SUMMARY
Gene expression is tightly controlled by Cyclin-dependent kinases (CDKs) which regulate the RNA Polymerase II (RNAPII) transcription cycle at discrete checkpoints. RNAPII pausing is a CDK9-controlled rate-limiting process that occurs shortly after initiation and is required for spatio-temporal control of transcription in multicellular organisms. We discovered that CDK9-mediated RNAPII pause-release is functionally opposed by a protein phosphatase 2A (PP2A) complex. PP2A dynamically competes for key CDK9 substrates, DSIF and RNAPII, and is recruited to transcription pausing sites by INTS6, a subunit of the Integrator complex. INTS6 depletion disrupts the Integrator-PP2A association and confers resistance to CDK9 inhibition. This results in unrestrained activity of CDK9 and dysregulation of acute transcriptional responses. Pharmacological PP2A activation amplifies RNAPII pausing mediated by CDK9 inhibitors and synergizes therapeutically in a model of MLL-rearranged leukemia. These data demonstrate that finely-tuned gene expression relies on the delicate balance of kinase and phosphatase activity throughout the transcription cycle.
HIGHLIGHTS
Loss of INTS6 confers resistance to CDK9 inhibition
INTS6 recruits PP2A to Integrator and chromatin
PP2A/INTS6 complexes functionally oppose CDK9
PP2A/INTS6 fine-tune acute transcriptional responses
Synergistic anti-cancer activity between PP2A activators and CDK9 inhibitors
Competing Interest Statement
The Johnstone laboratory receives funding support from Roche, BMS, Astra Zeneca, and MecRx.
