Recurrent R-spondin fusions in colon cancer

Abstract

Exomes, transcriptomes and copy-number alterations in a sample of more than 70 primary human colonic tumours were analysed in an attempt to characterize the genomic landscape; in addition to finding alterations in genes associated with commonly mutated signalling pathways, recurrent gene fusions involving R-spondin family members were also found to occur in approximately 10% of colonic tumours, revealing a potential new therapeutic target. An analysis of exomes, transcriptomes and copy-number alterations in more than 70 primary human colon tumours and matched normal controls has identified more than 35,000 protein-altering somatic mutations, most of which have been validated. In addition to alterations in genes involved in the Wnt pathway, chromatin remodelling and receptor-tyrosine-kinase signalling, the authors identify recurrent gene fusions involving R-spondin family members that collectively occur in 10% of colon tumors; as such they may provide a potential therapeutic target. There is evidence to suggest that these fusions may have a role in the activation of Wnt signalling and tumorigenesis. Identifying and understanding changes in cancer genomes is essential for the development of targeted therapeutics1. Here we analyse systematically more than 70 pairs of primary human colon tumours by applying next-generation sequencing to characterize their exomes, transcriptomes and copy-number alterations. We have identified 36,303 protein-altering somatic changes that include several new recurrent mutations in the Wnt pathway gene TCF7L2, chromatin-remodelling genes such as TET2 and TET3 and receptor tyrosine kinases including ERBB3. Our analysis for significantly mutated cancer genes identified 23 candidates, including the cell cycle checkpoint kinase ATM. Copy-number and RNA-seq data analysis identified amplifications and corresponding overexpression of IGF2 in a subset of colon tumours. Furthermore, using RNA-seq data we identified multiple fusion transcripts including recurrent gene fusions involving R-spondin family members RSPO2 and RSPO3 that together occur in 10% of colon tumours. The RSPO fusions were mutually exclusive with APC mutations, indicating that they probably have a role in the activation of Wnt signalling and tumorigenesis. Consistent with this we show that the RSPO fusion proteins were capable of potentiating Wnt signalling. The R-spondin gene fusions and several other gene mutations identified in this study provide new potential opportunities for therapeutic intervention in colon cancer.