Novel Spt5-Pol II inhibitors uncouple distinct activities and reveal additional regulatory roles

Spt5 is a conserved and essential transcription elongation factor that promotes proximal-promoter-pausing, promoter-escape, elongation and mRNA processing. Spt5 plays specific roles in transcription of inflammation and stress induced genes, and of tri-nucleotides expanded-repeat genes involved in inherited neurological pathologies. Using high throughput drug screen that utilizes the split Renilla luciferase (RL) complementation assay, we identified the first Spt5-Pol II inhibitors (SPIs). SPIs faithfully reproduced Spt5 knockdown effects on proximal-promoter-pausing, NF-κB activation and the expanded-repeat huntingtin gene in neuronal cells. Using SPIs we (i) identified Spt5 target genes that responded to Spt5 inhibition with profoundly distinct kinetics (ii) uncovered Spt5 metabolic regulatory role via GDF15, a food intake and body-weight inhibitory hormone (iii) unveiled a previously unknown role of Spt5 in promoting 3’-end processing of histone genes. Remarkably, while several SPIs affect all Spt5 functions, a few inhibit a single one, implying uncoupling and selective targeting of Spt5 activities. Thus, SPIs expand the understanding of Spt5-Pol II functions and are potential drugs against metabolic and neurodegenerative diseases.