Down-regulation of 14-3-3β exerts anti-cancer effects through inducing ER stress in human glioma U87 cells: Involvement of CHOP-Wnt pathway

We previously identified 14-3-3 beta as a tumor-specific isoform of 14-3-3 protein in astrocytoma, but its functional role in glioma cells and underlying mechanisms are poorly understood. In the present study, we investigated the effects of 14-3-3 beta inhibition in human glioma U87 cells using specific targeted small interfering RNA (siRNA). The results showed that 14-3-3 beta is highly expressed in U87 cells but not in normal astrocyte SVGp12 cells. Knockdown of 14-3-3 beta by Si-14-3-3 beta transfection significantly decreased the cell viability but increased the LDH release in a time-dependent fashion in U87 cells, and these effects were accompanied with G0/G1 cell cycle arrest and apoptosis. In addition, 14-3-3 beta knockdown induced ER stress in U87 cells, as evidenced by ER calcium release, increased expression of XBP1S mRNA and induction of ER related pro-apoptotic factors. Down-regulation of 14-3-3 beta significantly decreased the nuclear localization of beta-catenin and inhibited Topflash activity, which was shown to be reversely correlated with CHOP. Furthermore, Si-CHOP and sFRP were used to inhibit CHOP and Wnt, respectively. The results showed that the anti-cancer effects of 14-3-3 beta knockdown in U87 cells were mediated by increased expression of CHOP and followed inhibition of Wnt/beta-catenin pathway. In summary, the remarkable efficiency of 14-3-3 beta knockdown to induce apoptotic cell death in U87 cells may find therapeutic application for the treatment of glioma patients. (C) 2015 Elsevier Inc. All rights reserved.