Comparative Oncogenomic Analysis of Copy Number Alterations in Human and Zebrafish Tumors Enables Cancer Driver Discovery

Abstract

The identification of cancer drivers is a major goal of current cancer research. Finding driver genes within large chromosomal events is especially challenging because such alterations encompass many genes. Previously, we demonstrated that zebrafish malignant peripheral nerve sheath tumors (MPNSTs) are highly aneuploid, much like human tumors. In this study, we examined 147 zebrafish MPNSTs by massively parallel sequencing and identified both large and focal copy number alterations (CNAs). Given the low degree of conserved synteny between fish and mammals, we reasoned that comparative analyses of CNAs from fish versus human MPNSTs would enable elimination of a large proportion of passenger mutations, especially on large CNAs. We established a list of orthologous genes between human and zebrafish, which includes approximately two-thirds of human protein-coding genes. For the subset of these genes found in human MPNST CNAs, only one quarter of their orthologues were co-gained or co-lost in zebrafish, dramatically narrowing the list of candidate cancer drivers for both focal and large CNAs. We conclude that zebrafish-human comparative analysis represents a powerful, and broadly applicable, tool to enrich for evolutionarily conserved cancer drivers. Cancer is essentially a genetic disease, caused by serial genetic changes including point mutations and chromosome number abnormalities. The latter leads to copy number alterations of many genes. While there are usually thousands of these genetic changes in a given tumor, only a small fraction likely contribute to cancer development. One of the major challenges is to distinguish these cancer “driver” genes from “passenger” mutations that do not contribute to the cancer phenotype. In particular, identifying the driver genes on entire chromosomes that are frequently gained or lost in tumors remains a recalcitrant problem as these alterations contain so many genes. We demonstrate that, because the chromosomal location of genes is highly scrambled between zebrafish and human, the number of passenger genes can be dramatically reduced by comparing the genes in copy number alterations found in zebrafish and human tumors. Thus, our approach dramatically narrows down the list of candidate cancer drivers, and can accelerate discovery of novel cancer drivers and pathways that could inform future targeted therapy and personalized medicine.