The Inhibitor of Growth 1b (ING1b) is a type II tumor suppressor and a core member of HDAC-containing chromatin-modifying complexes. ING1b contributes to regulation of gene expression, DNA damage repair and stress signalling, cell growth and senescence, tumorigenesis and apoptosis. Mislocalization of ING1b and decreased levels of ING1b are commonly found in human tumors and cancer cell lines, suggesting the possibility of using ING1b levels as a prognostic marker in clinics. Consistent with a pro-apoptotic function, ING1b protein positively regulates p21 and bax gene expression, and ING1b overexpression promotes apoptosis in p53-dependent and p53-independent manners. The inactivation of apoptosis pathways that is frequently observed in cancer cells causes a dramatic decrease in the efficiency of many cancer treatments. The inactivation of ING1b and suppression of apoptosis in tumors and a greater sensitivity of cancer vs. normal cells to elevated levels of ING1b suggest that modulation of ING1b expression in tumors may serve as a viable approach for cancer therapy.

In this study we aim to expand our understanding of the molecular mechanism(s) by which ING1b promotes apoptosis in cancer cells. Consistent with a wide range of ING1b molecular functions, the protein displays a complex multidomain architecture. Here we define ING1b regions that are necessary for its apoptotic function to design minimal recombinant peptides with potent apoptosis-inducing properties. We previously noted that overexpression of a peptide containing multiple copies of the highly conserved Lamin Interacting Domain (LID) could induce apoptosis in a rapid and efficient way in several cancer cell line models. Here we report that peptides containing the third alpha helix (A3H) and NLS/NTS domains of the ING1b protein are able to induce apoptosis at levels comparable with those seen for full length ING1b protein. While the A3H region is necessary but not sufficient, the NLS domain is required, and partially sufficient, for induction of apoptosis. Cells overexpressing full length ING1b protein or the A3H-NLS peptide show similar changes in cell morphology characteristic of apoptosis, exhibit increased levels of PARP cleavage, and display similar levels of apoptosis as determined by FACS analysis using an Annexin V assay. Our ongoing studies will identify binding partners of the A3H-NLS peptide using mass spectrometry, and determine if the observed pro-apoptotic function of the A3H-NLS peptide requires the presence of these partners. Future experiments will assess the efficacy and specificity of the minimal peptide for controlling cancer cell growth and progression in cell lines and mouse breast cancer models via adenoviral delivery. Our long-term goal is to better define apoptosis pathways and to develop ING1b-based therapeutics for the selective induction of apoptosis in cancer cells.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B20.

Citation Format: Oleksandr Boyko, Karl Riabowol. Defining the minimal ING1b-derived peptide that is pro-apoptotic. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B20.