Abstract A013: Functional and clinical consequences of hotspot non-coding mutations upstream of the LEPROTL1 gene in bladder cancer
Authors: Butler Kelly , Lone Bilal , Dobbins Alexandra , Chakraborty Arup , Boudajadi Salah , Apolo Andrea , Banday Rouf 
Published: May 2024

Abstract
Recent whole-genome sequencing studies have unveiled intriguing hotspot mutations within non-coding genomic regions, yet their implications in cancer remain unknown. Here, we characterized the role of twin hotspot non-coding mutations upstream of the LEPROTL1 gene in bladder cancer: chr8: 29,952,919 G&gt;A and chr8: 29,952,919 C&gt;T. Either mutation is found in ~20% of bladder tumors, and the mutations do not typically co-occur. Through a comprehensive analysis integrating ChiP-seq, ATAC-seq, and Hi-C data from bladder cancer cell lines, we observed that these mutations co-localize with enhancer elements that interact with multiple nearby genes. In vitro dual luciferase reporter assays showed that both mutations are functional and likely affect gene expression in a genomic context. CRISPR-Cas9-mediated knocking out of the putative enhancer region identified LEPROTL1, DCTN6, and SARAF as target genes that are likely co-regulated, which was further supported by strong positive correlations of their mRNA expression in TCGA data. Isogenic cell clones generated by CRISPR-mediated base-editing showed that the mutations result in simultaneous upregulation of the three target genes, which were also expressed at higher levels in TCGA tumors harboring the non-coding mutations. Little is known about the function of LEPROTL1, DCTN6, and SARAF. Utilizing siRNA knockdown models complemented by live-cell imaging, viability assays, and cell cycle analysis, we found that they promote cell proliferation and cell cycle progression. Furthermore, our base-edited isogenic cell lines showed more rapid proliferation and cell cycle progression, as well as resistance to cisplatin. The mutations were also associated with shorter disease-specific survival in a TCGA cohort, and DCTN6 showed a negative association with overall survival. These results underscore the clinical significance of the non-coding mutations. Currently, we are assessing the effect of these mutations on tumor growth and cisplatin response in vivo using xenograft mouse models and evaluating the mechanisms by which LEPROTL1, DCTN6, and SARAF modulate cell cycle progression. Taken together, our data suggest that non-coding enhancer mutations near LEPROTL1 contribute to bladder carcinogenesis by increasing the expression of three co-regulated novel oncogenes, all of which were previously uncharacterized in bladder cancer. Since we found the mutations to be clinically significant, our study also raises the possibility of using the non-coding mutations and their target genes as clinical biomarkers and potential therapeutic drug targets.
Citation Format: Kelly Butler, Bilal Lone, Alexandra Dobbins, Arup Chakraborty, Salah Boudajadi, Andrea Apolo, Rouf Banday. Functional and clinical consequences of hotspot non-coding mutations upstream of the LEPROTL1 gene in bladder cancer [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr A013.