Original Article Silencing receptor EphA2 induces apoptosis and attenu- ates tumor growth in malignant mesothelioma

Receptor EphA2 over-expression is associated with the aggressive nature of growth in malignant meso- thelioma (MM) and silencing EphA2 with interference RNA suppressed MM proliferation. The mechanisms associated with targeting the EphA2 gene in MM were not clear. We sought to determine whether silencing EphA2 induces apop- tosis in MM cells by either extrinsic or intrinsic pathways. The receptor EphA2 signaling pathway may provide attrac- tive therapeutic strategy for MM. Apoptosis was determined by Cell Death ELISA in MM Cells transfected with siRNA- EphA2 and control siRNA. The gene expression profile of apoptosis pathways were analyzed by GEArray. Selected genes were further studied by quantitative PCR, Western analysis, and immunofluorescence. Caspases activities were measured by fluorescence spectrometer. Silencing EphA2 expression induced apoptosis in MMC. Apoptosis was characterized by FADD expression, activated caspase-8, caspase-3 and induction of Bax, Bak, and Bid as revealed by GEArray and protein fractionation assays. The expression of FADD, Bid, caspase-8, cytochrome-c and apaf-1 were significantly higher in the cytosolic fractions of EphA2-siRNA transfected cells. Furthermore, blocking the expression of caspase-8 by an inhibitor blunted FADD expression, indicating that caspase-8 is implicated in EphA2-siRNA in- duced apoptosis in MMC. Our data indicates that targeting the EphA2 gene by siRNA induced both extrinsic and in- trinsic apoptotic pathways in MM Cells. Receptor EphA2 inhibition may be an effective approach for inhibiting MM growth and a promising direction for MM therapy.