Abstract LB-098: Pooled shRNA screen uncovered the role of SEL1L, an ERAD (endoplasmic reticulum associated degradation) gene, in modulating temozolomide resistance in GBM
Authors: Arora Anjali , Tomar Vivek Singh , Thomas Sannu , Patil Vikas , Hoheisel Jörg , Somasundaram Kumaravel 
Published: August 2018

Abstract
Glioblastoma (GBM) is the most aggressive form of adult brain tumors with a poor median survival of less than 15 months. The alkylating agent temozolomide is used for chemotherapy for GBM. Regardless of the rigorous therapeutic regime, almost all cases develop resistance and recur. The mechanisms of the inherent and acquired resistance are less understood and demand in-depth research. We performed a pooled and bar-coded shRNA screen (5045 shRNAs) in a glioma cell line to identify mediators of temozolomide resistance in GBM. The data was analyzed by the HitSelect algorithm, and the top ranking genes imparting resistance (n=257) and sensitivity (n=256) were further subjected to gene set enrichment analysis (GSEA), Gene Ontology (GO) annotation and survival analysis in The Cancer Genome Atlas (TCGA) GBM cohort. An enrichment of translation and protein synthesis-related pathways was found in sensitivity genes, while enrichment of proliferation, metabolic processes, cytokine-cytokine receptor interaction and response to stress was found in resistance genes. Suppressor of Lin-12-Like Protein 1 (SEL1L) was identified as one of the top ranking genes in our screen that caused resistance to temozolomide. SEL1L is a component gene of the endoplasmic-reticulum-associated protein degradation (ERAD). It is known to play an important role in clearing misfolded proteins from cells, thus maintaining proteostasis. SEL1L was found to be a poor prognostic marker in the TCGA GBM cohort treated with temozolomide, as identified by univariate and Kaplan- Meier analysis. In vitro SEL1L knockdown resulted in a significant reduction of proliferation and in an increased sensitivity towards temozolomide. Upon temozolomide treatment of cells in the SEL1L knockdown condition, an increase in apoptosis was observed as measured by Annexin V staining. In vivo tumor showed increased SEL1L protein levels as compared to control brain and mice tumor that responded to temozolomide. We subjected to GSEA, (i) the genes that exhibited survival significance in the TCGA GBM cohort with temozolomide, as well as (ii) the genes that showed differential expression in the SEL1L low and high expression groups. Interestingly, both these analyses identified significant enrichment of overlapping pathways like TNFA mediated NF-kappaB signaling, EMT, IL6 STAT3 signaling, G2M checkpoint and E2F target genes, further highlighting the role of SEL1L in temozolomide resistance. This underscores that SEL1L is an important mediator for temozolomide resistance and is a poor prognosticator in GBM. SEL1L high expression correlates with various resistance-related signaling pathways. Our study emphasizes on the interplay between these pathways and the ERAD machinery in maintaining proteostasis in response to chemotherapeutic stress.
Citation Format: Anjali Arora, Vivek Singh Tomar, Sannu Thomas, Vikas Patil, Jörg Hoheisel, Kumaravel Somasundaram. Pooled shRNA screen uncovered the role of SEL1L, an ERAD (endoplasmic reticulum associated degradation) gene, in modulating temozolomide resistance in GBM [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 LB-098.