Chemical splicing modulators that bind to the spliceosome have provided an attractive avenue for cancer treatment. Splicing modulators induce accumulation and subsequent translation of a subset of intron-retained mRNAs. However, the biological effect of proteins containing translated intron sequences remains unclear. Here, we identify a number of truncated proteins generated upon treatment with the splicing modulator spliceostatin A (SSA) via genome-wide ribosome profiling and bio-orthogonal noncanonical 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 c-Jun N-terminal kinase (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.

与剪接体结合的化学剪接调节剂为癌症治疗提供了一条有吸引力的途径。剪接调节剂诱导内含子保留的 mRNA 子集的积累和随后的翻译。然而，含有翻译内含子序列的蛋白质的生物学效应仍不清楚。在这里，我们通过全基因组核糖体分析和生物正交非经典氨基酸标记 (BONCAT) 质谱法鉴定了用剪接调节剂剪接抑素 A (SSA) 处理后产生的许多截短蛋白。这些截短蛋白的一个子集具有本质上无序的区域，形成不溶性细胞凝聚物，并通过 c-Jun N 末端激酶 (JNK) 磷酸化触发蛋白毒性应激反应，从而抑制 mTORC1 通路。反过来，这会减少全局翻译。这些发现表明，产生来自内含子的易凝结蛋白的覆盖物会抑制翻译并防止进一步产生有害的截短蛋白。这种机制似乎有助于剪接调节剂的抗增殖和促凋亡活性。