Chromatin architecture is indirectly regulated by CDK7 transcriptional activity

Cyclin Dependent Kinase 7 (CDK7) is the core catalytic subunit of Cyclin Activating Kinase (CAK), a complex that has dual roles in cell cycle progression and transcription. While several CDK7 inhibitors are efficacious in preclinical models of cancer and have entered clinical trials, the mechanism(s) by which CDK7 promotes proliferation and cell viability is not well understood. Using triple negative breast cancer (TNBC) as a model, we found that inhibiting CDK7, either genomically or pharmacologically, induces mitotic dysfunction. Live and static cell imaging revealed that CDK7 inhibition prolongs mitosis and induces chromatin bridge formation, DNA double strand breaks, and abnormal nuclear features, all of which are indicative of mitotic catastrophe and chromosome instability. Transcriptome analyses revealed that CDK7 is essential for maintaining condensin complex gene expression, suggesting that CDK7 may sustain chromatin configuration, a role that extends beyond its impact on super-enhancers. Indeed, inhibiting CDK7 alters chromatin architecture consistent with condensin disruption. Confirming the importance of condensin regulation by CDK7, genetic suppression of a core subunit of this complex, structural maintenance of chromosome 2 (SMC2), phenocopies CDK7 inhibition. We report an undescribed role of CDK7 in maintaining chromatin structure and chromosome stability, as well as promoting proper mitoses, by sustaining condensin expression. Overall design: Hi-C study MDA-MB-231 cells treated with DMSO (Vehicle, Control) or THZ1 (CDK7 inhibitor, drug) in technical replicates.