Genome sequencing and RNA-motif analysis reveal novel damaging noncoding mutations in human tumors

A major challenge in cancer research is to determine the biological and clinical significance of somatic mutations in noncoding regions. This has been studied in terms of recurrence, functional impact, and association to individual regulatory sites, but the combinatorial contribution of mutations to common RNA regulatory motifs has not been explored. Therefore, we developed a new method, MIRA (mutation identification for RNA alterations), to perform an unbiased and comprehensive study of significantly mutated regions (SMR) affecting binding sites for RNA-binding proteins (RBP) in cancer. Extracting signals related to RNA-related selection processes and using RNA sequencing (RNA-seq) data from the same specimens, we identified alterations in RNA expression and splicing linked to mutations on RBP binding sites. We found SRSF10 and MBNL1 motifs in introns, HNRPLL motifs at 5 ⁰ UTRs, as well as 5 ⁰ and 3 ⁰ splice-site motifs, among others, with specific mutational patterns that disrupt the motif and impact RNA processing. MIRA facilitates the integrative analysis of multiple genome sites that operate collectively through common RBPs and aids in the interpretation of noncoding variants in cancer. MIRA is available at https://github.com/comprna/mira. Implications: The study of recurrent cancer mutations on potential RBP binding sites reveals new alterations in introns, untranslated regions, and long noncoding RNAs that impact RNA processing and provide a new layer of insight that can aid in the interpretation of noncoding variants in cancer genomes.