Abstract 331: Epithelial-mesenchymal transition confers resistance to complement-dependent cytotoxicity in lung cancer cells

Recent studies have implicated Epithelial-mesenchymal transition (EMT) in conferring several clinically relevant properties to cancer cells, in addition to initiating tumor metastasis. These include stem-cell like properties, resistance to targeted therapies and ability to evade immune surveillance. Pathway analysis of gene expression changes in TGF-β induced EMT identified the complement cascade as one of the significantly enriched pathway. Further analysis of the genes in the complement pathway revealed EMT-induced expression of complement inhibitors and decrease in expression of proteins essential for complement activity, suggesting resistance to complement dependent cytotoxicity (CDC) during EMT. We found lung cancer cells that undergo EMT showed marked decrease in C3 deposition and concomitant resistance to apoptosis by CDC as measured by 7-Aminoactinomycin D staining. Flow cytometric and RT-PCR analysis showed a significant increase in the CD59 expression on the surface of cells undergoing EMT, which is a potent inhibitor of formation of membrane attack complex that mediates complement dependent cell lysis. Furthermore, CD59 inhibition by siRNA mediated knock-down overcame the EMT-induced resistance to anti-EGFR antibody (Cetuximab) mediated CDC. The increase in CD59 was abrogated on disruption of TGF-β signaling as revealed by TGF- β Receptor kinase inhibitor and is dependent on Smad3 signaling. Chromatin immunoprecipitation analysis revealed increased occupancy of Smad3 on CD59 promoter, suggesting a direct regulation by Smad3. These results demonstrate that TGF-β-induced EMT confers another novel immune evasive mechanism to tumor cells that facilitates tumor progression and CD59 as a potential therapeutic target for enhancing the efficacy of anti-EGFR Antibody therapies and against tumor metastasis. 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 331. doi:1538-7445.AM2012-331