“Locking” CDK9 inhibition by activating integrator function in HIV transcription

The positive transcription elongation factor b (P-TEFb) is a critical host factor for HIV transcription, yet pharmacological inhibition of its CDK9 subunit yields transient suppression with cytotoxicity. We identify that the integrator-PP2A complex enhances the potency and durability of CDK9 inhibition without added toxicity. Activation of PP2A with the small-molecule SMAP-2, combined with a low dose of the CDK9 inhibitor AZD4573, suppresses HIV transcription in CD4 + T cells, persisting for 7 days after drug withdrawal. Mechanistically, the drug combination increases integrator recruitment and repressive chromatin marks, decreases RNA polymerase II occupancy and C-terminal domain (CTD) phosphorylation at HIV promoter, and reduces short and long HIV transcripts, without global T cell activation, proliferation or broad transcriptome changes. The drug combination's HIV-inhibiting effect is somewhat resistant against elevated HIV activity in the presence of cocaine or morphine. These findings reveal cooperative P-TEFb inhibition and integrator activation as a promising strategy for durable HIV silencing.