Remodeling oncogenic transcriptomes by small molecules targeting NONO

A large swath of the human proteome is dedicated to mRNA homeostasis, but most RNA-binding proteins lack chemical probes. Here, we report the discovery through phenotypic screening of electrophilic small molecules that swiftly (within 4 h) and stereospecifically decrease transcripts encoding the androgen receptor (AR) and its major V7 splice variant in human prostate cancer cells. We show by chemical proteomics that these compounds covalently engage cysteine-145 of the RNA-binding protein NONO. Broader profiling revealed that covalent NONO ligands suppress a discrete set of transcripts and proteins, including multiple oncogenic transcription factors, and impair the proliferation of cancer cells. These effects were not observed following genetic disruption of NONO, which instead blocked ligand activity. The covalent ligands promote accumulation of NONO in nuclear foci and at the first 5’ splice site of immature transcripts, pointing to a trapping mechanism that may prevent the compensatory action of the paralogous proteins PSPC1 and SFPQ, which were found to increase in cancer cells following genetic or chemical perturbation of NONO. These findings, taken together, designate NONO as a druggable RNA-binding protein that can be co-opted by covalent small molecules to suppress pro-tumorigenic transcriptional networks.