Abstract 259: Interplay between Bcl-2 and cFLIP in lymphoma disease progression is a function of an altered redox milieu

Abstract

Abstract Bcl-2 is associated with chemoresistance and despite the preponderance of evidence linking its anti-apoptotic function to hematologic cancers, it’s now emerging that overexpression of Bcl-2 is a feature shared by a host of cancers. Canonically, the death inhibitory activity of Bcl-2 is associated with its ability to prevent mitochondrial outer membrane permeabilization. However, recent evidence has highlighted a novel facet in the biology of Bcl-2, whereby enforced expression of Bcl-2 resulted in an increase in mitochondrial oxygen consumption and elevated levels of the reactive oxygen species (ROS), superoxide (O2-.). Alleviating the levels of intracellular O2-. sensitized Bcl-2 overexpressing cells to death receptor induced apoptosis via a robust increase in upstream caspase 8 activation. Using a variety of functional mutants of the NOX-activating small GTPase Rac1, we show a clear link between Bcl-2 induced apoptosis resistance and intracellular O2-.. In the search for the molecular target of this inhibitory signal, we now show that Bcl-2 overexpression is associated with an increase in the transcription and protein levels of the receptor inhibitory protein, cFLIP. We employed pharmacological and genetic approaches to modulated intracellular O2-. and present evidence cFLIP is transcriptionally regulated by O2-.; increase in cFLIP promoter activity and mRNA levels. Interestingly, inhibiting glycolysis also resulted in downregulation of cFLIP in a ROS-dependent manner. Notably, primary cells derived from patients with lymphoma also showed a significant downregulation of cFLIP when subjected to conditions that decrease O2-. and elicited enhanced sensitivity to TRAIL-induced apoptosis. Importantly, TCGA and Affy meta-cohorts’ analyses revealed consistent correlation trend: Bcl-2 and cFLIP (CFLAR) were positively correlated; Bcl-2 and SOD1 (superoxide dismutase 1) were negatively correlated. A strong negative correlation was also observed between CFLAR and SOD1. Furthermore, Kaplan-Meier analyses of overall survival (OS) were performed in the in-house High expression of either Bcl-2 or CFLAR conferred poor OS outcome. When stratified by CFLAR and Bcl-2 expressions, cases with higher expression of the two genes had the worst prognosis with the shortest median survival. Notably, DLBCL with high Bcl-2 and low SOD1 had the worst OS outcome, compared against expression levels of Bcl-2 and SOD1. Together, these findings point to a concordance between cFLIP and Bcl-2, which negatively correlates with SOD1 in driving lymphoma progression. Citation Format: Jayshree L. Hirpara, Shazib Pervaiz. Interplay between Bcl-2 and cFLIP in lymphoma disease progression is a function of an altered redox milieu [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 259.