Subtilase cytotoxin induces apoptosis in HeLa cells by mitochondrial permeabilization via activation of Bax/Bak, independent of C/EBF-homologue protein (CHOP), Ire1α or JNK signaling

Subtilase cytotoxin (SubAB) is an AB(5) cytotoxin produced by some strains of Shiga-toxigenic Escherichia colt The A subunit is a subtilase-like serine protease and cleaves an endoplasmic reticulum (ER) chaperone, BiP, leading to transient inhibition of protein synthesis and cell cycle arrest at G(1) phase, and inducing caspase-dependent apoptosis via mitochondrial membrane damage in Vero cells. Here we investigated the mechanism of mitochondrial permeabilization in HeLa cells SubAB-induced cytochrome c release into cytosol did not depend on mitochondrial permeability transition pore (PTP), since cyclosporine A did not suppress cytochrome c release SubAB did not change the expression of anti-apoptotic Bcl-2 or Bcl-XL and pro-apoptotic Box or Bak, but triggered Box and Bak conformational changes and association of Bax with Bak Silencing using siRNA of both bax and bak genes, but not bax, bak, or bun alone, resulted in reduction of cytochrome c release, caspase-3 activation. DNA ladder formation and cytotoxicity, indicating that Box and Bak were involved in apoptosis SubAB activated ER transmembrane transducers, Ire1 alpha, and cJun N-terminal kinase (JNK), and induced C/EBF-homologue protein (CHOP) To investigate whether these signals were involved in cytochrome c release by Bax activation, we silenced ire la, ink or chop. however, silencing did not decrease SubAB-induced cytochrome c release, suggesting that these signals were not necessary for SubAB-induced mitochondrial permeabilization by Bax activation (C) 2010 Elsevier Ltd All rights reserved