Abstract 2005: Identification of Bcl2L13 as a novel GBM oncoprotein

Abstract

Using in silico analysis of 272 GBM samples in the TGCA data set to find important cell death mechanisms in gliomapathogenesis, we identified differential expression of the novel Bcl2-Like13 protein (Bcl2L13). Bcl2L13 shares significant structural homology with Bcl-2 and Bcl-xL, but contains a unique 250 amino acid sequence that may point to unique, non-classical functions. Several studies have shown that Bcl2L13 expression correlates with increased chemotherapeutic resistance and unfavorable treatment outcome in leukemia and ZIC1-driven liposarcomas. These clinical data suggests that Bcl2L13 likely acts as an onco-protein in multiple cancers and may act in a similar manner in GBM. Using qRT-PCR and immunohistochemical analyses, we found that Bcl2L13 was highly overexpressed in >90% of GBM samples, but absent in adjacent normal brain. Using RNAi-loss- and cDNA complementation studies in glioma cell lines and glioma stem cells (GSCs), we determined that Bcl2L13 potently inhibits therapy-induced apoptosis by inhibiting mitochondrial outer membrane permeabalization (MOMP) and post-mitochondrial caspase-3 and -7 cleavage, likely acting in a similar manner as canonical Bcl-2 family proteins. Bcl2L13 overexpression also greatly increased cellular proliferation, and immunofluorescence and cell fractionalization experiments revealed that Bcl2L13 is localized at the mitochondria. To study the impact of Bcl2L13 on the progression of gliomagenesis in vivo, we orthotopically injected glioma cell lines with enforced expression of Bcl2L13-targeting shRNAs into immunocompromised SCID mice. Strikingly, neutralization of Bcl2L13 signaling increased overall glioma-free survival, which was associated with enhanced intratumoral apoptosis and decreased proliferative indices. To molecularly elucidate the mechanism by which Bcl2L13 exerts its anti-apoptotic effects, we performed a Yeast Two Hybrid screen and identified a select number of tumor suppressors and onco-proteins including ceramide synthase 2 (CerS2), (a regulator of MOMP) and O-6-methylguanine-DNA methyltransferase (MGMT), (an important prognostic indicator of telozolomide effectiveness) as Bcl2L13 interaction partners. Co-immunoprecipitations confirmed the interactions between Bcl2L13 and these proteins. Taken together, these results reveal that Bcl2L13 represents a novel anti-apoptotic, Bcl-2-like GBM oncoprotein that inhibits apoptosis progression and promotes tumor growth by impacting mitochondrial membrane physiology. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2005. doi:1538-7445.AM2012-2005