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

Abstract

The INK4A/ARF tumor suppressor locus is frequently inactivated in hepatocellular carcinoma (HCC), yet the consequences of this remain unknown. We recently described a HCC mouse model in which loss of the Ink4a/Arf locus accelerates the development of metastasis and enhances tumor cell migration and invasion in cell culture assays. We show here that knockdown of p19Arf in an HCC cell line increases invasion in cell culture assays. Furthermore, reintroduction of p19Arf into HCC cell lines lacking Ink4a/Arf inhibits tumor cell invasion, without affecting cell proliferation, or cell transformation as measured by soft agar colony formation. Inhibition of cell invasion by p19Arf was dependent on its C-terminal binding protein (CtBP) interaction domain but independent of Mdm2 binding and nucleolar localization. Indeed, RNA interference-mediated knockdown of CtBP1 or CtBP2 decreased cell invasion, and ectopic expression of CtBP2 enhanced tumor cell migration and invasion. Thus, our data indicate a novel role for the Arf tumor suppressor protein in regulating phenotypes associated with tumor progression and metastasis in HCC cells. [Cancer Res 2008;68(2):476-82]

Therapeutic targeting of C-terminal binding protein in human cancer

“…CtBP is a potential therapeutic target in cancer, therefore, due to its numerous pro-oncogenic properties. 7,16,17,19 Here we have samples for Class II tumors invariably contained detectable and comparatively high levels of CtBP1/2 protein, as also seen in matched normal samples from Class III tissues (where CtBP levels were the same in normal and tumor tissue; Fig. 5A, #7-9), but unlike the matched normal class I specimens (Fig.…”

“…CtBP transcription repressors represent potentially attractive cancer drug targets since they encode a potentially "druggable" dehydrogenase domain and their silencing by RNAi leads to anti-cancer effects, including apoptosis and abrogation of cancer cell migration/invasion. 10,[17][18][19] Based on the identification of MTOB as a CtBP substrate, as well as its reported cytotoxicity, the effect of MTOB on cell viability was determined in cell lines known to rely on CtBP for regulation of survival [HCT116 colon carcinoma wild type (+/+) or null (-/-) for p53 (Fig. 1A)].…”

“…activities, including EMT, 8 cell migration/invasion, 7,17,18 and cell survival 8,19 through repression of epithelial genes such as keratin-8 and E-cadherin and apoptosis genes such as Bik, Noxa, Puma and PERP. 8,20 Additionally, CtBP targets multiple growth inhibitory tumor suppressors for repression, including PTEN, p16…”

Pontin, a new mutant p53-binding protein, promotes gain-of-function of mutant p53

“…Some genes that require Pontin for their transcriptional regulation by mutp53, including STMN1, ADRB1, ITPR1, RIPK1, CtBP2, TPD52 and TOX3, have been suggested to have roles in tumorigenesis, especially for migration and metastasis. 30,31,[38][39][40][41] Results from ChIP assays show that mutp53 interacts with some target genes at their regulatory regions in a Pontin-dependent manner. It remains unclear why Pontin selectively regulates mutp53 transcriptional activity toward certain genes.…”

CtBPs promote mitotic fidelity through their activities in the cell nucleus

“…Other strategies to target the spindle assembly checkpoint, such as the use of aurora B inhibitors, are also under investigation as potential therapeutic strategies (Ditchfield et al, 2005). The disruption of CtBP chromatin-modifying complexes in order to disrupt mitotic fidelity may be a similarly valid approach, particularly given the other known tumour-promoting activity of CtBPs (Chinnadurai, 2009), such as suppression of senescence (Mroz et al, 2008) and apoptosis (Kovi et al, 2010) as well as enhancement of invasion (Chen et al, 2008). One concern with such an approach is the potential effects on normal cells; we previously showed that siRNA-targeting CtBPs induce mitotic aberrations in cultured non-transformed fibroblasts, in addition to a panel of breast cancer cell lines (Bergman et al, 2009).…”