Bim-dependent apoptosis follows IGFBP-5 down-regulation in neuroblastoma cells

The insulin-like growth factor (IGF) axis is frequently activated in neuroblastoma (NB) tumors and cell lines. We show that silencing endogenous expression of IGF Binding Protein-5 (IGFBP-5) in NB cells by using microRNA and siRNA causes mitochondrial apoptosis that is characterized by: (a) release of cytochrome C in the cytoplasm and activation of caspase 9; (b) Erk1 and Erk2 inhibition; and (c) upregulation of pro-apoptotic proteins Bim and Bax. Bim upregulation is caused, at least in part, by protein stabilization that may depend on inhibition of Erk1 and Erk2. Of interest, Bim knock-down by siRNA decreases apoptosis in IGFBP-5-interfered cells. Thus, inhibition of endogenously produced IGFBP-5 is associated with Bim-dependent apoptosis in NB cells.