C-Jun N-terminal kinases are required for oncolytic adenovirus-mediated autophagy

Oncolytic adenoviruses, such as Delta-24-RGD, are replication-competent viruses that are genetically engineered to induce selective cancer cell lysis. In cancer cells, Delta-24-RGD induces massive autophagy, which is required for efficient cell lysis and adenoviral spread. Understanding the cellular mechanisms underlying the regulation of autophagy in cells treated with oncolytic adenoviruses may provide new avenues to improve the therapeutic effect. In this work, we showed that cancer cells infected with Delta-24-RGD undergo autophagy despite the concurrent activation of the AKT/mTOR pathway. Moreover, adenovirus replication induced sustained activation of JNK proteins in vitro. ERK1/1 phosphorylation remained unchanged during adenoviral infection, suggesting specificity of JNK activation. Using genetic ablation and pharmacological inactivation of JNK, we unequivocally demonstrated that cells infected with Delta-24-RGD required JNK activation. Thus, genetic co-ablation of JNK1 and JNK2 genes or inhibition of JNK kinase function rendered Delta-24-RGD–treated cells resistant to autophagy. Accordingly, JNK activation induced phosphorylation of Bcl-2 and prevented the formation of Bcl-2/Beclin 1 autophagy suppressor complexes. Using an orthotopic model of human glioma xenograft, we showed that treatment with Delta-24-RGD induced phosphorylation and nuclear translocation of JNK, as well as phosphorylation of Bcl-2. Collectively, our data identified JNK proteins as an essential mechanistic link between Delta-24-RGD infection and autophagy in cancer cells. Activation of JNK without inactivation of the AKT/mTOR pathway constitutes a distinct molecular signature of autophagy regulation that differentiates Delta-24-RGD adenovirus from the mechanism used by other oncolytic viruses to induce autophagy and provides a new rationale for the combination of oncolytic viruses and chemotherapy.