Abstract 1119: Quaking (Qki) loss enhances stemness of glioma stem cells through regulating intracellular vesicle trafficking system

Abstract

Abstract Glioma stem cells (GSCs) have higher self-renewal capacity than neural stem cells (NSCs), yet the underlying molecular mechanism is less clear. Here we report the generation of a novel conditional KO allele of Quaking (Qki), a tumor suppressor in glioblastoma with RNA binding activity. When Qki was deleted in Nestin-CreERT2;QkiL/L mice, the NSC population, which is characterized by long-term BrdU retention and GFAP+/Nestin+ double positive staining, was greatly increased, indicating that Qki deletion enhances NSC self-renewal. To determine whether Qki deletion promotes gliomagenesis, we generated a Nestin-CreERT2;QkiL/L;PtenL/L;p53L/L cohort, in which 92% of the mice developed glioblastoma with a median survival of 105 days. However, the Nestin-CreERT2;PtenL/L;p53L/L cohort did not develop any glioma up to a year; therefore Qki deletion greatly promotes gliomagenesis. Transcriptomic and proteomic profiling coupled with PAR-CLIP (Photoactivatable-Ribonucleoside-Enhanced Crosslinking and Immunoprecipitation) analyses revealed that genes involved in intracellular vesicle trafficking were greatly enriched by Qki deletion. Specifically, 34% of the genes up-regulated by Qki deletion are involved in receptor delivery, and 39% of the genes down-regulated by Qki deletion are subunits of receptor degradation machineries such as endosomes and lysosomes. High level of receptor delivery and low level of receptor degradation concomitantly enrich receptors on the membrane and enhance the activity of the receptors that are involved in maintaining stemness, including RTK, Notch1 and Frizzled. Lower lysosomal activity induced by Qki deletion also leads to defective mitophagy, which consequently leads to accumulation of damaged mitochondria, high level of ROS, and genomic instability in Qki-deficient NSCs. We identified that genomic instability induced by Qki deletion led to accumulation of classical glioblastoma-associated mutations such as copy number gains of PDGFRa, Cyclin D1 and Cyclin D3. Taken together, our data suggest that Qki loss-induced endolysosomal defects promotes gliomagenesis through both reducing receptor degradation and inducing genomic instability. Citation Format: Jian Hu, Takashi Shingu. Quaking (Qki) loss enhances stemness of glioma stem cells through regulating intracellular vesicle trafficking system [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1119.