Overexpression of Bcl-2 induces STAT-3 activation via an increase in mitochondrial superoxide

Abstract

We recently reported a novel interaction between Bcl-2 and Rac1 and linked that to the ability of Bcl-2 to induce a pro-oxidant state in cancer cells. To gain further insight into the functional relevance of this interaction, we utilized computer simulation based on the protein pathway dynamic network created by Cellworks Group Inc. STAT3 was identified among targets that positively correlated with Rac1 and/or Bcl-2 expression levels. Validating this, the activation level of STAT3, as marked by p-Tyr705, particularly in the mitochondria, was significantly higher in Bcl-2-overexpressing cancer cells. Bcl-2-induced STAT3 activation was a function of GTP-loaded Rac1 and NADPH oxidase (Nox)-dependent increase in intracellular superoxide (O2•−). Furthermore, ABT199, a BH-3 specific inhibitor of Bcl-2, as well as silencing of Bcl-2 blocked STAT3 phosphorylation. Interestingly, while inhibiting intracellular O2•− blocked STAT3 phosphorylation, transient overexpression of wild type STAT3 resulted in a significant increase in mitochondrial O2•− production, which was rescued by the functional mutants of STAT3 (Y705F). Notably, a strong correlation between the expression and/or phosphorylation of STAT3 and Bcl-2 was observed in primary tissues derived from patients with different sub-sets of B cell lymphoma. These data demonstrate the presence of a functional crosstalk between Bcl-2, Rac1 and activated STAT3 in promoting a permissive redox milieu for cell survival. Results also highlight the potential utility of a signature involving Bcl-2 overexpression, Rac1 activation and STAT3 phosphorylation for stratifying clinical lymphomas based on disease severity and chemoresistance.

Cell death through the ages: The ICDS 25th Anniversary Meeting

“…Shazib Pervaiz (National University of Singapore, Singapore) highlighted the historical dogma of the balance between BCL‐2 and BAX and the importance of this balance for cell survival versus the commitment to cell death. Pervaiz demonstrated a non‐canonical anti‐apoptotic function of BCL‐2 by computational modeling, whereby active BCL‐2 interacts with GTP‐bound RAS‐related C3 botulinum toxin substrate 1 (RAC1) to confer apoptotic resistance . This research highlights a potential dual therapeutic approach for treating lymphomas overexpressing RAC1 or active BCL‐2.…”

How does estrogen work on autophagy?

“…Functional crosstalk between BCL2, RAC1, and activated STAT3 exists and promotes a permissive redox milieu for cell survival [84]. STAT3 signaling events occur downstream of MMP14/MT1-MMP (matrix metallopeptidase 14).…”

Cross Talk Between Cellular Redox State and the Antiapoptotic Protein Bcl-2

“…levels was also associated with the downstream activation of signal transducer and activator of transcription 3 (STAT3), which was mediated through a function of Rac1 (79). Overexpression of Bcl-2 induced phosphorylation of STAT3 on Tyr705, which was mediated by increased O 2 .…”