Abstract 1724: Pancreatic cancer stem cell metastasis and mitochondrial respiration is dependent on the the ISG15-mediated ubiquitin-like modification process known as ISGylation

Abstract

Abstract We recently discovered that CSCs of distinct solid tumors (e.g. pancreatic, colon, and liver) contain intracellular vesicles coated in the ATP-dependent transporter ABCG2, which act as a sink for the accumulation of riboflavin (vitamin B2). Using autofluorescence and other CSC markers, such as CD133, we have begun to dissect CSCs at the genetic and protein level. Using RNAseq to transcriptionally distinguish CSCs from non-CSCs, we observed that pancreatic CSCs of different primary PDAC tumors exhibit a transcriptional gene activation signature belonging to the Type I interferon (IFN) signaling pathway. In particular, CSCs up-regulate the interferon-stimulated gene 15, a 165 amino acid (17kDa) protein that is induced by Type I IFN treatment and functions to ISGylate proteins, a ubiquitin-like modification process whereby ISG15 can be covalently linked to cytoplasmic and nuclear proteins. We have discovered that CSCs not only upregulate the expression of monomeric ISG15, but numerous proteins within CSCs are ISGylated, the level of ISGylation correlates with their metastatic capacity and knockdown of ISG15 ablates pancreatic CSCs functions, such as self-renewal, migration and invasion in vivo and mitochondrial respiration. Thus, our data indicate that the ISGylayion pathway is active in CSCs and plays an important role in the “stem-like” properties of these cells. We have also elucidated the mechanism underlying the differential regulation of ISG15 in CSCs versus non-CSCs. Specifically, using over expression lentiviral vector systems and pharmacological inhibitors (i.e. BRD4 inhibitor JQ-1), we show that MYC controls the expression of miR22, a micro-RNA that targets, among others transcripts, a number of Interferon Regulatory Factors (IRFs) that are essential for intracellular IFN signaling, including ISG15 expression. CSCs express low levels of MYC and miR-22, relieving the inhibitory block on IRFs and subsequent ISG15 signaling. As expected, over expression of MYC increases miR-22 levels and blocks IRF-mediated ISG15 expression. While the intricacies of these complex and distinct pathways still need to be unraveled at the CSC level, our data suggest that MYC may be a key universal player in these pathways, and targeting ISG15 in CSCs may represent a unique approach to altering the biology of CSCs. Citation Format: Bruno Sainz, Sonia Alcala Sanchez, Mireia Vallespinos. Pancreatic cancer stem cell metastasis and mitochondrial respiration is dependent on the the ISG15-mediated ubiquitin-like modification process known as ISGylation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1724.