Noxa mitochondrial targeting domain induces necrosis via VDAC2 and mitochondrial catastrophe.

Noxa, a Bcl-2 homology 3 (BH3)-only protein of the Bcl-2 family, is responsive to cell stresses and triggers apoptosis by binding the prosurvival Bcl-2-like proteins Mcl1, Bcl, and Bcl2A1. Although the Noxa BH3 domain is necessary to induce apoptosis, the mitochondrial targeting domain (MTD) of Noxa functions as a pronecrotic domain, an inducer of mitochondrial fragmentation, and delivery to mitochondria. In this study, we demonstrate that the extended MTD (eMTD) peptide induces necrotic cell death by interaction with the VDAC2 protein. The eMTD peptide penetrates the cell membrane, causing cell membrane blebbing, cytosolic calcium influx, and mitochondrial swelling, fragmentation, and ROS generation. The MTD domain binds VDACs and opens the mitochondrial permeability transition pore (mPTP) in a CypD-independent manner. The opening of mPTP induced by eMTD is inhibited either by down-regulation of VDAC2 or by the VDACs inhibitor DIDS. These results indicate that the MTD domain of Noxa causes mitochondrial damage by opening mPTP through VDACs, especially VDAC2, during necrotic cell death.