A novel regulatory mechanism of U2 spliceosome proteostasis that controls the transcriptome and therapy response in cancer [RNAseq_CUTLL1_shSF3B1_MapR]

Aberrant splicing is an important cause of cancer, and the production of noncanonical, cancer-specific, mRNA transcripts associate with transformation. Studies have focused on characterizing the effect of spliceosome mutations on disease progression. Here, we have uncovered a novel mode of regulation of the U2 complex component SF3B1 in leukemia via lysosomal degradation. Elevated levels of SF3B1 protein control splicing and active transcription via direct interaction with the general transcriptional machinery and are critical for leukemia growth due to the control of cell cycle and DNA damage response-related transcripts, such as the serine/threonine kinase CHEK2. We further exploited these findings to show that clinically-used SF3B1 inhibitors synergize with transcriptional inhibitors, CHEK2 inhibitors and chemotherapy drugs to block leukemia growth. Our study provides the proof-of-principle for post-translational regulation of the splicing machinery via the lysosome and associated splicing-dependent and -independent roles of the U2 complex in cancer, that can be exploited for therapeutic purposes. 3 million/per group CUTLL1 cells were treat with DMSO or 3nm E7107 for 24h and harvest cells straightly follow the protocol from Kavitha Sarma’s lab[67]. The protein GST-RNaseH-MNase and GST-RNaseH mut-MNase were provided by Kavitha Sarma.