Arylsulfonamide mediated RBM39 degradation causes aberrant splicing of mitotic kinesins

Certain arylsulfonamides (ArSulfs) induce an interaction between the E3 ligase substrate adaptor DCAF15 and the critical splicing factor RBM39, ultimately causing its degradation. Although molecules like the ArSulfs, which interfere with splicing decisions, are exciting potential medicines, the molecular glue mechanism of RBM39 degradation introduces complex pleiotropic effects that are difficult to untangle. For example, DCAF15 inhibition, RBM39 degradation, and the downstream proteome effects of splicing changes will all cause different yet overlaid effects. As such the precise cell-killing mechanism by RBM39 loss is largely unknown. By overlaying transcriptome and proteome datasets, we distinguish transcriptional from post-transcriptional effects, pinpointing those proteins most impacted by splicing changes. Our proteomic profiling of several ArSulfs suggests a selective DCAF15/ArylSulf/RBM39RRM2 interaction with a narrow degradation profile. We identify two mitotic kinesin motor proteins that are aberrantly spliced upon RBM39 degradation, and we demonstrate that these are likely contributors to the antiproliferative activity of ArSulfs.