pro-oncogenic functions along with the previously characterized CtBP co-repressor function.

ZNF750 interacts with KLF4 and RCOR1, KDM1A, and CTBP1/2 chromatin regulators to repress epidermal progenitor genes and induce differentiation genes

“…Transcriptional activation or repression by RCOR1 and CTBP1/2 likely depends on the specific transcription factors and chromatin regulators with which they are associated, as shown here. We found that ZNF750 is required for full association of RCOR1, KDM1A, and CTBP1/2 with specific genomic sites, consistent with the previously described recruitment of these general chromatin regulators to specific sites by other transcription factors (Lin et al 2010;Paliwal et al 2012). It is possible that additional ZNF750-interacting proteins identified by mass spectrometry may also be involved in distinguishing the ZNF750-activating and ZNF750-repressing complexes.…”

“…RCOR1 and CTBP1/2 have known roles in transcriptional repression in a complex with KDM1A (Shi et al 2003;Lee et al 2005). Roles for RCOR1 and CTBP1/2 in transcriptional activation have also been described, but the mechanism is not well understood (Fang et al 2006;Jin et al 2007;Abrajano et al 2010;Paliwal et al 2012). Transcriptional activation or repression by RCOR1 and CTBP1/2 likely depends on the specific transcription factors and chromatin regulators with which they are associated, as shown here.…”

Nicotinamide Phosphoribosyltransferase in Malignancy: A Review

“…63 An increased NADH/NAD ratio strengthens CtBP binding to its cellular targets, enhancing resistance to proteolytic digestion and promoting cell migration, partially through the metastases-promoting Tiam1 protein. [64][65][66] Increased iNampt expression increases intracellular NAD levels, while hypoxia increases the NADH/NAD + ratio. Thus, increased tumor iNampt combined with hypoxia could lead to pro-carcinogenesis events via CtBP activation.…”

“…Thus, increased tumor iNampt combined with hypoxia could lead to pro-carcinogenesis events via CtBP activation. 13,[64][65][66] Van Horssen et al 67 demonstrated that pharmacologic or genetic suppression of iNampt lowered NADH levels and glioma cell migration, while extracellular supplementation with NAD + or iNampt re-expression abolished these effects. Cellular mobility was also associated with a lowered internal pH determined by the lactate dehydrogenase dependent pyruvate-lactate conversion, suggesting that tumor hypoxia may promote cell migration.…”

Inhibition of C-terminal binding protein attenuates transcription factor 4 signaling to selectively target colon cancer stem cells

“…17 However, more recent evidence points to a more diverse role in which CtBP can be both an activator as well as repressor of gene expression depending on the partnering transcription factor, as well as cell context. 15,18 In fact, in a drosophila model, CtBP was proposed as an activator of TCF-4 signaling in gene and context specific manner. 19 We and others have shown that TCF-4 signaling plays a key role in colonic CSC growth and self-renewal.…”