Oncolytic adenoviral vectors which employ the survivin promoter induce glioma oncolysis via a process of beclin-dependent autophagy

Survivin has gained attention as a tumor-specific marker which is upregulated in a variety of neoplasms. Although the survivin protein is implicated in anti-apoptotic tumor pathways, little is known about the function of the survivin promoter. In this study, we constructed a conditionally replicative adenoviral vector (CRAd) that utilizes the survivin promoter and examined the mechanism of CRAd induced cell death in malignant glioma. Our results indicate that CRAd vectors which utilize the survivin promoter effectively replicate in glioma cells and exhibit a high oncolytic effect. The survivin-mediated CRAd appeared to induce apoptosis as measured by Annexin/7-AAD. Caspase-3 and BAX mRNAs were upregulated based on microarray data, however, Western blot analysis of infected cells showed no evidence of elevated caspase-3, BAX, or p53 protein expression. Of note, at each time point infected glioma cells showed no evidence of activated BAD or AKT. The inhibition of AKT signaling led us to examine autophagy in infected cells. Electron micrographs of virally infected glioma cells suggested autophagosomal-mediated cell death and selective blocking of beclin with siRNA prevented autophagy. These results indicate that the survivin promoter enhances viral replication and induces autophagy of infected glioma cells via a beclin-dependent mechanism.