Rottlerin induces pro-apoptotic endoplasmic reticulum stress through the protein kinase C-δ-independent pathway in human colon cancer cells

Abstract

Rottlerin, a compound reported to be a PKC d-selective inhibitor, has been shown to induce growth arrest or apoptosis of human cancer cell lines. In our study, rottlerin dose-dependently induced apoptotic cell death in colon carcinoma cells. Treatment of HT29 human colon carcinoma cells with rottlerin was found to induce a number of signature ER stress markers; phosphorylation of eukaryotic initiation factor-2a (eIF-2a), ER stress-specific XBP1 splicing, and up-regulation of glucose-regulated protein (GRP)-78 and CCAAT/enhancer-binding proteinhomologous protein (CHOP). However, suppression of PKC d expression by siRNA or overexpression of WT-PKC d and DN-PKC d did not abrogate the rottlerinmediated induction of CHOP. These results suggest that rottlerin induces up-regulation of CHOP via PKC d-independent pathway. Furthermore, down-regulation of CHOP expression using CHOP siRNA attenuated rottlerininduced apoptosis. Taken together, the present study thus provides strong evidence to support an important role of ER stress response in mediating the rottlerin-induced apoptosis. Keywords Rottlerin Endoplasmic reticulum stress Apoptosis CHOP Unfolded protein response