Inhibition of autophagy enhances dynamin inhibitor-induced apoptosis via promoting Bak activation and mitochondrial damage in human Jurkat T cells

Abstract

Treatment of Jurkat T cells with the dynamin inhibitor, myristyl trimethyl ammonium bromides (MiTMAB) caused cytokinesis impairment and apoptotic DNA fragmentation along with down-regulation of anti-apoptotic BAG3 and Mcl-1 levels, Bak activation, mitochondrial membrane potential (Δψm) loss, activation of caspase-9 and -3, and PARP cleavage, without accompanying necrosis. Bcl-xL overexpression completely abrogated these MiTMAB-induced mitochondrial damage and resultant caspase cascade activation, except for impaired cytokinesis and down-regulated BAG3 and Mcl-1 levels. Additionally, autophagic responses including Akt-mTOR pathway inhibition, formation of acridine orange-stainable acidic vesicular organelles, LC3-I/II conversion, and p62/SQSTM1 down-regulation were detected regardless of Bcl-xL overexpression. The autophagy inhibitors 3-methyladenine and LY294002 enhanced MiTMAB-induced apoptotic sub-G1 peak, BAG3 and Mcl-1 down-regulation, Bak activation, Δψm loss, and caspase activation. These results indicate that MiTMAB-caused cytokinesis failure leads to concomitant induction of apoptosis and cytoprotective autophagy, and suggest that inhibition of autophagy is a promising strategy to augment antitumor activity of MiTMAB.

Keywords: BAG3 and Mcl-1 down-regulation; Cytokinesis arrest; Cytoprotective autophagy; Dynamin inhibitor; MiTMAB; Mitochondrial apoptosis.