Targeting CDK12/CYCLIN K induces a gene activation program which is mediated by P-TEFb

Regulation of transcription in human cells is a multistep process controlled by coordinated actions of host transcription factors and their associated kinases. Despite major advances, fundamental gaps still remain in understanding how transcriptional programs are dynamically regulated. Gene expression of Human immunodeficiency virus (HIV) is tightly controlled by the cellular transcription machinery, providing a powerful model for studying transcription regulation. Such gene expression regulation is clinically significant, as HIV persists in long-lived reservoirs even under antiretroviral therapy. Here, we show that selective targeting of CDK12/CYCLIN K (CCNK) induces a global gene activation program, which is mediated by positive transcription elongation factor b (P-TEFb). CDK12/CCNK targeting reshapes promoter-proximal and gene bodies landscape at chromatin, and promotes release of P-TEFb from its inhibitory 7SK snRNP complex. Additional transcriptomic profiling reveals preferential upregulation of P-TEFb-target genes, accompanied by induction of relatively short genes and repression of CDK12-regulated DNA damage response pathways. In HIV- infected cells, targeting CDK12/CCNK activates a robust viral gene expression, accompanied with latency reversal and importantly, synergistic reactivation effects when combined with latency- reversing agents. Together, these results uncover a previously unrecognized compensatory interplay between transcriptional kinases that rewires the cellular gene expression program with implications for HIV latency reversal and cancer biology.