Differential Functions of Splicing Factors in Breast-Cancer Initiation and Metastasis

SUMMARY Misregulation of alternative splicing is a hallmark of human tumors; yet to what extent and how it contributes to malignancy are only beginning to be unraveled. Here, we define which members of the splicing factor SR and SR-like families contribute to breast cancer, and uncover differences and redundancies in their targets and biological functions. We first identify splicing factors frequently altered in human breast tumors, and then assay their oncogenic functions using breast organoid models. Importantly we demonstrate that not all splicing factors affect mammary tumorigenesis. Specifically, upregulation of either SRSF4, SRSF6 or TRA2β promotes cell transformation and invasion. By characterizing the targets of theses oncogenic factors, we identify a shared set of spliced genes associated with well-established cancer hallmarks. Finally, we demonstrate that the splicing factor TRA2β is regulated by the MYC oncogene, plays a role in metastasis maintenance in vivo , and its levels correlate with breast-cancer-patient survival.