βIII-tubulin can act as a brake on extrinsic apoptosis in pancreatic cancer

Abstract

The microtubule protein beta III-tubulin is a prognostic, pro-survival, and chemoresistance factor in multiple malignancies, including pancreatic ductal adenocarcinoma (PDAC). However, the precise survival mechanisms controlled by beta III-tubulin in cancer remain unknown. Here, we discovered a link between beta III-tubulin and the activation of caspase 8-mediated extrinsic apoptosis. Silencing beta III-tubulin in PDAC cells activated caspase 8, leading to decreased cell viability and growth both in vitro and in vivo. beta III-tubulin knockdown also increased the sensitivity of PDAC cells to extrinsic cell death signals, including TNF-related apoptosis-inducing ligand (TRAIL), TNF alpha, and FasL. Furthermore, we demonstrated that beta III-tubulin knockdown in PDAC cells, in the absence or presence of TRAIL, increased diffusion and clustering of the TRAIL death receptor DR5 at the cell membrane, inducing extrinsic apoptosis. Nanoparticle delivery of beta III-tubulin siRNA to mouse PDAC tumours reduced tumour growth and increased responsiveness to TRAIL therapy. In patient-derived human PDAC explants, beta III-tubulin silencing reduced tumour cell frequency and improved sensitivity to TRAIL. Finally, we showed that high beta III-tubulin expression in the human PDAC stroma was independently prognostic for poor overall survival. Taken together, silencing beta III-tubulin represents an innovative strategy to activate a suicide signal in PDAC cells and render them more sensitive to microenvironment- and chemotherapy-derived death signals.