Redox sensor CtBP mediates hypoxia-induced tumor cell migration

Abstract

The rapid growth and poor vascularization of solid tumors expose cancer cells to hypoxia, which promotes the metastatic phenotype by reducing intercellular adhesion and increasing cell motility and invasiveness. In this study, we found that hypoxia increased free NADH levels in cancer cells, promoting CtBP recruitment to the E-cadherin promoter. This effect was blocked by pyruvate, which prevents the NADH increase. Furthermore, hypoxia repressed Ecadherin gene expression and increased tumor cell migration, effects that were blocked by CtBP knockdown. We propose that CtBP senses levels of free NADH to control expression of cell adhesion genes, thereby promoting tumor cell migration under hypoxic stress.NADH ͉ E-cadherin ͉ metastasis ͉ HIF1␣ ͉ adhesion T he ability of tumors to metastasize is a hallmark of malignancy. A critical event during metastasis is the reduction of adhesion, which facilitates tumor cell invasion into surrounding tissues and vascular channels, ultimately leading to the development of new sites of cancer progression. E-cadherin-mediated cell-cell adhesion is essential for maintaining the homeostasis and architecture of epithelial tissues. Down-regulation of Ecadherin expression occurs concomitantly with dedifferentiation and invasion of epithelial cells during tumorigenesis (1, 2). Consequently, E-cadherin and its associated complex are thought to be key mediators of tumor cell invasion (3).Highly aggressive, rapidly growing tumors are exposed to hypoxia, which occurs as a consequence of high metabolic activity and inadequate blood supply (4). It has been proposed that hypoxia is the initiating event that sets tumors on the road to metastasis (5). We have shown that the transcriptional corepressor CtBP has the unique ability to sense levels of free nuclear NADH and transmit this information to complexes that regulate gene expression (6). Transcription of E-cadherin and several other cell adhesion proteins is known to be repressed by CtBP (7) via ZEB and other factors believed to interact with the E-cadherin promoter (8,9). CtBP binding to these transcriptional repressors is induced by elevations in free NADH (6). We propose that the redox-sensing property of CtBP provides a regulatory switch for E-cadherin expression under hypoxic conditions.In this study, we show that the transcriptional corepressor CtBP has a central role in cancer cell migration in response to hypoxia. Hypoxia increases free NADH levels, which promotes CtBP recruitment to the E-cadherin promoter, repressing Ecadherin gene expression and increasing tumor cell migration. Thus, the pathway we have described links tumor hypoxia to cell migration through NADH regulation of CtBP function.

RETRACTED: Metabolic regulation of SIRT1 transcription via a HIC1:CtBP corepressor complex

“…To assess whether 2-DG affected CtBP binding to HIC1, we performed coimmunoprecipitation assays. Under control conditions, the association of HIC1 and CtBP was readily apparent ( (24), we treated cells with pyruvate, which similarly reduces free NADH levels (18), and obtained identical results (data not shown).…”

“…5A). This effect was partially blocked by treatment with pyruvate, which drives NADH to NAD ϩ (18). A complete reversal of the hypoxia effect occurred after treatment with 2-DG.…”

“…CtBP has previously been shown to mediate the hypoxia-induced repression of E-cadherin (18). We show here that the redox changes induced by the glycolytic inhibitor 2-deoxyglucose (2-DG) decrease CtBP interaction with the transcriptional repressor, HIC1 (hypermethylated in cancer; 19).…”

“…Next, we tested whether SIRT1 transcription is regulated in the opposite direction through hypoxia, which increases NADH concentration by Ϸ4-fold (18). Overnight exposure of cells to hypoxia (1% O 2 ) lowered levels of SIRT1 transcript (Fig.…”

The conserved NAD(H)-dependent corepressor CTBP-1 regulates Caenorhabditis elegans life span

“…CtBP represses transcription by recruiting multiple histone modifying enzymes including the histone H3 lysine 9 (H3K9) methyltransferase G9a/HMTase1 and the histone H3 lysine 4 (H3K4) demethylase LSD1 (3,8). Previous studies suggest a role for CtBP in mouse development, apoptosis, and hypoxia-induced tumor migration (9)(10)(11)(12). However, by and large, the biology of CtBP is still incompletely understood.…”