Targeting of C-terminal binding protein (CtBP) by ARF results in p53-independent apoptosis

Area of Science:

• Oncology
• Molecular Biology
• Cell Biology

Background:

• ARF (Alternative Reading Frame) is a tumor suppressor that inhibits MDM2, a negative regulator of p53.
• Loss of ARF in p53-null mice broadens the tumor spectrum and decreases tumor latency, suggesting p53-independent functions.

Purpose of the Study:

• To investigate the mechanism of p53-independent tumor suppression by ARF.
• To identify proteins interacting with ARF using a yeast two-hybrid screen.

Main Methods:

• Yeast two-hybrid screening to identify ARF-interacting proteins.
• In vitro and in vivo assays to confirm ARF interactions with CtBP1 and CtBP2.
• Assessment of proteasome-dependent CtBP degradation upon ARF interaction.
• Evaluation of p53-independent apoptosis induction by ARF-mediated CtBP degradation or CtBP knockdown in colon cancer cells.

Main Results:

• C-terminal binding protein 2 (CtBP2), an antiapoptotic transcriptional corepressor, was identified as an ARF-interacting protein.
• ARF interacts with both CtBP1 and CtBP2, leading to their proteasome-dependent degradation.
• ARF-induced CtBP degradation and CtBP small interfering RNA (siRNA) treatment both induced p53-independent apoptosis in colon cancer cells.
• ARF's ability to induce apoptosis is dependent on its interaction with CtBP, as CtBP overexpression reversed ARF-induced apoptosis.

Conclusions:

• CtBP proteins are putative targets for ARF-mediated p53-independent tumor suppression.
• ARF induces apoptosis by degrading CtBP proteins, offering a novel therapeutic target for cancers lacking p53 function.