RNA-seq analysis in breast cancer cell lines BT549 WT and SF3A3 5'UTR DSL3 edited.
Splicing is a central RNA-based process commonly altered in human cancers; however, how the splicing machinery is co-opted during tumorigenesis remains largely unresolved. Here we identify the splice factor SF3A3 at the nexus of an oncogenic translation program that rewires splicing to promote tumorigenesis. Our results suggest that key spliceosomal networks centered on the essential core U2-associated factor, SF3A3, are exquisitely controlled at the translation level during oncogenic stress. Upon oncogene activation, SF3A3 translation is rapidly enabled via a conserved internal stem-loop structure embedded in the transcript 5' untranslated region (UTR). Uncoupled SF3A3 translation leads to alternative splicing of several mRNAs involved in mitochondrial dynamics, and induces a metabolic switch that fuels cancer initiation properties in MYC-driven breast tumorigenesis in vivo. Finally, we compelling show that SF3A3 is post-transcriptionally altered and predicts for poor prognosis in aggressive triple negative breast cancers. Together, these findings unveil a highly dynamic regulatory network that interfaces mRNA splicing and translation to orchestrate cancer gene expression networks. Overall design: 2 sets of samples including wild-type (WT)  and CRISPR/CAS9 edited SF3A3 5'UTR (DSL3) were included in the study. Each sample was prepared in the biologically indpendent, matched triplicates.