The interferon-inducible gene IFI16, a member of the HIN200 family, triggers primary endothelial cell apoptosis through caspase 2 and caspase 3 pathway

IFI16, an Interferon (IFN)-inducible gene in humans, is a member of the 200-amino acid repeat family of genes HIN200. We previously reported that enforced IFI16 expression in the first 48 h suppressed cell proliferation and resulted in upregulation of inflammatory molecules in human endothelial cells (EC). However, the fate of IFI16-overexpressing EC after inhibition of cell growth has not been clarified so far. Here, we show that IFI16 was sufficient to induce apoptosis, as measured by sub-G1 accumulation, Annexin V binding, and TUNEL analysis in the next 72 h after its overexpression. Activation of caspase 2 and caspase 3 was required for the full apoptotic effect, whereas their inactivation either by specific siRNAs or caspase-2 inhibitor abrogate cell death. IFI16 knockdown by specific siRNA partially prevented EC apoptosis triggered by IFN-beta priming followed by poly rI:rC treatment, proving its physiological relevance in IFN-mediated cell death. Finally, expression of a dominantnegative mutant of IKK2 kinase or treatment with AS602868, an inhibitor of IKK2 activity, halting IkB a degradation and NF-kB activation, resulted in lack of caspase 2 activation and apoptosis induction. We concluded that the IFN-inducible gene IFI16 may contribute to IFN-mediated inhibition of EC cell growth and tube morphogenesis by triggering caspase 2- and caspase 3-mediated programmed cell death through the NF-kB pathway