Abstract 5105: Aberrant CLK1 splicing is a key dependency factor in pediatric high-grade gliomas
Authors: Naqvi Ammar S. , Seghal Priyanka , Corbett Ryan , Rathi Komal , Ennis Brian , Zhang Bo , Brown Miguel , Miller Daniel , Kraya Adam , Dybas Joseph , Hayer Katharina , Arif Shehbeel , Geng Zhuangzhuang , Chroni Antonia , Lahiri Aditya , Conkrite Karina , Hollawell Madison , Diskin Sharon , Madsen Peter , Foster Jessica B. , Koptyra Mateusz P. , Thomas-Tikhonenko Andrei , Resnick Adam , Storm Phillip J. , Rokita Jo Lynne 
Published: March 2024

Abstract
Pediatric brain cancer is the leading cause of disease-related mortality in children. With a paucity of therapeutically targetable alterations, there is a pressing need to identify effective strategies for many of these tumors. In this study, we systematically examine aberrant alternative splicing in pediatric brain tumors from the Open Pediatric Brain Tumor Atlas, and additional tumors from the Children's Brain Tumor Network and the Pacific Pediatric Neuro-Oncology Consortium (n = 1831). Notably, high-grade gliomas (HGGs), including those with and without H3 histone mutations, were enriched in the upper quartile of all tumors with high splicing burden (SB). HGGs demonstrated the greatest SB heterogeneity of all tumor types and we identified a total of 19,229 aberrant splicing events in 8,577 genes in midline tumors compared to non-tumor brainstem controls (ΔPSI &gt;= |.20|, p &lt; 0.05). We next integrated protein annotations from the UniProt Knowledgebase to assess and prioritize differential alternative splicing events affecting protein function. This approach led to the discovery of 3,754 splice variants in 5,036 genes resulting in the gain or ablation of functional sites. The protein kinase CDC-like kinase 1 (CLK1), a recognized master splicing factor and cell-cycle modulator, exhibited aberrant splicing of exon 4, whereby inclusion promoted the gain of two known phosphorylation sites. Additionally, we observed a strong correlation between CLK1 splicing, its own RNA expression and proteomic activity of the Serine/Arginine-rich (SR) family of splicing factors. The distribution of exon 4 splicing was significantly different (p = 0.019) between tumors with low vs high splicing burden; tumors with high splicing burden had increased exon 4 inclusion. Further, we performed experimental modulation of CLK1 exon 4 aberrant splicing in the brain tumor cell line KNS42 and demonstrated that forced exon 4 skipping leads to reduced CLK1 protein abundance and significantly reduces cell proliferation (p &lt; 0.01 vs. control). Following bulk RNA-Seq analysis of these cell lines, we identified that forced CLK1 exon 4 skipping resulted in 4,518 dysregulated genes enriched for known cancer pathways such as mitotic spindle, E2F targets, and G2M checkpoint. Our data suggest a role for CLK1 in driving transcriptional dysregulation in pediatric high-grade gliomas and uncover a potential therapeutic vulnerability.
Citation Format: Ammar S. Naqvi, Priyanka Seghal, Ryan Corbett, Komal Rathi, Brian Ennis, Bo Zhang, Miguel Brown, Daniel Miller, Adam Kraya, Joseph Dybas, Katharina Hayer, Shehbeel Arif, Zhuangzhuang Geng, Antonia Chroni, Aditya Lahiri, Karina Conkrite, Madison Hollawell, Sharon Diskin, Peter Madsen, Jessica B. Foster, Mateusz P. Koptyra, Andrei Thomas-Tikhonenko, Adam Resnick, Phillip J. Storm, Jo Lynne Rokita. Aberrant CLK1 splicing is a key dependency factor in pediatric high-grade gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5105.