The spliceosome is a therapeutic vulnerability in MYC-driven cancer

c-MYC (MYC) overexpression or hyperactivation is one of the most common drivers of human cancer. Despite intensive study, the MYC oncogene remains recalcitrant to therapeutic inhibition. MYC is a transcription factor, and many of its pro-tumorigenic functions have been attributed to its ability to regulate gene expression programs(1–3). Notably, oncogenic MYC activation has also been shown to increase total RNA and protein production in many tissue and disease contexts(4–7). While such increases in RNA and protein production may endow cancer cells with pro-tumor hallmarks, this elevation in synthesis may also generate new or heightened burden on MYC-driven cancer cells to properly process these macromolecules(8). Herein, we discover the spliceosome as a new target of oncogenic stress in MYC-driven cancers. We identify BUD31 as a MYC-synthetic lethal gene, and demonstrate that BUD31 is a component of the core spliceosome required for its assembly and catalytic activity. Core spliceosomal factors (SF3B1, U2AF1, and others) associated with BUD31 are also required to tolerate oncogenic MYC. Notably, MYC hyperactivation induces an increase in total pre-mRNA synthesis, suggesting an increased burden on the core spliceosome to process pre-mRNA. In contrast to normal cells, partial inhibition of the spliceosome in MYC-hyperactivated cells leads to global intron retention, widespread defects in pre-mRNA maturation, and deregulation of many essential cell processes. Importantly, genetic or pharmacologic inhibition of the spliceosome in vivo impairs survival, tumorigenicity, and metastatic proclivity of MYC-dependent breast cancers. Collectively, these data suggest that oncogenic MYC confers a collateral stress on splicing and that components of the spliceosome may be therapeutic entry points for aggressive MYC-driven cancers.