Bz-423 superoxide signals B cell apoptosis via Mcl-1, Bak, and Bax

Abstract

Bz-423 is a pro-apoptotic 1,4-benzodiazepine with therapeutic properties in murine models of lupus demonstrating selectivity for autoreactive lymphocytes. Bz-423 modulates the F1F0-ATPase, inducing the formation of superoxide within the mitochondrial respiratory chain, which then functions as a second messenger initiating apoptosis. In order to understand some of the features that contribute to the increased sensitivity of lymphocytes, we report the signaling pathway engaged by Bz-423 in a Burkitt lymphoma cell line (Ramos). Following the generation of superoxide, Bz-423-induced apoptosis requires the activation of Bax and Bak to induce mitochondrial outer membrane permeabilization and cytochrome c release. Knockdown of the BH3-only proteins Bad, Bim, Bik, and Puma inhibits Bz-423 apoptosis, suggesting that these proteins serve as upstream sensors of the oxidant stress induced by Bz-423. Treatment with Bz-423 results in superoxide-dependent Mcl-1 degradation, implicating this protein as the link between Bz-423-induced superoxide and Bax and Bak activation. In contrast to fibroblasts, B cell death induced by Bz-423 is independent of c-Jun N-terminal kinase. These results demonstrate that superoxide generated from the mitochondrial respiratory chain as a consequence of a respiratory transition can signal a specific apoptotic response that differs across cell types.

ABT‐263 enhances sorafenib‐induced apoptosis associated with Akt activity and the expression of Bax and p21(CIP1/WAF1) in human cancer cells

“…Bax deficiency causes blocking of cell death signalling and changes in chemosensitivity to drug-induced apoptosis in many cell types (Blatt et al, 2009). p21 (CIP1/WAF1), a potent cyclindependent kinase inhibitor, inhibits the activity of the cyclin-CDK complexes, and thus has functions as a regulator of cell cycle progression (Ding et al, 2008;Hoeferlin et al, 2011).…”

Apoptotic Signaling Activated by Modulation of the F0F1-ATPase: Implications for Selective Killing of Autoimmune Lymphocytes

“…Bz-423-induced O 2 . does not engage the ASK1-JNK pathway in Ramos B cells; instead Bax/Bak-dependent apoptosis is mediated by functional activation of BH3-only proteins in this cell type (Blatt et al, 2009). Although JNK is activated in Bz-423-treated Jurkat cells, it is not necessary for apoptosis and its activation is delayed relative to the timing defined in MEFs.…”

“…In contrast, Bz-423-induced O 2 . does not activate ASK1-JNK signaling in B cells (Blatt et al, 2009). To determine whether the ASK1-JNK pathway is engaged in T cells, phospho-JNK was measured in Bz-423-treated Jurkat cells.…”

“…Because . signals degradation of Mcl-1 in B cells (Blatt et al, 2009), we sought to determine whether a similar mechanism contributes to activation of Bak in Jurkat cells. Although levels of Bcl-x L were stable, Mcl-1 was reduced by Bz-423 to Ͻ50% of control levels after 4 h, and continued to fall to Ͻ10% by 8 h (Fig.…”

“…In contrast, Bz-423-induced O 2 . does not activate the ASK1-JNK pathway in more sensitive Ramos B cells (Blatt et al, 2009). Instead, degradation of the antiapoptotic Bcl-2 family protein Mcl-1 and functional activation of proapoptotic BH3-only proteins link the O 2 .…”