Abstract 4313: Protein synthesis modulates paraptotic death induced by inhibition of cyclophilins in glioblastoma (GBM) cells

Abstract

Abstract In this study, we investigated the mechanisms underlying cell death induced by the small molecule cyclophilin inhibitor NIM811. NIM811 effectively killed GBM cells through a non-apoptotic pathway, as there was no nuclear shrinkage or caspase activation. Instead, death was preceded by dramatic cytosolic vacuolization, stemming from enlargement of the endoplasmic reticulum (ER). RNA-seq revealed upregulation of genes pertinent to the unfolded protein response (UPR) and autophagy. Western blotting for UPR and autophagy mediators also supported a transient UPR signaling and compromised autophagy during prolonged NIM811 treatment. By utilizing a bicistronic reporter plasmid, we independently quantitated Cap-dependent and Cap-independent translation. We further assessed the long-term effects mediated by different short-term paraptosis inhibitors via colony formation assay. We find that NIM811 initiates paraptosis in GBM cells, due to an abnormal upregulation of protein translation that caused accumulation of misfolded or unfolded proteins in ER. Transient activation of pro-survival autophagy and UPR signals were shutdown during prolonged treatment with NIM811, thus allowing cell death to occur. Cycloheximide was previously reported by others to suppress paraptosis. In our studies, we find instead that it temporarily delayed vacuole formation, but actually enhanced paraptotic cell death in the long term. The mTOR inhibitors rapamycin or torin-2 rescued cells from NIM811 induced paraptosis by sustaining autophagy and the UPR, and specifically restrained cap-dependent translation. We propose that ER vacuolization could be a protective response generated by cells to isolate defective proteins within the ER in order to prevent misfolded aggregates to interfere with cellular homeostasis. For that reason, simply inhibiting vacuole formation without clearing protein accumulation in the ER was insufficient to prevent cell death. These findings aid our understanding of cellular mechanisms that contribute to non-apopotic death. Moreover, this work underlines the importance of evaluating cellular responses in cell death experiments over multiple time frames to judge the true impact. Citation Format: Lin Wang, Justin Gundelach, Richard Bram. Protein synthesis modulates paraptotic death induced by inhibition of cyclophilins in glioblastoma (GBM) cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4313. doi:10.1158/1538-7445.AM2017-4313