Splicing modulators elicit global translational repression by condensate-prone proteins translated from introns

Chemical splicing modulators that bind to the spliceosome have provided an attractive venue for cancer treatment. Splicing modulators induce accumulation and subsequent translation of a subset of intron-retained mRNAs. Yet, the biological effect of proteins containing translated intron sequences remains unclear. Here we identified a number of truncated proteins generated upon treatment with the splicing modulator spliceostatin A (SSA) using genome-wide ribosome profiling and bio-orthogonal non-canonical amino-acid tagging (BONCAT) mass spectrometry. A subset of these truncated proteins has intrinsically disordered regions, forms insoluble cellular condensates, and triggers the proteotoxic stress response through JNK phosphorylation, thereby inhibiting the mTORC1 pathway. In turn, this reduces global translation. These findings indicate that creating an overburden of condensate-prone proteins derived from introns represses translation and prevents further production of harmful truncated proteins. This mechanism appears to contribute to the antiproliferative and proapoptotic activity of splicing modulators. Overall design: Broadly, the objective of the study is to understand how cells cope with the aberrant splicing. We sought for the fates of each transcripts upon splicing modulation by a small molecule compound, spliceostatin A (SSA). Also, SSA is antitumor compound but the reason for the selective killing of cancer cells in vitro and in vivo has been unrevealed. Our study provides insight over it as well. we treated the HeLa S3 cells with either 100ng/mL SSA or two replicates with methanol (MeOH) (solvent for SSA as negative control) for 6 hours. Same cell lysate was simultaneously used to prepare RNA-seq and Ribosome profiling libraries.