Transcriptional Responses to IFN-γ Require Mediator Kinase-Dependent Pause Release and Mechanistically Distinct CDK8 and CDK19 Functions.

Transcriptional responses to external stimuli remain poorly understood. Using global nuclear run-on followed by sequencing (GRO-seq) and precision nuclear run-on sequencing (PRO-seq), we show that CDK8 kinase activity promotes RNA polymerase II pause release in response to interferon-γ (IFN-γ), a universal cytokine involved in immunity and tumor surveillance. The Mediator kinase module contains CDK8 or CDK19, which are presumed to be functionally redundant. We implemented cortistatin A, chemical genetics, transcriptomics, and other methods to decouple their function while assessing enzymatic versus structural roles. Unexpectedly, CDK8 and CDK19 regulated different gene sets via distinct mechanisms. CDK8-dependent regulation required its kinase activity, whereas CDK19 governed IFN-γ responses through its scaffolding function (i.e., it was kinase independent). Accordingly, CDK8, not CDK19, phosphorylates the STAT1 transcription factor (TF) during IFN-γ stimulation, and CDK8 kinase inhibition blocked activation of JAK-STAT pathway TFs. Cytokines such as IFN-γ rapidly mobilize TFs to "reprogram" cellular transcription; our results implicate CDK8 and CDK19 as essential for this transcriptional reprogramming. • Mediator kinases CDK8 and CDK19 are distinct transcription regulators in the IFN-γ pathway • CDK8 acts as a kinase while CDK19 functions as a scaffold in driving IFN-γ gene profiles • CDK8 and CDK19 activate distinct gene sets • Mediator kinase CDK8 promotes polymerase II pause release during the IFN-γ response Steinparzer et al. discover that the Mediator kinases CDK8 and CDK19 are functionally and mechanistically distinct transcription regulators in the IFN-γ antiviral program: CDK8 and CDK19 activate distinct gene sets, and they do so in kinase-dependent (CDK8) and kinase-independent (CDK19) ways. Further, CDK8 kinase activity promotes RNAPII pause release. [ABSTRACT FROM AUTHOR]