Regulation of complement-dependent cytotoxicity by TGF-β-induced epithelial-mesenchymal transition.

The process of epithelial-mesenchymal transition (EMT), in addition to being an initiating event for tumor metastasis, is implicated in conferring several clinically relevant properties to disseminating cancer cells. These include stem cell-like properties, resistance to targeted therapies and ability to evade immune surveillance. Enrichment analysis of gene expression changes during transforming growth factor-β (TGF-β)-induced EMT in lung cancer cells identified complement cascade as one of the significantly enriched pathway. Further analysis of the genes in the complement pathway revealed an increase in the expression of complement inhibitors and a decrease in the expression of proteins essential for complement activity. In this study, we tested whether EMT confers resistance to complement-dependent cytotoxicity (CDC) in lung cancer cells and promotes tumor progression. CD59 is a potent inhibitor of membrane attack complex that mediates complement-dependent cell lysis. We observed a significant increase in the CD59 expression on the surface of cells after TGF-β-induced EMT. Furthermore, CD59 knockdown restored susceptibility of cells undergoing EMT to cetuximab-mediated CDC. TGF-β-induced CD59 expression during EMT is dependent on Smad3 but not on Smad2. Chromatin immunoprecipitation analysis confirmed that Smad3 directly binds to the CD59 promoter. Stable knockdown of CD59 in A549 cells inhibited experimental metastasis. These results demonstrate that TGF-β-induced EMT and CD59 expression confers an immune-evasive mechanism to disseminating tumor cells facilitating tumor progression. Together, our data demonstrates that CD59 inhibition may serve as an adjuvant to enhance the efficacy of antibody-mediated therapies, as well as to inhibit metastasis in lung cancer.