Apo2L/TRAIL induction and nuclear translocation of inositol hexakisphosphate kinase 2 during IFN-β-induced apoptosis in ovarian carcinoma

Publisher Website
Google Scholar
Abstract
Previously, we have reported that overexpression of IHPK2 (inositol hexakisphosphate kinase 2) sensitized NIH-OVCAR-3 ovarian carcinoma cell lines to the growth-suppressive and apoptotic effects of IFN-β (interferon-β) treatment and γ-irradiation. In the present study, we demonstrate that Apo2L/TRAIL (Apo2L/tumour-necrosis-factor-related apoptosis-inducing ligand) is a critical mediator of IFN-induced apoptosis in these cells. Compared with IFN-α2, IFN-β is a more potent inducer of Apo2L/TRAIL and IHPK2 activity. Overexpression of IHPK2 converts IFN-α2-resistant cells into cells that readily undergo apoptosis in response to IFN-α2. In untreated cells transfected with IHPK2-eGFP (where eGFP stands for enhanced green fluorescent protein), the fusion protein is localized to the cytoplasm and perinuclear region. After treatment with IFN-β, IHPK2-eGFP translocated to the nucleus. In cells transfected with mutant IHPK2-NLS-eGFP (where NLS stands for nuclear localization sequence), containing point mutations in the NLS, the fusion protein remained trapped in the cytoplasm, even after IFN-β treatment. Cells expressing mutant NLS mutation were more resistant to IFN-β. The IC50 value of IHPK2-expressing cells was 2–3-fold lower than vector control. The IC50 value of NLS-mutant-expressing cells was 3-fold higher than vector control. Blocking antibodies to Apo2L/TRAIL or transfection with a dominant negative Apo2L/TRAIL receptor (DR5Δ) inhibited the antiproliferative effects of IFN-β. Thus overexpression of IHPK2 enhanced apoptotic effects of IFN-β, and expression of the NLS mutant conferred resistance to IFN-β. Apo2L/TRAIL expression and nuclear localization of IHPK2 are both required for the induction of apoptosis by IFN-β in ovarian carcinoma.