The Alternative Reading Frame Tumor Suppressor Antagonizes Hypoxia-Induced Cancer Cell Migration via Interaction with the COOH-Terminal Binding Protein Corepressor

Abstract

The alternative reading frame (ARF) tumor suppressor exerts both p53-dependent and p53-independent activities critical to the prevention of cancer in mice and humans. Recent evidence from mouse models suggests that when p53 is absent, further loss of ARF can widen the tumor spectrum, and potentiate invasion and metastasis. A major target of the p53-independent activity of ARF is the COOH-terminal binding protein (CtBP) family of metabolically regulated transcriptional corepressors, which are degraded upon acute exposure to the ARF protein. CtBPs are activated under conditions of metabolic stress, such as hypoxia, to repress epithelial and proapoptotic genes, and can mediate hypoxia-induced migration of cancer cells. The possibility that ARF could suppress tumor cell migration as part of its p53-independent activities was thus explored. Small-interfering RNA (siRNA)-mediated knockdown of ARF in human lung carcinoma cells led to increased cell migration, especially during hypoxia, and this effect was blocked by concomitant treatment with CtBP2 siRNA. Introduction of ARF into p53 and ARF-null human colon cancer cells inhibited hypoxia-induced migration. Furthermore, overexpression of CtBP2 in ARF-expressing cells enhanced cell migration, and an ARF mutant defective in CtBP-family binding was impaired in its ability to inhibit cell migration induced by CtBP2. ARF depletion or CtBP2 overexpression was associated with decreased PTEN expression and activation of the phosphatidylinositol 3-kinase pathway, and a phosphatidylinositol 3-kinase inhibitor blocked CtBP2-mediated cell migration. Thus, ARF can suppress cell migration by antagonizing CtBP2 and the phosphatidylinositol 3-kinase pathway, and these data may explain the increased aggressiveness of ARF-null tumors in mouse models.

The Corepressor CTBP2 Is a Coactivator of Retinoic Acid Receptor/Retinoid X Receptor in Retinoic Acid Signaling

“…CTBP is part of the corepressor complex, CoREST and is involved in repression of tumor suppressor genes such as CDH1 (encoding E-cadherin), PTEN, and CDKN2A (37)(38)(39)(40)(41). In the present study, we found that suppression of Ctbp2, but not of Ctbp1, confers RA resistance, suggesting the unique attribute of Ctbp2 as a coactivator in RA signaling (Fig.…”

CtBP2 Modulates the Androgen Receptor to Promote Prostate Cancer Progression

“…CtBPs have PLDS domains that interact with histone-modifying enzymes, such as HDAC, LSD1, and G9a, to modulate histone acetylation and methylation levels. Although the CTBP family is associated with cancer, the roles of CtBPs in cancer vary depending on the cancer type (27)(28)(29).…”

p19Arf Inhibits the Invasion of Hepatocellular Carcinoma Cells by Binding to C-terminal Binding Protein

“…Arf inhibits the hypoxia-induced migration of H1299 human lung carcinoma cells in a p53-independent and CtBPdependent manner (35), and previous studies have indicated that CtBP can regulate the migration of this cell line, although cell invasion was not assayed in these studies (20). Significantly, the leucine 46 residue, which is critical for the Arf-CtBP interaction, is one of six invariant residues conserved across several species, including human, mouse, chicken, pig, and opossum (32).…”