The minor spliceosome is a second RNA splicing system in eukaryotes and is essential for the correct expression of ∼700 genes containing at least one minor intron. This subset of genes, which represents only 3.5% of all protein coding genes, is enriched in processes essential for the rapid growth and survival of cancer cells, including MAPK signalling, DNA damage repair, cell cycle progression and DNA replication. The minor spliceosome is distinguished from the major spliceosome (responsible for all other RNA splicing) by several unique protein and small nuclear RNA (snRNA) components, including the U11/U12 snRNP 65K protein encoded by Rnpc3 and the U12 snRNA.
We used several genetically engineered zebrafish and mouse models of cancer to demonstrate that heterozygous Rnpc3 mutation reduces tumour burden in liver, lung and gastric adenocarcinoma, and prolongs the survival of mice with follicular lymphoma and acute myeloid leukemia. The effects of impaired minor splicing are due, at least in part, to the induction of DNA damage and activation of a Tp53-dependent transcriptional program that restricts tumour burden by inducing cell cycle arrest and apoptosis. Importantly, these anti-tumour effects produce no toxicity to normal tissues. To investigate the underlying mechanism/s of minor splicing inhibition we used siRNAs to knock down RNPC3 and the U12 snRNA expression in the human A549 lung adenocarcinoma cell line. Disruption of these components recapitulated the anti-growth and anti-survival effects we observed in our in vivo cancer models. Using transcriptome-wide RNA-sequencing and functional assays, we demonstrated that accumulation of DNA damage culminated in apoptosis, cell cycle arrest/senescence.
Collectively, these results suggest that targeting the minor spliceosome may provide a broad-spectrum approach to cancer therapy with a viable therapeutic window.