Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease with a 5-year survival rate under 5%. Whereas activated pancreatic stellate cells (PaSC) are important players in PDAC stroma, simultaneously targeting both cancer and stromal cells can be beneficial for cancer therapy. We previously reported that the phytochemical rottlerin dose-dependently reduces PaSC viability through dysregulation of autophagy and induction of apoptosis, and attenuates tumor progression in PDAC experimental models. Interestingly, both rottlerin and metformin have been shown to affect mitochondrial function, and metformin has been demonstrated to induce AMPK-dependent, CHOP-mediated cell death. Here we further studied the mechanisms underlying cell death and autophagy in rottlerin-treated mouse PaSC. Rottlerin rapidly depolarized mitochondrial membrane, increased oxygen consumption and decreased cellular ATP levels and the expression of the mitochondrial transmembrane protein TOM20, suggesting mitochondrial damage. Rottlerin dysregulated autophagy as indicated by rapid and prolonged increasing in LC3I-LC3II conversion and p62/SQSTM1 accumulation. However, rottlerin-induced LC3II did not further change in the presence of inhibitors of autophagic flux, suggesting that rottlerin blocks autophagy progression in PaSC. In addition, rottlerin induced marked AMPK activation and inhibited mTOR signaling. In contrast to metformin, AMPKα1/2 knockdown had no effect on rottlerin-induced inhibition of mTOR signaling and cell viability. Furthermore, rottlerin induced ER stress as manifested by persistent activation of the PERK pathway and upregulation of proapoptotic transcription factor CHOP. Importantly, rottlerin-induced apoptosis was greatly reduced in PaSC isolated from CHOP null mice. In summary, these data indicate that rottlerin reduces PaSC viability through impairing mitochondrial function, inhibiting mTOR signaling and inducing prolonged ER stress. Specifically, CHOP induction plays an important role in determining cell-fate in mitochondria-targeting agents, such as rottlerin and metformin.
Citation Format: Hsin-Yuan Su, Richard Waldron, Raymond Gong, Stephen Pandol, Aurelia Lugea. Rottlerin induces ER stress-mediated cell death in pancreatic stellate cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1769. doi:10.1158/1538-7445.AM2015-1769